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Detecting Majorana Fermion Induced Crossed Andreev Reflection, Lei Fang 2017 The Graduate Center, City University of New York

Detecting Majorana Fermion Induced Crossed Andreev Reflection, Lei Fang

All Graduate Works by Year: Dissertations, Theses, and Capstone Projects

This dissertation is devoted to a study of detecting the Majorana fermion induced crossed Andreev reflection.

Majorana fermions are particles that constitute their own antiparticles. In condensed matter physics, Majorana fermions are zero energy modes that reside at edges or around vortices of topological superconductors. The special properties of Majorana fermions result in their potential to conduct topological quantum computation, which has been attracting a lot of current research. One of the most important issues in the field of the Majorana fermion physics now is to detect their existence in realistic systems. Among many classes of detecting methods, a transport ...


Kinetics Of Restricted Solid-On-Solid Models Of Film Growth, James W. Evans, M. C. Bartelt 2017 Iowa State University

Kinetics Of Restricted Solid-On-Solid Models Of Film Growth, James W. Evans, M. C. Bartelt

James W. Evans

We consider the kinetics of irreversible film growth in solid-on-solid models with various restrictions on the adsorption (or growth) sites. We show how the master equations for the probabilities of subconfigurations of filled sites can be analyzed exactly to obtain coverages and spatial correlations for the first several layers. These provide an efficient framework for analysis of the early-stage growth kinetics, and indicate rapid attainment of asymptotic behavior. We illustrate the (1+1)- and (2+1)-dimensional cases for the simplest restricted solid-on-solid condition, and various modifications.


Novel Half-Metallic And Spin-Gapless Heusler Compounds, Yunlong Jin 2017 University of Nebraska-Lincoln

Novel Half-Metallic And Spin-Gapless Heusler Compounds, Yunlong Jin

Theses, Dissertations, and Student Research: Department of Physics and Astronomy

This thesis is devoted to experimental studies of Heusler compounds CoFeCrAl, CoFeCrX (X = Si, Ge) and Mn2PtSn. These Heusler alloys present an interesting class of ferromagnetic materials for spintronic applications since they are predicted to be spin gapless semiconductors and have half-metallic properties with 100 % spin polarization at the Fermi level. In this thesis, the structural, magnetic, spin-polarization and electron- transport properties of the fabricated alloys were studied. CoFeCrAl thin films deposited on MgO exhibit nearly perfect epitaxy and a high degree of L21 Heusler order. All considered types of chemical disorder destroy the spin-gapless semiconductivity of ...


Crossover In The Magnetic Response Of Single-Crystalline Ba1−Xkxfe2as2 And Lifshitz Critical Point Evidenced By Hall Effect Measurements, Yong Liu, Thomas A. Lograsso 2017 Iowa State University

Crossover In The Magnetic Response Of Single-Crystalline Ba1−Xkxfe2as2 And Lifshitz Critical Point Evidenced By Hall Effect Measurements, Yong Liu, Thomas A. Lograsso

Thomas A. Lograsso

We report on the doping evolution of magnetic susceptibility χ(T) and Hall coefficient RH in high-quality Ba1−xKxFe2As2 (0.13≤x≤1) single crystals. It is found that the normal-state magnetic susceptibility of Ba1−xKxFe2As2 compounds undergoes a crossover from linear-T dependence in the undoped and underdoped samples into KFe2As2-type magnetic response in the overdoped samples with increasing K content. Although magnetic susceptibility χ(T) of optimally doped samples (0.34≤x≤0.47) still follows a monotonic increase with increasing temperature, a big hump around 300 K emerges. As x exceeds 0.53, a broad peak forms in ...


Neutron-Scattering Measurements Of Spin Excitations In Lafeaso And Ba(Fe0.953co0.047)2as2: Evidence For A Sharp Enhancement Of Spin Fluctuations By Nematic Order, Qiang Zhang, Rafael M. Fernandes, Jagat Lamsal, Jiaqiang Yan, Songxue Chi, Gregory S. Tucker, Daniel K. Pratt, Jeffrey W. Lynn, R. William McCallum, Paul C. Canfield, Thomas A. Lograsso, Alan I. Goldman, David Vaknin, Robert J. McQueeney 2017 Iowa State University

Neutron-Scattering Measurements Of Spin Excitations In Lafeaso And Ba(Fe0.953co0.047)2as2: Evidence For A Sharp Enhancement Of Spin Fluctuations By Nematic Order, Qiang Zhang, Rafael M. Fernandes, Jagat Lamsal, Jiaqiang Yan, Songxue Chi, Gregory S. Tucker, Daniel K. Pratt, Jeffrey W. Lynn, R. William Mccallum, Paul C. Canfield, Thomas A. Lograsso, Alan I. Goldman, David Vaknin, Robert J. Mcqueeney

Thomas A. Lograsso

Inelastic neutron scattering is employed to investigate the impact of electronic nematic order on the magnetic spectra of LaFeAsO and Ba(Fe0.953Co0.047)2As2. These materials are ideal to study the paramagnetic-nematic state, since the nematic order, signaled by the tetragonal-to-orthorhombic transition at TS, sets in well above the stripe antiferromagnetic ordering at TN. We find that the temperature-dependent dynamic susceptibility displays an anomaly at TS followed by a sharp enhancement in the spin-spin correlation length, revealing a strong feedback effect of nematic order on the low-energy magnetic spectrum. Our findings can be consistently described by a model that ...


Upper Critical Field Of Kfe2as2 Under Pressure: A Test For The Change In The Superconducting Gap Structure, Valentin Taufour, Neda Foroozani, Makariy A. Tanatar, Jinhyuk Lim, Udhara S. Kaluarachchi, Stella K. Kim, Yong Liu, Thomas A. Lograsso, Vladimir G. Kogan, Ruslan Prozorov, Sergey L. Bud'ko, James S. Schilling, Paul C. Canfield 2017 Iowa State University

Upper Critical Field Of Kfe2as2 Under Pressure: A Test For The Change In The Superconducting Gap Structure, Valentin Taufour, Neda Foroozani, Makariy A. Tanatar, Jinhyuk Lim, Udhara S. Kaluarachchi, Stella K. Kim, Yong Liu, Thomas A. Lograsso, Vladimir G. Kogan, Ruslan Prozorov, Sergey L. Bud'ko, James S. Schilling, Paul C. Canfield

Thomas A. Lograsso

ARTICLE TEXT
SUPPLEMENTAL MATERIAL
REFERENCES

ABSTRACT

We report measurements of electrical resistivity under pressure to 5.8 GPa, magnetization to 6.7 GPa, and ac susceptibility to 7.1 GPa in KFe2As2. The previously reported change of slope in the pressure dependence of the superconducting transition temperature Tc(p) at a pressure p∗∼1.8 GPa is confirmed, and Tc(p) is found to be nearly constant above p∗ up to 7.1 GPa. The T−p phase diagram is very sensitive to the pressure conditions as a consequence of the anisotropic uniaxial pressure dependence of Tc. Across p∗, a ...


Magnetic Excitations And Anomalous Spin-Wave Broadening In Multiferroic Fev2o4, Qiang Zhang, Mehmet Ramazanoglu, Songxue Chi, Yong Liu, Thomas A. Lograsso, David Vaknin 2017 Iowa State University

Magnetic Excitations And Anomalous Spin-Wave Broadening In Multiferroic Fev2o4, Qiang Zhang, Mehmet Ramazanoglu, Songxue Chi, Yong Liu, Thomas A. Lograsso, David Vaknin

Thomas A. Lograsso

We report on the different roles of two orbital-active Fe2+ at the A site and V3+ at the B site in the magnetic excitations and on the anomalous spin-wave broadening in FeV2O4. FeV2O4 exhibits three structural transitions and successive paramagnetic (PM)–collinear ferrimagnetic (CFI)–noncollinear ferrimagnetic (NCFI)/ferroelectric transitions. The high-temperature tetragonal/PM–orthorhombic/CFI transition is accompanied by the appearance of a large energy gap in the magnetic excitations due to strong spin-orbit-coupling-induced anisotropy at the Fe2+ site. While there is no measurable increase in the energy gap from the orbital ordering of V3+ at the orthorhombic/CFI–tetragonal ...


Magnetic And Structural Transitions In La0.4na0.6fe2as2 Single Crystals, J.-Q. Yan, S. Nandi, B. Saparov, P. Čermák, Y. Xiao, Y. Su, W. T. Jin, A. Schneidewind, Th. Brückel, R. W. McCallum, T. A. Lograsso, B. C. Sales, D. G. Mandrus 2017 Oak Ridge National Laboratory

Magnetic And Structural Transitions In La0.4na0.6fe2as2 Single Crystals, J.-Q. Yan, S. Nandi, B. Saparov, P. Čermák, Y. Xiao, Y. Su, W. T. Jin, A. Schneidewind, Th. Brückel, R. W. Mccallum, T. A. Lograsso, B. C. Sales, D. G. Mandrus

Thomas A. Lograsso

La0.4Na0.6Fe2As2 single crystals have been grown out of an NaAs flux in an alumina crucible and characterized by measuring magnetic susceptibility, electrical resistivity, specific heat, as well as single-crystal x-ray and neutron diffraction. La0.4Na0.6Fe2As2 single crystals show a structural phase transition from a high-temperature tetragonal phase to a low-temperature orthorhombic phase at Ts=125 K. This structural transition is accompanied by an anomaly in the temperature dependence of electrical resistivity, anisotropic magnetic susceptibility, and specific heat. Concomitant with the structural phase transition, the Fe moments order along the a direction with an ordered moment of 0 ...


Imprinting Bulk Amorphous Alloy At Room Temperature, Song-Yi Kim, Eun-Soo Park, Ryan T. Ott, T. A. Lograsso, Moo-young Huh, Do-Hyang Kim, Jürgen Eckert, Min-Ha Lee 2017 Korea Institute of Industrial Technology

Imprinting Bulk Amorphous Alloy At Room Temperature, Song-Yi Kim, Eun-Soo Park, Ryan T. Ott, T. A. Lograsso, Moo-Young Huh, Do-Hyang Kim, Jürgen Eckert, Min-Ha Lee

Thomas A. Lograsso

We present investigations on the plastic deformation behavior of a brittle bulk amorphous alloy by simple uniaxial compressive loading at room temperature. A patterning is possible by cold-plastic forming of the typically brittle Hf-based bulk amorphous alloy through controlling homogenous flow without the need for thermal energy or shaping at elevated temperatures. The experimental evidence suggests that there is an inconsistency between macroscopic plasticity and deformability of an amorphous alloy. Moreover, imprinting of specific geometrical features on Cu foil and Zr-based metallic glass is represented by using the patterned bulk amorphous alloy as a die. These results demonstrate the ability ...


Fermi Surface Reconstruction In (Ba1−Xkx)Fe2as2 (0.44≤X≤1) Probed By Thermoelectric Power Measurements, Halyna Hodovanets, Yong Liu, Anton Jesche, Sheng Ran, Eun Deok Mun, Thomas A. Lograsso, Sergey L. Bud'ko, Paul C. Canfield 2017 Iowa State University

Fermi Surface Reconstruction In (Ba1−Xkx)Fe2as2 (0.44≤X≤1) Probed By Thermoelectric Power Measurements, Halyna Hodovanets, Yong Liu, Anton Jesche, Sheng Ran, Eun Deok Mun, Thomas A. Lograsso, Sergey L. Bud'ko, Paul C. Canfield

Thomas A. Lograsso

We report in-plane thermoelectric power measurements on single crystals of (Ba1−xKx)Fe2As2(0.44≤x≤1). We observe a minimum in the S|T=const versus x at x∼0.55 that can be associated with the change in the topology of the Fermi surface, a Lifshitz transition, related to the electron pockets at the center of M point crossing the Fermi level. This feature is clearly observable below ∼75 K. Thermoelectric power also shows a change in the x∼0.8–0.9 range, where the maximum in the thermoelectric power collapses into a plateau. This Lifshitz transition ...


Specific Heat Investigation For Line Nodes In Heavily Overdoped Ba1−Xkxfe2as2, J. S. Kim, G. R. Stewart, Yong Liu, Thomas A. Lograsso 2017 University of Florida

Specific Heat Investigation For Line Nodes In Heavily Overdoped Ba1−Xkxfe2as2, J. S. Kim, G. R. Stewart, Yong Liu, Thomas A. Lograsso

Thomas A. Lograsso

Previous research has found that the pairing symmetry in the iron-based superconductor Ba1−xKxFe2As2 changes from nodeless s wave near optimally doped, x≈0.4−0.55 and Tc>30K, to nodal (either d wave or s wave) at the pure end point, x=1 and Tc<4K. Intense theoretical interest has been focused on this possibility of changing pairing symmetry, where in the transition region both order parameters would be present and time-reversal symmetry would be broken. Here we report specific heat measurements in zero and applied magnetic fields down to 0.4 K of three individual single crystals ...


Formation Mechanism Of Superconducting Phase And Its Three-Dimensional Architecture In Pseudo-Single-Crystal Kxfe2−Yse2, Yong Liu, Qingfeng Xing, Warren E. Straszheim, Jeff Marshman, Pai Pedersen, Richard McLaughlin, Thomas A. Lograsso 2017 Ames Laboratory

Formation Mechanism Of Superconducting Phase And Its Three-Dimensional Architecture In Pseudo-Single-Crystal Kxfe2−Yse2, Yong Liu, Qingfeng Xing, Warren E. Straszheim, Jeff Marshman, Pai Pedersen, Richard Mclaughlin, Thomas A. Lograsso

Thomas A. Lograsso

We report how the superconducting phase forms in pseudo-single-crystal KxFe2−ySe2. In situ scanning electron microscopy (SEM) observation reveals that, as an order-disorder transition occurs, on cooling, most of the high-temperature iron-vacancy-disordered phase gradually changes into the iron-vacancy-ordered phase, whereas a small quantity of the high-temperature phase retains its structure and aggregates to the stripes with more iron concentration but less potassium concentration compared to the iron-vacancy-ordered phase. The stripes that are generally recognized as the superconducting phase are actually formed as a remnant of the high-temperature phase with a compositional change after an “imperfect” order-disorder transition. It should be ...


Physical Properties Of Single Crystalline R Mg 2 Cu 9 ( R = Y , Ce − Nd , Gd − Dy , Yb ) And The Search For In-Plane Magnetic Anisotropy In Hexagonal Systems, Tai Kong, William R. Meier, Qisheng Lin, Scott M. Saunders, S. L. Bud’ko, Rebecca Flint, Paul C. Canfield 2017 Iowa State University

Physical Properties Of Single Crystalline R Mg 2 Cu 9 ( R = Y , Ce − Nd , Gd − Dy , Yb ) And The Search For In-Plane Magnetic Anisotropy In Hexagonal Systems, Tai Kong, William R. Meier, Qisheng Lin, Scott M. Saunders, S. L. Bud’Ko, Rebecca Flint, Paul C. Canfield

Paul C. Canfield

Single crystals ofRMg2Cu9 (R = Y, Ce-Nd, Gd-Dy, Yb) were grown using a high-temperature solution growth technique and were characterized by measurements of room-temperature x-ray diffraction, temperature-dependent specific heat, and temperature- and field-dependent resistivity and anisotropic magnetization. YMg2Cu9 is a nonlocal- moment-bearing metal with an electronic specific heat coefficient, γ ∼ 15 mJ/mol K2. Yb is divalent and basically non-moment-bearing in YbMg2Cu9. Ce is trivalent in CeMg2Cu9 with two magnetic transitions being observed at 2.1 K and 1.5 K. PrMg2Cu9 does not exhibit any magnetic phase transition down to 0.5 K. The other members being studied (R = Nd ...


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 2017 Iowa State University

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 ...


C60-Induced Devil's Staircase Transformation On A Pb/Si(111) Wetting Layer, Lin-Lin Wang, Duane D. Johnson, Michael C. Tringides 2017 Ames Laboratory

C60-Induced Devil's Staircase Transformation On A Pb/Si(111) Wetting Layer, Lin-Lin Wang, Duane D. Johnson, Michael C. Tringides

Duane D. Johnson

Density functional theory is used to study structural energetics of Pb vacancy cluster formation on C60/Pb/Si(111) to explain the unusually fast and error-free transformations between the “Devil's Staircase” (DS) phases on the Pb/Si(111) wetting layer at low temperature (∼110K). The formation energies of vacancy clusters are calculated in C60/Pb/Si(111) as Pb atoms are progressively ejected from the initial dense Pb wetting layer. Vacancy clusters larger than five Pb atoms are found to be stable with seven being the most stable, while vacancy clusters smaller than five are highly unstable, which agrees ...


Wave Propagation Inside Random Media, Xiaojun Cheng 2017 The Graduate Center, City University of New York

Wave Propagation Inside Random Media, Xiaojun Cheng

All Graduate Works by Year: Dissertations, Theses, and Capstone Projects

This thesis presents results of studies of wave scattering within and transmission through random and periodic systems. The main focus is on energy profiles inside quasi-1D and 1D random media.

The connection between transport and the states of the medium is manifested in the equivalence of the dimensionless conductance, g, and the Thouless number which is the ratio of the average linewidth and spacing of energy levels. This equivalence and theories regarding the energy profiles inside random media are based on the assumption that LDOS is uniform throughout the samples. We have conducted microwave measurements of the longitudinal energy profiles ...


Ferroelectric-Domain-Patterning-Controlled Schottky Junction State In Monolayer Mos2, Zhiyong Xiao, Jingfeng Song, David K. Ferry, Stephen Ducharme, Xia Hong 2017 University of Nebraska-Lincoln

Ferroelectric-Domain-Patterning-Controlled Schottky Junction State In Monolayer Mos2, Zhiyong Xiao, Jingfeng Song, David K. Ferry, Stephen Ducharme, Xia Hong

Stephen Ducharme Publications

We exploit scanning-probe-controlled domain patterning in a ferroelectric top layer to induce nonvolatile modulation of the conduction characteristic of monolayer MoS2 between a transistor and a junction state. In the presence of a domain wall, MoS2 exhibits rectified I-V characteristics that are well described by the thermionic emission model. The induced Schottky barrier height ΦeffB varies from 0.38 to 0.57 eV and is tunable by a SiO2 global back gate, while the tuning range of ΦeffB depends sensitively on the conduction-band-tail trapping states. Our work points to a new route to ...


Determining The Grain Size Of Polycrystalline Diamond For High Energy Density Experiments, Lauren Barmore 2017 Northwestern University

Determining The Grain Size Of Polycrystalline Diamond For High Energy Density Experiments, Lauren Barmore

Undergraduate Research and Arts Exposition

The High Energy Density Sciences group at SLAC National Accelerator Laboratory uses shock waves produced by the Linac Coherent Light Source to dynamically compress polycrystalline diamond samples. Compressing these polycrystalline samples allows us to use x-ray diffraction to study the changes to the structure as it experiences high pressure conditions. Polycrystalline diamond is valuable to study because it can be formed into ablator capsules for use in inertial confinement fusion reactions. As a result of the shock compression, the polycrystalline diamond samples undergo dynamic compression, a combination of stress and strain. To understand how dynamic compression takes place in a ...


Electronic And Magnetic Properties Of Carbon-Based And Boron-Based Nano Materials, Rosi Gunasinghe 2017 Clark Atlanta University

Electronic And Magnetic Properties Of Carbon-Based And Boron-Based Nano Materials, Rosi Gunasinghe

Electronic Theses & Dissertations Collection for Atlanta University & Clark Atlanta University

The structural and electronic properties of covalently and non-covalently functionalized graphene are investigated by means of first-principles density-functional-theory. The electronic characteristics of non-covalently functionalized graphene by a planar covalent organic framework (COF) are investigated. The aromatic central molecule of the COF acts as an electron donor while the linker of the COF acts as an electron acceptor. The concerted interaction of donor acceptor promotes the formation of planar COF networks on graphene. The distinctive electronic properties of covalently functionalized fluorinated epitaxial graphene are attributed to the polar covalent C–F bond. The partial ionic character of the C–F bond ...


Surface Geometry And Heat Flux Effect On Thin Wire Nucleate Pool Boiling Of Subcooled Water In Microgravity, Troy Munro, Andrew Fassman, Heng Ban, JR Dennision 2017 Utah State University

Surface Geometry And Heat Flux Effect On Thin Wire Nucleate Pool Boiling Of Subcooled Water In Microgravity, Troy Munro, Andrew Fassman, Heng Ban, Jr Dennision

Heng Ban

In the summer of 2010, undergraduates from the USU Get Away Special team flew a nucleate pool boiling experiment on NASA’s Weightless Wonder to study nucleate boiling heat transfer in microgravity. The motivation of this research was to understand the effects of surface geometry and heat flux applied to a thin wire heater for the design and development of efficient thermal management systems for space applications. The specific objectives were to observe and characterize behaviors of boiling onset, steady state heat transfer, and bubble dynamics with respect to nucleate boiling of subcooled water.. Using three thin platinum wire geometries ...


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