Tunable reentrant Kondo effect in quantum dots coupled to metal-superconducting hybrid reservoirs

We elaborate on the recently introduced concept of the reentrant Kondo effect in quantum impurities/dots coupled to hybrid metal-semiconductor contacts [G. Diniz et al., Phys. Rev. B 101, 125115 (2020)]. By noticing the equivalence of the originally suggested semiconducting arrangement to an analogous three-terminal quantum dot setup with a normal and two phase-biased superconducting leads introduced in our recent work [P. Zalom et al., Phys. Rev. B 103, 035419 (2021)], we put this effect into a new physical context, which gives us a fresh look on the problem. First, we identify the superconducting counterpart of the reentrant Kondo effect and, consequently, reveal its fragility with respect to an underlying doublet-singlet quantum phase transition induced by the particle-hole asymmetry of the reservoir densities of states. This is pertinent (even if previously unnoticed) also in the original as well as extended semiconducting setups, where it puts stringent conditions on the symmetry of the contact density of states. Furthermore, we analyze the experimental feasibility of observing the reentrant Kondo effect in its superconducting realization concluding that even present-day experiments might see the onset of the reentrant behavior, but fully developed Kondo features cannot be reached due to the required vast separation of energy/temperature scales.