Quasiparticle Beam Research Articles

Ballistic Quasiparticle Generation and Propagation in Superfluid 3He–B

Ballistic quasiparticles are produced by means of a supercritically driven wire resonator in 3He-B at temperatures below 0.25 TC. At 0 bar pressure the observed critical velocity of the wire is about 9 mm/s relative to the container (or about 18 mm/s relative to the maximum superfluid back flow). This velocity scales with (Δ/pF) as a function of pressure, confirming that pair-breaking of the superfluid is the dissipation mechanism. At higher temperatures, the scattering of existing quasiparticles leads to dissipation at much lower velocities. The ballistic propagation of a pulse of quasiparticles through the superfluid is demonstrated by the mechanical force it applies to a second wire resonator at a distance of up to 6 mm. The detector is incorporated into a SQUID circuit to yield an ultra-sensitive force detector. We observe strong signals at the detector at the same frequency as the power dissipation in the generating wire, and of a magnitude proportional to the power dissipation. The order of magnitude of these signals agrees with a simple theoretical model of ballistic quasiparticle propagation. Comparison of the received forces from a number of different driving wires suggests that the quasiparticles are emitted with almost cylindrical symmetry, with a low flux emitted parallel to the wire axis. The phase of the received signals at 0 bar indicates that the propagation is rapid. The small reduction in signal as the temperature is raised shows that the attenuation of the quasiparticle beam is low. Future experiments are proposed on the influence of Andreev scattering of quasiparticles from a super flow field.

Tunneling of quasiparticles between two weakly coupled systems of superfluid helium

Quasiparticle tunneling in a weakly coupled system of liquid helium is theoretically studied, in analogy with normal electron tunneling of superconductor junctions. Chemical potential difference in this case is to be created across the junction by a superfluid flow parallel to the junction. Calculation shows that a collimated beam of quasiparticles would show several divergences of tunneling current at specific angles of incidence or at specific values of superfluid velocity, while no divergence is expected for the integrated current, which is an important difference from the case of superconductor junctions.