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 Tc

1986: the new superconductors

La1.84Sr0.16CuO4 Tc = 40K

the new superconductors: pnictides Tc = 56K

Wolfgang Jeitschko

2006 Hirano; 2008 Jorend

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 Tc

• strong coupling of soft lattice mode to conduction electrons

• no lattice distortion when Tc occurs first

Batterman and Barrett Phys. Rev. 145, 296 (1966)

Schilling V3Si: TMartensitic / Tc

highest Tc 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 Tcboundary 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