Surface dynamics of the layered ruthenate Ca1.9Sr0.1RuO4
The strong coupling between electronic, lattice, orbital, and spin degrees of freedom in transition metal oxides implies that the symmetry breaking at the surface of these materials should lead to a rich surface phase diagram and interesting new physics. Here we investigate the surface phases of the Ca{sub 2-x}Sr{sub x}RuO{sub 4} system that (in bulk) can be tuned from a Mott insulator (x = 0) to a p-wave superconductor (x = 2) without changing the electron count. This system therefore displays a bandwidth controlled metal-insulator transition. Electronic and structural properties of these surfaces are studied by variable temperature High Resolution Electron Energy Loss Spectroscopy (HREELS) and Low Energy Electron Diffraction (LEED). It is found that broken symmetry on the Sr{sub 2}RuO{sub 4} surface results in the rotation of RuO{sub 4} octahedra relative to bulk positions along the c-axis, changing the relative in-plane Ru-O bond length and shifting the surface phonon energies. The substitution of Ca ions in Sr{sub 2}RuO{sub 4} crystals results in a rotation plus a tilt of the RuO{sub 6} octahedra creating a Mott-insulator phase. In particular, Ca{sub 1.9}Sr{sub 0.1}RuO{sub 4} exhibits a Mott transition below 154 K in bulk single crystals. However, with HREELS, we observed phonon and conductivity dynamics at the surface of Ca{sub 1.9}Sr{sub 0.1}RuO{sub 4} crystals below {approx}130 K, indicating a lower surface Mott transition temperature than in the bulk.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 859556
- Report Number(s):
- P04-121489; TRN: US200522%%215
- Journal Information:
- Physica Status Solidi B (Basic Research), Vol. 241, Issue 10
- Country of Publication:
- United States
- Language:
- English
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