Superconductivity and structural variation of the electron-correlated layer systems Sr(Pd1-xTx)(2)Ge-2 (T = Co, Ni, Rh; 0 <= x <= 1)

No Thumbnail Available
Issue Date
2012-01-31
Authors
Wang, J.W.
Chen, I.A.
Hung, T.L.
You, Y.B.
Ku, H.C.
Hsu, Y.Y.
Ho, J. C.
Chen, Y.Y.
Advisor
Citation

Wang J.W., Chen I.A., Hung T.L., You Y.B., Ku H.C., et al. 2012. "Superconductivity and structural variation of the electron-correlated layer systems Sr(Pd1-xTx)(2)Ge-2 (T = Co, Ni, Rh; 0 <= x <= 1)". Physical Review B - Condensed Matter and Materials Physics. 85 (2).

Abstract

Superconductivity variations deduced from the x-ray diffraction and the magnetic and heat-capacity measurements in the pseudoternary Sr(Pd1-xTx)(2)Ge-2 layer system [Pd(4d(8)), T = Co(3d(7)), Ni(3d(8)), or Rh(4d(7)); 0 <= x <= 1] are reported. For the BaFe2As2-type tetragonal structure, the degenerate nd(7) or nd(8) orbitals of transitionmetal T are split by c-axis squeezed TGe4 tetrahedral crystal field in the T-Ge layer. For the isoelectronic Sr(Pd1-xNix)(2)Ge-2 system, the superconducting transition temperature T-c decreases monotonically from 3.12 K for 4d-band SrPd2Ge2 to 0.92 K for 3d-band SrNi2Ge2, where major contributions of conduction electrons are from the half filled dispersive three-dimensional (3D)-like upper-lying nd(xz,yz) bands. For the Sr(Pd1-xRhx)(2)Ge-2 system, T-c decreases to 2.40 K with 25% of 4d(7) Rh substitution. For the Sr(Pd1-xCox)(2)Ge-2 system, T-c decreases sharply to 2.58 K with only 3% of 3d(7) Co substitution. No superconductivity is e! xpected for SrRh2Ge2 and SrCo2Ge2 with lower density of states in d(xz,yz) bands due to down shift of Fermi energy E-F by one less electron per transition metal. The lower T-c of the present electron-overdoped (nd(7) or nd(8)) compound is due to dispersive 3D-like nd(xz,yz) conduction bands with weak electron correlation, in comparison with the less-electron-doped (3d(6.1)) 22-K superconductor BaFe1.8Co0.2As2 or the hole-doped (3d(5.9)) 38-K superconductor Ba0.6K0.4Fe2As2 where electron contribution is from less dispersive 2D-like lower-lying 3d(xy) conduction band with stronger electron correlation.

Table of Content
Description
Click on the DOI link below to access the article (may not be free).
publication.page.dc.relation.uri