Strongly anisotropic spin response as a signature of the helical regime in Rashba nanowires

TL;DR

This paper demonstrates that the helical regime in Rashba nanowires can be identified by a strongly anisotropic spin susceptibility, providing a new experimental signature that complements conductance measurements.

Contribution

It reveals that the helical regime exhibits a unique anisotropic spin response, which can serve as an experimental signature distinguishing it from other regimes.

Findings

Spin susceptibility is exponentially suppressed along one spin direction in the helical regime.

No low-frequency spin fluctuations occur along the suppressed direction.

Spin measurements can identify the helical regime independently of conductance data.

Abstract

Rashba nanowires in a magnetic field exhibit a helical regime when the spin-orbit momentum is close to the Fermi momentum, k_F \approx k_{SO}. We show that this regime is characterized by a strongly anisotropic electron spin susceptibility, with an exponentially suppressed signal along one direction in spin space, and that there are no low frequency spin fluctuations along this direction. Since the spin response in the gapless regime k_F \not \approx k_{SO} has a power law behavior in all three directions, spin measurements provide a signature of the helical regime that complements spin-insensitive conductance measurements.