The ground state of a mixture of two species of fermionic atoms in 1D optical lattice

In this paper, we investigate the ground state properties of a mixture of two species of fermionic atoms in one-dimensional optical lattice, as described by the asymmetric Hubbard model. The quantum phase transition from density wave to phase separation is investigated by studying both the corresponding charge order parameter and quantum entanglement. A rigorous proof that even for the single hole doping case, the density wave is unstable to the phase separation in the infinite U limit, is given. Therefore, our results are quite instructive for both on-going experiments on strongly correlated cold-atomic systems and traditional heavy fermion systems.Comment: 9 pages, 10 figures, extended versio

Lower bound for the segregation energy in the Falicov-Kimball model

In this work, a lower bound for the ground state energy of the Falicov-Kimball model for intermediate densities is derived. The explicit derivation is important in the proof of the conjecture of segregation of the two kinds of fermions in the Falicov-Kimball model, for sufficiently large interactions. This bound is given by a bulk term, plus a term proportional to the boundary of the region devoid of classical particles. A detailed proof is presented for density n=1/2, where the coefficient 10^(-13) is obtained for the boundary term, in two dimensions. With suitable modifications the method can also be used to obtain a coefficient for all densities.Comment: 8 pages, 2 figure

Simple theory for spin-lattice relaxation in metallic rare earth ferromagnets

The spin-lattice relaxation time $\tau_{SL}$ is a key quantity both for the dynamical response of ferromagnets excited by laser pulses and as the speed limit of magneto-optical recording. Extending the theory for the electron paramagnetic resonance of magnetic impurities to spin-lattice relaxation in ferromagnetic rare earths we calculate $\tau_{SL}$ for Gd and find a value of 48 ps in very good agreement with time-resolved spin-polarized photoemission experiments. We argue that the time scale for $\tau_{SL}$ in metals is essentially given by the spin-orbit induced magnetocrystalline anisotropy energy.Comment: 18 pages revtex, 5 uuencoded figure

Equivalence of the Falicov-Kimball and Brandt-Mielsch forms for the free energy of the infinite-dimensional Falicov-Kimball model

Falicov and Kimball proposed a real-axis form for the free energy of the Falicov-Kimball model that was modified for the coherent potential approximation by Plischke. Brandt and Mielsch proposed an imaginary-axis form for the free energy of the dynamical mean field theory solution of the Falicov-Kimball model. It has long been known that these two formulae are numerically equal to each other; an explicit derivation showing this equivalence is presented here.Comment: 4 pages, 1 figure, typeset with ReVTe

Linear and nonlinear optical characteristics of the Falicov-Kimball model

We calculate the linear and nonlinear optical properties of the Falicov-Kimball model for a mixed-valent system within the self-consistent mean-field approximation. Second-harmonic generation can only occur if the mixed-valent state has a built-in coherence between the itinerant d-electrons and the localized f-holes. By contrast, second-harmonic generation cannot occur for solutions of the model with f-site occupation as a good quantum number. As an experimental test of coherence in mixed-valent compounds we propose a measurement of the dynamic second-order susceptibility.Comment: 4 pages, 2 PostScript figures, to appear in Physical Review Letter

Symmetries of microcanonical entropy surfaces

Symmetry properties of the microcanonical entropy surface as a function of the energy and the order parameter are deduced from the invariance group of the Hamiltonian of the physical system. The consequences of these symmetries for the microcanonical order parameter in the high energy and in the low energy phases are investigated. In particular the breaking of the symmetry of the microcanonical entropy in the low energy regime is considered. The general statements are corroborated by investigations of various examples of classical spin systems.Comment: 15 pages, 5 figures include

Higher order contributions to Rashba and Dresselhaus effects

We have developed a method to systematically compute the form of Rashba- and Dresselhaus-like contributions to the spin Hamiltonian of heterostructures to an arbitrary order in the wavevector k. This is achieved by using the double group representations to construct general symmetry-allowed Hamiltonians with full spin-orbit effects within the tight-binding formalism. We have computed full-zone spin Hamiltonians for [001]-, [110]- and [111]-grown zinc blende heterostructures (D_{2d},C_{4v},C_{2v},C_{3v} point group symmetries), which are commonly used in spintronics. After an expansion of the Hamiltonian up to third order in k, we are able to obtain additional terms not found previously. The present method also provides the matrix elements for bulk zinc blendes (T_d) in the anion/cation and effective bond orbital model (EBOM) basis sets with full spin-orbit effects.Comment: v1: 11 pages, 3 figures, 8 table

Disproportionation Phenomena on Free and Strained Sn/Ge(111) and Sn/Si(111) Surfaces

Distortions of the $\sqrt3\times\sqrt3$ Sn/Ge(111) and Sn/Si(111) surfaces are shown to reflect a disproportionation of an integer pseudocharge, $Q$, related to the surface band occupancy. A novel understanding of the $(3\times3)$-1U (``1 up, 2 down'') and 2U (``2 up, 1 down'') distortions of Sn/Ge(111) is obtained by a theoretical study of the phase diagram under strain. Positive strain keeps the unstrained value Q=3 but removes distorsions. Negative strain attracts pseudocharge from the valence band causing first a $(3\times3)$-2U distortion (Q=4) on both Sn/Ge and Sn/Si, and eventually a $(\sqrt3\times\sqrt3)$-3U (``all up'') state with Q=6. The possibility of a fluctuating phase in unstrained Sn/Si(111) is discussed.Comment: Revtex, 5 pages, 3 figure