Abstract
Contrary to previous studies that identified the ground state crystal structure of the entire Co series ( is a rare earth) as orthorhombic , we show that YCo undergoes a structural phase transition at K. Single crystal neutron diffraction data reveal that at the trigonal prisms formed by a cobalt atom and its six nearest-neighbor yttrium atoms experience distortions accompanied by notable changes of the Y-Co distances. The formation of the low-temperature phase is accompanied by a pronounced lattice distortion and anomalies seen in heat capacity and resistivity measurements. Density functional theory calculations reveal a dynamical instability of the structure of YCo. In particular, a transversal acoustic phonon mode along the direction has imaginary frequencies at . Employing inelastic neutron scattering measurements we find a strong damping of the phonon mode below a critical temperature . The observed structural transformation causes the reduction of dimensionality of electronic bands and decreases the electronic density of states at the Fermi level that identifies YCo as a system with the charge density wave instability.
- Received 27 January 2013
DOI:https://doi.org/10.1103/PhysRevB.88.024117
©2013 American Physical Society