10 research outputs found
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 and , 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 for small values of leads to a Kondo
insulator-metal transition. Upon further enhancement of 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 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