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

TL;DR

This study explores how sodium doping affects the superconducting and charge-density-wave properties of BaTi2Sb2O, revealing the emergence of superconductivity at certain doping levels and characterizing its conventional nature.

Contribution

It provides the first detailed investigation of the interplay between charge-density-wave order and superconductivity in Ba1-xNaxTi2Sb2O using muSR and magnetometry.

Findings

Charge-density-wave order exists below 58 K in BaTi2Sb2O.

Superconductivity appears at x=0.25 with T_c around 5 K.

The superconducting state follows a conventional weak-coupling behavior.

Abstract

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 (muSR) and SQUID magnetometry. Our measurements reveal the absence of magnetic ordering below TDW = 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 density 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,bulk} = 4.5 K in the muSR 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.