EFFECTS OF ELECTRON-ELECTRON INTERACTIONS IN TWO DIMENSIONS

K. W. Becker, Peter Fulde

Dragana Popović

The fate of the metallic phase in parallel magnetic fields represents one of the major open issues in the studies of dilute, strongly interacting systems in two dimensions (2D). In this experiment, the temperature dependence of conductivity σ(T) of a 2D electron system in silicon has been studied in parallel magnetic fields B. At B = 0, the system displays a new and unexpected kind of metallic behavior with dσ/dT > 0, and a novel type of a metal-insulator transition,1 which occurs at a critical electron density nc(0). At low fields (B ≤ 2 T ), nc increases as nc(B) - nc(0) ∝ Bβ(β ≈ 0.9), and the zero-temperature conductivity scales as σ(ns, B, 0)/σ (ns, 0, 0) = f(Bβ/δn) (where δn = (ns - nc(0))/nc(0), and ns is electron density) as expected for a quantum phase transition. The metallic phase persists in fields up to 18 T, consistent with the saturation of nc at high fields. These results strongly suggest that the 2D metal may exist even for spinless electrons.

Myriam P. Sarachik, S. V. Kravchenko

Seiji Yunoki, Sadamichi Maekawa

Constantino Tsallis, Anna Chame

We discuss, within a real-space renormalization-group, interesting thermal effects (surface singularity at the bulk transition ; Ising-Heisenberg crossover) concerning the free surface of a semi-infinite d = 3 spin 1/2 anisotropic Heisenberg ferromagnet. Comparison with the Mermin-Wagner theorem and with experimental work is done.