Role of Coulomb correlations in the charge density wave of CuTe

A quasi-one-dimensional layered material CuTe undergoes a charge density wave (CDW) transition in Te chains with a modulation vector of q_CDW = (0.4, 0.0, 0.5). Here, using first-principles calculations, we demonstrate that the correlation effect of Cu is critical to stabilizing the 5 × 1 × 2 modulation of Te chains. The phonon calculation with the strong Coulomb correlation exhibits the imaginary phonon frequency at q_ph0 = (0.4, 0.0, 0.5), indicating the structural instability. The corresponding lattice distortion of the soft mode agrees well with the experimental modulation. These results demonstrate that the CDW transition in CuTe originates from the interplay of the Coulomb correlation and electron-phonon interaction. Furthermore, we investigated the stability of the CDW state in a CuTe monolayer, Similarly to its bulk structure, we find the phonon soft mode at q = (0.4, 0.0), indicating structural instability, which only appears with the correlation effect on Cu. Interestingly, by reducing the interlayer interactions, tuning of the CDW modulation may be possible, as demonstrated by the modulation pattern in quasi-one-dimensional Te chains being different from that in the bulk counterpart.
Reference
S. Kim, B. Kim, K. Kim, Physical Review B, 100, 054112 (2019)