arXiv subjects

L. De Leo

Publications and source records attributed to L. De Leo.

7 recordsLinked to original sources

arXiv2012

We've walked a million miles for one of these smiles

We derive a new, exact and transparent expansion for option smiles, which lends itself both to analytical approximation and, perhaps more importantly, to congenial numerical treatments. We show that the skew and the curvature of the smile can be computed as exotic options, for which the Hedged Monte Carlo method is particularly well suited. When applied to options on the S&P index, we find that the skew and the curvature of the smile are very poorly reproduced by the standard Edgeworth (cumulant) expansion. Most notably, the relation between the skew and the skewness is inverted at small and large vols, a feature that none of the model studied so far is able to reproduce. Furthermore, the around-the-money curvature of the smile is found to be very small, in stark contrast with the highly kurtic nature of the returns.

q-fin.PR↗

arXiv2009

Pseudogap opening and formation of Fermi arcs as an orbital-selective Mott transition in momentum space

We present an approach to the normal state of cuprate superconductors which is based on a minimal cluster extension of dynamical mean-field theory. Our approach is based on an effective two-impurity model embedded in a self-consistent bath. The two degrees of freedom of this effective model can be associated to the nodal and antinodal regions of momentum space. We find a metal-insulator transition which is selective in momentum space: At low doping quasiparticles are destroyed in the antinodal region, while they remain protected in the nodal region, leading to the formation of apparent Fermi arcs. We compare our results to tunneling and angular-resolved photoemission experiments on cuprates. At very low energy, a simple description of this transition can be given using rotationally invariant slave bosons.

cond-mat.str-el↗

arXiv2009

Trapping and cooling fermionic atoms into the Mott and Néel states

We perform a theoretical study of a fermionic gas with two hyperfine states confined to an optical lattice. We derive a generic state diagram as a function of interaction strength, particle number, and confining potential. We discuss the central density, the double occupancy and their derivatives as probes for the Mott state, connecting our findings to the recent experiment of Jördens et al. Using entropic arguments we compare two different strategies to reach the antiferromagnetic state in the presence of a trapping potential.

cond-mat.str-el↗

arXiv2008

Valence-Bond Dynamical Mean-Field Theory of Doped Mott Insulators with Nodal/Antinodal Differentiation

We introduce a valence-bond dynamical mean-field theory of doped Mott insulators. It is based on a minimal cluster of two orbitals, each associated with a different region of momentum space and hybridized to a self-consistent bath. The low-doping regime is characterized by singlet formation and the suppression of quasiparticles in the antinodal regions, leading to the formation of Fermi arcs. This is described in terms of an orbital-selective transition in reciprocal space. The calculated tunneling and photoemission spectra are consistent with the phenomenology of the normal state of cuprates. We derive a low-energy description of these effects using a generalization of the slave-boson method.

cond-mat.str-el↗

arXiv2007

Strong Correlations in a nutshell

We present the phase diagram of clusters made of two, three and four coupled Anderson impurities. All three clusters share qualitatively similar phase diagrams that include Kondo screened and unscreened regimes separated by almost critical crossover regions reflecting the proximity to barely avoided critical points. This suggests the emergence of universal paradigms that apply to clusters of arbitrary size. We discuss how these crossover regions of the impurity models might affect the approach to the Mott transition within a cluster extension of dynamical mean field theory.

cond-mat.str-el↗

arXiv2005

Surprises in the phase diagram of an Anderson impurity model for a single C$_{60}^{n-}$ molecule

We find by Wilson numerical renormalization group and conformal field theory that a three-orbital Anderson impurity model for a C$_{60}^{n-}$ molecule has a very rich phase diagram which includes non-Fermi-liquid stable and unstable fixed points with interesting properties, most notably high sensitivity to doping $n$. We discuss the implications of our results to the conductance behavior of C$_{60}$-based single-molecule transistor devices.

cond-mat.str-el↗

arXiv2003

Spin-Charge gauge approach to "Pseudogap": theory versus experiments

We propose an explanation of several experimental features related to the ``pseudogap'' in HTS cuprates in terms of a spin-charge gauge theory approach to the t-J model. The metal-insulator crossover as temperature decreases is explained from the competition between antiferromagnetism and dissipative charge dynamics. We show that gauge interactions bind spinon and holon into an electron resonance, whose recombination time shows up in the out-of-plane resistivity. The theoretical results are sistematically compared with experimental data, finding a very good agreement.

cond-mat.str-el↗