We performed a polarized Raman scattering study of quasi-one-dimensional superconductor K2Cr3As3. We detect two A 1 phonons and three E phonons. One of the A 1 modes exhibits a nearly temperature-independent Fano lineshape. Based on our first-principles calculations, we ascribe this mode to the in-phase vibrations of Cr atoms within one layer. This observation strongly suggests that the magnetic fluctuations in K2Cr3As3 are coupled to the electronic structure via the lattice.PACS numbers: 74.25. Kc, 74.25.nd, 63.20.kd Superconductivity in conventional materials is mediated by the electron-phonon interaction. When the electron-phonon coupling is strong enough, the spectral lineshape of Raman phonon excitations is characterized by an asymmetric profile called Fano lineshape [1]. Despite a superconducting transition temperature (T c ) up to 6.1 K comparable to that of conventional superconductors, the recently discovered quasi-one-dimensional superconductors A 2 Cr 3 As 3 (A = K, Rb, Cs) have exotic properties that tentatively earned them the label of unconventional superconductors [2][3][4], such as an abnormal power law divergence of the 75 As nuclear spin lattice relaxation rate near T c [5]. Penetration depth measurements suggest a nodal line in the superconducting gap [6] and a large zero temperature upper critical field H c2 (0) compared to the Pauli limit has been attributed to a spin triplet p-wave pairing [2], in agreement with a theoretical study revealing strong ferromagnetic fluctuations caused by the frustration of Cr moments within one layer [7]. Interestingly, CrAs itself exhibits superconductivity in proximity to a magnetic instability [8]. Moreover, theoretical calculations of the electronic density-of-states indicate a sizable renormalization factor in K 2 Cr 3 As 3 compatible with a large specific heat coefficient [2], suggesting significant electron correlations [9,10]. However, although some evidences push towards unconventional superconductivity in K 2 Cr 3 As 3 , this view is not universally accepted [11] and whether the electron-phonon interaction plays a key role in this material remains an open question.In this Letter, we report a polarized Raman scattering study of K 2 Cr 3 As 3 . We identify two and three phonon modes with the A 1 and E symmetries, respectively. Surprisingly, one of the A 1 phonons exhibits a Fano lineshape, nearly temperature-independent from 6 K to room temperature, which is characterized by a coupling strength factor 1/q = −0.29. Our theoretical analysis indicates that this mode involves the in-plane movement of the Cr atoms, which directly modulates the Cr-
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