Hidden Magnetic Texture in the Pseudogap Phase of High-Tc $YBa_{2}Cu_{3}O_{6.6}$

TL;DR

This study uncovers a hidden long-range translational symmetry-breaking magnetism in the pseudogap phase of high-Tc cuprate superconductors, revealing complex magnetic textures that could be key to understanding the pseudogap phenomenon.

Contribution

It reports the discovery of a previously undetected LT-breaking magnetism in YBa2Cu3O6.6, combining with known intra-unit cell magnetism to form a complex magnetic texture.

Findings

Magnetic correlations appear at the pseudogap onset temperature.

Magnetism exhibits a planar propagation wave vector, doubling or quadrupling the magnetic unit cell.

Magnetic moments are mainly perpendicular to CuO2 layers.

Abstract

Despite decades of intense researches, the enigmatic pseudo-gap (PG) phase of superconducting cuprates remains an unsolved mystery. In the last 15 years, various symmetry breakings in the PG state have been discovered, spanning an intra-unit cell (IUC) magnetism, preserving the lattice translational (LT) symmetry but breaking time-reversal symmetry and parity, and an additional incipient charge density wave breaking the LT symmetry upon cooling. However, none of these states can (alone) account for the partial gapping of the Fermi surface. Here we report a hidden LT-breaking magnetism uisng polarized neutron diffraction. Our measurements reveal magnetic correlations, in two different underdoped $\rm YBa_{2}Cu_{3}O_{6.6}$ single crystals, that settle at the PG onset temperature with i) a planar propagation wave vector $(\pi,0) \equiv (0,\pi)$, yielding a doubling or quadrupling of the magnetic unit cell and ii) magnetic moments mainly pointing perpendicular to the $CuO_{2}$ layers. The LT-breaking magnetism is at short range suggesting the formation of clusters of 5-6 unit cells. Together with the previously reported IUC magnetism, it yields a hidden magnetic texture of the $CuO_{2}$ unit cells hosting loop currents, forming large supercells which may be crucial for elucidating the PG puzzle.