Topic

# Critical field

About: Critical field is a research topic. Over the lifetime, 10622 publications have been published within this topic receiving 200795 citations. The topic is also known as: critical field & critical magnetic field strength.

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TL;DR: A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-O compound system at ambient pressure.

Abstract: A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-O compound system at ambient pressure. An estimated upper critical field H c2(0) between 80 and 180 T was obtained.

5,965 citations

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Bell Labs

^{1}TL;DR: In this paper, a solution of the linearized Gor'kov equations for the upper critical magnetic field of a bulk type-II superconductor is extended to include the effects of Pauli spin paramagnetism and spin-orbit impurity scattering.

Abstract: A previously obtained solution of the linearized Gor'kov equations for the upper critical magnetic field ${H}_{c2}$ of a bulk type-II superconductor is extended to include the effects of Pauli spin paramagnetism and spin-orbit impurity scattering. To carry out the calculation, it is necessary to introduce an approximation which assumes that spin-orbit scattering is infrequent in comparison with spin-independent scattering. It is found that spin-orbit scattering counteracts the effects of the spin paramagnetism in limiting the critical field and improves agreement between theory and experiment.

2,474 citations

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TL;DR: In this paper, a review of recent developments in the phenomenological description of unconventional superconductivity is presented, starting with the BCS theory of superconductivities with anisotropic Cooper pairing, and the group-theoretical derivation of the generalized Ginzburg-Landau theory for unconventional supercondivity.

Abstract: This article is a review of recent developments in the phenomenological description of unconventional superconductivity. Starting with the BCS theory of superconductivity with anisotropic Cooper pairing, the authors explain the group-theoretical derivation of the generalized Ginzburg-Landau theory for unconventional superconductivity. This is used to classify the possible superconducting states in a system with given crystal symmetry, including strong-coupling effects and spin-orbit interaction. On the basis of the BCS theory the unusual low-temperature properties and the (resonant) impurity scattering effects are discussed for superconductors with anisotropic pairing. Using the Ginzburg-Landau theory, the authors study several bulk properties of such superconductors: spontaneous lattice distortion, upper critical magnetic field, splitting of a phase transition due to uniaxial stress. Two possible mechanisms for ultrasound absorption are discussed: collective modes and damping by domain-wall motion. The boundary conditions for the Ginzburg-Landau theory are derived from a correlation function formulation and by group-theoretical methods. They are applied to a study of the Josephson and proximity effects if unconventional superconductors are involved there. The magnetic properties of superconductors that break time-reversal symmetry are analyzed. Examples of current and magnetic-field distributions close to inhomogeneities of the superconducting order parameter are given and their physical origin is discussed. Vortices in a superconductor with a multicomponent order parameter can exhibit various topological structures. As examples the authors show fractional vortices on domain walls and nonaxial vortices in the bulk. Furthermore, the problem of the possible coexistence of a superconducting and a magnetically ordered phase in an unconventional superconductor is analyzed. The combination of two order parameters that are almost degenerate in their critical temperature is considered with respect to the phase-transition behavior and effects on the lower and upper critical fields. Because heavy-fermion superconductors---which are possible realizations of unconventional superconductivity---have been the main motivation for the phenomenological studies presented here, the authors compare the theoretical results with the experimental facts and data. In particular, they emphasize the intriguing features of the compound U${\mathrm{Pt}}_{3}$ and consider in detail the alloy ${\mathrm{U}}_{1\ensuremath{-}x}{\mathrm{Th}}_{x}{\mathrm{Be}}_{13}$.

1,577 citations

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Bell Labs

^{1}TL;DR: In this paper, an examination of some recent reports dealing with the extremely high critical fields in certain hard superconductors was presented, and it was concluded that the critical fields for these BETA -wolfran compounds are so high that they may be effectively limited at low temperatures by the normal-state paramagnetism.

Abstract: An examination is presented of some recent reports dealing with the extremely high critical fields in certain hard superconductors. Observations of nuclear magnetic resonance in V/sub 3/Si and V/sub 3/Ga are shown to set a severe upper limit on the attainable critical field because of a reduction in the spin susceptibility of these materials in the superconducting state. Equations are derived for the maximum critical field using this limiting criterion. A table of maximum and estimated critical fields is presented for V/sub 2.95/ Ga, Nb/sub 3/ Sn, V/sub 3/Si, and V/sub 1.95/ Ga. It is concluded that the critical fields for these BETA -wolfran compounds are so high that they may be effectively limited at low temperatures by the normal-state paramagnetism. If this is the case, critical fields higher than about 300 kilogauss will not be realized unless materials can be discovered with high transition temperatures. (H.D.R.)

1,321 citations

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TL;DR: In this paper, the authors review the thermodynamic and electromagnetic properties of such systems in several limiting scenarios: (i) systems with on-site pairing which can be described by the extended negative-$U$ Hubbard model, at which it reduces to a system of tightly bound electron pairs (bipolarons) on a lattice, and the changeover from weak-attraction BCS-like superconductivity to the superfluidity of charged hard core bosons is examined.

Abstract: In narrow-band systems electrons can interact with each other via a short-range nonretarded attractive potential. The origin of such an effective local attraction can be polaronic or it can be due to a coupling between electrons and excitons or plasmons. It can also result from purely chemical (electronic) mechanisms, especially in compounds with elements favoring disproportionation of valent states. These mechanisms are discussed and an exhaustive list of materials in which such local electron pairing occurs is given. The authors review the thermodynamic and electromagnetic properties of such systems in several limiting scenarios: (i) Systems with on-site pairing which can be described by the extended negative-$U$ Hubbard model. The strong-attraction limit of this model, at which it reduces to a system of tightly bound electron pairs (bipolarons) on a lattice, is extensively discussed. These electron pairs behaving as hard-core charged bosons can exhibit a superconducting state analogous to that of superfluid $^{4}\mathrm{He}$ II. The change-over from weak-attraction BCS-like superconductivity to the superfluidity of charged hard-core bosons is examined. (ii) Systems with intersite pairing described by an extended Hubbard model with $Ug0$ and nearest-neighbor attraction and/or nearest-neighbor spin exchange as well as correlated hopping. (iii) A mixture of local pairs and itinerant electrons interacting via a charge-exchange mechanism giving rise to a mutually induced superconductivity in both subsystems. The authors discuss to what extent the picture of local pairing, and in particular superfluidity of hard-core charged bosons on a lattice, can be an explanation for the superconducting and normal-state properties of the high-${T}_{c}$ oxides: doped BaBi${\mathrm{O}}_{3}$ and the cuprates.

1,276 citations