Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
39,687
result(s) for
"SUPERCONDUCTORS"
Sort by:
mBot for makers : conceive, construct and code your own robots at home or in the classroom
\"The mBot is an educational Arduino robot that helps kids learn programming and electronics, alone or in the classroom. The mBot allows novices to start by tinkering, and to access higher-level features or add new components when inspiration strikes, without soldering or breadboarding! This flexibility allows raw beginners and experienced Makers to work at their own comfort level. Written by educators, this book cuts through much of the confusion resulting from the mBot documentation. It also saves you time when you're scaling up your mBots for home and classroom use by giving you creative project ideas you can use right away.\"--Back cover.
Book
Magnetic and Electronic Properties of Sr Doped Infinite-Layer NdNiOsub.2 Supercell: A Screened Hybrid Density Functional Study
To understand the influence of doping Sr atoms on the structural, magnetic, and electronic properties of the infinite-layer NdSrNiO[sub.2], we carried out the screened hybrid density functional study on the Nd[sub.9-n]SrnNi[sub.9]O[sub.18] (n = 0-2) unit cells. Geometries, substitution energies, magnetic moments, spin densities, atom- and lm-projected partial density of states (PDOS), spin-polarized band structures, and the average Bader charges were studied. It showed that the total magnetic moments of the Nd[sub.9]Ni[sub.9]O[sub.18] and Nd[sub.8]SrNi[sub.9]O[sub.18] unit cells are 37.4 and 24.9 emu g[sup.−1], respectively. They are decreased to 12.6 and 4.2 emu g[sup.−1] for the Nd[sub.7]Sr[sub.2]Ni[sub.9]O[sub.18]-Dia and Nd[sub.7]Sr[sub.2]Ni[sub.9]O[sub.18]-Par unit cells. The spin density distributions demonstrated that magnetic disordering of the Ni atoms results in the magnetism decrease. The spin-polarized band structures indicated that the symmetry of the spin-up and spin-down energy bands around the Fermi levels also influence the total magnetic moments. Atom- and lm-projected PDOS as well as the band structures revealed that Ni(d[sub.x2−y2]) is the main orbital intersecting the Fermi level. As a whole, electrons of Sr atoms tend to locate locally and hybridize weakly with the O atoms. They primarily help to build the infinite-layer structures, and influence the electronic structure near the Fermi level indirectly.
Journal Article
Coherent Oscillations in a SrRuOsub.3/BiFeOsub.3 Superlattice
We investigated the ultrafast dynamics of a SrRuO[sub.3]/BiFeO[sub.3] superlattice grown on a SrTiO[sub.3] substrate using a near infrared pump–probe technique at various temperatures. The superlattice exhibits a ferromagnetic order inherited from the SrRuO[sub.3] layer. The pump-induced changes in the reflectivity reveal periodic oscillations. We found that the oscillation frequency can be well explained by zone-folded acoustic phonon oscillations, whose dispersion depends on the sound velocity, density, and thickness within the supercell of each constituent layer. It is found that the observed oscillation frequency corresponds to the A[sub.1] mode, which suggests that oscillations are excited due to pump-induced expansion of the SrRuO[sub.3] layer that absorbs the pump photon. Temperature-dependent measurements reveal significant suppression of the oscillation amplitude in the ferromagnetic state. The suppressed amplitude is proportional to the square of the magnetization, M(T)[sup.2]. This phenomenon can be attributed to a strong magnetostriction effect of SrRuO[sub.3] that suppresses lattice expansion upon pumping.
Journal Article
Vortex Glass—Vortex Liquid Transition in BaFesub.2sub.2 and CaKFesub.4Assub.4 Superconductors from Multi-Harmonic AC Magnetic Susceptibility Studies
For practical applications of superconductors, understanding the vortex matter and dynamics is of paramount importance. An important issue in this context is the transition of the vortex glass, which is a true superconducting phase, into a vortex liquid phase having a linear dissipation. By using multi-harmonic susceptibility studies, we have investigated the vortex glass-vortex liquid phase transitions in CaKFe[sub.4]As[sub.4] and BaFe[sub.2](As[sub.0.68]P[sub.0.32])[sub.2] single crystals. The principle of our method relates the on-set of the third-harmonic susceptibility response with the appearance of a vortex-glass phase in which the dissipation is non-linear. Similar to the high-critical temperature cuprate superconductors, we have shown that even in these iron-based superconductors with significant lower critical temperatures, such phase transition can be treated as a melting in the sense of Lindemann's approach, considering an anisotropic Ginzburg-Landau model. The experimental data are consistent with a temperature-dependent London penetration depth given by a 3D XY fluctuations model. The fitting parameters allowed us to extrapolate the vortex melting lines down to the temperature of liquid hydrogen, and such extrapolation showed that CaKFe[sub.4]As[sub.4] is a very promising superconducting material for high field applications in liquid hydrogen, with a melting field at 20 K of the order of 100 T.
Journal Article
Ion-Selective Scattering Studied Using the Variable-Energy Electron Irradiation in the Basub.0.2Ksub.0.8Fesub.2Assub.2 Superconductor
Low-temperature variable-energy electron irradiation was used to induce non-magnetic disorder in a single crystal of a hole-doped iron-based superconductor, Ba[sub.1−x]K[sub.x]Fe[sub.2]As[sub.2], x = 0.80. To avoid systematic errors, the beam energy was adjusted non-consequently for five values between 1.0 and 2.5 MeV when sample resistance was measured in situ at 22 K. For all energies, the resistivity raises linearly with the irradiation fluence suggesting the creation of uncorrelated dilute point-like disorder (confirmed by simulations). The rate of the resistivity increase peaks at energies below 1.5 MeV. Comparison with calculated partial cross-sections points to the predominant creation of defects in the iron sublattice. Simultaneously, superconducting T[sub.c], measured separately between the irradiation runs, is monotonically suppressed as expected, since it depends on the total scattering rate, hence on the total cross-section, which is a monotonically increasing function of the energy. Our work experimentally confirms an often-made assumption of the dominant role of the iron sub-lattice in iron-based superconductors.
Journal Article
Elemental Substitution at Tl Site of Tlsub.1−xXIx/ICaCusub.2Osub.7 Superconductor with X = Cr, Bi, Pb, Se, and Te
The effects of elemental substitutions at the Tl site of a Tl[sub.1−x]Xx(Ba, Sr)CaCu[sub.2]O[sub.7] superconductor with X = Cr, Bi, Pb, Se, and Te were investigated. This study aimed to determine the elements that enhance and suppress the superconducting transition temperature of the Tl[sub.1−x]Xx(Ba, Sr)CaCu[sub.2]O[sub.7] (Tl-1212) phase. The selected elements belong to the groups of transition metal, post-transition metal, non-metal, and metalloid. The relationship between the transition temperature and ionic radius of the elements was also discussed. The samples were prepared by the solid-state reaction method. The XRD patterns showed a single Tl-1212 phase was formed in the non- and Cr-substituted (x = 0.15) samples. The Cr-substituted samples (x = 0.4) showed a plate-like structure with smaller voids. The highest superconducting transition temperatures (T[sub.c onset], T[sub.cχ′], and T[sub.p]) were also achieved by the Cr-substituted samples for x = 0.4 compositions. However, the substitution of Te suppressed the superconductivity of the Tl-1212 phase. J[sub.c inter] (T[sub.p]) for all samples was calculated to be in the range of 12-17 A/cm[sup.2]. This work shows that substitution elements with a smaller ionic radius tend to be more favorable in improving the superconducting properties of the Tl-1212 phase.
Journal Article
Cometal Addition Effect on Superconducting Properties and Granular Behaviours of Polycrystalline FeSesub.0.5Tesub.0.5
The enhanced performance of superconducting FeSe[sub.0.5]Te[sub.0.5] materials with added micro-sized Pb and Sn particles is presented. A series of Pb- and Sn-added FeSe[sub.0.5]Te[sub.0.5] (FeSe[sub.0.5]Te[sub.0.5] + xPb + ySn; x = y = 0-0.1) bulks are fabricated by the solid-state reaction method and characterized through various measurements. A very small amount of Sn and Pb additions (x = y ≤ 0.02) enhance the transition temperature (T[sub.c] [sup.onset]) of pure FeSe[sub.0.5]Te[sub.0.5] by ~1 K, sharpening the superconducting transition and improving the metallic nature in the normal state, whereas larger metal additions (x = y ≥ 0.03) reduce T[sub.c] [sup.onset] by broadening the superconducting transition. Microstructural analysis and transport studies suggest that at x = y > 0.02, Pb and Sn additions enhance the impurity phases, reduce the coupling between grains, and suppress the superconducting percolation, leading to a broad transition. FeSe[sub.0.5]Te[sub.0.5] samples with 2 wt% of cometal additions show the best performance with their critical current density, J[sub.c], and the pinning force, Fp, which might be attributable to providing effective flux pinning centres. Our study shows that the inclusion of a relatively small amount of Pb and Sn (x = y ≤ 0.02) works effectively for the enhancement of superconducting properties with an improvement of intergrain connections as well as better phase uniformity.
Journal Article
Evidence of topological superconductivity in planar Josephson junctions
Majorana zero modes—quasiparticle states localized at the boundaries of topological superconductors—are expected to be ideal building blocks for fault-tolerant quantum computing
1
,
2
. Several observations of zero-bias conductance peaks measured by tunnelling spectroscopy above a critical magnetic field have been reported as experimental indications of Majorana zero modes in superconductor–semiconductor nanowires
3
–
8
. On the other hand, two-dimensional systems offer the alternative approach of confining Majorana channels within planar Josephson junctions, in which the phase difference
φ
between the superconducting leads represents an additional tuning knob that is predicted to drive the system into the topological phase at lower magnetic fields than for a system without phase bias
9
,
10
. Here we report the observation of phase-dependent zero-bias conductance peaks measured by tunnelling spectroscopy at the end of Josephson junctions realized on a heterostructure consisting of aluminium on indium arsenide. Biasing the junction to
φ
≈ π reduces the critical field at which the zero-bias peak appears, with respect to
φ
= 0. The phase and magnetic-field dependence of the zero-energy states is consistent with a model of Majorana zero modes in finite-size Josephson junctions. As well as providing experimental evidence of phase-tuned topological superconductivity, our devices are compatible with superconducting quantum electrodynamics architectures
11
and are scalable to the complex geometries needed for topological quantum computing
9
,
12
,
13
.
Evidence is found for phase-tunable Majorana zero modes in scalable two-dimensional Josephson junctions produced by top-down fabrication.
Journal Article
Critical Current Density in Id/I-Wave Hubbard Superconductors
In this work, the Generalized Hubbard Model on a square lattice is applied to evaluate the electrical current density of high critical temperature d-wave superconductors with a set of Hamiltonian parameters allowing them to reach critical temperatures close to 100 K. The appropriate set of Hamiltonian parameters permits us to apply our model to real materials, finding a good quantitative fit with important macroscopic superconducting properties such as the critical superconducting temperature (T[sub.c]) and the critical current density (J[sub.c]). We propose that much as in a dispersive medium, in which the velocity of electrons can be estimated by the gradient of the dispersion relation ∇ε(k), the electron velocity is proportional to ∇E(k) in the superconducting state (where E(k)=[square root of (ε(k)−μ)[sup.2]+Δ[sup.2](k)] is the dispersion relation of the quasiparticles, and k is the electron wave vector). This considers the change of ε(k) with respect to the chemical potential (μ) and the formation of pairs that gives rise to an excitation energy gap Δ(k) in the electron density of states across the Fermi level. When ε(k)=μ at the Fermi surface (FS), only the term for the energy gap remains, whose magnitude reflects the strength of the pairing interaction. Under these conditions, we have found that the d-wave symmetry of the pairing interaction leads to a maximum critical current density in the vicinity of the antinodal k-space direction (π,0) of approximately 1.407236×10[sup.8] A/cm[sup.2], with a much greater current density along the nodal direction (π/2,π/2) of 2.214702×10[sup.9] A/cm[sup.2]. These results allow for the establishment of a maximum limit for the critical current density that could be attained by a d-wave superconductor.
Journal Article
Topological superconductivity in a phase-controlled Josephson junction
Topological superconductors can support localized Majorana states at their boundaries
1
–
5
. These quasi-particle excitations obey non-Abelian statistics that can be used to encode and manipulate quantum information in a topologically protected manner
6
,
7
. Although signatures of Majorana bound states have been observed in one-dimensional systems, there is an ongoing effort to find alternative platforms that do not require fine-tuning of parameters and can be easily scaled to large numbers of states
8
–
21
. Here we present an experimental approach towards a two-dimensional architecture of Majorana bound states. Using a Josephson junction made of a HgTe quantum well coupled to thin-film aluminium, we are able to tune the transition between a trivial and a topological superconducting state by controlling the phase difference across the junction and applying an in-plane magnetic field
22
. We determine the topological state of the resulting superconductor by measuring the tunnelling conductance at the edge of the junction. At low magnetic fields, we observe a minimum in the tunnelling spectra near zero bias, consistent with a trivial superconductor. However, as the magnetic field increases, the tunnelling conductance develops a zero-bias peak, which persists over a range of phase differences that expands systematically with increasing magnetic field. Our observations are consistent with theoretical predictions for this system and with full quantum mechanical numerical simulations performed on model systems with similar dimensions and parameters. Our work establishes this system as a promising platform for realizing topological superconductivity and for creating and manipulating Majorana modes and probing topological superconducting phases in two-dimensional systems.
Majorana bound states are created in a two-dimensional architecture by confining Majorana channels within a planar Josephson junction, using the phase difference across the junction and an in-plane magnetic field.
Journal Article