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