Effect of Mn impurities on the superconductivity inNaxCoO2∙yH2O

Abstract

To shed light on the symmetry of the superconducting order parameter in Na x CoO 2 · yH 2 O, the Mn doping effects are studied. X-ray absorption spectroscopy verifies that the doped Mn impurities occupy the Co sites and are with a valance close to +4. Impurity scattering by Mn is in the unitary limit that, however, does not lead to strong T c suppression. This absence of the strong impurity effects on T c is inconsistent with the simple picture of a sign-changing order parameter. Coexistence of the s-wave superconducting order parameter and the nodal one is proposed to reconcile all the existing experiments and has been implied by the specific heat experiments.

Superconductivity of cobalt oxide hydrate, Na (H3O) CoO2· yH2O

“…Although the Li ions themselves are, of course, non-magnetic, they should induce a skyrmion state around Li ion in the cuprate [108]. Mn 4+ -doping causes a similar reduction rate of 0.64 K/1% [106], although the Mn 4+ ions must be magnetic [107] (as is naturally expected). Preliminary data from one study support a ''small'' reduction rate due to Mn doping and no significant change in the reduction rate between nonmagnetic and magnetic ions.…”

“…In the case of non-s-wave superconductivity, T C is expected to be greatly reduced regardless of the types of impurities in a given sample. Three kinds of ions have been identified as impurities for the Co ions in BLH [105,106].…”

Induced magnetic moment by Mn doping in

“…Polycrystalline parent compounds of sodium cobalt oxides g À Na 0:7 Co 1Àz Mn z O 2 ðz ¼ 020:03Þ were prepared using a rapid heat-up procedure [4]. The resulting powders were immersed in the 3 M Br 2 =CH 3 CN solution for 5 days, followed by filtering and thorough washing with CH 3 CN and DI water.…”

“…However, there are presently only limited studies of impurity effects on Na x CoO 2 Á yH 2 O [3,4]. In particular, the Mn doping effects are studied to explore the symmetry of the superconducting order parameter in Na x CoO 2 Á yH 2 O [4]. It is therefore desirable to characterize the doped Mn ions in detail.…”

“…Knowledge of the mechanisms behind these effects would help to shed light on the mystery of Na x CoO 2 Á yH 2 O and the related compounds. However, there are presently only limited studies of impurity effects on Na x CoO 2 Á yH 2 O [3,4]. In particular, the Mn doping effects are studied to explore the symmetry of the superconducting order parameter in Na x CoO 2 Á yH 2 O [4].…”