Transmission-phase measurement of the 0.7 anomaly in a quantum point contact

TL;DR

This study measures the transmission phase in a quantum point contact at low carrier densities, revealing anomalous phase behavior in the 0.7 regime indicative of complex electron interactions and possible transition to a spin-incoherent Luttinger liquid.

Contribution

It provides the first direct measurement of transmission phase behavior in the 0.7 anomaly regime, linking phase shifts to electron interactions and spin states.

Findings

Monotonic phase shift in the first conductance plateau

Anomalous phase increase in the 0.7 regime

Evidence suggesting a transition to a spin-incoherent Luttinger liquid

Abstract

We measure the transmission phase of a quantum point contact (QPC) at a low carrier density in which electron interaction is expected to play an important role and anomalous behaviors are observed. In the first conductance plateau, the transmission phase shifts monotonically as the carrier density is decreased by the gate voltage. When the conductance starts to decrease, in what is often called the 0.7 regime, the phase exhibits an anomalous increase compared with the noninteracting model. The observation implies an increase in the wave vector as the carrier density is decreased, suggesting a transition to a spin-incoherent Luttinger liquid.