Pseudogap energy scale independent of charge-density-wave order in a high-Tc cuprate

In order to explain the emergence of the anomalous pseudogap state and high temperature superconductivity in the cuprates, intense research activity over three decades has focused on unravelling the connection between the various instabilities of the underdoped regime. In the high temperature superconductor (Ca_xLa_1-x)(Ba_1.75-xLa_0.25+x)Cu₃O_y (CLBLCO) isovalent chemical substitution produces smooth changes to the CuO₂ plane buckling and the Cu(II)-to-apical-oxygen distance, allowing us to study the interdependence of charge-density-wave (CDW) order, superconductivity and the pseudogap at constant hole doping in two adiabatically connected representations of the 123 cuprate structure. In this study, resonant soft x-ray scattering measurements reveal the first observation of incommensurate CDW correlations in CLBLCO and demonstrate a lack of correlation between T_CDW and the pseudogap crossover temperature (T*). This result poses a challenge for models in which the opening of the pseudogap at T* results from fluctuating CDW correlations.