Charge Order and Fluctuations in Bi2Sr2−xLaxCuO6+δ Revealed by 63,65Cu-Nuclear Magnetic Resonance

The discovery of a magnetic-field-induced charge-density-wave (CDW) order in the pseudogap state via nuclear magnetic resonance (NMR) studies has highlighted the importance of "charge" in the physics of high transition-temperature (T c) superconductivity in copper oxides (cuprates). Herein, after briefly reviewing the progress achieved in the last few years, we report new results of 63,65Cu-NMR measurements on the CDW order and its fluctuation in the single-layered cuprate Bi2Sr2− x Lax CuO6+ δ. The NMR spectrum under both in- and out-of-plane magnetic fields above H = 10 T indicates that the CDW replaces the antiferromagnetic order before superconductivity appears, but disappears before superconductivity is optimized. We found that the CDW onset temperature T CDW scales with the pseudogap temperature T*. Comparison between 63Cu and 65Cu NMR indicates that the spin–lattice relaxation process is dominated by charge fluctuations in the doping regions where the CDW appears as well as at the pseudogap end point (T* = 0). These results suggest that charge orders and fluctuations exist in multiple doping regions and over a quite wide temperature range.