Direct bulk-sensitive probe of 5f symmetry in URu2Si2.

Sundermann, Martin; Haverkort, Maurits W; Agrestini, Stefano; Al-Zein, Ali; Moretti Sala, Marco; Huang, Yingkai; Golden, Mark; de Visser, Anne et al. · Proc Natl Acad Sci U S A · 2016

basic_science · Level V

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Abstract

The second-order phase transition into a hidden order phase in URu<sub>2</sub>Si<sub>2</sub> goes along with an order parameter that is still a mystery, despite 30 years of research. However, it is understood that the symmetry of the order parameter must be related to the symmetry of the low-lying local electronic [Formula: see text]-states. Here, we present results of a spectroscopic technique, namely core-level nonresonant inelastic X-ray scattering (NIXS). This method allows for the measurement of local high-multipole excitations and is bulk-sensitive. The observed anisotropy of the scattering function unambiguously shows that the 5[Formula: see text] ground-state wave function is composed mainly of the [Formula: see text] with majority [Formula: see text] = [Formula: see text] + [Formula: see text] and/or [Formula: see text] singlet states. The incomplete dichroism indicates the possibility that quantum states of other irreducible representation are mixed into the ground state.