Nonlocal Potential Measurements of Quantum Conductors

Abstract

Multiterminal measurements of magnetoresistance fluctuations in silicon inversion-layer nanostructures are extended to probe spacings $L\ensuremath{\ll}{L}_{\ensuremath{\varphi}}$, the phase-preserving diffusion length. Unlike for $L>{L}_{\ensuremath{\varphi}}$, the sizes of the voltage fluctuations are independent of $L$, and have novel correlations consistent with independent potential fluctuations of each probe. The corresponding "conductance" fluctuations $\ensuremath{\delta}G(L)$ are $\ensuremath{\gg}\frac{{e}^{2}}{h}$; however, this can be understood if each pair of probes effectively measures voltage fluctuations at scale ${L}_{\ensuremath{\varphi}}$, determined by the condition $\ensuremath{\delta}G({L}_{\ensuremath{\varphi}})=\frac{{e}^{2}}{h}$.