Ian Bradley Tony Guénault Richard Haley Carolyn Matthews Ian Miller George Pickett Victor Tsepelin Martin Ward Rebecca Whitehead Kathryn Zaki Ian Bradley Tony Guénault Richard Haley Carolyn Matthews Ian Miller George Pickett Victor Tsepelin Martin Ward Rebecca Whitehead Kathryn Zaki Quasiparticle Shadows: Detecting Vortices in superfluid 3He-B at very low temperatures. Quasiparticle Shadows: Detecting Vortices in superfluid 3He-B at very low temperatures. Shaun Fisher

Ian Bradley Tony Guénault Richard Haley Carolyn Matthews Ian Miller George Pickett Victor Tsepelin Martin Ward Rebecca Whitehead Kathryn Zaki Ian Bradley Tony Guénault Richard Haley Carolyn Matthews Ian Miller George Pickett Victor Tsepelin Martin Ward Rebecca Whitehead Kathryn Zaki Quasiparticle Shadows: Detecting Vortices in superfluid 3He-B at very low temperatures. Quasiparticle Shadows: Detecting Vortices in superfluid 3He-B at very low temperatures. Introduction in 3 He Vibrating Wire Techniques Quasiparticle shadows Direct Andreev reflection measurements Quasiparticle Transmission measurements. Introduction in 3 He Vibrating Wire Techniques Quasiparticle shadows Direct Andreev reflection measurements Quasiparticle Transmission measurements.

Superfluid phases formed by Cooper pairs with S=1, L=1 3 He Phase Diagram

Vortices in the B-phase Formed by a 2  phase shift around the core Superfluid velocity, v S =  /2  r Circulation confined to the core and quantised :  =h/2m 3 Superfluid is distorted in the core, core size depends on pressure:  0 ~ 65nm to 15nm

The Vibrating Wire Resonator Wire thin to reduce relative internal friction ~3mm ~4 micron

I 0 e iwt

V 0 e iwt

Frequency V0V0 Resonant Voltage    f 2

At low T, damping arises from collisions with ballistic quasiparticle excitations. The excitations effectively exchange momentum between the wire and the walls of the cell.  f 2   exp(-  /kT)

Superfluid flow, v + pFv+ pFv

Quasiholes propagate through flow field

Quasiparticles Andreev Scattered into Quasiholes with very small momentum transfer

Fraction of flux Reflected =0.5[1-exp(p F v(r)/k B T)] v(r)=  /2  r,  =h/2m 3 Shadow half Width = p F  /2  k B T ln 2 ~8  100  K (vortex core size  0 ~ low P)

Thermal quasiparticle damping reduced due to Andreev Reflection from vortex lines

Take a thin slab of homogeneous vortex tangle of unit area, line density L and thickness  x Probability of qp passing within distance r of a vortex core is L  x r Mean qp energy =k B T Qps are Andreev scattered if p F v(r)> k B T v(r)=  /2  r, so qps scattered if they approach within a distance, r ~  p F /2  k B T Simple Estimate of vortex Line Density Quasiparticle Flux transmitted through thickness x is exp(-x/ ), decay length,  ~  2  k B T / L  p F

Oscillating the grid has a larger warming effect on the cell.

Take the ratio to give the fractional thermal damping

Giving the damping suppression by vortices. Investigate Recovery of Vortex Signal

At low grid velocities, independent loops are created which travel fast (~10 mm/s) and disperse rapidly. The rings have a range governed by mutual friction; x~R/q R=ring radius, q= mutual friction parameter (measured by Bevan et al at higher T)

2R~5  m

At low grid velocities, independent loops are created which travel fast (~10 mm/s) and disperse rapidly.

Above a critical grid velocity, the ring density becomes high enough for a cascade of reconnection to occur, rapidly creating fully-developed turbulence which disperses only slowly.

Summary Turbulence in 3 He-B at low Temperatures: Can easily be generated and detected using vibrating wire resonators Maximum line densities so-far produced are ~10 8 m -2, corresponding to a line spacing ~ 100  m Spatial extent ~ mm For wire resonators, turbulence generated above pair-breaking critical velocity v C =v L /3 For a grid, ballistic vortex rings generated above a velocity ~ 1mm/s, becoming turbulent above ~ 3mm/s can measure ring decay at higher temperatures Grid Turbulence decays similar to HeII (suggests Kolmogorov spectrum with ’~0.2  ). Need new techniques to better determine absolute line densities.