Regensburg 2000 – scientific programme

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TT: Tiefe Temperaturen

TT 5: Niederdimensionale Elektronensysteme

TT 5.1: Invited Talk

Monday, March 27, 2000, 15:00–15:30, H20

New phases of two-dimensional interacting electron systems — •Günther Meissner — Theoretische Physik, Universität des Saarlandes, Postfach 15 11 50, D-66041 Saarbrücken

A simple but rigorous many-body approach provides the study of the nature of novel competing phases of interacting two-dimensional (2D) electrons in high magnetic fields with partial Landau level filling. In the long wavelength limit the collective excitations of Laughlin’s incompressible quantum liquid can, e.g., be shown to have a finite gap (magneto-rotons) due to strong correlations in the density fluctuations of the centers of the cyclotron orbits at magic fractional filling factors of the lowest Landau level, contrary to those of the magnetic field-induced 2D Wigner crystal being gapless (magneto-phonons) due to broken magnetic translational invariance. The triangular lattice of the classical Wigner crystal predicted already 1976 and verified experimentally on liquid helium films 1979 turns out to be the ground state of this sort of a many-body system in the dilute electron or high magnetic field limit with the cyclotron orbits shrinking to points as the Larmor radius approaches zero. Methods of applying our approach to examine current approximations as, e.g., the single mode, the renormalized harmonic or the time-dependent Hartree-Fock approximation are indicated. Implications to be drawn about a kind of charge-density wave ordering at high-index partial Landau level filling from a comparison with recent experimental findings and with small system calculations will finally be discussed briefly.