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My research interests have been mainly focused on studying quantum many-body systems
from the theoretical and numerical sides.
My effort goes in two directions,
developing new methods to treat systems with strong electron correlation,
and studying how the interaction affects their physical properties.
The electronic structure of realistic systems has been studied by using a variational approach
based on resonating valence bond wave functions and quantum Monte Carlo techniques.
This approach can be extended to systems of remarkable
interest, such as the transition metals,
high Tc superconductors, and cerium!
Another powerful tool to study strongly-correlated materials
from first principles is the dynamical mean field theory
(DMFT), where a low-energy (usually multi-bands) Hubbard model
is solved within the DMFT approximation, which retains the full
many-body nature of the single site, embedded in a dynamical
medium. We developed improved ways to derive the low-energy
model, by dealing with a dynamical Hubbard
repulsion. ARPES spectral properties of iron-based
superconductors have been studied by means of this approach.
To improve upon the DMFT approximation (local self-energy), we worked on
combining it with GW, which gives the so-called GW+DMFT method.
We have done some work to understand the superconductivity
found in alkali-doped aromatic molecular crystals, such as the
K3Picene. We explained the experimental critical temperature
with a phonon driven mechanism. The electron-phonon coupling
has been computed by Wannier interpolation, with values
computed by density functional perturbation theory.
A joint experiment-theory collaboration yielded very
interesting results on the spintronic and topological properties of
BaNiS2. Unexpectedly,we found a very large Rashba
spin orbit (SO) coupling in this material, due to a huge
crystal field enhancement of the atomic Ni SO. The properties
and tunability of the Dirac states in BaNiS2
are currently under active investigation.
Another line of research we pursue is in the physics of low dimensional models.
The one dimensional electron gas
is the prototype for the description of quantum systems with reduced transversal dimensionality.
Recent advances in the field of cold atoms have allowed the realization of quasi one dimensional systems
also in optical lattices. It is particularly interesting to analyze the effect of the optical trap
on the phases of cold atom systems. This provides a way to interpret the experimental outcome.
Quantum Monte Carlo techniques are ideal tools to study one dimensional systems, as they usually give unbiased
numerical results in one dimension.
The physics of two dimensional Coulomb systems is fascinating and characterized by many peculiar properties.
In particular, the interplay between dimensionality and long-range interactions might lead to
the melting of the crystal through possible exotic phases in the charge sector. Anisotropic phases
such stripes or nematic fluids play a very important role in some theories of high Tc superconductivity, and have
also been suggested as a possible explanation of the metal insulator transition seen in two dimensional
electronic devices.
We proposed new algorithms to tackle the study of many-body problems,
such as new diffusion Monte Carlo techniques, that allow one to stochastically simulate realistic models with non-local pseudo-potentials.
A lattice regularized approach has been introduced,
which includes non-local potentials in a consistent variational way.
We worked on the extension of the standard diffusion Monte Carlo
method to deal with non-local potentials,
by combining the continuous drift-diffusion process with a discrete non local step.
The latter method can be implemented straightforwardly into previous existing codes,
and make them able to perform stable and accurate electronic structure
calculations. I contributed to the realization
of the TurboRVB code.
We developed a new way of performing molecular dynamics simulations with quantum nuclei driven by quantum Monte Carlo forces.
This opens the way to study nuclear quantum effects in
correlated systems. Within a path integral formalism, we
proposed recently an improved scheme of computing phonons in strongly
quantum anharmonic systems, relevant for the new class of
hydrogen-based superconductors.
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Last update 01/04/2021, Paris, France
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