Berlin 2015 – wissenschaftliches Programm
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, GQ = 2e2/h. An unexpected kink of the pinch-off curve near 0.7GQ 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 . 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 . 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 .
 A. Micolich, J. Phys.: Condens. Matter 23, 443201 (2011)
 F. Bauer et al., Nature 501, 73 (2013)