title: How many quantum phase transitions exist inside the superconducting dome of the iron pnictides?
abstract: Recent experiments on two iron-pnictide families suggest the existence of a single quantum phase transition inside the superconducting dome despite the fact that two separate transition lines--magnetic and nematic-cross the superconducting dome at T(c). Here we argue that these two observations are actually consistent. We show, using a microscopic model, that each order coexists with superconductivity for a wide range of parameters, and both transition lines continue into the superconducting dome below T(c). However, at some T(merge)<T(c), the two transitions merge and continue down to T=0 as a single simultaneous first-order nematic-magnetic transition. We show that superconductivity has a profound effect on the character of this first-order transition, rendering it weakly first order and allowing strong fluctuations to exist near the quantum phase transition.
authors: School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA. rfernand@umn.edu
authors: Rafael M
authors: RM
authors: Fernandes
authors: Saurabh
authors: S
authors: Maiti
authors: Peter
authors: P
authors: Wölfle
authors: Andrey V
authors: AV
authors: Chubukov