Terminal-coupling induced critical eigenspectrum transition in closed non-Hermitian loops.

A hallmark feature of non-Hermitian (NH) systems is the non-Hermitian skin effect (NHSE), in which the eigenenergy spectra of the system under open boundary conditions (OBC) and periodic boundary conditions (PBC) differ markedly from each other. In particular, the critical NHSE occurs in systems consisting of multiple non-Hermitian chains coupled in parallel where even an infinitesimally small inter-chain coupling can cause the thermodynamic-limit eigenenergy spectrum of the system to deviate significantly from the OBC spectra of the individual component chains. We overturn the conventional wisdom that multiple chains are required for such critical transitions by showing that such a critical effect can also be induced in a single finite-length non-Hermitian chain where its two ends are connected together by a weak terminal coupling to form a closed loop.

Higher Chern number states in curved periodic nanowires.

The coupling between the spin and momentum degrees of freedom due to spin-orbit interactions (SOI) suggests that the strength of the latter can be modified by controlling the motion of the charge carriers. In this paper, we investigate how the effective SOI can be modulated by constraining the motion of charge carriers to curved waveguides thereby introducing real-space geometric curvature in their motion. The change in the SOI can in turn induce topological phase transitions in the system.

Effective Hamiltonian for silicene under arbitrary strain from multi-orbital basis.

A tight-binding (TB) Hamiltonian is derived for strained silicene from a multi-orbital basis. The derivation is based on the Slater-Koster coupling parameters between different orbitals across the silicene lattice and takes into account arbitrary distortion of the lattice under strain, as well as the first and second-order spin-orbit interactions (SOI). The breaking of the lattice symmetry reveals additional SOI terms which were previously neglected.

Controllable p-n junctions in three-dimensional Dirac semimetal CdAs nanowires.

We demonstrate a controllable p-n junction in a three-dimensional Dirac semimetal (DSM) CdAs nanowire with two recessed bottom gates. The device exhibits four different conductance regimes with gate voltages, the unipolar (n-n and p-p) and bipolar (n-p and n-p) regimes, where p-n junctions are formed. The conductance in the p-n junction regimes decreases drastically when a magnetic field is applied perpendicular to the nanowire.

Group delay time and Hartman effect in strained Weyl semimetals.

The group delay time was theoretically studied in Weyl semimetals (WSMs) in the presence of strain. The Hartman effect, where the delay time for tunneling through a barrier tends to a constant for large barrier thickness, can be observed in WSMs when the incident angles [Formula: see text] and [Formula: see text], and the unidirectional strain tensor u and shear strain tensor u , are larger than some critical values. We show that the Hartman effect is strongly dependent on the strength of the unidirectional strain tensor u and the ratio of the shear strain tensor [Formula: see text].

Electrically tunable valley polarization in Weyl semimetals with tilted energy dispersion.

Tunneling transport across electrical potential barriers in Weyl semimetals with tilted energy dispersion is investigated. We report that the electrons around different valleys experience opposite direction refractions at the barrier interface when the energy dispersion is tilted along one of the transverse directions. Chirality dependent refractions at the barrier interface polarize the Weyl fermions in angle-space according to their valley index.

Anomalous Photothermoelectric Transport Due to Anisotropic Energy Dispersion in WTe.

Band structures are vital in determining the electronic properties of materials. Recently, the two-dimensional (2D) semimetallic transition metal tellurides (WTe and MoTe) have sparked broad research interest because of their elliptical or open Fermi surface, making distinct from the conventional 2D materials. In this study, we demonstrate a centrosymmetric photothermoelectric voltage distribution in WTe nanoflakes, which has not been observed in common 2D materials such as graphene and MoS.

Curvature induced quantum phase transitions in an electron-hole system.

In this work, we study the effect of introducing a periodic curvature on nanostructures, and demonstrate that the curvature can lead to a transition from a topologically trivial state to a non-trivial state. We first present the Hamiltonian for an arbitrarily curved nanostructure, and introduce a numerical scheme for calculating the bandstructure of a periodically curved nanostructure. Using this scheme, we calculate the bandstructure for a sinusoidally curved two-dimensional electron gas.

Quantum Dots Formed in Three-dimensional Dirac Semimetal CdAs Nanowires.

We demonstrate quantum dot (QD) formation in three-dimensional Dirac semimetal CdAs nanowires using two electrostatically tuned p-n junctions with a gate and magnetic fields. The linear conductance measured as a function of gate voltage under high magnetic fields is strongly suppressed at the Dirac point close to zero conductance, showing strong conductance oscillations. Remarkably, in this regime, the CdAs nanowire device exhibits Coulomb diamond features, indicating that a clean single QD forms in the Dirac semimetal nanowire.

Influence of Fermi arc states and double Weyl node on tunneling in a Dirac semimetal.

Most theoretical studies of tunneling in Dirac and the closely related Weyl semimetals have modeled these materials as single Weyl nodes described by the three-dimensional Dirac equation [Formula: see text]. The influence of scattering between the different valleys centered around different Weyl nodes, and the Fermi arc states which connect these nodes are hence not evident from these studies. In this work we study the tunneling in a thin film system of the Dirac semimetal NaBi consisting of a central segment with a gate potential, sandwiched between identical semi-infinite source and drain segments.

Quantum Capacitance of a Topological Insulator-Ferromagnet Interface.

We study the quantum capacitance in a topological insulator thin film system magnetized in the in-plane direction in the presence of an out-of-plane magnetic field and hexagonal warping. To first order, the modification in quantum capacitance due to hexagonal warping compared to the clean case, where both the in-plane magnetization and hexagonal warping are absent, is always negative, and increases in magnitude monotonically with the energy difference from the charge neutrality point. In contrast, the change in the quantum capacitance due to in-plane magnetization oscillates with the energy in general, except when a certain relation between the inter-surface coupling, out of plane Zeeman energy splitting and magnetic field strength is satisfied.

Dirac semimetal thin films in in-plane magnetic fields.

In this work we study the effects of in-plane magnetic fields on thin films of the Dirac Semimetal (DSM) NaBi where one of the in-plane directions is perpendicular to the k-separation between the two Weyl nodes that exist for each spin orientation. We show numerically that the states localized near the surfaces of these thin films are related to the Fermi arc states in semi-infinite slabs. Due to the anisotropy between the two in-plane directions, the application of a magnetic field along these directions have differing effects.