Superfluid $\beta$ phase of ${}^3\mathrm{He}$

It is known that in low magnetic fields the superfluid transition of ${}^3\mathrm{He}$ in nematic aerogel occurs into the polar phase. Using a vibrating aerogel resonator, we observe that in high magnetic fields this transition splits into two discrete transitions, occurring at different temperatures. According to theoretical models, a new superfluid phase—the $\beta$ phase—should be realized between these two transitions. The temperature range of existence of the new phase is measured as a function of magnetic field. The results are well consistent with theoretical expectations for the $\beta$ phase.

Figure 1

Scanning electron microscope image of the free surface of mullite aerogel sample.

Figure 2

The sketch of the experimental cell.

Figure 3

Temperature dependencies of FWHM (solid circles) and frequency (open circles) of the main resonance of the VW resonator measured in magnetic field of 10.25 kOe at excitation current of 0.4 mA. Arrows indicate the features we associate with $T_{P2}$, $T_{P1}$, $T_{A2}$, and $T_{A1}$. $T_c$ is a superfluid transition temperature of bulk ${}^3\mathrm{He}$ in zero magnetic field. $P=15.4\mathrm{bar}$.

Figure 4

Temperature dependencies of the FWHM of the main resonance of the VW resonator measured in magnetic fields of 10.25 (solid circles), 8.2 (open circles), 6.15 (open triangles), and 4.1 kOe (solid triangles) at corresponding excitation currents of 0.4, 0.5, 0.67, and 1 mA. For a better view, the arrows mark $P_1$, $P_2$, $A_1$, and $A_2$ features only for $H=4.1\mathrm{kOe}$. $\mathrm{P}=15.4\mathrm{bar}$.

Figure 5

$P_1–P_2$ splitting of the superfluid transition of ${}^3\mathrm{He}$ in nematic aerogel in magnetic field. Open and solid circles indicate transitions between distorted $\beta$ and $\beta$, $\beta$, and normal phases, respectively. Lines are linear approximations of experimental data.