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The breakdown of superfluidity in liquid 4He : an experimental test of Landau's theory.

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<mark>Journal publication date</mark>4/01/1977
<mark>Journal</mark>Philosophical Transactions of the Royal Society of London A
Issue number1320
Number of pages46
Pages (from-to)179-224
Publication StatusPublished
<mark>Original language</mark>English


A single pulse time of flight technique has been used to determine the drift velocity v of the negative ions injected into liquid 4He from a field emission source. Measurements of v as a function of temperature T, pressure P and electric field E are presented within the range: 0.29 < T < 0.5 K; 21 x 10^5 < P < 25 x 10^5 Pa; 1 < E < 300 kV/m. The experimental results are in good agreement with Landau's theory of superfluidity. The data are used to demonstrate the inapplicability of two theories of super critical dissipation: by Takken, based on an assumption of coherent roton emission; and by Bowley and Sheard, based on the assumption of incoherent single-roton emission. The results are, however, shown to be in excellent agreement with Bowley and Sheard's incoherent two-roton theory, and the data are used to derive a numerical value of the matrix element. characterizing two-roton emission. The surprising absence of the single-roton emission process is discussed, and an upper bound is placed on the relevant matrix element.