Quantum phase transition in ultrahigh mobility SiGe/Si/SiGe two-dimensional electron system

Abstract

The metal-insulator transition (MIT) is an exceptional test bed for studying strong electron correlations in two dimensions in the presence of disorder. In the present study, it is found that in contrast to previous experiments on lower-mobility samples, in ultra-high mobility SiGe/Si/SiGe quantum wells the critical electron density, nc, of the MIT becomes smaller than the density, nm, where the effective mass at the Fermi level tends to diverge. Near the topological phase transition expected at nm, the metallic temperature dependence of the resistance should be strengthened, which is consistent with the experimental observation of more than an order of magnitude resistance drop with decreasing temperature below ∼ 1 K.

Recent Developments in the Field of the Metal-Insulator Transition in Two Dimensions

“…[4][5][6][7]). The strongest drop of the resistance on the metallic side of the transition (up to a factor of 12) at sub-Kelvin temperatures was reported in 2D systems in SiGe/Si/SiGe quantum wells [8]; in spite of lower disorder, the drop of the resistance in GaAs-based structures never exceeded a factor of about 3. This discrepancy has been attributed particularly to the fact that electrons in silicon-based structures have two almost degenerate valleys, which further enhances the correlation effects [9,10].…”

Recent Developments in the Field of the Metal-Insulator Transition in Two Dimensions

“…[4][5][6][7]). The strongest drop of the resistance on the metallic side of the transition (up to a factor of 12) at sub-Kelvin temperatures was reported in 2D systems in SiGe/Si/SiGe quantum wells [8]; in spite of lower disorder, the drop of the resistance in GaAs-based structures never exceeded a factor of about 3. This discrepancy has been attributed particularly to the fact that electrons in silicon-based structures have two almost degenerate valleys, which further enhances the correlation effects [9,10].…”

Persistence of spin memory in a crystalline, insulating phase-change material

“…[7][8][9] Particularly for quantum materials whose properties are driven by strong spin-orbit coupling, systematically understanding the impact of disorder on spin-dependent electronic transport when approaching a strongly localized, insulating state remains an outstanding challenge, although in recent years also significant progress has been made. [10][11][12] In weakly disordered metals, spin lifetimes have long been studied using the unambiguous signature of electronic quantum interference: weak localization. Quantum corrections to diffusive metallic transport, known as weak localization, appear when disorder influences the physical properties of the material under study but does not yet dominate it.…”