Observation of an electromagnetic absorption peak in the millimeter wave range in liquid helium at the superfluid λ transition

Resonance Microwave Absorption in He II

“…Note that earlier the maximum of dielectric losses (f = 36.6 GHz) [10] and a sharp decrease in the Q-factor accompanied by hysteretic effects (f = 73.7 GHz) were also observed for the electromagnetic wave propagated in the liquid helium at temperatures in the vicinity of λpoint.…”

“…The losses can be brought about by consumption of the a.c. electric field energy of the wave to create phonons with energy 2 -4 K in He II. The process intensity rises on approaching the λ-point (see [10]) presumably due to the fluctuations in the vicinity of the phase transition. Fig.…”

“…It is expected that the electric component of a MW will generate superfluid and normal flows in He II which, in turn, will interact with the MW. In addition to previous studies of MW absorption in He II [9][10][11], we use microwaves of substantially higher frequencies comparable with typical frequencies of rotons.…”

A New Concept of Open ${\rm TE}_{011}$ Cavity

“…The relationship between r and l is monotonic; such property allows obtaining the resonance frequency of an arbitrary geometry. a 0 17.64 a 1 -522.62 a 2 7021 a 3 -54208.7 a 4 265156 a 5 -852422 a 6 1.80184E6 a 7 -2.4161E6 a 8 1.86592E6 a 9 -632737 Table. Coefficients of the 9 th degree polynomial function fitting the mode chart curve. The standard deviation of the fit is 1.06*10 -4 .…”

“…The millimeter wave region of the electromagnetic spectrum knew in the last years a rapidly growing activity, following the improved accessibility to these wavelengths guaranteed by the development in source and detector technology. A relevant effort was in particular dedicated to the realization of the basic passive components of a typical spectroscopic setup, as low-loss waveguides [1], polarizers [1,2], non-reciprocal elements [3], and resonators [4][5][6]. In the last case, the solutions commonly adopted at millimeter wavelengths are borrowed from the adjacent spectral regions, where the technology of the resonant cavities is well established.…”