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Open access publications by faculty, postdocs, and graduate students in the Department of Physics and Astronomy.
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Item Gilbert damping in metallic ferromagnets from Schwinger-Keldysh field theory: Intrinsically nonlocal, nonuniform, and made anisotropic by spin-orbit coupling(Physical Review B, 2024-01-12) Reyes-Osorio, Felipe; Nikolić, Branislav K.Understanding the origin of damping mechanisms in the magnetization dynamics of metallic ferromagnets is a fundamental problem for nonequilibrium many-body physics of systems in which quantum conduction electrons interact with localized spins assumed to be governed by the classical Landau-Lifshitz-Gilbert (LLG) equation. It is also of critical importance for applications because damping affects energy consumption and the speed of spintronic and magnonic devices. Since the 1970s, a variety of linear-response and scattering theory approaches have been developed to produce widely used formulas for computation of the spatially independent Gilbert scalar parameter as the magnitude of the Gilbert damping term in the LLG equation. The Schwinger-Keldysh field theory (SKFT), largely unexploited for this purpose, offers additional possibilities, such as to rigorously derive an extended LLG equation by integrating quantum electrons out. Here we derive such an equation whose Gilbert damping for metallic ferromagnets is nonlocal, i.e., dependent on all localized spins at a given time, and nonuniform, even if all localized spins are collinear and spin-orbit coupling (SOC) is absent. This is in sharp contrast to standard lore, in which nonlocal damping is considered to emerge only if localized spins are noncollinear—for such situations, direct comparison using the example of a magnetic domain wall shows that SKFT-derived nonlocal damping is an order of magnitude larger than the previously considered one. Switching on SOC makes such nonlocal damping anisotropic, in contrast to standard lore, in which SOC is usually necessary to obtain a nonzero Gilbert damping scalar parameter. Our analytical formulas, with their nonlocality being more prominent in low spatial dimensions, are fully corroborated by numerically exact quantum-classical simulations.Item Demonstration of high-throughput magnetic hysteresis measurements based on spintronic THz emission(Journal of Applied Physics, 2023-12-21) DeCamp, M. F.; Bhatt, S.; Hossain, M. T.; Wu, W.; Jungfleisch, M. B.Spintronic terahertz (THz) emitters have been shown to be a cost-efficient source for use in time-domain THz spectroscopy. The use of external magnetic fields to control the polarity of the THz emission provides an opportunity to measure the magnetization of spintronic materials as well as shaping THz emission. Here, we demonstrate an efficient method of measuring magnetic hysteresis with material sensitivity and speed several orders of magnitude greater than typical magnetometry methods. In addition, we utilize the rapid control of material magnetization for lock-in detection in time-domain THz spectroscopy of spintronic emitters. The ability to rapidly control and measure the material magnetization on very small volumes provides an opportunity to study magnetic hetero-structures with sub-micron spatial resolution.Item Analysis of neutron monitor count rates and timing distributions from latitude surveys(Journal of Physics: Conference Series, 2023-12-01) Yakum, P.; Khamphakdee, S.; Nuntiyakul, W.; Sáiz, A.; Ruffolo, D.; Evenson, P.; Bangliang, C.; Seripienlert, A.; Jiang, P.; Chuanraksasat, P.Neutron monitors continuously record the hadronic part of secondary atmospheric radiation on the ground, which originates from primary cosmic rays. In Thailand, we developed a mobile neutron monitor housed inside a standard-size shipping container named "Changvan." It contains three neutron-sensitive proportional counters set up in the typical NM64 layout. However, the central counter doesn't have the lead producer, leading us to refer to it as a "semi-leaded" neutron monitor. We examined cosmic ray spectral variations on two latitude surveys during 2018-2019 and 2019-2020. This work examines the ratio of count rates between leaded and unleaded setups, which shows notable variation based on geomagnetic cutoff rigidity, suggesting a sensitivity to the cosmic ray spectrum. This measurement could be implemented at stationary stations. The unleaded counter, shielded by the reflector with a higher count from nearby lead, may have advantages over a bare one. Furthermore, we explore alternative techniques to identify spectral changes in Galactic cosmic rays using Changvan data. We analyze using time delay histograms to determine the leader fraction (L) of neutrons that are not preceded by another neutron from the same primary cosmic ray. We also examine other parameters, including the alpha (α) parameter and pulse rate (PR), which can be compared with count rates (CR). Our findings indicate that the ratios of L and α are not significantly affected by geomagnetic cutoff rigidity. In contrast, CR and PR exhibit significant dependency and show opposite trends.Item Monte Carlo Simulation and measurement of Calibration Neutron Monitor count rate dependence on proximity to water(Journal of Physics: Conference Series, 2023-12-01) Duangjai, B.; Nuntiyakul, W.; Seripienlert, A.; Pagwhan, A.; Chaiwongkhot, K.; Sáiz, A.; Ruffolo, D.; Evenson, P.Due to their global availability, neutron monitors play a crucial role in measuring time variations in the Galactic cosmic ray flux. A portable calibration neutron monitor (CalMon) is useful for intercalibrating various neutron monitors to ensure accurate measurements. A common technique to ensure that the calibration is done in a consistent environment is to place the CalMon at some height above a wide container (such as a portable swimming pool) filled with water. This study investigates the impact of CalMon height and water depth on the count rate ratio relative to a standard 18NM64 count rate recorded nearby (CalMon/18NM64). We compare simulated data from the FLUKA Monte Carlo package to experimental data from [1] to demonstrate the statistical accuracy of our simulation. Using the simulation results, we then extend the study of the proximity-to-water effect on the counting rate. In this work, we present a preliminary empirical model by analyzing the CalMon/18NM64 as a function of CalMon to water distance. Overall, our study enhances understanding of the response of calibration monitors (now often called "mini-neutron monitors") operated in various locations worldwide, and validates the Monte Carlo techniques used to model the response of the global neutron monitor network.Item Pulse selection algorithm for NM64 neutron detector(Journal of Physics: Conference Series, 2023-12-01) Kittiya, A.; Nuntiyakul, W.; Chaiwongkhot, K.; Sáiz, A.; Ruffolo, D.; Seripienlert, A.; Evenson, P.We propose an algorithm to sepearate pile-up pulses in neutron detectors by utilizing a standard pulse. For this method to be effective, the data must consist mostly of isolated pulses. First, we define a reference pulse by averaging a sample of clearly isolated pulses. Then, for an arbitrary signal, we calculate a shape deviation by summing up the squared residuals between it and the reference pulse. The pulse with the greatest shape deviation is removed from the process. We then recalculate the reference pulse and repeat until the remaining pulses have shape deviation within a threshold. These remaining pulses exhibit a very good linear trend between area and height, allowing us to screen those suspected as pile-ups. A pulse much higher than the final reference pulse, despite being in the area-height-trend and having low shape deviation, is considered a pile-up of two identical pulses. The final reference pulse is fitted to a function defined by two pieces of Gaussian-multiplied polynomial, normalized, and called the standard pulse. We attempted to fit the pile-up pulse with one standard pulse to separate pile-up pulses. If the sum of squared normalized residuals is higher than some threshold, we add one more pulse, try fitting again, and repeat up to three pulses. We apply this algorithm to the pulses collected from one counter at the Princess Sirindhorn Neutron Monitor station at the summit of Doi Inthanon Mountain, Chiang Mai, Thailand, measured by an oscilloscope. The algorithm correctly separates obvious pile-up cases, allowing to record individual pulse timing with improved accuracy. However, we found small pulses, usually belong to gamma rays, that blend with neutron pulse and pass 100 mV output filtration. After removing those under 100 mV, the pulse area distribution of the separated pile-up is consistent with that of single pulses except at very small pulse sizes.Item Application of collisional analysis to the differential velocity of solar wind ions(Frontiers in Astronomy and Space Sciences, 2024-01-09) Johnson, E.; Maruca, B. A.; McManus, M.; Stevens, M.; Klein, K. G.; Mostafavi, P.Collisional analysis combines the effects of collisional relaxation and large-scale expansion to quantify how solar wind parameters evolve as the plasma expands through the heliosphere. Though previous studies have applied collisional analysis to the temperature ratio between protons (ionized hydrogen) and α-particles (fully ionized helium), this is the first study to explore α-proton differential flow with collisional analysis. First, the mathematical model for the collisional analysis of differential flow was derived. Then, this model was applied to individual in-situ observations from Parker Solar Probe (PSP; r = 0.1–0.27 au) to generate predictions of the α-proton differential flow in the near-Earth solar wind. A comparison of these predicted values with contemporaneous measurements from the Wind spacecraft (r = 1.0 au) shows strong agreement, which may imply that the effects of expansion and Coulomb collisions have a large role in governing the evolution of differential flow through the inner heliosphere.Item Low temperature spin relaxation length exceeding 3 μm in highly conductive copper channels(Journal of Applied Physics, 2023-10-14) Shen, Xingyu; Ji, YiDespite extensive studies of spin transport in metallic structures, it remains a challenge to achieve spin relaxation length well above 1 μm in metals even at low temperatures. We explore nonlocal spin transport in Cu channels with a cross section of 0.5 × 0.5 μm2, which exhibit superior values of electrical conductivity and residual resistivity ratio (RRR). Based on structures fabricated in a single batch, we found an average spin relaxation length of λCu = 3.2± 0.7 μm and an average spin relaxation time of τs = 120 ± 50 ps at 30 K. Substantial variations of λCu, RRR, and resistivity pcu are found among the structures and the three quantities correlate well to one another. The most conductive Cu channel in the batch yields λCu = 5.3 ± 0.8 μm and ts = 250± 80 ps. These superior values exceed expectations for metals and can be attributed to reduced spin relaxation from grain boundaries and surfaces.Item The Eruption of a Magnetic Flux Rope Observed by Solar Orbiter and Parker Solar Probe(The Astrophysical Journal, 2023-09-28) Long, David M.; Green, Lucie M.; Pecora, Francesco; Brooks, David H.; Strecker, Hanna; Orozco-Suárez, David; Hayes, Laura A. Hayes; Davies, Emma E.; Amerstorfer, Ute V.; Mierla, Marilena; Lario, David; Berghmans, David; Zhukov, Andrei N.; Rüdisser, Hannah T.Magnetic flux ropes are a key component of coronal mass ejections, forming the core of these eruptive phenomena. However, determining whether a flux rope is present prior to eruption onset and, if so, the rope's handedness and the number of turns that any helical field lines make is difficult without magnetic field modeling or in situ detection of the flux rope. We present two distinct observations of plasma flows along a filament channel on 2022 September 4 and 5 made using the Solar Orbiter spacecraft. Each plasma flow exhibited helical motions in a right-handed sense as the plasma moved from the source active region across the solar disk to the quiet Sun, suggesting that the magnetic configuration of the filament channel contains a flux rope with positive chirality and at least one turn. The length and velocity of the plasma flow increased from the first to the second observation, suggesting evolution of the flux rope, with the flux rope subsequently erupting within ∼5 hr of the second plasma flow. The erupting flux rope then passed over the Parker Solar Probe spacecraft during its encounter (13), enabling in situ diagnostics of the structure. Although complex and consistent with the flux rope erupting from underneath the heliospheric current sheet, the in situ measurements support the inference of a right-handed flux rope from remote-sensing observations. These observations provide a unique insight into the eruption and evolution of a magnetic flux rope near the Sun.Item State-Insensitive Trapping of Alkaline-Earth Atoms in a Nanofiber-Based Optical Dipole Trap(PRX Quantum, 2023-10-12) Kestler, G.; Ton, K.; Filin, D.; Cheung, C.; Schneeweiss, P.; Hoinkes, T.; Volz, J.; Safronova, M.S.; Rauschenbeutel, A.; Barreiro, J.T.Neutral atoms that are optically trapped using the evanescent fields surrounding optical nanofibers are a promising platform for developing quantum technologies and exploring fundamental science, such as quantum networks and many-body physics of interacting photons. Building on the successful advancements with trapped alkali atoms, here we trap strontium-88 atoms, an alkaline-earth element, in a state-insensitive, nanofiber-based optical dipole trap using the evanescent fields of an optical nanofiber. Employing a two-color, double magic-wavelength trapping scheme, we realize state-insensitive trapping of the atoms for the kilohertz-wide 5s21S0−5s5p3P1,|m|=1 intercombination transition, which we verify by performing high-resolution spectroscopy for an atom-surface distance of about 300 nm. This allows us to experimentally find and verify the state insensitivity of the trap nearby a theoretically predicted magic wavelength of 435.827(25) nm, a necessary step to confirm precision atomic physics calculations. Alkaline-earth atoms also exhibit nonmagnetic ground states and ultranarrow linewidth transitions making them ideal candidates for atomic clocks and precision metrology applications, especially with state-insensitive traps. Additionally, given the low collisional scattering length specific to strontium-88, this work also lays the foundation for developing versatile and robust matter-wave atomtronic circuits over nanophotonic waveguides.Item Observation of ultrafast ballistic orbital transport(Nature Nanotechnology, 2023-08-07) Jungfleisch, M. BenjaminTerahertz emission spectroscopy reveals long-distance ballistic orbital-angular-momentum transport in tungsten. While most electronic devices so far are based on the electron’s charge or its spin degree of freedom, electrons can also carry orbital angular momentum. Orbitronics (orbital electronics), which focuses on the electron’s orbital angular momentum1, is much less explored than the field of spintronics, especially at terahertz (THz) frequencies2,3. However, orbitronics promises higher-density information transfer over longer distances in many materials than would be possible with spin currents. Furthermore, utilizing the electron’s orbital angular momentum L offers distinct advantages: (1) orbital current is an emergent property from Bloch states in a solid, comprising many atoms and, hence, orbital angular momentum transfer can be arbitrarily large1, whereas the spin angular momentum S of one electron is limited to 1/2h. This may hinder efficient transport and control of information in spintronic devices. (2) The conversion of orbital angular momentum to charge currents does not rely on spin–orbit coupling, suggesting that many more materials could potentially be harnessed for interfacing angular-momentum-based devices with charge-based devices4. Despite these advantages, it has been experimentally challenging to unambiguously distinguish L and S transport and their conversion into charge currents. Furthermore, it has been unclear if L transport could be used similarly to S transport at ultrafast timescales, potentially leading to efficient THz devices5,6.Item Probing Ion Configurations in the KcsA Selectivity Filter with Single-Isotope Labels and 2D IR Spectroscopy(Journal of the American Chemical Society, 2023-08-23) Ryan, Matthew J.; Gao, Lujia; Valiyaveetil, Francis I.; Zanni, Martin T.; Kananenka, Alexei A.The potassium ion (K+) configurations of the selectivity filter of the KcsA ion channel protein are investigated with two-dimensional infrared (2D IR) spectroscopy of amide I vibrations. Single 13C–18O isotope labels are used, for the first time, to selectively probe the S1/S2 or S2/S3 binding sites in the selectivity filter. These binding sites have the largest differences in ion occupancy in two competing K+ transport mechanisms: soft-knock and hard-knock. According to the former, water molecules alternate between K+ ions in the selectivity filter while the latter assumes that K+ ions occupy the adjacent sites. Molecular dynamics simulations and computational spectroscopy are employed to interpret experimental 2D IR spectra. We find that in the closed conductive state of the KcsA channel, K+ ions do not occupy adjacent binding sites. The experimental data is consistent with simulated 2D IR spectra of soft-knock ion configurations. In contrast, the simulated spectra for the hard-knock ion configurations do not reproduce the experimental results. 2D IR spectra of the hard-knock mechanism have lower frequencies, homogeneous 2D lineshapes, and multiple peaks. In contrast, ion configurations of the soft-knock model produce 2D IR spectra with a single peak at a higher frequency and inhomogeneous lineshape. We conclude that under equilibrium conditions, in the absence of transmembrane voltage, both water and K+ ions occupy the selectivity filter of the KcsA channel in the closed conductive state. The ion configuration is central to the mechanism of ion transport through potassium channels.Item 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.Item The Trans-Heliospheric Survey(Astronomy & Astrophysics, 2023-07-24) Maruca, Bennett A.; Qudsi, Ramiz A.; Alterman, B. L.; Walsh, Brian M.; Korreck, Kelly E.; Verscharen, Daniel; Bandyopadhyay, Riddhi; Chhiber, Rohit; Chasapis, Alexandros; Parashar, Tulasi N.; Matthaeus, William H.; Goldstein, Melvyn L.Context. Though the solar wind is characterized by spatial and temporal variability across a wide range of scales, long-term averages of in situ measurements have revealed clear radial trends: changes in average values of basic plasma parameters (e.g., density, temperature, and speed) and a magnetic field with a distance from the Sun. Aims. To establish our current understanding of the solar wind's average expansion through the heliosphere, data from multiple spacecraft needed to be combined and standardized into a single dataset. Methods. In this study, data from twelve heliospheric and planetary spacecraft - Parker Solar Probe (PSP), Helios 1 and 2, Mariner 2 and 10, Ulysses, Cassini, Pioneer 10 and 11, New Horizons, and Voyager 1 and 2 - were compiled into a dataset spanning over three orders of magnitude in heliocentric distance. To avoid introducing artifacts into this composite dataset, special attention was given to the solar cycle, spacecraft heliocentric elevation, and instrument calibration. Results. The radial trend in each parameter was found to be generally well described by a power-law fit, though up to two break points were identified in each fit. Conclusions. These radial trends are publicly released here to benefit research groups in the validation of global heliospheric simulations and in the development of new deep-space missions such as Interstellar Probe.Item Winds and magnetospheres from stars and planets: similarities and differences(Proceedings of the International Astronomical Union, 2023-08-16) Owocki, StanBoth stars and planets can lose mass through an expansive wind outflow, often constrained or channeled by magnetic fields that form a surrounding magnetosphere. The very strong winds of massive stars are understood to be driven by line-scattering of the star’s radiative momentum, while in the Sun and even lower-mass stars a much weaker mass loss arises from the thermal expansion of a mechanically heated corona. In exoplanets around such low-mass stars, the radiative heating and wind interaction can lead to thermal expansion or mechanical ablation of their atmospheres. Stellar magnetospheres result from the internal trapping of the wind outflow, while planetary magnetospheres are typically shaped by the external impact from the star’s wind. But in both cases the stressing can drive magnetic reconnection that results in observable signatures such as X-ray flares and radio outbursts. This review will aim to give an overview of the underlying physics of these processes with emphasis on their similarities and distinctions for stars vs. planets.Item Getting started: How a supersonic stellar wind is initiated from a hydrostatic surface(Proceedings of the International Astronomical Union, 2022-11-30) Owocki, StanMost 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.Item 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.Item Patellofemoral Joint Loading Progression Across 35 Weightbearing Rehabilitation Exercises and Activities of Daily Living(American Journal of Sports Medicine, 2023-06-05) Song, Ke; Silva, Rodrigo Scattone; Hullfish, Todd J.; Silbernagel, Karin Grävare; Baxter, Josh R.Background: Exercises that provide progressive therapeutic loading are a central component of patellofemoral pain rehabilitation, but quantitative evidence on patellofemoral joint loading is scarce for a majority of common weightbearing rehabilitation exercises. Purpose: To define a loading index to quantify, compare, rank, and categorize overall loading levels in the patellofemoral joint across 35 types of weightbearing rehabilitation exercises and activities of daily living. Study Design: Descriptive laboratory study. Methods: Model-estimated knee flexion angles and extension moments based on motion capture and ground-reaction force data were used to quantify patellofemoral joint loading in 20 healthy participants who performed each exercise. A loading index was computed via a weighted sum of loading peak and cumulative loading impulse for each exercise. The 35 rehabilitation exercises and daily living activities were then ranked and categorized into low, moderate, and high “loading tiers” according to the loading index. Results: Overall patellofemoral loading levels varied substantially across the exercises and activities, with loading peak ranging from 0.6 times body weight during walking to 8.2 times body weight during single-leg decline squat. Most rehabilitation exercises generated a moderate level of patellofemoral joint loading. Few weightbearing exercises provided low-level loading that resembled walking or high-level loading with both high magnitude and duration. Exercises with high knee flexion tended to generate higher patellofemoral joint loading compared with high-intensity exercises. Conclusion: This study quantified patellofemoral joint loading across a large collection of weightbearing exercises in the same cohort. Clinical Relevance: The visualized loading index ranks and modifiable worksheet may assist clinicians in planning patient-specific exercise programs for patellofemoral pain rehabilitation.Item 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.Item Quantum classical approach to spin and charge pumping and the ensuing radiation in terahertz spintronics: Example of the ultrafast light-driven Weyl antiferromagnet Mn3Sn(Physical Review B, 2023-05-15) Suresh, Abhin; Nikolić, Branislav K.The interaction of a femtosecond laser pulse with magnetic materials has been intensely studied for more than two decades in order to understand ultrafast demagnetization in single magnetic layers or terahertz emission from their bilayers with nonmagnetic spin-orbit (SO) materials. However, in contrast to well-understood spin and charge pumping by dynamical magnetization in spintronic systems driven by microwaves or current injection, analogous processes in light-driven magnets and radiation emitted by them remain largely unexplained due to the multiscale nature of the problem. Here we develop a multiscale quantum-classical formalism—where conduction electrons are described by quantum master equation (QME) of the Lindblad type, classical dynamics of local magnetization is described by the Landau-Lifshitz-Gilbert (LLG) equation, and incoming light is described by classical vector potential, while outgoing electromagnetic radiation is computed using the Jefimenko equations for retarded electric and magnetic fields—and apply it to a bilayer of antiferromagnetic Weyl semimetal Mn3Sn, hosting noncollinear local magnetization, and SO-coupled nonmagnetic material. Our QME+LLG+Jefimenko scheme makes it possible to understand how a femtosecond laser pulse directly generates spin and charge pumping and electromagnetic radiation by the Mn3Sn layer, including both odd and even high harmonics (of the pulse center frequency) up to order n≤7. The directly pumped spin current then exerts spin torque on local magnetization whose dynamics, in turn, pumps additional spin and charge currents radiating in the terahertz range. By switching on and off LLG dynamics and SO couplings, we unravel which microscopic mechanism contributes the most to emitted terahertz radiation—charge pumping by local magnetization of Mn3Sn in the presence of it own SO coupling is far more important than standardly assumed (for other types of magnetic layers) spin pumping and subsequent spin-to-charge conversion within the adjacent nonmagnetic SO-coupled material.Item 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.