Probing “Cosmological” Defects in Superfluid ${}^3\mathrm{He}\mathrm{\text{−}}\mathrm{B}$ with a Vibrating-Wire Resonator

We report on the observation of an anomalously high damping measured by a vibrating-wire resonator (VWR) immersed into superfluid ${}^3\mathrm{He}\mathrm{\text{−}}\mathrm{B}$ at ultralow temperatures. The observed dissipation is orders of magnitude above that corresponding to friction with the dilute normal fraction and superfluid vortices. A clear pinning behavior is also observed, as well as a strong magnetic field dependence. Our analysis points to the interaction of the VWR with a planar topological defect, analogue to cosmological vacua defects, as proposed by Salomaa and Volovik.

Figure 1

Bolometric cell containing superfluid ${}^3\mathrm{He}$. The $\varphi =4.5\mu \mathrm{m}$-VWR ($T$-VWR) serves for thermometry and the $\varphi =13\mu \mathrm{m}$-VWR (heater) for the bolometric calibration.

Figure 2

Collapse of the resonance line on lowering the drive at fields below 60–70 mT. This behavior was observed in all of the 4 anomalous experimental runs in which we went to lower fields. The resonance frequency decrease at low drives indicates the enhancement of the oscillating mass.

Figure 3

Strongly nonlinear force-velocity relation of anomalously damped $T$-VWR at 55 mT. The collapse of the response at low drives suggests a pinning of the wire. $F_p$ is defined as the force at which the VWR response deviates from the linear high velocity extrapolation by a factor 2.

Figure 4

Dramatic increase of the pinning force as the field is lowered to a critical field. The vertical arrows indicate the fields at which the $T$-VWR was completely trapped, before the spontaneous and sudden disappearance of the anomalous damping or pinning effect.

Figure 5

Suggested scenario of the domain wall in the superfluid, when present on the $T$-VWR. The defect thickness is of the order of ${\xi }_0\sim 90\mathrm{nm}$. Note that the oscillation amplitude $X$ is generally much smaller than the VWR diameter $\Phi =4.5\mu \mathrm{m}$.