Magnetic Dynamics in Iron-based Superconductors Probed by Neutron Spectroscopy PDF Download
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Author: Alice Elizabeth Taylor
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Alice Elizabeth Taylor
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Franziska Hammerath
Publisher: Springer Science & Business Media
ISBN: 3834824232
Category : Science
Languages : en
Pages : 183
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Nuclear Magnetic Resonance (NMR) has been a fundamental player in the studies of superconducting materials for many decades. This local probe technique allows for the study of the static electronic properties as well as of the low energy excitations of the electrons in the normal and the superconducting state. On that account it has also been widely applied to Fe-based superconductors from the very beginning of their discovery in February 2008. This dissertation comprises some of these very first NMR results, reflecting the unconventional nature of superconductivity and its strong link to magnetism in the investigated compounds LaO1–xFxFeAs and LiFeAs.
Author: Leland Weldon Harriger
Publisher:
ISBN:
Category :
Languages : en
Pages : 196
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Presented within are neutron scattering studies detailing the spin dynamics of BaNi[subscript x]Fe2[subscript x]As2 for x = 0 (parent), 0.04 (underdoped), and 0.1 (optimal) dopings, and FeSe[subscript x]Te1[subscript x] for x = 0 (parent), 0.3 (underdoped), and 0.4 (optimal) dopings. These recently discovered Fe-based superconducting compounds are strikingly similar, in many respects, to the cuprate class of unconventional superconductors and share qualitatively similar phase diagrams consisting of a long range ordered magnetic ground state in the parents which, upon doping, is supplanted in favor of superconductivity. The dopings discussed herein allow us to tune through the phase diagram, beginning with long range ordered parents and ending with optimally doped superconductors with short range magnetic correlations. For BaFe2As2, the excitations in the ordered state are strongly damped and persist up to 300meV. Low energies excitations are centered around Q[subscript AMF] and disperse towards the zone boundary with increasing energy. Only scattering above 100meV is effected when warming above T[subscript N]. In underdoped x = 0.04 BaNi[subscript x]Fe2−[subscript x]As2, we find an order of magnitude reduction in the coupling between layers and a corresponding crossover from 3D to 2D magnetism. In coauthor work on optimal doped x = 0.1 BaNi[subscript x]Fe2−[subscript x]As2 we establish the existence of a 3D resonance mode in the superconducting state. Excitations at optimal doping above the resonance are very similar to the paramagnetic scattering observed in the parent and consists of diffuse scattering below 100meV while above this threshold the signal has similar dispersion, linewidths, and intensity as the ordered state. For FeTe, I discuss our existing efforts and data collection aimed at addressing issues associated with calculating the effective moment from Q, E-integrated data. Tuning through the phase diagram to the x = 0.3 underdoped FeSe[subscript x]Te1−[subscript x] system we find filamentary superconductivity with magnetic spectral weight sitting at both the AFM and nesting vector. Upon reaching x = 0.4 optimal doping, the scattering completely transfers over to the nesting vector and a 2D resonance mode appears below T[subscript c].
Author: Xingye Lu
Publisher: Springer
ISBN: 981104998X
Category : Technology & Engineering
Languages : en
Pages : 127
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This book studies the structural, magnetic and electronic properties of, as well as magnetic excitations in, high-temperature BaFe2-xNixAs2 superconductors using neutron diffraction and neutron spectroscopic methods. It describes the precise determination of the phase diagram of BaFe2-xNixAs2, which demonstrates strong magnetoelastic coupling and avoided quantum criticality driven by short-range incommensurate antiferromagnetic order, showing cluster spin glass behavior. It also identifies strong nematic spin correlations in the tetragonal state of uniaxial strained BaFe2-xNixAs2. The nematic correlations have similar temperature and doping dependence as resistivity anisotropy in detwinned samples, which suggests that they are intimately connected. Lastly, it investigates doping evolution of magnetic excitations in overdoped BaFe2-xNixAs2 and discusses the links with superconductivity. This book includes detailed neutron scattering results on BaFe2-xNixAs2 and an introduction to neutron scattering techniques, making it a useful guide for readers pursuing related research.
Author: Aliaksei Charnukha
Publisher: Springer Science & Business Media
ISBN: 3319011928
Category : Technology & Engineering
Languages : en
Pages : 139
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This thesis combines highly accurate optical spectroscopy data on the recently discovered iron-based high-temperature superconductors with an incisive theoretical analysis. Three outstanding results are reported: (1) The superconductivity-induced modification of the far-infrared conductivity of an iron arsenide with minimal chemical disorder is quantitatively described by means of a strong-coupling theory for spin fluctuation mediated Cooper pairing. The formalism developed in this thesis also describes prior spectroscopic data on more disordered compounds. (2) The same materials exhibit a sharp superconductivity-induced anomaly for photon energies around 2.5 eV, two orders of magnitude larger than the superconducting energy gap. The author provides a qualitative interpretation of this unprecedented observation, which is based on the multiband nature of the superconducting state. (3) The thesis also develops a comprehensive description of a superconducting, yet optically transparent iron chalcogenide compound. The author shows that this highly unusual behavior can be explained as a result of the nanoscopic coexistence of insulating and superconducting phases, and he uses a combination of two complementary experimental methods - scanning near-field optical microscopy and low-energy muon spin rotation - to directly image the phase coexistence and quantitatively determine the phase composition. These data have important implications for the interpretation of data from other experimental probes.
Author: George Reiter
Publisher: Springer Science & Business Media
ISBN: 1468474901
Category : Science
Languages : en
Pages : 359
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This NATO Advanced Research Workshop was held at a time when there was little consensus as to the mechanism for high temperature superconductivity, in the context of a world undergoing major changes in its political alignments and sense of the possibility for the future. It was characterized by generosity in the sharing of our uncertainties and speculations, as was appropriate for both the subject matter and the context. The workshop was organized, of necessity around the experimental work, as is this volume. Where the theoretical work is directly relevant to particular experiments, it is included in the appropriate sections with them. Most of the participants felt strongly that magnetic fluctuations played an important role in the mechanism for high T c, although with the exception of the IlS R work reported by Luke showing results inconsistent with the anyon picture, and the work on flux phases by Lederer, the mechanism remained an issue in the background. A major focus was the phenomenological interpretation of the NMR data.
Author:
Publisher: Elsevier
ISBN: 0128020938
Category : Science
Languages : en
Pages : 534
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Book Description
Neutron Scattering - Magnetic and Quantum Phenomena provides detailed coverage of the application of neutron scattering in condensed matter research. The book's primary aim is to enable researchers in a particular area to identify the aspects of their work where neutron scattering techniques might contribute, conceive the important experiments to be done, assess what is required to carry them out, write a successful proposal for one of the major user facilities, and perform the experiments under the guidance of the appropriate instrument scientist. An earlier series edited by Kurt Sköld and David L. Price, and published in the 1980s by Academic Press as three volumes in the series Methods of Experimental Physics, was very successful and remained the standard reference in the field for several years. This present work has similar goals, taking into account the advances in experimental techniques over the past quarter-century, for example, neutron reflectivity and spin-echo spectroscopy, and techniques for probing the dynamics of complex materials of technological relevance. This volume complements Price and Fernandez-Alonso (Eds.), Neutron Scattering - Fundamentals published in November 2013. Covers the application of neutron scattering techniques in the study of quantum and magnetic phenomena, including superconductivity, multiferroics, and nanomagnetism Presents up-to-date reviews of recent results, aimed at enabling the reader to identify new opportunities and plan neutron scattering experiments in their own field Provides a good balance between theory and experimental techniques Provides a complement to Price and Fernandez-Alonso (Eds.), Neutron Scattering - Fundamentals published in November 2013
Author: Keith M. Taddei
Publisher:
ISBN: 9781369000177
Category : Iron-based superconductors
Languages : en
Pages : 236
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Book Description
With nearly innumerable applications, superconductivity stands as a holy grail in the research of quantum phenomena. Understanding the mechanism that begets the fabled pairing of electrons which leads to zero resistance is the most significant undertaking in order to bring to fruition all of superconductivity's splendor. Yet the interaction which couples electrons in the most promising family of superconductors known as unconventional superconductors, which show the highest Tc's and largest upper critical fields remains a mystery. Intense study over the past several decades on the cuprate superconductors has allowed for the identification of several candidate mechanisms --- cardinal of which is magnetic fluctuations --- however as of yet the question still remains. Recently, the discovery of the iron-based superconductors has provided another fruitful avenue through which this mechanism can be probed. Excitingly in these materials superconductivity not only arises near a magnetic instability - a situation which is expected to be particularly suited for engendering superconductivity should magnetic fluctuations be the pairing mechanism - but also exhibit the microscopic co-existence of the two presumably adversarial phenomena. In the work presented here the powerful techniques of neutron and x-ray diffraction will be used to study two particularly interesting members of this family: the intercalated iron-selenide CsxFe 2--xSe2 and two members of the iron-arsenide 122 family (BaFe2(As1--xPx)2 and Sr1--xNaxFe2As 2). Though isostructural at high temperatures, these two materials behave remarkably differently and the idiosyncratic manifestations of superconductivity and ordered magnetism in either give clues as to how the latter might stabilize the former. The iron-selenides will be shown to exhibit a complex phase space with phase separation leading to stabilization of magnetism and superconductivity in separate phases. The structure, behavior and complex vacancy ordering of this phase-separated state will be elucidated and the superconductivity attributed to a pseudo-stable minority phase. Detailed phase diagrams will be constructed for the related BaFe2(As1--xPx) 2 and Sr1--xNaxFe2 As2 compounds leading to a direct comparison of the effects driving of either doping regime. A strong magneto-elastic coupling will be established in both of these materials and a new magnetic phase will be mapped in Sr1--xNaxFe2As2. These observations will lead to a discussion of the role of magnetic fluctuations in the overall behavior of the material. The results of inelastic and elastic diffraction experiments will be combined with the results of the local probe M?ssbauer spectroscopy technique in order to determine magnetic fluctuations as the primary order parameter in the phase evolution of the iron-based superconductors, and therefore their importance in establishment of superconductivity as the ground state of these materials.
Author: Peter D. Johnson
Publisher: Springer
ISBN: 3319112546
Category : Technology & Engineering
Languages : en
Pages : 452
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This volume presents an in-depth review of experimental and theoretical studies on the newly discovered Fe-based superconductors. Following the Introduction, which places iron-based superconductors in the context of other unconventional superconductors, the book is divided into three sections covering sample growth, experimental characterization, and theoretical understanding. To understand the complex structure-property relationships of these materials, results from a wide range of experimental techniques and theoretical approaches are described that probe the electronic and magnetic properties and offer insight into either itinerant or localized electronic states. The extensive reference lists provide a bridge to further reading. Iron-Based Superconductivity is essential reading for advanced undergraduate and graduate students as well as researchers active in the fields of condensed matter physics and materials science in general, particularly those with an interest in correlated metals, frustrated spin systems, superconductivity, and competing orders.
Author: Miaoyin Wang (Researcher in physics)
Publisher:
ISBN:
Category : Metal oxide semiconductors
Languages : en
Pages : 128
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In most iron-based and copper-oxide superconductors, the Tc̳ [superconducting critical temperature] gradually increases upon charge carrier doping or isovalent doping. In the under-doped regime of electron-doped BaFe2As2 [Barium Iron 2 Arsenic 2], the superconductivity appears before the complete suppression of AF [antiferromagnetic] long-range order, creating a SC-AF [superconducting-antiferromagnetic] coexisting area. The interplay between long-range magnetic order and superconductivity was studied using a triple-axis thermal neutron spectrometer under an in-plane magnetic field. The suppression of superconductivity and the enhancement of long-range AF order were discovered under 11 Tesla, suggesting the competing nature of these two phases and the itinerant nature of iron-pnictides. We also measured the evolution of the neutron spin resonance in under-doped BaFe1̣ 925Ni0̣ 075As2 [Barium Iron 1.925 Nickel 0.075 As 2] and in over-doped BaFe1̣ 85Ni0̣ 15As2 [Barium Iron 1.85 Nickel 0.15 As 2]. Combining the previous results, we were able to compare the evolution of the neutron spin resonance energies in both BaFe2−x̳Nix̳As2 [Barium Iron (2-x) Nickel (x) Arsenic 2] and BaFe2−x̳Cox̳As2 [Barium Iron (2-x) Cobalt (x) Arsenic 2]. In late 2010, another type of iron-based superconductor alkali iron selenide A0̣ 8Fe1̣ 6+y̳Se2 [Alkali 0.8 Iron (1.6+y) Selenium 2 ] (or "245 system") was discovered. It is a unique system among the family of unconventional (high-Tc̳ [superconducting critical temperature]) superconductors because of its novel phase diagram, insulating parent compounds and huge magnetic moment. Using the inelastic time-of-flight technique, we are able to show that the parent compound can be described well by a local Heisenberg model. The follow up experiments on a superconducting sample (below and above Tc̳) and insulating samples (below and above Tn̳ [Neel Temperature]) provide a more detailed comparison and show more evidence that the alkali iron selenide system is rather different from either itinerant iron-pnictides or local copper-oxide systems.
