+publisher:"University of Florida" +contributor:("Stewart, Gregory R")

University of Florida

1. Rowe, Wenya. Spin Fluctuation Theory for Unconventional Superconductivity in Antiferromagnetic Metals.

Degree: PhD, Physics, 2014, University of Florida

► The understanding of unconventional superconductivity is still a challenge for condensed matter physicists. To understand the interplay between antiferromagnetic order and superconductivity is crucial for… (more)

▼ The understanding of unconventional superconductivity is still a challenge for condensed matter physicists. To understand the interplay between antiferromagnetic order and superconductivity is crucial for the development of unconventional superconductivity theory, not only because the antiferromagnetic state coexists with superconductivity in many materials such as cuprates, iron-based pnictides, heavy fermions and organic superconductors, but also because spin fluctuations near a magnetically ordered phase have been proposed to possibly mediate superconductivity. In Chapter 1, we introduce the mechanism of spin fluctuations and review important categories of unconventional superconductors. In Chapter 2 we review elements of the relevant theory of magnetism. We discuss the differences between localized and itinerant approaches to study magnetism. We focus on cuprates which have a simple one-band Fermi surface. We use the Hubbard model to describe the band structure of the cuprates, and introduce the mean field phase diagram of electron-doped cuprates. In Chapter 3, we study the dynamic susceptibility of cuprates in the pure antiferromagnetic state and in the coexistence state of antiferromagnetism and superconductivity. We identify the key features of particle-hole spin excitations which are affected by the next-nearest neighbor hopping, t^′. We compare the different spin wave features between electron- and hole-doped cuprates. We conclude that the long range commensurate antiferromagnetic state is unstable on the hole doped side within the self-consistent-mean field theory due to the negative spin-stiffness. In the coexistence state, we see the spin resonance peak caused by superconductivity as well as the Goldstone mode in the spin excitation spectrum. Last we present the instability analysis of superconductivity from spin fluctuations in the antiferromagnetic state. We derive the superconducting pairing potentials and the gap equations for the spin singlet and triplet pairings. We separate the singlet potentials into longitudinal and transverse channels and expand the them around the pocket's center in the small pocket limit. Our result shows on the electron-doped side the leading symmetry is d_x^2-y²-wave and on the hole-doped side it is p-wave. This implies that from the paramagnetic state to the antiferromagnetic state, the superconducting gap has a smooth transition on the electron-doped side whereas the gap has to change symmetry on the hole-doped side. We conjecture that this may account for the lack of bulk coexistence of antiferromagnetic and superconducting order on the hole-doped side of the cuprates phase diagram. ( en ) Advisors/Committee Members: HIRSCHFELD,PETER J (committee chair), KUMAR,PRADEEP (committee member), STEWART,GREGORY R (committee member), PHILLPOT,SIMON R (committee member).

Subjects/Keywords: Cuprates; Doping; Electrons; Fermi surfaces; Magnetism; Magnons; Sine function; Superconductivity; Superconductors; Symmetry; antiferromagnetism – superconductivity

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APA (6^th Edition):

Rowe, W. (2014). Spin Fluctuation Theory for Unconventional Superconductivity in Antiferromagnetic Metals. (Doctoral Dissertation). University of Florida. Retrieved from https://ufdc.ufl.edu/UFE0046580

Chicago Manual of Style (16^th Edition):

Rowe, Wenya. “Spin Fluctuation Theory for Unconventional Superconductivity in Antiferromagnetic Metals.” 2014. Doctoral Dissertation, University of Florida. Accessed March 08, 2021. https://ufdc.ufl.edu/UFE0046580.

MLA Handbook (7^th Edition):

Rowe, Wenya. “Spin Fluctuation Theory for Unconventional Superconductivity in Antiferromagnetic Metals.” 2014. Web. 08 Mar 2021.

Vancouver:

Rowe W. Spin Fluctuation Theory for Unconventional Superconductivity in Antiferromagnetic Metals. [Internet] [Doctoral dissertation]. University of Florida; 2014. [cited 2021 Mar 08]. Available from: https://ufdc.ufl.edu/UFE0046580.

Council of Science Editors:

Rowe W. Spin Fluctuation Theory for Unconventional Superconductivity in Antiferromagnetic Metals. [Doctoral Dissertation]. University of Florida; 2014. Available from: https://ufdc.ufl.edu/UFE0046580

University of Florida

2. Tam, Gordon N. 22 K Superconductivity Induced in AeFe2As2 Post-Growth via Reactive Gases ( Subscripts on the numbers in AeFe2As2).

Degree: PhD, Physics, 2019, University of Florida

URL: https://ufdc.ufl.edu/UFE0054337

► Iron based superconductors are among the least understood superconductors. One aspect that has puzzled researchers for nearly as long as their existence since discovery is… (more)

Subjects/Keywords: fluorine – iron – superconductivity

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APA (6^th Edition):

Tam, G. N. (2019). 22 K Superconductivity Induced in AeFe2As2 Post-Growth via Reactive Gases ( Subscripts on the numbers in AeFe2As2). (Doctoral Dissertation). University of Florida. Retrieved from https://ufdc.ufl.edu/UFE0054337

Chicago Manual of Style (16^th Edition):

Tam, Gordon N. “22 K Superconductivity Induced in AeFe2As2 Post-Growth via Reactive Gases ( Subscripts on the numbers in AeFe2As2).” 2019. Doctoral Dissertation, University of Florida. Accessed March 08, 2021. https://ufdc.ufl.edu/UFE0054337.

MLA Handbook (7^th Edition):

Tam, Gordon N. “22 K Superconductivity Induced in AeFe2As2 Post-Growth via Reactive Gases ( Subscripts on the numbers in AeFe2As2).” 2019. Web. 08 Mar 2021.

Vancouver:

Tam GN. 22 K Superconductivity Induced in AeFe2As2 Post-Growth via Reactive Gases ( Subscripts on the numbers in AeFe2As2). [Internet] [Doctoral dissertation]. University of Florida; 2019. [cited 2021 Mar 08]. Available from: https://ufdc.ufl.edu/UFE0054337.

Council of Science Editors:

Tam GN. 22 K Superconductivity Induced in AeFe2As2 Post-Growth via Reactive Gases ( Subscripts on the numbers in AeFe2As2). [Doctoral Dissertation]. University of Florida; 2019. Available from: https://ufdc.ufl.edu/UFE0054337

University of Florida

3. Wang, Yan. Theory of Gap Symmetry and Structure in Fe-Based Superconductors.

Degree: PhD, Physics, 2014, University of Florida

URL: https://ufdc.ufl.edu/UFE0046628

► We consider a series of problems related to determining the origin of superconductivity in the recently discovered iron pnictide and chalcogenide materials, where the common… (more)

Subjects/Keywords: Anisotropy; Cuprates; Electrons; Fermi surfaces; Magnetic fields; Sine function; Specific heat; Superconductivity; Superconductors; Symmetry; chalcogenide – disordered – gap – impurity – pairing – pnictide – rpa – spinfluctuation – structure – sts – superconductivity – superconductor – symmetry – vortex

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Wang, Y. (2014). Theory of Gap Symmetry and Structure in Fe-Based Superconductors. (Doctoral Dissertation). University of Florida. Retrieved from https://ufdc.ufl.edu/UFE0046628

Chicago Manual of Style (16^th Edition):

Wang, Yan. “Theory of Gap Symmetry and Structure in Fe-Based Superconductors.” 2014. Doctoral Dissertation, University of Florida. Accessed March 08, 2021. https://ufdc.ufl.edu/UFE0046628.

MLA Handbook (7^th Edition):

Wang, Yan. “Theory of Gap Symmetry and Structure in Fe-Based Superconductors.” 2014. Web. 08 Mar 2021.

Vancouver:

Wang Y. Theory of Gap Symmetry and Structure in Fe-Based Superconductors. [Internet] [Doctoral dissertation]. University of Florida; 2014. [cited 2021 Mar 08]. Available from: https://ufdc.ufl.edu/UFE0046628.

Council of Science Editors:

Wang Y. Theory of Gap Symmetry and Structure in Fe-Based Superconductors. [Doctoral Dissertation]. University of Florida; 2014. Available from: https://ufdc.ufl.edu/UFE0046628

University of Florida

4. Timmerwilke, John M. Point Contact Studies of Iron Based Superconductors.

Degree: PhD, Physics, 2013, University of Florida

URL: https://ufdc.ufl.edu/UFE0045403

► This work presents spectroscopic measurements on Cobalt doped Barium Iron Arsenide at different dopings. The technique used is Point-Contact Spectroscopy, PCS. This technique is well… (more)

Subjects/Keywords: Anisotropy; Crystals; Doping; Electric potential; Electrons; Spectroscopy; Superconductivity; Superconductors; Symmetry; Uniform Resource Locators; iron-based – point-contact – superconductivity

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Timmerwilke, J. M. (2013). Point Contact Studies of Iron Based Superconductors. (Doctoral Dissertation). University of Florida. Retrieved from https://ufdc.ufl.edu/UFE0045403

Chicago Manual of Style (16^th Edition):

Timmerwilke, John M. “Point Contact Studies of Iron Based Superconductors.” 2013. Doctoral Dissertation, University of Florida. Accessed March 08, 2021. https://ufdc.ufl.edu/UFE0045403.

MLA Handbook (7^th Edition):

Timmerwilke, John M. “Point Contact Studies of Iron Based Superconductors.” 2013. Web. 08 Mar 2021.

Vancouver:

Timmerwilke JM. Point Contact Studies of Iron Based Superconductors. [Internet] [Doctoral dissertation]. University of Florida; 2013. [cited 2021 Mar 08]. Available from: https://ufdc.ufl.edu/UFE0045403.

Council of Science Editors:

Timmerwilke JM. Point Contact Studies of Iron Based Superconductors. [Doctoral Dissertation]. University of Florida; 2013. Available from: https://ufdc.ufl.edu/UFE0045403

University of Florida

5. MISHRA,VIVEK. Fluctuation, Disorder and Inhomogeneity in Unconventional Superconductors.

Degree: PhD, Physics, 2011, University of Florida

URL: https://ufdc.ufl.edu/UFE0042738

► In this dissertation, I present the results of theoretical investigations of the effect of fluctuations Advisors/Committee Members: Hirschfeld, Peter J (committee chair), (more)

Subjects/Keywords: Critical temperature; Doping; Electrons; Fermi surfaces; Impurities; Inhomogeneity; Low temperature; Magnetic fields; Superconductors; Thermal conductivity; DISORDERED – FERMI – IRON – MODELS – NODE – SUPERCONDUCTING – SUPERFLUID – THERMAL – UNCONVENTIONAL – UNDERDOPED

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

MISHRA,VIVEK. (2011). Fluctuation, Disorder and Inhomogeneity in Unconventional Superconductors. (Doctoral Dissertation). University of Florida. Retrieved from https://ufdc.ufl.edu/UFE0042738

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Chicago Manual of Style (16^th Edition):

MISHRA,VIVEK. “Fluctuation, Disorder and Inhomogeneity in Unconventional Superconductors.” 2011. Doctoral Dissertation, University of Florida. Accessed March 08, 2021. https://ufdc.ufl.edu/UFE0042738.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

MLA Handbook (7^th Edition):

MISHRA,VIVEK. “Fluctuation, Disorder and Inhomogeneity in Unconventional Superconductors.” 2011. Web. 08 Mar 2021.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Vancouver:

MISHRA,VIVEK. Fluctuation, Disorder and Inhomogeneity in Unconventional Superconductors. [Internet] [Doctoral dissertation]. University of Florida; 2011. [cited 2021 Mar 08]. Available from: https://ufdc.ufl.edu/UFE0042738.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Council of Science Editors:

MISHRA,VIVEK. Fluctuation, Disorder and Inhomogeneity in Unconventional Superconductors. [Doctoral Dissertation]. University of Florida; 2011. Available from: https://ufdc.ufl.edu/UFE0042738

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

University of Florida

6. Boyd, Gregory. Thermodynamic and Transport Properties of Unconventional Superconductors and Multiferroics.

Degree: PhD, Physics, 2010, University of Florida

URL: https://ufdc.ufl.edu/UFE0042391

► Often, the phase diagram for a given material can be quite complex, presenting evidence for multiple orders and it is the task of the condensed… (more)

▼ Often, the phase diagram for a given material can be quite complex, presenting evidence for multiple orders and it is the task of the condensed matter community to describe and quantify knowledge of these properties. Significant insight can often be gained by comparing model calculations of basic thermodynamic and transport properties of a material with experiment. Here we consider two classes of novel materials whose rich phase diagrams are actively under investigation: unconventional superconductors and multiferroics. In 2006, H.Hosono discovered a new class of iron-based superconducting materials which are not conventional superconductors. After the initial discovery, there is a range of questions of immediate interest; foremost among them is what is the structure and symmetry of the superconducting state, a question which took roughly a decade to answer for the cuprate superconductors. We present calculations that help reveal the structure of the superconducting gap using angle dependent specific heat measurements. We then calculate the electronic Raman scattering intensity for several polarizations of light and different models of disorder, providing information about the anisotropy and location of nodes in the superconducting gap. Understanding the influence of disorder is considered crucial because currently conflicting experimental results may be due to differences in sample quality. Recently, there has also been interest in multiferroics: materials with simultaneous non-zero polarization and magnetic order. We present calculations of fundamental thermodynamic properties, mean field behavior for the simplest ferromagnetic-ferroelectric, characterize topological defects, and use the perturbative renormalization group to help understand the critical point, as a beginning towards understanding the multitude multiferroic materials with increasingly complex magnetic and polar order. ( en ) Advisors/Committee Members: Hirschfeld, Peter J. (committee chair), Matchev, Konstantin T. (committee member), Dorsey, Alan T. (committee member), Maslov, Dmitrii (committee member), Stewart, Gregory R. (committee member), Phillpot, Simon R. (committee member).

Subjects/Keywords: Cuprates; Doping; Impurities; Magnetic fields; Magnetism; Physics; Quasiparticles; Specific heat; Superconductors; Symmetry; cuprate, multiferroic, pnictide, superconductor

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Boyd, G. (2010). Thermodynamic and Transport Properties of Unconventional Superconductors and Multiferroics. (Doctoral Dissertation). University of Florida. Retrieved from https://ufdc.ufl.edu/UFE0042391

Chicago Manual of Style (16^th Edition):

Boyd, Gregory. “Thermodynamic and Transport Properties of Unconventional Superconductors and Multiferroics.” 2010. Doctoral Dissertation, University of Florida. Accessed March 08, 2021. https://ufdc.ufl.edu/UFE0042391.

MLA Handbook (7^th Edition):

Boyd, Gregory. “Thermodynamic and Transport Properties of Unconventional Superconductors and Multiferroics.” 2010. Web. 08 Mar 2021.

Vancouver:

Boyd G. Thermodynamic and Transport Properties of Unconventional Superconductors and Multiferroics. [Internet] [Doctoral dissertation]. University of Florida; 2010. [cited 2021 Mar 08]. Available from: https://ufdc.ufl.edu/UFE0042391.

Council of Science Editors:

Boyd G. Thermodynamic and Transport Properties of Unconventional Superconductors and Multiferroics. [Doctoral Dissertation]. University of Florida; 2010. Available from: https://ufdc.ufl.edu/UFE0042391

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