Superfluid density of He in 98% aerogel in small magnetic fields

We performed low-frequency sound measurements on He in 98% aerogel in a magnetic field that was varied between 0 and 2130 G at a fixed pressure of 27.9 bar. We monitor the frequency of the second sound like sslowd mode, which is the manifestation of superfluidity of He in the presence of correlated disorder, and use its temperature dependence to calculate the superfluid fraction rs /r. We observed no field dependence of the rssTd /r, other than an increase in the temperature range where the A-like sA*d phase is metastable. Both the A* and B phases have a smaller rssTd /r than that of bulk He, and the ratio rs A* /rs B is <0.5 over the whole temperature range. The A* phase does not reappear on warming from the B phase until a field in excess of 1270 Gauss is applied.