arXiv subjects

Arindam Ghosh

Publications and source records attributed to Arindam Ghosh.

At least 37 records · Page 2Linked to original sources

arXiv2022

New Results on Generalization of Jordan centralizers over matrix rings

This paper presents a study on Jordan maps over matrix rings with some functional equations related to additive maps on these rings. We first show that every Jordan left (right) centralizer over a matrix ring is a left (right) centralizer. Moreover, every two-sided centralizer over the matrix ring is of a particular form. Further, we prove that any additive map satisfying functional equations over matrix rings becomes a two-sided centralizer. Finally, we conclude our work with some results on the Jordan left $\star$- centralizer over matrix rings and establish some results on functional equations that arise for the $\star$-centralizer.

math.RA↗

arXiv2022

Graphene-Induced Energy Transfer for Quantitative Membrane Biophysics at Sub-Nanometer Resolution

Graphene-induced energy transfer (GIET) is a recently developed fluorescence-spectroscopic technique that achieves sub-nanometric optical localization of fluorophores along the optical axis of a microscope. GIET is based on the near-field energy transfer from an optically excited fluorescent molecule to a single sheet of graphene. It has been successfully used for estimating inter-leaflet distances of single lipid bilayers, and for investigating the membrane organization of living mitochondria. In this study, we use GIET to measure the cholesterol-induced subtle changes of membrane thickness at the nanoscale. We quantify membrane thickness variations in supported lipid bilayers (SLBs) as a function of lipid composition and increasing cholesterol content. Our findings demonstrate that GIET is an extremely sensitive tool for investigating nanometric structural changes in bio-membranes.

physics.optics↗

arXiv2022

Spin-orbit coupling-enhanced valley ordering of malleable bands in twisted bilayer graphene on WSe2

New phases of matter can be stabilized by a combination of diverging electronic density of states, strong interactions, and spin-orbit coupling. Recent experiments in magic-angle twisted bilayer graphene (TBG) have uncovered a wealth of novel phases as a result of interaction-driven spin-valley flavour polarization. In this work, we explore correlated phases appearing due to the combined effect of spin-orbit coupling-enhanced valley polarization and large density of states below half filling ($ν\lesssim 2$) of the moiré band in a TBG coupled to tungsten diselenide. We observe anomalous Hall effect, accompanied by a series of Lifshitz transitions, that are highly tunable with carrier density and magnetic field. Strikingly, the magnetization shows an abrupt sign change in the vicinity of half-filling, confirming its orbital nature. The coercive fields reported are about an order of magnitude higher than previous studies in graphene-based moiré systems, presumably aided by a Stoner instability favoured by the van Hove singularities in the malleable bands. While the Hall resistance is not quantized at zero magnetic fields, indicative of a ground state with partial valley polarization, perfect quantization and complete valley polarization are observed at finite fields. Our findings illustrate that singularities in the flat bands in the presence of spin-orbit coupling can stabilize ordered phases even at non-integer moiré band fillings.

cond-mat.mes-hall↗

arXiv2022

Tuning exciton complexes in twisted bilayer WSe2 at intermediate misorientation

Twist angle modifies the band alignment, screening, and interlayer (IL) coupling in twisted bilayers (tBLs) of transition metal dichalcogenides. Intermediate misorientation (twist angles > 15 degrees) bilayers (BLs) offer a unique opportunity to tune excitonic behavior within these concurrent physical mechanisms but are seldom studied. In this paper, we measure many-body excitonic complexes in monolayer (ML), natural BL, and tBL WSe2. Neutral biexciton (XX) is observed in tBL, while being undetected in nonencapsulated ML and BL, demonstrating unique effects of disorder screening in tBLs. The XX as well as charged biexciton are robust to thermal dissociation and are controllable by electrostatic doping. Vanishing of momentum-indirect IL excitons with increasing electron doping is demonstrated in tBL, resulting from the near alignment of Q-K and K-K valleys. Intermediate misorientation samples offer a high degree of control of excitonic complexes while offering possibilities for studying exciton-phonon coupling, band alignment, and screening.

physics.optics↗

arXiv2022

Non-uniform magnetic field as a booster for quantum speed limit: faster quantum information processing

We probe the quantum speed limit (QSL) of an electron when it is trapped in a non-uniform magnetic field. We show that the QSL increases to a large value, but within the regime of causality, by choosing a proper variation in magnetic fields. We also probe the dependence of QSL on spin of electron and find that it is higher for spin-down electron in the relativistic regime. This can be useful in achieving a faster speed of transmission of quantum information. Further, we use the Bremermann--Bekenstein bound to find a critical magnetic field that bridges the gap between non-relativistic and relativistic treatments and relates to the stability of matter. An analytical framework is developed. We also provide a plausible experimental design to supplement our theory.

quant-ph↗

arXiv2022

Low-resource Low-footprint Wake-word Detection using Knowledge Distillation

As virtual assistants have become more diverse and specialized, so has the demand for application or brand-specific wake words. However, the wake-word-specific datasets typically used to train wake-word detectors are costly to create. In this paper, we explore two techniques to leverage acoustic modeling data for large-vocabulary speech recognition to improve a purpose-built wake-word detector: transfer learning and knowledge distillation. We also explore how these techniques interact with time-synchronous training targets to improve detection latency. Experiments are presented on the open-source "Hey Snips" dataset and a more challenging in-house far-field dataset. Using phone-synchronous targets and knowledge distillation from a large acoustic model, we are able to improve accuracy across dataset sizes for both datasets while reducing latency.

eess.AS↗

arXiv2022

Towards 6G Communications: Architecture, Challenges, and Future Directions

The cellular network standard is gradually stepping towards the 6th Generation (6G). In 6G, the pioneering and exclusive features, such as creating connectivity even in space and under water, are attracting Governments, organizations and researchers to spend time, money, effort extensively in this area. In the direction of intelligent network management and distributed secured systems, Artificial Intelligence (AI) and blockchain are going to form the backbone of 6G, respectively. However, there is a need for the study of the 6g architecture and technology, such that researchers can identify the scopes of improvement in 6G. Therefore, in this survey, we discuss the primary requirements of 6G along with its overall architecture and technological aspects. We also highlight crucial challenges and future research directions in 6G networks, which can lead to the successful practical implementation of 6G, as per the objective of its introduction in next generation cellular networks.

cs.NI↗

arXiv2021

Emergence of broken-symmetry states at half-integer band fillings in twisted bilayer graphene

The dominance of Coulomb interactions over kinetic energy of electrons in narrow, non-trivial moiré bands of magic-angle twisted bilayer graphene (TBG) gives rise to a variety of correlated phases such as correlated insulators, superconductivity, orbital ferromagnetism, Chern insulators and nematicity. Most of these phases occur at or near an integer number of carriers per moiré unit cell. Experimental demonstration of ordered states at fractional moiré band-fillings at zero applied magnetic field $B$, is a challenging pursuit. In this letter, we report the observation of states near half-integer band-fillings of $ν\approx 0.5$ and $\pm3.5$ at $B\approx 0$ in TBG proximitized by tungsten diselenide (WSe$_2$) through magnetotransport and thermoelectricity measurements. A series of Lifshitz transitions due to the changes in the topology of the Fermi surface implies the evolution of van Hove singularities (VHSs) of the diverging density of states (DOS) at a discrete set of partial fillings of flat bands. Furthermore, at a band filling of $ν\approx-0.5$, a symmetry-broken Chern insulator emerges at high $B$, compatible with the band structure calculations within a translational symmetry-broken supercell with twice the area of the original TBG moiré cell. Our results are consistent with a spin/charge density wave ground state in TBG in the zero $B$-field limit.

cond-mat.mes-hall↗

arXiv2021

Quantum Hall interferometry in triangular domains of marginally twisted bilayer graphene

Quantum Hall (QH) interferometry provides an archetypal platform for the experimental realization of braiding statistics of fractional QH states. However, the complexity of observing fractional statistics requires phase coherence over the length of the interferometer, as well as suppression of Coulomb charging energy. Here, we demonstrate a new type of QH interferometer based on marginally twisted bilayer graphene (mtBLG), with a twist angle $θ$ $\approx$ $0.16$ $^{\circ}$. With the device operating in the QH regime, we observe distinct signatures of electronic Fabry-Pérot (FP) and Aharonov-Bohm (AhB)-oscillations of the magneto-thermopower in the density-magnetic field phase-space, at Landau level filling factors $ν=4$,$8$. We find that QH interference effects are intrinsic to the triangular AB/BA domains in mtBLG that show diminished Coulomb charging effects. Our results demonstrate phase-coherent interference of QH edge modes without any additional gate-defined complex architecture, which may be beneficial in experimental realizations of non-Abelian braiding statistics.

cond-mat.mes-hall↗

arXiv2021

Leveraging Pretrained Models for Automatic Summarization of Doctor-Patient Conversations

Fine-tuning pretrained models for automatically summarizing doctor-patient conversation transcripts presents many challenges: limited training data, significant domain shift, long and noisy transcripts, and high target summary variability. In this paper, we explore the feasibility of using pretrained transformer models for automatically summarizing doctor-patient conversations directly from transcripts. We show that fluent and adequate summaries can be generated with limited training data by fine-tuning BART on a specially constructed dataset. The resulting models greatly surpass the performance of an average human annotator and the quality of previous published work for the task. We evaluate multiple methods for handling long conversations, comparing them to the obvious baseline of truncating the conversation to fit the pretrained model length limit. We introduce a multistage approach that tackles the task by learning two fine-tuned models: one for summarizing conversation chunks into partial summaries, followed by one for rewriting the collection of partial summaries into a complete summary. Using a carefully chosen fine-tuning dataset, this method is shown to be effective at handling longer conversations, improving the quality of generated summaries. We conduct both an automatic evaluation (through ROUGE and two concept-based metrics focusing on medical findings) and a human evaluation (through qualitative examples from literature, assessing hallucination, generalization, fluency, and general quality of the generated summaries).

cs.CL↗

arXiv2021

Defects-Assisted Piezoelectric Response in Liquid Exfoliated MoS2 Nanosheets

We report piezoelectric response in liquid phase exfoliated MoS2 nanosheets with desired structure and morphology. The piezoelectric effect in liquid phase exfoliated few layers of MoS2 flakes is interesting as it may allow the scalable fabrication of electronic devices such as self-powered electronics, piezoelectric transformers, antennas and more. The piezo force microscopy (PFM) measurements were used to quantify the amplitude and phase loop, which shows strong piezoelectric coefficient. Herein, the piezoelectric response in few layers of MoS2 is attributed to the defects formed in it during the synthesis procedure. The presence of defects is confirmed by XPS analysis

cond-mat.mtrl-sci↗

arXiv2021

Spontaneous time reversal symmetry breaking at individual grain boundaries in graphene

Graphene grain boundaries have attracted interest for their ability to host nearly dispersionless electronic bands and magnetic instabilities. Here, we employ quantum transport and universal conductance fluctuations (UCF) measurements to experimentally demonstrate a spontaneous breaking of time reversal symmetry (TRS) across individual GBs of chemical vapour deposited graphene. While quantum transport across the GBs indicate spin-scattering-induced dephasing, and hence formation of local magnetic moments, below $T\lesssim 4$ K, we observe complete lifting of TRS at high carrier densities ($n \gtrsim 5\times 10^{12}$cm$^{-2}$) and low temperature ($T\lesssim 2$ K). An unprecedented thirty times reduction in the UCF magnitude with increasing doping density further supports the possibility of an emergent frozen magnetic state at the GBs. Our experimental results suggest that realistic GBs of graphene can be a promising resource for new electronic phases and spin-based applications.

cond-mat.mes-hall↗

arXiv2020

Exact Solutions and Symmetry Analysis of a Boussinesq type Equation for Longitudinal Waves through a Magneto-Electro-Elastic Circular Rod

In this work the longitudinal wave equation through magneto-electro-elastic circular rod is studied analytically. Painlevé test is performed to check integrability of the equation. Exact solitary wave solutions are found by homogeneous balance method and Tanh method and are plotted using suitable values of physical parameters. A similar solution to an earlier related work [17, 20] is obtained. However we have obtained a new solution as well. Lie symmetry analysis has been done and similarity reduction of the equation is presented. Numerical results related to phase velocity etc for different materials has been derived and compared.

nlin.SI↗

arXiv2020

Excess entropy and breakdown of semiclassical description of thermoelectricity in twisted bilayer graphene close to half filling

In moiré systems with twisted bilayer graphene (tBLG), the amplification of Coulomb correlation effects at low twist angles ($θ$) is a result of nearly flat low-energy electronic bands and divergent density of states (DOS) at van Hove singularities (vHS). This not only causes superconductivity, Mott insulating states, and quantum anomalous Hall effect close to the critical (or magic) angle $θ= θ_{c} \approx 1.1^\circ$, but also unconventional metallic states that are claimed to exhibit non-Fermi liquid (NFL) excitations. However, unlike superconductivity and the correlation-induced gap in the DOS, unambiguous signatures of NFL effects in the metallic state remain experimentally elusive. Here we report simultaneous measurement of electrical resistivity ($ρ$) and thermoelectric power ($S$) in tBLG at $θ\approx 1.6^\circ$. We observe an emergent violation of the semiclassical Mott relation in the form of excess $S$ close to half-filling. The excess $S$ ($\approx 2$ $μ$V/K at low temperature $T \sim 10$ K) persists up to $\approx 40$ K, and is accompanied by metallic $T$-linear $ρ$ with transport scattering rate ($τ^{-1}$) of near-Planckian magnitude $τ^{-1} \sim k_{B}T/\hbar$. The combination of non-trivial electrical transport and violation of Mott relation provides compelling evidence of NFL physics intrinsic to tBLG, at small twist angle and half-filling.

cond-mat.mes-hall↗

arXiv2020

Gate-controllable electronic trap detection in dielectrics

Gate controllable electronic trap detection method has been demonstrated by regulating the gate potential of MIS devices. This method is based on shift of capacitance voltage (CV) curve as well as flatband voltage (VFB) measure in less than 10 micro-seconds due to injection or ejection of electrons through the metal gate. Using this method, an electronic trap energy distribution was measured in the HfO2 dielectric film and it confirms a maximum number of traps (Delta_NT) of 1.7x1012 cm-2 corresponding to an energy level (Delta_EIL) of 0.45 eV above silicon conduction band (Si-ECB). In comparison, ZrO2-based MIS devices showed a broader distribution of electronic traps throughout the band gap. However, HfO2 contained more than 60% traps in deep level compared to 50% in ZrO2, which establishes the effects of material variation.

physics.app-ph↗

arXiv2020

Evidence of Lifshitz transition in thermoelectric power of ultrahigh mobility bilayer graphene

Resolving low-energy features in the density of states (DOS) holds the key to understanding wide variety of rich novel phenomena in graphene based 2D heterostructures. Lifshitz transition in bilayer graphene (BLG) arising from trigonal warping has been established theoretically and experimentally. Nevertheless, the experimental realization of its effects on the transport properties has been challenging because of its relatively low energy scale ($\sim 1$ meV). In this work, we demonstrate that the thermoelectric power (TEP) can be used as an effective probe to investigate fine changes in the DOS of BLG. We observe additional entropy features in the vicinity of the charge neutrality point (CNP) in gapped BLG. This apparent violation of Mott formula can be explained quantitatively by considering the effects of trigonal warping, thereby serving as a possible evidence of a Lifshitz transition.

cond-mat.mes-hall↗

arXiv2019

Observation of excess resistance anomaly at resistive transitions in Ag/Au nanostructures

The resistive transition in nanocomposite films of silver (Ag) nanoclusters of ~ 1 nm diameter embedded in gold (Au) matrix exhibits an anomalous resistance peak at the onset of the transition, even for transition temperatures as high as 260 K. The maximum value of the resistance ranges between ~ 30% - 300% above that of the normal state depending on devices as well as lead configuration within a single device. The excess resistance regime was observed in about 10% of the devices, and extends from ~ 10 - 100 K. Application of magnetic field of 9 T was found to partially suppress the excess resistance. From the critical current behavior, as well as negative differential resistance in the current-voltage characteristics, we discuss the possibility of interacting phase slip centers and alternate physical scenarios that may cause the excess resistance in our system.

cond-mat.supr-con↗

arXiv2019

Evolution of high-frequency Raman modes and their doping dependence in twisted bilayer MoS2

Twisted van der Waals heterostructures unravel a new platform to study strongly correlated quantum phases. The interlayer coupling in these heterostructures is sensitive to twist angles ($θ$) and key to controllably tune several exotic properties. Here, we demonstrate a systematic evolution of the interlayer coupling strength with twist angle in bilayer $\mathrm{MoS_{2}}$ using a combination of Raman spectroscopy and classical simulations. At zero doping, we show a \textit{monotonic} increment of the separation between the $\mathrm{A_{1g}}$ and $\mathrm{E^{1}_{2g}}$ mode frequencies as $θ$ decreases from $10^{\circ} \to 1^{\circ}$, which saturates to that for a bilayer at small twist angles. Furthermore, using doping-dependent Raman spectroscopy we reveal $θ$ dependent softening and broadening of the $\mathrm{A_{1g}}$ mode, whereas the $\mathrm{E^{1}_{2g}}$ mode remains unaffected. Using first principles-based simulations we demonstrate large (weak) electron-phonon coupling for the $\mathrm{A_{1g}}$ ($\mathrm{E^{1}_{2g}}$) mode explaining the experimentally observed trends. Our study provides a non-destructive way to characterize the twist angle, the interlayer coupling and establishes the manipulation of phonons in twisted bilayer $\mathrm{MoS_{2}}$ (twistnonics).

cond-mat.mtrl-sci↗