Perfect Diamagnetism Research Articles

Effect of the Er-substitution on critical current density in glass-ceramic Bi2Sr2Ca2(Cu3−xErx)O10+δ superconducting system

Bi2Sr2Ca2Cu3−xErxO10+δ (x=0.0, 0.5 and 1.0) samples were manufactured using conventional glass-ceramic technique and their structural, magnetic and flux pinning properties were studied. The onset temperature of diamagnetic signal decreased by the Er-substitution. The x=0.5 Er-substituted sample showed perfect diamagnetism, which is attributed to secondary phases acting as pinning centers in the crystal structure. Jc of the samples was calculated by using Bean's equation. The highest Jc value was obtained for x=0.5 Er-substitution. The results suggest that the Er ions in the host material act as pinning centers which lead to the increase of Jc.

On the dynamics of the Meissner effect

The question of how a metal becoming superconducting expels a magnetic field is addressed. It is argued that the conventional theory of superconductivity has not answered this question despite its obvious importance. We argue that the growth of the superconducting region into the normal region and associated expulsion of magnetic field from the superconducting region can only be understood if it is accompanied by motion of charge from the superconducting region into the normal region. From a microscopic point of view it is shown that the perfect diamagnetism of superconductors requires that superconducting electrons reside in orbits of spatial extent , with the London penetration depth. Associated with this physics, the spin–orbit interaction of the electron magnetic moment and the positively charged ionic background gives rise to a ‘Spin Meissner’ effect, the generation of a macroscopic spin current near the surface of superconductors. We point out that both the Meissner and the Spin Meissner effect can be understood dynamically under the assumption that the superfluid condensate wavefunction does not screen itself, just like the for an electron in a hydrogen atom. We argue that the conventional theory of superconductivity cannot explain the Meissner effect because it does not contain the physical elements discussed here.

The synthesis and magnetic structure of the iron selenide Ba0.8Fe2Se2

The BaxFe2-ySe2 (x=0.8) single crystal has been synthesized by using the one step technique at relatively lower temperatures. We have investigated structural properties of samples by using the XRD, SEM-EDX and magnetic properties. The SEM results clearly demonstrate that Ba ions are intercalated in the FeSe lattice. XRD result shows that the sample prepared has multi-phase structure. According to our M-H measurements perfect diamagnetism has been observed only in low field at 5 K. In addition, those curves indicate that the high field value and some impurities reveal ferromagnetic interactions. The superconducting transition was observed at around Tc≈10.9 K.

Experimento demonstrativo de levitação supercondutora: Ferramenta para problematização de conceitos físicos

<p>Em meados da década de 1980, os ditos supercondutores cerâmicos foram descobertos. Estes materiais se destacam por possuírem temperaturas de transição superiores à do nitrogênio líquido (<italic>T</italic> = 77 K). Este líquido criogênico possui um custo e facilidade de obtenção muito mais vantajosos se comparado com o hélio líquido (<italic>T</italic> = 4, 2 K). Assim, as possibilidades de aplicações desses materiais se ampliaram. Tais aplicações se adequam, em geral, aos esforços por buscas de fontes de energia limpas e a estruturação de uma sociedade sustentável por conta das propriedades dos supercondutores (por exemplo, resistividade nula e diamagnetismo perfeito). Neste trabalho apresentaremos a montagem de um experimento de levitação supercondutora que pode ser usado em problematizações a alunos do ensino médio além de incentivá-los a optarem por uma carreira científica.</p>

Synthesis and characterization of superconductor Bi3O2S3

Bulk and nanoscale powder layered superconductor Bi3O2S3 have been successfully prepared via conventional solid-state reaction route. The diffraction peaks observed for Bi3O2S3, except for the small impurity peaks belong to Bi28O32(SO4)10, can be indexed to the orthorhombic (I4/mmm tetragonal) phase for Bi3O2S3 with cell constants a=3.961Å, c=41.316Å. The pill comprised of nanoscale Bi3O2S3 behaves like insulator. However the zero resistivity of bulk Bi3O2S3 is observed at 4.62K. The superconductivity is also proved by the Meissner effect from the zero-field cooled and field cooled dc magnetization measurements, and the diamagnetic susceptibility which reflects shielding volume fraction of superconductor at 2K is about −0.031emuOe−1g−1, indicating a perfect diamagnetism.

The Annealing Effects in the Iron-Based Superconductor FeTe0.8Se0.2 Prepared by the Self-Flux Method

FeTe0.8Se0.2 single crystals as-cast and post-annealed were prepared by the self-flux method. We have investigated the structural properties of samples by using the XRD, scanning electron microscope (SEM), energy dispersive X-ray (EDX), and magnetic techniques. The SEM results clearly demonstrate that Te ions are quite well substituted for Se ions in the FeSe lattice for the samples. From the XRD and EDX spectra of the both samples, it has been concluded that the post-annealing causes no change in the tetragonal structure of FeTe0.8Se0.2. According to M–H measurements, the perfect diamagnetism has been observed only in low field at 5 and 10 K temperatures. The trend of the magnetization versus temperature curves, measured under a magnetic field of 10 Oe, also support our conclusion about diamagnetic contribution in FeTe0.8Se0.2 single crystal explored in this study. The as-cast and post-annealed samples show the onset of diamagnetism at temperatures, $T_{\mathrm {c.on}}^{\text {mag}}$ , 12.45 and 13.27 K, respectively. In addition, those curves indicate that the high field value and some impurities reveal ferromagnetic interactions.

Effects of post-annealing and cobalt co-doping on superconducting properties of (Ca,Pr)Fe2As2 single crystals

In order to clarify the origin of anomalous superconductivity in (Ca,RE)Fe2As2 system, Pr doped and Pr,Co co-doped CaFe2As2 single crystals were grown by the FeAs flux method. These samples showed two-step superconducting transition with Tc1=25–42K, and Tc2<16K, suggesting that (Ca,RE)Fe2As2 system has two superconducting components. Post-annealing performed for these crystals in evacuated quartz ampoules at various temperatures revealed that post-annealing at ∼400°C increased the c-axis length for all samples. This indicates that as-grown crystals have a certain level of strain, which is released by post-annealing at ∼400°C. Superconducting properties also changed dramatically by post-annealing. After annealing at 400°C, some of the co-doped samples showed large superconducting volume fraction corresponding to the perfect diamagnetism below Tc2 and high Jc values of 104–105Acm−2 at 2K in low field, indicating the bulk superconductivity of (Ca,RE)Fe2As2 phase occurred below Tc2. On the contrary, the superconducting volume fraction above Tc2 was always very small, suggesting that 40K-class superconductivity observed in this system is originating in the local superconductivity in the crystal.

AC Losses in Sn-Doped Bi1.6Pb0.4Sr2(Ca1-xSnx)2Cu3Oδ Superconductors

Measurements of complex AC susceptibilityχ = χ + χas a function of temperature have been carried out on Sn-doped Bi1.6Pb0.4Sr2(Ca1-xSnx)2Cu3Oδsuperconductor samples prepared via the conventional solid state reaction method. All the samples exhibit perfect diamagnetism below 109 K. Theχ (T)curves display two-step features, indicating the presence of mixed phases and therefore weakening of the grains' coupling. The amount of shielded volume in Sn-free samples is greater than that in Sn-doped samples. The intrinsic peak due to the small AC losses within the grain was not observed in theχ (T)curves for all samples. However, the coupling peak,TP, for Sn-free samples at an applied field of 1.0 Oe was observed at 89 K and shifted to a lower temperature ranging from 59 K to 64.2 K in Sn-doped samples. The amounts of hysteresis losses above theTPin all doped samples were smaller than that of the Sn-free sample. Therefore, the effect of Sn doping suppressed the inter-granular critical current,Jcm, and the presence of weak links that coupled the superconducting grains.Keywords: BSCCO, AC Losses, Sn-doped, Superconductor

Magnetic detectability of a finite size paramagnet/superconductor cylindrical cloak

Cloaking of static magnetic fields by a finite thickness type-II superconductor tube surrounded by a coaxial paramagnet shell is studied. On the basis of exact solutions to the London and Maxwell equations, it is shown that perfect cloaking is realizable for arbitrary geometrical parameters including the thin film case for both constituents. In contrast to the previous approximate studies assuming perfect diamagnetism of the superconductor constituent, it is proven that cloaking provides simultaneously full undetectability, that is the magnetic moment of the structure completely vanishes as well as all high-order multipole moments as soon as the uniform field outside remains unaffected.

Observation of the Meissner-Ochsenfeld Effect and the Absence of the Meissner State in UCoGe

We present low field magnetization and susceptibility measurements made on a single crystal of the ferromagnetic superconductor UCoGe. The interplay between ferromagnetism and superconductivity comes into view in the study of hysteresis along the c axis (easy magnetization axis). The Meissner state (perfect diamagnetism) could not be observed in very low magnetic fields for all three crystallographic directions, implying that the sample is always in the mixed state. Notwithstanding, the Meissner-Ochsenfeld effect (reversible flux expulsion) occurs and is found to be anisotropic. For the c axis in low fields, it is proportional to the bulk magnetization M (and thus to the population of domains) and not to the applied magnetic field H. On a microscopic level, our interpretation of these results implies that flux is expelled independently from each domain proportional to its volume.

Complete tailor-made inverse filter for image processing of scanning SQUID microscope

By introducing a numerical image processing technique, the resolution of scanning SQUID microscope (SSM) has been improved beyond the “naive” limit determined by the size of the pickup (sensor) coil. Our image processing is developed by taking account of the specific characteristics of SSM apparatus, including detailed shape of the coil and its perfect diamagnetism, in a tailor-made manner. The actual experiment has been done for nano-scale superconducting Pb network, and the magnetic field structures apparently smaller than the size of the pickup coil were made visible by our method.

Meissner effect, diamagnetism, and classical physics—a review

We review the literature on what classical physics says about the Meissner effect and the London equations. We discuss the relevance of the Bohr-van Leeuwen theorem for the perfect diamagnetism of superconductors and conclude that the theorem is based on invalid assumptions. We also point out results in the literature that show how magnetic flux expulsion from a sample cooled to superconductivity can be understood as an approach to the magnetostatic energy minimum. These results have been published several times but many textbooks on magnetism still claim that there is no classical diamagnetism, and virtually all books on superconductivity repeat Meissner’s 1933 statement that flux expulsion has no classical explanation.

Superconductivity: 100th Anniversary of Its Discovery and Its Future

Superconducting technologies are reviewed as the integration of various technologies by considering its research history, present status, future prospects, and the application to energy, transportation, and communications. Superconductivity involves a persistent current, perfect diamagnetism, and the Josephson effect, and is a unique phenomenon that cannot be imitated. After the discovery of superconductivity 100 years ago, as long as half a century was required to clarify its difficult mechanism. To date, the applications of superconductivity have been limited to specific purposes that require ultimate performance. The reason for this undoubtedly lies in the cooling penalty. In addition, to exploit the advantages of superconductivity, it has been necessary to wait until elaborated composite materials, whose fabrication requires nanotechnologies, reached the desired level. Spurred on by the discovery of high-temperature superconductivity, this year, we celebrate the 100th anniversary of the discovery of superconductivity, which is predicted to play a key role in realizing a sustainable global environment and in human society in the future.

Effect of doping on structural and superconducting properties in Ca1−xNaxFe2As2single crystals (x=0.5, 0.6, 0.75)

We study the correlation between crystalline structure and superconducting properties in Na-doped Ca${}_{1\ensuremath{-}x}$Na${}_{x}$Fe${}_{2}$As${}_{2}$ single crystals for three chemical compositions ($x$ = 0.5, 0.6, 0.75). We find the maximum superconducting transition temperature ${T}_{c}$ \ensuremath{\sim} 33.4 K at $x$ \ensuremath{\sim} 0.75. The Na substitution causes the decrease of the a-b crystallographic axes and the increase of the $c$ axis in the tetragonal phase. The single crystals show perfect diamagnetism, indicating full superconducting volume. The anisotropy ratio for the upper critical field near the superconducting transition temperature is \ensuremath{\gamma} = 1.85 \ifmmode\pm\else\textpm\fi{} 0.05, independently of the Na content. A narrow vortex liquid phase was detected in the sample with highest ${T}_{c}$ ($x$ = 0.75), consistent with the expectations based on a Lindemann criterion. The analysis of the critical currents shows no evidence of correlated pinning and indicates that the pinning arises from a combination of several mechanisms. At low fields, pinning by random nanoparticles dominates. At higher fields, a small and field independent ${J}_{\mathrm{c}}$ in the optimally doped crystal may originate in the simultaneous presence of sparse large nanoparticles and a much denser distribution of smaller particles, with the sparse pins producing a caging effect that constrains the volume of the vortex bundle associated with the denser and weaker defects.

Ultracold fermions in real or fictitious magnetic fields: BCS-BEC evolution and type-I–type-II transition

We study ultracold neutral fermion superfluids in the presence of fictitious magnetic fields, as well as charged fermion superfluids in the presence of real magnetic fields. Charged fermion superfluids undergo a phase transition from type-I to type-II superfluidity, where the magnetic properties of the superfluid change from being a perfect diamagnet without vortices to a partial diamagnet with the emergence of the Abrikosov vortex lattice. The transition from type-I to type-II superfluidity is tuned by changing the scattering parameter (interaction) for fixed density. We also find that neutral fermion superfluids such as $^{6}\mathrm{Li}$ and $^{40}\mathrm{K}$ are extreme type-II superfluids and are more robust to the penetration of a fictitious magnetic field in the BCS-BEC crossover region near unitarity, where the critical fictitious magnetic field reaches a maximum as a function of the scattering parameter (interaction).

Magnetic Response in Quantized Spin Hall Phase of Correlated Electrons

We investigate the magnetic response in the quantized spin Hall (SH) phase of layered-honeycomb lattice system with intrinsic spin-orbit coupling lambda_SO and on-site Hubbard U. The response is characterized by a parameter g= 4 U a^2 d / 3, where a and d are the lattice constant and interlayer distance, respectively. When g< (sigma_{xy}^{s2} mu)^{-1}, where sigma_{xy}^{s} is the quantized spin Hall conductivity and mu is the magnetic permeability, the magnetic field inside the sample oscillates spatially. The oscillation vanishes in the non-interacting limit U -> 0. When g > (sigma_{xy}^{s2} mu)^{-1}, the system shows perfect diamagnetism, i.e., the Meissner effect occurs. We find that superlattice structure with large lattice constant is favorable to see these phenomena. We also point out that, as a result of Zeeman coupling, the topologically-protected helical edge states shows weak diamagnetism which is independent of the parameter g.

Superconducting Phenomena and Electromagnetism I

One hundred years have passed since the discovery of superconductivity. Over this time, the science, especially in the area of physics, relating to superconductivity has improved dramatically. However, no appreciable progress has been made in the education of superconductivity in relation to primary electromagnetism. A superconductor is a unique material in which Ohm's law is not applicable to the flow of electric current. If this physical point is carefully considered, a new perspective on electromagnetic properties emerges. In this series of lectures, electromagnetic phenomena in superconductors are examined from various aspects. The first lecture deals primarily with the magnetic phenomena occurring in the vicinity of superconductors while they are in the Meissner-Ochsenfeld state, showing perfect diamagnetism. It is shown that by introducing this magnetic phenomenon to the present E-B analogy, the style of teaching primary electromagnetism can be dramatically changed. In accordance with this analogy, it would even have been possible to predict the existence of superconductors in the 19th century after the formulation of the Maxwell theory. This kind of discussion reinforces the E-B analogy. The introduction of superconductivity makes it possible to directly derive the magnetic energy through a mechanical action working against the magnetic force. In contrast, the magnetic energy can be derived only after teaching electromagnetic induction in existing textbooks. Other merits of introducing superconductivity are also discussed.

SOLVING THE SCHRÖDINGER AND DIRAC EQUATIONS FOR A HYDROGEN ATOM IN THE UNIVERSE'S STRONGEST MAGNETIC FIELDS WITH THE FREE COMPLEMENT METHOD

The free complement method for solving the Schr¨ odinger and Dirac equations has been applied to the hydrogen atom in extremely strong magnetic fields. For very strong fields such as those observed on the surfaces of white dwarf and neutron stars, we calculate the highly accurate non-relativistic and relativistic energies of the hydrogen atom. We extended the calculations up to field strengths that exceed the strongest magnetic field (∼10 15 G) ever observed in the universe on a magnetar surface. These are the first reported accurate quantum mechanical calculations ever to include such strong fields. Certain excited state bands in extremely strong fields showed perfect diamagnetism with an infinite number of degenerate states with the same energies as for a hydrogen atom in the absence of a field. Our method of solving the Schr¨ odinger and Dirac equations provides an accurate theoretical

Classical Perfect Diamagnetism: Expulsion of Current from the Plasma Interior

The vanishing of generalized helicity is shown to be the necessary and sufficient condition for a perfect conductor to display perfect diamagnetism, considered to be the defining attribute of a conventional superconductor. Although conventional superconductivity is brought about by quantum correlations in classical systems, prepared in the state of zero initial helicity (helicity is a constant of the motion for a perfect conductor), it can mimic the superconductor's behavior.

Quantum condensates classified in superconductivity with topology in the Minkowski space-time

A substantial problem in the macroscopic theory of pure superconductivity has been left forgotten for a long time since London and London in 1935. An impression survived that the Meissner effect is more substantial than the zero-resistivity. But, the London equation [I], the Newtonian equation of motion, was abandoned, whereas the London equation [II], derived from the Maxwell equations, was postulated. The London equation [II] included the logical gap [ α ] in real time, whereas the London equation [I] has been ignored without even noting the logical gap [ β ] in space. Microscopically, after the publication of F. London's book and the discovery of the isotope effect in 1950, the success of the Bardeen--Cooper--Schrieffer (BCS) theory in 1957 was likely to have finally given the definitive explanation on superconductivity by proving only the London equation [II] that claimed the coherent condensation of Cooper pairs in the momentum space. Since then, these arguments have been regarded to be a standard among various preceding theories. Meanwhile, the London equation [I] has faded away and has been long-forgotten. But we must not abandon the London equation [I], and, rather, retrieve it. We later recognized also that the DC-component of a persistent current can never be determined by using the Fourier transform analysis, because of its singularity at ω = 0 and q = 0 with huge differences of space-time domain. Quite recently, in 2003, we first recognized a proper and harmonious view to simultaneously account for (i) the zero-resistivity in an open system with (i-c) the resultant persistent current in a closed system, and (ii) the perfect diamagnetism at T ≅ 0 K in the space-time aspects in terms of the gauge field theory. Here, we further clarify where and how we have lost and found a properly perspective view of the superconductivity. Here, we eliminate two logical gaps [ α ] and [ β ] by using the gauge field theory for further clarifying a position of the previous and present works. We especially classify superconductors with topology which eventually leads us such as (ii-2D) magnetic flux quantization in a ring. By projecting the 3-dimensional BCS-theory with the concept of ‘coherence’ among an enormous number of Bosons like Cooper pairs onto the (1 + 3)-dimensional Minkowski space-time [β = (v/c) = 0], we clarify responses of the ground state Ψ macro at T ≅ 0 K in a set of the basic equations, for (i) the zero-resistivity, [E K − qφ( R )] = 0 at ω = 0 and (ii) the perfect diamagnetism [ℏK − qA ( R )] = 0 at q = 0 as an inevitable consequence at the gauge fields in the proper theory of superconductivity.