Current Jets, Disorder, and Linear Magnetoresistance in the Silver Chalcogenides

The inhomogeneous distribution of excess or deficient silver atoms lies behind the large and linear transverse magnetoresistance displayed by ${\mathrm{Ag}}_{2\pm \delta }\mathrm{Se}$ and ${\mathrm{Ag}}_{2\pm \delta }\mathrm{Te}$, introducing spatial conductivity fluctuations with length scales independent of the cyclotron radius. We report a negative, nonsaturating longitudinal magnetoresistance up to at least 60 T, which becomes most negative where the bands cross and the effect of conductivity fluctuations is most acute. Thinning samples down to $10\mu \mathrm{m}$ suppresses the negative response, revealing the essential length scale in the problem and paving the way for designer magnetoresistive devices.

Figure 1

Normalized magnetoresistance of $n$-type ${\mathrm{Ag}}_{2+\delta }\mathrm{Se}$ under (a) transverse and (b) longitudinal magnetic field at a series of temperatures. The transverse response is large, positive, and essentially linear with magnetic field, while a crossover to linear but negative magnetoresistance occurs in the longitudinal configuration.

Figure 2

A voltage drop across the thickness of $p$-type ${\mathrm{Ag}}_{2-\delta }\mathrm{Se}$ develops under a longitudinal magnetic field, revealing distorted current flows across the sample as the source of the negative magnetoresistance (illustrated in the inset).

Figure 3

Normalized longitudinal magnetoresistance vs sample thickness for ${\mathrm{Ag}}_{2-\delta }\mathrm{Se}$ at $T=30\mathrm{K}$. The negative component of the magnetoresistance decreases with thinning, vanishing by $15\mu \mathrm{m}$. This sets the inhomogeneity length scale in the problem. Inset: The transverse magnetoresistance is independent of sample thickness, shown here for 15 and $400\mu \mathrm{m}$.

Figure 4

Normalized longitudinal magnetoresistance as a function of magnetic field for (a) electron- and (b) hole-doped silver telluride at a series of temperatures. Pronounced negative magnetoresistance emerges in both limits.