Berlin 2015 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 102: Transport: Quantum Dots, Quantum Wires, Point Contacts 2 (jointly with HL)

TT 102.7: Hauptvortrag

Donnerstag, 19. März 2015, 16:45–17:15, A 053

Microscopic Origin of the 0.7-Anomaly in Quantum Point Contacts: Correlations in 1D — Florin Bauer¹, Jan Heyder¹, Dawid Borowsky¹, D. Taubert¹, D. Schuh², B. Bruognolo¹, Werner Wegscheider³, Jan von Delft¹, and •Stefan Ludwig¹ — ¹Fakultät für Physik, LMU München — ²Institut für Angew. Physik, Universität Regensburg — ³ETH Zurich, Switzerland

Quantum point contacts (QPCs), the ultimate building blocks of quantum electronic circuits, are 1D constrictions in a 2D electron system (2DES). When a QPC is pinched off, its conductance famously decreases in integer steps of the conductance quantum, G_Q = 2e²/h. An unexpected kink of the pinch-off curve near 0.7G_Q with an intriguing dependence on temperature, magnetic field and source-drain voltage, the 0.7-anomaly, has been subject of debates for the last two decades [1]. In this talk I will show that the divergence of the 1D density of states (DOS) at low energies, a prerequisite of the quantized conductance, is also the origin of the 0.7-anomaly. It naturally arises from strong correlations fostered by an enhanced DOS. They cause an anomalous increase of the spin susceptibility and back-scattering. Our microscopic model is built on a combination of systematic measurements of a highly tunable QPC and detailed numerical calculations [2]. We discuss commonalities and differences to previous more phenomenological attempts to explain the 0.7-anomaly, namely the model of spontaneous spin polarization and the Kondo model [1].

[1] A. Micolich, J. Phys.: Condens. Matter 23, 443201 (2011)

[2] F. Bauer et al., Nature 501, 73 (2013)