Observation of Pinning Mode of Stripe Phases of 2D Systems in High Landau Levels

Abstract

We study the radio-frequency diagonal conductivities of the anisotropic stripe phases of higher Landau levels near half-integer fillings. In the hard direction, in which larger dc resistivity occurs, the spectrum exhibits a striking resonance, while in the orthogonal, easy direction, no resonance is discernible. The resonance is interpreted as a pinning mode of the stripe phase.

Onset of quantum criticality in the topological-to-nematic transition in a two-dimensional electron gas at filling factor ν=5/2

“…Our recent measurements 26 revealed that the ground state at ν = 5/2 undergoes a pressure-driven quantum phase transition from the FQHS to a stripe phase [27][28][29][30][31][32][33][34][35][36][37] . In this experiment the two-dimensional electron gas was not exposed to an in-plane magnetic field or any other externally applied symmetry breaking fields 26 .…”

“…This FQHS, similarly to all other FQHSs 3,4 , is topologically ordered, it is believed to belong to the Pfaffian universality class [5][6][7][8][9][10][11][12][13][14][15][16][17] , and it is thought to support non-Abelian excitations 5 . Within the framework of the composite fermion theory 18,19 , the ν = 5/2 FQHS can be understood as being due to pairing of composite fermions, a pairing driven by the residual attractive interactions between the composite fermions 5,20-25 .Our recent measurements 26 revealed that the ground state at ν = 5/2 undergoes a pressure-driven quantum phase transition from the FQHS to a stripe phase [27][28][29][30][31][32][33][34][35][36][37] . In this experiment the two-dimensional electron gas was not exposed to an in-plane magnetic field or any other externally applied symmetry breaking fields 26 .…”

Spin and Charge Ordering in the Quantum Hall Regime

“…In the same experiment, the stripe period was determined to 3.6 · . Apart from that, pinning mode resonances have been observed as reported earlier for the bubble phase [114,115]. Interestingly, in the case of the stripe phase, a resonance only occurs if the electric field of the microwave signal is oriented along the hard axis.…”

“…The temperature dependence of the transport anisotropy at = 9 ⁄2 has been analyzed and was found to be consistent with the predictions of a nematic phase [111,112]. Apart from that, resonances in the microwave absorption have been observed and interpreted as pinning modes of the stripe crystal [114,115]. Yet, with these techniques microscopic details remain elusive.…”

“…When driven by an oscillating electric field, the electron system responds in a collective manner, a so-called pinning mode, if the external frequency matches the resonance frequency set by the pinning potential. The existence of such a pinning mode has been inferred from resonances in the microwave conductivity around 200 MHz [102] for the bubble phase and 100 MHz [114] for the stripe phase. If the excitation frequency is higher than the pinning mode resonance frequency, a phase shift between the electric field and the charge modulation occurs as for any classical driven oscillator.…”