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AlSb and AlAs have attracted renewed interest in recent years as promising photovoltaic (PV) materials due to significant light absorption, eco-friendliness, and low cost. Here, density functional theory (DFT) in combination with the non-equilibrium Green's function method (NEGF) has been used to compute the temperature-dependent PV parameters of nanoscale AlSb and AlAs p-n junction solar cell devices. In particular, the influence of electron-phonon coupling (EPC) and spin-orbit coupling (SOC) on the PV properties of these devices is investigated. Our results highlight the importance of inclusion of EPC in evaluating the ab initio PV properties of p-n junctions at finite temperatures. At non-zero temperatures, the PV parameters can differ significantly compared to those at zero temperature due to phonon-assisted tunnelling of charge carriers across the p-n junction. In particular, the mobility of low-effective-mass carriers at the p-n junction is found to be enhanced by phonon scattering, which in turn results in improved PV transport properties. The short-circuit current (J sc) at 300 K proved to be 21.7% (16.2%) higher for AlSb (AlAs) than that at 0 K. On the other hand, the open-circuit voltage (V oc) at 300 K proved to be 19.1% (16.7%) lower for AlSb (AlAs) than that at 0 K. J sc is higher in AlSb than in AlAs due to higher phonon-influenced mobility of low-effective-mass carriers. Overall, our study strongly suggests the importance of inclusion of EPC and hence phonon scattering in the first-principles quantitative determination of PV parameters of solar cells. The estimates obtained in this study may be utilized as input ab initio parameters in continuum-model-based multi-scale simulations of AlSb and AlAs p-n homo-junction solar cells. • Photovoltaic (PV) parameters of nanoscale AlSb and AlAs p-n junction are studied using DFT + NEGF methods. • PV properties investigated under influence of electron-phonon coupling and spin-orbit coupling. • The phonon scattering with low effective mass carriers across the p-n junction influence the PV transport properties. [ABSTRACT FROM AUTHOR]

The origin of the ubiquitous low-frequency shoulder on the longitudinal optical (LO) phonon fundamental in the Raman spectra of CdSe quantum dots is examined. This feature is usually assigned as a "surface optical" (SO) phonon, but it is only slightly affected by modifying the surface through exchanging ligands or adding a semiconductor shell. Here we present excitation profile data showing that the low-frequency shoulder loses intensity as the excitation is tuned to longer wavelengths, closer to resonance with the lowest-energy 1Se-1S3/2 excitonic transition. Calculations of the resonance Raman spectra are carried out using a fully atomistic model with an empirical force field to calculate the phonon modes and the standard effective mass approximation envelope function model to calculate the electron and hole wave functions. When a force field of the Tersoff type is used, the calculated spectra closely resemble the experimental ones in showing mainly the higher-frequency LO phonon with 1Se-1S3/2 resonance but showing intensity in lower-frequency features with 1Pe-1P3/2 resonance. These calculations indicate that the main LO phonon peak involves largely motion of the interior atoms, while the low-frequency shoulder is more equally distributed throughout the crystal but not surface-localized. Interestingly, very different results are obtained with the widely used Coulomb plus Lennard-Jones force field developed by Rabani, which predicts far more disordered structures and more localized phonon modes for the nanocrystals compared with the Tersoff-type potential.

The role of the electronic system in high energy displacement cascades is explored. The energy exchange between the electronic and the atomic subsystem is described by the electron–phonon coupling. The electronic effects on the damage accumulation due to 100 keV Ni ion cascades in nickel, a prototype system to a large group of nickel-based high entropy alloys, are investigated for overlapping cascades. It is shown that the energy exchange between the two subsystems affects microstructure evolution, resulting in the formation of smaller clusters and more isolated defects. This effect is more significant for the vacancy cluster formation and size distribution.

The nitrogen-vacancy (NV) center in diamond is a solid-state defect qubit with favorable coherence time up to room temperature, which could be harnessed in several quantum-enhanced sensor and quantum communication applications, and has a potential in quantum simulation and computing. The quantum control largely depends on the intricate details about the electronic structure and states of the NV center, the radiative and nonradiative rates between these states, and the coupling of these states to external spins, electric, magnetic, and strain fields, and temperature. This review shows how first-principles calculations contributed to understanding the properties of the NV center and briefly discusses the issues to be solved toward the full ab initio description of solid-state defect qubits.

Abstract Understanding the physics of strongly correlated electronic systems has been a central issue in condensed matter physics for decades. In transition metal oxides, strong correlations characteristic of narrow d bands are at the origin of remarkable properties such as the opening of Mott gap, enhanced effective mass, and anomalous vibronic coupling, to mention a few. SrVO3 with V4+ in a 3d1 electronic configuration is the simplest example of a 3D correlated metallic electronic system. Here, the authors' focus on the observation of a (roughly) quadratic temperature dependence of the inverse electron mobility of this seemingly simple system, which is an intriguing property shared by other metallic oxides. The systematic analysis of electronic transport in SrVO3 thin films discloses the limitations of the simplest picture of e–e correlations in a Fermi liquid (FL); instead, it is shown show that the quasi‐2D topology of the Fermi surface (FS) and a strong electron–phonon coupling, contributing to dress carriers with a phonon cloud, play a pivotal role on the reported electron spectroscopic, optical, thermodynamic, and transport data. The picture that emerges is not restricted to SrVO3 but can be shared with other 3d and 4d metallic oxides.

The electronic structure and the electron‐phonon couplings in a novel mass‐production‐compatible Al2O3/TiO2 2D electron system (2DES) are investigated using resonant inelastic soft X‐ray scattering. The experimental data from the samples of various TiO2 thicknesses unequivocally show that the Ti3+ state indeed exists at the deep interface to serve as an n‐type dopant for the 2DES. The electronic structure of Ti3+ species is scrutinized as entirely separated from that of the Ti4+ host lattice. Furthermore, features of sub‐eV energy loss phonon modes are clearly observed, indicating substantial electron‐phonon coupling effects. Such low energy loss features are enhanced in thinner TiO2 samples, implying that polaronic local lattice deformation is enhanced due to the presence of Ti3+. These findings suggest that the 2DES properties can be controlled via well‐established TiO2 engineering, thereby enthroning the binary oxide heterostructure as a promising candidate for 2DES device applications. [ABSTRACT FROM AUTHOR]

Understanding the physics of strongly correlated electronic systems has been a central issue in condensed matter physics for decades. In transition metal oxides, strong correlations characteristic of narrow d bands are at the origin of remarkable properties such as the opening of Mott gap, enhanced effective mass, and anomalous vibronic coupling, to mention a few. SrVO3 with V4+ in a 3d1 electronic configuration is the simplest example of a 3D correlated metallic electronic system. Here, the authors' focus on the observation of a (roughly) quadratic temperature dependence of the inverse electron mobility of this seemingly simple system, which is an intriguing property shared by other metallic oxides. The systematic analysis of electronic transport in SrVO3 thin films discloses the limitations of the simplest picture of e–e correlations in a Fermi liquid (FL); instead, it is shown show that the quasi‐2D topology of the Fermi surface (FS) and a strong electron–phonon coupling, contributing to dress carriers with a phonon cloud, play a pivotal role on the reported electron spectroscopic, optical, thermodynamic, and transport data. The picture that emerges is not restricted to SrVO3 but can be shared with other 3d and 4d metallic oxides. [ABSTRACT FROM AUTHOR]

Electron-phonon coupling affects the properties of two-dimensional (2D) materials significantly, leading to a series of novel phenomena. Inelastic light scattering provides a powerful experimental tool to explore electron-phonon interaction in 2D materials. This review gives an overview of the basic theory and experimental advances of electron-phonon coupling in 2D materials detected by Raman and Brillouin scattering, respectively. In the Raman scattering part, we review Raman spectroscopy studies of electron-phonon coupling in graphene, transition metal disulfide compounds, van der Waals heterostructures, strongly correlated systems, and 2D magnetic materials. In the Brillouin scattering part, we extensively introduce Brillouin spectroscopy in non-van der Waals 2D structures, including temperature sensors for phonons and magnons, interfacial Dzyaloshinsky-Moriya interaction and spin torque in multilayer magnetic structures, as well as exciton-polariton in semiconductor quantum well. [ABSTRACT FROM AUTHOR]

Resonance Raman spectra and absolute differential Raman cross-sections have been measured for CdSe nanocrystals in both the wurtzite and zincblende crystal forms at four excitation wavelengths from 457.9 to 514.5 nm. The frequency and bandshape of the longitudinal optical (LO) phonon fundamental is essentially identical for both crystal forms at each excitation wavelength. The LO phonon overtone to fundamental intensity ratio appears to be slightly higher for the wurtzite form, which may suggest slightly stronger exciton-phonon coupling from the Fröhlich mechanism in the wurtzite form. The LO fundamental Raman cross-sections are very similar for both crystal forms at each excitation wavelength. © 2012 Elsevier B.V. All rights reserved.

In this work, oxygen vacancies in MgAl2O4 crystal were investigated using the first-principles. The Heyd-Scuseria-Ernzerhof (HSE) was adopted to reproduce the experimental band gap. The finite-size correction scheme was applied to eliminate the unreal interaction between charged defects and their periodic images. Finally, taking into account of the electron-phonon coupling, we obtained the optical spectra of the F and F+ centres. The absorption peaks for the F and F+ centres are at 5.04 eV and 4.67 eV, respectively. Furthermore, we calculate the emission peak for the F centre is 3.28 eV. Comparing with the experimental results, the emission peak at 2.15 eV is related to the F+ centre. [ABSTRACT FROM AUTHOR]

Perovskite variants have attracted wide interest because of the lead-free nature and strong self-trapped exciton (STE) emission. Divalent Sn(II) in CsSnX3 perovskites is easily oxidized to tetravalent Sn(IV), and the resulted Cs2SnCl6 vacancy-ordered perovskite variant exhibits poor photoluminescence property although it has a direct band gap. Controllable doping is an effective strategy to regulate the optical properties of Cs2SnX6. Herein, combining the first principles calculation and spectral analysis, we attempted to understand the luminescence mechanism of Te4+-doped Cs2SnCl6 lead-free perovskite variants. The chemical potential and defect formation energy are calculated to confirm theoretically the feasible substitutability of tetravalent Te4+ ions in Cs2SnCl6 lattices for the Sn-site. Through analysis of the absorption, emission/excitation, and time-resolved photoluminescence (PL) spectroscopy, the intense green-yellow emission in Te4+:Cs2SnCl6 was considered to originate from the triplet Te(IV) ion 3P1→1S0 STE recombination. Temperature-dependent PL spectra demonstrated the strong electron-phonon coupling that inducing an evident lattice distortion to produce STEs. We further calculated the electronic band structure and molecular orbital levels to reveal the underlying photophysical process. These results will shed light on the doping modulated luminescence properties in stable lead-free Cs2MX6 vacancy-ordered perovskite variants and be helpful to understand the optical properties and physical processes of doped perovskite variants. [ABSTRACT FROM AUTHOR]

Metal halide perovskites have drawn tremendous attention in optoelectronic applications owing to the rapid development in photovoltaic and light‐emitting diode devices. More recently, these materials are demonstrated as excellent gain media for laser applications due to their large absorption coefficient, low defect density, high charge carrier mobility, long carrier diffusion length, high photoluminescence quantum yield, and low Auger recombination rate. Despite the great progress in laser applications, the development of perovskite lasers is still in its infancy and the realization of electrically pumped lasers has not yet been demonstrated. To accelerate the development of perovskite‐based lasers, it is important to understand the fundamental photophysical characteristics of perovskite gain materials. Here, the structure and gain behavior in various perovskite materials are discussed. Then, the effects of charge carrier dynamics and electron–phonon interaction on population inversion in different types of perovskite materials are analyzed. Further, recent advances in perovskite‐based lasers are also highlighted. Finally, a perspective on perovskite material design is presented and the remaining challenges of perovskite lasers are discussed. [ABSTRACT FROM AUTHOR]

Tin oxide‐encapsulated tin nanoparticles (Sn@SnOx NCs) are in situ prepared by a modified DC arc‐discharge plasma process. The as‐prepared Sn@SnOx NCs are typically 50–70 nm in diameter with 6 nm of the SnOx shell. The diameter of Sn@SnOx NCs is 50–80 nm and the thickness of the SnOx shell increases to ≈25 nm after heat treatment in a vacuum tube furnace. The effect of SnOx shell thickness on the electrical properties of Sn@SnOx NCs is measured by the four‐probe technique. The results show that the resistivity is described using Bloch–Grüneisen's equation with SnOx shell thickness‐dependent resistivity and SnOx shell thickness‐dependent Debye temperature above the superconducting transition temperature Tc. Superconductivity occurs in both Sn@SnOx NCs with different shell thicknesses when the temperature is lower than Tc. The Tc of the two NCs (3.98 K, 4.15 K) is slightly higher than that of the metal block (3.73 K) due to the electron‐scattering effect of the particles' surface shell. The resistances of the two samples below Tc show an exponential decay mode, which is the result of the thermally activated phase slip (TAPS) and quantum phase slip (QPS). [ABSTRACT FROM AUTHOR]

The discovery of slow hot carrier cooling in hybrid organic–inorganic lead halide perovskites (HOIPs) has provided exciting prospects for efficient solar cells that can overcome the Shockley–Queisser limit. Questions still loom over how electron‐phonon interactions differ from traditional polar semiconductors. Herein, the electron‐phonon coupling (EPC) strength of common perovskite films (MAPbBr3, MAPbI3, CsPbI3, and FAPbBr3) is obtained using transient absorption spectroscopy by analyzing the hot carrier cooling thermodynamics via a simplified two‐temperature model. Density function theory calculations are numerically performed at relevant electron‐temperatures to confirm experiments. Further, the variation of carrier‐temperature over a large range of carrier‐densities in HOIPs is analyzed, and an "S‐shaped" dependence of the initial carrier‐temperature to carrier‐density is reported. The phenomenon is attributed to the dominance of the large polaron screening and the destabilization effect which causes an increasing‐decreasing fluctuation in temperature at low excitation powers; and a hot‐phonon bottleneck which effectively increases the carrier temperature at higher carrier‐densities. The turning point in the relationship is indicative of the critical Mott density related to the nonmetal‐metal transition. The EPC analysis provides a novel perspective to quantify the energy transfer in HOIPs, electron‐lattice subsystem, and the complicated screening‐bottleneck interplay is comprehensively described, resolving the existing experimental contradictions. [ABSTRACT FROM AUTHOR]

In the present report, optical and Raman spectral properties were extensively studied. Ni-doped CuO nanoparticles were prepared using the sol–gel method. X-ray diffraction patterns confirm that the prepared particles have the space group of C2h6 with monoclinic structure. Optical studies show that there is a broad absorption spectrum in the whole visible regime due to surface plasmon oscillations (SPR). Raman spectral measurements taken using 532 nm excitation found that three Raman peaks centred at 276 cm−1 (Ag), 330 cm−1 (Bg) and 616 cm−1 (Bg), respectively. Doping of Ni ions shows a redshift in Raman peak position. In the present work, the influence of Ni doping on electron–phonon coupling and phonon lifetimes has been studied extensively. [ABSTRACT FROM AUTHOR]

Superconducting materials have garnered widespread attention due to their zero-resistance characteristic and complete diamagnetism. After more than 100 years of exploration, various high-temperature superconducting materials including cuprates, nickelates, iron-based compounds, and ultra-high pressure multi-hydrides have been discovered. However, the practical application of these materials is severely hindered by their poor ductility and/or the need for high-pressure conditions to maintain structural stability. To address these challenges, we first provide a new thought to build high-temperature superconducting materials based on few-hydrogen metal-bonded hydrides under ambient pressure. We then review the related research efforts in this article. Moreover, based on the bonding type of atoms, we classify the existing important superconducting materials and propose the new concepts of pseudo-metal and quasi-metal superconductivity, which are expected to be helpful for the design of new high-temperature superconducting materials in the future., (© 2024 IOP Publishing Ltd.)

Electron-phonon (e-p) coupling plays a crucial role in various physical phenomena, and regulation of e-p coupling is vital for the exploration and design of high-performance materials. However, the current research on this topic lacks accurate quantification, hindering further understanding of the underlying physical processes and its applications. In this work, we demonstrate quantitative regulation of e-p coupling, by pressure engineering and in-situ spectroscopy. We successfully observe both a distinct vibrational mode and a strong Stokes shift in layered CrBr 3 , which are clear signatures of e-p coupling. This allows us to achieve precise quantification of the Huang-Rhys factor S at the actual sample temperature, thus accurately determining the e-p coupling strength. We further reveal that pressure efficiently regulates the e-p coupling in CrBr 3 , evidenced by a remarkable 40% increase in S value. Our results offer an approach for quantifying and modulating e-p coupling, which can be leveraged for exploring and designing functional materials with targeted e-p coupling strengths., (© 2024 IOP Publishing Ltd.)

The electron-phonon (e-ph) interactions are pivotal in shaping the electrical and thermal properties, and in particular, determining the carrier dynamics and transport behaviors in optoelectronic devices. By employing pump-probe spectroscopy and ultrafast microscopy, the consequential role of e-ph coupling strength in the spatiotemporal evolution of hot electrons is elucidated. Thermal transport across the metallic interface is controlled to regulate effective e-ph coupling factor G eff in Au and Au/Cr heterostructure, and their impact on nonequilibrium transport of hot electrons is examined. Via the modulation of buried Cr thickness, a strong correlation between G eff and the diffusive behavior of hot electrons is found. By enhancing G eff through the regulation of thermal transport across interface, there is a significant reduction in e-ph thermalization time, the maximum diffusion length of hot electrons, and lattice heated area which are extracted from the spatiotemporal evolution profiles. Therefore, the increased G eff significantly weakens the diffusion of hot electrons and promotes heat relaxation of electron subsystems in both time and space. These insights propose a robust framework for spatiotemporal investigations of G impact on hot electron diffusion, underscoring its significance in the rational design of advanced optoelectronic devices with high efficiency., (© 2024 Wiley‐VCH GmbH.)

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 )., (© 2024 Wiley-VCH GmbH.)

Resonance Raman spectra and absolute differential Raman cross-sections have been measured for CdSe nanocrystals in both the wurtzite and zincblende crystal forms at four excitation wavelengths from 457.9 to 514.5 nm. The frequency and bandshape of the longitudinal optical (LO) phonon fundamental is essentially identical for both crystal forms at each excitation wavelength. The LO phonon overtone to fundamental intensity ratio appears to be slightly higher for the wurtzite form, which may suggest slightly stronger exciton-phonon coupling from the Fröhlich mechanism in the wurtzite form. The LO fundamental Raman cross-sections are very similar for both crystal forms at each excitation wavelength. © 2012 Elsevier B.V. All rights reserved.

Abstract Charge and thermal transport in a crystal is carried by free electrons and phonons (quantized lattice vibration), the two most fundamental quasiparticles. Above the Debye temperature of the crystal, phonon‐mediated thermal conductivity (κL) is typically limited by mutual scattering of phonons, which results in κL decreasing with inverse temperature, whereas free electrons play a negligible role in κL. Here, an unusual case in charge‐density‐wave tantalum disulfide (1T‐TaS2) is reported, in which κL is limited instead by phonon scattering with free electrons, resulting in a temperature‐independent κL. In this system, the conventional phonon–phonon scattering is alleviated by its uniquely structured phonon dispersions, while unusually strong electron‐phonon (e‐ph) coupling arises from its Fermi surface strongly nested at wavevectors in which phonons exhibit Kohn anomalies. The unusual temperature dependence of thermal conduction is found as a consequence of these effects. The finding reveals new physics of thermal conduction, offers a unique platform to probe e‐ph interactions, and provides potential ways to control heat flow in materials with free charge carriers. The temperature‐independent thermal conductivity may also find thermal management application as a special thermal interface material between two systems when the heat conduction between them needs to be maintained at a constant level.

The temperature dependence of photoluminescence (PL) emission is a valuable tool for investigating carrier localization, recombination, and carrier–phonon interactions. Herein, electron–phonon couplings in lead sulfide (PbS) quantum dots (QDs) and lead sulfide/manganese tellurite (PbS/MnTe) QDs is reported. The effect of temperature on the PL emission of PbS and PbS/MnTe was explored within a temperature range of 10 to 300 K. When temperature increased, PL emission was blue-shifted due to the confinement effect. The gradual broadening of the full width at half maximum (FWHM) with increasing temperature indicates electron–phonon interactions. An analysis based on the Boson model revealed that the values of the exciton acoustic phonon coupling coefficient, σ, and temperature-dependent linewidth, γ, for PbS/MnTe were larger than those for PbS, indicating stronger exciton longitudinal-optical–phonon coupling in the compound structure.

Abstract Thermoelectric multilayer thin films used in nanoscale energy conversion have been receiving increasing attention in both academic research and industrial applications. Thermal transport across multilayer interface plays a key role in improving thermoelectric conversion efficiency. In this study, the cross-plane thermal conductivities of nano-constructed Sb2Te3/(Cu, Ag, Au, Pt) thermoelectric multilayer thin films have been measured using time-domain thermoreflectance method. The interface morphology features of multilayer thin film samples were characterized by using scanning and transmission electron microscopes. The effects of interface microstructure on the cross-plane thermal conductivities of the multilayer thin films have been extensively examined and the thermal transfer mechanism has been explored. The results indicated that electron–phonon coupling occurred at the semiconductor/metal interface that strongly affected the cross-plane thermal conductivity. By appropriately optimizing the period thickness of the metal layer, the cross-plane thermal conductivity can be effectively reduced, thereby improving the thermoelectric conversion efficiency. This work presents both experimental and theoretical understanding of the thermal transport properties of Sb2Te3/metal multilayer thin film junctions with important implications for exploring a novel approach to improving the thermoelectric conversion efficiency.

Two-dimensional (2D) superconductors are important both for the basic understanding of pairing mechanism and potential applications in nanosuperconducting quantum interference devices. In this work, we explore the phonon-mediated superconductivity of hole-doped and lithium-deposited monolayer BC2N by first-principles calculations. Our results reveal that the hole-doped planar BC2N cannot superconduct due to weak electron–phonon coupling (EPC) with λ = 0.07. When lithium is deposited on the monolayer, the EPC constant is enhanced significantly to 0.52 and the superconducting transition temperature Tc is determined to be 3.58 K. Because more phonons, in particular the out-of-plane modes, are triggered to participate in the EPC process, the Tc is higher than 1.4 K of Ca-deposited graphene, 1.3 K of Li-deposited stanene, and 3 K of doped WS2 and NbSe2. It is also found that tensile biaxial strain weakens the EPC and leads to a decreased superconducting transition temperature. Our findings will provide a new guideline for designing novel 2D superconductors and enrich the potential application of 2D BC2N. [ABSTRACT FROM AUTHOR]

Due to the subtle interplay of site-to-site electronic couplings, exciton delocalization, nonadiabatic effects, and vibronic couplings, quantum dynamical studies are needed to elucidate the details of ultrafast photoinduced energy and charge transfer events in organic multichromophoric systems. In this vein, we review an approach that combines first-principles parameterized lattice Hamiltonians with accurate quantum dynamical simulations using advanced multiconfigurational methods. Focusing on the elementary transfer steps in organic functional materials, we address coherent exciton migration and creation of charge transfer excitons in homopolymers, notably representative of the poly(3-hexylthiophene) material, as well as exciton dissociation at polymer:fullerene heterojunctions. We emphasize the role of coherent transfer, trapping effects due to high-frequency phonon modes, and thermal activation due to low-frequency soft modes that drive a diffusive dynamics. [ABSTRACT FROM AUTHOR]

The mechanical properties of superconducting NdBa2Cu3O7 and non-superconducting NdBa2Cu3O6.60 have been measured between 80 and 300 K at 10 MHz. An anomaly in the longitudinal sound velocity indicating lattice-softening tendency between 160 and 230 K was observed in non-superconducting NdBa2Cu3O6.60 but not in superconducting NdBa2Cu3O7 (critical temperature, Tc = 93 K). The Debye temperature θD increased when the oxygen content was increased where θD = 313 K for NdBa2Cu3O6.6 and θD = 370 K for NdBa2Cu3O7 indicating hardening of the material with the superconducting phase. The electron-phonon coupling constant of the superconducting sample in the conventional three-dimensional BCS theory was λ = 0.67, and in the two-dimensional van Hove scenario, λvH = 0.046. The related elastic moduli of the samples are also reported in this paper. [ABSTRACT FROM AUTHOR]

With the trend of Moore's law, the decreasing size and fine structure of semiconductor devices, batteries and bio-medical devices increasingly require the higher performance of thermal interface materials (TIMs). The micro/nano structure of these materials will influence the working efficiency and operation life of TIMs. To improve the quality of TIMs, researchers applied new methods on synthesis routine, structure modification, simulation modelling and measurements. In this article, the types of thermal interface materials, for example, single component TIMs, metal-polymer composite TIMs, nonmetal-polymer composite TIMs were summarized. The principle of electron-phonon coupling and its impact on the thermal transport within micro/nano-scale composite materials including lattice vibration, electron-phonon scattering were reviewed. Typical models of electron-phonon coupling like SMAMM was introduced. The equipment and methods such as time domain thermal reflection and 3ω for measuring the interfacial thermal conductance were also introduced, and the development and application of electron-phonon theory in the future was also prospected. [ABSTRACT FROM AUTHOR]

Development of ultrafast lasers and nonlinear optical techniques over the last two decades provides tools to access real-time dynamics of low energy excitations in superconductors. For example, time-resolved THz spectroscopy and time- and angular-resolved photoemission spectroscopy provide access to the real-time dynamics of the superconducting gap amplitude. Such studies enable determination of microscopic parameters like quasi-particle recombination rates, pair-breaking rates and electron–boson coupling constants. Recently, intense THz pulses have been used to probe the nonlinear dynamics, including observation of collective modes. Moreover, using low-frequency electromagnetic pulses, there are several reports of amplification of superconductivity in both conventional and unconventional superconductors. Starting with a brief historical overview of the pioneering work, where non-equilibrium phenomena in superconductors were investigated using quasi-continuous excitation, we review some of the insights that are provided by using real-time approaches. We focus on conventional BCS superconductors, whose ground state is reasonably well understood, and address similarities and open questions related to the corresponding studies in high- T c superconductors. [ABSTRACT FROM AUTHOR]

Transition metal nitrides have recently gained attention in the fields of plasmonics, plasmon‐enhanced photocatalysis, photothermal applications, and nonlinear optics because of their suitable optical properties, refractory nature, and large laser damage thresholds. This work reports comparative studies of the transient response of films of titanium nitride (TiN), zirconium nitride (ZrN), and gold (Au) under femtosecond excitation. Broadband transient optical characterization helps to adjudicate earlier, somewhat inconsistent reports regarding hot electron lifetimes based upon single wavelength measurements. These pump–probe experiments show sub‐picosecond transient dynamics only within the epsilon‐near‐zero window of the refractory metals. The dynamics are dominated by photoinduced interband transitions resulting from ultrafast electron energy redistribution. The enhanced reflection modulation in the epsilon‐near‐zero window makes it possible to observe the ultrafast optical response of these films at low pump fluences. These results indicate that electron–phonon coupling in TiN and ZrN is 25–100 times greater than in Au. Strong electron–phonon coupling drives the sub‐picosecond optical response and facilitates greater lattice heating compared to Au, making TiN and ZrN promising for photothermal applications. The spectral response and dynamics of TiN and ZrN are only weakly sensitive to pump fluence and pump excitation energy. However, the magnitude of the response is much greater at higher pump photon energies and higher fluences, reaching peak observed values of 15% in TiN and 50% in ZrN in the epsilon‐near‐zero window. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) alters zero bandgap of graphene to achieve photoluminescence (PL), while the low quantum yield (generally: PLQY < 1%) seriously restricts its further development in practical applications. Here we employ two-step fluorination strategy to controllably modify GO, achieving island structure of aromatic regions in continuous phase of fluorine regions. The fluorinated product (FGO) presents a high PLQY of 66%, far exceeding the largest value (21.2%) reported for modifications of GO. We systematically and meticulously investigate fluorine effect of FGO during whole PL evolution. In excitation process, the coexistence of fluorine and aromatic regions in FGO is responsible for new electronic bandgap structure then multitudinous excited electrons produce, thus providing foundation for strong PL. In emission process, Raman measurements show that the weaker electron-phonon interactions in FGO result in slower nonradiative decay. It is attributed to that FGO possesses larger rigidity, as demonstrated by temperature-dependent fluorescence spectra, broadband dielectric measurements, density functional theory calculations and infrared spectra. Interestingly, different types of fluorine-related groups in FGO play different roles. That is, unoriented CF 2 and CF 3 groups realize passivation of defects, and C–F bonds perpendicular to graphene plane contribute to weakening interlayer interactions, both greatly enhancing PL. A simple and effective two-step fluorination means for GO is performed to controllably prepare FGO with a high PLQY of 66%. The advantages are that the introduction of fluorine creates a new electronic bandgap structure, weakens electron-phonon interactions, increases rigidity and reduces interlayer interactions. During which different types of fluorine-related groups in FGO play different roles in enhancing PL. Image 1 [ABSTRACT FROM AUTHOR]

Recently, the AlB2-type compounds (such as AlB2 and MgB2) which exhibit Dirac Nodal Line (DNLs) semimetal on their electronic band structure and Phononic Weyl Nodal Straight Lines (PTWNLs) on their phonon spectrum, have received wide attentions on their novel properties. Up to date, no comparative studies have been investigated on their electronic structures, phonon spectrum, and electron phonon coupling (EPC) under the conditions of carrier doping and strain engineering. Here, we systemically investigate their above properties under carrier doping and strain engineering by first-principles calculations. The results show that the superconducting transition temperature Tc can be enhanced by electron doping and tensile strain. For AlB2, the tensile strain of 6% can enhance Tc to 10.25 K and with the doping concentrate of 0.1 e- per cell can enhance Tc reach to 9.89 K. Moreover, the physical quantities related to superconductivity of AlB2 are more affected by carrier doping than MgB2. Our results provide a theoretical reference to explore the correlation between electronic and phonon topological properties in AlB2-type materials. [ABSTRACT FROM AUTHOR]

With strong electron-phonon coupling, the self-trapped excitons are usually formed in materials, which leads to the local lattice distortion and localized excitons. The self-trapping strongly depends on the dimensionality of the materials. In the three-dimensional case, there is a potential barrier for self-trapping, whereas no such barrier is present for quasi-one-dimensional systems. Two-dimensional (2D) systems are marginal cases with a much lower potential barrier or nonexistent potential barrier for the self-trapping, leading to the easier formation of self-trapped states. Self-trapped excitons emission exhibits a broadband emission with a large Stokes shift below the bandgap. 2D perovskites are a class of layered structure material with unique optical properties and would find potential promising optoelectronic. In particular, self-trapped excitons are present in 2D perovskites and can significantly influence the optical and electrical properties of 2D perovskites due to the soft characteristic and strong electron-phonon interaction. Here, we summarized the luminescence characteristics, origins, and characterizations of self-trapped excitons in 2D perovskites and finally gave an introduction to their applications in optoelectronics. [ABSTRACT FROM AUTHOR]

The problem of the description of the strong interaction of the InAs/GaAs exciton quantum dot (QD) grown by molecular-beam epitaxy with acoustic phonon and electron reservoirs is studied. A nonperturbative solution to the self-energy function of the exciton quantum dot is found. It is shown that these functions at temperatures higher than 10 K differ significantly from those obtained within in the Born approximation. The accurate calculation of the self-energy function of the exciton QD makes it possible to solve the problem of decoherence and dephasing of quantum states, which opens the way to develop single-photon sources necessary in quantum calculations and quantum communication. [ABSTRACT FROM AUTHOR]