The renormalization of electronic eigenenergies due to electron-phonon coupling is sizable in many materials with light atoms. This effect, often neglected in ab-initio calculations, can be computed using the perturbation-based Allen-Heine-Cardona theory in the adiabatic or non-adiabatic harmonic approximation. After a short description of the numerous recent progresses in this field, and a brief overview of the theory, we focus on the issue of phonon wavevector sampling convergence, until now poorly understood. Indeed, the renormalization is obtained numerically through a q-point sampling inside the BZ. For q-points close to G, we show that a divergence due to non-zero Born effective charge appears in the electron-phonon matrix elements, leading to a divergence of the integral over the BZ for band extrema. Although it should vanish for non-polar materials, unphysical residual Born effective charges are usually present in ab-initio calculations. Here, we propose a solution that improves the coupled q-point convergence dramatically. For polar materials, the problem is more severe: the divergence of the integral does not disappear in the adiabatic harmonic approximation, but only in the non-adiabatic harmonic approximation. In all cases, we study in detail the convergence behavior of the renormalization as the q-point sampling goes to infinity and the imaginary broadening parameter goes to zero. This allows extrapolation, thus enabling a systematic way to converge the renormalization for both polar and non-polar materials. Finally, the adiabatic and non-adiabatic theory, with corrections for the divergence problem, are applied to the study of five semiconductors and insulators: a-AlN, b-AlN, BN, diamond and silicon. For these five materials, we present the zero-point renormalization, temperature dependence, phonon-induced lifetime broadening and the renormalized electronic bandstructure.
Spin injection using ferromagnetic semiconductors at room temperature is a building block for the realization of spin-functional semiconductor devices. Nevertheless, this has been very challenging due to the lack of reliable room-temperature ferromagnetism in well-known group IV and III-V based semiconductors. Here, we demonstrate room-temperature spin injection by using spin pumping in a (Ga,Fe)Sb / BiSb heterostructure, where (Ga,Fe)Sb is a ferromagnetic semiconductor (FMS) with high Curie temperature (TC) and BiSb is a topological insulator (TI). Despite the very small magnetization of (Ga,…
Electron correlation in semiconductors and insulators via symbolic regression
Oden Institute for Computational Engineering and Sciences, The University of Texas at Austin（德克萨斯大学奥斯汀分校奥登计算工程与科学研究所）；Department of Physics, The University of Texas at Austin（德克萨斯大学奥斯汀分校物理系）
Motivated by the fact that septuple-atomic-layer MnBi$_2$Te$_4$ can be structurally viewed as the combination of double-atomic-layer MnTe intercalating into quintuple-atomic-layer Bi$_2$Te$_3$, we present a general approach of constructing twelve septuple-atomic-layer $α_i$- and $β_i$-$MA_2Z_4$ monolayer family (\emph{i} = 1 to 6) by intercalating MoS$_2$-type $MZ$$_2$ monolayer into InSe-type A$_2$Z$_2$ monolayer. Besides reproducing the experimentally synthesized $α_1$-MoSi$_2$N$_4$, $α_1$-WSi$_2$N$_4$ and $β_5$-MnBi$_2$Te$_4$ monolayer materials, another 66 thermodynamically and dynamically…
In this work we study, theoretically, electronic mobility of the silicon carbide semiconductor in the 3C phase, named 3C-SiC. 3C-SiC has shown great potential for applications in extreme conditions. Thus, the study of the electronic mobility of this semiconductor is of great interest. In this work were theoretically deduced: drift velocity, displacement and mobility of the charge carriers in the n-type doped 3C-SiC semiconductor, subjected to a constant electric field. The dependence of these transport properties as a function of the intensity of the electric field and temperature was analyzed…
The dispersion law of plasmons running along thin wires with radius $a$ is known to be practically linear. We show that in a wire with a dielectric constant $κ$ much larger than that of its environment $κ_e$, such dispersion law crosses over to a dispersionless three-dimensional-like law when the plasmon wavelength becomes shorter than the length $(a/2) \sqrt{(κ/κ_e)\ln(κ/2κ_e)}$ at which the electric field lines of a point charge exit from the wire to the environment. This happens both in trivial semiconductor wires and wires of three-dimensional topological insulators.
Atomic scale electronic structure of the ferromagnetic semiconductor Cr2Ge2Te6
Cr_2Ge_2Te_6是一种具有范德华型层状结构的本征铁磁半导体材料，是一种很有前途的新型电子和自旋电子器件材料。在这里，我们结合扫描隧道显微镜和第一性原理计算研究的电子结构的Cr2 Ge 2 Te 6。Tunnel光谱揭示了一个令人惊讶的大的能级位移和变化的能隙大小的铁磁顺磁相变，以及一个特殊的双峰电子状态的Cr-网站缺陷。这些特征可以通过密度泛函理论的计算得到定量的解释，揭示了电子结构和磁序之间的密切关系。这些发现为Cr2 Ge 2 Te 6的微观电子结构和磁序起源提供了重要的新线索。
Structural phase transitions between semiconductors and topological insulators have rich applications in nanoelectronics but are rarely found in two-dimensional (2D) materials. In this work, by combining ab initio computations and evolutionary structure search, we investigate two stable 2D forms of gold(I) telluride (Au$_{2}$Te) with square symmetry, noted as s(I)- and s(II)-Au$_{2}$Te. s(II)-Au$_{2}$Te is the global minimum structure and is a room-temperature topological insulator. s(I)-Au$_{2}$Te is a direct-gap semiconductor with high carrier mobilities and unusual in-plane negative Poisson…
Relativistic First-Principles Full Potential Calculations of Electronic and Structural Properties of group IIIA-VA semiconductors based on Zeroth Order Regular Approximation (ZORA) Hamiltonian
The search for exotic new topological states of matter in widely accessible materials, for which the manufacturing process is mastered, is one of the major challenges of the current topological physics. Here we predict higher order topological insulator state in quantum wells based on the most common semiconducting materials. By successively deriving the bulk and boundary Hamiltonians, we theoretically prove the existence of topological corner states due to cubic symmetry in quantum wells with double band inversion. We show that the appearance of corner states does not depend solely on the cry…
Electronic transport under hydrostatic pressure and peculiar properties of the impurity energy spectrum in semiconductor arsenides of n-type: InAs, CdSnAs2, CdGeAs2 and GaAs
