Fractional microwave-induced resistance oscillations

We develop a systematic theory of microwave-induced oscillations in magnetoresistivity of a 2D electron gas in the vicinity of fractional harmonics of the cyclotron resonance, observed in recent experiments. We show that in the limit of well-separated Landau levels the effect is dominated by the multiphoton inelastic mechanism. At moderate magnetic field, two single-photon mechanisms become important. One of them is due to resonant series of multiple single-photon transitions, while the other originates from microwave-induced sidebands in the density of states of disorder-broadened Landau levels.Comment: 3 pages, 2 figures; Proceedings of EP2DS17 to be published in Physica E; less technical version of arXiv:0707.099

Resonating-valence-bond structure of Gutzwiller-projected superconducting wave functions

Gutzwiller-projected (GP) wave functions have been widely used for describing spin-liquid physics in frustrated magnets and in high-temperature superconductors. Such wave functions are known to represent states of the resonating-valence-bond (RVB) type. In the present work I discuss the RVB structure of a GP singlet superconducting state with nodes in the spectrum. The resulting state for the undoped spin system may be described in terms of the "path integral" over loop coverings of the lattice, thus extending the known construction for RVB states. The problem of the topological order in GP states may be reformulated in terms of the statistical behavior of loops. The simple example of the projected d-wave state on the square lattice demonstrates that the statistical behavior of loops is renormalized in a nontrivial manner by the projection.Comment: 6 pages, 4 figures, some numerical data adde

Multi-field continuum theory for medium with microscopic rotations

We derive the multi-field, micropolar-type continuum theory for the two-dimensional model of crystal having finite-size particles. Continuum theories are usually valid for waves with wavelength much larger than the size of primitive cell of crystal. By comparison of the dispersion relations, it is demonstrated that in contrast to the single-field continuum theory constructed in our previous paper the multi-field generalization is valid not only for long but also for short waves. We show that the multi-field model can be used to describe spatially localized short- and long wavelength distortions. Short-wave external fields of forces and torques can be also naturally taken into account by the multi-field continuum theory.Comment: 14 pages, 4 figures, submitted to International Journal of Solids and Structure

Technological Transfers, Limited Commitment and Growth

This paper examines the effect on economic growth and welfare of the access to external financing which results in technological transfers to a developing country from the rest of the world. We consider a two-sector stochastic growth model and compute optimal accumulation mechanisms in the environments which differ in the extent to which the borrowing contracts are enforced. Furthermore, we examine different assumptions concerning the default punishment and their implications for growth, welfare and borrowing patterns. We show that under limited commitment lack of technological transfers may result in scarce capital flows to developing countries and substantially reduce their growth opportunities. Presence of technological transfers in this environment induces a developing country to use foreign capital to both smooth consumption and invest more heavily in all the sectors of the economy including those unaffected by the productivity benefits. Our findings suggest that technological transfers may play a role of an important enforcement mechanism. In addition, our model can account for the rich structure of observed capital flows to low- and middle income countriesIncentive compatibility, technological diffusion, international capital flows, default risk, numerical algorithm.