Universal bulk charge-density-wave (CDW) correlations in the cuprate superconductors

The recent observation of bulk CDW order in YBa$_{2}$Cu$_{3}$O$_{8+\delta}$(YBCO) in competition with superconductivity is a significant development [1,2]. Using Cu $L$-edge resonant X-ray scattering, we also observe bulk CDW order in HgBa$_{2}$CuO$_{4+\delta}$(Hg1201; $T_{c}=$72K). The correlations appear below $T_{CDW}\approx $200K, well below the pseudogap temperature $T^{\ast }\approx $320K associated with unusual magnetism [3], but coincident with the onset of Fermi-liquid-like charge transport [4,5]. In contrast to YBCO, we observe no decrease of the CDW amplitude below $T_{c}$, and the correlation length is short and temperature independent. CDW correlations therefore are a universal property of underdoped cuprates, enhanced by low structural symmetry and a magnetic field [1,2], but fundamentally not in significant competition with superconductivity. We also discuss the relationship between the CDW modulation wave vector and the Fermi surface area extracted from QO experiments [6]. \\[4pt] [1] G. Ghiringhelli \textit{et al.}, Science \textbf{337}, 821 (2012).\\[0pt] [2] J. Chang \textit{et al.}, Nature Phys. \textbf{8}, 871 (2012).\\[0pt] [3] Y. Li \textit{et al.}, Phys. Rev B \textbf{84}, 224508 (2011).\\[0pt] [4] N. Bari\v{s}i\'c \textit{et al.}, PNAS \textbf{110}, 12235 (2013).\\[0pt] [5] S.I. Mirzaei \textit{et al.}, PNAS \textbf{110}, 5774 (2013).\\[0pt] [6] N. Bari\v{s}i\'{c} \textit{et al.}, Nature Physics (2013), doi:10.1038/nphys2792.