Spintronic signatures of Klein tunneling in topological insulators

Abstract

Klein tunneling, the perfect transmission of normally incident Dirac electrons across a potential barrier, has been widely studied in graphene and explored to design switches, albeit indirectly. We show that Klein tunneling maybe easier to detect for spin-momentum locked electrons crossing a PN junction along a three dimensional topological insulator surface. In these topological insulator PN junctions (TIPNJs), the spin texture and momentum distribution of transmitted electrons can be measured electrically using a ferromagnetic probe for varying gate voltages and angles of current injection. Based on transport models across a TIPNJ, we show that the asymmetry in the potentiometric signal between PP and PN junctions and its overall angular dependence serve as a direct signature of Klein tunneling.

Conductance-Matrix Symmetries of a Three-Terminal Hybrid Device

“…In two-terminal superconductor-semiconductor devices, observed asymmetries in the subgap conductance [22] have been suggested to arise from a dissipative fermionic reservoir, effectively acting as a third lead [23], although, as in the normal-conducting case [3], biasdependence of the self-consistent potential can also cause a deviation from symmetry [24]. Multi-terminal super-conducting devices are a topic of particular interest, as they can be used for MZM [25][26][27][28][29][30][31], Cooper-pair splitter [32,33], and multi-terminal Josephson studies [34][35][36][37][38]. In multi-terminal superconducting quantum dot devices, bias asymmetries have been observed [39], and a relationship between nonlocal conductance and the bound-state charge has been proposed [40,41].In this Letter, we report a symmetry analysis of the conductance matrix measured in a three-terminal, superconductor-semiconductor hybrid device.…”

Majorana-Weyl crossings in topological multiterminal junctions

“…As a consequence, the Andreev-Weyl crossings would manifest themselves through a quantized transconductance, in units of 4e 2 /h, between two voltage-biased terminals [2,3]. This prediction was subsequently extended to junctions with three terminals in an external magnetic field [4,5].…”

Phase-coherent caloritronics with ordinary and topological Josephson junctions

“…In addition to the growing interest in topological materials, there has been an interest in systems that allow for the simulation of topologically nontrivial band structures with trivial materials. A particular emphasis has been devoted to multi-terminal Josephson junctions [91][92][93][94][95]. Here, the superconducting phase differences form the analogon of crystal momenta while the Andreev bound state energies correspond to the energy bands in a crystal.…”

“…For a junction with at least four terminals, three independent superconducting phase differences form a sufficiently large number of degrees of freedom to mimic the behavior of Weyl points in the Andreev spectrum [91,92,95]. Similary, in three-terminal junctions, the two superconducting phases together with a magnetic flux through the junction can be used to realize nontrivial Andreev bound state spectra of interest [93,94]. In addition to the potential of simulating topological band structures, multi-terminal Josephson junctions are also of interest for phase-coherent caloritronics [90].…”

“…[90], it is also shown that the circulator efficiency is quite robust with respect to the disorder. As this device has been shown to be a prototype for simulating topologically nontrivial band structures [93,94], it will be worthwhile to explore the topological nature in thermal conductance of the multiterminal Josephson junctions.…”