  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 e_a in the point
contact. From the grayscale plot we extract the constant normal subband edges
e_0, e_1, ... and most notably the bias dependent anomalous subband edge
e'_0(mu_d) split off from e_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.
