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Condensed Matter Physics

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Full-Text Articles in Physics

Uncompensated Polarization In Incommensurate Modulations Of Perovskite Antiferroelectrics, Tao Ma, Zhongming Fan, Bin Xu, Tae-Hoon Kim, Ping Lu, Laurent Bellaiche, Matthew J. Kramer, Xiaoli Tan, Lin Zhou Sep 2019

Uncompensated Polarization In Incommensurate Modulations Of Perovskite Antiferroelectrics, Tao Ma, Zhongming Fan, Bin Xu, Tae-Hoon Kim, Ping Lu, Laurent Bellaiche, Matthew J. Kramer, Xiaoli Tan, Lin Zhou

Xiaoli Tan

Complex polar structures of incommensurate modulations (ICMs) are revealed in chemically modified PbZrO3 perovskite antiferroelectrics using advanced transmission electron microscopy techniques. The Pb-cation displacements, previously assumed to arrange in a fully-compensated antiparallel fashion, are found to be either antiparallel but with different magnitudes, or in a nearly orthogonal arrangement in adjacent stripes in the ICMs. Ab initio calculations corroborate the low-energy state of these arrangements. Our discovery corrects the atomic understanding of ICMs in PbZrO3-based perovskite antiferroelectrics.


Studying Near-Critical And Super-Critical Fluids In Reduced Gravity, Christian Hawkins, Ana Oprisan, Carole Lecoutre-Chabot, Yves Garrabos, Daniel Beysens Aug 2019

Studying Near-Critical And Super-Critical Fluids In Reduced Gravity, Christian Hawkins, Ana Oprisan, Carole Lecoutre-Chabot, Yves Garrabos, Daniel Beysens

Journal of the South Carolina Academy of Science

Critical and supercritical fluids have a variety of applications, from use as machine lubricants in high pressure or high temperature environments to the manufacturing of materials such as aerogel. The optical properties of fluids undergo rapid changes near the critical point resulting in a rapid increase in turbidity known as critical opalescence. These optical changes can be used to probe the universality of critical behavior. As a fluid approaches the critical point, the compressibility rapidly increases. In a gravitational field, this increase in compressibility leads to near-critical fluids stratifying by phase and density, making it difficult to observe the optical ...


Correlations Between Short- And Long-Time Relaxation In Colloidal Supercooled Liquids And Glasses, Chandan K. Mishra, Xiaoguang Ma, Piotr Habdas, Kevin B. Aptowicz, A. G. Yodh Aug 2019

Correlations Between Short- And Long-Time Relaxation In Colloidal Supercooled Liquids And Glasses, Chandan K. Mishra, Xiaoguang Ma, Piotr Habdas, Kevin B. Aptowicz, A. G. Yodh

Physics

Spatiotemporal dynamics of short- and long-time structural relaxation are measured experimentally as a function of packing fraction, φ, in quasi-two-dimensional colloidal supercooled liquids and glasses. The relaxation times associated with long-time dynamic heterogeneity and short-time intracage motion are found to be strongly correlated and to grow by orders of magnitude with increasing φ toward dynamic arrest. We find that clusters of fast particles on the two timescales often overlap, and, interestingly, the distribution of minimum-spatial-separation between closest nonoverlapping clusters across the two timescales is revealed to be exponential with a decay length that increases with φ. In total, the experimental ...


Fatigue-Resistant High-Performance Elastocaloric Materials Via Additive Manufacturing, Huilong Hou, Emrah Simsek, Tao Ma, Nathan S. Johnson, Suxin Qian, Cheikh Cissé, Drew Stasak, Naila Al Hasan, Lin Zhou, Yunho Hwang, Reinhard Radermacher, Valery I. Levitas, Matthew J. Kramer, Mohsen Asle Zaeem, Aaron P. Stebner, Ryan T. Ott, Jun Cui, Ichiro Takeuchi Aug 2019

Fatigue-Resistant High-Performance Elastocaloric Materials Via Additive Manufacturing, Huilong Hou, Emrah Simsek, Tao Ma, Nathan S. Johnson, Suxin Qian, Cheikh Cissé, Drew Stasak, Naila Al Hasan, Lin Zhou, Yunho Hwang, Reinhard Radermacher, Valery I. Levitas, Matthew J. Kramer, Mohsen Asle Zaeem, Aaron P. Stebner, Ryan T. Ott, Jun Cui, Ichiro Takeuchi

Valery I. Levitas

Elastocaloric cooling, which exploits the latent heat released and absorbed as stress-induced phase transformations are reversibly cycled in shape memory alloys, has recently emerged as a frontrunner in non-vapor-compression cooling technologies. The intrinsically high thermodynamic efficiency of elastocaloric materials is limited only by work hysteresis. Here, we report on creating high-performance low-hysteresis elastocaloric cooling materials via additive manufacturing of Titanium-Nickel (Ti-Ni) alloys. Contrary to established knowledge of the physical metallurgy of Ti-Ni alloys, intermetallic phases are found to be beneficial to elastocaloric performances when they are combined with the binary Ti-Ni compound in nanocomposite configurations. The resulting microstructure gives rise ...


Self-Consistent Two-Gap Description Of Mgb2 Superconductor, Hyunsoo Kim, Kyuil Cho, Makariy A. Tanatar, Valentin Taufour, Stella K. Kim, Sergey L. Bud’Ko, Paul C. Canfield, Vladimir G. Kogan, Ruslan Prozorov Aug 2019

Self-Consistent Two-Gap Description Of Mgb2 Superconductor, Hyunsoo Kim, Kyuil Cho, Makariy A. Tanatar, Valentin Taufour, Stella K. Kim, Sergey L. Bud’Ko, Paul C. Canfield, Vladimir G. Kogan, Ruslan Prozorov

Paul C. Canfield

A self-consistent two-gap γ -model is used to quantitatively describe several thermodynamic properties of MgB 2 superconductor. The superconducting coupling matrix, νij , was obtained from the fitting of the superfluid density in the entire superconducting temperature range. Using this input, temperature-dependent superconducting gaps, specific heat, and upper critical fields were calculated with no adjustable parameters and compared with the experimental data as well as with the first-principles calculations. The observed agreement between fit and data shows that γ -model provides adequate quantitative description of the two-gap superconductivity in MgB 2 and may serve as a relatively simple and versatile self-consistent ...


Composition-Dependent Stability Of The Medium-Range Order Responsible For Metallic Glass Formation, Feng Zhang, Min Ji, Xiao-Wei Fang, Yang Sun, Cai-Zhuang Wang, Mikhail I. Mendelev, Matthew J. Kramer, Ralph E. Napolitano, Kai-Ming Ho Aug 2019

Composition-Dependent Stability Of The Medium-Range Order Responsible For Metallic Glass Formation, Feng Zhang, Min Ji, Xiao-Wei Fang, Yang Sun, Cai-Zhuang Wang, Mikhail I. Mendelev, Matthew J. Kramer, Ralph E. Napolitano, Kai-Ming Ho

Ralph E. Napolitano

The competition between the characteristic medium-range order corresponding to amorphous alloys and that in ordered crystalline phases is central to phase selection and morphology evolution under various processing conditions. We examine the stability of a model glass system, Cu–Zr, by comparing the energetics of various medium-range structural motifs over a wide range of compositions using first-principles calculations. We focus specifically on motifs that represent possible building blocks for competing glassy and crystalline phases, and we employ a genetic algorithm to efficiently identify the energetically favored decorations of each motif for specific compositions. Our results show that a Bergman-type motif ...


A Computational Study Of Diffusion In A Glass-Forming Metallic Liquid, T. Wang, F. Zhang, L. Yang, X. W. Fang, S. H. Zhou, Matthew J. Kramer, Cai-Zhuang Wang, Kai-Ming Ho, Ralph E. Napolitano Aug 2019

A Computational Study Of Diffusion In A Glass-Forming Metallic Liquid, T. Wang, F. Zhang, L. Yang, X. W. Fang, S. H. Zhou, Matthew J. Kramer, Cai-Zhuang Wang, Kai-Ming Ho, Ralph E. Napolitano

Ralph E. Napolitano

Liquid phase diffusion plays a critical role in phase transformations (e.g. glass transformation and devitrification) observed in marginal glass forming systems such as Al-Sm. Controlling transformation pathways in such cases requires a comprehensive description of diffusivity, including the associated composition and temperature dependencies. In the computational study reported here, we examine atomic diffusion in Al-Sm liquids using ab initio molecular dynamics (AIMD) and determine the diffusivities of Al and Sm for selected alloy compositions. Non-Arrhenius diffusion behavior is observed in the undercooled liquids with an enhanced local structural ordering. Through assessment of our AIMD result, we construct a general ...


A Diffraction Paradox: An Unusually Broad Diffraction Background Signals Ideal Graphene, Shen Chen, Michael Horn-Von Hoegen, Patricia A. Thiel, Michael C. Tringides Aug 2019

A Diffraction Paradox: An Unusually Broad Diffraction Background Signals Ideal Graphene, Shen Chen, Michael Horn-Von Hoegen, Patricia A. Thiel, Michael C. Tringides

Patricia A. Thiel

The realization of the unusual properties of 2-d materials requires the formation of large domains of single layer thickness, extending over the mesoscale. It is found that the formation of ideal graphene on SiC, contrary to textbook diffraction , is signaled by a strong bell-shaped-component (BSC) around the (00) and G(10), but not the SiC(10) spots.The BSC is also seen for graphene on metals, because single layer uniform graphene with large lateral size can also be grown. It is only seen by electron diffraction and not with X-ray or He-scattering experiments. Most likely it originates from the spatial ...


Fatigue-Resistant High-Performance Elastocaloric Materials Via Additive Manufacturing, Huilong Hou, Emrah Simsek, Tao Ma, Nathan S. Johnson, Suxin Qian, Cheikh Cissé, Drew Stasak, Naila Al Hasan, Lin Zhou, Yunho Hwang, Reinhard Radermacher, Valery I. Levitas, Matthew J. Kramer, Mohsen Asle Zaeem, Aaron P. Stebner, Ryan T. Ott, Jun Cui, Ichiro Takeuchi Aug 2019

Fatigue-Resistant High-Performance Elastocaloric Materials Via Additive Manufacturing, Huilong Hou, Emrah Simsek, Tao Ma, Nathan S. Johnson, Suxin Qian, Cheikh Cissé, Drew Stasak, Naila Al Hasan, Lin Zhou, Yunho Hwang, Reinhard Radermacher, Valery I. Levitas, Matthew J. Kramer, Mohsen Asle Zaeem, Aaron P. Stebner, Ryan T. Ott, Jun Cui, Ichiro Takeuchi

Aerospace Engineering Publications

Elastocaloric cooling, which exploits the latent heat released and absorbed as stress-induced phase transformations are reversibly cycled in shape memory alloys, has recently emerged as a frontrunner in non-vapor-compression cooling technologies. The intrinsically high thermodynamic efficiency of elastocaloric materials is limited only by work hysteresis. Here, we report on creating high-performance low-hysteresis elastocaloric cooling materials via additive manufacturing of Titanium-Nickel (Ti-Ni) alloys. Contrary to established knowledge of the physical metallurgy of Ti-Ni alloys, intermetallic phases are found to be beneficial to elastocaloric performances when they are combined with the binary Ti-Ni compound in nanocomposite configurations. The resulting microstructure gives rise ...


Strongly Correlated Systems Under High Magnetic Field: A Mixed Landau Levels Description For Fractional Quantum Hall Effect, Sumanta Bandyopadhyay Aug 2019

Strongly Correlated Systems Under High Magnetic Field: A Mixed Landau Levels Description For Fractional Quantum Hall Effect, Sumanta Bandyopadhyay

Arts & Sciences Electronic Theses and Dissertations

Strong correlation among electrons under high magnetic field gives rise to an entirely new arena of emergent physics, namely fractional quantum Hall effect. Such systems have entirely different elementary degrees of freedom and generally, demand non-perturbative approaches to develop a better understanding. In the literature, there are several analytical methodologies and numerical toolkits available to study such a system. Clustering of zeros, parent Hamiltonian, off-diagonal order parameter, parton construction, matrix product states are to be named among a few of those popular methodologies in the existing literature. Most of these methods work well in the lowest Landau level or holomorphic ...


Tuning Phase-Stability And Short-Range Order Through Ai-Doping In (Cocrfemn)100-Xaix High Entropy Alloys, Prashant Singh, Amalraj Marshal, Andrei V. Smirnov, Aayush Sharma, Ganesh Balasubramanian, K. G. Pradeep, Duane D. Johnson Aug 2019

Tuning Phase-Stability And Short-Range Order Through Ai-Doping In (Cocrfemn)100-Xaix High Entropy Alloys, Prashant Singh, Amalraj Marshal, Andrei V. Smirnov, Aayush Sharma, Ganesh Balasubramanian, K. G. Pradeep, Duane D. Johnson

Ganesh Balasubramanian

For (CoCrFeMn)100−xAlx high-entropy alloys, we investigate the phase evolution with increasing Al content (0≤x≤20 at.%). From first-principles theory, aluminum doping drives the alloy structurally from fcc to bcc separated by a narrow two-phase region (fcc+bcc), which is well supported by our experiments. Using KKR-CPA electronic-structure calculations, we highlight the effect of Al doping on the formation enthalpy (alloy stability) and electronic dispersion of (CoCrFeMn)100−xAlx alloys. As chemical short-range order indicates the nascent local order, and entropy changes, as well as expected low-temperature ordering behavior, we use KKR-CPA-based thermodynamic linear response to predict the ...


Dependence Of The Absolute Value Of The Penetration Depth In (Ba1–X Kx) Fe2 As2 On Doping, Avior Almoalem, Alon Yagil, Kyuil Cho, Serafim Teknowijoyo, Makariy A. Tanatar, Ruslan Prozorov, Yong Liu, Thomas A. Lograsso, Ophir M. Auslaender Aug 2019

Dependence Of The Absolute Value Of The Penetration Depth In (Ba1–X Kx) Fe2 As2 On Doping, Avior Almoalem, Alon Yagil, Kyuil Cho, Serafim Teknowijoyo, Makariy A. Tanatar, Ruslan Prozorov, Yong Liu, Thomas A. Lograsso, Ophir M. Auslaender

Thomas A. Lograsso

We report magnetic force microscopy (MFM) measurements on the iron-based superconductor Ba1−xKxFe2As2. By measuring locally the Meissner repulsion with the magnetic MFM tip, we determine the absolute value of the in-plane magnetic penetration depth (λab) in underdoped, optimally doped, and overdoped samples. The results suggest an abrupt increase of λab as doping is increased from xopt, which is potentially related to the presence of a quantum critical point. The response of superconducting vortices to magnetic forces exerted by the MFM tip for x=0.19 and 0.58 is compatible with previously observed structural symmetries at those doping levels.


Self-Consistent Two-Gap Description Of Mgb2 Superconductor, Hyunsoo Kim, Kyuil Cho, Makariy A. Tanatar, Valentin Taufour, Stella K. Kim, Sergey L. Bud’Ko, Paul C. Canfield, Vladimir G. Kogan, Ruslan Prozorov Aug 2019

Self-Consistent Two-Gap Description Of Mgb2 Superconductor, Hyunsoo Kim, Kyuil Cho, Makariy A. Tanatar, Valentin Taufour, Stella K. Kim, Sergey L. Bud’Ko, Paul C. Canfield, Vladimir G. Kogan, Ruslan Prozorov

Ames Laboratory Accepted Manuscripts

A self-consistent two-gap γ -model is used to quantitatively describe several thermodynamic properties of MgB 2 superconductor. The superconducting coupling matrix, νij , was obtained from the fitting of the superfluid density in the entire superconducting temperature range. Using this input, temperature-dependent superconducting gaps, specific heat, and upper critical fields were calculated with no adjustable parameters and compared with the experimental data as well as with the first-principles calculations. The observed agreement between fit and data shows that γ -model provides adequate quantitative description of the two-gap superconductivity in MgB 2 and may serve as a relatively simple and versatile self-consistent ...


Computational Studies Of Thermal Properties And Desalination Performance Of Low-Dimensional Materials, Yang Hong Aug 2019

Computational Studies Of Thermal Properties And Desalination Performance Of Low-Dimensional Materials, Yang Hong

Student Research Projects, Dissertations, and Theses - Chemistry Department

During the last 30 years, microelectronic devices have been continuously designed and developed with smaller size and yet more functionalities. Today, hundreds of millions of transistors and complementary metal-oxide-semiconductor cells can be designed and integrated on a single microchip through 3D packaging and chip stacking technology. A large amount of heat will be generated in a limited space during the operation of microchips. Moreover, there is a high possibility of hot spots due to non-uniform integrated circuit design patterns as some core parts of a microchip work harder than other memory parts. This issue becomes acute as stacked microchips get ...


Non-Fermi-Liquid Behaviors Associated With A Magnetic Quantum-Critical Point In Sr(Co{1-X}Ni{X})2as2 Single Crystals, Nediadath S. Sangeetha, Lin-Lin Wang, Andrei V. Smirnov, Volodymyr Smetana, A.-V. Mudring, Duane D. Johnson, Makariy A. Tanatar, Ruslan Prozorov, David C. Johnston Jul 2019

Non-Fermi-Liquid Behaviors Associated With A Magnetic Quantum-Critical Point In Sr(Co{1-X}Ni{X})2as2 Single Crystals, Nediadath S. Sangeetha, Lin-Lin Wang, Andrei V. Smirnov, Volodymyr Smetana, A.-V. Mudring, Duane D. Johnson, Makariy A. Tanatar, Ruslan Prozorov, David C. Johnston

Duane D. Johnson

Electron-doped Sr(Co{1-x}Ni{x})2As2 single crystals with compositions x = 0 to 0.9 were grown out of self-flux and SrNi2As2 single crystals out of Bi flux. The crystals were characterized using single-crystal x-ray diffraction (XRD), magnetic susceptibility chi(H,T), isothermal magnetization M(H,T), heat capacity Cp(H,T), and electrical resistivity ho(H,T) measurements versus applied magnetic field H and temperature T. The chi(T) data show that the crystals exhibit an antiferromagnetic (AFM) ground state almost immediately upon Ni doping on the Co site. Ab-initio electronic-structure calculations for x = 0 and x = 0 ...


Hole Doping And Antiferromagnetic Correlations Above The Néel Temperature Of The Topological Semimetal (Sr1-X Kx) Mnsb2, Yong Liu, Farhan Islam, Kevin W. Dennis, Wei Tian, Benjamin G. Ueland, Robert J. Mcqueeney, David Vaknin Jul 2019

Hole Doping And Antiferromagnetic Correlations Above The Néel Temperature Of The Topological Semimetal (Sr1-X Kx) Mnsb2, Yong Liu, Farhan Islam, Kevin W. Dennis, Wei Tian, Benjamin G. Ueland, Robert J. Mcqueeney, David Vaknin

Ames Laboratory Accepted Manuscripts

Neutron diffraction and magnetic susceptibility studies of orthorhombic single crystal (Sr0.97K0.03)MnSb2 confirm the three-dimensional (3D) C-type antiferromagnetic (AFM) ordering of the Mn2+ moments at TN=305±3 K, which is slightly higher than that of the parent SrMnSb2 with TN=297±3 K. Susceptibility measurements of the K-doped and parent crystals above TN are characteristic of 2D AFM systems. This is consistent with high-temperature neutron diffraction of the parent compound that displays persisting 2D AFM correlations well above TN to at least ∼560 K with no evidence of a ferromagnetic phase. Analysis of the de Haas–van ...


Single Pair Of Weyl Fermions In The Half-Metallic Semimetal Eucd2as2, Lin-Lin Wang, Na Hyun Jo, Brinda Kuthanazhi, Yun Wu, Robert J. Mcqueeney, Adam Kaminski, Paul C. Canfield Jul 2019

Single Pair Of Weyl Fermions In The Half-Metallic Semimetal Eucd2as2, Lin-Lin Wang, Na Hyun Jo, Brinda Kuthanazhi, Yun Wu, Robert J. Mcqueeney, Adam Kaminski, Paul C. Canfield

Paul C. Canfield

Materials with the ideal case of a single pair of Weyl points (WPs) are highly desirable for elucidating the unique properties of Weyl fermions. EuC d 2 A s 2 is an antiferromagnetic topological insulator or Dirac semimetal depending on the different magnetic configurations. Using first-principles band-structure calculations, we show that inducing ferromagnetism in EuC d 2 A s 2 can generate a single pair of WPs from splitting the single pair of antiferromagnetic Dirac points due to its half-metallic nature. Analysis with a low-energy effective Hamiltonian shows that a single pair of WPs is obtained in EuC d 2 ...


Temperature-Dependent Anisotropies Of Upper Critical Field And London Penetration Depth, V. G. Kogan, Ruslan Prozorov, A. E. Koshelev Jul 2019

Temperature-Dependent Anisotropies Of Upper Critical Field And London Penetration Depth, V. G. Kogan, Ruslan Prozorov, A. E. Koshelev

Ames Laboratory Accepted Manuscripts

We show on a few examples of one-band materials with spheroidal Fermi surfaces and anisotropic order parameters that anisotropies γH of the upper critical field and γλ of the London penetration depth depend on temperature, a feature commonly attributed to multiband superconductors. The parameters γH and γλ may have opposite temperature dependences or may change in the same direction depending on the Fermi-surface shape and on the character of the gap nodes. For two-band systems, the behavior of anisotropies is affected by the ratios of bands densities of states, Fermi velocities, anisotropies, and order parameters. We investigate in detail the ...


Electronic Structure Of The Topological Superconductor Candidate Au2pb, Yun Wu, Gil Drachuck, Lin-Lin Wang, Duane D. Johnson, Przemyslaw Swatek, Benjamin Schrunk, Daixiang Mou, Lunan Huang, Sergey L. Bud’Ko, Paul C. Canfield, Adam Kaminski Jul 2019

Electronic Structure Of The Topological Superconductor Candidate Au2pb, Yun Wu, Gil Drachuck, Lin-Lin Wang, Duane D. Johnson, Przemyslaw Swatek, Benjamin Schrunk, Daixiang Mou, Lunan Huang, Sergey L. Bud’Ko, Paul C. Canfield, Adam Kaminski

Duane D. Johnson

We use magnetization measurements, high-resolution angle-resolved photoemission spectroscopy (ARPES), and density functional theory (DFT) calculations to study the electronic properties of Au2Pb, a topological superconductor candidate. The magnetization measurements reveal three discontinuities at 40, 51, and 99 K that agree well with reported structural phase transitions. To measure the band structure along desired crystal orientations, we utilized polishing, sputtering, and annealing to obtain clean flat sample surfaces. ARPES measurements of the Au2Pb (111) surface at 110 K shows a shallow hole pocket at the center and flower-petal-like surface states at the corners of the Brillouin zone. These observations match the ...


Electronic Structure Of The Topological Superconductor Candidate Au2pb, Yun Wu, Gil Drachuck, Lin-Lin Wang, Duane D. Johnson, Przemyslaw Swatek, Benjamin Schrunk, Daixiang Mou, Lunan Huang, Sergey L. Bud’Ko, Paul C. Canfield, Adam Kaminski Jul 2019

Electronic Structure Of The Topological Superconductor Candidate Au2pb, Yun Wu, Gil Drachuck, Lin-Lin Wang, Duane D. Johnson, Przemyslaw Swatek, Benjamin Schrunk, Daixiang Mou, Lunan Huang, Sergey L. Bud’Ko, Paul C. Canfield, Adam Kaminski

Paul C. Canfield

We use magnetization measurements, high-resolution angle-resolved photoemission spectroscopy (ARPES), and density functional theory (DFT) calculations to study the electronic properties of Au2Pb, a topological superconductor candidate. The magnetization measurements reveal three discontinuities at 40, 51, and 99 K that agree well with reported structural phase transitions. To measure the band structure along desired crystal orientations, we utilized polishing, sputtering, and annealing to obtain clean flat sample surfaces. ARPES measurements of the Au2Pb (111) surface at 110 K shows a shallow hole pocket at the center and flower-petal-like surface states at the corners of the Brillouin zone. These observations match the ...


High-Tc Superconductivity In Cakfe4 As4 In Absence Of Nematic Fluctuations, W.-L. Zhang, William R. Meier, Tai Kong, Paul C. Canfield, G. Blumberg Jul 2019

High-Tc Superconductivity In Cakfe4 As4 In Absence Of Nematic Fluctuations, W.-L. Zhang, William R. Meier, Tai Kong, Paul C. Canfield, G. Blumberg

Paul C. Canfield

We employ polarization-resolved Raman spectroscopy to study the multiband stoichiometric Tc = 35 K superconductor CaKFe4As4. We do not detect Pomeranchuk-like electronic nematic fluctuations which were universally observed in the XY (B2g) symmetry Raman response for most families of the Fe-based superconductors. In the superconducting state we observe, consistent with a nodeless order parameter, a full spectral weight suppression at low energies and the emergence of a composite pair-breaking coherence feature at energies between 12 and 20 meV. We analyze the superconductivity-induced phonon self-energy effects and give an estimation for the electron-phonon coupling constant λΓ=0.0015 which is insufficient ...


Ultrahigh Elastically Compressible And Strain-Engineerable Intermetallic Compounds Under Uniaxial Mechanical Loading, Gyuho Song, Vladislav Borisov, William Meier, Mingyu Xu, Keith J. Dusoe, John T. Sypek, Roser Valentí, Paul C. Canfield, Seok-Woo Lee Jul 2019

Ultrahigh Elastically Compressible And Strain-Engineerable Intermetallic Compounds Under Uniaxial Mechanical Loading, Gyuho Song, Vladislav Borisov, William Meier, Mingyu Xu, Keith J. Dusoe, John T. Sypek, Roser Valentí, Paul C. Canfield, Seok-Woo Lee

Paul C. Canfield

Intermetallic compounds possess unique atomic arrangements that often lead to exceptional material properties, but their extreme brittleness usually causes fracture at a limited strain of less than 1% and prevents their practical use. Therefore, it is critical for them to exhibit either plasticity or some form of structural transition to absorb and release a sufficient amount of mechanical energy before failure occurs. This study reports that the ThCr2Si2-structured intermetallic compound (CaFe2As2) and a hybrid of its structure (CaKFe4As4) with 2 µm in diameter and 6 µm in height can exhibit superelasticity with strain up to 17% through a reversible, deformation-induced ...


Lack Of Superconductivity In The Phase Diagram Of Single-Crystalline Eu(Fe1-Xcox)(2)As-2 Grown By Transition Metal Arsenide Flux, Gang Wang, William R. Meier, Warren E. Straszheim, Joshua Slagle, Sergey L. Bud’Ko, Paul C. Canfield Jul 2019

Lack Of Superconductivity In The Phase Diagram Of Single-Crystalline Eu(Fe1-Xcox)(2)As-2 Grown By Transition Metal Arsenide Flux, Gang Wang, William R. Meier, Warren E. Straszheim, Joshua Slagle, Sergey L. Bud’Ko, Paul C. Canfield

Paul C. Canfield

The interplay of magnetism and superconductivity (SC) has been a focus of interest in condensed matter physics for decades. EuF e 2 A s 2 has been identified as a potential platform to investigate interactions between structural, magnetic, and electronic effects as well as the coexistence of magnetism and SC with similar transition temperatures. However, there are obvious inconsistencies in the reported phase diagrams of Eu ( F e 1 − x C o x ) 2 A s 2 crystals grown by different methods. For transition metal arsenide (TMA)-flux-grown crystals, even the existence of SC is uncertain. Here we reexamine the ...


Tuning Phase-Stability And Short-Range Order Through Ai-Doping In (Cocrfemn)100-Xaix High Entropy Alloys, Prashant Singh, Amalraj Marshal, Andrei V. Smirnov, Aayush Sharma, Ganesh Balasubramanian, K. G. Pradeep, Duane D. Johnson Jul 2019

Tuning Phase-Stability And Short-Range Order Through Ai-Doping In (Cocrfemn)100-Xaix High Entropy Alloys, Prashant Singh, Amalraj Marshal, Andrei V. Smirnov, Aayush Sharma, Ganesh Balasubramanian, K. G. Pradeep, Duane D. Johnson

Duane D. Johnson

For (CoCrFeMn)100−xAlx high-entropy alloys, we investigate the phase evolution with increasing Al content (0≤x≤20 at.%). From first-principles theory, aluminum doping drives the alloy structurally from fcc to bcc separated by a narrow two-phase region (fcc+bcc), which is well supported by our experiments. Using KKR-CPA electronic-structure calculations, we highlight the effect of Al doping on the formation enthalpy (alloy stability) and electronic dispersion of (CoCrFeMn)100−xAlx alloys. As chemical short-range order indicates the nascent local order, and entropy changes, as well as expected low-temperature ordering behavior, we use KKR-CPA-based thermodynamic linear response to predict the ...


Enhanced Thermoelectric Performance Of Mg2 Si1−X Snx Codoped With Bi And Cr, Vikram, Duane D. Johnson, Aftab Alam Jul 2019

Enhanced Thermoelectric Performance Of Mg2 Si1−X Snx Codoped With Bi And Cr, Vikram, Duane D. Johnson, Aftab Alam

Duane D. Johnson

Magnesium silicides are favorable thermoelectric materials considering resource abundance and cost. Chromium (Cr) doping in magnesium silicides has not yet been explored. Using first-principles calculations, we have studied the stability of Mg2Si with chromium (1.85, 3.7, 5.55, and 6.25% Cr) and tin (12.5 and 50% Sn). Three Mg2Si compounds doped with Sn, (Sn + Bi), and (Sn + Bi + Cr) are used to explain doping effects on thermoelectric performance. Notably, Cr behaves nonmagnetically for ≤2%Cr, after which ferromagnetic ordering is favored (≤12.96% Cr), despite its elemental antiferromagnetic state. With alloying of Sn (70.4%), Mg2Si ...


Two-Dimensional Ordering And Collective Magnetic Excitations In The Dilute Ferromagnetic Topological Insulator (Bi0.95 Mn0.05)2 Te3, David Vaknin, Daniel M. Pajerowski, Deborah L. Schlagel, Kevin W. Dennis, Robert Mcqueeney Jul 2019

Two-Dimensional Ordering And Collective Magnetic Excitations In The Dilute Ferromagnetic Topological Insulator (Bi0.95 Mn0.05)2 Te3, David Vaknin, Daniel M. Pajerowski, Deborah L. Schlagel, Kevin W. Dennis, Robert Mcqueeney

Deborah L. Schlagel

Employing elastic and inelastic neutron scattering (INS) techniques, we report on the microscopic properties of the ferromagnetism in the dilute magnetic topological insulator (Bi0.95Mn0.05)2 Te3. Neutron diffraction of polycrystalline samples shows the ferromagnetic (FM) ordering is long range within the basal plane, and mainly two dimensional (2D) in character with short-range correlations between layers below T C ≈ 13 K. Remarkably, we observe gapped and collective magnetic excitations in this dilute magnetic system. The excitations appear typical of quasi-2D FM systems despite the severe broadening of short-wavelength magnons which is expected from the random spatial distribution of Mn ...


Anisotropy And Orbital Moment In Sm-Co Permanent Magnets, Bhaskar Das, Renu Choudhary, Ralph Skomski, Balamurugan Balasubramanian, Arjun K. Pathak, Durga Paudyal, David J. Sellmyer Jul 2019

Anisotropy And Orbital Moment In Sm-Co Permanent Magnets, Bhaskar Das, Renu Choudhary, Ralph Skomski, Balamurugan Balasubramanian, Arjun K. Pathak, Durga Paudyal, David J. Sellmyer

Ames Laboratory Accepted Manuscripts

Structural and magnetic properties of iron-free and iron-substituted SmCo5 have been investigated theoretically and experimentally. The nanocrystalline ribbons of SmCo5−xFex(0≤x≤2), which were produced by rapid solidification, crystallize in the hexagonal CaCu5 structure for x≤0.75. Small Fe additions (x=0.25) substantially improve the coercivity, from 0.45 to 2.70 T, which we interpret as combined intrinsic and extrinsic effect. Most of our findings are consistent with past samarium-cobalt research, but some are at odds with findings that have seemingly been well established through decades of rare-earth transition-metal research. In particular, our local spin-density ...


Antiferromagnetic Stacking Of Ferromagnetic Layers And Doping-Controlled Phase Competition In Ca1−X Srx Co2−Y As2, Bing Li, Yuriy Sizyuk, Nediadath S. Sangeetha, John M. Wilde, Pinaki Das, W. Tian, David C. Johnston, Alan I. Goldman, Andreas Kreyssig, Peter P. Orth, Robert J. Mcqueeney, Benjamin G. Ueland Jul 2019

Antiferromagnetic Stacking Of Ferromagnetic Layers And Doping-Controlled Phase Competition In Ca1−X Srx Co2−Y As2, Bing Li, Yuriy Sizyuk, Nediadath S. Sangeetha, John M. Wilde, Pinaki Das, W. Tian, David C. Johnston, Alan I. Goldman, Andreas Kreyssig, Peter P. Orth, Robert J. Mcqueeney, Benjamin G. Ueland

Ames Laboratory Accepted Manuscripts

In search of a quantum phase transition between the two-dimensional (2D) ferromagnetism of CaCo2−yAs2 and stripe-type antiferromagnetism in SrCo2 As2, we instead find evidence for 1D magnetic frustration between magnetic square Co layers. We present neutron-diffraction data for Ca1−x Srx Co2−y As2 that reveal a sequence of x -dependent magnetic transitions which involve different stacking of 2 D ferromagnetically aligned layers with different magnetic anisotropy. We explain the x-dependent changes to the magnetic order by utilizing classical analytical calculations of a 1D Heisenberg model where single-ion magnetic anisotropy and frustration of antiferromagnetic nearest- and next-nearest-layer exchange interactions ...


Tuning Phase-Stability And Short-Range Order Through Ai-Doping In (Cocrfemn)100-Xaix High Entropy Alloys, Prashant Singh, Amalraj Marshal, A. V. Smirnov, Aayush Sharma, Ganesh Balasubramanian, K. G. Pradeep, Duane D. Johnson Jul 2019

Tuning Phase-Stability And Short-Range Order Through Ai-Doping In (Cocrfemn)100-Xaix High Entropy Alloys, Prashant Singh, Amalraj Marshal, A. V. Smirnov, Aayush Sharma, Ganesh Balasubramanian, K. G. Pradeep, Duane D. Johnson

Ames Laboratory Accepted Manuscripts

For (CoCrFeMn)100−xAlx high-entropy alloys, we investigate the phase evolution with increasing Al content (0≤x≤20 at.%). From first-principles theory, aluminum doping drives the alloy structurally from fcc to bcc separated by a narrow two-phase region (fcc+bcc), which is well supported by our experiments. Using KKR-CPA electronic-structure calculations, we highlight the effect of Al doping on the formation enthalpy (alloy stability) and electronic dispersion of (CoCrFeMn)100−xAlx alloys. As chemical short-range order indicates the nascent local order, and entropy changes, as well as expected low-temperature ordering behavior, we use KKR-CPA-based thermodynamic linear response to predict the ...


Effect Of Nickel Substitution On Magnetism In The Layered Van Der Waals Ferromagnet Fe3 Gete2, Gil Drachuck, Zaher Salman, Morgan W. Masters, Valentin Taufour, Tej Lamichhane, Qisheng Lin, Warren E. Straszheim, Sergey L. Bud’Ko, Paul C. Canfield Jul 2019

Effect Of Nickel Substitution On Magnetism In The Layered Van Der Waals Ferromagnet Fe3 Gete2, Gil Drachuck, Zaher Salman, Morgan W. Masters, Valentin Taufour, Tej Lamichhane, Qisheng Lin, Warren E. Straszheim, Sergey L. Bud’Ko, Paul C. Canfield

Qisheng Lin

We have grown a series of nickel-substituted single crystals of the layered ferromagnet (FM) Fe3GeTe2. The large single-crystalline samples of (Fe1−xNix)3GeTe2 with x=0–0.84 were characterized with single-crystal x-ray diffraction, magnetic susceptibility, electrical resistance, and muon spin spectroscopy. We find Fe can be continuously substituted with Ni with only a minor structural variation. In addition, FM order is suppressed from TC=212K for x=0 down to TC=50Kfor x=0.3, which is accompanied by a strong suppression of saturated and effective moments, and Curie-Weiss temperature. Beyond x=0.3, the FM order is continuously ...