The interplay between different ordering tendencies of superconducting materials is complicated. Recently, intertwined orders have been proposed from a new perspective that focuses on the cooperation of different orders. To explore the underlying physics of intertwined orders, the discovery of several electronic orders in the kagome superconductors AV₃Sb₅ (A represents K, Rb, or Cs) provides a promising platform.  

The Japanese word “kagome” refers to a bamboo basket woven pattern. This two-dimensional (2D) lattice pattern is endowed with various band structures such as flat bands, Dirac points, and van Hove singularities. Earlier theory predicted unusual superconductivity and a large variety of electronic orders near the van Hove singularities in a 2D kagome lattice.  

Prof. CHEN's group, in previous studies, illuminated the triple-Q charge density wave (CDW) and a novel electronic nematicity, and found the unusual competition of superconductivity and CDW state in pressure experiments. 

Based on this previous research, the researchers further investigated the evolution of CDW and superconductivity in CsV₃Sb₅ under pressure. An emergent CDW state was observed between the pressures of P_c1≈0.58 GPa and P_c2≈2.0 GPa where superconductivity was strongly suppressed. However, when the pressure reached P_c2, the emergent CDW was suppressed and superconductivity dominated. These findings suggest strong competition between CDW and superconductivity. 

Moreover, through the nuclear spin-lattice relaxation measurement, the researchers found evidence of pressure-independent charge fluctuations above the CDW transition temperature, suggesting the existence of electronic correlation effects in the 2D kagome lattice. Conventional superconductors showed a Hebel-Slichter coherent peak below the superconducting transition temperature. But this peak was not observed in CsV₃Sb₅, thus indicating a possibly unconventional superconductivity in this pressurized kagome superconductor. 

The study reveals the evolution of kagome superconductors and new electronic correlation effects in kagome superconductors, paving the way for exploring more about their unconventional superconductivity.