Conduction threshold and pinning frequency of magnetically induced Wigner solid

Abstract

The 2D quantum system of electrons at a GaAs/GaAlAs heterojunction in high magnetic field at low temperature is shown to exhibit conduction typical of pinned charge-density waves. Crossover from Ohmic conduction occurs on the same boundary at which radio-frequency resonances signal the onset of transverse elasticity. A further small non-Ohmic region is isolated from the main area by a v-j quantum-Hall-effect phase. The relationship found between the threshold conduction field and the resonance frequency is well accounted for by a model of a pinned electron crystal.

Pinning modes of high-magnetic-field Wigner solids with controlled alloy disorder

“…The insulator is understood as a form of Wigner solid 2-14 , a state of matter composed of charge carriers arranged to minimize their mutual repulsion while constrained to a fixed density by charge neutrality. The role of the disorder is crucial in producing the insulating behavior, since the Wigner solid is necessarily pinned by any disorder.The spectra of the low ν insulating phases of 2DES exhibit a microwave or rf resonance 6-9,12,13 that is identified as a pinning mode 7,9,[12][13][14][15] , in which pieces of the solid oscillate collectively about their pinned positions. This disorder-induced mode is a powerful tool for study of solid phases in 2DES, which occur under many conditions 14 besides the low ν insulator.…”

Studies of the extreme quantum limit of 2D hole systems

“…This is consistent with the formation of a magnetically induced Wigner solid stablised by strong Landau level mixing. strong de-pinning and a current proportional to applied voltage [10]. The fit is remarkably good until a value ETn above which we see an almost constant relatively low differential resistance.…”

Microwave pinning modes near Landau fillingν=1in two-dimensional electron systems with alloy disorder

“…In two-dimensional electron systems (2DES) in high magnetic field, B, Wigner solids [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] pinned by residual disorder occur for sufficiently small Landau level filling factor, ν. At the low-ν termination of the fractional quantum Hall effect (FQHE) series, such a solid can appear in dc transport as an insulating phase.…”

“…The resonances are understood as pinning modes [13][14][15][16][17][18]28 , in which pieces of the solid oscillate within the disorder potential. The relation between the disorder and the resonance frequency and lineshape is only partially understood.…”

“…Microwave spectroscopy is known to directly measure pinned solids in high magnetic field, since these solids exhibit resonances in their microwave spectra 10,13,16,17,[21][22][23]26,27 . The resonances are understood as pinning modes [13][14][15][16][17][18]28 , in which pieces of the solid oscillate within the disorder potential.…”