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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Conductor on molded barrel magnet assembly and associated systems and methods

A Conductor on Molded Barrel (COMB) magnet assembly optimized for High Temperature Superconducting (HTS) materials. The magnet assembly comprises a magnetic coil(s) carried by a conductor support structure and configured in cosine-theta geometry. Created using additive manufacturing, the conductor support structure features a continuous cable channel that fittedly carries and positions elongated straight portion(s) of the magnetic coil(s) parallel to a magnetic axis. The conductor support structure may be cylindrically shaped and longitudinally bored, with the continuous cable channel comprising an outer channel portion (distal on the cylinder) and an inner channel portion (proximal on the cylinder). A transition hole that joins the outer channel portion and the inner channel portion allows a single magnetic coil to be wound along both the outer and inner surfaces of the conductor support structure. The conductor support structure may be fabricated as longitudinally-symmetrical halves, and secured for operation using azimuthal and/or midplane shims.

Kashikhin, Vadim V.↗
DOE OSTI2021

Spectroscopic study of the coupling effect between the two gaps of magnesium diboride on its RF properties

This program studied the two-gap nature of magnesium diboride and its possible effects on the superconducting rf properties of this material. Magnesium diboride (MgB 2 ) is a BCS superconductor with a superconducting critical temperature of 39 K, high critical current density and no weak link behavior across the grain boundary. These properties make this material ideal for both power applications and electronic devices. In particular, the high superconducting critical temperature and high thermodynamic field suggests that MgB 2 could be an ideal material also for superconducting radio frequency (SRF) cavities operating at a much higher temperature than Nb cavities and, therefore, reducing noticeably the cryogenics costs. However, MgB 2 is a two gap superconductor and it has been suggested that the RF properties are dominated by the smaller gap, which would make this material not competitive with Nb and especially Nb 3 Sn. The main problem does not seem to be the double-gap nature of this material but rather the weak-coupling of the two gaps that in the presence of an RF field suppresses superconductivity all together at fields much lower than the thermodynamic field. The main goal of this proposal is to address the fundamental question of the coupling between the two gaps in MgB 2 and understand if it is possible to control it and ultimately improve the RF performance of MgB 2 . The project studied these questions by measuring the density of states in the presence of an in-plane current and focused on the effect of controlled disorder. Disorder, indeed, provides an important knob to tune the properties of MgB2 and provides the possibility of changing the coupling between the two bands, making this material a competitive material for SRF applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Ubiquitous coexisting electron-mode couplings in high-temperature cuprate superconductors

In conventional superconductors, electron-phonon coupling plays a dominant role in generating superconductivity. In high-temperature cuprate superconductors, the existence of electron coupling with phonons and other boson modes and its role in producing high-temperature superconductivity remain unclear. The evidence of electron-boson coupling mainly comes from angle-resolved photoemission (ARPES) observations of ~70-meV nodal dispersion kink and ~40-meV antinodal kink. However, the reported results are sporadic and the nature of the involved bosons is still under debate. Here we report findings of ubiquitous two coexisting electron-mode couplings in cuprate superconductors. By taking ultrahigh-resolution laser-based ARPES measurements, we found that the electrons are coupled simultaneously with two sharp modes at ~70meV and ~40meV in different superconductors with different dopings, over the entire momentum space and at different temperatures above and below the superconducting transition temperature. These observations favor phonons as the origin of the modes coupled with electrons and the observed electron-mode couplings are unusual because the associated energy scales do not exhibit an obvious energy shift across the superconducting transition. We further find that the well-known “peak-dip-hump” structure, which has long been considered a hallmark of superconductivity, is also omnipresent and consists of “peak-double dip-double hump” finer structures that originate from electron coupling with two sharp modes. These results provide a unified picture for the ~70-meV and ~40-meV energy scales and their evolutions with momentum, doping and temperature. In conclusion, they provide key information to understand the origin of these energy scales and their role in generating anomalous normal state and high-temperature superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Enhanced charge density wave coherence in a light-quenched, high-temperature superconductor

Superconductivity and charge density waves (CDWs) are competitive, yet coexisting, orders in cuprate superconductors. To understand their microscopic interdependence, a probe capable of discerning their interaction on its natural length and time scale is necessary. We use ultrafast resonant soft x-ray scattering to track the transient evolution of CDW correlations in YBa 2 Cu 3 O 6+x after the quench of superconductivity by an infrared laser pulse. We observe a nonthermal response of the CDW order characterized by a near doubling of the correlation length within ≈1 picosecond of the superconducting quench. Our results are consistent with a model in which the interaction between superconductivity and CDWs manifests inhomogeneously through disruption of spatial coherence, with superconductivity playing the dominant role in stabilizing CDW topological defects, such as discommensurations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Ambient-pressure 151-K superconductivity in HgBa 2 Ca 2 Cu 3 O 8+δ via pressure quench

Superconductivity has been a vigorously researched topic since its discovery in 1911. Raising the superconducting transition temperature (T c ) has been the main driving force behind such long-sustained efforts due to its potential for impacting humanity and the fundamental knowledge gained from understanding this macroscopic coherent quantum state at high temperatures. The successful development of high-T c superconductivity will make possible extraordinarily efficient generation, delivery, and utilization of energy and could also enable the development of controlled fusion while impacting other burgeoning fields like quantum computation and quantum electronics. However, progress has been hindered by a longstanding plateau in the record ambient-pressure T c , unchanged since 1993. Subsequent significant advancements in T c have been achieved only under high pressures, preventing the realization of superconductivity’s full potential. To directly address this challenge, we developed a pressure-quench protocol (PQP) to stabilize pressure-induced/-enhanced superconducting states at ambient pressure. Here, we achieve a record ambient-pressure T c of 151 K in the cuprate HgBa 2 Ca 2 Cu 3 O 8+δ via PQP. The experimental results are further supported by synchrotron X-ray diffraction measurements and phonon and electronic structure calculations. This breakthrough opens avenues for stabilizing and exploring ambient-pressure high-T c superconducting states and other quantum states that have been previously only accessible under pressure, paving the way for deeper understanding and practical applications of high-T c superconductivity and beyond.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Magnetic flux trapping in hydrogen-rich high-temperature superconductors

Recent discoveries of superconductivity in various hydrides at high pressures have shown that a critical temperature of superconductivity can reach near-room-temperature values. However, experimental studies are limited by high-pressure conditions, and electrical transport measurements have been the primary technique for detecting superconductivity in hydrides. Here we implement a non-conventional protocol for the magnetic measurements of superconductors in a SQUID magnetometer and probe the trapped magnetic flux in two near-room-temperature superconductors H 3 S and LaH 10 at high pressures. Contrary to traditional magnetic susceptibility measurements, the magnetic response from the trapped flux is almost unaffected by the background signal of the diamond anvil cell due to the absence of external magnetic fields. The behaviour of the trapped flux generated under zero-field-cooled and field-cooled conditions proves the existence of superconductivity in these materials. We reveal that the absence of a pronounced Meissner effect is associated with the very strong pinning of vortices inside the samples. This approach can also be a tool for studying multiphase samples or samples that have a low superconducting fraction at ambient pressure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

On the Analysis of the Tin-Inside-H 3 S Mössbauer Experiment

Here, a simple analysis is presented of the particular experiment used to prove the bulk nature of very-high-Tc superconductivity in H 3 S compound under ultra-high pressure. In the experiment, an internal magnetic field was sensed by the synchrotron Mössbauer spectroscopy in tin placed inside the H 3 S sample. The experiment showed peculiar anisotropy with respect to the direction of the applied field at first sight. By considering actual experimental geometries and parameters of the experiment, we show that this particular observation is consistent with the expectations for a regular type-II superconductor with Meissner expulsion and pinning.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

High-temperature phonon-mediated superconductivity in monolayer Mg 2 B 4 C 2

A two-dimensional material – Mg 2 B 4 C 2 , belonging to the family of the conventional superconductor MgB 2 , is theoretically predicted to exhibit superconductivity with critical temperature T c estimated in the 47–48 K range (predicted using the McMillian-Allen-Dynes formula) without any tuning of external parameters such as doping, strain, or substrate-induced effects. The origin of such a high intrinsic T c is ascribed to the presence of strong electron-phonon coupling and large density of states at the Fermi level. This system is obtained after replacing the chemically active boron-boron surface layers in a MgB 2 slab by chemically inactive boron-carbon layers. Hence, the surfaces of this material are inert. Our calculations confirm the stability of 2D Mg 2 B 4 C 2 . We also find that the key features of this material remain essentially unchanged when its thickness is increased by modestly increasing the number of inner MgB 2 layers.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Anisotropy and isotope effect in superconducting solid hydrogen

Elucidating the phase diagram of solid hydrogen is a key objective in condensed matter physics. Several decades ago, it was proposed that at low temperatures and high pressures, solid hydrogen would be a metal with a high superconducting transition temperature. This transition to a metallic state can happen through the closing of the energy gap in the molecular solid or through a transition to an atomic solid. Recent experiments have managed to reach pressures in the range of 400–500 GPa, providing valuable insights. There is strong evidence suggesting that metallization via either of these mechanisms occurs within this pressure range. Computational and experimental studies have identified multiple promising crystal phases, but the limited accuracy of calculations and the limited capabilities of experiments prevent us from determining unequivocally the observed phase or phases. Therefore, it is crucial to investigate the superconducting properties of all the candidate phases. Recently, we reported the superconducting properties of the C2/c-24, Cmca-12, Cmca-4 and I41/amd-2 phases, including anharmonic effects. Here, we report the effects of anisotropy on superconducting properties using Eliashberg theory. Then, we investigate the superconducting properties of deuterium and estimate the size of the isotope effect for each phase. We find that the isotope effect on superconductivity is diminished by anharmonicity in the C2/c-24 and Cmca-12 phases and enlarged in the Cmca-4 and I41/amd-2 phases. Our anharmonic calculations of the C2/c-24 phase of deuterium agree closely with the most recent experiment by Loubeyre et al (2022 Phys. Rev. Lett.29 035501), indicating that the C2/c-24 phase remains the leading candidate in this pressure range, and has a strong anharmonic character. These characteristics can serve to distinguish among crystal phases in experiment. Furthermore, expanding our understanding of superconductivity in pure hydrogen holds significance in the study of high-T c hydrides.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Suppression of superconductivity by anisotropic strain near a nematic quantum critical point

In most unconventional and high-temperature superconductors, superconductivity emerges as a nearby symmetry-breaking phase is suppressed by chemical doping or pressure. This has led to the belief that the fluctuations associated with the symmetry-breaking phase are beneficial, if not responsible, for the superconducting pairing. A direct test to verify this hypothesis is to observe a decrease of the superconducting critical temperature (T c ) by applying the symmetry-breaking conjugate field that suppresses the dynamic fluctuations of the competing order. However, most of the competing phases in unconventional superconductors break translational symmetry, requiring a spatially modulated conjugate field that is difficult to realize experimentally. Here, we show that anisotropic strain, the conjugate field of nematicity, reduces the T c of an iron pnictide. For optimally doped samples we show a fivefold reduction of T c with less than one per cent of strain. For underdoped samples, T c becomes zero yielding a fully metallic ground state. In addition to providing direct evidence of the role played by the nematic fluctuations in the formation of the superconducting state, these results demonstrate tunable mechanical control of a high-temperature superconductor, an important step forward for technological applications of superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

High magnetic field response of superconductivity dome in quantum artificial high−⁢𝑇 𝐶 superlattices with variable geometry

It is known that cuprate artificial high-𝑇 𝐶 superlattices (AHTS) with period 𝑑, composed of quantum wells confining interface space charge in stoichiometric Mott insulator layers (𝑆), with thickness 𝐿, at the interface with overdoped normal metallic cuprate layers (𝑁) show a superconducting dome by tuning the geometric 𝐿 over 𝑑 ratio of the SNSN superlattice with the top predicted by quantum material design engineering quantum size effects. Here we report high-field magnetotransport measurements up to 41 Tesla of AHTS across the entire superconducting dome. The results show the universal upward-concave behavior of the temperature-dependent upper critical magnetic field in low-𝑇 𝐶 samples at the rising edge and drop edge of the dome, providing strong evidence consistent with two-band superconductivity in agreement with multigap theory used for quantum design of the SNSN superlattices. The measured superconducting coherence length demonstrates that atomic-scale engineering controls not only the critical temperature but also the intrinsic pair size at Fano-Feshbach resonances physics paving the way toward next-generation quantum devices and shedding light on unconventional superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Dual-phase superconductivity in high-pressure high-temperature synthesized TaNbZrHfTi

We report on a novel TaNbZrHfTi-based high entropy alloy (HEA) which demonstrates distinctive dual-phase superconductivity. The HEA was synthesized under high pressures and high temperatures starting from a ball milled mixture of elemental metals in a large-volume Paris–Edinburgh cell with P ≈ 6 GPa and T = 2300 K. The synthesized HEA is a phase mixture of BCC (NbTa)0.45(ZrHfTi)0.55 with Tc1 = 6 K and FCC (NbTa)0.04(ZrHfTi)0.96 with Tc2 = 3.75 K. The measured magnetic field parameters for the HEA are lower critical field, Hc1(0) = 31 mT, and a relatively high upper critical field, Hc2(0) = 4.92 T. This dual-phase system is further characterized by the presence of a second magnetization peak, or the fishtail effect, observed in the virgin magnetization curves. This phenomenon, which does not distort the field-dependent magnetization hysteresis loops, suggests intricate pinning mechanisms that could be potentially tuned for optimized performance. The manifestation of these unique features in HEA superconductivity reinforces phase-dependent superconductivity and opens new avenues in the exploration of novel superconducting materials.

Materials Science↗
DOE OSTI2022

Topological d -wave superconductivity in two dimensions

Despite intensive searches for topological superconductors, the realization of topological superconductivity remains under debate. Previous proposals for the topological s-wave, p-wave, and chiral d-wave superconductivity have both advantages and disadvantages. In this review, we discuss two-dimensional topological superconductivity based on the non-chiral d-wave superconductors. It is shown that the noncentrosymmetric d-wave superconductors become topological superconductors under an infinitesimal Zeeman field without fine-tuning of parameters. Additionally, Floquet engineering for introducing the Zeeman field in a controllable way is also proposed. When the two-dimensional noncentrosymmetric superconductors are stacked to recover the global inversion symmetry, the field-induced parity transition may occur, and the high-field odd-parity superconducting state realizes various topological phases depending on the stacking structures. Two-dimensional heterostructures of strongly correlated electron systems, which have been developed by recent experiments, are proposed as a platform of the high-temperature topological superconductivity and the interplay of topology and strong correlations in superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Low-Pressure Electrochemical Synthesis of Complex High-Pressure Superconducting Superhydrides

There is great current interest in multicomponent superhydrides due to their unique quantum properties under pressure. A remarkable example is the ternary superhydride Li 2 MgH 16 computationally identified to have an unprecedented high superconducting critical temperature T c of ~470 K at 250 GPa. However, the very high synthesis pressures required remains a significant hurdle for detailed study and potential applications. In this Letter, we evaluate the feasibility of synthesizing ternary Li-Mg superhydrides by the recently proposed pressure-potential (P 2 ) method that uniquely combines electrochemistry and applied pressure to control synthesis and stability. Furthermore, the results indicate that it is possible to synthesize Li-Mg superhydrides at modest pressures by applying suitable electrode potentials. Using pressure alone, no Li-Mg ternary hydrides are predicted to be thermodynamically stable, but in the presence of electrode potentials, both Li 2 MgH 16 and Li 4 MgH 24 can be stabilized at modest pressures. Three polymorphs are predicted as ground states of Li 2 MgH 16 below 300 GPa, with transitions at 33 and 160 GPa. The highest pressure phase is superconducting, while the two at lower pressures are not. Our findings point out the potentially important role of the P 2 method in controlling phase stability of complex multicomponent superhydrides.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Hot Hydride Superconductivity Above 550 K

The search for room temperature superconductivity has accelerated in the last few years driven by experimentally accessible theoretical predictions that indicated alloying dense hydrogen with other elements could produce conventional superconductivity at high temperatures and pressures. These predictions helped inform the synthesis of simple binary hydrides that culminated in the discovery of the superhydride LaH 10 with a superconducting transition temperature T c of 260 K at 180 GPa. We have now successfully synthesized a metallic La-based superhydride with an initial T c of 294 K. When subjected to subsequent thermal excursions that promoted a chemical reaction to a higher order system, the Tc onset was driven irreversibly to 556 K. X-ray characterization confirmed the formation of a distorted LaH 10 based backbone that suggests the formation of ternary or quaternary compounds with substitution at the La and/or H sites. The results provide evidence for hot superconductivity, aligning with recent predictions for higher order hydrides under pressure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Synthesis and structure of carbon-doped H 3 S compounds at high pressure

Understanding of recently reported putative close-to-room-temperature superconductivity in C-S-H compounds at 267 GPa demands a reproducible synthesis protocol as well as knowledge of the compounds' structure and composition. Here, we synthesized C-S-H compounds with various carbon compositions at high pressures from elemental carbon C and methane CH 4 , sulfur S, and molecular hydrogen H 2 . Here, we focus on compounds synthesized using methane as these allow a straightforward determination of their structure and composition by combining single-crystal x-ray diffraction and Raman spectroscopy. We applied a two-stage synthesis of [(CH 4 ) x (H 2 S) (1-x) ] 2 H 2 compounds with various compositions by first reacting sulfur and mixed methane-hydrogen fluids and forming CH 4 -doped H 2 S crystals at 0.5-3 GPa and then by growing single crystals of the desired hydrogen-rich compound. Raman spectroscopy applied to this material shows the presence of CH 4 molecules incorporated into the lattice and allows the determination of the CH 4 content, while single-crystal x-ray diffraction results suggest that the methane molecules substitute H 2 S molecules. The structural behavior of these compounds is very similar to the previously investigated methane-free crystals demonstrating a transition from Al 2 Cu type I4/mcm molecular crystal to a modulated molecular structure at 20-30 GPa and back to the same basic I4/mcm structure in an extended modification with greatly modified Raman spectra. This latter phase demonstrates a distortion into a Pnma structure at 132-159 GPa and then transforms into a common Im$\bar{3}$m H 3 S phase at higher pressures; however, no structural anomaly is detected near 220 GPa, where a sharp upturn in T c has been reported.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Anisotropic superconductivity in the spin-vortex antiferromagnetic superconductor CaK(Fe 0.95 Ni 0.05 ) 4 As 4

High critical temperature superconductivity often occurs in systems where an antiferromagnetic order is brought near T = 0 K by slightly modifying pressure or doping. CaKFe 4 As 4 is a superconducting, stoichiometric iron-pnictide compound showing optimal superconducting critical temperature with T c as large as 35 K. Doping with Ni induces a decrease in T c and the onset of spin-vortex crystal (SVC) antiferromagnetic order, which consists of spins pointing inwards to or outwards from alternating As sites on the diagonals of the in-plane square Fe lattice. In this work we study the band structure of CaK(Fe 0.95 Ni 0.05 ) 4 As 4 (T c = 10 K, T SVC = 50 K) using quasiparticle interference with a scanning tunneling microscope and show how the SVC modifies the band structure and induces a fourfold superconducting gap anisotropy.

36 MATERIALS SCIENCE↗