Observation of a Raman-active phonon with Fano line shape in the quasi-one-dimensional superconductorK2Cr3As3

Abstract

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-

Multiband One-Dimensional Electronic Structure and Spectroscopic Signature of Tomonaga-Luttinger Liquid Behavior in K2Cr3AsWatson1, Feng2, Nicholson3 et al. 2017Phys. Rev. Lett.593410View full textAdd to dashboardCite

“…While spin fluctuations could still be relevant to both these discussions, deviation from Fermi liquid behavior is certainly expected in the context of these ARPES results, which show an absence of low-energy quasiparticle excitations. The ARPES results also demand a different explanation of the anomalously large Sommerfeld coefficient [1,4], other than the picture of quasiparticles renormalized by electron-electron (or electron-phonon [31,32]) interactions. We predict that STM studies would show a similar power law behavior to our observations [33].…”

Cs133andAs75NMR investigation of the normal metallic state of quasi-one-dimensionalZhi1, Lee2, Imai3 et al. 2016Phys. Rev. B276280View full textAdd to dashboardCite

“…Early measurements of bulk physical properties such as electrical resistivity ρ [4][5][6], electronic specific heat coefficient γ [4][5][6], bulk magnetic susceptibility χ bulk [4][5][6] and other measurements [7][8][9] suggested that K 2 Cr 3 As 3 may exhibit strongly correlated phenomena owing to Cr 3d electrons [10,11]. The nominal valence of Cr is +2.33, assuming As 3− and K + with no vacancies.…”

Strong-coupling electron-phonon superconductivity in noncentrosymmetric quasi-one-dimensionalK2Cr3As3

“…In addition, zero-field μSR measurements show the presence of an internal magnetic field in the superconducting state, although the magnetic field is more than 100 times smaller than that observed in Sr 2 RuO 4 . Raman scattering studies of phonons with frequencies greater than 100 cm −1 also show very weak electron-phonon coupling that is too small to account for the observed superconductivity in this material [13]. In addition to these experimental observations, various first principles and Hubbard model based theoretical studies also find that a triplet superconducting state mediated by magnetic fluctuations is likely to be present in K 2 Cr 3 As 3 [14][15][16][17][18][19].…”