Interlayer spin-singlet pairing induced by magnetic interactions in an antiferromagnetic superconductor

Abstract

It is shown that interlayer spin-singlet Cooper pairing is induced by magnetic interactions in a metallic antiferromagnet of stacked conductive layers in which each layer is ferromagnetically polarized and they order antiferromagnetically in stacking direction. As a result, the antiferromagnetic long-range order and superconductivity coexist at low temperatures. It is shown that T AF Ͼ T c except for in a very limited parameter region unless T AF = 0, where T AF and T c denote the antiferromagnetic and superconducting transition temperatures, respectively. It is found that the exchange field caused by the spontaneous staggered magnetization does not affect superconductivity at all, even if it is very large. The resultant superconducting order parameter has a horizontal line node and is isotropic in spin space in spite of the anisotropy of the background magnetic order. We discuss the possible relevance of the present mechanism to the antiferromagnetic heavy fermion supercon-In this paper, we show that interlayer spin-singlet Cooper pairing is induced by magnetic interactions in a certain kind of metallic antiferromagnet. We consider a layered system of itinerant electrons in which each layer is ferromagnetically polarized but the majority-spin alternates in stacking direction. Therefore the magetic order is characterized by the wave vector Q = ͑0,0, / c͒, where we have assumed the a and b crystal axes to be parallel to the layers, and the c axis in the stacking direction, and c denotes the c axis lattice constant. It is also shown that the exchange field caused by spontaneous staggered magnetization does not influence superconductivity, however large it is.The heavy fermion superconductors, such as UPd 2 Al 3 and CePt 3 Si, can be candidates of the present mechanism. The antiferromagnetic long-range order is considered to be characterized by the wave vector Q = ͑0,0, / c͒, both in UPd 2 Al 3 ͑Ref. 1͒ and in CePt 3 Si. 2 Superconducting transitions have been observed at T c = 2.0 and 0.7 K, below the antiferromagnetic transition temperatures T AF = 14.3 and 2.2 K, in UPd 2 Al 3 ͑Ref. 3͒ and CePt 3 Si, 4 respectively. It has been suggested that the magnetic moment is large, i.e., 0.85 B /U, in UPd 2 Al 3 , 3 but small, i.e., 0.16 B / Ce, in CePt 3 Si. 2 The order parameter of interlayer spin-singlet pairing has a horizontal line node. This also agrees with the experimental results in the compound UPd 2 Al 3 . The existence of the line node is suggested by the nuclear magnetic resonance ͑NMR͒ measurement, 5 in which the Hebel-Slichter peak was absent, and T 1 −1 ϰ T 3 was observed. The singlet state is supported by the presence of NMR Knight shift 5 and the Pauli limited upper critical field. 6,7 In recent angle resolved magnetothermal transport measurements, 8 twofold oscillation in the rotation perpendicular to the ab plane was observed, while no oscillation was observed in rotation in the ab plane. These experimental results are reproduced by the order parameter of the form of ⌬͑k͒ = ⌬ 0 cos͑k z c͒.Coexistence of...

Non-centrosymmetric Superconductivity and Antiferromagnetic Order: Microscopic Discussion of CePt3Si

“…4 is obtained without taking into account the canting of AFM moment in contrast to ref. 15 where the AFM coupling to the local moment is assumed to explain a similar property. Another mechanism to enhance the spin susceptibility below T c has been proposed by Fujimoto, which is based on a strong particle-hole asymmetry.…”