arXiv subjects

Ayan Roy Chaudhuri

Publications and source records attributed to Ayan Roy Chaudhuri.

15 recordsLinked to original sources

arXiv2026

Anisotropic exciton-polaritons reveal non-Hermitian topology in van der Waals materials

Topological band theory has expanded into various domains in applied physics, offering significant potential for future technologies. Recent developments indicate that unique bulk band topology perceived for electrons can be realized in a system of light-matter quasiparticles with reduced crystal symmetry by utilizing tunable light-matter interaction. In this work we realize topologically non-trivial energy band dispersion of exciton-polaritons confined in two-dimensional anisotropic materials inside an optical microcavity, and show the emergence of exceptional points (EPs) due to non-Hermitian topology arising from excitonic dipole oscillators with finite quasiparticle lifetime. Fourier-plane imaging reveals two pairs of EPs connected by bulk Fermi arcs for each of the transverse electric and magnetic polarized modes. An anisotropic Lorentz oscillator model captures the exact band dispersion observed in our experiment in two-dimensional momentum space. Our findings establish anisotropic two-dimensional materials as a platform for exploring non-Hermitian topological physics, with implications for polarization-controlled optical technologies.

physics.optics↗

arXiv2025

Zero-Threshold PT-Symmetric Polariton-Raman Laser

Anisotropy endows topological aspects in optical systems and furnishes a platform to explore non-Hermitian physics, which can be harnessed for the polarization-selective amplification of light. Here, we show a zero-threshold Raman laser can be achieved in an anisotropic optical microcavity via polarization-controlled optical pumping. A loss-gain mechanism between two polarized Stokes modes arises naturally via polarization-dependent stimulated scattering and anisotropic Raman gain of the active layered material inside the microcavity. A Parity-Time (PT) symmetric Hamiltonian has been proposed to explain the emergence of a single polarization mode, essential for achieving a zero-threshold lasing condition. Additionally, intensity correlation measurements of the Stokes modes validate the coherence properties of the emitted light. Our realization of the zero-threshold Raman laser in anisotropic microcavity can open up a new research direction exploring non-Hermitian and topological aspects of light in anisotropic two-dimensional materials.

cond-mat.mes-hall↗

arXiv2023

Emergent room-temperature ferroelectricity in spark-plasma sintered DyCrO$_3$ and LaCrO$_3$

Identification of novel multiferroic materials with high-ordering temperatures remains at the forefront of condensed matter physics research. In this regard, the antiferromagnetic RCrO$_3$ compounds (like GdCrO$_3$) constitute a promising class of multiferroic compounds, which, however, mostly become ferroelectric concomitant with the antiferromagnetic ordering much below room-temperature, arising from a subtle competition between the ferroelectric off-centering mode and a non-polar antiferrodistortive rotation mode that inhibits ferroelectricity. Recently, room-temperature ferroelectricity of structural origin, arising from off-centering displacements of R and Cr ions, has been identified in spark-plasma sintered GdCrO$_3$ [Suryakanta Mishra et al., Phys. Rev. B 104, L180101 (2021)]. Interestingly, some of the experimentally observed non-ferroelectric RCrO$_3$ compounds have been theoretically predicted to host similar ferroelectric instabilities. Here, we have identified two such non-ferroelectric RCrO3 compounds, one DyCrO$_3$ (which is reported as a quantum paraelectric) and another LaCrO$_3$ (which is paraelectric), and using a modified synthesis protocol involving spark-plasma-sintering (SPS), we have been successful in engineering an intrinsic room-temperature ferroelectricity in the paramagnetic state, driven by noncentrosymmetric structural phase in both SPS sintered DyCrO$_3$ and LaCrO$_3$, in contrast to room-temperature paraelectricity in solid-state synthesized DyCrO$_3$ and LaCrO$_3$. While the ferroelectricity in SPS-prepared DyCrO$_3$ and LaCrO$_3$ is stable at room-temperature, it undergoes an irreversible transition from a ferroelectric (Pna2$_1$) phase to a paraelectric (Pbnm) phase at 440 K. Significantly, SPS-sintered LaCrO$_3$, which undergoes antiferromagnetic ordering at 290 K, emerges as a promising near room-temperature multiferroic material.

cond-mat.mtrl-sci↗

arXiv2023

Anisotropic exciton polariton pairs as a platform for PT-symmetric non-Hermitian physics

Non-Hermitian systems with parity-time (PT) symmetry have been realized using optical constructs in the classical domain, leading to a plethora of non-intuitive phenomena. However, PT-symmetry in purely quantum non-Hermitian systems like microcavity exciton-polaritons has not been realized so far. Here we show how a pair of nearly orthogonal sets of anisotropic exciton-polaritons can offer a versatile platform for realizing multiple spectral degeneracies called Exceptional Points (EPs) and propose a roadmap to achieve a PT-symmetric system. Polarization-tunable coupling strength creates one class of EPs, while Voigt EPs are observed for specific orientations where splitting of polariton modes due to birefringence is compensated by Transverse Electric (TE) -Transverse Magnetic (TM) mode splitting. Thus, paired sets of polarized anisotropic microcavity exciton-polaritons can offer a promising platform not only for fundamental research in non-Hermitian quantum physics and topological polaritons, but also, we propose that it will be critical for realizing zero threshold lasers.

cond-mat.mes-hall↗

arXiv2022

Evolution of Resistive Switching Characteristics in WO3-x-based MIM Devices by Tailoring Oxygen Deficiency

We report on resistive switching (RS) characteristics of W/WO3-x/Pt-based thin film memristors modulated by precisely controlled oxygen non-stoichiometry. RS properties of the devices with varied oxygen vacancy (VO) concentration have been studied by measuring their DC current voltage properties. Switchability of the resistance states in the memristors have been found to depend strongly on the VOs concentration in the WO3-x layer. Depending on x, the memristors exhibited forming-free bipolar, forming-required bipolar and non-formable characteristics. Devices with high VOs concentration (~1*1021 cm-3) exhibited lower initial resistance and memory window of only 15, which has been increased to ~6500 with reducing VOs concentration to ~5.8*1020 cm-3. Forming-free, stable RS with memory window of ~2000 have been realized for a memristor possessing VOs concentration of ~6.2*1020 cm-3. Investigation of the conduction mechanism suggests that tailoring VOs concentration modifies the formation and dimension of the conducting filaments as well as the Schottky barrier height at WO3-x/Pt interface which deterministically modulates RS characteristics of the WO3-x based memristors.

physics.app-ph↗

arXiv2022

Nitrogen doped In$_2$O$_3$-ZnO nanocomposite thin film based sensitive and selective ethanol sensor

Nanocomposite metal oxide thin films exhibit assuring qualities in the field of gas sensors because of the collective opportunities provided by the heterointerface formation. In this work, we present the synthesis of nitrogen doped mesoporous In$_2$O$_3$-ZnO nano-composite thin films by simple wet chemical method using urea as the nitrogen precursor. SEM investigation suggests formation of mesoporous nano-composite thin films, where the uniformity of surface pore distribution depends on the relative proportion of In$_2$O$_3$ and ZnO in the composites. HRTEM investigation suggest formation of sharp interfaces between N-In$_2$O$_3$ and N-ZnO grains in the nano-composite thin films. The nano-composite thin films have been tested for their ethanol sensing performance over an extensive range of temperature, ethanol vapor concentration and relative humidity. Nitrogen doped nano-composite thin film with equal proportion of In$_2$O$_3$ and ZnO exhibits excellent ethanol sensing performance at a reasonable operating temperature (~94 % at 200 °C for 50 ppm of ethanol), fast response time (~two seconds), stability over time, enhanced resilience against humidity and selectivity to ethanol over various other volatile organic compounds.

cond-mat.mtrl-sci↗

arXiv2021

Nitrogen incorporated Zinc oxide thin film for efficient ethanol detection

Zinc oxide which is a n-type semiconducting metal oxide (SMO) has been a promising material for detecting ethanol vapor. However, pure ZnO based ethanol sensors often suffer from high working temperature, cross sensitivity towards methanol and poor stability against humidity. Doping ZnO with various metal ions has been widely explored as a proficient approach to improve its ethanol sensing properties, while anionic dopants have been rarely considered. Here in we demonstrate the effect of nitrogen doping on the ethanol sensing characteristics of ZnO thin films. Nitrogen doped ZnO (N-ZnO) thin films have been synthesized following sol-gel technique with urea as nitrogen precursor. Ethanol sensing characteristics of the N-ZnO thin film has been com-pared with pure ZnO sensor over a wide range of temperature and relative humidity conditions. The N-ZnO sensor exhibits significantly large ethanol sensing response at a lower operating temperature (~99 % at 225 °C vs ~81 % at 250 °C for ZnO), faster response time (12 s vs 33 s for ZnO), long term stability, improved resilience against humidity and selectivity towards ethanol over methanol and acetone. The experimental observations have been supplemented by estimating the adsorption energies of ethanol on ZnO and N-ZnO surface using density functional theory (DFT) calculations. We discuss that the microscopic origin of improved ethanol sensing of N-ZnO is related to the facile adsorption of ethanol molecules on the oxide surface which is promoted by modification of electronic properties of ZnO by the nitrogen dopant atoms.

cond-mat.mtrl-sci↗

arXiv2021

Interfacial anisotropic exciton-polariton manifolds in ReS$_2$

Light-matter coupling in van der Waal's materials holds significant promise in realizing Bosonic condensation and superfluidity. The underlying semiconductor's crystal asymmetry, if any, can be utilized to form anisotropic half-light half-matter quasiparticles. We demonstrate generation of such highly anisotropic exciton-polaritons at the interface of a biaxial layered semiconductor, stacked on top of a distributed Bragg reflector. The spatially confined photonic mode in this geometry couples with polarized excitons and their Rydberg states, creating a system of highly anisotropic polariton manifolds, displaying Rabi splitting of up to 68 meV. Rotation of the incident beam polarization is used to tune coupling strength and smoothly switch regimes from weak to strong coupling, while also enabling transition from one three-body coupled oscillator system to another. Light-matter coupling is further tunable by varying the number of weakly coupled optically active layers. Our work provides a versatile method of engineering devices for applications in polarization-controlled polaritonics and optoelectronics.

cond-mat.mes-hall↗

arXiv2020

Engineering room-temperature multiferroicity in Bi and Fe codoped BaTiO3

Fe doping into BaTiO3, stabilizes the paraelectric hexagonal phase in place of the ferroelectric tetragonal one [P. Pal et al. Phys. Rev. B, 101, 064409 (2020)]. We show that simultaneous doping of Bi along with Fe into BaTiO3 effectively enhances the magnetoelectric (ME) multiferroic response (both ferromagnetism and ferroelectricity) at room-temperature, through careful tuning of Fe valency along with the controlled-recovery of ferroelectric-tetragonal phase. We also report systematic increase in large dielectric constant values as well as reduction in loss tangent values with relatively moderate temperature variation of dielectric constant around room-temperature with increasing Bi doping content in Ba1-xBixTi0.9Fe0.1O3 (0<x<0.1), which makes the higher Bi-Fe codoped sample (x=0.08) promising for the use as room-temperature high-k dielectric material. Interestingly, x=0.08 (Bi-Fe codoped) sample is not only found to be ferroelectrically (~20 times) and ferromagnetically (~6 times) stronger than x=0 (only Fe-doped) at room temperature, but also observed to be better insulating (larger bandgap) with indirect signatures of larger ME coupling as indicated from anomalous reduction of magnetic coercive field with decreasing temperature. Thus, room-temperature ME multiferroicity has been engineered in Bi and Fe codoped BTO (BaTiO3) compounds.

cond-mat.mtrl-sci↗

arXiv2020

Origin and tuning of room-temperature multiferroicity in Fe doped BaTiO$_3$

Simultaneous co-existence of room-temperature(T) ferromagnetism and ferroelectricity in Fe doped BaTiO$_3$ (BTO) is intriguing, as such Fe doping into tetragonal BTO, a room-T ferroelectric (FE), results in the stabilization of its hexagonal polymorph which is FE only below $\sim$80K. Here, we investigate its origin and show that Fe-doped BTO has a mixed-phase room-temperature multiferroicity, where the ferromagnetism comes from the majority hexagonal phase and a minority tetragonal phase gives rise to the observed weak ferroelectricity. In order to achieve majority tetragonal phase (responsible for room-T ferroelectricity) in Fe-doped BTO, we investigate the role of different parameters which primarily control the PE hexagonal phase stability over the FE tetragonal one and identify three major factors namely, the effect of ionic size, Jahn-Teller (J-T) distortions and oxygen vacancies (OVs), to be primarily responsible. The effect of ionic size which can be qualitatively represented using the Goldschmidt's tolerance (GT) factor seems to be the major dictating factor for the hexagonal phase stability. The understanding of these factors not only enables us to control them but also, achieve suitable co-doped BTO compound with enhanced room-T multiferroic properties.

cond-mat.mtrl-sci↗

arXiv2019

Hydrogen sensing characteristics of perovskite based calcium doped BiFeO3 thin films

Perovskite oxide based thin film gas sensors have long been considered as potential alternatives to commonly investigated binary metal oxides based sensors. BiFeO3, which is a prototype of p-type perovskite based semiconducting oxides, has recently drawn significant attention for its promising gas sensing characteristics. In the present work, the hydrogen sensing characteristics of calcium doped BiFeO3 has been reported by varying the film thickness, doping concentration, operating temperature, and test gas concentration. The films were deposited on glass substrates by sol-gel route using spin coating. X-ray diffraction analyses confirmed formation of phase pure films and scanning electron microscopy confirmed their uniform and dense microstructure. The Ca-doped BiFeO3 sensors exhibit higher sensitivity compared to pure BiFeO3 sensors. It is reported that the film thickness and Ca doping concentration play major role to control hydrogen sensing characteristics of the deposited films. The sensor based on 15% Ca-doped BiFeO3 sensor exhibited very high sensitivity (~212 % at 500 ppm H2), and excellent selectivity towards hydrogen at a moderate operating temperature (~250 °C).The enhanced gas sensing response of the doped BiFeO3 films has been attributed to the higher oxygen vacancy concentration induced by incorporation of aliovalent Ca2+.

cond-mat.mtrl-sci↗

arXiv2009

Investigation of biferroic properties in La0.6Sr0.4MnO3/0.7 Pb(Mg1/3Nb2/3)O3 0.3 PbTiO3 epitaxial bilayered heterostructures

Epitaxial bilayered thin films consisting of La0.6Sr0.4MnO3 (LSMO) and 0.7 Pb(Mg1/3Nb2/3)O3 0.3 PbTiO3 (PMN-PT) layers of relatively different thicknesses were fabricated on LaNiO3 coated LaAlO3 (100) single crystal substrates by pulsed laser ablation technique. Ferroelectric and ferromagnetic characteristics of these heterostructures confirmed their biferroic nature. The magnetization and ferroelectric polarization of the bilayered heterostructures were enhanced with increasing PMN-PT layer thickness owing to the effect of lattice strain. Dielectric properties of these heterostructures studied over a wide range of temperature under different magnetic field strength suggested a possible role of elastic strain mediated magnetoelectric coupling behind the observed magneto-dielectric effect in addition to the influence of rearrangement of the interfacial charge carriers under an applied magnetic field.

cond-mat.mtrl-sci↗

arXiv2008

Magnetocapacitive La0.6Sr0.4MnO3 0.7Pb(Mg0.33Nb0.67)O3 0.3PbTiO3 epitaxial heterostructures

Epitaxial heterostructures of La0.6Sr0.4MnO3 0.7Pb(Mg0.33Nb0.67)O3 0.3PbTiO3 were fabricated on LaNiO3 coated LaAlO3 (100) substrates by pulsed laser ablation. Ferromagnetic and ferroelectric hysteresis established their biferroic nature. Dielectric behviour studied under different magnetic fields over a wide range of frequency and temperatures revealed that the capacitance in these heterostructures varies with the applied magnetic field. Appearance of magnetocapacitance and its dependence on magnetic fields, magnetic layer thickness, temperature and frequency indicated a combined contribution of strain mediated magnetoelectric coupling, magnetoresistance of the magnetic layer and Maxwell Wagner effect on the observed properties.

cond-mat.mtrl-sci↗

arXiv2007

Realization of biferroic properties in La0.6Sr0.4MnO3 0.7Pb(Mg0.33Nb0.67)O3 0.3(PbTiO3) epitaxial superlattices

A set of symmetric and asymmetric superlattices with ferromagnetic La0.6Sr0.4MnO3 and ferroelectric 0.7Pb(Mg0.33Nb0.67)O3 0.3(PbTiO3) as the constituting layers were fabricated on LaNiO3 coated (100) oriented LaAlO3 substrates using pulsed laser ablation. The crystallinity, magnetic and ferroelectric properties were studied for all the superlattices. All the superlattice structures exhibited a ferromagnetic behavior over a wide range of temperatures between 10K and 300K, whereas only the asymmetric superlattices exhibited a reasonably good ferroelectric behaviour. Strong influence of an applied magnetic field was observed on the ferroelectric properties of the asymmetric superlattices. Studies were conducted towards understanding the influence of conducting LSMO layers on the electrical responses of the heterostructures. The absence of ferroelectricity in the symmetric superlattice structures has been attributed to their high leakage characteristics. The effect of an applied magnetic field on the ferroelectric properties of the asymmetric superlattices indicated strong influence of the interfaces on the properties. The dominance of the interface on the dielectric response was confirmed by the observed Maxwell Wagner type dielectric relaxation in these heterostructures.

cond-mat.mtrl-sci↗

arXiv2006

Interface dominated biferroic La0.6Sr0.4MnO3/0.7Pb(Mg0.33Nb0.66)O3 0.3PbTiO3 epitaxial superlattices

Superlattices composed of ferromagnetic La0.6Sr0.4MnO3 and ferroelectric 0.7Pb(Mg0,33Nb0.66)O3 0.3(PbTiO3) layers were fabricated on (100) LaAlO3 substrates by pulsed laser deposition technique. Ferromagnetic and frequency independent ferroelectric hysteresis characteristics established the biferroic nature of the superlattices. Influence of magnetic field was observed in tuning the P-E characteristics of the superlattices. Similar effect was observed on application of a high DC electric field to the samples. The nature of the observed ferroelectric properties and their modulation by applied magnetic and electric fields were thus discussed in connection to existence of dielectric passive layers at the ferroelectric/ferromagnetic interface.

cond-mat.mtrl-sci↗