Showing 1–15 of 15 results for author: Shah, D

A Contactless Heat Engine Driven by Nonreciprocal Fluctuation-Induced Torques

Authors: Dhruv Shah, Kiryl Asheichyk, David Gelbwaser-Klimovsky, Noah Graham, Mehran Kardar, Matthias Krüger

Abstract: We describe a contactless heat engine in which quantum and thermal electromagnetic fluctuations act as the working medium. The setup consists of two concentric cylinders held at different temperatures. The inner cylinder stably levitates within the outer one due to repulsive nonequilibrium Casimir forces. The chirality of the setup is broken by using nonreciprocal dielectric materials, akin to app… ▽ More We describe a contactless heat engine in which quantum and thermal electromagnetic fluctuations act as the working medium. The setup consists of two concentric cylinders held at different temperatures. The inner cylinder stably levitates within the outer one due to repulsive nonequilibrium Casimir forces. The chirality of the setup is broken by using nonreciprocal dielectric materials, akin to application of a magnetic field along the common cylinder axis. Using Rytov fluctuational electrodynamics, we show that heat transfer and torque can be expressed in terms of an angular-momentum-resolved heat flux density, $Φ_n(ω)$: each exchanged photon carries energy $\hbar ω$ and angular momentum $\hbar n$. In reciprocal media contributions from modes $n$ and $-n$ cancel and there is no net torque; nonreciprocity breaks this symmetry and powers rotation of the inner cylinder. Even in the absence of contact, electromagnetic fluctuations produce a frictional torque opposing rotation that we compute. This enables computation of characteristic steady state rotations, and estimation of the engine efficiency (which remains bounded by the Carnot limit). The cylindrical setup provides a natural realization of fluctuation-induced angular-momentum transfer and a possible route toward nanoscale contactless engines. △ Less

Submitted 23 June, 2026; originally announced June 2026.

Comments: 6 pages, 1 figure

From Knowledge to Action: Outcomes of the 2025 Large Language Model (LLM) Hackathon for Applications in Materials Science and Chemistry

Authors: Aritra Roy, Kevin Shen, Andrew MacBride, Awwal Oladipupo, Mudassra Taskeen, Wojtek Treyde, Ruaa A. E. A. Abakar, Ahmad D. Abbas, Elsayed Abdelfatah, Abbas A. Abdullahi, Seham S. Abyah, Chahd Rahyl Adjmi, Fariha Agbere, Savyasanchi Aggarwal, Muhammad Ahmed, Tasnim Ahmed, Motasem Ajlouni, Mattias Akke, Hussein AlAdwan, Anwaar S. Alazani, Zahra A. Alharbi, Wajd A. Aljulyhi, Mohammed A. AlKubaish, Fatima A. Almahri, Sayed A. Almohri , et al. (328 additional authors not shown)

Abstract: Large language models (LLMs) are rapidly changing how researchers in materials science and chemistry discover, organize, and act on scientific knowledge. This paper analyzes a broad set of community-developed LLM applications in an effort to identify emerging patterns in how these systems can be used across the scientific research lifecycle. We organize the projects into two complementary categori… ▽ More Large language models (LLMs) are rapidly changing how researchers in materials science and chemistry discover, organize, and act on scientific knowledge. This paper analyzes a broad set of community-developed LLM applications in an effort to identify emerging patterns in how these systems can be used across the scientific research lifecycle. We organize the projects into two complementary categories: Knowledge Infrastructure, systems that structure, retrieve, synthesize, and validate scientific information; and Action Systems, systems that execute, coordinate, or automate scientific work across computational and experimental environments. The submissions reveal a shift from single-purpose LLM tools toward integrated, multi-agent workflows that combine retrieval, reasoning, tool use, and domain-specific validation. Prominent themes include retrieval-augmented generation as grounding infrastructure, persistent structured knowledge representations, multimodal and multilingual scientific inputs, and early progress toward laboratory-integrated closed-loop systems. Together, these results suggest that LLMs are evolving from general-purpose assistants into composable infrastructure for scientific reasoning and action. This work provides a community snapshot of that transition and a practical taxonomy for understanding emerging LLM-enabled workflows in materials science and chemistry. △ Less

Submitted 4 May, 2026; originally announced May 2026.

Comments: This paper reflects contributions from hundreds of researchers worldwide through an event, follow-on discussions, and project development exploring LLM applications in materials science and chemistry. While unconventional, it captures a timely, broad, and efficient community exploration of a rapidly evolving field and offers value to the arXiv community

Granular aluminum induced superconductivity in germanium for hole spin-based hybrid devices

Authors: Giorgio Fabris, Paul Falthansl-Scheinecker, Devashish Shah, Daniel Michel Pino, Maksim Borovkov, Anton Bubis, Kevin Roux, Dina Sokolova, Alejandro Andres Juanes, Tommaso Costanzo, Inas Taha, Aziz Genç, Jordi Arbiol, Stefano Calcaterra, Afonso De Cerdeira Oliveira, Daniel Chrastina, Giovanni Isella, Ruben Seoane Souto, Maria Jose Calderon, Ramon Aguado, Jose Carlos Abadillo-Uriel, Georgios Katsaros

Abstract: In superconductor-semiconductor hybrid structures, superconductivity and spin polarization are competing effects as magnetic fields break Cooper pairs. They can be combined using thin films and in-plane magnetic fields, an approach that enabled the pursuit of Majorana zero modes, Kitaev chains, and Andreev spin qubits (ASQs), but remains challenging for materials with small in-plane $g$-factors or… ▽ More In superconductor-semiconductor hybrid structures, superconductivity and spin polarization are competing effects as magnetic fields break Cooper pairs. They can be combined using thin films and in-plane magnetic fields, an approach that enabled the pursuit of Majorana zero modes, Kitaev chains, and Andreev spin qubits (ASQs), but remains challenging for materials with small in-plane $g$-factors or when out-of-plane fields are required. We demonstrate that granular aluminium (grAl), composed of nanometre-scale aluminium grains embedded in an amorphous oxide matrix, can overcome this limitation. By depositing grAl on Ge/SiGe heterostructures, we induce a hard superconducting gap with BCS peaks at $305~μ\mathrm{eV}$ and magnetic-field resilience for both the in-plane and out-of-plane directions, allowing Zeeman splitting of Yu-Shiba-Rusinov (YSR) states beyond $50~μ\mathrm{eV}$ (12 GHz). Leveraging this robustness, we reveal signatures of hole physics and discuss a driving mechanism for ASQs regardless of the strength of the Rashba spin-orbit coupling in planar germanium. △ Less

Submitted 25 August, 2026; v1 submitted 24 February, 2026; originally announced February 2026.

Low-Noise Quantum Dots in Ultra-Shallow Ge/SiGe Heterostructures for Prototyping Hybrid Semiconducting-Superconducting Devices

Authors: M. Borovkov, Y. Schell, D. Sokolova, K. Roux, P. Falthansl-Scheinecker, G. Fabris, D. Shah, J. Saez-Mollejo, R. Previdi, I. Taha, Aziz Genç, J. Arbiol, S. Calcaterra, A. D. C. Oliveira, D. Chrastina, G. Isella, A. Bubis, G. Katsaros

Abstract: Planar germanium is currently the only semiconducting platform where high-coherence spin qubits and proximity-induced superconductivity have each been demonstrated. Recent research into spin qubits in Ge/SiGe heterostructures has focused on increasing the thickness of the SiGe capping layer, reporting improvements in the electrostatic noise levels. Meanwhile, heterostructures with thinner capping… ▽ More Planar germanium is currently the only semiconducting platform where high-coherence spin qubits and proximity-induced superconductivity have each been demonstrated. Recent research into spin qubits in Ge/SiGe heterostructures has focused on increasing the thickness of the SiGe capping layer, reporting improvements in the electrostatic noise levels. Meanwhile, heterostructures with thinner capping layers remain rather unexplored, despite the potential advantages for proximity-induced superconductivity. Here, we study a Ge/SiGe heterostructure with a thin SiGe cap $d \approx 4\ \mathrm{nm}$ and investigate its viability to host low-noise quantum dots. To keep the thermal budget compatible with superconducting layers, low-temperature oxide deposition processes were developed and implemented for the gate dielectrics. The charge-noise level of fabricated devices is estimated to be $1.8 \pm 1.0\ μ\mathrm{eV}/\sqrt{\mathrm{Hz}}$, comparable to devices fabricated on shallow heterostructures $\left(d \sim 20\ \mathrm{nm}\right)$ with high-temperature deposited oxides. Low charge-noise levels, together with the straightforward integration of superconductors, make this heterostructure an attractive platform for prototyping hybrid semiconducting-superconducting devices. △ Less

Submitted 10 March, 2026; v1 submitted 24 February, 2026; originally announced February 2026.

Full Shapiro spectroscopy of current-phase relationships

Authors: Maxim Tjøtta, Devashish Shah, Kanishk Modi, Marco Valentini, Rubén Seoane Souto, Georgios Katsaros, Jeroen Danon

Abstract: Extracting the current-phase relationship (CPR) of a single superconducting junction is challenging in practice and traditionally involves embedding the junction in a larger superconducting circuit containing SQUIDs and/or resonators. Applying ac driving to the junction has proven to be a viable and less invasive way to extract information about the few lowest harmonics of the CPR, by locating the… ▽ More Extracting the current-phase relationship (CPR) of a single superconducting junction is challenging in practice and traditionally involves embedding the junction in a larger superconducting circuit containing SQUIDs and/or resonators. Applying ac driving to the junction has proven to be a viable and less invasive way to extract information about the few lowest harmonics of the CPR, by locating the integer and fractional Shapiro steps in the IV-curve of the driven junction. Here, we present an alternative driving-based method that allows to extract the full harmonic content of a CPR in a non-invasive way, by fitting the measured critical currents of the driven junction as a function of driving power. We test our method, both using numerical simulations and in experiments, and we show that it works very accurately, also in the presence of noise. △ Less

Submitted 18 November, 2025; originally announced November 2025.

Prediction of Large Events in Directed Sandpiles

Authors: Dhruv Shah

Abstract: The degree of predictability of large avalanche events in the directed sandpile model is studied. A waiting time based prediction strategy which exploits the local anticorrelation of large events is discussed. With this strategy we show analytically and numerically that large events are predictable to some extent, and that this predictability persists in the thermodynamic limit. We introduce anoth… ▽ More The degree of predictability of large avalanche events in the directed sandpile model is studied. A waiting time based prediction strategy which exploits the local anticorrelation of large events is discussed. With this strategy we show analytically and numerically that large events are predictable to some extent, and that this predictability persists in the thermodynamic limit. We introduce another strategy which predicts large avalanches in the future based on the present excess density in the sandpile. We obtain the exact conditional probabilities for large events given an excess density, and use this to determine the exact form of the ROC predictability curves. We show that for this strategy, the model is predictable only for finite lattice sizes, and unpredictable in the thermodynamic limit. This behaviour is to be contrasted with previously established numerical studies carried out for Manna sandpiles. △ Less

Submitted 2 August, 2025; originally announced August 2025.

Comments: 19 pages, 18 figures

Enhanced Crystallization and Evaporation Retardation in Mixed Surfactant Systems at the Air-Water Interface: A Study on Chain Length Compatibility and Molecular Ratio

Authors: Kulsuma Begum, Abhijeet Das, Dinesh O. Shah, Sanjeev Kumar

Abstract: Effects of chain length compatibility and molecular ratio on the two-dimensional crystallization of a binary mixed surfactant system with non-identical molecular size and its consequence on retardation to water evaporation are described via Langmuir Blodgett films. The mixed monolayers corresponding to 1:3 exhibit minimal area per molecule owing to identical chain length. The maximum crystallizati… ▽ More Effects of chain length compatibility and molecular ratio on the two-dimensional crystallization of a binary mixed surfactant system with non-identical molecular size and its consequence on retardation to water evaporation are described via Langmuir Blodgett films. The mixed monolayers corresponding to 1:3 exhibit minimal area per molecule owing to identical chain length. The maximum crystallization was also observed at this ratio from BAM images at constant surface pressure. The prominent changes in the physical properties of the analyzed system, for the 1:3 molecular ratio, are attributed to the augmented stability mediated by the hexagonal closed packing and packing behavior in the mixed monolayer. The observation was validated from a random ball mixing model and simulation study. The maximum retardation to evaporation was also observed for the 1:3 molecular ratio and is attributed to augmented stability and spreading of the monolayers at the air-water interface. △ Less

Submitted 22 March, 2025; originally announced March 2025.

Preserving Coulomb blockade in transport spectroscopy of quantum dots, by dynamical tunnel-barrier compensation

Authors: Varsha Jangir, Devashish Shah, Sounak Samanta, Siddarth Rastogi, Harvey E. Beere, David A. Ritchie, Kantimay Das Gupta, Suddhasatta Mahapatra

Abstract: Surface-gated quantum dots (QDs) in semiconductor heterostructures represent a highly attractive platform for quantum computation and simulation. However, in this implementation, the barriers through which the QD is tunnel-coupled to source and drain reservoirs (or neighboring QDs) are usually non-rigid, and capacitively influenced by the plunger gate voltage (VP). In transport spectroscopy measur… ▽ More Surface-gated quantum dots (QDs) in semiconductor heterostructures represent a highly attractive platform for quantum computation and simulation. However, in this implementation, the barriers through which the QD is tunnel-coupled to source and drain reservoirs (or neighboring QDs) are usually non-rigid, and capacitively influenced by the plunger gate voltage (VP). In transport spectroscopy measurements, this leads to complete suppression of current and lifting of Coulomb blockade, for large negative and positive values of VP, respectively. Consequently, the charge-occupancy of the QD can be tuned over a rather small range of VP. By dynamically tuning the tunnel barriers to compensate for the capacitive effect of VP, here we demonstrate a protocol which allows the Coulomb blockade to be preserved over a remarkably large span of charge-occupancies, as demonstrated by clean Coulomb diamonds and well-resolved excited state features. The protocol will be highly beneficial for automated tuning and identification of the gatevoltage-space for optimal operation of QDs, in large arrays required for a scalable spin quantum computing architecture. △ Less

Submitted 22 September, 2024; originally announced September 2024.

Comments: 5 pages, 5 figures, 1 table

Non Gaussian statistics in static and dynamic Galton boards

Authors: Dhruv Shah, R. K. Shishir, Manjaree, Shreya Pithva, T. Y. Booritth Balaji, Rahul Agarwal Singh

Abstract: Perturbing the arrangements of pegs on a static Galton board can result in non-trivial stationary distributions, which in the continuum limit correspond to departure from regular gaussian behavior. Two such distributions are obtained. Further, the distributions generated for a dynamic galton board under external forcing in a general direction are obtained by solution of the corresponding stochasti… ▽ More Perturbing the arrangements of pegs on a static Galton board can result in non-trivial stationary distributions, which in the continuum limit correspond to departure from regular gaussian behavior. Two such distributions are obtained. Further, the distributions generated for a dynamic galton board under external forcing in a general direction are obtained by solution of the corresponding stochastic differential equations. Exact cumulant generating functions for the distribution are presented for forcing in one dimension. An approximate expression, correct to first order in the forcing amplitude, is presented for the case of two dimensions. Both cases show nontrivial departures from the static gaussian solution. △ Less

Submitted 2 July, 2024; v1 submitted 30 April, 2024; originally announced April 2024.

Comments: 10 pages

A Survey on Evaluation Metrics for Synthetic Material Micro-Structure Images from Generative Models

Authors: Devesh Shah, Anirudh Suresh, Alemayehu Admasu, Devesh Upadhyay, Kalyanmoy Deb

Abstract: The evaluation of synthetic micro-structure images is an emerging problem as machine learning and materials science research have evolved together. Typical state of the art methods in evaluating synthetic images from generative models have relied on the Fréchet Inception Distance. However, this and other similar methods, are limited in the materials domain due to both the unique features that char… ▽ More The evaluation of synthetic micro-structure images is an emerging problem as machine learning and materials science research have evolved together. Typical state of the art methods in evaluating synthetic images from generative models have relied on the Fréchet Inception Distance. However, this and other similar methods, are limited in the materials domain due to both the unique features that characterize physically accurate micro-structures and limited dataset sizes. In this study we evaluate a variety of methods on scanning electron microscope (SEM) images of graphene-reinforced polyurethane foams. The primary objective of this paper is to report our findings with regards to the shortcomings of existing methods so as to encourage the machine learning community to consider enhancements in metrics for assessing quality of synthetic images in the material science domain. △ Less

Submitted 3 November, 2022; originally announced November 2022.

Comments: Accepted in Neural Information Processing Systems (NeurIPS) 2022 Workshop on AI for Accelerated Materials Design (AI4Mat). Selected as spotlight paper for workshop

ACM Class: I.2.m; J.2

Hybrid Magneto Photonic Material Structure for Plasmon Assisted Magnetic Switching

Authors: Alan Hwader Chu, Bradlee Beauchamp, Deesha Shah, Aveek Dutta, Alexandra Boltasseva, Vladimir M. Shalaev, Ernesto E. Marinero

Abstract: We have proposed the use of surface plasmon resonances at the interface of hybrid magneto-photonic heterostructures [Opt. Mat. Exp., 7, 4316 (2017)] for all-optical control of the macroscopic spin orientation in nanostructures in fs time scales. This requires strong spin-photon coupling for the resonant enhancement of opto-magnetic fields, generated through the inverse Faraday effect, in magnetic… ▽ More We have proposed the use of surface plasmon resonances at the interface of hybrid magneto-photonic heterostructures [Opt. Mat. Exp., 7, 4316 (2017)] for all-optical control of the macroscopic spin orientation in nanostructures in fs time scales. This requires strong spin-photon coupling for the resonant enhancement of opto-magnetic fields, generated through the inverse Faraday effect, in magnetic nanostructures with perpendicular anisotropy. Here we report on the development of nm thick interlayers to control the growth orientation of hcp-Co alloys grown on refractory plasmonic materials to align the magnetic axis out-of-plane, thereby meeting key requirements for the realization of ultrafast magneto-photonic devices. △ Less

Submitted 11 September, 2020; v1 submitted 16 June, 2020; originally announced June 2020.

Comments: 14 pages, 7 figures

Controlling the plasmonic properties of ultrathin TiN films at the atomic level

Authors: Deesha Shah, Alessandra Catellani, Harsha Reddy, Nathaniel Kinsey, Vladimir Shalaev, Alexandra Boltasseva, Arrigo Calzolari

Abstract: By combining first principles theoretical calculations and experimental optical and structural characterization such as spectroscopic ellipsometry, X-ray spectroscopy, and electron microscopy, we study the dielectric permittivity and plasmonic properties of ultrathin TiN films at an atomistic level. Our results indicate a remarkably persistent metallic character of ultrathin TiN films and a progre… ▽ More By combining first principles theoretical calculations and experimental optical and structural characterization such as spectroscopic ellipsometry, X-ray spectroscopy, and electron microscopy, we study the dielectric permittivity and plasmonic properties of ultrathin TiN films at an atomistic level. Our results indicate a remarkably persistent metallic character of ultrathin TiN films and a progressive red shift of the plasmon energy as the thickness of the film is reduced. The microscopic origin of this trend is interpreted in terms of the characteristic two-band electronic structure of the system. Surface oxidation and substrate strain are also investigated to explain the deviation of the optical properties from the ideal case. This paves the way to the realization of ultrathin TiN films with tailorable and tunable plasmonic properties in the visible range for applications in ultrathin metasurfaces and flexible optoelectronic devices. △ Less

Submitted 17 December, 2017; originally announced December 2017.

Comments: 24 pages, 8 Figures, research article

Generalized four-point characterization method for resistive and capacitive contacts

Authors: Brian S. Kim, Wang Zhou, Yash D. Shah, Chuanle Zhou, N. Işık, M. Grayson

Abstract: In this paper, a four-point characterization method is developed for resistive samples connected to either resistive or capacitive contacts. Provided the circuit equivalent of the complete measurement system is known including coaxial cable and connector capacitances as well as source output and amplifier input impedances, a frequency range and capacitive scaling factor can be determined, whereby… ▽ More In this paper, a four-point characterization method is developed for resistive samples connected to either resistive or capacitive contacts. Provided the circuit equivalent of the complete measurement system is known including coaxial cable and connector capacitances as well as source output and amplifier input impedances, a frequency range and capacitive scaling factor can be determined, whereby four-point characterization can be performed. The technique is demonstrated with a discrete element test sample over a wide frequency range using lock-in measurement techniques from 1 Hz - 100 kHz. The data fit well with a circuit simulation of the entire measurement system. A high impedance preamplifier input stage gives best results, since lock-in input impedances may differ from manufacturer specifications. The analysis presented here establishes the utility of capacitive contacts for four-point characterizations at low frequency. △ Less

Submitted 25 August, 2011; originally announced August 2011.

Comments: 21 pages, 10 figures

Electronic Properties of Carbon Nanotubes Calculated from Density Functional Theory and the Empirical pi-Bond Model

Authors: Deep Shah, Nicolas A. Bruque, Khairul Alam, Roger K. Lake, Rajeev R. Pandey

Abstract: The validity of the DFT models implemented by FIREBALL for CNT electronic device modeling is assessed. The effective masses, band gaps, and transmission coefficients of semi-conducting, zigzag, (n,0) carbon nanotubes (CNTs) resulting from the ab initio tight-binding density functional theory (DFT) code FIREBALL and the empirical, nearest-neighbor pi-bond model are compared for all semiconducting… ▽ More The validity of the DFT models implemented by FIREBALL for CNT electronic device modeling is assessed. The effective masses, band gaps, and transmission coefficients of semi-conducting, zigzag, (n,0) carbon nanotubes (CNTs) resulting from the ab initio tight-binding density functional theory (DFT) code FIREBALL and the empirical, nearest-neighbor pi-bond model are compared for all semiconducting n values 5 <(=) n <(=) 35. The DFT values for the effective masses differ from the pi-bond values by +(-) 9% over the range of n values, 17 <(=) n <(=) 29, most important for electronic device applications. Over the range 13 <(=) n <(=) 35, the DFT bandgaps are less than the empirical bandgaps by 20-180 meV depending on the functional and the n value. The pi-bond model gives results that differ signifcantly from the DFT results when the CNT diameter goes below 1 nm due to the large curvature of the CNT. The pi-bond model quickly becomes inaccurate away from the bandedges for a (10, 0) CNT, and it is completely inaccurate for n <(=) 8. △ Less

Submitted 9 April, 2007; originally announced April 2007.

Comments: J. Computational Electronics (accepted, 20 February 2007)

Counting good truth assignments of random k-SAT formulae

Authors: Andrea Montanari, Devavrat Shah

Abstract: We present a deterministic approximation algorithm to compute logarithm of the number of `good' truth assignments for a random k-satisfiability (k-SAT) formula in polynomial time (by `good' we mean that violate a small fraction of clauses). The relative error is bounded above by an arbitrarily small constant epsilon with high probability as long as the clause density (ratio of clauses to variabl… ▽ More We present a deterministic approximation algorithm to compute logarithm of the number of `good' truth assignments for a random k-satisfiability (k-SAT) formula in polynomial time (by `good' we mean that violate a small fraction of clauses). The relative error is bounded above by an arbitrarily small constant epsilon with high probability as long as the clause density (ratio of clauses to variables) alpha<alpha_{u}(k) = 2k^{-1}\log k(1+o(1)). The algorithm is based on computation of marginal distribution via belief propagation and use of an interpolation procedure. This scheme substitutes the traditional one based on approximation of marginal probabilities via MCMC, in conjunction with self-reduction, which is not easy to extend to the present problem. We derive 2k^{-1}\log k (1+o(1)) as threshold for uniqueness of the Gibbs distribution on satisfying assignment of random infinite tree k-SAT formulae to establish our results, which is of interest in its own right. △ Less

Submitted 14 July, 2006; originally announced July 2006.

Comments: 13 pages, 1 eps figure