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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Topological Surface Superconductivity via Josephson Coupling in Bi 2 Te 3 /Nb

Since discoveries of protected conducting surface states, topological superconducting qubits have enchanted quantum science as prime elements in future fault-tolerant devices, particularly those based on Josephson junctions containing topological insulators. Still, Josephson coupling is often eclipsed by other proximity effects that can dilute topological superconducting pairing at the nontrivial insulator’s boundaries. Here, however, using an ultra-low-temperature scanning tunneling microscope, we detect Josephson physics in topological Bi 2 Te 3 films on superconducting Nb. At low temperatures, a previously undetected proximity gap varies little with Bi 2 Te 3 thickness and the density of states exhibits normal and superconducting components. Such observations are rationalized via Josephson pair tunneling through the (nearly) insulating Bi 2 Te 3 bulk, creating a rare, pure topological superconducting sheet. Our findings establish routes toward accessible topological superconducting states in qubits.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Tunable superconductivity coexisting with the anomalous Hall effect in a transition metal dichalcogenide

Transition metal dichalcogenides display a high technological potential due to their wide range of electronic ground states. Here, we unveil that by tuning hydrostatic pressure P, a cascade of electronic phase transitions can be induced in the few-layer transition metal dichalcogenide 1 T ’-WS 2 . As P increases, we observe the suppression of superconductivity with the concomitant emergence of an anomalous Hall effect (AHE) at P ≈ 1.15 GPa. Above 1.6 GPa, we uncover a reentrant superconducting state emerging from a state still exhibiting AHE. This superconducting state competes with the AHE state and shows a marked increase in superconducting anisotropy with respect to the ambient pressure phase, suggesting a distinct pairing symmetry. We demonstrate that 1 T ’-WS 2 concomitantly transitions into a strong topological phase with different band orbital characters and Fermi surfaces contributing to the superconductivity. These findings position 1T’-WS 2 as a tunable superconductor, wherein superconductivity, AHE, and band features can be tuned reversibly.

Superconducting properties and materials↗
DOE OSTI2024

Superconductivity in pressurized trilayer La 4 Ni 3 O 10-$δ$ single crystals

In this study, the pursuit of discovering new high-temperature superconductors that diverge from the copper-based model has profound implications for explaining mechanisms behind superconductivity and may also enable new applications. Here our investigation shows that the application of pressure effectively suppresses the spin–charge order in trilayer nickelate La 4 Ni 3 O 10-δ single crystals, leading to the emergence of superconductivity with a maximum critical temperature (T c ) of around 30 K at 69.0 GPa. The d.c. susceptibility measurements confirm a substantial diamagnetic response below T c , indicating the presence of bulk superconductivity with a volume fraction exceeding 80%. In the normal state, we observe a strange metal behaviour, characterized by a linear temperature-dependent resistance extending up to 300 K. Furthermore, the layer-dependent superconductivity observed hints at a unique interlayer coupling mechanism specific to nickelates, setting them apart from cuprates in this regard. Our findings provide crucial insights into the fundamental mechanisms underpinning superconductivity, while also introducing a new material platform to explore the intricate interplay between the spin–charge order, flat band structures, interlayer coupling, strange metal behaviour and high-temperature superconductivity.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Observation of cupratelike nonlinear terahertz responses in superconducting infinite-layer nickelates via two-dimensional coherent spectroscopy

The 𝑑-wave pairing symmetry in newly discovered infinite-layer nickelates remains highly debated compared to the widely accepted 𝑑-wave superconductivity in cuprates, despite recent intense efforts using equilibrium optical and electrical transport measurements. A complementary approach involves characterizing THz coherent nonlinear responses, which is currently lacking but needed, as it would offer new insights into the superconducting gap structure by characterizing Higgs modes and quasiparticle excitations. Here, in this study, we report THz 2D coherent spectroscopy (THz-2DCS) responses from the superconducting state in an infinite-layer nickelate. The 2D spectra clearly demonstrate the absence of hallmark signatures of 𝑠-wave pairing symmetry, such as resonant 2⁢Δ peaks at superconducting gaps. Instead, we observe gapless 2D spectra in the nickelate, centered around the THz driving frequency, with no noticeable shift as the temperature increases. These findings closely resemble the nodal superconductivity behavior expected in cuprates. Together with our simulations, these findings suggest that 2⁢Δ signatures in the 2D spectra of 𝑑-wave gap structures can be obscured by significant nodal quasiparticle excitations at arbitrarily low energies. This contrasts with the long-lived Higgs modes, observed as distinct 2⁢Δ peaks in a controlled THz-2DCS experiment on niobium, a representative example of dirty-limit s-wave superconductors. Our results have implications for understanding the unconventional superconductivity in nickelates and highlight the need to explore their coherent nonlinear dynamics.

Pairing mechanisms↗
DOE OSTI2025

Possible unconventional surface superconductivity in the half-Heusler compound YPtBi

Here, we report an extensive study of the noncentrosymmetric half-Heusler superconductor YPtBi, revealing an unusual relation between bulk superconductivity and the possible appearance of surface superconductivity on the (111) oriented surface, at temperatures up to three times the bulk transition temperature. Transport measurements confirmed the low carrier density of the material and its bulk superconducting transition, which was also observed in ac susceptibility through mutual inductance (MI) measurements. However, a weak signature of superconductivity in the MI measurements appeared much above the bulk transition temperature, which was further observed in scanning tunneling spectroscopy, pointing to a possible surface superconducting state. Polar Kerr effect measurements suggest that while the bulk superconductor may exhibit an unusual nodal superconducting state, only the surface state breaks time reversal symmetry. Complementary tunneling measurements on LuPtBi are used to establish the observations on YPtBi, while density-functional theory calculations may shed light on the origin of this unusual surface state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Cryogenic growth of aluminum: Structural morphology, optical properties, superconductivity, and microwave dielectric loss

We explore the molecular beam epitaxy synthesis of superconducting aluminum thin films grown on c-plane sapphire substrates at cryogenic temperatures of 6 K and compare their behavior with films synthesized at room temperature. We demonstrate that cryogenic growth increases structural disorder, producing crystalline grains that modify the optical, electrical, and superconducting properties of aluminum. We observe that cryogenic deposition changes the color of aluminum from fully reflective to yellow and correlate the pseudodielectric function and reflectance with structural changes in the film. We find that smaller grain sizes enhance the superconductivity of aluminum, increasing its critical temperature and critical field. We then estimate the superconducting gap and coherence length of Cooper pairs in aluminum in the presence of disorder. In conclusion, we fabricate superconducting microwave resonators on these films and find that, independently of the growth temperature, the system is dominated by two-level system loss with similar quality factors in the high- and low-power regimes. We further measure a higher kinetic inductance in the cryogenically grown films.

36 MATERIALS SCIENCE↗
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 OSTI2025

Sketched Nanoscale KTaO 3 -Based Superconducting Quantum Interference Device

The discovery of two-dimensional superconductivity in LaAlO 3 /KTaO 3 (111) and (110) interfaces has raised significant interest in this system. In this paper, we report the first successful fabrication of a direct current superconducting quantum interference device (dc-SQUID) in the KTO system. The key device elements, superconducting weak links, are created by conductive atomic force microscope lithography, which can reversibly control the conductivity at the LAO/KTO (110) interface with nanoscale resolution. The periodic modulation of the SQUID critical current 𝐼 c ⁡(𝐵) with magnetic field corresponds well with our theoretical modeling, which reveals a large kinetic inductance of the superconducting two-dimensional electron gas in KTO. The kinetic inductance of the SQUID is tunable by electrical gating from the back, due to the large dielectric constant of KTO. The demonstration of weak links and SQUIDs in KTO broadens the scope for exploring the underlying physics of KTO superconductivity, including the role of spin-orbit coupling, pairing symmetry, and inhomogeneity. It also promotes KTO as a versatile platform for a growing family of quantum devices, which could be applicable in the realm of quantum computing and information.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Hund's coupling governed orbital-selective superconductivity in Ba 1−𝑥 ⁢K 𝑥⁢ Fe 2 ⁢As 2

Understanding how strong electronic correlations shape superconductivity remains a central challenge in quantum materials. In multiorbital systems, correlations driven by Hund's coupling can differentiate the behavior of individual orbitals, producing the so-called Hund's metal state. How such orbital-selectivity also governs superconducting pairing, however, has remained largely unexplored experimentally. Here, in this study, we use high-resolution angle-resolved photoemission spectroscopy to systematically map the superconducting gap structure across the phase diagram of the representative iron-based superconductor Ba 1−x K x Fe 2 As 2 . We find that superconductivity evolves in a strongly orbital-dependent manner: the gap associated with the d xy orbital collapses beyond optimal doping while pairing on the d xz /d yz orbitals persists. This behavior mirrors the orbital-selective correlations observed in the normal state and reveals a direct connection between Hund's metal physics and the superconducting pairing landscape. Our results demonstrate that superconducting gaps themselves can serve as a sensitive probe of orbital-dependent correlations and suggest that Hund's coupling plays a central role in shaping pairing in multiorbital superconductors.

Corbae, Elena [SLAC National Accelerator Laborator↗
DOE OSTI2026

Superconducting phase diagram of multilayer square-planar nickelates

The discovery of superconductivity in square-planar nickelates has offered a rich materials platform to explore the origins of high-temperature superconductivity. However, experimental investigations have largely been limited to the infinite-layer R NiO 2 ( R , rare earth) nickelates. For this work we constructed a phase diagram of multilayer square-planar Nd n+1 Ni n O 2n+2 compounds and found signatures of superconductivity for dimensionality n = 4 to 8. Upon decreasing n , the superconducting anisotropy evolves owing to 4ƒ electron effects, and electronic structure characteristics approach cuprate-like behavior. Magnetic fluctuations persist from within the superconducting regime and into the overdoped, nonsuperconducting regime. The superconducting regime overlaps with that of chemically doped infinite-layer nickelates, demonstrating underlying commonalities as well as differences across varying structural realizations of square-planar nickelates. Our work establishes this layered template for creating new nickel-based superconductors.

36 MATERIALS SCIENCE↗
DOE OSTI2024

ARPES detection of superconducting gap sign in unconventional superconductors

The superconducting gap symmetry is crucial in understanding the underlying superconductivity mechanism. Angle-resolved photoemission spectroscopy (ARPES) has played a key role in determining the gap symmetry in unconventional superconductors. However, it has been considered so far that ARPES can only measure the magnitude of the superconducting gap but not its phase; the phase has to be detected by other phase-sensitive techniques. Here we propose a method to directly detect the superconducting gap sign by ARPES. This method is successfully validated in a cuprate superconductor Bi 2 Sr 2 CaCu 2 O 8+δ with a well-known d-wave gap symmetry. When two bands have a strong interband interaction, the resulted electronic structures in the superconducting state are sensitive to the relative gap sign between the two bands. Our present work provides an approach to detect the gap sign and can be applied to various superconductors, particularly those with multiple orbitals like the iron-based superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

The superconducting diode effect in Josephson junctions fabricated from a structurally chiral superconductor

The superconducting diode effect occurs in superconducting materials in which both time-reversal and inversion symmetry are broken. The recently observed chirality-induced spin selectivity effect demonstrates that chiral materials break both symmetries. Thus, a Josephson junction interface with the left-handed structure on one side of the junction and the right-handed structure on the other should exhibit a diode effect. Here, we report the electrical transport properties of right-handed/left-handed and right-handed/right-handed devices fabricated from single crystals of the structurally chiral superconductor Mo 3 Al 2 C. Fraunhofer-like magnetic diffraction patterns confirm the presence of the Josephson effect in all but one of our devices. A magnetic-field-induced superconducting diode effect is demonstrated in the right-handed/left-handed devices by a statistically significant difference in I c + and ∣ I c −∣, with a maximum asymmetry of 5%. The intrinsic superconducting diode effect is not observed in the right-handed/right-handed devices. We provide an explanation for the presence of the superconducting diode effect in the right-handed/left-handed devices.

superconducting devices↗
DOE OSTI2026

Conventional superconductivity in single-crystalline BiPt

Binary Bi-Pd/Pt systems have attracted a lot of interest because of their topologically nontrivial nature along with superconductivity. We report the structural and superconducting properties of high-quality single-crystalline BiPt using a comprehensive range of experimental techniques, including X-ray diffraction, electron microscopy, muon spin rotation/relaxation (𝜇⁢SR), magnetization, resistivity, and heat capacity. Our findings establish that BiPt is a weak type-II superconductor with a transition temperature (𝑇 𝑐 ) of 1.2 K which exhibits pronounced anisotropic superconducting characteristics attributed to its hexagonal crystal structure. Magnetization and electronic transport studies reveal that BiPt lies within the dirty limit, while 𝜇⁢SR and heat capacity data indicate conventional 𝑠-wave superconductivity that maintains time-reversal symmetry. Here, this work provides valuable insights into the pairing symmetry and superconducting mechanism of topologically trivial BiPt, a sound comparison system for other Bi-based topologically nontrivial superconductors.

Demagnetization↗
DOE OSTI2024

Tunneling Spectroscopy at Megabar Pressures: Determination of the Superconducting Gap in Sulfur

The recent discovery of high-temperature, high-pressure superconductors, such as hydrides and nickelates, has opened exciting avenues in studying high-temperature superconductivity. The primary superconducting properties of these materials are well characterized by measuring various electrical and magnetic properties, despite the challenges posed by the high-pressure environment. Experimental microscopic insight into the pairing mechanism of these superconductors is even more challenging, due to the lack of direct probes of the superconducting gap structures at high pressure conditions. Here, we have developed a planar tunnel junction technique for diamond anvil cells and present ground-breaking tunneling spectroscopy measurements at megabar pressures. We determined the superconducting gap of elemental sulfur at 160 GPa, a key constituent of the high-temperature superconductor H 3 S . High quality tunneling spectra indicate that β -Po phase sulfur is a type II superconductor with a single s -wave gap with a gap value 2 Δ ( 0 ) = 5.6 meV . This technique is compatible with superconducting compounds synthesized in diamond anvil cells and provides insight into the pairing mechanism in novel superconductors under high-pressure conditions. Published by the American Physical Society 2024

36 MATERIALS SCIENCE↗
DOE OSTI2025

Robust Nodal Behavior in the Thermal Conductivity of Superconducting UTe 2

The superconducting state of the heavy-fermion metal UTe 2 has attracted considerable interest because of evidence of spin-triplet Cooper pairing and nontrivial topology. Progress on these questions requires identifying the presence or absence of nodes in the superconducting gap function and their dimension. In this article, we report a comprehensive study of the influence of disorder on the thermal transport in the superconducting state of UTe 2 . Through detailed measurements of the magnetic-field dependence of the thermal conductivity in the zero-temperature limit, we obtain clear evidence of the presence of point nodes in the superconducting gap for all samples with transition temperatures ranging from 1.6 to 2.1 K obtained by different synthesis methods, including a refined self-flux method. This robustness implies the presence of symmetry-imposed nodes throughout the range studied, further confirmed via disorder-dependent calculations of the thermal transport in a model with a single pair of nodes. In addition to capturing the temperature dependence of the thermal conductivity up to 𝑇 𝑐 , this model provides some information about the locations of the nodes, suggesting a 𝐵 1⁢𝑢 or 𝐵 2⁢𝑢 symmetry for the superconducting order parameter. Additionally, comparing the new, ultrahigh conductivity samples to older samples reveals a crossover between a low-field and a high-field regime at a single value of the magnetic field in all samples. In the high-field regime, the thermal conductivity at different disorder levels differs from each other by a simple offset, suggesting that some simple principle determines the physics of the mixed state, a fact which may illuminate trends observed in other clean nodal superconductors.

spin-triplet pairing↗
DOE OSTI2025

Probing Non-Equilibrium Pair-Breaking and Quasiparticle Dynamics in Nb Superconducting Resonators Under Magnetic Fields

We conducted a comprehensive study of the non-equilibrium dynamics of Cooper pair breaking, quasiparticle (QP) generation, and relaxation in niobium (Nb) cut from superconducting radio-frequency (SRF) cavities, as well as various Nb resonator films from transmon qubits. Using ultrafast pump–probe spectroscopy, we were able to isolate the superconducting coherence and pair-breaking responses. Our results reveal both similarities and notable differences in the temperature- and magnetic-field-dependent dynamics of the SRF cavity and thin-film resonator samples. Moreover, femtosecond-resolved QP generation and relaxation under an applied magnetic field reveals a clear correlation between non-equilibrium QPs and the quality factor of resonators fabricated by using different deposition methods, such as DC sputtering and high-power impulse magnetron sputtering. These findings highlight the pivotal influence of fabrication techniques on the coherence and performance of Nb-based quantum devices, which are vital for applications in superconducting qubits and high-energy superconducting radio-frequency applications.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Structural Phase Separation and Enhanced Superconductivity in La 1.875 Ba 0.125 CuO 4 Under Uniaxial Strain

Strain engineering has attracted significant attention in recent years due to its capability in tuning lattice and electronic structures of quantum materials. Using moderate uniaxial compressive strain, structural phase separation is induced in the low-temperature phase of x = 1/8 La 2-x Ba x CuO 4 (LBCO) single crystals. These structures are low temperature tetragonal (LTT), low temperature less orthorhombic (LTLO), and a plastically deformed nano-domain structure (PDNS), comprised of few-nanometer-sized orthorhombic domains within an amorphous matrix. These three structures exhibit distinct superconducting behaviors. The volume fraction of the LTT structure is suppressed with increasing strain, while its superconducting transition temperature increases and broadens. The LTLO structure exhibits a sharp superconducting transition above 32 K, which increases up to ≈ 36 K at maximum strain. The PDNS phase exhibits a very broad superconducting transition and persists even after removing the strain. This study illustrates the sensitivity of superconductivity to the structure of the LBCO sample near its stripe instability.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

In Situ Local Imaging of Ferromagnetism and Superconductivity in RbEuFe 4 As 4

The coexistence of superconductivity and ferromagnetism is an intrinsically interesting research focus in condensed matter physics but the study is limited by low superconducting (T c ) and magnetic (T m ) transition temperatures in related materials. Here, we used a scanning superconducting quantum interference device to image the in-situ diamagnetic and ferromagnetic responses of RbEuFe 4 As 4 with high T c and T m . We observed significant suppression of superfluid density in vicinity of the magnetic phase transition, signifying fluctuation-enhanced magnetic scatterings between Eu spins and Fe 3d conduction electrons. Intriguingly, we observed multiple ferromagnetic domains which should be absent in an ideal magnetic helical phase. The formation of these domains demonstrates a weak c-axis ferromagnetic component probably arising from Eu spin-canting effect, indicative of possible superconductivity-driven domain Meissner and domain vortex-antivortex phases as revealed in EuFe 2 (As 0.79 P 0.21 ) 2 . Finally, our observations highlight RbEuFe 4 As 4 is a unique system which includes multiple interplay channels between superconductivity and ferromagnetism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗