2010/07/30 by A. P. Petrović, R. Lortz, Rolf Lortz +13 · 1 citation
Chemistry · Materials Science · Physics and Astronomy · #Charge density wave #Condensed matter physics #Density of states #Inorganic Chemistry and Materials #Iron-based superconductors research #Lattice (music) #Organic and Molecular Conductors Research #Phonon #Physics #Superconductivity #cond-mat.str-el #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevb.82.235128
published as Physical Review B 82 235128 (2010) · 16 pages, 13 figures
arxiv created 2010/07/30 · openalex publication_date 2010/12/21 · arxiv updated 2013/03/06 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present electronic-structure calculations, electrical resistivity data, and the first specific-heat measurements in the normal and superconducting states of quasi-one-dimensional M2Mo6Se6 (M=Tl,In,Rb). Rb2Mo6Se6 undergoes a metal-insulator transition at \ensuremath∼170 K: electronic-structure calculations indicate that this is likely to be driven by the formation of a dynamical charge-density wave. However, Tl2Mo6Se6 and In2Mo6Se6 remain metallic down to low temperature, with superconducting transitions at Tc=4.2 K and 2.85 K, respectively. The absence of any metal-insulator transition in these materials is due to a larger in-plane bandwidth, leading to increased interchain hopping which suppresses the density wave instability. Electronic heat-capacity data for the superconducting compounds reveal an exceptionally low density of states D_EF=0.055 states eV^\ensuremath-1 atom^\ensuremath-1, with BCS fits showing 2\ensuremathΔ/kBTc\ensuremath≥5 for Tl2Mo6Se6 and 3.5 for In2Mo6Se6. Modeling the lattice specific heat with a set of Einstein modes, we obtain the approximate phonon density of states F(\ensuremathω). Deconvolving the resistivity for the two superconductors then yields their electron-phonon transport coupling function \ensuremathαtr2F(\ensuremathω). In Tl2Mo6Se6 and In2Mo6Se6, F(\ensuremathω) is dominated by an optical ``guest ion'' mode at \ensuremath∼5 meV and a set of acoustic modes from \ensuremath∼10 to 30 meV. Rb2Mo6Se6 exhibits a similar spectrum; however, the optical phonon has a lower intensity and is shifted to \ensuremath∼8 meV. Electrons in Tl2Mo6Se6 couple strongly to both sets of modes, whereas In2Mo6Se6 only displays significant coupling in the 10--18 meV range. Although pairing is clearly not mediated by the guest ion phonon, we believe it has a beneficial effect on superconductivity in Tl2Mo6Se6, given its extraordinarily large coupling strength and higher Tc compared to In2Mo6Se6.