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Search Results: 1 - 10 of 5508 matches for " Philipp Werner "
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(4+1)-Dimensional Quantum Hall Effect & Applications to Cosmology
Philipp Werner
Physics , 2012,
Abstract: This work discusses the (4+1)-dimensional generalization of the Quantum Hall Effect and its relation to axion electrodynamics.
Krylov implementation of the hybridization expansion impurity solver and application to 5-orbital models
Andreas Laeuchli,Philipp Werner
Physics , 2009, DOI: 10.1103/PhysRevB.80.235117
Abstract: We present an implementation of the hybridization expansion impurity solver which employs sparse matrix exact-diagonalization techniques to compute the time evolution of the local Hamiltonian. This method avoids computationally expensive matrix-matrix multiplications and becomes advantageous over the conventional implementation for models with 5 or more orbitals. In particular, this method will allow the systematic investigation of 7-orbital systems (lanthanide and actinide compounds) within single-site dynamical mean field theory. We illustrate the power and usefulness of our approach with dynamical mean field results for a 5-orbital model which captures some aspects of the physics of the iron based superconductors.
Polarized Superfluidity in the imbalanced attractive Hubbard model
Akihisa Koga,Philipp Werner
Physics , 2010, DOI: 10.1143/JPSJ.79.064401
Abstract: We investigate the attractive Hubbard model in infinite spatial dimensions by means of dynamical mean-field theory. Using a continuous-time Monte Carlo algorithm in the Nambu formalism as an impurity solver, we directly deal with the superfluid phase in the population imbalanced system. By calculating the superfluid order parameter, the magnetization, and the density of states, we discuss how the polarized superfluid state is realized in the attractive Hubbard model at quarter filling. We find that a drastic change in the density of states is induced by spin imbalanced populations in the superfluid state.
Nonequilibrium dynamical mean-field calculations based on the non-crossing approximation and its generalizations
Martin Eckstein,Philipp Werner
Physics , 2010, DOI: 10.1103/PhysRevB.82.115115
Abstract: We solve the impurity problem which arises within nonequilibrium dynamical mean-field theory for the Hubbard model by means of a self-consistent perturbation expansion around the atomic limit. While the lowest order, known as the non-crossing approximation (NCA), is reliable only when the interaction U is much larger than the bandwidth, low-order corrections to the NCA turn out to be sufficient to reproduce numerically exact Monte Carlo results in a wide parameter range that covers the insulating phase and the metal-insulator crossover regime at not too low temperatures. As an application of the perturbative strong-coupling impurity solver we investigate the response of the double occupancy in the Mott insulating phase of the Hubbard model to a dynamical change of the interaction or the hopping, a technique which has been used as a probe of the Mott insulating state in ultracold fermionic gases.
Low temperature properties of the infinite-dimensional attractive Hubbard model
Akihisa Koga,Philipp Werner
Physics , 2011, DOI: 10.1103/PhysRevA.84.023638
Abstract: We investigate the attractive Hubbard model in infinite spatial dimensions by combining dynamical mean-field theory with a strong-coupling continuous-time quantum Monte Carlo method. By calculating the superfluid order parameter and the density of states, we discuss the stability of the superfluid state. In the intermediate coupling region above the critical temperature, the density of states exhibits a heavy fermion behavior with a quasi-particle peak in the dense system, while a dip structure appears in the dilute system. The formation of the superfluid gap is also addressed.
Relaxation dynamics of the Kondo lattice model
Philipp Werner,Martin Eckstein
Physics , 2012, DOI: 10.1103/PhysRevB.86.045119
Abstract: We study the relaxation properties of the Kondo lattice model using the nonequilibrium dynamical mean field formalism in combination with the non-crossing approximation. The system is driven out of equilibrium either by a magnetic field pulse which perturbs the local singlets, or by a sudden quench of the Kondo coupling. For relaxation processes close to thermal equilibrium (after a weak perturbation), the relaxation time increases substantially as one crosses from the local moment regime into the heavy Fermi liquid. A strong perturbation, which injects a large amount of energy, can rapidly transform the heavy Fermi liquid into a local moment state. Upon cooling, the heavy Fermi liquid reappears in a two-stage relaxation, where the first step opens the Kondo gap and the second step corresponds to a slow approach of the equilibrium state via a nonthermal pathway.
Cluster Monte Carlo Algorithms for Dissipative Quantum Systems
Philipp Werner,Matthias Troyer
Physics , 2005, DOI: 10.1143/PTPS.160.395
Abstract: We review efficient Monte Carlo methods for simulating quantum systems which couple to a dissipative environment. A brief introduction of the Caldeira-Leggett model and the Monte Carlo method will be followed by a detailed discussion of cluster algorithms and the treatment of long-range interactions. Dissipative quantum spins and resistively shunted Josephson junctions will be considered.
Damping of Bloch oscillations in the Hubbard model
Martin Eckstein,Philipp Werner
Physics , 2011, DOI: 10.1103/PhysRevLett.107.186406
Abstract: Using nonequilibrium dynamical mean-field theory, we study the isolated Hubbard model in a static electric field in the limit of weak interactions. Linear response behavior is established at long times, but only if the interaction exceeds a critical value, below which the system exhibits an AC-type response with Bloch oscillations. The transition from AC to DC response is defined in terms of the universal long-time behavior of the system, which does not depend on the initial condition.
Ultra-fast photo-carrier relaxation in Mott insulators with short-range spin correlations
Martin Eckstein,Philipp Werner
Physics , 2014,
Abstract: We compute the time-resolved photoemission spectrum after photo-doping in a two-dimensional Mott-Hubbard insulator. We find that the relaxation rate of high-energy photo-doped electrons in the paramagnetic phase scales with the strength of the nearest-neighbor spin correlations, which implies a pronounced increase of the relaxation times with temperature and excitation density. Finite doping, in contrast, opens additional scattering channels and leads to a faster relaxation. To obtain our results we have implemented a nonequilibrium version of the dynamical cluster approximation (DCA), which, in contrast to single-site dynamical mean-field theory, captures the effect of short-range correlations.
Superconductivity in the two-band Hubbard model
Akihisa Koga,Philipp Werner
Physics , 2014, DOI: 10.1103/PhysRevB.91.085108
Abstract: We study the two-band Hubbard model in infinite dimensions by solving the dynamical mean-field equations with a strong coupling continuous-time quantum Monte Carlo method and show that an $s$-wave superconducting state can be stabilized in the repulsively interacting case. We discuss how this superconducting state competes with the metallic and paired Mott states. The effects of the Hund coupling and crystalline electric field are also addressed.
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