Disordered dimer state in electron-doped Sr3Ir2O7

Spin excitations are explored in the electron-doped spin-orbit Mott insulator (Sr1−xLax)3Ir2O7. As this bilayer square lattice system is doped into the metallic regime, long-range antiferromagnetism vanishes, yet a spectrum of gapped spin excitation remains. Excitation lifetimes are strongly damped with increasing carrier concentration, and the energy-integrated spectral weight becomes nearly momentum independent as static spin order is …