New Phases Stabilized by Anisotropic Impurity in $^3$He

We have introduced anisotropic impurity into superfluid $^3$He using well-characterized silica aerogel samples negatively strained by mechanical compression along the cylinder axis by $\approx 10\%$, $20\%$, and $30\%$. Using NMR measurements, we determined the temperature-magnetic field phase diagrams for these amounts of strain. In previous work it was found that in the presence of negative strain of $\approx 20\%$ the superfluid A-phase is only stable above a critical magnetic field, $H_c$.\footnote{ J.I.A. Li {\it et al.}, Phys. Rev. Lett. \textbf{112}, 115303 (2014).} We have found $H_c^2$ increases linearly with strain. By comparing the measured NMR longitudinal resonance frequency to results from unstrained isotropic aerogel, we have determined that in the presence of negative strain the B-phase evolves into a new anisotropic phase. This new anisotropic phase is more stable than the A-phase for fields below $H_c$. This work was supported by the National Science Foundation, DMR-1103625.