Evidence for Charge Instability in theCuO3Chains ofPrBa2Cu3O7from63,65CuNMR

NMR and NQR measurements have been performed on Cu(1) chain sites in ${\mathrm{PrBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ between 300 and 4.2 K. The spin-lattice relaxation rate $1/T_1$ has been measured in the whole temperature range 4.2–300 K. Static and dynamic NMR and NQR parameters undergo a crossover at 180 K and an energy gap opens at $T^{†}\approx 120\mathrm{K}$, as revealed by the temperature dependence of $1/T_1$. These results are consistent with a charge density wave occurring in the quasi-one-dimensional ${\mathrm{CuO}}_3$ chains and reveal the internal electronic properties of the chains in the “123” compounds.