Search NASA⌕ Search

SEARCH · Search NASA

Results for “London penetration depth”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

54 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Superconductivity and phase diagrams of CaK(Fe 1- x Mn x ) 4 As 4 single crystals

In order to study the effects of Mn substitution on the superconducting and magnetic ground state of CaKFe 4 As 4 (T c = 35 K), members of the CaK (Fe 1–x Mn x ) 4 As 4 series have been synthesized by high-temperature solution growth in single-crystalline form and characterized by elemental analysis, thermodynamic, and transport measurements. These measurements show that the superconducting transition temperature decreases monotonically and is finally suppressed below 1.8 K as x is increased from 0 to 0.036. For x values greater than 0.016, signatures of a magnetic transition can be detected in both thermodynamic and transport measurements in which kinklike features allow for the determination of the transition temperature T* that increases as Mn substitution increases. Here, a temperature-composition (T–x) phase diagram is constructed, revealing a half-dome of superconductivity with the magnetic transition temperature T* appearing near 26 K for x ~ 0.017 and rising slowly up to 33 K for x ~ 0.036. In addition to the creation of the T–x phase diagram for CaK(Fe 1–x Mn x ) 4 As 4 , specific-heat data are used to track the jump in specific heat at T c ; the CaK(Fe 1–x Mn x ) 4 As 4 data do not follow the scaling of ΔC p with $T$$^{3}_{c}$ as many of the other Fe-based superconducting systems do. These data suggest that, as magnetic pair breaking is present, the jump in C p for a given T c is reduced. Elastoresistivity coefficients 2m 66 and m 11 – m 12 as a function of temperature are also measured. 2m 66 and m 11 – m 12 are qualitatively similar to CaK(Fe 1–x Ni x ) 4 As 4 . This may indicate that the magnetic order in Mn-substituted system may be still the same as CaK(Fe 1–x Mn x ) 4 As 4 . Superconductivity of CaK(Fe 1–x Mn x ) 4 As 4 is also studied as a function of magnetic field. A clear change in H' c2 (T)/T c , where H' c2 (T) is dH' c2 (T)/dT, at x ~ 0.015 is observed and probably is related to change of the Fermi surface due to magnetic order. Coherence lengths and the London penetration depths are also calculated based on H c1 and H c2 data. Coherence lengths as the function of x also show the changes near x = 0.015, again consistent with Fermi-surface changes associated with the magnetic ordering seen for higher-x values.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Full superconducting gap in the candidate topological superconductor In 1-x Pb x Te for x = 0.2

High-pressure synthesis techniques have allowed for the growth of samples on the indium-rich side of (Pb,In)Te, which have increased superconducting transition temperatures compared to lead-rich compounds. Here, we present measurements of the temperature dependence of the London penetration depth Δλ(T) in the compound In 0.8 Pb 0.2 Te, which shows a bulk T c,onset of ~ 4.75 K. The results indicate fully gapped BCS-like behavior, ruling out odd-parity topologically nontrivial A 2u , pairing, however, odd-parity A 1u , pairing is still possible. Critical field values measured below 1 K and other superconducting parameters are also presented.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Superconductivity and magnetic and transport properties of single-crystalline CaK ( Fe 1 – x Cr x ) 4 As 4

Members of the CaK (Fe 1–x Cr x ) 4 As 4 series have been synthesized by high-temperature solution growth in single-crystalline form and characterized by x-ray diffraction, elemental analysis, and magnetic and transport measurements. The effects of Cr substitution on the superconducting and magnetic ground states of CaKFe 4 As 4 (T c = 35 K) have been studied. These measurements show that the superconducting transition temperature decreases monotonically and is finally suppressed below 1.8 K as x is increased from 0 to 0.038. For x-values greater than 0.012, signatures of a magnetic transition can be detected in magnetic measurements with the associated features in the transport measurements becoming detectable for x ≥ 0.038. The magnetic transition temperature increases in a roughly linear manner as Cr substitution increases. A temperature-composition (T – x) phase diagram is constructed, revealing a half-dome of superconductivity with the magnetic transition temperature, T*, appearing near 22 K for x ~ 0.017 and rising slowly up to 60 K for x ~ 0.077. The T – x phase diagrams for CaK (Fe 1–x T x ) 4 As 4 for T = Cr and Mn are essentially the same despite the nominally different band filling; this is in marked contrast to T = Co and Ni series for which the T – x diagrams scale by a factor of 2, consistent with the different changes in band filling Co and Ni would produce when replacing Fe. Superconductivity of CaK (Fe 1–x Cr x ) 4 As 4 is also studied as a function of magnetic field. A clear change in $H^{'}_{c2}$ (T)/T c , where $H^{'}_{c2}$ (T) is dH c2 (T)/dT, at x ~ 0.012 is observed and probably is related to a change of the Fermi surface due to magnetic order. Further, coherence length and the London penetration depths are also calculated based on H c1 and H c2 data. Both of them as a function of x show changes near x = 0.012, again consistent with Fermi surface changes associated with the magnetic ordering seen for higher x-values.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Constraints on a split superconducting transition under uniaxial strain in Sr 2 RuO 4 from scanning SQUID microscopy

More than two decades after the discovery of superconductivity in Sr 2 RuO 4 , it is still unclear whether the order parameter has a single component or two degenerate components. For any two-component scenario, application of uniaxial strain is expected to lift the degeneracy, generating two distinct phase transitions. The presence of a second (lower-temperature) transition may be observable by probes that are sensitive to changes in the London penetration depth, λ, as a function of temperature, T. Furthermore, we use scanning SQUID microscopy combined with a uniaxial strain device to test for a second transition under strain. We only observe a single transition. Within the temperature range where a second transition has been suggested by μSR measurements, we further place a tight upper bound of less than 1% on the change in the zero temperature superfluid density n s ∝ λ –2 (0) due to a second transition, suggesting that such a transition does not occur. These results constrain theories of the order parameter in Sr 2 RuO 4 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Isotope effect and critical magnetic fields of superconducting YH 6 : A Migdal-Eliashberg theory approach

The emergence of near-ambient temperature superconductivity under pressure in metal hydride systems has motivated a desire to further understand such remarkable properties, specifically critical magnetic fields. Here, YH 6 is suggested to be a departure from conventional superconductivity, due to apparent anomalous behavior. Using density functional calculations in conjunction with Migdal-Eliashberg theory we show that in YH 6 the critical temperature and the isotope effect under pressure, as well as the high critical fields, are consistent with strong-coupling conventional superconductivity, a property anticipated to extend to other related systems. Furthermore, strong-coupling corrections occur to the expected BCS values for the isotope effect coefficient (α), Ginzburg-Landau parameter [κ 1 ⁡(T)], London penetration depth [λ L (T)], electromagnetic coherence length [ξ⁡(T)], and the energy gap (Δ 0 ).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Electron irradiation reveals robust fully gapped superconductivity in LaNiGa 2

The effects of 2.5-MeV electron irradiation were studied in the superconducting phase of single crystals of LaNiGa 2 , using measurements of electrical transport and radio-frequency magnetic susceptibility. The London penetration depth is found to vary exponentially with temperature, suggesting a fully gapped Fermi surface. The inferred superfluid density is close to that of a single-gap weak-coupling isotropic s – wave superconductor. Superconductivity is extremely robust against nonmagnetic point-like disorder induced by electron irradiation. Our results place strong constraints on the previously proposed triplet pairing state by requiring fine-tuned impurity scattering amplitudes and are most naturally explained by a sign-preserving, weak-coupling, and approximately momentum-independent singlet superconducting state in LaNiGa 2 , which does not break time-reversal symmetry. Finally, we discuss how our findings could be reconciled with previous measurements that indicated magnetic signatures in the superconducting phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Anisotropic multiband superconductivity in 2 M − WS 2 probed by controlled disorder

The intrinsically superconducting Dirac semimetal 2 M − WS 2 is a promising candidate for realizing proximity-induced topological superconductivity in its protected surface states. A precise characterization of the bulk superconducting state is essential to understand the nature of surface superconductivity in the system. Here, we report a detailed experimental study of the temperature-dependent London penetration depth, λ ( T ) , the upper critical field, H c 2 ( T ) , and the effects of nonmagnetic disorder on these quantities, as well as on the superconducting transition temperature T c in single crystals of 2 M − WS 2 . We observe a power-law variation of λ ( T ) ∝ T 3 at temperatures below 0.35 T c . Nonmagnetic pointlike disorder induced by 2.5 MeV electron irradiation at various doses results in a significant suppression of T c . These observations are markedly different from expectations for a fully gapped isotropic s − wave superconductor. Together with the substantial increase of slope, d H c 2 / d T | T = T c , with increasing disorder, our results suggest a strongly anisotropic s + + multiband superconducting state. These results have direct consequences for the expected proximity-induced superconductivity of the topological surface states. Published by the American Physical Society 2024

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1991

Elliptical flux vortices in YBa2Cu3O7

The most energetically favorable vortex in YBa2Cu3O7 forms perpendicular to an anisotropic plane. This vortex is elliptical in shape and is distinguished by an effective interchange of London penetration depths from one axis of the ellipse to another. By generalizing qualitatively from the isotropic to the anisotropic case, we suggest that the flux flow resistivity for the vortex that forms perpendicular to an anistropic plane should have a preferred direction. Similar reasoning indicates that the Kosterlitz-Thouless transition temperature for a vortex mediated transition should be lower if the vortex is elliptical in shape.

Hickman, H.↗
DOE OSTI2026

Magnetic flux distribution, quasiparticle spectroscopy, and quality factors in Nb films for superconducting qubits

Niobium is a practical material platform for superconducting microwave circuits; however, device-level performance can vary significantly depending on film growth and processing conditions. We compare three epitaxial Nb films grown on $c-$plane sapphire substrates under nominally identical conditions, except for the deposition temperature. To correlate internal quality factors, $Q_{\mathrm {i}}$, with material properties, we combine magneto-optical imaging of magnetic flux distribution with quasiparticle spectroscopy via measurements of the London penetration depth, $λ(T)$. In the low-$Q_{\mathrm i}$ film, there is a lesser ability to screen the magnetic field and an irregular temperature variation of $λ(T)$, implying the existence of localized in-gap states. High $Q_{\mathrm i}$ films show the opposite trend. We conclude that our measurements provide an efficient method for characterizing and optimizing superconducting films for quantum informatics applications.

Datta, Amlan [Ames Lab; Iowa State U.]↗
DOE OSTI2026

Effect of metal encapsulation on bulk superconducting properties of niobium thin films used in qubits

Niobium metal occupies nearly 100% of the volume of a typical 2D transmon device. While the aluminum Josephson junction is of utmost importance, maintaining quantum coherence across the entire device means that pair-breaking in Nb leads, capacitive pads, and readout resonators can be a major source of decoherence. The established contributors are surface oxides and hydroxides, as well as absorbed hydrogen and oxygen. Metal encapsulation of freshly grown surfaces with non-oxidizing metals, preferably without breaking the vacuum, is a successful strategy to mitigate these issues. While the positive effects of encapsulation are undeniable, it is important to understand its impact on the macroscopic behavior of niobium films. We present a comprehensive study of the bulk superconducting properties of Nb thin films encapsulated with gold and palladium/gold, and compare them to those of bare Nb films. Magneto-optical imaging, magnetization, resistivity, and London and Campbell penetration depth measurements reveal significant differences in encapsulated samples. Both sputtered, and epitaxial Au-capped films exhibit the highest residual resistivity ratio and superconducting transition temperature, as well as the lowest upper critical field, London penetration depth, and critical current. These results are in good agreement with the microscopic theory of anisotropic normal and superconducting states of Nb. We conclude that pair-breaking in the bulk of niobium films, driven by disorder throughout the film rather than just at the surface, is a significant source of quantum decoherence in transmons. We also conclude that gold capping not only passivates the surface but also affects the properties of the entire film, significantly reducing the scattering rate due to defects likely induced by surface diffusion if the film is not protected immediately after fabrication.

Datta, Amlan [Ames Lab; Iowa State U.]↗
DOE OSTI2024

Conventional single-gap $s-$wave superconductivity and hidden peak effect in single crystals of Mo$_8$Ga$_{41}$ superconductor

London and Campbell penetration depths were measured in single crystals of the endohedral gallide cluster superconductor, Mo _8 8 Ga _41 41 . The full temperature range superfluid density, \rho_s(T) ρ s ( T ) , is consistent with the clean isotropic s- s − wave weak-coupling BCS theory without any signs of the second gap or strong coupling. The temperature dependence of the Campbell length is hysteretic between zero-field cooling (ZFC) and field-cooling (FC) protocols, indicating an anharmonic vortex pinning potential. The field dependence of the effective critical current density, j_{c}(H) j c ( H ) , reveals an unusual result. While in the ZFC protocol, j_{c}(H) j c ( H ) is monotonically suppressed by the magnetic field, it exhibits a profound “hidden” peak effect in the FC protocol, that is, without a vortex density gradient. We suggest a possible novel mechanism for such a peak effect, which involves both static and dynamic aspects of vortex pinning.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Emergent Chern-Simons interactions in 3+1 dimensions

Parity-violating superconductors can support a low-dimension local interaction that becomes, upon condensation, a purely spatial Chern-Simons term. Solutions to the resulting generalized London equations can be obtained from solutions of the ordinary London equations with a complex penetration depth, and suggest several remarkable physical phenomena. The problem of flux exclusion by a sphere brings in an anapole moment, the problem of current-carrying wires brings in an azimuthal magnetic field, and the problem of vortices brings in currents along the vortices. We demonstrate that interactions of this kind, together with a conceptually related dimensionally reduced Chern-Simons interaction, can arise from physically plausible microscopic interactions. Published by the American Physical Society 2024

Materials Science↗
DOE OSTI2022

SuperScreen: An open-source package for simulating the magnetic response of two-dimensional superconducting devices

Quantitative understanding of the spatial distribution of magnetic fields and Meissner screening currents in two-dimensional (2D) superconductors and mesoscopic thin film superconducting devices is critical to interpreting the results of magnetic measurements of such systems. Here, we introduce SuperScreen, an open-source Python package for simulating the response of 2D superconductors to trapped flux and applied time-independent or quasi-DC magnetic fields for any value of the effective magnetic penetration depth, Λ. Given an applied magnetic field, SuperScreen solves the 2D London equation using an efficient matrix inversion method to obtain the Meissner currents and magnetic fields in and around structures composed of one or more superconducting thin films of arbitrary geometry with spatially nonuniform magnetic penetration depth. SuperScreen can be used to model screening effects and calculate self- and mutual-inductance in superconducting devices, and simulate the magnetic response of inhomogeneous 2D superconductors.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Evidence for current suppression in superconductor–superconductor bilayers

Superconducting radio frequency (SRF) cavities, which are critical components in many particle accelerators, need to be operated in the Meissner state to avoid strong dissipation from magnetic vortices. For a defect-free superconductor, the maximum attainable magnetic field for operation is set by the superheating field, B sh , which directly depends on the surface current. In heterostructures composed of different superconductors, the current in each layer depends not only on the properties of the individual material, but also on the electromagnetic response of the adjacent layers through boundary conditions at the interfaces. Three prototypical bilayers [Nb 1–x Ti x N (50 nm)/Nb, Nb 1–x Ti x N (80 nm)/Nb, and, Nb 1–x Ti x N (160 nm)/Nb] are investigated here by depth-resolved measurements of their Meissner screening profiles using low energy muon spin rotation (LE-µSR). From fits to a model based on London theory (with appropriate boundary and continuity conditions), a magnetic penetration depth for the thin Nb 1–x Ti x N layers of λ Nb 1–x Ti x N = 182.5(31) nm is found, in good agreement with literature values for the bulk alloy. Using the measured λ Nb 1–x Ti x N , the maximum vortex-free field, B max , of the superconductor-superconductor (SS) bilayer structure was estimated to be 610(40) mT. The strong suppression of the surface current in the Nb 1–x Ti x N layer suggests an optimal thickness of ~ 1.4λ Nb 1–x Ti x N = 261(14) nm.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Anomalous Superfluid Density in a Disordered Charge-Density-Wave Material: Pd-Intercalated ErTe 3

We image local superfluid density in single crystals of Pd-intercalated ErTe 3 below the superconducting critical temperature T c , well below the onset temperature T CDW of (disordered) charge-density-wave order. We find no detectable inhomogeneities on micron scales. Furthermore, we observe a rapid increase of the superfluid density below T c , deviating from the behavior expected in a conventional Bardeen-Cooper-Schrieffer superconductor, and show that the temperature dependence is qualitatively consistent with a combination of quantum and thermal phase fluctuations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
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↗
DOE OSTI2022

SuperScreen: An open-source package for simulating the magnetic response of two-dimensional superconducting devices

Quantitative understanding of the spatial distribution of magnetic fields and Meissner screening currents in two-dimensional (2D) superconductors and mesoscopic thin film superconducting devices is critical to interpreting the results of magnetic measurements of such systems. Here, we introduce SuperScreen, an open-source Python package for simulating the response of 2D superconductors to trapped flux and applied time-independent or quasi-DC magnetic fields for any value of the effective magnetic penetration depth, Λ. Given an applied magnetic field, SuperScreen solves the 2D London equation using an efficient matrix inversion method to obtain the Meissner currents and magnetic fields in and around structures composed of one or more superconducting thin films of arbitrary geometry. Further, SuperScreen can be used to model screening effects and calculate self- and mutual-inductance in thin film superconducting devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Insights Into Thermal Runaway Mechanisms: Fast Tomography Analysis of Metal Agglomerates in Lithium-Ion Batteries

Thermal Runaway (TR) in lithium-ion batteries (LIB) is a critical technological and social concern. Whilst such events are rare, TR is characterized by uncontrollable heating leading to catastrophic failures. To deepen the understanding of the failure process and subsequently develop more accurate TR prediction models and as a result safer battery systems, we present in this work high-speed X-ray tomography for in-depth investigations of the copper current collector melting and agglomeration during TR. The melting process presents valuable real-time internal information about heat evolution during TR, previously challenging to access but crucially important for validating TR models. In this work, controlled failure studies combined with high-speed X-ray tomography were performed on two different commercial LIB models, subjecting them to both external heating and nail penetration to induce TR. Through real-time observation via high-speed tomography, followed by segmentation, rendering, and analysis, the formation of copper agglomerates was qualitatively and quantitatively characterized and visualized for the first time. Agglomerates tended to form either from the battery's outermost layers or centrally, depending on the method of TR initiation, and gives an indirect insight into the internal temperature evolution and distribution. Moreover, an initial comparative analysis between the battery models also revealed differences in agglomerate size, which has been linked to the thicker copper current collectors of one of the cell models. We further discuss the impact of larger copper agglomerates on heat distribution and safety. This study not only sheds light on the intricate dynamics of TR in LIBs but also underscores the pivotal role of 'gold-standard' imaging techniques in advancing battery safety, crucial for the robust modeling of TR and the future design of electric vehicle safety systems.

25 ENERGY STORAGE↗