Denis Konstantinov

Quantum Dynamics Unit

OIST Graduate University

New Quantum Phenomena in

Electrons on Helium

under

Microwave Excitation

University Paris-Sud, March 18, 2015

理化学研究場 RIKAGAKUKENKYUJYO - RIKEN

Japan’s largest research institute

Largest campus - 15 min from

downtown Tokyo

Over 3,000 researches

My previous affiliation

Wako campus

Okinawa Institute of Science and Technology - OIST

45 Research Units in Neuroscience,

Biology, Physics and Chemistry

350 researches (approximately half are

not Japanese)

Graduate University since 2013

Present affiliation

No divisions into departments

Collaborators

Experiment

Kimitoshi Kono, RIKEN

Hanako Isshiki, RIKEN

Hikota Akimoto, RIKEN

Alexei Chepelianskii, University Paris-Sud

Theory

Yuriy Monarkha, ILTPE, Kharkov

Mark Dykman, Michigan State University

Masa Watanabe, RIKEN

- Electrons on helium versus 2DEG in semiconductors

- Electrons under microwave excitation

- Microwave-induced Zero-Resistance States (ZRS)

- Future directions

Talk Outline

- Recent interests

Polarization attraction

4

32

1

14

1

e

epol

RRRd

eRU

'

'

)(

)()(

Liquid He

e

e

ez

,)(e

epolz

ezU

2

005.0)1(4

)1(

Liquid He

'3Rd

eR

'R

e

Liquid He

z

yx

Sommer, 1964

Potential barrier ~1 eV

Liquid He

The Pauli exclusion principle -

electron avoids He atoms

e

electron bubble

20

Surface barrier

Vacuum

z>0 Helium

z<0

~1 meV (10 K)

0)(2

2

''

z

z

mEzψ n

nn

Equation of motion in z-direction:

Hydrogen-like spectrum: 2n

RyEn

Surface-state electrons (SSE)

E

||p10 K

Total energy:

m

pEE n

2

2

||

2D motion

||BB

due to spin

AlGaAs GaAs

Energy band

Complement to degenerate 2DEG in

Si MOSFETs and GaAs heterostructures

Comparison with traditional 2DES

• Crystalline interface

• Dielectric constant ε= 10

• Effective mass = 0.067 me

• g-factor = -0.44

• Electron density ns> 5x1010 cm-2

• Liquid/Superfluid interface

• Dielectric constant ε= 1

• Effective mass = 1.0 me

• g-factor = 2

• Electron density ns< 2x109 cm-2

Limited by surface instability!

-e filament

electrodes

Phase diagram

Temperature (K)

Density (

cm

-2)

Fermi liquid

Wigner solid

Coulomb liquid

0.01 0.1 1 10

106

108

1010

1012

EonH

e

s

s

f

Cp

n

mne

E

Vr

2

0

2

4

*

Tk

ne

E

V

B

s

th

Cp

0

2

4

Quantum fluctuations

Thermal fluctuations

Relevant energies

Typical electron densities

ns< 2x109 cm-2

Scattering (elastic)

- e-

liquid

He vapor

ripplons

- Scattering at helium vapor atoms

T

QTNvapor exp2/3

- Scattering at surface waves (ripplons)

T

Tk

N

B

q

q

1

1

exp

Shirahama et al. 1995

Highest mobility known!

2

n2

n

E

+

+

+ + +

+

10 nm

Past work

T

(K)

Grimes & Adams,

PRL 42, 795 (1979)

C.C.Grimes & Brown

PRL 32, 280 (1974)

2m

1m

n=1

n=2

12 EE

Microwave radiation

Interesting many-body physics

Coupled plasmon-ripplon modes

Edge magneto-plasons

Grimes and Brown, Platzman

Dahm, Williams, Glattli, Lea

mm-MW pulse

Low decoherence

Identification of well-defined qubits:

I0> and I1> states of individual surface electrons

Reliable state preparation:

Below 1 K almost all qubits will be in the quantum ground state I0>

T1=100 μs

Scalability!

1

E2

E3

E

+ + +

Recent interest: proposal for qubits

Resistive Detection of resonance

E1

E2

Microwave radiation

E

IV

1C 2C

eR

Sommer-Tanner method DK et al. PRL 2007

90 95 100

0.4

0.5

0.6

0.7

F (V/cm)

-1 (

M

)

T=0.5 K

E

||k

m

kEE n

2

2

||

2

2D energy subbands

90 95 100

0.4

0.5

0.6

0.7

E (V/cm)

-1 (

M

)

T=0.5 K

Decay due to elastic scattering

Very fast thermalization T >>T

sdecay

89 1010

see

1110~ p

Cooling due to inelastic scattering

sE

64 1010

e

decay

Electron Heating

Optical bistability

Estimate using mean-field approximation:

1122

1zzC

tc ctn

nnn

rr

ezz

3

2

11 Liquid He

Eeff

c

DK et al. PRL 2009

n=1

n=2

||k

E

)2/1( lEE cn n=1

n=2

l

E

c

m

kEE n

2

2

||

2

2D energy subbands

What is we apply magnetic field?

1

2

||

How to suppress heating?

Probe by transport measurements

l

E

c1E

2E

How do we probe it?

- apply resonant microwaves

12 EE

- measure DC conductivity

)( 22

2

effce

effs

xxm

ne

Relaxation dynamics must depend on ratio: cc

EE

12

Experiment

Experimental setup

- Leak-tight copper cell

- Kapton windows for MW

- Liquid height 1.3 mm

- Tuning by Stark shift in perp. electric field

0.2 0.4 0.6 0.80

5

10

15

xx (

10

-11 S

)

Magentic field (T)

T = 0.2 K

ns = 1.1x10

6 cm

-2

w/o MW

4 5 6 7 8 90

5

10

15

xx (

10

-11 S

)

/c

/2=79 GHz

DK and Kono, PRL 2010

222

xy

xx

xyxx

xxxx

0 xx

Tensor relation:

Vanishing conductivity: 0xx

4 5 6 7 8 90

5

10

15

xx (

10

-11

-1)

/c

Vanishing resistance!

ZRS – Zero Resistance States

DK and Kono, PRL 2010

Mani et al. Nature 2002 Possible explanations:

Electron pairing due to excitons

Dynamical symmetry breaking

Disorder-assisted transitions

Ponderomotive force near contacts

Microwave stabilization of edge states

Nonequilibrium population of LL

(Nature 2002)

(PRL 2003, PRB 2009)

(PRL 2003, Nature 2003)

(PRL 2003, PRB 2003-2010)

(PRB 2010)

(PRB 2011)

(highlights in Phys. Today 2003,

Science 2003, Nature 2004)

ZRS in heterostructures

Mechanism of oscillations in EonHe

)(),()(~

',

'',',

'

',inteB

nn

Tk

nnnnnn

nn

nner eqS

q

qq

)(),()(

',

'',

'

',

'

',eB

nn

Tk

nnnnnn

nn

nn

B

eqSTk

q

qq

non-zero for nonequilibrium population

derivative of DSF DSF

n=1

n=2

Tilted LL in dc-field

5 6 7 8 9 10 11 12-5.0x10

8

0.0

5.0x108

1.0x109

(

s-1)

21

/c

T=0.2 K

ns=5x10

6 cm

-2

eff

Yu. P. Monarkha Linear transport theory

Eac

Zero-resistance states

There exists (some) mechanism

leading to absolute negative σxx

σxx )(2

2

zV

Vjt

s

rs

t

kk

2~

exp

Instability and formation of current domains

Andreev, Aleiner, Millis, PRL 2003

Andreev et al. PRL 2003

σxx

Non-dissipative current domains

Photocurrent experiment

+

Iinner

Iouter Microwave

modulation

ON/OFF

-0.3

0.0

0.3

Pho

tocurr

ent

(pA

)

0 1 2 3

-0.3

0.0

0.3

Time (s)

ON ON OFF OFF DK, Chepelianskii, Kono, J. Phys. Soc. Jpn. 2012

Current Amps

MW When MW switched ON

Positive image charge released

Electrons moved away

Fix B-field

at minima

of σxx

e- redistribution and self-oscillations

+

liquid He

When MW switched ON

Electrons deplete from the center

AND accumulate at the edge

(large fraction up to 50% )

DK, M. Watanabe, K. Kono J. Phys. Soc. Jpn.

(2013)

OFF ON

In certain range of e- density

appears self-organized

(audio-frequency) oscillations

Compressibility experiment

+

Current Amp

+ Vc Vg > Vc

~ Vac

A. Chepelianskii et al. Nature

Communication, in press

iac

Can directly measure compressibility

ac

g

e idV

dn~defined by

Recent experiment in RIKEN

Vanishing compressibility!

Single-electron detection

Yury Mukharsky, CEA, Saclay, France

E. Rousseau et al. PRB 79, 045406 (2009)

Helium Pool

0.7 m deep

SET

2 m

Gate

Injector

550 nm

Pool

40 nm

Guard

Royal Holloway

University of London

Mike Lea, RHUL, London, UK

G. Papageorgiou et al. APL 86, 153106 (2005)

Qubits with long decoherence

Fluctuating magnetic field due to

Rashba effect (spin-orbit interaction):

SH osˆ

|| Ep

- T2 exceeding 100 sec

- Qubit coupling by dipole interaction [S. A. Lyon, Phys. Rev. A, 74,

052338]

Towards a hybrid quantum computer

Cavity Trap

Progress: APS March Meeting 2012

• Strong coupling to RF cavity

• Electron-electron coupling via a

single photon

• Manipulation of spin states via spin-

orbit coupling

Summary

- Electrons on helium: unique model system

- New quantum phenomena under MW excitation

- Some remarkable progress in quantum engineering

- Still exciting object of study!

Yuriy Moukharskii, Sacley: SET

David Rees, NCTU-RIKEN Joint Laboratory: Point Contact

David Shuster, University of Chicago and

Andreas Fragner,Yell University: Cavity QED

end more..

Mike Lee, University of London Royal Holloway and Steve Lyon, Princeton: CCD device