Electronic Nematicities in the Titanium Pnictide Oxide Superconductors BaTi2(As1−xSbx)2O

The titanium pnicide oxide superconductor is studied via the measurements of resistivity and Seebeck coefficient S on the solid solution samples of BaTi 2 (As 1-x Sb x ) 2 O.The composition dependence of the nematic charge-density-wave (CDW) order below T a is reported.Upon cooling below T a , the |S| suddenly increases for 0 ≤ x ≤ 0.6 while decreases for 0.8 ≤ x ≤ 1, indicating that parts of the hole and electron Fermi surfaces are lost at the transitions, respectively.Thus, the nematic CDW order changes its character at x ~ 0.7.Since the superconductivity appears only for 0.9 ≤ x ≤ 1, the hole Fermi surfaces must be responsible for the superconductivity in the titanium pnictide oxides.