ICPS 2014

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8:30-9:00
Invited: Hermann Sellier
Wigner Crystallization in Quantum Point Contacts Revealed by Scanning Gate Microscopy

In addition to quantized conductance plateaus at multiples of 2e²/h, quantum point contacts in 2DEGs often show a shoulder at 0.7(2e²/h), which cannot be explained by single-particle theories. At very low temperature, this 0.7 anomaly shades off and a zero-bias anomaly emerges. Different theoretical models have been proposed but none is fully satisfactory. Here we present new experimental results using a scanning gate microscope to change in-situ the potential landscape with a sharp polarized tip. Approaching the tip towards the point contact produces an oscillatory splitting of the zero-bias anomaly correlated with large modulations of the 0.7 anomaly. These oscillations cannot be explained by interference effects, and are interpreted as the signature of a many-body localized state induced by strong Coulomb interactions at low electron density. This state is revealed by the Kondo screening from the leads, giving a conductance peak at zero (resp. finite) bias for an odd (resp. even) number of electrons that is tuned by the tip position. Our interpretation is supported by electrostatic simulations showing that the electron density in the contact meets the criterion for 1D Wigner crystallization below the first plateau. It points in the same direction as a recent experiment with six surface gates that gave indications for the presence of emergent localized states. Our result contributes to resolving a complex mesoscopic problem involving strongly interacting electrons in a non-uniform potential landscape.

Co-authors: Boris Brun, Frederico Martins, Sebastien Faniel, Benoit Hackens, Antonella Cavanna, Christian Ulysse, Abdelkarim Ouerghi, Ulf Gennser, Dominique Mailly, Guillaume Bachelier, Serge Huant, Vincent Bayot, Marc Sanquer

9:00-9:15
Oral: Aleksey Kozikov
Inducing & Controlling Aharonov-Bohm Oscillations with a Scanning Gate
Co-authors: Richard Steinacher, Clemens Roessler, Christian Reichl, Werner Wegscheider, Thomas Ihn, Klaus Ensslin

9:15-9:30
Oral: Yoshitaka Nishihara
Precise Shot Noise Measurement in a Clean Quantum Point Contact
Co-authors: Teruo Ono, Tomonori Arakawa, Takahiro Tanaka, Shota Norimoto, Kensuke Kobayashi, Thomas Ihn, Clemens Rössler, Klaus Ensslin

9:30-9:45
Oral: Chunlin Yu
Magnetic Field-Enhanced Cooper Pair Co-Tunneling in InSb Nanowire Josephson Quantum Devices
Co-authors: Mingtang Deng, Philippe Caroff, Kimberly Thelander, Hongqi Xu

9:45-10:00
Oral: Scott Dietrich
Dynamics of Quantal Heating of 2D Electrons in Crossed Electric & Quantizing Magnetic Fields
Co-authors: William Mayer, Sergey Vitkalov, Alexey Bykov

10:00-10:15
Oral: Lars Duggen
Bloch-Like Oscillations in Finite Quantum Structures
Co-authors: Morten Willatzen, Benny Lassen, Lok C. Lew Van Yoon

10:15-10:30
Oral: Dmitri Efetov
Andreev Spectroscopy in the Quantum Hall Regime in Bilayer Graphene
Co-authors: Clevin Handschin, Jean-Damian Pillet, Lei Wang, Cory Dean, Philip Kim