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Register a new userPhonon lineshapes in the vortex state of the phonon-mediated superconductor YNi$_2$B$_2$C
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We present an inelastic neutron scattering study of phonon lineshapes in the vortex state of the type-II superconductor YNi$_2$B$_2$C. In a previous study [Phys. Rev. Lett. textbf{101}, 237002 (2008)] it was shown that certain phonons exhibit a clear signature of the superconducting gap $2Delta$ on entering the superconducting state. Our interest was to find out whether or not the lineshape of such phonons reflects the inhomogeneous nature of the vortex state induced by a magnetic field smaller than the upper critical field $B_{c2}$ .We found that this is indeed the case because the observed phonon lineshapes can be well described by a model considering the phonon as a local probe of the spatial variation of the superconducting gap. We found that even at $B=3,rm{T}$, where the inter-vortex distance is less than $300,$AA, the phonon lineshape still shows evidence for a variation of the gap.
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We report an inelastic neutron scattering investigation of phonons with energies up to 159 meV in the conventional superconductor YNi$_2$B$_2$C. Using the SWEEP mode, a newly developed time-of-flight technique involving the continuous rotation of a single crystal specimen, allowed us to measure a four dimensional volume in (Q,E) space and, thus, determine the dispersion surface and linewidths of the $A_{1g}$ (~ 102 meV) and $A_u$ (~ 159 meV) type phonon modes for the whole Brillouin zone. Despite of having linewidths of $Gamma = 10 meV$, $A_{1g}$ modes do not strongly contribute to the total electron-phonon coupling constant $lambda$. However, experimental linewidths show a remarkable agreement with ab-initio calculations over the complete phonon energy range demonstrating the accuracy of such calculations in a rare comparison to a comprehensive experimental data set.
We present synchrotron x-ray diffraction studies revealing that the lattice of thulium borocarbide is distorted below T_Q = 13.5 K at zero field. T_Q increases and the amplitude of the displacements is drastically enhanced, by a factor of 10 at 60 kOe, when a magnetic field is applied along [100]. The distortion occurs at the same wave vector as the antiferromagnetic ordering induced by the a-axis field. A model is presented that accounts for the properties of the quadrupolar phase and explains the peculiar behavior of the antiferromagnetic ordering previously observed in this compound.
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