Roton propagation and phonon-roton scattering in He II

Journal Article · Thu Apr 01 04:00:00 EST 1976 · Phys. Rev., B, v. 13, no. 7, pp. 2898-2909

DOI:https://doi.org/10.1103/PhysRevB.13.2898· OSTI ID:4015508

Narayanamurti, V; Dynes, R C

The propagation characteristics of high-energy excitations in He II are studied as a function of pressure, temperature, and frequency by means of a superconducting Sn fluorescent generator and a Sn tunnel detector and time-of- flight techniques. At saturated vapor pressure and low temperatures (T approx. = 0.1 K) and with the detector energy gap possessing its full value ( approx. 14 K), a single well-defined pulse is observed to arrive at a time corresponding to that expected for the first echo (three traverses of the cell) of a low-energy phonon. This ''echo pulse'' disappears as the pressure is raised to 10 +- 2 bar and one observes a driven roton second sound at higher pressures. The echo pulse is interpreted as arising from a collinear interaction near the detector of a low- energy phonon with ''fast'' rotons (group velocity approximately equals the sound velocity c$sub 0$) by means of a three-particle interaction (phonon + roton $Yields$ roton) first suggested by Pitaevskii. The data indicate that this Pitaevskii process turns off at high pressures and only the four-particle process (phonon + roton $Yields$ phonon + roton) remains. With increasing magnetic field on the detector, ballistic phonons are observed as expected. The scattering of these ballistic phonons and a cloud of rotons are probed by means of a novel double-pulse technique and provides strong evidence for the existence of this collinear three-particle interaction at low pressures. (AIP)

• Research Organization: Bell Laboratories, Murray Hill, New Jersey
• Sponsoring Organization: USDOE
• NSA Number: NSA-33-031609
• OSTI ID: 4015508
• Journal Information: Phys. Rev., B, v. 13, no. 7, pp. 2898-2909, Journal Name: Phys. Rev., B, v. 13, no. 7, pp. 2898-2909; ISSN PLRBA
• Country of Publication: United States
• Language: English

Related Subjects

*HELIUM II-- ROTONS
640700*
EXCITATION
N66100* --Physics (Low Temperature)--Superfluidity
PHONONS
SCATTERING
SECOND SOUND