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Persistent URL http://purl.org/net/epubs/work/66060
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Record Id 66060
Title Phonon-roton modes of liquid ^4He beyond the roton in the porous medium MCM-41
Abstract We present neutron scattering measurements of the phonon-roton (P-R) mode of superfluid 4He 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. Only one previous measurement in porous media (in aerogel) with low statistical precision has been reported. At T=0.5 K, we find that 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 4He. 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=2Δ where Δ is the roton energy, Δ=0.74 ± 0.01 meV in MCM-41. This upper limit means the P-R mode decays to two rotons if its energy exceeds 2Δ. 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=2ΔL, where ΔL=0.60 meV is the energy of the roton-like minimum of the layer mode. Rather the P-R mode and the layer modes observed in porous media appear to be quite different modes with little interaction between them.
Organisation ISIS , ISIS-OSIRIS , STFC
Keywords ISIS 2013
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Language English (EN)
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Journal Article Phys Rev B 88, no. 2 (2013): 024510. doi:10.1103/PhysRevB.88.024510 2013