arXiv subjects

Topojit Debnath

Publications and source records attributed to Topojit Debnath.

10 recordsLinked to original sources

arXiv2026

Radio-Frequency-Driven Reshaping of the Mesoscale Charge-Density-Wave Landscape in 1T-TaS2 Thin-Film Devices

Radio-frequency excitation directly reshapes the mesoscale charge-density-wave landscape in quasi-two-dimensional 1T-TaS2 thin films. Under combined RF and DC bias, the hysteretic current-voltage characteristics associated with the nearly commensurate-incommensurate transition are strongly altered, displaying RF-driven collapse, branching, and multiple step-like features that depend on frequency and drive amplitude. In-situ Raman measurements show enhanced intensity and linewidth narrowing of low-frequency CDW phonon modes, consistent with reduced dephasing and increased coherence of the periodic lattice distortion under RF drive. This behavior is captured by combining an overdamped time-dependent Ginzburg-Landau description of the commensurate CDW with a morphology-informed percolative resistor-capacitor transport model. The simulations indicate that oscillatory driving anneals frustrated domain configurations, reduces domain-wall density, and reorganizes the discommensuration network, while the transport model reproduces the resulting hysteresis, avalanche-like pathways, and RF-induced conductance steps. RF driving therefore provides an effective route for controlling collective electron-phonon order and accessing metastable transport states in 1T-TaS2, with implications for reconfigurable RF electronics, memory, and unconventional computing based on correlated materials.

cond-mat.mtrl-sci↗

arXiv2026

Phonon Signatures of Near-Room-Temperature Phase Transition in Quasi-One-Dimensional Bi4I4 Topological van der Waals Material

The quasi-one-dimensional material Bi4I4 hosts two crystallographically similar polymorphs that realize distinct topological insulating phases separated by a first-order structural transition near room temperature. This transition occurs without a change in space group, arising instead from a subtle rearrangement of chain stacking registry. Polarization-resolved Raman spectroscopy directly resolves this structural-topological phase transition through abrupt, hysteretic modifications of the phonon spectrum. Angle-dependent measurements establish the symmetry of the dominant Raman-active modes and require a complex Raman tensor formalism to account for absorption-induced phase effects. Across the transition, selected phonon modes exhibit discontinuous, reversible shifts in frequency, linewidth, and relative intensity despite the absence of a space-group change. Density functional theory calculations reproduce the direction of the observed phonon renormalizations and confirm their sensitivity to stacking-dependent force constants. These results demonstrate that polarization-resolved Raman spectroscopy can detect subtle stacking-driven structural rearrangements that underlie topological band character, even when global crystallographic symmetry remains unchanged. The obtained results provide valuable insights into the interplay among lattice dynamics, structural distortions, and topological properties in this class of low-dimensional materials, with strong potential for unique functionalities.

cond-mat.mtrl-sci↗

arXiv2025

Quantum Spin Singlet and Classical N\'eel-Ordered Ground States in MoX3 (X = I, Br) Spin-3/2 Dimerized Antiferromagnetic Chain Crystals

We report that MoX3 (X = I, Br) are rare van der Waals materials that exhibit signatures of both quantum spin chains with a spin singlet ground state and classical Neel order. Bulk single crystals grown by chemical vapor transport exhibit classical antiferromagnetic ground states with a transition temperature of ~40 K as revealed by susceptibility and specific heat measurements. Above 40 K, the susceptibilities show the large, broad peaks associated with a quantum spin-singlet ground state and large singlet-triplet gaps of 21 meV and 25 meV. Monte Carlo simulations, density matrix renormalization-group calculations for finite spin-3/2 chains, and density functional theory reproduce the experimental behavior, confirming the interplay between strong one-dimensional intrachain and weak three-dimensional interchain couplings. MoX3 offers a unique platform for exploring quantum magnetism and magnetic excitations at the atomic chain limit, as these materials combine a 1D van der Waals motif, spin chain behavior, and classical interchain order.

cond-mat.str-el↗

arXiv2025

Giant Gate Response of the Charge in an Electron-Lattice Condensate

Efficient electrical capacitive control is important for the next generation of ultra-low-power and ultra-fast electronics and energy-storage devices. Correlated electronic phases offer a powerful route to enhancing field-effect control beyond the limits of conventional capacitive gating. In such systems, modest gate voltages can couple to an order parameter, producing responses far larger than expected from the electrostatics of non-interacting carriers. It was demonstrated that electron-electron interactions, in which the exchange and correlation energies among electrons lower the chemical potential of an electron system as the electron density increases, can significantly increase the effective capacitance over its geometric capacitance value. Here, we show that the electron-lattice or electron-phonon correlations in charge density wave (CDW) condensate can lead to a giant gate response with the corresponding capacitance enhancement. This unusual phenomenon is demonstrated in the quasi-one-dimensional CDW material, where the gate-induced change in CDW charge density exceeds predictions based on geometrical gate capacitance by one to two orders of magnitude. This "giant gating" effect arises from the coupling of the electric field to the CDW electron-lattice condensate, demonstrating a mechanism for massively amplifying gate response via collective electronic behavior. We quantify the effect by determining the quantum capacitance of the CDW charge and by constructing a band diagram for the gated CDW device. The obtained results can lead to an alternative strategy for continuing the downscaling of the transistor feature size in electronic technology.

cond-mat.str-el↗

arXiv2024

Topological magnonic properties of an antiferromagnetic chain

The magnonic excitations of a dimerized, one-dimensional, antiferromagnetic chain can be trivial or topological depending on the signs and magnitudes of the alternating exchange couplings and the anisotropy. The topological phase that occurs when the signs of the two different exchange couplings alternate is qualitatively different from that of the Su-Schrieffer-Heeger model. A material that may exhibit these properties is the quasi-one-dimensional material MoI$_3$ that consists of dimerized chains weakly coupled to adjacent chains. The magnetic ground state and its excitations are analyzed both analytically and numerically using exchange and anisotropy parameters extracted from density functional theory calculations.

cond-mat.mes-hall↗

arXiv2023

Phonon States in NbTe$_4$ and TaTe$_4$ Quasi-One-Dimensional van der Waals Crystals

We report the results of polarization-dependent Raman spectroscopy of phonon states in single-crystalline quasi-one-dimensional NbTe$_4$ and TaTe$_4$ van der Waals materials. The measurements were conducted in the wide temperature range from 80 K to 560 K. Our results show that although both materials have identical crystal structures and symmetries, there is a drastic difference in the intensity of their Raman spectra. While TaTe4 exhibits well-defined peaks through the examined frequency and temperature ranges, NbTe4 reveals extremely weak Raman signatures. The measured spectral positions of the phonon peaks agree with the phonon band structure calculated using the density-functional theory. We offer possible reasons for the in-tensity differences between the two van der Waals materials. Our results provide insights into the phonon properties of NbTe$_4$ and TaTe$_4$ van der Waals materials and indicate the potential of Raman spectroscopy for studying charge-density-wave quantum condensate phases.

cond-mat.mtrl-sci↗

arXiv2022

Specifics of the Elemental Excitations in "True One-Dimensional" MoI$_3$ van der Waals Nanowires

We report on the temperature evolution of the polarization-dependent Raman spectrum of exfoliated MoI$_3$, a van der Waals material with a "true one-dimensional" crystal structure that can be exfoliated to individual atomic chains. The temperature evolution of several Raman features reveals anomalous behavior suggesting a phase transition of a magnetic origin. Theoretical considerations indicate that MoI$_3$ is an easy-plane antiferromagnet with alternating spins along the dimerized chains and with inter-chain helical spin ordering. The calculated frequencies of the phonons and magnons are consistent with the interpretation of the experimental Raman data. The obtained results shed light on the specifics of the phononic and magnonic states in MoI$_3$ and provide a strong motivation for future study of this unique material with potential for spintronic device applications.

cond-mat.mes-hall↗

arXiv2021

Metallic vs. Semiconducting Properties of Quasi-One-Dimensional Tantalum Selenide van der Waals Nanoribbons

We conducted a tip-enhanced Raman scattering spectroscopy (TERS) and photoluminescence (PL) study of quasi-1D TaSe3 nanoribbons exfoliated onto gold substrates. At a selenium deficiency of ~0.25 (Se/Ta=2.75,), the nanoribbons exhibit a strong, broad PL peak centered around ~920 nm (1.35 eV), suggesting their semiconducting behavior. Such nanoribbons revealed a strong TERS response under 785-nm laser excitation, allowing for their nanoscale spectroscopic imaging. Nanoribbons with a smaller selenium deficiency of ~0.15 (Se/Ta=2.85) did not show any PL or TERS response. The confocal Raman spectra of these samples agree with the previously-reported spectra of metallic TaSe3. The differences in the optical response of the nanoribbons examined in this study suggest that even small variations in Se content can induce changes in electronic structure, causing samples to exhibit either metallic or semiconducting character. The temperature-dependent electrical measurements of devices fabricated with both types of materials corroborate these observations. The density-functional-theory calculations revealed that incorporation of an oxygen atom in a Se vacancy can result in band gap opening and thus enable the transition from a metal to a semiconductor. However, the predicted bandgap is substantially smaller than that derived from PL data. These results indicate that the properties of van der Waals materials can vary significantly depending on stoichiometry, defect types and concentration, and possibly environmental and substrate effects. In view of this finding, local probing of nanoribbon properties with TERS becomes essential to understanding such low-dimensional systems.

cond-mat.mtrl-sci↗

arXiv2020

Thermal conductivity of the quasi-1D materials TaSe3 and ZrTe3

The high breakdown current densities and resilience to scaling of the metallic transition metal trichalcogenides TaSe3 and ZrTe3 make them of interest for possible interconnect applications, and it motivates this study of their thermal conductivities and phonon properties. These crystals consist of planes of strongly bonded one-dimensional chains more weakly bonded to neighboring chains. Phonon dispersions and the thermal conductivity tensors are calculated using density functional theory combined with an iterative solution of the phonon Boltzmann transport equation. The phonon velocities and the thermal conductivities of TaSe3 are considerably more anisotropic than those of ZrTe3. The maximum LA velocity in ZrTe3 occurs in the cross-chain direction, and this is consistent with the strong cross-chain bonding that gives rise to large Fermi velocities in that direction. The thermal conductivities are similar to those of other metallic two-dimensional transition metal dichalcogenides. At room temperature, a significant portion of the heat is carried by the optical modes. In the low frequency range, the phonon lifetimes and mean free paths in TaSe3 are considerably shorter than those in ZrTe3. The shorter lifetimes in TaSe3 are consistent with the presence of lower frequency optical branches and zone-folding features in the acoustic branches that arise due to the doubling of the TaSe3 unit cell within the plane.

cond-mat.mtrl-sci↗

arXiv2020

Properties of Shape-Engineered Phoxonic Crystals: Brillouin-Mandelstam Spectroscopy and Ellipsometry Study

We report the results of Brillouin-Mandelstam spectroscopy and Mueller matrix spectroscopic ellipsometry of the nanoscale "pillar with the hat" periodic silicon structures, revealing intriguing phononic and photonic properties. It has been theoretically shown that periodic structures with properly tuned dimensions can act simultaneously as phononic and photonic - phoxonic - crystals, strongly affecting the light-matter interactions. Acoustic phonon states can be tuned by external boundaries, either as a result of phonon confinement effects in individual nanostructures, or as a result of artificially induced external periodicity, as in the phononic crystals. The shape of the nanoscale pillar array was engineered to ensure the interplay of both effects. The Brillouin-Mandelstam spectroscopy data indicated strong flattening of the acoustic phonon dispersion in the frequency range from 2 GHz to 20 GHz and the phonon wave vector extending to the higher-order Brillouin zones. The specifics of the phonon dispersion dependence on the pillar arrays orientation suggest the presence of both periodic modulation and spatial localization effects for the acoustic phonons. The ellipsometry data reveal a distinct scatter pattern of four-fold symmetry due to nanoscale periodicity of the pillar arrays. Our results confirm the dual functionality of the nanostructured shape-engineered structure and indicate a possible new direction for fine-tuning the light-matter interaction in the next generation of photonic, optoelectronic, and phononic devices.

physics.app-ph↗