Competition between reduced delocalization and charge transfer effects for a two-band Hubbard model

We use the embedding approach for a dynamical mean-field method to investigate the electronic properties of a semi-infinite two band Hubbard model at half- and quarter-filling. Two effects determine the degree of correlation at the surface: first, there will charge transfer between the surface and the bulk, and, secondly, electrons at the surface are less delocalized due to the reduced coordination number. We determine the result of these two effects and compute the quasiparticle weight. It is shown that depletion of charge from the surface to the bulk at quarter-filling competes with enhanced correlation effects; the net result is that at quarter-filling the quasi particle weight at the surface is approximately equal to the bulk quasi particle weight. Only when the charge transfer approaches zero at large interaction strengths does the quasi particle weight at the surface become lower than that in the bulk.Comment: Accepted to Phys. Rev.

Surface effects in doping a Mott insulator

The physics of doping a Mott insulator is investigated in the presence of a solid-vacuum interface. Using the embedding approach for dynamical mean field theory we show that the change in surface spectral evolution in a doped Mott insulator is driven by a combination of charge transfer effects and enhanced correlation effects. Approaching a Mott insulating phase from the metallic side, we show that a dead layer forms at the surface of the solid, where quasiparticle amplitudes are exponentially suppressed. Surface correlation and charge transfer effects can be strongly impacted by changes of the hopping integrals at the surface.Comment: accepted in Phys. Rev.

Metallic surface of a bipolaronic insulator

We investigate the possibility that the surface of a strongly coupled electron-phonon system behaves differently from the bulk when the relevant parameters are inhomogeneous due to the presence of the interface. We consider parameter variations which make the surface either more metallic or more insulating than the bulk. While it appears impossible to stabilize a truly insulating surface when the bulk is metallic, the opposite situation can be realized. A metallic surface can indeed be decoupled from a bipolaronic insulator realized in the bulk.Comment: Accepted to PR

Surface Polaron Formation in the Holstein model

The effect of a solid-vacuum interface on the properties of a strongly coupled electron-phonon system is analyzed using dynamical mean-field theory to solve the Holstein model in a semi-infinite cubic lattice. Polaron formation is found to occur more easily (i.e., for a weaker electron-phonon coupling) on the surface than in the bulk. On the other hand, the metal-insulator transition associated to the binding of polarons takes place at a unique critical strength in the bulk and at the surface.Comment: 5 pages, 3 figure

Phase diagram of Holstein-Kondo lattice model at half-filling

We study the Kondo lattice model which is modified by the Holstein term, involving both the Kondo exchange coupling and the electron-phonon coupling constants, characterized by $J$ and $g$, respectively. The model is solved by employing the dynamical mean-field theory in conjunction with exact diagonalization technique. A zero temperature phase diagram of symmetry unbroken states at half filling is mapped out which exhibits an interplay between the two interactions and accounts for both spin and charge fluctuations. When the Kondo exchange coupling is dominant the system is in Kondo insulator state. Increasing $g$ for small values of $J$ leads to a Kondo insulator-metal transition. Upon further enhancement of $g$ a transition to the bipolaronic insulating phase takes place. Also a small region with non-Fermi liquid behavior is found near the Kondo insulator-metal transition

Bad metallic transport in a cold atom Fermi-Hubbard system

Charge transport is a revealing probe of the quantum properties of materials. Strong interactions can blur charge carriers resulting in a poorly understood "quantum soup". Here we study the conductivity of the Fermi-Hubbard model, a testing ground for strong interaction physics, in a clean quantum system - ultracold $^6$Li in a 2D optical lattice. We determine the charge diffusion constant in our system by measuring the relaxation of an imposed density modulation and modeling its decay hydrodynamically. The diffusion constant is converted to a resistivity, which exhibits a linear temperature dependence and exceeds the Mott-Ioffe-Regel limit, two characteristic signatures of a bad metal. The techniques we develop here may be applied to measurements of other transport quantities, including the optical conductivity and thermopower

Correlation-driven electronic multiferroicity in TMTTF2-X organic crystals

Using a combination of density functional theory and dynamical mean field theory we show that electric polarization and magnetism are strongly intertwined in TMTTF2-X (X=PF6, AsF6, and SbF6) organic crystals. Electronic correlations induce a charge-ordered state which, combined with the molecular dimerization, gives rise to a finite electronic polarization and to a ferroelectric state. The value of the electronic polarization is enhanced by the onset of antiferromagnetism showing a sizable magnetoelectric effect which predicts the multiferroic behavior of TMTTF2-X compounds

Data for "Bad metallic transport in a cold atom Fermi-Hubbard system"

Data associated with arXiv:1802.0945