Open Access Publications

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Open access publications by faculty, postdocs, and graduate students in the Department of Physics and Astronomy.

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3D MHD models of the centrifugal magnetosphere from a massive star with an oblique dipole field Get access Arrow
(Monthly Notices of the Royal Astronomical Society, 2023-02-01) ud-Doula, Asif; Owocki, Stanley P.; Russell, Christopher; Gagné, Marc; Daley-Yates, Simon
We present results from new self-consistent 3D magnetohydrodynamics (MHD) simulations of the magnetospheres from massive stars with a dipole magnetic axis that has a non-zero obliquity angle (β) to the star’s rotation axis. As an initial direct application, we compare the global structure of co-rotating discs for nearly aligned (β = 5°) versus half-oblique (β = 45°) models, both with moderately rapid rotation (∼0.5 critical). We find that accumulation surfaces broadly resemble the forms predicted by the analytical rigidly rotating magnetosphere model, but the mass buildup to near the critical level for centrifugal breakout against magnetic confinement distorts the field from the imposed initial dipole. This leads to an associated warping of the accumulation surface towards the rotational equator, with the highest density concentrated in wings centred on the intersection between the magnetic and rotational equators. These MHD models can be used to synthesize rotational modulation of photometric absorption and H α emission for a direct comparison with observations.
Ammonia dimer: extremely fluxional but still hydrogen bonded
(Nature Communications, 2022-03-18) Aling, Jing; Szalewicz, Krzysztof; van der Avoird, Ad
In the 1980s, Nelson, Fraser, and Klemperer (NFK) published an experimentally derived structure of the ammonia dimer dramatically different from the structure determined computationally, which led these authors to the question “Does ammonia hydrogen bond?". This question has not yet been answered satisfactorily. To answer it, we have developed an ab initio potential energy surface (PES) for this dimer at the limits of the current computational capabilities and performed essentially exact six-dimensional calculations of the vibration-rotation-tunneling (VRT) spectra of NH3-NH3 and ND3-ND3, obtaining an unprecedented agreement with experimental spectra. In agreement with other recent electronic structure calculations, the global minimum on the PES is in a substantially bent hydrogen-bonded configuration. Since the bottom of the PES is exceptionally flat, the dimer is extremely fluxional and the probability of finding it in configurations that are not hydrogen bonded is high. Nevertheless, the probability of hydrogen-bonded configurations is large enough to consider the ammonia dimer to be hydrogen bonded. We also show that NFK’s inference that the ammonia dimer is nearly rigid actually results from unusual cancellations between quantum effects that generate differences in spectra of different isotopologues.
Assessment of Directionally Solidified Eutectic Sm–Fe(Co)–Ti Alloys as Permanent Magnet Materials
(IEEE Transactions on Magnetics, 2023-05-29) Gabay, Alexander M.; Han, Chaoya; Ni, Chaoying; Hadjipanayis, George C.
Sm–Fe–Ti and Sm–Fe 0.8 Co 0.2 –Ti alloys were prepared via arc-melting and directionally solidified on a water-cooled copper hearth. The as-solidified alloys featured cells of the Sm(Fe,Co,Ti) 12 –Ti(Fe,Co) 2+δ –(α-Fe) lamellar eutectic. The lamellae of Sm(Fe,Co,Ti) 12 phase with a crystal structure of the ThMn12 type were less than 0.2 μm thick, and had their [001] easy-magnetization directions oriented along the temperature gradient of the solidification. The eutectic microstructure led to an increased coercivity, especially in the Co-added alloys. Below 250 °C, this coercivity was found not to vary much with temperature with a temperature coefficient of -0.18 %/°C. However, the modest absolute values, reaching only 0.7 kOe, are insufficient for utilization of the directionally solidified alloys as anisotropic permanent magnets.
Bimetal–organic frameworks derived tuneable Co nanoparticles embedded in porous nitrogen-doped carbon nanorods as high-performance electromagnetic wave absorption materials
(Journal of Materials Chemistry C, 2021-05-04) Pan, Jiannan; Yang, Huadong; Hong, Qu; Wen, Hui-Min; Xiao, John Q.; Hu, Jun
The in situ pyrolysis of metal–organic-frameworks (MOFs) is an effective strategy to prepare magnetic metal nanoparticle (NP) doped porous carbon materials. These composite materials have shown great potential as high performance electromagnetic wave (EMW) absorption materials. So far, the precise control of composite composition and structure has remained a major challenge in constructing highly porous composites with uniformly distributed NPs. In this work, we report a facile route to synthesize tuneable Co NPs embedded in porous nitrogen-doped carbon (Co/NC) nanorods through the direct thermolysis of the bimetal–organic framework (CoZn–ZIF) precursor. By adjusting the proportion of Co2+ in the MOF precursor, the content and distribution of Co NPs in the composite absorber change accordingly. When the molar ratio between Co2+ and Zn2+ is 3 : 1, the carbonized composites exhibit the largest external surface area and the best EMW absorption performance. With a filler mass loading of merely 15 wt%, the minimum reflection loss (RLmin) reaches −52.3 dB at 10.1 GHz with a thin layer thickness of 2.5 mm. The largest effective absorption bandwidth (EAB) of 5.0 GHz (11.1–16.1 GHz) is achieved in a 2.0 mm thick sample. The qualified bandwidth can be up to 14.5 GHz (3.5–18.0 GHz) with the integrated thickness from 1.0 mm to 5.5 mm. The enhanced conductive/magnetic losses, strong interfacial/dipolar/defect polarization, hierarchical pore structure and the geometric effect endow the Co/NC absorber with improved impedance matching and enhanced attenuation of EMW. This work provides a good direction for the future study of MOF-derived lightweight and efficient EMW absorbing materials.
Calculations of multipole transitions in Sn II for kilonova analysis
(The European Physical Journal D, 2023-07-03) Bondarev, A. I.; Gillanders, J. H.; Cheung, C.; Safronova, M. S.; Fritzsche, S.
We use the method that combines linearized coupled-cluster and configuration interaction approaches for calculating energy levels and multipole transition probabilities in singly ionized tin ions. We show that our calculated energies agree very well with the experimental data. We present probabilities of magnetic dipole and electric quadrupole transitions and use them for the analysis of the AT2017gfo kilonova emission spectra. This study demonstrates the importance and utility of accurate atomic data for forbidden transitions in the examination of future kilonova events.
Centrifugal breakout reconnection as the electron acceleration mechanism powering the radio magnetospheres of early-type stars
(Monthly Notices of the Royal Astronomical Society, 2022-04-27) Owocki, S. P.; Shultz, M. E.; ud-Doula, A.; Chandra, P.; Das, B.; Leto, P.
Magnetic B-stars often exhibit circularly polarized radio emission thought to arise from gyrosynchrotron emission by energetic electrons trapped in the circumstellar magnetosphere. Recent empirical analyses show that the onset and strength of the observed radio emission scale with both the magnetic field strength and the stellar rotation rate. This challenges the existing paradigm that the energetic electrons are accelerated in the current sheet between opposite-polarity field lines in the outer regions of magnetized stellar winds, which includes no role for stellar rotation. Building on recent success in explaining a similar rotation-field dependence of H α line emission in terms of a model in which magnetospheric density is regulated by centrifugal breakout (CBO), we examine here the potential role of the associated CBO-driven magnetic reconnection in accelerating the electrons that emit the observed gyrosynchrotron radio. We show in particular that the theoretical scalings for energy production by CBO reconnection match well the empirical trends for observed radio luminosity, with a suitably small, nearly constant conversion efficiency ϵ ≈ 10−8. We summarize the distinct advantages of our CBO scalings over previous associations with an electromotive force, and discuss the potential implications of CBO processes for X-rays and other observed characteristics of rotating magnetic B-stars with centrifugal magnetospheres.
Combinational Vibration Modes in H2O/HDO/D2O Mixtures Detected Thanks to the Superior Sensitivity of Femtosecond Stimulated Raman Scattering
(Journal of Physical Chemistry B, 2023-06-01) Pastorczak, Marcin; Duk, Katsiaryna; Shahab, Samaneh; Kananenka, Alexei A.
Overtones and combinational modes frequently play essential roles in ultrafast vibrational energy relaxation in liquid water. However, these modes are very weak and often overlap with fundamental modes, particularly in isotopologues mixtures. We measured VV and HV Raman spectra of H2O and D2O mixtures with femtosecond stimulated Raman scattering (FSRS) and compared the results with calculated spectra. Specifically, we observed the mode at around 1850 cm–1 and assigned it to H–O–D bend + rocking libration. Second, we found that the H–O–D bend overtone band and the OD stretch + rocking libration combination band contribute to the band located between 2850 and 3050 cm–1. Furthermore, we assigned the broad band located between 4000 and 4200 cm–1 to be composed of combinational modes of high-frequency OH stretching modes with predominantly twisting and rocking librations. These results should help in a proper interpretation of Raman spectra of aqueous systems as well as in the identification of vibrational relaxation pathways in isotopically diluted water.
Comparing spin injection in Fe75Co25/Bi2Te3 at GHz and optical excitations
(Applied Physics Letters, 2023-02-13) Sharma, Vinay; Nepal, Rajeev; Wu, Weipeng; Pogue, E. A.; Kumar, Ravinder; Kolagani, Rajeswari; Gundlach, Lars; Jungfleisch, M. Benjamin; Budhani, Ramesh C.
Spin-to-charge conversion (S2CC) processes in thin-film heterostructures have attracted much attention in recent years. Here, we describe the S2CC in a 3D topological insulator Bi2Te3 interfaced with an epitaxial film of Fe75Co25. The quantification of spin-to-charge conversion is made with two complementary techniques: ferromagnetic resonance based inverse spin Hall effect (ISHE) at GHz frequencies and femtosecond light-pulse induced emission of terahertz (THz) radiation. The role of spin rectification due to extrinsic effects like anisotropic magnetoresistance (AMR) and planar Hall effects (PHE) is pronounced at the GHz timescale, whereas the THz measurements do not show any detectible signal, which could be attributed to AMR or PHE. This result may be due to (i) homodyne rectification at GHz, which is absent in THz measurements and (ii) laser-induced thermal spin current generation and magnetic dipole radiation in THz measurements, which is completely absent in GHz range. The converted charge current has been analyzed using the spin diffusion model for the ISHE. We note that regardless of the differences in timescales, the spin diffusion length in the two cases is comparable. Our results aid in understanding the role of spin pumping timescales in the generation of ISHE signals.
Crystal Structure Predictions for 4-Amino-2,3,6-trinitrophenol Using a Tailor-Made First-Principles-Based Force Field
(Crystal Growth and Design, 2022-01-24) Metz, Michael P.; Shahbaz, Muhammad; Song, Hongxing; Vogt-Maranto, Leslie; Tuckerman, Mark E.; Szalewicz, Krzysztof
Predictions of crystal structures from first-principles electronic structure calculations and molecular simulations have been performed for an energetic molecule, 4-amino-2,3,6-trinitrophenol. This physics-based approach consists of a series of steps. First, a tailor-made two-body potential energy surface (PES) was constructed with recently developed software, autoPES, using symmetry-adapted perturbation theory based on a density-functional theory description of monomers [SAPT(DFT)]. The fitting procedure ensures asymptotic correctness of the PES by employing a rigorous asymptotic multipole expansion, which seamlessly integrates with SAPT(DFT) interaction energies. Next, crystal structure prediction (CSP) was performed by generating possible crystal structures with rigid molecules, minimizing these structures using the SAPT(DFT) force field, and running isothermal–isobaric molecular dynamics (MD) simulations with flexible molecules based on the tailor-made SAPT(DFT) intermolecular force field and a generic/SAPT(DFT) intramolecular one. This workflow led to the experimentally observed structure being identified as one of the forms with the lowest lattice energy, demonstrating the success of a first-principles, bottom-up approach to CSP. Importantly, we argue that the accuracy of the intermolecular potential, here the SAPT(DFT)-based potential, is determinative of the crystal structure, while generic/SAPT(DFT) force fields can be used to represent the intramolecular potential. This force field approach simplifies the CSP workflow, without significantly compromising the accuracy of the prediction.
Detection of astrophysical tau neutrino candidates in IceCube
(The European Physical Journal C, 2022-11-15) IceCube Collaboration; Abbasi, R.; Ackermann, M.; Adams, J.; et al.
High-energy tau neutrinos are rarely produced in atmospheric cosmic-ray showers or at cosmic particle accelerators, but are expected to emerge during neutrino propagation over cosmic distances due to flavor mixing. When high energy tau neutrinos interact inside the IceCube detector, two spatially separated energy depositions may be resolved, the first from the charged current interaction and the second from the tau lepton decay. We report a novel analysis of 7.5 years of IceCube data that identifies two candidate tau neutrinos among the 60 “High-Energy Starting Events” (HESE) collected during that period. The HESE sample offers high purity, all-sky sensitivity, and distinct observational signatures for each neutrino flavor, enabling a new measurement of the flavor composition. The measured astrophysical neutrino flavor composition is consistent with expectations, and an astrophysical tau neutrino flux is indicated at 2.8σ significance.
Direct detection of ultralight dark matter bound to the Sun with space quantum sensors
(Nature Astronomy, 2022-12-05) Tsai, Yu-Dai; Eby, Joshua; Safronova, Marianna S.
Recent advances in quantum sensors, including atomic clocks, enable searches for a broad range of dark matter candidates. The question of the dark matter distribution in the Solar system critically affects the reach of dark matter direct detection experiments. Partly motivated by the NASA Deep Space Atomic Clock and the Parker Solar Probe, we show that space quantum sensors present new opportunities for ultralight dark matter searches, especially for dark matter states bound to the Sun. We show that space quantum sensors can probe unexplored parameter space of ultralight dark matter, covering theoretical relaxion targets motivated by naturalness and Higgs mixing. If a two-clock system were able to make measurements on the interior of the solar system, it could probe this highly sensitive region directly and set very strong constraints on the existence of such a bound-state halo in our solar system. We present sensitivity projections for space-based probes of ultralight dark matter, which couples to electron, photon and gluon fields, based on current and future atomic, molecular and nuclear clocks.
Direct probing of strong magnon–photon coupling in a planar geometry
(Quantum Science and Technology, 2022-10-31) Kaffash, Mojtaba T.; Wagle, Dinesh; Rai, Anish; Meyer, Thomas; Xiao, John Q.; Jungfleisch, M. Benjamin
We demonstrate direct probing of strong magnon–photon coupling using Brillouin light scattering (BLS) spectroscopy in a planar geometry. The magnonic hybrid system comprises a split-ring resonator loaded with epitaxial yttrium iron garnet thin films of 200 nm and 2.46 μm thickness. The BLS measurements are combined with microwave spectroscopy measurements where both biasing magnetic field and microwave excitation frequency are varied. The cooperativity for the 200 nm-thick YIG films is 1.1, and larger cooperativity of 29.1 is found for the 2.46 μm-thick YIG film. We show that BLS is advantageous for probing the magnonic character of magnon–photon polaritons, while microwave absorption is more sensitive to the photonic character of the hybrid excitation. A miniaturized, planar device design is imperative for the potential integration of magnonic hybrid systems in future coherent information technologies, and our results are a first stepping stone in this regard. Furthermore, successfully detecting the magnonic hybrid excitation by BLS is an essential step for the up-conversion of quantum signals from the microwave to the optical regime in hybrid quantum systems.
Effect of Strongly Magnetized Electrons and Ions on Heat Flow and Symmetry of Inertial Fusion Implosions
(Physical Review Letters, 2022-05-11) Bose, A.; Peebles, J.; Walsh, C. A.; Frenje, J. A.; Kabadi, N. V.; Adrian, P. J.; Sutcliffe, G. D.; Johnson, M. Gatu; Frank, C. A.; Davies, J. R.; Betti, R.; Glebov, V. Yu.; Marshall, F. J.; Regan, S. P.; Stoeckl, C.; Campbell, E. M.; Sio, H.; Moody, J.; Crilly, A.; Appelbe, B. D.; Chittenden, J. P.; Atzeni, S.; Barbato, F.; Forte, A.; Li, C. K.; Seguin, F. H.; Petrasso, R. D.
This Letter presents the first observation on how a strong, 500 kG, externally applied B field increases the mode-two asymmetry in shock-heated inertial fusion implosions. Using a direct-drive implosion with polar illumination and imposed field, we observed that magnetization produces a significant increase in the implosion oblateness (a 2.5× larger P2 amplitude in x-ray self-emission images) compared with reference experiments with identical drive but with no field applied. The implosions produce strongly magnetized electrons (ωeτe≫1) and ions (ωiτi>1) that, as shown using simulations, restrict the cross field heat flow necessary for lateral distribution of the laser and shock heating from the implosion pole to the waist, causing the enhanced mode-two shape.
Electron energy dissipation in a magnetotail reconnection region
(Physics of Plasmas, 2023-08-08) Burch, J. L.; Genestreti, K. J.; Heuer, S. V.; Chasapis, A.; Torbert, R. B.; Gershman, D. J.; Bandyopadhyay, R.; Pollock, C. J.; Matthaeus, W. H.; Nakamura, T. K. M.; Egedal, J.
The four Magnetospheric Multiscale spacecraft encountered a reconnection region in the Earth's magnetospheric tail on 11 July 2017. Previous publications have reported characteristics of the electron diffusion region, including its aspect ratio, the reconnection electric field, plasma wave generation from electron beams in its vicinity, and energetic particles in the Earthward exhaust. This paper reports on the investigation of conversion of electromagnetic energy to electron kinetic energy (by J·E) and the ensuing conversion of electron beam energy to electron thermal energy via the pressure–strain interaction. The main result is that omnidirectional, compressive dissipation of electron energy dominates in the positive J·E region, while incompressive parallel dissipation dominates in the inflow region where J·E is small. The existence of parallel electric fields in the inflow region supports previous suggestions that electron trapping by these fields contributes to the parallel dissipation. All of the results are reproduced quantitatively within a factor of two with a 2.5-D particle-in-cell simulation.
Electroweak monopoles and magnetic dumbbells in grand unified theories
(Physical Review D, 2021-05-20) Lazarides, G.; Shafi, Q.
We use the SU(5) model to show the presence in grand unified theories of an electroweak monopole and a magnetic dumbbell (“meson”) made up of a monopole-antimonopole pair connected by a Z-magnetic flux tube. The monopole is associated with the spontaneous breaking of the weak SU(2)L gauge symmetry by the induced vacuum expectation value of a heavy scalar SU(2)L triplet with zero weak hypercharge contained in the adjoint Higgs 24-plet. This monopole carries a Coulomb magnetic charge of (3/4)(2π/e) as well as Z-magnetic charge, where 2π/e denotes the unit Dirac magnetic charge. Its total magnetic charge is √3/8(4π/e), which is in agreement with the Dirac quantization condition. The monopole weighs about 700 GeV, but because of the attached Z-magnetic tube it exists, together with the antimonopole, in a magnetic dumbbell configuration whose mass is expected to lie in the TeV range. The presence of these topological structures in SU(5) and SO(10) and in their supersymmetric extensions provides an exciting new avenue for testing these theories in high-energy colliders.
Energy transfer in reconnection and turbulence
(Physical Review E, 2021-12-21) Adhikari, S.; Parashar, T. N.; Shay, M. A.; Matthaeus, W. H.; Pyakurel, P. S.; Fordin, S.; Stawarz, J. E.; Eastwood, J. P.
Reconnection and turbulence are two of the most commonly observed dynamical processes in plasmas, but their relationship is still not fully understood. Using 2.5D kinetic particle-in-cell simulations of both strong turbulence and reconnection, we compare the cross-scale transfer of energy in the two systems by analyzing the generalization of the von Kármán Howarth equations for Hall magnetohydrodynamics, a formulation that subsumes the third-order law for steady energy transfer rates. Even though the large scale features are quite different, the finding is that the decomposition of the energy transfer is structurally very similar in the two cases. In the reconnection case, the time evolution of the energy transfer also exhibits a correlation with the reconnection rate. These results provide explicit evidence that reconnection dynamics fundamentally involves turbulence-like energy transfer.
Factors influencing hydrogen peroxide versus water inclusion in molecular crystals
(Physical Chemistry Chemical Physics, 2022-04-28) Wiscons, Ren A.; Nikhar, Rahul; Szalewicz, Krzysztof; Matzger, Adam J.
Hydrate formation is often unavoidable during crystallization, leading to performance degradation of pharmaceuticals and energetics. In some cases, water molecules trapped within crystal lattices can be substituted for hydrogen peroxide, improving the solubility of drugs and detonation performance of explosives. The present work compares hydrates and hydrogen peroxide solvates in two ways: (1) analyzing structural motifs present in crystal structures accessed from the Cambridge Structural Database and (2) developing potential energy surfaces for water and hydrogen peroxide interacting with functional groups of interest at geometries relevant to the solid state. By elucidating fundamental differences in local interactions that can be formed with molecules of hydrogen peroxide and/or water, the analyses presented here provide a foundation for the design and selection of candidate molecules for the formation of hydrogen peroxide solvates.
Getting started: How a supersonic stellar wind is initiated from a hydrostatic surface
(Proceedings of the International Astronomical Union, 2022-11-30) Owocki, Stan
Most of a star’s mass is bound in a hydrostatic equilibrium in which pressure balances gravity. But if at some near-surface layer additional outward forces overcome gravity, this can transition to a supersonic, outflowing wind, with the sonic point, where the outward force cancels gravity, marking the division between hydrostatic atmosphere and wind outflow. This talk will review general issues with such transonic initiation of a stellar wind outflow, and how this helps set the wind mass loss rate. The main discussion contrasts the flow initiation in four prominent classes of steady-state winds: (1) the pressure-driven coronal wind of the sun and other cool stars; (2) line-driven winds from OB stars; (3) a two-stage initiation model for the much denser winds from Wolf-Rayet (WR) stars; and (4) the slow “overflow” mass loss from highly evolved giant stars. A follow on discussion briefly reviews eruptive mass loss, with particular focus on the giant eruption of η Carinae.
High-performance HZO/InAlN/GaN MISHEMTs for Ka-band application
(Semiconductor Science and Technology, 2023-02-01) Cui, Peng; Moser, Neil; Chen, Hang; Xiao, John Q.; Chabak, Kelson D.; Zeng, Yuping
This paper reports on the demonstration of microwave power performance at 30 GHz on InAlN/GaN metal–insulator–semiconductor high electron mobility transistor (MISHEMT) on silicon substrate by using the Hf0.5Zr0.5O2 (HZO) as a gate dielectric. Compared with Schottky gate HEMT, the MISHEMT with a gate length (LG) of 50 nm presents a significantly enhanced performance with an ON/OFF current ratio (ION/IOFF) of 9.3 × 107, a subthreshold swing of 130 mV dec−1, a low drain-induced barrier lowing of 45 mV V−1, and a breakdown voltage of 35 V. RF characterizations reveal a current gain cutoff frequency (fT) of 155 GHz and a maximum oscillation frequency (fmax) of 250 GHz, resulting in high (fT × fmax)1/2 of 197 GHz and the record high Johnson's figure-of-merit (JFOM = fT × BV) of 5.4 THz V among the reported GaN MISHEMTs on Si. The power performance at 30 GHz exhibits a maximum output power of 1.36 W mm−1, a maximum power gain of 12.3 dB, and a peak power-added efficiency of 21%, demonstrating the great potential of HZO/InAlN/GaN MISHEMTs for the Ka-band application.
Inner shell excitation by strong field laser rescattering: optimal laser conditions for high energy recollision
(Journal of the Optical Society of America B, 2021-11-15) Kelley, L.; Germain, Z.; Jones, E. C.; Milliken, D.; Walker, Barry C.
We address the challenge of finding the optimal laser intensity and wavelength to drive high-energy, strong field rescattering and report the maximum yields of K-shell and LI-shell hole creation. Surprisingly, our results show laser-driven rescattering is able to create inner shell holes in all atoms from lithium to uranium with the interaction spanning from the deep IR to x-ray free electron laser sources. The calculated peak rescattering follows a simple scaling with the atomic number and laser wavelength. The results show it is possible to describe the ideal laser intensity and wavelength for general high-energy laser rescattering processes.

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