Optical evidence for bonding-antibonding splitting in IrTe2

We combined optical spectroscopy with first principles calculations to reveal the electronic signatures of Ir dimer formation in the q=(1/5,0,1/5) high resistivity phase of IrTe2. Our measurements uncover two interband transitions into the unoccupied dxy antibonding orbital, one from mixed iridium/tellurium bands, the other from the dxy bonding orbital of the dimerized Ir centers. The bonding-antibonding splitting demonstrates that iridium, not tellurium, plays the dominant role in stabilizing the low temperature phase of IrTe2 through localized bonding orbital formation.