Evolution of charge density waves from three-dimensional to quasi-two-dimensional in kagome superconductors Cs(V1-xMx)3Sb5 (M = Nb, Ta)

The kagome material AV3Sb5 (A = K, Rb, Cs) with geometry frustration hosts nontrivial topological elec-tronic structures, electronic nematicity, the charge density wave (CDW), and superconductivity, providing an ideal platform to study the interplay between these phases. Specifically, in pressurized or substituted CsV3Sb5, the relationship between CDW and superconductivity is unusual and remains to be fully understood. Recently, coexisting and competing 2 x 2 x 4 and 2 x 2 x 2 CDW phases were discovered in CsV3Sb5. To investigate the evolution of the CDW phases with the substitution of V atoms, we performed x-ray diffraction experiments on Cs(V(1-x)Tax)(3)Sb-5 and Cs(V(1-x)Nbx)(3)Sb-5. Our results indicate that in all substituted samples, the discrete CDW reflection points in pristine CsV3Sb5 change to rodlike structures along the c* direction. This suggests that the long-ranged three-dimensional CDW becomes quasi-two-dimensional by the substitution of V by Ta/Nb. Moreover, our temperature-dependent measurements show that there is no hysteresis behavior of CDW signals, indicating that even a slight substitution of Nb or Ta as low as 0.021 and 0.04, respectively, can easily suppress the 2 x 2 x 4 CDW phase. These findings uncover the CDW evolution upon substitution of V atoms in CsV3Sb5, providing insights into the microscopic mechanism of CDW and helping to understand the interplay between intertwined phases and superconductivity.