Song He

NEW LIQUID PHASE AND METAL-INSULATOR TRANSITION IN SI MOSFETS

We argue that there is a new liquid phase in the two-dimensional electron system in Si MOSFETs at low enough electron densities. The recently observed metal-insulator transition results as a crossover from the percolation transition of the liquid phase through the disorder landscape in the system below the liquid-gas critical temperature. The consequences of our theory are discussed for variety of physical properties relevant to the recent experiments.

Theory of ballistic electron transport through quantized constrictions

Abstract We numerically calculate the quantum conductance of narrow constrictions directly from the Kubo formula by using the recursive Greens function technique. We study effects of temperature, elastic and inelastic scattering, and, the shape and the size of the constriction on the conductance quantization phenomenon. We find the quantization to be quite fragile, being destroyed by having either too high or too low a temperature, and, by elastic and inelastic scattering. We find quantum resonance structure on the conductance plateau, arising from quantum reflection at the sharp edges of the constriction (or, from the impurities), which disappears as the temperature is raised or the constriction is made smoother.

THEORY OF ELECTRON TRANSPORT THROUGH QUANTUM CONSTRICTIONS IN SEMICONDUCTOR NANOSTRUCTURES

Detailed numerical results are presented for the calculated conductance of quantum point contacts, or, narrow constrictions between high mobility two-dimensional electron systems fabricated on semiconductor nanostructures. The conductance is calculated from the two-terminal multichannel transmission matrix formalism using the recursive single-particle Green’s function technique. The Green’s functions are obtained recursively for a tight-binding two-dimensional disordered Anderson lattice model representing the constriction. The conductance is calculated as a function of the shape and the size of the constriction (i.e., its geometry), the temperature, and, the elastic disorder in the system. Our main results, which are consistent with experimental findings, are: (1) increase of elastic scattering destroys the quantization; (2) for a fixed amount of disorder (i.e., for a given value of the elastic mean free path), the conductance quantization is poorer for longer constrictions; (3) in general, the quantizat...

Collective Mode of Semion Systems

The ground and the excited states of a two-dimensional anyon system are studied via finite-size numerical calculations and single-mode approximation in a spherical geometry. It is shown that Laughlins mean field theory gives an accurate description of the ground state properties. We find, consistent with earlier analytic theories, that the collective mode of the system exhibits a linear dispersion in the long wavelength limit, and predict a novel roton minimum at a finite value of the wavenumber q. We also discuss the consequences on the anyon spectrum of having a model repulsive interaction between the particles.

Optical and transport properties of one-dimensional quantum wire structures

Abstract We calculate optical and transport properties of semiconductor quantum wire structures and compare our theoretical results with available experimental data. Optical properties are calculated by developing a theory for the far-infrared electromagnetic response of the system in the multi-subband occupancy situation, including effects of both intra-subband and inter-subband excitations and the modecoupling between them. Transport properties are calculated for the currently experimentally interesting quantum constriction structures from the ballistic to the diffusive regime by using the recursive Greens function technique. Good agreement between our theory and experiment is found for both optical and transport properties.