arXiv subjects

Arnold Kiefer

Publications and source records attributed to Arnold Kiefer.

3 recordsLinked to original sources

arXiv2026

Negative magnetoresistance in strained $α$-Sn and $α$-SnGe films in an in-plane magnetic field

To test the hypothesis that the chiral anomaly is responsible for negative magnetoresitance (MR) in \atn{}, we have studied magnetotransport in strained, epitaxial films of pure \aSn{} and the alloy \aSnGe{} that are in the Dirac semimetal and 3D topological insulator state, respectively. We have observed for both states a negative MR with current either parallel or transverse to the in-plane magnetic field, but with a different dependence of MR on $\vec{B}$ strength. Our results are inconsistent with the chiral anomaly and suggest that other mechanisms may be responsible for negative MR in the Dirac/Weyl semimetal phase of \aSn{}. We also discuss several factors in sample design and material quality that may be contributing to the incongruous observations of MR reported in studies of strained \atn{} films.

cond-mat.mtrl-sci↗

arXiv2024

Interplay between strain and size quantization in a class of topological insulators based on inverted-band semiconductors

We consider surface states in semiconductors with inverted-band structures, such as $α$-Sn and HgTe. The main interest is the interplay of the effect of a strain of an arbitrary sign and that of the sample finite size. We consider, in particular, a model system comprised of a gapless semiconductor (e.g. HgTe or $α$-Sn) of finite-width sandwiched between layers of a regular-band semiconductor (e.g. CdTe or InSb). We clarify the origin of various transitions that happen at a given strain with the change of the sample thickness, in particular the transition between the Dirac semimetal and quasi-3D (quantized) topological insulator. Our conclusion opposes those reached recently by the majority of researchers. We show that near the transition point the surface state cannot be treated as a truly topological one since the parameters of the problem are such that an appreciable overlap of the surface states' wave functions located at opposite boundaries occur. As a result, a spin-conserving, elastic impurity scattering between the states located at opposite boundaries will induce substantial backscattering and destroy the robustness of the surface state. For the k-p Kane model we derive hard-wall boundary conditions in the case when the regular-band materials form high barriers for the carriers of the inner inverted-band semiconductor (for example, CdTe/HgTe/CdTe and CdTe/$α$-Sn/CdTe cases). We show that in this case the boundary conditions have universal and simple form and allow investigation of the realistic case of finite mass of the heavy-hole band, and comparison of the results obtained within the Kane and Luttinger models. In particular, a new type of surface states (wing states) developes with application of strain in the Kane model and is absent in the Luttinger model.

cond-mat.mes-hall↗

arXiv2021

Revisiting the physical origin and nature of surface states in inverted-band semiconductors

We revisit the problem of surface states in semiconductors with inverted band structures, such as $α$-Sn and HgTe. We unravel the confusion that arose over the past decade regarding the origin of the surface states, their topological nature, and the role of strain. Within a single minimalistic description, we reconcile different solutions found in the 1980s with the results obtained from modern-day numerical simulations, allowing us to unambiguously identify all branches of surface states around the $Γ$-point of the Brillouin zone in different regimes. We also show that strain is a smooth "deformation" to the surface states, following the usual continuity principle of physics, and not leading to any drastic change of the physical properties in these materials, in contrast to what has recently been advanced in the literature. We consider biaxial in-plane strain that is either tensile or compressive, leading to different branches of surface states for topological insulators and Dirac semimetals, respectively. Our model can help in interpreting numerous experiments on topological surface states originating from inverted-band semiconductors.

cond-mat.mes-hall↗