Paramagnetic tunneling systems and their contribution to the polarization echo in glasses (extended)

Startling magnetic effects on the spontaneous polarization echo in some silicate glasses at low and ultra-low temperatures have been reported in the last decade or so. Though some progress in search of an explanation has been made by considering the nuclear quadrupole dephasing of tunneling particles, here we show that the effect of a magnetic field can be understood quantitatively by means of a special tunnel mechanism associated with paramagnetic impurities. For the Fe-, Cr- and Nd-contaminated glasses we provide reasonable fits to the published data as a function of applied magnetic field and temperature

Critical behavior of the compact 3d U(1) gauge theory on isotropic lattices

We report on the computation of the critical point of the deconfinement phase transition, critical indices and the string tension in the compact three dimensional U(1) lattice gauge theory at finite temperatures. The critical indices govern the behavior across the deconfinement phase transition in the pure gauge U(1) model and are generally expected to coincide with the critical indices of the two-dimensional XY model. We studied numerically the U(1) model for N_t=8 on lattices with spatial extension ranging from L=32 to L=256. Our determination of the infinite volume critical point on the lattice with N_t=8 differs substantially from the pseudo-critical coupling at L=32, found earlier in the literature and implicitly assumed as the onset value of the deconfined phase. The critical index $\nu$ computed from the scaling of the pseudo-critical couplings with the extension of the spatial lattice agrees well with the XY value $\nu$=1/2. On the other hand, the index $\eta$ shows large deviation from the expected universal value. The possible reasons of such behavior are discussed in details.Comment: 15 pages, 7 figures; version accepted for publication on J. Stat. Mech