Spin-wave excitations in antiferromagnetically ordered YbCo2Si2

Research on quantum phase transitions continue to be in the focus in condensed matter physics, because systems at quantum criticality show quite unusual low temperature properties including unconventional superconductivity in some cases. The heavy-fermion compound YbRh2Si2 is a model system to study quantum criticality. Isostructural YbCo2Si2 can be considered as the magnetically well ordered counterpart allowing for the investigation of the spin excitations in the antiferromagnetic state below TN∼1.7 K. The system exhibits well-defined spin waves in the two ordered phases with distinct dispersion. Although the dispersion along several principal directions are almost unchanged between the low temperature commensurate and the high temperature incommensurate phase, some marked differences are observed in the vicinity of (0 0 1). The results help to understand the basic magnetic interactions in this heavy-fermion compound.