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Articles 1 - 20 of 20
Full-Text Articles in Condensed Matter Physics
Charge Effects In Bilayer Electric Transport, Christopher Czech
Charge Effects In Bilayer Electric Transport, Christopher Czech
All Theses
The mathematical isomorphism between the layer index in a bilayer system and the spin index in a spin-polarized system is used to draw an analogy between phenomena that occur in the two systems as a result of the electron-electron (e-e) interaction. First, the classical case of the Coulomb drag, a phenomenon resulting from momentum transfer through e-e collisions, is reviewed for both bilayer systems and spin-polarized systems. Then, the spin-backflow phenomenon, a result of the interaction-induced changes in the local quasiparticle energy that affects the charge transport in spin-polarized systems is presented. Finally, the iso-spin correlation is exploited to establish …
Spin Density Wave Phases In Semiconductor Superlattice, Liqiu Zheng
Spin Density Wave Phases In Semiconductor Superlattice, Liqiu Zheng
All Dissertations
We discuss the existence of spin instabilities and of possible ground states with broken spin symmetry in the presence of a tilted magnetic field for several semiconductor heterostructures. In each instance, the fundamental premise of our study is the existence of a spin degeneracy, controlled by tuning various experimentally controllable parameters, that permits the apparition of spin-flip processes driven entirely by the many-body Coulomb interaction. If in the case of a single quantum well, the spin instabilities trigger an abrupt paramagnetic to ferromagnetic phase transition, we demonstrate that in superlattices, at low temperatures, a stable spin density wave ($SDW$) ground …
Reversal Of Spin Polarization In Fe/Gaas (001) Driven By Resonant Surface States: First-Principles Calculations, Athanasios N. Chantis, Kirill D. Belashchenko, D. L. Smith, Evgeny Y. Tsymbal, Mark Van Schilfgaarde, R. C. Albers
Reversal Of Spin Polarization In Fe/Gaas (001) Driven By Resonant Surface States: First-Principles Calculations, Athanasios N. Chantis, Kirill D. Belashchenko, D. L. Smith, Evgeny Y. Tsymbal, Mark Van Schilfgaarde, R. C. Albers
Evgeny Tsymbal Publications
A minority-spin resonant state at the Fe/GaAs(001) interface is predicted to reverse the spin polarization with the voltage bias of electrons transmitted across this interface. Using a Green's function approach within the local spin-density approximation, we calculate the spin-dependent current in a Fe/GaAs/Cu tunnel junction as a function of the applied bias voltage. We find a change in sign of the spin polarization of tunneling electrons with bias voltage due to the interface minority-spin resonance. This result explains recent experimental data on spin injection in Fe/GaAs contacts and on tunneling magnetoresistance in Fe/GaAs/Fe magnetic tunnel junctions.
Bias Voltage Dependence Of Tunneling Anisotropic Magnetoresistance In Magnetic Tunnel Junctions With Mgo And Al2O3 Tunnel Barriers, Li Gao, Xin Jiang, See-Hun Yang, John D. Burton, Evgeny Y. Tsymbal, Stuart S. P. Parkin
Bias Voltage Dependence Of Tunneling Anisotropic Magnetoresistance In Magnetic Tunnel Junctions With Mgo And Al2O3 Tunnel Barriers, Li Gao, Xin Jiang, See-Hun Yang, John D. Burton, Evgeny Y. Tsymbal, Stuart S. P. Parkin
Evgeny Tsymbal Publications
Tunneling anisotropic magnetoresistance (TAMR) is observed in tunnel junctions with transition metal electrodes as the moments are rotated from in-plane to out-of-plane in sufficiently large magnetic fields that the moments are nearly parallel to one another. A complex angular dependence of the tunneling resistance is found with twofold and fourfold components that vary strongly with bias voltage. Distinctly different TAMR behaviors are obtained for devices formed with highly textured crystalline MgO(001) and amorphous Al2O3 tunnel barriers. A tight-binding model shows that a fourfold angular dependence can be explained by the presence of an interface resonant state that …
Effect Of Tip Resonances On Tunnelling Anisotropic Magnetoresistance In Ferromagnetic Break Junctions: A First-Principles Study, John D. Burton, Renat F. Sabirianov, Julian P. Velev, O. N. Mryasov, Evgeny Y. Tsymbal
Effect Of Tip Resonances On Tunnelling Anisotropic Magnetoresistance In Ferromagnetic Break Junctions: A First-Principles Study, John D. Burton, Renat F. Sabirianov, Julian P. Velev, O. N. Mryasov, Evgeny Y. Tsymbal
Materials Research Science and Engineering Center: Faculty Publications
First-principles calculations of electron tunneling transport in nanoscale Ni and Co break-junctions reveal strong dependence of the conductance on the magnetization direction, an effect known as tunneling anisotropic magnetoresistance TAMR. An important aspect of this phenomenon stems from resonant states localized in the electrodes near the junction break. The energy and broadening of these states is strongly affected by the magnetization orientation due to spin-orbit coupling, causing TAMR to be sensitive to bias voltage on a scale of a few millivolts. Our results bear a resemblance to recent experimental data and suggest that TAMR driven by resonant states is a …
The Thermoelectric Properties Investigation Of Ir3Ge7 Typed Representatives, Huqin Zhang
The Thermoelectric Properties Investigation Of Ir3Ge7 Typed Representatives, Huqin Zhang
All Theses
Energy conversion is employed to power generation utilizing the Seebeck effect or cooling utilizing the Peltier effect. Herein, we study several Ir3Ge7 typed semiconductor materials for potential thermoelectric energy conversion. Mo3Sb7, crystallizing in Ir3Ge7 type, can be rendered semiconducting by a partial Sb-Te substitution without noticeable structure changes, resulting in Mo3Sb5Te2 with 55 valence electrons per formula unit. Meanwhile, large cubic voids in the Mo3Sb5Te2 crystal structure provide the possibility of filling the voids with small cations to decrease the …
Comparison Between Steady State And Laser Flash Techniques, Justine Andrews
Comparison Between Steady State And Laser Flash Techniques, Justine Andrews
All Theses
Thermoelectrics is a promising avenue of energy conservation. A material is deemed a good thermoelectric material when it portrays certain material characteristics. These characteristics include a high thermopower and electrical conductivity and a low thermal conductivity. This thesis focuses on the methods of measuring a material's thermal conductivity.
The steady state method is a measurement technique used in the low temperature thermal conductivity measurements. This technique assures that the system and sample are at equilibrium before a measurement point is taken. As a result the measurements are both precise and accurate.
The laser flash technique measures a sample's thermal conductivity …
Comparison Of Thermoelectric Properties Of Arc-Melted And Hot-Pressed Half-Heuslers, Brad Edwards
Comparison Of Thermoelectric Properties Of Arc-Melted And Hot-Pressed Half-Heuslers, Brad Edwards
All Theses
Relatively low thermal conductivity and great electrical properties in combination with wide tuning parameters through doping make half-Heuslers high potential thermoelectric materials. In this study we plan to investigate the effects of hot-pressing and arc-melting on the thermoelectric properties of ZrNiSn0.975Sb0.025, and Hf0.75Zr0.25NiSn0.975Sb0.025 samples. Also, the effects of electron and phonon scattering due to the insertion of small 50 nm particles within the sample were investigated in ZrNiSn0.975Sb0.025 +4% Al2O3 and Hf0.75Zr0.25NiSn0.975Sb0.025 +4% Al2O …
Electronic Structure Of Mos2 Nanotubes, Lingyun Xu
Electronic Structure Of Mos2 Nanotubes, Lingyun Xu
All Dissertations
First-principles methods enable one to study the electronic structure of solids, surfaces, or clusters as accurately as possible with moderate computational effort.
So we used a first-principles electronic structure method to calculate the electronic structure of free-standing layer of MoS2 with ABA and ABC stacking. Our results suggest MoS2 with ABA stacking which appears as an insulator has an energy gap of 1.64 eV. The covalent bonds between molybdenum and sulfur atoms are strong enough to form this gap. The ABC stacking will break the symmetry and becomes metallic. The valance and impurities calculations show the rigid-band picture …
Quantum Analysis Of A Linear Dc Squid Mechanical Displacement Detector, M. P. Blencowe, E. Buks
Quantum Analysis Of A Linear Dc Squid Mechanical Displacement Detector, M. P. Blencowe, E. Buks
Dartmouth Scholarship
We provide a quantum analysis of a dc SQUID mechanical displacement detector within the subcritical Josephson current regime. A segment of the SQUID loop forms the mechanical resonator and motion of the latter is transduced inductively through changes in the flux threading the loop. Expressions are derived for the detector signal response and noise, which are used to evaluate the position and force detection sensitivity. We also investigate cooling of the mechanical resonator due to detector back reaction.
Defect-Mediated Properties Of Magnetic Tunnel Junctions, Julian P. Velev, Mikhail Ye. Zhuravlev, Kirill D. Belashchenko, Sitaram S. Jaswal, Evgeny Y. Tsymbal, T. Katayama, S. Yuasa
Defect-Mediated Properties Of Magnetic Tunnel Junctions, Julian P. Velev, Mikhail Ye. Zhuravlev, Kirill D. Belashchenko, Sitaram S. Jaswal, Evgeny Y. Tsymbal, T. Katayama, S. Yuasa
Evgeny Tsymbal Publications
Defects play an important role in the properties of metal oxides which are currently used as barrier layers in magnetic tunnel junctions (MTJs). We study the effect of O vacancies on the interlayer exchange coupling (IEC) and tunneling magnetoresistance (TMR) in Fe–MgO–Fe tunnel junctions. Measurements of IEC in fully epitaxial Fe–MgO–Fe(001) tunnel junctions show IEC is antiferromagnetic (AFM) for small MgO thickness but changes sign and then vanishes for large barrier thickness. First-principles calculations based on density functional theory demonstrate that the presence of neutral O vacancies (F-centers) in the MgO barrier can explain this behavior. Resonant tunneling …
Raman Spectroscopic Evidence For Anharmonic Phonon Lifetimes And Blueshifts In 1d Structures, Rahul Rao
Raman Spectroscopic Evidence For Anharmonic Phonon Lifetimes And Blueshifts In 1d Structures, Rahul Rao
All Dissertations
Anharmonic effects in two different quasi-1D systems were probed via micro-Raman spectroscopy. In the first system, we observed upshifts of peaks in the Raman spectra for b-Ga2O3 nanowires grown along the [110] growth direction compared those present in bulk b-Ga2O3. Contrary to our Raman studies on -Ga2O3 nanowires, downshifts in the Raman spectrum for b-Ga2O3 nanowires grown along [401] direction has also been reported by other research groups. We attribute these Raman shifts to the growth direction-induced lattice strains (compressive and tensile) present in the nanowires, and present a model based on the quasi-harmonic density functional theory to support our …
Nondiffusive Spin Dynamics In A Two-Dimensional Electron Gas, Christopher P. Weber, J. Orenstein, B. Andrei Bernevig, Shou-Cheng Zhang, Jason Stephens, D. D. Awschalom
Nondiffusive Spin Dynamics In A Two-Dimensional Electron Gas, Christopher P. Weber, J. Orenstein, B. Andrei Bernevig, Shou-Cheng Zhang, Jason Stephens, D. D. Awschalom
Physics
We describe measurements of spin dynamics in the two-dimensional electron gas in GaAs=GaAlAs quantum wells. Optical techniques, including transient spin-grating spectroscopy, are used to probe the relaxation rates of spin polarization waves in the wave vector range from zero to 6 x 104 cm-1. We find that the spin polarization lifetime is maximal at a nonzero wave vector, in contrast with expectations based on ordinary spin diffusion, but in quantitative agreement with recent theories that treat diffusion in the presence of spin-orbit coupling
Interface Effects In Spin-Dependent Tunneling, Evgeny Y. Tsymbal, Kirill D. Belashchenko, Julian P. Velev, Sitaram S. Jaswal, Mark Van Schilfgaarde, Ivan I. Oleynik, Derek A. Stewart
Interface Effects In Spin-Dependent Tunneling, Evgeny Y. Tsymbal, Kirill D. Belashchenko, Julian P. Velev, Sitaram S. Jaswal, Mark Van Schilfgaarde, Ivan I. Oleynik, Derek A. Stewart
Evgeny Tsymbal Publications
In the past few years the phenomenon of spin dependent tunneling (SDT) in magnetic tunnel junctions (MTJs) has aroused enormous interest and has developed into a vigorous field of research. The large tunneling magnetoresistance (TMR) observed in MTJs garnered much attention due to possible application in random access memories and magnetic field sensors. This led to a number of fundamental questions regarding the phenomenon of SDT. One such question is the role of interfaces in MTJs and their effect on the spin polarization of the tunneling current and TMR. In this paper we consider different models which suggest that the …
Ferroelectric Properties Of Langmuir-Blodgett Copolymer Films At The Nanoscale, A. Tolstousov, R. V. Gaynutdinov, R. Tadros-Morgane, Herbert Kliem, Stephen Ducharme, Vladimir M. Fridkin
Ferroelectric Properties Of Langmuir-Blodgett Copolymer Films At The Nanoscale, A. Tolstousov, R. V. Gaynutdinov, R. Tadros-Morgane, Herbert Kliem, Stephen Ducharme, Vladimir M. Fridkin
Stephen Ducharme Publications
Langmuir-Blodgett (LB) films are well known structures prepared as a result of successive transfer of monolayers (ML) from the gas-liquid interface onto solid substrates. One impressive possibility of LB method is the opportunity to vary the thickness of the film to an accuracy of one transfer, which could coincide with one ML. The ferroelectric properties of a copolymer of vinylidene fluoride and trifluorethylene P[VDF-TrFE] prepared by LB deposition are investigated in the region of a few monolayers.
Magnetic Enhancement In Cobalt-Manganese Alloy Clusters, Shuangye Yin, Ramiro Moro, Xiaoshan Xu, Walter A. De Heer
Magnetic Enhancement In Cobalt-Manganese Alloy Clusters, Shuangye Yin, Ramiro Moro, Xiaoshan Xu, Walter A. De Heer
Xiaoshan Xu Papers
Magnetic moments of CoNMnM and CoNVM clusters (N ≤ 60; M ≤ N/3) are measured in molecular beams using the Stern-Gerlach deflection method. Surprisingly, the per atom average moments of CoNMnM clusters are found to increase with Mn concentration, in contrast to bulk CoMn. The enhancement with Mn doping is found to be independent of cluster size and composition in the size range studied. Meanwhile, CoNVM clusters show reduction of average moments with increasing V doping, consistent with what is expected in bulk CoV. The results are …
Investigation Of The Catalytic And Structural Roles Of Conserved Histidines Of Human Coproporphyrinogen Oxidase Using Site-Directed Mutagenesis, Shani J. Gitter, Christopher L. Cooper, Jon A. Frieson, Timothy D. Lash, Marjorie A. Jones
Investigation Of The Catalytic And Structural Roles Of Conserved Histidines Of Human Coproporphyrinogen Oxidase Using Site-Directed Mutagenesis, Shani J. Gitter, Christopher L. Cooper, Jon A. Frieson, Timothy D. Lash, Marjorie A. Jones
Faculty Publications – Chemistry
Background: The catalytic contribution of four conserved histidines of human coproporphyrinogen oxidase (CPO) has been investigated using site-directed mutagenesis to change histidine (H) into alanine (A). Material/Methods: The wild-type and mutant enzyme forms were analyzed for their ability to utilize coproporphyrinogen-III, mesoporphvrinogen-VI, and harderoporphyrinogen as substrates. Results: Wild-type CPO had specific activities of 4.9 +/- 0.9 nmole product/min/mg for coproporphyrinogen-III, 1.7 +/- 0.7 nmole ptoduct/min/mg for mesoporphyrinogen-VI, and 5.1 +/- 1.8 nmole product/min/mg for harderoporphyrinogen. The four mutant enzymes were catalytically competent With all three substrates, but to varying degrees. The most affected Mutant was the H158A enzyme which exhibited …
An Evaluation Of Supercritical Drying And Peg/Freeze Drying Of Waterlogged Archaeological Wood, Eric Schindelholz, Robert Blanchette, Desmond C. Cook, Michael Drews, Steve Hand, Benjamin Held, Joel Jurgens, Betty Seifert
An Evaluation Of Supercritical Drying And Peg/Freeze Drying Of Waterlogged Archaeological Wood, Eric Schindelholz, Robert Blanchette, Desmond C. Cook, Michael Drews, Steve Hand, Benjamin Held, Joel Jurgens, Betty Seifert
Physics Faculty Publications
This study was undertaken to evaluate the physical effects of drying waterlogged archaeological wood using supercritical carbon dioxide as compared to air drying and the popular polyethylene glycol (PEG)/freeze drying method. Previous studies have shown supercritical drying to be a potentially advantageous alternative to current methods of drying waterlogged wood through reduced processing time, minimal shrinkage, and increased success for reversibility. Samples in the form of blocks and planks of a few centimeters in size were prepared from two archaeological waterlogged wood sources and grouped into three treatment sets: one for air drying, one for PEG/freeze drying, and the other …
Hologram-Based Humidity Indicator For Domestic And Packaging Applications, Izabela Naydenova, Raghavendra Jallapuram, Vincent Toal, Suzanne Martin
Hologram-Based Humidity Indicator For Domestic And Packaging Applications, Izabela Naydenova, Raghavendra Jallapuram, Vincent Toal, Suzanne Martin
Conference Papers
A passive indicator for Relative Humidity based on a photopolymer recorded hologram has been developed. The indicator works on the principle that the wavelength reconstructed by a reflection hologram is dependent on the spacing between the fringe planes of the hologram. As the Relative Humidity changes, the hologram swells or shrinks and the apparent colour of the reconstructed image changes. The response time, operational range and reversibility of the indicator have been studied in a controlled humidity environment. Response times from less than a minute to tens of minutes depending on the holograms physical properties have been measured. Indicators with …
Atomic Motion In Ferromagnetic Break Junctions: Comment And Response, S.-F. Shi, David C. Ralph, Andrei Sokolov, Chunjuan Zhang, Evgeny Y. Tsymbal, Jody G. Redepenning, Bernard Doudin
Atomic Motion In Ferromagnetic Break Junctions: Comment And Response, S.-F. Shi, David C. Ralph, Andrei Sokolov, Chunjuan Zhang, Evgeny Y. Tsymbal, Jody G. Redepenning, Bernard Doudin
Evgeny Tsymbal Publications
Authors’ response
In their comment, Shi and Ralph emphasize that conductance of Ni point contacts produced by an electro-migration technique can occasionally exhibit two-level fluctuations (TLF), mimicking the discrete steps in the conductance of the point contacts as a function of the applied magnetic-field direction. They explain the nature of these steps in terms of atomic motion rather than intrinsic electronic effect. We emphasize in this reply that our results, obtained on a different magnetic material synthesized by a different method, do not show a