Second-order charge-density-wave transition in single crystals of La3Co4Sn13La_{3}Co_{4}Sn_{13}

We present the temperature dependence of the electrical resistivity, the magnetic susceptibility, and the specificheat of a high-quality single crystal of La3Co4Sn13. As opposed to earlier reports on this system, these bulkproperties exhibit clear anomalies at the phase transition at T ∗ = 151(1) K, while the present data confirm thesecond-order character of this transition. X-ray diffraction with synchrotron radiation is used to solve the fourfoldsuperstructure in space group I213 as it exists belowT ∗ in the charge-density-wave (CDW) state of La3Co4Sn13.Unlike conventional CDW systems, we have observed hysteresis between the zero-field-cooled and field-cooledmagnetization below the CDW transition. This discrepancy can be attributed to a possible magnetic instabilityarising out of correlations of Co in the lattice, developing at the CDWtransition. The crystal structure shows thatany modifications of the electronic state of Co might be due to modified binding characteristics of the Sn atomscomprising the trigonal prismatic coordination of Co, while the coordination of Co itself is hardly changed atthe phase transition. The superconducting transition is observed at Tsc = 2.85(2) K. The superconducting energygap is estimated as 5 K on the basis of the specific heat measured down to 0.1 K. These results suggest thatLa3Co4Sn13 is a conventional weak-electron-phonon-coupling superconductor