Two-dimensional nature of superconductivity in the intercalated layered systems LixHfNCl and LixZrNCl:: Muon spin relaxation and magnetization measurements -: art. no. 134522

We report muon spin relaxation (muSR) and magnetization measurements, together with synthesis and characterization, of the Li-intercalated layered superconductors LixHfNCl and LixZrNCl with/without cointercalation of THF (tetrahydrofuran) or propylene carbonate. The three-dimensional superfluid density n(s)/m* (superconducting carrier density/effective mass) as well as the two-dimensional superfluid density n(s2D)/m(ab)* [two-dimensional (2D) area density of superconducting carriers/ab-plane effective mass] have been derived from the muSR results of the magnetic-field penetration depth lambda(ab) observed with external magnetic field applied perpendicular to the 2D honeycomb layer of HfN/ZrN. In a plot of T-c versus n(s2D)/m(ab)*, most of the results lie close to the linear relationship found for underdoped high-T-c cuprate (HTSC) and layered organic BEDT (bis(ethylenedithio)) superconductors. In LixZrNCl without THF intercalation, the superfluid density and T-c for x=0.17 and 0.4 do not show much difference, reminiscent of muSR results for some overdoped HTSC systems. Together with the absence of dependence of T-c on average interlayer distance among ZrN/HfN layers, these results suggest that the 2D superfluid density n(s2D)/m(ab)* is a dominant determining factor for T-c in the intercalated nitride-chloride systems. We also report muSR and magnetization results on depinning of flux vortices, and the magnetization results for the upper critical field H-c2 and the penetration depth lambda. A reasonable agreement was obtained between muSR and magnetization estimates of lambda. We discuss the two-dimensional nature of superconductivity in the nitride-chloride systems based on these results.