Browsing by Author "Nityananda Acharyya"

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Temperature-Dependent Broadband Terahertz Behavior of Metal-Free Multiwalled Carbon Nanotubes
(American Chemical Society, 2024) Mangababu Akkanaboina; Nityananda Acharyya; Shreeya Rane; Gopal Kulkarni; Shyamal Mondal; Saloni Sharma; Shubhda Srivastava; Bipin Kumar Gupta; Dibakar Roy Chowdhury
This study focuses on the temperature-dependent terahertz (THz) response of a metal-catalyst-free multiwalled carbon nanotubes (MWCNTs) film. The presence of metal catalyst particles challenges the understanding of pure response of the MWCNTs; hence, a distinct method is adopted for the development of pure MWCNTs excluding metal catalyst particles. Utilizing the MWCNTs obtained by this method, a film of ∼40 μm thickness is drop-casted on a high-resistance Si substrate. With the help of terahertz time domain spectroscopy (THz-TDS), the MWCNTs films are characterized for the broadband frequency range (0.2-1 THz) with temperature variation from 24 to 123 °C. Our experiments reveal that an increase in the sample temperature leads to a decrease in THz transmissions due to enhanced THz conductivity. Further, decreasing temperature brings back its response in the reverse manner; however, the two paths are slightly deviated from each other, inducing a temperature-induced hysteresis effect. We attribute this to the temperature-dependent THz response of MWCNTs to π-electron transitions and the existence of defect states. Moreover, the establishment of scattering junctions at high temperature is dedicated to the observed hysteresis effect. Our study also reveals the applicability of these MWCNTs films as THz broadband absorbers, low pass filters, and modulators. Hence, this study can be very useful in incorporating low-dimensional materials in order to realize THz quantum devices. © 2024 American Chemical Society.
Thermally tunable dual channel toroidal metasurface on VO2 platform
(American Institute of Physics, 2025) S. N. Yogitha; Nityananda Acharyya; Abhishek Mishra; Akkanaboina Mangababu; Amit Kumar Verma; Dhanvir Singh Rana; Dibakar Roy Chowdhury
Active modulation of electromagnetic response in terahertz (THz) regime has gathered plenty of attention owing to its multifunctional applications. In this regard, metasurfaces integrated with VO2 as active material can create compelling pathways for actively controlling terahertz propagation. Hence, we have demonstrated a design of dual toroidal active metasurface by realizing plasmonic split-ring resonators on the VO2 thin film for dynamic and real-time control over THz wave propagation. These metasurfaces exhibit agile modulation of multiple resonances by exploiting insulator-to-metal transition (IMT) phenomena exhibited by VO2. For this purpose, sample temperature is varied from 26 to 110 °C. It is observed that at 110 °C, VO2 conductivity increased significantly resulting in a 46% peak amplitude modulation with respect to room temperature. Besides temperature induced tunability mediated by VO2 activated IMT, these metasurfaces manifest temperature tunable electric, magnetic, and toroidal modes which is further validated by rigorous multipole analysis. Hence, these outcomes provide a framework for implementing VO2 based temperature tunable THz metadevices for futuristic applications such as thermal sensors, modulators, terahertz switching, tunable absorbers, and photonic memory. © 2025 Author(s).