arXiv subjects
Publications and source records attributed to T. Portengen.
We discuss the emergence of an orthogonality catastrophe in the response of a composite fermion liquid as the filling factor νapproaches 1/2m, where m=1,2,3.... A tunneling experiment is proposed in which dramatic changes in the I-V characteristic should be observable as νis varied. Explicit I-V characteristics calculated within the so-called Modified Random Phase Approximation, are provided for ν=1/3 -> ν=1/2.
A novel type of charged excitation, known as a Skyrmion, has recently been discovered in quantum Hall systems with filling factor near ν= 1. A Skyrmion -- which can be thought of as a topological twist in the spin density of the electron gas -- has the same charge as an electron, but a much larger spin. In this review we present a detailed theoretical investigation of the optical properties of Skyrmions. Our results provide means for the optical detection of Skyrmions using photoluminescence (PL) spectroscopy. We first consider the optical properties of Skyrmions in disordered systems. A calculation of the luminescence energy reveals a special optical signature which allows us to distinguish between Skyrmions and ordinary electrons. Two experiments to measure the optical signature are proposed. We then turn to the optical properties of Skyrmions in pure systems. We show that, just like an ordinary electron, a Skyrmion may bind with a hole to form a Skyrmionic exciton. The Skyrmionic exciton can have a lower energy than the ordinary magnetoexciton. The optical signature of Skyrmions is found to be a robust feature of the PL spectrum in both disordered and pure systems.
We investigate the properties of a Skyrmionic exciton consisting of a negatively charged Skyrmion bound to a mobile valence hole. A variational wave function is constructed which has the generalized total momentum P as a good quantum number. It is shown that the Skyrmionic exciton can have a larger binding energy than an ordinary magnetoexciton and should therefore dominate the photoluminescence spectrum in high-mobility quantum wells and heterojunctions where the electron-hole separation exceeds a critical value. The dispersion relation for the Skyrmionic exciton is discussed.
The photoluminescence spectrum of quantized Hall states near filling factor ν= 1 is investigated theoretically. For ν>= 1 the spectrum consists of a right-circularly polarized (RCP) line and a left-circularly polarized (LCP) line, whose mean energy: (1) does not depend on the electron g factor for spin-1/2 quasielectrons, (2) does depend on g for charged spin-texture excitations (skyrmions). For ν< 1 the spectrum consists of a LCP line shifted down in energy from the LCP line at ν>= 1. The g-factor dependence of the red shift of the LCP line determines the nature of the negatively charged excitations.
We present a theory of the linear and nonlinear optical characteristics of the insulating phase of the Falicov-Kimball model within the self-consistent mean-field approximation. The Coulomb attraction between the itinerant d-electrons and the localized f-holes gives rise to a built-in coherence between the d and f-states, which breaks the inversion symmetry of the underlying crystal, leading to: (1) electronic ferroelectricity, (2) ferroelectric resonance, and (3) a nonvanishing susceptibility for second-harmonic generation. As experimental tests of such a built-in coherence in mixed-valent compounds we propose measurements of the static dielectric constant, the microwave absorption spectrum, and the dynamic second-order susceptibility.
We calculate the linear and nonlinear optical properties of the Falicov-Kimball model for a mixed-valent system within the self-consistent mean-field approximation. Second-harmonic generation can only occur if the mixed-valent state has a built-in coherence between the itinerant d-electrons and the localized f-holes. By contrast, second-harmonic generation cannot occur for solutions of the model with f-site occupation as a good quantum number. As an experimental test of coherence in mixed-valent compounds we propose a measurement of the dynamic second-order susceptibility.