CPM Seminar

Microwave and rf spectroscopy of two-dimensional electron solids and stripes

Lloyd Engel

National High Magnetic Field Laboratory
Tallahassee

Two-dimensional electron systems (2DES) in high magnetic field are well known for the integer and fractional quantum Hall effects, but also have ground states with broken spatial symmetry, including crystalline solids, and phases with stripes of charge density. The archetypical electron solid, expected to be the ground state of disorder-free 2DES in the high magnetic field or low density limit, is the Wigner crystal, a triangular lattice of electrons stabilized by their mutual repulsion.

We have found that a striking rf or microwave resonance in the spectrum is a generic feature of the electron solids or stripes, with observed resonance frequencies ranging from 70 MHz to 10 GHz. The electron solids are insulators due to pinning by disorder, and the resonances are interpreted as “pinning modes”, in which crystalline domains oscillate within the disorder potential. After introducing the phenomenology of the resonances for the phase terminating the fractional quantum Hall effect series at low Landau level filling, I will present results on several of the higher-filling solid and striped phases.