Metal-insulator transition in pyrochlore Eu2Ir2O7 studied by infrared spectroscopy*

The large family of pyrochlores with formula A$_2$B$_2$C$_7$ attracted a lot of early attention due to strong geometric magnetic frustration. Recent band structure calculations predict that the iridate pyrochlores A$_2$Ir$_2$O$_7$ may have nontrivial topological states. We will report the results of an infrared spectroscopic study of the metal-insulator transition in Eu$_2$Ir$_2$O$_7$ single crystal and Y$_2$Ir$_2$O$_7$ polycrystal. We will report the broad band IR reflection as a function of temperature for an overview of the M-I transition and the low frequency transmission which is more sensitive for detection of a 10 meV gap[1] and other possible excitations. We will discuss possible implications of the semimetal Weyl states. [1] J.J. Ishikawa et al., Phys. Rev. B 85, 245109 (2012).