From hidden-order to antiferromagnetism: electronic structure changes in Fe-doped URu$_{2}$Si$_{2}$

TL;DR

This study investigates the electronic structure changes associated with the hidden-order to antiferromagnetic phase transition in URu$_2$Si$_2$, revealing that interaction strength modifications near the Fermi level drive the transition.

Contribution

It demonstrates that non-rigid changes in the Fermi surface, driven by interaction strength variations, are key to understanding the hidden-order to antiferromagnetic phase transition in URu$_2$Si$_2$.

Findings

Fermi surface topography is similar in HO and AFM phases.

Electron pocket sizes differ between HO and AFM phases.

Interaction strength near the Fermi level influences the phase transition.

Abstract

In matter, any spontaneous symmetry breaking induces a phase transition characterized by an order parameter, such as the magnetization vector in ferromagnets, or a macroscopic many-electron wave-function in superconductors. Phase transitions with unknown order parameter are rare but extremely appealing, as they may lead to novel physics. An emblematic, and still unsolved, example is the transition of the heavy fermion compound URu$_2$Si$_2$ (URS) into the so-called hidden-order (HO) phase when the temperature drops below $T_0 = 17.5$K. Here we show that the interaction between the heavy fermion and the conduction band states near the Fermi level has a key role in the emergence of the HO phase. Using angle resolved photoemission spectroscopy, we find that while the Fermi surfaces of the HO and of a neighboring antiferromagnetic (AFM) phase of well-defined order parameter have the same topography, they differ in the size of some, but not all, of their electron pockets. Such a non-rigid change of the electronic structure indicates that a change in the interaction strength between states near the Fermi level is a crucial ingredient for the HO-to-AFM phase transition.