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Big Facility Physics 26th Jan 2004

Condensed Matter Physics

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“Big Facility” Physics in Grenoble

ESRF: X-raysILL: neutrons



“Big Facility” Physics near Zurich

- Paul Scherrer InstitutSS: muons

SINQ: neutronsSLS: X-rays



Low energy muons for investigation of:

Magnetic fields in thin films and surfaces



The apparatus for producing

a beam of low energy muons



muons are implanted in the sample surface<= HERE at a tuneable energy of 1 - 30 keV

the muons come in <= HERE with 4 MeVenergy and are spin-polarisedOriginal apparatus designed

and constructed by E. Morenzoni at Paul Scherrer Institut

F ie ld d irection at sam ple position

Sam ple C ryostat

Positronte lescopes

C onica llens

G ate Valve

TriggerD etector

E inzel lens Low Energy (keV)m uon beam

Spin

Surface m uon beam(K .E . = 4 M eV)

M oderator

M irror

E inzel lens(LN cooled)2

Einzel lens

Velocity

Spin

Velocity

Entry scin tilla tor



WHY USE (+ve) MUONS ?

•its spin precessesin the local B-field

•the e+ tends to be emitted along the

muon spin direction

•the spin-polarised muon arrives in the sample

•it decays, giving an e+ in about 2 s



After implanting a large number of muons... =>

The muon spin sweeps around like a lighthouse- the probability of an e+ arriving

at a fixed detector =>

oscillates (and decays) with time (after implantation)



... which has been implanted at a known depth - - controlled by its energy...

The frequency of precession measures the magnetic field AT the muon ...



First ever measurement of field profile on a nm scale just inside a superconductor

Field

Distance below surface of YBCO

T.J. Jackson et al. Phys. Rev. Lett. 84, 4958-4961 (2000)

increasing temperature



Current Developments

new samples:

•low Tc super-conducting films

•ferromagnetic-normal and ferro-superconducting multilayers

•CMR+HighTc films

•micro-structured superconductors

- and a new x 10 intensity muon beamline being developed at PSI

a new muon moderation cryostat - developed in Birmingham



Magnetic Flux Lines in superconductorsEach flux line

Carries a flux of 0 = h/2e

Flux lines

Current

Current

Type-II superconducto

r

Motion



F

T

H

Fc

Liquid

Moving Bragg glass

Smectic

PlasticVortex Glass

Bragg glass

D=3

Vortex Matter H -T Phase DiagramVortex Matter Dynamical Phase Diagram

H

T

normal state

vortex solid

vortex liquid

Hc2

Tc

Meissner state



Detected by small-angle neutron diffraction SANS



Diffraction pattern from

a Flux Lattice in

niobium

EPSRC – funded 11 T cryomagnet



Results from YBCO => Phys Rev Lett, Feb 2004

B = 1 T pattern

Four stretche

d triangul

ar lattices

at low fields



Results from YBCO => Phys Rev Lett, Feb 2004

B = 11 T pattern

Square lattice of flux lines at

high fields

Due to fourfold symmetry of d-

wave flux line cores



Calculations of flux lattice structure and energy

s-wave: but forced to be square

d-wave: orientation rotated 45

deg

d-wave observed orientatio

n

lowest energy



Future Work – mainly on “Vortex Matter”• flux lattice structures and pairing mechanisms in

unconventional superconductors

• flux lattice melting in low-Tc superconductors

• X-ray observation of flux line cores

• flux line motion and motion-induced ordering

• flux-line-like molecular structures

• Other neutron scattering, including inelastic neutron

scattering studies of fluctuations near QCP in Sr3Ru2O7



Future Developments in neutron scattering

Spallation Neutron Source, Oak Ridge USA



European Spallation Source?

Probably in the UK

ILL will be competitive

for the next 10 years

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