Measuring Overlaps in Mesoscopic Spin Glasses via Conductance Fluctuations

We consider the electronic transport in a mesoscopic metallic spin glass. We show that the distribution of overlaps between spin configurations can be inferred from the reduction of the conductance fluctuations by the magnetic impurities. Using this property, we propose new experimental protocols to probe spin glasses directly through their overlaps.

Figure 1

Proposed experimental protocol: the temperature is cycled between $T_{\exp }$ and $T^{\prime }>T_g$ in successive runs labeled by $n$. Measurements of the magneto-conductance are done at $T_{\exp }$ after some equilibration time $t_w$. Different runs $n$ and $m$ correspond to different spins states $\{{\overrightarrow{S}}_i^{(n)}\}$ and $\{{\overrightarrow{S}}_i^{(m)}\}$ at the same temperature $T_{\exp }$. The average correlations $⟨\delta G_n\delta G_m{⟩}_B$ between the corresponding magnetoconductance provides a determination of the overlap $Q_{nm}$ between the two spin configurations. Repeating this process gives access to the (nonaverage) overlap distribution for the waiting time $t_w$.