High temperature singlet-based magnetism from Hund\u2019s rule correlations

Lin Miao ,Yang Zhao ,Hailang He ,Gabriel Kotliar ,Yi‐De Chuang ,Shanta Saha ,Zhijun Xu ,J W Lynn ,J R Jeffries ,Rourav Basak ,Chang-Jong Kang ,Erica Kotta ,Yishuai Xu ,Sheng Ran ,Yilin Wang ,Jonathan D Denlinger ,Pegor Aynajian ,Nicholas P Butch ,Ioannis Giannakis ,L Andrew Wray

doi:10.1038/s41467-019-08497-3

Abstract

Uranium compounds can manifest a wide range of fascinating many-body phenomena, and are often thought to be poised at a crossover between localized and itinerant regimes for 5f electrons. The antiferromagnetic dipnictide USb2 has been of recent interest due to the discovery of rich proximate phase diagrams and unusual quantum coherence phenomena. Here, linear-dichroic X-ray absorption and elastic neutron scattering are used to characterize electronic symmetries on uranium in USb2 and isostructural UBi2. Of these two materials, only USb2 is found to enable strong Hund’s rule alignment of local magnetic degrees of freedom, and to undergo distinctive changes in local atomic multiplet symmetry across the magnetic phase transition. Theoretical analysis reveals that these and other anomalous properties of the material may be understood by attributing it as the first known high temperature realization of a singlet ground state magnet, in which magnetism occurs through a process that resembles exciton condensation.

Highlights

Uranium compounds can manifest a wide range of fascinating many-body phenomena, and are often thought to be poised at a crossover between localized and itinerant regimes for 5f electrons
Density functional theory suggests that the charge and spin density on uranium are significantly modified by itinerancy effects[14,15], as we will discuss in the analysis below, making it difficult to address this question from secondary characteristics such as the local or ordered moment
X-ray absorption spectra (XAS) of UBi2 and USb2 were measured by the total electron yield (TEY) method, revealing curves that are superficially similar but quantitatively quite different (Fig. 2a)

Summary

Introduction

Uranium compounds can manifest a wide range of fascinating many-body phenomena, and are often thought to be poised at a crossover between localized and itinerant regimes for 5f electrons. Linear-dichroic X-ray absorption and elastic neutron scattering are used to characterize electronic symmetries on uranium in USb2 and isostructural UBi2 Of these two materials, only USb2 is found to enable strong Hund’s rule alignment of local magnetic degrees of freedom, and to undergo distinctive changes in local atomic multiplet symmetry across the magnetic phase transition. X-ray absorption (XAS) at the uranium O-edge and numerical modeling are used to evaluate the low energy atomic multiplet physics of USb2 and UBi2, revealing only USb2 to have significant Hund’s rule correlations These investigations yield the prediction that USb2 must be a uniquely robust realization of a singlet-ground-state magnet, in which magnetic moments appear via the occupation of low-energy excited states on a non-magnetic background (Fig. 1c). The evolution of crystal field symmetries and magnetic ordered moment across the antiferromagnetic phase transition is measured with linear dichroism (XLD) and elastic neutron scattering, confirming that the magnetic transition in USb2 occurs through an exotic process that resembles exciton condensation

Methods

Results

Conclusion