A long-standing controversial issue in the quest to understand the superconductivity in cuprates is
the nature of the enigmatic pseudogap region of the phase diagram. Especially important is whether
the pseudogap state is a distinct thermodynamic phase characterized by broken symmetries below
the onset temperature T*. Here we report torque-magnetometry measurements of anisotropic
susceptibility within the ab planes in orthorhombic YBCO with exceptionally high precision. The
in-plane anisotropy along  direction (Cu-O-Cu direction) displays a significant increase with
a distinct kink at T*, showing a remarkable scaling behavior with respect to T/T* in a wide doping
range. The analysis reveals that the rotational symmetry breaking (nematicity) sets in at T* in the
limit where the effect of orthorhombicity is eliminated. We also performed the same measurements
on simple tetragonal Hg1201 with single CuO2 layer. Two-fold susceptibility anisotropy emerges
spontaneously at T*, providing direct evidence of the broken rotational symmetry. These firmly
establish that the nematic phase transition is universal in high-Tc cuprates. Surprisingly, unlike
YBCO, the diagonal nematicity along  direction develops in Hg1201. Furthermore, the
nematicity in Hg1201 appears to compete with CDW.
Thermodynamic evidence for a nematic phase transition at the onset of pseudogap in YBCO and Hg1201.
Retrieved from the University of Minnesota Digital Conservancy,
Content distributed via the University of Minnesota's Digital Conservancy may be subject to additional license and use restrictions applied by the depositor.