NCTS (South)


DATE2013-09-23

TIME12:00

PLACER49223, Second Physics Building , NCKU

FIELDQuantum Information Science

SPEAKER Prof. David Rees - NCTU-RIKEN Joint Laboratory, Institute of Physics, NCTU

TITLEClassical Electron Transport in Point Contacts and Nanowires with Surface-State Electrons on Liquid Helium

ABSTRACTWe present transport measurements of electrons "floating" above the surface of liquid helium, confined in microchannel devices. Our experiments, in which we measure electron transport through nanoconstrictions formed by split-gate electrodes beneath the helium surface, serve as a classical analogue to the well-known quantum point contact. Because the surface electron density is lower than those usually observed in Fermi 2DEGs in semiconductor heterostructures, the electron system is nondegenerate. In addition, the Coulomb interaction between electrons is essentially unscreened. Electrons on helium can therefore be described as a classical electron system, the ground state being the classical Wigner crystal.

We first investigate transport in our split-gate device at temperatures above 1 K, at which the electrons form a strongly-correlated electron liquid[1]. As the constriction is opened the conductance of the device increases in a step-like manner, reminiscent of quantised conductance steps in QPC devices. However, in our device, the conductance steps arise due to the increasing number of electrons able to pass sideby-side through the constriction, a classical many-body effect. At lower temperatures, when the system forms a Wigner crystal, these steps develop into peak-like features which, with the aid of molecular dynamics simulations, we show to be due to the onset of pinning when the electron lattice is arranged in a commensurate manner around the constriction[2].

Lastly, we investigate electron transport in long, thin channels, the effective width of which can be controlled electrostatically[3]. We show that the reentrant melting of the quasi-one-dimensional electron lattice, which occurs as the number of electron chains in the nanowire increases, also produces oscillations in current. These transport features allow us to count the number of chains in the system, from 1 up to several tens of electron rows. Our experiment demonstrates that electrons on helium are a useful system for investigating the dynamical properties of strongly-correlated systems in confined geometry.

[1] D.G. Rees et al., Phys. Rev. Lett. 106, 026803 (2011).
[2] D.G. Rees, H. Totsuji and K. Kono, Phys. Rev. Lett. 108, 176801 (2012).
[3] H. Ikegami, H. Akimoto, D.G. Rees and K. Kono, Phys. Rev. Lett. 109, 236802(2012).