کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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1815780 | 1525262 | 2007 | 6 صفحه PDF | دانلود رایگان |
We show for the first time high-resolution excitation spectra of bulk superfluid and liquid 4He obtained in a wide energy range (0–3 meV) in a broad temperature interval 0.6–2.5 K. The experiments were performed at 0.4 bar constant liquid pressure on the time-of-flight crystal analyser neutron spectrometer IRIS at the ISIS Facility. There is a real gap in resolution between neutron spin echo or exact-backscattering spectroscopy and other conventional time-of-flight or triple-axis-spectrometer measurements, which at the moment can only be covered by IRIS. The unique combination of high resolution and wide dynamic range accessible on this inverted geometry spectrometer allowed for a non-conventionally detailed line-shape analysis of the roton excitations and made possible the separation of the roton and the higher-energy broad components. We provide the high-resolution evidence of a remainder single-phonon response at the extrapolated roton energy above Tλ. We conclude that the superfluid phase transition manifests itself in the strong slowdown of the variation of the single-phonon line shape with increasing temperature, rather than in the total disappearance of the signal.
Journal: Physica B: Condensed Matter - Volume 388, Issues 1–2, 15 January 2007, Pages 43–48