Spin fluctuation induced Weyl semimetal state in the paramagnetic phase of EuCd2As2

Weyl fermions as emergent quasiparticles can arise in Weyl semimetals (WSMs) in which the energy bands are nondegenerate, resulting from inversion or time-reversal symmetry breaking. Nevertheless, experimental evidence for magnetically induced WSMs is scarce. Here, using photoemission spectroscopy, we observe that the degeneracy of Bloch bands is already lifted in the paramagnetic phase of EuCd2As2. We attribute this effect to the itinerant electrons experiencing quasi-static and quasi\u2013long-range ferromagnetic fluctuations. Moreover, the spin-nondegenerate band structure harbors a pair of ideal Weyl nodes near the Fermi level. Hence, we show that long-range magnetic order and the spontaneous breaking of time-reversal symmetry are not essential requirements for WSM states in centrosymmetric systems and that WSM states can emerge in a wider range of condensed matter systems than previously thought

Heydemann interpolation correction for energy linearization of soft X ray monochromators

Material science research in the soft X ray regime at the Swiss Light Source accommodates five beamlines where the monochromators rely on in vacuum angular encoders for positioning mirror and gratings. Despite the factory calibration of the quadrature signals from these rotary encoders, the energy linearization for spectroscopic data requires accurate calibration of the encoder quadrature signals. We characterize the interpolation errors and describe the Heydemann correction algorithm for the quadrature signals for improving the energy linearization on a scale comparable with the incremental encoder interpolation interval. Experimental data are shown where such errors produce sizeable effects in soft X ray spectroscopy and for which the correction algorithm efficiently improves the short range non linearit

Observation of Two Nondispersive Magnetic Excitations in NiO by Resonant Inelastic Soft-X-Ray Scattering

We present high resolution (E ¼ 120 meV) resonant inelastic X-ray scattering data measured at the Ni L3 edge (2p3=2 ! 3d) on the paradigmatic antiferromagnetic oxide NiO. Spectra reveal clear signatures of magnetic excitations at 95 and 190 meV whose energy seems independent from transferred momentum. These spectral features are well reproduced by a single Ni2þ ion model in an effective exchange field. Within this local model the two magnetic excitations are characterized by a variation of the atomic magnetic moment along the local ordering direction (S) of one and two units. The S¼ 2 case has different nature from bimagnons observed in optical Raman spectra, for which S¼ 0