Does a persistent current exist in a superfluid helium film?

Wagner, F. E.

doi:10.1007/bf00654405

Cited by 9 publications

(3 citation statements)

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“…Although such currents have been observed in filter material 1 and Vycor, 2 previous attempts to observe these currents in similar open geometries have not been successful. 3 ' 4 This led to the suggestion that high-quantum-number circulation states may be very unstable. 4 Recent experiments 5,6 in saturated films have shown this suggestion to be incorrect for those films.…”

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confidence: 99%

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Stability of Persistent Currents in Unsaturated SuperfluidHe4Films

Telschow

Hallock

1976

Phys. Rev. Lett.

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Phys. Chem. Liq. 2, 213 (1971). 12 C. A. Tracy and B 0 M. McCoy, Phys. Rev. B JL2, 368 (1975).We report the first observation of persistent currents in unsaturated superfluid 4 He films on a large-diameter glass substrate in an open geometry. Although such currents have been observed in filter material 1 and Vycor, 2 previous attempts to observe these currents in similar open geometries have not been successful. 3 ' 4 This led to the suggestion that high-quantum-number circulation states may be very unstable. 4 Recent experiments 5,6 in saturated films have shown this suggestion to be incorrect for those films. We present here the first measurements of the stability of persistent currents in unsaturated superfluid films as a function of film thickness at constant temperature and observe a strong thickness dependence for films thinner than about 12 atomic layers. Currently it is believed that thermally activated dissipation is responsible for the decay of persistent currents near critical velocity. 7 The observed behavior of our decays places strong restrictions on models used in this theory in the case of films. The decay of the flow velocity becomes immeasurably small for films thicker than 12 atomic layers. For these thicker films we find the circulation stable with respect to translation and to changes in the film thickness through condensation and evaporation.The persistent currents are produced on the outside of a cylindrical Pyrex glass ring with posts 13 A. . attached to it schematically shown in Fig. 1(a). To produce the thin films investigated here the entire apparatus is enclosed in a copper cell where the pressure is maintained at a value below the saturated vapor pressure at the chosen operating temperature of 1.45 K. The film thick-GLASS .SUBSTRATE HEATERS ^^" ^\ Nef^5 ^^^^ HEATER S H f^^^L^C^AL. STRIPS V S2 ~4 , Is 1 " 0 -^A 1 V S 3 V S1 FIG. 1. (a) Pyrex glass ring substrate of average perimeter l t +l 2 =21.15± 0.2 cm. The long-to shortflow-path ratio l 2 /l t is 15.63 with height of 0.73 cm and thickness of 0 o 24 cm. The aluminum strips are on the outer side and directly opposite the two posts. (b) Schematic of the flow paths. We report the first measurements of the stability of persistent currents in unsaturated 4 He films in an open geometry. Persistent currents are generated without rotation and exhibit several features which place strong restrictions on models of thermally activated dissipation in thin films. 1484

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“…910 The wirewound heater S and an extra aluminum strip heater S H were used to generate and destroy persistent currents as will be described later. The application of heat by heater Q results in a film flow velocity V s3 related to Q by Q=p sf V s3 xdP 3 …”

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Stability of Persistent Currents in Unsaturated SuperfluidHe4Films

Telschow

Hallock

1976

Phys. Rev. Lett.

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“…In Ref. 3 it was speculated that the reason for this metastability is a fast decay of the high quantized cylindrical .container.…”

Section: V = (V~o -V2) 1/2 (2)mentioning

confidence: 99%

Persistent currents in saturated He II films detected through film flow measurements: Addendum to ?Does a persistent current exist in a superfluid helium film??

Wagner

1976

J Low Temp Phys

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The existence of a persistent current in a saturated He ll film which is adsorbed on the walls of a container of typical dimensions 1 cm is demonstrated. The persistent current is produced by rotation and detected by measuring the critical film flow rate.The conditions for the successful excitation of persistent currents in saturated helium films are still unexplored. In one case t'z persistent currents in saturated helium films have been successfully generated inside closed annuli made of metal or glass capillaries. In these experiments persistent currents are detected via the kinetic energy of the mass flow, which excites level oscillations in partly filled containers connected to the loop. No persistent currents have been observed in cylindrical containers of typical dimension 1 cm. 3"4 Here the cylinder, whose walls were covered by the film, was rotated in an attempt to produce a superfluid mass flow. The detection of persistent currents was by measuring either the critical film flow rate as a function of the container wall velocity 3 or the Doppler shift of the third sound velocity. 4In this paper we describe experiments in which we have observed persistent currents in saturated films adsorbed on the walls of a comparatively large cylindrical container. The presence of a persistent current was demonstrated by measuring the critical film flow rate R c. Film flow could be thermally induced in a cylindrical container parallel to the axis about which it could *"Does a Persistent

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