Direct observation of melted Mott state evidenced from Raman scattering in 1T-TaS_2 single crystal

The evolution of electron correlation and charge density wave(CDW)in 1T-TaS_2 single crystal has been investigated by temperature-dependent Raman scattering,which undergoes two obvious peaks of A_(1g) modes about 70.8 cm~(-1) and 78.7 cm~(-1) at 80 K,respectively.The former peak at 70.8 cm~(-1) is accordant with the lower Hubbard band,resulting in the electron-correlation-driven Mott transition.Strikingly,the latter peak at 78.7 cm~(-1) shifts toward low energy with increasing the temperature,demonstrating the occurrence of nearly commensurate CDW phase(melted Mott phase).In this case,phonon transmission could be strongly coupled to commensurate CDW lattice via Coulomb interaction,which likely induces appearance of hexagonal domains suspended in an interdomain phase,composing the melted Mott phase characterized by a shallow electron pocket.Combining electronic structure,atomic structure,transport properties with Raman scattering,these findings provide a novel dimension in understanding the relationship between electronic correlation,charge order,and phonon dynamics.     

Band engineering and precipitation enhance thermoelectric performance of SnTe with Zn-doping

We have systematically studied the thermoelectric properties in Zn-doped Sn Te.Strikingly,band convergence and embedded precipitates arising from Zn doping,can trigger a prominent improvement of thermoelectric performance.In particular,the value of dimensionless figure of merit z T has increased by 100% and up to ~ 0.5 at 775 K for the optimal sample with 2% Zn content.Present findings demonstrate that carrier concentration and effective mass play crucial roles on the Seebeck coefficient and power factor.The obvious deviation from the Pisarenko line(Seebeck coefficient versus carrier concentration) due to Zn-doping reveals the convergence of valence bands.When the doping concentration exceeds the solubility,precipitates occur and lead to a reduction of lattice thermal conductivity.In addition,bipolar conduction is suppressed,indicating an enlargement of band gap.The Zn-doped Sn Te is shown to be a promising candidate for thermoelectric applications.