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arXiv 2022年

作者： Waters, Dacen Thompson, Ellis Arreguin-Martinez, Esmeralda Fujimoto, Manato Ren, Yafei Watanabe, Kenji Taniguchi, Takashi Cao, Ting Xiao, Di Yankowitz, Matthew Department of Physics University of Washington SeattleWA98195 United States Intelligence Community Postdoctoral Research Fellowship Program University of Washington SeattleWA98195 United States Department of Materials Science and Engineering University of Washington SeattleWA98195 United States Department of Physics Osaka University Osaka560-0043 Japan Research Center for Functional Materials National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan International Center for Materials Nanoarchitectonics National Institute for Materials Science 1-1 Namiki Tsukuba305-0044 Japan

Moiré patterns formed by stacking atomically-thin van der Waals crystals with a relative twist angle can give rise to dramatic new physical properties [1, 2]. The study of moiré materials has so far been limited to structures comprising no more than a few vdW sheets, since a moiré pattern localized to a single two-dimensional interface is generally assumed to be incapable of appreciably modifying the properties of a bulk three-dimensional crystal. Layered semimetals such as graphite offer a unique platform to challenge this paradigm, owing to distinctive properties arising from their nearly-compensated electron and hole bulk doping. Here, we perform transport measurements of dual-gated devices constructed by slightly rotating a monolayer graphene sheet atop a thin bulk graphite crystal. We find that the moiré potential transforms the electronic properties of the entire bulk graphitic thin film. At zero and small magnetic fields, transport is mediated by a combination of gate-tunable moiré and graphite surface states, as well as coexisting semimetallic bulk states that do not respond to gating. At high field, the moiré potential hybridizes with the graphitic bulk states owing to the unique properties of the two lowest Landau bands of graphite. These Landau bands facilitate the formation of a single quasi–two-dimensional hybrid structure in which the moiré and bulk graphite states are inextricably mixed. Our results establish twisted graphene-graphite as the first in a new class of mixed-dimensional moiré materials. Copyright © 2022, The Authors. All rights reserved.

关键词： Thin films

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Evaluating the Potential to Constrain Dark Matter Annihilation with Fermi-LAT Observations of Ultra-Faint Compact Stellar Systems

arXiv

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arXiv 2024年

作者： Circiello, Antonio McDaniel, Alex Drlica-Wagner, Alex Karwin, Christopher Ajello, Marco Mauro, Mattia Di Sánchez-Conde, Miguel Á. Department of Physics and Astronomy Clemson University 4 ClemsonSC29631 United States Department of Physics and Astronomy Clemson University ClemsonSC29631 United States Fermi National Accelerator Laboratory P.O. Box 500 BataviaIL60510 United States Kavli Institute for Cosmological Physics University of Chicago ChicagoIL60637 United States Department of Astronomy and Astrophysics University of Chicago ChicagoIL60637 United States NASA Postdoctoral Program Fellow NASA Goddard Space Flight Center GreenbeltMD20771 United States Istituto Nazionale di Fisica Nucleare Sezione di Torino Via P. Giuria 1 Torino10125 Italy Instituto de Física Teórica UAM-CSIC Universidad Autónoma de Madrid C/ Nicolás Cabrera 13-15 Madrid28049 Spain Departamento de Física Teórica Universidad Autónoma de Madrid M-15 MadridE-28049 Spain

Recent results from numerical simulations and models of galaxy formation suggest that recently discovered ultra-faint compact stellar systems (UFCSs) in the halo of the Milky Way (MW) may be some of the smallest and faintest galaxies. If this is the case, these systems would be attractive targets for indirect searches of weakly interacting massive particle (WIMP) dark matter (DM) annihilation due to their relative proximity and high expected DM content. In this study, we analyze 14.3 years of gamma-ray data collected by the Fermi-LAT coincident with 26 UFCSs. No significant excess gamma-ray emission is detected, and we present gamma-ray flux upper limits for these systems. Assuming that the UFCSs are dark-matter-dominated galaxies consistent with being among the faintest and least massive MW dwarf spheroidal (dSphs) satellite galaxies, we derive the projected sensitivity for a dark matter annihilation signal. We find that observations of UFCSs have the potential to yield some of the most powerful constraints on DM annihilation, with sensitivity comparable to observations of known dSphs and the Galactic center. This result emphasizes the importance of precise kinematic studies of UFCSs to empirically determine their DM content. Copyright © 2024, The Authors. All rights reserved.

关键词： Stars

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Ramsey Envelope Modulation in NV Diamond Magnetometry

arXiv

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arXiv 2022年

作者： Oon, Jner Tzern Tang, Jiashen Hart, Connor A. Olsson, Kevin S. Turner, Matthew J. Schloss, Jennifer M. Walsworth, Ronald L. Department of Physics University of Maryland College ParkMD20742 United States Quantum Technology Center University of Maryland College ParkMD20742 United States Department of Electrical Engineering and Computer Science University of Maryland College ParkMD20742 United States Intelligence Community Postdoctoral Research Fellowship Program University of Maryland College ParkMD20742 United States Lincoln Laboratory Massachusetts Institute of Technology LexingtonMA02421 United States

Nitrogen-vacancy (NV) spin ensembles in diamond provide an advanced magnetic sensing platform, with applications in both the physical and life sciences. The development of isotopically engineered 15NV diamond offers advantages over naturally occurring 14NV for magnetometry, due to its simpler hyperfine structure. However, for sensing modalities requiring a bias magnetic field not aligned with the sensing NV axis, the absence of a quadrupole moment in the 15N nuclear spin leads to pronounced envelope modulation effects in time-dependent measurements of 15NV spin evolution. While such behavior in spin echo experiments are well studied, analogous effects in Ramsey measurements and the implications for magnetometry remain under-explored. Here, we derive the modulated 15NV Ramsey response to a misaligned bias field, using a simple vector description of the effective magnetic field on the nuclear spin. The predicted modulation properties are then compared to experimental results, revealing significant magnetic sensitivity loss if unaddressed. We demonstrate that double-quantum coherences of the NV S = 1 electronic spin states dramatically suppress these envelope modulations, while additionally proving resilient to other parasitic effects such as strain heterogeneity and temperature shifts. © 2022, CC BY.

关键词： Spin dynamics

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A METHOD OF ENHANCING SOURCE DETECTION SENSITIVITY IN GAUSSIAN NOISE, WITH APPLICATION TO PSR 1937+21 AND GW150914

arXiv

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arXiv 2020年

作者： Lieu, Richard Lackeos, Kristen A. Department of Physics University of Alabama HuntsvilleAL35899 United States NASA Postdoctoral Program Fellow NASA Marshall Space Flight Center HuntsvilleAL35812 United States

The Gaussian phase noise of intensity time series is demonstrated to be drastically reduced when the raw voltage data are digitally filtered through an arbitrarily large number n of orthornormal bandpass profiles (eigen-filters) sharing the same intensity bandwidth, and the resulting intensity series are co-added. Specifically, the relative noise variance of the summed series at the resolution of one coherence time or less, goes down with increasing n as 1/n, although (consistent with the radiometer equation) the advantage gradually disappears when the series is bin averaged to lower resolution. Thus the algorithm is designed to enhance the sensitivity of detecting transients that are smoothed out by time averaging and too faint to be visible in the noisy unaveraged time series, as demonstrated by the simulation of a weak embedded time varying signal of either a periodic nature or a fast and unrepeated pulse. The algorithm is then applied to a 10 minute observation of the pulsar PSR 1937+21 by the VLA, where the theoretical predictions were verified by the data. Moreover, it is shown that microstructures within the time profile are better defined as the number n of filters used increases, and a periodic signal of period 1.86 × 10−5 s (53.9 kHz) is discovered in the pulse profile. Lastly, we apply the algorithm to the first binary black hole merger detected by LIGO, GW150914. We find the SNR of the mean peak intensity increases as √n and cross correlation of the event between the LIGO-Hanford-Livingston detector pair increases with filter order n. Copyright © 2020, The Authors. All rights reserved.

关键词： Time series

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Machine Learning for Improved Current Density Reconstruction from 2D Vector Magnetic Images

arXiv

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arXiv 2024年

作者： Reed, Niko R. Bhutto, Danyal Turner, Matthew J. Daly, Declan M. Oliver, Sean M. Tang, Jiashen Olsson, Kevin S. Langellier, Nicholas Ku, Mark J.H. Rosen, Matthew S. Walsworth, Ronald L. Department of Physics University of Maryland College ParkMD United States Quantum Technology Center University of Maryland College ParkMD United States Joint Quantum Institute University of Maryland College ParkMD United States Department of Biomedical Engineering Boston University BostonMA United States A. A. Martinos Center for Biomedical Imaging Massachusetts General Hospital CharlestownMA United States Department of Electrical and Computer Engineering University of Maryland College ParkMD United States The MITRE Corporation McLeanVA22102 United States Intelligence Community Postdoctoral Research Fellowship Program University of Maryland College ParkMD20742 United States Department of Physics Harvard University CambridgeMA United States Department of Materials Science and Engineering University of Delaware NewarkDE19716 United States Department of Physics and Astronomy University of Delaware NewarkDE19716 United States Harvard Medical School 25 Shattuck St. BostonMA United States

The reconstruction of electrical current densities from magnetic field measurements is an important technique with applications in materials science, circuit design, quality control, plasma physics, and biology. Analytic reconstruction methods exist for planar currents, but break down in the presence of high spatial frequency noise or large standoff distance, restricting the types of systems that can be studied. Here, we demonstrate the use of a deep convolutional neural network for current density reconstruction from two-dimensional (2D) images of vector magnetic fields acquired by a quantum diamond microscope (QDM). Trained network performance significantly exceeds analytic reconstruction for data with high noise or large standoff distances. This machine learning technique can perform quality inversions on lower SNR data, significantly reducing the data collection time and permitting reconstructions of weaker and three-dimensional current sources. © 2024, CC BY.

关键词： Magnetic fields

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Anomalous Second Harmonic Generation from Atomically Thin MnBi2Te4

arXiv

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arXiv 2022年

作者： Fonseca, Jordan Diederich, Geoffrey M. Ovchinnikov, Dmitry Cai, Jiaqi Wang, Chong Yan, Jiaqiang Xiao, Di Xu, Xiaodong Department of Physics University of Washington SeattleWA98195 United States Intelligence Community Postdoctoral Research Fellowship Program University of Washington SeattleWA98195 United States Department of Materials Science and Engineering University of Washington SeattleWA98195 United States Materials Science and Technology Division Oak Ridge National Laboratory Oak RidgeTN37831 United States Department of Materials Science and Engineering University of Tennessee KnoxvilleTN37996 United States

MnBi2Te4 is a van der Waals topological insulator with intrinsic intralayer ferromagnetic exchange and A-type antiferromagnetic (AFM) interlayer coupling. Theoretically, it belongs to a class of structurally centrosymmetric crystals whose layered antiferromagnetic order breaks inversion symmetry for even layer numbers, making optical second harmonic generation (SHG) an ideal probe of the coupling between the crystal and magnetic structures. Here, we perform magnetic field and temperature dependent SHG measurements on MnBi2Te4 flakes ranging from bulk to monolayer thickness. We find that the dominant SHG signal from MnBi2Te4 is unexpectedly unrelated to both magnetic state and layer number. We suggest that surface SHG is the likely source of the observed strong SHG, whose symmetry matches that of the MnBi2Te4-vacuum interface. Our results highlight the importance of considering the surface contribution to inversion symmetry-breaking in van der Waals centrosymmetric magnets. Copyright © 2022, The Authors. All rights reserved.

关键词： Harmonic generation

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First-Principle-Integrated Study of Blazar Synchrotron Radiation and Polarization Signatures from Magnetic Turbulence

arXiv

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arXiv 2023年

作者： Zhang, Haocheng Marscher, Alan P. Guo, Fan Giannios, Dimitrios Li, Xiaocan Negro, Michela NASA Postdoctoral Program United States NASA Goddard Space Flight Center GreenbeltMD20771 United States Institute for Astrophysical Research Boston University BostonMA02215 United States Theoretical Division Los Alamos National Lab Los AlamosNM87545 United States Department of Physics and Astronomy Purdue University West LafayetteIN47907 United States Dartmouth College HanoverNH03750 United States University of Maryland Baltimore County BaltimoreMD21250 United States Center for Research and Exploration in Space Science and Technology NASA/GSFC GreenbeltMD20771 United States

Blazar emission is dominated by nonthermal radiation processes that are highly variable across the entire electromagnetic spectrum. Turbulence, which can be a major source of nonthermal particle acceleration, can widely exist in the blazar emission region. The Turbulent Extreme Multi-Zone (TEMZ) model has been used to describe turbulent radiation signatures. Recent particle-in-cell (PIC) simulations have also revealed the stochastic nature of the turbulent emission region and particle acceleration therein. However, radiation signatures have not been systematically studied via first-principle-integrated simulations. In this paper, we perform combined PIC and polarized radiative transfer simulations to study synchrotron emission from magnetic turbulence in the blazar emission region. We find that the multi-wavelength flux and polarization are generally characterized by stochastic patterns. Specifically, the variability time scale and average polarization degree (PD) are governed by the correlation length of the turbulence. Interestingly, magnetic turbulence can result in polarization angle (PA) swings with arbitrary amplitudes and duration, in either direction, that are not associated with changes in flux or PD. Surprisingly, these swings, which are stochastic in nature, can appear either bumpy or smooth, although large amplitude swings (> 180◦) are very rare, as expected. Our radiation and polarization signatures from first-principle-integrated simulations are consistent with the TEMZ model, except that in the latter there is a weak correlation, with zero lag, between flux and degree of polarization. Copyright © 2023, The Authors. All rights reserved.

关键词： Polarization

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Large Interferometer For Exoplanets (LIFE): XIII. The Value of Combining Thermal Emission and Reflected Light for the Characterization of Earth Twins

arXiv

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arXiv 2024年

作者： Alei, E. Quanz, S.P. Konrad, B.S. Garvin, E.O. Kofman, V. Mandell, A. Angerhausen, D. Mollière, P. Meyer, M.R. Robinson, T. Rugheimer, S. ETH Zurich Institute for Particle Physics & Astrophysics Wolfgang-Pauli-Str. 27 Zurich8093 Switzerland NASA Postdoctoral Program Fellow NASA Goddard Space Flight Center GreenbeltMD United States ETH Zurich Department of Earth Sciences Sonneggstrasse 5 Zurich8092 Switzerland NASA Goddard Space Flight Center GreenbeltMD United States American University 4400 Massachusetts Ave NW WashingtonDC20016 United States Max-Planck-Institut für Astronomie Königstuhl 17 Heidelberg69117 Germany Department of Astronomy The University of Michigan West Hall 323 1085 S. University Avenue Ann ArborMI48109 United States Lunar & Planetary Laboratory University of Arizona TucsonAZ United States Department of Physics and Astronomy York University 4700 Keele St. TorontoONM3J 1P3 Canada

Context. Following the recommendations to NASA (in the Astro2020 Decadal survey) and ESA (through the Voyage2050 process), the search for life on exoplanets will be a priority in the next decades. Two concepts for direct imaging space missions are being developed for this purpose: the Habitable Worlds Observatory (HWO), and the Large Interferometer for Exoplanets (LIFE). These two concepts operate in different spectral regimes: HWO is focused on reflected light spectra in the ultraviolet/visible/near-infrared (UV/VIS/NIR), while LIFE will operate in the mid-infrared (MIR) to capture the thermal emission of temperate exoplanets. Aims. In this study we aim to assess the potential of HWO and LIFE in characterizing a cloud-free Earth twin orbiting a Sun-like star at 10 parsec distance both as separate missions and in synergy with each other. We aim to quantify the increase in information that can be gathered by joint atmospheric retrievals on a habitable planet. Methods. We perform Bayesian retrievals on simulated data obtained by a HWO-like and a LIFE-like mission separately, then jointly. We consider the baseline spectral resolutions currently assumed for these concepts and use two increasingly complex noise simulations, obtained using state-of-the-art noise simulators. Results. A HWO-like concept would allow to strongly constrain H2O, O2, and O3, in the atmosphere of a cloud-free Earth twin, while the atmospheric temperature profile is not well constrained (with an average uncertainty ≈ 100 K). LIFE-like observations would strongly constrain CO2, H2O, O3 and provide stronger constraints on the thermal atmospheric structure and surface temperature (down to ≈ 10 K uncertainty). For all the investigated scenarios, both missions would provide an upper limit on CH4. A joint retrieval on HWO and LIFE data would accurately define the atmospheric thermal profile and planetary parameters. It would decisively constrain CO2, H2O, O2, and O3 and find weak constraints on CO and C

关键词： Interferometers

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Magneto-optics in a van der Waals magnet tuned by self-hybridized polaritons

arXiv

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arXiv 2023年

作者： Dirnberger, Florian Quan, Jiamin Bushati, Rezlind Diederich, Geoffrey Florian, Matthias Klein, Julian Mosina, Kseniia Sofer, Zdenek Xu, Xiaodong Kamra, Akashdeep García-Vidal, Francisco J. Alù, Andrea Menon, Vinod M. Department of Physics City College of New York New YorkNY10031 United States Department of Physics The Graduate Center City University of New York New YorkNY10016 United States Photonics Initiative CUNY Advanced Science Research Center New YorkNY10031 United States Department of Electrical Engineering City College of the City University of New York New YorkNY10031 United States Intelligence Community Postdoctoral Research Fellowship Program University of Washington SeattleWA United States Department of Physics Department of Materials Science and Engineering University of Washington SeattleWA United States Department of Electrical and Computer Engineering Department of Physics University of Michigan Ann ArborMI48109 United States Department of Materials Science and Engineering Massachusetts Institute of Technology CambridgeMA02139 United States Department of Inorganic Chemistry University of Chemistry and Technology Prague Technickaá 5 Prague 6166 28 Czech Republic Universidad Autónoma de Madrid MadridE- 28049 Spain

Controlling quantum materials with light is of fundamental and technological importance. By utilizing the strong coupling of light and matter in optical cavities [1–3], recent studies were able to modify some of their most defining features [4–6]. In this work, we study the magneto-optical properties of a van der Waals magnet that supports strong coupling of photons and excitons even in the absence of external cavity mirrors. In this material – the layered magnetic semiconductor CrSBr – emergent light-matter hybrids called polaritons are shown to significantly increase the spectral bandwidth of correlations between the magnetic, electronic, and optical properties, enabling largely tunable optical responses to applied magnetic fields and magnons. Our results highlight the importance of exciton-photon self-hybridization in van der Waals magnets and motivate novel directions for the manipulation of quantum material properties by strong light-matter coupling. © 2023, CC BY.

关键词： Van der Waals forces

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Bayesian Analysis for Remote Biosignature Identification on exoEarths (BARBIE) III: Introducing the KEN

arXiv

引用

arXiv 2024年

作者： Latouf, Natasha Himes, Michael D. Mandell, Avi M. Moore, Michael Dane Kofman, Vincent Villanueva, Geronimo L. Stark, Chris Department of Physics and Astronomy George Mason University 4400 University Drive MS 3F3 FairfaxVA22030 United States NASA Goddard Space Flight Center 8800 Greenbelt Road GreenbeltMD20771 United States Sellers Exoplanents Environment Collaboration 8800 Greenbelt Road GreenbeltMD20771 United States NASA Postdoctoral Program Fellow NASA Goddard Space Flight Center 8800 Greenbelt Road GreenbeltMD20771 United States Morgan State University 1700 E Cold Spring Lane BaltimoreMD21251 United States NASA Goddard Space Flight Center GreenbeltMD United States Business Integra Inc. BethesdaMD United States Sellers Exoplanets Environment Collaboration 8800 Greenbelt Road GreenbeltMD20771 United States Integrated Space Science and Technology Institute Department of Physics American University WashingtonDC United States

We deploy a newly-generated set of geometric albedo spectral grids to examine the detectability of methane (CH4) in the reflected-light spectrum of an Earth-like exoplanet at visible and near-infrared wavelengths with a future exoplanet imaging mission. By quantifying the detectability as a function of signal-to-noise ratio (SNR) and molecular abundance, we can constrain the best methods of detection with the high-contrast space-based coronagraphy slated for the next generation telescopes such as the Habitable Worlds Observatory (HWO). We used 25 bandpasses between 0.8 and 1.5 μm. The abundances range from a modern-Earth level to an Archean-Earth level, driven by abundances found in available literature. We constrain the optimal 20%, 30%, and 40% bandpasses based on the effective SNR of the data, and investigate the impact of spectral confusion between CH4 and H2O on the detectability of each one. We find that a modern-Earth level of CH4 is not detectable, while an Archean Earth level of CH4 would be detectable at all SNRs and bandpass widths. Crucially, we find that CH4 detectability is inversely correlated with H2O abundance, with required SNR increasing as H2O abundance increases, while H2O detectability depends on CH4 abundance and selected observational wavelength, implying that any science requirements for the characterization of Earth-like planet atmospheres in the VIS/NIR should consider the abundances of both species in tandem. © 2024, CC0.

关键词： Exoplanets

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