QFS2016 Book of Abstracts

Abstracts

O3.9

Multi-particle excitations in superfluid

He investigated as a function

of pressure

Beauvois K.(1, 2, 3), Campbell C. E.(4), Dawidowski J.(5), F˚ak B.(1, 6, 7),

Godfrin H.(2, 3), Krotscheck E.(8, 9), Lauter H.-J.(10), Lichtenegger T.(8, 9),

Ollivier J.(1), Sultan A.(2, 3, 7)

1) Institut Laue-Langevin, 6, rue Jules Horowitz, 38042 Grenoble, France

2) Univ. Grenoble Alpes, Inst NEEL, F-38000 Grenoble, France

3) CNRS, Inst NEEL, F-38042 Grenoble, France

4) School of Physics and Astronomy, Univ. of Minnesota, Minneapolis MN

55455, USA

5) Comisi´on Nacional de Energ´ıa At´omica and CONICET, Argentina

6) Univ. Grenoble Alpes, INAC-SPSMS, F-38000 Grenoble, France

7) CEA, INAC-SPSMS, F-38000 Grenoble, France

8) Department of Physics, University at Buffalo, SUNY Buffalo NY 14260, USA

9) Institute for Theoretical Physics, Johannes Kepler University, A4040 Linz,

Austria

10) Spallation Neutron Source, ORNL, Oak Ridge, Tennessee 37831, USA

The dynamic structure function S(q,E) of superfluid

He has been measured

at very low temperatures for pressures up to 10 bars, in the multi-excitation

regime. The neutron scattering measurements were performed at the Institut

Laue-Langevin on the time-of-flight spectrometer IN5. Our measurements at

saturated vapour pressure [1] display a very rich landscape of multi-excitations,

including a “ghost phonon” and other remarkable features which are found to

depend on pressure in agreement with the Dynamic Many-Body theory [2].

[1] K. Beauvois et al., arXiv:1605.02638v1, to be published.

[2] C. E. Campbell, E. Krotscheck, and T. Lichtenegger, Phys. Rev. B 91, 184510

(2015).

O3.10

Correlations in the low-density Fermi gas:Fermi-Liquid state,

Dimerization, and BCS Pairing

Fan, H.-H.(1, 2), Krotscheck E.(1, 2), Zillich, R. E.(2)

(1) Department of Physics, University at Buffalo, SUNY Buffalo NY 14260,

USA

(2) Institute for Theoretical Physics, Johannes Kepler University, A4040 Linz,

Austria

We present ground state calculations for low-density Fermi gases the optimized

Fermi-Hypernetted Chain integral equation method which provides, in the density

regimes of interest, an accuracy better than one percent. As a function of density

and/or coupling strength we encounter an instability of the normal state of the

system which is characterized by a divergence of the scattering length indicating

phonon-exchange driven dimerization. We then study, in the stable regime, the

superfluid gap and its dependence on the density and the interaction strength.

The most important finite-range corrections are a direct manifestation of the

many-body nature of the system.