Kondo effect in Quantum dots / Carbon nanotubes

1
Kondo effect in Quantum dots / Carbon nanotubes

• Journal Club 2008/05/20
• Fan Wu

2
Kondo effect
L. Kouwenhoven, L. Glazman. Revival of the Kondo
effect. Physics World, 1, 33 (2001)
odd e in QD
magnetic impurities
normal metal
SC
even e in QD
even
odd
3
s 0.22 for spin-half system
Nature 408, 342 (2000)
4

• SWNT with gold leads
• Kondo ridge for odd-N at B0
• Bubbles for even-N at B0, yet ridges can be
  formed at certain field BC, which related with
  ground state (singlet S0) - lowest excited state
  (triplet S1) energy gap Dt-s as

M. Pustilnik, et al., Quantumdots with even
number of electrons Kondo effect in a finite
magnetic field. Phys. Rev. Lett. 84, 1756 (2000).
5

• 12nm gold bridge on Al/Al2O3
• Electromigration forms grain quantum dot,
  with/without submonolayer of cobalt
• Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction
  introduce split zero-bias peak (SZBP)

6

• Competition between the Kondo effect (energy
  scale TK) and the RKKY coupling of the spin
  (interaction strength I)

7
Nature 434, 484 (2005)
8

• Ti/Au electrodes with CVD grown SWNT
• dB orbital Kondo effect induced by anticrossing
  band

• Unusually high TK 7.7K, ascribed to the
  enhanced degeneracy (one electron SU(4) and
  two-electron singlettriplet Kondo

B1.5T
9
(No Transcript)
10

• Cr/Au electrodes with CVD grown SWNT

Ng 1, 3
SU(2)
Ng 2
11

• InAs quantum dots with Ti/Al electrodes
• Competition between Kondo and SC DltltkBT, Kondo
  survive with SC leads DgtgtkBT, Coulomb blockade

12
TK TK/(21/s-1)1/2, G(TK) G0/2, s0.22 for
spin-half system
13

• Cr/Au electrodes with CVD grown SWNT

14
Coulomb energy U 2.9 meV,orbital splitting
0.7 meV, single-particle level spacing DE 3.5
meV.

• Inelastic cotunneling with second-order
  perturbation