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Full-Text Articles in Physics

Improved Strategies For Dnp-Enhanced 2d 1h-X Heteronuclear Correlation Spectroscopy Of Surfaces, Takeshi Kobayashi, Frederic Perras, Umesh Chaudhary, Igor I. Slowing, Wenyu Huang, Aaron D. Sadow, Marek Pruski Nov 2017

Improved Strategies For Dnp-Enhanced 2d 1h-X Heteronuclear Correlation Spectroscopy Of Surfaces, Takeshi Kobayashi, Frederic Perras, Umesh Chaudhary, Igor I. Slowing, Wenyu Huang, Aaron D. Sadow, Marek Pruski

Aaron D. Sadow

We demonstrate that the dynamic nuclear polarization (DNP)-enhanced 1H-X heteronuclear correlation (HETCOR) measurements of surface species are better accomplished by using proton-free solvents. This approach notably prevents HETCOR spectra from being obfuscated by the solvent-derived signals otherwise present in DNP measurements. Additionally, in the hydrogen-rich materials studied here, which included functionalized mesoporous silica nanoparticles and metal organic frameworks, the use of proton-free solvents afforded higher sensitivity gains than the commonly used solvents containing protons. We also explored the possibility of using a solvent-free sample formulation and the feasibility of indirect detection in DNP-enhanced HETCOR experiments.


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.


Competing Phases And Orbital-Selective Behaviors In The Two-Orbital Hubbard-Holstein Model, Shaozhi Li, Ehsan Khatami, Steven Johnston Dec 2016

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 coupling, 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 ...