A double quantum dot spin valve

Arunav Bordoloi,Lucia Sorba,Valentina Zannier,Christian Schönenberger,Andreas Baumgartner

doi:10.1038/s42005-020-00405-2

Arunav Bordoloi, Lucia Sorba + Show 3 more

Open Access

https://doi.org/10.1038/s42005-020-00405-2

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Journal: Communications Physics	Publication Date: Aug 6, 2020
Citations: 27	License type: open-access

Affiliation: University of Basel, Istituto Nanoscienze

Abstract

A most fundamental goal in spintronics is to electrically tune highly efficient spin injectors and detectors, preferably compatible with nanoscale electronics and superconducting elements. These functionalities can be obtained using semiconductor quantum dots, spin-polarized by a ferromagnetic split-gate, which we demonstrate in a double quantum dot spin valve with two weakly coupled quantum dots in series, with individual split gates magnetized in parallel or anti-parallel. In tunneling magnetoresistance experiments we find a strongly reduced spin valve conductance for the two anti-parallel configurations, with a single dot polarization of ~27%. This value can be significantly improved by a small external magnetic field and optimized gate voltages, which results in a continuously electrically tunable quantum dot spin polarization of ±80%. Such versatile quantum dot spin filters are compatible with superconducting electronic elements and suitable for single spin projection and correlation experiments, as well as initialization and read-out of spin qubits.

Highlights

A most fundamental goal in spintronics is to electrically tune highly efficient spin injectors and detectors, preferably compatible with nanoscale electronics and superconducting elements
Most of the present concepts rely on electrical contacts to ferromagnetic reservoirs[1], or on magnetic tunnel barriers[21], with significant obstacles[22] such as a low polarization (20%–40%)[23], the magneto-Coulomb effect[24,25], the conductivity mismatch at the metallic ferromagnet–semiconductor interface[26], or large global external magnetic fields[8,27], suppressing the superconductivity and changing significantly the band structure
We demonstrate this concept in tunneling magnetoresistance (TMR)

Summary

Introduction

A most fundamental goal in spintronics is to electrically tune highly efficient spin injectors and detectors, preferably compatible with nanoscale electronics and superconducting elements. In tunneling magnetoresistance experiments we find a strongly reduced spin valve conductance for the two anti-parallel configurations, with a single dot polarization of ~27% This value can be significantly improved by a small external magnetic field and optimized gate voltages, which results in a continuously electrically tunable quantum dot spin polarization of ±80%. A reliable and versatile technique to measure the spin degree of freedom remains elusive, especially for superconductor hybrid devices, where spin phenomena are crucial, e.g., in entanglement generation in solids[18,19], or demonstrating topological superconductivity in Majorana-type devices[20] Such experiments require highly efficient and gate-tunable spin injectors and detectors in situ of an active device. Using a simple DQD-SV model allows us to extract a corresponding large, electrically tunable QD spin polarization of up to ±80%, which can, in principle, be further improved to the theoretical limit of 100%

Methods

Results

Conclusion