Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

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

TT 102.8: Talk

Thursday, March 19, 2015, 17:15–17:30, A 053

Spin dynamics in a quantum point contact showing the 0.7-anomaly — •Dennis Schimmel^1,2, Florian Bauer^1,2, Jan Heyder^1,2, and Jan von Delft^1,2 — ¹Ludwig-Maximilians-Universitaet Muenchen — ²Arnold Sommerfeld Center for Theoretical Physics

The 0.7-anomaly in the first conductance step of a quantum point contact is believed to arise from an interplay of geometry, spin dynamics and interaction effects. Various scenarios have been proposed to explain it, each evoking a different concept, including spontaneous spin polarization, or a quasi-localized state, or ferromagnetic spin fluctuations, or a van Hove ridge (a geometry-induced maximum in the density of states). Though these scenarios differ substantially regarding numerous details, they all imply anomalous dynamics for the spins in the vicinity of the QPC. Our model consists of a one-dimensional system with a parabolic barrier. Interactions are restricted to a central region around the barrier and short-range. The leads are solved exactly and the central region is then treated using the functional renormalization group within a coupled ladder approximation scheme. Within this setup, we have performed a detailed study of the spin dynamics in the central region by calculating the dynamical spin-spin correlation function χ(x,x′,ω) = ∫₀^∞⟨ S_z(x,t) S_z(x′,0) ⟩ e^{i ω t} . We will discuss its behavior as function of frequency, interaction strength and gate voltage and comment on the implications of these results for each of the above-mentioned scenarios.