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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Shockwave-Loading-Induced Enhancement of T c in Superconducting Bi 2 Sr 2 CaCu 2 O 8+δ

Here, we report a shockwave method for altering the properties of the superconductor material Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212). We find that the superconducting transition temperature (T c ) increases from 84 K for the pristine sample to 94 K for the sample treated at a temperature and pressure of ~1200 K and ~31 GPa, respectively. X-ray diffraction and transmission electron microscopy characterizations indicate that this T c enhancement arises from a phase transition from pristine Bi2212 to a mixture of superconducting Bi2212 and semiconducting Bi 2 Sr 2 CuO 6+δ (Bi2201) during the shockwave treatment. The shockwave-treated sample exhibits n-type semiconductor properties (with an on-off ratio ~5), in contrast to the pure metallic pristine sample. This study offers an alternative route for modifying the superconducting properties via a shockwave treatment. Furthermore, this method may provide a new approach for studying other temperature- and pressure-sensitive materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Superconducting and normal-state anisotropy of the doped topological insulator Sr 0.1 Bi 2 Se 3

Sr x Bi 2 Se 3 and the related compounds Cu x Bi 2 Se 3 and Nb x Bi 2 Se 3 have attracted considerable interest, as these materials may be realizations of unconventional topological superconductors. Superconductivity with T c ~3 K in Sr x Bi 2 Se 3 arises upon intercalation of Sr into the layered topological insulator Bi 2 Se 3 . Here we elucidate the anisotropy of the normal and superconducting state of Sr 0.1 Bi 2 Se 3 with angular dependent magnetotransport and thermodynamic measurements. High resolution x-ray diffraction studies underline the high crystalline quality of the samples. We demonstrate that the normal state electronic and magnetic properties of Sr 0.1 Bi 2 Se 3 are isotropic in the basal plane while we observe a large two-fold in-plane anisotropy of the upper critical field in the superconducting state. In conclusion, our results support the recently proposed odd-parity nematic state characterized by a nodal gap of Eu symmetry in Sr x Bi 2 Se 3 .

36 MATERIALS SCIENCE↗
DOE OSTI2019

Edge effect pinning in mesoscopic superconducting strips with non-uniform distribution of defects

Transport characteristics of nano-sized superconducting strips and bridges are determined by an intricate interplay of surface and bulk pinning. In the limiting case of a very narrow bridge, the critical current is mostly defined by its surface barrier, while in the opposite case of very wide strips it is dominated by its bulk pinning properties. Here we present a detailed study of the intermediate regime, where the critical current is determined, both, by randomly placed pinning centres and by the Bean-Livingston barrier at the edge of the superconducting strip in an external magnetic field. We use the time-dependent Ginzburg-Landau equations to describe the vortex dynamics and current distribution in the critical regime. Our studies reveal that while the bulk defects arrest vortex motion away from the edges, defects in their close vicinity promote vortex penetration, thus suppressing the critical current. We determine the spatial distribution of the defects optimizing the critical current and find that it is in general non-uniform and asymmetric: the barrier at the vortex-exit edge influence the critical current much stronger than the vortex-entrance edge. Furthermore, this optimized defect distribution has a more than 30% higher critical current density than a homogeneously disorder superconducting film.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Evidence for unconventional superconductivity and nontrivial topology in PdTe

Abstract PdTe is a superconductor with T c ~ 4.25 K. Recently, evidence for bulk-nodal and surface-nodeless gap features has been reported in PdTe. Here, we investigate the physical properties of PdTe in both the normal and superconducting states via specific heat and magnetic torque measurements and first-principles calculations. Below T c , the electronic specific heat initially decreases in T 3 behavior (1.5 K < T < T c ) then exponentially decays. Using the two-band model, the superconducting specific heat can be well described with two energy gaps: one is 0.372 meV and another 1.93 meV. The calculated bulk band structure consists of two electron bands (α and β) and two hole bands (γ and η) at the Fermi level. Experimental detection of the de Haas-van Alphen (dHvA) oscillations allows us to identify four frequencies ( F α = 65 T, F β = 658 T, F γ = 1154 T, and F η = 1867 T for H // a ), consistent with theoretical predictions. Nontrivial α and β bands are further identified via both calculations and the angle dependence of the dHvA oscillations. Our results suggest that PdTe is a candidate for unconventional superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Coupled electronic and magnetic excitations in the cuprates and their role in the superconducting transition

The formation of Cooper pairs, a bound state of two electrons of opposite spin and momenta by exchange of a phonon, is a defining feature of conventional superconductivity. In the cuprate high temperature superconductors, even though the superconducting state also consists of Cooper pairs, the pairing mechanism remains intensely debated. Here, we investigate superconducting pairing in the Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) cuprate by employing spectral functions obtained from angle-resolved photoemission as input to the Bethe-Salpeter equation. Assuming Cooper pairing is driven by spin fluctuations, we construct the spin-fluctuation-mediated pairing interaction and use it to compute the eigenfunctions and eigenvalues of the Bethe-Salpeter equation for multiple Bi2212 samples. The leading d-wave eigenvalue increases as the temperature is decreased toward $T_c$, reaching a value of approximately 1 at the $T_c$ corresponding to each doping value. This suggests that spin fluctuations can approximately account for $T_c$ and mediate pairing in the cuprate superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Fractional magnetoresistance oscillations in spin-triplet superconducting rings

Abstract Half-quantum vortices in spin-triplet superconductors are predicted to host Majorana zero modes and may provide a viable platform for topological quantum computation. Recent works also suggested that, in thin mesoscopic rings, the superconducting pairing symmetry can be probed via Little-Parks-like magnetoresistance oscillations of periodicity Φ 0 = h /2 e that persist below the critical temperature. Here we use the London limit of Ginzburg-Landau theory to study these magnetoresistance oscillations resulting from thermal vortex tunneling in spin-triplet superconducting rings. For a range of temperatures in the presence of disorder, we find magnetoresistance oscillations with an emergent fractional periodicity Φ 0 / n , where the integer n ≥ 3 is entirely determined by the ratio of the spin and charge superfluid densities. These fractional oscillations can unambiguously confirm the spin-triplet nature of superconductivity and directly reveal the tunneling of half-quantum vortices in real-world candidate materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Superconductivity with extremely large upper critical fields in Nb2Pd0.81S5

Here, we report the discovery of superconductivity in a new transition metal-chalcogenide compound, i.e. Nb2Pd0.81S5, with a transition temperature Tc > 6.6 K. Despite its relatively low Tc, it displays remarkably high and anisotropic superconducting upper critical fields, e.g. m0Hc2 (T R 0 K) . 37 T for fields applied along the crystallographic b-axis. For a field applied perpendicularly to the b-axis, m0Hc2 shows a linear dependence in temperature which coupled to a temperature-dependent anisotropy of the upper critical fields, suggests that Nb2Pd0.81S5 is a multi-band superconductor. This is consistent with band structure calculations which reveal nearly cylindrical and quasi-one-dimensional Fermi surface sheets having hole and electron character, respectively. The static spin susceptibility as calculated through the random phase approximation, reveals strong peaks suggesting proximity to a magnetic state and therefore the possibility of unconventional superconductivity.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Robust antiferromagnetism preventing superconductivity in pressurized (Ba 0.61 K 0.39 )Mn 2 Bi 2

BaMn 2 Bi 2 possesses an iso-structure of iron pnictide superconductors and similar antiferromagnetic (AFM) ground state to that of cuprates, therefore, it receives much more attention on its properties and is expected to be the parent compound of a new family of superconductors. When doped with potassium (K), BaMn 2 Bi 2 undergoes a transition from an AFM insulator to an AFM metal. Consequently, it is of great interest to suppress the AFM order in the K-doped BaMn 2 Bi 2 with the aim of exploring the potential superconductivity. Here, we report that external pressure up to 35.6 GPa cannot suppress the AFM order in the K-doped BaMn 2 Bi 2 to develop superconductivity in the temperature range of 300 K–1.5 K, but induces a tetragonal (T) to an orthorhombic (OR) phase transition at ~20 GPa. Theoretical calculations for the T and OR phases, on basis of our high-pressure XRD data, indicate that the AFM order is robust in the pressurized Ba 0.61 K 0.39 Mn 2 Bi 2 . Utlimately, both of our experimental and theoretical results suggest that the robust AFM order essentially prevents the emergence of superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Critical field of two-dimensional superconducting Sn{sub 1-x}/Si{sub x} bimetallic composite cluster assembled films with energetic cluster impact deposition

Sn{sub 1-x}/Si{sub x} cluster assembled films have been prepared by an energetic cluster impact deposition using a plasma-gas-condensation cluster beam deposition apparatus. Transmission electron microscope images indicated that individual clusters have composite morphologies, where Sn and Si were separated from each other. The superconducting critical magnetic fields, H{sub c}, of Sn{sub 1-x}/Si{sub x} cluster assembled films were measured and found to be much higher than the critical magnetic field of the bulk Sn. We estimated the H{sub c} values by using a theory of the superconducting thin film. The estimated values are in good agreement with the experiments, indicating that the Sn{sub 1-x}/Si{sub x} cluster assembled films can be regarded as a two-dimensional system although thickness, t, of Sn{sub 1-x}/Si{sub x} cluster assembled films (t Almost-Equal-To 1000 nm) is thicker than conventional superconducting thin film (t < 100 nm).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Effect of injected spins with different polarized orientations on the superconductivity of La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/La{sub 1.85}Sr{sub 0.15}CuO{sub 4} thin films

The influence of spin-polarized quasi-particle injection on the superconductivity of epitaxial La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/La{sub 1.85}Sr{sub 0.15}CuO{sub 4} composite thin films is systematically investigated. Different electrode configurations on the same specimen are designed to study the role of spin injection. It is found that the upper critical field and flux pinning potential are reduced by the spin injection, especially for the field parallel to ab-plane. The manipulation of superconductivity by the spin polarization orientations of injected quasi-particles possibly originates from the different suppressions on the superconducting pairing strength, which is considered to be related to the local antiferromagnetic spin fluctuations in La{sub 1.85}Sr{sub 0.15}CuO{sub 4}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Unsteady heat dissipation in accelerator superconducting coils insulated with porous ceramic insulation in normal and supercritical helium conditions

To investigate the unsteady heat dissipation in accelerator superconducting coils insulated with porous ceramic insulation, two experimental mock-ups reproducing the thermal and the mechanical conditions of a superconducting coils were produced. The mock-ups with compressive load of 10 MPa and 20 MPa were tested at normal (T = 4.23 K and p = 1 bar) and supercritical helium conditions (T = 4.23 K and p = 2.0 to 3.75 bar) during unsteady heat dissipation. The paper presents the experimental results of temperature rise in both superconducting coils as a function of time for a wide range of a localized heat load varying from 0.1 kJ/m{sup 3} up to 12.8 MJ m{sup −3} per pulse. A numerical model of the transient process in these coils has been developed and the computations are compared with the experimental results.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Single-crystal superconducting nanowires of NbSe{sub 2} fabricated by reactive plasma etching

We present the preparation and measurements of nanowires of single-crystal NbSe{sub 2}. These nanowires were prepared on ultrathin (≲10 nm) flakes of NbSe{sub 2} mechanically exfoliated from a bulk single crystal using a process combining electron beam lithography and reactive plasma etching. The electrical contacts to the nanowires were prepared using Ti/Au. Our technique, which overcomes several limitations of methods developed previously for fabricating superconducting nanowires, also allows for the preparation of complex superconducting nanostructures with a desired geometry. Current-voltage characteristics of individual superconducting single-crystal nanowires with widths down to 30 nm and cross-sectional areas as low as 270 nm{sup 2} were measured.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Non-uniform absorption of terahertz radiation on superconducting hot electron bolometer microbridges

We interpret the experimental observation of a frequency-dependence of superconducting hot electron bolometer (HEB) mixers by taking into account the non-uniform absorption of the terahertz radiation on the superconducting HEB microbridge. The radiation absorption is assumed to be proportional to the local surface resistance of the HEB microbridge, which is computed using the Mattis-Bardeen theory. With this assumption the dc and mixing characteristics of a superconducting niobium-nitride (NbN) HEB device have been modeled at frequencies below and above the equilibrium gap frequency of the NbN film.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Stress dependent oxidation of sputtered niobium and effects on superconductivity

We report on the suppression of room temperature oxidation of DC sputtered niobium films and the effects upon the superconductive transition temperature, T{sub c}. Niobium was sputter-deposited on silicon dioxide coated 150 mm wafers and permitted to oxidize at room temperature and pressure for up to two years. Resistivity and stress measurements indicate that tensile films greater than 400 MPa resist bulk oxidation with measurements using transmission electron microscope, electron dispersive X-ray spectroscopy, x-ray photoelectric spectroscopy, and secondary ion mass spectrometry confirming this result. Although a surface oxide, Nb{sub 2}O{sub 5}, consumed the top 6–10 nm, we measure less than 1 at. % oxygen and nitrogen in the bulk of the films after the oxidation period. T{sub c} measurements using a SQUID magnetometer indicate that the tensile films maintained a T{sub c} approaching the dirty superconductive limit of 8.4 K after two years of oxidation while maintaining room temperature sheet resistance. This work demonstrates that control over niobium film stress during deposition can prevent bulk oxidation by limiting the vertical grain boundaries ability to oxidize, prolonging the superconductive properties of sputtered niobium when exposed to atmosphere.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Raising gradient limitations in 2.1 GHz superconducting photonic band gap accelerator cavities

We report results from recent 2.1 GHz superconducting radio frequency (SRF) photonic band gap (PBG) resonator experiments at Los Alamos. Two 2.1 GHz PBG cells with elliptical rods were fabricated and tested at high power in a liquid helium bath at the temperatures of 4 K and below 2 K. The described SRF PBG cells were designed with a particular emphasis on changing the shape of the PBG rods to reduce peak surface magnetic fields and at the same time to preserve its effectiveness at damping higher-order-modes. The superconducting PBG cavities have great potential for damping long-range wakefields in SRF accelerator structures without affecting the fundamental accelerating mode. The cells performed in accordance with simulation's predictions and the maximum achieved accelerating gradient was 18.3 MV/m. This represents a 30% increase over gradients previously demonstrated in superconducting PBG cavities with round rods.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Joint measurement of current-phase relations and transport properties of hybrid junctions using a three junctions superconducting quantum interference device

We propose a scheme to measure both the current-phase relation and differential conductance dI/dV of a superconducting junction, in the normal and the superconducting states. This is done using a dc Superconducting Quantum Interference Device with two Josephson junctions in parallel with the device under investigation and three contacts. As a demonstration, we measure the current-phase relation and dI/dV of a small Josephson junction and a carbon nanotube junction. In this latter case, in a regime where the nanotube is well conducting, we show that the non-sinusoidal current phase relation we find is consistent with the theory for a weak link, using the transmission extracted from the differential conductance in the normal state. This method holds great promise for future investigations of the current-phase relation of more exotic junctions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Electrical modulation of superconducting critical temperature in liquid-gated thin niobium films

We demonstrate that the superconducting critical temperature (T{sub c}) of thin niobium films can be electrically modulated in a liquid-gated geometry device. T{sub c} can be suppressed and enhanced by applying positive and negative gate voltage, respectively, in a reversible manner within a range of about 0.1 K. At a fixed temperature below T{sub c}, we observed that the superconducting critical current can be modulated by gate voltage. This result suggests a possibility of an electrically controlled switching device operating at or above liquid helium temperature, where superconductivity can be turned on or off solely by the applied gate voltage.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

A cryogen-free ultralow-field superconducting quantum interference device magnetic resonance imaging system

Magnetic resonance imaging (MRI) at microtesla fields using superconducting quantum interference device (SQUID) detection has previously been demonstrated, and advantages have been noted. Although the ultralow-field SQUID MRI technique would not need the heavy superconducting magnet of conventional MRI systems, liquid helium required to cool the low-temperature detector still places a significant burden on its operation. We have built a prototype cryocooler-based SQUID MRI system that does not require a cryogen. The SQUID detector and the superconducting gradiometer were cooled down to 3.7 K and 4.3 K, respectively. We describe the prototype design, characterization, a phantom image, and areas of further improvements needed to bring the imaging performance to parity with conventional MRI systems.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗