Magnetic excitations in YbCo2Si2

Quantum phase transitions and their origin are still open issues of current research in condensed matter physics. Although YbRh2Si2 is a model system to study quantum criticality, microscopic studies by neutron scattering are prevented because of the large absorption of Rh for neutrons, the small ordered moment and the small available samples. Instead, we investigated YbCo2Si2 being isoelectronic and isostructural to YbRh2Si2. YbCo2Si2 orders antiferromagnetically below TN ∼1.7 K in an incommensurate structure and changes to a commensurate structure below TL ∼0.9 K. Using inelastic neutron scattering we studied in detail the spin excitations in the low temperature commensurate phase. Well-defined spin excitations exhibiting distinct dispersion have been detected. The results contribute to the general understanding of the magnetic interactions in YbCo2Si2.