Abstract
We report the first observation of cyclotron resonance in the hidden-order phase of ultraclean crystals, which allows the full determination of angle-dependent electron-mass structure of the main Fermi-surface sheets. We find an anomalous splitting of the sharpest resonance line under in-plane magnetic-field rotation. This is most naturally explained by the domain formation, which breaks the fourfold rotational symmetry of the underlying tetragonal lattice. The results reveal the emergence of an in-plane mass anisotropy with hot spots along the [110] direction, which can account for the anisotropic in-plane magnetic susceptibility reported recently. This is consistent with the “nematic” Fermi liquid state, in which itinerant electrons have unidirectional correlations.
- Received 12 April 2012
DOI:https://doi.org/10.1103/PhysRevLett.109.036401
© 2012 American Physical Society