Search

In ultrawide bandgap (UWBG) nitride and oxide semiconductors, increased bandgap (Eg) correlates with greater ionicity and strong electron–phonon coupling. This limits mobility through phonon scattering, localizes carriers via polarons and self-trapping, broadens optical transitions via dynamic disorder, and modifies the breakdown field. Herein, we use polarized optical transmission spectroscopy from 77 to 633 K to investigate the Urbach energy (Eu) for many orientations of Fe- and Sn-doped β-Ga2O3 bulk crystals. We find Eu values ranging from 60 to 140 meV at 293 K and that static (structural defects plus zero-point phonons) disorder contributes more to Eu than dynamic (finite temperature phonon-induced) disorder. This is evidenced by lack of systematic Eu anisotropy, and Eu correlating more with x-ray diffraction rocking-curve broadening than with Sn-doping. The lowest measured Eu are ∼10× larger than for traditional semiconductors, pointing out that band tail effects need to be carefully considered in these materials for high field electronics. We demonstrate that, because optical transmission through thick samples is sensitive to sub-gap absorption, the commonly used Tauc extraction of a bandgap from transmission through Ga2O3 >1–3 μm thick is subject to errors. Combining our Eu(T) from Fe-doped samples with Eg(T) from ellipsometry, we extract a measure of an effective electron–phonon coupling that increases in weighted second order deformation potential with temperature and a larger value for E||b than E||c. The large electron–phonon coupling in β-Ga2O3 suggests that theories of electrical breakdown for traditional semiconductors need expansion to account not just for lower scattering time but also for impact ionization thresholds fluctuating in both time and space. [ABSTRACT FROM AUTHOR]

Polarons, which arise from the intricate interplay between excess electrons and/or holes and lattice vibrations (phonons), represent quasiparticles pivotal to the electronic behavior of materials. This review reaffirms the established classification of small and large polarons, emphasizing its relevance in the context of recent advances in understanding lead halide perovskites' behavior. The distinct characteristics of large and small polarons stem from the electron–phonon interaction range, which exerts a profound influence on materials' characteristics and functionalities. Concurrently, lead halides have emerged with exceptional opto‐electronic properties, featuring prolonged carrier lifetimes, low recombination rates, high defect tolerance, and moderate charge carrier mobilities; these characteristics make them a compelling contender for integration of optoelectronic devices. In this review, the formation of both small and large polarons within the lattice of lead halide perovskites, elucidating their role in protecting photogenerated charge carriers from recombination processes, is discussed. As optoelectronic devices continue to advance, this review underscores the importance of unraveling polaron dynamics to pave the way for innovative strategies for enhancing the performance of next‐generation photovoltaic technologies. Future research should explore novel polaronic effects using advanced computational and experimental techniques, enhancing our understanding and unlocking new applications in materials science and device engineering. [ABSTRACT FROM AUTHOR]

Terahertz (THz) electromagnetic interference (EMI) shielding materials is crucial for ensuring THz electromagnetic protection and information confidentiality technology. Here, it is demonstrated that high electrical conductivity and strong absorption of THz electromagnetic radiation by type‐II Dirac semimetal PdTe2 film make it a promising material for EMI shielding. Compared to MXene film, a commonly used metallic 2D material, the PdTe2 film demonstrates a remarkable 40.36% increase in average EMI shielding efficiency per unit thickness within a broadband THz frequency range. Furthermore, it is demonstrated that a photoinduced long life‐time THz transparency in Dirac semimetal PdTe2 films is attributed to the formation of small polarons due to the strong electron‐phonon coupling. A 15 nm‐thick PdTe2 film exhibits a photoinduced change of EMI SE of 1.1 dB, a value exceeding three times that measured on MXene film with a similar pump fluence. This work provides insights into the fundamental photocarrier properties in type‐II Dirac semimetals that are essential for designing advanced THz optoelectronic devices. [ABSTRACT FROM AUTHOR]

Halide perovskites emerged as a revolutionary family of high-quality semiconductors for solar energy harvesting and energy-efficient lighting. There is mounting evidence that the exceptional optoelectronic properties of these materials could stem from unconventional electron-phonon couplings, and it has been suggested that the formation of polarons and self-trapped excitons could be key to understanding such properties. By performing first-principles simulations across the length scales, here we show that halide perovskites harbor a uniquely rich variety of polaronic species, including small polarons, large polarons, and charge density waves, and we explain a variety of experimental observations. We find that these emergent quasiparticles support topologically nontrivial phonon fields with quantized topological charge, making them nonmagnetic analog of the helical Bloch points found in magnetic skyrmion lattices. [ABSTRACT FROM AUTHOR]

Hydrogen-based compounds have been found to exhibit high superconducting critical temperature ( T c ) through the electron–phonon coupling mechanism under ultrahigh pressure. Herein, a new two-dimensional transition metal dichalcogenide material is constructed, namely, the Janus WSH monolayer. It is formed by replacing one layer of S atoms in the WS2 monolayer with H atoms. Then the electronic structure, phonon dispersion, electron–phonon coupling, and superconductivity are investigated by first-principles calculations. The results show that the introduction of H atoms helps to flatten the electronic dispersion and leads to high electronic density of states at the Fermi level, resulting in strong electron–phonon coupling. Additionally, the softening of phonon modes from the hybridization of in-plane W atomic vibrations and out-of-plane H atomic vibrations boosts the electron–phonon coupling further. The strong interactions between electrons and phonons lead to phonon-mediated superconductivity in Janus WSH monolayer with a calculated T c being about 23.1 K. This is the highest T c predicted in WS2-based materials at present, which indicates that hydrogenation is a great way to improve the T c of transition metal dichalcogenide materials. [ABSTRACT FROM AUTHOR]

Polar optical phonon modes of wurtzite triangular nanowires (NWs) with three different cross sections, including the hemi-equilateral triangle (HET), the isosceles right triangle (IRT), and the equilateral triangle (ET), are deduced and analyzed using the dielectric continuum model. The exact and analytical phonon states of exactly confined (EC) modes in nitride NWs with HET, IRT, and ET cross sections are derived. The characteristic frequency of EC phonon modes in the triangular nitride NW systems is specified. Fröhlich electron–phonon interaction Hamiltonians in wurtzite NWs with three types of triangular cross sections are obtained. It is found from the numerical results that, among the three types of GaN NWs, the electron–phonon coupling of EC modes in NWs with an HET cross section is the weakest one, that in NWs with an ET cross section is the strongest one, and that in NWs with an IRT cross section is in the middle. The electrostatic potentials of EC modes in HET NWs are neither symmetric nor antisymmetric. The potential functions of EC modes in the ET NW structures have one (three) symmetric axis (axes) as the quantum numbers p and q take fractions (integers). The potential functions of EC modes in IRT NWs behave either symmetrically or anti-symmetrically, which are closely dependent on the parities of the quantum numbers p and q. With the increase of order-number of EC modes, the electron–phonon coupling becomes weaker and weaker. This reveals that cross-sectional morphology of quantum structures has an important influence on the symmetries of phonon modes and electron–phonon coupling strengths in low-dimensional quantum systems. [ABSTRACT FROM AUTHOR]

We derive a formulation of mixed quantum–classical dynamics for modeling electronic carriers interacting with phonons in reciprocal space. For dispersionless phonons, we start by expressing the real-space classical coordinates in terms of complex variables. Taking these variables as a Fourier series then yields the reciprocal-space coordinates. Evaluating the electron–phonon interaction term through Ehrenfest's theorem, we arrive at a reciprocal-space formalism that is equivalent to mean-field mixed quantum–classical dynamics in real space. This equivalence is numerically verified for the Holstein and Peierls models, for which we find the reciprocal-space Hellmann–Feynman forces to involve momentum-derivative contributions in addition to the position-derivative terms commonly seen in real space. To illustrate the advantage of the reciprocal-space formulation, we present a proof of concept for the inexpensive modeling of low-momentum carriers interacting with phonons using a truncated reciprocal-space basis, which is not possible within a real-space formulation. [ABSTRACT FROM AUTHOR]

In this work, the role of spin‐orbit coupling (SOC) in ATl3 (A = Ca, Y, La, and Th) and La3Tl is investigated by theoretical investigation of their structural, electronic, elastic, mechanical, phonon, and electron–phonon interaction properties. The effect of SOC on the electronic band structures of these compounds is that some of the degeneracies at the high symmetry points that would exist in a scalar relativistic calculation without SOC are removed by considering this coupling. The replacement of La and Tl atoms in LaTl3 increases the value of the density of states at the Fermi level N(EF$E_{\text{F}}$) by a factor of 2.1. Furthermore, this replacement makes almost all phonon modes in La3Tl softer than those in LaTl3. Both softer phonon modes and higher N(EF$E_{\text{F}}$) make the electron–phonon interaction in La3Tl much stronger than in LaTl3. The presence of SOC increases the Tc$T_{\text{c}}$ values of LaTl3 by 34% (from 1.151 to 1.542 K) and of ThTl3 by 65% (from 0.479 to 0.793 K), resulting in good agreement with the corresponding experimental values of 1.63 and 0.87 K. The inclusion of SOC also improves the agreement with the experiment for Tc$T_{\text{c}}$ values of CaTl3, YTl3, and La3Tl. [ABSTRACT FROM AUTHOR]

A three-terminal nanoscale refrigeration concept based on a vibron-coupled quantum dot hybrid system coupled to two contacts and a phonon bath is proposed and analyzed in detail. While investigating the non-trivial role of electron–phonon interactions, we show that, although they are well known to be detrimental from a general refrigeration perspective, they can be engineered to favorably improve the trade-off between the cooling power (CP) and the coefficient-of-performance (COP). Furthermore, an additional improvement in the trade-off can be facilitated by applying a high thermal bias. However, the allowed maximum of the thermal bias being strongly limited by the electron–phonon coupling, in turn, determines the lowest achievable temperature of the cooled body. It is further demonstrated that such interactions drive a phonon flow between the dot and bath whose direction and magnitude depend on the temperature difference between the dot and bath. To justify its impact in optimizing the peak CP and COP, we show that a weak coupling with the bath is preferable when the phonons relax through it and a strong coupling is suitable in the opposite case when the phonons are extracted from the bath. Finally, in studying the effect of asymmetry in electronic couplings, we show that a stronger coupling is favorable with the contact whose temperature is closer to that of the bath. Combining these aspects, we believe that this study could offer important guidelines for a possible realization of molecular and quantum dot thermoelectric refrigerator. [ABSTRACT FROM AUTHOR]

The modeling of coupled electron–ion dynamics including a quantum description of the nuclear degrees of freedom has remained a costly and technically difficult practice. The kinetic model for electron–phonon interaction provides an efficient approach to this problem, for systems evolving with low amplitude fluctuations, in a quasi-stationary state. In this work, we propose an extension of the kinetic model to include the effect of coherences, which are absent in the original approach. The new scheme, referred to as Liouville–von Neumann + Kinetic Equation (or LvN + KE), is implemented here in the context of a tight-binding Hamiltonian and employed to model the broadening, caused by the nuclear vibrations, of the electronic absorption bands of an atomic wire. The results, which show close agreement with the predictions given by Fermi's golden rule (FGR), serve as a validation of the methodology. Thereafter, the method is applied to the electron–phonon interaction in transport simulations, adopting to this end the driven Liouville–von Neumann equation to model open quantum boundaries. In this case, the LvN + KE model qualitatively captures the Joule heating effect and Ohm's law. It, however, exhibits numerical discrepancies with respect to the results based on FGR, attributable to the fact that the quasi-stationary state is defined taking into consideration the eigenstates of the closed system rather than those of the open boundary system. The simplicity and numerical efficiency of this approach and its ability to capture the essential physics of the electron–phonon coupling make it an attractive route to first-principles electron–ion dynamics. [ABSTRACT FROM AUTHOR]

Electron–phonon interaction strongly affects and often limits charge transport in organic semiconductors (OSs). However, approaches to its experimental probing are still in their infancy. In this study, we probe the local electron–phonon interaction (quantified by the charge-transfer reorganization energy) in small-molecule OSs by means of Raman spectroscopy. Applying density functional theory calculations to four series of oligomeric OSs—polyenes, oligofurans, oligoacenes, and heteroacenes—we extend the previous evidence that the intense Raman vibrational modes considerably contribute to the reorganization energy in several molecules and molecular charge-transfer complexes, to a broader scope of OSs. The correlation between the contribution of the vibrational mode to the reorganization energy and its Raman intensity is especially prominent for the resonance conditions. The experimental Raman spectra obtained with various excitation wavelengths are in good agreement with the theoretical ones, indicating the reliability of our calculations. We also establish for the first time relations between the spectrally integrated Raman intensity, the reorganization energy, and the molecular polarizability for the resonance and off-resonance conditions. The results obtained are expected to facilitate the experimental studies of the electron–phonon interaction in OSs for an improved understanding of charge transport in these materials. [ABSTRACT FROM AUTHOR]

Electron–phonon interaction in bulk and nanoflakes of MoS2 is investigated using Raman spectroscopy. Resonant Raman spectroscopic studies carried out on bulk and liquid exfoliated nanoflakes of MoS2 revealed a second order Raman mode (called the “b” mode), whose frequency in the case of nanoflakes was found to be largely different from that in bulk MoS2. Temperature dependent Raman spectra show larger variation in the frequency of the “b” mode in bulk MoS2 as compared to that in nanoflakes of MoS2. This anomalous behavior of the “b” mode could be attributed to the stronger electron–phonon coupling occurring in bulk MoS2, due to higher electron concentration in the same, as compared to that in nanoflakes of MoS2. A larger sulfur vacancy in bulk MoS2 as compared to that of nanoflakes was found to be responsible for higher electron concentrations. These findings are supported by energy dispersive x-ray analysis and x-ray photoelectron spectroscopic studies carried out on bulk and nanoflakes of MoS2. The present study suggests a more sensitive probe for the estimation of electron concentrations in the low limit range by following the “b” mode in resonance Raman spectra. [ABSTRACT FROM AUTHOR]

We analyze the influence of electron–phonon (e–ph) interaction in a model for electron transfer (ET) processes in DNA in terms of the envelope function approach for spinless electrons. We are specifically concerned with the effect of e–ph interaction on the coherence of the ET process and how to model the interaction of DNA with phonon reservoirs of biological relevance. We assume that the electron bearing orbitals are half filled and derive the physics of e–ph coupling in the vicinity in reciprocal space. We find that at half filling, the acoustical modes are decoupled to ET at first order, while optical modes are predominant. The latter are associated with inter-strand vibrational modes in consistency with previous studies involving polaron models of ET. Coupling to acoustic modes depends on electron doping of DNA, while optical modes are always coupled within our model. Our results yield e–ph coupling consistent with estimates in the literature, and we conclude that large polarons are the main result of such e–ph interactions. This scenario will have strong consequences on decoherence of ET under physiological conditions due to relative isolation from thermal equilibration of the ET mechanism. [ABSTRACT FROM AUTHOR]

The electron–phonon interaction is central to condensed matter, e.g. through electrical resistance, superconductivity or the formation of polarons, and has a strong impact on observables such as band gaps or optical spectra. The most common framework for band energy corrections is the Fröhlich model, which often agrees qualitatively with experiments in polar materials, but has limits for complex cases. A generalized version includes anisotropic and degenerate electron bands, and multiple phonons. In this work, we identify trends and outliers for the Fröhlich models on 1260 materials. We test the limits of the Fröhlich models and their perturbative treatment, in particular the large polaron hypothesis. Among our extended dataset most materials host perturbative large polarons, but there are many instances that are non-perturbative and/or localize on distances of a few bond lengths. We find a variety of behaviors, and analyze extreme cases with huge zero-point renormalization using the first-principles Allen-Heine-Cardona approach. [ABSTRACT FROM AUTHOR]

A new approach to establishing a strong electron-phonon interaction in heterostructures is proposed. A three-layer structure consisting of an ionic substrate, a semiconductor film, and a covering dielectric (with air or vacuum possibly serving as such a dielectric) is examined. Interface optical phonons emerge near the heterointerface. Their parameters are governed by the dielectric properties of the substrate. It is demonstrated that the effective mass of carriers in the film is altered in the presence of interface phonons. Depending on the substrate ionicity, the magnitude of this change may vary from several tens to hundreds of percent. It is shown that the conditions for strong electron-phonon interaction may be established in a large number of semiconductor films. Measurements of the effective mass of carriers in identical films positioned on different substrates should make it possible to identify a transition from a weak electron-phonon interaction to a strong one. [ABSTRACT FROM AUTHOR]

We analyze the effect of longitudinal optical phonons on the energy states of electrons in a nanowire in the presence of Rashba interaction and an in-plane magnetic field. Due to the electron–phonon interaction, an energy splitting appears at zero wave vector accompanied by a downward shift of the dispersion relation in the absence of external magnetic fields. The splitting increases linearly with the product of the Rashba parameter and the dimensionless constant characterizing the Fröhlich Hamiltonian. It also induces an enhancement in the g -factor that is inversely proportional to the strength of the magnetic field. Moreover, we calculate the contribution of Rashba intersubband coupling (RIC) to the electron energy. This contribution does not influence the g -factor for the case of parallel magnetic field to the nanowire, but it causes reduction in it by increasing the angle between the nanowire and the field. [ABSTRACT FROM AUTHOR]

We have studied four 2D layered perovskites, including OA2PbI4 (RP phase), ODAPbI4 and BDAPbI4 (DJ phase), (GA)MAPbI4 (ACI phase), where OA is [(CmH2m+1)NH3](m = 8), ODA is [NH3(CH2)mNH3](m = 8), BDA is [NH3(CH2)mNH3](m = 4), and GA is [C(NH2)3]; RP, DJ, and ACI means Ruddlesden–Popper, Dion–Jacobson and alternating cations in the interlayer, respectively. The temperature dependence of absorption and photoluminescence (PL) spectra have been measured. From which the average phonon energy (electron-phonon interaction strength) is analyzed as around 34 (80), 47 (184), 50 (402), and 63 (758) with the unit of meV for OA2PbI4, ODAPbI4, BDAPbI4, and (GA)MAPbI4, respectively. Larger phonon energy indicates the involvement of more phonons in organic spacer layer, with the corresponding stronger electron-phonon interaction. Furthermore, ultrafast transient absorption spectroscopy proves that, when the excitation photon energy is serval hundred meV higher than bandgap, the excitons still are the major photoexcitations in OA2PbI4, but polarons are major one in ODAPbI4, BDAPbI4, and (GA)MAPbI4 films, no matter the excitonic transitions dominate the absorption at their band edges. This work proves the organic spacers can regulate electron–phonon interaction then optoelectronic properties in 2D perovskites profoundly, which have implications toward future rational design for relevant devices. [ABSTRACT FROM AUTHOR]

Based on the derivation of the equation of state for systems with a fractional power spectrum, the relationship between the van der Waals constant and the fractional derivative order has been established. The fractional model of electron–phonon interaction has received additional consideration, which may be pertinent when interpreting the experimental results. This model is valuable for describing superconductivity at high temperatures because it predicts relatively large values for the electron–phonon interaction constant. [ABSTRACT FROM AUTHOR]

Layered BiCuXO (X = S, Se, and Te) compounds attract much attention recently because of their superior thermoelectric properties. However, the major shortcoming of these compounds is the relatively large electrical resistance. Exploring the mechanism of electrical scattering of BiCuXO can give some hints on how to optimize their electrical conductivity. Here, we compared electrical and magnetotransport properties of degenerate semiconductor BiCuXO. These compounds show metallic electrical properties, and the in-plane resistivity is linearly dependent on the temperature at the high-temperature regime (>150 K). The magnetoresistance of these compounds is approximately quadratically dependent on the square of magnetic field B, and magnetoresistance decreases from 10%–16% to 0.5% when the temperature is increased from 2 to 300 K. The Hall measurements substantiate that the electrical carriers of BiCuXO are holes, which perhaps come from Bi vacancies. The electron-optical-phonon interaction is the major mechanism of electron scattering when the temperature is higher than 80 K. Analyzing the linear coefficient ρxx-T of BiCuXO (X = S, Se, and Te) suggests that the averaged electron-phonon interaction of BiCuSO is nearly six times larger than that of BiCuSeO/BiCuTeO. Based on the Thomas-Fermi model, compared with BiCuSO, the weak electron-phonon interaction in BiCuSeO/BiCuTeO could be attributed to a highly screened Coulomb interaction between electrons and ions. This work may be useful to optimize the electrical properties of BiCuXO to satisfy the requirement of thermoelectric materials. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenide (TMD) semiconductors are two-dimensional materials with great potential for the future of nano-optics and nano-optoelectronics as well as the rich and exciting development of basic research. The influence of an external magnetic field on a TMD monolayer raises a new question: to unveil the behavior of the magneto-polaron resonances (MPRs) associated with the phonon symmetry inherent in the system. It is shown that the renormalized Landau energy levels are modified by the interplay of the long-range Pekar–Fröhlich (PF) and short-range deformation potential (DP) interactions. This leads to a new series of MPRs involving the optical phonons at the center of the Brillouin zone. The coupling of the two Landau levels with the LO and A 1 optical phonon modes provokes resonant splittings of double avoided-crossing levels giving rise to three excitation branches. This effect appears as bigger energy gaps at the anticrossing points in the renormalized Landau levels. To explore the interplay between the MPRs, the electron-phonon interactions (PF and DP) and the couplings between adjacent Landau levels, a full Green's function treatment for the evaluation of the energy and its life-time broadening is developed. A generalization of the two-level approach is performed for the description of the new MPR branches. The obtained results are a guideline for the magneto-optical experiments in TMDs, where three MPR peaks should be observable. [ABSTRACT FROM AUTHOR]

Electron–phonon interactions play a crucial role in nano-electronic device performance. As the accurate calculation of these interactions requires huge computational resources, reduction of this burden without losing accuracy poses an important challenge. Here, we investigate the electron–phonon interactions of nano-devices using two first-principles-based methods in numerically efficient manners. The first method is the Lowest Order Approximation (LOA) version of the computationally burdensome self-consistent Born approximation method. The LOA method incorporates the effect of each phonon mode on the electronic current perturbatively. In this work, we theoretically resolve the discrepancy between two conventional approaches of direct LOA calculation. To validate the correct approach, we compared its output with a completely different method (second method) named Special Thermal Displacement (STD) method. The STD method uses non-interacting transport calculation of the displaced atomic configuration of a device. We apply both methods to two thin-film nanodevices: 2D silicon junctionless FET and n-i-n FET. Both methods justify each other by providing similar results and exhibiting important quantum phenomena, such as phonon-assisted subthreshold swing degradation and tunneling. [ABSTRACT FROM AUTHOR]

Physics of the multiferroic interfaces is currently understood mostly within a phenomenological framework based on screening of the polarization field and depolarizing charges. Additional effects still unexplored are the band dependence of the interfacial charge modulation and the associated changes of the electron-phonon interaction, coupling the charge and lattice degrees of freedom. Here, multiferroic heterostructures of the colossal-magnetoresistance manganite La1-xSrxMnO3 buried under ferroelectric BaTiO3 and PbZrxTi1-xO3 are investigated using soft-X-ray angle-resolved photoemission. The experimental band dispersions from the buried La1-xSrxMnO3 identify coexisting two-dimensional hole and three-dimensional electron charge carriers. The ferroelectric polarization modulates their charge density, affecting the coupling of the 2D holes and 3D electrons with the lattice which forms large Fröhlich polarons inherently reducing mobility of the charge carriers. Our k-resolved results on the orbital occupancy, band filling and electron-lattice interaction in multiferroic oxide heterostructures modulated by the ferroelectric polarization disclose most fundamental physics of these systems needed for further progress of beyond-CMOS ferro-functional electronics. A deeper understanding of the coupling at the interface of multiferroics heterostructures is being achieved by the use of synchrotron radiation techniques. Here, the authors use k-resolved soft X-ray photoemission spectroscopy and first principles calculations to investigate the band structure of several multiferroic heterostructures, isolating the distinct signature of the interface. [ABSTRACT FROM AUTHOR]

We have studied strong correlation effects and localization in metallic systems. Strong correlation effects and localization occurred in metallic systems due to strong electron-electron interactions and strong electron phonon coupling. Strong electron-phonon interactions have been found in such materials as cuprates, fullerides and manganites. The interplay of electronelectron and electron-phonon interactions in these correlated systems leaded to coexistence of or competition between various phases such as super conductivity, charge-density-wave or spin-density wave phases or formation of novel non Fermi liquid phases, polarons, bipolarons and so on. We have considered Holstein-Hubbard model for our work. The Holstein-Hubbard model provides on over simplified description of both electron-electron and electron-phonon interactions, it retains to be the relevant ingredients of a system in which electrons experience simultaneously an instantaneous short range repulsion and a phonon-mediated retarded attraction. In spite of its formal simplicity, it is not exactly solvable even in one dimension. So quantum simulators of Fermi-Hubbard modes based on either fermionic atoms inoptical lattice or electrons in artificial quantum dot crystals have been used. In our work a classical analog simulator was theoretically proposed for the two site Holstein-Hubbard model based on light transport in engineered waveguide lattices, which is capable of reproducing the temporal dynamics of the quantum model in Fock space as spatial evolution in photonic lattice. We have found that in the strong correlation regime the periodic temporal dynamics exhibited by the Holstein-Hubbard Hamiltonian, related to the excitation Holstein polarons has been explained in terms of generalized Bloch oscillations of a single particle in a semi-infinite inhomogeneous tight binding lattice. Light transport in two dimensional photonic lattices simulated in Fock space the hopping dynamics of two correlated electrons on a one dimensional lattice and exploited to visualize such phenomena as correlated tunneling of bond electron-electron molecules and their coherent motion under the action of d.c. or a.c. fields. The obtained results were found in good agreement with previous results. [ABSTRACT FROM AUTHOR]

Theoretical studies available in the literature suggest that the compound YH10 is a promising candidate for a high-temperature superconductor with a phase transition temperature TC close to room temperature. Numerical solutions of the classical Eliashberg equations at 250 GPa led to the critical temperature of about TC = 326 K. As expected, YH10 belongs to the group of superconductors with strong electron-phonon coupling, similar to others with TC above 200 K, for example, H3S, LaH10, or YH6. In 2018, a series of experiments were conducted, and the experimental verifications confirming the existence of a high-temperature superconducting state in LaH10 turned out to be groundbreaking. At the time, it seemed that such confirmation concerning YH10 would come very quickly. Unfortunately, so far there have been no successful experimental measurements on the high-temperature YH10 superconducting phase. The aim of this work is to show the effect of the vertex corrections to the electron-phonon interaction on the value of the critical temperature of YH10 at 250 GPa. Thus, it was shown that by including more complex equations into the calculations (the formalism of Eliashberg equations with the vertex corrections), the estimated value of the metal-superconductor phase transition temperature lowers significantly to TC = 245:75 K. Furthermore, we point out that the influence of temperature on the effective electron mass exhibits a similar tendency as that concerning the LaH10 superconductor we studied earlier. [ABSTRACT FROM AUTHOR]

In cuprate superconductors, a pronounced maximum of superconducting T c max is observed in compounds that have an in-plane Cu–O distance a C u - O close to ∼ 1.92 angstroms. On the other hand, direct measurements of the electron–phonon coupling λ ⟨ ω 2 ⟩ as a function of a C u - O show a clear linear correlation, implying that T c max is a strongly non-linear function of λ ⟨ ω 2 ⟩ . Conventional superconductivity theories based on the electron–phonon interaction predict a monotonic dependence of T c max on λ ⟨ ω 2 ⟩ , which makes them incompatible with the observed behavior. The observed crossover behavior as a function of λ ⟨ ω 2 ⟩ suggests that T c max occurs at the crossover from weak to strong coupling, which is also associated with the onset of carrier localization. A coexistence, with a dynamical exchange of localized and itinerant carriers in a two-component superconductivity scenario are in agreement with the observed anomalous behavior and are suggested to be the key to understanding the mechanism for achieving high T c max . [ABSTRACT FROM AUTHOR]

Theoretical studies available in the literature suggest that the compound YH10 is a promising candidate for a high-temperature superconductor with a phase transition temperature TC close to room temperature. Numerical solutions of the classical Eliashberg equations at 250 GPa led to the critical temperature of about TC = 326 K. As expected, YH10 belongs to the group of superconductors with strong electron-phonon coupling, similar to others with TC above 200 K, for example, H3S, LaH10, or YH6. In 2018, a series of experiments were conducted, and the experimental verifications confirming the existence of a high-temperature superconducting state in LaH10 turned out to be groundbreaking. At the time, it seemed that such confirmation concerning YH10 would come very quickly. Unfortunately, so far there have been no successful experimental measurements on the high-temperature YH10 superconducting phase. The aim of this work is to show the effect of the vertex corrections to the electron-phonon interaction on the value of the critical temperature of YH10 at 250 GPa. Thus, it was shown that by including more complex equations into the calculations (the formalism of Eliashberg equations with the vertex corrections), the estimated value of the metal-superconductor phase transition temperature lowers significantly to TC = 245:75 K. Furthermore, we point out that the influence of temperature on the effective electron mass exhibits a similar tendency as that concerning the LaH10 superconductor we studied earlier. [ABSTRACT FROM AUTHOR]

The coupling between electrons and phonons is ubiquitous in condensed matter physics. In recent years, with the rise of two dimensional (2D) materials, electron–phonon interaction exhibits unique characteristics compared with their three‐dimensional counterparts. In this paper, research progress of electron–phonon interaction in 2D materials is briefly reviewed, mainly focus on thermoelectric device, conventional superconductor, field effect transistor, and photoelectric device. Firstly, electron–phonon interaction on thermoelectric application of 2D materials is concluded according to recent reports, and strategies to increase figure of merit are discussed. Next, strong electron–phonon coupling strength is essential for increasing transition temperature of superconductors. Conversely, electron–phonon interaction inhibits the carrier mobility for transport process. By summarizing research works in the past years, its role on the performance of 2D materials‐based field effect transistors is fully evaluated. Furthermore, the influences of electron–phonon interaction on light–matter interaction in 2D materials are briefly overviewed. Finally, some outlooks in the field are prospected. In a word, understanding electron–phonon interaction in 2D materials establishes strategically important directions for manipulating physical properties and optimizing device design. [ABSTRACT FROM AUTHOR]

The carrier–phonon interaction in semiconductor quantum dots (QDs) can greatly affect the optical preparation of the excited state. For resonant excitation used in the Rabi preparation scheme, the polaron is formed accompanied by the emission of a phonon wave packet, leading to a degradation of preparation fidelity. In this article, phonon wave packets for different coherent excitation schemes are analyzed. One example is the adiabatic rapid passage scheme relying on a chirped excitation. Herein, also a phonon wave packet is emitted, but the preparation fidelity can still be approximately unity. A focus is on the phonon impact on a recently proposed swing‐up scheme, induced by two detuned pulses. Similar to the Rabi scheme, a degradation and a phonon wave packet emission are found, despite the detuning. If the swing‐up frequency coincides with the maximum of the phonon spectral density, a series of wave packets is emitted yielding an even stronger degradation. The insight gained from our results further helps in designing an optimal preparation scheme for QDs. [ABSTRACT FROM AUTHOR]

La 0.8 Ca 0.2 Mn 0.5 Ni 0.5 O 3 NTC (negative thermal coefficient) thermo-sensitive material was prepared using a conventional solid-state reaction method. From the structural results, we found that the material is pure and crystallizes in the orthorhombic structure with a Pnma space group. It is found that the La 0.8 Ca 0.2 Mn 0.5 Ni 0.5 O 3 ceramic can be used as an NTC thermistor compound in specific temperature sensors and attenuators. Based on Holsten's theory, detailed electrical investigations concerning the nature of the activated small polaron hopping mechanism were reported. The temperature dependence of the DC conductance was used to determine the electrical conduction processes that govern the transport properties of La 0.8 Ca 0.2 Mn 0.5 Ni 0.5 O 3. Hence, the DC mechanisms exhibit changes from the variable range hopping at very low temperatures to the non-adiabatic small polaronic hopping at T = 210 K. In the intermediate temperature range, the semiconductor behavior of La 0.8 Ca 0.2 Mn 0.5 Ni 0.5 O 3 was attributed to the contribution of the tunneling transport process. At various temperatures, the conductance spectra were discussed based on Jonscher and Bruce's laws. Contributions of the overlapping-large-polaron-tunneling, the correlated barrier hopping, the quantum mechanical tunneling, and the non-overlapping small polaron tunneling mechanisms to the transport properties were observed in the dispersive region of the conductance spectra. In addition, Summerfield scaling and corrected Summerfield scaling approaches prove that the charge mobility is temperature-dependent. The positive value of the correction parameter α = 1.2 confirms the presence of interactions in the studied sample. [ABSTRACT FROM AUTHOR]

Quasi-particle formed by electron and the dressed deformed lattice is important to accurately interpret the properties of various disordered/amorphous materials. However, a unified understanding of the drag effect, in particular the negative Coulomb drag in hopping systems, remains an open challenge. This work proposes a theoretic framework to account for both positive and negative Coulomb drag in dual-1D-hopping systems by considering both the electron-electron correlation and the electron-phonon correlation. It is found that lattice relaxation in the active line of the hopping system may give rise to an inverse energetic pumping force in the passive line, causing negative Coulomb drag. The mobility of the negative coulomb drag can approach the scale of 10−5cm2V−1s−1, especially at low temperature, high carrier-density, and narrow inter-spacing separation. More intriguingly, the positive drag could be recovered by varying the energy fluctuation and suppressing the electron-phonon interactions, but with a much lower magnitude. Our work could serve as a universal model for the Coulomb drag effect in the hopping system. [ABSTRACT FROM AUTHOR]

Engineering of phonons, that is, collective lattice vibrations in crystals, is essential for manipulating physical properties of materials such as thermal transport, electron‐phonon interaction, confinement of lattice vibration, and optical polarization. Most approaches to phonon‐engineering have been largely limited to the high‐quality heterostructures of III–V compound semiconductors. Yet, artificial engineering of phonons in a variety of materials with functional properties, such as complex oxides, will yield unprecedented applications of coherent tunable phonons in future quantum acoustic devices. In this study, artificial engineering of phonons in the atomic‐scale SrRuO3/SrTiO3 superlattices is demonstrated, wherein tunable phonon modes are observed via confocal Raman spectroscopy. In particular, the coherent superlattices led to the backfolding of acoustic phonon dispersion, resulting in zone‐folded acoustic phonons in the THz frequency domain. The frequencies can be largely tuned from 1 to 2 THz via atomic‐scale precision thickness control. In addition, a polar optical phonon originating from the local inversion symmetry breaking in the artificial oxide superlattices is observed, exhibiting emergent functionality. The approach of atomic‐scale heterostructuring of complex oxides will vastly expand material systems for quantum acoustic devices, especially with the viability of functionality integration. [ABSTRACT FROM AUTHOR]

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 FROM AUTHOR]

La 0.7 Ca 0.18 Ba 0.12 Mn 0.95 Sn 0.05 O 3 compound has been successfully prepared by the solid-state reaction route. The structural, electrical, magnetotransport properties, as well as the temperature coefficient of resistance, were experimentally characterized and discussed. Rietveld's refinement of the X-ray diffractogram revealed that the compound crystallizes in an orthorhombic structure with a Pnma space group. The estimated crystallite size is about 43 nm. The SEM micrographs revealed the granular nature and polygonal grain shape of the sample. The electrical resistivity curves, carried out between 20 and 300 K, show a metal-to-insulator transition and an upturn at a very low-temperature range (20 K < T < 32 K). The magnetoresistance maximum value reached 23.23% at 20 K under 1 Tesla. The temperature coefficient of resistance curves exhibits a slight characteristic peak around TMI, and its value is around 1.96%. Fitting the electrical resistivity curves in the metallic region ( 32 K < T ≤ T MI ) confirms that the resistivity behavior is governed by a combination of residual resistivity, electron–electron scattering process, and electron–phonon interaction, whereas in the insulating region ( T ≥ θ D / 2 ), it is governed by adiabatical small polarons hopping. [ABSTRACT FROM AUTHOR]

We have studied the characteristic feature of coherent photon transport in a semiconductor waveguide. We have presented a semiconductor master equation formalism that accurately simulated coherent input or output coupling of semiconductor cavity quantum electrodynamics systems such as planar photonic crystals and micropillar cavities. The role of quantized multiphoton effects pointed out the possible failure of weak excitation approximation, which was found to fail even for low input powers and small mean cavity photon numbers. For increasing field strengths, possible failure of the semiclassical approach was taken into account. In the weak coupling regime, higher order quantum correlation effects, were shown to be significant. We have introduced the general theoretical technique to simulate coherent photon transport outside both the weak excitation approximation and the semi classical approximation. Electron-phonon interactions at a microscopic level were derived using polaron transformation. We have demonstrated that substantial deviations from the weak excitation approximation resulted for very small mean photon numbers. We have modified the master equation approach to include the mechanism of electron-acoustic scattering and studied the impact of electron-phonon interaction on incoherent scattering and coherent renormalization of the exciton cavity coupling rate, qualitative differences from simple Lorentzian decay model containing quantum dot were found. We have also studied the transmission of light in the strong coupling regime and simulated a phase gate. We have found that coupling to an acoustic phonon bath caused considerable qualitative changes in light propagation characteristics modeled by a simple pure dephasing process. We have used the model to simulate a conditional phasegate. The obtained results were found in good agreement with previously obtained results. [ABSTRACT FROM AUTHOR]

We study ground-state properties of a two-site, two-electron Holstein model describing two molecules coupled indirectly via electron-phonon interaction by using both exact diagonalization and self-consistent diagrammatic many-body perturbation theory. The Hartree and self-consistent Born approximations used in the present work are studied at different levels of self-consistency. The governing equations are shown to exhibit multiple solutions when the electron-phonon interaction is sufficiently strong, whereas at smaller interactions, only a single solution is found. The additional solutions at larger electron-phonon couplings correspond to symmetry-broken states with inhomogeneous electron densities. A comparison to exact results indicates that this symmetry breaking is strongly correlated with the formation of a bipolaron state in which the two electrons prefer to reside on the same molecule. The results further show that the Hartree and partially self-consistent Born solutions obtained by enforcing symmetry do not compare well with exact energetics, while the fully self-consistent Born approximation improves the qualitative and quantitative agreement with exact results in the same symmetric case. This together with a presented natural occupation number analysis supports the conclusion that the fully self-consistent approximation describes partially the bipolaron crossover. These results contribute to better understanding how these approximations cope with the strong localizing effect of the electron-phonon interaction. [ABSTRACT FROM AUTHOR]

We analyze the renormalization of the electron mass due to the electron–phonon interaction and interaction constant λ associated with this renormalization in the models of acoustic and optical phonons in a wide range of characteristic phonon frequencies ω0 both in the adiabatic limit, when this frequency is substantially lower than Fermi energy εF, as well as in the antiadiabatic limit, when the characteristic frequency is substantially higher than the width of the seed electron band. It is shown that in the antiadiabatic limit, λ is inversely proportional to the characteristic phonon frequency, and in view of the smallness of this constant, the Migdal theorem holds in this limit also. We consider the effect of disorder and strong electron correlations of the electron–phonon renormalization of the electron mass and constant λ. In the adiabatic limit, mass renormalization λ is slightly suppressed by impurity scattering, which is due to a decrease in the density of states at the Fermi level. Electron correlations in this limit suppress insignificantly the electron–phonon interaction constant λ in a correlated metal, while in the Mott insulator, λ ≈ 0. The electron–phonon interaction hampers the Mott metal–insulator transition, which makes possible the restoration of the quasiparticle peak and a sharp increase in constant λ with the Debye frequency in the insulator near the Mott transition. In the antiadiabatic limit, neither disorder nor strong electron correlations noticeably affect the electron–phonon renormalization of the mass and effective constant λ ~ εF/ω0. [ABSTRACT FROM AUTHOR]

Large-radius excitons in polar crystals are considered. It is shown that translation invariant description of excitons interacting with a phonon field leads to a nonzero contribution of phonons into the exciton ground state energy only in the case of weak or intermediate electron-phonon coupling. A conclusion is made that self-trapped excitons cannot exist in the limit of strong coupling. Peculiarities of the absorption and emission spectra of translation invariant excitons in a phonon field are discussed. Conditions when the hydrogen-like exciton model remains valid in the case of electron-phonon interaction are found. [ABSTRACT FROM AUTHOR]

The addition of active, nonlinear, and nonreciprocal functionalities to passive piezoelectric acoustic wave technologies could enable all-acoustic and therefore ultra-compact radiofrequency signal processors. Toward this goal, we present a heterogeneously integrated acoustoelectric material platform consisting of a 50 nm indium gallium arsenide epitaxial semiconductor film in direct contact with a 41° YX lithium niobate piezoelectric substrate. We then demonstrate three of the main components of an all-acoustic radiofrequency signal processor: passive delay line filters, amplifiers, and circulators. Heterogeneous integration allows for simultaneous, independent optimization of the piezoelectric-acoustic and electronic properties, leading to the highest performing surface acoustic wave amplifiers ever developed in terms of gain per unit length and DC power dissipation, as well as the first-ever demonstrated acoustoelectric circulator with an isolation of 46 dB with a pulsed DC bias. Finally, we describe how the remaining components of an all-acoustic radiofrequency signal processor are an extension of this work. Radio frequency signal processing (RFSP) currently involves a mix of components with differing operation principles, which hinders miniaturisation. Here, Hackett et al. succeed in creating acoustic non-reciprocal circulators, amplifiers, and passive filters, paving the way for all acoustic single-chip RFSP. [ABSTRACT FROM AUTHOR]

The formation of large polarons and bipolarons and related in-gap states in lightly-doped cuprates is studied in the strong electron–phonon coupling regime. The ground-state energies, binding energies and binding radius of strong-coupling large (bi)polarons are calculated using the continuum model and adiabatic approximation taking into account both the short- and long-range electron–phonon interactions. The obtained results show that the binding energies of such large (bi)polarons in the cuprates are progressively increased with decrease in the high frequency dielectric constant 𝜀 ∞ and ratio η = 𝜀 ∞ / 𝜀 0 (where 𝜀 0 is the static dielectric constant). As a result, large (bi)polarons become nearly small (bi)polarons. It is shown that hole carriers strongly interact with acoustic and optical phonons and their self-trapping leads to the formation of (bi)polaronic states in the charge-transfer (CT) gap of the cuprates. As the cuprate system is doped, the CT gap of the parent compound is filled in with low-energy (bi)polaronic states. The calculated energies of such (bi)polaronic states are in good agreement with the experimentally observed energies of new states appearing in the CT gap of the parent cuprates. The calculated values of the binding radius of large polarons are also well consistent with the existing experimental data. [ABSTRACT FROM AUTHOR]

In this work, we investigated the formation of Tl-Se layers followed by doping with metal cations. A two-stage adsorption/diffusion process used to form Tl-Se layers involves (a) selenization in potassium selenotrithionate solution followed by (b) treatment with Tl+ precursor solutions. These layers have been successfully doped with Cu+/Cu2+, Ga3+ and Ag+ cations using a cation exchange reaction. The resulting chemical compositions of Tl-Se and Tl-M-Se (M = Cu, Ga, Ag) layers were investigated using the EDS and AAS methods. The bulk elemental composition and the Tl/Se molar ratio of the Tl-Se layers varied with the concentration of the Tl+ precursor solution, the exposure time in the Tl+ precursor solution, and the form of the Tl+ in the solution, whereas the EDS analysis showed that the surface was slightly enriched in thallium. The optical properties of the formed layers were studied. These layers were identified using room temperature reflection spectrum, the values of absorption edge, bandgap (Eg), band tail width (Urbach energy, EU) of the localised states, Steepness parameter (s) and electron-phonon interaction (Ee-p). [ABSTRACT FROM AUTHOR]

A thorough understanding of the microscopic picture of heat conduction in solids is critical to a broad range of applications, from thermal management of microelectronics to more efficient thermoelectric materials. The transport properties of phonons, the major microscopic heat carriers in semiconductors and insulators, particularly their scattering mechanisms, have been a central theme in microscale heat conduction research. In the past two decades, significant advancements have been made in computational and experimental efforts to probe phonon-phonon, phonon-impurity, and phonon-boundary scattering channels in detail. In contrast, electron-phonon scatterings were long thought to have negligible effects on thermal transport in most materials under ambient conditions. This article reviews the recent progress in first-principles computations and experimental methods that show clear evidence for a strong impact of electron-phonon interaction on phonon transport in a wide variety of technologically relevant solid-state materials. Under thermal equilibrium conditions, electron-phonon interactions can modify the total phonon scattering rates and renormalize the phonon frequency, as determined by the imaginary part and the real part of the phonon self-energy, respectively. Under nonequilibrium transport conditions, electron-phonon interactions can affect the coupled transport of electrons and phonons in the bulk through the "phonon/electron drag" mechanism as well as the interfacial thermal transport. Based on these recent results, we evaluate the potential use of electron-phonon interactions to control thermal transport in solids. We also provide an outlook on future directions of computational and experimental developments. [ABSTRACT FROM AUTHOR]

The magneto-optical absorption properties, including magneto-optical absorption coefficient (MOAC) and its line-width, or the full-width at half-maximum (FWHM), of a GaAs/Ga 1 - s Al s As quantum well with a finite semi-parabolic potential are studied under the combined effects of the Al-doped concentration (s), the hydrostatic pressure (P), and the temperature (T). The MOAC is expressed as a function of photon energy for distinct values of s, P, T, and the well-width (L z) when the electron-phonon interaction is included. The energy separation as well as the intensity and position of absorption peaks depend on these parameters. The variation of the FWHM of absorption peaks is used to study absorption characteristics as a function of s, P, T, and L z . The temperature-dependent FWHM is found to qualitatively consistent with experimental observations. [ABSTRACT FROM AUTHOR]

The artificial stacking of nanohybrid films helps to enhance their properties and thus intrigues researchers to explore this possibility in emerging technologies. The layer-by-layer approach was used to fabricate samples of zinc sulfide/reduced graphene oxide (ZnS/rGO) by using spin coating technique. The structure and optoelectronic properties has been extensively studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV–VIS-NIR spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Hall measurements. Raman spectrum elucidates the phonon contribution of ZnS and breathing mode of κ-point phonons and sp2 bonds of carbon atoms of rGO. The electron-phonon interactions reveal reduction in electron mobility and enhancement in holes contribution with rGO content leading to surface charge transfer doping (SCTD). XPS results explain the valence band edge and conduction band edge to form type-I band alignment to reconfirm carrier-type reversal. A change in the dispersion of refractive indices along with a small rise in the value of absorption coefficient in terahertz (THz) region for ZnS/rGO nanocomposite films has been observed. These results will open up new opportunities to furthering the science of this technologically important class of materials for future electronics. [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]

An improved Lee-Low-Pines intermediate coupling method is used to study the energies and binding energies of bound polarons in a wurtzite ZnO/MgxZn1-xO quantum well. The contributions from different branches of long-wave optical phonons, i.e., confined optical phonons, interface optical phonons, and half-space optical phonons are considered. In addition to electron-phonon interaction, the impurity-phonon interaction, and the anisotropy of material parameters, such as phonon frequency, electron effective mass, and dielectric constant, are also included in our computation. Ground-state energies, binding energies and detailed phonon contributions from various phonons as functions of well width, impurity position and composition are presented. Our result suggests that total phonon contribution to ground state and binding energies in the studied wurtzite ZnO/Mg0.3Zn0.7O quantum wells varies between 28-23meV and 62-45meV, respectively, which are much larger than the corresponding values (about 3.2-1.8meV and 1.6-0.3 meV) in GaAs/Al0.3Ga0.7As quantum wells. For a narrower quantum well, the phonon contribution mainly comes from interface and half-space phonons, for a wider quantum well, most of phonon contribution originates from confined phonons. The contribution from all the phonon modes to binding energies increases slowly either when impurity moves far away from the well center in the z direction or with the increase in magnesium composition (x). It is found that different phonons have different influences on the binding energies of bound polarons. Furthermore, the phonon contributions to binding energies as functions of well width, impurity position, and composition are very different from one another. In general, the electron-optical phonon interaction and the impurity center-optical phonon interaction play an important role in electronic states of ZnO-based quantum wells and cannot be neglected. [ABSTRACT FROM AUTHOR]

The magneto transport of Ruddlesden–Popper, La2-2xSr1+2xMn2O7 (0.42≤x≤0.52), 2-dimensional bilayered manganites have been investigated in a broad temperature range. The samples have been synthesized using the solid-state reaction method. Rietveld refinement of the X-ray diffraction data indicates the tetragonal structure formation with I4/mmm space group. The resistivity curves of the samples present a general characteristic of metal-insulator (MI) transition at certain temperature (TMI). Besides, for samples with x = 0.48, 0.50, and 0.52, at a certain temperature (TCO) well below TMI the charge ordering is also evident. Furthermore, the samples display a shallow upturn in resistivity below Tmin due to the Kondo like spin scattering effect, weak localization and electron-phonon interaction. The high temperature semiconducting (T>TMI) region, the resistivity curve follows the 3D Mott's variable hopping transport mechanism. The overall suppression of resistivity accounts for a substantial magnetoresistance by applying a magnetic field and the characteristic change in TMI, TCO, and Tmin are discussed. Temperature-dependent magnetization demonstrates the suppression of ferromagnetism and evident of antiferromagnetic nature with an apparent charge ordering with increasing concentration of Sr2+. [ABSTRACT FROM AUTHOR]

Trigonal α − G a 2 O 3 is an ultrawideband semiconductor with potential applications in power electronics and ultraviolet opto-electronic devices. In this Letter, we calculate the low field electron mobility in α − G a 2 O 3 from first principles calculations. The effect of all the 30 phonon modes is taken into account for the transport calculation. The phonon dispersion and the Raman and Infrared spectra are calculated under the density functional perturbation theory formalism and compared with experiments. The electron–phonon interaction (EPI) elements on a dense reciprocal space grid are obtained using the Wannier function interpolation. The full energy dispersion of the phonons is included in both the polar and nonpolar EPI calculations. The electron mobility is then evaluated incorporating the effects of the polar, nonpolar, and ionized impurity scattering using Rode's iterative method. At room temperature, the low field isotropic average electron mobility is estimated to be ∼220 c m 2 / V s predominantly limited by the polar optical phonon scattering at a doping density of 1.0 × 1 0 15 c m − 3 . The anisotropy in the mobility arising from the phonon scattering is also evaluated. Temperature and dopant concentration variation of mobility is also studied, which can help in optimization of the growth for transport measurements. [ABSTRACT FROM AUTHOR]

The current–voltage characteristics of silicon photodiodes before and after irradiation by γ-quanta with an energy of 1.25 MeV and an irradiation dose of 0.5 mrad are investigated. It is established that the reverse currents are determined by the Poole–Frenkel mechanism in a strong electric field with the influence of electron–phonon interaction. A procedure is developed and the parameters of the electron–phonon interaction described by the single-coordinate configuration model are calculated from the reverse current–voltage characteristics. It is assumed that divacancy-oxygen centers in silicon, which determine the reverse photodiode currents, are formed due to γ-ray irradiation. [ABSTRACT FROM AUTHOR]