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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Phonon-Mediated Long-Range Attractive Interaction in One-Dimensional Cuprates

Establishing a minimal microscopic model for cuprates is a key step towards the elucidation of a high-T c mechanism. By a quantitative comparison with a recent in situ angle-resolved photoemission spectroscopy measurement in doped 1D cuprate chains, our simulation identifies a crucial contribution from long-range electron-phonon coupling beyond standard Hubbard models. Using reasonable ranges of coupling strengths and phonon energies, we obtain a strong attractive interaction between neighboring electrons, whose strength is comparable to experimental observations. Additionally, nonlocal couplings play a significant role in the mediation of neighboring interactions. Considering the structural and chemical similarity between 1D and 2D cuprate materials, this minimal model with long-range electron-phonon coupling will provide important new insights on cuprate high-T c superconductivity and related quantum phases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Prevailing Charge Order in Overdoped La 2 – x Sr x CuO 4 beyond the Superconducting Dome

The extremely overdoped cuprates are generally considered to be Fermi liquid metals without exotic orders, whereas the underdoped cuprates harbor intertwined states. Contrary to this conventional wisdom, using Cu L 3 -edge and O K-edge resonant x-ray scattering, we reveal a charge order (CO) correlation in overdoped La 2–x⁢ Sr x ⁢CuO 4 (0.35 ≤ x ≤0.6) beyond the superconducting dome. This CO has a periodicity of ~6 lattice units with correlation lengths of ~20 lattice units. It shows similar in-plane momentum and polarization dependence and dispersive excitations as the CO of underdoped cuprates, but its maximum intensity differs along the c direction and persists up to 300 K. This CO correlation cannot be explained by the Fermi surface instability and its origin remains to be understood. Finally, our results suggest that CO is prevailing in the overdoped metallic regime and requires a reassessment of the picture of overdoped cuprates as weakly correlated Fermi liquids.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Prediction of s ± -Wave Superconductivity Enhanced by Electronic Doping in Trilayer Nickelates La 4 Ni 3 O 10 under Pressure

Motivated by the recently reported signatures of superconductivity in trilayer La 4 ⁢Ni 3 ⁢O 10 under pressure, here we comprehensively study this system using ab initio and random-phase approximation techniques. Without electronic interactions, the Ni d 3z 2 –r 2 orbitals show a bonding-antibonding and nonbonding splitting behavior via the O p z orbitals inducing a “trimer” lattice in La 4⁢ Ni 3 ⁢O 10 , analogous to the dimers of La 3 ⁢Ni 2 ⁢O 7 . The Fermi surface consists of three electron sheets with mixed e g orbitals, and a hole and an electron pocket made up of the d 3⁢z 2 –r 2 orbital, suggesting a Ni two-orbital minimum model. In addition, we find that superconducting pairing is induced in the s ± -wave channel due to partial nesting between the M = (π,π) centered pockets and portions of the Fermi surface centered at the Γ = (0,0) point. With changing electronic density n, the s ± instability remains leading and its pairing strength shows a domelike behavior with a maximum around n = 4.2 ( ~6.7% electron doping). The superconducting instability disappears at the same electronic density as that in the new 1313 stacking La 3 ⁢Ni 2 ⁢O 7 , correlated with the vanishing of the hole pocket that arises from the trilayer sublattice, suggesting that the high-T c superconductivity of La 3⁢ Ni 2 ⁢O 7 does not originate from a trilayer and monolayer structure. Furthermore, we confirm the experimentally proposed spin state in La 4 ⁢Ni 3 ⁢O 10 with an in-plane (π, π) order and antiferromagnetic coupling between the top and bottom Ni layers, and spin zero in the middle layer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Electronic structure of the alternating monolayer-trilayer phase of La 3 Ni 2 O 7

Recent studies of La 3 Ni 2 O 7 have identified a bilayer (2222) structure and an unexpected alternating monolayer-trilayer (1313) structure, both of which feature signatures of superconductivity near 80 K under high pressures. Using angle-resolved photoemission spectroscopy, we measure the electronic structure of 1313 samples. In contrast to the previously studied 2222 structure, we find that the 1313 structure hosts a flat band with a markedly different binding energy, as well as an additional electron pocket and band splittings. By comparison to local-density approximation calculations, we find renormalizations of the Ni-d z 2 and Ni-d x 2 -y 2 derived bands to be about 5 to 7 and about 4 respectively, suggesting strong correlation effects. These results reveal important differences in the electronic structure brought about by the distinct structural motifs with the same stoichiometry. Such differences may be relevant to the putative high temperature superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Homogeneous superconducting gap in Dy Ba 2 Cu 3 O 7 - δ synthesized by oxide molecular beam epitaxy

Much of what is known about high-temperature cuprate superconductors stems from studies based on two surface analytical tools, angle-resolved photoemission spectroscopy (ARPES) and spectroscopic imaging scanning tunneling microscopy (SI-STM). A question of general interest is whether and when the surface properties probed by ARPES and SI-STM are representative of the intrinsic properties of bulk materials. We find this question is prominent in thin films of a rarely studied cuprate Dy Ba 2 Cu 3 O 7 - δ DBCO). We synthesize DBCO films by oxide molecular beam epitaxy and study them by in situ ARPES and SI-STM. Both ARPES and SI-STM show that the surface DBCO layer is different from the bulk of the film—it is heavily underdoped, while the doping level in the bulk is close to optimal doping evidenced by bulk-sensitive mutual inductance measurements. ARPES shows the typical electronic structure of a heavily underdoped CU O 2 plane and two sets of one-dimensional bands originating from the CuO chains with one of them gapped. SI-STM reveals two different energy scales in the local density of states, with one (at ~ 18 meV ) corresponding to the superconductivity and the other one (at ~ 90 meV ) to the pseudogap. Finally, while the pseudogap shows large variations over the length scale of a few nanometers, the superconducting gap is very homogeneous. This indicates that the pseudogap and superconductivity are of different origins.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Ultrathin epitaxial MgB 2 on SiC: Substrate surface-polarity-dependent properties

High-quality, ultrathin superconducting films are required for advanced devices such as hot-electron bolometers, superconducting nanowire single-photon detectors, and quantum applications. Using hybrid physical-chemical vapor deposition, we show that MgB 2 films as thin as 4 nm can be fabricated on the carbon-terminated 6⁢H-SiC (0001) surface with a superconducting transition temperature above 33 K and a rms roughness of 0.7 nm. Remarkably, the film quality is a function of the SiC surface termination, with the C-terminated surface preferred to the Si-terminated surface. To understand the MgB 2 thin film/SiC substrate interactions giving rise to this difference, we characterized the interfacial structures using Rutherford backscattering spectroscopy/channeling, electron-energy-loss spectroscopy, and x-ray photoemission spectroscopy. The MgB 2 /SiC interface structure is complex and different for the two terminations. Both terminations incorporate substantial unintentional oxide layers influencing MgB 2 growth and morphology, but with a different extent, intermixing, and interface chemistry. In this paper, we report measurements of transport, resistivity, and the critical superconducting temperature of MgB 2 /SiC that are different for the two terminations, and they link interfacial structure variations to observed differences. The result shows that the C face of SiC is a preferred substrate for the deposition of ultrathin superconducting MgB 2 films.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Large response of charge stripes to uniaxial stress in La 1.475 Nd 0.4 Sr 0.125 CuO 4

The La-based "214"cuprates host several symmetry-breaking phases, including superconductivity, charge and spin order in the form of stripes, and a structural orthorhombic-to-tetragonal phase transition. Therefore these materials are an ideal system to study the effects of uniaxial stress onto the various correlations that pervade the cuprate phase diagram. We report resonant x-ray scattering experiments on La 1.475 Nd 0.4 Sr 0.125 CuO 4 (LNSCO-125) that reveal a significant response of charge stripes to uniaxial tensile stress of ~0.1GPa. These effects include a reduction of the onset temperature of stripes by ~50K, a 29-K reduction of the low-temperature orthorhombic-to-tetragonal transition, competition between charge order and superconductivity, and a preference for stripes to form along the direction of applied stress. Altogether, we observe a dramatic response of the electronic properties of LNSCO-125 to a modest amount of uniaxial stress.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Planar Thermal Hall Effect from Phonons in Cuprates

A surprising “planar” thermal Hall effect, whereby the field is parallel to the current, has recently been observed in a few magnetic insulators; this effect has been attributed to exotic excitations such as Majorana fermions or chiral magnons. Here, we investigate the possibility of a planar thermal Hall effect in three different cuprate materials, in which the conventional thermal Hall conductivity 𝜅 xy (with an out-of-plane field perpendicular to the current) is dominated by either electrons or phonons. Our measurements show that the planar 𝜅 xy from electrons in cuprates is zero, as expected from the absence of a Lorentz force in the planar configuration. By contrast, we observe a sizable planar 𝜅 xy in those samples where the thermal Hall response is due to phonons, even though it should, in principle, be forbidden by the high crystal symmetry. Our findings call for a careful reexamination of the mechanisms responsible for the phonon thermal Hall effect in insulators.

Cuprates↗
DOE OSTI2021

YBCO-on-Kapton: Material for High-Density Quan-tum Computer Interconnects with Ultra-Low Thermal Conductance

Development of practical quantum computers would require 1000's of qubits and equally large number of read-outs, bias and drive lines. New materials that combine low passive loss and good RF properties are needed. In this study we report performance of signal interconnects comprised of high-temperature YBCO films that are exfoliated from a metal substrate and transferred to a E-Kapton tape. The technology offers low-loss transition be-tween 60 K to sub-mK environments and interfacing with off-shelf flexible silicon electronics. We demonstrate < 1 dB/m at-tenuation at 6 GHz at 77 K. The microstrip assemblies demon-strated no degradation upon multiple cycles to liquid Nitrogen and conduction cooling down to 18 K. We discuss designs of a practical high-density signal cable with passive heat load well below 1 μW per line. The YBCO-on-Kapton technology offers a practical pathway to large error-corrected quantum computing systems.

47 OTHER INSTRUMENTATION↗