Many-body effects on the $\rho_{xx}$ ringlike structures in two-subband wells

TL;DR

This study investigates the many-body effects on ringlike structures in the longitudinal resistivity of two-subband quantum wells, revealing phase transitions and collapse phenomena influenced by temperature, magnetic field tilt, and electron interactions.

Contribution

It introduces a detailed theoretical analysis of the shape, spin polarization, and collapse of resistivity rings considering many-body interactions and phase transitions.

Findings

Rings break at low temperatures due to quantum Hall ferromagnetic transition.

High spin polarization (~50%) observed within rings, consistent with NMR data.

Rings collapse at a critical tilt angle due to interplay of anticrossings and exchange-correlation effects.

Abstract

The longitudinal resistivity $\rho_{xx}$ of two-dimensional electron gases formed in wells with two subbands displays ringlike structures when plotted in a density--magnetic-field diagram, due to the crossings of spin-split Landau levels (LLs) from distinct subbands. Using spin density functional theory and linear response, we investigate the shape and spin polarization of these structures as a function of temperature and magnetic-field tilt angle. We find that (i) some of the rings "break" at sufficiently low temperatures due to a quantum Hall ferromagnetic phase transition, thus exhibiting a high degree of spin polarization ($\sim 50 $%) within, consistent with the NMR data of Zhang \textit{et al.} [Phys. Rev. Lett. {\bf 98}, 246802 (2007)], and (ii) for increasing tilting angles the interplay between the anticrossings due to inter-LL couplings and the exchange-correlation (XC) effects leads to a collapse of the rings at some critical angle $\theta_c$, in agreement with the data of Guo \textit{et al.} [Phys. Rev. B {\bf 78}, 233305 (2008)].