Increase in charge-density-wave potential of 1T-TaSxSe2-x -: art. no. 245123

We present a detailed angle-resolved photoemission (ARPES) study on changes in the electronic structure of layered transition-metal dichalcogenides 1T-TaSxSe2-x caused by the increase of charge-density-wave (CDW) potential. No significant difference in the spectral features taken at 300 K is shown between 1T-TaS1.2Se0.8 and 1T-TaS1.5Se0.5. In contrast to that, the spectral features at 90 K are different. At the 0.4GammaM point, which is located close to the Fermi wave number along the GammaM line, the spectral feature just below the Fermi level (E-F) shifts to the high-binding-energy side in 1T-TaS1.5Se0.5, but not in 1T-TaS1.2Se0.8. Around the 0.65GammaM point, the energy gap due to the splitting of the Ta 5d band caused by the formation of the CDW grows by cooling in the both materials. The gap size at 90 K in 1T-TaS1.5Se0.5 is larger than that in 1T-TaS1.2Se0.8. At the M point, an energy shift of the spectral feature at the binding energy of 1 eV is clearly shown by cooling in both materials. The results imply that the influence of the CDW-related potential of 1T-TaS1.5Se0.5 in the insulating CDW phase at 90 K is larger than that in 1T-TaS1.2Se0.8 in the metallic CDW phase at 90 K. Based on a model calculation of the spectral function, which captures the main features of the ARPES spectra quite well qualitatively, we conclude that the metal-insulator transition in 1T-TaSxSe2-x is driven by the narrowing of the band width of the Ta 5d band straddling E-F, which is induced by the increase in the CDW-related potential.