Phonon-roton modes in liquid
                    <sup>4</sup>
                    He coincide with Bose-Einstein condensation

Bossy, J.; Ollivier, Jacques; Schober, H.; Glyde, H. R.

doi:10.1209/0295-5075/98/56008

Cited by 17 publications

(41 citation statements)

References 48 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This is consistent with the peak in the density of states (DOS) of phonons in bulk polycrystalline helium between the grains observed previously. 39,46,47 The large peak at ω = 0 is elastic scattering, S(Q, ω = 0), from the amorphous solid in the pores. The elastic scattering from the polycrystalline solid is confined to Bragg peaks and the Q in Fig.…”

Section: Resultsmentioning

confidence: 99%

Excitations of amorphous solid helium

et al. 2012

Self Cite

View full text Add to dashboard Cite

We present neutron scattering measurements of the dynamic structure factor, S(Q, ω), of amorphous solid helium confined in 47Å pore diameter MCM-41 at pressure 48.6 bar. At low temperature, T = 0.05 K, we observe S(Q, ω) of the confined quantum amorphous solid plus the bulk polycrystalline solid between the MCM-41 powder grains. No liquid-like phonon-roton modes, other sharply defined modes at low energy (ω < 1.0 meV) or modes unique to a quantum amorphous solid that might suggest superflow are observed. Rather the S(Q, ω) of confined amorphous and bulk polycrystalline solid appear to be very similar. At higher temperature (T > 1 K), the amorphous solid in the MCM-41 pores melts to a liquid which has a broad S(Q, ω) peaked near ω ≃ 0 characteristic of normal liquid 4 He under pressure. Expressions for the S(Q, ω) of amorphous and polycrystalline solid helium are presented and compared. In previous measurements of liquid 4 He confined in MCM-41 at lower pressure the intensity in the liquid roton mode decreases with increasing pressure until the roton vanishes at the solidification pressure (38 bars), consistent with no roton in the solid observed here.

show abstract

Section: Resultsmentioning

confidence: 99%

Excitations of amorphous solid helium

et al. 2012

Self Cite

View full text Add to dashboard Cite

show abstract

“…In porous media 19,[21][22][23][24]26,[28][29][30][31]34 and in helium films, 35,38,39 a layer mode is also observed. This is a mode that propagates in the 1-4 liquid layers adjacent to the porous media walls.…”

Section: Figmentioning

confidence: 87%

“…The minimum energy is typically ∆ L ≃ 0.5-0.65 meV which is significantly lower than the P-R mode roton minimum, ∆ = 0.742 ± 0.001 eV in bulk liquid 4 He. Both ∆ and ∆ L decrease with increasing pressure 30 .…”

Section: Figmentioning

confidence: 90%

Phonon-roton modes of liquid4He beyond the roton in the porous medium MCM-41

et al. 2013

Self Cite

View full text Add to dashboard Cite

We present neutron scattering measurements of the phonon-roton (P-R) mode of superfluid 4 He confined in 47 Å MCM-41 at T = 0.5 K at wave vectors, Q, beyond the roton wave vector (QR = 1.92 Å−1 ). Measurements beyond the roton require access to high wave vectors (up to Q = 4 Å−1 ) with excellent energy resolution and high statistical precision. The present results show for the first time that at T = 0.5 K the P-R mode in MCM-41 extends out to wave-vector Q ≃ 3.6 Å−1 with the same energy and zero width (within precision) as observed in bulk superfluid 4 He. Layer modes in the roton region are also observed. Specifically, the P-R mode energy, ωQ, increases with Q for Q > QR and reaches a plateau at a maximum energy ωQ = 2∆ where ∆ is the roton energy, ∆ = 0.74 ± 0.01 meV in MCM-41. This upper limit means the P-R mode decays to two rotons when its energy exceeds 2∆. It also means that the P-R mode does not decay to two layers modes. If the P-R could decay to two layer modes, ωQ would plateau at a lower energy, ωQ = 2∆L where ∆L = 0.60 meV is the energy of the roton like minimum of the layer mode. The observation of the P-R mode with energy up to 2∆ shows that the P-R mode and the layer modes are independent modes with apparently little interaction between them.

show abstract

“…In fully filled porous media at SVP, the P-R mode energy is the same as in the bulk liquid within precision, both at low T and as a function of T in all porous media investigated. 12,[17][18][19][20][21][22] To date, the layer mode is observed 12,18,[20][21][22][23][24][25][26][27][28] at wave vectors 1.7Å −1 < Q < 2.3 A −1 only, denoted the roton region. At these wave vectors, the layer mode energy, ω L , has a roton like dispersion with an energy minimum near Q = 2.1Å −1 .…”

Section: 13mentioning

confidence: 99%

“…At this minimum, the mode is denoted the "layer roton" and has an energy, ∆ L , that lies 0.2-0.3 meV below the bulk roton minimum, ∆ = 0.742 ± 0.001 meV. For this reason, the superfluid density at intermediate temperatures 15 and the specific heat 21,29 in porous media are governed by exciting the lower energy layer mode (rather than the P-R mode).…”

Section: 13mentioning

confidence: 99%

Localized Bose-Einstein condensation in disordered liquidHe4films

2015

Self Cite

View full text Add to dashboard Cite

We present neutron scattering measurements of the phonon-roton and layer modes of liquid helium films adsorbed in 25Å pore diameter gelsil as a function of temperature. The goal is to determine whether the well-defined phonon-roton and layer modes observed at low temperature at partial fillings of the porous media persist as well-defined modes at higher temperatures above the superfluid phase, as is the case of fully filled pores (3D liquid). We find that well defined P-R modes exist in films at temperatures well above the superfluid phase. This is the case at all fillings investigated. Liquid 4 He in porous media is an example of a Bose liquid in disorder. The existence of P-R modes above Tc suggests the existence of patches or islands of Bose condensed liquid having long range order (localized Bose-Einstein condensation (LBEC)) above Tc. The interpretation is that the welldefined P-R modes propagate in the patches of BEC. Gelsil partially filled with liquid helium shows the same LBEC behavior as found previously in fully filled gelsil (as in a 3D liquid).

show abstract

Phonon-roton modes in liquid ⁴ He coincide with Bose-Einstein condensation

Cited by 17 publications

References 48 publications

Excitations of amorphous solid helium

Excitations of amorphous solid helium

Phonon-roton modes of liquid4He beyond the roton in the porous medium MCM-41

Localized Bose-Einstein condensation in disordered liquidHe4films

Contact Info

Product

Resources

About

Phonon-roton modes in liquid 4 He coincide with Bose-Einstein condensation

Cited by 17 publications

References 48 publications

Excitations of amorphous solid helium

Excitations of amorphous solid helium

Phonon-roton modes of liquid4He beyond the roton in the porous medium MCM-41

Localized Bose-Einstein condensation in disordered liquidHe4films

Contact Info

Product

Resources

About

Phonon-roton modes in liquid ⁴ He coincide with Bose-Einstein condensation