Conductance through a helical state in an Indium antimonide nanowire

J Kammhuber,L P Kouwenhoven,M C Cassidy,A Vuik,S R Plissard,Ö Gül,F Pei,M Wimmer,E P A M Bakkers,M P Nowak,D Car

doi:10.1038/s41467-017-00315-y

Abstract

The motion of an electron and its spin are generally not coupled. However in a one-dimensional material with strong spin-orbit interaction (SOI) a helical state may emerge at finite magnetic fields, where electrons of opposite spin will have opposite momentum. The existence of this helical state has applications for spin filtering and cooper pair splitter devices and is an essential ingredient for realizing topologically protected quantum computing using Majorana zero modes. Here, we report measurements of a quantum point contact in an indium antimonide nanowire. At magnetic fields exceeding 3 T, the 2 e2/h conductance plateau shows a re-entrant feature toward 1 e2/h which increases linearly in width with magnetic field. Rotating the magnetic field clearly attributes this experimental signature to SOI and by comparing our observations with a numerical model we extract a spin-orbit energy of approximately 6.5 meV, which is stronger than the spin-orbit energy obtained by other methods.

Highlights

The motion of an electron and its spin are generally not coupled
The spin-orbit interaction (SOI) is a relativistic effect where a charged particle moving in an electric field E with momentum k and velocity v = k/m0, experiences an effective magnetic field BSO = (−1/m0c)k × E in its rest frame
The electric field arises from a symmetry breaking that is either intrinsic to the underlying crystal lattice in which the carriers move, known as the Dresselhaus SOI1, or an artificially induced asymmetry in the confinement potential due to an applied electric field, or Rashba[2] SOI

Summary

Results

Emergence of the helical gap a quantum point contact. Figure 1a shows a schematic image of a typical QPC device. 4, 5 including both SOI with strength α and Zeeman splitting EZ = gμBB, where g is the g-factor, μB the Bohr magneton and B the magnetic field strength When the chemical potential μ is tuned by the external gate voltage, it first aligns with the bottom of both bands resulting in conductance at 1·G0 before reducing from 1·G0 to 0.5·G0 when μ is positioned inside the gap This conductance reduction with a width scaling linearly with increasing Zeeman energy, is a hallmark of transport through a helical state.

20 EZeeman

Discussion

Methods