Electronically phase-separated charge-density waves in Lu ₂Ir₃Si₅

We report the investigation of charge density waves (CDW's) in Lu ₂Ir₃Si₅ by electron diffraction and dark-field imaging in transmission electron microscopy using superlattice diffraction spots. The CDW state is confirmed by the presence of superlattice reflections. Most interestingly, the CDW state at low temperatures is found to be electronically phase separated, with the coexistence of CDW domains and low-temperature normal phase domains. With a change in temperature, unlike other typical incommensurate CDW systems in which commensurability varies with temperature, we find that commensurability remains unchanged in the present case and that the predominant change is in the redistribution of the area ratio of the two coexisting phases, which is clearly revealed in the dark-field images obtained from the CDW superlattice reflections. The electronic phase separation in the CDW state of Lu₂Ir₃Si₅ is unprecedented in CDW systems, and its temperature dependence is also anomalous.