In this paper we study the problem of nding an exact ground state of a two-dimensional J Ising spin glass on a square lattice with nearest neighbor interactions and periodic boundary conditions when there is a concentration p of negative bonds, with p ranging between 0:1 and 0:9. With our exact algorithm we can determine ground states of grids of sizes up to 50 50 in a moderate amount of comput...

This paper is a continuation of our previous analysis [2] of partition functions zeros in models with first-order phase transitions and periodic boundary conditions. Here it is shown that the assumptions under which the results of [2] were established are satisfied by a large class of lattice models. These models are characterized by two basic properties: The existence of only a finite number o...

In this paper we study the problem of nding an exact ground state of a two-dimensional J Ising spin glass on a square lattice with nearest neighbor interactions and periodic boundary conditions when there is a concentration p of negative bonds, with p ranging between 0:1 and 0:9. With our exact algorithm we can determine ground states of grids of sizes up to 50 50 in a moderate amount of comput...

We study the sawtooth lattice of a coupled spin 1/2 Heisenberg system, a variant of the railroad trestle lattice. The ground state of this system is twofold degenerate with periodic boundary conditions and supports kink antikink excitations, which are distinct in this case, unlike the railroad trestle lattice. The resulting low temperature thermodynamics is compared with the recently discovered...

Abstract. A d-dimensional quantum model system confined to a general hypercubical geometry with linear spatial size L and “temporal size” 1/T ( T temperature of the system) is considered in the spherical approximation under periodic boundary conditions. For a film geometry in different space dimensions 1 2 σ < d < 3 2 σ , where 0 < σ ≤ 2 is a parameter controlling the decay of the long-range in...

A d–dimensional quantum model system confined to a general hypercubical geometry with linear spatial size L and " temporal size " 1/T (T-temperature of the system) is considered in the spherical approximation under periodic boundary conditions. For a film geometry in different space dimensions 1 2 σ < d < 3 2 σ , where 0 < σ ≤ 2 is a parameter controlling the decay of the long–range interaction...

We study a model for itinerant, strongly interacting fermions where a judicious tuning of the interactions leads to a supersymmetric Hamiltonian. On the triangular lattice this model is known to exhibit a property called superfrustration, which is characterized by an extensive ground state entropy. Using a combination of numerical and analytical methods we study various ladder geometries obtain...

We propose a new Ising spin glass model on Z of Edwards-Anderson type, but with highly disordered coupling magnitudes, in which a greedy algorithm for producing ground states is exact. We find that the procedure for determining (infinite volume) ground states for this model can be related to invasion percolation with the number of ground states identified as 2 , where N = N (d) is the number of...

The 1/r2 quantum many body problem, and the closely related Haldane-Shastry 1/r2 Heisenberg chain, are the subject of intense theoretical study at present, due in part to their relationship to an ideal gas obeying fractional statistics (see [1] for a review). One direction of study has been the exact calculation of some ground state correlation functions [1-5]. Let us briefly summarize the main...

We study entanglement renormalization group transformations for the ground states of a spin model, called cubic code model HA in three dimensions, in order to understand long-range entanglement structure. The cubic code model has degenerate and locally indistinguishable ground states under periodic boundary conditions. In the entanglement renormalization, one applies local unitary transformatio...