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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Recovered supernova Ia rate from simulated LSST images
(Astronomy & Astrophysics, 2024-05-24) Petrecca, V.; Botticella, M. T.; Cappellaro, E.; Greggio, L.; Sánchez, B. O.; Möller, A.; Sako, M.; Graham, M. L.; Paolillo, M.; Bianco, F.; the LSST Dark Energy Science Collaboration
Aims. The Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) will revolutionize time-domain astronomy by detecting millions of different transients. In particular, it is expected to increase the number of known type Ia supernovae (SN Ia) by a factor of 100 compared to existing samples up to redshift ∼1.2. Such a high number of events will dramatically reduce statistical uncertainties in the analysis of the properties and rates of these objects. However, the impact of all other sources of uncertainty on the measurement of the SN Ia rate must still be evaluated. The comprehension and reduction of such uncertainties will be fundamental both for cosmology and stellar evolution studies, as measuring the SN Ia rate can put constraints on the evolutionary scenarios of different SN Ia progenitors. Methods. We used simulated data from the Dark Energy Science Collaboration (DESC) Data Challenge 2 (DC2) and LSST Data Preview 0 to measure the SN Ia rate on a 15 deg2 region of the “wide-fast-deep” area. We selected a sample of SN candidates detected in difference images, associated them to the host galaxy with a specially developed algorithm, and retrieved their photometric redshifts. We then tested different light-curve classification methods, with and without redshift priors (albeit ignoring contamination from other transients, as DC2 contains only SN Ia). We discuss how the distribution in redshift measured for the SN candidates changes according to the selected host galaxy and redshift estimate. Results. We measured the SN Ia rate, analyzing the impact of uncertainties due to photometric redshift, host-galaxy association and classification on the distribution in redshift of the starting sample. We find that we are missing 17% of the SN Ia, on average, with respect to the simulated sample. As 10% of the mismatch is due to the uncertainty on the photometric redshift alone (which also affects classification when used as a prior), we conclude that this parameter is the major source of uncertainty. We discuss possible reduction of the errors in the measurement of the SN Ia rate, including synergies with other surveys, which may help us to use the rate to discriminate different progenitor models.
Large Rashba spin splittings in bulk and monolayer of BiAs
(Physical Review Materials, 2024-05-20) Zubair, Muhammad; Evangelista, Igor; Khalid, Shoaib; Medasani, Bharat; Janotti, Anderson
There is great interest in developing new materials with Rashba split bands near the Fermi level for spintronics. Using first-principles calculations, we predict BiAs as a semiconductor with large Rashba splitting in bulk and monolayer forms. Bulk BiAs has a layered crystal structure with two atoms in a rhombohedral primitive cell, derived from the structure of the parent Bi and As elemental phases. It is a narrow band gap semiconductor, and it shows a combination of Rashba and Dresselhaus spin splitting with a characteristic spin texture around the L point in the Brillouin zone of the hexagonal conventional unit cell. It has sizable Rashba energies and Rashba coupling constants in the valence and conduction bands at the band edges. The 2D monolayer of BiAs has a much larger band gap at Γ, with a circular spin texture characteristic of a pure Rashba effect. The Rashba energy and Rashba coupling constant of monolayer BiAs are large compared to other known 2D materials and rapidly increase under biaxial tensile strain.
Natural-linewidth measurements of the 3⁢𝐶 and 3⁢𝐷 soft-x-ray transitions in Ni xix
(Physical Review A, 2024-06-10) Shah, Chintan; Kühn, Steffen; Bernitt, Sonja; Steinbrügge, René; Togawa, Moto; Berger, Lukas; Buck, Jens; Hoesch, Moritz; Seltmann, Jörn; Kozlov, Mikhail G.; Porsev, Sergey G.; Gu, Ming Feng; Porter, F. Scott; Pfeifer, Thomas; Leutenegger, Maurice A.; Cheung, Charles; Safronova, Marianna S.; Crespo López-Urrutia, José R.
We used the monochromatic soft-x-ray beamline P04 at the synchrotron-radiation facility PETRA III to resonantly excite the strongest 2⁢𝑝−3⁢𝑑 transitions in neonlike Nixix ions, [2⁢𝑝6]𝐽=0→[(2⁢𝑝5)1/23⁢𝑑3/2]𝐽=1 and [2⁢𝑝6]𝐽=0→[(2⁢𝑝5)3/23⁢𝑑5/2]𝐽=1, respectively dubbed 3⁢𝐶 and 3⁢𝐷, achieving a resolving power of 15 000 and signal-to-background ratio of 30. We obtain their natural linewidths, with an accuracy of better than 10%, as well as the oscillator-strength ratio 𝑓⁡(3⁢𝐶)/𝑓⁡(3⁢𝐷)=2.51⁢(11) from analysis of the resonant fluorescence spectra. These results agree with those of previous experiments, earlier predictions, and our own advanced calculations.
Turbulence and particle energization in twisted flux ropes under solar-wind conditions
(Astronomy & Astrophysics, 2024-06-04) Pezzi, O.; Trotta, D.; Benella, S.; Sorriso-Valvo, L.; Malara, F.; Pucci, F.; Meringolo, C.; Matthaeus, W. H.; Servidio, S.
Context. The mechanisms regulating the transport and energization of charged particles in space and astrophysical plasmas are still debated. Plasma turbulence is known to be a powerful particle accelerator. Large-scale structures, including flux ropes and plasmoids, may contribute to confining particles and lead to fast particle energization. These structures may also modify the properties of the turbulent, nonlinear transfer across scales. Aims. We aim to investigate how large-scale flux ropes are perturbed and, simultaneously, how they influence the nonlinear transfer of turbulent energy toward smaller scales. We then intend to address how these structures affect particle transport and energization. Methods. We adopted magnetohydrodynamic simulations perturbing a large-scale flux rope in solar-wind conditions and possibly triggering turbulence. Then, we employed test-particle methods to investigate particle transport and energization in the perturbed flux rope. Results. The large-scale helical flux rope inhibits the turbulent cascade toward smaller scales, especially if the amplitude of the initial perturbations is not large (∼5%). In this case, particle transport is inhibited inside the structure. Fast particle acceleration occurs in association with phases of trapped motion within the large-scale flux rope.
MEMS-actuated terahertz metamaterials driven by phase-transition materials
(Frontiers of Optoelectronics, 2024-05-27) Huang, Zhixiang; Wu, Weipeng; Herrmann, Eric; Ma, Ke; Chase, Zizwe A.; Searles, Thomas A.; Jungfleisch, M. Benjamin; Wang, Xi
The non-ionizing and penetrative characteristics of terahertz (THz) radiation have recently led to its adoption across a variety of applications. To effectively utilize THz radiation, modulators with precise control are imperative. While most recent THz modulators manipulate the amplitude, frequency, or phase of incident THz radiation, considerably less progress has been made toward THz polarization modulation. Conventional methods for polarization control suffer from high driving voltages, restricted modulation depth, and narrow band capabilities, which hinder device performance and broader applications. Consequently, an ideal THz modulator that offers high modulation depth along with ease of processing and operation is required. In this paper, we propose and realize a THz metamaterial comprised of microelectromechanical systems (MEMS) actuated by the phase-transition material vanadium dioxide (VO2). Simulation and experimental results of the three-dimensional metamaterials show that by leveraging the unique phase-transition attributes of VO2, our THz polarization modulator offers notable advancements over existing designs, including broad operation spectrum, high modulation depth, ease of fabrication, ease of operation condition, and continuous modulation capabilities. These enhanced features make the system a viable candidate for a range of THz applications, including telecommunications, imaging, and radar systems. Graphical Abstract available at: https://doi.org/10.1007/s12200-024-00116-4
Ultrastrong magnon-magnon coupling and chiral spin-texture control in a dipolar 3D multilayered artificial spin-vortex ice
(Nature Communications, 2024-05-14) Dion, Troy; Stenning, Kilian D.; Vanstone, Alex; Holder, Holly H.; Sultana, Rawnak; Alatteili, Ghanem; Martinez, Victoria; Kaffash, Mojtaba Taghipour; Kimura, Takashi; Oulton, Rupert F.; Branford, Will R.; Kurebayashi, Hidekazu; Iacocca, Ezio; Jungfleisch, M. Benjamin; Gartside, Jack C.
Strongly-interacting nanomagnetic arrays are ideal systems for exploring reconfigurable magnonics. They provide huge microstate spaces and integrated solutions for storage and neuromorphic computing alongside GHz functionality. These systems may be broadly assessed by their range of reliably accessible states and the strength of magnon coupling phenomena and nonlinearities. Increasingly, nanomagnetic systems are expanding into three-dimensional architectures. This has enhanced the range of available magnetic microstates and functional behaviours, but engineering control over 3D states and dynamics remains challenging. Here, we introduce a 3D magnonic metamaterial composed from multilayered artificial spin ice nanoarrays. Comprising two magnetic layers separated by a non-magnetic spacer, each nanoisland may assume four macrospin or vortex states per magnetic layer. This creates a system with a rich 16N microstate space and intense static and dynamic dipolar magnetic coupling. The system exhibits a broad range of emergent phenomena driven by the strong inter-layer dipolar interaction, including ultrastrong magnon-magnon coupling with normalised coupling rates of Δf/ν =0.57, GHz mode shifts in zero applied field and chirality-control of magnetic vortex microstates with corresponding magnonic spectra.
Giant enhanced stability of the quantum electron solid from a weakened electron-electron interaction in double-layer MoS 2
(Physical Review B, 2024-03-19) Chui, S. T.; Huang, Meizhen; Wu, Zefei; Wang, Ning
The melting temperature of the quantum electron solid in double-layer two-dimensional MoS2 stacked on opposite sides of a thin layer of BN is larger than previous single-layer results in Si-MOSFETs and bilayer estimates by four orders of magnitude. This giant enhancement of the stability of the solid comes from a shear modulus μ that is an order of magnitude larger than expected and comes from a weakened electron-electron interaction due to the screening by the polarization charges at the interfaces of the experimental structure. We found that the short-range part of the interelectron Coulomb potential actually provides for a negative contribution to μ and makes the lattice less stable. The weakening of this short-range contribution enhances μ by an order of magnitude. This large μ, together with a larger energy scale e2/ab for a smaller Bohr radius ab for the experimental structure, leads to a high melting temperature and makes possible using the structure as a practical logic device. Our understanding of this phenomenon guides us in optimizing its design. The large melting temperature and the small zero-temperature critical density agrees with experimental results extracted from the density and temperature dependence of the Coulomb drag resistance.
Using ZDI maps to determine magnetic forces and torques at the photospheres of early-type stars
(Monthly Notices of the Royal Astronomical Society, 2024-04-30) MacDonald, James; Natan, Tali; Petit, Véronique; Kochukhov, Oleg; Shultz, Matthew E.
We use the magnetic field components measured by Zeeman Doppler imaging (ZDI) to calculate the stellar surface force and torque due to magnetic stresses for the fast rotators σ Ori E, 36 Lyn, and CU Vir, and the slow rotator τ Sco. If we assume the stars have spherical photospheres, the estimated torques give spin-down time-scales no larger than 7 × 105 yr. For σ Ori E, the predicted spin-down time-scale, ≃ 6000 yr, is much less than the observationally measured time-scale of ≃ 106 yr. However, for CU Vir, we find that the spin-down time-scale from its ZDI map is 7 × 105 yr in good agreement with its average rate of spin-down from 1960 to 2010. With the exception of τ Sco, the net force due to magnetic stresses at the stellar surface are large compared to the surface-integrated pressure. We discuss possible reasons for the large values of the forces (and torques), and suggest that the likely explanation is that rotation and the magnetic stresses create significant departures from spherical symmetry.
COVID-19 Questions for Physics Exams
(The Physics Teacher, 2024-02-01) Wallace, Colin Scott; Deardorff, Duane; Young, Daniel; Churukian, Alice D.
Physics instructors are always looking for questions and activities that both are tractable to students and illuminate real-life applications of physics. This is especially true in Introductory Physics for the Life Sciences (IPLS), where many students enter with the belief that physics is merely a “weed-out” course that has little to do with their majors and career goals.1 Authentic applications of physics to the life sciences help dispel this myth. The COVID-19 pandemic provides numerous examples of the relevance of physics to current events and the life sciences. Physics principles are used both to model the spread of the disease and to develop technologies that curb its transmission. Given the disruption COVID-19 has wrought on almost every aspect of life, physics content related to the pandemic inevitably captures students’ attention. Few topics are more relevant to their lives, at the time of writing, than COVID-19. While previous papers report on the effects of COVID-19 on physics instruction,2 COVID-related curricular materials have not been widely disseminated. This paper looks at how information about the disease can be incorporated into the assessment aspect of a class. Specifically, we share a sample of exam questions we have used to assess IPLS students since the beginning of the COVID-19 pandemic. Since they are exam questions, they are written such that they can be answered by a student in a short period of time as part of a larger timed assessment. Consequently, they are not meant to investigate every possible application of physics to COVID-19. They are also not meant to be collaborative activities that require a substantial amount of time, and potentially interdisciplinary knowledge to solve, although we have used them to assess the knowledge of students who have come through an IPLS sequence using such activities.3 Instructors looking for inspiration as they develop an activity may find these questions to be a fruitful launching point. These questions can also be used by other instructors on exams or developed into interactive in-class problem-solving activities.4 The questions below assess content from three different parts of our IPLS sequence: scaling, diffusion, and electricity. The following sections show the sample exam questions, describe their solutions and their relevance to our IPLS sequence, and discuss students’ performance in answering these questions.
Band Engineering of ErAs:InGaAlBiAs Nanocomposite Materials for Terahertz Photoconductive Switches Pumped at 1550 nm
(Advanced Functional Materials, 2024-04-18) Acuna, Wilder; Wu, Weipeng; Bork, James; Doty, Mathew F.; Jungfleisch, M. Benjamin; Gundlach, Lars; Zide, Joshua M. O.
Terahertz technology has the potential to have a large impact in myriad fields, such as biomedical science, spectroscopy, and communications. Making these applications practical requires efficient, reliable, and low-cost devices. Photoconductive switches (PCS), devices capable of emitting and detecting terahertz pulses, are a technology that needs more efficiency when working at telecom wavelength excitation (1550 nm) to exploit the advantages this wavelength offers. ErAs:InGaAs is a semiconductor nanocomposite working at this energy; however, high dark resistivity is challenging due to a high electron concentration as the Fermi level lies in the conduction band. To increase dark resistivity, ErAs:InGaAlBiAs material is used as the active material in a PCS detecting Terahertz pulses. ErAs nanoparticles reduce the carrier lifetime to subpicosecond values required for short temporal resolution, while ErAs pins the effective Fermi level in the host material bandgap. Unlike InGaAs, InGaAlBiAs offers enough freedom for band engineering to have a material compatible with a 1550 nm pump and a Fermi level deep in the bandgap, meaning low carrier concentration and high dark resistivity. Band engineering is possible by incorporating aluminum to lift the conduction band edge to the Fermi level and bismuth to keep a bandgap compatible with 1550 nm excitation.
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.
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.
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.
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.
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.
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.
Low temperature spin relaxation length exceeding 3 μm in highly conductive copper channels
(Journal of Applied Physics, 2023-10-14) Shen, Xingyu; Ji, Yi
Despite 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.
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.
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.
Observation of ultrafast ballistic orbital transport
(Nature Nanotechnology, 2023-08-07) Jungfleisch, M. Benjamin
Terahertz 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.

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