We use neutron absorption in rotating 3He-B to heat locally a 10 micrometer-size volume into normal phase. When the heated region cools back in microseconds, vortex lines are formed. We record with NMR the number of lines as a function of superflow velocity and compare to the Kibble-Zurek theory of vortex-loop freeze-out from a random network of defects. The measurements confirm the calculated loop-size distribution and show that also the superfluid state itself forms as a patchwork of competing A and B phase blobs. This explains the A to B transition in supercooled neutron-irradiated 3He-A.
Postscript from: Los Alamos, Zaragoza, Trieste, Paris, Augsburg, Southampton, Moscow.
It is now well-recognized that the Universe may behave like a condensed matter system in which several phase transitions have taken place. Superconductors and the superfluid phases of 3He are condensed matter systems with useful similarities to the Universe: they both contain Bose fields (order parameter) and Fermions (quasiparticles) which interact in a way similar to the interaction of Higgs and gauge particles with fermions in particle physics. This analogy allows us to simulate many properties of the cosmologically relevant physical (particle physics) vacuum in condensed matter, while direct experiments in particle physics are still far from realization. Recently, the anomalous generation of momentum (called ``momentogenesis'') was experimentally confirmed in 3He: in the non-trivial background of a moving 3He vortex, quantum effects gave rise to the production of quasiparticles with momentum which were detected by measuring the force on the vortex. This phenomenon is based on the same physics as the anomalous generation of matter in particle physics and bears directly on the cosmological problem of why the Universe contains much more matter than antimatter (``baryogenesis''). Here we report the experimental observation of the effect opposite to momentogenesis: the conversion of quasiparticle momentum into a non-trivial order parameter configuration or ``texture''. The corresponding process in a cosmological setting would be the creation of a primordial magnetic field due to changes in the matter content.
Postscript from: Los Alamos, Zaragoza, Trieste, Paris, Augsburg, Southampton, Moscow.
A new experiment has been performed to study the formation of topological defects (quantized vortices) during rapid quenches of liquid 4-He through the superfluid transition, with particular care taken to minimise vortex creation via conventional hydrodynamic flow processes. It is found that the generated vortices, if any, are being produced at densities at least two orders of magnitude less than might be expected on the basis of the Kibble-Zurek mechanism.
The early Universe is believed to have undergone a sequence of very rapid phase transitions. Defect formation in these transitions has been suggested as the source for the anisotropy in the cosmic background radiation and the large-scale structure in the distribution of visible mass. So far controlled laboratory experiments have not been performed on homogeneous second order phase transitions as a function of transition speed and a freeze-out of topological defects has not been convincingly demonstrated. Recently a new phenomenon was discovered in rotating superfluid 3He-B: the formation of quantized vortices within bulk superflow in the presence of ionizing radiation. This ``mini bang'' allows one to explore the superfluid transition within the clean bulk medium on the microsecond time scale. The experiment appears to provide the first quantitative test of the theories on defect formation in a time-dependent second order phase transition. This is one example among several analogies, such as baryogenesis or generation of primordial magnetic fields, where quantized vortices and other defects in the 3He superfluids provide a connection to quantum field theory and its applications to cosmology.
Postscript from: Los Alamos, Zaragoza, Trieste, Paris, Augsburg, Southampton, Moscow.
Proceeding of Cosmo 97, August 1997, Ambleside UK . Proc. Cosmo 97, World Scientific, 1998.
Recent measurements in superfluid 3He-B have been interpreted as evidence in support of the Kibble-Zurek hypothesis for the formation of defects in the early Universe. The superfluid 3He analogue to the cosmic string is the quantum vortex. We report here the first observations on the production and decay of this vorticity in superfluid 3He-B at temperatures down to ~110microK. We detect the heat evolution of the decaying vorticity after neutron irradiation of a small superfluid 3He-B sample. We interpret the decay process in terms of a simple exponential time constant which varies inversely proportional to the quasiparticle excitation number density in the superfluid. We also observe that the fraction of the neutron energy deposited in the vorticity is consistent with the earlier measurements which supported the Kibble-Zurek hypothesis.
Proceedings of Quantum Fluids and Solids meeting , Amherst Mass, June 1998; J. Low Temp. Phys. (in press - to be published November 1998)
Recent measurements in superfluid 3He-B have been interpreted as evidence in support of the Kibble-Zurek hypothesis for the formation of defects in the early Universe. The superfluid 3He analogue to the cosmic string is the quantum vortex. We report here the preliminary attempts to detect the heat evolution from the decay of this vorticity in superfluid 3He-B at temperatures down to ~110 microK. We produce vorticity by neutron irradiation of a small superfluid 3He-B sample and attempt to measure the heat released as the vorticity decays. We detect a long time scale heat release and find that the lifetime of this decay varies inversely proportional to the quasiparticle excitation number density in the superfluid. However, we have yet to be convinced that this heat is from the decay of vorticity.