Modes of Atomic Motions in Liquid Helium by Inelastic Scattering of Neutrons

Henshaw, D. G.; Woods, A. D. B.

doi:10.1103/physrev.121.1266

Cited by 387 publications

(126 citation statements)

References 29 publications

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“…6(a) [60]. The system loses superfluidity with this mechanism well below T BE = 3.2 K. Although its energy ω rtn corresponds to about 4k B T c , the thermal excitation to the roton minimun has a large weight in the phase space thanks to a substantial momentum transfer of ∼ 2.0Å −1 , and ω rtn becomes a primary determining factor for T c .…”

Section: Excitation: Magnetic Resonance Mode As a Roton Analoguementioning

confidence: 99%

“…The YBCO data in (a) shows even further reduction from this "TKT jump" [57] value as the Tc is approached. 4 He observed by neutron scattering [60]. (b) The plot of Tc versus energy of the roton minimum of bulk superfluid 4 He (values for both axes multiplied by a factor 60) measured under applied pressures [61], compared with the relationship seen in HTSC systems for the energies of the neutron resonance mode at (π, π) [15][16][17][18] and the Raman A1g mode [19][20][21][22].…”

Section: Acknowledgmentmentioning

confidence: 99%

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Condensation, excitation, pairing, and superfluid density in high-T_c superconductors: the magnetic resonance mode as a roton analogue and a possible spin-mediated pairing

Uemura¹

2004

J. Phys.: Condens. Matter

100

123

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To find out a primary determing factor of Tc and a pairing mechanism in high-Tc cuprates, we combine the muon spin relaxation results on ns/m * (superconducting carrier density / effective mass), accumulated over the last 15 years, with the results from neutron and Raman scattering, STM, specific heat, Nernst effect and ARPES measurements. We identify the neutron magnetic resonance mode as an analogue of roton minimum in the superfluid 4 He, and argue that ns/m * and the resonance mode energy ωres play a primary role in determining Tc in the underdoped region. We propose a picture that roton-like excitations in the cuprates appear as a coupled mode, which has the resonance mode for spin and charge responses at different momentum transfers but the same energy transfers, as detected respectively, by the neutron S=1 mode and the Raman S=0 A1g mode. We shall call this as the "hybrid spin/charge roton". After discussing the role of dimensionality in condensation, we propose a generic phase diagram of the cuprates with spatial phase separation in the overdoped region as a special case of the BE-BCS crossover conjecture where the superconducting coupling is lost rapidly in the overdoped region. Using a microscopic model of charge motion resonating with antiferomagnetic spin fluctuations, we propose a possibility that the hybrid spin/charge roton and higher-energy spin fluctuations mediate the superconducting pairing. In this model, the resonance modes can be viewed as a meson-analogue and the "dome" shape of the phase diagram can be understood as a natural consequence of departure from the competing Mott insulator ground state via carrier doping.

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Section: Excitation: Magnetic Resonance Mode As a Roton Analoguementioning

confidence: 99%

Section: Acknowledgmentmentioning

confidence: 99%

Condensation, excitation, pairing, and superfluid density in high-T_c superconductors: the magnetic resonance mode as a roton analogue and a possible spin-mediated pairing

Uemura¹

2004

J. Phys.: Condens. Matter

100

123

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“…Calculating the excitation energy requires knowledge of the process by which the photons impart momentum and energy to the BEC. Analogously, excitations in superfluid 4 He were observed indirectly, by measuring the momenta and the energies of scattered neutrons [6]. The phonon energy is much larger than that of a free particle with the same momentum, and consists mostly of interaction energy between the phonon and the condensate.…”

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confidence: 99%

Direct Observation of the Phonon Energy in a Bose-Einstein Condensate by Tomographic Imaging

et al. 2002

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The momentum and energy of phonons in a Bose-Einstein condensate are measured directly from a time-of-flight image by computerized tomography. We find that the same atoms that carry the momentum of the excitation also carry the excitation energy. The measured energy is in agreement with the Bogoliubov spectrum. Hydrodynamic simulations are performed which confirm our observation.In a Bose-Einstein condensate (BEC), the long wavelength excitations are phonons, characterized by a linear dispersion relation, as well as a wave function consisting of atoms with positive and negative momenta. Both the dispersion relation and the wave function were measured indirectly, by Bragg spectroscopyA two-photon Bragg process coherently imparts an energy ω and momentum k, determined by the frequency difference and the angle between the Bragg beams, to the condensate [3]. In Bragg spectroscopy, the two-photon energy ω is varied, and the response of the BEC to the two-photon Bragg transition is observed [4] [5] [1]. Thus, the directly measured energy is the photon energy. Calculating the excitation energy requires knowledge of the process by which the photons impart momentum and energy to the BEC. Analogously, excitations in superfluid 4 He were observed indirectly, by measuring the momenta and the energies of scattered neutrons [6]. The phonon energy is much larger than that of a free particle with the same momentum, and consists mostly of interaction energy between the phonon and the condensate. When the trapping potential is turned off, all the interaction energy is transformed into kinetic energy during a short acceleration period [7].In this letter we present a direct measurement of this energy from time-of-flight (TOF) images of the released atoms. Previously the ground state interaction energy of the condensate was also measured from TOF absorption images [7]. Since absorption images provide only the density of the cloud integrated along the axis of the absorption beam, whereas energy measurements require knowledge of the full density distribution, fits to model functions of the density were needed [7]. Here we use computerized tomography of the TOF absorption images, in which the cylindrical symmetry of the cloud is used to reconstruct the full density profile from a single absorption image.Several measurements are performed using this technique. First, the ground state interaction energy of a released, unexcited BEC is measured and compared to the value extracted from a fit to the radial size of the absorption image. Second, the density distribution of a Bragg-excited condensate is reconstructed. A clear separation between a released-phonon cloud and a condensate cloud, which is not clear in the original absorption image, is visible. The energy and momentum added to the cloud by the Bragg pulse are measured from the reconstructed image. In this way the excitation energy is found without sweeping through frequencies, and by looking directly at images of the atoms. Finally, the energy carried by the released phonons is meas...

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“…This dispersion underpins our understanding of superfluidity in helium, and explains many experiments on heat capacity and superfluid critical velocity. What is now called the "rotonmaxon" dispersion in He II has been precisely measured in neutron scattering experiments [3,4] and is generally considered a hallmark of Bose superfluids in the strong interaction regime.The roton-maxon dispersion carries a number of intriguing features that distinguish excitations in different regimes. The low-lying excitations are acoustic phonons with energy E = pv s , where p is the momentum and v s is the sound speed.…”

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confidence: 99%

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Roton-Maxon Excitation Spectrum of Bose Condensates in a Shaken Optical Lattice

et al. 2015

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We present experimental evidence showing that an interacting Bose condensate in a shaken optical lattice develops a roton-maxon excitation spectrum, a feature normally associated with superfluid helium. The roton-maxon feature originates from the double-well dispersion in the shaken lattice, and can be controlled by both the atomic interaction and the lattice modulation amplitude. We determine the excitation spectrum using Bragg spectroscopy and measure the critical velocity by dragging a weak speckle potential through the condensate -both techniques are based on a digital micromirror device. Our dispersion measurements are in good agreement with a modified Bogoliubov model.PACS numbers: 03.75. Kk, 05.30.Jp, 37.10.Jk, In his seminal papers in the 1940s [1,2], L. D. Landau formulated the theory of superfluid helium-4 (He II) and showed that the energy-momentum relation (dispersion) of He II supports two types of elementary excitations: acoustic phonons and gapped rotons. This dispersion underpins our understanding of superfluidity in helium, and explains many experiments on heat capacity and superfluid critical velocity. What is now called the "rotonmaxon" dispersion in He II has been precisely measured in neutron scattering experiments [3,4] and is generally considered a hallmark of Bose superfluids in the strong interaction regime.The roton-maxon dispersion carries a number of intriguing features that distinguish excitations in different regimes. The low-lying excitations are acoustic phonons with energy E = pv s , where p is the momentum and v s is the sound speed. At higher momenta, the dispersion exhibits both a local maximum at p = p m with energy E = ∆ m and a minimum at p = p r with energy E = ∆ r . The elementary excitations associated with this maximum and minimum are known as maxons and rotons, respectively. The roton excitations, in particular, are known to reduce the superfluid critical velocity below the sound speed. This is best understood based on the Landau criterion for superfluidity in which the critical velocity set by the roton minimum v c ≈ ∆ r p r is lower than the sound speed v s . The roton minimum also suggests the emergence of density wave order [5] and dynamical instability [6].To explore the properties of these unconventional excitations, many theoretical works have proposed schemes for producing the roton-maxon dispersion outside of the He II system. Many proposals have been devoted to atomic systems with long-range or enhanced interactions, e.g. dipolar gases [6][7][8], Rydberg-excited condensates [9], or resonantly interacting gases [10]. Other candidates are 2D Bose gases [11,12], spinor condensates [13,14], and spin-orbit coupled condensates [15,16]. Experimentally, mode softening resulting from cavity-induced interaction has recently been reported [17], which provides strong evidence for an underlying rotonlike excitation spectrum.In this Letter, we generate and characterize an asymmetric roton-maxon excitation spectrum based on a Bose-Einstein condensate (BEC) in a one dimensio...

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Modes of Atomic Motions in Liquid Helium by Inelastic Scattering of Neutrons

Cited by 387 publications

References 29 publications

Condensation, excitation, pairing, and superfluid density in high-T_c superconductors: the magnetic resonance mode as a roton analogue and a possible spin-mediated pairing

Condensation, excitation, pairing, and superfluid density in high-T_c superconductors: the magnetic resonance mode as a roton analogue and a possible spin-mediated pairing

Direct Observation of the Phonon Energy in a Bose-Einstein Condensate by Tomographic Imaging

Roton-Maxon Excitation Spectrum of Bose Condensates in a Shaken Optical Lattice

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Modes of Atomic Motions in Liquid Helium by Inelastic Scattering of Neutrons

Cited by 387 publications

References 29 publications

Condensation, excitation, pairing, and superfluid density in high-Tc superconductors: the magnetic resonance mode as a roton analogue and a possible spin-mediated pairing

Condensation, excitation, pairing, and superfluid density in high-Tc superconductors: the magnetic resonance mode as a roton analogue and a possible spin-mediated pairing

Direct Observation of the Phonon Energy in a Bose-Einstein Condensate by Tomographic Imaging

Roton-Maxon Excitation Spectrum of Bose Condensates in a Shaken Optical Lattice

Contact Info

Product

Resources

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Condensation, excitation, pairing, and superfluid density in high-T_c superconductors: the magnetic resonance mode as a roton analogue and a possible spin-mediated pairing

Condensation, excitation, pairing, and superfluid density in high-T_c superconductors: the magnetic resonance mode as a roton analogue and a possible spin-mediated pairing