Anisotropic transport in unidirectional lateral superlattice around half-filling of the second Landau level

TL;DR

This study observes transport anisotropy in unidirectional superlattices near half-filling of the second Landau level, indicating possible stripe phase stabilization influenced by external modulation and magnetic fields.

Contribution

It demonstrates the emergence of anisotropic transport features at specific ratios of superlattice period to magnetic length, revealing the influence of external parameters on stripe phase formation.

Findings

Transport anisotropy peaks at specific a/l ratios.

Anisotropic features are enhanced by in-plane magnetic fields perpendicular to the grating.

External periodic modulation stabilizes stripe phases at the second Landau level.

Abstract

We have observed marked transport anisotropy in short period (a=92 nm) unidirectional lateral superlattices around filling factors nu=5/2 and 7/2: magnetoresistance shows a sharp peak for current along the modulation grating while a dip appears for current across the grating. By altering the ratio a/l (with l=sqrt{hbar/eB_perp} the magnetic length) via changing the electron density n_e, it is shown that the nu=5/2 anisotropic features appear in the range 6.6 alt a/l alt 7.2 varying their intensities, becoming most conspicuous at a/l simeq 6.7. The peak/dip broadens with temperature roughly preserving its height/depth up to 250 mK. Tilt experiments reveal that the structures are slightly enhanced by an in-plane magnetic field B_| perpendicular to the grating but are almost completely destroyed by B_| parallel to the grating. The observations suggest the stabilization of a unidirectional charge-density-wave or stripe phase by weak external periodic modulation at the second Landau level.