arXiv subjects

P. Sémon

Publications and source records attributed to P. Sémon.

22 records · Page 2Linked to original sources

arXiv2014

Ergodicity of the Hybridization-Expansion Monte Carlo Algorithm for Broken-Symmetry States

With the success of dynamical mean field theories, solvers for quantum-impurity problems have become an important tool for the numerical study of strongly correlated systems. Continuous-time Quantum Monte Carlo sampling of the expansion in powers of the hybridization between the ``impurity'' and the bath provides a powerful solver when interactions are strong. Here we show that the usual updates that add or remove a pair of creation-annihilation operators are rigorously not ergodic for several classes of broken-symmetries that involve spatial components. We show that updates with larger numbers of simultaneous updates of pairs of creation-annihilation operators remedy this problem. As an example, we apply the four operator updates that are necessary for ergodicity to the case of d-wave superconductivity in plaquette dynamical mean-field theory for the one-band Hubbard model. While the results are qualitatively similar to those previously published, they are quantitatively better that previous ones, being closer to those obtained by other approaches.

cond-mat.str-el↗

arXiv2012

c-axis resistivity, pseudogap, superconductivity and Widom line in doped Mott insulators

Layered doped Mott insulators, such as the cuprates, show unusual temperature dependence of the resistivity. Intriguingly, the resistivity perpendicular to the CuO$_2$ planes, $ρ_c(T)$, shows both metallic ($dρ_c/dT > 0$) and semi-conducting ($dρ_c/dT<0$) behavior. We shed light on this puzzle by calculating $ρ_c$ for the two-dimensional Hubbard model within plaquette cellular dynamical mean-field theory and strong-coupling continuous-time quantum Monte Carlo as the impurity solver. The temperature, $T$, and doping, $δ$, dependencies of $ρ_c$ are controlled by the first-order transition between pseudogap and correlated metal phases from which superconductivity can emerge. On the large doping side of the transition $ρ_c(T)$ is metallic, while on the low-doping side $ρ_c(T)$ changes from metallic to semi-conducting behavior with decreasing $T$. As a function of doping, the jump in $ρ_c$ across the first-order transition evolves into a sharp crossover at higher temperatures. This crossover coincides with the pseudogap temperature $T^*$ in the single-particle density of states, the spin susceptibility and other observables. Such coincidence in crossovers is expected along the continuation of the first-order transition into the super-critical regime, called the Widom line. This implies that not only the dynamic and the thermodynamic properties but also the DC transport in the normal state are governed by the hidden first-order transition. $ρ_c(T)$ has a high-temperature quasi-linear regime where it can exceed the Mott-Ioffe-Regel limit and when it has a minimum it is nearly parallel to the Widom line.

cond-mat.str-el↗

arXiv2012

Pseudogap temperature as a Widom line in doped Mott insulators

The pseudogap refers to an enigmatic state of matter with unusual physical properties found below a characteristic temperature $T^*$ in hole-doped high-temperature superconductors. Determining $T^*$ is critical for understanding this state. Here we study the simplest model of correlated electron systems, the Hubbard model, with cluster dynamical mean-field theory to find out whether the pseudogap can occur solely because of strong coupling physics and short nonlocal correlations. We find that the pseudogap characteristic temperature $T^*$ is a sharp crossover between different dynamical regimes along a line of thermodynamic anomalies that appears above a first-order phase transition, the Widom line. The Widom line emanating from the critical endpoint of a first-order transition is thus the organizing principle for the pseudogap phase diagram of the cuprates. No additional broken symmetry is necessary to explain the phenomenon. Broken symmetry states appear in the pseudogap and not the other way around.

cond-mat.str-el↗

arXiv2012

Strong coupling superconductivity, pseudogap and Mott transition

An intricate interplay between superconductivity, pseudogap and Mott transition, either bandwidth driven or doping driven, occurs in materials. Layered organic conductors and cuprates offer two prime examples. We provide a unified perspective of this interplay in the two-dimensional Hubbard model within cellular dynamical mean-field theory on a $2\times 2$ plaquette and using the continuous-time quantum Monte Carlo method as impurity solver. Both at half filling and at finite doping, the metallic normal state close to the Mott insulator is unstable to d-wave superconductivity. Superconductivity can destroy the first-order transition that separates the pseudogap phase from the overdoped metal, yet that normal state transition leaves its marks on the dynamic properties of the superconducting phase. For example, as a function of doping one finds a rapid change in the particle-hole asymmetry of the superconducting density of states. In the doped Mott insulator, the dynamical mean-field superconducting transition temperature $T_c^d$ does not scale with the order parameter when there is a normal-state pseudogap. $T_c^d$ corresponds to the local pair formation temperature observed in tunneling experiments and is distinct from the pseudogap temperature.

cond-mat.str-el↗