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Bulk n-type SrTiO3 (STO) has long been known to possess a superconducting ground state at an exceptionally dilute carrier density. This has raised questions about the applicability of the BCS-Eliashberg paradigm with its underlying adiabatic assumption. However, recent experimental reports have set the pairing gap to the critical temperature ( T c ) ratio at the BCS value for superconductivity in Nb-doped STO, even though the adiabaticity condition the BCS pairing requires is satisfied over the entire superconducting dome only by the lowest branch of optical phonons. In spite of the strong implications these reports have on specifying the pairing glue, they have not proved sufficient in explaining the magnitude of the optimal doping. This motivated us to apply density functional theory to Nb-doped STO to analyze how the phonon band structures and the electron–phonon coupling evolve with doping. To describe the very low doping concentration, we tuned the homogeneous background charge, from which we obtained a first-principles result on the doping-dependent phonon frequency that is in good agreement with experimental data for Nb-doped STO. Using the EPW code, we obtain the doping-dependent phonon dispersion and the electron–phonon coupling strength. Within the framework of our calculation, we found that the electron–phonon coupling forms a dome in a doping range lower than the experimentally observed superconducting dome of the Nb-doped STO. Additionally, we examined the doping dependence of both the orbital angular momentum quenching in the electron–phonon coupling and the phonon displacement correlation length and found the former to have a strong correlation with our electron–phonon coupling in the overdoped region. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) layered materials have received much attention due to the unique properties stemming from their van der Waals (vdW) interactions, quantum confinement, and many-body interactions of quasi-particles, which drive their exotic optical and electronic properties, making them critical in many applications. Here, we review our past years' findings, focusing on many-body interactions in 2D layered materials, including phonon anharmonicity, electron–phonon coupling (e-ph), exciton dynamics, and phonon anisotropy based on temperature (polarization)-dependent Raman spectroscopy and Photoluminescence (PL). Our review sheds light on the role of quasi-particles in tuning the material properties, which could help optimize 2D materials for future applications in electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Strong electron‐phonon coupling can hinder exciton transport and induce undesirable non‐radiative recombination, resulting in a shortened exciton diffusion distance and constrained exciton dissociation in organic solar cells (OSCs). Therefore, suppressing electron‐phonon coupling is crucially important for achieveing high‐performance OSCs. Here, we employ the solid additive to regulating electron‐phonon coupling in OSCs. The planar configuration of SA1 confers a significant advantage in suppressing lattice vibrations in the active layers, reducing the scattering of excitons by phonons. Consequently, a slow but sustained hole transfer process is identified in the SA1‐assisted film, indicating an enhancement in hole transfer efficiency. Prolonged exciton diffusion length and exciton lifetime are achieved in the blend film processed with SA1, attributed to a low non‐radiative recombination rate and low energetic disorder for charge carrier transport. As a result, a high efficiency of 20 % was achieved for ternary device with a remarkable short‐circuit current. This work highlights the important role of suppressing electron‐phonon coupling in improving the photovoltaic performance of OSCs. [ABSTRACT FROM AUTHOR]

Layered ternary type‐II Weyl semimetals demonstrate promising applications in high‐performance and broadband optoelectronics, therefore it is crucial to gain insights into their photocarriers' dynamics. In this work, the probing polarization dependence of non‐equilibrium dynamics in NbIrTe4 is investigated by using transient reflectivity spectroscopy. Following photoexcitation at 3.18 eV, the dynamical response of 1.59 eV probe pulse exhibits a strong dependence on probe polarization. The relaxation comprises two components: a rapid recovery of ≈0.6 ps attributed to the electron–phonon scattering, and an anomalous slow recovery spanning hundreds of picoseconds attributed to the photoinduced quasi‐particle. The polarization dependence of rapid relaxation time τ is indicative of the in‐plane anisotropy of electron–phonon coupling in NbIrTe4. The slow relaxation modulated by a latest reported 16 cm−1 coherent phonon also shows strong probing polarization dependence, further revealing the anisotropic nature of electron–phonon coupling and the possibility of anisotropic lattice distortion, as well as photoinduced polaron, under ultrafast photoexcitation in NbIrTe4. The dynamical anisotropy in NbIrTe4 has provided valuable guidance for the application of NbIrTe4 in polarization‐sensitive nonlinear optics or optoelectronic devices and offers insights into the unique carrier transport as well as phonon transport properties of this newly established topological material. [ABSTRACT FROM AUTHOR]

Strong electron‐phonon coupling can hinder exciton transport and induce undesirable non‐radiative recombination, resulting in a shortened exciton diffusion distance and constrained exciton dissociation in organic solar cells (OSCs). Therefore, suppressing electron‐phonon coupling is crucially important for achieveing high‐performance OSCs. Here, we employ the solid additive to regulating electron‐phonon coupling in OSCs. The planar configuration of SA1 confers a significant advantage in suppressing lattice vibrations in the active layers, reducing the scattering of excitons by phonons. Consequently, a slow but sustained hole transfer process is identified in the SA1‐assisted film, indicating an enhancement in hole transfer efficiency. Prolonged exciton diffusion length and exciton lifetime are achieved in the blend film processed with SA1, attributed to a low non‐radiative recombination rate and low energetic disorder for charge carrier transport. As a result, a high efficiency of 20 % was achieved for ternary device with a remarkable short‐circuit current. This work highlights the important role of suppressing electron‐phonon coupling in improving the photovoltaic performance of OSCs. [ABSTRACT FROM AUTHOR]

Recent experiments suggest a new paradigm toward novel colossal magnetoresistance (CMR) in a family of materials EuM2X2 (M = Cd, In, Zn; X = P, As), distinct from the traditional avenues involving Kondo-Ruderman-Kittel-Kasuya-Yosida crossovers, magnetic phase transitions with structural distortions, or topological phase transitions. Here, we use angle-resolved photoemission spectroscopy and density functional theory calculations to explore their origin, particularly focusing on EuCd2P2. While the low-energy spectral weight royally tracks that of the resistivity anomaly near the temperature with maximum magnetoresistance (TMR) as expected from transport-spectroscopy correspondence, the spectra are completely incoherent and strongly suppressed with no hint of a Landau quasiparticle. Using systematic material and temperature dependence investigation complemented by theory, we attribute this nonquasiparticle caricature to the strong presence of entangled magnetic and lattice interactions, a characteristic enabled by the p-f mixing. Given the known presence of ferromagnetic clusters, this naturally points to the origin of CMR being the scattering of spin-polarized polarons at the boundaries of ferromagnetic clusters. These results are not only illuminating to investigate the strong correlations and topology in EuCd2X2 family, but, in a broader view, exemplify how multiple cooperative interactions can give rise to extraordinary behaviors in condensed matter systems. [ABSTRACT FROM AUTHOR]

In recent years, as two-dimensional (2D) materials have been widely used in electronic devices, searching for 2D high superconducting transition temperature ( T c ) superconductors has also attracted great attentions. In this work, based on first-principles calculations and Eliashberg equation, the electronic structure, electron-phonon coupling (EPC) and possible superconductivity of alkali metal-deposited monolayer BC: MBC (M = Na, K) are studied. The results show that MBC (M = Na, K) are metallic and potential superconductors. The calculated EPC constants of MBC (M = Na, K) are 0.97 and 1.48, respectively. The strong coupling of MBC (M = Na, K) mainly origins from the coupling between electrons with the in-plane vibration modes of C and B atoms. The T c of MBC (M = Na, K) are 34.1 K and 41.7 K, respectively, and the T c of NaBC can be increased to 45.6 K under 2% biaxial tensile strain, and the T c of KBC can be boosted to 53.8 K under 1% biaxial tensile strain. It is anticipated that the predicted monolayer MBC (M = Na, K) and its strained cases can be realized in future experiments. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) van der Waals (vdW) materials have been an exciting area of research ever since scientists first isolated a single layer of graphene. Single layer magnetic materials can provide a pathway for vdW heterostructures with magnetic properties. While most of the magnetic vdW materials exhibit ordering transitions in the bulk, here we report a successful exfoliation of a triangular lattice S = 1 antiferromagnet NiGa S , which already demonstrates exotic magnetism in the bulk material. We establish the number of layers of the material by atomic force microscopy (AFM) and detail a careful characterization using Raman and optical spectroscopy to demonstrate how the optical, electronic, and structural properties of NiGa S change as a function of sample thickness. Optical measurements and electronic structure calculations of bulk versus monolayer NiGa S confirm the material to be a Mott insulator with an electronic gap of about 1.5 eV, which slightly increases for layers below 10 L. We conclude with a theoretical analysis of the possibility of doping monolayer NiGa S by proximity to a metal. [ABSTRACT FROM AUTHOR]

Finding high‐temperature superconductivity in light‐weight element containing compounds at atmosphere pressure is currently a research hotspot but has not been reached yet. Here it is proposed that hard or superhard materials can be promising candidates to possess the desirable high‐temperature superconductivity. By studying the electronic structures and superconducting properties of H and Li doped c‐BN within the framework of the first‐principles, it is demonstrated that the doped c‐BN are indeed good superconductors at ambient pressure after undergoing the phase transition from the insulating to metallic behavior, though holding different nature of metallization. Li doped c‐BN is predicted to exhibit the superconducting transition temperature of ≈58 K, while H doped c‐BN has stronger electron–phonon interaction and possesses a higher transition temperature of 122 K. These results and findings thus point out a new direction for exploring the ambient‐pressure higher‐temperature superconductivity in hard or superhard materials. [ABSTRACT FROM AUTHOR]

The highest ambient‐pressure Tc among binary compounds is 40 K (MgB2). Higher Tc is achieved in high‐pressure hydrides or multielement cuprates. Alternatively, are explored superconducting properties of binary, metastable sub‐oxides, that may emerge under extremely low oxygen partial pressure. The emphasis is on the rock‐salt structure, which is known to promote superconductivity, and exploring AlO, ScO, TiO, and NbO. Dynamic lattice stability is achieved by introducing metal and oxygen vacancies in the fashion of Nb1−xO1−x‐type structure (x = ¼). The electron‐phonon (e‐ph) coupling is remarkably large in Al1−xO1−x and Ti1−xO1−x (λ ≈ 2 at x = ¼), with Tc ≈ 35 K according to the Allen–Dynes equation. Significantly, the coupling strength is comparable to that in high‐pressure hydrides, yet, in contrast to hydrides and MgB2, the coupling is largely driven by low frequency phonons. Sc1−xO1−x and Nb1−xO1−x show significantly smaller λ and Tc. Further, hydrogen intercalation to boost λ and Tc is investigated. Only Ti1−x(O1−xHx) and Nb1−x(O1−xHx) are dynamically stable upon intercalation, where H, respectively, decreases and increases Tc. The effect of H doping on electronic structure and Tc is discussed. Altogether, the study suggests that metal sub‐oxides are promising compounds to achieve strong e‐ph coupling at ambient pressure. [ABSTRACT FROM AUTHOR]

Hydrogenated metal borides have attracted much attention due to their potential high-temperature superconductivity. Here, we propose a new strategy for hydrogen intercalation tuning the stability and superconductivity of the boron honeycomb sublattice, and predict an unprecedented layered compound Na2B2H, which hosts excellent superconductivity. Strikingly, the superconducting transition temperature (Tc) of Na2B2H reaches 42 K at ambient pressure. The Tc value can be further increase to 63 K under 5% biaxial tensile strain. The excellent superconductivity originates from the strong electron-phonon coupling between the σ-bonding bands near the Fermi level and the B-B stretching optical E′ modes. The interstitial electron localization and crystal orbitals of the H-intercalated Na ion layer well match the boron honeycomb lattice and act as a chemical template to stabilize the B layer. Furthermore, the introduction of hydrogen tuned the Fermi level, and the coupling vibration of Na and H ions effectively enhanced the dynamic stability of the structure. Na2B2H represents a new family of layered high-temperature superconductors, and the strategy of stabilizing the honeycomb boron sublattice via chemical template hosts great potential for application to more layered compounds. [ABSTRACT FROM AUTHOR]

The introduction of superconductivity in graphene systems is highly desirable from both fundamental physics and application perspectives. In this article, a superlattice strategy to develop a series of Li‐doped graphene is reported: deposition type‐I (Li2C6, Li2C8, LiC6, Li3C24, LiC12, LiC16, Li2C36, LiC24), intercalation type‐II (LiC4, Li2C12, LiC8, LiC12, LiC16), and coexisting deposition and intercalation type‐III (Li3C12). With increasing concentration of Li atoms, both metallicity, and electron–phonon coupling (EPC) has dramatically increased, which is favorable for the emergence of superconductivity in the screened Li–C compounds. Notably, graphene superlattice structures with intercalated Li2 atoms have higher stability, while Li1‐deposited graphene at the same concentration produces higher Tc. Among them, type‐I‐Li2C6, type‐I‐Li2C8, type‐II‐LiC4, and type‐III‐Li3C12 are phonon‐mediated superconductors with high transition temperatures (Tc) of 18, 12, 3.4, and 14 K, respectively. The EPC of type‐I‐Li2C6, type‐I‐Li2C8, and type‐III‐Li3C12 mainly arises from the coupling of the C‐2pz electron states with the low‐frequency (0–800 cm−1) deposition‐Lixy/Liz, and out‐of‐plane‐Cz vibrations. In contrast, the high‐frequency (800–1600 cm−1) vibration modes of in‐plane‐Cxy atoms are mainly responsible for the Tc of type‐II‐LiC4. The findings provide comprehensive insights into the superconductivity limit of Li‐doped graphene. [ABSTRACT FROM AUTHOR]

Several multi‐hydrogen hydrides have exhibited high critical temperature (Tc) superconductivity, but the requirement for ultrahigh pressures limits their applications. Here, high‐throughput calculations are utilized to investigate the superconductivity in few‐hydrogen metal‐bonded (FHMB) perovskites (PVSKs) AHM3 characterized with perfect ambient‐pressure stability. AHM3 is classified into two groups, d and sp superconductors, and provide three indicators that accurately describe AHM3 superconductivity. i) Tc of d superconductors is positively correlated with the number of unpaired d electrons from M atoms; ii) A suitably sized octahedral interstice of H atom is essential for sp superconductors; iii) The introduction of H will further improve the superconductivity, when the M atom has a lower electronegativity than H. ZnHCr3 and ZnHAl3, perfectly meeting the requirements aforementioned, exhibit the highest Tc of 30 and 80 K among the d and sp superconductors, respectively. The results are helpful for understanding the electron–phonon coupling (EPC) mechanism in few‐hydrogen metal‐bonded perovskites and facilitate realizations of ambient‐pressure high‐Tc superconductivity in hydrides. [ABSTRACT FROM AUTHOR]

Achieving superconductivity at room temperature (RT) is a holy grail in physics. Recent discoveries on high‐Tc superconductivity in binary hydrides H3S and LaH10 at high pressure have directed the search for RT superconductors to compress hydrides with conventional electron–phonon mechanisms. Here, an exceptional family of superhydrides is predicated under high pressures, MH12 (M = Mg, Sc, Zr, Hf, Lu), all exhibiting RT superconductivity with calculated Tcs ranging from 313 to 398 K. In contrast to H3S and LaH10, the hydrogen sublattice in MH12 is arranged as quasi‐atomic H2 units. This unique configuration is closely associated with high Tc, attributed to the high electronic density of states derived from H2 antibonding states at the Fermi level and the strong electron–phonon coupling related to the bending vibration of H2 and H‐M‐H. Notably, MgH12 and ScH12 remain dynamically stable even at pressure below 100 GPa. The findings offer crucial insights into achieving RT superconductivity and pave the way for innovative directions in experimental research. [ABSTRACT FROM AUTHOR]

In recent years, there has been a growing emphasis on the exploration of sustainable and eco-friendly materials well-suited for advanced applications in the realms of thermoelectrics and optoelectronics. Lead-free halide double perovskites have emerged as a compelling class of materials in this context. Nevertheless, despite their potential utility, thorough investigations into their thermal transport characteristics remain limited. In this systematic investigation, we employ density functional theory (DFT) and post-DFT techniques to elucidate the essential stability parameters, transport properties, and carrier-lattice interactions of the metal halide-based Cs2MGaBr6 (X = Li, Ga) double perovskites. Our assessment of structural stability involves a meticulous description of stability index parameters and the optimization of pristine structures using the GGA-PBE potential. Additionally, we calibrate the electronic structure while taking spin–orbit coupling (SOC) effects into consideration by using a combination of GGA and GGA + mBJ potentials. Our findings reveal that the TB-mBJ derived band gaps of 1.82 eV and 1.78 eV for Cs2LiGaBr6 and Cs2NaGaBr6 reside within the visible spectrum, prompting further investigation into their thermal transport characteristics. Moreover, we analyze the phonon characteristics and vibrational modes, extending our investigation to examine the electron–phonon coupling strength. The scrutiny of the Fröhlich coupling constant and the Feynman polaron radius unveils a stronger electron–phonon coupling strength. In the domain of thermoelectrics, the significant figure of merit (zT) values of 1.08 and 1.04 for Cs2LiGaBr6 and Cs2NaGaBr6, respectively, emphasize the considerable potential of these materials for deployment in renewable energy applications. Furthermore, our computational investigation into optical properties, including the dielectric constant, optical absorption, and refractive index, demonstrates optimal performance within the visible spectrum. Specifically, elevated absorption coefficient values of 30 × 10 4 cm - 1 for Cs2LiGaBr6 and 40 × 10 4 cm - 1 for Cs2NaGaBr6 are noted across visible and infrared spectra, highlighting their promising potential in optoelectronic and solar cell technologies. [ABSTRACT FROM AUTHOR]

We present a study of electrical and thermal transport in Weyl semimetal WTe2 down to 0.3 K. The Wiedemann-Franz law holds below 2 K and a downward deviation starts above. The deviation is more pronounced in cleaner samples, as expected in the hydrodynamic picture of electronic transport, where a fraction of electron-electron collisions conserve momentum. Phonons are the dominant heat carriers and their mean-free-path does not display a Knudsen minimum. This is presumably a consequence of weak anharmonicity, as indicated by the temperature dependence of the specific heat. Frequent momentum exchange between phonons and electrons leads to quantum oscillations of the phononic thermal conductivity. Bloch-Grüneisen picture of electron-phonon scattering breaks down at low temperature when Umklapp ph-ph collisions cease to be a sink for electronic flow of momentum. Comparison with semi-metallic Sb shows that normal ph-ph collisions are amplified by anharmonicity. In both semimetals, at cryogenic temperature, e-ph collisions degrade the phononic flow of energy but not the electronic flow of momentum. [ABSTRACT FROM AUTHOR]

A recent theoretical study (Xu in Proc R Soc A Math Phys Eng Sci 477:20200913, 2021) has derived conditions on the coefficients of Jeffreys-type equation to predict thermal oscillations and resonance during phonon hydrodynamics in non-metallic solids. Thermal resonance, in which the temperature amplitude attains a maximum value (peak) in response to an external exciting frequency source, is a phenomenon pertinent to the presence of underdamped thermal oscillations and explicit finite speed for the thermal wave propagation. The present work investigates the occurrence condition for thermal resonance phenomenon during the electron–phonon interaction process in metals based on the hyperbolic two-temperature model. First, a sufficient condition for underdamped electron and lattice temperature oscillations is discussed by deriving a critical frequency (a material characteristic). It is shown that the critical frequency of thermal waves near room temperature, during electron–phonon interactions, may be on the order of terahertz ( 10 - 20 THz for Cu and Au, i.e., lying within the terahertz gap). It is found that whenever the natural frequency of metal temperature exceeds this frequency threshold, the temperature oscillations are of underdamped type. However, this condition is not necessary, since there is a small frequency domain, below this threshold, in which the underdamped thermal wave solution is available but not effective. Otherwise, the critical damping and the overdamping conditions of the temperature waves are determined numerically for a sample of pure metals. The thermal resonance conditions in both electron and lattice temperatures are investigated. The occurrence of resonance in both electron and lattice temperature is conditional on violating two distinct critical values of frequencies. When the natural frequency of the system becomes larger than these two critical values, an applied frequency equal to such a natural frequency can drive both electron and lattice temperatures to resonate together with different amplitudes and behaviors. However, the electron temperature resonates earlier than the lattice temperature. [ABSTRACT FROM AUTHOR]

Recent reports of room-temperature, ambient pressure superconductivity in copper-substituted lead phosphate apatite, commonly referred to as LK99, have prompted numerous theoretical and experimental studies into its properties. As the electron–phonon interaction is a common mechanism for superconductivity, the electron–phonon coupling strength is an important quantity to compute for LK99. In this work, we compare the electron–phonon coupling strength among the proposed compositions of LK99. The results of our study are in alignment with the conclusion that LK99 is a candidate for low-temperature, not room-temperature, superconductivity if electron–phonon interaction is to serve as the mechanism. [ABSTRACT FROM AUTHOR]

One‐third of monolayer of Sn adatoms on a Ge(111) substrate forms a 2D triangular lattice with one unpaired electron per site. The system presents a metal–insulator transition when decreasing the temperature and it is known to exhibit strong electron–phonon coupling at 120–150 K. Herein, a study of the electronic band structure for α‐Sn/Ge(111) between 150 and 5 K is reported. Both the experimental Fermi surfaces and the energy dispersions along high symmetry directions as a function of the temperature are presented. At 5 K it is observed a weakly or low‐dispersing spectral feature, exhibiting an extended gap in the reciprocal space. This feature is derived from the topmost occupied band, which is metallic at high temperature and which develops a kink associated with the strong electron–phonon coupling. The spectral evolution is partially explained with an increase of the electron–phonon coupling when decreasing the temperature. The increase of the electron–phonon coupling at low temperatures gives light into the new physics of this 2D system. The bandwidth is progressively reduced when reducing the temperature, enhancing the electronic correlation effects, and triggering the Mott transition. [ABSTRACT FROM AUTHOR]

Since the discovery of the high-temperature superconductors H3S and LaH10 under high pressure, compressed hydrides have received extensive attention as promising candidates for room-temperature superconductors. As a result of current high-pressure theoretical and experimental studies, it is now known that almost all the binary hydrides with a high superconducting transition temperature (T c) require extremely high pressure to remain stable, hindering any practical application. In order to further lower the stable pressure and improve superconductivity, researchers have started exploring ternary hydrides and had many achievements in recent years. Here, we discuss recent progress in ternary hydrides, aiming to deepen the understanding of the key factors regulating the structural stability and superconductivity of ternary hydrides, such as structural motifs, bonding features, electronic structures, electron–phonon coupling, etc. Furthermore, the current issues and challenges of superconducting ternary hydrides are presented, together with the prospects and opportunities for future research. [ABSTRACT FROM AUTHOR]

Localized excitation in traditional organic photocatalysts typically prevents the generation and extraction of photo‐induced free charge carriers, limiting their activity enhancement under illumination. Here, we enhance delocalized photoexcitation of small molecular photovoltaic catalysts by weakening their electron‐phonon coupling via rational fluoro‐substitution. The optimized 2FBP‐4F catalyst we develop here exhibits a minimized Huang–Rhys factor of 0.35 in solution, high dielectric constant and strong crystallization in the solid state. As a result, the energy barrier for exciton dissociation is decreased, and more importantly, polarons are unusually observed in 2FBP‐4F nanoparticles (NPs). With the increased hole transfer efficiency and prolonged charge carrier lifetime highly related to enhanced exciton delocalization, the PM6 : 2FBP‐4F heterojunction NPs at varied concentration exhibit much higher optimized photocatalytic activity (207.6–561.8 mmol h−1 g−1) for hydrogen evolution than the control PM6 : BP‐4F and PM6 : 2FBP‐6F NPs, as well as other reported photocatalysts under simulated solar light (AM 1.5G, 100 mW cm−2). [ABSTRACT FROM AUTHOR]

Localized excitation in traditional organic photocatalysts typically prevents the generation and extraction of photo‐induced free charge carriers, limiting their activity enhancement under illumination. Here, we enhance delocalized photoexcitation of small molecular photovoltaic catalysts by weakening their electron‐phonon coupling via rational fluoro‐substitution. The optimized 2FBP‐4F catalyst we develop here exhibits a minimized Huang–Rhys factor of 0.35 in solution, high dielectric constant and strong crystallization in the solid state. As a result, the energy barrier for exciton dissociation is decreased, and more importantly, polarons are unusually observed in 2FBP‐4F nanoparticles (NPs). With the increased hole transfer efficiency and prolonged charge carrier lifetime highly related to enhanced exciton delocalization, the PM6 : 2FBP‐4F heterojunction NPs at varied concentration exhibit much higher optimized photocatalytic activity (207.6–561.8 mmol h−1 g−1) for hydrogen evolution than the control PM6 : BP‐4F and PM6 : 2FBP‐6F NPs, as well as other reported photocatalysts under simulated solar light (AM 1.5G, 100 mW cm−2). [ABSTRACT FROM AUTHOR]

This paper investigates a wide‐band emitting red phosphor, an advancement that solves shortcomings including the re‐absorption of the yellow phosphor in the blue light area and a lack of red spectrum components which result in low color rendering and an uneven white light tone. An examination through femtosecond, Raman, and low‐temperature spectroscopy demonstrates why this phosphor has large Stokes shift (SS = 7.5×103 cm−1) and wide half‐peak width with a full‐width at half maximum (FWHM) of more than 170 nm. In these samples, it is importantly observed that larger lattice causes smaller electron–phonon coupling of Eu2+ activator, and meanwhile leads to less temperature dependency of emission peak width. The obtained sample, after cation replacement in (Ca1‐xSrx)7(SiO3)6Cl2: Eu2+ (CSSC: Eu2+), exhibits an emission spectrum covers the range from 450 to 800 nm while its excitation range is below 450 nm, in which not reabsorb the blue light. This matches well with blue phosphors that can also be excited by near‐ultraviolet chips. The fabricated white light‐emitting diode (w‐LED) device has an ideal color rendering index and correlated color temperature (Ra = 90.5, CCT = 3894 K), making it an excellent candidate material for white LED illumination. [ABSTRACT FROM AUTHOR]

High open‐circuit voltage (Voc) organic solar cells (OSCs) have received increasing attention because of their promising application in tandem devices and indoor photovoltaics. However, the lack of a precise correlation between molecular structure and stacking behaviors of wide band gap electron acceptors has greatly limited its development. Here, we adopted an asymmetric halogenation strategy (AHS) and synthesized two completely non‐fused ring electron acceptors (NFREAs), HF‐BTA33 and HCl‐BTA33. The results show that AHS significantly enhances the molecular dipoles and suppresses electron‐phonon coupling, resulting in enhanced intramolecular/intermolecular interactions and decreased nonradiative decay. As a result, PTQ10 : HF‐BTA33 realizes a power conversion efficiency (PCE) of 11.42 % with a Voc of 1.232 V, higher than that of symmetric analogue F‐BTA33 (PCE=10.02 %, Voc=1.197 V). Notably, PTQ10 : HCl‐BTA33 achieves the highest PCE of 12.54 % with a Voc of 1.201 V due to the long‐range ordered π–π packing and enhanced surface electrostatic interactions thereby facilitating exciton dissociation and charge transport. This work not only proves that asymmetric halogenation of completely NFREAs is a simple and effective strategy for achieving both high PCE and Voc, but also provides deeper insights for the precise molecular design of low cost completely NFREAs. [ABSTRACT FROM AUTHOR]

High open‐circuit voltage (Voc) organic solar cells (OSCs) have received increasing attention because of their promising application in tandem devices and indoor photovoltaics. However, the lack of a precise correlation between molecular structure and stacking behaviors of wide band gap electron acceptors has greatly limited its development. Here, we adopted an asymmetric halogenation strategy (AHS) and synthesized two completely non‐fused ring electron acceptors (NFREAs), HF‐BTA33 and HCl‐BTA33. The results show that AHS significantly enhances the molecular dipoles and suppresses electron‐phonon coupling, resulting in enhanced intramolecular/intermolecular interactions and decreased nonradiative decay. As a result, PTQ10 : HF‐BTA33 realizes a power conversion efficiency (PCE) of 11.42 % with a Voc of 1.232 V, higher than that of symmetric analogue F‐BTA33 (PCE=10.02 %, Voc=1.197 V). Notably, PTQ10 : HCl‐BTA33 achieves the highest PCE of 12.54 % with a Voc of 1.201 V due to the long‐range ordered π–π packing and enhanced surface electrostatic interactions thereby facilitating exciton dissociation and charge transport. This work not only proves that asymmetric halogenation of completely NFREAs is a simple and effective strategy for achieving both high PCE and Voc, but also provides deeper insights for the precise molecular design of low cost completely NFREAs. [ABSTRACT FROM AUTHOR]

Two-dimensional superconductors, especially the covalent metals such as borophene, have received significant attention due to their new fundamental physics, as well as potential applications. Furthermore, the bilayer borophene has recently ignited interest due to its high stability and versatile properties. Here, the mechanical and superconducting properties of bilayer- δ 6 borophene are explored by means of first-principles computations and anisotropic Migdal–Eliashberg analytics. We find that the coexistence of strong covalent bonds and delocalized metallic bonds endows this structure with remarkable mechanical properties (maximum 2D-Young's modulus of ~570 N/m) and superconductivity with a critical temperature of ~20 K. Moreover, the superconducting critical temperature of this structure can be further boosted to ~46 K by applied strain, which is the highest value known among all borophenes or two-dimensional elemental materials. [ABSTRACT FROM AUTHOR]

The discovery of covalent H3 S and clathrate structure LaH10 with excellent superconducting critical temperatures at high pressures has facilitated a multitude of research on compressed hydrides. However, their superconducting pressures are too high (generally above 150 GPa), thereby hindering their application. In addition, making room-temperature superconductivity close to ambient pressure in hydrogen-based superconductors is challenging. In this work, we calculated the chemically "pre-compressed" Be-H by heavy metals Th and Ce to stabilize the superconducting phase near ambient pressure. An unprecedented ThBeH8 (CeBeH8) with a "fluorite-type" structure was predicted to be thermodynamically stable above 69 GPa (76 GPa), yielding a Tc of 113 K (28 K) decompressed to 7 GPa (13 GPa) by solving the anisotropic Migdal-Eliashberg equations. Be-H vibrations play a vital role in electron-phonon coupling and structural stability of these ternary hydrides. Our results will guide further experiments toward synthesizing ternary hydride superconductors at mild pressures. [ABSTRACT FROM AUTHOR]

Structural mosaic of rare-earth tri-tellurides (RTe3) inlaid with non-classical structural motifs like the 2D-polytelluride square nets has attracted immense attention owing to their enigmatic chemical bonding, unconventional structure, and harboring charge density wave (CDW) ground states. GdTe3, an archetypal RTe3, is a natural heterostructure of charged and van der Waals (vdW) layers, formed by intercalating vdW gap separated 2D square telluride nets … between the charged double corrugated slabs of n[GdTe]+. Here, we have investigated the evolution of structural distortions along with the electrical and thermal transport properties of GdTe3 across its CDW transition through X-ray pair distribution function analysis, thermal conductivity measurements, Raman spectroscopy and first principles theoretical calculations. The results reveal that the unusual structure of GdTe3 engenders a large anisotropic lattice thermal conductivity by concomitantly hampering the phonon propagation along parallel to the spark plasma sintering (SPS) pressing direction via chemical bonding hierarchy while facilitating phonon propagation along perpendicular to the SPS pressing direction through the metallic Te sheets and phason channel. The low lattice thermal conductivity is attributed to the strong vibrational anharmonicity caused by CDW-induced concerted local lattice distortions of both Gd-Te slab and Te square net, and the robust electron-phonon coupling. [ABSTRACT FROM AUTHOR]

Highlights: The soft 2D material reduces the coupling strength between carriers and longitudinal optical phonons, releasing the mechanical stress of lattice vibration. The power conversion efficiency of rigid devices and flexible devices reaches 25.5% and 23.4%, respectively. This study presents experimental evidence of the dependence of non-radiative recombination processes on the electron–phonon coupling of perovskite in perovskite solar cells (PSCs). Via A-site cation engineering, a weaker electron–phonon coupling in perovskite has been achieved by introducing the structurally soft cyclohexane methylamine (CMA+) cation, which could serve as a damper to alleviate the mechanical stress caused by lattice oscillations, compared to the rigid phenethyl methylamine (PEA+) analog. It demonstrates a significantly lower non-radiative recombination rate, even though the two types of bulky cations have similar chemical passivation effects on perovskite, which might be explained by the suppressed carrier capture process and improved lattice geometry relaxation. The resulting PSCs achieve an exceptional power conversion efficiency (PCE) of 25.5% with a record-high open-circuit voltage (VOC) of 1.20 V for narrow bandgap perovskite (FAPbI3). The established correlations between electron–phonon coupling and non-radiative decay provide design and screening criteria for more effective passivators for highly efficient PSCs approaching the Shockley–Queisser limit. [ABSTRACT FROM AUTHOR]

Though YB6 and LaB6 share the same crystal structure, atomic valence electron configuration, and phonon modes, they exhibit drastically different phonon-mediated superconductivity. YB6 superconducts below 8.4 K, giving it the second-highest critical temperature of known borides, second only to MgB2. LaB6 does not superconduct until near-absolute zero temperatures (below 0.45 K), however. Though previous studies have quantified the canonical superconductivity descriptors of YB6's greater Fermi-level (Ef ) density of states and higher electron-phonon coupling (EPC), the root of this difference has not been assessed with full detail of the electronic structure. Through chemical bonding, we determine low-lying, unoccupied 4f atomic orbitals in lanthanum to be the key difference between these superconductors. These orbitals, which are not accessible in YB6, hybridize with π B-B bonds and bring this π-system lower in energy than the σ B-B bonds otherwise at Ef. This inversion of bands is crucial: the optical phonon modes we show responsible for superconductivity cause the σ-orbitals of YB6 to change drastically in overlap, but couple weakly to the π-orbitals of LaB6. These phonons in YB6 even access a crossing of electronic states, indicating strong EPC. No such crossing in LaB6 is observed. Finally, a supercell (the M k-point) is shown to undergo Peierls-like effects in YB6, introducing additional EPC from both softened acoustic phonons and the same electron-coupled optical modes as in the unit cell. Overall, we find that LaB6 and YB6 have fundamentally different mechanisms of superconductivity, despite their otherwise near-identity. [ABSTRACT FROM AUTHOR]

In recent years, there has been a growing emphasis on the exploration of sustainable and eco-friendly materials well-suited for advanced applications in the realms of thermoelectrics and optoelectronics. Lead-free halide double perovskites have emerged as a compelling class of materials in this context. Nevertheless, despite their potential utility, thorough investigations into their thermal transport characteristics remain limited. In this systematic investigation, we employ density functional theory (DFT) and post-DFT techniques to elucidate the essential stability parameters, transport properties, and carrier-lattice interactions of the metal halide-based Cs2MGaBr6 (X = Li, Ga) double perovskites. Our assessment of structural stability involves a meticulous description of stability index parameters and the optimization of pristine structures using the GGA-PBE potential. Additionally, we calibrate the electronic structure while taking spin–orbit coupling (SOC) effects into consideration by using a combination of GGA and GGA + mBJ potentials. Our findings reveal that the TB-mBJ derived band gaps of 1.82 eV and 1.78 eV for Cs2LiGaBr6 and Cs2NaGaBr6 reside within the visible spectrum, prompting further investigation into their thermal transport characteristics. Moreover, we analyze the phonon characteristics and vibrational modes, extending our investigation to examine the electron–phonon coupling strength. The scrutiny of the Fröhlich coupling constant and the Feynman polaron radius unveils a stronger electron–phonon coupling strength. In the domain of thermoelectrics, the significant figure of merit (zT) values of 1.08 and 1.04 for Cs2LiGaBr6 and Cs2NaGaBr6, respectively, emphasize the considerable potential of these materials for deployment in renewable energy applications. Furthermore, our computational investigation into optical properties, including the dielectric constant, optical absorption, and refractive index, demonstrates optimal performance within the visible spectrum. Specifically, elevated absorption coefficient values of 30 × 10 4 cm - 1 for Cs2LiGaBr6 and 40 × 10 4 cm - 1 for Cs2NaGaBr6 are noted across visible and infrared spectra, highlighting their promising potential in optoelectronic and solar cell technologies. [ABSTRACT FROM AUTHOR]

Single‐component white‐light emitters are ideal for solid‐state lighting applications. Here, the dual‐emission white light in the 3D Cs2NaInCl6:0.1 Sb3+ crystal is successfully achieved by the high‐pressure treatment strategy. Upon compression, the remarkable self‐trapped exciton (STE) emission enhancement is observed at 20.6 GPa due to the tilting and twisting of inorganic octahedron caused by the phase transition of Cs2NaInCl6:0.1 Sb3+ crystal. Intriguingly, after undergoing the high‐pressure treatment, in addition to the blue high‐energy emission from the STEs, [SbCl6]3− exhibits the orange low‐energy emission from STEs, which is ascribed to the remaining local distortion of inorganic octahedron resulting from the presence of residual amorphous phase in the local region upon decompression. Furthermore, coherent phonon generation and density functional theory calculations indicate that the electrons exhibit a strong coupling to A1g stretch mode and T2gIn bending mode in Cs2NaInCl6:0.1 Sb3+. After high‐pressure treatment, the coupling between the electrons and the T2gIn bending mode disappears, suggesting local octahedral symmetry disruption due to residual amorphous structures induced by high‐pressure treatment. This work unveils the relationship between the electron‐phonon coupling and the STE emission and offers a new strategy to design and synthesize the new single‐component white‐light metal halide perovskites. [ABSTRACT FROM AUTHOR]

To assess the potential optoelectronic applications of metal‐halide perovskites, it is critical to have a detailed understanding of the nature and dynamics of interactions between carriers and the polar lattices. Here, the electronic and structural dynamics of bismuth‐based perovskite Cs3Bi2I9 are revealed by transient reflectivity and ultrafast electron diffraction. A cross‐examination of these results combined with theoretical analyses allows the identification of the major carrier–phonon coupling mechanism and the associated time scales. It is found that carriers photoinjected into Cs3Bi2I9 form self‐trapped excitons on an ultrafast time scale. However, they retain most of their energy, and their coupling to Fröhlich‐type optical phonons is limited at early times. Instead, the long‐lived excitons exert an electronic stress via deformation potential and develop a prominent, sustaining strain field as coherent acoustic phonons in 10 ps. From sub‐ps to ns and beyond, a similar extent of the atomic displacements is found throughout the different stages of structural distortions, from limited local modulations to a coherent strain field to the Debye–Waller random atomic motions on longer times. The current results suggest the potential use of bismuth‐based perovskites for applications other than photovoltaics to take advantage of the carriers' stronger self‐trapping and long lifetimes. [ABSTRACT FROM AUTHOR]

Lead‐free halide double perovskites (HDPs) have emerged as a new generation of thermochromic materials. However, further materials development and mechanistic understanding are required. Here, a highly stable HDP Cs2NaFeCl6 single crystal is synthesized, and its remarkable and fully reversible thermochromism with a wide color variation from light‐yellow to black over a temperature range of 10 to 423 K is investigated. First‐principles, density functional theory (DFT)‐based calculations indicate that the thermochromism in Cs2NaFeCl6 is an effect of electron–phonon coupling. The temperature sensitivity of the bandgap in Cs2NaFeCl6 is up to 2.52 meVK−1 based on the Varshni equation, which is significantly higher than that of lead halide perovskites and many conventional group‐IV, III–V semiconductors. Meanwhile, this material shows excellent environmental, thermal, and thermochromic cycle stability. This work provides valuable insights into HDPs' thermochromism and sheds new light on developing efficient thermochromic materials. [ABSTRACT FROM AUTHOR]

Electron‐phonon interactions, crucial in condensed matter, are rarely seen in Metal–Organic Frameworks (MOFs). Detecting these interactions typically involves analyzing luminescence in lanthanide‐ or actinide‐based compounds. Prior studies on Ln‐ and Ac‐based MOFs at high temperatures revealed additional peaks, but these were too faint for thorough analysis. In our research, we fabricated a high‐quality, crystalline uranium‐based MOF (KIT‐U‐1) thin film using a layer‐by‐layer method. Under UV light, this film showed two distinct "hot bands," indicating a strong electron‐phonon interaction. At 77 K, these bands were absent, but at 300 K, a new emission band appeared with half the intensity of the main luminescence. Surprisingly, a second hot band emerged above 320 K, deviating from previous findings in rare‐earth compounds. We conducted a detailed ab‐initio analysis employing time‐dependent density functional theory to understand this unusual behaviour and to identify the lattice vibration responsible for the strong electron‐phonon coupling. The KIT‐U‐1 film's hot‐band emission was then utilized to create a highly sensitive, single‐compound optical thermometer. This underscores the potential of high‐quality MOF thin films in exploiting the unique luminescence of lanthanides and actinides for advanced applications. [ABSTRACT FROM AUTHOR]

In recent years, there has been a growing emphasis on the exploration of sustainable and eco-friendly materials well-suited for advanced applications in the realms of thermoelectrics and optoelectronics. Lead-free halide double perovskites have emerged as a compelling class of materials in this context. Nevertheless, despite their potential utility, thorough investigations into their thermal transport characteristics remain limited. In this systematic investigation, we employ density functional theory (DFT) and post-DFT techniques to elucidate the essential stability parameters, transport properties, and carrier-lattice interactions of the metal halide-based Cs2MGaBr6 (X = Li, Ga) double perovskites. Our assessment of structural stability involves a meticulous description of stability index parameters and the optimization of pristine structures using the GGA-PBE potential. Additionally, we calibrate the electronic structure while taking spin–orbit coupling (SOC) effects into consideration by using a combination of GGA and GGA + mBJ potentials. Our findings reveal that the TB-mBJ derived band gaps of 1.82 eV and 1.78 eV for Cs2LiGaBr6 and Cs2NaGaBr6 reside within the visible spectrum, prompting further investigation into their thermal transport characteristics. Moreover, we analyze the phonon characteristics and vibrational modes, extending our investigation to examine the electron–phonon coupling strength. The scrutiny of the Fröhlich coupling constant and the Feynman polaron radius unveils a stronger electron–phonon coupling strength. In the domain of thermoelectrics, the significant figure of merit (zT) values of 1.08 and 1.04 for Cs2LiGaBr6 and Cs2NaGaBr6, respectively, emphasize the considerable potential of these materials for deployment in renewable energy applications. Furthermore, our computational investigation into optical properties, including the dielectric constant, optical absorption, and refractive index, demonstrates optimal performance within the visible spectrum. Specifically, elevated absorption coefficient values of 30 × 10 4 cm - 1 for Cs2LiGaBr6 and 40 × 10 4 cm - 1 for Cs2NaGaBr6 are noted across visible and infrared spectra, highlighting their promising potential in optoelectronic and solar cell technologies. [ABSTRACT FROM AUTHOR]

Excited-states play a crucial role in the optical absorption and luminescence of solids and hence their accurate information is highly desired. Herein, we attempt to seize the excited-states information of Mn4+ ions in K2SiF6 microcrystals via measuring and calculating their variable-temperature photoluminescence excitation (PLE) spectra. At cryogenic temperatures, an unpredicted splitting of the high-excited-state is observed. Moreover, the two-split high-excited-state levels are further revealed to primarily couple with the two hyperfine split modes of quasi-localized v2 vibration in the distorted Mn-F6 octahedral configuration, whereas the coupling strengths are found to be substantially different from each other. The slightly split vibrational mode is firmly supported by the low-temperature Raman spectra. Jahn-Teller lattice distortion is believed to be responsible for the observed splitting of the electronic high-excited-state and the quasi-localized vibrational mode. [ABSTRACT FROM AUTHOR]

Gallium antimonide (GaSb) is a III-V semiconductor of technological interest for low-power, high-mobility field-effect transistors, as well as for mid-wave infrared detectors. In such devices, GaSb interfaces with other III–V semiconductors with different lattice constants that can induce strain in the GaSb layers. Two dominant limiting factors in hot carrier relaxation are the intra-valley and the inter-valley electron–phonon (e-ph) scattering. In GaSb, these are sensitive to the Γ –L energy ordering, which depend intimately on the strain. Here, we report ab initio calculations of electronic structure, phonon dispersion, e-ph scattering and relaxation times for GaSb as a function of strain. As observed previously for other group IV and III-V semiconductors, our results show strong anisotropy, a strong contribution from LO phonons, and the need to go beyond the deformation potential scattering. For GaSb, the main finding is that a compressive strain between 0.4% and 0.6% converts GaSb from a direct-bandgap semiconductor to an indirect-bandgap semiconductor, with dramatic changes in the competing scattering rates and carrier relaxation times. [ABSTRACT FROM AUTHOR]

Bismuth halide perovskites are highly promising for various applications owing to their lower toxicity and greater environmental stability. The temperature‐dependent color tunability of these materials renders them a strong contender for use in smart window applications and temperature sensors. To delve deeper into their properties, the thermochromism and fundamental lattice dynamics are investigated in bismuth halide perovskites through the transmutation of cation and anions, specifically focusing on Cs3Bi2Br9, MA3Bi2Br9, Cs2AgBiBr6, and Cs2AgBiCl6 perovskites. Absorption spectroscopy and powder‐XRD patterns as a function of temperature reveal that 2D‐layered Cs3Bi2Br9 and MA3Bi2Br9 perovskites exhibit significantly greater bandgap changes and thermal expansion compared to 3D connected Cs2AgBiCl6 and Cs2AgBiBr6 perovskites attributed to more space in the 2D connected lattice. The reduction in bandgap and color variation in these perovskites stems from the intricate interplay between electron‐phonon interactions and thermal expansion. Notably, it is found that the type of cation and anion play a crucial role in influencing the degree of thermochromism, as the electron‐phonon coupling depends on this transformation. This study sheds new light on the fundamental mechanisms underlying the thermochromic behavior of bismuth halide perovskites and paves the way for the rational design and engineering of novel thermochromic materials with tailored properties. [ABSTRACT FROM AUTHOR]

Many issues concerning the origin of high-temperature superconductivity (HTS) are still under debate. For example, how the magnetic order varies with doping and its relationship with the superconducting temperature (Tc); and why Tc always peaks near the quantum critical point. In this paper, taking hole-doped La2CuO4 as a classical example, we employ the first-principles band structure and total energy calculations with Monte Carlo simulations to explore how the symmetry-breaking magnetic ground state evolves with hole doping and the origin of a dome-shaped superconductivity region in the phase diagram. We demonstrate that the local antiferromagnetic order and doping play key roles in determining the electron-phonon coupling, thus Tc. Initially, the La2CuO4 possesses a checkerboard local antiferromagnetic ground state. As the hole doping increases, Tc increases with the enhanced electron-phonon coupling strength. But as the doping increases further, the strength of the antiferromagnetic interaction weakens and spin fluctuation increases. At the critical doping level, a magnetic phase transition occurs that reduces the local antiferromagnetism-assisted electron-phonon coupling, thus diminishing the Tc. The superconductivity disappears in the heavily overdoped region when the ferromagnetic order dominates. These observations could account for why cuprates have a dome-shaped superconductivity region in the phase diagram. Our study, thus, contributes to a fundamental understanding of the correlation between doping, local magnetic order, and superconductivity of HTS. [ABSTRACT FROM AUTHOR]

The charge density wave (CDW) instability, usually occurring in low-dimensional metals, has been a topic of interest for longtime. However, some very fundamental aspects of the mechanism remain unclear. Recently, a plethora of new CDW materials, a substantial fraction of which is two-dimensional or even three-dimensional, has been prepared and characterised as bulk and/or single-layers. As a result, the need for revisiting the primary mechanism of the instability, based on the electron–hole instability established more than 50 years ago for quasi-one-dimensional (quasi-1D) conductors, has clearly emerged. In this work, we consider a large number of CDW materials to revisit the main concepts used in understanding the CDW instability, and emphasise the key role of the momentum dependent electron–phonon coupling in linking electronic and structural degrees of freedom. We argue that for quasi-1D systems, earlier weak coupling theories work appropriately and the energy gain due to the CDW and the concomitant periodic lattice distortion (PLD) remains primarily due to a Fermi surface nesting mechanism. However, for materials with higher dimensionality, intermediate and strong coupling regimes are generally at work and the modification of the chemical bonding network by the PLD is at the heart of the instability. We emphasise the need for a microscopic approach blending condensed matter physics concepts and state-of-the-art first-principles calculations with quite fundamental chemical bonding ideas in understanding the CDW phenomenon in these materials. [ABSTRACT FROM AUTHOR]

Electron–phonon coupling (EPC) and phonon–phonon scattering (PPS) are at the core of the microscopic physics mechanisms of vast quantum materials. However, to date, there are rarely reports that these two processes can be spatially separated, although they are usually temporally detached with different characteristic lifetimes. Here, by employing ultrafast spectroscopy to investigate the photo‐carrier ultrafast dynamics in a LaCoO3 thin film on a (100) SrTiO3 substrate, intriguing evidence is found that the two interactions are indeed spatially separated. The EPC mainly occurs in the thin film, whereas PPS is largely in the substrate, especially at the several atomic layers near the interface. Across‐interface penetration and decay of optical phonons into acoustic phonons thus naturally occur. An EPC strength λEg = 0.30 is also obtained and an acoustic phonon mode at 45.3 GHz is observed. The finding lays out a cornerstone for future quantum nano device designs. [ABSTRACT FROM AUTHOR]

Hybrid inorganic/organic systems (HIOS) open new avenues for tailoring them with respect to desired features and functions by exploiting the respective advantages of their components. Therefore, these materials are actively explored in many experimental studies and devices. On the theory side, similar investigations are rather scarce as such interfaces, in addition to exhibiting large unit cells, require highest‐level theories to be described reliably. Consequently, hybrid materials pose a challenge for electronic structure theory, starting from density‐functional theory to methods beyond, particularly many‐body perturbation theory. This concerns both conceptual aspects and computational bottlenecks. In this perspective, the performance of state‐of‐the‐art theoretical approaches applied to HIOS is summarized, mainly focusing on optoelectronic properties. Recent achievements, open challenges, and urgent needs are addressed. [ABSTRACT FROM AUTHOR]

Using first-principles calculations, we predict a new type of two-dimensional (2D) beryllium(Be)-decorated T-graphene named BeC2, where Be atoms are inserted into C–C bonds linking the carbon tetrarings of T-graphene. The band structure shows that BeC2 is metallic, thus, the possible phonon-mediated superconductivity is explored based on the Eliashberg equation. The calculated electron-phonon coupling (EPC) constant λ is up to 4.07, and the corresponding superconducting critical temperature (Tc) is 72.1 K, approaching the liquid nitrogen temperature. The reason for the high Tc is the strong EPC. And it is proved to be an anisotropic single-gap superconductor by analyzing the superconducting gap Δk of BeC2. The electronic susceptibility calculation shows strong nesting effect in BeC2. Since rare 2D superconductors show such a strong EPC constant λ which originates from the coupling between electrons in C–pz orbital and in-plane vibrations of Be and C atoms, the predicted BeC2 provides a new platform for investigating strong EPC 2D superconductor. [ABSTRACT FROM AUTHOR]

Perovskites have been recognized as a class of promising materials for optoelectronic devices. We intentionally include excessive Cs+ cations in precursors in the synthesis of perovskite CsPbBr3 nanocrystals and investigate how the Cs+ cations influence the lattice strain in these perovskite nanocrystals. Upon light illumination, the lattice strain due to the addition of alkali metal Cs+ cations can be compensated by light–induced lattice expansion. When the Cs+ cation in precursors is about 10% excessive, the electron–phonon coupling strength can be reduced by about 70%, and the carrier cooling can be slowed down about 3.5 times in lead halide perovskite CsPbBr3 nanocrystals. This work reveals a new understanding of the role of Cs+ cations, which take the A–site in ABX3 perovskite and provide a new way to improve the performance of perovskites and their practical devices further. [ABSTRACT FROM AUTHOR]

Understanding the full electron–phonon and phonon–phonon interaction effects in semiconductors is crucial for tuning electronic and phonon transport properties with the purpose to the enhancement of thermoelectric performances. In this work, based on the detailed investigations on 2D lead phosphorene (PbP) by using the first‐principle calculations, it is demonstrated that, in α−$\alpha -$, β−$\beta -$, and γ−$\gamma -$PbP, the electron–phonon interactions are significantly stronger than conventional group‐IV monolayers such as silicene by five orders in magnitude, and intravalley scatterings dominate over the intervalley scattering due to less degenerate band extrema near Fermi level. Based on the selection‐rule analysis, it is found that the symmetry breaking in the janus γ phase compared to the higher‐symmetry α phase allows fewer symmetry operations, leading to more allowed scattering channels for electrons and phonons, subsequently suppressing the electron and phonon transport in γ−$\gamma -$PbP. Due to the low Debye temperatures, and strong four‐phonon interactions, the lattice thermal conductivities at room temperature in these monolayers are sharply decreased. Finally, it is found that the maximum thermoelectric figure of merits for these three monolayers reach 0.90/0.24/1.25 at room temperature, respectively. This work not only paves the way for the promising applications of PbP monolayers in thermoelectric devices, but also suggests that symmetry breaking and strong high‐order phonon–phonon interactions are crucial to identifying excellent thermoelectric materials. [ABSTRACT FROM AUTHOR]

Broadband emission induced by self‐trapped excitons (STEs) in double halide perovskites (DHPs) has received continuous attention in recent years. However, the comprehensive understanding of the STEs formation mechanism is still in its early stage. The corresponding roles of different B‐site cations also remain unclear in these advanced materials. The lack of an effective STEs database for DHPs hinders the efficient discovery of potential optoelectronic materials with strong STEs. Herein, a systematic STEs database is built for DHPs through density functional theory (DFT) calculations and proposed a highly efficient predictive machine learning (ML) model of the Huang–Rhys factor S for the first time. Results reveal the different contributions of two B‐site metal cations to the formation of STEs in DHPs, which helps to understand the in‐depth nature of STEs. Based on the accurate predictions of the effective phonon frequency ωLO$\left(\omega\right)_{\text{LO}}$ , it is further realized that the prediction of S without conducting the time‐consuming phonon property calculations of DHPs offers new opportunities for exploring the STEs. Combining DFT calculations and ML techniques, this study supplies an effective approach to efficiently discover the potential novel optoelectronic materials, which provides important guidance for the future exploration of promising solid‐state phosphors. [ABSTRACT FROM AUTHOR]

Recently, it was demonstrated that inelastic helium atom scattering from conducting surfaces provides a direct measurement of the surface electron–phonon coupling constant (mass enhancement factor λ) via the temperature or the incident wave vector dependence of the Debye–Waller exponent. Here, previous published as well as unpublished helium atom scattering diffraction data from the vicinal surfaces of copper (Cu(11α), with α = 3, 5, 7) and aluminum (Al(221) and Al(332)) were analyzed to determine λ. The results suggested an enhancement with respect to the corresponding data for the low-index surfaces (111) and (001) above the roughening transition temperature. The specific role of steps compared to that of terraces is briefly discussed. [ABSTRACT FROM AUTHOR]

To explore carbide superconductors with higher transition temperature, two novel carbon structures of cage‐network are designed and their superconductivity is studied by doping metals. MC6 and MC10 are respectively identified as C24 and C32 cage‐network structures. This study finds that both carbon structures drive strong electron–phonon interaction and can exhibit superconductivity above liquid nitrogen temperature. Importantly, the superconducting transition temperatures above 100 K are predicted to be achieved in C24‐cage‐network systems doped by Na, Mg, Al, In, and Tl at ambient pressure, which is far higher than those in graphite, fullerene, and other carbides. Meanwhile, the superconductivity of cage‐network carbides is also found to be sensitive to the electronegativity and concentration of dopant M. The result indicates that the higher transition temperatures can be obtained by optimizing the carbon‐cage‐network structures and the doping conditions. The study suggests that the carbon‐cage‐network structure is a direction to explore high‐temperature superconducting carbides. [ABSTRACT FROM AUTHOR]

The electron-phonon interaction can reveal the microscopic mechanism of heat transfer in metals. The two-step heat conduction considering electron-phonon interaction has become an effective theoretical model for extreme environments, such as micro-scale and ultrafast processes. In this work, the two-step heat transfer model is further extended by considering the Burgers heat conduction model with the second-order heat flux rate for electrons. Then, a novel generalized electron-phonon coupling thermoelasticity is proposed with the Burgers electronic heat transfer. Then, the problem of one-dimensional semi-infinite copper strip subject to a thermal shock at one side is studied by the Burgers two-step (BTS) model. The thermoelastic analytical solutions are systematically derived in the Laplace domain, and the numerical Laplace inversion method is adopted to obtain the transient responses. The new model is compared with the parabolic two-step (PTS) model and the hyperbolic two-step (HTS) model. The results show that in ultrafast heating, the BTS model has the same wave front jump as the HTS model. The present model has the faster wave speed, and predicts the bigger disturbed regions than the HTS model. More deeply, all two-step models also have the faster wave speeds than one-step models. This work may benefit the theoretical modeling of ultrafast heating of metals. [ABSTRACT FROM AUTHOR]