Abstract
Superconductivity in a three-orbital model for the Γ3 crystalline electric field (CEF) ground state is investigated by applying the random phase approximation. In this model, we assume an antiferromagnetic interaction between the Γ7 and Γ8 orbitals to stabilize the Γ3 CEF state among f2 states. This interaction may induce spin-singlet pairing between electrons in these orbitals. If we consider the onsite pairing state composed of the Γ7 and Γ8 orbitals, it has the Eg symmetry. Indeed, we find that the Eg spin-singlet superconducting state is realized in a wide parameter region. Possible coexistence of the superconductivity and quadrupole order is also discussed.
Highlights
In the vicinity of the antiferromagnetically ordered phase, unconventional superconductivity[1,2] has been observed in many materials, and the relation between the superconductivity and magnetism has been a central issue in condensed matter physics
Superconductivity has been found in PrT2X20 (T = transition metal element, X = Zn, Al) in which the crystalline electric field (CEF) ground state of the f 2 electronic configuration in a Pr3+ ion is the Γ3 doublet[3,4,5,6,7,8,9]
We study the three-orbital model for the Γ3 CEF state composed of the Γ7 and Γ8 orbitals.[21]
Summary
In the vicinity of the antiferromagnetically ordered phase, unconventional superconductivity[1,2] has been observed in many materials, and the relation between the superconductivity and magnetism has been a central issue in condensed matter physics. The magnetic-fluctuation-mediated superconducting mechanism has been widely discussed. It is interesting to investigate unconventional superconductivity caused by other mechanisms. There may be a route to unconventional superconductivity other than the spin fluctuation mechanism in the Γ3 system. Superconductivity has been found in PrT2X20 (T = transition metal element, X = Zn, Al) in which the CEF ground state of the f 2 electronic configuration in a Pr3+ ion is the Γ3 doublet[3,4,5,6,7,8,9] (strictly, in PrRh2Zn20, the CEF ground state is the Γ23 doublet due to symmetry lowering at the Pr site induced by a structural transition[8]). The relation between the superconductivity and the quadrupole degrees of freedom has been attracting much attention
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