Manipulating Molecular Spins at the Nanometer Scale

薛其坤

清华大学物理系

Acknowledgements段文晖 (Tsinghua University, Beijing)裘晓辉 (National Center for Nanoscience & Technology, Beijing)张 平 (Institute of Appl. Phys. & Computa. Math. Beijing)

Members: 陈 曦 马旭村 贾金锋

季帅华 付英双 张 童 吴 蕊

Molecule Based Spintronics

NO

COOH

NO

COOH

electrode electrode

N

S1. Molecule-electrode (metal)

interaction

2. Molecule-molecule interaction

3. Spin-polarized electrons

(injection, transport, manipulation, detection…)

(under external fields)

……

Essential but Challenging!

Content

I. IntroductionII. ExperimentIII. Kondo Effect (MnPc)IV. Zeeman Effect (CoPc)V. Gap States (Mn & Cr)VI. Summary

localized spin + surface

I. Introduction

Anderson Model

I. Introduction

Three parameters: Ed: energy of molecular levelU: Coulomb energy

△~|V|2N: peak width

metal molecule

I. IntroductionAnderson Model Parameters: Ed , U, △

I. Introduction

Kondo Effect Discovered in the 1930sExplained in the 1960s

Interaction between spin and environment

I. Introduction

Kondo

DOS(EF)

I. IntroductionAnderson Model

localized spin + surface

I. Introduction

Kondo

ZeemanQuantum Size Effect (thin film)

Superconducivity

substrate

film

localized spin + surface

I. Introduction

Quantum Size Effect ZeemanKondo

MagnetismSuperconductivity

………

Platform

II. Experiment

Our Molecules

II. Experiment

Our Surface

(111)

Tc=7.2K

Pb (111) thin films on Si

Si

Pb thin films on Si

Superconductivity (Tc): SCIENCE 306, 1915 (2004) Growth kinetics: PRL 92, 106104 (2004)Electron-phonon coupling : PRL 95, 096802 (2005) Upper critical field : PRL 95, 247005 (2005) Surface diffusion: PRL 95, 266102 (2006) Kondo resonance: PRL 99, 156601 (2007) Surface chemical reactivity: PNAS 104, 9204 (2007) ……

Si(111)Pb

Material Properties Modulated by QSE

Superconductivity (Tc) oscillation

PHYSICAL REVIEW LETTERS 15 April 1963

J. M. Blatt and C. J. ThompsonPRL 10, 332 (1963)

22 23 24 25 26 27 28

5.1

5.4

5.7

6.0

6.3

6.6

Tc (K

)

Thickness (ML)22 23 24 25 26 27 28

Thickness (ML)

Guo, Zhang et al., SCIENCE 306, 1915 (2004)Zhang et al., PRL 96, 096802 (2005)

Our tool: STM

Imaging ManipulationSpectroscopy

II. Experiment

Our Instrument

Unisoku UHV ultra-LT (400mK) high magnetic field (11T) STM

II. Experiment

II. ExperimentOur Instrument

Ji et al., PRL (in press)

III. Kondo EffectManipulation

III. Kondo Effect

Kondo Effect

0

122 J

KT D eD

ρ

π

−Δ=

0

1 1( )d d

JUπρ ε ε

Δ= +

+2

0Vπ ρΔ =

Energy spectra for an Anderson impurity system

Without hybridization With hybridization In the Kondo regime below TK.

20

11 12 ( )2

02 d dV

UKT D V e

ρε ερ

−+

+=

J: coupling of spins and conduction electrons

ρ0: density of states of host

Direct observation at single atoms/molecule level by STM

Science 280, 567(1998) M. CrommiePRL80, 2893 (1998)

Wolf-Dieter Schneider

Ce/Ag(111)Co/Au(111)

3d transition metal on Au (111): Ti, V, Cr, Mn, Fe, Co, and Ni.

Nature 403, 512(2000) D. M. Eigler

Co/Cu(111)

MnPc on Pb(111)

CoPc

1.4nm

III. Kondo EffectMnPc

Modulation of Kondo Effect by QSE

III. Kondo Effect

STM Manipulation

III. Kondo Effect

Kondo Resonance

The same molecule

on the same surface under the same measurement conditions!

Fano Lineshape

In tunneling experiments:

Resonance width: 2 2 B KK TΓ =

' 2

'2

( )( )1

dI qVdV

εε+

∝+

0'B K

eV EK T

ε −=

STM tip

Magnetic atom

III. Kondo EffectKondo Temperature Fu et al., PRL 99, 156601 (2007)

III. Kondo Effect

Oxide surface

Pb(111)PbO

III. Kondo Effect

Splitted Kondo

III. Kondo Effect

Kondo Mapping

IV. Zeeman

IV. Zeeman

Pb

CoPc/Pb(111)

IV. Zeeman

T=0.4K

△ ↑

IV. Zeeman

IETS via Single Spin Flipping

on 2nd layer

123

45

Pb

Spin-flip IETS

σe + σie

dI/dV

eV0-gμBB gμBB

σe

Ef

Ef

gμBB

gμBB eV

Mn Atom Chains

Hirjibehedin et al., Science 312, 1021(2006)

IV. Zeeman

Measurement of g-factor of single molecule

1

11

N

N i ii

H J S S−

+=

= ⋅∑Heisenberg model:

Dimer:(3rd layer CoPc)

2 2 21 2 1 2[( ) ]

2JH S S S S= + − −

1E JΔ =

Model Calculations

Trimer:(4th layer)

2 2 21 2 3 1 3 2[( ) ( ) ]

2JH S S S S S S= + + − + − 1 AE JSΔ =

12AS >

1E JΔ =12AS =

Tetramer:(5th layer)

2 21 2 3 1 3

2 2 22 3 4 2 4 2 3

[( ) ( )2

( ) ( ) ( ) ]

JH S S S S S

S S S S S S S

= + + − +

+ + + − + − +

1E JΔ =12AS =only for 2 1.5E JΔ =

Manipulation of single-molecule spin-states

-6 -4 -2 0 2 4 6

0.4

0.6

0.8

1.0

1.2

Sca

led

dI/d

V

Sample bias(mV)

3T 5T 7T 9T 11T

g=2.038

Spin-flip IETS

Bg BμΔ=

Isolated momentZeeman ↔ Kondo

-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6

0.5

1.0

1.5

2.0

2.5

Sca

led

dI/d

V

Sample bias(mV)

3T 5T 7T 9T 11T

Kondo resonance

1st

Ji et al., PRL (in press)

V. Gap StatesGap States

Pb Mn

U ↑

V. Magnetic

Superconductor Gap States

Cr, Mn on Pb(111)U ↑

Single Atom Spectroscopy

VI. SummaryTopic

Spin states of adsorbatesToolbox

Low temperature (B) STMSingle molecule manipulation

Scanning tunneling spectroscopyInelastic tunneling spectroscopy (IETS) via single spin flip

Gap states in superconductorProgress

Kondo effect modulation via QSEMagnetic coupling between molecules

Manipulating spin states at single molecular levelPerspective

Organic magnetismMolecular spintronicsMolecular recognition

Single atom reaction detection……

Thank you very much!!!

localized spin + surface

I. Introduction

Quantum Size Effect ZeemanKondo

MagnetismSuperconductivity

………

Superconductive film

Platform

magnetic atom/molecule

Atomically flat Pb films on Si(111)

2μmx2μm

Si(111) 0.1º

Thickness: 7nm (24ML)Uniformity: ~centimeter

Pb(bulk): coherent length 87nm

2D electronic system1D Square Potential Well-tunable L

Pb

QSE对电子结构和超导的影响

Superconductivity (Tc) oscillation

PHYSICAL REVIEW LETTERS 15 April 1963

J. M. Blatt and C. J. ThompsonPRL 10, 332 (1963)

22 23 24 25 26 27 28

5.1

5.4

5.7

6.0

6.3

6.6

Tc (K

)

Thickness (ML)22 23 24 25 26 27 28

Thickness (ML)

Guo, Zhang et al., SCIENCE 306, 1915 (2004)Zhang et al., PRL 96, 096802 (2005)

Single domain (111) structure

Si

N N+1N-1

500nm x500nm

10ML 12ML

Oxygen adsorption on PbO2 (~120L @LN2)

10ML, 12ML: more sites11ML: less sites

10ML: θ=0.2453

11ML: θ=0.0831

3 times!

11ML

Oscillating oxidation on Pb(111) surface

121411 13

1512ML

11ML

13ML

QSE on Surface Oxidation of Pb(111)

400nmx400nm

400nmx400nm

SiPb

odd even odd evenodd eveneven

12 1411 1315

PNAS 104, 9204 (2007)Xucun Ma et al.,

PbO

12 14 16

Silicon

e e

In the same metal Pb island,

the behaviors of electrons are different

o2

Surface Reactivity & LDOS at EF (O2/Pb)

• oxygen clusters

■ oxides

Reactivity

LDOS at EF

Xucun Ma et al., PNAS 104, 9202 (2007)

Kondo EffectMagnetic impurity

Metal host

Kondo Temperature TK

Initial state

final stateTK