ABSTRACT
The two different light-matter interactions between visible and infrared light are not switchable because control mechanisms have not been elucidated so far, which restricts the effective spectral range in light-sensing devices. In this study, modulation of the effective spectral range is demonstrated using the metal-insulator transition of MoS2. Nondegenerate MoS2 exhibits a photoconductive effect in detecting visible light. In contrast, degenerate MoS2 responds only to mid-infrared (not visible) light by displaying a photoinduced heating effect via free carrier absorption. Depending on the doping level, the optical behavior of MoS2 simulates the photoconductivity of either the semiconductor or the metal, further indicating that the optical metal-insulator transition is coherent with its electrical counterpart. The electrical switchability of MoS2 enables the development of an unprecedented and novel design optical sensor that can detect both visible and mid-IR (wavelength of 9.6 µm) ranges with a singular optoelectronic device.
ABSTRACT
The 1D wire TaS3 exhibits metallic behavior at room temperature but changes into a semiconductor below the Peierls transition temperature (Tp), near 210 K. Using the 3ω method, we measured the thermal conductivity κ of TaS3 as a function of temperature. Electrons dominate the heat conduction of a metal. The Wiedemann-Franz law states that the thermal conductivity κ of a metal is proportional to the electrical conductivity σ with a proportional coefficient of L0, known as the Lorenz number-that is, κ=σLoT. Our characterization of the thermal conductivity of metallic TaS3 reveals that, at a given temperature T, the thermal conductivity κ is much higher than the value estimated in the Wiedemann-Franz (W-F) law. The thermal conductivity of metallic TaS3 was approximately 12 times larger than predicted by W-F law, implying L=12L0. This result implies the possibility of an existing heat conduction path that the Sommerfeld theory cannot account for.
