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

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 $T_o$, 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

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

Effective action approach to strongly correlated fermion systems

We construct a new functional for the single particle Green's function, which is a variant of the standard Baym Kadanoff functional. The stability of the stationary solutions to the new functional is directly related to aspects of the irreducible particle hole interaction through the Bethe Salpeter equation. A startling aspect of this functional is that it allows a simple and rigorous derivation of both the standard and extended dynamical mean field (DMFT) equations as stationary conditions. Though the DMFT equations were formerly obtained only in the limit of infinite lattice coordination, the new functional described in the work, presents a way of directly extending DMFT to finite dimensional systems, both on a lattice and in a continuum. Instabilities of the stationary solution at the bifurcation point of the functional, signal the appearance of a zero mode at the Mott transition which then couples t o physical quantities resulting in divergences at the transition.Comment: 9 page

Kepadatan dan Keanekaragaman Meiofauna di Perairan Sungai Meureudu Kecamatan Meureudu Kabupaten Pidie Jaya

Research on the density and diversity of meiofauna is very important because of limited information about the meiofauna. This research has been conducted during April-May 2016. The purpose of this study is to determine the density and diversity in the waters of the Meureudu River, Pidie Jaya District. The method of this research used was purposive sampling, which stations the total is 36 samples. 11 species of meiofauna was found with a total of 240 individuals, namely, Cumacea sp. with the density of 518.4 ind/m2, Kalipthorincia sp. with the density of 2629.7 ind/m2, Annulonemertes sp. with the density of 925.9 ind/m2, Spiroplectammina biformis with the density of 296.32 ind/m2, Amphipoda with the density of 333.31 ind/m2, Eggerelloides scabrous with the density of 296.25 ind/m2, Patagonacyther senescens with the density of 481.47 ind/m2, Copepods with the density of 518.5 ind/m2, Cyatholainus sp. with the density of 2037.1 ind/m2, Acari sp. with the density of 444.41 ind/m2, and Amoria betavus with the density of 407.41 ind/m2. The higest density is Kalipthorincia sp. and the lowest is Spiroplectammina biformis. The diversity of meiofauna in Merureudu River is medium

Distribusi dan Kelimpahan Meiofauna di Perairan Kuala Jeumpa Kecamatan Jeumpa, Kabupaten Bireuen

This study was conducted to determine the abundance and distribution of meiofauna in the Kuala Jeumpa waters, Jeumpa subdistrict, Bireuen regency. Sampling was conducted in April until May 2016. Purposive sampling method was used to determine the 3 stations of data collection, which includes downstream, upstream and estuary area, and then the data was analyzed in the laboratory. The results obtained from the abundance of meiofauna ranging from 222 ind/m2 - 3963 ind/m2 was made up of an abundance of Acarina sp. 222 ind/m2, abundance of Annulonemertes sp. 593 ind/m2, abundance of Cumacea sp. 481 ind/m2, abundance of Cyatholaimus sp. 3963 ind/m2, abundance of Eggerelloides scabrous 630 ind/m2, abundance of Kalipthorincia sp. 1037 ind/m2, abundance of Patagonacyther senescens 556 ind/m2, abundance of Syllides sp. 1593 ind/m2 and an abundance of Decapoda 407 ind/m2. Meiofauna with the highest abundance in the Kuala Jeumpa waters is Cyatholaimus sp. and the lowest was Acarina sp. Distribution Acarina sp. to Decapoda is clustered. The conclusion that the abundance of meiofauna ranging between 222 ind/m2 - 3963 ind/m2. The types of sediment are smooth sand and medium sand