Search NASA⌕ Search

SEARCH · Search NASA

Results for “emerging modes”

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.

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Transport in helical Luttinger liquids in the fractional quantum Hall regime

Abstract Domain walls in fractional quantum Hall ferromagnets are gapless helical one-dimensional channels formed at the boundaries of topologically distinct quantum Hall (QH) liquids. Naïvely, these helical domain walls (hDWs) constitute two counter-propagating chiral states with opposite spins. Coupled to an s-wave superconductor, helical channels are expected to lead to topological superconductivity with high order non-Abelian excitations 1–3 . Here we investigate transport properties of hDWs in the ν = 2/3 fractional QH regime. Experimentally we found that current carried by hDWs is substantially smaller than the prediction of the naïve model. Luttinger liquid theory of the system reveals redistribution of currents between quasiparticle charge, spin and neutral modes, and predicts the reduction of the hDW current. Inclusion of spin-non-conserving tunneling processes reconciles theory with experiment. The theory confirms emergence of spin modes required for the formation of fractional topological superconductivity.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

The Role of Seasonality and the ENSO Mode in Central and East Pacific ENSO Growth and Evolution

Abstract A cyclostationary linear inverse model (CSLIM) is used to investigate the seasonal growth of tropical Pacific Ocean El Niño–Southern Oscillation (ENSO) events with canonical, central Pacific (CP), or eastern Pacific (EP) sea surface temperature (SST) characteristics. Analysis shows that all types of ENSO events experience maximum growth toward final states occurring in November and December. ENSO events with EP characteristics also experience growth into May and June, but CP events do not. A single dominant “ENSO mode,” growing from an equatorial heat content anomaly into a characteristic ENSO-type SST pattern in about 9 months (consistent with the delayed/recharge oscillator model of ENSO), is essential for the predictable development of all ENSO events. Notably, its seasonality is responsible for the late-calendar-year maximum in ENSO amplification. However, this ENSO mode alone does not capture the observed growth and evolution of diverse ENSO events, which additionally involve the seasonal evolution of other nonorthogonal Floquet modes. EP event growth occurs when the ENSO mode is initially “covered up” in combination with other Floquet modes. The ENSO mode’s slow seasonal evolution allows it to emerge while the other modes rapidly evolve and/or decay, leading to strongly amplifying and more predictable EP events. CP events develop when the initial state has a substantial contribution from Floquet modes with meridional mode–like SST structures. Thus, while nearly all ENSO events involve the seasonally varying ENSO-mode dynamics, the diversity and predictability of ENSO events cannot be understood without identifying contributions from the remaining Floquet modes. Significance Statement The purpose of this study is to identify structures that lead to seasonal growth of diverse types of El Niño–Southern Oscillation (ENSO) events. An important contribution from this study is that it uses an observationally constrained, empirically derived seasonal model. We find that processes affecting the evolution of diverse ENSO events are strongly seasonally dependent. ENSO events with eastern equatorial Pacific sea surface temperature (SST) characteristics are closely related to a single “ENSO mode” that resembles theoretical models of ENSO variability. ENSO events that have central equatorial Pacific SST characteristics include contributions from additional “meridional mode” structures that evolve via different physical processes. These findings are an important step in evaluating the seasonal predictability of ENSO diversity.

Vimont, Daniel J.↗
DOE OSTI2021

Constraints on quasinormal modes and bounds for critical points from pole-skipping

We consider a holographic thermal state and perturb it by a scalar operator whose associated real-time Green’s function has only gapped poles. These gapped poles correspond to the non-hydrodynamic quasinormal modes of a massive scalar perturbation around a Schwarzschild black brane. Relations between pole-skipping points, critical points and quasinormal modes in general emerge when the mass of the scalar and hence the dual operator dimension is varied. First, this novel analysis reveals a relation between the location of a mode in the infinite tower of quasinormal modes and the number of pole-skipping points constraining its dispersion relation at imaginary momenta. Second, for the first time, we consider the radii of convergence of the derivative expansions about the gapped quasinormal modes. These convergence radii turn out to be bounded from above by the set of all pole-skipping points. Furthermore, a transition between two distinct classes of critical points occurs at a particular value for the conformal dimension, implying close relations between critical points and pole-skipping points in one of those two classes. We show numerically that all of our results are also true for gapped modes of vector and tensor operators.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Vacancies and spin-phonon coupling in CrSi 0.8 Ge 0.1 Te 3

We report temperature-dependent Raman scattering and magnetization studies of van der Waals ferromagnetic compound CrSi 0.8 Ge 0.1 Te 3 . Magnetic susceptibility measurements revealed dominant ferromagnetic interactions below T C which shift to the lower values due to the presence of vacancies. A Raman active mode, additional to the ones predicted by symmetry in the parent compounds, has been observed. This A g symmetry mode most likely emerges as a consequence of the atomic vacancies on Si/Ge site. Presence of the strong spin–phonon coupling at temperature around 210 K is indicated by deviations from conventional phonon self-energy temperature dependence of all analysed modes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Study on Application of Distributed Network of Sensors with List Mode for NMAC Literature Review

Nuclear material accounting and control (NMAC) for nuclear security detects, deters, and resolves questions related to unauthorized removal (i.e. theft) or misuse of nuclear material. NMAC also serves as a key insider threat mitigation measure and aids in recovery of nuclear material that is missing. Effective nuclear security depends on NMAC for timely and accurate information about nuclear material types, quantities, and locations. Bulk nuclear material processing facilities, however, present unique challenges for effective NMAC due to the presence of large quantities of material in-process and the accumulation of residual material holdup within process equipment. These holdup accumulations can obscure accurate physical inventory taking and complicate efforts to resolve NMAC irregularities at the facility level. Bulk material monitoring systems often rely on material balance calculations and indirect measurement techniques, which may mask protracted theft of smaller amounts of nuclear material. These monitoring limitations have generated increased interest in continuous monitoring technologies, including distributed non-destructive assay (NDA) sensor networks capable of providing real-time or near-real-time measurement of material movement and accumulation within bulk processing environments. Recent advancements in distributed networks of NDA radiation detectors and sensing technologies provide an opportunity to address these limitations. Although such distributed sensor networks have been implemented in select facilities for IAEA Safeguards applications, their potential for supporting NMAC functions specifically tailored to nuclear security objectives remains largely unexplored. Furthermore, emerging list-mode data acquisition technologies have reached high technology readiness levels, enabling time-correlated detection of nuclear events across multiple temporal scales. These capabilities provide enhanced opportunities for accurate holdup measurement, continuous process monitoring, and improved detection of material theft or misuse over time. The increasing global expansion of civil nuclear power and development of related bulk material processing facilities, including those supporting high-assay low-enriched uranium (HALEU) and other advanced reactor fuel fabrication, further increases the need for advanced measurement and monitoring strategies for NMAC.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

The Role of Optical Phonon Confinement in the Infrared Dielectric Response of III–V Superlattices

Polar dielectrics are key materials of interest for infrared (IR) nanophotonic applications due to their ability to host phonon-polaritons that allow for low-loss, subdiffractional control of light. The properties of phonon-polaritons are limited by the characteristics of optical phonons, which are nominally fixed for most “bulk” materials. Superlattices composed of alternating atomically thin materials offer control over crystal anisotropy through changes in composition, optical phonon confinement, and the emergence of new modes. In particular, the modified optical phonons in superlattices offer the potential for so-called crystalline hybrids whose IR properties cannot be described as a simple mixture of the bulk constituents. To date, however, studies have primarily focused on identifying the presence of new or modified optical phonon modes rather than assessing their impact on the IR response. Here, this study focuses on assessing the impact of confined optical phonon modes on the hybrid IR dielectric function in superlattices of GaSb and AlSb. Using a combination of first principles theory, Raman, FTIR, and spectroscopic ellipsometry, the hybrid dielectric function is found to track the confinement of optical phonons, leading to optical phonon spectral shifts of up to 20 cm -1 . These results provide an alternative pathway toward designer IR optical materials.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Unveiling horizons in quantum critical collapse

Critical gravitational collapse offers a unique window into regimes of arbitrarily high curvature, culminating in a naked singularity arising from smooth initial data — thus providing a dynamical counterexample to weak cosmic censorship. Near the critical regime, quantum effects from the collapsing matter are expected to intervene before full quantum gravity resolves the singularity. Despite its fundamental significance, a self-consistent treatment has so far remained elusive. In this work, we perform a one-loop semiclassical analysis using the robust anomaly-based method in the canonical setup of Einstein gravity minimally coupled to a free, massless scalar field. Focusing on explicitly solvable near-critical solutions in both 2 + 1 and 3 + 1 dimensions, we analytically solve the semiclassical Einstein equations and obtain controlled, quantitative results for several long-standing questions within the dominant s-wave sector. We find that regularity uniquely selects a Boulware-like quantum state, encoding genuine vacuum polarization effects from the collapsing matter. Remarkably, the resulting quantum corrections manifest as a growing mode. Horizon-tracing analyses, incorporating both classical and quantum modes, reveal the emergence of a finite mass gap, signaling a phase transition from classical Type II to quantum-modified Type I behavior, thereby providing a quantum enforcement of the weak cosmic censorship. The most non-trivial aspect of our analysis involves dealing with non-conformal matter fields in explicitly time-dependent critical spacetimes. Along the way, we uncover intriguing and previously underexplored features of quantum field theory in curved spacetime.

2D Gravity↗
DOE OSTI2023

Tunable ferroelectricity in oxygen-deficient perovskites with Grenier structure

Using first-principles calculations, we predict that tunable ferroelectricity can be realized in oxide perovskites with the Grenier structure and ordered oxygen vacancies. Specifically, we show that R 1/3 A 2/3 FeO 2.67 solids (where R is a rare-earth ion and A an alkaline-earth cation) exhibit polar phases, with a spontaneous polarization tunable by an appropriate choice of R and A. We find that larger cations combined with small R elements lead to a maximum in the polarization and to a minimum in the energy barriers required to switch the sign of the polarization. Ferroelectricity arises from cooperative distortions of octahedral and tetrahedral units, where a combination of rotational and sliding modes controls the emergence of polarization within three-dimensional connected layers. Our results indicate that polar Grenier phases of oxide perovskites are promising materials for microelectronic applications and, in general, for the study of phenomena emerging from breaking inversion symmetry in solids.

Electronic devices↗
DOE OSTI2020

Impact of stalk on directly driven inertial confinement fusion implosions

Low-mode asymmetries have emerged as one of the primary challenges to achieving high-performing inertial confinement fusion (ICF) implosions. In direct-drive ICF, an important potential seed of such asymmetries is the capsule stalk mount, the impact of which has remained a contentious question. In this paper, we describe the results from an experiment on the OMEGA laser with intentional offsets at varying angles to the capsule stalk mount, which clearly demonstrates the impact of the stalk mount on implosion dynamics. The angle between stalk and offset is found to significantly impact observables. Specifically, a larger directional flow is observed in neutron spectrum measurements when the offset is toward rather than away from the stalk, while an offset at 42° to the stalk gives minimal directional flow but still generates a large flow field in the implosion. No significant directional flow is seen due to stalk only. Time-integrated x-ray images support these flow observations. A trend is also seen in implosion yield, with lower yield obtained for offsets with a smaller angle than with a larger angle toward the stalk. Radiation hydrodynamic simulations using 2D DRACO and 2D/3D Chimera not including the stalk mount and using 2D xRAGE including the stalk mount are brought to bear on the data. The yield trend, the minimal directional flow with stalk only, and the larger flow enhancement observed with the offset toward the stalk are all reproduced in the xRAGE simulations. Finally, the results strongly indicate that the stalk impact must be considered and mitigated to achieve high-performing implosions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Natural hot-ion modes in a rotating plasma

We report that in steady state, the fuel cycle of a fusion plasma requires inward particle fluxes of fuel ions. These particle flows are also accompanied by heating. In the case of classical transport in a rotating cylindrical plasma, this heating can proceed through several distinct channels depending on the physical mechanisms involved. Some channels directly heat the fuel ions themselves, whereas others heat electrons. Which channel dominates depends, in general, on the details of the temperature, density and rotation profiles of the plasma constituents. However, remarkably, under relatively few assumptions concerning these profiles, if the α particles, the by-products of the fusion reaction, can be removed directly by other means, then a hot-ion mode tends to emerge naturally.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Braiding of Majorana zero modes in vortex cores

Here, we demonstrate the successful simulation of $\sqrt{𝑍-}$, $\sqrt{𝑋-}$, and 𝑋-quantum gates using Majorana zero modes (MZMs) that emerge in magnetic vortices located in topological superconductors. We compute the transition probabilities and geometric phase differences accounting for the full many-body dynamics and show that qubit states can be read out by fusing the vortex core MZMs and measuring the resulting charge density. We visualize the gate processes using the time- and energy-dependent nonequilibrium local density of states. Our results demonstrate the feasibility of employing vortex core MZMs for the realization of fault-tolerant topological quantum computing.

Majorana bound states↗
DOE OSTI2025

A study of resistive peeling–ballooning modes across spherical tokamaks

We investigate how non-ideal-magnetohydrodynamics (MHD) effects, in particular plasma resistivity, impact the peeling–ballooning stability thresholds in spherical tokamaks. This analysis follows the discovery of resistive kink-peeling modes in ELMing National Spherical Torus Experiment (NSTX) discharges. In the present study we extend this modeling to ELMing pulses in the Mega Ampere Spherical Tokamak (MAST) and MAST—Upgrade (MAST-U), where we find a clear resistive scaling for peeling–ballooning modes. While in NSTX ideal-MHD predicts stability for ELMing discharges, in MAST-U we find that the plasma is slightly unstable to peeling–ballooning modes, but is fully stabilized once diamagnetic effects are considered in terms of a growth rate normalization. A resistive power law scaling is calculated for these modes on MAST-U, which lies in between that of tearing modes and resistive interchange modes. A comparison between M3D-C1 and NIMROD shows reasonable agreement for this scaling. Resistivity destabilizes the modes and the peeling–ballooning unstable domain is considerably expanded in both, MAST and MAST-U. In addition to the MAST/-U pulses we also analyze resistive PB stability in a NSTX-similarity discharge on DIII-D. While having a different aspect ratio from NSTX, this discharge uses NSTX-like shaping parameters, toroidal field and plasma current. By considering these discharges alongside NSTX cases, we identify conditions influencing the onset of resistive peeling–ballooning modes. Furthermore, our findings indicate that magnetic shear in the pedestal region is closely linked to the emergence of resistive edge modes.

MAST-U↗
DOE OSTI2022

Insights into the possible existence of a soft dipole mode in He 8

With an extreme neutron-to-proton ratio of N/Z = 3, 8 He provides an ideal laboratory for the study of a variety of exotic phenomena, such as the emergence of a soft dipole mode that is dominated by transitions into the continuum. In this contribution, a covariant density-functional theory (DFT) framework is used to compute ground-state properties and the dipole response of 8 He. Although 8 He is admittedly too light for DFT to be applicable, the great merit of the approach is that the spurious contamination associated with the center-of-mass motion is guaranteed to decouple from the physical response. Given that a strong mixing between the isoscalar and isovector dipole modes is expected for a system with such a large neutron-proton asymmetry as 8 He, the narrow structures that emerged at low energies in the isovector dipole response are attributed to the shift of the spurious strength to zero (or near zero) excitation energy. Furthermore, the theoretical framework implemented here disfavors the emergence of a soft dipole mode in 8 He.

6 ≤ A ≤ 19↗
DOE OSTI2025

Two-Frequency RF Fields Induced Multipactor in Coaxial Transmission Lines

Multipactor is a nonlinear discharge phenomenon that occurs in vacuum RF systems, potentially leading to signal distortion, power loss, and even permanent damage to high-power components. This study presents a detailed investigation of two-surface multipactor in coaxial transmission lines under two-frequency excitation, using one-dimensional (1D) Monte Carlo simulations validated by three-dimensional (3D) Particle-in-Cell (PIC) results and experimental data. Introducing a second carrier mode is shown to suppress multipactor by reshaping and shrinking the susceptibility region, with the extent and location of suppression strongly dependent on the device aspect ratio and the relative phase of the second mode. Distinct suppression patterns emerge across different frequency–gap distance (fd) regimes, and in certain cases, susceptibility expansion is also observed. The study identifies and distinguishes pure and mixed multipactor modes in coaxial geometry, where analytical mode boundaries are not readily defined. Unlike planar systems, pure-mode regions in coaxial structures overlap with mixed-mode domains, complicating classification. Image charge forces are found to have minimal effect on susceptibility thresholds but do influence electron growth rates. These findings provide new insights into waveform-driven control of multipactor in high-power RF systems.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Majorana zero modes in impurity-assisted vortex of LiFeAs superconductor

The iron-based superconductor is emerging as a promising platform for Majorana zero mode, which can be used to implement topological quantum computation. One of the most significant advances of this platform is the appearance of large vortex level spacing that strongly protects Majorana zero mode from other low-lying quasiparticles. Despite the advantages in the context of physics research, the inhomogeneity of various aspects hampers the practical construction of topological qubits in the compounds studied so far. Here we show that the stoichiometric superconductor LiFeAs is a good candidate to overcome this obstacle. By using scanning tunneling microscopy, we discover that the Majorana zero modes, which are absent on the natural clean surface, can appear in vortices influenced by native impurities. Our detailed analysis reveals a new mechanism for the emergence of those Majorana zero modes, i.e. native tuning of bulk Dirac fermions. The discovery of Majorana zero modes in this homogeneous material, with a promise of tunability, offers an ideal material platform for manipulating and braiding Majorana zero modes, pushing one step forward towards topological quantum computation.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Phonon-induced collective modes in spin-orbit coupled polar metals

We study the interplay between collective electronic and lattice modes in polar metals in an applied magnetic field aligned with the polar axis. Static spin-orbit coupling leads to the appearance of a particle-hole spin-flip continuum that is gapped at low energies in a finite field. We find that a weak spin-orbit assisted coupling between electrons and polar phonons induces the emergence of electronic collective modes. The strength of the applied magnetic field tunes the number of modes and their energies, which can lie both above and below the particle-hole continuum. For a range of field values, we identify Fano-type interference between the electronic continuum and phonons. Here, we show that signatures of these collective modes can be observed in optical spectroscopy experiments, and we provide the corresponding theoretical predictions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Robust nonlinear isolators based on frozen mode exceptional point degeneracies

We introduce a class of imperfection-protected nonlinear isolators designed to operate at exceptional point degeneracies (EPDs) of the Bloch modes of periodic photonic structures. These Bloch EPDs are responsible for slow light and the emergence of a scattering frozen mode regime (FMR). When a weak spectral asymmetry is introduced, the group velocity in their proximity varies sharply, boosting the directional nature of the nonlinear interactions and leading to extreme isolation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Coupling of electronic transition to ferroelectric order in a 2D semiconductor

A ferroelectric material often exhibits a soft transverse optical (TO) phonon mode which governs its phase transition. Charge coupling to this ferroelectric soft mode may further mediate emergent physical properties, including superconductivity and defect tolerance in semiconductors. However, direct experimental evidence for such coupling is scarce. Here we show that a photogenerated coherent phonon couples strongly to the electronic transition above the bandgap in the van der Waals (vdW) two-dimensional (2D) ferroelectric semiconductor NbOI 2 . Using terahertz time-domain spectroscopy and first-principles calculations, we identify this mode as the TO phonon responsible for ferroelectric order. This exclusive coupling occurs only with the above-gap electronic transition and is absent in the valence band as revealed by resonant inelastic X-ray scattering. Our findings suggest a new role of the soft TO phonon mode in electronic and optical properties of ferroelectric semiconductors.

36 MATERIALS SCIENCE↗