S. Maekawa (IMR, Tohoku University) Spin, Charge and Orbital and their Excitations in Transition Metal Oxides Contents: i) Spin-charge separation in one-dimensional cupr ates, ii) Non-linear optical response due to spin-charge separation, iii) Orbital in High Tc cuprates, iv) Anomalous transport properties due to orbital, v) Thermo-electric response due to spin and orbi tal, (Hong Kong, Dec. 18, 2006)
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S. Maekawa (IMR, Tohoku University) Spin, Charge and Orbital and their Excitations in Transition Metal Oxides Contents: i) Spin-charge separation in one-dimensional.
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S. Maekawa(IMR, Tohoku University)
Spin, Charge and Orbital and their Excitations in Transition Metal Oxides
Contents: i) Spin-charge separation in one-dimensional cuprates, ii) Non-linear optical response due to spin-charge separation, iii) Orbital in High Tc cuprates, iv) Anomalous transport properties due to orbital, v) Thermo-electric response due to spin and orbital,
(Hong Kong, Dec. 18, 2006)
Internal degrees of freedom of electron
Spin Magnet
Charge Electric Current
z
xy
Oxygen
d(3z2r2)d(x2y2)
d(xy) d(yz) d(zx)
Orbital (Shape of wave function: Shape of electron)
Hong Kong Conference
December 18, 2006
Anomalous Electronic Latticesin Cobaltates
S. Maekawa, W. Koshibae and N. Bulut(IMR, Tohoku University, Sendai)
Co - Oxides in triangular lattice
(NaxCoO2 and NaxCoO2・ yH2O)
i) Review of Unconventional properties
ii) Orbital degeneracy in the frustrated lattice
crystal lattice vs. electron lattice
unconventional properties
x Co3+ (3d6) and (1 x) Co4+ (3d5) in CoO6 units
CoO6
octahedron
•Crystal Structure
CoO2 layer
edge-shared CoO6 units
Na layer
CoO2 layer
Na layer
CoO2 layer
In NaxCoO2,
K. Takada, H. Sakurai, E. Takayama-Muromachi, F. Izumi, R.A. Dilanian, T. Sasaki, Nature 422, 53 (2003).
Superconductivity in water-intercalated NaxCoO2·yH2O
Na layer
CoO2 layer
H2O
In cubic CoO6 units,
Co3+eg
t2g
Co4+
Co3+ (3d6)S = 0
Co4+ (3d5)S = 1/2
z
x
y
d(3z2r2)d(x2y2)
d(xy) d(yz) d(zx)
5 - 3d orbitals
eg
t2g
NaxCoO2:
Anomalous physical properties in CoO2 layer:
i. Giant Hall effect at T R.T. NaxCoO2
(Y. Wang, et al., cond-mat/0305455)ii. Ferromagnetism
[Bi2xPbxSr2O4]yCoO2, Tc 3.2 K(I. Tsukada et al., J. Phys. Soc. Jpn. 70, 834 (’01).)
iii. Giant thermopower at T R.T.NaxCoO2
(I. Terasaki, Y. Sasago, and K. Uchinokura, PRB56, 12685(’97).)[Bi2xPbxSr2O4]yCoO2
(T. Yamamoto et al., Jpn. J. Appl. Phys. 39, L747 (’00).) Ca3Co4O9
(A. C. Masset et al., PRB62, 166 (’00).)iv. Superconductivity
NaxCoO2·yH2O(K. Takada et al., Nature 422, 53 (’03).)
v. Charge ordering NaxCoO2
(Foo et al., cond-mat/0312174)vi. Antiferromagnetism
Na0.5CoO2
(T. Uemura et al.)
I. Terasaki, Y. Sasago, and K. Uchinokura, PRB56, 12685(’97).
Y. Wang et al., cond-mat/0305455
Novel physics in CoO2 layer with triangular structure
1. Kagomé lattice hidden in CoO2 layer(WK and SM: PRL 91, 257003 (’03), NB, WK and SM: PRL 95, 037001 (05))
2. Anomalous physical properties: - Superconductivity (G. Khaliullin, WK and SM: PRL93, 176401(’04))
- Hall effect (WK, A. Oguri and SM: unpublished)
- Thermopower and Nernst effect(WK and SM: PRL 87, 236603 (’01). )