Exciton Superfluidity

1
Exciton Superfluidity Related Phenomena
2
Fermion-Pair (BCS) Theory
Spin-Up Electrons
µ
Spin-Down Holes
3
Fermion-Pair BCS Theory
Spin-Up Electrons
µ
Energy Gain
Spin-Down Holes
4
Fermion-Pair BCS Theory
Conduction Band
µ
Energy Gain
Valence Band
5
Spin Coherent States
6
Desperately Seeking Semi-metals
Common Fermi Surface
py
px
7
graphene
Phil Wallace - Physical Review 1947 Geim AHM
Physics Today August 2007
8
Excitons Elementary Excitations of Intrinsic
Semiconductors
h
9
(No Transcript)
10
Walter Kohn David Sherrington RMP (1970)
11
Tunnel Experiment
12
Landau Levels
13
Lowest Landau Level
Orbit Center Ladder Operator
14
Whats Special about Quantum Hall
Ferromagnets II. QH Superfluids
15
Bilayer Excitonic Superfluidity
16
Spontaneous Interband Coherence is Exciton
Condensation
17
Exciton Condensation in Bilayers
2D eh Bilayer
Ec EV
Lezovik 1975
Kuramoto 1978
18
Mean-Field Theory Description
WHAT?
Spontaneous Interlayer Coherence
19
Counterflow Superfluidity
top
bottom
Moon et al. PRB 51 (1995)
20
quantum Hall ferromagnets
21
Heisenberg QHF (?1)
Halperin Helv. Phys. Acta (1982) Herb Fertig
PRB (1989) Wen Zee PRL (2002)
Only state SN/2 ?111
22
d/l Perturbation Theory
Joglekar AHM (2000) Burkov AHM (2002)
23
Spin Coherent States
24
Classifying QHFs
Jungwirth AHM PRB (2000)
easy plane
easy axis
d
25
Bilayer MFT Phase Diagram
Cote, Brey AHM (1992)
26
Merons
Moon, Yang et al. PRB (1995)
27
An Experimenter
28
Andreev Scattering
Superconductor
29
Exciton Superflow in pictures
T R
B R
layers in series
30
Exciton Superflow in pictures
T R
Loop geometry
31

• Exciton condensation is interlayer coherence is
  layer pseudospin ferromagnetism and occurs in QH
  bilayers
• Exciton condensation does lead to spectacular
  electrical effects when you can do separate
  contacting

32
but what about Kohn and Sherrington?
condensate KE
Preferred phase
33
Critical Current
Energy Functional
Energy Conservation
Critical Current
34
Tunnel Experiment
35

• Exciton condensation is interlayer coherence is
  layer pseudospin ferromagnetsim
• Exciton condensation does lead to spectacular
  electrical effects when you can do separate
  contacting

36
Quantum Hall Edge States
Skipping Orbits
37
Edge States
?i kF/2p
kF0
kF1
38
Drag Experiment
39
Exciton Superfluidity Related Phenomena