Strain-induced quantum phase transitions probed by electron spin resonance

Physical Review B: Condensed Matter and Materials Physics. 2025. Vol. 111. No. 23. Article 235413.

Андреева С. А., Щепетильников А. В., Nikolaev G. A., Khisameeva A. R., Ya.V. Fedotova, Reichl C., Wegscheider W., Kukushkin I. V.

We examine the quantum phase transitions in a two-dimensional electron system hosted at a high-quality wide AlAs quantum well, with a particular focus on the integer filling factor of 𝜈=2 in the regime of the quantum Hall effect. The observed transitions are induced by the application of external strain to the structure and are manifested by a substantial change in the longitudinal resistance of the sample. The anisotropy of the 𝑔 factor permitted us to capture the spin resonances of electrons occupying the two in-plane valleys independently. An analysis of their amplitudes enabled us to attribute these transitions to the macroscopic modification of the valley “pseudospin” polarization, i.e., relative valley occupation, and to uncover the pseudospin evolution around these transitions.

Ключевые слова: quantum Hall effect, two-dimensional electron system, electron spin resonance, valley degree of freedom