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Stress‐tuned metal‐insulator transition in Si:B: dynamical scaling

Uniaxial stress S was used to tune the critical density of barely metallic Si:B at low temperatures through the metal‐insulator transition. For all values of stress and temperature, the DC conductivity exhibits an excellent fit to the scaling form σ(S, T) = ATμ/zν f[(S — Sc)/T1/zν] on both sides of the transition. Finite temperature scaling yields a critical conductivity exponent μ = 1.6, considerably larger than the value obtained in experiments where the transition was crossed by varying the dopant concentration. Direct comparison of the temperature dependence of stressed and unstressed Si:B suggests that the stress‐driven and concentration‐driven metal‐insulator transitions are not equivalent. We show that the conductivity in the critical region on the metallic side follows σc ∝ T1/2, the form that has been calculated and observed in the perturbative region for weakly disordered metals. The conductivity in the insulating phase follows the Efros‐Shklovskii form, σ(S, T) ∝ exp([—(S — Sc)zν/T]1/2), expected for variable‐range hopping in the presence of Coulomb interactions, with a prefactor ∝T1/2 corresponding to the temperature dependence of the critical curve.