Michele Fabrizio

 

E-mail

fabrizio (at) sissa.it

Office

A 305

Web

Tel

+39 040 3787 457

Fax

+39 040 3787 249

Vita

I was born in 1964. I got the PhD in 1992 at SISSA. After spending two years as a post-Doc in the Theory group of Prof. Nozières at the ILL in Grenoble, I got a position as assistant professor in the Condensed Matter Theory Group of SISSA. In 2000 I was nominated associate professor.

Research

My research activity in the past years has been mostly focused on Strongly Correlated Systems. The topics I am currently most interested in are:

  • Out-of-equilibrium phenomena in correlated systems.

The electronic properties of correlated systems are generally controlled by distinct energy scales that cover a wide energy range, from the high-energy Hubbard bands down to the quasiparticle coherence energy, from the atomic Coulomb exchange down to the magnetic super-exchange. The energy that is suddenly injected to drive out-of-equilibrium the correlated system can therefore induce a substantial redistribution of spectral weight over a wide energy interval with unpredictable outcomes.  Furthermore, since most of the spectral weight is believed to be concentrated in the incoherent Hubbard bands, it is not immediately obvious how energy injected in these bands could be dissipated and the system finally relax. These and other open questions make this subject quite challenging. We have shown that by properly including time-dependence into a Gutzwiller-type of variational wavefunction it is possible to uncover the Hubbard bands and study their dynamics as well as that one of the low-energy coherent quasiparticles. This approximate variational approach is very simple and flexible and in principle can be adapted to study many cases of interest, e.g. how a Mott transistor works, etc..

  • Realistic modeling of transport across magnetic nanocontacts.

A magnetic nanocontact coupled to non-magnetic leads must undergo Kondo effect, because spin-symmetry cannot be locally broken. Since Kondo effect is a genuine many-body phenomenon, conventional electronic structure calculations are unable to capture it, hence describe ab-initio the correct transport behavior. We have proposed a novel working scheme that combines together ab-initio with many-body techniques. This allows to identify the magnetic moment that is involved in the Kondo effect and the strength of the Kondo exchange, which is important to determine the energy scale that controls the low-temperature behavior, i.e. the Kondo temperature. There is however the possibility that a magnetic nanocontact could retain its moment down to zero temperature eluding the Kondo effect. This case would for instance occur should the exchange be ferromagnetic. If the leads are ferromagnetic or nearly ferromagnetic metals, a ferromagnetic exchange with the contact is likely to appear. This scenario has been so far not much explored but could have interesting consequences.

  • Variational description of correlated electron and boson systems.

We have shown along the past years that variational wavefunctions of the Gutzwiller type can provide a quite accurate description of correlated models even in the Mott insulating phase. These wavefunctions in their simplest form can be also studied analytically by the so-called Gutzwiller approximation. However it is often necessary to implement a Jastrow factor  in the wavefunction to get more sensible results, especially in the insulating phases. In this case a numerical calculation is compulsory. However, in both cases a variational optimization can be performed and since the method is simple enough, it is suitable to treat lots of different models. More recently we have studied in great detail the disordered Bose Hubbard model and other studies are in progress.

Most recent publications (all my publications can be found on the arXiv)

  1. P. Lucignano, M. Fabrizio, and A. Tagliacozzo, Suppression of Kondo-assisted cotunneling in a spin-1 quantum dot with spin-orbit interaction, Phys. Rev. B 82, 161306 (2010).
  2. M. Schiro` and M. Fabrizio, Time-Dependent Mean Field Theory for Quench Dynamics in Correlated Electron Systems, Phys. Rev. Lett. 105, 076401 (2010).
  3. J. Carrasquilla, F. Becca, A. Trombettoni, and M. Fabrizio, Characterization of the Bose-glass phase in low-dimensional lattices, Phys. Rev. B 81, 195129 (2010).
  4. P. Lucignano, M. Fabrizio, and A. Tagliacozzo, Destruction of Kondo correlations in a four electron quantum dot with spin-orbit interactions, Physica E 42, 860 (2010).
  5. G. Borghi, M. Fabrizio, and E. Tosatti, Strongly correlated metal interfaces in the Gutzwiller approximation, Phys. Rev. B 81, 115134 (2010).
  6. N. Lanata`, P. Barone, and M. Fabrizio, Superconductivity in the doped bilayer Hubbard model, Phys. Rev. B 80, 224524 (2009).
  7. P. Gentile, L. De Leo, M. Fabrizio, and E. Tosatti, Lack of Kondo screening at nanocontacts of nearly magnetic metals, EPL 87, 27014 (2009).
  8. P. Lucignano, R. Mazzarello, A. Smogunov, M. Fabrizio, and E. Tosatti, Kondo conductance in an atomic nanocontact from first principles, Nature Materials 8, 563 (2009).
  9. M. Capone, M. Fabrizio, C. Castellani, and E. Tosatti, Colloquium: Modeling the unconventional superconducting properties of expanded A(3)C(60) fullerides, Rev. Mod. Phys. 81, 943 (2009).
  10. M. Schiro` and M. Fabrizio, Real-time diagrammatic Monte Carlo for nonequilibrium quantum transport, Phys. Rev. B 79, 153302 (2009).
  11. G. Borghi, M. Fabrizio, and E. Tosatti, Surface Dead Layer for Quasiparticles Near a Mott Transition, Phys. Rev. Lett. 102, 066806 (2009).
  12. M.E. Pezzoli, F. Becca, M. Fabrizio, and G.E. Santoro, Local moments and magnetic order in the two-dimensional Anderson-Mott transition, Phys. Rev. B 79, 033111 (2009).
  13. N. Lanata’, P. Barone, and M. Fabrizio, Fermi-surface evolution across the magnetic phase transition in the Kondo lattice model, Phys. Rev. B 78, 155127 (2008).
  14. P. Lucignano, G.E. Santoro, M. Fabrizio, and E. Tosatti, Two-level physics in a model metallic break junction, Phys. Rev. B 78, 155418 (2008).
  15. P. Barone, R. Raimondi, M. Capone, C. Castellani, and M. Fabrizio, Gutzwiller scheme for electrons and phonons: The half-filled Hubbard-Holstein model, Phys. Rev. B 77, 235115 (2008).
  16. M. Capello, F. Becca, M. Fabrizio, and S. Sorella, Mott transition in bosonic systems: Insights from the variational approach, Phys. Rev. B 77, 144517 (2008).
  17. M. Schiro`, M. Capone, M. Fabrizio, and C. Castellani, Strongly correlated superconductivity arising in a pseudogap metal, Phys. Rev. B 77, 104522 (2008).