11 April 2023 Niels Bohr Institute – University of Copenhagen

Josephson junctions and spin-electronics with single wall carbon nanotubes

Experiment: Jeppe Holm, Henrik Ingerslev Jørgensen, Kasper Grove-Rasmussen, Jonas Hauptmann, Poul Erik LindelofTheory: Jens Paaske, Karsten Flensberg,

Niels Bohr Institute & Nano-Science CenterUniversity of Copenhagen, Denmark

Symposium on Quantum Phenomena and Devices at Low Temperatures 28.-30.3.2008, ULTI users meeting, Finland

CARDEQ(ULTRA-1D)SECOQCERA QISTFTP (DK)NTT BRL

Content11 April 2023 Niels Bohr Institute – University of Copenhagen

1. Single wall carbon nanotubes by CVD2. Nanotube synthesis in its enfancy3. Biasspectroscopy4. Importance of contact resistance5. Renormalization shifts6. Exchange fields from ferromagnetic contacts7. Spin reversal by the gatevoltage8. Giaever tunneling through SWCNT9. Josephson tunneling through SWCNT

11 April 2023 Niels Bohr Institute – University of Copenhagen

CVD growth of Single-Wall Carbon Nanotubes (SWCNT)

Argon

Hydrogen

CVD oven (850 oC) Methane

11 April 2023 Niels Bohr Institute – University of Copenhagen

Carbon nanotubesarmchair Zig-Zag Chiral

(10,10) (15,0) (12,8)

1 nm

11 April 2023 Niels Bohr Institute – University of Copenhagen

Rope of single wall carbon nanotubes

10 nm

TEM picture

11 April 2023 Niels Bohr Institute – University of Copenhagen

SWCNT with topgates and backgates

10/26/2005

Bandstructure of Carbon nanotubes

(N, M) = (5, 5) (N, M) = (10, 5)

Metallic tubes (but…) Wide-gap semiconducting tubes

Chirality determines bandstructure

11 April 2023 Niels Bohr Institute – University of Copenhagen

__ __

__ __

__ __

__ __

__ __

__ __

__

__

__ __

source drain

Quantum dot

barriere barriere

Vgate

Vsd

Vsd

0 -

Vgate

* * * *___________

Transconductance ~ 3e2/h

Quantum DotsBias-spectroscopy

11 April 2023 Niels Bohr Institute – University of Copenhagen

Fabry-Perot/Kondo/Coulomb

K. Grove-Rasmussen et al.

J. New Physics (2006)

Coulomb blockade shells)

Adding 285 electrons,one by one...

88 odd-occupiedcharge states withzero-bias Kondo ridge.

11 April 2023 Niels Bohr Institute – University of Copenhagen

4 shell Kondo resonances

Vg

Jeppe Holm, MSc

The standard diamond

H He Li Be

B C N O

F Ne Na Mg

... ... ... ...

Shell-filling

11 April 2023 Niels Bohr Institute – University of Copenhagen

Kondo resonance

.

The standard shell diamonds

Inelastic cotunneling

Elastic cotunneling (S=½ Kondo)

New type of diamondsGatedependent excitation energies

30

21

7

53 are unidentified

11 April 2023

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_ _

Renormalization effects *** *

_ __ _

_ _

_ __ _

_ _

_ __ _

_ _

- large transmission

- small transmission

Tunneling-renormalized diamonds (Theory)

Diamond edges are skewed

Widths of diamonds are different

11 April 2023 Niels Bohr Institute – University of Copenhagen

Relative width of the different diamonds

11 April 2023 Niels Bohr Institute – University of Copenhagen

Exchange field*

Hauptmann, Paaske, Lindelof, Nature Physics, April 2008

*Ideas of Patsupathy et al. (2004) Martinek et al. (2005)

11 April 2023 Niels Bohr Institute – University of Copenhagen

Exchange field and external

field

Hauptmann, Paaske, Lindelof, Nature Physics, April 2008

11 April 2023 Niels Bohr Institute – University of Copenhagen

Gate influence on exchange field

11 April 2023 Niels Bohr Institute – University of Copenhagen

Renormalizationllevel shift for

various Vg and B

Hauptmann, Paaske, Lindelof, Nature Physics, April 2008

Theory of Martinek et al.PRB 72, 121302 (2005)

- - - 2. Order perurbation theory

11 April 2023 Niels Bohr Institute – University of Copenhagen

-10 -5 0 5 10

-6

-3

0

3

6

Vgate [V]

Vsd

[mV]

PdNbPd-SWCNT-PdNbPd (5/70/5nm)• Gap around zero bias, width corresponding to 4• Clear Coulomb blockade diamonds

Vsd = 2

Superconducting Giaever tunnelling

Henrik I. Jørgensen, Kasper Grove-Rasmussen and PEL

11 April 2023 Niels Bohr Institute – University of Copenhagen

-3 -2 -1 0 1 2 30.00

0.05

0.10

0.15

0.20

0.25

QPQP

ES

dI/

dV

[e

2/h

]

Vsd [mV]

A B

GS

GS

GS

QP

QP

2

-2

=20uV (5nA)Ec = 5-6 meV = 0.275 meVE = 2-3 meV

Ec, E >>>>

PdNbPd-SWCNT-PdNbPd (Coulomb blockade)

Henrik I. Jørgensen, Kasper Grove-Rasmussen and PEL

S-SWCNT-S

E

11 April 2023 Niels Bohr Institute – University of Copenhagen

Designed Bias circuit to superconducting SWCNT

11 April 2023 Niels Bohr Institute – University of Copenhagen

Josephson effect & p junctions

H.I. Jørgensen et al., Nano Letters 7, 2441 (2007)

TiAlTi-SWCNT-TiAlTiTc=0.75 KD=0.1 meV

T=75 mK

11 April 2023 Niels Bohr Institute – University of Copenhagen

Ic (Vg)

H.I. Jørgensen et al., Nano Letters 7, 2441 (2007)

Summary

11 April 2023 Niels Bohr Institute – University of Copenhagen

- Fabrication of SWCNTs is still rudimentary- Contacts resistance < = < h/4e2 crucial, but it is not well

controlled (~30%)- We found a new renormalization effect in SWCNT- We measured a magnetic exchange field (~2 T) in

SWCNT with ferromagnetic contacts- We are for the first time able to reverse a single electron

spin in a quantum dot by tuning a backgate voltage- We optimized the Josephson supercurrent by a bias circuit

(up to 2.5 nA, D/eRJ=4.5 A)- We studied S-SWCNT-S p - Josephson junction