  Transport and magnetic properties along with high resolution valence band
photoemission study of disordered double perovskite Sr$_{2}$TiIrO$_{6}$ has
been investigated. Insulator to insulator transition along with a magnetic
transition concurrently occurs at 240 K. Comparison of valence band
photoemission with band structure calculations suggests that the spin orbit
coupling as well as electron correlation are necessary to capture the line
shape and width of the Ir 5$d$ band. Room temperature valence band
photoemission spectra show negligibly small intensity at Fermi energy, $E_{F}$.
Fermi cut-off is observed at low temperatures employing high resolution. The
spectral density of states at room temperature exhibits $|E-E_{F}|^{2}$ energy
dependence signifying the role of electron-electron interaction. This energy
dependence changes to $|E-E_{F}|^{3/2}$ below the magnetic transition
evidencing the role of electron-magnon coupling in magnetically ordered state.
The evolution of pseudogap ($\pm$12 meV) explains the sudden increase in
resistivity ($\rho$) below 50 K in this disordered system. The temperature
dependent spectral density of states at $E_{F}$ exhibiting $T^{1/2}$ behaviour
verifies Altshuler-Aronov theory for correlated disordered systems.
