Quantization of the band at the surface of charge density wave material 2H-TaSe₂

By using angle-resolved photoemission spectroscopy (ARPES) combined with the first-principles electronic structure calculations, we report the quantized states at the surface of a single crystal 2H-TaSe₂. We have observed sub-bands of quantized states at the three-dimensional Brillouin zone center due to a highly dispersive band with light effective mass along k_z direction. The quantized sub-bands shift upward towards E_F while the bulk band at \varGamma shifts downward with the decrease of temperature across charge density wave (CDW) formation. The band shifts could be intimately related to the CDW. While neither the two-dimensional Fermi-surface nesting nor purely strong electron-phonon coupling can explain the mechanism of CDW in 2H-TaSe₂, our experiment may ignite the interest in understanding the CDW mechanism in this family.