Searching for a Supersolid in Cold Atom Optical Lattices

We suggest a technique for the observation of a predicted supersolid phase in extended Bose-Hubbard models which are potentially realizable in cold atom optical lattice systems. In particular, we discuss important subtleties arising from the existence of the trapping potential which leads to an externally imposed (as opposed to spontaneous) breaking of translational invariance. We show, by carefully including the trapping potential in our theoretical formalism, that noise correlations could prove instrumental in identifying the supersolid and density wave phases. We also find that the noise correlation peak width scales inversely with the relative size of trapped Mott domains.Comment: 5 pages, 4 figure

Spin Polarization Dependence of Carrier Effective Mass in Semiconductor Structures: Spintronic Effective Mass

We introduce the concept of a spintronic effective mass for spin-polarized carriers in semiconductor structures, which arises from the strong spin-polarization dependence of the renormalized effective mass in an interacting spin-polarized electron system. The majority-spin many-body effective mass renormalization differs by more than a factor of 2 at rs=5 between the unpolarized and the fully polarized two-dimensional system, whereas the polarization dependence (~15%) is more modest in three dimensions around metallic densities (rs~5). The spin-polarization dependence of the carrier effective mass is of significance in various spintronic applications.Comment: Final versio

Ground-state of graphene in the presence of random charged impurities

We calculate the carrier density dependent ground state properties of graphene in the presence of random charged impurities in the substrate taking into account disorder and interaction effects non-perturbatively on an equal footing in a self-consistent theoretical formalism. We provide detailed quantitative results on the dependence of the disorder-induced spatially inhomogeneous two-dimensional carrier density distribution on the external gate bias, the impurity density, and the impurity location. We find that the interplay between disorder and interaction is strong, particularly at lower impurity densities. We show that for the currently available typical graphene samples, inhomogeneity dominates graphene physics at low ($\lesssim 10^{12}$ cm$^{-2}$) carrier density with the density fluctuations becoming larger than the average density.Comment: Final version, accepted for publication in Phys. Rev. Let

An evaluation of physical and biogeochemical processes regulating perennial suboxic conditions in the water column of the Arabian Sea

Monthly oxygen budgets for the subsurface Arabian Sea (100-1000 m) are constructed on the basis of Modular Ocean Model and recently collected oxygen data. The model results are in agreement with the observed pattern. The model results revealed that Oxygen Minimum Zone (OMZ) in the Arabian Sea is regulated largely by physical processes in association with biogeochemical cycling of oxygen. This results in perennial suboxic conditions in the water column with no significant seasonal variability. Maintenance of OMZ during non-monsoon seasons, when oligotrophic conditions prevail in surface layers, occurs through low supply of oxygen by physical pump aided by continued oxygen consumption in the oxidation of organic matter produced during monsoons. On the other hand, formation of anoxic conditions during monsoons, when higher sinking fluxes of carbon occur, is prevented by higher flux of oxygen by the physical pump. Hence, suboxic conditions in the Arabian Sea are maintained by physical pump with moderation from monsoonal biological pump. The residence time of the Arabian Sea intermediate waters (100-1000 m) was computed to be 6.5 years with rapid replacement during monsoons. The oxygen consumption rates are also high during monsoons compared with non-monsoon seasons. The carbon regeneration rates computed based on the water mass-mixing model, bacterial carbon demand, and electron transport system activity in the subsurface layers are in agreement with oxygen consumption rates estimated based on this model

Condensates induced by interband coupling in a double-well lattice

We predict novel inter-band physics for bosons in a double-well lattice. An intrinsic coupling between the s and px band due to interaction gives rise to larger Mott regions on the phase diagram at even fillings than the ones at odd fillings. On the other hand, the ground state can form various types of condensates, including a mixture of single-particle condensates of both bands, a mixture of a single-particle condensate of one band and a pair-condensate of the other band, and a pair-condensate composed of one particle from one band and one hole from the other band. The predicted phenomena should be observable in current experiments on double-well optical lattices.Comment: Published versio

Electrical neurostimulation for chronic pain: on selective relay of sensory neural activities in myelinated nerve fibers

Chronic pain affects about 100 million adults in the US. Despite their great need, neuropharmacology and neurostimulation therapies for chronic pain have been associated with suboptimal efficacy and limited long-term success, as their mechanisms of action are unclear. Yet current computational models of pain transmission suffer from several limitations. In particular, dorsal column models do not include the fundamental underlying sensory activity traveling in these nerve fibers. We developed a (simple) simulation test bed of electrical neurostimulation of myelinated nerve fibers with underlying sensory activity. This paper reports our findings so far. Interactions between stimulation-evoked and underlying activities are mainly due to collisions of action potentials and losses of excitability due to the refractory period following an action potential. In addition, intuitively, the reliability of sensory activity decreases as the stimulation frequency increases. This first step opens the door to a better understanding of pain transmission and its modulation by neurostimulation therapies