Electronic Structure and the Origin of the Phase Transition in BaAg₂As₂ Revealed by ARPES and REXS Studies

Transition metal pnictides in 122 families are rich with fantastic quantum phenomena such as spin density wave (SDW) in BaFe₂As₂[1], superconductivity (SC) and charge density wave (CDW) in SrPt₂As₂[2] and BaPt₂As₂[3]. In the meanwhile, BaPt₂As₂ and SrPt₂As₂ shares CaBe₂Ge₂-type structure while BaFe₂As₂ crystallizes in ThCr₂Si₂-type structure. Studying the interplay among SDW, SC and CDW and their relationship with crystal structure and structural transition is of wide interests. BaAg₂As₂, as a newly-discovered transition metal pnictide adopted to ThCr₂Si₂-type structure, possess a phase transition at 138K in resistivity whose origin is still unknown[4]. To study the mechanism, we applied systematic angle-resolved photoemission spectroscopy (ARPES) combined with resonant elastic soft X-ray scattering (REXS) and identified the exact structural transition and density-wave-like transition in it for the first time.

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