The availability of ab initio electronic calculations and the concomitant techniques for deriving the corresponding lattice dynamics have been profusely used for calculating thermodynamic and vibrational properties of semiconductors, as well as their dependence on isotopic masses. The latter have been compared with experimental data for elemental and binary semiconductors with different isotopic compositions. Here we present theoretical and experimental data for several vibronic and thermodynamic properties of CuGa2, a canonical ternary semiconductor of the chalcopyrite family. Among these properties are the lattice parameters, the phonon dispersion relations and densities of states (projected on the Cu, Ga, and S constituents), the specific heat and the volume thermal expansion coefficient. The calculations were performed with the ABINIT and VASP codes within the LDA approximation for exchange and correlation and the results are compared with data obtained on samples with the natural isotope composition for Cu, Ga and S, as well as for isotope enriched samples.
Detailed first principles calculations of the structural, electronic and optical properties of two representatives of the chalcopyrite group of compounds (LiInSe2 and LiInTe2) are reported in the present paper. Both materials are shown to be the direct band gap semiconductors. Analysis of the electronic properties showed that the degree of covalency increases if Se is substituted by Te. Calculations of the optical properties of both crystals allowed getting reliable approximation of the refractive index as a function of the wavelength. All calculated results were compared with the available ex…
The correct treatment of d electrons is of prime importance in order to predict the electronic properties of the prototype chalcopyrite semiconductors. The effect of d states is linked with the anion displacement parameter u, which in turn influences the bandgap of these systems. Semilocal exchange-correlation functionals which yield good structural properties of semiconductors and insulators often fail to predict reasonable u because of the underestimation of the bandgaps arising from the strong interplay between d electrons. In the present study, we show that the meta-generalized gradient ap…
We observe significant effects of structural distortion on electronic and optical properties of CdGa_2X_4 (X = S, Se, Te) defect chalcopyrite. The calculation is carried out within Density functional theory based tight binding linear muffin tin orbital (TB-LMTO) method. Structural parameters and band gap of CdGa_2X_4 agree well with the available experimental values within LDA limit. Change in band gap due to structural distortion is 3.63%, 4.0%, and 8.8% respectively. We observe significant change in optical properties also due to this effect. Effects on optical properties come mainly from op…
Influence of composition and external hydrostatic pressure on the structural, electronic, and optical properties of the CuGa1-xAlxS2 (x=0, 0.25, 0.5, 0.75, 1.0) chalcopyrite semiconductor was analyzed by means of the first-principles calculations. Dielectric functions and optical absorption spectra were calculated for all considered aluminum concentrations. The pressure coefficients of the calculated band gaps and position of the lowest in energy absorption peaks were extracted from the calculated results. One of the main results is that substitution of 25% of gallium by aluminum (thus forming…
We have carried out ab-initio calculation and study of structural and electronic properties of AgAlM2 (M = S, Se, Te) chalcopyrite semiconductors using Density Functional Theory (DFT) based self consistent Tight binding Linear Muffin Tin orbital (TB-LMTO) method. Calculated equlibrium values of lattice constants, anion displacement parameter (u), tetragonal distortion (η = c/2a) and bond lengths have good agreement with experimental values. Our study suggests these semiconductors to be direct band gap semiconductors with band gaps 1.98 eV, 1.59 eV and 1.36 eV respectively. These are in good ag…
The electronic structure, linear and nonlinear optical properties have been calculated for CuInX2 (X=S, Se, Te) chalcopyrite-structure single crystals using the state-of-the-art full potential linear augmented plane wave (FP-LAPW) method. We present results for band structure, density of states, and imaginary part of the frequency-dependent linear and nonlinear optical susceptibilities. We find that these crystals are semiconductors with direct band gaps. We have calculated the birefringence of these crystals. The birefringence is negative for CuInS2 and CuInSe2 while it is positive for CuInTe…
Four ternary semiconductors with the chalcopyrite structure (BeCN2, BeSiN2, MgCN2, and MgSiN2) were studied using the first principles methods. The structural, electronic, optical and elastic properties were calculated. All these materials were found to be the indirect band gap semiconductors, with the calculated band gaps in the range from 3.46 eV to 3.88 eV. Comparison of the degree of covalency/ionicity of the chemical bonds in these compounds was performed. Anisotropy of the optical properties of these tetragonal crystals was demonstrated by calculating the real and imaginary parts of the …
If magnetic semiconductors are ever to find wide application in real spintronic devices, their magnetic and electronic properties will require tailoring in much the same way that band gaps are engineered in conventional semiconductors. Unfortunately, no systematic understanding yet exists of how, or even whether, properties such as Curie temperatures and band gaps are related in magnetic semiconductors. Here we explore theoretically these and other relationships within 64 members of a single materials class, the Mn-doped II-IV-V2 chalcopyrites, three of which are already known experimentally t…
We have studied the structural and electronic properties of defect chalcopyrite semiconductors AAl2Se4 (A = Ag, Cu, Cd, Zn) using Density Functional Theory (DFT) based first principle technique within Tight binding Linear Muffin Tin orbital (TB-LMTO) method. Our calculated structural parameters such as lattice constants, anion displacement parameter (u), tetragonal distortion (η = c/2a), bond lengths and bulk modulus are in good agreement with other work. Our band structure calculation suggests that these compounds are direct band gap semiconductors having band gaps 2.40, 2.50, 2.46 and 2.82 e…
We use the Surface Green Function Matching (SGFM) method and a tight-binding hamiltonian to calculate the (100)-surface electronic band structure and local density of states of the series of Cu-based A^{I}B^{III}C2^{VI} chalcopyrites . We find four surface states in the optical gap energy region of s-p character and three surface states in the conduction band region of p-character. We show the trends of different characteristics within the series by means of figures and tables so that the quantitave behavior can be evaluated as well. We did not find Frontier Induced Semi-Infinite states of non…
The ground state band structure, magnetic moments, charges and population numbers of electronic shells of Cu and Fe atoms have been calculated for chalcopyrite CuFeS2 using density functional theory. The comparison between our calculation results and experimental data (X-ray photoemission, X-ray absorption and neutron diffraction spectroscopy) has been made. Our calculations predict a formal oxidation state for chalcopyrite as Cu$^{1+}$Fe$^{3+}$S$_{2}$$^{2-}$. However, the assignment of formal valence state to transition metal atoms appears to be oversimplified. It is anticipated that the vale…
Anharmonicity Driven by Vacancy Ordering Unlocks High-performance Thermoelectric Conversion in Defective Chalcopyrites II-III$_2$-VI$_4$
Ningbo University（宁波大学）；University of the Basque Country (UPV/EHU)（巴斯克大学）；Centro de Física de Materiales (CFM-MPC), CSIC-UPV/EHU（材料物理中心（CFM-MPC），西班牙国家研究委员会-巴斯克大学）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；Dartmouth College（达特茅斯学院）；Technical University of Darmstadt（达姆施塔特工业大学）；Technische Universität Wien（维也纳工业大学）；Linköping University（林雪平大学）；Suzhou Laboratory（苏州实验室）；Gusu Laboratory of Materials（姑苏材料实验室）
We present a systematic assessment of the structural properties, the electronic density of states, the charge densities, and the phase stabilities of AgInSe$_2$ and AuInSe$_2$ using screened exchange hybrid density functional theory, and compare their properties to those of CuInSe$_2$. For AgInSe$_2$, hybrid density functional theory properly captures several experimentally measured properties, including the increase in the band gap and the change in the direction of the lattice distortion parameter $u$ in comparison to CuInSe$_2$. While the electronic properties of AuInSe$_2$ have not yet bee…
The bulk photovoltaic effect generates intrinsic photocurrents in materials without inversion symmetry. Shift current is one of the bulk photovoltaic phenomena related to the Berry phase of the constituting electronic bands: photo-excited carriers coherently shift in real space due to the difference in the Berry connection between the valence and conduction bands. Ferroelectric semiconductors and Weyl semimetals are known to exhibit such nonlinear optical phenomena. Here we consider chalcopyrite semiconductor ZnSnP$_2$ which lacks inversion symmetry and calculate the shift current conductivity…
Electronic and transport properties of CuGaTe$_2$, a hole-doped ternary copper based chalcopyrite type semiconductor, are studied using calculations within the Density Functional Theory and solving the Boltzmann transport equation within the constant relaxation time approximation. The electronic bandstructures are calculated by means of the full-potential linear augmented plane wave method, using the Tran-Blaha modified Becke-Johnson potential. The calculated band gap of 1.23 eV is in agreement with the experimental value of 1.2 eV. The carrier concentration- and temperature dependent thermoel…
Accurate and efficient prediction of the band gaps and optical spectra of chalcopyrite semiconductors from a non-empirical range-separated dielectric-dependent hybrid: Comparison with many-body perturbation theory
Using first-principles electronic structure calculations we identify the anion vacancies in II-VI and chalcopyrite Cu-III-VI2 semiconductors as a class of intrinsic defects that can exhibit metastable behavior. Specifically, we predict persistent electron photoconductivity (n-type PPC) caused by the oxygen vacancy VO in n-ZnO, and persistent hole photoconductivity (p-type PPC) caused by the Se vacancy VSe in p-CuInSe2 and p-CuGaSe2. We find that VSe in the chalcopyrite materials is amphoteric having two "negative-U" like transitions, i.e. a double-donor transition e(2+/0) close to the valence …
Molecular dynamics simulations of a Xe monolayer sliding on Ag(001) and Ag(111) are carried out in order to ascertain the microscopic origin of friction. For several values of the electronic contribution to the friction of individual Xe atoms, the intra-overlayer phonon dissipation is calculated as a function of the corrugation amplitude of the substrate potential, which is a pertinent parameter to consider. Within the accuracy of the numerical results and the uncertainty with which the values of the relevant parameters are known at present, we conclude that electronic and phononic dissipation…
By using density functional theory, we have studied vibrational features, Raman activities, and electronic properties of ultrathin hydrogen-passivated diamond nanowires (H-DNWs). Confinement imposes the softening of transverse acoustic modes and the hardening of the low-optical modes. Higher frequencies optical modes are more influenced by the surface termination effect. Surface effect splits transverse (TO) and longitudinal (LO) optical modes with a redshift from the bulk diamond. Electronic inspection shows that the surface terminated hydrogen atoms have the main contribution to the conducti…
Disentangling electronic and phononic contributions to high-temperature superconductivity in X2MH6 hydrides
Jimei University（集美大学）；Xiamen University（厦门大学）；Iowa State University（爱荷华州立大学）；Guangdong University of Technology（广东工业大学）；Ames National Laboratory, U.S. Department of Energy（美国能源部艾姆斯国家实验室）
Unveiling the nature of the bosonic excitations that mediate the formation of Cooper pairs is a key issue for understanding unconventional superconductivity. A fundamen- tal step toward this goal would be to identify the relative weight of the electronic and phononic contributions to the overall frequency (Ω) dependent bosonic function, Π(Ω). We perform optical spectroscopy on Bi2212 crystals with simultaneous time- and frequency-resolution; this technique allows us to disentangle the electronic and phononic contributions by their different temporal evolution. The strength of the interaction (…
Recently a stable monolayer of antimony in buckled honeycomb structure called antimonene was successfully grown on 3D topological insulator Bi$_2$Te$_3$ and Sb$_2$Te$_3$, which displays semiconducting properties. By first principle calculations, we systematically investigate the phononic, electronic and optical properties of $α-$ and $β-$ allotropes of monolayer arsenene/antimonene. We investigate the dynamical stabilities of these four materials by considering the phonon dispersions. The obtained electronic structures reveal the direct band gap of monolayer $α-$As/Sb and indirect band gap of …
Band structure and optical properties of defect- Chalcopyrite type semiconductor ZnIn$_2$Te$_4$ have been studied by TB-LMTO first principle technique. The optical absorption calculation suggest that ZnIn$_2$Te$_4$ is a direct-gap semiconductor having a band gap of 1.40 eV., which confirms the experimentally measured value. The calculated complex dielectric-function $ε(E) = ε_1(E) + iε_2(E)$ reveal distinct structures at energies of the critical points in the Brillouin zone.
The thermoelectric properties of n type nanoscale three dimensional (3D) Si phononic crystals (PnCs) with spherical pores are studied. Density functional theory and Boltzmann transport equation under the relaxation time approximation are applied to study the electronic transport coefficients, electrical conductivity, Seebeck coefficient and electronic thermal conductivity. We found that the electronic transport coefficients in 3D Si PnC at room temperature (300 K) change very little compared with that of Si, for example, electrical conductivity and electronic thermal conductivity is decreased …
Electronic Raman scattering and optical phonon self-energies are studied on single crystals of $LuB_{12}$ with different isotopic composition in the temperature region 10-650K and at pressures up to 10 GPa. The shape and energy position of the spectral peaks depend on the magnitude of the probed wave vector, temperature, and symmetry of excitations. We simulated experimental spectra using electronic structure obtained in the density function theory and taking into account the electron-phonon scattering. The emergence of a broad continuum in the spectra is identified with the inelastic scatteri…
First-principles calculations, within the framework of density functional theory, have been performed on the well-studied 2H and the less explored 1T$^{\prime}$ phase of single-layer MoS$_{2}$. We have addressed the strain-induced tunability of the electronic and phononic properties of both phases, and compared their stability against the applied strain. By considering a large number of strain profiles for both tensile and compressive stress, we have found that the electronic properties of both 2H and 1T$^{\prime}$ phases are sensitive to the direction of the applied strain and can be tuned in…
Over the past thirty years, it has been consistently observed that surface engineering of colloidal nanocrystals (NC) is key to their performance parameters. In the case of lead chalcogenide NCs, for example, replacing thiols with halide anion surface termination has been shown to increase power conversion efficiency in NC-based solar cells. To gain insight into the origins of these improvements, we perform ab initio molecular dynamics (AIMD) on experimentally-relevant sized lead sulfide (PbS) NCs constructed with thiol or Cl, Br, and I anion surfaces. The surface of both the thiol- and halide…
We study the electron and phonon spectral functions as well as superconductivity for a two dimensional electron gas couped to dipolar phonons via small-momentum transfer scattering. The results reported here are obtained through sign-problem-free quantum Monte-Carlo simulation. Hence aside from modeling there is no further approximations. Our results can be relevant to the high-temperature superconductor at the interface between a unit-cell-thick FeSe and SrTiO3.
Thermoelectrics as a way to use waste heat, is essential in electronic industries, but its low performance at operational temperatures makes it inappropriate in practical applications. Tailoring graphene can change its properties. In this work, we are interested in studying the transport properties of S-shape graphene structures with the single vacancy (SV) and double vacancy (DV) models. The structures are composed of a chiral part, which is an armchair graphene nanoribbon, and two zigzag graphene ribbons. We investigate the changes in the figure of merit by means of the Seebeck coefficient, …
We present a dynamical study on the nonlinear conduction behaviour in the commensurate charge-density-wave phase of the quasi-one-dimensional conductor DCNQI$_2$Cu below 75 K. We can accurately simulate magnitude and time-dependence of the measured conductivity in response to large voltage pulses by accounting for the energy exchange between the phononic and electronic subsystems by means of an electrothermal model. Our simulations reveal a distinct non-equilibrium population of optical phonon states with an average energy of E$_{ph}$ = 19 meV being half the activation energy of about $Δ$E$_a$…
Thermoelectrics (TE) materials manifest themselves in direct conversion of temperature differences to electric power and vice versa. Despite remarkable advances have been achieved in the past decades for various TE systems, the energy conversion efficiencies of TE devices, which is characterized by a dimensionless figure-of-merit (ZT ), remain a generally poor factor that severely limits their competitiveness and range of employment. The bottleneck for substantially boosting ZT coefficient lies in the strong interdependence of the physical parameters involved in electronic and phononic transpo…
We report ab initio calculations of the electronic band structure, the corresponding optical spectra, and the phonon dispersion relations of trigonal alpha-HgS (cinnabar). The calculated dielectric functions are compared with unpublished optical measurements by Zallen and coworkers. The phonon dispersion relations are used to calculate the temperature and isotopic mass dependence of the specific heat which has been compared with experimental data obtained on samples with the natural isotope abundances of the elements Hg and S (natural minerals and vapor phase grown samples) and on samples prep…
We report on the complex dielectric tensor components of four chalcopyrite semiconductors in the optical energy range (1.4-5.2 eV, from 0.9 eV for CuInSe2) determined at room temperature by spectroscopic ellipsometry. Our results were obtained on single crystals of CuInSe2, CuGaSe2, CuInS2, and CuGaS2. Values of refractive indices n, extinction coefficients k and normal-incidence reflectivity R in the two different polarizations are given and compared with earlier data where available. We analyze in detail the structures of the dielectric function observed in the studied energy region. Critica…
Extreme Terahertz Nonlinear Phononics by Coherence-Imprinted Control of Hybrid Order
Ames National Laboratory（艾姆斯国家实验室）；Department of Physics and Astronomy, Iowa State University（爱荷华州立大学物理与天文系）；Centre for Quantum Physics, Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), School of Physics, Beijing Institute of Technology（北京理工大学物理学院先进光电量子架构与测量教育部重点实验室量子物理中心）；Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology（北京理工大学北京纳米光子学与超精细光电系统重点实验室）；Key Laboratory for Laser Plasmas (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University（上海交通大学物理与天文学院激光等离子体教育部重点实验室）；Zhangjiang Institute for Advanced Study and Tsung-Dao Lee Institute, Shanghai Jiao Tong University（上海交通大学张江高等研究院及李政道研究所）
Interplay between electronic and phononic energy dissipation channels in the adsorption of CO on Cu(110)
Instituto de Física Rosario (IFIR), CONICET-UNR（罗萨里奥物理研究所）；Universidad Nacional de Rosario（罗萨里奥国立大学）；Universidad Autónoma de Madrid（马德里自治大学）；Universidad del País Vasco (UPV/EHU)（巴斯克地区大学）；Centro de Física de Materiales CFM/MPC (CSIC-UPV/EHU)（材料物理中心）；Donostia International Physics Center DIPC（圣塞巴斯蒂安国际物理中心）
While condensed matter systems host both Fermionic and Bosonic quasi-particles, reliably predicting and empirically verifying topological states is only mature for Fermionic electronic structures, leaving topological Bosonic excitations sporadically explored. This is unfortunate, as Bosonic systems such a phonons offer the opportunity to assess spinless band structures where nodal lines can be realized without invoking special additional symetries to protect against spin-orbit coupling. Here we combine first-principles calculations and meV-resolution inelastic x-ray scattering to demonstrate t…
Phosphorene, an emerging elemental two-dimensional (2D) direct band gap semiconductor with fascinating structural and electronic properties distinctively different from other 2D materials such as graphene and MoS2, is promising for novel nanoelectronic and optoelectronic applications. Phonons, as one of the most important collective excitations, are at the heart for the device performance, as their interactions with electrons and photons govern the carrier mobility and light-emitting efficiency of the material. Here, through a detailed first-principles study, it is demonstrated that monolayer …
Electron-phonon-driven charge density waves can in some circumstances allow electronic correlations to become predominant, driving a system into a Mott insulating state. New insights into both the Mott state and preceding charge density wave may result from observations of the coupled dynamics of their underlying degrees of freedom. Here, tunneling injection of single electrons into the upper Hubbard band of the Mott charge-density-wave material 1T-TaS2 reveals extraordinarily narrow electronic excitations which couple to amplitude mode phonons associated with the charge density wave's periodi…
We report the structural and electronic properties of chalcopyrite semiconductors CuInSe2, CuIn2 Se4 and Cu0.5Li0.5InSe2. Our calculation is based on Density functional Theory within tight binding linear muffin-tin orbital (TB-LMTO) method. The calculated lattice constants, anion displacement (u), tetragonal distortion (η = c/2a) and bond lengths agree well with experimental values. Our result shows these compounds are direct band gap semiconductors. Our calculated band gaps, 0.79eV and 1.08 eV of CuInSe2 and Cu0.5Li0.5InSe2 respectively agree well with the experimental values within the limit…
The principle of detailed balance between electrons and phonons in presence of excitonic effects
Dipartimento di Fisica, Università di Roma La Sapienza（罗马大学物理系）；Theory and Simulation of Materials (THEOS), and National Centre for Computational Design and Discovery of Novel Materials (MARVEL), École Polytechnique Fédérale de Lausanne（洛桑联邦理工学院材料理论与模拟中心及国家计算设计与发现新材料中心）；Dipartimento di Scienze e Metodi dell’Ingegneria, Università di Modena e Reggio Emilia（摩德纳与雷焦艾米利亚大学工程科学与方法系）
Three-, four-, and six-fold excitations have significantly extended the subjects of condensed matter physics. There is an urgent need for a realistic material that can have coexisting 3-, 4-, and 6-fold excitations. However, these materials are uncommon because these excitations in electronic systems are usually broken by spin-orbit coupling (SOC) and normally far from the Fermi level. Unlike the case in electronic systems, the phonon systems with negligible SOC effect, not constrained by the Pauli exclusion principle, provide a feasible platform to realize these excitations in a wide frequenc…
Following the emergence of many novel two-dimensional (2-D) materials beyond graphene, interest has grown in exploring implications for fundamental physics and practical applications, ranging from electronics, photonics, phononics, to thermal management and energy storage. In this Colloquium, we first summarize and compare the phonon properties, such as phonon dispersion and relaxation time, of pristine 2-D materials with single layer graphene to understand the role of crystal structure and dimension on thermal conductivity. We then compare the phonon properties, contrasting idealized 2-D crys…
Moiré lattices which consist of parallel but staggered periodic lattices have been extensively explored due to their salient physical properties, such as van Hove singularities[1, 2], commensurable incommensurable transitions[3], non-Abelian gauge potentials[4], fractional quantum Hall effects[5-7], van der Waals interfaces[8, 9] and unconventional superconductivity[10, 11]. However, there are limited demonstrations of such concepts for classical wave systems. Here, we realized gauge fields in one-dimensional Moiré phononic lattices consisting of two superimposed periodic patterns which mismat…
The discovery of topological quantum states marks a new chapter in both condensed matter physics and materials sciences. By analogy to spin electronic system, topological concepts have been extended into phonons, boosting the birth of topological phononics (TPs). Here, we present a high-throughput screening and data-driven approach to compute and evaluate TPs among over 10,000 materials. We have clarified 5014 TP materials and classified them into single Weyl, high degenerate Weyl, and nodal-line (ring) TPs. Among them, three representative cases of TPs have been discussed in detail. Furthermo…
