title: Intra-unit-cell nematic charge order in the titanium-oxypnictide family of superconductors.
abstract: Understanding the role played by broken-symmetry states such as charge, spin and orbital orders in the mechanism of emergent properties, such as high-temperature superconductivity, is a major current topic in materials research. That the order may be within one unit cell, such as nematic, was only recently considered theoretically, but its observation in the iron-pnictide and doped cuprate superconductors places it at the forefront of current research. Here, we show that the recently discovered BaTi2Sb2O superconductor and its parent compound BaTi2As2O form a symmetry-breaking nematic ground state that can be naturally explained as an intra-unit-cell nematic charge order with d-wave symmetry, pointing to the ubiquity of the phenomenon. These findings, together with the key structural features in these materials being intermediate between the cuprate and iron-pnictide high-temperature superconducting materials, render the titanium oxypnictides an important new material system to understand the nature of nematic order and its relationship to superconductivity.
authors.affiliation: Department of Physics, Columbia University, New York, New York 10027, USA.
authors.forename: Benjamin A
authors.initials: BA
authors.lastname: Frandsen
authors.affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: Emil S
authors.initials: ES
authors.lastname: Bozin
authors.affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: Hefei
authors.initials: H
authors.lastname: Hu
authors.affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: Yimei
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo, Kyoto 615-8510, Japan.
authors.forename: Yasumasa
authors.initials: Y
authors.lastname: Nozaki
authors.affiliation: Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo, Kyoto 615-8510, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kageyama
authors.affiliation: Department of Physics, Columbia University, New York, New York 10027, USA.
authors.forename: Yasutomo J
authors.initials: YJ
authors.lastname: Uemura
authors.affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: Wei-Guo
authors.initials: WG
authors.lastname: Yin
authors.affiliation: 1] Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA [2] Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA.
authors.forename: Simon J L
authors.initials: SJ
authors.lastname: Billinge