Spatially Inhomogeneous Superconducting State near $H_{c2}$ in UPd${}_2$Al${}_3$

Abstract

We have performed ${}^{27}$Al-NMR measurements on single-crystalline UPd${}_2$Al${}_3$ with the field parallel to the $c$ axis to investigate the superconducting (SC) properties near the upper critical field of superconductivity $H_{c2}$. The broadening of the NMR linewidth below 14~K indicates the appearance of the internal field at the Al site, which originates from the antiferromagnetically ordered moments of U 5$f$ electrons. In the SC state well below ${\mu }_0{H}_{c2}$ = 3.4~T, the broadening of the NMR linewidth due to the SC diamagnetism and a decrease in the Knight shift are observed, which are well-understood by the framework of spin-singlet superconductivity. In contrast, the Knight shift does not change below $T_{\mathrm{c}}(H)$, and the NMR spectrum is broadened symmetrically in the SC state in the field range of 3~T $<{\mu }_{0}H<{\mu }_0{H}_{c2}$. The unusual NMR spectrum near $H_{c2}$ suggests that a spatially inhomogeneous SC state such as the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state would be realized.

5 pages, 5 figures

References in corpus (2)

• Evidence of Andreev bound states as a hallmark of the FFLO phase in $\kappa$-(BEDT-TTF)${}_2$Cu(NCS)${}_2$
• Spin susceptibility of Andreev bound states

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