Phonons at high energies studied by time-of-flight neutron spectroscopy: the case of YNi2B2C

We used the so-called SWEEP mode implemented at the ARCS chopper spectrometer at the Spallation Neutron Source (SNS), Oak Ridge National Laboratory, in order to study phonons in the conventional superconductor YNi2B2C at energies from 35 meV up to 160 meV. The SWEEP mode involves a continuous but asynchronous rotation of the single crystal specimen enabling coverage of a continuous four dimensional volume in reciprocal space and energy. Essential to this method is that, in the event mode at SNS, scattered neutrons are recorded individually with a complete set of information. Rotating the sample with an angular speed of 0.1° per second neutrons from a specific pulse can be assigned to a specific angle of the sample and, hence, a specific point in reciprocal space. We applied this new data collection mode to the case of the conventional superconductor YNi2B2C (Tc = 15.2 K). Here, the impact on superconductivity of A1g-type phonon modes with energies around 100 meV was debated in different DFT calculations. We were able to measure phonon energies and line widths over the largest part of the spectrum. Completed by previous triple-axis measurements we provide a rare comparison between calculated lattice dynamical properties and a comprehensive experimental data set. (author)