Coulomb Drag in a Strongly Correlated Double Layer 2D

Electron System

Melinda KelloggJames Eisenstein Loren Pfeiffer Ken West

Ie-

V

e-

e-

e-

GaAsGaAs

180Å 99Å 180Å

~ 106 cm2/V•s

nlayer = 5.3 x1010 cm-2

drive

D

I

VD

Coulomb Drag

Al0.9Ga0.1As

Bilayer QHE Phase Diagram

Murphy et al., 1994

4

3

2

1

00.100.050.00

NO QHE

QHE

Tunneling

d__

l

Temperature Dependence in Zero Field

6

4

2

0

D(

)

543210T(K)

2~ TD

0.6

0.4

0.2

0.0

543210T(K)

2TD

Deviation from quadratic behavior -- no phonon peak

Kim, Nayak, Demler & Das Sarma 2000

Bonesteel, McDonald,

Ussishkin & Stern, 1998

Above Tc, Pairing Fluctuations

• We have discovered an enhancement inthe drag resistivity at total = 1.

• This enhancement appears well above thebilayer QHE phase boundary.

• This enhancement persists when the layer densities are unbalanced.