In-Plane Charge Modulation below $T_c$ and Charge-Density-Wave Correlations in the Chain Layer in ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{O}_7$

Nuclear quadrupole resonance (NQR) measurements have been performed on Cu(2) plane sites and Cu(1) chain sites in fully doped ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ between 300 and 4.2 K. The sharp increase of the Cu(1) NQR linewidth across the superconducting transition and the T dependence of the Cu(1) spin lattice relaxation rate confirm the existence of a charge-density-wave state (CDW) in the chains. The simultaneous broadening of the Cu(2) linewidth below $T_c$ and the anomalous T dependence of Cu(1) and Cu(2) NQR parameters indicate that these in-chain CDW correlations are strongly involved in the appearance of an in-plane charge modulated structure below $T_c$.