Anomalous Surface Behavior of Sr₃Ir₂O₇

The temperature dependent low-energy electron diffraction (LEED) studies on Sr₃Ir₂O₇(001) show a behavior that contradicts the expected Debye-Waller scattering. According to Debye-Waller scattering, a finite Debye temperature would imply a decrease in LEED scattering intensities with increasing temperature, but this is not observed between room temperature and roughly 400 K in Sr₃Ir₂O₇ at low electron kinetic energies. Instead, there is a significant enhancement in the intensities of the LEED diffraction spots before an attenuation in intensity sets in, with increasing temperature. Hence, there is an anomaly in the surface behavior of Sr₃Ir₂O₇ which contradicts the Debye-Waller scattering theory. However, at higher kinetic energies, the LEED intensity behavior becomes more characteristic of a finite Debye temperature. This anomaly in the surface behavior of Sr₃Ir₂O₇(001) might be attributed to temperature-induced surface segregation, strong correlation, a structural transition or an insulator-metal phase transition. By carrying out angle resolved X-ray photoemission spectroscopy, surface segregation has been excluded as a cause of the observed anomaly. Electron transport measurements however indicate a carrier activation energy in close agreement with LEED.