This paper presents the results of a functional-integral approach to dynamics two-state system coupled dissipative environment. It is primarily an extended account obtained over last four years by authors; while they try provide some background for orientation, it emphatically not intended as comprehensive review literature on subject. Its contents include (1) exact and general prescription reduction, under appropriate circumstances, problem tunneling between two wells in presence...

It is argued that the long-wavelength, low-temperature behavior of a two-dimensional quantum Heisenberg antiferromagnet can be described by nonlinear $\ensuremath{\sigma}$ model in two space plus one time dimension, at least range parameters where has long-range order zero temperature. The properties are analyzed approximately using one-loop renormalization-group method. When $T=0$, long-wavelength finite temperatures purely classical model, with renormalized fluctuations. correlation length...

We propose that the enigmatic pseudogap phase of cuprate superconductors is characterized by a hidden broken symmetry d(x^2-y^2)-type. The transition to this state rounded disorder, but in limit disorder made sufficiently small, crossover should reveal itself be such transition. ordered breaks time-reversal, translational, and rotational symmetries, it invariant under combination any two. discuss these ideas context ten specific experimental properties cuprates, make several predictions,...

Recent neutron-scattering data for the spin-correlation length in ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$ can be fitted quantitatively with an analysis of quantum mechanical nonlinear \ensuremath{\sigma} model two space dimensions. The coupling constant must chosen range where isolated ${\mathrm{CuO}}_{2}$ layer has antiferromagnetic order at T=0. parameters are consistent spin-wave theory nearest-neighbor spin-(1/2 Heisenberg antiferromagnet on a square lattice.

A quantitative analysis of a recent model high-temperature superconductors based on an interlayer tunneling mechanism is presented. This can account well for the observed magnitudes high transition temperatures in these materials and implies gap that does not change sign, be substantially anisotropic, has same symmetry as crystal. The experimental consequences explored so far are consistent with observations.

The authors study a symmetric two-state system with "bare" tunneling frequency ${\ensuremath{\Delta}}_{0}$, dimensionless Ohmic dissipation coefficient $\ensuremath{\alpha}$, and heat-bath cutoff ${\ensuremath{\omega}}_{c}$. Defining ${\ensuremath{\Delta}}_{r}\ensuremath{\equiv}{\ensuremath{\Delta}}_{0}{(\frac{{\ensuremath{\Delta}}_{0}}{{\ensuremath{\omega}}_{c}})}^{\frac{\ensuremath{\alpha}}{(1\ensuremath{-}\ensuremath{\alpha})}}$ for $\ensuremath{\alpha}<1$...

Quantum fluctuations in a microscopic model of Josephson junction including dissipative effects, parametrized by $\ensuremath{\eta}=\frac{\ensuremath{\hbar}}{2\ensuremath{\pi}{e}^{2}R}$ with $R$ the resistance, are discussed. It is shown that parameter space divides sharply into two regions: One which scaling trajectories lead to vanishing mean tunneling rate at $T=0$ and other they do not.

Four-component massive and massless Dirac fermions in the presence of long range Coulomb interaction chemical potential disorder exhibit striking fermionic quantum criticality. For an odd number flavors fermions, sign mass distinguishes topological trivial band insulator phases, gapless semi-metallic phase corresponds to critical point that separates two. Up a strength disorder, remains stable, universality class direct transition between two insulating phases is unchanged. Beyond undergoes...

A theory of the electronic properties doped fullerenes is proposed in which correlation effects within single fullerene molecules play a central role, and qualitative predictions are made which, if verified, would support this hypothesis. Depending on effective intrafulllerene electron-electron repulsion interfullerene hopping amplitudes (which should depend dopant species, among other things), calculations indicate possibilities singlet superconductivity ferromagnetism.

The magnetic properties of CuGe${\mathrm{O}}_{3}$ are shown to be well described by the one-dimensional Heisenberg $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\frac{1}{2}$ model with competing antiferromagnetic interactions. Provided that exchange is moderately large but smaller than critical value required produce a gap in excitation spectrum without lattice dimerization, agrees variety experimental properties. It argued interactions general feature organic charge transfer...

We have used Monte Carlo simulation, lattice dynamics in the harmonic approximation, and solution of hypernetted-chain equation to study classical two-dimensional one-component plasma. find a fluid phase for $\ensuremath{\Gamma}=\frac{{e}^{2}{(\ensuremath{\pi}n)}^{\frac{1}{2}}}{{k}_{B}T}<~125\ifmmode\pm\else\textpm\fi{}15$ solid higher $\ensuremath{\Gamma}$. The shows directional long-range order. In positional order is lost as thermodynamic limit approached. also present results...

A theoretical analysis is presented of the problem onset global phase coherence in granular superconductors and Josephson-junction arrays. It shown that ratio $\frac{(\frac{h}{{e}^{2}})}{R}$, where $R$ resistance, plays an important role thermodynamics. This due to quantum fluctuations order parameter occurs superconductivity only because both a statistical as well dynamical variable. The theory provides natural qualitative explanation recent experiments Orr, Jaeger, Goldman, Kuper.

We discuss the recently discovered two-dimensional metal-insulator transition in zero magnetic field light of scaling theory localization. demonstrate that observed symmetry relating conductivity and resistivity follows directly from quantum critical behavior associated with such a transition. In addition, we show very general considerations imply any disordered metal is perfect metal, but most likely not Fermi liquid.

Critical behavior of Ising spin-glass with $\ifmmode\pm\else\textpm\fi{}J$ distribution is discussed. The results are based on the high-temperature series expansion Edwards-Anderson susceptibility in powers $w (=\frac{{tanh}^{2}J}{\mathrm{kT}})$ for 2D, 3D, and 4D "cubic" lattices to orders 19, 17, 15, respectively. lengths comparable best available pure model. While 3D systems exhibit transitions at finite temperatures, 2D a zero-temperature transition power-law divergence (in inverse...

A one-dimensional Ising model in a transverse field can be mapped onto system of spinless fermions with $p$-wave superconductivity. In the weak-coupling BCS regime, it exhibits zero-energy Majorana mode at each end chain. Here, we consider variation model, which represents superconductor longer-ranged kinetic energy and pairing amplitudes, as is likely to occur more realistic systems. It possesses richer zero-temperature phase diagram has several quantum transitions. From an exact solution...

We obtain exact exterior solutions of a rotating infinite cylinder. In addition to two different obtained before, new solution is found which finite on the axis. It seems that these three exhaust possibilities.

We consider the π-electrons on surface of a single molecule C60 (fullerene) interacting via an on-site repulsive interaction U. show that, for large range parameters, energy to add two electrons is less than twice one electron each molecules. Thus, at scales greater molecular diameter, there strong effective attraction between purely electronic origin. This can readily produce superconductivity. The effect appears be insensitive details model considered.

The nuclear-magnetic-resonance spin-lattice relaxation time (${T}_{1}$) and electron-paramagnetic-resonance (EPR) linewidth (${\ensuremath{\Gamma}}_{\ensuremath{\perp}}^{s}$) are calculated for ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$. large broadening of the EPR at room temperature is shown to narrow with increasing as (\ensuremath{\xi}/a${)}^{3}$, where \ensuremath{\xi} two-dimensional spin-correlation length a lattice constant. NMR ${T}_{1}$ first lengthens...

Recent experiments on the onset of superconductivity in granular films have raised a number interesting issues regarding role quantum fluctuations phase variable. We model film as an ordered array Josephson-coupled grains, and we take into account quasiparticle tunneling via method Ambegaokar, Eckern, Sch\"on. The superconductivity, at T=0, occurs when value normal-state sheet resistance has critical order h/4${e}^{2}$, which is not very sensitive to capacitance grains.

By using a combination of hydrodynamics, scaling, and renormalization-group analysis, fit to the simulations classical rotor model, we can predict form dynamic structure factor $S(\mathrm{k}, \ensuremath{\omega})$ two-dimensional quantum Heisenberg antiferromagnet at low temperatures, if zero-temperature spin-stiffness constant ${\ensuremath{\rho}}_{s}$ magnetic susceptibility ${\ensuremath{\chi}}_{\ensuremath{\perp}}^{0}$ are known. These results should be applicable inelastic neutron...

The dynamics of a two-state system coupled to the dissipative degrees freedom environment appears in many different contexts. In this paper we have given general formulation problem as well detailed comparison two priori very heat baths: (a) collection harmonic oscillators system, and (b) fermions system. Consideration such baths is motivated by assertion that weakly excited states can be modeled elementary excitations following Landau. Our conclusion case Ohmic dissipation...