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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Quaternary borocarbides: New class of intermetallic superconductors

Our recent discovery of superconductivity (SC) in the four-element multiphase Y-Ni-B-C system at an elevated temperature (TC approximately 12 K) has opened up great possibilities of identifying new superconducting materials and generating new physics. Superconductivity with Tc (greater than 20 K) higher than that known so far in bulk intermetallics has been observed in multiphase Y-Pd-B-C and Th-Pd-B-C systems and a family of single phase materials RENi2B2C (RE= Y, rare earth) have been found. Our investigations show YNi2B2C to be a strong coupling hard type-II SC. HC2(T) exhibits an unconventional temperature dependence. Specific heat and magnetization studies reveal coexistence of SC and magnetism in RNi2B2C (R = Ho, Er, Tm) with magnetic ordering temperatures (Tc approximately 8 K, 10.5 K, 11 K and Tm approximately 5 K, approximately 7K, approximately 4 K respectively) that are remarkably higher than those in known magnetic superconductors . Mu-SR studies suggest the possibility of Ni atoms carrying a moment in TmNi2B2C. Resistivity results suggests a double re-entrant transition (SC-normal-SC) in HoNi2B2C. RENi2B2C (RE = Ce, Nd, Gd) do not show SC down to 4.2 K. The Nd- and Gd-compounds order magnetically at approximately 4.5 K and approximately 19.5 K, respectively. Two SC transitions are observed in Y-Pd-B-C (Tc approximately 22 K, approximately 10 K) and in Th-Pd-B-C (Tc approximately 20 K, approximately 14 K) systems, which indicate that there are at least two structures which support SC in these borocarbides. In our multiphase ThNi2B2C we observe SC at approximately 6 K. No SC was seen in multiphase UNi2B2C, UPd2B2C, UOs2Ge2C and UPd5B3C(0.35) down to 4.2 K. Tc in YNi2B2C is depressed by substitutions (Gd, Th and U at Y-sites and Fe, Co at Ni-sites).

Nagarajan, R.↗
NASA NTRS1989

Characterizations of electrical properties of highT(sub c) superconducting materials

The automated data acquisition system developed in the Space Science Laboratory at Marshall Space Flight Center for measuring electrical properties of high temperature superconductors is described. The acquisition system, consisting of a computer and computer-controlled hardware, allows large numbers of voltage, current, temperature, and magnetic measurements to be performed on bulk and thin film samples. Typical results are shown characterizing transition temperature (T sub c), critical current density (J sub c), and magnetic properties of bulk high T(sub c) materials as a function of temperature.

Sisk, R. C.↗
NASA NTRS1991

Chemical spray pyrolysis of Tl-Ba-Ca-Cu-O high-T(sub c) superconductors for high-field bitter magnets

The deposition of Tl-Ba-Ca-Cu-O thick films by spray pyrolyzing a Ba-Ca-Cu-O precursor film and diffusing thallium into the film to form the superconducting phase is examined. This approach was taken to reduce exposure to thallium and its health and safety hazards. The Tl-Ba-Ca-Cu-O system was selected because it has very attractive features which make it appealing to device and manufacturing engineering. Tl-Ba-Ca-Cu-O will accommodate a number of superconducting phases. This attribute makes it very forgiving to stoichiometric fluctuations in the bulk and film. It has excellent thermal and chemical stability, and appears to be relatively insensitive to chemical impurities. Oxygen is tightly bound into the systems, consequently there is no orthorhombic (conductor) to tetragonal (insulator) transition which would affect a component's lifetime. More significantly, the thallium based superconductors appear to have harder magnetic properties than the other high-Tc oxide ceramics. Estimates using magnetoresistance measurements indicate that at 77 K Tl2Ba2CaCu2O10 will have an upper critical field, H(sub c2) fo 26 Tesla for applied fields parallel to the c-axis and approximately 1000 Tesla for fields oriented in the a-b plane. Results to date have shown that superconducting films can be reproducibly deposited on 100 oriented MgO substrates. One film had a zero resistance temperature of 111.5 K. Furthermore, x ray diffraction analysis of the films showed preferential c-axis orientation parallel to the plane of the substrate. These results have now made it possible to consider the manufacture of a superconducting tape wire which can be configured into a topology useful for high-field magnet designs. The research which leads to the preparation of these films and plans for further development are reviewed.

Derochemont, L. Pierre↗
DOE OSTI2021

Electronic Origin of T c in Bulk and Monolayer FeSe

FeSe is classed as a Hund’s metal, with a multiplicity of d bands near the Fermi level. Correlations in Hund’s metals mostly originate from the exchange parameter J, which can drive a strong orbital selectivity in the correlations. The Fe-chalcogens are the most strongly correlated of the Fe-based superconductors, with d xy the most correlated orbital. Yet little is understood whether and how such correlations directly affect the superconducting instability in Hund’s systems. By applying a recently developed ab initio theory, we show explicitly the connections between correlations in d xy and the superconducting critical temperature T c . Starting from the ab initio results as a reference, we consider various kinds of excursions in parameter space around the reference to determine what controls T c . We show small excursions in J can cause colossal changes in T c . Additionally we consider changes in hopping by varying the Fe-Se bond length in bulk, in the free standing monolayer M-FeSe, and M-FeSe on a SrTiO 3 substrate (M-FeSe/STO). The twin conditions of proximity of the dxy state to the Fermi energy, and the strength of J emerge as the primary criteria for incoherent spectral response and enhanced single- and two-particle scattering that in turn controls T c . Using c-RPA, we show further that FeSe in monolayer form (M-FeSe) provides a natural mechanism to enhance J. We explain why M-FeSe/STO has a high T c , whereas M-FeSe in isolation should not. Our study opens a paradigm for a unified understanding what controls Tc in bulk, layers, and interfaces of Hund’s metals by hole pocket and electron screening cloud engineering.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Strongly-overdoped $\mathrm{La}$ 2- $_{x}$$\mathrm{Sr}$$_{x}$$\mathrm{CuO}$ 4 : Evidence for Josephson-coupled grains of strongly-correlated superconductor

The interpretation of how superconductivity disappears in cuprates at large hole doping has been controversial. To address this issue, here we present an experimental study of single-crystal and thin film samples of La 2-x Sr x CuO 4 (LSCO) with x ≥0.25. In particular, measurements of bulk susceptibility on LSCO crystals with x = 0.25 indicate an onset of diamagnetism at T c1 =38.5 K, with a sharp transition to a phase with full bulk shielding at T c2 =18 K, independent of field direction. Strikingly, the in-plane resistivity only goes to zero at T c2 . Inelastic neutron scattering on 0.25 crystals confirms the presence of low-energy incommensurate magnetic excitations with reduced strength compared to lower doping levels. The ratio of the spin gap to T c2 is anomalously large. Our results are consistent with a theoretical prediction for strongly overdoped cuprates by Spivak, Oreto, and Kivelson, in which superconductivity initially develops within disconnected self-organized grains characterized by a reduced hole concentration, with bulk superconductivity occurring only after superconductivity is induced by proximity effect in the surrounding medium of higher hole concentration. Beyond the superconducting-to-metal transition, local differential conductance measurements on an LSCO thin film suggest that regions with pairing correlations survive, but are too dilute to support superconducting order. Future experiments will be needed to test the degree to which these results apply to overdoped cuprates in general.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1991

Levitation of superconducting composites

The inverse levitation of a high temperature superconductor polymer composite consisting of powdered quench melt growth Ba2YCu3O(7-delta) and cyanoacrylate is reported. Magnetic hysteresis loop measurements for the composite are compared to those measured for the bulk material prior to powdering. Differences in the flux pining capability between the two material forms are small but significant.

Chiang, C. K.↗
DOE OSTI2024

Absence of a bulk signature of a charge density wave in hard x-ray measurements of UTe 2

The long-sought pair density wave (PDW) is an exotic phase of matter in which charge density wave (CDW) order is intertwined with the amplitude or phase of coexisting, superconducting order. Originally predicted to exist in copper-oxides, circumstantial evidence for PDW order now exists in a variety of materials. Recently, scanning tunneling microscopy (STM) studies have reported evidence for a three-component CDW at the surface of the heavy-fermion superconductor, UTe 2 , persisting below its superconducting transition temperature [Aishwarya et al., Nature 618, 928933 (2023); Gu et al., Nature 618, 921927 (2023); LaFleur et al., Nat. Commun. 15, 4456 (2024)]. Here, in this study, we use hard x-ray diffraction measurements on crystals of UTe 2 at 𝑇 = 1.9 and 12 K to search for a bulk signature of this CDW. Using STM measurements as a constraint, we calculate the expected locations of CDW superlattice peaks and sweep a large volume of reciprocal space in search of a signature. We fail to find any evidence for a CDW near any of the expected superlattice positions in many Brillouin zones. We estimate an upper bound on the CDW lattice distortion of 𝑢 max ≲ 4×10 −3 Å. Our results suggest that the CDW observed in STM is either purely electronic, somehow lacking a signature in the lattice, or is restricted to the material surface.

Kengle, Caitlin S.↗
DOE OSTI2022

Anomalous Shiba states in topological iron-based superconductors

We demonstrate the formation of robust zero energy modes close to magnetic impurities in the iron-based superconductor FeSe 1–x Te x . We find that the Zeeman field generated by the impurity favors a spin-triplet inter-orbital pairing as opposed to the spin-singlet intra-orbital pairing prevalent in the bulk. The preferred spin-triplet pairing preserves time-reversal symmetry and is topological, as robust, topologically-protected zero modes emerge at the boundary between regions with different pairing states. Moreover, the zero modes form Kramers doublets that are insensitive to the direction of the spin polarization or to the separation between impurities. Here, we argue that our theoretical results are consistent with recent experimental measurements on FeSe 1–x Te x .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1988

Gauged Q-balls

Classical non-topological soliton configurations are considered within the theory of a complex scalar field with a gauged U symmetry. Their existence and stability against dispersion are demonstrated and some of their properties are investigated analytically and numerically. The soliton configuration is such that inside the soliton the local U symmetry is broken, the gauge field becomes massive and for a range of values of the coupling constants the soliton becomes a superconductor pushing the charge to the surface. Furthermore, because of the repulsive Coulomb force, there is a maximum size for these objects, making impossible the existence of Q-matter in bulk form. Also briefly discussed are solitons with fermions in a U gauge theory.

Lee, Kimyeong↗
DOE OSTI2023

Antiferromagnetism and Superconductivity

This work under the rubrique of Antiferromagnetism and Superconductivity covers significant aspects of the most important and highest quality of superconductors in the class of quantum materials and the influence of magnetism on the superconducting state. These compounds include high temperature superconductors, pnictide iron-based superconductors, and topological superconductors. Special note is given that crystal growth of uranium based superconductors was performed with equipment created at Northwestern University for this purpose using novel ultra-high vacuum, electron-beam, float zone refining and crystal growth, producing the best quality of bulk single crystals of UPt3 in the literature with RRR=1546.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Oscillating paramagnetic Meissner effect and Berezinskii-Kosterlitz-Thouless transition in underdoped Bi2Sr2CaCu2O8+δ

ABSTRACT Superconducting phase transitions in two dimensions lie beyond the description of the Ginzburg-Landau symmetry-breaking paradigm for three-dimensional superconductors. They are Berezinskii-Kosterlitz-Thouless (BKT) transitions of paired-electron condensate driven by the unbinding of topological excitations, i.e. vortices. The recently discovered monolayers of layered high-transition-temperature (${{{T}}}_{{\rm C}}$) cuprate superconductor Bi2Sr2CaCu2O8+δ (Bi2212) meant that this 2D superconductor promised to be ideal for the study of unconventional superconductivity. But inhomogeneity posed challenges for distinguishing BKT physics from charge correlations in this material. Here, we utilize the phase sensitivity of scanning superconducting quantum interference device microscopy susceptometry to image the local magnetic response of underdoped Bi2212 from the monolayer to the bulk throughout its phase transition. The monolayer segregates into domains with independent phases at elevated temperatures below ${{{T}}}_{{\rm C}}$. Within a single domain, we find that the susceptibility oscillates with flux between diamagnetism and paramagnetism in a Fraunhofer-like pattern up to ${{{T}}}_{{\rm C}}$. The finite modulation period, as well as the broadening of the peaks when approaching ${{{T}}}_{{\rm C}}$ from below, suggests well-defined vortices that are increasingly screened by the dissociation of vortex-antivortex plasma through a BKT transition. In the multilayers, the susceptibility oscillation differs in a small temperature regime below ${{{T}}}_{{\rm C}}$, consistent with a dimensional crossover led by interlayer coupling. Serving as strong evidence for BKT transition in the bulk, we observe a sharp jump in phase stiffness and paramagnetism at small fields just below ${{{T}}}_{{\rm C}}$. These results unify the superconducting phase transitions from the monolayer to the bulk underdoped Bi2212, and can be collectively referred to as the BKT transition with interlayer coupling.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Signatures of a spin-active interface and a locally enhanced Zeeman field in a superconductor-chiral material heterostructure

A localized Zeeman field, intensified at heterostructure interfaces, could play a crucial role in a broad area including spintronics and unconventional superconductors. Conventionally, the generation of a local Zeeman field is achieved through magnetic exchange coupling with a magnetic material. However, magnetic elements often introduce defects, which could weaken or destroy superconductivity. Alternatively, the coupling between a superconductor with strong spin-orbit coupling and a nonmagnetic chiral material could serve as a promising approach to generate a spin-active interface. Here, we leverage an interface superconductor, namely, induced superconductivity in noble metal surface states, to probe the spin-active interface. Our results unveil an enhanced interface Zeeman field, which selectively closes the surface superconducting gap while preserving the bulk superconducting pairing. The chiral material, i.e., trigonal tellurium, also induces Andreev bound states (ABS) exhibiting spin polarization. The field dependence of ABS manifests a substantially enhanced interface Landég-factor (g eff ~ 12), thereby corroborating the enhanced interface Zeeman energy.

Science & Technology - Other Topics↗
DOE OSTI2024

Single-gap isotropic s- wave superconductivity in single crystals AuSn 4

In this article, London, λ L (T), and Campbell, λ C (T), penetration depths were measured in single crystals of a topological superconductor candidate AuSn 4 . At low temperatures, λ L (T) is exponentially attenuated and, if fitted with the power law, λ(T) ~ T n , gives exponents n > 4, indistinguishable from the isotropic single s- wave gap Bardeen-Cooper-Schrieffer (BCS) asymptotic. The superfluid density fits perfectly in the entire temperature range to the BCS theory. The superconducting transition temperature, T c = 2.40 ± 0.05 K, does not change after 2.5 MeV electron irradiation, indicating the validity of the Anderson theorem for isotropic s- wave superconductors. Campbell penetration depth before and after electron irradiation shows no hysteresis between the zero-field cooling (ZFC) and field cooling (FC) protocols, consistent with the parabolic pinning potential. Interestingly, the critical current density estimated from the original Campbell theory decreases after irradiation, implying that a more sophisticated theory involving collective effects is needed to describe vortex pinning in this system. In general, our thermodynamic measurements strongly suggest that the bulk response of the AuSn 4 crystals is fully consistent with the isotropic s- wave weak-coupling BCS superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2001

Formation of Y(x)Nd(1-x) Ba2Cu3O(7-delta) (0 = or < x < or = 0.7) Superconductors from an Undercooled Melt Via Aero-Acoustic Levitation

Melt processing of RE123 superconductors has gained importance in recent years. While the first high temperature superconductors (HTSCs) were made using traditional ceramic press and sinter technology, recent fabrication efforts have employed alternate processing techniques including laser ablation and ion beam assisted deposition for thin film fabrication of tapes and wires and melt growth for bulk materials. To optimize these techniques and identify other potential processing strategies, phase relation studies on HTSCs have been conducted on a wide variety of superconducting compounds using numerous processing strategies. This data has enhanced the understanding of these complex systems and allowed more accurate modeling of phase interactions. All of this research has proved useful in identifying processing capabilities for HTSCs but has failed to achieve a breakthrough for wide spread application of these materials. This study examines the role of full to partial substitution of Nd in the Y123 structure under rapid solidification conditions. Aero-acoustic levitation (AAL) was used to levitate and undercool RE123 in pure oxygen binary alloys with RE = Nd an Y along a range of compositions corresponding to Y(x)Nd(1-x) Ba2Cu3O(7-delta) (0 = or < x < or = 0.7) which were melted by a CO2 laser. Higher Y content spheres could not be melted in the AAL and were excluded from this report. Solidification structures were examined using scanning electron microscopy, electron dispersive spectroscopy, and powder x-ray diffraction to characterize microstructures and identify phases.

Gustafson, D. E.↗
DOE OSTI2021

Biasing topological charge injection in topological matter

Here we explore the interplay between topologies in the momentum and real spaces to formulate a thermodynamic description of nonequilibrium injection of topological charges under external bias. We show that the edge modes engendered by the momentum-space topology can play a functional role of connecting the external reservoirs to the bulk transport of topological charges in the real space. We illustrate our general results with two examples: the spin-torque injection of skyrmions in an electrically biased integer quantum Hall system, and the vortex injection in a topological $p + ip$ superconductor coupled to heat reservoirs. Based on the universal fractional entropy of the Majorana zero modes bound to the vortices, their controllable injection proposed in this work could provide a route for creating and manipulating Majorana fermions.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Frieze charge-stripes in a correlated kagome superconductor

In kagome metals, geometric frustration, electronic correlations and band topology combine to produce a wide range of intriguing phenomena. Among them, CsCr$_3$Sb$_5$ offers an opportunity to investigate unconventional superconductivity in a strongly correlated kagome system, with indications of frustrated magnetism and quantum criticality. Here, we demonstrate a cascade of density-wave transitions with distinct symmetries in bulk single crystals of CsCr$_3$Sb$_5$. Using spectroscopic imaging scanning tunneling microscopy, we uncover a unidirectional density wave that breaks all mirror symmetries -- resembling a chiral density wave -- but that also retains a mirror glide symmetry. We refer to this as a frieze charge stripe order phase, as its symmetry properties correspond to one of the fundamental frieze symmetry groups. A combination of high-resolution imaging, Fourier analysis and theoretical simulations reveal the key role of sublattice degrees of freedom in stabilizing this phase, characterized by internal chiral textures of opposite handedness. These findings suggest that superconductivity in CsCr$_3$Sb$_5$ emerges from this distinct density wave state and provide fresh insight into realizing electronic phases governed by frieze symmetry groups in quantum materials.

Cheng, Siyu [Boston College, Chestnut Hill, MA (Un↗
DOE OSTI2024

Vortex phase diagram of the kagome superconductor CsV 3 ⁢Sb 5

The screening response of the kagome superconductor CsV 3 ⁢Sb 5 was obtained from high-resolution ac mutual inductance measurements. At zero applied magnetic field and low temperatures, we observe no evidence for gapless quasiparticles, while near T c we find evidence for enhanced fluctuations. A rich vortex state appears above H c⁢1 ≈30 Oe, exhibiting successive emergence of vortex phases. For a fixed magnetic field, lowering the temperature below T c⁡ (H) leads to a wide range of vortex liquid state in a landscape of weak pinning potential, which gives rise to an irreversibility line. Further lowering the temperature, we identify the vortex melting line followed by the peak effect manifested in enhanced vortex pinning strength and critical current. Finally, we suggest that such an unusual behavior, where the peak effect region is fully contained within the vortex lattice state below the irreversibility line, is a consequence of the strong anisotropy and weak bulk pinning in CsV 3 ⁢Sb 5 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Nematic transitions in iron pnictide superconductors imaged with a quantum gas

The Scanning Quantum Cryogenic Atom Microscope (SQCRAMscope) uses an atomic Bose–Einstein condensate to measure magnetic fields emanating from solid-state samples. The quantum sensor does so with unprecedented d.c. sensitivity at micrometre resolution, from room to cryogenic temperatures. An additional advantage of the SQCRAMscope is the preservation of optical access to the sample so that magnetometry imaging of, for example, electron transport may be performed in concert with other imaging techniques. Here, we apply this multimodal imaging capability to the study of nematicity in iron pnictide high-temperature superconductors, where the relationship between electronic and structural symmetry breaking resulting in a nematic phase is under debate. We combine the SQCRAMscope with an in situ microscope that measures optical birefringence near the surface. This enables simultaneous and spatially resolved detection of both bulk and near-surface manifestations of nematicity via transport and structural deformation channels, respectively. By performing local measurements of emergent resistivity anisotropy in iron pnictides, we observe sharp, nearly concurrent transport and structural transitions. More broadly, these measurements demonstrate the SQCRAMscope’s ability to reveal important insights into the physics of complex quantum materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗