Emergence of a novel correlated-electron metal in a 2D electron gas

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• Dr. Vijay Narayan, Semiconductor Physics Group, Cavendish Laboratory
• Thursday 12 June 2014, 11:00-11:30
• Pippard Lecture Theatre, Cavendish Laboratory, Department of Physics.

If you have a question about this talk, please contact Leona Hope-Coles.

This seminar is being given as part of the recruitment process for the Early Career Lectureships. Members of the Department are encouraged to attend as the selection panel would welcome any feedback by email to hod@phy.cam.ac.uk

ABSTRACT: Two-dimensional electron gases (2DEGs) are a rich playground for inter-electron interactions and host to several fascinating phenomena such as the quantum Hall effect, the fractional quantum Hall effect and the 2D ‘metal-to-insulator transition’. They are ideal test beds to observe the delicate interplay of the many-body Coulomb potential and disorder which theoretically has been predicted to give rise to very rich electronic phase behaviour.

In this talk I will present some of my recent experimental studies on the thermopower (S) of GaAs-based mesoscopic 2DEGs where I am looking for novel electron phase behaviour. I will start with an introduction to many-electron physics in 2DEGs, and then briefly discuss why S is a powerful probe of such many-body effects, before going into the experimental results. Remarkably, the data suggest a density-driven transition between two distinct electron phases both of which show metal-like transport. Interestingly, neither S nor the electrical resistivity ρ show any indication of the more conventional 2D metal-insulator transition even when ρ is two orders of magnitude greater than the resistance quantum h/e². Instead, as n is lowered, the 2DEG shows an abrupt departure from simple, non-interacting, Drude metal-like behaviour to strongly-interacting, correlated-electron behaviour. The latter include (i) A metallic character as evidenced by the linear T-dependence of S and T-independent nature of ρ even when ρ >> h/e²; (ii) strong oscillations and even sign changes in S while ρ is absolutely monotonic; and (iii) exceedingly large S-values of ~100 mV/K at 1.5 K. Furthermore, in the T-dependence of S, there is an earlier onset of phonon drag as compared to the non-interacting phase signifying a sharp reduction in the number of charge carriers. This reduction cannot be simply explained by the gating action used to tune n and is a strong indicator of correlated electron behaviour. I will conclude with an explanation of these results based on a picture of the 2DEG tending towards a spatially ordered state as n is reduced and in which collective electron excitations mediate both thermal and electrical transport.

This talk is part of the Special Departmental Seminars series.

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