Origin of enhanced charge density wave in the kagome superconductor ${\mathrm{CsV}}_{3-x}{\mathrm{Mo}}_x{\mathrm{Sb}}_5$

The topological kagome superconductor ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ exhibits rich quantum phenomenology of correlated electronic phases including unconventional charge order and superconductivity. Understanding how the singularities inherent to the kagome lattice are linked to the observed many-body phases is a topic of great interest. Here, by using Shubnikov–de Haas oscillation measurements, we report the detailed evolution of electronic band structures in ${\mathrm{CsV}}_{3-x}{\mathrm{Mo}}_x{\mathrm{Sb}}_5$ single crystals, where Mo substitution causes a suppression of superconductivity and an enhanced charge density wave. The obvious decrease of oscillation frequency $\left(F_{\beta }\right)$ corresponding to the nontrivial band from 72 to 59 T and smaller cyclotron effective mass $(\sim 0.069m_e)$ reveal that the van Hove singularities from the vanadium orbitals near $M$ are abnormally lifted and promote the nesting condition for the charge density wave. Meanwhile, the electric conduction changes from a hole-dominated multiband feature to a single electron band feature and the anomalous Hall effect becomes stronger. In conjunction with the simple schematics of band structures, the promoted Fermi-surface nesting is dominant in the unusual enhanced charge density wave, offering insight to comprehend the delicate interaction between the intertwined orders in this kagome system.