Is the Orbital-Selective Mott Phase Stable against Interorbital Hopping?

The localization-delocalization transition is at the heart of strong correlation physics. Recently, there is great interest in multiorbital systems where this transition can be restricted to certain orbitals, leading to an orbital-selective Mott phase (OSMP). Theoretically, the OSMP is widely studied for kinetically decoupled orbitals, but the effect of interorbital hopping remains unclear. Here, we show how nonlocal interorbital hopping leads to local hybridization in single-site dynamical mean-field theory (DMFT). Under fairly general circumstances, this implies that, at zero temperature, the OSMP, involving the Mott-insulating state of one orbital, is unstable against interorbital hopping to a different, metallic orbital. We further show that the coherence scale below which all electrons are itinerant is very small and gets exponentially suppressed even if the interorbital hopping is not overly small. Within this framework, the OSMP with interorbital hopping may thus reach down to extremely low temperatures T, but not to T = 0. Accordingly, it is part of a coherence-incoherence crossover and not a quantum critical point. We present analytical arguments supported by numerical results using the numerical renormalization group as a DMFT impurity solver. We also compare our findings with previous slave-spin studies.

Automated summary

This study investigates the impact of interorbital hopping on the localization-delocalization transition and finds that, at zero temperature, the orbital-selective Mott phase is unstable against interorbital hopping and transforms into a different metallic orbital. Additionally, the coherence scale for all electrons to become itinerant is very small and exponentially suppressed, even with non-small interorbital hopping. This implies that the orbital-selective Mott phase can reach extremely low temperatures, but not T = 0, and is part of a coherence-incoherence crossover rather than a quantum critical point.