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Full-Text Articles in Physics

Tuning Of Charge Density Wave Transitions In Laauxsb2 By Pressure And Au Stoichiometry, Li Xiang, Dominic H. Ryan, Warren E. Straszheim, Paul C. Canfield, Sergey L. Bud’Ko Sep 2020

Tuning Of Charge Density Wave Transitions In Laauxsb2 By Pressure And Au Stoichiometry, Li Xiang, Dominic H. Ryan, Warren E. Straszheim, Paul C. Canfield, Sergey L. Bud’Ko

Ames Laboratory Accepted Manuscripts

Two charge density wave transition can be detected in LaAuSb2 at similar to 110 and similar to 90K by careful electrical transport measurements. Whereas control of the Au site occupancy in LaAuxSb2 (for 0.9 less than or similar to x less than or similar to 1.0) can suppress each of these transitions by similar to 80K, the application of hydrostatic pressure can completely suppress the lower transition by similar to 7.5kbar and the upper transition by similar to 17kbar. Clear anomalies in the resistance as well as the magnetoresistance are observed to coincide with the pressures at ...


Magnetism And Its Coexistence With Superconductivity In Cak(Fe0.949ni0.051)(4)As-4: Muon Spin Rotation/Relaxation Studies, Rustem Khasanov, Gediminas Simutis, Yurii G. Pashkevich, Tatyana Shevtsova, William R. Meier, Mingyu Xu, Sergey L. Bud’Ko, Vladimir G. Kogan, Paul C. Canfield Sep 2020

Magnetism And Its Coexistence With Superconductivity In Cak(Fe0.949ni0.051)(4)As-4: Muon Spin Rotation/Relaxation Studies, Rustem Khasanov, Gediminas Simutis, Yurii G. Pashkevich, Tatyana Shevtsova, William R. Meier, Mingyu Xu, Sergey L. Bud’Ko, Vladimir G. Kogan, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

The magnetic response of CaK(Fe0.949Ni0.051)(4)As-4 was investigated by means of the muon spin rotation/relaxation. The long-range commensurate magnetic order sets in below the Neel temperature T-N = 50.0(5) K. The density-functional theory calculations have identified three possible muon stopping sites. The experimental data were found to be consistent with only one type of magnetic structure, namely, the long-range magnetic spin-vortex-crystal order with the hedgehog motif within the ab plane and the antiferromagnetic stacking along the c direction. The value of the ordered magnetic moment at T approximate to 3 K was estimated to ...


Lightwave Terahertz Quantum Manipulation Of Nonequilibrium Superconductor Phases And Their Collective Modes, M. Mootz, Jigang Wang, I. E. Perakis Aug 2020

Lightwave Terahertz Quantum Manipulation Of Nonequilibrium Superconductor Phases And Their Collective Modes, M. Mootz, Jigang Wang, I. E. Perakis

Ames Laboratory Accepted Manuscripts

We present a gauge-invariant density matrix description of nonequilibrium superconductor (SC) states with spatial and temporal correlations driven by intense terahertz (THz) lightwaves. We derive superconductor Bloch-Maxwell equations of motion that extend Anderson pseudospin models to include the Cooper pair center-of-mass motion and electromagnetic propagation effects. We thus describe quantum control of dynamical phases, collective modes, quasiparticle coherence, and high nonlinearities during cycles of carrier wave oscillations, which relates to our recent experiments. Coherent photogeneration of a nonlinear supercurrent with a dc component, achieved via condensate acceleration by an effective lightwave field, dynamically breaks the equilibrium inversion symmetry. Experimental signatures ...


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 ...


Free Charge Carrier Properties In Two-Dimensional Materials And Monoclinic Oxides Studied By Optical Hall Effect, Sean Knight Aug 2020

Free Charge Carrier Properties In Two-Dimensional Materials And Monoclinic Oxides Studied By Optical Hall Effect, Sean Knight

Theses, Dissertations, and Student Research from Electrical & Computer Engineering

In this dissertation, optical Hall effect (OHE) measurements are used to determine the free charge carrier properties of important two-dimensional materials and monoclinic oxides. Two-dimensional material systems have proven useful in high-frequency electronic devices due to their unique properties, such as high mobility, which arise from their two-dimensional nature. Monoclinic oxides exhibit many desirable characteristics, for example low-crystal symmetry which could lead to anisotropic carrier properties. Here, single-crystal monoclinic gallium oxide, an AlInN/GaN-based high-electron-mobility transistor (HEMT) structure, and epitaxial graphene are studied as examples. To characterize these material systems, the OHE measurement technique is employed. The OHE is a ...


Multi-Metallic Conduction Cooled Superconducting Radio-Frequency Cavity With High Thermal Stability, Gianluigi Ciovati, Gary Cheng, Uttar Pudasaini, Robert A. Rimmer Jul 2020

Multi-Metallic Conduction Cooled Superconducting Radio-Frequency Cavity With High Thermal Stability, Gianluigi Ciovati, Gary Cheng, Uttar Pudasaini, Robert A. Rimmer

Physics Faculty Publications

Superconducting radio-frequency cavities are commonly used in modern particle accelerators for applied and fundamental research. Such cavities are typically made of high-purity, bulk Nb and with cooling by a liquid helium bath at a temperature of ∼2 K. The size, cost and complexity of operating a particle accelerator with a liquid helium refrigerator make the current cavity technology not favorable for use in industrial-type accelerators. We have developed a multi-metallic 1.495 GHz elliptical cavity conductively cooled by a cryocooler. The cavity has a ∼2 μm thick layer of Nb3Sn on the inner surface, exposed to the rf ...


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.


Generalized Magnetoelectronic Circuit Theory And Spin Relaxation At Interfaces In Magnetic Multilayers, G. G. Baez Flores, Alexey Kovalev, Mark Van Schilfgaarde, K. D. Belashchenko Jun 2020

Generalized Magnetoelectronic Circuit Theory And Spin Relaxation At Interfaces In Magnetic Multilayers, G. G. Baez Flores, Alexey Kovalev, Mark Van Schilfgaarde, K. D. Belashchenko

Faculty Publications, Department of Physics and Astronomy

Spin transport at metallic interfaces is an essential ingredient of various spintronic device concepts, such as giant magnetoresistance, spin-transfer torque, and spin pumping. Spin-orbit coupling plays an important role in many such devices. In particular, spin current is partially absorbed at the interface due to spin-orbit coupling. We develop a general magnetoelectronic circuit theory and generalize the concept of spin-mixing conductance, accounting for various mechanisms responsible for spin-flip scattering. For the special case when exchange interactions dominate, we give a simple expression for the spin-mixing conductance in terms of the contributions responsible for spin relaxation (i.e., spin memory loss ...


Fabrication Of Magnetocaloric La(Fe,Si)13 Thick Films, N H. Dung, N B. Doan, P De Rango, L Ranno, Karl G. Sandeman, N M. Dempsey Jun 2020

Fabrication Of Magnetocaloric La(Fe,Si)13 Thick Films, N H. Dung, N B. Doan, P De Rango, L Ranno, Karl G. Sandeman, N M. Dempsey

Publications and Research

La(Fe,Si)13–based compounds are considered to be very promising magnetocaloric materials for magnetic refrigeration applications. Many studies have focused on this material family but only in bulk form. In this paper we report on the fabrication of thick films of La(Fe,Si)13, both with and without post-hydriding. These films exhibit magnetic and structural properties comparable to bulk materials. We also observe that the ferromagnetic phase transition has a negative thermal hysteresis, a phenomenon not previously found in this material but which may have its origins in the availability of a strain energy reservoir, as in ...


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 ...


Magnetic, Thermal, And Electronic-Transport Properties Of Eumg2bi2 Single Crystals, Santanu Pakhira, Makariy A. Tanatar, David C. Johnston Jun 2020

Magnetic, Thermal, And Electronic-Transport Properties Of Eumg2bi2 Single Crystals, Santanu Pakhira, Makariy A. Tanatar, David C. Johnston

Ames Laboratory Accepted Manuscripts

The trigonal compound EuMg2Bi2 has recently been discussed in terms of its topological band properties. These are intertwined with its magnetic properties. Here detailed studies of the magnetic, thermal, and electronic-transport properties of EuMg2Bi2 single crystals are presented. The Eu+2 spins 7/2 in EuMg2Bi2 exhibit an antiferromagnetic (AFM) transition at a temperature T-N = 6.7 K, as previously reported. By analyzing the anisotropic magnetic susceptibility chi data below T-N in terms of molecular-field theory (MFT), the AFM structure is inferred to be a c-axis helix, where the ordered moments in the hexagonal ab-plane layers are aligned ferromagnetically in ...


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 ...


Ground-State Properties Of The Hubbard Model In One And Two Dimensions From The Gutzwiller Conjugate Gradient Minimization Theory, Zhuo Ye, Feng Zhang, Yong-Xin Yao, Cai-Zhuang Wang, Kai-Ming Ho May 2020

Ground-State Properties Of The Hubbard Model In One And Two Dimensions From The Gutzwiller Conjugate Gradient Minimization Theory, Zhuo Ye, Feng Zhang, Yong-Xin Yao, Cai-Zhuang Wang, Kai-Ming Ho

Ames Laboratory Accepted Manuscripts

We introduce Gutzwiller conjugate gradient minimization (GCGM) theory, an ab initio quantum many-body theory for computing the ground-state properties of infinite systems. GCGM uses the Gutzwiller wave function but does not use the commonly adopted Gutzwiller approximation (GA), which is a major source of inaccuracy. Instead, the theory uses an approximation that is based on the occupation probability of the on-site configurations, rather than approximations that decouple the site-site correlations as used in the GA. We test the theory in the one-dimensional and two-dimensional Hubbard models at various electron densities and find that GCGM reproduces energies and double occupancies in ...


Physics 516: Electromagnetic Phenomena (Spring 2020), Philip C. Nelson May 2020

Physics 516: Electromagnetic Phenomena (Spring 2020), Philip C. Nelson

Department of Physics Papers

These course notes are made publicly available in the hope that they will be useful. All reports of errata will be gratefully received. I will also be glad to hear from anyone who reads them, whether or not you find errors: pcn@upenn.edu.


Symmetry And Interface Considerations For Interactions On Mos2, Prescott E. Evans May 2020

Symmetry And Interface Considerations For Interactions On Mos2, Prescott E. Evans

Theses, Dissertations, and Student Research: Department of Physics and Astronomy

The critical role of symmetry, in adsorbate-MoS2 interactions, has been demonstrated through a variety of electronic structure, topology, and catalytic studies of MoS2 and MoS2 composites.A combination of density functional theory and experiment exhibiting diiodobenzene isomer dependent adsorption rates highlight frontier orbital symmetry as key to adsorption on MoS2. It is clear that the geometry and symmetry of MoS2 influences the creation and stability of surface defects, that in turn affect catalytic activity and a myriad of other applications. We have shown that surface reactions such the methanol to methoxy reaction can create defects ...


First-Principles Prediction Of Incipient Order In Arbitrary High-Entropy Alloys: Exemplified In Ti0.25crfenialx, Prashant Singh, Andrei V. Smirnov, Aftab Alam, Duane D. Johnson May 2020

First-Principles Prediction Of Incipient Order In Arbitrary High-Entropy Alloys: Exemplified In Ti0.25crfenialx, Prashant Singh, Andrei V. Smirnov, Aftab Alam, Duane D. Johnson

Materials Science and Engineering Publications

Multi-principal-element alloys, including high-entropy alloys, experience segregation or partially-ordering as they are cooled to lower temperatures. For Ti0.25CrFeNiAlx, experiments suggest a partially-ordered B2 phase, whereas CALculation of PHAse Diagrams (CALPHAD) predicts a region of L21+B2 coexistence. We employ first-principles density-functional theory (DFT) based electronic-structure approach to assess stability of phases of alloys with arbitrary compositions and Bravais lattices (A1/A2/A3). In addition, DFT-based linear-response theory has been utilized to predict Warren-Cowley short-range order (SRO) in these alloys, which reveals potentially competing long-range ordered phases. The resulting SRO is uniquely analyzed using concentration-waves analysis for occupation probabilities ...


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 ...


First-Order Ferromagnetic Transitions Of Lanthanide Local Moments In Divalent Compounds: An Itinerant Electron Positive Feedback Mechanism And Fermi Surface Topological Change, Eduardo Mendive-Tapia, Durga Paudyal, Leon Petit, Julie B. Staunton May 2020

First-Order Ferromagnetic Transitions Of Lanthanide Local Moments In Divalent Compounds: An Itinerant Electron Positive Feedback Mechanism And Fermi Surface Topological Change, Eduardo Mendive-Tapia, Durga Paudyal, Leon Petit, Julie B. Staunton

Ames Laboratory Accepted Manuscripts

Around discontinuous (first-order) magnetic phase transitions, the strong caloric response of materials to the application of small fields is widely studied for the development of solid-state refrigeration. Typically strong magnetostructural coupling drives such transitions and the attendant substantial hysteresis dramatically reduces the cooling performance. In this context, we describe a purely electronic mechanism which pilots a first-order paramagnetic-ferromagnetic transition in divalent lanthanide compounds and which explains the giant nonhysteretic magnetocaloric effect recently discovered in a Eu2In compound. There is a positive feedback between the magnetism of itinerant valence electrons and the ferromagnetic ordering of local f-electron moments, which appears as ...


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.


An Analysis Of The Debate Over Creation, Evolution, And The Timeline Of The Universe At An Ecumenical Christian University, Mason Pohlman Apr 2020

An Analysis Of The Debate Over Creation, Evolution, And The Timeline Of The Universe At An Ecumenical Christian University, Mason Pohlman

Honors Theses

Throughout a significant portion of history and within modern culture, the fields of science and religion appear to be competing for the same holds in a person’s belief system. Universities are where academics and the sciences are the prevailing held truth, while in churches, the Bible reigns as supreme authority. However, in a Christian academic setting, the predominate school of thought in belief systems might turn into a little more of a melting pot. By analyzing gathered personal data (via surveys and interviews), one can begin to piece together the predominate thoughts on the apparent conflict between religion and ...


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.


Gapless Dirac Surface States In The Antiferromagnetic Topological Insulator Mnbi2 Te4, Przemyslaw Swatek, Yun Wu, Lin-Lin Wang, Kyungchan Lee, Benjamin Schrunk, Jiaqiang Yan, Adam Kaminski Apr 2020

Gapless Dirac Surface States In The Antiferromagnetic Topological Insulator Mnbi2 Te4, Przemyslaw Swatek, Yun Wu, Lin-Lin Wang, Kyungchan Lee, Benjamin Schrunk, Jiaqiang Yan, Adam Kaminski

Ames Laboratory Accepted Manuscripts

We used angle-resolved photoemission spectroscopy (ARPES) and density functional theory calculations to study the electronic properties of MnBi2Te4, a material that was predicted to be an intrinsic antiferromagnetic (AFM) topological insulator. In striking contrast to earlier literature showing a full gap opening between two surface band manifolds on the (0001) surface, we observed a gapless Dirac surface state with a Dirac point sitting at EB=−280meV. Furthermore, our ARPES data revealed the existence of a second Dirac cone sitting closer to the Fermi level. Surprisingly, these surface states remain intact across the AFM transition. The presence of gapless Dirac states ...


Magnetic Forces In The Absence Of A Classical Magnetic Field, Ismael L. Paiva, Yakir Aharonov, Jeff Tollaksen, Mordecai Waegell Apr 2020

Magnetic Forces In The Absence Of A Classical Magnetic Field, Ismael L. Paiva, Yakir Aharonov, Jeff Tollaksen, Mordecai Waegell

Mathematics, Physics, and Computer Science Faculty Articles and Research

It is shown that, in some cases, the effect of discrete distributions of flux lines in quantum mechanics can be associated with the effect of continuous distributions of magnetic fields with special symmetries. In particular, flux lines with an arbitrary value of magnetic flux can be used to create energetic barriers, which can be used to confine quantum systems in specially designed configurations. This generalizes a previous work where such energy barriers arose from flux lines with half-integer fluxons. Furthermore, it is shown how the Landau levels can be obtained from a two-dimensional grid of flux lines. These results suggest ...


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.


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.


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 ...


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 ...