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Is there a Bose condensate in
Supersolid
helium?
Collaborators•
M. A. Adams (ISIS) •
O. Kirichek (ISIS)•
R. B. E. Down (ISIS)
“Measurement of the kinetic energy and lattice constant
•
in hcp
solid helium at temperatures 0.07-0.4 K”
M. A. Adams, J. Mayers, O. Kirichek and R.B.E. Down
•
Phys. Rev. Lett. 98
085301 Feb 2007
Experimental evidence
Liquid He4 is 100% superfluid
at T=0 Solid He4 is ~2% superfluid
at T=0
E. L. Andronikashvili, (1946) E. Kim and M. H. W. ChanScience 305
2004
ρS
0
1
2).exp(),()( ∫∫ Ψ= rrpsrsp didn
r=r1 s=r2
..rN
Bose –Einstein Condensation
(a)Ψ(r,s) is a non zero function of r
over length scales ~ L
(b) Ψ(r,s) has phase correlations over distances ~L
Fractional weight of condensate peak = f
Momentum distribution
Non-zero over length scales ~L
Ground state of liquid 4He
Phase correlations over distances ~L
Ψ(r,s) is connected over macroscopiclength scales between phase coherentpoints e.g. 1 and 2
2
1
Ψ(r,s)
Loops in Ψ(r,s)
over macroscopic (cm) length scales
Mass flow must be quantisedover macroscopic length scales
Single valued wave function
∫ =mnhdv rr).(
Normal viscous processescannot occur → zero viscosity at T=0
Ψ(r,s)
in solid
Can still be connected over macro lengthscales if enough vacancies are present
Solid can “flow”
if
(a) Flow conserves mass density
(b) wave function is connected
At least ~10% vacancies →~10% condensate fraction
If BEC of atoms is the origin of supersolidity,
reducing T should
•
Decrease kinetic energy.
•
Increase vacancy concentration.
RotatingAu Foil
Beam Direction
OCylinder of solid He4 inDilution fridge
92 Back scatteringdetectors
VESUVIO Measurement
he can
can
He4
Binned data
from 92 detectors Binned data after can subtraction.Dotted line is resolution function
liquid
O
single crystal high purity He4X
polycrystal
high purity He4□
10ppm He3 polycrystal
solid
J. Mayers, F. Albergamo, D. Timms Physica
B
276
(2000) 811
σ
MKE
223 22σh
=
T (K) (101) (002) (100)
0.070 2.758 (7) 3.1055
(300)
0.115 2.759 (7) 3.1055
(300)
0.150 2.758 (7) 3.1056 (300)
0.400 2.759 (7) 3.1055 (300)
Measured hcp
lattice spacings
SingleCrystalPure He4
PowderPure He4 0.075 2.758 (2) 2.934 (4) 3.131 (2)
PowderHe4+10ppm He3
0.075 2.757 (3) 2.940(3) 3.128 (2)
Conclusions
•
No change in KE, no change in vacancy concentration through SS transition.
•
Implies SS transition quite different to SF transition in liquid.
•
Probably not BEC in crystalline helium.
S. O. Diallo,J.V. Pearce, R. T. Azuah, O. Kirichek, J.W. Taylor, and H. R. GlydePRL 98, 205301 May 2007n0
= 0:10 ±
1:20% at T 80 mK
n0
= 0:08 ±
0:78% at T 120 mK
A S Ritner, J D Reppy
PRL 98, 175302 May 2007
Supersolid
fraction reduced by annealing.
Glassy phase?
Recent Experiments
Proposed experiment (POLARIS)
Perform in situ NCRIF experiment
Measure diffraction with and without supersolidity