Conventional superconductivity and charge-density-wave ordering in Ba1-xNaxTi2Sb2O

We have investigated the low-temperature physical properties of BaTi2Sb2O and Ba1-xNaxTi2Sb2O (x = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3) by means of muon spin rotation (mu SR) and SQUID magnetometry. Our measurements reveal the absence of magnetic ordering below T-DW = 58 K in the parent compound. Therefore the phase transition at this temperature observed by magnetometry is most likely due to the formation of a charge-denisty wave (CDW). Upon substitution of barium by sodium in Ba1-xNaxTi2Sb2O we find for x = 0.25 superconductivity with a maximum T-c = 5.1 K in the magnetization and a bulk T-c,T-bulk = 4.5 K in the mu SR measurements. The temperature dependency of the London penetration depth lambda(-2)(T) of the optimally doped compound can be well explained within a conventional weak-coupling scenario in the clean limit.