Quantum And Classical Transport Of 2d Electrons In The Presence Of Long And Short Range Disorder, 2018 The Graduate Center, City University of New York

#### Quantum And Classical Transport Of 2d Electrons In The Presence Of Long And Short Range Disorder, Jesse Kanter

*All Dissertations, Theses, and Capstone Projects*

This work focuses on the study of electron transport of 2-D electron gas systems in relation to both fundamental properties of the systems such as disorder and scattering mechanisms, as well as unique magnetoresistance (MR) effects. A large portion of the discussion is built around the use of an in plane magnetic field to vary the ratio between the Zeeman energy between electrons of different spins and the Landau level spacing, creating a tool to control the quantization of the density of states (DOS).

This tool is first used to isolate Quantum Positive Magnetoresistance (QPMR), which grants insight to the ...

Measuring The Practical Particle-In-A-Box: Orthorhombic Perovskite Nanocrystals, 2018 West Chester University of Pennsylvania

#### Measuring The Practical Particle-In-A-Box: Orthorhombic Perovskite Nanocrystals, Brandon Mitchell, Eric Herrmann, Junhao Lin, Leyre Gomez, Chris De Weerd, Yasufumi Fujiwara, Kazutomo Suenaga, Tom Gregorkiewicz

*Physics*

A connection between condensed matter physics and basic quantum mechanics is demonstrated as we use the fundamental 3D particle-in-a-box model to explain the optical properties of semiconductor nanocrystals, which are substantially modified due to quantum confinement. We also discuss recent advances in the imaging and measurement capabilities of transmission electron microscopy, which have made it possible to directly image single nanocrystals while simultaneously measuring their characteristic absorption energies. We introduce the basic theory of nanocrystals and derive a simplified expression to approximate the optical bandgap energy of an orthorhombic nanocrystal. CsPbBr3 perovskite nanocrystals are used to demonstrate this model due ...

Nodeless Superconductivity In The Type-Ii Dirac Semimetal Pdte 2 : London Penetration Depth And Pairing-Symmetry Analysis, 2018 Iowa State University and Ames Laboratory

#### Nodeless Superconductivity In The Type-Ii Dirac Semimetal Pdte 2 : London Penetration Depth And Pairing-Symmetry Analysis, Serafim Teknowijoyo, Na Hyun Jo, Mathias S. Scheurer, Makariy A. Tanatar, Kyuil Cho, Sergey L. Bud’Ko, Peter Orth, Paul C. Canfield, Ruslan Prozorov

*Ames Laboratory Accepted Manuscripts*

Superconducting gap structure was probed in type-II Dirac semimetal PdTe2 by measuring the London penetration depth using the tunnel diode resonator technique. At low temperatures, the data for two samples are well described by a weak-coupling exponential fit yielding λ(T=0)=230 nm as the only fit parameter at a fixed Δ(0)/Tc≈1.76, and the calculated superfluid density is consistent with a fully gapped superconducting state characterized by a single gap scale. Electrical resistivity measurements for in-plane and inter-plane current directions find very low and nearly temperature-independent normal-state anisotropy. The temperature dependence of resistivity is typical ...

Aftershocks In Slowly Compressed Bulk Metallic Glasses: Experiments And Theory, 2018 University of Illinois at Urbana-Champaign

#### Aftershocks In Slowly Compressed Bulk Metallic Glasses: Experiments And Theory, Louis W. Mcfaul, Wendelin Wright, Xiaojun Gu, Jonathan T. Uhl, Karin A. Dahmen

*Faculty Journal Articles*

We observe two distinct interevent time patterns in the slip avalanches of compressed bulk metallic glasses (BMGs). Small slip avalanches cluster together in time, but large slip avalanches recur roughly periodically. We compare the timing patterns of BMG slip avalanches with timing patterns of earthquakes and with the predictions of a mean-field model. The time clustering of small avalanches is similar to the known time clustering of earthquake foreshocks and aftershocks.

Modeling Recombination In Solar Cells, 2018 Macalester College

#### Modeling Recombination In Solar Cells, Paul Chery

*Macalester Journal of Physics and Astronomy*

Solar cells are a competitive alternative to nonrenewable energy sources such as fossil fuels. However, the efficiency of these devices is limited by photogenerated carrier recombination. We use a finite difference numerical model to study recombination phenomena in the absorber layer of solar cells including alternate recombination models and the effects of spatial distribution of recombination centers. We compare the effect of using the constant lifetime approximation for recombination to the full Shockley-Read-Hall expression in Silicon solar cells and find that the constant lifetime approximation holds for high defect densities but not for high photon flux densities. Finally, we simulate ...

Magnetoresistance In Lubi And Ybi Semimetals Due To Nearly Perfect Carrier Compensation, 2018 Polish Academy of Sciences

#### Magnetoresistance In Lubi And Ybi Semimetals Due To Nearly Perfect Carrier Compensation, Orest Pavlosiuk, Przemyslaw Swatek, Dariusz Kaczorowski, Piotr Wiśniewski

*Ames Laboratory Accepted Manuscripts*

Monobismuthides of lutetium and yttrium are shown as representatives of materials which exhibit extreme magnetoresistance and magnetic-field-induced resistivity plateaus. At low temperatures and in magnetic fields of 9 T, the magnetoresistance attains orders of magnitude of 104% and 103%, on YBi and LuBi, respectively. Our thorough examination of electron-transport properties of both compounds shows that observed features are the consequence of nearly perfect carrier compensation rather than of possible nontrivial topology of electronic states. The field-induced plateau of electrical resistivity can be explained with Kohler scaling. An anisotropic multiband model of electronic transport describes very well the magnetic field dependence ...

Antiferromagnetic Order In Cak(Fe1-Xnix)(4)As-4 And Its Interplay With Superconductivity, 2018 Iowa State University and Ames Laboratory

#### Antiferromagnetic Order In Cak(Fe1-Xnix)(4)As-4 And Its Interplay With Superconductivity, Andreas Kreyssig, John M. Wilde, Anna E. Böhmer, W. Tian, William R. Meier, Bing Li, Benjamin G. Ueland, Mingyu Xu, Sergey L. Bud’Ko, Paul C. Canfield, Robert J. Mcqueeney, Alan I. Goldman

*Ames Laboratory Accepted Manuscripts*

The magnetic order in CaK(Fe1−xNix)4 As4 (1144) single crystals (x=0.051 and 0.033) has been studied by neutron diffraction. We observe magnetic Bragg peaks associated with the same propagation vectors as found for the collinear stripe antiferromagnetic (AFM) order in the related BaFe2As2 (122) compound. The AFM state in 1144 preserves tetragonal symmetry and only a commensurate, noncollinear structure with a hedgehog spin-vortex crystal (SVC) arrangement in the Fe plane and simple AFM stacking along the c direction is consistent with our observations. The SVC order is promoted by the reduced symmetry in the FeAs ...

Quantum Fields In Extreme Backgrounds, 2018 Washington University in St. Louis

#### Quantum Fields In Extreme Backgrounds, Leandro Medina De Oliveira

*Arts & Sciences Electronic Theses and Dissertations*

Quantum field theories behave in interesting and nontrivial ways in the presence of intense electric and/or magnetic fields. Describing such behavior correctly, particularly at finite (nonzero) temperature and density, is of importance for particle physics, nuclear physics, astrophysics, condensed matter physics, and cosmology. Incorporating these conditions as external parameters also provides useful probes into the nonperturbative structure of gauge theories.

In this work, formalism for describing matter in a variety of extreme conditions is developed and implemented. We develop several expansions of one-loop finite temperature effects for spinor particles in the presence of magnetic fields, including the effects of ...

Chiral Topological Insulator Of Magnons, 2018 University of Nebraska - Lincoln

#### Chiral Topological Insulator Of Magnons, Bo Li, Alexey Kovalev

*Faculty Publications, Department of Physics and Astronomy*

We propose a magnon realization of 3D topological insulator in the AIII (chiral symmetry) topological class. The topological magnon gap opens due to the presence of Dzyaloshinskii-Moriya interactions. The existence of the topological invariant is established by calculating the bulk winding number of the system. Within our model, the surface magnon Dirac cone is protected by the sublattice chiral symmetry. By analyzing the magnon surface modes, we confirm that the backscattering is prohibited. By weakly breaking the chiral symmetry, we observe the magnon Hall response on the surface due to opening of the gap. Finally, we show that by changing ...

Vibrational Relaxation Theory For Systems Embedded In Microscopically Specified Reservoirs, 2018 University of New Mexico

#### Vibrational Relaxation Theory For Systems Embedded In Microscopically Specified Reservoirs, Anastasia Aemilia Ierides

*Physics & Astronomy ETDs*

This dissertation is a study of the theoretical framework of the practical as well as fundamental problem of the process of relaxation to equilibrium of quantum mechanical systems. The fundamental aspect is concerned with the simultaneous occurrence of decoherence and population equilibration. The practical aspect deals with experimental observations of vibrational relaxation of molecules embedded in liquids or solids. The systems include, but are not limited to, the nondegenerate dimer and harmonic oscillator, in one case weak and in the other strong, interaction with a thermal bath. The time dependence of the energy and the temperature dependence of the relaxation ...

Properties Of Epitaxial Sr0.5ba0.5mno3 Films From First-Principles, 2018 University of Arkansas, Fayetteville

#### Properties Of Epitaxial Sr0.5ba0.5mno3 Films From First-Principles, Temuujin Bayaraa

*Theses and Dissertations*

Magnetoelectric multiferroics, that possess coupled magnetic and electric degrees of freedom, have been receiving ever renewed attention for more than 15 years since they hold promise for the design of novel devices exploiting their cross-coupling.

In this thesis, we present the results of first-principles studies on physical properties of multiferroic Sr0.5Ba0.5MnO3 films under epitaxial compressive and tensile strains, and chemical ordering. We start by reviewing multiferroic materials, a magnetoelectric coupling mechanism and then we give a brief introduction to the first-principles computational methods that are involved in this study.

Here, we report that Sr0.5Ba0.5MnO3 (SBM) films ...

Optimization Of Cuinxga1-Xse2 Solar Cells With Post Selenization, 2018 The Graduate Center, City University of New York

#### Optimization Of Cuinxga1-Xse2 Solar Cells With Post Selenization, Zehra Cevher

*All Dissertations, Theses, and Capstone Projects*

The chalcopyrite semiconductor CuIn_{x}Ga_{1-x}Se_{2} is considered as the most promising material for high efficiency thin film solar cells due to its exceptional radiation stability, tunable direct bandgap, high light absorption coefficient and low cost preparation methods. In this thesis, we present the systematic investigation of the deposition conditions to optimize the CuIn_{x}Ga_{1-x}Se_{2 }device performance using the two-step deposition method. Further, we utilized nonlinear optical methods to investigate the deposition parameters to optimize the bulk and interface properties of photovoltaic devices.

First, we investigated the deposition parameters to optimize the structural ...

Pressure-Temperature Phase Diagrams Of Cak(Fe1-Xnix)(4)As-4 Superconductors, 2018 Iowa State University and Ames Laboratory

#### Pressure-Temperature Phase Diagrams Of Cak(Fe1-Xnix)(4)As-4 Superconductors, Li Xiang, William R. Meier, Mingyu Xu, Udhara S. Kaluarachchi, Sergey L. Bud’Ko, Paul C. Canfield

*Ames Laboratory Accepted Manuscripts*

The pressure dependence of the magnetic and superconducting transitions and that of the superconducting upper critical field are reported for CaK(Fe1-xNix)(4)As-4, the first example of an Fe-based superconductor with spin-vortex-crystal-type magnetic ordering. Resistance measurements were performed on single crystals with two substitution levels (x = 0.033,0.050) under hydrostatic pressures up to 5.12 GPa and in magnetic fields up to 9 T. Our results show that, for both compositions, magnetic transition temperatures T-N are suppressed upon applying pressure; the superconducting transition temperatures T-c are suppressed by pressure as well, except for x = 0.050 in ...

Measuring The Double Layer Capacitance Of Electrolytes With Varied Concentrations, 2018 Linfield College

#### Measuring The Double Layer Capacitance Of Electrolytes With Varied Concentrations, Geoffrey Rath

*Senior Theses*

When electric potentials are applied from an electrolytic fluid to a metal, a double layer capacitor, C_{dl}, develops at the interface. The layer directly at the interface is called the Stern layer and has a thickness equal to roughly the size of the ions in the fluid. The next layer, the diffuse layer, arises from the gathering of like charges in the Stern layer. This layer is the distance needed for ionic charges to return to equilibrium. This distance, called the Debye length, λ, depends on the square root of the electrolyte concentration. To study the properties of the ...

Doping Evolution Of Spin Fluctuations And Their Peculiar Suppression At Low Temperatures In Ca(Fe1-Xcox)(2)As-2, 2018 Iowa State University and Ames Laboratory

#### Doping Evolution Of Spin Fluctuations And Their Peculiar Suppression At Low Temperatures In Ca(Fe1-Xcox)(2)As-2, A. Sapkota, Pinaki Das, A. E. Böhmer, Benjamin G. Ueland, D. L. Abernathy, Sergey L. Bud’Ko, Paul C. Canfield, Andreas Kreyssig, Alan I. Goldman, Robert J. Mcqueeney

*Ames Laboratory Accepted Manuscripts*

Results of inelastic neutron scattering measurements are reported for two annealed compositions of Ca(Fe1-xCox)(2)As-2, x = 0.026 and 0.030, which possess stripe-type antiferromagnetically ordered and superconducting ground states, respectively. In the AFM ground state, well-defined and gapped spin waves are observed for x = 0.026, similar to the parent CaFe2As2 compound. We conclude that the well-defined spin waves are likely to be present for all x corresponding to the AFM state. This behavior is in contrast to the smooth evolution to overdamped spin dynamics observed in Ba(Fe1-xCox)(2)As-2, wherein the crossover corresponds to microscopically ...

Standard And Anomalous Wave Transport Inside Random Media, 2018 The Graduate Center, City University of New York

#### Standard And Anomalous Wave Transport Inside Random Media, Xujun Ma

*All Dissertations, Theses, and Capstone Projects*

This thesis is a study of wave transport inside random media using random matrix theory. Anderson localization plays a central role in wave transport in random media. As a consequence of destructive interference in multiple scattering, the wave function decays exponentially inside random systems. Anderson localization is a wave effect that applies to both classical waves and quantum waves. Random matrix theory has been successfully applied to study the statistical properties of transport and localization of waves. Particularly, the solution of the Dorokhov-Mello-Pereyra-Kumar (DMPK) equation gives the distribution of transmission.

For wave transport in standard one dimensional random systems in ...

Using First-Principles Calculations To Screen For Fragile Magnetism: Case Study Of Lacrge 3 And Lacrsb 3, 2018 Ames Laboratory

#### Using First-Principles Calculations To Screen For Fragile Magnetism: Case Study Of Lacrge 3 And Lacrsb 3, Manh Cuong Nguyen, Valentin Taufour, Sergey L. Bud’Ko, Paul C. Canfield, Vladimir P. Antropov, Cai-Zhuang Wang, Kai-Ming Ho

*Ames Laboratory Accepted Manuscripts*

In this paper, we present a coupled experimental/theoretical investigation of pressure effect on the ferromagnetism of LaCrGe3 and LaCrSb3 compounds. The magnetic, electronic, elastic, and mechanical properties of LaCrGe3 and LaCrSb3 at ambient condition are studied by first-principles density-functional theory calculations. The pressure dependences of the magnetic properties of LaCrGe3 and LaCrSb3 are also investigated. The ferromagnetism in LaCrGe3 is rather fragile, with a ferro- to paramagnetic transition at a relatively small pressure (around 7 GPa from our calculations, and 2 GPa in experiments). The key parameter controlling the magnetic properties of LaCrGe3 is found to be the proximity ...

Physics 516: Electromagnetic Phenomena (Spring 2018), 2018 University of Pennsylvania

#### Physics 516: Electromagnetic Phenomena (Spring 2018), Philip C. Nelson

*Department of Physics Papers*

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

Unconventional Pairing Symmetry Of Interacting Dirac Fermions On A Π -Flux Lattice, 2018 Beihang University

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

*Faculty Publications*

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 fully gapped. The results ...

Multimode Jahn-Teller Effect In Bulk Systems: A Case Of The Nv0 Center In Diamond, 2018 Ames Laboratory

#### Multimode Jahn-Teller Effect In Bulk Systems: A Case Of The Nv0 Center In Diamond, Jianhua Zhang, Cai-Zhuang Wang, Zizhong Zhu, Qing Huo Liu, Kai-Ming Ho

*Ames Laboratory Accepted Manuscripts*

The multimode Jahn-Teller (JT) effect in a bulk system of a neutral nitrogen-vacancy ( N V 0 ) center in diamond is investigated via first-principles density-functional-theory calculations and the intrinsic distortion path (IDP) method. The adiabatic potential energy surface of the electronic ground state of the N V 0 center is calculated based on the local spin-density approximation. Our calculations confirm the presence of the dynamic Jahn-Teller effect in the ground 2 E state of the N V 0 center. Within the harmonic approximation, the IDP method provides the reactive path of JT distortion from unstable high-symmetry geometry to stable low-symmetry energy ...