Arrested Kondo effect and hidden order in URu_2Si_2

TL;DR

This paper develops a first-principles method to analyze the electronic spectrum of URu_2Si_2, revealing the nature of its hidden order and its connection to magnetism, Kondo effects, and broken symmetry phases.

Contribution

It introduces a novel first-principles approach to identify the order parameter and electronic states in correlated materials, specifically applied to URu_2Si_2.

Findings

Identification of the hidden order parameter as a complex order parameter a.

Observation of a multichannel Kondo effect below 70K that is arrested by crystal field splitting.

Unified description of hidden order and antiferromagnetic phases via a complex order parameter a.

Abstract

Complex electronic matter exhibit subtle forms of self organization which are almost invisible to the available experimental tools, but which have dramatic physical consequences. One prominent example is provided by the actinide based heavy fermion material URu_2Si_2. At high temperature, the U-5f electrons in URu_2Si_2 carry a very large entropy. This entropy is released at 17.5K via a second order phase transition to a state which remains shrouded in mystery, and which was termed a "hidden order" state. Here we develop a first principles theoretical method to analyze the electronic spectrum of correlated materials as a function of the position inside the unit cell of the crystal, and use it to identify the low energy excitations of the URu_2Si_2. We identify the order parameter of the hidden order state, and show that it is intimately connected with magnetism. We present first principles results for the temperature evolution of the electronic states of the material. At temperature below 70K U-5f electrons undergo a multichannel Kondo effect, which is arrested at low temperature by the crystal field splitting. At lower temperatures, two broken symmetry states emerge, characterized by a complex order parameter \psi. A real $\psi$ describes the hidden order phase, and an imaginary \psi corresponds to the large moment antiferromagnetic phase, thus providing a unified picture of the two broken symmetry phases, which are realized in this material.