Nonlocal Potential Measurements of Quantum Conductors

Multiterminal measurements of magnetoresistance fluctuations in silicon inversion-layer nanostructures are extended to probe spacings $L\ll L_{\phi }$, the phase-preserving diffusion length. Unlike for $L>\mathrm{}{L}_{\phi }$, 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 $\delta G\left(L\right)\mathrm{}$ are $\gg \frac{e^2}{h}$; however, this can be understood if each pair of probes effectively measures voltage fluctuations at scale $L_{\phi }$, determined by the condition $\delta G\left(L_{\phi }\right)=\frac{e^2}{h}$.