Physikalisches Institut, Goethe-Universität, Frankfurt am Main, Germany.
Phys Rev Lett. 2011 Nov 11;107(20):206803. doi: 10.1103/PhysRevLett.107.206803. Epub 2011 Nov 7.
We present temperature-dependent conductivity data obtained on a sample set of nanogranular Pt-C with finely tuned intergrain tunnel coupling strength g. For samples in the strong-coupling regime g > g(C), characterized by a finite conductivity for T→0, we find a logarithmic behavior at elevated temperatures and a crossover to a √T behavior at low temperatures over a wide range of coupling strengths g(C) ≈ 0.25 < g ≤ 3. The experimental observation for g > 1 is in very good agreement with recent theoretical findings on ordered granular metals in three spatial dimensions. The results indicate a validity of the predicted universal conductivity behavior that goes beyond the immediate range of the approach used in the theoretical derivation.
我们呈现了一组经过精细调控的纳米颗粒 Pt-C 样品的温度相关电导率数据，这些样品的颗粒间隧道耦合强度为 g。对于处于强耦合 regime 的样品（g > g(C)），其特征是在 T→0 时存在有限的电导率，我们发现高温下呈现对数行为，低温下呈现 √T 行为，跨越了很宽的耦合强度范围 g(C) ≈ 0.25 < g ≤ 3。对于 g > 1 的实验观测结果与最近关于三空间维度有序颗粒金属的理论发现非常吻合。这些结果表明，预测的普遍电导率行为在理论推导中使用的方法的直接范围之外仍然有效。
