Magnetotransport subband spectroscopy in InAs nanowires

Spin-Resolved Magneto-Tunneling and Giant Anisotropic g-Factor in Broken Gap InAs-GaSb Core-Shell Nanowires

We experimentally and computationally investigate the magneto-conductance across the radial heterojunction of InAs-GaSb core-shell nanowires under a magnetic field, B, up to 30 T and at temperatures in the range 4.2-200 K. The observed double-peak negative differential conductance markedly blue-shifts with increasing B. The doublet accounts for spin-polarized currents through the Zeeman split channels of the InAs (GaSb) conduction (valence) band and exhibits strong anisotropy with respect to B orientation and marked temperature dependence. Envelope function approximation and a semiclassical (WKB) approach allow to compute the magnetic quantum states of InAs and GaSb sections of the nanowire and to estimate the B-dependent tunneling current across the broken-gap interface. Disentangling different magneto-transport channels and a thermally activated valence-to-valence band transport current, we extract the g-factor from the spin-up and spin-down dI/dV branch dispersion, revealing a giant, strongly anisotropic g-factor in excess of 60 (100) for the radial (tilted) field configurations.

Chiral Topological Superconductivity in Superconductor-Obstructed Atomic Insulator-Ferromagnetic Insulator Heterostructures

Implementing topological superconductivity (TSC) and Majorana states (MSs) is one of the most significant and challenging tasks in both fundamental physics and topological quantum computations. In this work, taking the obstructed atomic insulator (OAI) Nb_{3}Br_{8}, s-wave superconductor (SC) NbSe_{2}, and ferromagnetic insulator (FMI) CrI_{3} as an example, we propose a new setup to realize the 2D chiral TSC and MSs in the SC/OAI/FMI heterostructure, which could avoid the subband problem effectively and has the advantage of huge Rashba spin-orbit coupling. As a result, the TSC phase can be stabilized in a wide region of chemical potential and Zeeman splitting, and four distinct TSC phases with superconducting Chern number N=-1,-2,-3, 3 can be achieved. Moreover, a 2D Bogoliubov-de Gennes Hamiltonian based on the triangular lattice of obstructed Wannier charge centers, combined with the s-wave superconductivity paring and Zeeman splitting, is constructed to understand the whole topological phase diagram analytically. These results expand the application of OAIs and pave a new way to realize the TSC and MSs with unique advantages.

Crossover from Coulomb blockade to ballistic transport in InAs nanowire devices

We report on the observation of a crossover from the single electron Coulomb blockade regime to the ballistic transport in individual InAs semiconducting nanowire devices. The InAs nanowires studied here were grown by molecular-beam epitaxy (MBE), which provides a clean system to study the intrinsic electrons transport in a quasi-one-dimensional system. Quantized conductance plateaus are observed for an InAs nanowire-based device by changing the Fermi level with a global back gate at low temperature, suggesting the ballistic transport of electrons. Further lowering the temperature, we observe the Coulomb blockade phenomenon with the formation of the quantum dot between the two normal metal contacts. By increasing the electron density, the characteristic Fabry-Pérot oscillations are observed, which further provides evidence for the ballistic nature of transport in the InAs nanowire device. Our observations indicate that high-quality InAs nanowires grown by MBE behave as clean quantum wires at low temperatures, which enables us to investigate novel phenomena in the quasi-one-dimensional system.

The interplay between Zeeman splitting and spin-orbit coupling in InAs nanowires

Coupling of the electron orbital motion and spin, i.e., spin-orbit coupling (SOC) leads to nontrivial changes in energy-level structures, giving rise to various spectroscopies and applications. The SOC in solids generates energy-band inversion or splitting under zero or weak magnetic fields, which is required for topological phases or Majorana fermions. Here, we examined the interplay between the Zeeman splitting and SOC by performing the transport spectroscopy of Landau levels (LLs) in indium arsenide nanowires under a strong magnetic field. We observed the anomalous Zeeman splitting of LLs, which depends on the quantum number of LLs as well as the electron spin. We considered that this observation was attributed to the interplay between the Zeeman splitting and the SOC. Our findings suggest an approach of generating spin-resolved chiral electron transport in nanowires.

Spiral Modes and the Observation of Quantized Conductance in the Surface Bands of Bismuth Nanowires

When electrons are confined in two-dimensional materials, quantum-mechanical transport phenomena and high mobility can be observed. Few demonstrations of these behaviours in surface spin-orbit bands exist. Here, we report the observation of quantized conductance in the surface bands of 50-nm Bi nanowires. With increasing magnetic fields oriented along the wire axis, the wires exhibit a stepwise increase in conductance and oscillatory thermopower, possibly due to an increased number of high-mobility spiral surface modes based on spin-split bands. Surface high mobility is unexpected since bismuth is not a topological insulator and the surface is not suspended but in contact with the bulk. The oscillations enable us to probe the surface structure. We observe that mobility increases dramatically with magnetic fields because, owing to Lorentz forces, spiral modes orbit decreases in diameter pulling the charge carriers away from the surface. Our mobility estimates at high magnetic fields are comparable, within order of magnitude, to the mobility values reported for suspended graphene. Our findings represent a key step in understanding surface spin-orbit band electronic transport.

Schottky barrier and contact resistance of InSb nanowire field-effect transistors

Understanding of the electrical contact properties of semiconductor nanowire (NW) field-effect transistors (FETs) plays a crucial role in the use of semiconducting NWs as building blocks for future nanoelectronic devices and in the study of fundamental physics problems. Here, we report on a study of the contact properties of Ti/Au, a widely used contact metal combination, when contacting individual InSb NWs via both two-probe and four-probe transport measurements. We show that a Schottky barrier of height [Formula: see text] is present at the metal-InSb NW interfaces and its effective height is gate-tunable. The contact resistance ([Formula: see text]) in the InSb NWFETs is also analyzed by magnetotransport measurements at low temperatures. It is found that [Formula: see text] in the on-state exhibits a pronounced magnetic field-dependent feature, namely it is increased strongly with increasing magnetic field after an onset field [Formula: see text]. A qualitative picture that takes into account magnetic depopulation of subbands in the NWs is provided to explain the observation. Our results provide solid experimental evidence for the presence of a Schottky barrier at Ti/Au-InSb NW interfaces and can be used as a basis for design and fabrication of novel InSb NW-based nanoelectronic devices and quantum devices.