1. Routes for finding superconductors based on structural trends
Workshop on Digital
Design of Materials - 09/2013
Routes for finding superconductors based on structural trends
Pascoal G. Pagliuso
Grupo de Propriedades Ópticas e Magnéticas dos Sólidos (GPOMS)
Instituto de Física ``Gleb Wataghin'', UNICAMP – Campinas -SP
UC - Irvine
CBPF

2. Outline I. HFS in similar crystal structures
II. The role of dimensionality and crystal structures
(CEF – single ion anisotropy)
III. Possible relationship with FeAs-based intermetallic
IV. The role of local distortion of FeAs bonds
V. Substitution effects on the localization character
and orbital degrees of freedom of the Fe 3d bands
VI. Implications in new materials search
and suggestions for digital design

4. CemMnIn3m+2n -Ce2CoIn8 CeRh1-x(Ir,Co)xIn5 [1,2] Ce2Rh1-xIrxIn8 [3,4,5]
TC  1.0 K
  600 mJ/K2 mole Ce
[1] Pagliuso et al, Physica B, 312, 129 (2002).
[2] Pagliuso et al, Phys.Rev B, 64, (R) (2001).
[3] E.N. Hering et al Physica B, 378, 423 (2006).
[4] E.N. Hering, Physica B, 403, 780 (2008);
[5] E. N. Hering, C. Adriano, et al, PRB (2011).

5. c/a as control parameter for Tc
Is there an intrisic parameter in this plot, which depends on c/a and determines TC?
Tuning:
JRKKY TK
- CEF
P.G. Pagliuso et al. PRB, (R) (2002); Physica B , 129 (2002).

7. TN evolution for RmAnIn3m+2n(m = 1,2 ; n =0,1)
RE moments ordered along
c-axis.
RE moments in the ab-plane.
Garcia, E. Miranda, et al. JAP (2006)
P.G. Pagliuso et al. Physical Review B. 62, (2000) also PRB 2001.

8. INS and XAS CEF study in Ce-M-In
T. Willers et al.
A. Severing et al. PRB (2010)
A.D. Christianson et al PRB (2004).

9. Extrapolation of CEF trend to Ce-based materials
cubic
tetragonal
TRKKY TK TN
isotropic
anisotropic
anisotropic
anisotropic
(increasing of g-anisotropy)
Strong
magnetic-fluctuations??
Frustrated local
moments + hybridization

10. 1-1-5 – FeAs-intermetallics ?
M. S. Torikachvilli et al. PRB 2008.
Marianne Rotter al. New J. of Phys. (2009).

11. FeAs-based superconductors
Common Structural parameter: FeAs4 tetrahedral
Common Electronic parameter: SDW magnetic instability
J. Paglione and R. L. Greene. Nature Physics 6, 645 (2010).

12. Resultados – EXAFS
E. Granado et al. PRB 83, (2011)

13. Site specific ESR on Fe-based Intermetallic Compounds

14. Ho  g-value or IT
H  relaxation and inhomogeneity
I   (T)

15. ESR Results P. F. S. Rosa et al. submitted to PRL (2013).
Eu 2+
P. F. S. Rosa et al. PHYSICAL REVIEW B 86, (2012)
P. F. S. Rosa et al. submitted to PRL (2013).

16. ESR - Results P. F. S. Rosa et al. submitted to PRL (2013).
P. F. S. Rosa et al. PHYSICAL REVIEW B 86, (2012)
P. F. S. Rosa et al. submitted to PRL (2013).

17. z y x

18. xy occupation increasesz y x
Smaller dFe-As with chemical substitution, hydrostatic pressure and magnetic field in the plane!
SDW Phase vanishes
xy occupation increases

19. Implications for designing materials
To increase TC for magnetically mediated SC:
Tsf, characteristic T for spin fluctuations high
Tunable carrier density
Quasi 2-d helps a lot; maybe not much 2-d needed – increase c/a – tune CEF GS
Need bigger bandwidths to increase Tsf, but keep optimized Tc/Tsf - 3d spins in the active layer.
1-1-5 e 2-1-8
1-2-2
2-1-4, etc

20. Examples for Digital Design?
2-1-8
1-2-2
2-1-4
1) Bi2CuIn8
3d single band at FS? Which symmetry?
2) CaFeSn5
Fe 3d T2g at the Fermi level?
dxy with larger occupation?
3) Yb2CoAs4
Yb3+GS Ising like?
Energy scale of 4-electrons?