Advisor(s)

Sergey Kravchenko

Contributor(s)

Donald Heiman, Latika Menon, Jeffrey B. Sokoloff

Date of Award

2011

Date Accepted

12-2011

Degree Grantor

Northeastern University

Degree Level

Ph.D.

Degree Name

Doctor of Philosophy

Department or Academic Unit

College of Science, Department of Physics

Keywords

thermopower, condensed matter physics, strongly correlated electrons

Subject Categories

Electron transport, Thermoelectricity

Disciplines

Physics

Abstract

The discovery of the Metal-Insulator Transition at B = 0 in strongly correlated two-dimensional electron systems with low disorder has lead to investigations into related phenomena in this regime of signicant electron-electron interactions. Diverging spin susceptibility has been observed in parallel magnetic fields which was traced to an enhancement of the effective mass (albeit to values only up to 4 times band mass of electrons in Si) at low electron densities corresponding to strong electron-electron interactions. Below a certain density n close to the critical density of the MIT, the electron spins are spontaneously polarized which is interpreted as a phase transition to either a Wigner crystal or a ferromagnetic electron liquid.

We have performed experiments to measure the diffusion thermopower in low disordered Si-MOSFETs with high electron mobilities. The measured values of thermopower are observed to diverge at a particular disorder-independent electron density, nt. The thermopower is linear with temperature, consistent with the Mott formula for diffusion thermopower. The effective mass values are seen to be enhanced up to 25 times the band mass as the density nt is approached.

The two-parameter (disorder and interactions) scaling theory by Punnoose and Finkel'stein accurately describes the metallic behavior near the MIT without any fitting parameters. We have extended the earlier results to even lower temperatures and we observe that once the effects of changes in the valley degeneracy due to splitting and intervalley scattering are taken into account, the two-parameter theory still provides accurate predictions.

We have investigated the electron transport properties of strongly correlated 2D systems at temperatures of the order of the Fermi temperature and we have found qualitative agreement with the analogy with hydrodynamics of liquid He relating the viscosity to the resistivity.

Document Type

Dissertation

Rights Information

copyright 2011

Rights Holder

Anish Mokashi


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