Fig. 4: Near-field electrodynamics of thermally activated carrier of few-layer WTe2.
From: Terahertz response of monolayer and few-layer WTe2 at the nanoscale
a Temperature dependence of thermally activated carrier densities at different gap sizes calculated (Supplementary Note 6) based on the band structure investigated by ARPES [12]. b Near-field spectroscopic response of the thermally activated carriers of a model 2L WTe2 with \(\Delta =-10\,{{{{\mathrm{meV}}}}}\). The green shaded region represents the power spectrum of the THz probe. c Right panel: temperature dependent WL signal calculation based on LRM for 1L (black curve), 2L (blue curve), and 3L (red curve) WTe2 with gap sizes 60 meV, −10 meV, and −20 meV respectively. Along with the model, nano-THz data of 1L, 2L, and 3L WTe2 are displayed with squares. The error-bars are the standard deviations of the extracted data in regions indicated in Fig. 2b. Both the model curves and experiment points are normalized to the substrate value. Left panel: the gap-size dependent near-field signal of 2L (blue) and 3L (red) at 44 K. The signal level is strongly suppressed when the gap is close to zero or positive. d, e Hypothetical band structure of semimetallic 2L WTe2 (left) and insulating 1L WTe2 [12] with a bandgap \(\Delta > 60\,{{{{\mathrm{meV}}}}}\) (right).
