Quantum Monte Carlo evidence for d-wave pairing in the two-dimensional Hubbard model at a van Hove singularity

Quantum Monte Carlo study of the Hubbard model with next-nearest-neighbor hopping t': pairing and magnetism

Using the finite-temperature determinant quantum Monte Carlo (DQMC) algorithm, we study the pairing symmetries of the Hubbard Hamiltonian with next-nearest-neighbor (NNN) hopping t' on square lattices. By varying the value of t', we find that the d-wave pairing is suppressed by the onset of t', while the p + ip-wave pairing tends to emerge for low electron density and t' around -0.7. Together with the calculation of the anti-ferromagnetic and ferromagnetic spin correlation function, we explore the relationship between anti-ferromagnetic order and the d-wave pairing symmetry, and the relationship between ferromagnetic order and the p + ip-wave pairing symmetry. Our results may be useful for the exploration of the mechanism of the electron pairing symmetries, and for the realization of the exotic p + ip-wave superconductivity.

Frustration effects at finite temperature in the half filled Hubbard model

We investigate the finite temperature properties of the half filled Hubbard model in two dimensions, with onsite interaction (U), in presence of (frustrating) next nearest neighbor hopping (t') using a semiclassical approximation scheme. We show that introduction oft' results in a finite temperature pseudogapped (PG) phase that separates the smallUFermi liquid and largeUMott insulator. We map out the PG to normal metal crossover temperature scale (T*) as a function ofUandt'. We demonstrate that in the PG phase, the quadratic dependence of resistivity on temperature is violated due to thermally induced spin fluctuations. We conclude with exact diagonalization calculations, that complement our finite temperature results, and indicate the presence of a frustration driven PG state between the Fermi liquid and the Mott insulator at zero temperature as well.