Unusual upper critical field of the ferromagnetic superconductor UCoGe

Abstract

We report upper critical field $B_{c2}(T)$ measurements on a single-crystalline sample of the ferromagnetic superconductor UCoGe. $B_{c2}(0)$ obtained for fields applied along the orthorhombic axes exceeds the Pauli limit for $B\parallel a,b$ and shows a strong anisotropy $B_{c2}^a\simeq B_{c2}^b\gg B_{c2}^c$. This provide evidence for an equal spin pairing state and a superconducting gap function of axial symmetry with point nodes along the c axis, which is also the direction of the uniaxial ferromagnetic moment $m_0=0.07{\mu }_B$. An unusual curvature or kink is observed in the temperature variation of $B_{c2}$, which possibly indicates UCoGe is a two-band ferromagnetic superconductor.

4 pages, accepted for publication in PRL

References in corpus (2)

• Superconductivity on the border of weak itinerant ferromagnetism in UCoGe
• On the theory of superconductivity in ferromagnetic superconductors with triplet pairing

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