Abstract
We consider electron–electron interaction effects in quantum point contacts on the first quantization plateau, taking into account all scattering processes. We compute the low-temperature linear and nonlinear conductance, shot noise and thermopower, by perturbation theory and a self-consistent nonperturbative method. On the conductance plateau, the low-temperature corrections are solely due to momentum-nonconserving processes that change the relative number of left- and right-moving electrons. This leads to a suppression of the conductance for increasing temperature or voltage. The size of the suppression is estimated for a realistic saddle-point potential, and is largest in the beginning of the conductance plateau. For large magnetic field, interaction effects are strongly suppressed by the Pauli principle, and hence the first spin-split conductance plateau has a much weaker interaction correction. For the nonperturbative calculations, we use a self-consistent nonequilibrium Green's function approach, which suggests that the conductance saturates at elevated temperatures. These results are consistent with many experimental observations related to the so-called 0.7 anomaly.
Highlights
Conductance quantization in a quantum point contact (QPC), first observed in 1988[1], constitutes a classic textbook effect of mesoscopic physics
Such a quasi-bound state was found in spin density functional theory (SDFT) calculations[13], and models based on this picture appear to reproduce several essential observations related to the 0.7 anomaly
Several publications have suggested that electron-electron interactions alone may already result in a reduced conductance in a QPC at elevated temperatures, without the need for additional assumptions of spin polarization or a localized state[17, 18, 19, 20, 21, 22, 23]
Summary
Conductance quantization in a quantum point contact (QPC), first observed in 1988[1], constitutes a classic textbook effect of mesoscopic physics. While phenomenological models[9], assuming the existence of a density-dependent spin gap, can provide rather good fits to experimental data, the presumed static spin polarization due to interactions within the local QPC region is not expected in the presence of unpolarized bulk reservoirs Along this line of thinking, it was recently conjectured that spin symmetry-broken mean-field or density functional theory calculations are unable to recover the correct T dependence of the conductance[10, 11, 12]. A number of microscopic theories assume the existence of a quasi-bound state in the QPC region, leading to a Kondo-type scenario, as encountered in transport through interacting quantum dots[13, 14] Such a quasi-bound state was found in spin density functional theory (SDFT) calculations[13], and models based on this picture appear to reproduce several essential observations related to the 0.7 anomaly. Several publications have suggested that electron-electron (ee) interactions alone may already result in a reduced conductance in a QPC at elevated temperatures, without the need for additional assumptions of spin polarization or a localized state[17, 18, 19, 20, 21, 22, 23]
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