Physics news on the Internet: November 2023

VVDmitriev (P LKapitza IPPRAS) and his co-authors have become the first to carry out the observation of b-phase of superfluid He in nematic aerogel in a strong magnetic field [1]. Under ordinary conditions, superfluid He has only two phases (A and B). In a strongmagnetic field, however, it splits into new phases with different spin compositions of an ensemble of Cooper pairs. If, in addition, He is confined in nematic aerogel (a loose medium of siliceous filaments or another substance) with co-directed filaments, then a strong anisotropy and a polar phasemay appear. EV Surovtsev (IPP RAS and MIPT) predicted in [2, 3] that, under such conditions, He, when cooled, will transfer to the so-called b-phase instead of the purely polar phase, and then to a deformed b-phase with further cooling. Used in the new experiment was nematic aerogel of mullite (a mineral of the silicate class) with elongated pores, in which solid He layers on the filament surface were replaced by He. The aerogel was fixed in a mechanical cavity, and the resonance properties of this system as a function of temperature were examined. The transition of He into one phase or another was accompanied by a change in the superfluid component density and thus affected the resonant frequency and the shape of the resonance curve. This method was used to register the predicted transitions to a superfluid b-phase and a deformed b-phase. The temperature range of the b-phase was found to be proportional to the magnetic field value. For superfluid He phases in aerogel, see also [4].