Triangular-layered NiGa2S4, contrary to intuitive expectation, does not form a noncollinear antiferromagnetic structure, as do isoelectronic NaCrO2 and LiCrO2. Instead, the local magnetic moments remain disordered down to the lowest measured temperature. To get more insight into this phenomenon, we have performed first principles calculations of the first, second end third neighbors exchange in...

We show that the recently constructed exact solution of the SU(2|2) extended Hub-bard model on a one-dimensional lattice provides a complete set of 4 L eigenstates of the hamiltonian, where L is the length of the lattice.

One of the core problems in materials science is how the interactions between electrons in a solid give rise to properties like ∗This work was partially supported by the National Science Foundation under Grant 0313390, and Department of Energy, Office of Science, SciDAC grant DEFC02 06ER25793. Wenbin Chen was also supported in part by the China Basic Research Program under the grant 2005CB32170...

Rigorous justification of the Hubbard-Stratonovich transformation for the Pruisken-Schäfer type of parameterisations of real hyperbolic O(m,n)−invariant domains remains a challenging problem. We show that a naive choice of the volume element invalidates the transformation, and put forward a conjecture about the correct form which ensures the desired structure. The conjecture is supported by com...

We consider the coarse-graining of a lattice system with continuous spin variable. In the first part, two abstract results are established: sufficient conditions for a logarithmic Sobolev inequality with constants independent of the dimension (Theorem 3) and sufficient conditions for convergence to the hydrodynamic limit (Theorem 8). In the second part, we use the abstract results to treat a sp...

The Hubbard model is a “highly oversimplified model” for electrons in a solid which interact with each other through extremely short ranged repulsive (Coulomb) interaction. The Hamiltonian of the Hubbard model consists of two pieces; Hhop which describes quantum mechanical hopping of electrons, and Hint which describes nonlinear repulsive interaction. Either Hhop or Hint alone is easy to analyz...

We derive an upper bound on the ground state energy of the 3D repulsive Hubbard model on the cubic lattice agreeing in the low density limit with the known asymptotic expression of the ground state energy of the dilute Fermi gas in the continuum. As a corollary, we prove an old conjecture on the low density behavior of the 3D Hubbard model, i.e., that the total spin of the ground state vanishes...

In the context of the dynamical mean-field theory (DMFT) of the Hubbard model, we study the behavior of the compressibility near the density driven Mott transition at finite temperatures. We demonstrate this divergence using DMFT and quantum Monte Carlo simulations in the one-band and the two-band Hubbard model. We supplement this result with considerations based on the Landau theory framework,...

We study the properties of a quantum impurity embedded in a superconducting host. The superconductor is described by the negative U Hubbard model while the impurity introduces a repulsive interaction to the system. We discuss the influence of this ‘on-impurity’ Coulomb repulsion on the local properties (density of states, electron pairing) of the superconductor. We show the condition of π like ...