ARPES Study on the Electronic Structure and Superconducting Gap of Reentrant C₄ Phase in (Sr_,Na)Fe₂As₂

The relationship between magnetism, nematicity and superconductivity is important in understanding the superconductivity mechanism of the iron-based superconductors. Recently, reentrant C₄ tetragonal magnetic phase has been identified as a universal behavior within a narrow doping range in the hole-doped 122 iron-based superconductors in the nematic phase. Here we report high resolution laser-based angle-resolved photoemission (ARPES) measurements on the (Sr_,Na)Fe₂As₂ superconductors which exhibits reentrant C₄ magnetic phase. We measured the electronic structure distortion caused by the reentrant C₄ magnetic phase and the superconducting gap structure. Our results provide new insight in understanding the reentrant C₄ magnetic phase and superconductivity in the iron-based superconductors.