Two superconducting domes separated by a possible Lifshitz transition in LaFeAs1−xPxO

Abstract

Two distinct superconducting (SC) domes were discovered in the phase diagram of P-doped iron pnictide superconductors LaFeAs1−xPxO with x ranging from 0 to 1. The first SC dome is centered around x = 0.3 and then disappears as P content increases to x = 0.5. For x > 0.5, a second SC dome appears, and Tc reaches another maximum at x = 0.7. Although the maximum of Tc in the two domes is close to each other, the estimated upper critical field (Hc2) is much larger in the first SC dome, implying a difference in the nature between the two SC domes. Further band calculations and thermopower measurements suggest that there could be a Lifshitz transition in the electronic structure between the two SC domes.