In most charge density wave (CDW) systems of different material classes, ranging from traditional correlated systems in low-dimension to recent topological systems with Kagome lattice, superconductivity emerges when the system is driven toward the quantum critical point (QCP) of CDW via external parameters of doping and pressure. Despite this rather universal trend, the essential hinge between CDW and superconductivity has not been established yet. Here, the evidence of coupling between electron and CDW fluctuation is reported, based on a temperature- and intercalation-dependent kink in the angle-resolved photoemission spectra of 2H-PdxTaSe2. Kinks are observed only when the system is in the CDW phase, regardless of whether a long- or short-range order is established. Notably, the coupling strength is enhanced upon long-range CDW suppression, albeit the coupling energy scale is reduced. Interestingly, the estimation of the superconducting critical temperature by incorporating the observed coupling characteristics into McMillan's equation yields results closely resembling the known values of the superconducting dome. The results thus highlight a compelling possibility that this new coupling mediates Cooper pairs, which provides new insights into the competing relationship not only for CDW but also for other competing orders.
The authors acknowledge the helpful discussions with Y. Bang, H.\\u2010Y. Choi, and E.\\u2010G. Moon. This research was supported by the National R&D Program (No. 2020K1A3A7A09080366), the Creative Materials Discovery Program (No. 2015M3D1A1070672), and the Basic Science Resource Program (Nos. 2020R1A4A2002828 and 2018R1D1A1B07050869) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT. The use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE\\u2010AC02\\u201076SF00515. The work at SNU was financially supported by the National Research Foundation of S. Korea through 2019R1A2C2090648, 2019M3E4A1080227, and 2021R1A6C101B418. This research was supported by the KRISS (Korea Research Institute of Standards and Science) MPI (Materials Parts Instruments) Lab. program. The work at the Ajou University was supported by the NRF funded by the Ministry of Education (Nos. 2021R1A6A1A10044950 and RS\\u20102023\\u201000285390). The reproduction of the data has been performed using facilities at the IBS Center for Correlated Electron Systems, Seoul National University, and UVSOR Synchrotron Facility in the Institute of Molecular Science.
