11/04/23

www.neel.cnrs.fr

1

Subnanosecond spectral diffusionof a single quantum dot in a nanowire

G. Sallen, A. Tribu, T. Aichele*, R. André, L. Besombes,C. Bougerol, M. Richard, S. Tatarenko, K. Kheng, and J.-Ph. Poizat

CEA/CNRS/UJF joint team "Nanophysics and semi-conductors"Institut Néel and INAC, Grenoble, France

* Present address :Physics Institute, Humboldt University, Berlin, Germany

11/04/23

www.neel.cnrs.fr

2

Spectral diffusion

Random spectral jumps of a narrow lineas a result of fluctuating environment

Described by two parameters : diffusion amplituded : diffusion time

2.3322.3302.328Energy (eV)

d < : motional narrowing(dephasing)Lorentzian lineshape

A. Berthelot et al, Nat Phys (2006)

d > : wandering line :Gaussian lineshape

Besombes et al, PRB (2002)

Spectral diffusion of a single emitter

Standard method :Record spectra time serieTime resolution > 1 ms

* Resonant excitation of afluctuating line, photon correlationon the luminescence.Time resolution > 1µsZambusch et al, PRL (1993)

* Photon-correlation Fourierspectroscopy.Time resolution > 20 µsCoolen et al, PRL (2008)

Alternative methods :

Our method

Photon correlations on parts of the line :

Best time resolution : 90 ps

W holeLine

d

H s ide

L s ide

C X

2.3302.3282.326Energy (eV)

L side H sidet

t

t

1

0

g(2

) CX(L

,H,

)

-20 -10 0 10 20Delay (ns)

1

0g(2

) CX(L

,L,

)

2

1

0

g(2

) CX(

) c)

d)

e)

d

CX

Whole lineauto-correlation

L sideAuto-correlation

L- Hcross-correlation

Results

W holeLine

d

H s ide

L s ide

C X

2.3302.3282.326Energy (eV)

L side H sidea)

b)

t

t

t

Slow detectors : time resolution = 800ps

1.2

1.0

0.8

0.6

0.4

0.2

0.0

g(2) (L

,H,

)

-10 0 10Delay (ns)

2.3302.325Energy (eV)

2.3302.325Energy (eV)

Robustness with respect to energy slot size

Cross-correlation

The cross-correlation does not depend on the size of the energy slots

2.3302.327Energy (eV)

2.3302.327Energy (eV)

1.2

1.0

0.8

0.6

0.4

0.2

0.0

g(2) (L

,H,

)

-10 0 10Delay (ns)

Robustness with respect to energy separation

The probability of a spectral jump does not depend on its amplitude

Cross-correlation

~ 400 nm

~ 10 nm

Our sample

Single CdSe quantum dot inserted in a ZnSe nanowire

2.342.332.32Energy (eV)

XX

CX

X

Lifetimes : X = 500 ps CX = 650 ps CX = 450 ps

Antibunching @ T=220K : Tribu et al, NanoLett (2008)

Photon correlation spectroscopy : Sallen et al, PRB (2009)

1.5

1.4

1.3

1.2

1.1

1.0Line

wid

th (

meV

)

302520151050Excitation power (µW)

0.6

0.4

0.2

0.0

Diff

usi

on r

ate

(ns-1

)

Diffusion rate vs excitation power

T=4K

T=10K

CX to X diffusion rate

Spectral diffusion of theCX line (T=4K, T=10K)

10K/4K => Etrap= 1.1 meV

Linewidth = cste => Single charge exploring the traps

PCXsat

Spectral diffusion possible scenario

Conductionband

QD

1.1 meV

ZnSe CdSe ZnSe

10 nm

~3 nm

5

4

3

2

1

0

g(2

) X-X

X(L

,H,

)

-4 -2 0 2 4 Delay (ns)

5

4

3

2

1

0

g(2

) X-X

X(H

,H,

)

2.2362.234E (eV)

2.2182.2162.214E (eV)

2.2362.234 E (eV)

2.2182.2162.214E (eV)

XX

X

XX

X

Cascadepeak

2.2402.2302.2202.210Energy (eV)

XXCX

X

The sign of the energy shiftinduced by the fluctuatingenvironment is the sameon X and XX.

Correlated spectral diffusion

XX

X

Fast detectors : time resolution= 90ps

Conclusions

* Simple and robust method to measure spectral diffusionwith 90 ps resolution

(4 orders of magnitude improvementcompared to best existing resolution).

* Spectral duration time gives the under whichthere is no spectral diffusion.

* Opens new possibilities for the investigation of the very localenvironnement of single emitters.