Excitation spectrum in two-dimensional superfluid ⁴He

• Veröffentlicht in: Физика низких температур
• Datum: 2013
• ISSN: 0132-6414
• Hauptverfasser: Arrigoni, F., Vitali, E., Galli, D.E., Reatto, L.
• Format: Artikel
• Sprache: Englisch
• Veröffentlicht: Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України 2013
• Schlagworte: Сверхтекучесть в низкоразмерных системах и в условиях ограниченной геометрии
• Online Zugang: https://nasplib.isofts.kiev.ua/handle/123456789/118751
• Назва журналу: Digital Library of Periodicals of National Academy of Sciences of Ukraine
• Zitieren: Excitation spectrum in two-dimensional superfluid ⁴He / F. Arrigoni, E. Vitali, D.E. Galli, L. Reatto// Физика низких температур. — 2013. — Т. 39, № 9. — С. 1021–1030. — Бібліогр.: 37 назв. — англ.

In this work we perform an ab-initio study of an ideal two-dimensional sample of
 ⁴He atoms, a model for
 ⁴He
 films adsorbed on several kinds of substrates. Starting from a realistic hamiltonian we face the microscopic study
 of the excitation phonon–roton spectrum of the system at zero temperature. Our approach relies on path integral
 ground state Monte Carlo projection methods, allowing to evaluate exactly the dynamical density correlation
 functions in imaginary time, and this gives access to the dynamical structure factor of the system S(q, ), containing
 information about the excitation spectrum E(q), resulting in sharp peaks in S(q, ). The actual evaluation of
 S(q, ) requires the inversion of the Laplace transform in ill-posed conditions, which we face via the genetic inversion
 via falsification of theories technique. We explore the full density range from the region of spinodal decomposition
 to the freezing density, i.e., 0.0321 Å⁻²
 – 0.0658 Å⁻². In particular we follow the density dependence
 of the excitation spectrum, focusing on the low-wave vector behavior of E(q), the roton dispersion, the strength
 of single quasiparticle peak, Z(q), and the static density response function, (q). As the density increases, the
 dispersion E(q) at low-wave vector changes from a superlinear (anomalous dispersion) trend to a sublinear (normal
 dispersion) one, anticipating the crystallization of the system; at the same time the maxon–roton structure,
 which is barely visible at low density, becomes well developed at high densities and the roton wave vector has a
 strong density dependence. Connection is made with recent inelastic neutron scattering results from highly ordered
 silica nanopores partially filled with
 ⁴He.