Anisotropic excitonic magnetism from discrete C 4 symmetry in CeRhIn 5

• Published in: Physical review. B 2024-08, Vol.110 (6), Article 064434
• Main Authors: Brener, D. J., Mallo, I. Rodriguez, Lane, H., Rodriguez-Rivera, J. A., Schmalzl, K., Songvilay, M., Guratinder, K., Petrovic, C., Stock, C.
• Format: Article
• Language: English
• Subjects: Condensed Matter; Physics
• ISSN: 2469-9950; 2469-9969
• DOI: 10.1103/PhysRevB.110.064434

Anisotropy in strongly correlated materials is a central parameter in determining the electronic ground state and is tuned through the local crystalline electric field. This is notably the case in the CeCo x Rh 1 − x In 5 system where the ground-state wave function can provide the basis for antiferromagnetism and/or unconventional superconductivity. We develop a methodology to understand the local magnetic anisotropy and experimentally investigate with neutron spectroscopy applied to antiferromagnetic ( T N = 3.8 K ) CeRhIn 5 , which is isostructural to d -wave superconducting ( T c = 2.3 K ) CeCoIn 5 . Through diagonalizing the local crystal field Hamiltonian with discrete tetragonal C 4 point group symmetry and coupling these states with the random phase approximation, we find two distinct modes polarized along the crystallographic c and a − b planes, agreeing with experiment. The anisotropy and bandwidth, underlying the energy scale of these modes, are tuneable with a magnetic field which we use experimentally to separate in energy single and multiparticle excitations thereby demonstrating the instability of excitations polarized within the crystallographic a − b plane in CeRhIn 5 . We compare this approach to a S eff = 1 2 parametrizations and argue for the need to extend conventional SU(2) theories of magnetic excitations to utilize the multilevel nature of the underlying crystal-field basis states constrained by the local point-group C 4 symmetry.