1,565 research outputs found
Orbital selective crossover and Mott transitions in an asymmetric Hubbard model of cold atoms in optical lattices
We study the asymmetric Hubbard model at half-filling as a generic model to
describe the physics of two species of repulsively interacting fermionic cold
atoms in optical lattices. We use Dynamical Mean Field Theory to obtain the
paramagnetic phase diagram of the model as function of temperature, interaction
strength and hopping asymmetry. A Mott transition with a region of two
coexistent solutions is found for all nonzero values of the hopping asymmetry.
At low temperatures the metallic phase is a heavy Fermi-liquid, qualitatively
analogous to the Fermi liquid state of the symmetric Hubbard model. Above a
coherence temperature, an orbital-selective crossover takes place, wherein one
fermionic species effectively localizes, and the resulting bad metallic state
resembles the non-Fermi liquid state of the Falicov-Kimball model. We compute
observables relevant to cold atom systems such as the double occupation, the
specific heat and entropy and characterize their behavior in the different
phases
Weak coupling study of decoherence of a qubit in disordered magnetic environments
We study the decoherence of a qubit weakly coupled to frustrated spin baths.
We focus on spin-baths described by the classical Ising spin glass and the
quantum random transverse Ising model which are known to have complex
thermodynamic phase diagrams as a function of an external magnetic field and
temperature. Using a combination of numerical and analytical methods, we show
that for baths initally in thermal equilibrium, the resulting decoherence is
highly sensitive to the nature of the coupling to the environment and is
qualitatively different in different parts of the phase diagram. We find an
unexpected strong non-Markovian decay of the coherence when the random
transverse Ising model bath is prepared in an initial state characterized by a
finite temperature paramagnet. This is contrary to the usual case of
exponential decay (Markovian) expected for spin baths in finite temperature
paramagnetic phases, thereby illustrating the importance of the underlying
non-trivial dynamics of interacting quantum spinbaths.Comment: 12 pages, 18 figure
Phase diagram of the asymmetric Hubbard model and an entropic chromatographic method for cooling cold fermions in optical lattices
We study the phase diagram of the asymmetric Hubbard model (AHM), which is
characterized by different values of the hopping for the two spin projections
of a fermion or equivalently, two different orbitals. This model is expected to
provide a good description of a mass-imbalanced cold fermionic mixture in a 3D
optical lattice. We use the dynamical mean field theory to study various
physical properties of this system. In particular, we show how
orbital-selective physics, observed in multi-orbital strongly correlated
electron systems, can be realized in such a simple model. We find that the
density distribution is a good probe of this orbital selective crossover from a
Fermi liquid to a non-Fermi liquid state.
Below an ordering temperature , which is a function of both the
interaction and hopping asymmetry, the system exhibits staggered long range
orbital order. Apart from the special case of the symmetric limit, i.e.,
Hubbard model, where there is no hopping asymmetry, this orbital order is
accompanied by a true charge density wave order for all values of the hopping
asymmetry. We calculate the order parameters and various physical quantities
including the thermodynamics in both the ordered and disordered phases. We find
that the formation of the charge density wave is signaled by an abrupt increase
in the sublattice double occupancies. Finally, we propose a new method,
entropic chromatography, for cooling fermionic atoms in optical lattices, by
exploiting the properties of the AHM. To establish this cooling strategy on a
firmer basis, we also discuss the variations in temperature induced by the
adiabatic tuning of interactions and hopping parameters.Comment: 16 pages, 19 fig
Law School Admissions: A Different View
Contrary to the impression that may have been created by some recent articles, most law schools do not conduct their admissions procedure by the numbers. Critics of law school admissions practices cite statistics that can be misleading and tend to inflate the number of law school applicants. The solution to the admissions crisis may be to spread the applicants over more schools
Neurophysiology
Contains reports on three research projects.Bell Telephone Laboratories, IncorporatedNational Institutes of HealthTeagle Foundation, IncorporatedUnited States Air Force (WADD Contract AF33(616)-7783
The Disadvantaged Student and Preparation for Legal Education: The New York University Experience
The law school commitment to enroll more minority students is a decision which can have many and varied ramifications for the law school as an institution. Minority students will bring new perspectives, different needs a total outlook on life and law potentially at variance with that of the majority culture in which most law school faculties and students have been educated. The resulting challenge to accepted norms can be met by the law schools in many ways--it can be ignored, creating frustration and anger, or it can be utilized creatively, expanding the horizons of the law school to include hitherto unperceived areas of thought and endeavor. The latter alternative was the approach of New York University, whose minority students, in conjunction with certain majority student organizations, called for and received law school reforms altering the framework of the legal education process at NYU
Methane Flow through Organic-Rich Nanopores : The Key Role of Atomic-Scale Roughness
We perform a detailed study of methane flow through nanoporous kerogen. Using molecular dynamics and modeling the kerogen pore with an amorphous carbon nanotube (a-CNT), we show that the reported flow enhancement over Hagen−Poisseuile flow is mainly due to the smoothness, on an atomic scale, of the CNTs. It acts in two ways: first, it helps the mobility of the adsorbed layer; second, and even more important for the flow enhancement, it prevents the dependency on the inverse of the channel length (L) from developing. While the former can incrementally contribute to the flow, the latter effect can explain the orders of magnitude found in comparison to macroscopic results.Instituto de Investigaciones FisicoquÃmicas Teóricas y Aplicada
Polynomial evaluation over finite fields: new algorithms and complexity bounds
An efficient evaluation method is described for polynomials in finite fields.
Its complexity is shown to be lower than that of standard techniques when the
degree of the polynomial is large enough. Applications to the syndrome
computation in the decoding of Reed-Solomon codes are highlighted.Comment: accepted for publication in Applicable Algebra in Engineering,
Communication and Computing. The final publication will be available at
springerlink.com. DOI: 10.1007/s00200-011-0160-
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