Broken rotational and translational symmetries in the pseudogap phase of cuprates*

A large in-plane anisotropy of the Nernst coefficient in YBCO is found to set in precisely at the pseudogap temperature $T^\star$ throughout the doping phase diagram [1]. This implies that the pseudogap phase is an electronic state that breaks the four-fold rotational symmetry of the copper-oxide planes. At a somewhat lower temperature, of order $T^\star$/2, the positive Hall and Seebeck coefficients of YBCO start dropping, and they reach large negative values at $T = 0$, in the normal state accessed by applying high magnetic fields [2,3]. We interpret this in terms of an electron pocket forming in the Fermi surface of YBCO as a result of a Fermi-surface reconstruction caused by some order which breaks the translational symmetry of the lattice. Because very similar transport anomalies are observed in Eu-LSCO [4], where they coincide with the onset of stripe order, we infer that some form of stripe order is also at play in YBCO, and argue that the pseudogap phase is a precursor region of stripe (or spin-density-wave) fluctuations [5]. \\[4pt] [1] R. Daou {\it et al.}, Nature {\bf 463}, 519 (2010). \\[0pt] [2] J. Chang {\it et al.}, Physical Review Letters {\bf 104}, 057005 (2010). \\[0pt] [3] D. LeBoeuf, arXiv:1009.2078. \\[0pt] [4] O. Cyr-Choini\`ere {\it et al.}, Nature {\bf 458}, 743 (2009). \\[0pt] [5] L. Taillefer, Annual Review of Condensed Matter Physics {\bf 1}, 51 (2010); arXiv:1003.2972.