Berlin 2012 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 62: Quantum Dots and Wires: Transport Properties I (mainly Quantum Wires)

HL 62.1: Talk

Wednesday, March 28, 2012, 15:00–15:15, EW 203

Low Temperature Conductance Quantization in GaAs Quantum Wires — •Christian Scheller¹, Gilad Barak², Loren N. Pfeiffer³, Ken W. West³, Amir Yacoby², and Dominik M. Zumbühl¹ — ¹Dep. of Physics, University of Basel, Switzerland — ²Dep. of Physics, Harvard University, Cambridge, Massachusetts, USA — ³Bell Labs, Lucent Technologies, Murray Hill, New Jersey, USA

We present low temperature quantum transport measurements of cleaved edge overgrowth quantum wires fabricated in GaAs-AlGaAs. When the electron density in the wire is varied using a gate voltage, pronounced conductance plateaus are observed. However, the conductance values of the plateaus are strongly suppressed below the universally expected multiples of 2 e²/h [1]. For the lowest mode, the plateau conductance saturates at ≈ 1 e²/h at low temperatures T<80 mK and zero external magnetic field. This seems to suggest that the spin degeneracy is lifted, consistent with recent theory [2] predicting helical nuclear magnetism in the Luttinger liquid regime. Using the same setup and a similar chip carrier, we demonstrate electron temperatures down to 11 mK in metallic Coulomb blockade thermometers, suggesting that the sample cools far below 80 mK. We employ transport spectroscopy to investigate the system and further use resistively detected NMR in an attempt to elucidate the role of the nuclear spins. [1] "Nonuniversal Conductance Quantization in Quantum Wires", A.Yacoby et al., Phys. Rev. Lett. 77, 4612 (1996). [2] "Nuclear magnetism and electron order in interacting one-dimensional conductors", Bernd Braunecker, Pascal Simon, and Daniel Loss, Phys. Rev. B80, 165119 (2009).