Shot Noise and conductance spectroscopy on a single molecule junction

Oren TalMichael Krieger, Rik Hortensius, Bas Leerink

Robert Thijssen, Darko Djukic and Jan van Ruitenbeek

Leiden University,Netherlands

Capri Spring School 2007

Electron-Vibration Interaction

-80 -60 -40 -20 0 20 40 60 80-0.2

0.0

0.96

0.98

1.00

d2 I/dV

2 (ar

b. u

nits

)

d

I/dV

(G0)

Bias voltage (mV)

Inelastic Electron Tunneling SpectroscopyTypically low conductance ~10-5G0

Djukic et al. Phys. Rev. B (R). 71 (2005), 161402Thygesen et al. Phys. Rev. Lett. 94 (2005), 036807

Point Contact SpectroscopyTypically high conductance ~1G0

C2H2

Stipe et al. Rev. Sci. Inst.70 (1999), 137

H2

heGo 22

-60 -40 -20 0 20 40 600.97

0.98

0.99

dI/d

V [G

0]

Bias Voltage [mV]

Pt+H2O

Conductance curves of different molecular junctions

-60-40-20 0 20 40 600.22

0.24

0.26

0.28

dI/d

V [G

0]

Bias Voltage [mV]

Pt+H2O

-80 -40 0 40 800.30

0.32

0.34

0.36

0.38

0.40

dI/d

V [G

0]

Bias Voltage [mV]

Ag+O2

-60 -40 -20 0 20 40 600.92

0.94

0.96

0.98

1.00

dI/

dV [G

0]

Bias Voltage [mV]

Pt+H2

Step up

Step down

heGo 22

“step up” to “step down” shape transition as a function of conductance

-60 -40 -20 0 20 40 600.45

0.50

0.55

0.60

0.65

0.70Pt+H2O

dI/d

V [G

0]

Bias Voltage [mV]

Step size and direction in conductance curves

-60 -40 -20 0 20 40 600.45

0.50

0.55

0.60

0.65

0.70

dI/

dV

[G0]

-60-40-20 0 20 40 600.22

0.24

0.26

0.28

Bias Voltage [mV]

-60 -30 0 30 600.97

0.98

0.99

L. de la Vega, A. Martín-Rodero, N. Agraït, and A. Levy Yeyati, PRB 73, 075428 (2006)

Low Transmission

5.0

HighTransmission

5.0

(M. Paulsson et al. PRB 72, 201101R (2005) similar 0.5 transition)

Deviation from a single channel model

Single channel model:transition between “step up” to “step down”at 5.0

Do we have more then a single transmission channel for a Pt-H2O -Pt junction?

Shot Noise measurements

In our experiment:transition between “step up” to “step down”at GoG 65.0

i ih

eG

22

i i

i iiI eIS

)1(

2

i ih

eG

22

Shot noise in point contacts

τ1

τi

…

Shot noise in Pt+H2O single molecule junction

6

The transition between to occurs above 5.0 5.0 GoG 01.052.0

0.0 0.1 0.2 0.3 0.4 0.50

1

2

3

4

Fullshotnoise 1=0.48

2=0.04

Exc

ess

nois

e [1

0-2

6 A

2/H

z]

Bias Current [A]

GoG 01.052.0

0.0 0.2 0.4 0.6 0.80

1

2

3

4

1=0.95

2=0.05

Fullshotnoise

Exc

ess

nois

e [1

0-26

A2 /

Hz]

Bias Current [A]

GoG 01.000.1

At the main transmission channel has 5.0GoG 01.052.0

Conclusions

Point contact spectroscopy : The effect of electron - vibration interactions on the differential conductanceis inverted at a certain conductance. Shot noise measurements: More than a single transmission channel through the Pt-H2O-Pt junction

Using the combination of point contact spectroscopy and shot noisemeasurements the apparent deviation from the relevant models could beresolved.

Open question: what is the role of transmission channel mixing due to electron – vibration interactions?

Acknowledgments

Prof. Jan van Ruitenbeek

Michael KriegerRik HortensiusBas Leerink Robert ThijssenDarko DjukicChristian Martin Sander Otte

Ruud van EgmondBert Crama

Electron-Phonon Interaction

V

dI/dV

0V

Point Contact SpectroscopyTypically high transmission probability

V

dI/dV

0V

Inelastic Electron Tunneling SpectroscopyTypically low transmission probability

LeV

R

R

E

11

k

E

eV

e

e

i i

i iiI eIS

)1(

2

i ih

eG

22

Shot noise in point contacts

5 10 15 20

4x10-18

6x10-18

8x10-1810-17

0.8A

G=1.00+/-0.01G0

Tot

al n

oise

[V2 /

Hz]

Frequency [KHz]

0A

Lock-in

I-V

Spectrum Analyser

100100

1000 1000

100MFaraday cage

dipstick

PC

cryostat

battery

S1

S2

0.0 0.2 0.4 0.6 0.80

1

2

3

4

1=0.95

2=0.05F=0.095

Fullshotnoise

Exc

ess

nois

e [1

0-26

A2 /

Hz]

Bias Current [A]

Shot noise in Pt+H2O single molecule junction

6

0.0 0.1 0.2 0.3 0.4 0.50

1

2

3

4

Fullshotnoise 1=0.48

2=0.04F=0.554

G = 0.52 +/-0.01G0

Exc

ess

nois

e [1

0-2

6 A

2/H

z]

Bias Current [A]

At about G=0.5G0 the main transmission channel has 5.0

The transition between to occurs above 5.0 5.0 GoG 01.052.0

GoG 01.052.0 GoG 01.000.1

“ Elastic” and inelastic contributions

6

J. K. Viljan et al. PRB 72, 245415 (2005)

0 2 4 60

1000

2000

3000

Vb=0.1V

nu

mb

er

of c

ou

nts

Conductance (G0)

Pt

Conductance histograms: Pt

8 10 12 14 16 180

1

2

3

4

5

Co

nd

uct

an

ce (G

0)

Piezo voltage (V)

Pt

Conductance histograms: Pt+H2O

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00

500

1000

1500

2000

2500

30000.96G0 Vb=0.2V

1.16G0

Pt + H2O

No

. o

f co

un

ts

Conductance [G0]

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00

500

1000

1500

2000

2500

3000

1.00G0

0.20G0

Vb=0.1V

0.60G0

Pt + H2O

No

. o

f co

un

ts

Conductance [G0]

>at lower bias voltages lower peaksare more pronounced.

Conductance traces

0.30

1

2

3

4

C

on

du

cta

nce

(G0)

Piezo voltage (V)

Pt+H2O

0.2 0.30

1

2

3

4

Co

nd

uct

an

ce (G

0)

Piezo voltage (V)

Pt+H2O

0.2 0.3 0.40

1

2

3

4

Co

nd

uct

an

ce (G

0)

Piezo voltage (V)

Pt+H2O

0.2 0.30

1

2

3

4

Co

nd

uct

an

ce (G

0)

Piezo voltage (V)

Pt+H2O

>Pt-H2O-Pt configurations with higher conductance then 1G0 (?)