Université de Fribourg

Dielectric breakdown of Mott insulators – doublon production and doublon heating

Eckstein, Martin ; Werner, Philipp

In: Journal of Physics: Conference Series, 2013, vol. 427, no. 1, p. 012005

Using dynamical mean-field theory and the non-crossing approximation as impurity solver, we study the response of a Mott insulator to strong dc electric fields. The breakdown of the Mott insulating state is triggered by field-induced creation of doublon-hole pairs. In a previous investigation, Ref. [1], it was found that the system approaches a long-lived quasi-steady state in which the current...

Université de Fribourg

Screening and nonlocal correlations in the extended Hubbard model from self-consistent combined GW and dynamical mean field theory

Ayral, Thomas ; Biermann, Silke ; Werner, Philipp

In: Physical Review B, 2013, vol. 87, no. 12, p. 125149

We describe a recent implementation of the combined GW and dynamical mean field method (GW+DMFT) for the two-dimensional Hubbard model with onsite and nearest-neighbor repulsion. We clarify the relation of the GW+DMFT scheme to alternative approaches in the literature, and discuss the corresponding approximations to the free-energy functional of the model. Furthermore, we describe a numerically...

Université de Fribourg

Nonthermal Antiferromagnetic Order and Nonequilibrium Criticality in the Hubbard Model

Tsuji, Naoto ; Eckstein, Martin ; Werner, Philipp

In: Physical Review Letters, 2013, vol. 110, no. 13, p. 136404

We study dynamical phase transitions from antiferromagnetic to paramagnetic states driven by an interaction quench in the fermionic Hubbard model using the nonequilibrium dynamical mean-field theory. We identify two dynamical transition points where the relaxation behavior qualitatively changes: one corresponds to the thermal phase transition at which the order parameter decays critically slowly...

Université de Fribourg

Large temperature dependence of the number of carriers in co-doped BaFe₂As₂

Brouet, V. ; Lin, Ping-Hui ; Texier, Y. ; Bobroff, J. ; Taleb-Ibrahimi, A. ; Fèvre, P. Le ; Bertran, F. ; Casula, M. ; Werner, Philipp ; Biermann, S. ; Rullier-Albenque, F. ; Forget, A. ; Colson, D.

In: Physical Review Letters, 2013, vol. 110, no. 16, p. 167002

Using angle-resolved photoemission spectroscopy, we study the evolution of the number of carriers in Ba(Fe₁₋Cox)₂As₂ as a function of Co content and temperature. We show that there is a k-dependent energy shift compared to density functional calculations, which is large below 100 K at low Co contents and reduces the volume of hole and electron pockets by a factor 2. This k...

Université de Fribourg

Long-Range coulomb interactions in surface systems: a first-Principles description within self-Consistently combined GW and dynamical mean-Field theory

Hansmann, P. ; Ayral, T. ; Vaugier, L. ; Werner, Philipp ; Biermann, S.

In: Physical Review Letters, 2013, vol. 110, no. 16, p. 166401

Systems of adatoms on semiconductor surfaces display competing ground states and exotic spectral properties typical of two-dimensional correlated electron materials which are dominated by a complex interplay of spin and charge degrees of freedom. We report a fully ab initio derivation of low-energy Hamiltonians for the adatom systems Si(111):X, with X=Sn, Si, C, Pb, that we solve within...

Université de Fribourg

Gauge theory of topological phases of matter

Fröhlich, Jürg ; Werner, Philipp

In: EPL (Europhysics Letters), 2013, vol. 101, no. 4, p. 47007

We study the response of quantum many-body systems to coupling some of their degrees of freedom to external gauge fields. This serves to understand the current Green functions and transport properties of interacting many-body systems. Our analysis leads to a "gauge theory of states of matter" complementary to the well-known Landau theory of order parameters. We illustrate the power of our...

Université de Fribourg

Extracting spectral properties from Keldysh Green functions

Dirks, Andreas ; Eckstein, Martin ; Pruschke, Thomas ; Werner, Philipp

In: Physical Review E, 2013, vol. 87, no. 2, p. 023305

We investigate the possibility to assist the numerically ill-posed calculation of spectral properties of interacting quantum systems in thermal equilibrium by extending the imaginary-time simulation to a finite Schwinger-Keldysh contour. The effect of this extension is tested within the standard maximum entropy approach to analytic continuation. We find that the inclusion of real-time data...

Université de Fribourg

Spectral Properties of Correlated Materials: Local Vertex and Nonlocal Two-Particle Correlations from Combined GW and Dynamical Mean Field Theory

Ayral, Thomas ; Werner, Philipp ; Biermann, Silke

In: Physical Review Letters, 2012, vol. 109, no. 22, p. 226401

We present a fully self-consistent combined GW and dynamical mean field (DMFT) study of the extended two-dimensional Hubbard model. The inclusion of the local dynamical vertex stemming from the DMFT self-energy and polarization is shown to cure the known problems of self-consistent GW. We calculate momentum-resolved spectral functions, two-particle polarizations, and electron-loss spectra, as...

Université de Fribourg

Efficient implementation of the continuous-time hybridization expansion quantum impurity solver

Hafermann, Hartmut ; Werner, Philipp ; Gull, Emanuel

In: Computer Physics Communications, 2013, vol. 184, no. 4, p. 1280–1286

Strongly correlated quantum impurity problems appear in a wide variety of contexts ranging from nanoscience and surface physics to material science and the theory of strongly correlated lattice models, where they appear as auxiliary systems within dynamical mean-field theory. Accurate and unbiased solutions must usually be obtained numerically, and continuous-time quantum Monte Carlo algorithms,...

Université de Fribourg

Nonthermal symmetry-broken states in the strongly interacting Hubbard model

Werner, Philipp ; Tsuji, Naoto ; Eckstein, Martin

In: Physical Review B - Condensed Matter and Materials Physics, 2012, vol. 86, no. 20, p. 205101

We study the time evolution of the antiferromagnetic order parameter after interaction quenches in the Hubbard model. Using the nonequilibrium dynamical mean-field formalism, we show that the system, after a quench from intermediate to strong interaction, is trapped in a nonthermal state which is reminiscent of a photodoped state and protected by the slow decay of doublons. If the effective...