Critical Behavior of the Conductivity of Si:P at the Metal-Insulator Transition under Uniaxial Stress

We report new measurements of the electrical conductivity $\sigma$ of the canonical three-dimensional metal-insulator system Si:P under uniaxial stress $S$. The zero-temperature extrapolation of $\sigma (S,T\to 0)\sim |{S-S}_c{|}^{\mu }$ shows an unprecedently sharp onset of finite conductivity at $S_c$ with an exponent $\mu =1\mathrm{}$. The value of $\mu$ differs significantly from that of earlier stress-tuning results. Our data show dynamic $\sigma (S,T)$ scaling on both metallic and insulating sides, viz. $\sigma (S,T)={\sigma }_c\left(T\right)̇F^{\prime }\left(|{S-S}_c|/T^y\right)$ where ${\sigma }_c\left(T\right)$ is the conductivity at the critical stress $S_c$. We find $y=1\mathrm{}/z\nu =0.34\mathrm{}$ where $\nu$ is the correlation-length exponent and $z$ the dynamic critical exponent.