5 Common Concepts in correlated Fermi systemsscs.sa.infn.it/TCXIV/Download/Vollhardt/5_Common... ·...
Transcript of 5 Common Concepts in correlated Fermi systemsscs.sa.infn.it/TCXIV/Download/Vollhardt/5_Common... ·...
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Theory of correlated fermionic condensed matter
5. Common concepts in correlated Fermi systems
Supported by Deutsche Forschungsgemeinschaft through SFB 484
XIV. Training Course in the Physics of Strongly Correlated SystemsSalerno, October 9, 2009
Dieter Vollhardt
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• Common properties of correlated electrons and 3He
• Emergence in many-particle systems
Outline:
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Paradigm: Helium-3
NormalFermi liquid
Solid (bcc)disorderedspins
orderedspins
1. Normal state
3. localization-delocalizationtransition
2. Pair-correlated state
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NormalFermi liquid
Solid (bcc)disorderedspins
orderedspins
1. Normal state properties
3He
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3He Nuclear spin12
I
Fermion
Fermi-Dirac statistics
Fermi body/surface
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Fermi gas: Ground state
kx
ky
kz
Fermi sea
Fermi surface
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kx
ky
kz
Fermi gas: Excited states (T>0)
Switch on interaction adiabatically (d=3)
Exact k-states ("particles"): infinite life time
Particle
Hole
Fermi sea
Fermi surface
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Landau Fermi liquid
kx
ky
kz
Well-defined k-states ("quasiparticles") with - finite life time - effective mass- effective interaction
(Quasi-) Particle
(Quasi-) Hole
Fermi sea
Fermi surface
Landau (1956/58) 1-1 correspondence between k-states
= elementary excitationof an interacting Fermi system
Unique to fermions
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Universal Fermi liquid properties:
0*V V
mcm
c
0
01*
s saFm m
specific heat
spin susceptibility
compressibility0
01*
s
m mF
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0im *l V
T
mm
cT
3He Greywall (1983)
Simple metals
Potassium
T2 (K2)
C/T
(mJ/
mol
e K2 )
quasiparticle mass
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0im *l V
T
mm
cT
3He Greywall (1983)
Heavy fermions: UBe13,CeCu2Si2Stewart et al. (1983,1984)
quasiparticle mass
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3 lnV T Tc T
3He Greywall (1983)
Heavy fermions: UPt3Stewart et al. (1983,1984)
Eliashberg (1960)Doniach, Engelsberg (1966)Pethick, Carneiro (1973)Chubukov et al. (2005)Aleiner, Efetov (2006)
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3He
LandauFermi liquid
2 2* 1
2
1 5
*
.*
FF
B
F
mk
Km
Tk
Tm
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3He: Pressure dependence
Strong short-range, repulsive interactions •spin fluctuations strongly enhanced•density fluctuations strongly suppressed
Greywall (1983)
High susceptibility: “almost ferromagnetic liquid“?
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0
0
*1s asm m
F
Anderson, Brinkman (1975):
“Almost localized Fermi liquid“;vicinity of Mott transition
0
01*1s
as
m m F
3He: Pressure dependence
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Gutzwiller-Brinkman-Rice theoryGutzwiller (1963)Hubbard (1963)Kanamori (1963)
One-particle wave function(Hartree-Fock, BCS, etc.)
ˆ
†
, ,i j i i
i ji
ij
D
tH c c nU n
Gutzwiller wave functionˆ
0GDe
Metzner, DV (1988/89)d=1,: exact analytic evaluation possible
1 G GG
G G
HE
L
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Gutzwiller approximation (1963/65)
Brinkman, Rice (1970): 1*cU Um q
m
Describesmetal-insulator
("Mott") transition, application to V2O3
0Ed
1
nk
kkF
q
AG
GEL
0( ) ,q d dU
1Z
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Gutzwiller-Brinkman-Rice theory:Application to normal liquid 3He
DV (1984)
Gutzwiller approximationLandau Fermi liquid theory
liquid 3He:"almost localized Fermi liquid" (vicinity of Mott transition),not „almost ferromagnetic"
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Gutzwiller approximationLandau Fermi liquid theory
DV, Wölfle, Anderson (1987)
Generalization: Gutzwiller-Hubbardlattice gas model for 3He
Gutzwiller-Brinkman-Rice theory:Application to normal liquid 3He
DV (1984)
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Gebhard (1990)
Gutzwiller wave function in d
Metzner, DV (1989)
Gutzwiller approximationˆ0
UG
He
G GG
G G
HE
exact in d
d: Evaluation of EG 0for arbitrary
Multi-band generalization:
„Gutzwiller DFT“
Bünemann, Gebhard, Ohm, Weiser, Weber (2005)
Ferromagnetic Ni: Cut of Fermi surface
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NormalFermi liquid
Solid (bcc)disorderedspins
orderedspins
2. Pair-correlated state
Osheroff, Richardon, Lee (1972)
3He: P-T phase diagram
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3He: H-P-T phase diagram
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kx
ky
kz
Landau Fermi liquid
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kx
ky
k
k
Arbitrarily weak attraction Cooper instabilitykz
Universal fermionic property
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ξ0,k
,k
Arbitrarily weak attraction: Cooper pair ( , ; , ) k k
S=0(singlet)
0,2,4,... ( )L r
S=1(triplet)
1,3,5,... ( )L + r
0 ( ) r
( ) - r
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Cooper pairing of Fermions vs. Bose-Einstein condensation
Conventional superconductors
High TC superconductors
Superfluid 3He
0 10000 Å
0 150 Å
0 10 Å
BCS
Tightly packed bosons BEC0 1 Å
Cont
inuo
us
cros
sove
r?
Leggett (1980)New insights from BEC of cold atoms
Cooper pair: “Quasi-boson“
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B phase A phase
L=1, S=1
Order parameter matrix
Aiμ
3 ´3 ´2 =18 real numbers
Superfluid 3He
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_
"conventional" superfluidity/superconductivity
s-wave pairing
SO(3)S´SO(3)L´U(1)φ symmetry brokenLeggett (1975)Mineev (1980)Bruder, DV (1986)
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SO(3)S+L_
B phase
/ Bk TVc e
only stable phase in mean-field theory
Spontaneously broken spin-orbitsymmetry (SBSOS) Leggett (1972)
"unconventional" superfluidity
SO(3)S´SO(3)L´U(1)φ symmetry brokenLeggett (1975)Mineev (1980)Bruder, DV (1986)
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U(1)SzU(1)Lz- φ
´
A phase
3Vc T stabilization by
strong-coupling effects
"unconventional" superfluidity
SO(3)S´SO(3)L´U(1)φ symmetry brokenLeggett (1975)Mineev (1980)Bruder, DV (1986)
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Unconventional superconductivity
G ´ SO(3)S ´ T´ U(1)φ symmetry broken
G: point symmetry group of solid Anderson (1985)Volovik, Gorkov (1985)Ueda, Rice (1985)Blount (1985)
Example: Tetragonal crystal (D4h)
conventional D2h: unconventional
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UPt3
H-T phase diagramAdenwalla et al. (1990)Park, Joynt (1995)
T-P phase diagramv. Löhneysen, Trappmann,Taillefer (1992)
Unconventional superconductivity
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U1-xThxBe13 Ott et al. (1985)
Sr2RuO4 Maeno et al. (1994) triplet pairing
Other systems:
Unconventional superconductivity
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NormalFermi liquid
Solid (bcc)disorderedspins
orderedspins
3. Localization-delocalization transition
3He
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3He
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3He
Interaction
ln 2BS kS T
heating
anomalous("Pomeranchuk")effect
Clausius-Clapeyron eq.:
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V2O3 McWhan et al. (1971)
Correlationinduced("Mott-Hubbard")metal-insulatortransition
Interaction
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V2O3 McWhan et al. (1971)
Interaction
Clausius-Clapeyron eq.:
heating
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Localization-delocalization transition
V2O3: Mott metal-insulator transition
Interaction
metal
insulator
3He:liquid-solid transition
S T ln 2BS k
Interaction
ln 2BS kS T
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Strongly correlatedelectron materials:V2O3, NiSe2-xSx, κ-organics, ...
Helium-3
Universality due to Fermi statistics + correlations
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Peculiarities of Many-Particle Systems
and “Emergence“
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Interacting many-particle systems
e
e
r2er
Coulomb potential
Vacuum
Elementary (“bare”) particles + interactions
effective (“quasi”) particles + effective interactions N
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r2
/re er
Effective Yukawa potential
Electron gas: ScreeningSimplest approximation: Thomas-Fermi
e
e
Interacting many-particle systems
Elementary (“bare”) particles + interactions
effective (“quasi”) particles + effective interactions N
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r2
3 cos(2 )Fe k rr
Friedel oscillations
Electron gas: ScreeningBetter approximation: Lindhard
e
e
Interacting many-particle systems
Elementary (“bare”) particles + interactions
effective (“quasi”) particles + effective interactions N
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Electrons in solids
“Strong interaction” of electrons in localized orbitals
Interacting many-particle systems
Elementary (“bare”) particles + interactions
effective (“quasi”) particles + effective interactions N
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Interacting many-particle systems
Elementary (“bare”) particles + interactions
effective (“quasi”) particles + effective interactions N
Entirely new phenomena arise, e.g., phase transitions
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Strategy of Statistical Physics to detect Phase Transitions
( , )H V NHamiltonian of many-body system
( , )iE V N
Energy of microstate i
/( , , ) i BE k T
i
Z T V N e
Partition function
( , , ) lnBF T V N k T Z
Free energy
( , , ) ( , )G T P N N T P
Chemical potential
( ) ( , )n T PSingularity in Phase transition
Sum of analytic terms Z analytic ?!
infinitely many termsZ,μ can become
non-analytic
, , / . N V N V const Thermodynamic limit:
Lee, Yang (1952)
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Strategy of Statistical Physics to detect Phase Transitions
Thermodynamic limit unpredicted new phenomena Thermodynamic limit unpredicted new phenomena
( , )H V NHamiltonian of many-body system
( , )iE V N
Energy of microstate i
/( , , ) i BE k T
i
Z T V N e
Partition function
( , , ) lnBF T V N k T Z
Free energy
( , , ) ( , )G T P N N T P
Chemical potential
Sum of analytic terms Z analytic ?!
infinitely many termsZ,μ can become
non-analytic
, , / . N V N V const Thermodynamic limit:
Lee, Yang (1952)
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Entirely new phenomena, e.g., phase transitions
Interacting many-particle systems
N
Unpredicted “emergent” behavior
We used to think that if we knew one, we knew two, because one and one are two. We are finding out that we must learn a great deal more about 'and'.
Arthur Eddington (1882-1944)
We used to think that if we knew one, we knew two, because one and one are two. We are finding out that we must learn a great deal more about 'and'.
Arthur Eddington (1882-1944)
“More is different” Anderson (1972)
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EmergenceEmergence
Examples:
Superconductivity MagnetismGalaxy formation
TrafficWeatherStock market
AntsHuman bodyConsciousness
© The Institute for Complex Adaptive matter (ICAM)
Interacting many-particle systems
N
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New Developments & Perspectives
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1, 2, … multi-electron transfer in metalloproteincomplexes Photosynthesis
Explanation & prediction of properties of complex materials
Phase diagram of La1-xSrxMnO3
(i) Complex correlated electron materials
Kagome layer inZnCu3(OH)6Cl2(herbertsmithite):Spin liquid behavior
Cu
Hemberger et al. (2002)
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Explanation & prediction of properties of complex materials
Phase diagram of La1-xSrxMnO3
(i) Complex correlated electron materials
Kagome layer inZnCu3(OH)6Cl2(herbertsmithite):Spin liquid behavior
D A
damage & repair
1, 2, … multi-electrontransfer in DNA
e-
Hemberger et al. (2002)
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(ii) Quantum phase transitions
Quantumcritical
© DFG Research Unit (Augsburg-Dresden-Göttingen-Karlsruhe-Köln-München, 2007)
Non-Fermiliquid
Quantum critical point
• Non-Fermi liquid behavior • Emergence of novel degrees of freedom• New phases of matter
Driven by quantum fluctuations
ordered non-ordered
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(ii) Quantum phase transitions
Quantumcritical
© DFG Research Unit (Augsburg-Dresden-Göttingen-Karlsruhe-Köln-München, 2007)
Non-Fermiliquid
Quantum critical point
• Non-Fermi liquid behavior • Emergence of novel degrees of freedom• New phases of matter
antiferromagnetic non-magnetic
magnetic transition
H
Driven by quantum fluctuations
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(ii) Quantum phase transitions
• Non-Fermi liquid behavior • Emergence of novel degrees of freedom• New phases of matter
Driven by quantum fluctuations
Custers et al. (2003)
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(iii) Correlated electrons in non-equilibrium
Real time evolution of correlation phenomena, e.g., time-resolved optical photoemission
Perfetti et al. (2006)
Photoelectron intensityin Mott insulating phase
Required: Theory of non-equilibrium beyond linear response in correlated bulk materials
Required: Theory of non-equilibrium beyond linear response in correlated bulk materials
Pump-probe experiment
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Modugno et al. (2003)
Bosonic/fermionic atoms in optical lattices
(iv) Correlated fermionic/bosonic atoms in optical lattices
Observation of Fermi surface (40K atoms)
Köhl, Esslinger (2006)
High degree of tunability: “Many-body tool box”
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Jaksch et al. (1998)Hubbard model with ultracold atoms
Angular momentum Ltot = F N=2F+1 hyperfine states
SU(N) Hubbard models Honerkamp, Hofstetter (2004)
Cooper pairs
N=3, e.g. 6Li, U<0: Color superconductivity, baryon formation (QCD)Rapp et al. (2006)
(iv) Correlated fermionic/bosonic atoms in optical lattices
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Correlated many-particle systems:More manifold and fascinating than ever
D A
Non-Fermiliquid
Quantum critical point