scholarly journals Fluctuation diamagnetism around the superconducting transition in a cuprate crystal with a reduced Meissner fraction

2008 ◽  
Vol 77 (5) ◽  
Author(s):  
Jesús Mosqueira ◽  
Félix Vidal
Keyword(s):  
Superconducting Transition ◽  
Meissner Fraction

scholarly journals Synthesis, Characterization and Ageing of MgB2

2001 ◽  
Vol 689 ◽  
Author(s):  
A. Serquis ◽  
R. Schulze ◽  
Y. T. Zhu ◽  
J. Y. Coulter ◽  
D. E. Peterson ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Rietveld Analysis ◽  
Superconducting Transition ◽  
Superconducting Properties ◽  
Ambient Conditions ◽  
X Ray ◽  
Grain Sizes ◽  
Crystal Strain ◽  
Surface Decomposition ◽  
Meissner Fraction

ABSTRACTWe studied the influence of sample preparation and defects in the superconducting properties samples using atomic ratios of Mg:B=1:1 and Mg:B=1:2. Samples were characterized by SEM, and XRD, and the magnetization properties were examined in a SQUID magnetometer. The presence of Mg vacancies was determined by Rietveld analysis. Most of the samples exhibited sharp superconducting transitions with Tcs between 37–39 K.We found a strong correlation between the crystal strain and the Tc. This strain was related to the presence of Mg vacancies. In addition, results showed that some samples degraded with time when exposed to ambient conditions. In these samples the Tc did not change with time, but the superconducting transition became broader and the Meissner fraction decreased. This effect was only present in samples with poor connectivity between grains and smaller grain sizes. The degradation was related to a surface decomposition as observed by X-ray Photoelectron Spectroscopy. No correlation was found between this effect and the presence of Mg vacancies.

Microcalorimeters for X-Ray Spectroscopy

1988 ◽  
Vol 102 ◽  
pp. 41
Author(s):  
E. Silver ◽  
C. Hailey ◽  
S. Labov ◽  
N. Madden ◽  
D. Landis ◽  
...  
Keyword(s):  
High Resolution ◽  
High Efficiency ◽  
Thermal Response ◽  
Low Noise ◽  
High Resolution Spectroscopy ◽  
Superconducting Transition ◽  
Sapphire Substrates ◽  
Laboratory Plasmas ◽  
Adiabatic Demagnetization ◽  
Theoretical Predictions

The merits of microcalorimetry below 1°K for high resolution spectroscopy has become widely recognized on theoretical grounds. By combining the high efficiency, broadband spectral sensitivity of traditional photoelectric detectors with the high resolution capabilities characteristic of dispersive spectrometers, the microcalorimeter could potentially revolutionize spectroscopic measurements of astrophysical and laboratory plasmas. In actuality, however, the performance of prototype instruments has fallen short of theoretical predictions and practical detectors are still unavailable for use as laboratory and space-based instruments. These issues are currently being addressed by the new collaborative initiative between LLNL, LBL, U.C.I., U.C.B., and U.C.D.. Microcalorimeters of various types are being developed and tested at temperatures of 1.4, 0.3, and 0.1°K. These include monolithic devices made from NTD Germanium and composite configurations using sapphire substrates with temperature sensors fabricated from NTD Germanium, evaporative films of Germanium-Gold alloy, or material with superconducting transition edges. A new approache to low noise pulse counting electronics has been developed that allows the ultimate speed of the device to be determined solely by the detector thermal response and geometry. Our laboratory studies of the thermal and resistive properties of these and other candidate materials should enable us to characterize the pulse shape and subsequently predict the ultimate performance. We are building a compact adiabatic demagnetization refrigerator for conveniently reaching 0.1°K in the laboratory and for use in future satellite-borne missions. A description of this instrument together with results from our most recent experiments will be presented.

Observation by HVEM of the martensite transformation and the superconducting transition in Nb3Sn

1988 ◽  
Vol 46 ◽  
pp. 788-789
Author(s):  
M. A. Kirk ◽  
M. C. Baker ◽  
B. J. Kestel ◽  
H. W. Weber
Keyword(s):  
Thin Films ◽  
Low Temperature ◽  
Superconducting State ◽  
Martensite Transformation ◽  
Sputter Deposition ◽  
Diffusion Reaction ◽  
Solute Diffusion ◽  
Superconducting Transition ◽  
Twin Boundaries ◽  
Martensite Structure

It is well known that a number of compound superconductors with the A15 structure undergo a martensite transformation when cooled to the superconducting state. Nb3Sn is one of those compounds that transforms, at least partially, from a cubic to tetragonal structure near 43 K. To our knowledge this transformation in Nb3Sn has not been studied by TEM. In fact, the only low temperature TEM study of an A15 material, V3Si, was performed by Goringe and Valdre over 20 years ago. They found the martensite structure in some foil areas at temperatures between 11 and 29 K, accompanied by faults that consisted of coherent twin boundaries on {110} planes. In pursuing our studies of irradiation defects in superconductors, we are the first to observe by TEM a similar martensite structure in Nb3Sn.Samples of Nb3Sn suitable for TEM studies have been produced by both a liquid solute diffusion reaction and by sputter deposition of thin films.

INCREASED RESISTANCE BELOW THE SUPERCONDUCTING TRANSITION IN DISCONTINUOUS FILMS OF (SN)x AND INDIUM

1978 ◽  
Vol 39 (C6) ◽  
pp. C6-448-C6-450 ◽  
Author(s):  
M. W. Young ◽  
J. M.D. Thomas ◽  
C. J. Adkins ◽  
J. W. Tate
Keyword(s):  
Superconducting Transition

Prediction of phonon-mediated superconductivity in two-dimensional Mo2B2

2019 ◽  
Vol 7 (9) ◽  
pp. 2589-2595 ◽  
Author(s):  
Luo Yan ◽  
Tao Bo ◽  
Peng-Fei Liu ◽  
Bao-Tian Wang ◽  
Yong-Guang Xiao ◽  
...  
Keyword(s):  
Two Dimensional ◽  
Transition Temperatures ◽  
Superconducting Transition ◽  
Molybdenum Boride

We predict two new molybdenum boride monolayers as phonon-mediated superconductors with superconducting transition temperatures of 3.9 and 0.2 K.

scholarly journals Evolution of spin excitations from bulk to monolayer FeSe

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jonathan Pelliciari ◽  
Seher Karakuzu ◽  
Qi Song ◽  
Riccardo Arpaia ◽  
Abhishek Nag ◽  
...  
Keyword(s):  
Quantum Monte Carlo ◽  
Spin Dynamics ◽  
Spin Fluctuations ◽  
Superconducting Transition ◽  
Pairing Mechanism ◽  
Range Magnetic Order ◽  
X Ray Scattering ◽  
Spin Excitations ◽  
Order Of Magnitude ◽  
Long Range Magnetic Order

AbstractIn ultrathin films of FeSe grown on SrTiO3 (FeSe/STO), the superconducting transition temperature Tc is increased by almost an order of magnitude, raising questions on the pairing mechanism. As in other superconductors, antiferromagnetic spin fluctuations have been proposed to mediate SC making it essential to study the evolution of the spin dynamics of FeSe from the bulk to the ultrathin limit. Here, we investigate the spin excitations in bulk and monolayer FeSe/STO using resonant inelastic x-ray scattering (RIXS) and quantum Monte Carlo (QMC) calculations. Despite the absence of long-range magnetic order, bulk FeSe displays dispersive magnetic excitations reminiscent of other Fe-pnictides. Conversely, the spin excitations in FeSe/STO are gapped, dispersionless, and significantly hardened relative to its bulk counterpart. By comparing our RIXS results with simulations of a bilayer Hubbard model, we connect the evolution of the spin excitations to the Fermiology of the two systems revealing a remarkable reconfiguration of spin excitations in FeSe/STO, essential to understand the role of spin fluctuations in the pairing mechanism.

scholarly journals Importance of $${{d}}_{{{xy}}}$$ orbital and electron correlation in iron-based superconductors revealed by phase diagram for 1111-system

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tsuyoshi Kawashima ◽  
Shigeki Miyasaka ◽  
Hirokazu Tsuji ◽  
Takahiro Yamamoto ◽  
Masahiro Uekubo ◽  
...  
Keyword(s):  
Electron Correlation ◽  
Weak Coupling ◽  
Structural Parameters ◽  
Structural Flexibility ◽  
Superconducting Transition ◽  
Iron Based Superconductors ◽  
Wide Range ◽  
Band Filling ◽  
Iron Based ◽  
Correlation Strength

AbstractThe structural flexibility at three substitution sites in LaFeAsO enabled investigation of the relation between superconductivity and structural parameters over a wide range of crystal compositions. Substitutions of Nd for La, Sb or P for As, and F or H for O were performed. All these substitutions modify the local structural parameters, while the F/H-substitution also changes band filling. It was found that the superconducting transition temperature $$T_{\text{c}}$$ T c is strongly affected by the pnictogen height $$h_{Pn}$$ h Pn from the Fe-plane that controls the electron correlation strength and the size of the $$d_{xy}$$ d xy hole Fermi surface (FS). With increasing $$h_{Pn}$$ h Pn , weak coupling BCS superconductivity switches to the strong coupling non-BCS one where electron correlations and the $$d_{xy}$$ d xy hole FS may be important.

scholarly journals Kondo effect and superconductivity in niobium with iron impurities

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hansong Zeng ◽  
Dan Zhou ◽  
Guoqing Liang ◽  
Rujun Tang ◽  
Zhi H. Hang ◽  
...  
Keyword(s):  
Magnetic Moment ◽  
Low Temperatures ◽  
Kondo Effect ◽  
Film Structure ◽  
Kondo Temperature ◽  
Superconducting Transition ◽  
Interesting Phenomenon ◽  
Superconducting Device ◽  
Bcc Lattice ◽  
Device Applications

AbstractKondo effect is an interesting phenomenon in quantum many-body physics. Niobium (Nb) is a conventional superconductor important for many superconducting device applications. It was long thought that the Kondo effect cannot be observed in Nb because the magnetic moment of a magnetic impurity, e.g. iron (Fe), would have been quenched in Nb. Here we report an observation of the Kondo effect in a Nb thin film structure. We found that by co-annealing Nb films with Fe in Argon gas at above 400 $$^{\circ }$$ ∘ C for an hour, one can induce a Kondo effect in Nb. The Kondo effect is more pronounced at higher annealing temperature. The temperature dependence of the resistance suggests existence of remnant superconductivity at low temperatures even though the system never becomes superconducting. We find that the Hamann theory for the Kondo resistivity gives a satisfactory fitting to the result. The Hamann analysis gives a Kondo temperature for this Nb–Fe system at $$\sim $$ ∼ 16 K, well above the superconducting transition onset temperature 9 K of the starting Nb film, suggesting that the screening of the impurity spins is effective to allow Cooper pairs to form at low temperatures. We suggest that the mechanism by which the Fe impurities retain partially their magnetic moment is that they are located at the grain boundaries, not fully dissolved into the bcc lattice of Nb.

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