P. Sémon

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 2×2 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.

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.

Importance of subleading corrections for the Mott critical point

The interaction-induced metal-insulator transition should be in the Ising universality class. Experiments on layered organic superconductors suggest that the observed critical endpoint of the first-order Mott transition belongs instead to a different universality class. To address this question, we use dynamical mean-field theory and a cluster generalization that is necessary to account for short-range spatial correlations in two dimensions. Such calculations can give information on crossover effects, in particular quantum ones, that are not included in the simplest mean-field. In the cluster calculation, a canonical transformation that minimizes the sign problem in continuous-time quantum Monte Carlo calculations allows us to obtain very accurate results for double occupancy. These results show that there are important subleading corrections that can lead to apparent exponents that are different from mean-field. Experiments on optical lattices could verify our predictions.

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

Lazy skip-lists: An algorithm for fast hybridization-expansion quantum Monte Carlo

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Signatures of the Mott transition in the antiferromagnetic state of the two-dimensional Hubbard model

planes,

An organizing principle for two-dimensional strongly correlated superconductivity

\rho_c(T)

Entropy, frustration, and large thermopower of doped Mott insulators on the fcc lattice

, shows both metallic (

Benchmark of a modified iterated perturbation theory approach on the fcc lattice at strong coupling

d\rho_c/dT > 0

Antagonistic effects of nearest-neighbor repulsion on the superconducting pairing dynamics in the doped Mott insulator regime

) and semi-conducting (