Exciton Superfluidity

1
Exciton Superfluidity Related Phenomena
2
Semiconductor Roadmap
3
(No Transcript)
4
Two-Dimensional Electron Gas
5
Molecular Beam Epitaxy
heated cells
Al
Ga
As
ultra high vacuum
high quality GaAs substrate
6
Landau Levels
Cyclotron Orbit
7
Incompressible States Streda Formula
Compressibility
8
Integer Quantum Hall Effect
?xx
?xy/(h/e2)
9
Fractional Quantum Hall Effect
10
Bilayers
11
Separate Contacting
12
Tunnel Experiment
13
Drag Experiment
14
Counterflow Experiment
15
Quantum Hall
Magnetism
16
A Short History of Solid State Physics
17
Felix Bloch in his "Reminiscences of Heisenberg
and the early days of quantum mechanics"
explains how his investigation of the theory of
conductivity in metal led to what is now known
as the Bloch Theorem. "When I started to think
about it, I felt that the main problem was to
explain how the electrons could sneak by all the
ions in a metal so as to avoid a mean free path
of the order of atomic distances. Such a
distance was much too short to explain the
observed resistances... To make my life easy, I
began by considering wavefunctions in a
one-dimensional periodic potential. By straight
Fourier analysis I found to my delight that the
wave differed from the plane wave of free
electrons only by a periodic modulation.
18
Band Structure of Silicon
19
Electronic Properties of Solids
Bands Disorder Phonons Interactions
20
Ordered States Stoner Instability
21
Ordered States Stoner Instability
Spin Valve
22
Cooper Instability
Spin-up Electrons
µ
Energy Gain
Spin-down holes
23
Condensates
Bose-Einstein Condensates
24
Superconductivity
K. Onnes
25
Ordered States in the Quantum Hall Regime
26
QHF Stoner Criterion
Fogler Shklovskii (1995) Maude et al. (2005)
AX gt 1 ? QHF
27
Whats Special about Quantum Hall
Ferromagnets I. Skyrmions
28
Skrymion in 2D O(3) Ferromagnet
29
Quantum Hall Skyrmions
Sondhi et al. PRB 93
30
Skyrmions Size n0 LL
K
g
Fertig et al. PRB 94 97
31
Skyrmions in Ground State
Fertig et al. PRB 94 Barrett Tycko PRL 95
32
Skyrmion Crystal
Brey et al. PRL 95
33
Skyrmion Crystal Collective Excitations
Larmour
k1.5 phonons
k1 new
Cote et al. PRL 97
34
Whats Special about Quantum Hall
Ferromagnets II. QH Superfluids
35
Bilayer Excitonic Superfluidity
36
Spontaneous Interband Coherence is Exciton
Condensation
37
Desperately Seeking Semi-metals
Common Fermi Surface
py
px
38
graphene
Phil Wallace - Physical Review 1947 Geim AHM
Physics Today August 2007
39
Room Temperature Superfluid?
Bilayer Graphene
40
Exciton Condensation in Bilayers
2D eh Bilayer
Ec EV
Lezovik 1975
Kuramoto 1978
41
Mean-Field Theory Description
WHAT?
Spontaneous Interlayer Coherence
42
(No Transcript)
43
Counterflow Superfluidity
top
bottom
Moon et al. PRB 51 (1995)
44
Independent Contacting (better than Super)
45
An Experimenter
46
Andreev Scattering
Superconductor
47
Exciton Superflow in pictures
T R
B R
layers in series
48
Exciton Superflow in pictures
T R
Loop geometry
49
Exciton Superfluidity Related Phenomena