The natural van der Waals heterostructure $4H_b\text{−}{\text{TaS}}_2$ composed of alternating $1T$- and $1H\text{−}{\text{TaS}}_2$ layers serves as a platform for investigating the electronic correlations and layer-dependent properties of novel quantum materials. The temperature evolution of the conductivity spectra $\sigma (\omega )$ obtained through infrared spectroscopy elucidates the influence of band modifications associated with the charge-density-wave (CDW) superlattice on the $1T$ layer, resulting in a room-temperature energy gap, ${\mathrm{\Delta }}_{\mathrm{CDW}}\approx 0.35\mathrm{eV}$. Supported by density functional theory calculations, we attribute the behavior of interband transitions to the convergence of the layers, which amplifies the charge transfer from the $1T$ to the $1H$ layers, progressing as the temperature decreases. This phenomenon leads to an enhanced carrier density. The presence of an energy gap and the temperature-tunable charge transfer within the bulk of $4H_b\text{−}{\text{TaS}}_2$—driven by layer-dependent CDW states—contribute to a more comprehensive understanding of other complex compounds of transition-metal dichalcogenides.

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• Charge density waves
• Charge dynamics
• Optical conductivity
• 2-dimensional systems
• Transition metal dichalcogenides
• Density functional theory
• Fourier transform infrared spectroscopy