1. Niels Bohr Institute – University of Copenhagen
06 April 2017
Niels Bohr Institute – University of Copenhagen
Symposium on Quantum Phenomena and Devices at Low Temperatures , ULTI users meeting, Finland
Josephson junctions and spin-electronics with single wall carbon nanotubes
Experiment: Jeppe Holm, Henrik Ingerslev Jørgensen, Kasper Grove-Rasmussen, Jonas Hauptmann, Poul Erik Lindelof
Theory: Jens Paaske, Karsten Flensberg,
Niels Bohr Institute & Nano-Science Center
University of Copenhagen, Denmark
CARDEQ
(ULTRA-1D)
SECOQC
ERA QIST
FTP (DK)
NTT BRL

2. Niels Bohr Institute – University of Copenhagen
06 April 2017
Niels Bohr Institute – University of Copenhagen
Content
Single wall carbon nanotubes by CVD
Nanotube synthesis in its enfancy
Biasspectroscopy
Importance of contact resistance
Renormalization shifts
Exchange fields from ferromagnetic contacts
Spin reversal by the gatevoltage
Giaever tunneling through SWCNT
Josephson tunneling through SWCNT

3. CVD growth of Single-Wall Carbon Nanotubes (SWCNT)
06 April 2017
Niels Bohr Institute – University of Copenhagen
CVD growth of Single-Wall Carbon Nanotubes (SWCNT)
Argon
Hydrogen
CVD oven (850 oC) Methane

4. Carbon nanotubes armchair Zig-Zag Chiral
06 April 2017
Niels Bohr Institute – University of Copenhagen
Carbon nanotubes armchair Zig-Zag Chiral
1 nm
(10,10) (15,0) (12,8)

5. Rope of single wall carbon nanotubes
06 April 2017
Niels Bohr Institute – University of Copenhagen
Rope of single wall carbon nanotubes
TEM picture
10 nm

6. SWCNT with topgates and backgates
06 April 2017
Niels Bohr Institute – University of Copenhagen
SWCNT with topgates and backgates

7. Bandstructure of Carbon nanotubes
10/26/2005
Bandstructure of Carbon nanotubes
Metallic tubes (but…)
Wide-gap semiconducting tubes
(N, M) = (5, 5)
(N, M) = (10, 5)
Chirality determines bandstructure

8. Quantum Dots Bias-spectroscopy
06 April 2017
Niels Bohr Institute – University of Copenhagen
Quantum dot
Transconductance ~ 3e2/h __
__ __ __
__ __ __ __
__ __ __ __
barriere
Vsd
0 -
barriere
___________ * * * *
Quantum Dots Bias-spectroscopy
Vgate
Vsd
__ __ __ __
drain
source
Vgate

9. Fabry-Perot/Kondo/Coulomb
06 April 2017
Niels Bohr Institute – University of Copenhagen
Fabry-Perot/Kondo/Coulomb
K. Grove-Rasmussen et al.
J. New Physics (2006)

10. Coulomb blockade shells)
Adding 285 electrons,
one by one...
88 odd-occupied
charge states with
zero-bias Kondo ridge.

11. 4 shell Kondo resonances
06 April 2017
Niels Bohr Institute – University of Copenhagen
4 shell Kondo resonances Vg
Jeppe Holm, MSc

12. The standard diamond
Shell-filling H He Li Be B C N O F Ne Na Mg
...

13. Niels Bohr Institute – University of Copenhagen
06 April 2017
Niels Bohr Institute – University of Copenhagen
Kondo resonance .

14. The standard shell diamonds
Elastic cotunneling (S=½ Kondo)
Inelastic cotunneling

15. New type of diamonds Gatedependent excitation energies30 21 7
53 are unidentified

16. Renormalization effects
06 April 2017
Renormalization effects * * * *
- large transmission
- small transmission _
_ _ _
_ _ _
_ _ _
_ _

17. Tunneling-renormalized diamonds (Theory)
Diamond edges are skewed
Widths of diamonds are different

18. Relative width of the different diamonds
06 April 2017
Niels Bohr Institute – University of Copenhagen
Relative width of the different diamonds

19. Niels Bohr Institute – University of Copenhagen
06 April 2017
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)

20. Exchange field and external field
06 April 2017
Niels Bohr Institute – University of Copenhagen
Exchange field and external field
Hauptmann, Paaske, Lindelof, Nature Physics, April 2008

21. Gate influence on exchange field
06 April 2017
Niels Bohr Institute – University of Copenhagen
Gate influence on exchange field

22. Renormalizationllevel shift for various Vg and B
06 April 2017
Niels Bohr Institute – University of Copenhagen
Renormalizationllevel shift for various Vg and B
Order perurbation theory
Theory of Martinek et al.
PRB 72, (2005)
Hauptmann, Paaske, Lindelof, Nature Physics, April 2008

23. Superconducting Giaever tunnelling
06 April 2017
Niels Bohr Institute – University of Copenhagen
Superconducting Giaever tunnelling
PdNbPd-SWCNT-PdNbPd (5/70/5nm)
Gap around zero bias, width corresponding to 4
Clear Coulomb blockade diamonds
Vsd = 2
Henrik I. Jørgensen, Kasper Grove-Rasmussen and PEL

24. PdNbPd-SWCNT-PdNbPd (Coulomb blockade)
06 April 2017
Niels Bohr Institute – University of Copenhagen
PdNbPd-SWCNT-PdNbPd (Coulomb blockade) 2
-2
 =20uV (5nA)
Ec = 5-6 meV
 = meV
E = 2-3 meV   E 
S-SWCNT-S
Ec, E >>>>
Henrik I. Jørgensen, Kasper Grove-Rasmussen and PEL

25. Designed Bias circuit to superconducting SWCNT
06 April 2017
Niels Bohr Institute – University of Copenhagen
Designed Bias circuit to superconducting SWCNT

26. Josephson effect & p junctions
06 April 2017
Niels Bohr Institute – University of Copenhagen
Josephson effect & p junctions
T=75 mK
TiAlTi-SWCNT-TiAlTi
Tc=0.75 K
D=0.1 meV
H.I. Jørgensen et al., Nano Letters 7, 2441 (2007)

27. Niels Bohr Institute – University of Copenhagen
06 April 2017
Niels Bohr Institute – University of Copenhagen
Ic (Vg)
H.I. Jørgensen et al., Nano Letters 7, 2441 (2007)

28. Niels Bohr Institute – University of Copenhagen
06 April 2017
Niels Bohr Institute – University of Copenhagen
Summary
- 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