Manuela Capello

Unidirectional d -wave superconducting domains in the two-dimensional t − J model

Using the t-J model at x=1/8 doping, we investigate the emergence of spontaneous modulations in the d-wave superconducting resonating valence bond phase which may be connected to the recently observed pattern of unidirectional domains found in scanning tunneling microscopy studies of high-T_c superconductors [Y. Kohsaka et al., Science 315, 1380 (2007)]. Half-filled charge domains separated by four lattice spacings are found to form along one of the crystal axis leading to modulated superconductivity with {\it out-of-phase} d-wave order parameters in neighboring domains. Both renormalized mean-field theory and variational Monte Carlo calculations yield that the energies of modulated and uniform phases are very close to each other.

Superfluid to Mott-insulator transition in Bose-Hubbard models.

We study the superfluid-insulator transition in Bose-Hubbard models in one-, two-, and three-dimensional cubic lattices by means of a recently proposed variational wave function. In one dimension, the variational results agree with the expected Berezinskii-Kosterlitz-Thouless scenario of the interaction-driven Mott transition. In two and three dimensions, we find evidence that, across the transition, most of the spectral weight is concentrated at high energies, suggestive of preformed Mott-Hubbard sidebands. This result is compatible with the experimental data by Stoferle et al. [Phys. Rev. Lett. 92, 130403 (2004)].

Unconventional metal-insulator transition in two dimensions

We show, by using a correlated Jastrow wave function and a mapping onto a classical model, that the two-dimensional Mott transition in a simple half-filled one-band model can be unconventional and very similar to the binding-unbinding Kosterlitz-Thouless transition of vortices and antivortices, here identified by empty and doubly occupied sites. Within this framework, electrons strongly interact with collective plasmon excitations that induce anomalous critical properties on both sides of the transition. In particular, the insulating phase is characterized by a singular power-law behavior in the photoemission spectrum, which can be continuously connected to the fully projected insulating state relevant to strongly correlated low-energy models.

Stability of RVB hole stripes in high-temperature superconductors

Indications of density-wave states in underdoped cuprates, coming from recent scanning tunneling microscopy and Hall-resistance measurements, have raised concerns whether stripes could be stabilized in the superconducting phase of cuprate materials, even in the absence of antiferromagnetism. Here, we investigate this issue using state-of-the-art quantum Monte Carlo calculations of a

Mott transition in bosonic systems: Insights from the variational approach

t\text{\ensuremath{-}}J

From Luttinger liquid to Mott insulator : The correct low-energy description of the one-dimensional hubbard model by an unbiased variational approach

model. In particular we consider the stability of unidirectional hole domains in a modulated superconducting background by taking into account the effect of tetragonal-lattice distortions, next-nearest-neighbor hopping, and long-range Coulomb repulsion.

Variational description of Mott insulators

We study the Mott transition occurring for bosonic Hubbard models in one, two, and three spatial dimensions by means of a variational wave function benchmarked by Greens function Monte Carlo calculations. We show that a very accurate variational wave function, which is constructed by applying a long-range Jastrow factor to the noninteracting boson ground state, can describe the superfluid-insulator transition in any dimensionality. Moreover, by mapping the quantum averages over such a wave function into the partition function of a classical model, important insights into the insulating phase are uncovered. Finally, the evidence in favor of anomalous scenarios for the Mott transition in two dimensions is reported whenever additional long-range repulsive interactions are added to the Hamiltonian.

Unidirectional Charge Instability of the d-wave RVB Superconductor

We show that a particular class of variational wave functions reproduces the low-energy properties of the Hubbard model in one dimension. Our approach generalizes to finite on-site Coulomb repulsion the fully projected wave function proposed by Hellberg and Mele [Phys. Rev. Lett. 67, 2080 (1991)] for describing the Luttinger-liquid behavior of the doped

Imaging the effect of a non-magnetic impurity in a RVB superconductor

t\ensuremath{-}J

Jastrow theory of the Mott transition in bosonic Hubbard models

model. Within our approach, the long-range Jastrow factor emerges from a careful minimization of the energy, without assuming any parametric form for the long-distance tail. Specifically, in the conducting phase of the Hubbard model at finite hole doping, we obtain the correct power-law behavior of the correlations, with the exponents predicted by the Tomonaga-Luttinger theory. By decreasing the doping, the insulating phase is reached with a continuous change of the small-