Bias dependent subband edges and the 0.7 conductance anomaly

The 0.7 (2e(2)/h) conductance anomaly is studied in strongly confined, etched GaAs/GaAlAs quantum point contacts by measuring the differential conductance G as a function of source-drain bias V-sd and gate-source bias V-gs as well as a function of temperature. In the V-gs - V-sd plane we use a grayscale plot of the transconductance dG/dV(gs) to map out the bias dependent transitions between the normal and anomalous conductance plateaus. Any given transition is interpreted as arising when the bias controlled chemical potential mu(d) (mu(s)) Of the drain (source) reservoir crosses a subband edge epsilon(x) in the point contact. From the grayscale plot we extract the constant normal subband edges epsilon(0), epsilon(1),... and most notably the bias dependent anomalous subband edge epsilon(0)(')(mu(d)) split off from epsilon(0). We show by applying a finite-bias version of the recently proposed BCF model, how the bias dependence of the anomalous subband edge is the key to analyze various experimental observations related to the 0.7 anomaly.