Green-Function-Based Monte Carlo Method for Classical Fields Coupled to Fermions

Microscopic models of classical degrees of freedom coupled to non-interacting fermions occur in many different contexts. Prominent examples from solid state physics are descriptions of colossal magnetoresistance manganites and diluted magnetic semiconductors, or auxiliary field methods for correlated electron systems. Monte Carlo simulations are vital for an understanding of such systems, but notorious for requiring the solution of the fermion problem with each change in the classical field configuration. We present an efficient, truncation-free O(N) method on the basis of Chebyshev expanded local Green functions, which allows us to simulate systems of unprecedented size N.Comment: 4 pages, 3 figure

Scattering of charge carriers by point defects in bilayer graphene

Theory of scattering of massive chiral fermions in bilayer graphene by radial symmetric potential is developed. It is shown that in the case when the electron wavelength is much larger than the radius of the potential the scattering cross-section is proportional to the electron wavelength. This leads to the mobility independent on the electron concentration. In contrast with the case of single-layer, neutral and charged defects are, in general, equally relevant for the resistivity of the bilayer graphene.Comment: final versio

The Geothermal Probabilistic Cost Model with an Application to a Geothermal Reservoir at Heber, California

A financial accounting model that incorporates physical and institutional uncertainties was developed for geothermal projects. Among the uncertainties it can handle are well depth, flow rate, fluid temperature, and permit and construction times. The outputs of the model are cumulative probability distributions of financial measures such as capital cost, levelized cost, and profit. These outputs are well suited for use in an investment decision incorporating risk. The model has the powerful feature that conditional probability distribution can be used to account for correlations among any of the input variables. The model has been applied to a geothermal reservoir at Heber, California, for a 45-MW binary electric plant. Under the assumptions made, the reservoir appears to be economically viable

Possible field-tuned SIT in high-Tc superconductors: implications for pairing at high magnetic fields

The behavior of some high temperature superconductors (HTSC) such as $\rm La_{2-x}Sr_{x}CuO_{4}$ and $\rm Bi_{2}Sr_{2-x}La_xCuO_{6+\delta}$, at very high magnetic field, is similar to that of thin films of amorphous InOx near the magnetic field-tuned superconductor-insulator transition. Analyzing the InOx data at high fields in terms of persisting local pairing amplitude, we argue by analogy that local pairing amplitude also persists well into the dissipative state of the HTSCs, the regime commonly denoted as the "normal state" in very high magnetic field experiments.Comment: Revised figures and reference

Implementation of quantum maps by programmable quantum processors

A quantum processor is a device with a data register and a program register. The input to the program register determines the operation, which is a completely positive linear map, that will be performed on the state in the data register. We develop a mathematical description for these devices, and apply it to several different examples of processors. The problem of finding a processor that will be able to implement a given set of mappings is also examined, and it is shown that while it is possible to design a finite processor to realize the phase-damping channel, it is not possible to do so for the amplitude-damping channel.Comment: 10 revtex pages, no figure

Unraveling the acoustic electron-phonon interaction in graphene

Using a first-principles approach we calculate the acoustic electron-phonon couplings in graphene for the transverse (TA) and longitudinal (LA) acoustic phonons. Analytic forms of the coupling matrix elements valid in the long-wavelength limit are found to give an almost quantitative description of the first-principles based matrix elements even at shorter wavelengths. Using the analytic forms of the coupling matrix elements, we study the acoustic phonon-limited carrier mobility for temperatures 0-200 K and high carrier densities of 10^{12}-10^{13} cm^{-2}. We find that the intrinsic effective acoustic deformation potential of graphene is \Xi_eff = 6.8 eV and that the temperature dependence of the mobility \mu ~ T^{-\alpha} increases beyond an \alpha = 4 dependence even in the absence of screening when the full coupling matrix elements are considered. The large disagreement between our calculated deformation potential and those extracted from experimental measurements (18-29 eV) indicates that additional or modified acoustic phonon-scattering mechanisms are at play in experimental situations.Comment: 7 pages, 3 figure

Deviations from Matthiessen's Rule for SrRuO3{\rm SrRuO_3} and CaRuO3{\rm CaRuO_3}

We have measured the change in the resistivity of thin films of ${\rm SrRuO_3}$ and ${\rm CaRuO_3}$ upon introducing point defects by electron irradiation at low temperatures, and we find significant deviations from Matthiessen's rule. For a fixed irradiation dose, the induced change in resistivity {\it decreases} with increasing temperature. Moreover, for a fixed temperature, the increase in resistivity with irradiation is found to be {\it sublinear}. We suggest that the observed behavior is due to the marked anisotropic scattering of the electrons together with their relatively short mean free path (both characteristic of many metallic oxides including cuprates) which amplify effects related to the Pippard ineffectiveness condition

Transport Properties of a spinon Fermi surface coupled to a U(1) gauge field

With the organic compound $\kappa$-(BEDT-TTF)$_2$-Cu$_2$(CN)$_3$ in mind, we consider a spin liquid system where a spinon Fermi surface is coupled to a U(1) gauge field. Using the non-equilibrium Green's function formalism, we derive the Quantum Boltzmann Equation (QBE) for this system. In this system, however, one cannot a priori assume the existence of Landau quasiparticles. We show that even without this assumption one can still derive a linearized equation for a generalized distribution function. We show that the divergence of the effective mass and of the finite temperature self-energy do not enter these transport coefficients and thus they are well-defined. Moreover, using a variational method, we calculate the temperature dependence of the spin resistivity and thermal conductivity of this system.Comment: 12 page

Discrete diffraction and shape-invariant beams in optical waveguide arrays

General properties of linear propagation of discretized light in homogeneous and curved waveguide arrays are comprehensively investigated and compared to those of paraxial diffraction in continuous media. In particular, general laws describing beam spreading, beam decay and discrete far-field patterns in homogeneous arrays are derived using the method of moments and the steepest descend method. In curved arrays, the method of moments is extended to describe evolution of global beam parameters. A family of beams which propagate in curved arrays maintaining their functional shape -referred to as discrete Bessel beams- is also introduced. Propagation of discrete Bessel beams in waveguide arrays is simply described by the evolution of a complex $q$ parameter similar to the complex $q$ parameter used for Gaussian beams in continuous lensguide media. A few applications of the $q$ parameter formalism are discussed, including beam collimation and polygonal optical Bloch oscillations. \Comment: 14 pages, 5 figure

Effect of magnetic fluctuations on the normal state properties of Sr_2RuO_4

We investigate the normal state transport properties of Sr$_2$RuO$_4$ and we show that a consistent explanation of the experimental results can be obtained assuming that the system is near a quantum phase transition. Within the framework of a self-consistent spin fluctuation theory, we calculate the temperature variation of some relevant physical quantities and we discuss a possible microscopic origin of the quantum phase transition.Comment: 5 pages, 4 figures, to appear on Europhysics Letter