In-plane electron-phonon coupling anisotropy and multiple charge density wave orders in the superconductor Bi2Rh3Se2

The ternary chalcogenide superconductor Bi2Rh3Se2 was discovered to have charge density wave (CDW) order and electron-phonon coupling (EPC). However, it is still debated whether the phase transition at -240 K is a CDW one. Here, we systematically performed Raman scattering investigations on single-crystal Bi2Rh3Se2. Angle-resolved polarized Raman spectroscopic measurements reveal the in-plane anisotropic EPC in Bi2Rh3Se2, which inhibits the Raman intensity. Temperature-dependent x-ray diffraction and Raman measurements indicate the existence of the incommensurate (ICCDW) and commensurate (CCDW) CDW orders below -250 and -170 K, respectively, in Bi2Rh3Se2. The appearance of zone-folded phonon modes at -170 K confirms the CCDW-induced 2 x 2 reconstruction of the Brillouin zone. Semiquantitative analysis based on Landau theory of second-order phase transitions of CDW-correlated and uncorrelated phonon modes reflects extensive coupling between the phonons and CDW orders. Our findings elucidate the existence of CCDW and ICCDW and confirm the critical role of EPC in CDW transitions in Bi2Rh3Se2.