Raman spectroscopic study onBi2⁢Rh3⁢Se2: Two-dimensional Ising charge density wave and quantum fluctuations

The ternary chalcogenide Bi2⁢Rh3⁢Se2 was found to be a charge density wave (CDW) superconductor with a 2×2 periodicity. The key questions regarding the underlying mechanism of CDW state and its interplay with lattice and electronic properties remain to be explored. Here, based on the systematic Raman scattering investigations on single-crystalline Bi2⁢Rh3⁢Se2, we observed the fingerprinting feature of a CDW state, a collective amplitude mode at ∼39cm−1. The temperature evolution of Raman shift and linewidth for this amplitude mode can be well described by the critical behavior of two-dimensional (2D) Ising model, suggesting the interlayer interactions of Bi2⁢Rh3⁢Se2 are negligible when the CDW state is formed, as a consequence, the quantum fluctuations play an important role at low temperature. Moreover, the temperature dependence of Raman shift for the 𝐴9𝑔 mode deviates significantly from the expected anharmonic behavior when approaching the CDW transition temperature ∼240K, demonstrated that strong electron-phonon coupling plays a key role in the formation of CDW. Our results reveal that Bi2⁢Rh3⁢Se2 is an intriguing quasi-2D system to explore the quantum Ising model and modulate the correlations between CDW and superconductivity.