Broken rotational symmetry in the pseudogap phase of a high-Tc superconductor

Understand

The nature of the pseudogap phase is a central problem in the quest to understand high-Tc cuprate superconductors.

• A fundamental question is what symmetries are broken when that phase sets in below a temperature T*.
• There is evidence from both polarized neutron diffraction and polar Kerr effect measurements that time- reversal symmetry is broken, but at temperatures that differ significantly.
• Broken rotational symmetry was detected by both resistivity and inelastic neutron scattering at low doping and by scanning tunnelling spectroscopy at low temperature, but with no clear connection to T*.