Wavelet-induced renormalization group for the Landau-Ginzburg model

The scale hierarchy of wavelets provides a natural frame for renormalization. Expanding the order parameter of the Landau-Ginzburg/$\Phi^4$ model in a basis of compact orthonormal wavelets explicitly exhibits the coupling between scales that leads to non-trivial behavior. The locality properties of Daubechies' wavelets enable us to derive the qualitative renormalization flow of the Landau-Ginzburg model from Gaussian fluctuations in wavelet space.Comment: LATTICE99(Renormalization), LaTeX, 3 page

Comparisons of spectra determined using detector atoms and spatial correlation functions

We show how two level atoms can be used to determine the local time dependent spectrum. The method is applied to a one dimensional cavity. The spectrum obtained is compared with the mode spectrum determined using spatially filtered second order correlation functions. The spectra obtained using two level atoms give identical results with the mode spectrum. One benefit of the method is that only one time averages are needed. It is also more closely related to a realistic measurement scheme than any other definition of a time dependent spectrum.Comment: 8 pages, 8 figure

Wavelets as a variational basis of the XY model

We use Daubechies' orthonormal compact wavelets as a variational basis for the $XY$ model in two and three dimensions. Assuming that the fluctuations of the wavelet coefficients are Gaussian and uncorrelated, minimization of the free energy yields the fluctuation strength of wavelet coefficients at different scales, from which observables can be computed. This model is able to describe the low-temperature phase and makes a prediction about the phase transition temperature.Comment: 3 pages, postscript. Contribution to the Lattice 93 workshop (Dallas, Texas, October 1993

Detect Spinons via Spin Transport

Existence of spinons is the defining property of quantum spin liquids. These exotic excitations have (fractionalized) spin quantum number and no electric charge, and have been proposed to form Fermi surfaces in the recently discovered organic spin liquid candidates. However direct probes for them are still lacking. In this paper we propose to experimentally identify the spinons by measuring the spin current flowing through the spin liquid candidate materials, which would be a direct test for the existence of spin-carrying mobile excitations. By the nonequilibrium Green function technique we evaluate the spin current through the interface between a Mott insulator and a metal under a spin bias, and find that different kinds of Mott insulators, including quantum spin liquids, can be distinguished by different relations between the spin bias and spin current, In the end we will also discuss relations to experiments and estimate experimentally relevant parameters.Comment: 7 pages with appendix, 3 figure