Orientation of ground-state orbital in CeCoIn\(_5\) and CeRhIn\(_5\)

• Published in: arXiv.org
• Main Authors: Sundermann, M, Amorese, A, Strigari, F, Leedahl, B, Haverkort, M W, Gretarsson, H, Tjeng, L H, M Moretti Sala, Yavş, H, Bauer, E D, Rosa, P F S, Thompson, J D, Severing, A
• Format: Paper
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 25.06.2019
• Subjects: Crystal structure; Dipoles; Fermions; Inelastic scattering; Orientation; Phase diagrams; Unit cell; X-ray scattering
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1902.06726

We present core level non-resonant inelastic x-ray scattering (NIXS) data of the heavy fermion compounds CeCoIn\(_5\) and CeRhIn\(_5\) measured at the Ce \(N_{4,5}\)-edges. The higher than dipole transitions in NIXS allow determining the orientation of the \(\Gamma_7\) crystal-field ground-state orbital within the unit cell. The crystal-field parameters of the Ce\(M\)In\(_5\) compounds and related substitution phase diagrams have been investigated in great detail in the past; however, whether the ground-state wavefunction is the \(\Gamma_7^+\) (\(x^2\,-\,y^2\)) or \(\Gamma_7^-\) (\(xy\) orientation) remained undetermined. We show that the \(\Gamma_7^-\) doublet with lobes along the (110) direction forms the ground state in CeCoIn\(_5\) and CeRhIn\(_5\). For CeCoIn\(_5\), however, we find also some contribution of the first excited state crystal-field state in the ground state due to the stronger hybridization of 4\(f\) and conduction electrons, suggesting a smaller \(\alpha^2\) value than originally anticipated from x-ray absorption. A comparison is made to the results of existing density functional theory plus dynamical mean-field theory calculations.