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Ames Laboratory Accepted Manuscripts

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Full-Text Articles in Physics

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 ...


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 ...


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 ...


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.


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 ...


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 ...


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 ...


Reply To “Comment On ‘Magnetic Structure And Magnetization Of Z-Axis Helical Heisenberg Antiferromagnets With Xy Anisotropy In High Magnetic Fields Transverse To The Helix Axis At Zero Temperature’ ”, David C. Johnston Jan 2020

Reply To “Comment On ‘Magnetic Structure And Magnetization Of Z-Axis Helical Heisenberg Antiferromagnets With Xy Anisotropy In High Magnetic Fields Transverse To The Helix Axis At Zero Temperature’ ”, David C. Johnston

Ames Laboratory Accepted Manuscripts

The Comment criticizes the assumptions of the model I used. I was aware of the limitations of my model. However, my model is useful for fitting high-field magnetization versus transverse-field data for real helical Heisenberg antiferromagnets at temperatures much lower than their Néel temperatures and estimating their critical fields. To my knowledge, there existed no prior theory that could fit such experimental data over the entire field range of experiments. I welcome that the Comment calls for more accurate theory.


Magnetic Structure Of Selected Gd Intermetallic Alloys From First Principles, L. Petit, Z. Szotek, Durga Paudyal, Anis Biswas, Yaroslav Mudryk, Vitalij K. Pecharsky, J. B. Staunton Jan 2020

Magnetic Structure Of Selected Gd Intermetallic Alloys From First Principles, L. Petit, Z. Szotek, Durga Paudyal, Anis Biswas, Yaroslav Mudryk, Vitalij K. Pecharsky, J. B. Staunton

Ames Laboratory Accepted Manuscripts

Using first-principles calculations, based on disordered local moment (DLM) theory combined with the self-interaction corrected local spin density approximation (SIC-LSDA), we study magnetic correlations in the paramagnetic state of GdX(X=Cu, Zn, Ga, Ag, Cd, In, Au, Hg, and Tl) intermetallics and their alloys. The predicted magnetic orders and ordering temperatures that these correlations lead to are in overall good agreement with available experiments. The interactions between the Gd f-electron local moments are mediated by the valence electrons of the intermetallics which comprise both Gd and Xd bands as well as sp bands. There are RKKY-like features such as ...


Quasiperiodic Ordering In Thick Sn Layer On I-Al-Pd-Mn: A Possible Quasicrystalline Clathrate, Vipin Kumar Singh, Marek Mihalkovic, Marian Krajci, Shuvam Sarkar, Pampa Sadhukhan, M. Maniraj, Abhishek Rai, Katariina Pussi, Deborah L. Schlagel, Thomas A. Lograsso, Ajay Kumar Shukla, Sudipta Roy Barman Jan 2020

Quasiperiodic Ordering In Thick Sn Layer On I-Al-Pd-Mn: A Possible Quasicrystalline Clathrate, Vipin Kumar Singh, Marek Mihalkovic, Marian Krajci, Shuvam Sarkar, Pampa Sadhukhan, M. Maniraj, Abhishek Rai, Katariina Pussi, Deborah L. Schlagel, Thomas A. Lograsso, Ajay Kumar Shukla, Sudipta Roy Barman

Ames Laboratory Accepted Manuscripts

Realization of an elemental solid-state quasicrystal has remained a distant dream so far in spite of extensive work in this direction for almost two decades. In the present work, we report the discovery of quasiperiodic ordering in a thick layer of elemental Sn grown on icosahedral (i)-Al-Pd-Mn. The scanning tunneling microscopy (STM) images and the low-energy electron diffraction patterns of the Sn layer show specific structural signatures that portray quasiperiodicity but are distinct from the substrate. Photoemission spectroscopy reveals the existence of the pseudogap around the Fermi energy up to the maximal Sn thickness. The structure of the Sn ...


Raman Scattering From One And Two Magnons In Magnetoelectric Linipo4, D. Rigitano, David Vaknin, G. E. Barberis, E. Granado Jan 2020

Raman Scattering From One And Two Magnons In Magnetoelectric Linipo4, D. Rigitano, David Vaknin, G. E. Barberis, E. Granado

Ames Laboratory Accepted Manuscripts

Polarized Raman scattering in magnetoelectric LiNiPO4 shows a sharp resonant peak at 37 cm−1 in the magnetically ordered phase, originating from a one-magnon excitation of Ni2+S=1 localized moments at the zone center. Also, a broad component with maximum intensity at ∼65cm−1 is observed and successfully modeled in terms of light scattering from two-magnon excitations within the framework of the Fleury-Loudon theory using five relevant exchange parameters, providing an independent experimental confirmation of their values previously obtained with inelastic neutron scattering data in this material. An additional peak at 58 cm−1, already reported in previous works ...


Quantum Phase Transition Inside The Superconducting Dome Of Ba(Fe1-Xcox)2as2 From Diamond-Based Optical Magnetometry, Kamal R. Joshi, Naufer Nusran, Makariy A. Tanatar, Kyuil Cho, Sergey L. Bud’Ko, Paul C. Canfield, R. M. Fernandes, A. Levchenko, Ruslan Prozorov Jan 2020

Quantum Phase Transition Inside The Superconducting Dome Of Ba(Fe1-Xcox)2as2 From Diamond-Based Optical Magnetometry, Kamal R. Joshi, Naufer Nusran, Makariy A. Tanatar, Kyuil Cho, Sergey L. Bud’Ko, Paul C. Canfield, R. M. Fernandes, A. Levchenko, Ruslan Prozorov

Ames Laboratory Accepted Manuscripts

Unconventional superconductivity often emerges in close proximity to a magnetic instability. Upon suppressing the magnetic transition down to zero temperature by tuning the carrier concentration, pressure, or disorder, the superconducting transition temperature $T_c$ acquires its maximum value. A major challenge is the elucidation of the relationship between the superconducting phase and the strong quantum fluctuations expected near a quantum phase transition (QPT) that is either second order (i.e. a quantum critical point) or weakly first order. While unusual normal state properties, such as non-Fermi liquid behavior of the resistivity, are commonly associated with strong quantum fluctuations, evidence for its ...


Magnetic And Structural Transitions In Euag4as2 Studied Using 151eu Mössbauer Spectroscopy, D. H. Ryan, Sergey L. Bud’Ko, Chaowei Hu, N. Ni Dec 2019

Magnetic And Structural Transitions In Euag4as2 Studied Using 151eu Mössbauer Spectroscopy, D. H. Ryan, Sergey L. Bud’Ko, Chaowei Hu, N. Ni

Ames Laboratory Accepted Manuscripts

151Eu Mössbauer spectroscopy confirms that the europium in EuAg4As2 is fully divalent and that the spectrum at 5 K consists of a single, sharp magnetic pattern with a hyperfine field (Bhf) of 27.1(1) T and an isomer shift of −11.04(3) mm/s (relative to EuF3). The temperature dependence of the spectra shows that the ordering of the Eu moments proceeds via an incommensurate sine modulated structure starting at 15 K. The structure squares up below 9 K. A search for charge density or phonon softening signatures at the 120 K ...


The First-Order Magnetoelastic Transition In Eu2in: A 151eu Mössbauer Study, D. H. Ryan, Durga Paudyal, Francois Guillou, Yaroslav Mudryk, Arjun K. Pathak, Vitalij K. Pecharsky Dec 2019

The First-Order Magnetoelastic Transition In Eu2in: A 151eu Mössbauer Study, D. H. Ryan, Durga Paudyal, Francois Guillou, Yaroslav Mudryk, Arjun K. Pathak, Vitalij K. Pecharsky

Ames Laboratory Accepted Manuscripts

Our 151Eu Mössbauer investigation of Eu2In and Eu2Sn shows that the europium in both materials is fully divalent. We confirm the distinct thermodynamic orders of the magnetic transitions and reveal a remarkable difference between the magnetic environments of the europium atoms in the two compounds. Possible structural and electronic origins for these differences are discussed using DFT calculations.


Magnetic Structure Of Nd In Ndfeaso Studied By X-Ray Resonant Magnetic Scattering, M. G. Kim, J.-W. Kim, J.-Q. Yan, Alan I. Goldman, Andreas Kreyssig Dec 2019

Magnetic Structure Of Nd In Ndfeaso Studied By X-Ray Resonant Magnetic Scattering, M. G. Kim, J.-W. Kim, J.-Q. Yan, Alan I. Goldman, Andreas Kreyssig

Ames Laboratory Accepted Manuscripts

The magnetic structure of Nd in NdFeAsO compound has been investigated by x-ray resonant magnetic scattering at the Nd L2 edge (E=6.725 keV) at 1.7≤T≤15 K. At T=1.7 K we find that the Nd moments are aligned along the crystallographic c direction with the (1, 0, 0) propagation vector, and are arranged antiferromagnetically along the a direction and ferromagnetically along the b and c directions. At 1.7


Microstructure Evolution During Near-Tg Annealing And Its Effect On Shear Banding In Model Alloys, Meng-Hao Yang, Bei Cai, Yang Sun, Feng Zhang, Yi-Fan Wang, Cai-Zhuang Wang, Kai-Ming Ho Dec 2019

Microstructure Evolution During Near-Tg Annealing And Its Effect On Shear Banding In Model Alloys, Meng-Hao Yang, Bei Cai, Yang Sun, Feng Zhang, Yi-Fan Wang, Cai-Zhuang Wang, Kai-Ming Ho

Ames Laboratory Accepted Manuscripts

By performing extensive molecular dynamics simulations, we investigate the deformation behavior in Al90Sm10 and Cu64.5Zr35.5 alloys after elongated isothermal annealing in the vicinity of the glass-transition temperature (Tg). Different microstructural response to the annealing process was observed: Al90Sm10 maintains the glassy structure with improved energetic stability, enhanced short-range order (SRO), and a more pronounced spatial network that extends beyond the first atomic shell, while Cu64.5Zr35.5 forms nanocrystalline Laves Cu2Zr phases. Shear banding occurs in both annealed systems under shear loading. For Al90Sm10, the spatial network formed by the local clusters characterizing the SRO of the system ...


Energy Barriers For Pb Adatom Diffusion On Stepped Ultrathin Pb(111) Quantum Nanofilms: First-Principles Calculations, Yong Han, James W. Evans, Feng Liu Nov 2019

Energy Barriers For Pb Adatom Diffusion On Stepped Ultrathin Pb(111) Quantum Nanofilms: First-Principles Calculations, Yong Han, James W. Evans, Feng Liu

Ames Laboratory Accepted Manuscripts

Various properties of Pb(111) nanofilms, prototypical quantum films, have been studied extensively. However, key ab initio-level energy barriers for Pb adatom diffusion on stepped Pb(111) nanofilm surfaces are still not available. Using first-principles density functional theory, we calculate these barriers for films with thicknesses of few monolayers (ML). We find that two-atom exchange is always much more favorable than direct hopping to cross A- or B-type steps. Ehrlich-Schwoebel (ES) barriers for downward transport to a higher-coordination step-edge site depend strongly on the film thickness. For such transport from 2- to 1-ML terraces, or from 4- to 3-ML ...


Elastic Fields In Superconductors Caused By Moving Vortices, Vladimir G. Kogan Nov 2019

Elastic Fields In Superconductors Caused By Moving Vortices, Vladimir G. Kogan

Ames Laboratory Accepted Manuscripts

Strains in superconductors due to moving vortices and vortex lattices are discussed. It is shown that the energy stored in elastic strains increases with vortex velocity. For moving vortex lattices, the elastic energy depends on velocity orientation relative to the lattice having minimum for the velocity directed along one of the unit cell vectors of the moving lattice. It is shown that for supersonic motion, the vortex-induced stress field has a shape similar to supersonic shock waves.


Low Efficiency Roll-Off Phosphorescent Organic Light-Emitting Devices Using Thermally Activated Delayed Fluorescence Hosts Materials Based 1, 2, 4-Triazole Acceptor, Huixia Xu, Yaping Zhao, Jing Zhang, Di Zhang, Yanqin Miao, Joseph Shinar, Ruth Shinar, Hua Wang, Bingshe Xu Nov 2019

Low Efficiency Roll-Off Phosphorescent Organic Light-Emitting Devices Using Thermally Activated Delayed Fluorescence Hosts Materials Based 1, 2, 4-Triazole Acceptor, Huixia Xu, Yaping Zhao, Jing Zhang, Di Zhang, Yanqin Miao, Joseph Shinar, Ruth Shinar, Hua Wang, Bingshe Xu

Ames Laboratory Accepted Manuscripts

The host in phosphrescent organic light emitting devices (PhOLEDs), showing the thermally activated delayed fluorescence (TADF) charateristic, can effectively overcome the efficiency roll-off. Herein, six bipolar compounds with donor-π-acceptor (D-π-A) and D-π-A-π-D structures have been synthesized using 1,2,4-triazole derivative (TAZ) as an acceptor and phenothiazine (PTZ), phenoxazine (PXZ), and 9, 9-dimethylacridane (DMAC) as donors. The molecular structures were confirmed by 1H NMR, 13C NMR and X-ray single-crystal diffractions. The large steric hindrance endows these molecules with typical TADF features, including the small singlet-triplet energy splitting (Delta E-ST) of 0.08–0.30 eV and completely spatially separate highest ...


Lattice Distortion In The Spin-Orbital Entangled State In Rvo3 Perovskites, J.-Q. Yan, W. Tian, H. B. Cao, S. Chi, F. Ye, A. Llobet, A. Puretzky, Q. Chen, J. Ma, Y. Ren, J.-G. Cheng, J.-S. Zhou, M. A. Mcguire, Robert J. Mcqueeney Nov 2019

Lattice Distortion In The Spin-Orbital Entangled State In Rvo3 Perovskites, J.-Q. Yan, W. Tian, H. B. Cao, S. Chi, F. Ye, A. Llobet, A. Puretzky, Q. Chen, J. Ma, Y. Ren, J.-G. Cheng, J.-S. Zhou, M. A. Mcguire, Robert J. Mcqueeney

Ames Laboratory Accepted Manuscripts

We report a thorough study of Y0.7La0.3VO3 single crystals by measuring magnetic properties, specific heat, thermal conductivity, Raman scattering, x-ray and neutron diffraction with the motivation of revealing the lattice response to the spin-orbital entanglement in RVO3. Upon cooling from room temperature, the orbitally disordered paramagnetic state changes around T∗∼220 K to a spin-orbital entangled state which is then followed by a transition at TN = 116 K to C-type orbital-ordered (OO) and G-type antiferromagnetic ordered (AF) ground state. In the temperature interval TNyz/zxorbitals. However, this distortion is incompatible with the steric octahedral site distortion intrinsic to ...


Complex Oscillatory Decrease With Size In Diffusivity Of {100}-Epitaxially Supported 3d Fcc Metal Nanoclusters, King C. Lai, James W. Evans Oct 2019

Complex Oscillatory Decrease With Size In Diffusivity Of {100}-Epitaxially Supported 3d Fcc Metal Nanoclusters, King C. Lai, James W. Evans

Ames Laboratory Accepted Manuscripts

Diffusion and coalescence of supported 3D metal nanoclusters (NCs) leads to Smoluchowski Ripening (SR), a key pathway for catalyst degradation. Variation of the NC diffusion coefficient, DN, with size N (in atoms) controls SR kinetics. Traditionally, a form DN ∼ N−β was assumed consistent with mean-field analysis. However, KMC simulation of a stochastic model for diffusion of {100}-epitaxially supported fcc NCs mediated by surface diffusion reveals instead a complex oscillatory decrease of DN with N. Barriers for surface diffusion of metal atoms across and between facets, along step edges, etc., in this model are selected to accurately capture behavior ...