Effects In High-temperature Superconductors Research Articles

Bipolaron Theory of Field Effect in High-Temperature Superconductors

Bipolaron Theory of Field Effect in High-Temperature Superconductors

Bipolaron Theory of Field Effect in High-Temperature Superconductors

Bipolaron Theory of Field Effect in High-Temperature Superconductors

Material aspects of oxygen isotope effect studies in high-temperature superconductors

The article discusses issues related to the material aspects of the study of the oxygen isotope effect in High-temperature superconductors. These studies were initiated by Prof. K.A. Müller shortly after he and Dr. G. Bednorz discovered high-temperature superconductivity. Research on the isotope effect was carried out in the years 1991–1995, and then continued for various classes of superconductors and other strongly correlated electron systems. The paper presents methods of synthesis of complex oxide superconductors doped with isotopic oxygen-18. Methods for the determination of oxygen content and isotopic enrichment are also discussed.

Pressure effects in high-temperature superconductors: Pseudogap and barocaloric cooling as a spin-off

Some key results obtained in joint research projects with Alex Müller are summarized, concentrating on the application of pressure to perovskite materials. They include pressure effects on the pseudogap and information on the nature of the gap function observed for high-temperature superconductors by neutron scattering experiments as well as the invention of the barocaloric effect and its application for cooling.

The Born–Mayer–Huggins potential in high temperature superconductors

The Born–Mayer–Huggins potential which has been found the best suitable potential to study the YBa2Cu3O[Formula: see text] type high temperature superconductors is revisited in a new framework. A deeper insight in it reveals that the Born–Mayer parameters for different interactions in high temperature superconductor are not simple quantities but several thermodynamic and spatial functions enter the problem. Based on the new theory, the expressions for pressure, bulk modulus and Born–Mayer parameters have been derived and it is established that these quantities depend upon Gruneisen parameter which is the measure of the strength of anharmonic effects in high temperature superconductors. This theory has been applied to a specific model YBa2Cu3O[Formula: see text] crystal for the purpose of numerical estimates to justify the new results.

Extinction phenomenon for Spinor Ginzburg–Landau equations in three dimensions

Recent papers in physics literature have introduced coupled Ginzburg–Landau models for complex vector-valued order parameters in order to account for ferromagnetic or antiferromagnetic effects in high-temperature superconductors. In this paper, we study the spatial behavior of interacting components of coupled Ginzburg–Landau equations. We prove that the interspecies interaction leads to extinction in three dimensions.

Extinction phenomenon for Spinor Ginzburg-Landau equations

Recent papers in physics literature have introduced spinor Ginzburg-Landau model for complex vector-valued order parameters in order to account for ferromagnetic or antiferromagnetic effects in high-temperature superconductors. In this paper, we study the spatial behavior of interacting components of Spinor Ginzburg-Landau model. We prove the interspecies interaction leads to extinction, that is, configurations where one or more densities are null.

High resolution angle‐resolved photoemission spectroscopy on Cu‐based and Fe‐based high‐Tc superconductors

AbstractResearch on high temperature superconductivity has been a prominent topic in condensed matter physics. Angle‐resolved photoemission spectroscopy (ARPES) is a powerful technique in probing the electronic structure, energy gap and many‐body effects in high temperature superconductors, and other materials. In this paper, we first introduce our effort in developing vacuum ultra‐violet (VUV) laser‐based photoemission techniques, including angle‐resolved, spin‐resolved, time‐of‐flight electron energy analyzer‐based ones. Then, we highlight some of our recent results on Cu‐based high temperature superconductors utilizing our VUV laser‐based ARPES including many‐body effects in hole‐ and electron‐doped cuprates, superconducting gap and pseudogap, and the observation of Fermi pockets. In the last part of this paper, we briefly introduce our ARPES study on band structure, Fermi surface, superconducting gap, and many‐body effects in the newly discovered Fe‐based compounds.

Decomposition of Gauge Potential in Ginzburg–Landau Theory

Recently, Liu et al. proposed a so-called extended Anderson–Higgs mechanism by studying the (2+1)-dimensional Ginzburg–Landau model in the pseudogap region of high-Tc superconductor (Phys. Rev. B 65 (2002) 132513). We revisit this problem based on a general decomposition of the U(1) gauge potential. Using the bulk superconductor and superconduct ring as examples, we obtain a simpler expression for the extended Anderson–Higgs mechanism. In the former case we indicate that all the phase field can always be “eaten up" by the pure gauge term A||. In the latter case, we decompose the phase field as θ(x) = θ1(x) + θ2(x) and find that only the phase field θ1 connected with Anderson–Higgs mechanism can be canceled by the pure-gauge term A||. On the other hand, the remaining phase field θ2 connected with A⊥ is multi-valued, which can induce new physical effects such as A-B effect and flux quantization. It is natural to conclude that there is no longitudinal phase fluctuation effect in high-temperature superconductors since longitudinal phase θ1 is connected with pure-gauge term.

Reply to “Comment on ‘Isotope effect in high-Tcsuperconductors’ ”

Our paper on the isotope effect in high-temperature superconductors with cation substitutions presents a comprehensive analysis rooted completely in the experimental evidence. In this Reply we show that pair-breaking disorder, isotope effects, doping-induced variations in Tc and in the magnetic penetration depth, Coulomb's law, and Anderson's theorem are treated with correct physical and mathematical fundamentals. In contrast, the theory fostered in the Comment by Alexandrov and Zhao contradicts several specific experimental facts, eight of which are briefly discussed. Their Comment also uncritically repeats a previously discredited assertion of an isotope effect in the superconducting carrier mass, incorrectly assumes that cation doping continuously varies intrinsic superconducting parameters, unjustifiably assigns importance to data from samples with serious quality problems, and renders a false estimate of the pair-breaking strength.

Spinor Ginzburg–Landau equation and mean curvature flow

Recent papers in the physics literature have introduced spin-coupled (or spinor) Ginzburg–Landau models for complex vector-valued order parameters in order to account for ferromagnetic or antiferromagnetic effects in high-temperature superconductors. In this paper, we study the asymptotic behavior of solutions of the evolutionary spinor Ginzburg–Landau equation in three dimensions. We prove also that, asymptotically, the singularities evolve according to mean curvature flow in the sense of weak formulation.

The spinor Ginzburg–Landau model in dimension three

Recent papers in physics literature have introduced spin-coupled (or spinor) Ginzburg–Landau models for complex vector-valued order parameters in order to account for ferromagnetic or antiferromagnetic effects in high-temperature superconductors. In this paper, we study the asymptotic behavior of solutions to this model in dimension 3. It was also proven that limit singularities set is one-dimensional rectifiable, which consists of one or more line segments.

Self-organized networks and lattice effects in high-temperature superconductors

The entirely orbital self-organized dopant percolative filamentary model describes many counter-intuitive chemical trends in oxide superconductors quantitatively, especially the high superconductive transition temperatures Tc. According to rules previously used successfully for network glasees, the host networks are marginally stable mechanically, and the high Tc's are caused by network softening, which produces large electron-phonon interactions at interlayer dopants for states near the Fermi energy.

Comment on “Essence of intrinsic tunneling: Distinguishing intrinsic features from artifacts”

In a recent paper V.Zavaritsky has argued that interlayer ($c-$ axis) current-voltage characteristics of high temperature superconductors (HTSC) are Ohmic, and has claimed to disprove all findings of intrinsic tunnelling spectroscopy, as well as existence of the interlayer tunnelling and the intrinsic Josephson effect in HTSC, as such. In this comment I demonstrate, that the genuine interlayer current-voltage characteristics are strongly non-Ohmic, which undermines the basic postulate and the logical construction of the criticized paper.

FRACTIONAL DEGREE VORTICES FOR A SPINOR GINZBURG–LANDAU MODEL

Recent papers in the physics literature have introduced spin-coupled (or spinor) Ginzburg–Landau models for complex vector-valued order parameters in order to account for ferromagnetic or antiferromagnetic effects in high-temperature superconductors and in optically confined Bose–Einstein condensates. In this paper, we show that such models give rise to new types of vortices, with fractional degree and nontrivial core structure. We illustrate the various possibilites with some specific examples of Dirichlet problems in the unit disk.

Phonons in Hubbard ladders studied within the framework of the one-loop renormalization group

We study the effects of phonons in $N$-leg Hubbard ladders within the framework of a one-loop renormalization group. In particular, we explicitly demonstrate that the role of phonons changes {\em qualitatively} even in the simplest two-leg ladder, as compared to the single-chain system where phonons always dominate. Our numerical results suggest that in the spin-gapped phase of the two-leg ladder, the opening of the spin gap by electron-electron interaction also drives the electron-phonon interaction to strong coupling, but in a {\em subdominant} fashion. Therefore, even though the inclusion of phonons does not alter the phase, their subdominant relevance strongly renormalizes some physical properties below the energy scale of the spin gap. This might shine some light on the recent experiments showing an anomalous isotope effects in high-temperature superconductors.

Modulation of superconductivity by ferroelectric polarization in confined ferroelectric-superconductor-ferroelectric films

We show that the electric polarization at the interface with ultrathin superconducting (S) films sandwiched between ferroelectric (FE) layers allows achievement of substantially stronger modulation of inner carrier density and superconducting transition temperature as compared to FE-S bilayers typically used in superconducting FETs. We find that not only the larger penetration depths but also the pairing symmetry should be responsible for the fact that the electric field effect in high temperature superconductors is much stronger than in conventional systems. Discussing the advantages of multilayers, we propose a novel design concept for superconducting electric field-effect transistors based on ferroelectric films.

Local structural changes and photoinduced effects in high-temperature superconductors

Local structural changes and photoinduced effects in high-temperature superconductors

Des vortex fractionnaires pour un modèle Ginzburg–Landau spineur

Recent papers in the physics literature have introduced spin-coupled (or spinor) Ginzburg–Landau models for complex vector-valued order parameters in order to account for ferromagnetic or antiferromagnetic effects in high-temperature superconductors and in optically confined Bose–Einstein condensates. In this Note we observe that such models can lead to new types of vortices, with fractional degree and non-trivial core structure. To cite this article: S. Alama, L. Bronsard, C. R. Acad. Sci. Paris, Ser. I 337 (2003).

Novel boundary effect in high temperature superconductors: superconductivity induced by pseudogap proximity effect

The boundary between highly under-doped and over-doped cuprate superconductors is studied within the framework of the slave-boson mean-field theory of the t – J model. We assume that the under-doped region is in the pseudogap state and the singlet resonating valence bond (s-RVB) order is formed there. The over-doped region, on the other hand, is in a hole-rich state and the pseudogap is destroyed by the holes. Because of the proximity effect, the s-RVB order and high-density holes can coexist, leading to the superconducting behavior. Remarkably, the transition temperature of this “boundary superconductivity” exceeds the maximum superconducting transition temperature of the bulk region, thus possessing a new possibility of application for superconducting devices.