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20 August 2014 Niels Bohr Institute – University of Copenhagen Josephson junctions and spin-electronics with single wall carbon nanotubes Experiment: Jeppe.

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Presentation on theme: "20 August 2014 Niels Bohr Institute – University of Copenhagen Josephson junctions and spin-electronics with single wall carbon nanotubes Experiment: Jeppe."— Presentation transcript:

1 20 August 2014 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 Lindelof Theory: Jens Paaske, Karsten Flensberg, Niels Bohr Institute & Nano-Science Center University of Copenhagen, Denmark Symposium on Quantum Phenomena and Devices at Low Temperatures 28.-30.3.2008, ULTI users meeting, Finland CARDEQ (ULTRA-1D) SECOQC ERA QIST FTP (DK) NTT BRL

2 Content 20 August 2014 Niels Bohr Institute – University of Copenhagen 1.Single wall carbon nanotubes by CVD 2.Nanotube synthesis in its enfancy 3.Biasspectroscopy 4.Importance of contact resistance 5.Renormalization shifts 6.Exchange fields from ferromagnetic contacts 7.Spin reversal by the gatevoltage 8.Giaever tunneling through SWCNT 9.Josephson tunneling through SWCNT

3 20 August 2014 Niels Bohr Institute – University of Copenhagen CVD growth of Single-Wall Carbon Nanotubes (SWCNT) Argon Hydrogen CVD oven (850 oC) Methane

4 20 August 2014 Niels Bohr Institute – University of Copenhagen Carbon nanotubes armchair Zig-Zag Chiral (10,10) (15,0) (12,8) 1 nm

5 20 August 2014 Niels Bohr Institute – University of Copenhagen Rope of single wall carbon nanotubes 10 nm TEM picture

6 20 August 2014 Niels Bohr Institute – University of Copenhagen SWCNT with topgates and backgates

7 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

8 20 August 2014 Niels Bohr Institute – University of Copenhagen __ __ __ __ __ __ source drain Quantum dot barriere V gate V sd 0 - V gate **** ___________ Transconduct ance ~ 3e 2 /h Quantum Dots Bias-spectroscopy

9 20 August 2014 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 20 August 2014 Niels Bohr Institute – University of Copenhagen 4 shell Kondo resonances Vg Jeppe Holm, MSc

12 The standard diamond H He Li Be B C NO F Ne Na Mg Shell-filling

13 20 August 2014 Niels Bohr Institute – University of Copenhagen Kondo resonance.

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

15 New type of diamonds Gatedependent excitation energies 30 21 7 53 are unidentified

16 20 August 2014 _ Renormalization effects * * * * _ - large transmission - small transmission

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

18 20 August 2014 Niels Bohr Institute – University of Copenhagen Relative width of the different diamonds

19 20 August 2014 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 20 August 2014 Niels Bohr Institute – University of Copenhagen Exchange field and external field Hauptmann, Paaske, Lindelof, Nature Physics, April 2008

21 20 August 2014 Niels Bohr Institute – University of Copenhagen Gate influence on exchange field

22 20 August 2014 Niels Bohr Institute – University of Copenhagen Renormalizationl level 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

23 20 August 2014 Niels Bohr Institute – University of Copenhagen PdNbPd-SWCNT-PdNbPd (5/70/5nm) Gap around zero bias, width corresponding to 4  Clear Coulomb blockade diamonds V sd = 2  Superconducting Giaever tunnelling Henrik I. Jørgensen, Kasper Grove-Rasmussen and PEL

24 20 August 2014 Niels Bohr Institute – University of Copenhagen 22 -2   =20uV (5nA) Ec = 5-6 meV  = 0.275 meV  E = 2-3 meV Ec,  E >>  >>  PdNbPd-SWCNT-PdNbPd (Coulomb blockade) Henrik I. Jørgensen, Kasper Grove-Rasmussen and PEL    S-SWCNT-S EE

25 20 August 2014 Niels Bohr Institute – University of Copenhagen Designed Bias circuit to superconducting SWCNT

26 20 August 2014 Niels Bohr Institute – University of Copenhagen Josephson effect &  junctions H.I. Jørgensen et al., Nano Letters 7, 2441 (2007) TiAlTi-SWCNT-TiAlTi Tc=0.75 K  =0.1 meV T=75 mK

27 20 August 2014 Niels Bohr Institute – University of Copenhagen Ic (Vg) H.I. Jørgensen et al., Nano Letters 7, 2441 (2007)

28 Summary 20 August 2014 Niels Bohr Institute – University of Copenhagen - Fabrication of SWCNTs is still rudimentary - Contacts resistance < = < h/4e 2 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,  /eR J =4.5 A) -We studied S-SWCNT-S  - Josephson junction


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