Bias and temperature dependence of the 0.7 conductance anomaly in quantum point contacts

The 0.7 (2e(2)/h) conductance anomaly is studied in strongly confined, etch ed GaAs/GaAlAs quantum point contacts, by measuring the differential conduc tance as a function of source-drain and gate bias as well as a function of temperature. We investigate in detail how, fur a given gate voltage, the di fferential conductance depends on the finite bias voltage and find a so-cal led self-gating effect, which we correct for. The 0.7 anomaly at zero bias is found to evolve smoothly into a conductance plateau at 0.85 (2e(2)/h) at finite bias. On varying the gate voltage the transition between the 1.0 an d 0.85 (2e(2)/h) plateaus occurs for definite bias voltages, which define a gate-voltage-dependent energy difference Delta. This energy difference is compared with the activation temperature T-a extracted from the experimenta lly observed activated behavior of the 0.7 anomaly at low bias. We find Del ta = k(B)T(a), which lends support to the idea that the conductance anomaly is due to transmission through two conduction channels, of which the one w ith its subband edge Delta below the chemical potential becomes thermally d epopulated as the temperature is increased.