Scaling of the Magnetoconductivity of Silicon MOSFETs: Evidence for a Quantum Phase Transition in Two Dimensions

For a broad range of electron densities n and temperatures T, the in-plane magnetoconductivity of the two-dimensional system of electrons in silicon MOSFETs can be scaled onto a universal curve with a single parameter H_σ(n,T), where H_σ obeys the empirical relation H_σ0ex0ex=0ex0exA(n)[Δ(n)²+T²]1/2. The characteristic energy kBΔ associated with the magnetic field dependence of the conductivity decreases with decreasing density, and extrapolates to $0$ at a critical density n₀, signaling the approach to a zero-temperature quantum phase transition. We show that H_σ0ex0ex=0ex0exAT for densities near n₀.