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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

First characterisation of the MAGO cavity, a superconducting RF detector for kHz–MHz gravitational waves

Heterodyne detection using microwave cavities is a promising method for detecting high-frequency gravitational waves (GWs) or ultralight axion dark matter. In this work, we report on studies conducted on a spherical 2-cell cavity developed by the MAGO collaboration for high-frequency GWs detection. Although fabricated around 20 years ago, the cavity had not been used since. Due to deviations from the nominal geometry, we conducted a mechanical survey and performed room-temperature plastic tuning. Measurements and simulations of the mechanical resonances and electromagnetic properties were carried out, as these are critical for estimating the cavity’s GW coupling potential. Based on these results, we plan further studies in a cryogenic environment. The cavity characterisation does not only provide valuable experience for a planned physics run but also informs the future development of improved cavity designs.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

First Penning trap mass measurement of 36 Ca

Background: Isobaric quintets provide the best test of the isobaric multiplet mass equation (IMME) and can uniquely identify higher order corrections suggestive of isospin symmetry breaking effects in the nuclear Hamilto nian. The Generalized IMME (GIMME) is a novel microscopic interaction theory that predicts an extension to the quadratic form of the IMME. Only the A = 20, 32 T = 2 quintets have the exotic T z = –2 member ground state mass determined to high-precision by Penning trap mass spectrometry. Purpose: To establish A = 36 as the third high-precision T = 2 isobaric quintet with the T z = –2 member ground state mass measured by Penning trap mass spectrometry and provide the first test of the predictive power of the GIMME. Method: Here, a radioactive beam of neutron-deficient 36 Ca was produced by projectile fragmentation at the National Superconducting Cyclotron Laboratory. The beam was thermalized and the mass of 36 Ca + and 36 Ca 2+ measured by the Time of Flight - Ion Cyclotron Resonance method in the LEBIT 9.4 T Penning trap. Results: We measure the mass excess of 36 Ca to be ME= –6483.6(56) keV, an improvement in precision by a factor of 6 over the literature value. The new datum is considered together with evaluated nuclear data on the A = 36, T = 2 quintet. We find agreement with the quadratic form of the IMME given by isospin symmetry, but only coarse qualitative agreement with predictions of the GIMME. Conclusion: A total of three isobaric quintets have their most exotic members measured by Penning trap mass spectrometry. The GIMME predictions in the T = 2 quintet appear to break down for A = 32 and greater.

20 ≤ A ≤ 38↗
DOE OSTI2025

Detecting thermodynamic phase transition via explainable machine learning of photoemission spectroscopy

Identifying thermodynamic signatures of electronic phases, such as superconductivity, is challenging in low-dimensional materials due to strong fluctuations and low probing volume. Spectroscopic methods are often used to identify new bulk phases, but their main measurable quantity—electronic energy gaps—is no longer an effective order parameter in low-dimensional and fluctuating systems. Combining angle-resolved photoemission with a domain-adversarial neural network, we report a data-driven method to identify thermodynamic phase transitions solely based on single-particle spectra. We demonstrate 97.6% accuracy in cuprate superconductor Bi 2 Sr 2 CaCu 2 O 8+δ with strong superconducting fluctuations. This model notably compensates for the scarcity of experimental data by leveraging virtually inexhaustible simulated data. Further, its explainability reveals the crucial role of in-gap spectral weight in detecting phase fluctuations and thermodynamic transitions. Our work pinpoints the spectroscopic signatures of fluctuating orders and enables using spectroscopy for machine-learning-assisted material discovery for low-dimensional and strong coupling systems.

2D materials↗
DOE OSTI2021

Cryogenic single-port calibration for superconducting microwave resonator measurements

Superconducting circuit testing and materials loss characterization requires robust and reliable methods for the extraction of internal and coupling quality factors of microwave resonators. Additionally, a common method, imposed by limitations on the device design or experimental configuration, is the single-port reflection geometry, i.e. reflection-mode. However, impedance mismatches in cryogenic systems must be accounted for through calibration of the measurement chain while it is at low temperatures. In this paper, we demonstrate a data-based, single-port calibration using commercial microwave standards and a vector network analyzer with samples at millikelvin temperature in a dilution refrigerator, making this method useful for measurements of quantum phenomena. Finally, we cross reference our data-based, single-port calibration and reflection measurement with over-coupled 2D- and 3D-resonators against well established two-port techniques corroborating the validity of our method.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Floquet vortex states induced by light carrying an orbital angular momentum

Here, we propose a scheme to create an electronic Floquet vortex state by irradiating a two-dimensional semiconductor with a laser light carrying nonzero orbital angular momentum. We analytically and numerically study the properties of the Floquet vortex states, with methods analogous to the ones previously applied to the analysis of superconducting vortex states. We show that such Floquet vortex states are similar to superconducting vortex states, and they exhibit a wide range of tunability. To illustrate the potential utility of such tunability, we show how such states could be used for quantum state engineering.

2-dimensional systems↗
DOE OSTI2021

Identification of a new isomeric state in 76 Zn following the β decay of 76 Cu

Background: The evolution of nuclear shell structure far from stability can be explored by identifying and measuring the properties of isomers. Neutron-rich nuclei between the Z = 28 and Z = 50 closed shells have been the subject of recent studies which have identified a number of 0.1 - 10 µs isomers and measured detailed spectroscopic properties. Purpose: The purpose of this analysis was to identify and measure the properties of short-lived isomeric states populated following β decay in Z ≈ 30, N ≈ 50 nuclei near the doubly magic nucleus 78 Ni. Methods: Here, radioactive ions produced by beam fragmentation at the National Superconducting Cyclotron Laboratory were implanted into a CeBr 3 scintillator coupled to a pixelated photomultiplier tube. Ancillary arrays of HPGe clover and LaBr 3 detectors were positioned around the implantation detector to measure β-delayed γ rays. Results: The previously observed 2634-keV level in 76 Zn, populated following the β decay of 76 Cu, was identified as isomeric with a half-life of 25.4(4) ns. A combination of timing and γ-ray spectroscopy was used to confirm this assignment. Shell-model calculations were performed and indicate that this state may be a high-spin negativeparity state formed by the occupation of the ν0g 9/2 orbital. Conclusions: A new isomeric state in 76 Zn has been identified and its half-life was measured. Ambiguity about the structure of this state could be resolved with further experiments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Methods of controllable interstitial oxygen doping in niobium

A method for vacuum heat treating Nb, such as is used in superconducting radio frequency cavities, to engineer the interstitial oxygen profile with depth into the surface to conveniently optimize the low-temperature rf surface resistance of the material. An example application is heating of 1.3 GHz accelerating structures between 250-400° C. to achieve a very high quality factor of 5×1010 at 2.0 K. With data supplied by secondary ion mass spectrometry measurements, application of oxide decomposition and oxygen diffusion theory was applied to quantify previously unknown parameters crucial in achieving the oxygen alloy concentration profiles required to optimize the rf surface resistance. RF measurements of vacuum heat treated Nb superconducting radio frequency cavities confirmed the minimized surface resistance (higher Q0) previously expected only from 800° C. diffusive alloying with nitrogen.

Palczewski, Ari D.↗
DOE OSTI2021

Variational Discrete Action Theory

In this work, we propose the variational discrete action theory (VDAT) to study the ground state properties of quantum many-body Hamiltonians. VDAT is a variational theory based on the sequential product density matrix (SPD) ansatz, characterized by an integer $\mathscr{N}$, which monotonically approaches the exact solution with increasing $\mathscr{N}$. To evaluate the SPD, we introduce a discrete action and a corresponding integer time Green’s function. We use VDAT to exactly evaluate the SPD in two canonical models of interacting electrons: the Anderson impurity model and the d = ∞ Hubbard model. For the latter, we evaluate $\mathscr{N}$ = 2 – 4, where $\mathscr{N}$ = 2 recovers the Gutzwiller approximation (GA), and we show that $\mathscr{N}$ = 3, which exactly evaluates the Gutzwiller-Baeriswyl wave function, provides a truly minimal yet precise description of Mott physics with a cost similar to that of the GA. VDAT is a flexible theory for studying quantum Hamiltonians, competing both with state-of-the-art methods and simple, efficient approaches all within a single framework.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

MgPd 2 Sb : A Mg-based Heusler-type superconductor

Here, we report the synthesis and physical properties of a full Heusler compound, MgPd 2 Sb, which we found to show superconductivity below T c = 2.2 K . MgPd 2 Sb was obtained by a two-step solid-state reaction method and its purity and cubic crystal structure [Fm-3m, a = 6.4523(1) Å ] were confirmed by powder x-ray diffraction. Normal and superconducting states were studied by electrical resistivity, magnetic susceptibility, and heat capacity measurements. The results show that MgPd 2 Sb is a type-II, weak coupling superconductor ( λ e-p = 0.53 ). The observed pressure dependence of T c (ΔT c /p ≈ -0.23 K / GPa ) is one of the strongest reported for a superconducting Heusler compound. The electronic structure, phonons, and electron-phonon coupling in MgPd 2 Sb were theoretically investigated. The obtained results are in agreement with the experiment, confirming the electron-phonon coupling mechanism of superconductivity. We compare the superconducting parameters to those of all reported Heusler-type superconductors.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Superconductivity in electron-doped PbBi 2 ⁢Te 4

Single crystals of In-doped PbBi 2 ⁢Te 4 are synthesized via a conventional solid-state method. Chemical analysis and Hall measurements indicate that In replaces Pb, introducing n-type carriers, creating Pb 1–x ⁢In x ⁢Bi 2 ⁢Te 4 . A superconducting transition is observed with a maximum transition temperature around 2.06 K for Pb 1–x⁢ In x ⁢Bi 2 ⁢Te 4 . Field-dependent transport measurements reveal type-II superconductivity and yield a maximum upper critical field around 1.55 T. Thermodynamic data indicates bulk superconductivity in the BCS weak-coupling limit. Finally, our findings establish an ambient-pressure superconducting system in the AM 2 ⁢X 4 family, and doped PbBi 2 ⁢Te 4 as a promising platform for the study of topological superconductivity.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Analysis of diagonal G and subspace W approximations within fully self-consistent GW calculations for bulk semiconducting systems

Fully self-consistent GW (sc-GW) methods are now available to evaluate quasiparticle and spectral properties of various molecular and bulk systems. However, such techniques based on the full matrix of G and W are computationally demanding. Additionally, the routinely used single-shot GW approximation (G 0 W 0 ) has an undesirable dependency on the choice of initial exchange-correlation functional. In the literature, many so-called self-consistent GW methods are based on diagonal approximation of G and low-ranking approximation of W. It is thus worth checking how good such approximations are in comparison with the full matrix method. In this work, we consider AlAs, AlP, GaP, and ZnS as the prototype systems to perform sc-GW calculations by expressing the full G matrix using a plane-wave basis set. We compared our sc-GW results with the diagonal G and subspace W approximated sc-GW results (sc-GW-diagG and sc-GW-subW methods). In the sc-GW-diagG method, interacting G is expanded in the eigenvectors of noninteracting G such that only diagonal elements are retained, whereas the number of eigenmodes is truncated in sc-GW-subW calculations. A systematic analysis of the results obtained from the above techniques is presented. The differences in the quasiparticle band gap between the approximated and the full matrix sc-GW approaches are mostly less than 1.7%, which validates such widely adopted approximations, and also shows how such low-ranking approximation can be used to include higher-order terms such as the vertex correction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Characterization of Microwave Loss Using Multimode Superconducting Resonators

Measuring the losses arising from different materials and interfaces is crucial to improving the coherence of superconducting quantum circuits. Although this has been of interest for a long time, current studies can either only provide bounds to those losses, or require several devices for a complete characterization. In this work, we introduce a method to measure the microwave losses of materials and interfaces with a single multi-mode superconducting resonator. We demonstrate a formalism for analyzing the loss sensitivity of multi-mode systems and discuss the design strategies of multi-mode resonators for material loss studies. We present two types of multi-mode superconducting resonators for the study of bulk superconductors: the forky whispering-gallery-mode resonator (FWGMR) and the ellipsoidal cavity. We use these resonators to measure the surface dielectric, conductor, and seam losses of high-purity (5N5) aluminum and aluminum alloy (6061), as well as how they are affected by chemical etching, diamond turning, and thin-film coating. Here, we find that chemical etching and diamond turning reduce both the surface dielectric and conductive losses of high-purity aluminum, but provide no appreciable improvement to the seam. Coating the surfaces of diamond-turned aluminum alloys with e-beam evaporated or sputtered aluminum thinfilms significantly reduces all three losses under study. In addition, we study the effect of chemical etching on the surface of high-purity aluminum using transmission electron microscopy (TEM) and find that the chemical etching process creates a thinner and more uniform oxide layer, consistent with the observed improvement in the surface dielectric loss.

25 ENERGY STORAGE↗
DOE OSTI2021

Self-consistently renormalized spin-wave theory of layered ferromagnets on the honeycomb lattice

We develop a self-consistently renormalized spin-wave theory, within a mean-field approximation, for the two-dimensional Heisenberg ferromagnet with perpendicular easy-axis anisotropy on the honeycomb lattice, as well as its few-layer and bulk extensions. In this method, the magnetization dependence on temperature is found as the solution of the self-consistency equation. Furthermore, we account for the physical difference of surface and bulk layers by treating the layers as separate sublattices. Thus the method can be readily generalized to study various magnetic phenomena in a broad range of systems, including those comprising magnetically inequivalent sublattices. Using our theory, we calculate the temperature-dependent magnetization for two chromium-based layered van der Waals insulating magnets, Cr 2 Ge 2 Te 6 and CrI 3 , employing various sets of Heisenberg exchange and single-ion anisotropy values reported for these materials in the existing literature. As expected, we observe a strong dimensionality effect where the ordering temperature is reduced and its sensitivity on the anisotropy is enhanced with the decrease of dimensionality.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Accelerating Ultrafast Spectroscopy with Compressive Sensing

We report ultrafast spectroscopy is an important tool for studying photoinduced dynamical processes in atoms, molecules, and nanostructures. Typically, the time to perform these experiments ranges from several minutes to hours depending on the choice of spectroscopic method. It is desirable to reduce this time overhead not only to shorten time and laboratory resources, but also to make it possible to examine fragile specimens that quickly degrade during long experiments. In this article, we motivate using compressive sensing to significantly shorten data acquisition time by reducing the total number of measurements in ultrafast spectroscopy. We apply this technique to experimental data from ultrafast transient absorption spectroscopy and ultrafast terahertz spectroscopy and show that good estimates can be obtained with as low as 15% of the total measurements, implying a sixfold reduction in the data acquisition time.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Synergetic Ferroelectricity and Superconductivity in Zero-Density Dirac Semimetals near Quantum Criticality

Here, we study superconductivity in a three-dimensional zero-density Dirac semimetal in proximity to a ferroelectric quantum critical point. We find that the interplay of criticality, inversion-symmetry breaking, and Dirac dispersion gives rise to a robust superconducting state at the charge-neutrality point, where no Fermi surface is present. Using Eliashberg theory, we show that the ferroelectric quantum critical point is unstable against the formation of a ferroelectric density wave (FDW), whose fluctuations, in turn, lead to a first-order superconducting transition. Surprisingly, long-range superconducting and FDW orders are found to cooperate with each other, in contrast to the more usual scenario of phase competition. Therefore, we suggest that driving charge neutral Dirac materials, e.g., Pb x Sn 1–x Te, through a ferroelectric quantum critical point may lead to superconductivity intertwined with FDW order.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Developing and Running Quantum Algorithms for Chemistry and Materials (QAChMat) (Final Technical Report)

The goal of the project is to design, develop, and execute new computational methods on practical quantum computing platforms to simulate hard problems in chemical and materials sciences. We exploited the two leading quantum computing platforms of trapped atomic ion and superconducting qubits, established in laboratories at Duke University and the University of Maryland, to discover new simulation and computational methods for the study of quantum chemistry and materials.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Phase Transitions and the Thermodynamic Properties of the Potts Model with the Number of Spin States q = 4 on a Triangular Lattice

The phase transitions and the thermodynamic properties of the two-dimensional ferromagnetic Potts model with the number of spin states q = 4 on a triangular lattice are studied on the base of the Wang–Landau algorithm of the Monte Carlo method. The phase transition characters are analyzed using the method of the four-order Binder cumulants and the histogram analysis of the data. It is found that a first-order phase transition is observed in the model under study.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Spectral function of the Holstein polaron at finite temperature

Here we compute the Holstein polaron spectral function on a one-dimensional ring using the finite-temperature T Lanczos method. With increasing T additional features in the spectral function emerge even at temperatures below the phonon frequency. We observe a substantial spread of the spectral weight towards lower frequencies and the broadening of the quasiparticle (QP) peak. In the weak-coupling regime the QP peak merges with the continuum in the high-T limit. In the strong-coupling regime the main features of the low-T spectral function remain detectable up to the highest T used in our calculations. The effective polaron mass shows a nonmonotonic behavior as a function of T at small phonon frequency but increases with T at larger frequencies. The self-energy remains k independent even at elevated T in the frequency range corresponding to the polaron band, while at higher frequencies it develops a distinguishable k dependence. Analytical expressions for the first few frequency moments are derived, and they agree well with those extracted from numerical calculations in a wide-T regime.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗