Effect of Kondo resonance on optical third harmonic generation

We use the method of dynamical mean field thoery, to study the effect of Kondo resonance on optical third harmonic generation (THG) spectra of strongly correlated systems across the metal-insulator transition. We find that THG signals are proportional to the quasiparticle weight $z$ of the Kondo peak, and are precursors of Mott-Hubbard gap formation.Comment: ICM 2006 (kyoto) proceedin

Gapless chiral excitons in thin films of topological insulators

In a nanoscopic thin film of a strong topological insulator (TI) the Coulomb interaction in the channel that exchanges the two electrons with the same chirality in two different planes of the slab takes advantage of the minus sign resulting from such "exchange" and gives rise to a bound state between the positive energy states in one surface and the negative energy states in the opposite surfaces. Therefore particle and hole pairs in the {\em undoped} Dirac cone of the TI thin film form an inter-surface spin-singlet state that lies below the continuum of free particle-hole pairs. This mode is similar to the excitons of semiconductors, albeit formed between the electron and hole pairs from two different two-dimensional surfaces. For low-momenta the dispersion relation characterizing this collective mode is linear. Experimental comparison of two slabs with different thicknesses can capture the exponential dependence of the present effect on the slab thickness.Comment: Comments are welcom

Phenomenology of nn-nˉ{\bar n} Oscillations Revisited

We revisit the phenomenology of $n$-${\bar n}$ oscillations in the presence of external magnetic fields, highlighting the role of spin. We show, contrary to long-held belief, that the $n$-${\bar n}$ transition rate need not be suppressed, opening new opportunities for its empirical study.Comment: 15 pages, REVTeX; revised and rewritten to focus on SM spin-dependent effects, conclusions persis