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Full-Text Articles in Physics

Finite-Strain Scale-Free Phase-Field Approach To Multivariant Martensitic Phase Transformations With Stress-Dependent Effective Thresholds, Hamed Babaei, Valery I. Levitas Nov 2020

Finite-Strain Scale-Free Phase-Field Approach To Multivariant Martensitic Phase Transformations With Stress-Dependent Effective Thresholds, Hamed Babaei, Valery I. Levitas

Aerospace Engineering Publications

A scale-free phase-field model for martensitic phase transformations (PTs) at finite strains is developed as an essential generalization of small-strain models in Levitas et al. (2004) and Idesman et al. (2005). The theory includes finite elastic and transformational strains and rotations as well as anisotropic and different elastic properties of phases. The gradient energy term is excluded, and the model is applicable for any scale greater than 100 nm. The model tracks finite-width interfaces between austenite and the mixture of martensitic variants only; volume fractions of martensitic variants are the internal variables rather than order parameters. The concept of the ...


Substitutional And Interstitial Doping In Laco5 System For The Development Of Hard Magnetic Properties: A First Principles Study, Huseyin Ucar, Renu Choudhary, Durga Paudyal Sep 2020

Substitutional And Interstitial Doping In Laco5 System For The Development Of Hard Magnetic Properties: A First Principles Study, Huseyin Ucar, Renu Choudhary, Durga Paudyal

Ames Laboratory Accepted Manuscripts

We investigate here the changes in the electronic structure at the transition metal sites of the RE-TM5 structure (RE = Rare Earth, TM = Transition Metal) while doping the interstitial sites with nitrogen. LaCo5 compound is taken as the baseline compound owing to its critically needed intrinsic magnetic properties such as magneto-crystalline anisotropy energy (MAE) of ≈5 meV/fu [1] due to the contributions from the cobalt network. In addition, because of the lack of 4f electrons in lanthanum, complications originating from the treatment of the 4f localized electrons are absent in this compound; making it an ideal reference material to all ...


High Layer Uniformity Of 2-D Materials Surprisingly From Broad Features In Surface Electron Diffraction, Shen Chen, Michael Horn Von Hoegen, Patricia A. Thiel, Adam Kaminski, Benjamin Schrunk, Thanassis Speliotis, Edward Henry Conrad, Michael C. Tringides Sep 2020

High Layer Uniformity Of 2-D Materials Surprisingly From Broad Features In Surface Electron Diffraction, Shen Chen, Michael Horn Von Hoegen, Patricia A. Thiel, Adam Kaminski, Benjamin Schrunk, Thanassis Speliotis, Edward Henry Conrad, Michael C. Tringides

Chemistry Publications

Paradoxically a very broad diffraction background, named the Bell-Shaped-Component (BSC), has been established as a feature of graphene growth. Although the BSC has been present in the earlier literature it has been ignored. Recent diffraction studies as a function of electron energy have shown that the BSC is not related to scattering interference. The BSC is a very strong effect, but its origin is still unclear. Here, additional experiments are carried out as a function of temperature while monitoring changes in the intensity of different spots over the range that single-layer-graphene (SLG) grows. Quantitative fitting of the profiles shows that ...


Fifth-Degree Elastic Energy For Predictive Continuum Stress–Strain Relations And Elastic Instabilities Under Large Strain And Complex Loading In Silicon, Hao Chen, Nikolai A. Zarkevich, Valery I. Levitas, Duane D. Johnson, Xiancheng Zhang Aug 2020

Fifth-Degree Elastic Energy For Predictive Continuum Stress–Strain Relations And Elastic Instabilities Under Large Strain And Complex Loading In Silicon, Hao Chen, Nikolai A. Zarkevich, Valery I. Levitas, Duane D. Johnson, Xiancheng Zhang

Aerospace Engineering Publications

Materials under complex loading develop large strains and often phase transformation via an elastic instability, as observed in both simple and complex systems. Here, we represent a material (exemplified for Si I) under large Lagrangian strains within a continuum description by a 5th-order elastic energy found by minimizing error relative to density functional theory (DFT) results. The Cauchy stress—Lagrangian strain curves for arbitrary complex loadings are in excellent correspondence with DFT results, including the elastic instability driving the Si I → II phase transformation (PT) and the shear instabilities. PT conditions for Si I → II under action of cubic axial ...


Search For Encapsulation Of Platinum, Silver, And Gold At The Surface Of Graphite, Ann Lii-Rosales, Yong Han, Dapeng Jing, Michael C. Tringides, Patricia A. Thiel Jul 2020

Search For Encapsulation Of Platinum, Silver, And Gold At The Surface Of Graphite, Ann Lii-Rosales, Yong Han, Dapeng Jing, Michael C. Tringides, Patricia A. Thiel

Chemistry Publications

Using scanning tunneling microscopy, we show that Pt clusters can be encapsulated beneath the surface of graphite, whereas Ag and Au cannot. This is in complete agreement with independent predictions from density functional theory, which show that surface intercalation of single metal atoms is favorable for Pt, but unfavorable for Ag and Au. This supports the validity of using single-metal-atom energetics for predicting encapsulation of metal nanoparticles at the graphite surface. We also demonstrate that the optimal temperature for encapsulation scales with the cohesive energy of the metal.


Reynolds-Stress Modeling Of Cluster-Induced Turbulence In Particle-Laden Vertical Channel Flow, Michael C. Baker, Rodney O. Fox, Bo Kong, Jesse Capecelatro, Olivier Desjardins Jul 2020

Reynolds-Stress Modeling Of Cluster-Induced Turbulence In Particle-Laden Vertical Channel Flow, Michael C. Baker, Rodney O. Fox, Bo Kong, Jesse Capecelatro, Olivier Desjardins

Chemical and Biological Engineering Publications

Particle-laden flow in a vertical channel was simulated using a Reynolds-averaged Navier-Stokes two-fluid model including a Reynolds-stress model (RSM). Two sets of cases varying the overall mass loading were done using particle sizes corresponding to either a large or small Stokes number. Primary and turbulent statistics extracted from counterpart Eulerian-Lagrangian and Eulerian-Eulerian anisotropic-Gaussian simulations were used to inform parameters and closures applied in the RSM. While the behavior at the center of the channel compared well with the other simulations, including the transition from fully developed turbulent flow to relaminarization to cluster-induced turbulence as the mass loading increased, the behavior ...


Unprecedented Generation Of 3d Heterostructures By Mechanochemical Disassembly And Re-Ordering Of Incommensurate Metal Chalcogenides, Oleksandr Dolotko, Ihor Hlova, Arjun K. Pathak, Yaroslav Mudryk, Vitalij K. Pecharsky, Prashant Singh, Duane D. Johnson, Brett W. Boote, Jingzhe Li, Emily A. Smith, Scott L. Carnahan, Aaron J. Rossini, Lin Zhou, Ely M. Eastman, Viktor P. Balema Jun 2020

Unprecedented Generation Of 3d Heterostructures By Mechanochemical Disassembly And Re-Ordering Of Incommensurate Metal Chalcogenides, Oleksandr Dolotko, Ihor Hlova, Arjun K. Pathak, Yaroslav Mudryk, Vitalij K. Pecharsky, Prashant Singh, Duane D. Johnson, Brett W. Boote, Jingzhe Li, Emily A. Smith, Scott L. Carnahan, Aaron J. Rossini, Lin Zhou, Ely M. Eastman, Viktor P. Balema

Materials Science and Engineering Publications

Three-dimensional heterostructures are usually created either by assembling two-dimensional building blocks into hierarchical architectures or using stepwise chemical processes that sequentially deposit individual monolayers. Both approaches suffer from a number of issues, including lack of suitable precursors, limited reproducibility, and poor scalability of the preparation protocols. Therefore, development of alternative methods that enable preparation of heterostructured materials is desired. We create heterostructures with incommensurate arrangements of well-defined building blocks using a synthetic approach that comprises mechanical disassembly and simultaneous reordering of layered transition-metal dichalcogenides, MX2, and non-layered monochalcogenides, REX, where M = Ta, Nb, RE = Sm, La, and X = S, Se ...


Structure Of Chalcogen Overlayers On Au(111): Density Functional Theory And Lattice-Gas Modeling, Da-Jiang Liu, James W. Evans, Peter Spurgeon, Patricia A. Thiel Jun 2020

Structure Of Chalcogen Overlayers On Au(111): Density Functional Theory And Lattice-Gas Modeling, Da-Jiang Liu, James W. Evans, Peter Spurgeon, Patricia A. Thiel

Chemistry Publications

Ordering of different chalcogens, S, Se, and Te, on Au(111) exhibit broad similarities but also some distinct features, which must reflect subtle differences in relative values of the long-range pair and many-body lateral interactions between adatoms. We develop lattice-gas (LG) models within a cluster expansion framework, which includes about 50 interaction parameters. These LG models are developed based on density functional theory (DFT) analysis of the energetics of key adlayer configurations in combination with the Monte Carlo (MC) simulation of the LG models to identify statistically relevant adlayer motifs, i.e., model development is based entirely on theoretical considerations ...


First-Order Magnetic Phase Transition In Pr2in With Negligible Thermomagnetic Hysteresis, Anis Biswas, N. A. Zarkevich, Arjun Pathak, Oleksandr Dolotko, Ihor Z. Hlova, A. V. Smirnov, Yaroslav Mudryk, Duane D. Johnson, Vitalij K. Pecharsky Jun 2020

First-Order Magnetic Phase Transition In Pr2in With Negligible Thermomagnetic Hysteresis, Anis Biswas, N. A. Zarkevich, Arjun Pathak, Oleksandr Dolotko, Ihor Z. Hlova, A. V. Smirnov, Yaroslav Mudryk, Duane D. Johnson, Vitalij K. Pecharsky

Materials Science and Engineering Publications

Magnetic first-order phase transitions are key for the emergence of functionalities of fundamental and applied significance, including magnetic shape memory as well as magnetostrictive and magnetocaloric effects. Such transitions are usually associated with thermomagnetic hysteresis. We report the observation of a first-order transition in Pr2In from a paramagnetic to a ferromagnetic state at TC=57K without a detectable thermomagnetic hysteresis, which is also accompanied by a large magnetocaloric effect. The peculiar electronic structure of Pr2In exhibiting a large density of states near the Fermi energy explains the highly responsive magnetic behavior of the material. The magnetic properties of Pr2In are ...


Non-Equilibrium Growth Of Metal Clusters On A Layered Material: Cu On Mos2, Dapeng Jing, Ann Lii-Rosales, King C. Lai, Qiang Li, Jaeyoun Kim, Michael C. Tringides, James W. Evans, Patricia A. Thiel May 2020

Non-Equilibrium Growth Of Metal Clusters On A Layered Material: Cu On Mos2, Dapeng Jing, Ann Lii-Rosales, King C. Lai, Qiang Li, Jaeyoun Kim, Michael C. Tringides, James W. Evans, Patricia A. Thiel

Chemistry Publications

We use a variety of experimental techniques to characterize Cu clusters on bulk MoS2 formed via physical vapor deposition of Cu in ultrahigh vacuum, at temperatures ranging from 300 K to 900 K. We find that large facetted clusters grow at elevated temperatures, using high Cu exposures. The cluster size distribution is bimodal, and under some conditions, large clusters are surrounded by a denuded zone. We propose that defect-mediated nucleation, and coarsening during deposition, are both operative in this system. At 780 K, a surprising type of facetted cluster emerges, and at 900 K this type predominates: pyramidal clusters with ...


Pressure Tuning Of Structural And Magnetic Transitions In Euag4as2, Sergey L. Bud’Ko, Li Xiang, Chaowei Hu, Bing Shen, Ni Ni, Paul C. Canfield May 2020

Pressure Tuning Of Structural And Magnetic Transitions In Euag4as2, Sergey L. Bud’Ko, Li Xiang, Chaowei Hu, Bing Shen, Ni Ni, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

We report temperature-dependent measurements of ambient-pressure specific heat, magnetic susceptibility, anisotropic resistivity, and thermal expansion as well as in-plane resistivity under pressure up to 20.8 kbar on single crystals of EuAg4As2. Based on thermal expansion and in-plane electrical transport measurements at ambient pressure this compound has two, first-order, structural transitions in the 80–120 K temperature range. Ambient-pressure specific heat, magnetization, and thermal expansion measurements show a cascade of up to seven transitions between 8 and 16 K associated with the ordering of the Eu2+ moments. In-plane electrical transport is able to detect the more prominent of these transitions ...


Impact Of Nematicity On The Relationship Between Antiferromagnetic Fluctuations And Superconductivity In Fese0.91s0.09 Under Pressure, Khusboo Rana, Li Xiang, Paul W. Wiecki, Raquel A. Ribeiro, Guilherme Gorgen Lesseux, Anna E. Böhmer, Sergey L. Bud’Ko, Paul C. Canfield, Yuji Furukawa May 2020

Impact Of Nematicity On The Relationship Between Antiferromagnetic Fluctuations And Superconductivity In Fese0.91s0.09 Under Pressure, Khusboo Rana, Li Xiang, Paul W. Wiecki, Raquel A. Ribeiro, Guilherme Gorgen Lesseux, Anna E. Böhmer, Sergey L. Bud’Ko, Paul C. Canfield, Yuji Furukawa

Ames Laboratory Accepted Manuscripts

The sulfur-substituted FeSe system, FeSe1−xSx, provides a versatile platform for studying the relationship among nematicity, antiferromagnetism, and superconductivity. Here, by nuclear magnetic resonance (NMR) and resistivity measurements up to 4.73 GPa on FeSe0.91S0.09, we established the pressure- (p-) temperature (T) phase diagram in which the nematic state is suppressed with pressure showing a nematic quantum phase transition (QPT) around p=0.5GPa, two superconductivity (SC) regions separated by the QPT appear, and antiferromagnetic (AFM) phase emerges above ∼3.3GPa. From the NMR results up to 2.1 GPa, AFM fluctuations are revealed to be characterized by ...


Competing Magnetic Interactions In The Antiferromagnetic Topological Insulator Mnbi2te4, Bing Li, J.-Q. Yan, D. Pajerowski, Elijah Gordon, Ana-Marija Nedic, Y. Sizyuk, Liqin Ke, Peter P. Orth, David Vaknin, Robert J. Mcqueeney Apr 2020

Competing Magnetic Interactions In The Antiferromagnetic Topological Insulator Mnbi2te4, Bing Li, J.-Q. Yan, D. Pajerowski, Elijah Gordon, Ana-Marija Nedic, Y. Sizyuk, Liqin Ke, Peter P. Orth, David Vaknin, Robert J. Mcqueeney

Physics and Astronomy Publications

The antiferromagnetic (AFM) compound MnBi2Te4 is suggested to be the first realization of an AFM topological insulator. We report on inelastic neutron scattering studies of the magnetic interactions in MnBi2Te4 that possess ferromagnetic triangular layers with AFM interlayer coupling. The spin waves display a large spin gap and pairwise exchange interactions within the triangular layer are long ranged and frustrated by large next-nearest neighbor AFM exchange. The degree of frustration suggests proximity to a variety of magnetic phases, potentially including skyrmion phases, which could be accessed in chemically tuned compounds or upon the application of symmetry-breaking fields.


Ultrafast Control Of Excitonic Rashba Fine Structure By Phonon Coherence In The Metal Halide Perovskite Ch3nh3pbi3, Zhaoyu Liu, Chirag Vaswani, X. Yang, X. Zhao, Yongxin Yao, Z. Song, Di Cheng, Y. Shi, Liang Luo, Dinusha Herath Mudiyanselage, Chuankun Huang, Joong-Mok Park, Richard H. J. Kim, J. Zhao, Y. Yan, Kai-Ming Ho, Jigang Wang Apr 2020

Ultrafast Control Of Excitonic Rashba Fine Structure By Phonon Coherence In The Metal Halide Perovskite Ch3nh3pbi3, Zhaoyu Liu, Chirag Vaswani, X. Yang, X. Zhao, Yongxin Yao, Z. Song, Di Cheng, Y. Shi, Liang Luo, Dinusha Herath Mudiyanselage, Chuankun Huang, Joong-Mok Park, Richard H. J. Kim, J. Zhao, Y. Yan, Kai-Ming Ho, Jigang Wang

Ames Laboratory Accepted Manuscripts

We discover hidden Rashba fine structure in CH3NH3PbI3 and demonstrate its quantum control by vibrational coherence through symmetry-selective vibronic (electron-phonon) coupling. Above a critical threshold of a single-cycle terahertz pump field, a Raman phonon mode distinctly modulates the middle excitonic states with persistent coherence for more than ten times longer than the ones on two sides that predominately couple to infrared phonons. These vibronic quantum beats, together with first-principles modeling of phonon periodically modulated Rashba parameters, identify a threefold excitonic fine structure splitting, i.e., optically forbidden, degenerate dark states in between two bright ones with a narrow, similar to ...


Spin Dynamics In Antiferromagnetic Oxypnictides And Fluoropnictides: Lamnaso, Lamnsbo, And Bamnasf, Farhan Islam, Elijah Gordon, Pinaki Das, Yong Liu, Liquin Ke, Douglas L. Abernathy, Robert L. Mcqueeney, David Vaknin Apr 2020

Spin Dynamics In Antiferromagnetic Oxypnictides And Fluoropnictides: Lamnaso, Lamnsbo, And Bamnasf, Farhan Islam, Elijah Gordon, Pinaki Das, Yong Liu, Liquin Ke, Douglas L. Abernathy, Robert L. Mcqueeney, David Vaknin

Ames Laboratory Accepted Manuscripts

Inelastic neutron scattering (INS) from polycrystalline antiferromagnetic LaMnAsO, LaMnSbO, and BaMnAsF are analyzed using a J(1)-J(2)-J(c) Heisenberg model in the framework of the linear spin-wave theory. All three systems show clear evidence that the nearest- and next-nearest-neighbor interactions within the Mn square lattice layer (J(1) and J(2)) are both antiferromagnetic (AFM). However, for all compounds studied the competing interactions have a ratio of 2J(2)/J(1) < 1, which favors the square lattice checkerboard AFM structure over the stripe AFM structure. The interplane coupling Jc in all three systems is on the order of similar to 3 x 10(-4)J(1), rendering the magnetic properties of these systems with quasi-two-dimensional character. The substitution of Sb for As significantly lowers the in-plane exchange coupling, which is also reflected in the decrease of the Neel temperature, T-N. Although BaMnAsF shares the same MnAs sheets as LaMnAsO, their J(1) and J(2) values are substantially different. Using density functional theory, we calculate exchange parameters J(ij) to rationalize the differences among these systems.


Single-Atom-Layer Traps In A Solid Electrolyte For Lithium Batteries, Feng Zhu, Md Shafiqul Islam, Lin Zhou, Zhenqi Gu, Ting Liu, Xinchao Wang, Jun Luo, Ce-Wen Nan, Yifei Mo, Cheng Ma Apr 2020

Single-Atom-Layer Traps In A Solid Electrolyte For Lithium Batteries, Feng Zhu, Md Shafiqul Islam, Lin Zhou, Zhenqi Gu, Ting Liu, Xinchao Wang, Jun Luo, Ce-Wen Nan, Yifei Mo, Cheng Ma

Ames Laboratory Accepted Manuscripts

In order to fully understand the lithium-ion transport mechanism in solid electrolytes for batteries, not only the periodic lattice but also the non-periodic features that disrupt the ideal periodicity must be comprehensively studied. At present only a limited number of non-periodic features such as point defects and grain boundaries are considered in mechanistic studies. Here, we discover an additional type of non-periodic feature that significantly influences ionic transport; this feature is termed a “single-atom-layer trap” (SALT). In a prototype solid electrolyte Li0.33La0.56TiO3, the single-atom-layer defects that form closed loops, i.e., SALTs, are found ubiquitous by atomic-resolution electron ...


Competing Pairing Interactions Responsible For The Large Upper Critical Field In A Stoichiometric Iron-Based Superconductor Cakfe4as4, Matthew Bristow, William Knafo, Pascal Reiss, William R. Meier, Paul C. Canfield, Stephen J. Blundell, Amalia I. Coldea Apr 2020

Competing Pairing Interactions Responsible For The Large Upper Critical Field In A Stoichiometric Iron-Based Superconductor Cakfe4as4, Matthew Bristow, William Knafo, Pascal Reiss, William R. Meier, Paul C. Canfield, Stephen J. Blundell, Amalia I. Coldea

Physics and Astronomy Publications

The upper critical field of multiband superconductors is an important quantity that can reveal details about the nature of the superconducting pairing. Here we experimentally map out the complete upper-critical-field phase diagram of a stoichiometric superconductor, CaKFe4As4, up to 90T for different orientations of the magnetic field and at temperatures down to 4.2K. The upper critical fields are extremely large, reaching values close to ∼3Tc at the lowest temperature, and the anisotropy decreases dramatically with temperature, leading to essentially isotropic superconductivity at 4.2K. We find that the temperature dependence of the upper critical field can be well described ...


Light-Driven Raman Coherence As A Nonthermal Route To Ultrafast Topology Switching In A Dirac Semimetal, Chirag Vaswani, Lin-Lin Wang, Dinusha Herath Mudiyanselage, Q. Li, P. M. Lozano, G. D. Gu, Di Cheng, Boqun Song, Liang Luo, Richard H.J. Kim, Chuankun Huang, Zhiyan Liu, M. Mootz, I. E. Perakis, Yongxin Yao, Kai-Ming Ho, Jigang Wang Apr 2020

Light-Driven Raman Coherence As A Nonthermal Route To Ultrafast Topology Switching In A Dirac Semimetal, Chirag Vaswani, Lin-Lin Wang, Dinusha Herath Mudiyanselage, Q. Li, P. M. Lozano, G. D. Gu, Di Cheng, Boqun Song, Liang Luo, Richard H.J. Kim, Chuankun Huang, Zhiyan Liu, M. Mootz, I. E. Perakis, Yongxin Yao, Kai-Ming Ho, Jigang Wang

Ames Laboratory Accepted Manuscripts

A grand challenge underlies the entire field of topology-enabled quantum logic and information science: how to establish topological control principles driven by quantum coherence and understand the time dependence of such periodic driving. Here we demonstrate a few-cycle THz-pulse-induced phase transition in a Dirac semimetal ZrTe5 that is periodically driven by vibrational coherence due to excitation of the lowest Raman active mode. Above a critical THz-pump field threshold, there emerges a long-lived metastable phase, approximately 100 ps, with unique Raman phonon-assisted topological switching dynamics absent for optical pumping. The switching also manifests itself by distinct features: nonthermal spectral shape, relaxation ...


Localized Singlets And Ferromagnetic Fluctuations In The Dilute Magnetic Topological Insulator Sn0.95mn0.05te, David Vaknin, Santanu Pakhira, Deborah L. Schlagel, Farhan Islam, Jianhua Zhang, D. M. Pajerowski, Cai-Zhuang Wang, David C. Johnston, Robert J. Mcqueeney Apr 2020

Localized Singlets And Ferromagnetic Fluctuations In The Dilute Magnetic Topological Insulator Sn0.95mn0.05te, David Vaknin, Santanu Pakhira, Deborah L. Schlagel, Farhan Islam, Jianhua Zhang, D. M. Pajerowski, Cai-Zhuang Wang, David C. Johnston, Robert J. Mcqueeney

Ames Laboratory Accepted Manuscripts

The development of long-range ferromagnetic (FM) order in dilute magnetic topological insulators can induce dissipationless electronic surface transport via the quantum anomalous Hall effect. We measure the magnetic excitations in a prototypical magnetic topological crystalline insulator, Sn0.95Mn0.05Te, using inelastic neutron scattering. Neutron diffraction and magnetization data indicate that our Sn0.95Mn0.05Te sample has no FM long-range order above a temperature of 2 K. However, we observe slow, collective FM fluctuations (<70μeV), indicating proximity to FM order. We also find a series of sharp peaks originating from local excitations of antiferromagnetically (AF) coupled and isolated Mn-Mn dimers with JAF=460μeV. The simultaneous presence of collective and localized components in the magnetic spectra highlight different roles for substituted Mn ions, with competition between FM order and the formation of AF-coupled Mn-Mn dimers.


Manipulating Magnetism In The Topological Semimetal Eucd2as2, Na Hyun Jo, Brinda Kuthanazhi, Yun Wu, Erik I. Timmons, Tae-Hoon Kim, Lin Zhou, Lin-Lin Wang, Benjamin G. Ueland, Andriy Palasyuk, Dominic H. Ryan, Robert J. Mcqueeney, Kyungchan Lee, Benjamin Schrunk, Anton A. Burkov, Ruslan Prozorov, Sergey L. Bud’Ko, Adam Kaminski, Paul C. Canfield Apr 2020

Manipulating Magnetism In The Topological Semimetal Eucd2as2, Na Hyun Jo, Brinda Kuthanazhi, Yun Wu, Erik I. Timmons, Tae-Hoon Kim, Lin Zhou, Lin-Lin Wang, Benjamin G. Ueland, Andriy Palasyuk, Dominic H. Ryan, Robert J. Mcqueeney, Kyungchan Lee, Benjamin Schrunk, Anton A. Burkov, Ruslan Prozorov, Sergey L. Bud’Ko, Adam Kaminski, Paul C. Canfield

Physics and Astronomy Publications

EuCd2As2 is a magnetic semimetal that has the potential of manifesting nontrivial electronic states, depending on its low temperature magnetic ordering. Here, we report the successful synthesis of single crystals of EuCd2As2 that order ferromagnetically or antiferromagnetically depending on the level of band filling, thus allowing for the use of magnetism to tune the topological properties within the same host. We explored their physical properties via magnetization, electrical transport, heat capacity, and angle-resolved photoemission spectroscopy measurements and conclude that EuCd2As2 is an excellent, tunable system for exploring the interplay of magnetic ordering and topology.


Coherent Band-Edge Oscillations And Dynamic Longitudinal-Optical Phonon Mode Splitting As Evidence For Polarons In Perovskites, Zhaoyu Liu, Chirag Vaswani, Liang Luo, Di Cheng, X. Yang, Xin Zhao, Yongxin Yao, Z. Song, R. Brenes, R. J. H. Kim, J. Jean, V. Bulović, Y. Yan, Kai-Ming Ho, Jigang Wang Mar 2020

Coherent Band-Edge Oscillations And Dynamic Longitudinal-Optical Phonon Mode Splitting As Evidence For Polarons In Perovskites, Zhaoyu Liu, Chirag Vaswani, Liang Luo, Di Cheng, X. Yang, Xin Zhao, Yongxin Yao, Z. Song, R. Brenes, R. J. H. Kim, J. Jean, V. Bulović, Y. Yan, Kai-Ming Ho, Jigang Wang

Ames Laboratory Accepted Manuscripts

The coherence of collective modes, such as phonons and polarons, and their modulation of electronic states is long sought in complex systems, which is a crosscutting issue in photovoltaics and quantum electronics. In photovoltaic cells and lasers based on metal halide perovskites, the presence of polarons, i.e., photocarriers dressed by the macroscopic motion of charged lattice, assisted by terahertz (THz) longitudinal-optical (LO) phonons, has been intensely studied yet is still debated. This may be key for explaining the remarkable properties of the perovskite materials, e.g., defect tolerance, long charge lifetimes, and diffusion lengths. Here we use the intense ...


Interlayer Gap Widened Α-Phase Molybdenum Trioxide As High-Rate Anodes For Dual-Ion-Intercalation Energy Storage Devices, Minghao Yu, Hui Shao, Gang Wang, Fan Yang, Chaolun Liang, Patrick Rozier, Cai-Zhuang Wang, Xihong Lu, Patrice Simon, Xinliang Feng Mar 2020

Interlayer Gap Widened Α-Phase Molybdenum Trioxide As High-Rate Anodes For Dual-Ion-Intercalation Energy Storage Devices, Minghao Yu, Hui Shao, Gang Wang, Fan Yang, Chaolun Liang, Patrick Rozier, Cai-Zhuang Wang, Xihong Lu, Patrice Simon, Xinliang Feng

Ames Laboratory Accepted Manuscripts

Employing high-rate ion-intercalation electrodes represents a feasible way to mitigate the inherent trade-off between energy density and power density for electrochemical energy storage devices, but efficient approaches to boost the charge-storage kinetics of electrodes are still needed. Here, we demonstrate a water-incorporation strategy to expand the interlayer gap of α-MoO3, in which water molecules take the place of lattice oxygen of α-MoO3. Accordingly, the modified α-MoO3 electrode exhibits theoretical-value-close specific capacity (963 C g−1 at 0.1 mV s−1), greatly improved rate capability (from 4.4% to 40.2% at 100 mV s−1) and boosted cycling stability ...


Tip- And Plasmon-Enhanced Infrared Nanoscopy For Ultrasensitive Molecular Characterizations, Yilong Luan, Liam Mcdermott, F. Hu, Zhe Fei Mar 2020

Tip- And Plasmon-Enhanced Infrared Nanoscopy For Ultrasensitive Molecular Characterizations, Yilong Luan, Liam Mcdermott, F. Hu, Zhe Fei

Ames Laboratory Accepted Manuscripts

We propose a method for ultrasensitive infrared (IR) vibrational spectroscopy of molecules with nanoscale footprints by combining the tip enhancement of a scattering-type scanning near-field optical microscope (s-SNOM) and the plasmon enhancement of breathing-mode (BM) plasmon resonances of graphene nanodisks (GNDs). To demonstrate this, we develop a quantitative model that is capable of computing accurately the s-SNOM signals of nanoscale samples. With our modeling, we show that the s-SNOM tip can effectively excite gate-tunable BM plasmonic resonances in GNDs with strong field enhancement and sensitive dependence on the size of GND. Moreover, we demonstrate that the intense electric field of ...


London Penetration Depth At Zero Temperature And Near The Superconducting Transition, Vladimir G. Kogan, Makariy A. Tanatar, Ruslan Prozorov Mar 2020

London Penetration Depth At Zero Temperature And Near The Superconducting Transition, Vladimir G. Kogan, Makariy A. Tanatar, Ruslan Prozorov

Ames Laboratory Accepted Manuscripts

A simple relation is established between the zero-T penetration depth λ(0) and the slope of λ−2(T) near Tc, similar to Helfand-Werthamer's relation for Hc2(0) and the slope of Hc2(T) at Tc for the isotropic s-wave case with nonmagnetic scattering [E. Helfand and N. R. Werthamer, Phys. Rev. 147, 288 (1966)]. When the scattering parameter ρ=ℏv/2πTcℓ (v is the Fermi velocity and ℓ is the mean free path) varies from 1 to 10, the coefficient of proportionality between λ−2(0) and Tc(dλ−2/dT)Tc changes from 0.43 to 0 ...


Fundamentals Of Au(111) Surface Dynamics: Coarsening Of 2d Au Islands, Peter M. Spurgeon, King C. Lai, Yong Han, James W. Evans, Patricia A. Thiel Feb 2020

Fundamentals Of Au(111) Surface Dynamics: Coarsening Of 2d Au Islands, Peter M. Spurgeon, King C. Lai, Yong Han, James W. Evans, Patricia A. Thiel

Chemistry Publications

Au(111) surfaces play a central role in many applications, yet studies of fundamental aspects of their dynamics are limited. Thus, using Scanning Tunneling Microscopy (STM) at 300 K, we analyze the coarsening of first-layer 2D Au islands directly on the Au(111) substrate, and also of second-layer 2D Au islands. Specifically, we monitor the decay of Au first-layer islands with areas of about 100-500 nm^2 in the vicinity of larger islands or extended step edges over a period of approximately 40 hours - the relevant time scale for this process. Experimentally observed behavior is captured by analytic theory for ...


Light Control Of Surface–Bulk Coupling By Terahertz Vibrational Coherence In A Topological Insulator, Xu Yang, Liang Luo, Chirag Vaswani, Xin Zhao, Yongxin Yao, Di Cheng, Zhiyan Liu, Richard H. J. Kim, Xinyu Liu, Malgorzata Dobrowolska-Furdyna, Jacek K. Furdyna, Ilias E. Perakis, Cai-Zhuang Wang, Kai-Ming Ho, Jigang Wang Feb 2020

Light Control Of Surface–Bulk Coupling By Terahertz Vibrational Coherence In A Topological Insulator, Xu Yang, Liang Luo, Chirag Vaswani, Xin Zhao, Yongxin Yao, Di Cheng, Zhiyan Liu, Richard H. J. Kim, Xinyu Liu, Malgorzata Dobrowolska-Furdyna, Jacek K. Furdyna, Ilias E. Perakis, Cai-Zhuang Wang, Kai-Ming Ho, Jigang Wang

Ames Laboratory Accepted Manuscripts

The demand for disorder-tolerant quantum logic and spin electronics can be met by generating and controlling dissipationless spin currents protected by topology. Dirac fermions with helical spin-locking surface transport offer a way of achieving such a goal. Yet, surface-bulk coupling can lead to strong Dirac electron scattering with bulk carriers and phonons as well as impurities, assisted by such dissipative channel, which results in “topological breakdown”. Here, we demonstrate that coherent lattice vibrations periodically driven by a single-cycle terahertz (THz) pulse can significantly suppress such dissipative channel in topological insulators. This is achieved by reducing the phase space in the ...


Shapes Of Fe Nanocrystals Encapsulated At The Graphite Surface, Ann Lii-Rosales, Yong Han, Scott E. Julien, Olivier Pierre-Louis, Dapeng Jing, Kai-Tak Wan, Michael C. Tringides, James W. Evans, Patricia A. Thiel Feb 2020

Shapes Of Fe Nanocrystals Encapsulated At The Graphite Surface, Ann Lii-Rosales, Yong Han, Scott E. Julien, Olivier Pierre-Louis, Dapeng Jing, Kai-Tak Wan, Michael C. Tringides, James W. Evans, Patricia A. Thiel

Chemistry Publications

We describe and analyze in detail the shapes of Fe islands encapsulated under the top graphene layers in graphite. Shapes are interrogated using scanning tunneling microscopy. The main outputs of the shape analysis are the slope of the graphene membrane around the perimeter of the island, and the aspect ratio of the central metal cluster. Modeling primarily uses a continuum elasticity (CE) model. As input to the CE model, we use density functional theory to calculate the surface energy of Fe, and the adhesion energies between Fe and graphene or graphite. We use the shaft-loaded blister test (SLBT) model to ...


Extended Families Of Critical And Stationary Droplets For Nonequilibrium Phase Transitions In Spatially Discrete Bistable Systems, Chi-Jen Wang, Da-Jiang Liu, James W. Evans Feb 2020

Extended Families Of Critical And Stationary Droplets For Nonequilibrium Phase Transitions In Spatially Discrete Bistable Systems, Chi-Jen Wang, Da-Jiang Liu, James W. Evans

Ames Laboratory Accepted Manuscripts

Bistable nonequilibrium systems are realized in catalytic reaction-diffusion processes, biological transport and regulation, spatial epidemics, etc. Behavior in spatially continuous formulations, described at the mean-field level by reaction-diffusion type equations (RDEs), often mimics that of classic equilibrium van der Waals type systems. When accounting for noise, similarities include a discontinuous phase transition at some value, peq, of a control parameter, p, with metastability and hysteresis around peq. For each p, there is a unique critical droplet of the more stable phase embedded in the less stable or metastable phase which is stationary (neither shrinking nor growing), and with size diverging ...


Charge Density Wave Modulation In Superconducting Bapbo3/Babio3 Superlattices, D. T. Harris, N. G. Campbell, C. Di, Joong Mok Park, Liang Luo, H. Zhou, G.-Y. Kim, K. Song, S.-Y. Choi, Jigang Wang, M. S. Rzchowski, C. B. Eom Feb 2020

Charge Density Wave Modulation In Superconducting Bapbo3/Babio3 Superlattices, D. T. Harris, N. G. Campbell, C. Di, Joong Mok Park, Liang Luo, H. Zhou, G.-Y. Kim, K. Song, S.-Y. Choi, Jigang Wang, M. S. Rzchowski, C. B. Eom

Ames Laboratory Accepted Manuscripts

The isotropic, nonmagnetic doped BaBiO3 superconductors maintain some similarities to high-Tc cuprates, while also providing a cleaner system for isolating charge density wave (CDW) physics that commonly competes with superconductivity. Artificial layered superlattices offer the possibility of engineering the interaction between superconductivity and CDW. Here we stabilize a low-temperature, fluctuating short-range CDW order by using artificially layered epitaxial (BaPbO3)3m/(BaBiO3)m (m=1–10 unit cells) superlattices that are not present in the optimally doped BaPb0.75Bi0.25O3 alloy with the same overall chemical formula. Charge transfer from BaBiO3 to BaPbO3 effectively dopes the former and suppresses the long-range ...


Spin Waves Above And Below The Verwey Transition In Tbbafe2o5, Daniel M. Pajerowski, Daniel K. Pratt, Steven E. Hahn, Wei Tian, Garrett E. Granroth, Alexander I. Kolesnikov, Alexey A. Taskin, Yoichi Ando, Robert J. Mcqueeney Feb 2020

Spin Waves Above And Below The Verwey Transition In Tbbafe2o5, Daniel M. Pajerowski, Daniel K. Pratt, Steven E. Hahn, Wei Tian, Garrett E. Granroth, Alexander I. Kolesnikov, Alexey A. Taskin, Yoichi Ando, Robert J. Mcqueeney

Ames Laboratory Accepted Manuscripts

TbBaFe2O5+δ (TBFO) is a mixed valence compound with an antiferromagnetic order (TN=450K) that changes along with the crystal structure and conductivity upon cooling below a Verwey-like transition (TV=280K). This type of double-cell-layered perovskite is useful to study putative charge ordering in fractional valence systems because the crystal structure develops unique sites for the different valence states. While the evolution of the static magnetic structure in the different charge ordered states of TBFO is known, in this study we investigate the effect of charge ordering on the magnetic interactions. Dispersive magnetic excitations measured using single crystal inelastic neutron ...