One material - two ground states
14 Oct 2020





​​The structure of defects in Yb2Ti2O7. a For oxygen-depleted Yb2Ti2O7−δ the oxygen vacancies (gold) are located on the O(2) sites (blue), and neighbouring Ti4+ (green) are replaced by charge compensating Ti3+ (purple) ions that are slightly displaced away from the vacancy. b For stuffed Yb2(Ti2−xYbx)O7−x/2 neighbouring Ti4+ ions are replaced by Yb3+ (red) ions that are displaced towards the O(2) vacancy. The diffuse neutron scattering measured at T ~ 30 K in the (hk7) plane in c for oxygen depleted and d for stuffed samples is compared with the simulated scattering in e and f, calculated using the models shown in a and b, respectively. The contour diagrams are on a hot scale with an arbitrary maximum. 


​​​​The pyrochlore system Yb2Ti2O7 has attracted both experimental and theoretical interest as a model geometrically frustrated magnet with large quantum fluctuations. These studies have identified two possible ground states for the material, where the state formed is dependent on the individual sample, and its pressure. This suggests that low-level structural disorder could be causing the change in ground state preference.

By using neutron scattering on SXD, which is very sensitive to the vacancies and displacements of oxygen ions, the researchers were able to determine the structure of the defects in single crystals of Yb2Ti2O7. They found that isolated oxygen vacancies on the O(2) site stabilise the formation of the spin liquid ground state, whereas ideal defect-free samples exhibit long-range order, with a ferromagnetic ground state.

U​nderstanding the impact of these defects on the functionality of the pyrochlore system, and the competition between classically ordered systems and quantum states, could enable to development of novel quantum spin liquid phases.

Instrument: SXD, Merlin

Related publication: Role of defects in determining the magnetic ground state of ytterbium titanate. Nat Commun 10, 637 (2019)

DOI: 10.1038/s41467-019-08598-z

Funding: EPSRC

​Authors: DF Bowman (Royal Holloway, University of London), E Cemal (Royal Holloway, University of London, ILL), T Lehner (Royal Holloway, University of London), AR Wildes, L Mangin-Thro (ILL), GJ Nilsen (ILL, ISIS), MJ Gutmann, DJ Voneshen (ISIS), D Prabhakaran, AT Boothroyd (University of Oxford), DG Porter (Diamond Light Source), C Castelnovo (University of Cambridge), K Refson, JP Goff (Royal Holloway, University of London) 

Contact: Gianchandani, Shikha (STFC,RAL,ISIS)