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DOE OSTI2019

On the road to per cent accuracy – III. Non-linear reaction of the matter power spectrum to massive neutrinos

ABSTRACT We analytically model the non-linear effects induced by massive neutrinos on the total matter power spectrum using the halo model reaction framework of Cataneo et al. In this approach, the halo model is used to determine the relative change to the matter power spectrum caused by new physics beyond the concordance cosmology. Using standard fitting functions for the halo abundance and the halo mass–concentration relation, the total matter power spectrum in the presence of massive neutrinos is predicted to per cent-level accuracy, out to $k=10 \,{ h}\,{\rm Mpc}^{-1}$. We find that refining the prescriptions for the halo properties using N-body simulations improves the recovered accuracy to better than 1 per cent. This paper serves as another demonstration for how the halo model reaction framework, in combination with a single suite of standard Λ cold dark matter (ΛCDM) simulations, can recover per cent-level accurate predictions for beyond ΛCDM matter power spectra, well into the non-linear regime.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2025

Linear magnetoconductivity as a probe of time-reversal symmetry breaking

Several optical experiments have shown that in magnetic materials, the principal axes of response tensors can rotate as an odd function of an applied magnetic field. Here we offer a microscopic explanation of this effect, and we propose a closely related dc transport phenomenon—an off-diagonal symmetric conductivity, linear and odd in a magnetic field, which we refer to as linear magnetoconductivity (LMC). Although LMC has the same functional dependence on a magnetic field as the Hall effect, its origin is fundamentally different: LMC requires time-reversal symmetry to be broken even before a magnetic field is applied, and is therefore a sensitive probe of magnetism. We demonstrate LMC in three different ways: via a tight-binding toy model, a density functional theory calculation on MnPSe3, and a semiclassical treatment. The third approach identifies two distinct mechanisms yielding LMC: momentum-dependent band magnetization and Berry curvature. Finally, we propose an experimental geometry suitable for detecting LMC, and we demonstrate its applicability using Landauer-Büttiker simulations. Our results emphasize the importance of measuring the full conductivity tensor in magnetic materials, and they introduce LMC as a new transport probe of symmetry.

Sunko, V↗

DOE OSTI2015

Optimal mode transformations for linear-optical cluster-state generation

In this paper, we analyze the generation of linear-optical cluster states (LOCSs) via sequential addition of one and two qubits. Existing approaches employ the stochastic linear-optical two-qubit controlled-Z (CZ) gate with success rate of 1/9 per operation. The question of optimality of the CZ gate with respect to LOCS generation has remained open. We report that there are alternative schemes to the CZ gate that are exponentially more efficient and show that sequential LOCS growth is indeed globally optimal. We find that the optimal cluster growth operation is a state transformation on a subspace of the full Hilbert space. Finally, we show that the maximal success rate of postselected entangling n photonic qubits or m Bell pairs into a cluster is (1/2) n-1 and (1/4) m-1 , respectively, with no ancilla photons, and we give an explicit optical description of the optimal mode transformations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2025

Tomography of longitudinal phase space linearization for the generation of attosecond electron bunches

The generation of electron bunches on the attosecond timescale is important for a multitude of accelerator-based applications. Here, we report on a tomographic measurement of the (pre)linearized longitudinal phase space of a low charge 3 MeV electron bunch generated with the 1.6 cell Pegasus photoinjector for the generation of attosecond bunches. The nonlinear correlations in the longitudinal phase space induced by space charge at the photocathode, radiofrequency field curvature of the gun, and vacuum dispersion are compensated using a compact X-band linearizer. Then, the initial and compensated phase of the picosecond electron bunch is precisely reconstructed by neural network assisted tomographic reconstruction from momentum spectra at varying buncher linac phase. Finally, we combine the measured phase space shape with particle tracking simulations to show that electron bunches as short as 941 as develop downstream the beamline.

Beam control↗

DOE OSTI2021

Tunable Plasma Linearizer for Compensation of Nonlinear Energy Chirp

The removal of undesired nonlinear time-energy correlation (energy chirp) present in relativistic electron beams is crucial for many accelerator-based scientific applications, such as free-electron lasers, high-energy electron radiography, and MeV ultrafast electron microscopy. Here, we propose and demonstrate that a low-density plasma section can be used as a passive “linearizer” to significantly compensate for the nonlinear energy chirp imprinted on a beam by the curvature of the radio-frequency field in a conventional accelerator. Physically, the passage of the beam through the plasma excites a strong quasi-cosinoidal longitudinal decelerating wakefield that acts to mitigate the beam’s nonlinear energy chirp by superimposing a reverse chirp on the beam. Time-resolved phase-space measurements, combined with high-fidelity three-dimensional particle-in-cell simulations show that the longitudinal phase space of the beam core is almost completely linearized, leading to a fourfold reduction of the beam overall energy spread from 0.148% to 0.036% (FWHM).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

Giant linear magnetoelectric effect at the morphotropic phase boundary of epitaxial Sr 0.5 Ba 0.5 MnO 3 films

First-principles calculations are conducted to compute linear magnetoelectric coupling coefficients in epitaxial (001) Sr 0.5 Ba 0.5 MnO 3 films. A large enhancement of different linear magnetoelectric elements is found in a strained-induced morphotropic phase boundary region. Such enhancement is demonstrated to originate from the behavior of the dielectric susceptibility, thanks to a simple phenomenological model that is presently shown to be relevant and accurate. Finally, this work can thus provide a promising approach towards designing highly desired single-phase multiferroic with a colossal magnetoelectric conversion.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2015

Anisotropic magnetotransport and exotic longitudinal linear magnetoresistance in WTe 2 crystals

Recently, the WTe 2 semimetal, as a typical layered transition-metal dichalcogenide, attracted much attention due to an extremely large, non-saturating parabolic magnetoresistance in the perpendicular field. Here, we report a systematic study of the angular dependence of the magnetoresistance in a WTe 2 single crystal. The significant anisotropic magnetotransport behavior in different magnetic field directions and violation of the Kohler's rule are observed. Unexpectedly, when the applied field and excitation current are both parallel to the tungsten chains of WTe 2 , an exotic large longitudinal linear magnetoresistance as high as 1200% at 15T and 2K is identified. These results imply that the WTe 2 semimetal, due to its balanced hole and electron populations, seems to be the first material for which a large longitudinal linear magnetoresistance appears when the external magnetic field is parallel to the applied current. Finally, our work may stimulate studies of double-carrier correlated materials and the corresponding quantum physics.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Energy level alignment of self-assembled linear chains of benzenediamine on Au(111) from first principles

Using density functional theory (DFT) with van der Waals functionals, we calculate the adsorption energetics and geometry of benzenediamine (BDA) molecules on Au(111) surfaces. Our results demonstrate that the reported self-assembled linear chain structure of BDA, stabilized via hydrogen bonds between amine groups, is energetically favored over previously-studied monomeric phases. Moreover, using a model based on many-body perturbation theory within the GW approximation, we obtain approximate self-energy corrections to the DFT highest occupied molecular orbital (HOMO) energy associated with BDA adsorbate phases. As a result, we find that, independent of coverage, the HOMO energy of the linear chain phase is lower relative to the Fermi energy than that of the monomer phase, and in good agreement with values measured with ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2019

Dynamic linear response quantum algorithm

The dynamic linear response of a quantum system is critical for understanding both the structure and dynamics of strongly interacting quantum systems, including neutron scattering from materials, photon and electron scattering from atomic systems, and electron and neutrino scattering by nuclei. Here, we present a general algorithm for universal quantum computers to calculate the dynamic linear response function with controlled errors and to obtain information about specific final states that can be directly compared to experimental observations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2022

Quantum computation of nuclear observables involving linear combinations of unitary operators

Here we present the quantum computation of nuclear observables where the operators of interest are first decomposed in terms of the linear combination of unitaries. Then we utilize the Hadamard test and the linear combination of unitaries based methods to compute the expectation values. We apply these methods to calculate the electric quadrupole moment of the deuteron. The results are compared for the Jordan-Wigner transformation and Gray code encoding. We discuss the versatility of our approach that can be utilized in general to calculate several observables on a quantum computer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2016

One-dimensionality in atomic nuclei: A candidate for linear-chain α clustering in C 14

During the clustering of particles in atomic nuclei, the self-organization of various geometrical arrangements at the femtometer scale are produced as a result. Furthermore, the one-dimensional alignment of multiple a particles is known as linear-chain structure, evidence of which has been highly elusive. Here, we show via resonant elastic and inelastic a scattering of a radioactive Be-10 beam that excited states in the neutron-rich nucleus C-14 agree with recent predictions of linear-chain structure based on an antisymmetrized molecular dynamics model.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2020

Detecting axionlike dark matter with linearly polarized pulsar light

QCD axions or axionlike particles are among the most popular candidates for cold dark matter (DM) in the Universe. We proposed to detect axionlike DM, using linearly polarized pulsar light as a probe. Because of birefringence effect potentially caused by an oscillating galactic axion DM background, when pulsar light travels across the Galaxy, its linear polarization angle may vary with time. With a soliton + NFW galactic DM halo profile, we show that this strategy can potentially probe an axion-photon coupling as small as ~10 –13 GeV –1 for axion mass $m_a$ ~ 10 –22 –10 –20 eV , given the current measurement accuracy. An exclusion limit stronger than CAST (~ 10 –10 GeV –1 ) and SN1987A (~ 10 –11 GeV –1 ) could be extended up to $m_a$ ~ 10 –18 eV and ~10 –19 eV, respectively.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2024

Neutrino fast flavor oscillations with moments: Linear stability analysis and application to neutron star mergers

Providing an accurate modeling of neutrino physics in dense astrophysical environments such as binary neutron star mergers presents a challenge for hydrodynamic simulations. Nevertheless, understanding how flavor transformation can occur and affect the dynamics, the mass ejection, and the nucleosynthesis will need to be achieved in the future. Computationally expensive, large-scale simulations frequently evolve the first classical angular moments of the neutrino distributions. By promoting these quantities to matrices in flavor space, we develop a linear stability analysis of fast flavor oscillations using only the first two “quantum” moments, which notably requires generalizing the classical closure relations that appropriately truncate the hierarchy of moment equations in order to treat quantum flavor coherence. After showing the efficiency of this method on a well-understood test situation, we perform a systematic search of the occurrence of fast flavor instabilities in a neutron star merger simulation. Here, we discuss the successes and shortcomings of moment linear stability analysis, as this framework provides a time-efficient way to design and study better closure prescriptions in the future.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2019

Cosmic distance inference from purely geometric BAO methods: Linear point standard ruler and correlation function model fitting

Leveraging the baryon acoustic oscillations (BAO) feature present in clustering 2-point statistics, we aim to measure cosmological distances independently of the underlying background cosmological model. However this inference is complicated by late-time nonlinearities that introduce model and tracer dependencies in the clustering correlation function and power spectrum, which must be properly accounted for. With this in mind, we introduce the “purely geometric-BAO,” which provides a rigorous tool to measure cosmological distances without assuming a specific background cosmology. We focus on the 2-point clustering correlation function monopole, and show how to implement such an inference scheme employing two different methodologies: the linear point standard ruler (LP) and correlation-function model-fitting (CF-MF). For the first time we demonstrate how, by means of the CF-MF, we can measure very precisely the sound-horizon/isotropic-volume-distance ratio, r d /DV(z¯), while correctly propagating all the uncertainties. Using synthetic data, we compare the outcomes of the two methodologies, and find that the LP provides up to 50% more precise measurements than the CF-MF. Finally, we test a procedure widely employed in BAO analyses: fitting the 2-point function while fixing the cosmological and the non-linear-damping parameters at fiducial values. We find that this underestimates the distance errors by nearly a factor of 2. Furthermore, we recommend that this practice be reconsidered, whether for parameter determination or model selection.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

Linear magnetoresistance caused by mobility fluctuations in n -doped Cd 3 As 2

Cd 3 As 2 is a candidate three-dimensional Dirac semimetal which has exceedingly high mobility and nonsaturating linear magnetoresistance that may be relevant for future practical applications. We report magnetotransport and tunnel diode oscillation measurements on Cd 3 As 2 , in magnetic fields up to 65 T and temperatures between 1.5 and 300 K. We find that the nonsaturating linear magnetoresistance persists up to 65 T and it is likely caused by disorder effects, as it scales with the high mobility rather than directly linked to Fermi surface changes even when approaching the quantum limit. As a result of the observed quantum oscillations, we determine the bulk three-dimensional Fermi surface having signatures of Dirac behavior with a nontrivial Berry phase shift, very light effective quasiparticle masses, and clear deviations from the band-structure predictions. In very high fields we also detect signatures of large Zeeman spin splitting (g~16).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2016

Self-sustained micro mechanical oscillator with linear feedback

Autonomous oscillators, such as clocks and lasers, produce periodic signals without any external frequency reference. In order to sustain stable periodic motions, there needs to be external energy supply as well as nonlinearity built into the oscillator to regulate the amplitude. Usually, nonlinearity is provided by the sustaining feedback mechanism, which also supplies energy, whereas the constituent resonator that determines the output frequency stays linear. Here we propose a new self-sustaining scheme that relies on the nonlinearity originating from the resonator itself to limit the oscillation amplitude, while the feedback remains linear. We introduce a model to describe the working principle of the self-sustained oscillations and validate it with experiments performed on a nonlinear microelectromechanical (MEMS) based oscillator.

42 ENGINEERING↗

DOE OSTI2019

Electron-Phonon Coupling from Ab Initio Linear-Response Theory within the G W Method: Correlation-Enhanced Interactions and Superconductivity in Ba 1 - x K x BiO 3

We present a new first-principles linear-response theory of changes due to perturbations in the quasiparticle self-energy operator within the GW method. This approach, named GW perturbation theory ( GW PT), is applied to calculate the electron-phonon ( e -ph) interactions with the full inclusion of the GW nonlocal, energy-dependent self-energy effects, going beyond density-functional perturbation theory. Avoiding limitations of the frozen-phonon technique, GW PT gives access to e -ph matrix elements at the GW level for all phonons and scattering processes, and the computational cost scales linearly with the number of phonon modes (wave vectors and branches) investigated. We demonstrate the capabilities of GW PT by studying the e -ph coupling and superconductivity in Ba 0.6 K 0.4 BiO 3 . We show that many-electron correlations significantly enhance the e -ph interactions for states near the Fermi surface, and explain the observed high superconductivity transition temperature of Ba 0.6 K 0.4 BiO 3 as well as its doping dependence.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2020

Emergence of Topologically Nontrivial Spin-Polarized States in a Segmented Linear Chain

The synthesis of new materials with novel or useful properties is one of the most important drivers in the fields of condensed matter physics and materials science. Discoveries of this kind are especially significant when they point to promising future basic research and applications. Van der Waals bonded materials comprised of lower-dimensional building blocks have been shown to exhibit emergent properties when isolated in an atomically thin form. Here, we report the discovery of a transition metal chalcogenide in a heretofore unknown segmented linear chain form, where basic building blocks each consisting of two hafnium atoms and nine tellurium atoms (Hf 2 Te 9 ) are van der Waals bonded end-to-end. First-principle calculations based on density functional theory reveal striking crystal-symmetry-related features in the electronic structure of the segmented chain, including giant spin splitting and nontrivial topological phases of selected energy band states. In this work, atomic-resolution scanning transmission electron microscopy reveals single segmented Hf 2 Te 9 chains isolated within the hollow cores of carbon nanotubes, with a structure consistent with theoretical predictions. Van der Waals-bonded segmented linear chain transition metal chalcogenide materials could open up new opportunities in low-dimensional, gate-tunable, magnetic and topological crystalline systems.

36 MATERIALS SCIENCE↗