Where are the superconductors?

Z. Fisk, UC Irvine Digital Synthesis Workshop Boston University September 27, 2013 Supported by AFOSR MURI

(from J. Schilling)

timeline of maximum superconducting transition temperature T c

1986: the new superconductors

La 1.84

Sr 0.16

CuO 4 T c = 40K

the new superconductors: pnictides T c = 56K 2006 Hirano; 2008 Jorend Wolfgang Jeitschko

What is common here?

• all based on electron precise materials • charge separated layers • electronically anisotropic

competing order

M. Nicholas et al. Phys. Rev. B

76

, 052401 (2007)

generic cuprate phase diagram

BCS-type A15 superconductivity

• Peierls-type lattice distortion above T c • strong coupling of soft lattice mode to conduction electrons • no lattice distortion when T c occurs first

Batterman and Barrett Phys. Rev.

145

, 296 (1966)

Schilling V 3 Si: T Martensitic / T c

highest T c found in proximity to competing “ localized ” phase • holds for BCS, heavy Fermions, organics, cuprates and pnictides • the competing phase, afm in heavy Fermions, terminates where it intersects the T c boundary and does not extend into the superconducting phase • “ localized ” : in BCS, lattice distorted; in heavy Fermions, local moment magnetism; in cuprates, the psuedo-gap phase.

• electronics highly non-adiabatic • superconductivity runs in structures

• superconductivity appears as solution to unloading entropy of fluctuations • gaps out lower frequency fluctuations • It seems plausible that a connection between structure, character of fluctuations and superconductivity exists