Open Access Publications - Department of Physics and Astronomy

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

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Lipid–GPCR interactions in an asymmetric plasma membrane model
(Faraday Discussions, 2025-01-30) Ji, Jingjing; Lyman, Edward
We report simulations and analysis of the A2A adenosine receptor in its fully active state, in two different membrane environments. The first is a model in which the lipids are distributed asymmetrically according to recent lipidomics, simulations, and biophysical measurements, which together establish the distribution of lipids and cholesterol between the two leaflets. The second is the symmetrized version, which captures the membrane state following loss of lipid asymmetry. By comparing lipid–protein interactions between these two cases we show that solvation by phosphatidyl serine (PS) is insensitive to the loss of asymmetry—an abundance of positively charged sidechains around the cytoplasmic side of the receptor enriches solvation by PS in both membrane states. Cholesterol interactions are sensitive to the loss of asymmetry, with the abundance of cholesterol in the exoplasmic leaflet driving long-lived cholesterol interactions in the asymmetric state. However, one cholesterol interaction site on helix 6 is observed in both cases, and was also observed in earlier work with different membrane models, supporting its identification as a bona fide cholesterol binding site.
Measurement of Atmospheric Neutrino Oscillation Parameters Using Convolutional Neural Networks with 9.3 Years of Data in IceCube DeepCore
(Physical Review Letters, 2025-03-07) Abbasi, R.; Ackermann, M.; Adams, J.; Agarwalla, S. K.; Aguilar, J. A.; Ahlers, M.; Alameddine, J. M.; Amin, N. M.; Andeen, K.; et al.
The DeepCore subdetector of the IceCube Neutrino Observatory provides access to neutrinos with energies above approximately 5 GeV. Data taken between 2012 and 2021 (3387 days) are utilized for an atmospheric 𝜈𝜇 disappearance analysis that studied 150 257 neutrino-candidate events with reconstructed energies between 5 and 100 GeV. An advanced reconstruction based on a convolutional neural network is applied, providing increased signal efficiency and background suppression, resulting in a measurement with both significantly increased statistics compared to previous DeepCore oscillation results and high neutrino purity. For the normal neutrino mass ordering, the atmospheric neutrino oscillation parameters and their 1⁢𝜎 errors are measured to be Δ⁢m2 32=2.40+0.05−0.04×10−3 eV2 and sin2⁡𝜃23=0.54+0.04−0.03. The results are the most precise to date using atmospheric neutrinos, and are compatible with measurements from other neutrino detectors including long-baseline accelerator experiments.
Observation of Cosmic-Ray Anisotropy in the Southern Hemisphere with 12 yr of Data Collected by the IceCube Neutrino Observatory
(The Astrophysical Journal, 2025-03-07) Abbasi, R.; Ackermann, M.; Adams, J.; Agarwalla, S. K.; Aguado, T.; Aguilar, J. A.; Ahlers, M.; Alameddine, J. M.; Amin, N. M.; Andeen, K.; et al.
We analyzed the 7.92 × 1011 cosmic-ray-induced muon events collected by the IceCube Neutrino Observatory from 2011 May 13, when the fully constructed experiment started to take data, to 2023 May 12. This data set provides an up-to-date cosmic-ray arrival direction distribution in the Southern Hemisphere with unprecedented statistical accuracy covering more than a full period length of a solar cycle. Improvements in Monte Carlo event simulation and better handling of year-to-year differences in data processing significantly reduce systematic uncertainties below the level of statistical fluctuations compared to the previously published results. We confirm the observation of a change in the angular structure of the cosmic-ray anisotropy between 10 TeV and 1 PeV, more specifically in the 100–300 TeV energy range. For the first time, we analyzed the angular power spectrum at different energies. The observed variations of the power spectra with energy suggest relatively reduced large-scale features at high energy compared to those of medium and small scales. The large volume of data enhances the statistical significance at higher energies, up to the PeV scale, and smaller angular scales, down to approximately 6° compared to previous findings.
Engineering corner states by coupling two-dimensional topological insulators
(Physical Review B, 2025-01-06) Liu, Lizhou; An, Jiaqi; Ren, Yafei; Zhang, Ying-Tao; Qiao, Zhenhua; Niu, Qian
We theoretically find that the second-order topological insulator, i.e., corner states, can be engineered by coupling two copies of two-dimensional ℤ2 topological insulators with opposite spin helicities. As concrete examples, we utilize Kane-Mele models (i.e., graphene with intrinsic spin-orbit coupling) to realize the corner states by setting the respective graphenes as ℤ2 topological insulators with opposite intrinsic spin-orbit couplings. To exhibit its universality, we generalize our findings to other representative ℤ2 topological insulators, e.g., the Bernevig-Hughes-Zhang model. An effective model is presented to reveal the physical origin of the corner states. We further show that the corner states can also be designed in other topological systems, e.g., by coupling quantum anomalous Hall systems with opposite Chern numbers. Our work suggests that interlayer coupling can be treated as a simple and efficient strategy to drive two-dimensional lower-order topological insulators to the higher-order ones.
Dispersionless Nonhybrid Density Functional
(Journal of Chemical Theory and Computation, 2025-02-11) Rehman, Atta Ur; Szalewicz, Krzysztof
A dispersion-corrected density functional theory (DFT+D) method has been developed. It includes a nonhybrid dispersionless generalized gradient approximation (GGA) functional paired with a literature-parametrized dispersion function. The functional’s 9 adjustable parameters were optimized using a training set of 589 benchmark interaction energies. The resulting method performs better than other GGA-based DFT+D methods, giving a mean unsigned error of 0.33 kcal/mol. It even performs better than some more expensive meta-GGA or hybrid dispersion-corrected functionals. An important advantage of using the new functional is that its dispersion energy given by the D component is very close to the true dispersion energy at all intermolecular separations, whereas in other similarly accurate DFT+D approaches, such a dispersion contribution in the van der Waals minimum region is only a small fraction of the true value.
First Observation of the Complete Rotation Period of the Ultraslowly Rotating Magnetic O Star HD 54879
(The Astrophysical Journal, 2024-12-04) Erba, C.; Folsom, C. P.; David-Uraz, A.; Wade, G. A.; Seadrow, S.; Bellotti, S.; Fossati, L.; Petit, V.; Shultz, M. E.
HD 54879 is the most recently discovered magnetic O-type star. Previous studies ruled out a rotation period shorter than 7 yr, implying that HD 54879 is the second most slowly rotating known magnetic O-type star. We report new high-resolution spectropolarimetric measurements of HD 54879, which confirm that a full stellar rotation cycle has been observed. We derive a stellar rotation period from the longitudinal magnetic field measurements of P = 2562 +63 -58 days (about 7.02 yr). The radial velocity of HD 54879 has been stable over the last decade of observations. We explore equivalent widths and longitudinal magnetic fields calculated from lines of different elements, and conclude the atmosphere of HD 54879 is likely chemically homogeneous, with no strong evidence for chemical stratification or lateral abundance nonuniformities. We present the first detailed magnetic map of the star, with an average surface-magnetic-field strength of 2954 G, and a strength for the dipole component of 3939 G. There is a significant amount of magnetic energy in the quadrupole components of the field (23%). Thus, we find HD 54879 has a strong magnetic field with a significantly complex topology.
2025 roadmap on 3D nanomagnetism
(Journal of Physics: Condensed Matter, 2025-02-19) Gubbiotti, Gianluca; Barman, Anjan; Ladak, Sam; Bran, Cristina; et al.
The transition from planar to three-dimensional (3D) magnetic nanostructures represents a significant advancement in both fundamental research and practical applications, offering vast potential for next-generation technologies like ultrahigh-density storage, memory, logic, and neuromorphic computing. Despite being a relatively new field, the emergence of 3D nanomagnetism presents numerous opportunities for innovation, prompting the creation of a comprehensive roadmap by leading international researchers. This roadmap aims to facilitate collaboration and interdisciplinary dialogue to address challenges in materials science, physics, engineering, and computing. The roadmap comprises eighteen sections, roughly divided into three blocks. The first block explores the fundamentals of 3D nanomagnetism, focusing on recent trends in fabrication techniques and imaging methods crucial for understanding complex spin textures, curved surfaces, and small-scale interactions. Techniques such as two-photon lithography and focused electron beam-induced deposition enable the creation of intricate 3D architectures, while advanced imaging methods like electron holography and synchrotron x-ray tomography provide nanoscale spatial resolution for studying magnetization dynamics in three dimensions. Various 3D magnetic systems, including coupled multilayer systems, artificial spin-ice, magneto-plasmonic systems, topological spin textures, and molecular magnets are discussed. The second block introduces analytical and numerical methods for investigating 3D nanomagnetic structures and curvilinear systems, highlighting geometrically curved architectures, interconnected nanowire systems, and other complex geometries. Finite element methods are emphasized for capturing complex geometries, along with direct frequency domain solutions for addressing magnonic problems. The final block focuses on 3D magnonic crystals and networks, exploring their fundamental properties and potential applications in magnonic circuits, memory, and spintronics. Computational approaches using 3D nanomagnetic systems and complex topological textures in 3D spintronics are highlighted for their potential to enable faster and more energy-efficient computing.
Dynamic Imprints of Colliding-wind Dust Formation from WR 140
(The Astrophysical Journal Letters, 2025-01-20) Lieb, Emma P.; Lau, Ryan M.; Hoffman, Jennifer L.; Corcoran, Michael F.; Marin, Macarena Garcia; Gull, Theodore R.; Hamaguchi, Kenji; Han, Yinuo; Hankins, Matthew J.; Jones, Olivia C.; Madura, Thomas I.; Marchenko, Sergey V.; Matsuhara, Hideo; Millour, Florentin; Moffat, Anthony F. J.; Morris, Mark R.; Morris, Patrick W.; Onaka, Takashi; Perrin, Marshall D.; Rest, Armin; Richardson, Noel; Russell, Christopher M. P.; Sanchez-Bermudez, Joel; Soulain, Anthony; Tuthill, Peter; Weigelt, Gerd; William, Peredur M.
Carbon-rich Wolf–Rayet (WR) binaries are a prominent source of carbonaceous dust that contribute to the dust budget of galaxies. The "textbook" example of an episodic dust-producing WR binary, WR 140 (HD 193793), provides us with an ideal laboratory for investigating the dust physics and kinematics in an extreme environment. This study is among the first to utilize two separate JWST observations, from Cycle 1 ERS (2022 July) and Cycle 2 (2023 September), to measure WR 140's dust kinematics and confirm its morphology. To measure the proper motions and projected velocities of the dust shells, we performed a novel point-spread function (PSF) subtraction to reduce the effects of the bright diffraction spikes and carefully aligned the Cycle 2 to the Cycle 1 images. At 7.7 μm, through the bright feature common to 16 dust shells (C1), we find an average dust shell proper motion of 390 ± 29 mas yr−1, which equates to a projected velocity of 2714 ± 188 km s−1 at a distance of 1.64 kpc. Our measured speeds are constant across all visible shells and consistent with previously reported dust expansion velocities. Our observations not only prove that these dusty shells are astrophysical (i.e., not associated with any PSF artifact) and originate from WR 140, but also confirm the "clumpy" morphology of the dust shells, in which identifiable substructures within certain shells persist for at least 14 months from one cycle to the next. These results support the hypothesis that clumping in the wind collision region is required for dust production in WR binaries.
Phonons reveal coupled cholesterol-lipid dynamics in ternary membranes
(Biophysical Journal, 2024-12-03) Fitzgerald, James E.; Soloviov, Dmytro; Cai, Yong Q.; Heberle, Frederick A.; Ishikawa, Daisuke; Baron, Alfred Q.R.; Bolmatov, Dima; Zhernenkov, Mikhail; Lyman, Edward R.
Experimental studies of collective dynamics in lipid bilayers have been challenging due to the energy resolution required to observe these low-energy phonon-like modes. However, inelastic x-ray scattering (IXS) measurements—a technique for probing vibrations in soft and biological materials—are now possible with sub-meV resolution, permitting direct observation of low-energy, phonon-like modes in lipid membranes. Here, IXS measurements with sub-meV energy resolution reveal a low-energy optic-like phonon mode at roughly 3 meV in the liquid-ordered ðLoÞ and liquid-disordered phases of a ternary lipid mixture. This mode is only observed experimentally at momentum transfers greater than 5 nm 1 in the Lo system. A similar gapped mode is also observed in all-atom molecular dynamics (MD) simulations of the same mixture, indicating that the simulations accurately represent the fast, collective dynamics in the L o phase. Its optical nature and the Q range of the gap together suggest that the observed mode is due to the coupled motion of cholesterol-lipid pairs, separated by several hydrocarbon chains within the membrane plane. Analysis of the simulations provides molecular insight into the origin of the mode in transient, nanoscale substructures of hexagonally packed hydrocarbon chains. This nanoscale hexagonal packing was previously reported based on MD simulations and, later, by NMR measurements. Here, however, the integration of IXS and MD simulations identifies a new signature of the Lo substructure in the collective lipid dynamics, thanks to the recent confluence of IXS sensitivity and MD simulation capabilities.
Electron Dissipation and Electromagnetic Work
(JGR: Space Physics, 2024-10-14) Yang, Yan; Adhikari, Subash; Matthaeus, William H.
With the increase in technical capabilities of computer simulation in recent years, it has become feasible to quantify the degradation of fluid scale plasma and electromagnetic energies in favor of increases of internal energies. While it is understood that electromagnetic energy can be exchanged with fluid scale velocities, it is the pressure strain interaction that exchanges energy between fluid motions and internal energy. Here using simulations of both turbulence and reconnection we show that for electrons, the pressure strain and electromagnetic work are closely related and are frequently comparable when appropriate time and spatial averaging is applied. Otherwise, the instantaneous spatial averaged pressure strain and electromagnetic work are nearly equal for slowly evolving systems, like the reconnection case, while they differ significantly in rapidly evolving systems, like the turbulence case. This clarifies the relationship between these two quantities, which are each frequently used as measures of dissipation. Key Points - Time integrated volume averaged electromagnetic work does not formally or generally correspond to dissipation - Due to small electron mass, time integrated volume averaged pressure strain and electromagnetic work are nearly equal for electrons - Differences between instantaneous electromagnetic work and pressure strain can be considerable, but for electrons, these average to zero Plain Language Summary The electromagnetic field changes the fluid velocity of each type of plasma particle. Meanwhile, the pressure of each plasma species, interacts with nonuniform fluid velocities to produce heat. The intermediate steps are in general, complicated, but because electrons are so light, a special simplifying approximation holds, equating properly averaged electromagnetic work on electrons to the rate of increase of electron internal energy. This result may help clarify differences in how the reconnection and turbulence communities quantify “dissipation”.
The Role of Polarization for Bound States in Strong Fields
(Journal of Physics: Conference Series, 2024-11-01) Walker, B. C.; Jones, E. C.; Andreula, Z.; Gale, M. R.; Pham, M.; Wisely, J.
As atomic matter interacts with ultrastrong fields, the bound electrons are polarized and have ionization energies changed by Stark-shifting. The unprecedented range of laser intensities from 1015 W cm−2 to 1024 W cm−2 can take the interaction from the neutral atom to a bare nucleus. We have used an outer, single active electron approximation to calculate the polarization and Stark-shifted binding energy for ultraintense lasers interacting with highly charged ions at intensities from 1014 W cm−2 to 1022 W cm−2. The polarization of the bound state can result in a dipole moment and Stark shift that may be 0.1 e a0 and 50 Eh, respectively. At these high intensities, relativistic effects must also be considered. Across the intensity range of these studies, the magnetic field of the laser does not comparably affect the bound state of the atom; the impact of polarization and Stark shift exceed changes to the bound state wave function and binding energy from including relativity.
Constraints on dark matter from dynamical heating of stars in ultrafaint dwarfs. II. Substructure and the primordial power spectrum
(Physical Review D, 2024-10-15) Graham, Peter W.; Ramani, Harikrishnan
There is a large and growing interest in observations of small-scale structure in dark matter. We propose a new way to probe dark matter structures in the ∼10–108⁢𝑀⊙ range. This allows us to constrain the primordial power spectrum over shorter distances scales than possible with direct observations from the CMB. For 𝑘 in the range ∼10–1000 Mpc−1 our constraints on the power spectrum are orders of magnitude stronger than previous bounds. We also set some of the strongest constraints on dark matter isocurvature perturbations. Our method relies on the heating effect such dark matter substructures would have on the distribution of stars in an ultrafaint dwarf galaxy. Many models of inflation produce enhanced power at these short distance scales and can thus be constrained by our observation. Further, many dark matter models such as axion dark matter, self-interacting dark matter and dissipative dark matter, produce dense structures which could be constrained this way.
Multifilter UV to Near-infrared Data-driven Light-curve Templates for Stripped-envelope Supernovae
(The Astrophysical Journal: Supplement Series, 2024-11-29) Khakpash, Somayeh; Bianco, Federica B.; Modjaz, Maryam; Fortino, Willow F.; Gagliano, Alexander; Larison, Conor; Pritchard, Tyler A.
While the spectroscopic classification scheme for stripped-envelope supernovae (SESNe) is clear, and we know that they originate from massive stars that lost some or all of their envelopes of hydrogen and helium, the photometric evolution of classes within this family is not fully characterized. Photometric surveys, like the Vera C. Rubin Legacy Survey of Space and Time, will discover tens of thousands of transients each night, and spectroscopic follow-up will be limited, prompting the need for photometric classification and inference based solely on photometry. We have generated 54 data-driven photometric templates for SESNe of subtypes IIb, Ib, Ic, Ic-bl, and Ibn in U/u, B, g, V, R/r, I/i, J, H, Ks, and Swift w2, m2, w1 bands using Gaussian processes and a multisurvey data set composed of all well-sampled open-access light curves (165 SESNe, 29,531 data points) from the Open Supernova Catalog. We use our new templates to assess the photometric diversity of SESNe by comparing final per-band subtype templates with each other and with individual, unusual and prototypical SESNe. We find that SNe Ibn and SNe Ic-bl exhibit a distinctly faster rise and decline compared to other subtypes. We also evaluate the behavior of SESNe in the PLAsTiCC and ELAsTiCC simulations of LSST light curves, highlighting differences that can bias photometric classification models trained on the simulated light curves. Finally, we investigate in detail the behavior of fast-evolving SESNe (including SNe Ibn) and the implications of the frequently observed presence of two peaks in their light curves.
Cosmic-Ray Flux Correlation between MCMU and JBGO Neutron Monitors
(The Astrophysical Journal, 2024-11-08) Kittiya, A.; Nuntiyakul, W.; Seripienlert, A.; Madlee, S.; Sonsrettee, W.; Evenson, P.; Ruffolo, D.; Sáiz, A.; Oh, S.; Jung, J.
Neutron monitors (NMs) are large ground-based detectors of atmospheric secondary particles, mostly neutrons, from primary cosmic rays. Their sky direction and rigidity imply a well-defined incoming (asymptotic) direction in space. From 2015 December 16 to 2017 January 8, 6 of the 18 NM counters had been transferred from McMurdo to Jang Bogo, both in Antarctica, so data from similar detectors were recorded simultaneously at these two nearby NM stations. Autocorrelations of these NM count rates are well fit as the sum of three components: an exponential function and a cosine with a period of 1 day, both centered at zero lag, plus a constant. Fitting the cross correlation of the two count rates, the functions are no longer centered at zero lag. The best-fit cosine phase is at time lag −160.22 ± 0.12 minutes. Calculating cosmic-ray trajectories in Earth's magnetic field throughout the time interval, the mean difference in response-weighted asymptotic longitudes corresponds to time lag −169.41 ± 0.31 minutes, in close agreement with the observed lag. Thus, the cosine term is consistent with and provides a technique to cleanly measure the cosmic-ray anisotropy. In contrast, the peak term shows a time lag of –14.55 minutes, much closer to the –9.60 minutes lag in rotation due to the difference in geographic longitude. We find a similar behavior in the correlations between other pairs of stations. We propose that rapid fluctuations in the counting rate may be primarily due to cosmic-ray particles of very high energy.
Nonlinear multi-magnon scattering in artificial spin ice
(Nature Communications, 2023-06-09) Lendinez, Sergi; Kaffash, Mojtaba T.; Heinonen, Olle G.; Gliga, Sebastian; Iacocca, Ezio; Jungfleisch, M. Benjamin
Magnons, the quantum-mechanical fundamental excitations of magnetic solids, are bosons whose number does not need to be conserved in scattering processes. Microwave-induced parametric magnon processes, often called Suhl instabilities, have been believed to occur in magnetic thin films only, where quasi-continuous magnon bands exist. Here, we reveal the existence of such nonlinear magnon-magnon scattering processes and their coherence in ensembles of magnetic nanostructures known as artificial spin ice. We find that these systems exhibit effective scattering processes akin to those observed in continuous magnetic thin films. We utilize a combined microwave and microfocused Brillouin light scattering measurement approach to investigate the evolution of their modes. Scattering events occur between resonance frequencies that are determined by each nanomagnet’s mode volume and profile. Comparison with numerical simulations reveals that frequency doubling is enabled by exciting a subset of nanomagnets that, in turn, act as nanosized antennas, an effect that is akin to scattering in continuous films. Moreover, our results suggest that tunable directional scattering is possible in these structures.
The seventh blind test of crystal structure prediction: structure generation methods
(Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials, 2024-12-01) Hunnisett, Lily M.; Nyman, Jonas; Francia, Nicholas; Abraham, Nathan S.; et al.
A seventh blind test of crystal structure prediction was organized by the Cambridge Crystallographic Data Centre featuring seven target systems of varying complexity: a silicon and iodine-containing molecule, a copper coordination complex, a near-rigid molecule, a cocrystal, a polymorphic small agrochemical, a highly flexible polymorphic drug candidate, and a polymorphic morpholine salt. In this first of two parts focusing on structure generation methods, many crystal structure prediction (CSP) methods performed well for the small but flexible agrochemical compound, successfully reproducing the experimentally observed crystal structures, while few groups were successful for the systems of higher complexity. A powder X-ray diffraction (PXRD) assisted exercise demonstrated the use of CSP in successfully determining a crystal structure from a low-quality PXRD pattern. The use of CSP in the prediction of likely cocrystal stoichiometry was also explored, demonstrating multiple possible approaches. Crystallographic disorder emerged as an important theme throughout the test as both a challenge for analysis and a major achievement where two groups blindly predicted the existence of disorder for the first time. Additionally, large-scale comparisons of the sets of predicted crystal structures also showed that some methods yield sets that largely contain the same crystal structures.
XMM-Newton Perspective of the Unique Magnetic Binary-epsilon Lupi
(The Astrophysical Journal, 2024-10-11) Biswas, Ayan; Wade, Gregg A.; Chandra, Poonam; Petit, Veronique; Das, Barnali; Shultz, Matthew E.
The epsilon Lupi A (HD 136504) system stands out among magnetic massive binaries as the only short-period binary system in which both components have detectable magnetic fields. The proximity of the magnetospheres of the components leads to magnetospheric interactions, which are revealed as periodic pulses in the radio light curve of this system. In this work, we aim to investigate the magnetospheric interaction phenomenon in the X-ray domain. We observed this system with the XMM-Newton telescope, covering its orbital period. We observe variable X-ray emission with maximum flux near periastron, showing similarity with radio observations. The X-ray spectra show significantly elevated hard X-ray flux during periastron. We attribute the soft X-ray emission to individual magnetospheres, while the hard X-ray emission is explained by magnetospheric interaction, particularly due to magnetic reconnection. However, unlike in the radio, we do not find any significant short-term X-ray bursts. This exotic system may be an ideal target to study magnetospheric interactions in close binaries with organized magnetospheres.
Multistructured Accretion Flow of Sgr A*. I. Examination of a Radiatively Inefficient Accretion Flow Mode
(The Astrophysical Journal, 2024-10-08) Balakrishnan, Mayura; Corrales, Lia; Markoff, Sera; Nowak, Michael; Haggard, Daryl; Wang, Q. Daniel; Neilsen, Joey; Russell, Christopher M. P.; Calderón, Diego; Cuadra, Jorge
The extreme low-luminosity supermassive black hole Sgr A* provides a unique laboratory in which to test models of radiatively inefficient accretion flows (RIAFs). Previous fits to the quiescent Chandra ACIS-S spectrum found that a RIAF model with an equal inflow–outflow balance works well. In this work, we apply the RIAF model to the Chandra HETG-S spectrum obtained through the Chandra X-ray Visionary Program, which displays features suggestive of temperature and velocity structures within the plasma. A comprehensive forward model analysis accounting for the accretion flow geometry and HETG-S instrumental effects is required for a full interpretation of the quiescent Chandra HETG-S spectrum. We present a RIAF model that takes these effects into account. Our fits to the high-resolution grating spectrum indicate an inflow balanced by an outflow (s ∼ 1) alongside a temperature profile that appears shallower than what would be expected from a gravitational potential following 1/r. The data require that the abundance of iron relative to solar is ZFe < 0.32 Z⊙ (90% credible interval), much lower than the 2 Z⊙ metallicity measured in nearby late-type giants. While future missions like NewAthena will provide higher spectral resolution, source separation will continue to be a problem. Leveraging Chandra's unparalleled spatial resolution, which is not expected to be surpassed for decades, remains essential for detailed investigations of the densely populated Galactic center in X-rays.
Cavity-Mediated Enhancement of the Energy Transfer in the Reduced Fenna–Matthews–Olson Complex
(Journal of Chemical Theory and Computation, 2024-08-27) Herrera Rodríguez, Luis E.; Sindhu, Aarti; Rueda Espinosa, Kennet J.; Kananenka, Alexei A.
Strong light-matter interaction leads to the formation of hybrid polariton states and can alter the light-harvesting properties of natural photosynthetic systems without modifying their chemical structure. In the present study, we computationally investigate the effect of the resonant cavity on the efficiency and the rate of the population transfer in a quantum system coupled to the cavity and the dissipative environment. The parameters of the model system were chosen to represent the Fenna–Matthews–Olson natural light-harvesting complex reduced to the three essential sites. The dynamics of the total system was propagated using the hierarchical equations of motion. Our results show that the strong light-matter interaction can accelerate the population transfer process compared to the cavity-free case but at the cost of lowering the transfer efficiency. The transition to the strong coupling regime was found to coincide with the degeneracy of polariton eigenvalues. Our findings indicate the potential and the limit of tuning the energy transfer in already efficient natural light-harvesting systems.
Photoexcited Energy Relaxation in Porphyrin Nanorings
(Journal of Physical Chemistry C, 2024-08-19) Rueda Espinosa, Kennet J.; Kananenka, Alexei A.
Natural photosynthetic systems convert solar energy to chemical energy with an extremely high efficiency. Synthetic chromophore arrays are promising models for understanding and mimicking energy migration in natural light-harvesting systems. To duplicate the structure and function of natural systems, a multitude of cyclic porphyrin arrays have been synthesized over the past several decades. In a recent breakthrough [Nat. Chem. 2022, 14, 1436–1442], synthetic butadiyne-linked porphyrin nanorings have been shown to exhibit excitation energy transfer on the same timescale and length scale as the natural light-harvesting complex LH2 and with comparable efficiency. In the pursuit of understanding the fundamental underpinnings of the exciton dynamics in such systems, we combined time-dependent density functional theory with the hierarchical equation of motion approach and performed a systematic study of population dynamics, coherence length, and the energy transfer in linear and cyclic multiporphyrin nanostructures with and without the butadiyne moiety. In very good agreement with experiments, we showed that the ultrafast delocalization process of the exciton in symmetric structures occurs during the first 300 fs after the excitation. Migration and localization of the excitation in segments with π-conjugation links happen on a timescale of tens of picoseconds. We also found that coherence length dynamics in multiporphyrin systems are very robust to the environmental effects. Another notable feature of butadiyne-linked porphyrin nanorings is that their energy transfer efficiency can exceed 80%.

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