Specific heat and dispersion curve for helium II

Donnelly, Russell J.; Donnelly, J. A.; Hills, R. N.

doi:10.1007/bf00117839

Cited by 161 publications

(112 citation statements)

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“…The fit yields a line width of 0:035 cm In bulk liquid He, the roton energy amounts to ca. 6:0 cm ÿ1 [19], which is close to the rotational energy of the (J 1:5) level of free NO. The excess energy when relaxing from the J 0 1:5 to the J 00 0:5 in the gas phase amounts to EJ 2BJ 00 4:965 cm ÿ1 .…”

Section: H Y S I C a L R E V I E W L E T T E R S Week Ending 18 Novemsupporting

confidence: 63%

High-Resolution Spectroscopy of NO in Helium Droplets: A Prototype for Open Shell Molecular Interactions in a Quantum Solvent

Haeften

Metzelthin²,

Rudolph³

et al. 2005

Phys. Rev. Lett.

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We have measured the high-resolution infrared spectrum of the radical NO in the 2 1=2 state in superfluid helium nanodroplets. The features are attributed to the -doubling splitting and the hyperfine structure. The hyperfine interaction is found to be unaffected by the He solvation. For the -doubling splitting, we find a considerable increase by 55% compared to the gas phase. This is explained by a confinement of the electronically excited NO states by the surrounding He. The rotational level spacing is decreased to 76% of the gas phase value. The IR transition to the J 1:5 state is found to be homogeneously broadened. We attribute both observations to the coupling between the molecular rotation and phonon/roton excitations in superfluid 4 He droplets. DOI: 10.1103/PhysRevLett.95.215301 PACS numbers: 67.40.Fd, 33.15.Pw, 33.20.Ea, 33.20.Wr Spectroscopy of molecules in He nanodroplets is a very promising technique for investigating chemical reactions at ultralow temperatures. In such reactions, radicals play an important role [1]. It is, therefore, of interest to probe the influence of the He environment on a radical. While at present quite a number of closed shell molecules have been studied in He droplets [2], only little is known about the influence of the helium droplets on the spectra [3] and the electronic structure of radicals. The infrared spectra of many radicals exhibit hyperfine splitting and -type doubling. These effects are well known in the gas phase but have never been studied in solvents.In this Letter, we report the measurement of the IR spectrum of NO in He droplets. NO is an open shell molecule and has a 2 1=2 electronic ground state. The rotational levels of NO show hyperfine structure and -type doubling. While the hyperfine splitting reflects the magnetic interaction, -type doubling arises from rotational interaction of the ground state with higher electronic states. The coupling to the higher electronic or ÿ states splits the degenerate energy levels of the 2 1=2ground state. We will show that the droplets increase the magnitude of the -type doubling and discuss the implications for the electronically excited states of NO within the He solvent. The lower rotational energy levels of NO lie in the interesting region of the collective excitations of superfluid He. In particular, they are close to the roton excitations. NO is therefore a good candidate to investigate the role of these excitations in the rotational energy relaxation or in the shift of the rotational levels, as recently pointed out by theory [4,5]. For this purpose, NO as a diatomic molecule is ideal because it has only a single vibrational mode. The vibrational energy is much larger than the collective excitations of liquid He (1875 cm ÿ1 10 cm ÿ1 ). Therefore, vibrational relaxation is extremely slow.The experiments have been carried out using a new apparatus at Bochum. The setup is similar to that used by Hartmann et al. and explained in detail elsewhere [5,6]. Here we give only a brief description. Helium is expanded at 40 ...

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Section: H Y S I C a L R E V I E W L E T T E R S Week Ending 18 Novemsupporting

confidence: 63%

High-Resolution Spectroscopy of NO in Helium Droplets: A Prototype for Open Shell Molecular Interactions in a Quantum Solvent

Haeften

Metzelthin²,

Rudolph³

et al. 2005

Phys. Rev. Lett.

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“…The narrow energy resolution of these measurements reveals that the energy of the elementary excitation comes up to twice the roton energy, 2∆, at Q = 2.8Å −1 and the energy remains constant at 2∆ between Q 3.0Å −1 and the end point of the dispersion curve at Q = 3.6Å −1 . The width of the peak is also unobservably small from Q = 2.8Å −1 out to the end point, W = 2Γ < 20 µeV.The energy and lifetime of the elementary phonon-roton excitations (EE) in superfluid 4 He are accurately known at low wave vector up to the roton wave vector, Q ∼ 1.92Å −1 at SVP [1][2][3][4][5]. However, the energy and lifetime of the EE for wave vectors beyond the roton, 2.5 < Q < 3.6Å −1 , are much less well determined.…”

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confidence: 99%

“…The energy and lifetime of the elementary phonon-roton excitations (EE) in superfluid 4 He are accurately known at low wave vector up to the roton wave vector, Q ∼ 1.92Å −1 at SVP [1][2][3][4][5]. However, the energy and lifetime of the EE for wave vectors beyond the roton, 2.5 < Q < 3.6Å −1 , are much less well determined.…”

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Excitations in superfluid ⁴ He beyond the roton

Glyde¹,

Gibbs²,

Stirling³

et al. 1998

Europhys. Lett.

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PACS. 67.40Db -Quantum statistical theory; ground state, elementary excitations. PACS. 61.12−q -Neutron diffraction and scattering.Abstract. -High-energy resolution inelastic neutron scattering data on excitations in superfluid and normal 4 He at SVP at wave vectors Q beyond the roton, 2.0 ≤ Q ≤ 4.0Å −1 , are presented. The narrow energy resolution of these measurements reveals that the energy of the elementary excitation comes up to twice the roton energy, 2∆, at Q = 2.8Å −1 and the energy remains constant at 2∆ between Q 3.0Å −1 and the end point of the dispersion curve at Q = 3.6Å −1 . The width of the peak is also unobservably small from Q = 2.8Å −1 out to the end point, W = 2Γ < 20 µeV.The energy and lifetime of the elementary phonon-roton excitations (EE) in superfluid 4 He are accurately known at low wave vector up to the roton wave vector, Q ∼ 1.92Å −1 at SVP [1][2][3][4][5]. However, the energy and lifetime of the EE for wave vectors beyond the roton, 2.5 < Q < 3.6Å −1 , are much less well determined. This is chiefly because the intensity in the single EE component of the observed dynamic structure factor, S(Q, ω), decreases rapidly with increasing Q beyond the roton and this peak "sits" on a sloping broad component of S(Q, ω) so that high instrument resolution is required to determine the peak position accurately. The excitations at Q values beyond the roton (BTR) are also much less well understood [6-10] and microscopic calculations of the EE energy [11][12][13] reproduce the observed EE energies less well for Q > 2.5Å −1 . In 1959, Pitaevskii proposed that the energy of the single EE, ω Q , had an upper limit. When the energy reached the energy of a pair of lower energy EE's, the single EE would decay into this pair. The single EE energy could not exceed this pair energy without decaying. The pair having the lowest energy which meets the conservation conditions for decay is two rotons. The ω Q should not exceed 2∆. In this picture, at the Q value where ω Q reaches 2∆, the single EE should also broaden. Earlier measurements [14][15][16][17] suggest that ω Q exceeds 2∆ for Q > 2.8Å −1 , particularly at higher pressure. The energies of Cowley and Woods for Q > 2.8Å −1 have been adopted as c EDP Sciences

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“…In particular, in a Bose superfluid, it plays fundamental roles for the superfluidity [2]. Phonon has been observed in various systems such as superfluid 4 He [3], superconducting films [4], atomic superfluid fermi gases [5], as well as Bose-Einstein condensation (BEC) of cold atomic gases [6]. Due to the high degree of controllability, BEC of cold atomic gases offers an opportunity to study novel properties of phonons in the superfluid phase.…”

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Anomalous enhancement of quasiparticle current near a potential barrier in a Bose-Einstein condensate

Tsuchiya

Ōhashi

2008

Phys. Rev. A

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We investigate tunneling properties of Bogoliubov phonons in a Bose-Einstein condensate. We find the anomalous enhancement of the quasiparticle current Jq carried by Bogoliubov phonons near a potential barrier, due to the supply of the excess current from the condensate. This effect leads to the increase of quasiparticle transmission probability in the low energy region found by Kovrizhin et al.. We also show that the quasiparticle current twists the phase of the condensate wavefunction across the barrier, leading to a finite Josephson supercurrent Js through the barrier. This induced supercurrent flows in the opposite direction to the quasiparticle current so as to cancel out the enhancement of Jq and conserve the total current J = Jq + Js.PACS numbers: 03.75. Kk,03.75.Lm,67.85.De Phonon in a superfluid system is an example of Goldstone mode which appears in various fields of physics associated with spontaneous broken symmetry [1]. It is a manifestation of broken (global) U (1) symmetry which underlies the macroscopic quantum nature of the system, and a key to understand the low energy properties of superfluids. In particular, in a Bose superfluid, it plays fundamental roles for the superfluidity [2]. Phonon has been observed in various systems such as superfluid 4 He [3], superconducting films [4], atomic superfluid fermi gases [5], as well as Bose-Einstein condensation (BEC) of cold atomic gases [6]. Due to the high degree of controllability, BEC of cold atomic gases offers an opportunity to study novel properties of phonons in the superfluid phase.Bogoliubov phonon [7] in a BEC has been a longstanding issue of investigation in cold atomic gases [8].In the last few years, quantum tunneling of Bogoliubov phonon has attracted much attention [9,10,11,12,13,14]. Since Bogoliubov phonon is a collective excitation of a BEC, its tunneling property has specific features which are quite different from that of free particles. In fact, an anomalous tunneling property of Bogoliubov phonon has been predicted in [9,10]. It has been shown that the transmission probability of Bogoliubov phonon through a potential barrier increases at low energies and always unity in the zero-energy limit, irrespective of the height of the barrier [9,10]. Although several mechanisms were proposed in [10,11], the underlying physics of this anomalous tunneling has not been understood yet.In this paper, we report alternative anomalous tunneling properties of Bogoliubov phonons. We find that the quasiparticle current is not conserved, but greatly enhanced near the potential barrier at low incident energies, due to the excess current supplied from the condensate. This anomalous enhancement of the quasiparticle current increases the transmission probability of Bogoliubov phonon in the low energy region, which is consistent with the tunneling property in [9,10]. In addition, we show that the quasiparticle current twists the phase of the condensate wavefunction, leading to a Josephson supercurrent through the barrier. The excess part of the quasip...

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Specific heat and dispersion curve for helium II

Cited by 161 publications

References 24 publications

High-Resolution Spectroscopy of NO in Helium Droplets: A Prototype for Open Shell Molecular Interactions in a Quantum Solvent

High-Resolution Spectroscopy of NO in Helium Droplets: A Prototype for Open Shell Molecular Interactions in a Quantum Solvent

Excitations in superfluid ⁴ He beyond the roton

Anomalous enhancement of quasiparticle current near a potential barrier in a Bose-Einstein condensate

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Specific heat and dispersion curve for helium II

Cited by 161 publications

References 24 publications

High-Resolution Spectroscopy of NO in Helium Droplets: A Prototype for Open Shell Molecular Interactions in a Quantum Solvent

High-Resolution Spectroscopy of NO in Helium Droplets: A Prototype for Open Shell Molecular Interactions in a Quantum Solvent

Excitations in superfluid 4 He beyond the roton

Anomalous enhancement of quasiparticle current near a potential barrier in a Bose-Einstein condensate

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Excitations in superfluid ⁴ He beyond the roton