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| Author | : Guichuan Yu |
| Publisher | : |
| Total Pages | : 244 |
| Release | : 2008 |
| Genre | : |
| ISBN | : |
| Author | : Xingye Lu |
| Publisher | : Springer |
| Total Pages | : 127 |
| Release | : 2017-07-10 |
| Genre | : Technology & Engineering |
| ISBN | : 981104998X |
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 | : Jun Zhao |
| Publisher | : |
| Total Pages | : 126 |
| Release | : 2010 |
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| ISBN | : |
We carried out systematic neutron scattering experiments to investigate the magnetic properties and their relationship to the high-Tc superconductivity, when the materials are tuned from their antiferromagnetic (AF) parent compounds to the superconducting regime. We observed resonance mode in the electron doped cuprate Nd[subscript 1.85]Ce[subscript 0.15]CuO[subscript 4], demonstrating that the resonance is a general phenomenon in cuprate superconductors regardless of hole- or electron-doping. In Pr[subscript 0.88]LaCe[subscript 0.12]CuO[subscript 4], the local susceptibility displays two distinct energy scales that are broadly consistent with the bosonic modes revealed by scanning tunneling microscopy experiments. These results indicate the presence of very strong electron spin excitations couplings in electron doped cuprates. Shortly after the discovery of high-Tc superconductivity in the Fe pnictides, we discovered that the magnetic phase diagram of CeFeAsO[subscript 1-x]F[subscript x] is remarkably similar to that of the cuprates. Besides CeFeAsO, similar magnetic and lattice structures are also observed in PrFeAsO and SrFe[subscript 2]As[subscript 2] systems. Neutron scattering measurements show that in SrFe[subscript 2]As[subscript 2], the spectrum of magnetic excitations consists of a Bragg peak at the elastic position, a spin gap, and sharp spin-wave excitations at higher energies. Based on the observed dispersion relation, we estimated the effective magnetic exchange coupling using a Heisenberg model. In order to study the nature of the exchange interactions in the parent compound of Fe pnictides, we studied the high energy spin-wave excitations in CaFe2As2. Although the spin waves in the entire Brillouin zone can be described by an effective three-dimensional anisotropic Heisenberg Hamiltonian, the magnetism in this system is neither purely local nor purely itinerant; rather it is a complicated mix of the two. When the Fe pnictide is tuned into superconducting regime with doping, the low energy spin fluctuation is dominated by a resonance mode. In the optimally electron doped BaFe[subscript 1.9]Ni[subscript 0.1]As[subscript 2], application of a magnetic field that suppresses the superconductivity and superconducting gap energy also reduces the intensity and energy of the resonance. These results suggest that the energy of the resonance is proportional to the electron pairing energy, and thus indicate that spin fluctuations are intimately related to the mechanism of high Tc superconductivity.
| Author | : |
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| Total Pages | : |
| Release | : 2014 |
| Genre | : |
| ISBN | : |
Understanding the interplay between magnetism and superconductivity continues to be a "hot" topic in modern condensed matter physics. The discovery of high-temperature superconductivity in iron-based materials in 2008 provided an unique opportunity to compare and contrast these materials with traditional high-Tc copper oxide superconductors. Neutron scattering plays an important role in determining the dynamical spin properties in these materials. This proposal is a continuation of previous DOE supported proposal. This report summarizes the final progress we have made over from May 2005 till Aug. 2013. Overall, we continue to carry out extensive neutron scattering experiments on Fe-based materials, focusing on understanding their magnetic properties. In addition, we have established a materials laboratory at UT that has allowed us to grow these superconductors. Because neutron scattering typically demands a large amount of samples, by growing these materials in our own laboratory, we can now pursuit neutron scattering experiments over the entire electronic phase diagram, focusing on regions of interests. The material synthesis laboratory at UT was established entirely with the support of DOE funding. This not only allowed us to carry out neutron scattering experiments, but also permit us to provide samples to other US/International collaborators for studying these materials.
| Author | : |
| Publisher | : Elsevier |
| Total Pages | : 534 |
| Release | : 2015-11-29 |
| Genre | : Science |
| ISBN | : 0128020938 |
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 | : Cui Guangji |
| Publisher | : World Scientific |
| Total Pages | : 632 |
| Release | : 1990-02-01 |
| Genre | : |
| ISBN | : 9814696811 |
| Author | : Mengshu Liu (Physicist) |
| Publisher | : |
| Total Pages | : 148 |
| Release | : 2014 |
| Genre | : Condensed matter |
| ISBN | : |
Presented within are neutron scattering studies of several different high temperature superconducting materials: BaFe1.9Ni0.1As2 [Barium Iron Nickel Arsenic], BaFe1.85Ni0.15As2 [Barium Iron Nickel Arsenic], Ba0.67K0.33Fe2As2 [Barium Potassium Iron Arsenic], and Pr0.88LaCe0.12CuO4-y [Praseodymium Lanthanum Cerium Copper Oxide]. The main focus is on the magnetic excitations within the systems. For BaFe1.9Ni0.1As2 [Barium Iron Nickel Arsenic], we measured the intensity of its magnetic excitations and compared the results with excitations in antiferromagnetic non-superconducting BaFe2As2 [Barium Iron Arsenic]. We find electron-doping only affects spin excitations below 100 meV while the total size of the magnetic moment and the energy distribution do not change much. It shows that the magnetic moments in both materials are similar to insulating copper oxides, an indicator of the importance of strong electron correlations in high temperature superconductivity. For both BaFe1.85Ni0.15As2 [Barium Iron Nickel Arsenic] and Ba0.67K0.33Fe2As2 [Barium Potassium Iron Arsenic], we use polarized inelastic neutron scattering to study their low-energy spin excitations and their spatial anisotropy. Our neutron polarization analysis reveals that magnetic excitations are isotropic for the in-plane and out-of-plane components in both the normal and superconducting states for BaFe1.85Ni0.15As2 [Barium Iron Nickel Arsenic], while in Ba0.67K0.33Fe2As2 [Barium Potassium Iron Arsenic] large difference in spin gaps were found. A comparison of these results with those of undoped BaFe2As2 [Barium Iron Arsenic] and optimally electron-doped BaFe1.9Ni0.1As2 [Barium Iron Nickel Arsenic] suggests that the spin anisotropy observed Ba0.67K0.33Fe2As2 [Barium Potassium Iron Arsenic] are likely due to their proximity to their parent compound, where spin anisotropy exists below TN [Neel Temperature], while the neutron spin resonance is isotropic in the overdoped regime, consistent with a singlet to triplet excitation. For as-grown and optimal superconducting Pr0.88LaCe0.12CuO4-y [Praseodymium Lanthanum Cerium Copper Oxide] (PLCCO), we measured their magnetic excitations over a wide energy range, and compared their corresponding results. The spectra is considerably larger throughout the whole zone in as-grown PLCCO, than in the optimal superconducting PLCCO, which is very different from the BaFe2As2 [Barium Iron Arsenic] system.
| Author | : Z. X. Zhao |
| Publisher | : World Scientific |
| Total Pages | : 640 |
| Release | : 1990 |
| Genre | : Technology & Engineering |
| ISBN | : 9789810201227 |
http://www.worldscientific.com/worldscibooks/10.1142/0957
| Author | : Eugene M. Motoyama |
| Publisher | : |
| Total Pages | : |
| Release | : 2009 |
| Genre | : |
| ISBN | : |
While the mechanism for the high transition temperatures (Tc) in the cuprate superconductors remains unsolved, antiferromagnetic fluctuations on the copper-oxygen sheets are thought to play an important role. Long-range antiferromagnetic order is present in the undoped insulating parent compounds, whereas superconductivity is observed when these materials are doped with a sufficient number of holes or electrons. Because these two phases are well separated on the hole-doped side of the phase diagram, the interplay between antiferromagnetism and superconductivity is perhaps better studied in the electron-doped compounds, where the two phases appear to overlap. In this Thesis work, single crystals of electron-doped Nd{2-x}Ce{x}CuO4 (NCCO) were grown over a wide range of cerium concentration, and the following two neutron scattering studies were performed on these crystals. In the first study, an energy-integrating neutron scattering method is used to measure the two-dimensional instantaneous magnetic correlation length as a function of temperature and doping. For x 0.12, the correlation length diverges at the same temperature at which magnetic Bragg peaks appear, as expected. For x 0.12, on the other hand, the correlation length remains finite down to the lowest measured temperatures. Since bulk superconductivity is only found above about x=0.13, this shows that there is no genuine coexistence between superconductivity and long-range antiferromagnetic order, which was previously thought to extend to x = 0.17. The second study is the first inelastic neutron scattering investigation of an electron-doped cuprate superconductor in an applied magnetic field. This experiment measures how the weakening of superconductivity due to a magnetic field affects the antiferromagnetic response. An advantage of the electron-doped cuprates is that the critical field Hc2 required to completely suppress superconductivity is relatively low (~10 T). In zero field, the antiferromagnetic excitation spectrum of NCCO (x=0.166) is gapped below 2.5 meV. The gap energy is found to decrease linearly with applied field and to extrapolate to zero near Hc2. The observed behavior indicates that the non-superconducting ground state is similar to the (zero-field) paramagnetic state at temperatures above Tc, and thus that superconductivity and antiferromagnetism are not competing orders in this part of the phase diagram.
| Author | : Jason Stewart Gardner |
| Publisher | : |
| Total Pages | : |
| Release | : 1996 |
| Genre | : |
| ISBN | : |
