Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 33
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Book Description
Over the past 35 years, research on unconventional superconductivity in heavy-fermion systems has evolved from the surprising observations of unprecedented superconducting properties in compounds that convention dictated should not superconduct at all to performing explorations of rich phase spaces in which the delicate interplay between competing ground states appears to support emergent superconducting states. Here, we review the current understanding of superconductivity in heavy-fermion compounds and identify a set of characteristics that is common to their unconventional superconducting states. Furthermore, these core properties are compared with those of other classes of unconventional superconductors such as the cuprates and iron-based superconductors. Finally, we speculate on the prospects for future research in this field and how new advances might contribute towards resolving the long-standing mystery of how unconventional superconductivity works.
Author: Emma Elizabeth Pearson
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Andrey Zakharov
Publisher:
ISBN:
Category :
Languages : en
Pages : 100
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Author: V.P. Mineev
Publisher: CRC Press
ISBN: 9789056992095
Category : Science
Languages : en
Pages : 204
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Book Description
Unconventional superconductivity (or superconductivity with a nontrivial Cooper pairing) is believed to exist in many heavy-fermion materials as well as in high temperature superconductors, and is a subject of great theoretical and experimental interest. The remarkable progress achieved in this field has not been reflected in published monographs and textbooks, and there is a gap between current research and the standard education of solid state physicists in the theory of superconductivity. This book is intended to meet this information need and includes the authors' original results.
Author: Tanno Vorenkamp
Publisher:
ISBN:
Category :
Languages : en
Pages : 160
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Author: Yogesh Pratap Singh
Publisher:
ISBN:
Category : Fermions
Languages : en
Pages : 137
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Book Description
The current research interest in heavy fermion (HF) materials is for their unconventional superconductivity, their quantum critical behavior and the breakdown of Fermi liquid (FL) theory. Presently, we lack a universal understanding of the breakdown of the FL behavior in these materials. However, there are evidences which suggest that the breakdown of the FL behavior and the unconventional superconducting (SC) pairing could be the result of a zero temperature phase transition, taking place at a quantum critical point (QCP). Heavy fermions are f-electron materials in which local moments at each lattice site interact with the spin of the conduction electrons sitting at that site via an exchange coupling. There are two energy scales that result from this interaction, the Kondo temperature TK (temperature below which the local moments are screened by the spins of the conduction electrons), and the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, which characterize the induced coupling between two local moments. These two energy scales can be tuned by external parameters such as magnetic field, pressure, and chemical substitution. Such a tuning provides an opportunity to study the rich physics of these materials. This dissertation work presents experimental and theoretical studies on ab unique member of Ce-115 family of heavy fermions, i.e., Ce1-xYbxCoIn5. In the Ce-115 family of HFs, Cerium (Ce) contributes the f-electrons to form a Kondo lattice. The substitution of Ce ions by other rare earths is a widely used approach to study this system. Our selection of ytterbium for substituting Ce-site is unique in the sense that Yb appears in the intermediate valence state in this system (unlike any other substitution), thus giving rise to many of the unusual properties, which helped in the understanding the underlying physics of SC pairing, quantum criticality and non-Fermi liquid behavior in this HF. For the purpose of the studies presented in this dissertation, we utilized electronic, magneto- and thermal transport measurements. These measurements were done under high magnetic fields and pressures wherever needed. We developed a new method to identify the field-induced QCP in this material by studying its normal state. We utilized this method to locate QCP in the parent compound CeCoIn5 and determined its evolution with Yb doping in Ce1-xYbxCoIn5. Our findings show that quantum criticality in this system is suppressed by doping with Yb and a zero field QCP is obtained for the x = 0.20 Yb-doping level. Our studies also show the evolution of the many-body electronic state as the Kondo lattice of Ce moments is transformed into an array of Ce impurities with Yb-doping. Specifically, we observe a crossover from the predominantly localized Ce moment regime to the predominantly itinerant Yb f-electronic state regime. In the crossover regime, the magneto-transport behavior of the system indicates single impurity behavior of Ce ions. This result is surprising because the resistivity and specific heat measurements suggest significant amount of coherent scattering in the system. We attribute this unusual behavior to the hybridization of conduction electrons with mixed valence Yb ions, giving rise to an intermediate energy scale (TK ~ 14 K) between the single impurity regime of Ce and Ce Kondo lattice regime. Even more intriguing are the results at even higher Yb-doping levels. Large enough Yb concentrations show an increased coherence, unlike any other member of the Ce-115 family. We also identified another QCP at a higher Yb concentration of x = 0.75. An equally interesting feature in the doping dependence of this compound is the survival of NFL behavior throughout the phase diagram. The sub-linear temperature dependence of resistivity across the whole range of Yb concentrations suggests the presence of an unconventional scattering mechanism for the conduction electrons. Thus although the quantum spin fluctuations are suppressed at around 20 % of Yb doping, the NFL behavior is observed for the whole family. Our finding of an additional high doping QCP very well explains the large value of the Sommerfeld's coefficient and the persistent NFL behavior over the whole Yb-doping range. Given the complete suppression of the antiferromagnetic fluctuations for x > 0.20 and the very robust coherence and superconductivity, the possible electron pairing mechanism may involve an exchange of virtual magnetic fluctuations or a more unconventional mechanism involving virtual fluctuations into higher lying Ce crystalline field multiplets. We analyze theoretically the dependence of the superconducting critical temperature and Kondo lattice coherence temperature on pressure for both cases of clean and disordered systems. We use the approach of the large-N mean field theory, which works very well for Kondo lattice systems.
Author: Corneliu Florin Miclea
Publisher: Cuvillier Verlag
ISBN: 3867277087
Category :
Languages : en
Pages : 165
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Author: Ryuji Okazaki
Publisher: Springer Science & Business Media
ISBN: 4431545921
Category : Technology & Engineering
Languages : en
Pages : 114
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Book Description
In this thesis, the author investigates hidden-order phase transition at T0 = 17.5 K in the heavy-fermion URu2Si2. The four-fold rotational symmetry breaking in the hidden order phase, which imposes a strong constraint on the theoretical model, is observed through the magnetic torque measurement. The translationally invariant phase with broken rotational symmetry is interpreted as meaning that the hidden-order phase is an electronic “nematic” phase. The observation of such nematicity in URu2Si2 indicates a ubiquitous nature among the strongly correlated electron systems. The author also studies the superconducting state of URu2Si2 below Tc = 1.4 K, which coexists with the hidden-order phase. A peculiar vortex penetration in the superconducting state is found, which may be related to the rotational symmetry breaking in the hidden-order phase. The author also identifies a vortex lattice melting transition. This transport study provides essential clues to the underlying issue of quasiparticle dynamics as to whether a quasiparticle Bloch state is realized in the periodic vortex lattice.
Author: Dirk Manske
Publisher: Springer Science & Business Media
ISBN: 9783540212294
Category : Science
Languages : en
Pages : 244
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Book Description
This book presents a theory for unconventional superconductivity driven by spin excitations. Using the Hubbard Hamiltonian and a self-consistent treatment of the spin excitations, the interplay between magnetism and superconductivity in various unconventional superconductors is discussed. In particular, the monograph applies this theory for Cooper-pairing due to the exchange of spin fluctuations to the case of singlet pairing in hole- and electron-doped high-Tc superconductors, and to triplet pairing in Sr2RuO4. Within the framework of a generalized Eliashberg-like treatment, calculations of both many normal and superconducting properties as well as elementary excitations are performed. The results are related to the phase diagrams of the materials which reflect the interaction between magnetism and superconductivity.
Author: William Knafo
Publisher:
ISBN: 9789811265792
Category :
Languages : en
Pages : 0
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Book Description
Correlated-electron systems offer a unique playground for discovering and studying new quantum states of matter, at the crossway between itinerant quantum magnetism and unconventional superconductivity. The understanding of their basic properties, although needing experimental environments which cannot be transposed at industrial scales, will surely benefit within mid- and long-term perspectives to future revolutionary applications in the domains of applied physics, micro and nano-electronics, energetics.As textbook examples of quantum magnets and unconventional superconductors, heavy-fermion compounds offer a fertile ground for testing new concepts in condensed matter. Quantum magnetic phase transitions can be easily tuned experimentally, leading to a large variety of electronic ground states, from a heavy Fermi liquid to long-range magnetic-order and unconventional superconducting phases. This book written by William Knafo, an expert in correlated-electron physics, proposes a systematic and thorough review on the experimental advances in the study of magnetism in heavy-fermion metals over the last decades. The phase diagrams of these quantum materials under multiple sets of tuning parameters, the questions of the dual localized-itinerant nature of the f-electrons and of the critical role of magnetic fluctuations, in relation with nearby quantum magnetic phase transitions and the stabilization of superconductivity, are carefully addressed.
