Measurements of the kinetic energy of 4 He through the superfluid transition

J. Mayers, F. Albergamo, David N. Timms

B. Fåk, H. R. Glyde

J. Mayers, C. Andreani, D. Colognesi

Measurements of the kinetic energy of atoms in liquid have been made using neutron Compton scattering at wavevector transfers between 90 and . The kinetic energy shows a marked decrease from 16.2 K at a temperature of 2.5 K, to 13.9 K at 1.3 K. Three different measurements were made using energy analysers with different resolutions. Good agreement was obtained between the measurements using different resolutions and with previous measurements and calculations of the kinetic energies. For the best-resolution data, a line shape analysis was made in order to derive the non-Gaussian components of the momentum distribution. Values of kinetic energies are consistent with a Bose condensate fraction of . The measurements show that eV neutron scattering provides an accurate method of measuring kinetic energies in quantum fluids.

V. P. Peshkov

A. S. Alexandrov, Iorwerth O. Thomas

It has been well known that quantum fluctuations induce a macroscopic phase transition from a superfluid to a Mott insulator phase driven by the repulsive potential energy in the ground state of dense bosonic systems on a lattice. We find a quantum phase transition from the homogeneous to an inhomogeneous Bose-condensate strongly affected or sometimes driven by the kinetic energy dispersion in dilute bosonic superfluids, which provides a clear identification of the superfluid state.

Cécile Carcy, Sascha Hoinka, Marcus Lingham +4 more

We present an experimental study of the high-energy excitation spectra of unitary Fermi gases. Using focused beam Bragg spectroscopy, we locally probe atoms in the central region of a harmonically trapped cloud where the density is nearly uniform, enabling measurements of the dynamic structure factor for a range of temperatures both below and above the superfluid transition. Applying sum rules to the measured Bragg spectra, we resolve the characteristic behavior of the universal contact parameter, C, across the superfluid transition. We also employ a recent theoretical result for the kinetic (second-moment) sum rule to obtain the internal energy of gases at unitarity.