Nernst effect, quasiparticles, and d-density waves in cuprates

We examine the possibility that the large Nernst signal observed in the pseudogap regime of hole-doped cuprates originates from quasiparticle transport in a state with d-density wave (DDW) order, proposed by S. Chakravarty et al. [Phys. Rev. B 63, 094503 (2001)]. We find that the Nernst coefficient can be moderately enhanced in magnitude by DDW order, and is generally of negative sign. Thus, the quasiparticles of the DDW state cannot account for the large and positive Nernst signal observed in the pseudogap phase of the cuprates. However, the general considerations outlined in this paper may be of broader relevance, in particular to the recent measurements of Bel et al. in NbSe_2 and CeCoIn_5 [Phys. Rev. Lett. 91, 066602 (2003); ibid. 92, 217002 (2004)].Comment: 9 pages, 3 figures; published versio

Multispin correlations and pseudo-thermalization of the transient density matrix in solid-state NMR: free induction decay and magic echo

Quantum unitary evolution typically leads to thermalization of generic interacting many-body systems. There are very few known general methods for reversing this process, and we focus on the magic echo, a radio-frequency pulse sequence known to approximately "rewind" the time evolution of dipolar coupled homonuclear spin systems in a large magnetic field. By combining analytic, numerical, and experimental results we systematically investigate factors leading to the degradation of magic echoes, as observed in reduced revival of mean transverse magnetization. Going beyond the conventional analysis based on mean magnetization we use a phase encoding technique to measure the growth of spin correlations in the density matrix at different points in time following magic echoes of varied durations and compare the results to those obtained during a free induction decay (FID). While considerable differences are documented at short times, the long-time behavior of the density matrix appears to be remarkably universal among the types of initial states considered - simple low order multispin correlations are observed to decay exponentially at the same rate, seeding the onset of increasingly complex high order correlations. This manifestly athermal process is constrained by conservation of the second moment of the spectrum of the density matrix and proceeds indefinitely, assuming unitary dynamics.Comment: 12 Pages, 9 figure

Biot-Savart correlations in layered superconductors

We discuss the superconductor to normal phase transition in an infinite-layered type-II superconductor in the limit where the Josephson coupling between layers is negligible. We model each layer as a neutral gas of thermally excited pancake vortices. We assume the dominant interaction between vortices in the same and in different layers is the electromagnetic interaction between the screening currents induced by these vortices. Our main result, obtained by exactly solving the leading order renormalization group flow, is that the phase transition in this model is a Kosterlitz--Thouless transition despite being a three--dimensional system. While the transition itself is driven by the unbinding of two-dimensional pancake vortices, an RG analysis of the low temperature phase and a mean-field theory of the high temperature phase reveal that both phases possess three-dimensional correlations. An experimental consequence of this is that the jump in the measured in-plane superfluid stiffness, which is a universal quantity in 2d Kosterlitz-Thouless theory, will receive a small non--universal correction (of order 1% in Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$). This overall picture places some claims expressed in the literature on a more secure analytical footing and also resolves some conflicting views.Comment: 16 pages, 2 figures; minor typos corrected, references adde

Photophoresis of topical steroids in the treatment of severe forms of lichen ruber planus of oral mucosa

The objective of the study is to search for new methods of treatment for lichen ruber planus with high efficacy, few complications and side effects, as well as providing a long-term therapeutic effect. The authors used the method of photophoresis (red LED radiation + topical steroid) in the combination treatment of 40 patients with severe forms of lichen ruber planu

Photophoresis of topical steroids in the treatment of severe forms of lichen ruber planus of oral mucosa

The objective of the study is to search for new methods of treatment for lichen ruber planus with high efficacy, few complications and side effects, as well as providing a long-term therapeutic effec

On bipartite Rokhsar-Kivelson points and Cantor deconfinement

Quantum dimer models on bipartite lattices exhibit Rokhsar-Kivelson (RK) points with exactly known critical ground states and deconfined spinons. We examine generic, weak, perturbations around these points. In d=2+1 we find a first order transition between a ``plaquette'' valence bond crystal and a region with a devil's staircase of commensurate and incommensurate valence bond crystals. In the part of the phase diagram where the staircase is incomplete, the incommensurate states exhibit a gapless photon and deconfined spinons on a set of finite measure, almost but not quite a deconfined phase in a compact U(1) gauge theory in d=2+1! In d=3+1 we find a continuous transition between the U(1) resonating valence bond (RVB) phase and a deconfined staggered valence bond crystal. In an appendix we comment on analogous phenomena in quantum vertex models, most notably the existence of a continuous transition on the triangular lattice in d=2+1.Comment: 9 pages; expanded version to appear in Phys. Rev. B; presentation improve

Signatures of Electronic Nematic Phase at Isotropic-Nematic Phase Transition

The electronic nematic phase occurs when the point-group symmetry of the lattice structure is broken, due to electron-electron interactions. We study a model for the nematic phase on a square lattice with emphasis on the phase transition between isotropic and nematic phases within mean field theory. We find the transition to be first order, with dramatic changes in the Fermi surface topology accompanying the transition. Furthermore, we study the conductivity tensor and Hall constant as probes of the nematic phase and its transition. The relevance of our findings to Hall resistivity experiments in the high-$T_c$ cuprates is discussed.Comment: 5 pages, 3 figure