Anomalous spiked structures in ESR signals from the chiral helimagnet CrNb3S6

We have performed X-band electron spin resonance (ESR) measurements on a single crystal of the metallic chiral helimagnet CrNb3S6 from 3.5 to 180 K and for the external magnetic fields Hext , up to 4 kOe, perpendicular to the c axis (the helical axis of CrNb3S6). This field-crystalline configuration is expected to provide the chiral soliton lattice (CSL) state in this system. The main resonance line can be fit with a Dysonian function above Tc = 127 K, but additional features in the spectra were observed below 105 K. Specifically, spiked anomalies superposed on the main signals were observed for magnetic fields between Hc1 and Hc2 that are the appearing and disappearing fields of the spiked anomalies, respectively. The resulting magnetic field vs temperature phase diagram possesses three regions, which are interpreted as different dynamical responses in the CSL phase. In addition, the values of Hc2 are close to those reported by the d2M/dH2 curve [Tsuruta et al., Phys. Rev. B 93, 104402 (2016)]. Furthermore, the field range between Hc1 and Hc2, where the spiked anomalies exist, depends on the field direction and shifts to higher fields when turning to the c axis, thereby providing additional evidence that these spiked anomalies must be related to the chiral soliton dynamics