Particle Collisions and Negative Nonlocal Response of Ballistic Electrons

TL;DR

This paper predicts negative nonlocal resistance in the ballistic electron regime, challenging its use as a hydrodynamic signature and highlighting the role of memory effects and log divergence in electron kinetics.

Contribution

It demonstrates that negative resistance can occur in ballistic regimes, not just hydrodynamic ones, and reveals the enhancement of this effect by memory-related log divergence.

Findings

Negative resistance occurs in ballistic electron regimes.

Negative resistance is not exclusive to hydrodynamic flow.

Memory effects enhance negative response via log divergence.

Abstract

An electric field that builds in the direction against current, known as negative nonlocal resistance, arises naturally in viscous flows and is thus often taken as a telltale of this regime. Here we predict negative resistance for the ballistic regime, wherein the ee collision mean free path is greater than the length scale at which the system is being probed. Therefore, negative resistance alone does not provide strong evidence for the occurrence of the hydrodynamic regime; it must thus be demoted from the rank of a smoking gun to that of a mere forerunner. Furthermore, we find that negative response is log-enhanced in the ballistic regime by the physics related to the seminal Dorfman-Cohen log divergence due to memory effects in the kinetics of dilute gases. The ballistic regime therefore offers a unique setting for exploring these interesting effects due to electron interactions.