20 research outputs found
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
Antagonistic effects of nearest-neighbor repulsion on the superconducting pairing dynamics in the doped Mott insulator regime
The nearest-neighbor superexchange-mediated mechanism for d_{x^2-y^2}-wave
superconductivity in the one-band Hubbard model faces the challenge that
nearest-neighbor Coulomb repulsion can be larger than superexchange. To answer
this question, we use cellular dynamical mean-field theory (CDMFT) with a
continuous-time quantum Monte Carlo solver to determine the superconducting
phase diagram as a function of temperature and doping for on-site repulsion
and nearest-neighbor repulsion . In the underdoped regime,
increases the CDMFT superconducting transition temperature even
though it decreases the superconducting order parameter at low temperature for
all dopings. However, decreases in the overdoped regime. We gain
insight into these paradoxical results through a detailed study of the
frequency dependence of the anomalous spectral function, extracted at finite
temperature via the MaxEntAux method for analytic continuation. A systematic
study of dynamical positive and negative contributions to pairing reveals that
even though has a high-frequency depairing contribution, it also has a low
frequency pairing contribution since it can reinforce superexchange through
. Retardation is thus crucial to understand pairing in doped Mott
insulators, as suggested by previous zero-temperature studies. We also comment
on the tendency to charge order for large and on the persistence of d-wave
superconductivity over extended- or s+d-wave.Comment: Latex, 16 pages, 8 figure
The convex hull for a random acceleration process in two dimensions
We compute exactly the mean perimeter and the mean area of the
convex hull of a random acceleration process of duration T in two dimensions.
We use an exact mapping that relates, via Cauchy's formulae, the computation of
the perimeter and the area of the convex hull of an arbitrary two dimensional
stochastic process [x(t); y(t)] to the computation of the extreme value
statistics of the associated one dimensional component process x(t). The latter
can be computed exactly for the one dimensional random acceleration process
even though the process in non-Markovian. Physically, our results are relevant
in describing theaverage shape of a semi-flexible ideal polymer chain in two
dimensions.Comment: 17 pages, 7 figures, accepeted in Journal of Physics A: Mathematical
and Theoretica