Abstract:

The quantum second virial coefficient Bq of 3He↑ gas is determined in the temperature range 0.001-4 K from the Beth-Uhlenbeck formula. The corresponding phase shifts are calculated from the Lippmann-Schwinger equation using a highly-accurate matrix-inversion technique. A positive Bq corresponds to an overall repulsive interaction; whereas a negative Bq represents an overall attractive interaction. It is found that in the low-energy limit, Bq tends to increase with increasing spin polarization. The compressibility Z is evaluated as another measure of nonideality of the system. Z becomes most significant at low temperatures and increases with polarization. From the pressure-temperature (P-T) behavior of 3He↑  at low T, it is deduced that P decreases with increasing T below 8 mK.