Quantum
Fluids and Solids, Superfluids, Atomic Clusters
The
research field of this activity is the microscopic study of the effect
of confinement on the properties of strongly interacting Bosons. Today,
confinement effects are one of the key themes of the theoretical
research in condensed matter. In fact the reciprocal action of the
confining potential with the interparticle interaction can let to new
quantum phenomena driven by amplified correlation effects. One example
of this mechanism is the recent (probable) observation of a supersolid phase (a solid
with Bose-Einstein condensation, BEC) in the phase diagram of solid 4He [Kim
and Chan, Science 305, 1941 (2004)].
The physical systems under investigations are 4He systems at very low
temperatures in the superfluid phase or in the solid phase, where we are
studying also para-hydrogen (p-H2) systems.
The project will use state of the art quantum simulation methods (Quantum Monte Carlo methods; recently we have introduced a new exact method: the Shadow Path Integral Ground State, SPIGS) developed for strongly interacting systems.
Some activities under development:
1)
Exact calculation with the SPIGS technique of the Bose-Einstein
condensate fraction in a commensurate and incommensurate solid 4He;
2)
Study of the vacancy concentration in the ground state of quantum
solids;
3)
Study of elementary excitations in liquid 4He (phonons, rotons) and in
solid 4He (phonons,
vacancy waves, vacancy-interstitial waves);
4)
Study of 4He solid systems in presence of defects like dislocation,
grain boundaries, interstitials etc.;
5)
Study of 4He solids doped with charged impurities;
6)
Development of Quantum Monte Carlo methods.
Study of nodal regions (where the local density goes to zero) in an elementary cell of a para-hydrogen solid with a Quantum Monte Carlo simulation with the SPIGS technique. [D.E. Galli, L. Reatto and W.M. Saslow, Phys. Rev. B 76 052503 (2007); D.E. Galli and L. Reatto, J. Low Temp. Phys. 136, 343 (2004)]
Calculation of the one-body density matrix (on the left) with a Quantum Monte Carlo simulation (on the right) of solid 4He; the long range order present in the density matrix corresponds to the presence of BEC [D.E. Galli, M. Rossi, and L. Reatto, Phys. Rev. B71, 140506 (2005)]
Quantum Monte Carlo study of 4He confined in nanopores [(a) M. Rossi, D.E. Galli and L.
Reatto, Phys. Rev. B72, 064516 (2005); (b) M. Rossi, D.E. Galli and L. Reatto, AIP Conference Proceedings Vol. 850, pp. 356-357 (2006)]
-"Layer by layer solidification of 4He in narrow porous media", M. Rossi, D.E. Galli and L. Reatto, Phys. Rev. B72, 064516 (2005).
-"Bose-Einstein condensation in solid 4He", D.E. Galli, M. Rossi, and L. Reatto, Phys. Rev. B71, 140506 (2005).
-"The Shadow Path Integral Ground State Method: Study of Confined Solid 4He", D.E. Galli and L. Reatto, J. Low Temp. Phys. 136, 343 (2004).
-"Alkali and alkali--earth ions in 4He systems", M. Rossi, M. Verona, D.E. Galli and L. Reatto, Phys. Rev. B69, 212510 (2004).
-"Disorder Phenomena in Quantum Solids with Vacancies", D.E. Galli and L. Reatto, J. Low Temp. Phys. 134, 121 (2004).
-"Vacancy excitation spectrum in solid 4He and longitudinal phonons", D.E. Galli and L. Reatto, Phys. Rev. Lett. 90, 175301 (2003).
-"Recent progress in simulation of the ground state of many Boson systems", D.E. Galli and L. Reatto, Mol. Phys. 101, 1697 (2003).