Comment on ``Evidence for Anisotropic State of Two-Dimensional Electrons in High Landau Levels''

TL;DR

This paper comments on previous findings of anisotropic electronic states in 2D systems, clarifying measurement discrepancies and emphasizing that the true resistivity anisotropy is smaller than some measurements suggest, leaving its origin unexplained.

Contribution

It clarifies the discrepancy between different measurement techniques of resistivity anisotropy in 2D electron systems and emphasizes the geometric effects influencing resistance measurements.

Findings

Hall bar measurements accurately reflect resistivity anisotropy

Square sample resistance measurements are exponentially enhanced by geometry

The origin of the resistivity anisotropy remains unknown

Abstract

In a recent letter M. Lilly et al [PRL 82, 394 (1999)] have shown that a highly anisotropic state can arise in certain two dimensional electron systems. In the large square samples studied, resistances measured in the two perpendicular directions are found to have a ratio that may be 60 or larger at low temperature and at certain magnetic fields. In Hall bar measurements, the anisotropy ratio is found to be much smaller (roughly 5). In this comment we resolve this discrepancy by noting that the anisotropy of the underlying sheet resistivities is correctly represented by Hall bar resistance measurements but shows up exponentially enhanced in resistance measurements on square samples due to simple geometric effects. We note, however, that the origin of this underlying resistivity anisotropy remains unknown, and is not addressed here.