Topological charge, spin and heat transistor

TL;DR

This paper explores a topological device that enables robust control of charge, spin, and heat currents through topological effects and Majorana modes, functioning as a transistor with quantized and switchable transport properties.

Contribution

It introduces a novel topological device combining superconductor and quantum spin Hall insulator to control charge, spin, and heat currents via topological effects and Majorana modes.

Findings

Quantized charge, spin, and heat pumping related to topological invariants.

Majorana zero mode switches off current pumping.

Device functions as a robust topological charge, spin, and heat transistor.

Abstract

Spin pumping consists in the injection of spin currents into a non-magnetic material due to the precession of an adjacent ferromagnet. In addition to the pumping of spin the precession always leads to pumping of heat, but in the presence of spin-orbital entanglement it also leads to a charge current. We investigate the pumping of charge, spin and heat in a device where a superconductor and a quantum spin Hall insulator are in proximity contact with a ferromagnetic insulator. We show that the device supports two robust operation regimes arising from topological effects. In one regime, the pumped charge, spin and heat are quantized and related to each other due to a topological winding number of the reflection coefficient in the scattering matrix formalism -- translating to a Chern number in the case of Hamiltonian formalism. In the second regime, a Majorana zero mode switches off the pumping of currents owing to the topologically protected perfect Andreev reflection. We show that the interplay of these two topological effects can be utilized so that the device operates as a robust charge, spin and heat transistor.