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Condensed Matter Physics

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Full-Text Articles in Physics

In Situ Investigation Of Magnetism In Metastable Phases Of Levitated Fe83b17 During Solidification, D. G. Quirinale, D. Messina, G. E. Rustan, Andreas Kreyssig, Ruslan Prozorov, Alan I. Goldman Oct 2019

In Situ Investigation Of Magnetism In Metastable Phases Of Levitated Fe83b17 During Solidification, D. G. Quirinale, D. Messina, G. E. Rustan, Andreas Kreyssig, Ruslan Prozorov, Alan I. Goldman

A. I. Goldman

In situ measurements of structure, density, and magnetization on samples of Fe83B17 using an electrostatic levitation furnace allow us to identify and correlate the magnetic and structural transitions in this system during its complex solidification process. In particular, we identify magnetic ordering in the metastable Fe23B6/ fcc Fe coherently grown structures and primitive tetragonal Fe3B metastable phase in addition to characterizing the equilibrium Fe2B phase. Our measurements demonstrate that the incorporation of a tunnel-diode oscillator circuit within an electrostatic levitation furnace enables investigations of the physical properties of high-temperature metastable structures.


Distinct Pressure Evolution Of Coupled Nematic And Magnetic Orders In Fese, Anna E. Böhmer, Karunakar Kothapalli, Wageesha T. Jayasekara, John M. Wilde, Bing Li, Aashish Sapkota, Benjamin G. Ueland, Pinaki Das, Yumin Xiao, Wenli Bi, Jiyong Zhao, E. Ercan Alp, Sergey L. Bud’Ko, Paul C. Canfield, Alan I. Goldman, Andreas Kreyssig Oct 2019

Distinct Pressure Evolution Of Coupled Nematic And Magnetic Orders In Fese, Anna E. Böhmer, Karunakar Kothapalli, Wageesha T. Jayasekara, John M. Wilde, Bing Li, Aashish Sapkota, Benjamin G. Ueland, Pinaki Das, Yumin Xiao, Wenli Bi, Jiyong Zhao, E. Ercan Alp, Sergey L. Bud’Ko, Paul C. Canfield, Alan I. Goldman, Andreas Kreyssig

A. I. Goldman

We present a microscopic study of nematicity and magnetism in FeSe over a wide temperature and pressure range using high-energy x-ray diffraction and time-domain Mössbauer spectroscopy. The low-temperature magnetic hyperfine field increases monotonically up to ∼ 6 GPa. The orthorhombic distortion initially decreases under increasing pressure but is stabilized at intermediate pressures by cooperative coupling to the pressure-induced magnetic order. Close to the reported maximum of the superconducting critical temperature at p = 6.8 GPa , the orthorhombic distortion suddenly disappears and a new tetragonal magnetic phase occurs. The pressure and temperature evolution of the structural and magnetic order parameters suggests that ...


Heisenberg Model Analysis On Inelastic Powder Neutron Scattering Data Using Parent And K Doped Bamn2as2 Samples, Mehmet Ramazanoglu, Aashish Sapkota, Abhishek Pandey, Jagat Lamsal, Douglas L. Abernathy, Jennifer L. Niedziela, Matthew B. Stone, R. Salci, D. A. Acar, F. O. Oztirpan, Şener Ozonder, Andreas Kreyssig, Alan I. Goldman, David C. Johnston, Robert J. Mcqueeney Oct 2019

Heisenberg Model Analysis On Inelastic Powder Neutron Scattering Data Using Parent And K Doped Bamn2as2 Samples, Mehmet Ramazanoglu, Aashish Sapkota, Abhishek Pandey, Jagat Lamsal, Douglas L. Abernathy, Jennifer L. Niedziela, Matthew B. Stone, R. Salci, D. A. Acar, F. O. Oztirpan, Şener Ozonder, Andreas Kreyssig, Alan I. Goldman, David C. Johnston, Robert J. Mcqueeney

A. I. Goldman

Low temperature powder inelastic neutron scattering measurements were performed on three different powder samples; parent BaMn2As2,12.5% K-doped Ba0.875K0.125Mn2As2 and 25% K-doped Ba(0.75)K0.25Mn2As2. The Heisenberg Model involving J1‐J2‐Jz coupling constants were compared to the data by a powder integration routine using Monte Carlo integration methods. The best magnetic parameters were selected using a chi-square test where model intensities were compared to the full (q,E) dependence of magnetic scattering. A key step to this analysis is the characterization of the background which is formed mostly by phonon scattering intensities along with ...


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 Oct 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

A. I. Goldman

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 ...


Crystal Growth, Microstructure, And Physical Properties Of Srmnsb2, Yong Liu, Tao Ma, Warren E. Straszheim, Farhan Islam, Brandt A. Jensen, Wei Tian, Thomas Heitmann, R. A. Rosenberg, John M. Wilde, Bing Li, Andreas Kreyssig, Alan I. Goldman, Benjamin G. Ueland, Robert J. Mcqueeney, David Vaknin Oct 2019

Crystal Growth, Microstructure, And Physical Properties Of Srmnsb2, Yong Liu, Tao Ma, Warren E. Straszheim, Farhan Islam, Brandt A. Jensen, Wei Tian, Thomas Heitmann, R. A. Rosenberg, John M. Wilde, Bing Li, Andreas Kreyssig, Alan I. Goldman, Benjamin G. Ueland, Robert J. Mcqueeney, David Vaknin

A. I. Goldman

We report on the crystal and magnetic structures and magnetic and transport properties of SrMnSb2 single crystals grown by the self-flux method. Magnetic susceptibility measurements reveal an antiferromagnetic (AFM) transition at TN=295(3) K. Above TN, the susceptibility slightly increases and forms a broad peak at T∼420 K, which is a typical feature of two-dimensional magnetic systems. Neutron diffraction measurements on single crystals confirm the previously reported C-type AFM structure below TN. Both de Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) effects are observed in SrMnSb2 single crystals. Analysis of the oscillatory component by a Fourier transform shows ...


Competing Magnetic Phases And Itinerant Magnetic Frustration In Srco2 As2, Bing Li, Benjamin G. Ueland, W. T. Jayasekara, D. L. Abernathy, N. S. Sangeetha, David C. Johnston, Qing-Ping Ding, Yuji Furukawa, Peter P. Orth, Andreas Kreyssig, Alan I. Goldman, Robert J. Mcqueeney Oct 2019

Competing Magnetic Phases And Itinerant Magnetic Frustration In Srco2 As2, Bing Li, Benjamin G. Ueland, W. T. Jayasekara, D. L. Abernathy, N. S. Sangeetha, David C. Johnston, Qing-Ping Ding, Yuji Furukawa, Peter P. Orth, Andreas Kreyssig, Alan I. Goldman, Robert J. Mcqueeney

A. I. Goldman

Whereas magnetic frustration is typically associated with local-moment magnets in special geometric arrangements, here we show that SrCo2As2 is a candidate for frustrated itinerant magnetism. Using inelastic neutron scattering (INS), we find that antiferromagnetic (AF) spin fluctuations develop in the square Co layers of SrCo2As2 below T approximate to 100 K centered at the stripe-type AF propagation vector of (1/2, 1/2), and that their development is concomitant with a suppression of the uniform magnetic susceptibility determined via magnetization measurements. We interpret this switch in spectral weight as signaling a temperature-induced crossover from an instability toward ferromagnetism ordering to ...


Competing Magnetic Phases And Itinerant Magnetic Frustration In Srco2 As2, Bing Li, Benjamin G. Ueland, W. T. Jayasekara, D. L. Abernathy, N. S. Sangeetha, David C. Johnston, Qing-Ping Ding, Yuji Furukawa, Peter P. Orth, Andreas Kreyssig, Alan I. Goldman, Robert J. Mcqueeney Oct 2019

Competing Magnetic Phases And Itinerant Magnetic Frustration In Srco2 As2, Bing Li, Benjamin G. Ueland, W. T. Jayasekara, D. L. Abernathy, N. S. Sangeetha, David C. Johnston, Qing-Ping Ding, Yuji Furukawa, Peter P. Orth, Andreas Kreyssig, Alan I. Goldman, Robert J. Mcqueeney

Peter P. Orth

Whereas magnetic frustration is typically associated with local-moment magnets in special geometric arrangements, here we show that SrCo2As2 is a candidate for frustrated itinerant magnetism. Using inelastic neutron scattering (INS), we find that antiferromagnetic (AF) spin fluctuations develop in the square Co layers of SrCo2As2 below T approximate to 100 K centered at the stripe-type AF propagation vector of (1/2, 1/2), and that their development is concomitant with a suppression of the uniform magnetic susceptibility determined via magnetization measurements. We interpret this switch in spectral weight as signaling a temperature-induced crossover from an instability toward ferromagnetism ordering to ...


Suppression Of Antiferromagnetic Spin Fluctuations In Superconducting Cr0.8 Ru0.2, M. Ramazanoglu, Benjamin G. Ueland, D. K. Pratt, L. W. Harringer, J. W. Lynn, G. Ehlers, G. E. Granroth, Sergey L. Bud’Ko, Paul C. Canfield, Deborah L. Schlagel, Alan I. Goldman, Thomas A. Lograsso, Robert J. Mcqueeney Jul 2019

Suppression Of Antiferromagnetic Spin Fluctuations In Superconducting Cr0.8 Ru0.2, M. Ramazanoglu, Benjamin G. Ueland, D. K. Pratt, L. W. Harringer, J. W. Lynn, G. Ehlers, G. E. Granroth, Sergey L. Bud’Ko, Paul C. Canfield, Deborah L. Schlagel, Alan I. Goldman, Thomas A. Lograsso, Robert J. Mcqueeney

A. I. Goldman

Unconventional superconductivity (SC) often develops in magnetic metals on the cusp of static antiferromagnetic (AFM) order where spin fluctuations are strong. This association is so compelling that many SC materials are labeled as unconventional by proximity to an ordered AFM state. The Cr-Ru alloy system possesses such a phase diagram [see Fig. 1(a)]. Here we use inelastic neutron scattering to show that spin fluctuations are present in a SC Cr0.8Ru0.2 alloy (Tc=1.35 K). However, the neutron spin resonance, a possible signature of unconventional SC, is not observed. Instead, data indicate a spin gap of order ...


Using Controlled Disorder To Probe The Interplay Between Charge Order And Superconductivity In Nbse2, Kyuil Cho, M. Kończykowski, Serafim Teknowijoyo, Makariy A. Tanatar, J. Guss, P. B. Gartin, John M. Wilde, A. Kreyssig, Robert Mcqueeney, Alan I. Goldman, V. Mishra, P. J. Hirschfeld, Ruslan Prozorov Jul 2019

Using Controlled Disorder To Probe The Interplay Between Charge Order And Superconductivity In Nbse2, Kyuil Cho, M. Kończykowski, Serafim Teknowijoyo, Makariy A. Tanatar, J. Guss, P. B. Gartin, John M. Wilde, A. Kreyssig, Robert Mcqueeney, Alan I. Goldman, V. Mishra, P. J. Hirschfeld, Ruslan Prozorov

A. I. Goldman

The interplay between superconductivity and charge-density wave (CDW) in 2H-NbSe2 is not fully understood despite decades of study. Artificially introduced disorder can tip the delicate balance between two competing long-range orders, and reveal the underlying interactions that give rise to them. Here we introduce disorder by electron irradiation and measure in-plane resistivity, Hall resistivity, X-ray scattering, and London penetration depth. With increasing disorder, the superconducting transition temperature, Tc, varies non-monotonically, whereas the CDW transition temperature, TCDW, monotonically decreases and becomes unresolvable above a critical irradiation dose where Tcdrops sharply. Our results imply that the CDW ...


Magnetic-Field Effects On The Fragile Antiferromagnetism In Ybbipt, Benjamin G. Ueland, Andreas Kreyssig, E. D. Mun, J. W. Lynn, L. W. Harriger, D. K. Pratt, K. Prokeš, Z. Hüsges, R. Toft-Petersen, S. Sauerbrei, Scott M. Saunders, Yuji Furukawa, Sergey L. Bud’Ko, Robert J. Mcqueeney, Paul C. Canfield, Alan I. Goldman Jul 2019

Magnetic-Field Effects On The Fragile Antiferromagnetism In Ybbipt, Benjamin G. Ueland, Andreas Kreyssig, E. D. Mun, J. W. Lynn, L. W. Harriger, D. K. Pratt, K. Prokeš, Z. Hüsges, R. Toft-Petersen, S. Sauerbrei, Scott M. Saunders, Yuji Furukawa, Sergey L. Bud’Ko, Robert J. Mcqueeney, Paul C. Canfield, Alan I. Goldman

A. I. Goldman

We present neutron-diffraction data for the cubic-heavy-fermion YbBiPt that show broad magnetic diffraction peaks due to the fragile short-range antiferromagnetic (AFM) order persist under an applied magnetic-field H. Our results for H perpendicular to[(1) over bar 1 0] and a temperature of T = 0.14(1) K show that the (1/2,1/2,3/2) magnetic diffraction peak can be described by the same two-peak line shape found for mu H-0 = 0T below the Neel temperature of T-N = 0.4 K. Both components of the peak exist for mu H-0 less than or similar to 1.4 T ...


Dhital_Pnas.Pdf, Chetan Dhital Oct 2018

Dhital_Pnas.Pdf, Chetan Dhital

Chetan Dhital

No abstract provided.


Tailoring The Asymmetric Magnetoimpedance Response In Exchange-Biased Ni - Fe Multilayers, Ufuk Kilic, Carolina Ross, Carlos Garcia Sep 2018

Tailoring The Asymmetric Magnetoimpedance Response In Exchange-Biased Ni - Fe Multilayers, Ufuk Kilic, Carolina Ross, Carlos Garcia

Ufuk Kilic

The dependence of the asymmetric magnetoimpedance (MI) response on the directions of both the magnetic field and the exchange bias is studied for an [NiFe(60nm)/IrMn(35nm)]×5 multilayer system. The antiferromagnetic (AFM) layers create an exchange bias that shifts both the hysteresis loop and the MI response of NiFe; the strength of this coupling depends on the thicknesses of both the ferromagnetic layer and the AFM layer. Tuning the exchange-bias angle and the applied-magnetic-field direction provides a practical method to control the symmetry and the magnitude of the MI response. The observed asymmetric response can ...


Unconventional Pairing Symmetry Of Interacting Dirac Fermions On A Π -Flux Lattice, Huaiming Guo, Ehsan Khatami, Yao Wang, Thomas P. Devereaux, Rajiv R.P. Singh, Richard T. Scalettar Apr 2018

Unconventional Pairing Symmetry Of Interacting Dirac Fermions On A Π -Flux Lattice, Huaiming Guo, Ehsan Khatami, Yao Wang, Thomas P. Devereaux, Rajiv R.P. Singh, Richard T. Scalettar

Ehsan Khatami

The pairing symmetry of interacting Dirac fermions on the π-flux lattice is studied with the determinant quantum Monte Carlo and numerical linked-cluster expansion methods. The s- (i.e., extended s-) and d-wave pairing symmetries, which are distinct in the conventional square lattice, are degenerate under the Landau gauge. We demonstrate that the dominant pairing channel at strong interactions is an unconventional ds-wave phase consisting of alternating stripes of s- and d-wave phases. A complementary mean-field analysis shows that while the s- and d-wave symmetries individually have nodes in the energy spectrum, the ds channel is ...


Hyperpolarization Of Silicon Nanoparticles With Tempo Radicals, Jingzhe Hu, Nicholas Whiting, Pratip Bhattacharya Mar 2018

Hyperpolarization Of Silicon Nanoparticles With Tempo Radicals, Jingzhe Hu, Nicholas Whiting, Pratip Bhattacharya

Nicholas Whiting

Silicon-based particles can be hyperpolarized via dynamic nuclear polarization to enhance 29Si magnetic resonance signals. Application of this technique to nanoscale silicon particles has been limited because of the low signal enhancements achieved; it is hypothesized that this is due to the low number of endogenous electronic defects inherent to the particles. We introduce a method of incorporating exogenous radicals into silicon nanoparticle suspensions in order to improve the hyperpolarization of 29Si nuclear spins to levels sufficient for in vivo MR imaging. Calibration of radical concentrations and polarization times are reported for a variety of silicon particle sizes (30−200 ...


Unsupervised Machine Learning Account Of Magnetic Transitions In The Hubbard Model, Kelvin Ch'ng, Nick Vazquez, Ehsan Khatami Dec 2017

Unsupervised Machine Learning Account Of Magnetic Transitions In The Hubbard Model, Kelvin Ch'ng, Nick Vazquez, Ehsan Khatami

Ehsan Khatami

We employ several unsupervised machine learning techniques, including autoencoders, random trees embedding, and t-distributed stochastic neighboring ensemble (t-SNE), to reduce the dimensionality of, and therefore classify, raw (auxiliary) spin configurations generated, through Monte Carlo simulations of small clusters, for the Ising and Fermi-Hubbard models at finite temperatures. Results from a convolutional autoencoder for the three-dimensional Ising model can be shown to produce the magnetization and the susceptibility as a function of temperature with a high degree of accuracy. Quantum fluctuations distort this picture and prevent us from making such connections between the output of the autoencoder and physical ...


Superconductivity At Т≈200 K In Bismuth Cuprates Synthesized Using Solar Energy, J. G. Chigvinadze, Juana Vivó Acrivos, S. M. Ashimov, D. D. Gulamova, G. J. Donadze Oct 2017

Superconductivity At Т≈200 K In Bismuth Cuprates Synthesized Using Solar Energy, J. G. Chigvinadze, Juana Vivó Acrivos, S. M. Ashimov, D. D. Gulamova, G. J. Donadze

Juana Vivó Acrivos

When investigating low-frequency (0.1 Hz) oscillations of multiphase high-temperature cuprate superconductors (HTCS) Bi1,7Pb0,3Sr2Ca(n-1)CunOy (n=2-30), a wide attenuation peak (ΔT~100 К) with a maximum at Т≈200 К was detected. This peak was particularly pronounced in field cooling (FC) experiments, i.e. after abrupt cooling of the sample in the external magnetic field at the temperature Т<Тс with subsequent slow warming up to room temperature with invariance of the applied field. The attenuation peak height depended on the preliminary
orientation (before cooling) of the samples θ in the measured permanent magnetic field Н ...


Machine Learning Phases Of Strongly Correlated Fermions, Kelvin Ch'ng, Juan Carrasquilla, Roger G. Melko, Ehsan Khatami Aug 2017

Machine Learning Phases Of Strongly Correlated Fermions, Kelvin Ch'ng, Juan Carrasquilla, Roger G. Melko, Ehsan Khatami

Ehsan Khatami

Machine learning offers an unprecedented perspective for the problem of classifying phases in condensed matter physics. We employ neural network machine learning techniques to distinguish finite-temperature phases of the strongly-correlated fermions on cubic lattices. We show that a three-dimensional convolutional network trained on auxiliary field configurations produced by quantum Monte Carlo simulations of the Hubbard model can correctly predict the magnetic phase diagram of the model at the average density of one (half filling). We then use the network, trained at half filling, to explore the trend in the transition temperature as the system is doped away from half filling ...


Microscopic Origins Of The Large Piezoelectricity Of Leadfree (Ba,Ca)(Zr,Ti)O3, Yousra Nahas, Alireza Akbarzadeh, Sergei Prokhorenko, Sergey Prosandeev, Raymond Walter, Igor Kornev, Jorgé Íñiguez, Laurent Bellaiche Jun 2017

Microscopic Origins Of The Large Piezoelectricity Of Leadfree (Ba,Ca)(Zr,Ti)O3, Yousra Nahas, Alireza Akbarzadeh, Sergei Prokhorenko, Sergey Prosandeev, Raymond Walter, Igor Kornev, Jorgé Íñiguez, Laurent Bellaiche

Raymond Walter

In light of directives around the world to eliminate toxic materials in various technologies, finding lead-free materials with high piezoelectric responses constitutes an important current scientific goal. As such, the recent discovery of a large electromechanical conversion near room temperature in (1 x)Ba(Zr0.2Ti0.8)O3 x(Ba0.7Ca0.3)TiO3 compounds has directed attention to understanding its origin. Here, we report the development of a large-scale atomistic scheme providing a microscopic insight into this technologically promising material. We find that its high piezoelectricity originates from the existence of large ...


Weak Anti-Localization And Quantum Oscillations Of Surface States In Topological Insulator Bi2se2te, Lihong Bao, Liang He, Nicholas R. Meyer, Xufeng Kou, Peng Zhang, Zhi-Gang Chen, Alexei V. Fedorov, Trevor M. Riedemann, Thomas A. Lograsso, Kang L. Wang, Gary Tuttle, Faxian Xiu Jun 2017

Weak Anti-Localization And Quantum Oscillations Of Surface States In Topological Insulator Bi2se2te, Lihong Bao, Liang He, Nicholas R. Meyer, Xufeng Kou, Peng Zhang, Zhi-Gang Chen, Alexei V. Fedorov, Trevor M. Riedemann, Thomas A. Lograsso, Kang L. Wang, Gary Tuttle, Faxian Xiu

Gary Tuttle

Topological insulators, a new quantum state of matter, create exciting opportunities for studying topological quantum physics and for exploring spintronic applications due to their gapless helical metallic surface states. Here, we report the observation of weak anti-localization and quantum oscillations originated from surface states in Bi2Se2Te crystals. Angle-resolved photoemission spectroscopy measurements on cleaved Bi2Se2Te crystals show a well-defined linear dispersion without intersection of the conduction band. The measured weak anti-localization effect agrees well with the Hikami-Larkin-Nagaoka model and the extracted phase coherent length shows a power-law dependence with temperature ( ∼T−0.44), indicating the presence of the surface states. More ...


Toy Model For Uncommon Spin–Orbit-Driven Spin-Torque Terms .Pdf, Raymond Walter, Charles Paillard, Surendra Singh, Brahim Dkhil, Laurent Bellaiche May 2017

Toy Model For Uncommon Spin–Orbit-Driven Spin-Torque Terms .Pdf, Raymond Walter, Charles Paillard, Surendra Singh, Brahim Dkhil, Laurent Bellaiche

Raymond Walter

A toy model combining the angular magneto electric (AME) coupling Hamitonian (Mondal et al 2015 Phys. Rev. B 92 100402) with long-range magnetic dipolar interactions is used
to investigate spin-torque phenomena in a magnetic spin valve. It is found that such model (1) gives rise to spin-torque expressions that are analogous in form to those of the common spin-transfer torques; but also (2) predicts additional spin-torque terms, which are generated by an electrical current oriented along unconventional, in-plane directions. The magnitude of the AME induced terms is estimated and the conditions under which they may contribute signi cantly are explored. 


Modeling Out-Of-Plane Actuation In Thin-Film Nematic Polymer Networks: From Chiral Ribbons To Auto-Origami Boxes Via Twist And Topology, Vianney Gimenez-Pinto, Fangfu Ye, Badel Mbanga, Jonathan Selinger, Robin Selinger Mar 2017

Modeling Out-Of-Plane Actuation In Thin-Film Nematic Polymer Networks: From Chiral Ribbons To Auto-Origami Boxes Via Twist And Topology, Vianney Gimenez-Pinto, Fangfu Ye, Badel Mbanga, Jonathan Selinger, Robin Selinger

Jonathan Selinger

Various experimental and theoretical studies demonstrate that complex stimulus-responsive out-of-plane distortions such as twist of different chirality, emergence of cones, simple and anticlastic bending can be engineered and pre-programmed in a liquid crystalline rubbery material given a well-controlled director microstructure. Via 3-d finite element simulation studies, we demonstrate director-encoded chiral shape actuation in thin-film nematic polymer networks under external stimulus. Furthermore, we design two complex director fields with twisted nematic domains and nematic disclinations that encode a pattern of folds for an auto-origami box. This actuator will be flat at a reference nematic state and form four well-controlled bend distortions ...


Competing Phases And Orbital-Selective Behaviors In The Two-Orbital Hubbard-Holstein Model, Shaozhi Li, Ehsan Khatami, Steven Johnston Mar 2017

Competing Phases And Orbital-Selective Behaviors In The Two-Orbital Hubbard-Holstein Model, Shaozhi Li, Ehsan Khatami, Steven Johnston

Ehsan Khatami

We study the interplay between the electron-electron (e-e) and the electron-phonon (e-ph) interactions in the two-orbital Hubbard-Holstein model at half-filling using the dynamical mean-field theory. We find that the e-ph interaction, even at weak couplings, strongly modifies the phase diagram of this model and introduces an orbital-selective Peierls insulating phase (OSPI) that is analogous to the widely studied orbital-selective Mott phase (OSMP). At small e-e and e-ph couplings, we find a competition between the OSMP and the OSPI, while at large couplings, a competition occurs between Mott and charge-density-wave (CDW) insulating phases. We further demonstrate that the Hund's coupling ...


Properties Of Spacecraft Materials Exposed To Ionizing Radiation, Alex Souvall, Gregory Wilson, Katie Gamaunt, Ben Russon, Heather Tippets, Jr Dennison Mar 2017

Properties Of Spacecraft Materials Exposed To Ionizing Radiation, Alex Souvall, Gregory Wilson, Katie Gamaunt, Ben Russon, Heather Tippets, Jr Dennison

Katie Gamaunt

The effects of ionizing radiation damage on the various properties of spacecraft materials resulting from exposure in the Space Survivability Testing chamber (SST) are being studied with both ex situ and in situ tests. The SST is a ground based test facility designed to mimic low earth orbit (LEO), and geosynchronous orbit to test potential environmental-induced modifications to small satellites , and materials. Tests described here expose spacecraft materials to a Sr90 ionizing beta radiation source at room temperature and in high vacuum. Ex situ optical transmission/reflectivity measurements glass samples will monitor optical darkening. Properties of polymeric samples will ...


The Space Survivability Test Chamber, Katie Gamaunt, Heather Tippets, Alex Souvall, Ben Russon, Jr Dennison Mar 2017

The Space Survivability Test Chamber, Katie Gamaunt, Heather Tippets, Alex Souvall, Ben Russon, Jr Dennison

Katie Gamaunt

The Space Survivability Test chamber is a new ground-based research instrument being used for accelerated testing of environment-induced modifications of diverse samples. The chamber simulates space environment conditions, including neutral gas atmospheres and vacuum (<10-5 Pa) environments, temperature (~100 K to >450 K), ionizing radiation, electron fluxes (<10 eV to ~2½ MeV), and vacuum ultraviolet through mid-infrared photon fluxes. This versatile test chamber is well-suited for cost-effective testing of complete systems up to the size (< 20 cm dia.) of a 1U CubeSat, smaller components or electronics, and individual material samples. Multiple in-flux or in-situ space survivability and radiation exposure tests can be performed simultaneously, as well as ...


Measurement Of Effects Of Long Term Ionizing Radiation On High Efficiency Solar Arrays, Ben Russon, Heather Tippets, Gregory Wilson, Katie Gamaunt, Alex Souvall, Jr Dennison Mar 2017

Measurement Of Effects Of Long Term Ionizing Radiation On High Efficiency Solar Arrays, Ben Russon, Heather Tippets, Gregory Wilson, Katie Gamaunt, Alex Souvall, Jr Dennison

Katie Gamaunt

Degradation of power output efficiency for high-efficiency multilayer solar arrays due to ionizing radiation is measured using the Space Survivability Test chamber. Exposure to ionizing radiation disrupts the crystalline structure and can reduce solar array power output to the point that it no longer provides adequate output capacity. This can be a significant concern, particularly in the harsh environment of space where radiation dose rate is significantly higher and replacing components is often impossible. Ionizing radiation is simulated in a controlled environment to allow measurement and characterization of the power output of solar arrays, using a 100 mCi encapsulated Sr90 ...


Uv Degradation Effects: Terrestrial Versus Space Environment, Katie Gamaunt, Krysta Moser, Alex Souvall, Jr Dennison Mar 2017

Uv Degradation Effects: Terrestrial Versus Space Environment, Katie Gamaunt, Krysta Moser, Alex Souvall, Jr Dennison

Katie Gamaunt

The decrease in visible and ultraviolet transmission spectra of polymeric and glass spacecraft materials has been measured to determine the extent of degradation due to high energy UV radiation similar to the solar spectrum (both above and below the stratosphere). This project looked at the effects that the atmosphere has in regards to blocking UV radiation and thus, slowing down the UV degradation process. Materials such as quartz, borosilicate glass, sodium glasses, polyethylene, polyimide, and polyethylene terephthalate polymers were exposed to radiation from a focused high intensity deuterium lamp source, which generates radiation in the UVA and UVB spectrum. Duplicates ...


Synergistic Models Of Electron Emission And Transport Measurements Of Disordered Sio2, Jr Dennison, Jodie Corbridge Gillespie, Allen Andersen, Amberly Evans Jensen, Gregory Wilson, Justin Dekany, Alec M. Sim, Ryan Hoffmann Mar 2017

Synergistic Models Of Electron Emission And Transport Measurements Of Disordered Sio2, Jr Dennison, Jodie Corbridge Gillespie, Allen Andersen, Amberly Evans Jensen, Gregory Wilson, Justin Dekany, Alec M. Sim, Ryan Hoffmann

Jodie Corbridge Gillespie

A critical component in the prediction and mitigation of spacecraft charging issues is an accurate model of the charging, transport and electron emission properties of a broad array of materials used in the construction of spacecraft. The increased sensitivity, longer-duration missions, and ventures into more demanding environments only serve to heighten this need. One important way for the spacecraft charging community to address this issue is to expand the role of more fundamental materials physics. This includes the development of unifying theoretical models of the charge transport equations based on the creation, distribution, and occupancy of defect densities of states ...


Predictive Formula For Electron Range Over A Large Span Of Energies, Anne C. Starley, Gregory Wilson, Lisa Montierth Phillipps, Jr Dennison Mar 2017

Predictive Formula For Electron Range Over A Large Span Of Energies, Anne C. Starley, Gregory Wilson, Lisa Montierth Phillipps, Jr Dennison

Anne Starley

An empirical model developed by the Materials Research Group that predicts the approximate electron penetration depth—or range—of some common materials has been extended to predict the range for a broad assortment of other materials. The electron range of a material is the maximum distance electrons can travel through a material, before losing all of their incident kinetic energy. The original model used the Continuous-Slow-Down-Approximation for energy deposition in a material to develop a composite analytical formula which estimated the range from 10 MeV with an uncertainty of v, which describes the effective number of valence electrons. NV ...


Predictive Formula For Electron Range Over A Large Span Of Energy, Anne C. Starley, Jr Dennison Mar 2017

Predictive Formula For Electron Range Over A Large Span Of Energy, Anne C. Starley, Jr Dennison

Anne Starley

A model developed by the Materials Research Group that calculates electron penetration range of some common materials, has been greatly expanded with the hope that such extensions will predict the range in other, perhaps, more interesting materials. Developments in this extended model aid in predicting the approximate penetration depth into diverse classes of materials for a broad range of energetic incident electrons (<10 eV to>10 MeV, with better than 20% accuracy). The penetration depth—or range—of a material describes the maximum distance electrons can travel through a material, before losing all of its incident kinetic energy. This model has started to ...


Ex Situ Fabrication Of Field Emitters For Near Field Emission Scanning Electron Microscopy With Polarization Analysis, Taryl L. Kirk, Joseph Perrotta Dec 2016

Ex Situ Fabrication Of Field Emitters For Near Field Emission Scanning Electron Microscopy With Polarization Analysis, Taryl L. Kirk, Joseph Perrotta

Taryl Kirk

Research poster presented at the 2017 Rowan University Summer Undergraduate Research Program.