From hidden order to antiferromagnetism: Electronic structure changes in Fe-doped URu ₂ Si ₂

<jats:title>Significance</jats:title> <jats:p> The transition of <jats:inline-formula> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">U</mml:mi> <mml:mi mathvariant="normal">R</mml:mi> <mml:mi mathvariant="normal">u</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">S</mml:mi> <mml:mi mathvariant="normal">i</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> </jats:inline-formula> to an ordered state below 17.5 K has been a puzzle of condensed matter physics for over 30 y, earning it the soubriquet of the hidden-order (HO) state. Intriguingly, pressure or doping can transform the HO into an antiferromagnetic (AFM) state, of well-known symmetry. Here, by angle-resolved photoemission spectroscopy, the electronic structure of <jats:inline-formula> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">U</mml:mi> <mml:mi mathvariant="normal">R</mml:mi> <mml:mi mathvariant="normal">u</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">S</mml:mi> <mml:mi mathvariant="normal">i</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:math> </jats:inline-formula> in the HO phase is directly compared with its AFM counterpart. This reveals topographically identical Fermi surfaces; however, they differ by the size of some of their pockets. The overall nonrigid change of the electronic structure across the AFM/HO phase boundary indicates that a change in the interaction strength between states near the Fermi level is essential to stabilize the HO state. </jats:p>