Interfacial Energy of the Superfluid ${}^3\mathrm{H}\mathrm{e}$ $A\mathrm{\text{−}}B$ Phase Interface in the Zero-Temperature Limit

We have measured the surface energy of the interface between the $A$ and $B$ phases of superfluid ${}^3\mathrm{H}\mathrm{e}$ in the low temperature limit at zero pressure. Using a shaped magnetic field, we control the passage of the phase boundary through a small aperture. We obtain the interphase surface energy from the over- or undermagnetization required to force the interface through the aperture in both directions, yielding values of the surface tension and the interfacial contact angle. This is the first measurement of the interfacial energy in high magnetic fields and in the zero-temperature limit.

Figure 1

The inner experimental cell and the field profile used to manipulate the $A\mathrm{\text{−}}B$ phase interface.

Figure 2

The measured temperature as the interface moves through the cell during up and down ramps of the main solenoid current, versus the magnetic field at the grid relative to the equilibrium critical field $B_{AB}$. For labeled features see text. The horizontal dotted line marks the position of $B_{AB}$.

Figure 3

The field-gradient dependence of the excess magnetic field needed to pop the interface through the central aperture. Filled points: $B$ phase expanding into $A$ phase. Empty points: vice versa. The dashed line shows the calculated gradient dependence with the surface tension ${\sigma }_{AB}$ as a fitting parameter (see text).