Dipole-like dynamical nuclear spin polarization around a quantum point contact

TL;DR

This paper theoretically explores how a quantum point contact at finite magnetic field can induce a dipole-like nuclear spin polarization pattern, which can be distinguished from uniform polarization through conductance response to NMR.

Contribution

It introduces the concept of dipole-like nuclear polarization in a QPC at finite magnetic field and predicts its distinguishable experimental signature.

Findings

Dipole-like nuclear polarization occurs at conductance e^2/h in a spin-selective QPC.

The polarization pattern is spatially anti-symmetric, with zero polarization at the center.

The pattern can be experimentally identified via conductance response to NMR.

Abstract

We theoretically investigate the dynamical nuclear spin polarization in a quantum point contact (QPC) at finite magnetic field. We find that when the QPC is tuned to be spin selective, at the conductance of e^2/h, a finite bias induces a dipole-like (spatially anti-symmetric) nuclear polarization: at the QPC center the polarization is zero, while, for GaAs parameters, the nuclear spins down (up) are induced on the source (drain) side. We predict that the dipole-like polarization pattern can be distinguished from a uniform polarization due to a qualitatively different response of the QPC conductance to the NMR field.