Showing 1–23 of 23 results for author: More, S

Quantum Light Nano-Imaging

Authors: Michael Dapolito, Matthew Fu, Fuyang Tay, Suheng Xu, Yuchen Lin, Neil Hazra, Adam K. Williams, Samuel L. Moore, Rocco A. Vitalone, Jonas Kolker, Thomas Cherradi, Aaron Holman, Thomas P. Darlington, Mark E. Ziffer, Xavier Roy, Sebastian Will, Cory R. Dean, Mengkun Liu, A. J. Millis, Michael M. Fogler, Abhay N. Pasupathy, P. J. Schuck, D. N. Basov

Abstract: Entanglement and quantum correlations are central to the physics of quantum materials, yet they have remained notoriously difficult to access experimentally. Accessing these phenomena in solids requires quantum optical probes that operate at the native length and time scales of material excitations, below the diffraction limit of light. Developing the requisite tools has previously been infeasible… ▽ More Entanglement and quantum correlations are central to the physics of quantum materials, yet they have remained notoriously difficult to access experimentally. Accessing these phenomena in solids requires quantum optical probes that operate at the native length and time scales of material excitations, below the diffraction limit of light. Developing the requisite tools has previously been infeasible due to the weak intensities of state-of-the-art quantum light sources and the inefficiency of light coupling in near-field light-matter interactions. In this work, we address these challenges and report the development of a quantum light scattering-type scanning near-field optical microscope (q-SNOM) that enables quantum-optical studies of solid-state systems with nanoscale spatial resolution. As a first demonstration, we visualize the self-interference of single hybrid light-matter polaritons in the prototypical van der Waals semiconductor MoS2. We also introduce a polaritonic time-of-flight metrology that exploits the temporal correlations among entangled photons to observe the quasiparticle propagation dynamics at femtosecond time scales. This work establishes a new experimental paradigm for exploring quantum effects in materials at the nanoscale. △ Less

Submitted 1 July, 2026; v1 submitted 27 May, 2026; originally announced May 2026.

Building a Regional Data-Centric Materials Science Ecosystem for Processing-Rich Materials Innovation in the Great Plains

Authors: D. -M. Mei, K. Acharya, C. M. Adhikari, M. Adhikari, S. Aryal, B. V. Benson, K. Bhatta, S. Bhattarai, N. Budhathoki, A. M. Castillo, D. Chakraborty, S. Chhetri, S. Choudhury, T. A. Chowdhury, R. D. Cruz, B. Cui, S. Dhital, K. -M. Dong, R. Gapuz, A. Ghasemi, E. Z. Gnimpieba, B. D. S. Gurung, H. A. Hashim, R. I. Harry, K. -E. Hasin , et al. (30 additional authors not shown)

Abstract: Data-centric materials science is changing how materials are discovered, optimized, manufactured, and qualified, yet many deployment-limiting materials problems still depend on experimental, processing-rich, device-level, and field-relevant data that are difficult to capture in conventional materials databases. This perspective argues that the Great Plains and adjacent interior research corridor c… ▽ More Data-centric materials science is changing how materials are discovered, optimized, manufactured, and qualified, yet many deployment-limiting materials problems still depend on experimental, processing-rich, device-level, and field-relevant data that are difficult to capture in conventional materials databases. This perspective argues that the Great Plains and adjacent interior research corridor can make a distinctive national contribution by organizing distributed experimental assets into a trusted regional materials-data ecosystem. The proposed model emphasizes FAIR metadata, provenance, persistent sample identifiers, uncertainty-aware modeling, semi-closed-loop workflows, stackable workforce training, and tiered governance for academic, public, controlled-access, and industry-protected data. We identify five coupled barriers -- fragmented data, weak algorithm--laboratory translation, uneven access to cyberinfrastructure and technical staff, workforce gaps at the materials--data interface, and insufficient incentives for sharing and reuse -- and propose a staged roadmap for addressing them. A high-purity germanium pilot illustrates how regional strengths can be converted into reusable datasets, benchmark models, trained personnel, and decision-improving workflows. The broader message is that regional leadership in data-centric materials science will depend less on geographic concentration than on trustworthy data practices, interoperable infrastructure, cross-trained people, and application-driven materials challenges. △ Less

Submitted 19 May, 2026; originally announced May 2026.

Comments: 33 pages, 6 figures, and 8 tables

Van der Waals waveguide quantum electrodynamics probed by infrared nano-photoluminescence

Authors: Samuel L. Moore, Hae Yeon Lee, Nicholas Rivera, Yuzuka Karube, Mark Ziffer, Emanuil S. Yanev, Thomas P. Darlington, Aaron J. Sternbach, Madisen A. Holbrook, Jordan Pack, Xiaodong Xu, Cory R. Dean, Jonathan S. Owen, P. James Schuck, Milan Delor, Xiaoyang Zhu, James Hone, Dmitri N. Basov

Abstract: Atomically layered van der Waals (vdW) materials exhibit remarkable properties, including highly-confined infrared waveguide modes and the capacity for infrared emission in the monolayer limit. Here, we engineered structures that leverage both of these nano-optical functionalities. Specifically, we encased a photoluminescing atomic sheet of MoTe2 within two bulk crystals of WSe2, forming a vdW wav… ▽ More Atomically layered van der Waals (vdW) materials exhibit remarkable properties, including highly-confined infrared waveguide modes and the capacity for infrared emission in the monolayer limit. Here, we engineered structures that leverage both of these nano-optical functionalities. Specifically, we encased a photoluminescing atomic sheet of MoTe2 within two bulk crystals of WSe2, forming a vdW waveguide for the embedded light-emitting monolayer. The modified electromagnetic environment offered by the WSe2 waveguide alters MoTe2 spontaneous emission, a phenomenon we directly image with our interferometric nano-photoluminescence technique. We captured spatially-oscillating nanoscale patterns prompted by spontaneous emission from MoTe2 into waveguide modes of WSe2 slabs. We quantify the resulting Purcell-enhanced emission rate within the framework of a waveguide quantum electrodynamics (QED) model, relating the MoTe2 spontaneous emission rate to the measured waveguide dispersion. Our work marks a significant advance in the implementation of all-vdW QED waveguides. △ Less

Submitted 11 June, 2025; originally announced June 2025.

Comments: 14 pages, 5 Figues. Supplementary information can be found in the journal submission Nat. Photon. (2025)

Breaking the mold: overcoming the time constraints of molecular dynamics on general-purpose hardware

Authors: Danny Perez, Aidan Thompson, Stan Moore, Tomas Oppelstrup, Ilya Sharapov, Kylee Santos, Amirali Sharifian, Delyan Z. Kalchev, Robert Schreiber, Scott Pakin, Edgar A. Leon, James H. Laros III, Michael James, Sivasankaran Rajamanickam

Abstract: The evolution of molecular dynamics (MD) simulations has been intimately linked to that of computing hardware. For decades following the creation of MD, simulations have improved with computing power along the three principal dimensions of accuracy, atom count (spatial scale), and duration (temporal scale). Since the mid-2000s, computer platforms have however failed to provide strong scaling for M… ▽ More The evolution of molecular dynamics (MD) simulations has been intimately linked to that of computing hardware. For decades following the creation of MD, simulations have improved with computing power along the three principal dimensions of accuracy, atom count (spatial scale), and duration (temporal scale). Since the mid-2000s, computer platforms have however failed to provide strong scaling for MD as scale-out CPU and GPU platforms that provide substantial increases to spatial scale do not lead to proportional increases in temporal scale. Important scientific problems therefore remained inaccessible to direct simulation, prompting the development of increasingly sophisticated algorithms that present significant complexity, accuracy, and efficiency challenges. While bespoke MD-only hardware solutions have provided a path to longer timescales for specific physical systems, their impact on the broader community has been mitigated by their limited adaptability to new methods and potentials. In this work, we show that a novel computing architecture, the Cerebras Wafer Scale Engine, completely alters the scaling path by delivering unprecedentedly high simulation rates up to 1.144M steps/second for 200,000 atoms whose interactions are described by an Embedded Atom Method potential. This enables direct simulations of the evolution of materials using general-purpose programmable hardware over millisecond timescales, dramatically increasing the space of direct MD simulations that can be carried out. △ Less

Submitted 15 November, 2024; originally announced November 2024.

Journal ref: Journal of Chemical Physics 2025, 162(7), 072501

Plasmonic polarization sensing of electrostatic superlattice potentials

Authors: Shuai Zhang, Jordan Fonseca, Daniel Bennett, Zhiyuan Sun, Junhe Zhang, Ran Jing, Suheng Xu, Leo He, S. L. Moore, S. E. Rossi, Dmitry Ovchinnikov, David Cobden, Pablo. Jarillo-Herrero, M. M. Fogler, Philip Kim, Efthimios Kaxiras, Xiaodong Xu, D. N. Basov

Abstract: Plasmon polaritons are formed by coupling light with delocalized electrons. The half-light and half-matter nature of plasmon polaritons endows them with unparalleled tunability via a range of parameters, such as dielectric environments and carrier density. Therefore, plasmon polaritons are expected to be tuned when in proximity to polar materials since the carrier density is tuned by an electrosta… ▽ More Plasmon polaritons are formed by coupling light with delocalized electrons. The half-light and half-matter nature of plasmon polaritons endows them with unparalleled tunability via a range of parameters, such as dielectric environments and carrier density. Therefore, plasmon polaritons are expected to be tuned when in proximity to polar materials since the carrier density is tuned by an electrostatic potential; conversely, the plasmon polariton response might enable the sensing of polarization. Here, we use infrared nano-imaging and nano-photocurrent measurements to investigate heterostructures composed of graphene and twisted hexagonal boron nitride (t-BN), with alternating polarization in a triangular network of moiré stacking domains. We observe that the carrier density and the corresponding plasmonic response of graphene are modulated by polar domains in t-BN. In addition, we demonstrate that the nanometer-wide domain walls of graphene moirés superlattices, created by the polar domains of t-BN, provide momenta to assist the plasmonic excitations. Furthermore, our studies establish that the plasmon of graphene could function as a delicate sensor for polarization textures. The evolution of polarization textures in t-BN under uniform electric fields is tomographically examined via plasmonic imaging. Strikingly, no noticeable polarization switching is observed under applied electric fields up to 0.23 V/nm, at variance with transport reports. Our nano-images unambiguously reveal that t-BN with triangular domains acts like a ferrielectric, rather than ferroelectric claimed by many previous studies. △ Less

Submitted 25 June, 2024; originally announced June 2024.

Comments: 41 pages, 20 figures

Journal ref: Phys. Rev. X 15, 011019 (2025)

Extreme Metastability of Diamond and its Transformation to BC8 Post-Diamond Phase of Carbon

Authors: Kien Nguyen-Cong, Jonathan T. Willman, Joseph M. Gonzalez, Ashley S. Williams, Anatoly B. Belonoshko, Stan G. Moore, Aidan P. Thompson, Mitchell A. Wood, Jon H. Eggert, Marius Millot, Luis A. Zepeda-Ruiz, Ivan I. Oleynik

Abstract: Diamond possesses exceptional physical properties due to its remarkably strong carbon-carbon bonding, leading to significant resilience to structural transformations at very high pressures and temperatures. Despite several experimental attempts, synthesis and recovery of the theoretically predicted post-diamond BC8 phase remains elusive. Through quantum accurate, multi-million atom molecular dynam… ▽ More Diamond possesses exceptional physical properties due to its remarkably strong carbon-carbon bonding, leading to significant resilience to structural transformations at very high pressures and temperatures. Despite several experimental attempts, synthesis and recovery of the theoretically predicted post-diamond BC8 phase remains elusive. Through quantum accurate, multi-million atom molecular dynamics (MD) simulations, we have uncovered the extreme metastability of diamond at very high pressures, significantly exceeding its range of thermodynamic stability. We predict the post-diamond BC8 phase to be experimentally accessible only within a narrow high pressure-temperature region of the carbon phase diagram. The diamond to BC8 transformation proceeds through pre-melting followed by BC8 nucleation and growth in the metastable carbon liquid. We propose a double-shock compression pathway to achieve BC8 synthesis, which is currently being explored in theory-inspired experiments at the National Ignition Facility. △ Less

Submitted 22 January, 2024; v1 submitted 16 January, 2024; originally announced January 2024.

Simulation Guided Molecular Design of Hydrofluoroether Solvent for High Energy Batteries

Authors: Zhou Yu, Zhangxing shi, Sambasiva R. Bheemireddy, Ethan Kamphause, Xingyi Lyu, Mohammad Afsar Uddin, Zhiguang Li, Zhenzhen Yang, Tao Li, Jeffrey S. Moore, Lu Zhang, Lei Cheng

Abstract: Electrolyte design is critical for enabling next-generation batteries with higher energy densities. Hydrofluoroether (HFE) solvents have drawn a lot of attention as the electrolytes based on HFEs showed great promise to deliver highly desired properties, including high oxidative stability, ionic conductivity, as well as enhanced lithium metal compatibility. However, the structure-dynamics-properti… ▽ More Electrolyte design is critical for enabling next-generation batteries with higher energy densities. Hydrofluoroether (HFE) solvents have drawn a lot of attention as the electrolytes based on HFEs showed great promise to deliver highly desired properties, including high oxidative stability, ionic conductivity, as well as enhanced lithium metal compatibility. However, the structure-dynamics-properties relationships and design principles for high-performance HFE solvents are still poorly understood. Herein, we proposed four novel asymmetric HFE designs by systematically varying polyether and fluorocarbon structural building blocks. By leveraging molecular dynamics (MD) modeling to analyze the solvation structures and predict the properties of the corresponding 1 M lithium bis(fluorosulfonyl)imide (LiTFSI) solutions, we downselected the most promising candidate based on high conductivity, solvation species distribution, and oxidative stability for extensive electrochemical characterizations. The formulated electrolyte demonstrated properties consistent with the predictions from the simulations and showed much-improved capacity retention as well as Coulombic efficiency compared to the baseline electrolytes when cycled in lithium metal cells. This work exemplifies the construction of candidate electrolytes from building block functional moieties to engineer fundamental solvation structures for desired electrolyte properties and guide the discovery and rational design of new solvent materials. △ Less

Submitted 3 October, 2023; originally announced October 2023.

Comments: 18 pages, 1 Scheme, 6 figures

Visualizing moiré ferroelectricity via plasmons and nano-photocurrent in graphene/twisted-WSe2 structures

Authors: Shuai Zhang, Yang Liu, Zhiyuan Sun, Xinzhong Chen, Baichang Li, S. L. Moore, Song Liu, Zhiying Wang, S. E. Rossi, Ran Jing, Jordan Fonseca, Birui Yang, Yinming Shao, Chun-Ying Huang, Taketo Handa, Lin Xiong, Matthew Fu, Tsai-Chun Pan, Dorri Halbertal, Xinyi Xu, Wenjun Zheng, P. J. Schuck, A. N. Pasupathy, C. R. Dean, Xiaoyang Zhu , et al. (6 additional authors not shown)

Abstract: Ferroelectricity, a spontaneous and reversible electric polarization, is found in certain classes of van der Waals (vdW) material heterostructures. The discovery of ferroelectricity in twisted vdW layers provides new opportunities to engineer spatially dependent electric and optical properties associated with the configuration of moiré superlattice domains and the network of domain walls. Here, we… ▽ More Ferroelectricity, a spontaneous and reversible electric polarization, is found in certain classes of van der Waals (vdW) material heterostructures. The discovery of ferroelectricity in twisted vdW layers provides new opportunities to engineer spatially dependent electric and optical properties associated with the configuration of moiré superlattice domains and the network of domain walls. Here, we employ near-field infrared nano-imaging and nano-photocurrent measurements to study ferroelectricity in minimally twisted WSe2. The ferroelectric domains are visualized through the imaging of the plasmonic response in a graphene monolayer adjacent to the moiré WSe2 bilayers. Specifically, we find that the ferroelectric polarization in moiré domains is imprinted on the plasmonic response of the graphene. Complementary nano-photocurrent measurements demonstrate that the optoelectronic properties of graphene are also modulated by the proximal ferroelectric domains. Our approach represents an alternative strategy for studying moiré ferroelectricity at native length scales and opens promising prospects for (opto)electronic devices. △ Less

Submitted 12 September, 2023; originally announced September 2023.

Comments: 19 pages, 3 figures

Journal ref: Nature Communications 14, 6200 (2023)

Negative refraction in hyperbolic hetero-bicrystals

Authors: A. J. Sternbach, S. L. Moore, A. Rikhter, S. Zhang, R. Jing, Y. Shao, B. S. Y. Kim, S. Xu, S. Liu, J. H. Edgar, A. Rubio, C. Dean, J. Hone, M. M. Fogler, D. N. Basov

Abstract: We visualized negative refraction of phonon polaritons, which occurs at the interface between two natural crystals. The polaritons - hybrids of infrared photons and lattice vibrations - form collimated rays that display negative refraction when passing through a planar interface between the two hyperbolic van der Waals materials: molybdenum oxide ($MoO_3$) and isotopically pure hexagonal boron nit… ▽ More We visualized negative refraction of phonon polaritons, which occurs at the interface between two natural crystals. The polaritons - hybrids of infrared photons and lattice vibrations - form collimated rays that display negative refraction when passing through a planar interface between the two hyperbolic van der Waals materials: molybdenum oxide ($MoO_3$) and isotopically pure hexagonal boron nitride ($h^{11}BN$). At a special frequency $ω_0$, these rays can circulate along closed diamond-shaped trajectories. We have shown that polariton eigenmodes display regions of both positive and negative dispersion interrupted by multiple gaps that result from polaritonic level repulsion and strong coupling. △ Less

Submitted 7 July, 2023; v1 submitted 29 September, 2022; originally announced September 2022.

Programming moiré patterns in 2D materials by bending

Authors: Mäelle Kapfer, Bjarke S. Jessen, Megan E. Eisele, Matthew Fu, Dorte R. Danielsen, Thomas P. Darlington, Samuel L. Moore, Nathan R. Finney, Ariane Marchese, Valerie Hsieh, Paulina Majchrzak, Zhihao Jiang, Deepnarayan Biswas, Pavel Dudin, José Avila, Kenji Watanabe, Takashi Taniguchi, Søren Ulstrup, Peter Bøggild, P. J. Schuck, Dmitri N. Basov, James Hone, Cory R. Dean

Abstract: Moiré superlattices in twisted two-dimensional materials have generated tremendous excitement as a platform for achieving quantum properties on demand. However, the moiré pattern is highly sensitive to the interlayer atomic registry, and current assembly techniques suffer from imprecise control of the average twist angle, spatial inhomogeneity in the local twist angle, and distortions due to rando… ▽ More Moiré superlattices in twisted two-dimensional materials have generated tremendous excitement as a platform for achieving quantum properties on demand. However, the moiré pattern is highly sensitive to the interlayer atomic registry, and current assembly techniques suffer from imprecise control of the average twist angle, spatial inhomogeneity in the local twist angle, and distortions due to random strain. Here, we demonstrate a new way to manipulate the moiré patterns in hetero- and homo-bilayers through in-plane bending of monolayer ribbons, using the tip of an atomic force microscope. This technique achieves continuous variation of twist angles with improved twist-angle homogeneity and reduced random strain, resulting in moiré patterns with highly tunable wavelength and ultra-low disorder. Our results pave the way for detailed studies of ultra-low disorder moiré systems and the realization of precise strain-engineered devices. △ Less

Submitted 21 September, 2022; originally announced September 2022.

Journal ref: Science, 381, 2023, pp 677-681

Nanomechanical Resonators: Toward Atomic Scale

Authors: Bo Xu, Pengcheng Zhang, Jiankai Zhu, Zuheng Liu, Alexander Eichler, Xu-Qian Zheng, Jaesung Lee, Aneesh Dash, Swapnil More, Song Wu, Yanan Wang, Hao Jia, Akshay Naik, Adrian Bachtold, Rui Yang, Philip X. -L. Feng, Zenghui Wang

Abstract: The quest for realizing and manipulating ever smaller man-made movable structures and dynamical machines has spurred tremendous endeavors, led to important discoveries, and inspired researchers to venture to new grounds. Scientific feats and technological milestones of miniaturization of mechanical structures have been widely accomplished by advances in machining and sculpturing ever shrinking fea… ▽ More The quest for realizing and manipulating ever smaller man-made movable structures and dynamical machines has spurred tremendous endeavors, led to important discoveries, and inspired researchers to venture to new grounds. Scientific feats and technological milestones of miniaturization of mechanical structures have been widely accomplished by advances in machining and sculpturing ever shrinking features out of bulk materials such as silicon. With the flourishing multidisciplinary field of low-dimensional nanomaterials, including one-dimensional (1D) nanowires/nanotubes, and two-dimensional (2D) atomic layers such as graphene/phosphorene, growing interests and sustained efforts have been devoted to creating mechanical devices toward the ultimate limit of miniaturization--genuinely down to the molecular or even atomic scale. These ultrasmall movable structures, particularly nanomechanical resonators that exploit the vibratory motion in these 1D and 2D nano-to-atomic-scale structures, offer exceptional device-level attributes, such as ultralow mass, ultrawide frequency tuning range, broad dynamic range, and ultralow power consumption, thus holding strong promises for both fundamental studies and engineering applications. In this Review, we offer a comprehensive overview and summary of this vibrant field, present the state-of-the-art devices and evaluate their specifications and performance, outline important achievements, and postulate future directions for studying these miniscule yet intriguing molecular-scale machines. △ Less

Submitted 20 November, 2022; v1 submitted 15 August, 2022; originally announced August 2022.

Comments: 41 pages, 30 figures

Journal ref: ACS Nano 2022

Unzipping hBN with ultrashort mid-infrared pulses

Authors: Cecilia Y. Chen, Jared S. Ginsberg, Samuel L. Moore, M. Mehdi Jadidi, Rishi Maiti, Baichang Li, Sang Hoon Chae, Anjaly Rajendran, Gauri N. Patwardhan, Kenji Watanabe, Takashi Taniguchi, James Hone, D. N. Basov, Alexander L. Gaeta

Abstract: Manipulating the nanostructure of materials is critical for numerous applications in electronics, magnetics, and photonics. However, conventional methods such as lithography and laser-writing require cleanroom facilities or leave residue. Here, we describe a new approach to create atomically sharp line defects in hexagonal boron nitride (hBN) at room temperature by direct optical phonon excitation… ▽ More Manipulating the nanostructure of materials is critical for numerous applications in electronics, magnetics, and photonics. However, conventional methods such as lithography and laser-writing require cleanroom facilities or leave residue. Here, we describe a new approach to create atomically sharp line defects in hexagonal boron nitride (hBN) at room temperature by direct optical phonon excitation in the mid-infrared (mid-IR). We term this phenomenon "unzipping" to describe the rapid formation and growth of a <30-nm-wide crack from a point within the laser-driven region. The formation of these features is attributed to large atomic displacements and high local bond strain from driving the crystal at a natural resonance. This process is distinguished by (i) occurring only under resonant phonon excitation, (ii) producing highly sub-wavelength features, and (iii) sensitivity to crystal orientation and pump laser polarization. Its cleanliness, directionality, and sharpness enable applications in in-situ flake cleaving and phonon-wave-coupling via free space optical excitation. △ Less

Submitted 24 May, 2022; originally announced May 2022.

Comments: 11 pages, 4 figures

Machine Learning Interatomic Potential for Simulations of Carbon at Extreme Conditions

Authors: Jonathan T. Willman, Kien Nguyen-Cong, Ashley S. Williams, Anatoly B. Belonoshko, Stan G. Moore, Aidan P. Thompson, Mitchell A. Wood, Ivan I. Oleynik

Abstract: A Spectral Neighbor Analysis (SNAP) machine learning interatomic potential (MLIP) has been developed for simulations of carbon at extreme pressures (up to 5 TPa) and temperatures (up to 20,000 K). This was achieved using a large database of experimentally relevant quantum molecular dynamics (QMD) data, training the SNAP potential using a robust machine learning methodology, and performing extensiv… ▽ More A Spectral Neighbor Analysis (SNAP) machine learning interatomic potential (MLIP) has been developed for simulations of carbon at extreme pressures (up to 5 TPa) and temperatures (up to 20,000 K). This was achieved using a large database of experimentally relevant quantum molecular dynamics (QMD) data, training the SNAP potential using a robust machine learning methodology, and performing extensive validation against QMD and experimental data. The resultant carbon MLIP demonstrates unprecedented accuracy and transferability in predicting the carbon phase diagram, melting curves of crystalline phases, and the shock Hugoniot, all within 3% of QMD. By achieving quantum accuracy and efficient implementation on leadership class high performance computing systems, SNAP advances frontiers of classical MD simulations by enabling atomic-scale insights at experimental time and length scales. △ Less

Submitted 2 May, 2022; originally announced May 2022.

Visualizing Energy Transfer Between Redox-Active Colloids

Authors: Subing Qu, Zihao Ou, Yavuz Savsatli, Lehan Yao, Yu Cao, Elena C. Montoto, Hao Yu, Jingshu Hui, Bo Li, Julio A. N. T. Soares, Lydia Kisley, Brian Bailey, Elizabeth A. Murphy, Junsheng Liu, Christopher M. Evans, Charles M. Schroeder, Joaquín Rodríguez-López, Jeffrey S. Moore, Qian Chen, Paul V. Braun

Abstract: Redox-based electrical conduction in nonconjugated polymers has been explored less than a decade, yet is already showing promise as a new concept for electrical energy transport. Here using monolayers and sub-monolayers of touching micron-sized redox active colloids (RAC) containing high densities of ethyl-viologen (EV) side groups, intercolloid redox-based electron transport was directly observed… ▽ More Redox-based electrical conduction in nonconjugated polymers has been explored less than a decade, yet is already showing promise as a new concept for electrical energy transport. Here using monolayers and sub-monolayers of touching micron-sized redox active colloids (RAC) containing high densities of ethyl-viologen (EV) side groups, intercolloid redox-based electron transport was directly observed via fluorescence microscopy. This observation was enabled by the discovery that these RAC exhibit a highly non-linear electrofluorochromism which can be quantitatively coupled to the colloid redox state. By evaluating the quasi-Fickian nature of the charge transfer (CT) kinetics, the apparent CT diffusion coefficient DCT was extracted. Along with addressing more fundamental questions regarding energy transport in colloidal materials, this first real-time real-space imaging of energy transport within monolayers of redox-active colloids may provide insights into energy transfer in flow batteries, and enable design of new forms of conductive polymers for applications including organic electronics. △ Less

Submitted 1 November, 2024; v1 submitted 1 April, 2022; originally announced April 2022.

Comments: Main text: 10 pages, 3 figures; Supplementary Information: 17 pages, 18 figures

Pressure, temperature, and orientation dependent thermal conductivity of $α$-1,3,5-trinitro-1,3,5-triazinane ($α$-RDX)

Authors: Romain Perriot, Michael S. Powell, John D. Lazarz, C. A. Bolme, Shawn D. McGrane, David S. Moore, M. J. Cawkwell, Kyle J. Ramos

Abstract: We use reverse non-equilibrium molecular dynamics (RNEMD) simulations to determine the thermal conductivity in $α$-RDX in the <100>, <010>, and <001> crystallographic directions. Simulations are carried out with the Smith-Bharadwaj non-reactive empirical interatomic potential [Smith & Bharadwaj, J. Phys. Chem. B 103, 3570(1999)], which represents the thermo-elastic properties of RDX with good accu… ▽ More We use reverse non-equilibrium molecular dynamics (RNEMD) simulations to determine the thermal conductivity in $α$-RDX in the <100>, <010>, and <001> crystallographic directions. Simulations are carried out with the Smith-Bharadwaj non-reactive empirical interatomic potential [Smith & Bharadwaj, J. Phys. Chem. B 103, 3570(1999)], which represents the thermo-elastic properties of RDX with good accuracy. As an illustration, we report the temperature and pressure dependence of lattice constants of $α$-RDX, which compare well with experimental and ab initio results, as do linear and volume thermal expansion coefficients, which we also calculate. We find that the thermal conductivity depends linearly on the inverse temperature in the 200-400K regime due to the decrease in the phonon mean free path. The thermal conductivity also exhibits anisotropy, with a maximum difference at 300K of 24% between the <001> and <010> directions, an effect that remains when temperature increases. Thermal conductivity in the <100> direction is mostly between the two other directions, although crossovers are predicted with <001> at high temperature, and <010> at low temperature under pressure. We observe that the thermal conductivity varies linearly with pressure up to 4 GPa. The data are fitted to analytical functions for interpolation/extrapolation and use in continuum simulations. MD results are validated against experiments using impulsive stimulated thermal scattering (ISTS) on RDX single crystals at 293K and ambient pressure, showing good qualitative and quantitative agreement: same ordering between the three principal orientations, and an average error of 10% between the experiments and the model. These results provide confidence that the extracted analytical functions using the RNEMD methodology and the Smith-Bharadwaj potential can be applied to model the thermal conductivity of $α$-RDX. △ Less

Submitted 22 March, 2021; originally announced March 2021.

Nonlinear twistoptics at symmetry-broken interfaces

Authors: Kaiyuan Yao, Nathan R. Finney, Jin Zhang, Samuel L. Moore, Lede Xian, Nicolas Tancogne-Dejean, Fang Liu, Jenny Ardelean, Xinyi Xu, Dorri Halbertal, K. Watanabe, T. Taniguchi, Hector Ochoa, Ana Asenjo-Garcia, Xiaoyang Zhu, D. N. Basov, Angel Rubio, Cory R. Dean, James Hone, P. James Schuck

Abstract: Broken symmetries induce strong nonlinear optical responses in materials and at interfaces. Twist angle can give complete control over the presence or lack of inversion symmetry at a crystal interface, and is thus an appealing knob for tuning nonlinear optical systems. In contrast to conventional nonlinear crystals with rigid lattices, the weak interlayer coupling in van der Waals (vdW) heterostru… ▽ More Broken symmetries induce strong nonlinear optical responses in materials and at interfaces. Twist angle can give complete control over the presence or lack of inversion symmetry at a crystal interface, and is thus an appealing knob for tuning nonlinear optical systems. In contrast to conventional nonlinear crystals with rigid lattices, the weak interlayer coupling in van der Waals (vdW) heterostructures allows for arbitrary selection of twist angle, making nanomechanical manipulation of fundamental interfacial symmetry possible within a single device. Here we report highly tunable second harmonic generation (SHG) from nanomechanically rotatable stacks of bulk hexagonal boron nitride (BN) crystals, and introduce the term twistoptics to describe studies of optical properties in dynamically twistable vdW systems. We observe SHG intensity modulated by a factor of more than 50, polarization patterns determined by moiré interface symmetry, and enhanced conversion efficiency for bulk crystals by stacking multiple pieces of BN joined by symmetry-broken interfaces. Our study provides a foundation for compact twistoptics architectures aimed at efficient, scalable, and tunable frequency-conversion, and demonstrates SHG as a robust probe of buried vdW interfaces. △ Less

Submitted 20 August, 2020; v1 submitted 24 June, 2020; originally announced June 2020.

Comments: 23 Pages, 17 Figures

Journal ref: Science Advances 2021

Predicting the speed of epidemics spreading on networks

Authors: Sam Moore, Tim Rogers

Abstract: Global transport and communication networks enable information, ideas and infectious diseases now to spread at speeds far beyond what has historically been possible. To effectively monitor, design, or intervene in such epidemic-like processes, there is a need to predict the speed of a particular contagion in a particular network, and to distinguish between nodes that are more likely to become infe… ▽ More Global transport and communication networks enable information, ideas and infectious diseases now to spread at speeds far beyond what has historically been possible. To effectively monitor, design, or intervene in such epidemic-like processes, there is a need to predict the speed of a particular contagion in a particular network, and to distinguish between nodes that are more likely to become infected sooner or later during an outbreak. Here, we study these quantities using a message-passing approach to derive simple and effective predictions which are validated against epidemic simulations on a variety of real-world networks with good agreement. In addition to individualized predictions for different nodes, we find an overall sudden transition from low density to almost full network saturation as the contagion develops in time. Our theory is developed and explained in the setting of simple contagions on tree-like networks, but we are also able to show how the method extends remarkably well to complex contagions and highly clustered networks. △ Less

Submitted 12 February, 2020; originally announced February 2020.

Journal ref: Phys. Rev. Lett. 124, 068301, 2020

Seeing moiré superlattices

Authors: L. J. McGilly, A. Kerelsky, N. R. Finney, K. Shapovalov, E. -M. Shih, A. Ghiotto, Y. Zeng, S. L. Moore, W. Wu, Y. Bai, K. Watanabe, T. Taniguchi, M. Stengel, L. Zhou, J. Hone, X. -Y. Zhu, D. N. Basov, C. Dean, C. E. Dreyer, A. N. Pasupathy

Abstract: Moiré superlattices in van der Waals (vdW) heterostructures have given rise to a number of emergent electronic phenomena due to the interplay between atomic structure and electron correlations. A lack of a simple way to characterize moiré superlattices has impeded progress in the field. In this work we outline a simple, room-temperature, ambient method to visualize real-space moiré superlattices w… ▽ More Moiré superlattices in van der Waals (vdW) heterostructures have given rise to a number of emergent electronic phenomena due to the interplay between atomic structure and electron correlations. A lack of a simple way to characterize moiré superlattices has impeded progress in the field. In this work we outline a simple, room-temperature, ambient method to visualize real-space moiré superlattices with sub-5 nm spatial resolution in a variety of twisted vdW heterostructures including but not limited to conducting graphene, insulating boron nitride and semiconducting transition metal dichalcogenides. Our method utilizes piezoresponse force microscopy, an atomic force microscope modality which locally measures electromechanical surface deformation. We find that all moiré superlattices, regardless of whether the constituent layers have inversion symmetry, exhibit a mechanical response to out-of-plane electric fields. This response is closely tied to flexoelectricity wherein electric polarization and electromechanical response is induced through strain gradients present within moiré superlattices. Moiré superlattices of 2D materials thus represent an interlinked network of polarized domain walls in a non-polar background matrix. △ Less

Submitted 16 December, 2019; v1 submitted 13 December, 2019; originally announced December 2019.

Comments: 21 pages, 4 figures; updated text

Magnetic-Field Tuning of Light-Induced Superconductivity in Striped La$_{2-x}$Ba$_x$CuO$_4$

Authors: D. Nicoletti, D. Fu, O. Mehio, S. Moore, A. S. Disa, G. D. Gu, A. Cavalleri

Abstract: Optical excitation of stripe-ordered La$_{2-x}$Ba$_x$CuO$_4$ has been shown to transiently enhance superconducting tunneling between the CuO$_2$ planes. This effect was revealed by a blue-shift, or by the appearance of a Josephson Plasma Resonance in the terahertz-frequency optical properties. Here, we show that this photo-induced state can be strengthened by the application of high external magne… ▽ More Optical excitation of stripe-ordered La$_{2-x}$Ba$_x$CuO$_4$ has been shown to transiently enhance superconducting tunneling between the CuO$_2$ planes. This effect was revealed by a blue-shift, or by the appearance of a Josephson Plasma Resonance in the terahertz-frequency optical properties. Here, we show that this photo-induced state can be strengthened by the application of high external magnetic fields oriented along the c-axis. For a 7-Tesla field, we observe up to a ten-fold enhancement in the transient interlayer phase correlation length, accompanied by a two-fold increase in the relaxation time of the photo-induced state. These observations are highly surprising, since static magnetic fields suppress interlayer Josephson tunneling and stabilize stripe order at equilibrium. We interpret our data as an indication that optically-enhanced interlayer coupling in La$_{2-x}$Ba$_x$CuO$_4$ does not originate from a simple optical melting of stripes, as previously hypothesized. Rather, we speculate that the photo-induced state may emerge from activated tunneling between optically-excited stripes in adjacent planes. △ Less

Submitted 28 December, 2018; v1 submitted 14 March, 2018; originally announced March 2018.

Comments: 35 pages, 13 figures

Journal ref: Phys. Rev. Lett. 121, 267003 (2018)

Enhanced atomic layer etching of native aluminum oxide for ultraviolet optical applications

Authors: John Hennessy, Christopher S. Moore, Kunjithapatham Balasubramanian, April D. Jewell, Kevin France, Shouleh Nikzad

Abstract: We report on the development and application of an atomic layer etching (ALE) procedure based on alternating exposures of trimethylaluminum and anhydrous hydrogen fluoride (HF) implemented to controllably etch aluminum oxide. Our ALE process utilizes the same chemistry previously demonstrated in the atomic layer deposition of aluminum fluoride thin films, and can therefore be exploited to remove t… ▽ More We report on the development and application of an atomic layer etching (ALE) procedure based on alternating exposures of trimethylaluminum and anhydrous hydrogen fluoride (HF) implemented to controllably etch aluminum oxide. Our ALE process utilizes the same chemistry previously demonstrated in the atomic layer deposition of aluminum fluoride thin films, and can therefore be exploited to remove the surface oxide from metallic aluminum and replace it with thin fluoride layers in order to improve the performance of ultraviolet aluminum mirrors. This ALE process is modified relative to existing methods through the use of a chamber conditioning film of lithium fluoride, which is shown to enhance the loss of fluorine surface species and results in conformal layer-by-layer etching of aluminum oxide films. Etch properties were explored over a temperature range of 225 to 300 °C with the Al2O3 etch rate increasing from 0.8 to 1.2 Å per ALE cycle at a fixed HF exposure of 60 ms per cycle. The effective etch rate has a dependence on the total HF exposure, but the process is shown to be scalable to large area substrates with a post-etch uniformity of better than 2% demonstrated on 125 mm diameter wafers. The efficacy of the ALE process in reducing interfacial native aluminum oxide on evaporated aluminum mirrors is demonstrated with characterization by x-ray photoelectron spectroscopy and measurements of ultraviolet reflectance at wavelengths down to 120 nm. △ Less

Submitted 16 March, 2017; originally announced March 2017.

Journal ref: Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 35, 041512 (2017)

Microscale electromagnetic heating in heterogeneous energetic materials based on X-ray CT imaging

Authors: W. J. M. Kort-Kamp, N. L. Cordes, A. Ionita, B. B. Glover, A. L. Higginbotham Duque, W. L. Perry, B. M. Patterson, D. A. R. Dalvit, D. S. Moore

Abstract: Electromagnetic stimulation of energetic materials provides a noninvasive and nondestructive tool for detecting and identifying explosives. We combine structural information based on X-ray computed tomography, experimental dielectric data, and electromagnetic full-wave simulations, to study microscale electromagnetic heating of realistic three-dimensional heterogeneous explosives. We analyze the f… ▽ More Electromagnetic stimulation of energetic materials provides a noninvasive and nondestructive tool for detecting and identifying explosives. We combine structural information based on X-ray computed tomography, experimental dielectric data, and electromagnetic full-wave simulations, to study microscale electromagnetic heating of realistic three-dimensional heterogeneous explosives. We analyze the formation of electromagnetic hot spots and thermal gradients in the explosive-binder meso-structures, and compare the heating rate for various binder systems. △ Less

Submitted 4 December, 2015; originally announced December 2015.

Comments: 8 pages, 5 figures

Report number: LA-UR-15-29279

Journal ref: Phys. Rev. Applied 5, 044008 (2016)

Charge rearrangement and screening in a quantum point contact

Authors: Silvia Lüscher, Lindsay S. Moore, Tomaz Rejec, Yigal Meir, Hadas Shtrikman, David Goldhaber-Gordon

Abstract: Compressibility measurements, sensitive to charge rearrangements, are performed on a quantum point contact (QPC). Screening due to mobile charges in the QPC is quantitatively measured, using a second point contact to detect the screened electrical potential. These measurements are performed from pinch-off through the opening of the first few modes in the QPC. While the measured signal closely ma… ▽ More Compressibility measurements, sensitive to charge rearrangements, are performed on a quantum point contact (QPC). Screening due to mobile charges in the QPC is quantitatively measured, using a second point contact to detect the screened electrical potential. These measurements are performed from pinch-off through the opening of the first few modes in the QPC. While the measured signal closely matches a Thomas-Fermi-Poisson prediction, deviations from the classical behavior, in the form of additional dips, are apparent near the openings of the different modes, with the largest dip at the opening of the first mode. Density functional calculations attribute the first dip to exchange interactions. The other dips reflect the diverging density of states at the opening of each one-dimensional mode, which affects both kinetic and exchange contributions to the energy. △ Less

Submitted 24 June, 2007; v1 submitted 26 March, 2007; originally announced March 2007.

Comments: 6 pages, 5 figures. Published in PRL. Supplementary Information is included. Changes: Two references and journal reference added

Journal ref: Physical Review Letters 98, 196805 (2007)

A Tunable Anomalous Hall Effect in a Non-Ferromagnetic System

Authors: J. Cumings, L. S. Moore, H. T. Chou, K. C. Ku, S. A. Crooker, N. Samarth, D. Goldhaber-Gordon

Abstract: We measure the low-field Hall resistivity of a magnetically-doped two-dimensional electron gas as a function of temperature and electrically-gated carrier density. Comparing these results with the carrier density extracted from Shubnikov-de Haas oscillations reveals an excess Hall resistivity that increases with decreasing temperature. This excess Hall resistivity qualitatively tracks the parama… ▽ More We measure the low-field Hall resistivity of a magnetically-doped two-dimensional electron gas as a function of temperature and electrically-gated carrier density. Comparing these results with the carrier density extracted from Shubnikov-de Haas oscillations reveals an excess Hall resistivity that increases with decreasing temperature. This excess Hall resistivity qualitatively tracks the paramagnetic polarization of the sample, in analogy to the ferromagnetic anomalous Hall effect. The data are consistent with skew-scattering of carriers by disorder near the crossover to localization. △ Less

Submitted 30 December, 2005; originally announced December 2005.