B. Sriram Shastry

Exact ground state of a quantum mechanical antiferromagnet

We present some exact results for the ground state of a quantum mechanical antiferromagnetic model in the two dimensions with next-nearest neighbor interactions.

Decorated star-triangle relations and exact integrability of the one-dimensional Hubbard model

The exact integrability of the one-dimensional Hubbard model is demonstrated with the help of a novel set of triangle relations, the decorated star-triangle relations. The covering two-dimensional statistical mechanical model obeys the star-triangle or Yang-Baxter relation. A conjecture is presented for the eigenvalues of the transfer matrix.

Superconductivity in CoO 2 layers and the resonating valence bond mean-field theory of the triangular lattice t − J model

Motivated by the recent discovery of superconductivity in two-dimensional

Existence of Néel order in some spin-1/2 Heisenberg antiferromagnets

CoO_2

Persistent currents in a one-dimensional ring for a disordered Hubbard model.

layers, we present some possibly useful results of the resonating valence bond mean-field theory applied to the triangular lattice. An interesting time reversal breaking superconducting state arises from strongly frustrated interactions. Away from half filling, the order parameter is found to be complex, and yields a fully gapped quasiparticle spectrum. The sign of the hopping plays a crucial role in the analysis, and we find that superconductivity is as fragile for one sign as it is robust for the other.

Bloch Walls and Macroscopic String States in Bethe's Solution of the Heisenberg Ferromagnetic Linear Chain

Na_xCoO_2 \cdot yH_2O

Raman Scattering in Mott-Hubbard Systems

is argued to belong to the robust case, by comparing the local-density approximation fermi surface with an effective tight-binding model. The high-frequency Hall constant in this system is potentially interesting, since it is pointed out to increase linearly with temperature without saturation for T>Tdegeneracy.

Electrothermal transport coefficients at finite frequencies

The methods of Dyson, Lieb, and Simon are extended to prove the existence of Néel order in the ground state of the 3D spin-1/2 Heisenberg antiferromagnet on the cubic lattice. We also consider the spin-1/2 antiferromagnet on the cubic lattice with the coupling in one of the three lattice directions taken to ber times its value in the other two lattice directions. We prove the existence of Néel order for 0.16⩽r⩽1. For the 2D spin-1/2 model we give a series of inequalities which involve the two-point function only at short distances and each of which would by itself imply Néel order.

The theory of high- Tc superconductors — comparisons with experiment

We consider a one-dimensional Hubbard model in the presence of disorder. We compute the charge stiffness for a mesoscopic ring, as a function of the size L, which is a measure of the permanent currents. We find that for finite disorder the permanent currents of the system with repulsive interactions are larger than those of the system with attractive interactions. This counter intuitive result is due to the fact that local density fluctuations are reduced in the presence of repulsive interactions. Typeset using REVTEX

The origin of degeneracies and crossings in the 1d Hubbard model

We present a calculation of the lowest excited states of the Heisenberg ferromagnet in 1D for any wave vector. These turn out to be string solutions of Bethes equations with a macroscopic number of particles in them. They are identified as generalized quantum Bloch wall states, and a simple physical picture is provided for the same.