Magnetic Force Microscopy Studies Of Unconventional Superconductors
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Magnetic Force Microscopy Studies Of Unconventional Superconductors
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Author : Lan Luan
language : en
Publisher: Stanford University
Release Date : 2011
Magnetic Force Microscopy Studies Of Unconventional Superconductors written by Lan Luan and has been published by Stanford University this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
Superconductivity is among the most fascinating properties that a material can have. Below the transition temperature $T_c$, electrons condensate into a macroscopic quantum mechanical state and flow without dissipation. The quantum nature of the superconducting state also manifests in its magnetic properties. Superconductors fully expels magnetic field in a weak applied field, referred as Meissner effect. In an intermediate field, superconductors often contain microscopic whirlpools of electrons that carry quantized magnetic flux, called vortices. In this thesis, I present magnetic-force-microscopy (MFM) studies of unconventional superconductors both in the Meissner state and in the mix state. We extend the application of MFM beyond the conventional imaging mode and use it for quantitative analysis. In the mix state, we use MFM manipulating individual vortices with a high level of control and a known force to study the mechanics and dynamics of a single vortex in cuprate superconductors. In the Messiner state, we establish MFM as a novel local technique to measure the magnetic penetration depth $\lambda$ and implement it to study the pairing mechanism of iron-pnictide superconductors. Chapter 1 contains a brief introduction of MFM and its conventional application of imaging. We demonstrate high-spatial resolution images of isolated superconducting vortices. We show that by integrating images of isolated vortices at consecutive heights we are able to reconstruct the force between the MFM tip and vortices. We can also obtain the force by using a tip-vortex model. The two methods agree and both allow us to obtain the force used in vortex manipulation discussed in Chapter 2 and Chapter 3. Chapter 2 discusses the behavior of individual vortices in fully doped YBa$_2$Cu$_3$O$_{7-\delta}$ when subject to a local force. Because the anisotropy of fully doped YBa$_2$Cu$_3$O$_{7-\delta}$ is moderate, the vortex motion can be well described as an elastic string moving through a uniform three dimensional pinning landscape. We find an unexpected and marked enhancement of the response of a vortex to pulling when we wiggle it transversely. In addition, we find enhanced vortex pinning anisotropy that suggests clustering of oxygen vacancies in our sample. We demonstrate manipulation at the nanoscale with a level of control far beyond what has been reported before. We show that a dragged vortex can be used to probe deep into the bulk of the sample and to interact with microscopic structures much smaller than the tip size. Chapter 3 shows the vortex behavior in another limit. In an very underdoped YBa$_2$Cu$_3$O$_{6+x}$ single crystal, a cuprate superconductor with strong anisotropy, a vortex can be regarded as a stack of two-dimensional pancakes with weak interlayer Josephson coupling. We use the MFM tip to split the pancake stacks composing a single vortex and to produce a kinked structure. Our measurements highlight the discrete nature of stacks of pancake vortices in layered superconductors. We also measure the required force in the process, providing the first measurement of the interlayer coupling at the single vortex level. The discovery of iron-pnictide superconductors in 2008 motivates my efforts to locally measure the magnetic penetration depth $\lambda$, one of the two fundamental length scales in superconductors and known to be difficult to measure. Chapter 4 discusses the methodology of measuring $\lambda$ by MFM, which is based on the time-reversed mirror approximation an analytical model of the MFM tip-superconductor interaction in the Meissner state. A calibration run was performed on \YBCO\ single crystals with known $\lambda$. The same time-reversed mirror approximation can be applied to scanning SQUID sysceptometry (SSS) to measure the temperature variation of penetration depth $\Delta\lambda(T)\equiv\lambda(T)-\lambda(0)$. Chapter 5 includes brief introduction of the iron-pnictide superconductors. The multiple conduction bands and the vicinity of the superconducting phase to magnetic phase give additional challenges in $\lambda$ measurements. We demonstrated in this chapter on single crystals of Ba(Fe$_{0.95}$Co$_{0.05}$)$_2$As$_2$ that MFM can measure the absolute value of $\lambda$, as well as obtain its temperature dependence and spatial homogeneity. We observe that $\Delta\lambda(T)$ varies 20 times slower with temperature than previously reported by bulk techniques, and that $\rho_s(T)$ over the full temperature range is well described by a clean two-band fully gapped model, consistent with the proposed $s\pm$ pairing symmetry. Chapter 6 extends the measurements of $\rho_s(T)$ to the family Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ with Co doping level $x$ across the superconducting dome. We observe systematic evolution of $\rho_s(T)$ with $x$ that can be summarized as three main trends. First, $\rho_s(0)$ falls more quickly with $T_c$ on the underdoped side of the dome than on the overdoped. Second, the temperature variation of $\rho_s(T)$ at low temperature increases away from optimal doping. Third, $\rho_s(T)$ increases sharply with cooling through the superconducting transition temperature $T_c$ of both optimally doped and underdoped compounds. These observations hint an interplay between magnetism and superconductivity.
Magnetic Force Microscopy Studies Of Unconventional Superconductors
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Author : Lan Luan
language : en
Publisher:
Release Date : 2011
Magnetic Force Microscopy Studies Of Unconventional Superconductors written by Lan Luan and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
Superconductivity is among the most fascinating properties that a material can have. Below the transition temperature $T_c$, electrons condensate into a macroscopic quantum mechanical state and flow without dissipation. The quantum nature of the superconducting state also manifests in its magnetic properties. Superconductors fully expels magnetic field in a weak applied field, referred as Meissner effect. In an intermediate field, superconductors often contain microscopic whirlpools of electrons that carry quantized magnetic flux, called vortices. In this thesis, I present magnetic-force-microscopy (MFM) studies of unconventional superconductors both in the Meissner state and in the mix state. We extend the application of MFM beyond the conventional imaging mode and use it for quantitative analysis. In the mix state, we use MFM manipulating individual vortices with a high level of control and a known force to study the mechanics and dynamics of a single vortex in cuprate superconductors. In the Messiner state, we establish MFM as a novel local technique to measure the magnetic penetration depth $\lambda$ and implement it to study the pairing mechanism of iron-pnictide superconductors. Chapter 1 contains a brief introduction of MFM and its conventional application of imaging. We demonstrate high-spatial resolution images of isolated superconducting vortices. We show that by integrating images of isolated vortices at consecutive heights we are able to reconstruct the force between the MFM tip and vortices. We can also obtain the force by using a tip-vortex model. The two methods agree and both allow us to obtain the force used in vortex manipulation discussed in Chapter 2 and Chapter 3. Chapter 2 discusses the behavior of individual vortices in fully doped YBa$_2$Cu$_3$O$_{7-\delta}$ when subject to a local force. Because the anisotropy of fully doped YBa$_2$Cu$_3$O$_{7-\delta}$ is moderate, the vortex motion can be well described as an elastic string moving through a uniform three dimensional pinning landscape. We find an unexpected and marked enhancement of the response of a vortex to pulling when we wiggle it transversely. In addition, we find enhanced vortex pinning anisotropy that suggests clustering of oxygen vacancies in our sample. We demonstrate manipulation at the nanoscale with a level of control far beyond what has been reported before. We show that a dragged vortex can be used to probe deep into the bulk of the sample and to interact with microscopic structures much smaller than the tip size. Chapter 3 shows the vortex behavior in another limit. In an very underdoped YBa$_2$Cu$_3$O$_{6+x}$ single crystal, a cuprate superconductor with strong anisotropy, a vortex can be regarded as a stack of two-dimensional pancakes with weak interlayer Josephson coupling. We use the MFM tip to split the pancake stacks composing a single vortex and to produce a kinked structure. Our measurements highlight the discrete nature of stacks of pancake vortices in layered superconductors. We also measure the required force in the process, providing the first measurement of the interlayer coupling at the single vortex level. The discovery of iron-pnictide superconductors in 2008 motivates my efforts to locally measure the magnetic penetration depth $\lambda$, one of the two fundamental length scales in superconductors and known to be difficult to measure. Chapter 4 discusses the methodology of measuring $\lambda$ by MFM, which is based on the time-reversed mirror approximation an analytical model of the MFM tip-superconductor interaction in the Meissner state. A calibration run was performed on \YBCO\ single crystals with known $\lambda$. The same time-reversed mirror approximation can be applied to scanning SQUID sysceptometry (SSS) to measure the temperature variation of penetration depth $\Delta\lambda(T)\equiv\lambda(T)-\lambda(0)$. Chapter 5 includes brief introduction of the iron-pnictide superconductors. The multiple conduction bands and the vicinity of the superconducting phase to magnetic phase give additional challenges in $\lambda$ measurements. We demonstrated in this chapter on single crystals of Ba(Fe$_{0.95}$Co$_{0.05}$)$_2$As$_2$ that MFM can measure the absolute value of $\lambda$, as well as obtain its temperature dependence and spatial homogeneity. We observe that $\Delta\lambda(T)$ varies 20 times slower with temperature than previously reported by bulk techniques, and that $\rho_s(T)$ over the full temperature range is well described by a clean two-band fully gapped model, consistent with the proposed $s\pm$ pairing symmetry. Chapter 6 extends the measurements of $\rho_s(T)$ to the family Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ with Co doping level $x$ across the superconducting dome. We observe systematic evolution of $\rho_s(T)$ with $x$ that can be summarized as three main trends. First, $\rho_s(0)$ falls more quickly with $T_c$ on the underdoped side of the dome than on the overdoped. Second, the temperature variation of $\rho_s(T)$ at low temperature increases away from optimal doping. Third, $\rho_s(T)$ increases sharply with cooling through the superconducting transition temperature $T_c$ of both optimally doped and underdoped compounds. These observations hint an interplay between magnetism and superconductivity.
Scanning Squid Microscopy Of Unconventional Superconductivity And Frustrated Magnetism
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Author : Christopher Aaron Watson
language : en
Publisher:
Release Date : 2018
Scanning Squid Microscopy Of Unconventional Superconductivity And Frustrated Magnetism written by Christopher Aaron Watson and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018 with categories.
Scanning SQUID microscopy makes a unique contribution to the study of quantum materials, including unconventional superconductors and frustrated magnets, as it is a scanned probe technique and a highly quantitative magnetic probe. The ability to scan means that we are able to spatially resolve material properties, which is important as the samples tend to be complex lattices comprised of 3 or more elements, sometimes including dopants that are disordered by construction. Materials can never be grown perfectly, and this leads to a variety of possible material defects; additionally, materials that go through phase transitions, such as structural or magnetic transitions, will often have non-trivial domain structure that also leads to spatial variation. By spatially resolving such defects and domain boundaries, we are able to gain an understanding of how and why they interact with the properties under study. Chapters 2 and 3 serve as an introduction to the physics of SQUIDs and the art and science of scanning SQUID microscopy. These are directed primarily towards new students and practitioners, with the goal of reducing the learning curve for the technique, which can be quite challenging to overcome. Chapter 4 covers different measurement techniques that use scanning SQUID microscopy through short descriptions and case studies. The experiments covered include disordered Nb dot arrays, the split superconducting transition of PrOs4Sb12, the anisotropy of the penetration depth in single crystals of x = 1/8 LSCO, and magnetism in oxygen deficient LAO/STO heterostructures. In Chapter 5, I cover the integration of a piezoelectric-based strain cell with scanning SQUID microscopy and its implementation in studying the purported chiral superconductor, Sr2RuO4. The ability to tune anisotropic strain in situ provides a symmetry-breaking field that is compatible with SQUID electronics and promises to have many future applications. In this experiment, we ruled out the existence of a linear cusp in the response of the superconducting transition temperature to the applied anisotropic strain at the level predicted by theory. We do not rule out the possibility that Sr2RuO4 is a chiral order parameter, but it remains an open question why this signature would be smaller than predicted. The next chapter, Ch. 6, covers magnetic susceptibility measurements of bulk samples of x = 1/8. Samples at this doping show a reported bulk superconducting transition temperature much lower than those at both higher and lower dopings; furthermore, a cascade of phase transitions including structural transitions, charge ordering, and spin ordering occur as the temperature is reduced, and the transition to a bulk superconducting state is preceded by a diverging resistivity anisotropy that has led to the proposal of an exotic pair density wave state. We find instead that the superconducting transition in this material is grossly inhomogeneous, occurring at substantially higher temperatures in some regions, such as edges and terraces. This suggests that the resistivity anisotropy may be due to the percolation in two but not three dimensions of superconducting filaments along such defects. Chapter 7 focuses on the classical spin ice Ho2Ti2O7, a canonical example of frustrated magnetism. This work represents the first comprehensive study using scanning SQUID microscopy for magnetic flux noise spectroscopy, which we employed to disentangle the magnetic dynamics in our sample due to defects and theoretically predicted monopole-like excitations. We find that our data qualitatively deviate from simple models for spin ensembles in several ways that are consistent with the expectations for a dilute, low-mobility gas of magnetic monopoles. This technique promises to be essential in future studies of frustrated magnetic systems, including the search for quantum spin liquids. Chapter 8 covers work on engineered, exotic superconducting junctions. With devices comprised of the junction under study with conventional superconducting leads that close on one another to realize a ring structure, we are able to position our SQUID susceptometer over each device to conduct a measurement of the current-phase relationship. We demonstrate that the high transmission states at the surface of 3D topological insulator HgTe give rise to a distinctly non-sinusoidal current-phase relationship that is forward-skewed. The power of this technique is at least in part in our ability to measure many such devices in a single experiment, owing to the non-contact nature of the measurement. In concluding in Chapter 9, I attempt to tie together several overarching themes of my graduate work and give a coherent view of where scanning SQUID microscopy might be headed, including potential avenues for instrumentation development and new imaging modalities. The work contained in this thesis was conducted as part of the Stanford Institute for Materials and Energy Sciences and was funded by the Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract No. DE-AC02-76SF00515.
Low Temperature Magnetic Force Microscopy Studies Of Superconducting Niobium Films Microform
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Author : Mark A. Roseman
language : en
Publisher: National Library of Canada = Bibliothèque nationale du Canada
Release Date : 2001
Low Temperature Magnetic Force Microscopy Studies Of Superconducting Niobium Films Microform written by Mark A. Roseman and has been published by National Library of Canada = Bibliothèque nationale du Canada this book supported file pdf, txt, epub, kindle and other format this book has been release on 2001 with categories.
"Low temperature magnetic force microscopy studies of superconducting niobium films have been undertaken with the goal of studying the interplay between artificial pinning centers and magnetic vortices." --
Unconventional Superconductors
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Author : Gernot Goll
language : en
Publisher: Springer Science & Business Media
Release Date : 2006
Unconventional Superconductors written by Gernot Goll and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with Science categories.
This book offers a comprehensive summary of experiments that are especially suited to reveal the order-parameter symmetry of unconventional superconductors. It briefly introduces readers to the basic theoretical concepts and terms of unconventional superconductivity, followed by a detailed overview of experimental techniques and results investigating the superconducting energy gap and phase, plus the pairing symmetry. This review includes measurements of specific heat, thermal conductivity, penetration depth and nuclearmagnetic resonance and muon-spin rotation experiments. Further, point-contact and tunnelling spectroscopy and Josephson experiments are addressed. Current understanding is reviewed from the experimental point of view. With an appendix offering five tables with almost 200 references that summarize the present results from ambient pressure heavy-fermion and noncopper-oxide superconductors, the monograph provides a valuable resource for further studies in this field.
Vortices In Unconventional Superconductors And Superfluids
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Author : R.P. Huebener
language : en
Publisher: Springer Science & Business Media
Release Date : 2013-03-09
Vortices In Unconventional Superconductors And Superfluids written by R.P. Huebener and has been published by Springer Science & Business Media this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-03-09 with Technology & Engineering categories.
Presents a modern treatment of the physics of vortex matter, mainly applied to unconventional superconductors and superfluids but with extensions to other areas of physics.
Microwave Analysis Of Unconventional Superconductors With Coplanar Resonator Techniques
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Author : Gianluca Ghigo
language : en
Publisher: Springer Nature
Release Date : 2022-01-29
Microwave Analysis Of Unconventional Superconductors With Coplanar Resonator Techniques written by Gianluca Ghigo and has been published by Springer Nature this book supported file pdf, txt, epub, kindle and other format this book has been release on 2022-01-29 with Technology & Engineering categories.
This book provides a thorough overview of methods and approaches to the experimental characterization of superconductors at microwave frequencies, and includes a detailed description of the two main techniques, both based on the use of coplanar waveguide resonators, that the authors employed to investigate the properties of unconventional superconductors. In the second part several case studies are described, covering a large spectrum of materials and issues. Particular emphasis is given to recent hot topics concerning iron-based superconductors, both of fundamental nature and relevant for applications. The book is intended as a learning tool for researchers in the field, and serves as a guide providing inspiring examples of the use of coplanar resonator techniques to address key topics in the field of unconventional superconductivity.
Ruthenate And Rutheno Cuprate Materials
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Author : C. Noce
language : en
Publisher: Springer
Release Date : 2008-01-11
Ruthenate And Rutheno Cuprate Materials written by C. Noce and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008-01-11 with Technology & Engineering categories.
Ruthenate materials have come into focus recently because of their very interesting magnetic and superconducting properties. From the first international conference on this topic, the present volume has emerged as a first coherent account of the considerable body of work, both theoretical and experimental, gathered in this field within a short time span. The book has been written in the form of a set of lectures and tutorial reviews with the aim of providing the research community with both a comprehensive and modern source of reference and a tutorial introduction for postgraduate students and nonspecialists working in related areas.
High Magnetic Field Science And Its Application In The United States
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Author : National Research Council
language : en
Publisher: National Academies Press
Release Date : 2013-12-25
High Magnetic Field Science And Its Application In The United States written by National Research Council and has been published by National Academies Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-12-25 with Science categories.
The Committee to Assess the Current Status and Future Direction of High Magnetic Field Science in the United States was convened by the National Research Council in response to a request by the National Science Foundation. This report answers three questions: (1) What is the current state of high-field magnet science, engineering, and technology in the United States, and are there any conspicuous needs to be addressed? (2) What are the current science drivers and which scientific opportunities and challenges can be anticipated over the next ten years? (3) What are the principal existing and planned high magnetic field facilities outside of the United States, what roles have U.S. high field magnet development efforts played in developing those facilities, and what potentials exist for further international collaboration in this area? A magnetic field is produced by an electrical current in a metal coil. This current exerts an expansive force on the coil, and a magnetic field is "high" if it challenges the strength and current-carrying capacity of the materials that create the field. Although lower magnetic fields can be achieved using commercially available magnets, research in the highest achievable fields has been, and will continue to be, most often performed in large research centers that possess the materials and systems know-how for forefront research. Only a few high field centers exist around the world; in the United States, the principal center is the National High Magnetic Field Laboratory (NHMFL). High Magnetic Field Science and Its Application in the United States considers continued support for a centralized high-field facility such as NHFML to be the highest priority. This report contains a recommendation for the funding and siting of several new high field nuclear magnetic resonance magnets at user facilities in different regions of the United States. Continued advancement in high-magnetic field science requires substantial investments in magnets with enhanced capabilities. High Magnetic Field Science and Its Application in the United States contains recommendations for the further development of all-superconducting, hybrid, and higher field pulsed magnets that meet ambitious but achievable goals.
The Oxford Handbook Of Small Superconductors
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Author : A. V. Narlikar
language : en
Publisher: Oxford University Press
Release Date : 2017
The Oxford Handbook Of Small Superconductors written by A. V. Narlikar and has been published by Oxford University Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017 with Science categories.
Mesoscopic superconductors achieve a level of smallness that reveals the dominance of strange quantum effects. In a world driven by the miniaturization of electronic device technology, small superconductors acquire great relevance and timeliness for the development of ground breaking novel quantum devices.