Ultrasound attenuation and a P-B-T phase diagram of superfluid 3He in 98% aerogel

TL;DR

This study maps the phase diagram of superfluid 3He in 98% aerogel using ultrasound attenuation measurements, revealing unique magnetic field effects on the A-B transition compared to bulk superfluid.

Contribution

It provides the first detailed phase diagram of superfluid 3He in aerogel under varying pressure, temperature, and magnetic field, highlighting differences from bulk behavior.

Findings

A-B phase boundary shifts differently in aerogel than in bulk with increasing magnetic field.

Ultrasound attenuation effectively identifies phase transitions in superfluid 3He in aerogel.

The phase diagram shows a receding A-B boundary under magnetic field in aerogel.

Abstract

Longitudinal sound attenuation measurements in superfluid 3He in 98% aerogel were conducted at pressures between 14 and 33 bar and in magnetic fields up to 4.44 kG. The temperature dependence of the ultrasound attenuation in the A-like phase was determined for the entire superfluid region exploiting the field induced meta-stable A-like phase at the highest field. In the lower field, the A-B transition in aerogel was identified by a smooth jump in attenuation on both cooling and warming. Based on the transitions observed on warming, a phase diagram as a function of pressure (P), temperature (T) and magnetic field (B) is constructed. We find that the A-B phase boundary in aerogel recedes in a drastically different manner than in bulk in response to an increasing magnetic field. The implications of the observed phase diagram are discussed.