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

J. W. Wang, I. A. Chen, T. L. Hung, Y. B. You, H. C. Ku, Y. Y. Hsu, J. C. Ho, Y. Y. Chen

Research output: Contribution to journalArticle

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Abstract

Superconductivity variations deduced from the x-ray diffraction and the magnetic and heat-capacity measurements in the pseudoternary Sr(Pd 1-xT x) 2Ge 2 layer system [Pd(4d8), T= Co(3d7), Ni(3d8), or Rh(4d7); 0≤x≤1] are reported. For the BaFe 2As 2-type tetragonal structure, the degenerate nd7 or nd8 orbitals of transition metal T are split by c-axis squeezed TGe 4 tetrahedral crystal field in the T-Ge layer. For the isoelectronic Sr(Pd 1-xNi x) 2Ge 2 system, the superconducting transition temperature T c decreases monotonically from 3.12 K for 4d-band SrPd 2Ge 2 to 0.92 K for 3d-band SrNi 2Ge 2, 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(Pd 1-xRh x) 2Ge 2 system, T c decreases to 2.40K with 25% of 4d7 Rh substitution. For the Sr(Pd 1-xCo x) 2Ge 2 system, T c decreases sharply to 2.58 K with only 3% of 3d7 Co substitution. No superconductivity is expected for SrRh 2Ge 2 and SrCo 2Ge 2 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 (nd7 or nd8) compound is due to dispersive 3D-like nd xz,yz conduction bands with weak electron correlation, in comparison with the less-electron-doped (3d6.1) 22-K superconductor BaFe 1.8Co 0.2As 2 or the hole-doped (3d5.9) 38-K superconductor Ba 0.6K 0.4Fe 2As 2 where electron contribution is from less dispersive 2D-like lower-lying 3d xy conduction band with stronger electron correlation.

Original languageEnglish
Article number024538
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume85
Issue number2
DOIs
Publication statusPublished - 2012 Jan 31

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Superconductivity
superconductivity
Electrons
Electron correlations
Conduction bands
electrons
Superconducting materials
Transition metals
Substitution reactions
conduction bands
transition metals
substitutes
Fermi level
Superconducting transition temperature
Specific heat
conduction electrons
Diffraction
crystal field theory
x ray diffraction
X rays

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

Cite this

Superconductivity and structural variation of the electron-correlated layer systems Sr(Pd 1-xT x) 2Ge 2 (T = Co, Ni, Rh; 0≤x≤1). / Wang, J. W.; Chen, I. A.; Hung, T. L.; You, Y. B.; Ku, H. C.; Hsu, Y. Y.; Ho, J. C.; Chen, Y. Y.

In: Physical Review B - Condensed Matter and Materials Physics, Vol. 85, No. 2, 024538, 31.01.2012.

Research output: Contribution to journalArticle

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abstract = "Superconductivity variations deduced from the x-ray diffraction and the magnetic and heat-capacity measurements in the pseudoternary Sr(Pd 1-xT x) 2Ge 2 layer system [Pd(4d8), T= Co(3d7), Ni(3d8), or Rh(4d7); 0≤x≤1] are reported. For the BaFe 2As 2-type tetragonal structure, the degenerate nd7 or nd8 orbitals of transition metal T are split by c-axis squeezed TGe 4 tetrahedral crystal field in the T-Ge layer. For the isoelectronic Sr(Pd 1-xNi x) 2Ge 2 system, the superconducting transition temperature T c decreases monotonically from 3.12 K for 4d-band SrPd 2Ge 2 to 0.92 K for 3d-band SrNi 2Ge 2, 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(Pd 1-xRh x) 2Ge 2 system, T c decreases to 2.40K with 25{\%} of 4d7 Rh substitution. For the Sr(Pd 1-xCo x) 2Ge 2 system, T c decreases sharply to 2.58 K with only 3{\%} of 3d7 Co substitution. No superconductivity is expected for SrRh 2Ge 2 and SrCo 2Ge 2 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 (nd7 or nd8) compound is due to dispersive 3D-like nd xz,yz conduction bands with weak electron correlation, in comparison with the less-electron-doped (3d6.1) 22-K superconductor BaFe 1.8Co 0.2As 2 or the hole-doped (3d5.9) 38-K superconductor Ba 0.6K 0.4Fe 2As 2 where electron contribution is from less dispersive 2D-like lower-lying 3d xy conduction band with stronger electron correlation.",
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AU - Hung, T. L.

AU - You, Y. B.

AU - Ku, H. C.

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N2 - Superconductivity variations deduced from the x-ray diffraction and the magnetic and heat-capacity measurements in the pseudoternary Sr(Pd 1-xT x) 2Ge 2 layer system [Pd(4d8), T= Co(3d7), Ni(3d8), or Rh(4d7); 0≤x≤1] are reported. For the BaFe 2As 2-type tetragonal structure, the degenerate nd7 or nd8 orbitals of transition metal T are split by c-axis squeezed TGe 4 tetrahedral crystal field in the T-Ge layer. For the isoelectronic Sr(Pd 1-xNi x) 2Ge 2 system, the superconducting transition temperature T c decreases monotonically from 3.12 K for 4d-band SrPd 2Ge 2 to 0.92 K for 3d-band SrNi 2Ge 2, 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(Pd 1-xRh x) 2Ge 2 system, T c decreases to 2.40K with 25% of 4d7 Rh substitution. For the Sr(Pd 1-xCo x) 2Ge 2 system, T c decreases sharply to 2.58 K with only 3% of 3d7 Co substitution. No superconductivity is expected for SrRh 2Ge 2 and SrCo 2Ge 2 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 (nd7 or nd8) compound is due to dispersive 3D-like nd xz,yz conduction bands with weak electron correlation, in comparison with the less-electron-doped (3d6.1) 22-K superconductor BaFe 1.8Co 0.2As 2 or the hole-doped (3d5.9) 38-K superconductor Ba 0.6K 0.4Fe 2As 2 where electron contribution is from less dispersive 2D-like lower-lying 3d xy conduction band with stronger electron correlation.

AB - Superconductivity variations deduced from the x-ray diffraction and the magnetic and heat-capacity measurements in the pseudoternary Sr(Pd 1-xT x) 2Ge 2 layer system [Pd(4d8), T= Co(3d7), Ni(3d8), or Rh(4d7); 0≤x≤1] are reported. For the BaFe 2As 2-type tetragonal structure, the degenerate nd7 or nd8 orbitals of transition metal T are split by c-axis squeezed TGe 4 tetrahedral crystal field in the T-Ge layer. For the isoelectronic Sr(Pd 1-xNi x) 2Ge 2 system, the superconducting transition temperature T c decreases monotonically from 3.12 K for 4d-band SrPd 2Ge 2 to 0.92 K for 3d-band SrNi 2Ge 2, 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(Pd 1-xRh x) 2Ge 2 system, T c decreases to 2.40K with 25% of 4d7 Rh substitution. For the Sr(Pd 1-xCo x) 2Ge 2 system, T c decreases sharply to 2.58 K with only 3% of 3d7 Co substitution. No superconductivity is expected for SrRh 2Ge 2 and SrCo 2Ge 2 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 (nd7 or nd8) compound is due to dispersive 3D-like nd xz,yz conduction bands with weak electron correlation, in comparison with the less-electron-doped (3d6.1) 22-K superconductor BaFe 1.8Co 0.2As 2 or the hole-doped (3d5.9) 38-K superconductor Ba 0.6K 0.4Fe 2As 2 where electron contribution is from less dispersive 2D-like lower-lying 3d xy conduction band with stronger electron correlation.

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