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Full-Text Articles in Physics

Ternary Inorganic Electrides With Mixed Bonding, Junjie Wang, Qiang Zhu, Zhenhai Wang, Hideo Hosono Feb 2019

Ternary Inorganic Electrides With Mixed Bonding, Junjie Wang, Qiang Zhu, Zhenhai Wang, Hideo Hosono

Physics & Astronomy Faculty Publications

A high-throughput screening based on first-principles calculations was performed to search for new ternary inorganic electrides. From the available materials database, we identified three new thermodynamically stable materials (Li12Mg3Si4, NaBa2O, and Ca5Ga2N4) as potential electrides made by main group elements, in addition to the well known mayenite based electride (C12A7:e−). Different from those conventional inorganic electrides in which the excess electrons play only the role of anions, the three new materials, resembling the electrides found in simple metals under high pressure, possess mixed ionic and metallic bonding. The interplay between two competing mechanisms, together with the different crystal packing ...


Understanding And Manipulating The Thermal Conductance Of Sin Membranes In Sub-Kelvin Refrigerators And Sensors, Xiaohang Zhang Jan 2019

Understanding And Manipulating The Thermal Conductance Of Sin Membranes In Sub-Kelvin Refrigerators And Sensors, Xiaohang Zhang

Physics Graduate Theses & Dissertations

In superconducting transition-edge sensors (TES) and superconducting tunnel junction refrigerators, thermal conductance of the silicon nitride membrane is a key design character. Thermal conductance engineering in silicon nitride membrane is still challenging, especially not introducing extra noise to sensors and diminish its mechanical strength.

In this thesis, we introduce our new generation of macroscopic general-purpose refrigerator using superconducting tunnel junction. Using the product of the cooled mass and the temperature reduction as a performance metric, this work is a more than tenfold advance over previous efforts. Based on our model, a better understanding of phonon thermal conductance of silicon nitride ...


Scanning Tunneling Spectroscopy Investigations Of Superconducting-Doped Topological Insulators: Experimental Pitfalls And Results, Stefan Wilfert, Paolo Sessi, Zhiwei Wang, Henrik Schmidt, M. Carmen Martínez-Velarte, Seng Huat Lee, Yew San Hor, Alexander F. Otte, Yoichi Ando, Weida Wu, Matthias Bode Oct 2018

Scanning Tunneling Spectroscopy Investigations Of Superconducting-Doped Topological Insulators: Experimental Pitfalls And Results, Stefan Wilfert, Paolo Sessi, Zhiwei Wang, Henrik Schmidt, M. Carmen Martínez-Velarte, Seng Huat Lee, Yew San Hor, Alexander F. Otte, Yoichi Ando, Weida Wu, Matthias Bode

Yew San Hor

Recently, the doping of topological insulators has attracted significant interest as a potential route towards topological superconductivity. Because many experimental techniques lack sufficient surface sensitivity, however, definite proof of the coexistence of topological surface states and surface superconductivity is still outstanding. Here we report on highly surface sensitive scanning tunneling microscopy and spectroscopy experiments performed on Tl-doped Bi2Te3, a three-dimensional topological insulator which becomes superconducting in the bulk at TC=2.3 K. Landau level spectroscopy as well as quasiparticle interference mapping clearly demonstrated the presence of a topological surface state with a Dirac point energy ...


Rotational Symmetry Breaking In A Trigonal Superconductor Nb-Doped Bi₂Se₃, T. Asaba, B. J. Lawson, C. Tinsman, L. Chen, P. Corbae, G. Li, Y. Qiu, Yew San Hor, L. Fu, L. Li Oct 2018

Rotational Symmetry Breaking In A Trigonal Superconductor Nb-Doped Bi₂Se₃, T. Asaba, B. J. Lawson, C. Tinsman, L. Chen, P. Corbae, G. Li, Y. Qiu, Yew San Hor, L. Fu, L. Li

Yew San Hor

The search for unconventional superconductivity has been focused on materials with strong spin-orbit coupling and unique crystal lattices. Doped bismuth selenide (Bi2Se3) is a strong candidate, given the topological insulator nature of the parent compound and its triangular lattice. The coupling between the physical properties in the superconducting state and its underlying crystal symmetry is a crucial test for unconventional superconductivity. In this paper, we report direct evidence that the superconducting magnetic response couples strongly to the underlying trigonal crystal symmetry in the recently discovered superconductor with trigonal crystal structure, niobium (Nb)-doped Bi2Se3 ...


Scanning Tunneling Spectroscopy Investigations Of Superconducting-Doped Topological Insulators: Experimental Pitfalls And Results, Stefan Wilfert, Paolo Sessi, Zhiwei Wang, Henrik Schmidt, M. Carmen Martínez-Velarte, Seng Huat Lee, Yew San Hor, Alexander F. Otte, Yoichi Ando, Weida Wu, Matthias Bode Aug 2018

Scanning Tunneling Spectroscopy Investigations Of Superconducting-Doped Topological Insulators: Experimental Pitfalls And Results, Stefan Wilfert, Paolo Sessi, Zhiwei Wang, Henrik Schmidt, M. Carmen Martínez-Velarte, Seng Huat Lee, Yew San Hor, Alexander F. Otte, Yoichi Ando, Weida Wu, Matthias Bode

Physics Faculty Research & Creative Works

Recently, the doping of topological insulators has attracted significant interest as a potential route towards topological superconductivity. Because many experimental techniques lack sufficient surface sensitivity, however, definite proof of the coexistence of topological surface states and surface superconductivity is still outstanding. Here we report on highly surface sensitive scanning tunneling microscopy and spectroscopy experiments performed on Tl-doped Bi2Te3, a three-dimensional topological insulator which becomes superconducting in the bulk at TC=2.3 K. Landau level spectroscopy as well as quasiparticle interference mapping clearly demonstrated the presence of a topological surface state with a Dirac point energy ...


Universal Doping Evolution Of The Superconducting Gap Anisotropy In Single Crystals Of Electron-Doped Ba(Fe1-Xrhx)(2)As-2 From London Penetration Depth Measurements, Hyunsoo Kim, Makariy A. Tanatar, C. Martin, E. C. Blomberg, Ni Ni, Sergey L. Bud’Ko, Paul C. Canfield, Ruslan Prozorov Jun 2018

Universal Doping Evolution Of The Superconducting Gap Anisotropy In Single Crystals Of Electron-Doped Ba(Fe1-Xrhx)(2)As-2 From London Penetration Depth Measurements, Hyunsoo Kim, Makariy A. Tanatar, C. Martin, E. C. Blomberg, Ni Ni, Sergey L. Bud’Ko, Paul C. Canfield, Ruslan Prozorov

Ames Laboratory Accepted Manuscripts

Doping evolution of the superconducting gap anisotropy was studied in single crystals of 4d-electron doped Ba(Fe1-xRhx)(2)As-2 using tunnel diode resonator measurements of the temperature variation of the London penetration depth Delta lambda(T). Single crystals with doping levels representative of an underdoped regime x = 0.039 (T-c = 15.5 K), close to optimal doping x = 0.057 (T-c = 24.4 K) and overdoped x = 0.079 (T-c = 21.5 K) and x = 0.131 (T-c = 4.9 K) were studied. Superconducting energy gap anisotropy was characterized by the exponent, n, by fitting the data to the power-law ...


Current Induced Depairing And Mixed State Behavior In The Bite/Fete Interfacial Superconductor, Charles Louis Dean Ii Apr 2018

Current Induced Depairing And Mixed State Behavior In The Bite/Fete Interfacial Superconductor, Charles Louis Dean Ii

Theses and Dissertations

The Bi2Te3/FeTe heterostructure intersects several phenomena and key classes of materials in condensed matter physics: topological insulators, superconductivity, magnetism, and the physics of interfaces. While neither the topological insulator (BiTe) nor the iron chalcogenide (FeTe) are themselves superconductors, superconductivity forms in a thin 7nm interfacial layer between the two. The restricted dimensionality and the extraordinarily conductive normal state, possibly sourced by the topologically protected surface states, have led to the observation of novel phenomena such as the Likharev vortex explosion and transitions in behavior resulting from the interplay between current induced depairing and the Berezinski-Kosterlitz-Thouless regime. The measured depairing ...


Aspects Of Topology In Quantum Phases Of Matter: A Journey Through Lands Both Flat And Not, Abhinav Prem Jan 2018

Aspects Of Topology In Quantum Phases Of Matter: A Journey Through Lands Both Flat And Not, Abhinav Prem

Physics Graduate Theses & Dissertations

Topological quantum phases of matter are often characterized by the presence of fractionalized quasiparticles, which exhibit non-trivial braiding statistics or carry fractional quantum numbers, or of protected gapless surface states. In this thesis, we study topological phases in two and three spatial dimensions, from the perspective of searching for new exotic quantum phases and of characterizing their experimental signatures.

We first study topological defects in fermionic paired superfluids and discover that in the presence of a multiply quantized vortex, such a state hosts unpaired fermions in the BCS regime. We predict that these unpaired fermions will result in an experimentally ...


Potassium Doped Polyphenyls As A Potential High Temperature Organic Superconductor, Taylor Moon Jan 2018

Potassium Doped Polyphenyls As A Potential High Temperature Organic Superconductor, Taylor Moon

Undergraduate Honors Theses

A major focus in condensed matter physics is finding materials which display superconductiv- ity at high temperatures, and examining the underlying causes of this behavior. Organic supercon- ductors have remained limited to lower temperatures, until Wang et al. suggested in March 2017 that p-terphenyl becomes superconducting when doped in a 3:1 ratio with potassium, with a critical temperature of 123 K. The investigations of the material have been limited by the ability to mea- sure conductivity, a key defining trait of superconductors. This thesis describes the investigation of several methods for producing doped material with a continuous conducting region ...


Pressure Effects On Magnetism And Superconductivity, Udhara Sampath Kaluarachchi Jan 2018

Pressure Effects On Magnetism And Superconductivity, Udhara Sampath Kaluarachchi

Graduate Theses and Dissertations

This thesis summarizes experimental work using high pressure as a tuning parameter in the study of selected correlated electron systems at low temperatures. This thesis contains 8 chapters and 2 appendices. After giving the introduction in Chapter 1, experimental techniques are discussed in Chapter 2. Chapters 3 and 5 are devoted to pressure studies of ferromagnetic materials. In ferromagnetic systems, the appearance of quantum criticality is avoided either by a change of the second order transition to one of the first-order at a tricritical point or by the appearance of modulated, antiferromagnetic, phase. Chapter 3 summarizes the pressure study of ...


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 Nov 2017

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

Ames Laboratory Accepted Manuscripts

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 ...


Non-Centrosymmetric Superconductivity And Magnetism In The Presence Of Broken Symmetries, Mojammel Alam Khan Oct 2017

Non-Centrosymmetric Superconductivity And Magnetism In The Presence Of Broken Symmetries, Mojammel Alam Khan

LSU Doctoral Dissertations

Non-centrosymmetric (NC) superconducting and magnetic compounds have been synthesized and investigated using magnetic, specific heat, and transport measurements, as well as by neutron scattering and quantum oscillations. The crystal structures of NC compounds are defined by the lack of an inversion center. In NC superconductors, a finite antisymmetric spin orbit coupling originating from broken inversion symmetry results in unconventional Cooper pairing. Instead of a single spin channel, the order parameter is a mixture of spin-singlet and spin-triplet states. For NC magnetic compounds, the antisymmetric and isotropic spin interactions compete, leading to a helical ground state.

We have studied the NC ...


Effective One-Dimensional Coupling In The Highly Frustrated Square-Lattice Itinerant Magnet Caco 2 − Y As 2, Aashish Sapkota, B. G. Ueland, V. K. Anand, N. S. Sangeetha, D. L. Abernathy, M. B. Stone, J. L. Niedziela, D. C. Johnston, A. Kreyssig, A. I. Goldman, R. J. Mcqueeney Oct 2017

Effective One-Dimensional Coupling In The Highly Frustrated Square-Lattice Itinerant Magnet Caco 2 − Y As 2, Aashish Sapkota, B. G. Ueland, V. K. Anand, N. S. Sangeetha, D. L. Abernathy, M. B. Stone, J. L. Niedziela, D. C. Johnston, A. Kreyssig, A. I. Goldman, R. J. Mcqueeney

Ames Laboratory Accepted Manuscripts

Inelastic neutron scattering measurements on the itinerant antiferromagnet CaCo2−yAs2 at a temperature of 8 K reveal two orthogonal planes of scattering perpendicular to the Co square lattice in reciprocal space, demonstrating the presence of effective one-dimensional spin interactions. These results are shown to arise from near-perfect bond frustration within the J1-J2 Heisenberg model on a square lattice with ferromagnetic J1 and hence indicate that the extensive previous experimental and theoretical study of the J1-J2 Heisenberg model on local-moment square spin lattices should be expanded to include itinerant spin systems.


Pressure Induced Half-Collapsed-Tetragonal Phase In Cakfe4as4, Udhara Kaluarachchi, Valentin Taufour, Aashish Sapkota, Vladislav Borisov, Tai Kong, W. R. Meier, Karunakar Kothapalli, Benjamin G. Ueland, Andreas Kreyssig, Roser Valenti, Robert J. Mcqueeney, Alan I. Goldman, Sergey L. Bud'ko, Paul C. Canfield Oct 2017

Pressure Induced Half-Collapsed-Tetragonal Phase In Cakfe4as4, Udhara Kaluarachchi, Valentin Taufour, Aashish Sapkota, Vladislav Borisov, Tai Kong, W. R. Meier, Karunakar Kothapalli, Benjamin G. Ueland, Andreas Kreyssig, Roser Valenti, Robert J. Mcqueeney, Alan I. Goldman, Sergey L. Bud'ko, Paul C. Canfield

Ames Laboratory Accepted Manuscripts

We report the temperature-pressure phase diagram of CaKFe4As4 established using high-pressure electrical resistivity, magnetization, and high-energy x-ray diffraction measurements up to 6 GPa. With increasing pressure, both resistivity and magnetization data show that the bulk superconducting transition of CaKFe4As4 is suppressed and then disappears at p≳4 GPa. High-pressure x-ray data clearly indicate a phase transition to a collapsed tetragonal phase in CaKFe4As4 under pressure that coincides with the abrupt loss of bulk superconductivity near 4 GPa. The x-ray data, combined with resistivity data, indicate that the collapsed tetragonal transition line is essentially independent of pressure, occurring at 4.0 ...


Calorimetric Measurements Of Magnetic-Field-Induced Inhomogeneous Superconductivity Above The Paramagnetic Limit, Charles C. Agosta, Nathanael Alexander Fortune, Scott T. Hannahs, Shuyao Gu, Lucy Liang, Ju-Hyun Park, John A. Schleuter Jun 2017

Calorimetric Measurements Of Magnetic-Field-Induced Inhomogeneous Superconductivity Above The Paramagnetic Limit, Charles C. Agosta, Nathanael Alexander Fortune, Scott T. Hannahs, Shuyao Gu, Lucy Liang, Ju-Hyun Park, John A. Schleuter

Physics: Faculty Publications

We report the first magnetocaloric and calorimetric observations of a magnetic-field-induced phase transition within a superconducting state to the long-sought exotic Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state, first predicted over 50 years ago. Through the combination of bulk thermodynamic calorimetric and magnetocaloric measurements in the organic superconductor κ−(BEDT−TTF)2Cu(NCS)2 as a function of temperature, magnetic field strength, and magnetic field orientation, we establish for the first time that this field-induced first-order phase transition at the paramagnetic limit Hp is a transition to a higher-entropy superconducting phase, uniquely characteristic of the FFLO state. We also establish that this high-field ...


Crabbing System For An Electron-Ion Collider, Alejandro Castilla Apr 2017

Crabbing System For An Electron-Ion Collider, Alejandro Castilla

Physics Theses & Dissertations

As high energy and nuclear physicists continue to push further the boundaries of knowledge using colliders, there is an imperative need, not only to increase the colliding beams’ energies, but also to improve the accuracy of the experiments, and to collect a large quantity of events with good statistical sensitivity. To achieve the latter, it is necessary to collect more data by increasing the rate at which these pro- cesses are being produced and detected in the machine. This rate of events depends directly on the machine’s luminosity. The luminosity itself is proportional to the frequency at which the ...


Nonlinear Dynamics Of Vortices In Different Types Of Grain Boundaries, Ahmad K. Sheikhzada Apr 2017

Nonlinear Dynamics Of Vortices In Different Types Of Grain Boundaries, Ahmad K. Sheikhzada

Physics Theses & Dissertations

As a major component of linear particle accelerators, superconducting radio-frequency (SRF) resonator cavities are required to operate with lowest energy dissipation and highest accelerating gradient. SRF cavities are made of polycrystalline materials in which grain boundaries can limit maximum RF currents and produce additional power dissipation sources due to local penetration of Josephson vortices. The essential physics of vortex penetration and mechanisms of dissipation of vortices driven by strong RF currents along networks of grain boundaries and their contribution to the residual surface resistance have not been well understood. To evaluate how GBs can limit the performance of SRF materials ...


Angle-Resolved Photoemission Spectroscopy Study Of High Temperature Superconductor Cuprate, And Potential High Temperature Superconductors K-Doped P-Terphenyl And Trilayer Nickelate, Haoxiang Li Jan 2017

Angle-Resolved Photoemission Spectroscopy Study Of High Temperature Superconductor Cuprate, And Potential High Temperature Superconductors K-Doped P-Terphenyl And Trilayer Nickelate, Haoxiang Li

Physics Graduate Theses & Dissertations

The macroscopic quantum phenomenology of superconductivity has attracted broad interest from both scientific research and applications. Many exotic physics found in the first high TC superconductor family cuprate remain unsolved even after 30 years of intense study. Angle-Resolved Photoemission Spectroscopy (ARPES) provides the direct probe to the major information of the electronic interactions, which plays the key role in these exotic physics including high TC superconductivity. ARPES is also the best tool to study the electronic structure in materials that potentially hold high TC superconductivity, providing insight for materials research and design.

In this thesis, we present ...


Cryogenic Rf Test Of The First Srf Cavity Etched In An Rf Ar/Cl2 Plasma, J. Upadhyay, A. Palczewski, S. Popovic, A.-M. Valente-Feliciano, Do Im, H. L. Phillips, L. Vuskovic Jan 2017

Cryogenic Rf Test Of The First Srf Cavity Etched In An Rf Ar/Cl2 Plasma, J. Upadhyay, A. Palczewski, S. Popovic, A.-M. Valente-Feliciano, Do Im, H. L. Phillips, L. Vuskovic

Physics Faculty Publications

An apparatus and a method for etching of the inner surfaces of superconducting radio frequency (SRF) accelerator cavities are described. The apparatus is based on the reactive ion etching performed in an Ar/Cl2 cylindrical capacitive discharge with reversed asymmetry. To test the effect of the plasma etching on the cavity rf performance, a 1497 MHz single cell SRF cavity was used. The single cell cavity was mechanically polished and buffer chemically etched and then rf tested at cryogenic temperatures to provide a baseline characterization. The cavity's inner wall was then exposed to the capacitive discharge in a ...


Power Distribution Of Terahertz Emission From Hexagonal Bscco Microstrip Antennas, Andrew E. Davis Jan 2017

Power Distribution Of Terahertz Emission From Hexagonal Bscco Microstrip Antennas, Andrew E. Davis

Honors Undergraduate Theses

We analyze the distribution of coherent terahertz radiation from a regular hexagonal microstrip antenna (MSA) made from the high-Tc superconductor Bi2Sr2CaCu2O8+x (BSCCO). We discuss the C6v symmetry of the solutions of the wave equation on a hexagonal domain and distinguish between the closed-form and non-closed-form solutions. The closed-form wavefunctions of the transverse magnetic (TM) electromagnetic cavity modes are presented and formulas for the radiated power arising from the uniform part of the AC Josephson current and from the resonant cavity modes are derived. The wavefunctions and angular distribution of radiation ...


Rotational Symmetry Breaking In A Trigonal Superconductor Nb-Doped Bi₂Se₃, T. Asaba, B. J. Lawson, C. Tinsman, L. Chen, P. Corbae, G. Li, Y. Qiu, Yew San Hor, L. Fu, L. Li Jan 2017

Rotational Symmetry Breaking In A Trigonal Superconductor Nb-Doped Bi₂Se₃, T. Asaba, B. J. Lawson, C. Tinsman, L. Chen, P. Corbae, G. Li, Y. Qiu, Yew San Hor, L. Fu, L. Li

Physics Faculty Research & Creative Works

The search for unconventional superconductivity has been focused on materials with strong spin-orbit coupling and unique crystal lattices. Doped bismuth selenide (Bi2Se3) is a strong candidate, given the topological insulator nature of the parent compound and its triangular lattice. The coupling between the physical properties in the superconducting state and its underlying crystal symmetry is a crucial test for unconventional superconductivity. In this paper, we report direct evidence that the superconducting magnetic response couples strongly to the underlying trigonal crystal symmetry in the recently discovered superconductor with trigonal crystal structure, niobium (Nb)-doped Bi2Se3 ...


Exact Solution Of Quadratic Fermionic Hamiltonians For Arbitrary Boundary Conditions, Abhijeet Alase, Emilio Cobanera, Gerardo Ortiz, Lorenza Viola Aug 2016

Exact Solution Of Quadratic Fermionic Hamiltonians For Arbitrary Boundary Conditions, Abhijeet Alase, Emilio Cobanera, Gerardo Ortiz, Lorenza Viola

Open Dartmouth: Faculty Open Access Scholarship

We present a procedure for exactly diagonalizing finite-range quadratic fermionic Hamiltonians with arbitrary boundary conditions in one of D dimensions, and periodic in the remaining D−1. The key is a Hamiltonian-dependent separation of the bulk from the boundary. By combining information from the two, we identify a matrix function that fully characterizes the solutions, and may be used to construct an efficiently computable indicator of bulk-boundary correspondence. As an illustration, we show how our approach correctly describes the zero-energy Majorana modes of a time-reversal-invariant s-wave two-band superconductor in a Josephson ring configuration, and predicts that a fractional 4π-periodic Josephson ...


Wavelet Transform Of Optical Conductivity Of Bi2sr2cacu2o8+X In The Normal And Superconducting State, Patrick Janovick Jan 2016

Wavelet Transform Of Optical Conductivity Of Bi2sr2cacu2o8+X In The Normal And Superconducting State, Patrick Janovick

Williams Honors College, Honors Research Projects

This paper compares the wavelet transform of the optical conductivity of Bi2Sr2CaCu2O8+x in both the normal and the superconducting state. The wavelet transforms of the normal and superconducting state are also compared with wavelet transforms of the Drude model as well as the Lorentz model. The wavelet transform of the collected data for Bi2Sr2CaCu2O8+x is similar in shape to the Drude model. The wavelet transform of the collected data in the normal state corresponds to the Drude model with a high scattering rate and ...


The Effect Of Impurities On The Superconductivity Of Bscco-2212, John Vastola Jan 2016

The Effect Of Impurities On The Superconductivity Of Bscco-2212, John Vastola

Honors Undergraduate Theses

BSCCO-2212 is a high-temperature cuprate superconductor whose microscopic behavior is currently poorly understood. In particular, it is unclear whether its order parameter is consistent with s-wave or d-wave symmetry. It has been suggested that its order parameter might take one of several forms that are consistent with d-wave behavior. We present some calculations using the many-body theory approach to superconductivity that suggest that such order parameters would lead to a suppression of the critical temperature in the presence of impurities. Because some experiments have suggested the critical temperature of BSCCO-2212 is relatively independent of the concentration of impurities, this lends ...


Anyonic Superconductivity In A Modified Large-U Hubbard Model, Asim Gangopadhyaya, Prasanta Panigrahi Dec 2015

Anyonic Superconductivity In A Modified Large-U Hubbard Model, Asim Gangopadhyaya, Prasanta Panigrahi

Asim Gangopadhyaya

A modified large-U Hubbard model at half filling is analyzed by a mean-field approach. Preserving a local U(1) symmetry of the action, the fluctuations about half filling are studied in the spirit of the commensurate-flux-phase condition. The fluctuations then contribute a Chern-Simons term to the tree-level Lagrangian with a coefficient appropriate to that of a half fermion. With the Coulomb repulsion term, we study the low-energy excitations of the model and show the existence of superconductivity in the presence of a four-Fermi interaction term.


Dynamical Generation Of Floquet Majorana Flat Bands In S-Wave Superconductors, A. Poudel, G. Ortiz, L. Viola Apr 2015

Dynamical Generation Of Floquet Majorana Flat Bands In S-Wave Superconductors, A. Poudel, G. Ortiz, L. Viola

Open Dartmouth: Faculty Open Access Scholarship

We present quantum control techniques to engineer flat bands of symmetry-protected Majorana edge modes in s -wave superconductors. Specifically, we show how periodic control may be employed for designing time-independent effective Hamiltonians, which support Floquet Majorana flat bands, starting from equilibrium conditions that are either topologically trivial or only support individual Majorana pairs. In the first approach, a suitable modulation of the chemical potential simultaneously induces Majorana flat bands and dynamically activates a pre-existing chiral symmetry which is responsible for their protection. In the second approach, the application of effective parity kicks dynamically generates a desired chiral symmetry by suppressing ...


Electron Dynamics In High Temperature Superconductors Studied Using Angle And Time-Resolved Photoemission Spectroscopy, Stephen Patrick Parham Jan 2015

Electron Dynamics In High Temperature Superconductors Studied Using Angle And Time-Resolved Photoemission Spectroscopy, Stephen Patrick Parham

Physics Graduate Theses & Dissertations

High-Temperature Superconductivity (HTSC) has inspired decades of research since its discovery in 1986 but remains an enigmatic subject to this day. At the heart of this difficulty is the highly correlated electronic behavior that limits the usefulness of modern theoretical calculations. Angle-Resolved Photoemission Spectroscopy (ARPES) has proved an invaluable tool in the study of HTSC because it can directly measure this correlated behavior through its effects on the electronic scattering rate. However, the electronic scattering rates extracted by conventional ARPES analysis techniques can be up to an order of magnitude larger than those measured by other techniques (such as optical ...


Microscopic Theory Of The Knight Shift, Bianca Hall Jan 2015

Microscopic Theory Of The Knight Shift, Bianca Hall

Electronic Theses and Dissertations

This dissertation is the beginning of the development of a microscopic theory of the Knight shift. The Knight shift experiment has been used in superconductivity research throughout history, however, a complete understanding of the Knight shift in conventional as well as unconventional superconductors does not yet exist. Motivated by the results of a literature review, which discusses Knight shift anomalies in multiple superconducting materials, this research studies a new model of the Knight shift, which involves the processes involved in nuclear magnetic resonance measurements in metals. The result of this study is a microscopic model of nuclear magnetic resonance in ...


Nature Of Magnetic Excitations In The Iron Pnictides And Its Pertinence To Superconductivity As Studied By Inelastic Neutron Scattering, Gregory Scott Tucker Jan 2015

Nature Of Magnetic Excitations In The Iron Pnictides And Its Pertinence To Superconductivity As Studied By Inelastic Neutron Scattering, Gregory Scott Tucker

Graduate Theses and Dissertations

Unconventional superconductivity and antiferromagnetism are often found in close proximity to one another. For the series of compounds Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, which possesses both antiferromagnetism and superconductivity for the under-doped range of composition, this observation is certainly true. The close proximity, and in fact coexistence for under-doped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, of antiferromagnetism and superconductivity has encouraged speculation that antiferromagnetic spin fluctuations may mediate the electron pairing interaction in unconventional superconductors. Previous studies indicated that the spin fluctuations at optimally-doped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2 ...


Study Of Ferroelectric Oxides And Field Effect In Complex Oxides Heterostructures, Lu Jiang Aug 2014

Study Of Ferroelectric Oxides And Field Effect In Complex Oxides Heterostructures, Lu Jiang

Doctoral Dissertations

With the rapid development of technology, the need for novel materials and state-of-theart devices is growing fast. Complex oxides which have strongly correlated electrons are favorable candidates for materials industry, due to their rich phase diagrams and multiple functions. Especially, ferroelectric oxides is very promising materials in the industry for storage, due to their bistable polarization states triggered by external electrical field. This thesis is centered on ferroelectric oxides, analyzing their lattice structures and investigating the interface of ferroelectrics and other complex oxides to examine the potential of the heteostructures in the application in electronic devices.

The most notable feature ...