CDW and weak Kondo effect in a Dirac semimetal

Using angle-resolved photoemission spectroscopy (ARPES) and low-energy electron diffraction (LEED), together with density-functional theory (DFT) calculation, we report the formation of charge density wave (CDW) and its interplay with the Kondo effect and topological states in CeSbTe. The CDW is driven by the electron-phonon coupling (EPC) from the well-nested 2D Fermi surface (FS). The measured CDW gap is large and up to ~0.3 eV, thus explaining the robust CDW order up to very high temperatures. The gap is roughly isotropic in momentum space, except near the X point where the imperfect FS nesting leads to an energy gap less than 0.1 eV. The gap opening leads to a reduced density of states (DOS) near the Fermi level, which correspondingly suppresses the many-body Kondo effect, leading to very localized 4f electrons at 20 K and above. The topological Dirac cone at the X point is found to remain gapless

inside the CDW phase. Our results provide evidence for the competition between CDW and the Kondo effect in a Kondo lattice system. The robust CDW order in CeSbTe and related compounds provide an opportunity to search for the long-sought-after axionic insulator.