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DOE OSTI2025

Coulomb excitation of 80 Sr and the limits of the 𝑁 ≈ 𝑍 ≈ 40 island of deformation

The region of 𝑁 ≈ 𝑍 ≈ 40 has long been associated with strongly deformed nuclear configurations. The presence of this strong deformation was recently confirmed through lifetime measurements in 𝑁 ≈ 𝑍 Sr and Zr nuclei. Theoretically, however, these nuclei present a challenge due to the vast valence space required to incorporate all necessary orbitals. Recent state-of-the-art predictions indicate a near axial prolate deformation for 𝑁 = 𝑍 and 𝑁 = 𝑍+2 nuclei between 𝑁 = 𝑍 = 36 and 𝑁 = 𝑍 = 40. In this work we investigate the shores of this island of deformation through a sub-barrier Coulomb excitation study of the 𝑁 = 𝑍+4 nucleus, 80 Sr . Extracting a spectroscopic quadrupole moment of 𝑄 𝑠 ⁡($2^+_1$)= $0.5^{+0.8}_{−0.9}$𝑒⁢b, we find that 80 Sr is inconsistent with significant axial prolate deformation with a significance of 1.5⁢𝜎. This result, albeit with a large uncertainty, indicates that the predicted region of strong prolate deformation around 𝑁 = 𝑍 = 40 is tightly constrained to the quartet of nuclei: 76,78 Sr and 78,80 Zr .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

Ligand field exciton annihilation in bulk CrCl 3

The layered van der Waals material CrCl 3 exhibits very strongly bound ligand field excitons that control optoelectronic applications and are connected with magnetic ordering by virtue of their d-orbital origin. Time-resolved photoluminescence of these exciton populations at room temperature shows that their relaxation is dominated by exciton–exciton annihilation and that the spontaneous decay lifetime is very long. Furthermore, these observations allow the rough quantification of the exciton annihilation rate constant and contextualization in light of a recent theory of universal scaling behavior of the annihilation process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Excited state dynamics of azanaphthalenes reveal opportunities for the rational design of photoactive molecules

Abstract Various photoactive molecules contain motifs built on aza-aromatic heterocycles, although a detailed understanding of the excited state photophysics and photochemistry in such systems is not fully developed. To help address this issue, the non-adiabatic dynamics operating in azanaphthalenes under hexane solvation was studied following 267 nm excitation using ultrafast transient absorption spectroscopy. Specifically, the species quinoline, isoquinoline, quinazoline, quinoxaline, 1,6-naphthyridine, and 1,8-naphthyridine were investigated, providing a systematic variation in the relative positioning of nitrogen heteroatom centres within a bicyclic aromatic structure. Our results indicate considerable differences in excited state lifetimes, and in the propensity for intersystem crossingvsinternal conversion across the molecular series. The overall pattern of behaviour can be explained in terms of potential energy barriers and spin-orbit coupling effects, as demonstrated by extensive quantum chemistry calculations undertaken at the SCS-ADC(2) level of theory. The fact that quantum chemistry calculations can achieve such detailed and nuanced agreement with experimental data across a full set of six molecules exhibiting subtle variations in their composition provides an excellent example of the current state-of-the-art and is indicative of future opportunities for rational design of photoactive molecules.

Chemistry↗

DOE OSTI2026

Harnessing the Spin-Flip Radiative Lifetimes of Optically Addressable Molecular Qubits

Optically addressable molecular qubits based on spin-flip (SF) emissive transitions are promising candidates for quantum technologies due to their sharp luminescence lines and tunable optical-spin interfaces. Yet, the microscopic mechanisms controlling the spin-flip radiative lifetime of SF emitters, a key property for efficient spin readout, remain largely unexplored. Here, we present a computational study of several Cr 4+ and Mo 4+ pseudotetrahedral molecular qubits, and we identify chemical and structural features that influence the transition dipole moment associated with the SF emission, which, in turn, governs the SF radiative lifetime. We find that the magnitude of the dipole moment is governed by the multireference character of the spin-flip excited-state wave function, which can be modulated by tuning the energy separation between the d orbitals of the metal and the spin-pairing energy. Both parameters are sensitive to molecular symmetry, metal–ligand bond covalency, and bond anisotropy and leave room for modulation via ligand and metal design, as well as applied strain, which is relevant for sensing applications. Our findings provide a mechanistic framework for understanding and tuning the spin-flip radiative behavior of molecular qubits and SF emitters that may guide future advances in quantum information science.

molecular qubits↗

DOE OSTI2025

Polarization-resolved core exciton dynamics in LiF using attosecond transient absorption spectroscopy

The ability to control absorption by modifying the polarization of light presents an exciting opportunity to experimentally determine the orbital alignment of absorption features. Here, attosecond extreme ultraviolet (XUV) transient absorption spectroscopy is used to investigate the polarization dependence of core exciton dynamics in LiF thin films at the Li + K edge. XUV pulses excite electrons from the Li 1s core level into the conduction band, allowing for the formation of a p-orbital-like core exciton, aligned along the XUV light polarization axis. A sub-5 fs near-infrared (NIR) probe pulse then arrives at variable time delays, perturbing the XUV-excited states and allowing the coherence decay of the core exciton to be mapped. The coherence lifetimes are found to be ≈ 2.4 ± 0.4 fs, which is attributed to a phonon-mediated dephasing mechanism as in previous core exciton studies. The differential absorption features are also shown to be sensitive to the relative polarization of the XUV and NIR fields. The parallel NIR probe induces couplings between the initial XUV-excited p-like bright exciton and s-like dark excitons. When crossed pump and probe polarizations are used, the coupling between the bright and dark states is no longer dipole-allowed, and the transient absorption signal associated with the coupling is suppressed by approximately 90%. This interpretation is supported by simulations of a few-level model system, as well as analysis of the calculated band structure. Here, the results indicate that laser polarization can serve as a powerful experimental tool for exploring the orbital alignment of core excitonic states in solid-state materials.

Attosecond laser spectroscopy↗

DOE OSTI2026

Bimetallic Coinage Metal Complexes of Tetradentate ortho Ter arylene Ligands

The synthesis, structural and photophysical properties of five bimetallic coinage metal complexes of three tetradentate charge-transfer (CT) ligands are presented. The ligand structures incorporate donor/acceptor moieties electronically decoupled by ortho connection to a bridging biphenylene group. The M M distances observed in the crystal structures of the bimetallic complexes are shorter than the sum of the Van der Waals radii of the metal ions, suggesting stabilizing interactions between the d10 metal centers. Additionally, short distances between the bridging biphenylene and metal atoms suggest arylene metal interactions. Bimetallic Cu, Ag, and Au complexes of the ligand incorporating a carbazole donor and pyridyl acceptor (N2R22-) show absorption and emission energies that trend with the ionization potential of each metal, indicating metal character in the excited state. These properties contrast with our previously reported mononuclear Zn complex of N2R22-The structural and photophysical properties of five bimetallic d10 coinage metal complexes were presented. The M M distances observed in the crystal structures of the bimetallic complexes are shorter than the sum of the metals’ Van der Waals radii, suggesting attractive interactions between the d10 metal centers. Additionally, short distances between the bridging biphenylene and metal atoms suggest arylene metal interactions. The absorption and emission spectra of the bimetallic complexes redshift based on the oxidation potential of the metal ion. This suggests involvement of metal based orbitals in the excited state transitions of the bimetallic complexes, which was corroborated by molecular modeling. High photoluminescent quantum yields were observed in solution and in rigid media (up to PL = 0.75), and the excited state lifetimes in solution were found to exceed several microseconds.

Shariaty, Darius Allen [University of Southern Cal↗

DOE OSTI2025

The Effect of Core-Hole Shape on Attosecond Valence Electron Dynamics

Rapid X-ray ionization of a core electron is known to induce the attosecond motion of valence electrons; however, the effect of core-hole shape on the triggered dynamics remains relatively unknown. In this work, the sub-four fs response of prototypical functionalized/heterocyclic/polycyclic molecules was simulated using real-time time-dependent density functional theory (RT-TDDFT), a sudden approximation core-hole, and phenomenologically Auger–Meitner (AM) decay. These molecules included fluorobenzene, chlorobenzene, bromobenzene, phenol, thiophenol, pyridine, phosphorus, and azulene. It is observed that the valence electron dynamics are essentially independent of the core-hole created, provided that it is ionized from an inner-shell orbital and not an inner-valence orbital. This has broad implications for free-electron laser studies of X-ray pumped attosecond processes since the flexibility in edge allows for a wide range of experimental modalities, core-holes with longer AM lifetimes, and molecular targets.

aromatic compounds↗

DOE OSTI2024

Mitigating Band Tailing in Kesterite Solar Absorbers: Ab Initio Quantum Dynamics

Open-circuit voltage deficits are limiting factors in kesterite solar cells. Addressing this issue by suppressing band tailing and nonradiative charge recombination is essential for enhancing the performance. We employ ab initio nonadiabatic molecular dynamics to elucidate the origin of band tailing and charge losses and propose a mitigation strategy. The simulations show that Cu–Zn disorder, associated with antisite defect clusters [Cu Zn +Zn Cu ], is a significant source of band tailing in kesterites, as evidenced by the much larger Urbach energy in disordered than ordered kesterites. Cu–Zn disorder gives rise to new sulfur-centered coordination polyhedra, increases structural inhomogeneity, changes electrostatic potential at sulfur centers, and shifts the S(3p) orbital energy. Differences in the S(3p)/Cu(3d) and S(3p)/Sn(5s) hybridization strengths and the S(3p) orbital energy shift reduce the band gap by 0.37 eV. Furthermore, Cu–Zn disorder enhances vibrational motion of sulfur anions and surrounding cations, increasing band gap fluctuations by 15 meV. The stronger electron–phonon interactions reduce charge carrier lifetimes and limit the kesterite solar cell efficiency. Partial substitution of Zn with Cd facilitates structural ordering and significantly suppresses band tailing, particularly in disordered systems. The improvement can be attributed to the larger atomic radius and mass of Cd, which weakens bonding around the anion, suppresses S-related vibrations within the covalent tetrahedra, and reduces nonadiabatic coupling, thereby increasing charge carrier lifetimes. The reported results establish the key influence of cation disorder on band tailing and reduced charge carrier lifetimes in kesterites and highlight cation disorder engineering as a strategy to achieve high-efficiency kesterite solar cells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Luminescent N-heterocyclic carbene Cu( I ) complexes with N^O chelating ligands exhibit microsecond lifetimes and photocatalytic activity

To replace precious noble metal-based photosensitizers in applications involving photoinduced charge separation, energy transfer, or photocatalysis, Cu(I) complexes are considered to be cost-effective, earth-abundant, and sustainable alternatives. An emerging and effective design principle in Cu(I) photosensitizers involves heteroleptic structures where the HOMO and LUMO are spatially separated over two different ligands. In the present work, we introduce a complementary class of heteroleptic, three-coordinate copper photosensitizers that pairs variable N^O chelating ligands (8-hydroxyquinoline and 10-hydroxybenzo[h]quinoline) with a bulky 2,6-diisopropylphenyl-substituted N-heterocyclic carbene (NHC). In this design, both frontier orbitals are localized on the same ligand, the N^O chelate, such that structural modulation of the electron-rich N^O-chelates can substantially tune the energy levels of the HOMO and LUMO, thereby controlling the photoluminescence properties. Detailed photophysical and electrochemical experiments as well as DFT calculations suggest charge-transfer transitions with intra-ligand charge transfer (ILCT) character, involving the N^O ligands. This strategy successfully produced long triplet excited-state lifetimes (up to 44 µs) in compounds that are strong photoreductants (E([Cu] + /*[Cu] as negative as −2.0 V vs. the ferrocenium/ferrocene couple). These properties allow these photosensitizers to be used as photocatalysts in various transformations of organic compounds, such as hydrogenation of substituted benzophenones, hydrodehalogenation of aryl/alkyl halides (including challenging C–Cl bond activation) and E/Z isomerization of (E)-stilbene (an example of triplet–triplet energy transfer).

Chakraborty, Soumi [University of Houston, TX (Uni↗

DOE OSTI2025

Magnon damping and mode softening in quantum double-exchange ferromagnets

We present a comprehensive analysis of the magnetic excitations and electronic properties of fully quantum double-exchange ferromagnets, i.e. systems where ferromagnetic (FM) ordering emerges from the competition between spin, charge, and orbital degrees of freedom, but without the canonical approximation of using classical localized spins. Specifically, we investigate spin excitations within the Kondo lattice-like model, as well as a two-orbital Hubbard Hamiltonian in proximity to the orbital-selective Mott phase. Computational analysis of the magnon dispersion, damping, and spectral weight within these models reveals unexpected phenomena, such as magnon mode softening and the anomalous decoherence of magnetic excitations as observed in earlier experimental efforts, but explained here without the use of the phononic degrees of freedom. We show that these effects are intrinsically linked to incoherent spectral features near the Fermi level, which arise due to the quantum nature of the local (on-site) triplets. This incoherent spectrum leads to a Stoner-like continuum on which spin excitations scatter, governing magnon lifetime and strongly influencing the dynamical spin structure factor. Our study explores the transition from coherent to incoherent magnon spectra by varying the electron density. Furthermore, we demonstrate that the magnitude of the localized spin mitigates decoherence by suppressing the incoherent spectral contributions near the Fermi level. We also discuss the effective J 1 –J 2 spin Hamiltonian, which can accurately describe the large doping region characterized by the magnon-mode softening. Finally, we show that this behavior is also present in multiorbital models with partially filled orbitals, namely, in systems without localized spin moments, provided that the model is in a strong coupling regime. Our results potentially have far-reaching implications for understanding FM ordering in various multi-band systems. These findings establish a previously unknown direct connection between the electronic correlations of those materials and spin excitations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2024

Lifetimes of excited states in $^{16}$C as a benchmark for ab initio developments

Lifetimes of higher-lying states ($2_2^+$ and $4_1^+$) in 16 C have been measured, employing the Gammasphere and Microball detector arrays, as key observables to test and refine ab initio calculations based on interactions developed within chiral Effective Field Theory. The presented experimental constraints to these lifetimes of $\tau ({2_2^+}) = [244, 446]\,~\textrm{fs}$ and $\tau ({4_1^+}) = [1.8, 4]\,~\textrm{ps}$, combined with previous results on the lifetime of the $2_1^+$ state of 16 C, provide a rather complete set of key observables to benchmark the theoretical developments. We present No-Core Shell-Model calculations using state-of-the-art chiral 2- (NN) and 3-nucleon (3N) interactions at next-to-next-to-next-to-leading order for both the NN and the 3N contributions and a generalized natural-orbital basis (instead of the conventional harmonic-oscillator single-particle basis) which reproduce, for the first time, the experimental findings remarkably well. The level of agreement of the new calculations as compared to the CD-Bonn meson-exchange NN interaction is notable and presents a critical benchmark for theory.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2024

Excitonic Shockley-Read-Hall recombination in organic semiconductors

Trap-mediated recombination influences the performance of a wide range of electronic devices. The well-known Shockley-Read-Hall (SRH) expression for inorganic semiconductors is often invoked to describe the recombination rate in organic materials, although without a clear understanding of how its parameters relate to the underlying material properties or how it should be modified to account for the finite lifetime of exciton intermediates in, for example, the doped emissive layer of an organic light-emitting diode (OLED). Here, we formalize SRH recombination for organic semiconductors based on diffusive trapping and Langevin recombination. We show that including the exciton state suppresses the recombination rate in host-guest systems with type II energy level alignment whenever the interfacial gap between the host and guest molecular orbitals is comparable to the exciton energy. Furthermore, these results quantify the balance between bimolecular and trap-mediated recombination in doped OLED emissive layers, and indicate that devices with type II host-guest pairings can, in principle, beat the thermodynamic limit of their neat guest counterparts.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Nuclear structure of 157 Sm via 𝛽−decay of 157 Pm

Excited states of the neutron-rich nucleus 157 Sm were populated through the 𝛽−decay of 157 Pm , which has a tentatively assigned ground-state spin and parity of 𝐽 𝜋 =(5/2 − ). Over 30 levels have been observed, 16 of which are new, and over 45 new 𝛾-ray transitions have been placed in the level scheme. An evolution in the ground-state configurations for 𝑁 = 95 nuclei from 5/2 − ⁢[523] (Er/Yb), to 5/2 + ⁢[642] (Dy), to 3/2 − ⁢[521] (Sm/Gd) can be explained based on increasing deformation from 𝑍 = 70 to 𝑍 = 62 and the fact that these three orbitals are energetically close to each other at deformations near 𝛽 2 ≈ 0.25–0.3. Finally, tentative spin and parity assignments are made for most of the states below 1500 keV based on the decay properties of the levels and using excitation-energy systematics of the various orbitals observed in 𝑁 = 95 nuclei.

beta decay↗

DOE OSTI2025

Abrupt structural transition in exotic molybdenum isotopes unveils an isospin-symmetric island of inversion

Like electrons in atoms, protons and neutrons in nuclei occupy orbitals in a shell structure with energy gaps at magic numbers. Radioactive-beam experiments revealed the disappearance of magic numbers in some neutron-rich isotopes. In these nuclei, configurations involving particles excited across the shell gap gain correlation energy, becoming the ground state. Neutron-rich regions of the nuclear chart that exhibit this property are known as “Islands of Inversion”. Here we present the lifetime measurement of the first 2 + states in 84 Mo (N = Z) and 86 Mo (N = Z + 2) revealing an unexpected sharp structural change between them defining the edge of the region of deformation around 80 Zr. Similarly to the neutron-rich N = 40 Island of Inversion near 64 Cr where cross-shell excitations dominate, we identify this region as an Island of Inversion with symmetrical proton and neutron excitations that we term “Isospin-Symmetric Island of Inversion”. Three-nucleon forces are suggested to drive Mo isotope structural changes.

experimental nuclear physics↗

DOE OSTI2024

The Role and Lifetime of Dissociative Heterogeneous Processes in Improving Simulated Ozone on Mars

Abstract Ozone simulated in Mars Global Climate Models (MGCMs) is used to assess the underlying chemistry occurring in the atmosphere. Currently, ozone total column abundance (TCA) is under‐predicted in MGCMs by up to 120%, implying missing or inaccurate chemistry in models. Heterogeneous reactions of hydroxyl radicals (HO X ) have been offered as an explanation for some of this bias, because they cause ozone to increase at locations where it's currently under‐predicted. We use four simulations to compare modeled ozone TCA with observations from the UVIS spectrometer aboard the ExoMars Trace Gas Orbiter to improve the representation of heterogeneous processes and their impact on ozone. We use a gas‐phase only run, a dissociative scheme, an adsorbed HO X retention scheme, and a hybrid scheme that combines the dissociative mechanism with the retention of HO X on water ice. We find retention of HO X is dependent on water ice sublimation, and ozone abundance increases when water ice persists for longer periods (1–20 sols). Over time, the loss of HO X causes a depletion in H 2 O 2 concentration (HO X reservoir), and thus allows ozone concentration to increase. When adsorbed HO X are desorbed and dissociate into other by‐products, HO X are not immediately available to destroy ozone. This results in larger ozone concentrations than if desorbed HO X are released directly back into their gaseous states. When using the hybrid scheme, ozone TCA is increased up to 50% where the ozone deficit is greatest, demonstrating the best agreement with observations, and implying that HO X radicals are both retained when adsorbed and dissociate.

Brown, M. A. J.↗

DOE OSTI2025

M-Edge Spectroscopy of Transition Metals: Principles, Advances, and Applications

M-edge X-ray absorption spectroscopy (XAS), which probes 3p→3d transitions in first-row transition metals, provides detailed insights into oxidation states, spin-states, and local electronic structure with high element and orbital specificity. Operating in the extreme ultraviolet (XUV) region, this technique provides sharp multiplet-resolved features with high sensitivity to ligand field and covalency effects. Compared to K- and L-edge XAS, M-edge spectra exhibit significantly narrower full widths at half maximum (typically 0.3–0.5 eV versus >1 eV at the L-edge and >1.5–2 eV at the K-edge), owing to longer 3p core-hole lifetimes. M-edge measurements are also more surface-sensitive due to the lower photon energy range, making them particularly well-suited for probing thin films, interfaces, and surface-bound species. The advent of tabletop high-harmonic generation (HHG) sources has enabled femtosecond time-resolved M-edge measurements, allowing direct observation of ultrafast photoinduced processes such as charge transfer and spin crossover dynamics. This review presents an overview of the fundamental principles, experimental advances, and current theoretical approaches for interpreting M-edge spectra. We further discuss a range of applications in catalysis, materials science, and coordination chemistry, highlighting the technique’s growing impact and potential for future studies.

M-edge XANES↗

DOE OSTI2025

Dynamical Generation of Higher-Order Spin-Orbit Coupling, Topology, and Persistent Spin Texture in Light-Irradiated Altermagnets

Altermagnets have been identified as the third category of magnetic materials, exhibiting momentum-dependent spin splitting characterized by even powers of momentum. Here, in this Letter, we show that when subjected to elliptically polarized light, these materials serve as an exemplary framework for the dynamic generation of topological bands featuring higher-order spin-orbit coupling (SOC). Notably, while the generated Zeeman field remains invariant to the particular altermagnetic ordering, the induced higher-order SOCs are related to the magnitude and symmetry of the altermagnetic order. Specifically, we show that an altermagnet exhibiting 𝐤 2⁢𝑛 -spin splitting can generate odd-in-𝐤 spin-orbit couplings up to 𝐤 2⁢𝑛−1 . In the limit of circularly polarized light, the only correction is 𝑘 2⁢𝑛−1 , with all lower-order contributions being nullified. Interestingly, light-induced SOCs significantly impact the low-energy band topology, where their Chern numbers change by Δ⁢𝐶 = ±1, 2, 3 for 𝑑, 𝑔, 𝑖-wave altermagnets. Finally, we find a critical field in which a persistent spin texture is realized, a highly desirable state with predicted infinite spin lifetime. Our Letter showcases light as a powerful, controllable tool for engineering complex and exciting phenomena in altermagnets.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2025

Crystalline Order Yet Glass-Like Heat Transport Driven by Hidden Local Distortions as the Structural Origin of Ultralow Thermal Conductivity in AgErTe 2

Given their rich chemical diversity and the interplay among the p-, d-, and f-orbitals of chalcogens, transition metals, and lanthanides, respectively, rare-earth transition-metal chalcogenides exhibit a wide variety of structural, magnetic, and transport phenomena. As a result, they form a particularly appealing platform for investigating structure–property relationships, emergent electronic and magnetic behaviors, and thermal transport. Here we investigate AgErTe 2 as a model system to understand phonon-glass behavior in ordered crystalline solids, which establishes the design principles for thermal barrier coatings and next-generation thermoelectrics. The local bonding asymmetry and lattice softness suppress the inherently low lattice thermal conductivity, resembling the characteristics of amorphous materials. This suppression is significantly influenced by local off-centering of Ag atoms, which breaks lattice periodicity while maintaining global crystallinity. The presence of antibonding states just below the Fermi level, arising from Ag 4d and Te 5p orbital interactions, leads to lattice softening and destabilizes ideal tetrahedral coordination, resulting in a pseudo Jahn–Teller distortion. Furthermore, the coexistence of weaker, more polarizable Ag–Te bonds and stronger Er–Te bonds creates a complex vibrational landscape enriched with low-frequency modes and enhanced phonon scattering. A pronounced disparity in interatomic force constants gives rise to highly localized, low-energy optical phonons linked to Ag rattling. These flat vibrational modes exhibit strong coupling with transverse acoustic phonons, resulting in ultrashort phonon lifetimes and mean free paths approaching interatomic distances. These features collectively enhance phonon scattering across a broad range of length and energy scales. This work offers a framework for engineering suppressed thermal conductivity in crystalline systems without the introduction of alloying elements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗