Magnetoresistence engineering and singlet/triplet switching in InAs nanowire quantum dots with ferromagnetic sidegates

TL;DR

This study demonstrates electrically tunable magnetoresistance and singlet/triplet switching in InAs nanowire quantum dots with ferromagnetic sidegates, revealing complex tunneling behaviors and potential for spin-based quantum applications.

Contribution

It introduces a novel device with ferromagnetic sidegates enabling electrical control of magnetoresistance and spin states in InAs nanowire quantum dots, with detailed models explaining the observed phenomena.

Findings

Strong magnetoresistance observed with sharp switching up to 25%

Electrical tuning of MR sign and amplitude via ferromagnetic sidegates

Detection of singlet/triplet transitions in double dot regime

Abstract

We present magnetoresistance (MR) experiments on an InAs nanowire quantum dot device with two ferromagnetic sidegates (FSGs) in a split-gate geometry. The wire segment can be electrically tuned to a single dot or to a double dot regime using the FSGs and a backgate. In both regimes we find a strong MR and a sharp MR switching of up to 25\% at the field at which the magnetizations of the FSGs are inverted by the external field. The sign and amplitude of the MR and the MR switching can both be tuned electrically by the FSGs. In a double dot regime close to pinch-off we find {\it two} sharp transitions in the conductance, reminiscent of tunneling MR (TMR) between two ferromagnetic contacts, with one transition near zero and one at the FSG switching fields. These surprisingly rich characteristics we explain in several simple resonant tunneling models. For example, the TMR-like MR can be understood as a stray-field controlled transition between singlet and a triplet double dot states. Such local magnetic fields are the key elements in various proposals to engineer novel states of matter and may be used for testing electron spin-based Bell inequalities.