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

Abstract

The 0.7 (2e 2 /h) conductance anomaly is studied in strongly confined, etched GaAs/GaAlAs quantum point contacts, by measuring the differential conductance as a function of source-drain and gate bias as well as a function of temperature. We investigate in detail how, for a given gate voltage, the differential conductance depends on the finite bias voltage and find a so-called 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. Varying the gate voltage the transition between the 1.0 and the 0.85 (2e 2 /h) plateaus occurs for definite bias voltages, which defines a gate voltage dependent energy difference ∆. This energy difference is compared with the activation temperature Ta extracted from the experimentally observed activated behavior of the 0.7 anomaly at low bias. We find ∆ = kBTa which lends support to the idea that the conductance anomaly is due to transmission through two conduction channels, of which the one with its subband edge ∆ below the chemical potential becomes thermally depopulated as the temperature is increased.PACS 73.61.-r, 73.23.-b

The Influence of Device Geometry on Many-Body Effects in Quantum Point Contacts: Signatures of the 0.7 Anomaly, Exchange and Kondo

“…We observe that the peak width and height δG of the ZBA are not constant over the whole range 0 < G < 2e 2 /h (see also Figs. 6,7,8,9,10,11 and 12 in [19]). We choose to fit these parameters at G ∼ 0.3, where the peak height has a relative maximum.…”

“…Several models have been proposed that relate the 0.7 anomaly to a spontaneous spin splitting in zero magnetic field [5][6][7][8][9][10][11], since the 0.7 plateau evolves continuously into the spin-resolved plateau at 0.5(2e 2 /h) when an inplane magnetic field is applied. A recent theory paper [12] presented spin-density functional calculations of realistic QPC geometries that show that a localized state can exist near pinch-off in a QPC, providing a theoretical back-ground for the Kondo-like physics that was found experimentally [13].…”

Electrostatic effects in coupled quantum dot-point contact-single electron transistor devices

“…In a sample presented here, the oscillation amplitude is largest at V PC $ À1.3 V and V QD $ À1.47 V. They weaken and disappear deep in regions a and c. One can see from Fig. 2(b) that periodicity is not related to the conductance quantization of PC which was a subject of study in a number of works, [11][12][13] as the position and number of oscillations are not correlated with the conductance quantum plateaus at multiples or rational numbers of e 2 /h. There are more than ten periods of oscillations when G is below e 2 /h.…”

“…It can be explained either by the Coulomb blockade, or trans-conductance of the point contact in a regime of bound states. 11,12 In a latter case, the diamonds reflect quantization of conductance of the PC: differential conductance has peaks when transition between different conductance plateaus occurs. In our samples, oscillations are not correlated with integer plateaus or, recently discussed, 0.5, 0.7, and 0.9 ones of e 2 /h in the G, see Fig.…”

Conductance quantization and zero bias peak in a gated quantum wire

“…In AlGaAs/GaAs quantum point contacts (QPC) conductance plateaus occur at integral values of 2e 2 /h corresponding to an integral number of electric subbands carrying the transport current [1,2]. While integral conductance quantization can be understood from a single-electron picture [3][4][5], the widely observed 0.7 conductance feature observed in QPCs appears to involve manyelectron physics [6][7][8][9][10][11][12][13]. In this paper, we report conductance measurements on a 3 mm long quantum wire with seven cross channel gates.…”