Excitation of Rotons in Helium II by Cold Neutrons

Palevsky, H.; Otnes, K.; Larsson, K.E.

doi:10.1103/physrev.112.11

Cited by 74 publications

(40 citation statements)

References 9 publications

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“…Besides the well-known phonon mode, there is a clear parabolic minimum at finite quasimomentum in the excitation spectrum. Such a minimum is analogous to a roton excitation in the context of superfluid helium [118][119][120][121] and systems with long-range [122][123][124][125] (or finiterange [126,127]) interactions. However, in this regime the minimum at finite momentum originates from the double well structure of the linear spectrum.…”

Section: Bragg Spectroscopy Indicating Roton-like Excitationmentioning

confidence: 99%

Properties of spin–orbit-coupled Bose–Einstein condensates

et al. 2016

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The experimental and theoretical research of spin-orbit-coupled ultracold atomic gases has advanced and expanded rapidly in recent years. Here, we review some of the progress that either was pioneered by our own work, has helped to lay the foundation, or has developed new and relevant techniques. After examining the experimental accessibility of all relevant spin-orbit coupling parameters, we discuss the fundamental properties and general applications of spin-orbit-coupled Bose-Einstein condensates (BECs) over a wide range of physical situations. For the harmonically trapped case, we show that the ground state phase transition is a Dicke-type process and that spin-orbit-coupled BECs provide a unique platform to simulate and study the Dicke model and Dicke phase transitions. For a homogeneous BEC, we discuss the collective excitations, which have been observed experimentally using Bragg spectroscopy. They feature a roton-like minimum, the softening of which provides a potential mechanism to understand the ground state phase transition. On the other hand, if the collective dynamics are excited by a sudden quenching of the spin-orbit coupling parameters, we show that the resulting collective dynamics can be related to the famous Zitterbewegung in the relativistic realm. Finally, we discuss the case of a BEC loaded into a periodic optical potential. Here, the spin-orbit coupling generates isolated flat bands within the lowest Bloch bands whereas the nonlinearity of the system leads to dynamical instabilities of these Bloch waves. The experimental verification of this instability illustrates the lack of Galilean invariance in the system.

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Section: Bragg Spectroscopy Indicating Roton-like Excitationmentioning

confidence: 99%

Properties of spin–orbit-coupled Bose–Einstein condensates

et al. 2016

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“…The system enters into the solid phase when this gap tends to zero. The shape of the Landau spectrum has been confirmed by neutron-scattering experiments carried out in several different laboratories [9].…”

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confidence: 65%

Effective field theory forHe4

et al. 2006

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We introduce an effective scalar field theory to describe the 4 He phase diagram, which can be considered as a generalization of the XY model which gives the usual λ-transition. This theory results from a Ginzburg-Landau Hamiltonian with higher order derivatives, which allow to produce transitions between the superfluid, normal liquid and solid phases of 4 He. Mean field and Monte Carlo analyses suggest that this model is able to reproduce the main qualitative features of 4 He phase transitions.

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“…This dispersion relation for the liquid at low temperatures under its vapor pressure (i.e., essentially at zero pressure) has been determined in a very direct way by neutron scattering experiments. 13 Recently Henshaw and Woods 14 have repeated this kind of experiment for liquid helium at a pressure of 25.3 atm. Hence the dispersion relation is now known at these two pressures.…”

Section: B Pressure Dependence Of the Mobilitymentioning

confidence: 96%

Ion Motion in Superfluid Liquid Helium under Pressure

1961

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Recent investigations of superfluidity by a study of the mobilities of ions in liquid He n have been extended to the liquid under pressure. At a fixed temperature the positive-ion mobility decreases appreciably as the pressure is increased, particularly at low temperatures. At a fixed pressure the mobility increases less rapidly with decreasing temperature at higher pressures. The negative-ion mobility, smaller than that of the positive ion at zero pressure, becomes equal to that of the latter above 7 atm. In high electric fields and at high pressures, the drift velocity of the negative ions approaches a limiting value roughly equal to the Landau critical velocity for a body moving through the superfluid. The theory, which discusses the mobility in terms of ion scattering by rotons and phonons, is reviewed. It is pointed out that previously neglected effects concerned with the importance of small-angle scattering of the ion ought to be taken into account; some earlier estimates of scattering cross sections are revised accordingly. It is then shown that this theory, making use only of the known change of the roton dispersion relation with pressure, can account quantitatively for the observed pressure dependence of the positive-ion mobilities.

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Excitation of Rotons in Helium II by Cold Neutrons

Cited by 74 publications

References 9 publications

Properties of spin–orbit-coupled Bose–Einstein condensates

Properties of spin–orbit-coupled Bose–Einstein condensates

Effective field theory forHe4

Ion Motion in Superfluid Liquid Helium under Pressure

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