Subhadeep Datta’s research while affiliated with Jadavpur University and other places

We report a sequential two-step vapor deposition process for growing mixed-dimensional vdW materials, specifically Te nanowires (1D) and MoS2 (2D), on a single SiO2 wafer. Our growth technique offers a unique potential pathway to create large-scale, high-quality, defect-free interfaces. The assembled samples serve a twofold purpose: first, the as-prepared heterostructures (Te NW/MoS2) provide insights into the atomically thin depletion region of a 1D/2D vdW diode, as revealed by electrical transport measurements and density-functional-theory-based quantum transport calculations. The charge transfer at the heterointerface is confirmed using Raman spectroscopy and Kelvin probe force microscopy. We also observe modulation of the rectification ratio with varying applied gate voltage. Second, the nonhybrid regions on the substrate, consisting of the as-grown individual Te nanowires and MoS2 microstructures, are used to fabricate separate p- and n-type field-effect transistors (FETs), respectively. Furthermore, the ionic-liquid gating helps to realize a low-power complementary metal-oxide semiconductor (CMOS) inverter and all basic logic-gate operations using a pair of n- and p-FETs on the Si/SiO2 platform. This approach also demonstrates the potential for unifying diode and CMOS circuits on a single platform, opening opportunities for integrated analog and digital electronics.

The interaction of ultrasonic waves with piezoelectric materials provides a quantitative route to enhance electrical and mechanical coupling in van der Waals (vdW) heterostructures. Here, wire‐bonding tip‐assisted ultrasound (≈100 kHz) is presented as an effective approach to achieve piezoelectric transduction in monolayer MoS2 on Si/SiO2 substrates. Transient current measurements show reproducible sharp peaks with a peak‐to‐base ratio (Ipeak/Ibase ≈ 12) unique to monolayer MoS2, under an impact duration of 10–100 ms. Electrostatic gate voltage (Vg) and ultrasound power (WP) tunable piezocurrent exhibit 3–5 times higher sensitivity in the ON‐state (Vg ⩾ 0) compared to the OFF‐state. Multiple reflections of acoustic waves at source‐drain electrodes, with an increment in reflection coefficients, enhance the linewidth of peak currents, validated by microacoustic simulations of surface acoustic wave (SAW) propagation in submicron geometries. The localized strain and Joule heating under ultrasonic excitation may generate a temperature rise of ≈20 K, which reduces activation energy barriers, potentially enhancing reaction rates in temperature‐sensitive chemical processes, such as hydrogen peroxide decomposition. This thermal‐damage‐free method integrates with silicon‐based fabrication, establishing a robust platform for on‐chip catalysis and energy harvesting in FET‐based piezotransducers.

Magnons — wavelike spin excitations in magnets — transfer energy and information without moving charge, like ripples on water. Here, in FePS3, an antiferromagnetic insulator, magnons interact with the electrons of few-layer graphene when in a heterostructure, enabling spin waves to convert into electrical signals. In FePS3, magnons soften below 40 K, reducing stiffness with cooling, while few-layer graphene exhibits negative magnetoresistance at low fields (±0.2 T) up to 100 K, transitioning to positive beyond this point. This experiment also proposes a “magnon capacitor”, where spin waves regulate charge transport by influencing carrier dynamics at the interface. With possible applications in energy-efficient computing, this breakthrough advances next-generation spintronic technologies.

Magnetodielectric (MD) materials are important for their ability to spin-charge conversion, magnetic field control of electric polarization and vice versa. Among these, two-dimensional (2D) van der Waals (vdW) magnetic materials are of particular interest due to the presence of magnetic anisotropy (MA) originating from the interaction between the magnetic moments and the crystal field. Also, these materials indicate a high degree of stability in the long-range spin order and may be described using suitable spin Hamiltonians of the Heisenberg, XY, or Ising type. Recent reports have suggested effective interactions between magnetization and electric polarization in 2D magnets. However, MD coupling studies on layered magnetic materials are still few. This review covers the fundamentals of MD coupling by explaining related key terms. It includes the necessary conditions for having this coupling and sheds light on the possible microscopic mechanisms behind this coupling starting from phenomenological descriptions. Apart from that, this review classifies 2D magnetic materials into several categories for reaching out each and every class of materials. Additionally, this review summarizes recent advancements of some pioneer 2D MD materials. Last but not the least, the current review provides possible research directions for enhancing MD coupling in those and mentions the possibilities for future developments.

Magnetodielectric (MD) materials are important for their ability to spin-charge conversion, magnetic field control of electric polarization and vice versa. Among these, two-dimensional (2D) van der Waals (vdW) magnetic materials are of particular interest due to the presence of magnetic anisotropy (MA) originating from the interaction between the magnetic moments and the crystal field. Also, these materials indicate a high degree of stability in the long-range spin order and may be described using suitable spin Hamiltonians of the Heisenberg, XY, or Ising type. Recent reports have suggested effective interactions between magnetization and electric polarization in 2D magnets. However, MD coupling studies on layered magnetic materials are still few. This review covers the fundamentals of magnetodielectric coupling by explaining related key terms. It includes the necessary conditions for having this coupling and sheds light on the possible physical mechanisms behind this coupling starting from phenomenological descriptions. Apart from that, this review classifies 2D magnetic materials into several categories for reaching out each and every class of materials. Additionally, this review summarizes recent advancements of some pioneer 2D magnetodielectric materials. Last but not the least, the current review provides possible research directions for enhancing magnetodielectric coupling in those and mentions the possibilities for future developments.

The breaking of inversion symmetry combined with spin–orbit coupling, can give rise to intriguing quantum phases and collective excitations. Here, we report systematic temperature dependent Raman scattering and theoretical calculations of phonon modes across the inversion symmetry-breaking structural transitions in a quasi-one-dimensional compound (TaSe4)3I. Our investigation revealed the emergence of three additional Raman-active modes in Raman spectra of the low-temperature non-centrosymmetric (NC) structure of the material. From polarization dependent Raman spectra and phonon mode symmetry analysis, we have identified the origin of these three newly appeared additional Raman-active modes. Notably, two of these modes become Raman active due to the loss of inversion symmetry, while the third mode is identified as a soft phonon mode, arising from the distinctive vibrational motion of tantalum (Ta) atoms along the –Ta–Ta– chains. Furthermore, the temperature evolution of self-energy parameters indicates significant changes in the characteristics of the Raman modes across the transition. Latent heat measurements near the phase transition using Differential Scanning Calorimetry confirm the first-order nature of the transition. Theoretical analysis, including group theory and modeling, reaffirms the displacive first-order nature of the structural transition. Our findings establish (TaSe4)3I as a model quasi-one-dimensional system with broken inversion symmetry facilitated through a displacive first-order structural transition.

We investigate the pressure-driven structural and electronic evolution of PdSe$_2$ using powder X-ray diffraction, Raman spectroscopy, and first-principles calculations. Beyond 2.3 GPa, suppression of the Jahn-Teller distortion induces in-plane lattice expansion and metallization. Around 4.8 GPa, the interlayer $d_{z^2}-\pi^*$ orbital hybridization drives the dimensional crossover, facilitating the transformation from the 2D distorted to a 3D undistorted pyrite phase. Above 9 GPa, a novel phase emerges, characterized by octahedral distortions in the d orbitals of Pd. Structural analysis suggests the presence of marcasite (Pnnm) or arsenopyrite ($P2_1/c$) phase with orthorhombic and monoclinic configurations, respectively. Furthermore, the observed phonon anomaly and electronic structure modifications, including the emergence of flat bands in the high-pressure phases, elucidate the fundamental mechanisms underlying the previously reported exotic superconductivity with an enhanced critical temperature. These results highlight the pivotal role of dimensional crossover and structural transitions in tuning the electronic properties of puckered materials, providing pathways for novel functionalities.

We present a fully analytical model of hybridization between magnon, and phonons observed experimentally in magneto-Raman scattering in van der Waals (vdW) antiferromagnets (AFM). Here, the representative material, FePS3, has been shown to be a quasi-two-dimensional-Ising antiferromagnet, with additional features of spin-phonon coupling in the Raman spectra emerging below the N\'eel temperature (TN) of approximately 120 K. Using magneto-Raman spectroscopy as an optical probe of magnetic structure, we show that one of these Raman-active modes in the magnetically ordered state is a magnon with a frequency of 3.7 THz (~ 122 cm-1). In addition, one magnon band and three phonon bands are coupled via the magneto-elastic coupling evidenced by anti-crossing in the complete spectra. We consider a simple model involving only in-plane nearest neighbor exchange couplings (designed to give rise to a similar magnetic structure) and perpendicular anisotropy in presence of an out-of-plane magnetic field. Exact diagonalization of the Hamiltonian leads to energy bands which show that the interaction term gives rise to avoided crossings between the hybridized magnon and phonon branches. Realizing magnon-phonon coupling in two-dimensional (2D) AFMs is important for the verification of the theoretical predictions on exotic quantum transport phenomena like spin-caloritronics, topological magnonics, etc.

We report a sequential two-step vapor deposition process for growing mixed-dimensional van der Waals (vdW) materials, specifically Te nanowires (1D) and MoS$_2$ (2D), on a single SiO$_2$ wafer. Our growth technique offers a unique potential pathway to create large scale, high-quality, defect-free interfaces. The assembly of samples serves a twofold application: first, the as-prepared heterostructures (Te NW/MoS$_2$) provide insights into the atomically thin depletion region of a 1D/2D vdW diode, as revealed by electrical transport measurements and density functional theory-based quantum transport calculations. The charge transfer at the heterointerface is confirmed using Raman spectroscopy and Kelvin probe force microscopy (KPFM). We also observe modulation of the rectification ratio with varying applied gate voltage. Second, the non-hybrid regions on the substrate, consisting of the as-grown individual Te nanowires and MoS$_2$ microstructures, are utilized to fabricate separate p- and n-FETs, respectively. Furthermore, the ionic liquid gating helps to realize low-power CMOS inverter and all basic logic gate operations using a pair of n- and p- field-effect transistors (FETs) on Si/SiO$_2$ platform. This approach also demonstrates the potential for unifying diode and CMOS circuits on a single platform, opening opportunities for integrated analog and digital electronics.