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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Cathodes and electrolytes for rechargeable magnesium batteries and methods of manufacture

The invention relates to Chevrel-phase materials and methods of preparing these materials utilizing a precursor approach. The Chevrel-phase materials are useful in assembling electrodes, e.g., cathodes, for use in electrochemical cells, such as rechargeable batteries. The Chevrel-phase materials have a general formula of Mo 6 Z 8 (Z=sulfur) or Mo 6 Z 1 8-yZ 2 y (Z 1 =sulfur; Z 2 =selenium), and partially cuprated Cu 1 Mo 6 S 8 as well as partially de-cuprated Cu 1-x Mg x Mo 6 S 8 and the precursors have a general formula of M x Mo 6 Z 8 or M x Mo 6 Z 1 8-yZ 2 y , M=Cu. The cathode containing the Chevrel-phase material in accordance with the invention can be combined with a magnesium-containing anode and an electrolyte.

Kumta, Prashant N.↗
DOE OSTI2025

Quasiparticle description of angle-resolved photoemission spectroscopy for SrCuO 2

SrCuO 2 has long been considered a near-archetypal realization of a quasi-one-dimensional (1D) system of interacting electrons with short-range interactions. Within this framework, experimental observations - interpreted through the lens of the 1D Hubbard model - suggest that electron and hole excitations decay into two types of (unphysical) collective bosonic modes: "spinons", which carry the spin degree of freedom, and "holons", which carry the charge degree of freedom. This model, known as spin-charge separation, is most directly evidenced by angle-resolved photoemission spectroscopy (ARPES), where a photo-induced hole decays into a continuum of these excitations. Here we present an alternative perspective grounded in first-principles, self-consistent, and parameter-free many-body perturbation theory. In this revised quasiparticle framework, ARPES can be understood as a one-body effect arising from mild disorder in a long-range antiferromagnetic ground state. the emergence of the so-called spinon branch arises naturally from spin disorder, the anomalous linewidths are accurately captured, and we provide a compelling explanation for the spectral weight observed at the non-magnetic zone boundary. This reinterpretation provides a unified explanation for key experimental signatures previously attributed to spin-charge separation, including features observed in optical conductivity. Additionally, we show that SrCuO 2 exhibits a nontrivial interchain coupling that significantly influences both its one-particle and two-particle spectral functions. By comparing the spectral features of SrCuO 2 with those of La 2 CuO 4 , we argue that SrCuO 2 shares notable similarities with the two-dimensional cuprates-both being rooted in a common CuO 4 plaquette-based molecular orbital framework.

1D cuprates↗
DOE OSTI2026

Expert evaluation of LLM world models: A high-T c superconductivity case study

Large Language Models (LLMs) show great promise as a powerful tool for scientific literature exploration. However, their effectiveness in providing scientifically accurate and comprehensive answers to complex questions within specialized domains remains an active area of research. Using the field of high-temperature cuprates as an exemplar, we evaluate the ability of LLM systems to understand the literature at the level of an expert. We construct an expert-curated database of 1,726 scientific papers that covers the history of the field, and a set of 67 expert-formulated questions that probe deep understanding of the literature. We then evaluate six different LLM-based systems for answering these questions, including both commercially available closed models and a custom retrieval-augmented generation (RAG) system capable of retrieving images alongside text. Experts then evaluate the answers of these systems against a rubric that assesses balanced perspectives, factual comprehensiveness, succinctness, and evidentiary support. Among the six systems, two using RAG on curated literature outperformed existing closed models across key metrics, particularly in providing comprehensive and well-supported answers. We discuss promising aspects of LLM performances as well as critical short-comings of all the models. The set of expert-formulated questions and the rubric will be valuable for assessing expert level performance of LLM based reasoning systems.

36 MATERIALS SCIENCE↗
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

Revealing the frequency-dependent oscillations in the nonlinear terahertz response induced by the Josephson current

ABSTRACT Nonlinear responses of superconductors to intense terahertz radiation has been an active research frontier. Using terahertz pump-terahertz probe spectroscopy, we investigate the c-axis nonlinear optical response of a high-temperature superconducting cuprate. After excitation by a single-cycle terahertz pump pulse, the reflectivity of the probe pulse oscillates as the pump-probe delay is varied. Interestingly, the oscillatory central frequency scales linearly with the probe frequency, a fact widely overlooked in pump-probe experiments. By theoretically solving the nonlinear optical reflection problem on the interface, we show that our observation is well explained by the Josephson-type third-order nonlinear electrodynamics, together with the emission coefficient from inside the material into free space. The latter results in a strong enhancement of the emitted signal whose physical frequency is around the Josephson plasma edge. Our result offers a benchmark for and new insights into strong-field terahertz spectroscopy of related quantum materials.

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 OSTI2020

Detecting superconductivity out of equilibrium

Recent pump-probe experiments on underdoped cuprates and similar systems suggest the existence of a transient superconducting state above Tc. This poses the question of how to reliably identify the emergence of long-range order, in particular superconductivity, out of equilibrium. We investigate this point by studying a quantum quench in an extended Hubbard model and by computing various observables, which are used to identify (quasi-)long-range order in equilibrium. Our findings imply that, in contrast to current experimental studies, it does not suffice to study the time evolution of the optical conductivity to identify superconductivity. In turn, we suggest to utilize time-resolved angle-resolved photoemission spectroscopy experiments to probe for the formation of a condensate in the two-particle channel.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Absence of μ SR evidence for magnetic order in the pseudogap phase of Bi 2 + x Sr 2 - x CaCu 2 O 8 + δ

We present an extended zero-field muon spin relaxation (ZF-$µSR$) study of overdoped $Bi_{2+x}Sr_{2-x}\,CaCu_2O_{8+δ}$ (Bi2212) single crystals, intended to elucidate the origin of weak quasistatic magnetism previously detected by $µSR$ in the superconducting and normal states of optimallydoped and overdoped samples. New results on heavily-overdoped single crystals show a similar monotonically decreasing ZF-$µSR$ relaxation rate with increasing temperature that persists above the pseudogap (PG) temperature $T^*$ and does not evolve with hole doping ($p$). Additional measurements using an ultra-low background apparatus confirm that this behavior is an intrinsic property of Bi2212, which cannot be due to magnetic order associated with the PG phase. Instead we show that the temperature-dependent relaxation rate is most likely caused by structural changes that modify the contribution of the nuclear dipole fields to the ZF-$µSR$ signal. Finally, our results for Bi2212 emphasize the importance of not assuming the nuclear-dipole field contribution is independent of temperature in ZF-$µSR$ studies of high-temperature (high-$T_c$) cuprate superconductors, and do not support a recent $µSR$ study of $YBa_2Cu_3O_{6+x}$ that claims to detect magnetic order in the PG phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Scanning SQUID characterization of extremely overdoped La 2-x Sr x CuO 4

Recently, advances in film synthesis methods have enabled a study of extremely overdoped La 2 - x Sr x Cu O 4 . This has revealed a surprising behavior of the superfluid density as a function of doping and temperature, the explanation of which is vividly debated. One popular class of models posits electronic phase separation, where the superconducting phase fraction decreases with doping, while some competing phase (e.g., ferromagnetic) progressively takes over. A problem with this scenario is that all the way up to the dome edge the superconducting transition remains sharp, according to mutual inductance measurements. However, the physically relevant scale is the Pearl penetration depth Λ P , and this technique probes the sample on a length scale L that is much larger than Λ P . In the present paper, we use local scanning superconducting quantum interference device (SQUID) measurements that probe the susceptibility of the sample on the scale L << Λ P . Our SQUID maps show uniform landscapes of susceptibility and excellent overall agreement of the local penetration depth data with the bulk measurements. Overall, these results contribute an important piece to the puzzle of how high-temperature superconductivity vanishes on the overdoped side of the cuprate phase diagram.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Nature of the magnetic stripes in fully oxygenated La 2 CuO 4+y

We present triple-axis neutron scattering studies of static and dynamic magnetic stripes in an optimally oxygen-doped cuprate superconductor, La 2 CuO 4+y , which exhibits a clean superconducting transition at T c = 42 K. Polarization analysis reveals that the magnetic stripe structure is equally represented along both of the tetragonal crystal axes and that the fluctuating stripes display significant weight for in-plane as well as out-of-plane spin components. Both static magnetic order as well as low-energy fluctuations are fully developed in zero applied magnetic field and the low-energy spin fluctuations at ℏω = 0.3 – 10 meV intensify on cooling. We interpret this as an indication that superconductivity and low-energy spin fluctuations coexist microscopically in spatial regions which are separated from domains with static magnetic order.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Neutron scattering study of magnetic anisotropy in the tetragonal antiferromagnet Bi 2 CuO 4

In this work, we present a comprehensive study of magnon excitations in the tetragonal easy-plane antiferromagnet Bi 2 CuO 4 using inelastic neutron scattering and spin-wave analyses. The nature of low-energy magnons, and hence the anisotropy in this material, has been controversial. We show unambiguously that the low-energy magnon spectrum consists of a gapped and a gapless mode, which we attribute to out-of-plane and in-plane spin fluctuations, respectively. We modeled the observed magnon spectrum using linear spin-wave analysis of a minimal anisotropic spin model motivated by the lattice symmetry. By studying the magnetic field dependence of the (1,0,0) Bragg peak intensity and the in-plane magnon intensity, we observed a spin-flop transition in the ab plane at ~0.4 T, which directly indicates the existence of a small in-plane anisotropy that is classically forbidden. It is only by taking into account magnon zero-point fluctuations beyond the linear spin-wave approximation that we could explain this in-plane anisotropy and its magnitude, the latter of which is deduced from the critical field of the spin-flop transition. The microscopic origins of the observed anisotropic interactions are also discussed. We found that our data are inconsistent with a large Dzyaloshinskii-Moriya interaction, which suggests a potential departure of Bi 2 CuO 4 from the conventional theories of magnetic anisotropy for other cuprates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Implications of second harmonic generation for hidden order in Sr 2 CuO 2 Cl 2

Sr 2 CuO 2 Cl 2 (SCOC) is a model undoped cuprate with I4/mmm crystallographic symmetry, and a simple magnetic space group CAmca with associated magnetic point group mmm1'. However, recent second harmonic spectroscopy in the antiferromagnetic phase has challenged this picture, suggesting instead a magnetic point group 4/mm'm' that coexists with the antiferromagnetism and breaks the two orthogonal mirror planes containing the tetragonal c axis. Here, we analyze the symmetry of SCOC in light of the second harmonic results, and discuss possible ground states that are consistent with the data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Orbitally selective resonant photodoping to enhance superconductivity

Signatures of superconductivity at elevated temperatures above T c in high-temperature superconductors have been observed near 1/8 hole doping for photoexcitation with infrared or optical light polarized either in the CuO 2 plane or along the c axis. While the use of in-plane polarization has been effective for incident energies aligned to specific phonons, c-axis laser excitation in a broad range between 5 μm and 400 nm was found to affect the superconducting dynamics in striped La 1.88 5Ba 0.115 CuO 4 , with a maximum enhancement in the 1/ω dependence to the conductivity observed at 800 nm. This broad energy range, specifically 800 nm, is not resonant with any phonon modes, yet induced electronic excitations appear to be connected to superconductivity at energy scales well above the typical gap energies in the cuprates. A critical question is, What can be responsible for such an effect at 800 nm? Using time-dependent exact diagonalization, we demonstrate that the holes in the CuO 2 plane can be photoexcited into the charge reservoir layers at resonant wavelengths within a multiband Hubbard model. This orbitally selective photoinduced charge transfer effectively changes the in-plane doping level, which can lead to an enhancement of T c near the 1/8 anomaly.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Testing for pair density wave order in La 1.875 Ba 0.125 CuO 4

We report charge order is commonly believed to compete with superconducting order. An intertwined form of a superconducting wave function, known as pair density wave (PDW) order, has been proposed; however, direct evidence, theoretical or experimental, that it forms the ground state of any cuprate superconductor is lacking. As a test case, we consider La 2-x Ba x CuO 4 with x = 1/8, where charge and spin stripe orders within the CuO 2 planes compete with three-dimensional superconducting order. We report measurements of the superconducting critical current perpendicular to the planes in the presence of an in-plane magnetic field. The variation of the critical current with orientation of the field is inconsistent with a theoretical prediction specific to the PDW model. It appears, instead, that the orientation dependence of the critical-current density might be determined by a minority phase of d-wave superconductivity that is present as a consequence of doped-charge inhomogeneity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Pair density wave in the doped three-band Hubbard model on two-leg square cylinders

A pair density wave (PDW) is a superconducting (SC) state with a spatially modulated order parameter. Although much is known about the properties of the PDW state, its realization in microscopic models with divergent susceptibility has been challenging. Here, in this work, we report a density-matrix renormalization group study of a three-band Hubbard model (also known as the Emery model) for cuprates on long two-leg square cylinders. Upon light doping, we find that the ground state of the system is consistent with that of a PDW state with mutually commensurate and power-law SC, charge (CDW), and spin (SDW) density wave correlations. The SC correlations are dominant between neighboring Cu sites with d-wave pairing symmetry. Interestingly, we find that the near-neighbor interactions, especially the near-neighbor attractive V pd interaction between neighboring Cu and oxygen sites, can notably enhance the SC correlations while simultaneously suppressing the CDW correlations. For a modestly strong attractive V pd , the SC correlations become quasi-long-ranged with a divergent PDW susceptibility.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Enhanced superconductivity by near-neighbor attraction in the doped extended Hubbard model

A recent experiment has unveiled an anomalously strong electron-electron attraction in the one-dimensional copper-oxide chain Ba 2–x Sr x CuO 3+δ . While the effect of the near-neighbor electron attraction V in the one-dimensional extended Hubbard chain has been examined recently, its effect in the Hubbard model beyond the one-dimensional chain remains unclear. Here, in this work, we report a density matrix renormalization group study of the extended Hubbard model on long four-leg cylinders on the square lattice. We find that the near-neighbor electron attraction V can notably enhance the long-distance superconducting correlations while simultaneously suppressing the charge-density-wave (CDW) correlations. Specifically, for a modestly strong electron attraction, the superconducting correlations become dominant over the CDW correlations with a Luttinger exponent K sc ~1 and strong divergent superconducting susceptibility. Our results provide a promising way to realize long-range superconductivity in the doped Hubbard model. The relevance of our numerical results to cuprate materials is also discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Evolution of the Magnetic Excitations in Electron-Doped La 2 - x Ce x CuO 4

Here we investigated the high energy spin excitations in electron-doped La 2-x Ce x CuO 4 , a cuprate superconductor, by resonant inelastic x-ray scattering (RIXS) measurements. Efforts were paid to disentangle the paramagnon signal from non-spin-flip spectral weight mixing in the RIXS spectrum at Q ∥ =(0.6π,0) and (0.9π,0) along the (1 0) direction. Our results show that, for doping level x from 0.07 to 0.185, the variation of the paramagnon excitation energy is marginal. We discuss the implication of our results in connection with the evolution of the electron correlation strength in this system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Electron Glass Phase with Resilient Zhang-Rice Singlets in LiCu 3 ⁢O 3

LiCu 3 ⁢O 3 is an antiferromagnetic mixed valence cuprate where trilayers of edge-sharing Cu(II)O (3⁢d 9 ) are sandwiched in between planes of Cu(I) (3⁢d 10 ) ions, with Li stochastically substituting Cu(II). Angle-resolved photoemission spectroscopy (ARPES) and density functional theory reveal two insulating electronic subsystems that are segregated in spite of sharing common oxygen atoms: a Cu d z 2 /O p z derived valence band (VB) dispersing on the Cu(I) plane, and a Cu 3⁢d x 2 -y 2 /O 2⁢p x,y derived Zhang-Rice singlet (ZRS) band dispersing on the Cu(II)O planes. First-principle analysis shows the Li substitution to stabilize the insulating ground state, but only if antiferromagnetic correlations are present. Li further induces substitutional disorder and a 2D electron glass behavior in charge transport, reflected in a large 530 meV Coulomb gap and a linear suppression of VB spectral weight at E F that is observed by ARPES. Surprisingly, the disorder leaves the Cu(II)-derived ZRS largely unaffected. Finally, this indicates a local segregation of Li and Cu atoms onto the two separate corner-sharing Cu⁡(II)⁢O 2 sub-lattices of the edge-sharing Cu(II)O planes, and highlights the ubiquitous resilience of the entangled two hole ZRS entity against impurity scattering.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗