16.20 o11 b mallett
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High-Temperature Superconductors under pressure. NZIP2011 Ben Mallett Oct 2011
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Research 8: B Mallett
Transcript of 16.20 o11 b mallett
High-Temperature Superconductors under pressure.
NZIP2011
Ben MallettOct 2011
R. Hott et al, Supercondcuting materials: A topical overview, in “Frontiers in Superconducting Materials”, Springer-Verlag, 2004
Figure courtesy of S. Chong
Basic cuprate structure
YBa2Cu3O7-y
Figure courtesy of S. Chong
The phase diagram
J.L. Tallon, Frontier in Superconducting Materials; Oxygen in High-Tc Cuprate Superconductors, Springer-Verlag, 2004.
stripe phase
CuO
dx2-y2
2pσ
a
b
The undoped cuprates are anti-ferromagnetic, charge transfer insulators
The phase diagram
J.L. Tallon, Frontier in Superconducting Materials; Oxygen in High-Tc Cuprate Superconductors, Springer-Verlag, 2004.
stripe phase
Red triangles are external pressure measurement data reported by Wijngaarden et al., Physica B, 265, 128-135 (1999).
LnBa2Cu3O7-y
‘Chemical’ or ‘Internal’ pressure
Guillaume et al.
Measuring Antiferromagnetic superexchange strength, J, with Raman spectroscopy
Two excited magnons
LnBa2Cu3O6
J A
La2CuO4 data from - Aronson et al., Phys. Rev. B, 44, 4657 (1991)
YBa2Cu3O6.2 pressure data from - Maksimov et al., Phys. Rev. B, 49, 15385, (1994)
Red triangles are external pressure measurement data reported by Wijngaarden et al., Physica B, 265, 128-135 (1999).
Other energy scales?
• Pseudogap – although believed to scale with J…
• Proximity to the van Hove singularity in the Density of States.
• Pairing potential, V.
• Scattering rates.
• Dr. Jeff Tallon
• Dr. Grant Williams
• Raman lab guys (VUW)
• MacDiarmid Institute
• Prof. Alan Kaiser
• Prof. Thomas Wolf
• External pressure;
11 .cT K GPaP
~ 4P GPa
• Caveats;• Doping dependent• Charge transfer effects• For lower pressures;• Anisotropic pressure may have different effect• …
• Caveats;• Doping dependent• Charge transfer effects• For lower pressures;• Anisotropic pressure may have different effect• …
• Caveats;• Doping dependent• Charge transfer effects• For lower pressures;• Anisotropic pressure may have
different effect• …
Smaller ion size
-16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 120
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30Bi
2Sr
1.6-yA
yRE
0.4CuO
6+
Tc
[K]
S(300K) [V/K]
0.4La 0.2Ba, 0.4La 0.2Ca 0.4La 0.4Sm 0.4Nd 0.4Eu 0.4Gd
Bi2Sr1.6-yAyRE0.4CuO6+z
1
int~ 15 .cdT K GPadP
Caveat; Likely to be additional effects influencing/suppressing Tc.
• ; Pairing boson energy scale
• ; Density of states at the fermi level – in the normal-state.
• ; Pairing potential
11.13 expmf
B c BE
k TN V
B
EN
V
Hole dynamics
14, , , ,
, ,
ˆ ˆ ˆ ˆi j i j i j i jij ij ij
H t c c t c c J n n
S S
J xt Metal with residual AF correlations xt J
a
b
The Fermi surface
