33
_ _ _ __ _ _ _ _ __ _ _ _ _ __ _ _ _ _ __ _ _ _ _ __ _ _ _ _ __ _ _ _ _ SOLID STATE PHYSICS C. Vettier Institut Laue Langevin
_______________________________________
SOLID STATE PHYSICS
C. Vettier Institut Laue Langevin
_______________________________________
SOLID STATE PHYSICS
_______________________________________
SOLID STATE PHYSICS
• Understanding of bulk properties– Ground states– Susceptibilities– Simplifying but consistent patterns
• Characterisation of phase diagrams
– Structures– Relevant external fields
• Measure of fluctuations– Time and Space– Dynamical susceptibilty
_______________________________________
FRONTIERS IN SOLID STATE PHYSICS
Physics moves towards complexity
coupled degrees of freedom
low dimensionality
H. Ronnow et al., 2002
Electron charge, spin, orbit, Lattice
Soliton modes in CuGeO3
_______________________________________
FRONTIERS IN SOLID STATE PHYSICS
Biggest unsolved problems ?
plenty !
Self-organised complexity
Exotic superconductivity
Inhomogeneity
_______________________________________
FRONTIERS IN PHYSICS OF SOLIDS
Superconductivity
Discovery in 1911 – in Leiden
Successful model in 1957 - BCS
1986 Discovery of High Tc systems
Cuprates materials Bednorz & Müller
36 K, 90K and 130 K
Before mid-80’s
Tc restricted to below 23 K
_______________________________________
FRONTIERS IN PHYSICS OF SOLIDS
Superconductivity
Challenge :
Nature of couplings remains puzzling
despite an extraordinary activity
Applications
magnetic resonance imaging
power transport
_______________________________________
SUPERCONDUCTIVITY
model : glue-ing of electrons
attraction through lattice modes BCS
k
m
_______________________________________
SUPERCONDUCTIVITY
exotic couplingsmagnetism
Phonon wave
MagneticExciton wave
electron
s-wavepairs
d-wavepairs
electron
P. Coleman, 2001
No consensus on a global model
despite tremendous efforts
_______________________________________
SUPERCONDUCTIVITY
Neutrons : unique and necessary tool
Use all possible methods
Structures and motions of particles
Separation of lattice and magnetic effects
_______________________________________
BCS superconductivity
MgB2 Tc ~ 39 K
J. Nagamatsu et al., 2001
Mg
B
B
Resis
tivi
ty
Temperature (K)
0 20 40 60 80 100
Tc
0 10 20 30 40 50 60Temperature (K)
Su
scep
tib
ili
ty
Tc
_______________________________________
BCS superconductivity
Inelastic neutron scattering
R. Osborn et al., 2001
0 20 40 60 80 100Energy
(meV)
Ph
on
on
den
sit
y o
f sta
tes
B - bond stretching modes
Mg
B layer
-orbitals
-orbitals
MgB2
_______________________________________
BCS superconductivity
Aluminium doping destroys superconductivity
Electron dopingTemperature (K)
Su
scep
tib
ilit
y
Mg1-xAlxB2
J.S. Slusky et al., 2001
ZMg = 12
At. WeightMg = 24.3ZAL = 13
At. WeightAl = 27.0
_______________________________________
0 25 50 75 100 125 150 ENERGY
(meV)
20
15
10
5
0
Ph
on
on
den
sit
y o
f sta
tes
BCS superconductivity
B. Renker et al., 2002
Renormalisation of
phonon modes
Neutrons identify
key phonon modes
MgB2
AlB2
_______________________________________
BCS superconductivity
_______________________________________
BCS superconductivity
Vortex lattices
penetration depth
anisotropy
Small angle neutron scattering
_______________________________________
Ch. Dewhurst, B. Cubitt, 2002
SANS from Vortex Lattices in MgB2
Isotropic penetration depth
BCS superconductivity
_______________________________________
BCS superconductivity
Neutrons have unravelled the binding
mechanism in MgB2
More neutrons are needed to discover
couplings in exotic superconductors
_______________________________________
Exotic superconductivity
•Fluctuations
coupling of quasi - particles
•Neutron scattering
effects of lattice,
electron spins and charges
•Neutron polarisation
•Dynamics is essential
_______________________________________
Superconducting YBa2Cu3O7 Non-superconducting YBa2Cu3O6
Exotic superconductivity
Cuprate oxidesCharge reservoir
Neutron diffraction
_______________________________________
Phase diagram
anomalous metal
doping
metal
tem
pera
ture
HTc superconductors cuprate oxides
FLUCTUATIONS IN SOLIDS :THE GLOBAL VIEW
_______________________________________
QAF
FLUCTUATIONS IN SOLIDS :THE GLOBAL VIEW
Antiferromagnetic phase
Normal excitations : spin waves
_______________________________________
FLUCTUATIONS IN SOLIDS :THE GLOBAL VIEW
Antiferromagnetic phase
Superconducting phase
Doping
QAF QAF
_______________________________________
FLUCTUATIONS IN SOLIDS :THE GLOBAL VIEW
x=0.5x=0.52x=0.83x=0.92x=1
YBa2Cu3O6+x
X=0.5X=0.52X=0.83X=0.92X=1.00T = 2
K
Energy (meV)
0 10 20 30 40
Imag
inary
part
of
su
scep
tib
ilit
y
()
Magnetic response at QAF
slice in Q space
_______________________________________
FLUCTUATIONS IN SOLIDS :THE GLOBAL VIEW
Observation of resonance peak
YBCO6.85 J. Rossat-Mignod et al., 1991
Energy (meV)
Inte
nsit
y
QAF
_______________________________________
FLUCTUATIONS IN SOLIDS :THE GLOBAL VIEW
Extraction of magnetic response
Where is the interesting range in Q and energy?
Broad dynamical range
YBCO6.6 P. Dai et al., 1999
QA
F
_______________________________________ YBCO6.85 L.P. Regnault et al., 2002
En
erg
y (
meV
)
Q = Q - QAF in reciprocal lattice units
QA
F
resonance
FLUCTUATIONS IN SOLIDS :THE GLOBAL VIEW
Polarisation analysis Unusual
dispersion
Close look at resonance
_______________________________________
FLUCTUATIONS IN SOLIDS :THE GLOBAL VIEW
Obtaining more data is required
Broad range in frequency
from 1 neV to 100 meV
and Q space
Coupling to all degrees of freedom
polarisation analysis
_______________________________________
FLUCTUATIONS IN SOLIDS :THE GLOBAL VIEW
Phonon dispersion in YBa2 Cu3 O 7-x Egami et al., (2002)
Ph
on
on
en
erg
y
(meV
)
Q in reciprocal lattice units
Neutrons will be needed
to unravel the relevant couplings
_______________________________________
FLUCTUATIONS IN SOLIDS :THE GLOBAL VIEW
Many examples in other fields
Mapping a wide time and space domain
Quantum spin chains
M. Enderle et al., 2001
_______________________________________
FLUCTUATIONS IN SOLIDS :THE GLOBAL VIEW
• ESS offers unprecedented capabilities :
• flux
• coverage of (t,r) space
• neutron polarisation analysis
• ESS will allow to reach new scientific
frontiers
_______________________________________
BCS superconductivityMgB2 Tc ~ 39 K
Isotopic effects
Temperature (K)
Magneti
sati
on
Mg10B2Mg11B2
S.L. Bud’ko et al., 2001
Marginal shift with Mg isotope change
Mg
B
_______________________________________
Ch. Dewhurst ,B. Cubitt, 2002
Temperature (K)
Conventional BCS
No node in the gap
(Inte
nsi
ty)1
/2Vortex Lattice in MgB2
Isotropic penetration depth
BCS superconductivity
