Evgeny Plekhanov

Increasing d-wave superconductivity by on site repulsion

We study, through the variational Monte Carlo technique, an extended Hubbard model away from half filled band density which contains two competing nearest-neighbor interactions: a superexchange J favoring d-wave superconductivity and a repulsion V opposing it. We find that the on-site repulsion U effectively enhances the strength of J while suppressing that of V, thus favoring superconductivity. This result shows that attractions which do not involve charge fluctuations are very well equipped against strong electron-electron repulsion so much to get advantage from it.

The phase diagram of the extended anisotropic ferromagnetic-antiferromagnetic Heisenberg chain

Abstract. By using Density Matrix Renormalization Group (DMRG) technique we study the phase diagram of 1D extended anisotropic Heisenberg model with ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions. We analyze the static correlation functions for the spin operators both in- and out-of-plane and classify the zero-temperature phases by the range of their correlations. On clusters of 64, 100, 200, 300 sites with open boundary conditions we isolate the boundary effects and make finite-size scaling of our results. Apart from the ferromagnetic phase, we identify two gapless spin-fluid phases and two ones with massive excitations. Based on our phase diagram and on estimates for the coupling constants known from literature, we classify the ground states of several edge-sharing materials.

T = 0 phase diagram of the 1D Hubbard model with magnetic interactions in the narrow band limit

In this paper we study a generalization of the Hubbard model by considering spin-spin interactions described by the exchange constant J. An external magnetic field his also taken into account. In the narrowband limit and for the 1D case, we present the exact solution obtained in the framework of the Green’s function formalism, using the Composite Operator Method. We report the T = 0 phase diagram for both ferro (J > 0) and anti-ferro (J < 0) couplings. The competition of the different energy scales (U, J, and h; being U the local charge interaction) generates a variety of phases and different charge and spin orderings.

Spin and charge orderings in the atomic limit of the U-V-J model

In this paper we study a generalization of the 1D Hubbard model in the atomic limit by considering density-density and Ising-type spin-spin nearest neighbor (NN) interactions, parameterized by V and J, respectively. We present the T = 0 phase diagram for both ferro (J > 0) and anti-ferro (J < 0) coupling obtained in the narrow-band limit by means of an extension to zero-temperature of the transfer-matrix method. Based on the values of the Hamiltonian parameters, we identify a number of phases that involve orderings of the double occupancy, NN density and spin correlations.

XXZ-like phase in the F-AF anisotropic Heisenberg chain

By means of the Density Matrix Renormalization Group technique, we have studied the region where XXZ-like behavior is most likely to emerge within the phase diagram of the F-AF anisotropic extended (J-J’) Heisenberg chain. We have analyzed, in great detail, the equal-time two-spin correlation functions, both in- and out-of- plane, as functions of the distance (and momentum). Then, we have extracted, through an accurate fitting procedure, the exponents of the asymptotic power-law decay of the spatial correlations. We have used the exact solution of XXZ model (J’ = 0) to benchmark our results, which clearly show the expected agreement. A critical value of J’ has been found where the relevant power-law decay exponent is independent of the in-plane nearest-neighbor coupling.

d -wave pairing in lightly doped Mott insulators

We define a suitable quantity

Correlation-induced band suppression in the two-orbital Hubbard model

Z_c

T = 0 phase diagram of 1D extended anisotropic spin-½ Heisenberg model

that measures the pairing strength of two electrons added to the ground state wave function by means of the anomalous part of the one-particle Greens function.

Analysis of the magnetic response of the edge-sharing chain cuprate Li2CuO2 within TMRG

Z_c

Role of spin-orbit coupling in the electronic structure of IrO2

discriminates between systems described by one-electron states, like ordinary metals and band insulators, for which