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Coupled commensurate charge density wave and lattice distortion in Na 2 Ti 2 P n 2 O ( P n = As , Sb ) determined by x-ray diffraction and angle-resolved photoemission spectroscopy

DOI: 10.1103/PhysRevB.94.104515 DOI Help

Authors: N. R. Davies (Department of Physics, University of Oxford) , R. D. Johnson (Department of Physics, University of Oxford) , A. J Princep (Department of Physics, University of Oxford) , L A. Gannon (University of Oxford) , J.-z. Ma (Chinese Academy of Science; Swiss Light Source) , T. Qian (Chinese Academy of ScienceCollaborative Innovation Center of Quantum Matter) , P. Richard (Chinese Academy of ScienceCollaborative Innovation Center of Quantum Matter) , H. Li (Chinese Academy of Science) , M. Shi (Swiss Light Source) , H. Nowell (Diamond Light Source) , P. J. Baker (ISIS Facility, STFC Rutherford Appleton Laboratory) , Y. G. Shi (Chinese Academy of Science) , H. Ding (Chinese Academy of ScienceCollaborative Innovation Center of Quantum Matter) , J. Luo (Chinese Academy of Science) , Y. F. Guo (University of Oxford; ShanghaiTech University) , A. T. Boothroyd (University of Oxford)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Review B , VOL 94

State: Published (Approved)
Published: September 2016
Diamond Proposal Number(s): 10108

Abstract: We report single-crystal x-ray-diffraction measurements on Na 2 Ti 2 Pn 2 O(Pn=As,Sb) which reveal a charge superstructure that appears below the density wave transitions previously observed in bulk data. From symmetry-constrained structure refinements we establish that the associated distortion mode can be described by two propagation vectors q 1 =(1/2,0,l) and q 2 =(0,1/2,l) with l=0 (Sb) or l=1/2 (As) and primarily involves in-plane displacements of the Ti atoms perpendicular to the Ti-O bonds. We also present angle-resolved photoemission spectroscopy measurements, which show band folding and backbending consistent with a density wave with the same wave-vectors q 1 and q 2 associated with Fermi-surface nesting, and muon-spin relaxation data, which show no indication of spin density wave order. The results provide direct evidence for phonon-assisted charge density wave order in Na 2 Ti 2 Pn 2 O and fully characterize a proximate ordered phase that could compete with superconductivity in doped BaTi 2 Sb 2 O.

Subject Areas: Materials, Physics


Instruments: I19-Small Molecule Single Crystal Diffraction

Other Facilities: Swiss Light Source; Synchrotron Radiation Center;