Conductivity of Metallic Si:B near the Metal-Insulator Transition: Comparison between Unstressed and Uniaxially Stressed Samples

TL;DR

This study compares the low-temperature conductivity of p-type Si:B near the metal-insulator transition under different doping levels and uniaxial stress, revealing universal scaling behavior and a larger critical exponent under stress.

Contribution

It demonstrates that uniaxial stress induces a universal scaling of conductivity and provides a new critical exponent, highlighting differences from doping-tuned transitions.

Findings

Conductivity scales universally with stress and temperature.

Critical conductivity exponent is approximately 1.6 under stress.

Temperature dependence differs between stressed and unstressed samples.

Abstract

The low-temperature dc conductivities of barely metallic samples of p-type Si:B are compared for a series of samples with different dopant concentrations, n, in the absence of stress (cubic symmetry), and for a single sample driven from the metallic into the insulating phase by uniaxial compression, S. For all values of temperature and stress, the conductivity of the stressed sample collapses onto a single universal scaling curve. The scaling fit indicates that the conductivity of si:B is proportional to the square-root of T in the critical range. Our data yield a critical conductivity exponent of 1.6, considerably larger than the value reported in earlier experiments where the transition was crossed by varying the dopant concentration. The larger exponent is based on data in a narrow range of stress near the critical value within which scaling holds. We show explicitly that the temperature dependences of the conductivity of stressed and unstressed Si:B are different, suggesting that a direct comparison of the critical behavior and critical exponents for stress- tuned and concentration-tuned transitions may not be warranted.