Excitonic BEC in in Quantum Hall Bilayers

Ramin Abolfath NRCC Anton Burkov UCSB Jim Eisenstein Cal Tech. Steve Girvin Yale Yogesh Joglekar LANLJairo Sinova Texas A&M Ady Stern Weizmann Leo Radzihovsky UCAlvaro Nunez UTAEnrico Rossi UTAGiovanni Vignale UMC University of Texas at Austin

May 2005

Reference

Eisenstein and AHM Nature 432, 691 (2004)

Josephson Qubit

Devoret Walraff & Martinis cond-mat/0411

Non-linearNon-

Dissipative

Current - Spin-Torque

This feature allows you to specify a direct interactionbetween spin dependent current that is generated

in a ferromagnetic layer (polarizer), which isincident upon a second ferromagnetic layer

(analyzer) through a paramagnet.

**Click on regions of the menu for descriptions of the features.**

Landau Liftshitz Gilbert

Excitons – Elementary Excitations of Intrinsic Semiconductors

e-

h

h

e

Valence Band

Conduction Band

Excitonic BEC and Superfluidity?

Electron-Hole Pairs(n’,n)=(,) =Ferromagnetism(n’,n)=(c,v) = Excitonic BECs

(n’,n)=(TopLayer,BottomLayer) Order Parameter

Counterflow Superfluidity

AlGaAs AlGaAsGaAs

100 A

Quantum Well

e-

energ

y

Ga

As

Si

AlGaAs

GaAs

100 A

AlGaAs

Double Quantum Well

-

Quantum Wells

Ga As

ultra highvacuum

heated cells

high qualityGaAs substrate

Al

Molecular Beam Epitaxy

Pfeiffer - Bell Labs

Shayegan – Princeton

Electrons and Holes in the QH Regime

Add magnetic field

Particle-hole transformation

Assemble Bilayer

I

Ivoltmeter

voltmeter0

0

15

10

5

0

-5

-10

Hal

l Vol

tage

1050Magnetic Field

Electron-hole Pair Current

Superflow in Electron-Electron Bilayers

Kellogg and Eisenstein cond-mat/0401521

Hall Angle Not Large

σxx 1000 e2/h

300

200

100

0Tu

nn

elin

g C

on

du

cta

nce

(

10-9

-1

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-5 0 5Interlayer Voltage (mV)Interlayer Voltage

0

Tun

nelin

g ra

te

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Josephson-like Currents

Josephson Effect

J.J. Dynamics

eV = 0

Δ sin(φ) = Ibias

Correct Explanation?

300

200

100

0Tunn

elin

g C

ondu

ctan

ce

(10

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-5 0 5Interlayer Voltage (mV)0

Collective Dynamics & Dissipation

Ferromagnets vs. Josephson Junctions vs. Bilayers

J.J. Dynamics

Thin Film Ferromagnet

Dynamics

Joglekar TDHFA+SCBA

αφ >> αN

Joglekar & AHM PRB (2002)

Thin Film Ferromagnets Buhrman & Ralph, MSU, NIST, Orsay

Thin Film Ferromagnet

Dynamics

Spin Transfer

Transport Orbitals

eV

Condensate Orbitals

K = X l2

Coherent Edge Transport

Empl 10-6 eVΔQP 10-3 eV

G e2/h

Δt 10-9 eV

V* 10-6 Volts

Excitonic Bose Einstein Condensation

in Quantum Hall Bilayers !

Macroscopic Quantum Coherence

properties different from

both JJ’s and thin film magnets