Dresden 2011 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 64: Quantum Wires: Transport

HL 64.11: Vortrag

Mittwoch, 16. März 2011, 19:15–19:30, POT 251

The 0.7-anomaly of quantum point contacts — towards understanding its microscopic origin — •David Borowsky¹, Enrico Schubert¹, Daniela Taubert¹, Werner Wegscheider², and Stefan Ludwig¹ — ¹Center for NanoScience and Fakultät für Physik, Universität München, Germany — ²Solid State Physics Laboratory, ETH Zürich, Switzerland

The 0.7-anomaly of a quantum point contact (QPC) has been a subject of intense research since it was first studied in 1996 [1], but its microscopic origin is still controversially discussed. The temperature dependence of the conductance G at the 0.7-anomaly revealed a scaling behaviour reminiscent of the Kondo effect [2], which lead to an interpretation in terms of a quasi-bound state in the Kondo regime [3].

Motivated by many unanswered questions, we used highly tunable QPCs in the 2D electron system (2DES) of a GaAs/AlGaAs heterostructure to study the 0.7-anomaly. We measured G at the 0.7-anomaly as a function of the microscopic confinement potential and in-plane magnetic field. Our experiments show scaling behaviour as a function of magnetic field similar to the temperature dependence [2]. Our results favor a model predicting a magnetic susceptibility enhancement at the 1D-constriction which leads to phenomenologically similar behaviour as the Kondo effect of a quasi-bound state [4].

[1] Thomas et al, Phys. Rev. Lett., 1996, 77, 135 - 138

[2] Cronenwett et al, Phys. Rev. Lett., 2002, 88, 226805

[3] Meir et al, Phys. Rev. Lett., 2002, 89, 196802

[4] Jan von Delft (private communication)