2D layered double perovskites of (S-MPA)4AgBiI8 (MPA-AgBiI8) and (S-MPA)4CuBiI8 (MPA-CuBiI8) (S-MPA, S-beta-methylphenethylammonium) were synthesized with a hydrothermal method. The crystal structure of MPA-AgBiI8 was determined using single-crystal X-ray diffraction (scXRD). Powder XRD (pXRD) data suggest that the crystal structure of MPA-CuBiI8 is more complex than that of MPA-AgBiI8. UV-vis electronic absorption spectra of these perovskites reveal a bandgap of 2.03 eV for both. Short exciton lifetime from time-resolved photoluminescence (TRPL) results and low PL intensity of the Cu-based perovskite suggest a high density of trap states within the bandgap. Low frequency Raman spectra of both materials show distinct peaks and a slightly higher frequency for the Cu-based perovskite than the Ag-based perovskite. Density functional theory (DFT) calculations were conducted to simulate the low frequency Raman spectra and help explain the different phonon modes, which are collective vibrations of metal halide bond bending and stretching within the Ag- and Cu-centered octahedra coupled with MPA libration and twisting within the inorganic layer. The DFT results also quantified octahedral distortions in the two perovskites. This combined experimental and computational study provides new insights into the low frequency vibrations of 2D perovskites.

Neuromorphic computing is based on electronic devices that emulate both synaptic memory and neuronal activation within compact, energy-efficient architectures. Materials capable of supporting these distinct neuromorphic functions within a single chemical system are therefore highly desirable. Here we report on the switching behavior of epitaxial Cu2-x Se cubic thin films as a function of the copper concentration. Films with low Cu deficiency display volatile threshold switching with sharp turn-on, analogous to artificial neuron activation. In contrast, films with higher Cu deficiency exhibit nonvolatile memristive switching with analog conductance modulation and stable potentiation and depression, consistent with synaptic operation. Our results demonstrate that synaptic and neuron-like behaviors can be obtained by adjusting the stoichiometry within the Cu2-x Se material system.

Hybrid magnonic systems are promising platforms for quantum technologies, leveraging coherent coupling between magnons and phonons. Here, we demonstrate strong magnon–phonon coupling in CoFe nanomagnets, a material with high magnetostriction. Using time-resolved magneto-optical Kerr effect spectroscopy, we demonstrate strong coupling between magnonic and phononic modes in both polycrystalline and single-crystalline CoFe nanomagnets. Our findings reveal strong coupling with cooperativity values of C=20.04 for a polycrystalline CoFe nanomagnet and C=37.94 for a single-crystalline CoFe nanomagnet. The enhanced coupling strength in the single-crystalline CoFe nanomagnet is attributed to the higher magnetostriction in CoFe systems and lower intrinsic magnetic damping. This work highlights the critical role of material properties and crystalline structures in optimizing hybrid magnon–phonon systems for miniaturized quantum applications.

Thin films of the topological insulator (BiSb)2Te3 oriented along the [0001] direction were grown via molecular beam epitaxy on substrates of Al2O3 (0001) and MgF2 (110) single crystals, as well as on an epitaxial thin film of the antiferromagnetic insulator and predicted altermagnet MnF2 (110). Magnetoconductivity measurements of these samples showed close proximity of the Fermi level to the Dirac point and weak antilocalization at low temperature that was partially suppressed in the sample grown on the MnF2 layer. The magnetoconductivity data were fit to a model that describes the quantum corrections to the conductivity for the Dirac surface state of a three-dimensional topological insulator, from which values of the Fermi velocity and the phase coherence length of the surface state charge carriers were derived. The magnetoconductivity of the (BiSb)2Te3-MnF2 bilayer samples were fit to a model describing the crossover from weak antilocalization to weak localization due to magnetic doping. The results are consistent with the opening of an energy gap at the Dirac point in (BiSb)2Te3 due to magnetic proximity interactions of the topological surface states with the antiferromagnetic MnF2 insulator.

Thin films of the topological insulator (BiSb)$_2$Te$_3$ oriented along the [0001] direction were grown via molecular beam epitaxy on substrates of Al$_2$O$_3$ (0001) and MgF$_2$ (110) single crystals, as well as on an epitaxial thin film of the antiferromagnetic insulator MnF$_2$ (110). Magnetoconductivity measurements of these samples showed close proximity of the Fermi level to the Dirac point and weak antilocalization at low temperature that was partially suppressed in the sample grown on the MnF$_2$ layer. The magnetoconductivity data were fit to a model that describes the quantum corrections to the conductivity for the Dirac surface state of a 3-dimensional topological insulator, from which values of the Fermi velocity and the phase coherence length of the surface state charge carriers were derived. The magnetoconductivity of the (BiSb)$_2$Te$_3$ - MnF$_2$ bilayer samples were fit to a model describing the crossover from weak antilocalization to weak localization due to magnetic doping. The results are consistent with the opening of an energy gap at the Dirac point in the (BiSb)$_2$Te$_3$ due to magnetic proximity interactions of the topological surface states with the antiferromagnetic MnF$_2$ insulator.

Titan is the only known moon in the Solar System with a substantial atmosphere of N2 and CH4. However, its origin and evolution are not well understood. Titan’s present amount of atmospheric CH4 was predicted to be destroyed photochemically on very short timescales (~ 10 Myrs, Yung et al. 1984). This suggests that a methane resupply mechanism is necessary. The Huygens probe GCMS measurements of noble gases suggest that Titan’s atmosphere is likely linked to its interior instead of being incorporated during formation (Nieman et al., 2005). Recent theoretical modeling works of Titan’s atmosphere and interior suggest that its atmosphere could have originated partly by outgassing primordial organics in its interior (Neri et al. 2019; Miller et al. 2019). If this theory holds, volatiles like methane could be outgassing from Titan’s interior to sustain its current observed abundances. Insoluble organic matter (IOM) found in carbonaceous chondrites may serve as an analog for the organic material in Titan’s interior and provide experimental constraints on the outgassed component of its atmosphere (Thompson et al. 2021). By heating carbonaceous chondrite samples and measuring the abundances of their released volatiles, specifically methane, we may be able to connect what we see in the lab to species in Titan’s atmosphere today.We performed outgassing experiments using three primordial CM carbonaceous chondrites: Murchison, Aguas Zarcas, and Jbilet Winselwan. The first two are "fall" meteorite (1969 and 2019), and Jbilet Winselwan is a desert "find'' meteorite (2013). We used two sizes of samples for each CM chondrite for the measurements: a small grain sample with diameters < 20 µm and a normal grain sample with diameters of 20-100µm. Each sample underwent a step heating scheme where they are heated and held at every 100°C from room temperature to 1200° C. The whole heating scheme takes 12 hours. We continuously monitored the partial pressures of 10 outgassed mass peaks using a residual gas analyzer (RGA).We can estimate how much methane can be outgassed from the insoluble organics in the CM chondrites with the RGA data. We found that chondrite outgassing can resupply methane that can last for ~0.5-2 Gyrs. If organics indeed makes a significant fraction of Titan's interior, outgassing through thermal instability of Titan's interior can potentially resupply Titan's atmospheric methane for a period of time.

Quantum scars refer to eigenstates with enhanced probability density along unstable classical periodic orbits (POs). First predicted 40 years ago, scars are special eigenstates that counterintuitively defy ergodicity in quantum systems whose classical counterpart is chaotic. Despite the importance and long history of scars, their direct visualization in quantum systems remains an open field. Here we demonstrate that, by using an in-situ graphene quantum dot (GQD) creation and wavefunction mapping technique, quantum scars are imaged for Dirac electrons with nanometer spatial resolution and meV energy resolution with a scanning tunneling microscope. Specifically, we find enhanced probability densities in the form of lemniscate-shaped and streak-like patterns within our stadium-shaped GQDs. Both features show equal energy interval recurrence, consistent with predictions for relativistic quantum scars. By combining classical and quantum simulations, we demonstrate that the observed patterns correspond to two unstable POs that exist in our stadium-shaped GQD, thus proving they are both quantum scars. In addition to providing the first unequivocal visual evidence of quantum scarring, our work offers insight into the quantum-classical correspondence in relativistic chaotic quantum systems and paves the way to experimental investigation of other recently proposed scarring species such as perturbation-induced scars, chiral scars, and antiscarring.

Quantum scars refer to eigenstates with enhanced probability density along unstable classical periodic orbits. First predicted 40 years ago1, scars are special eigenstates that counterintuitively defy ergodicity in quantum systems whose classical counterpart is chaotic2,3. Despite the importance and long history of scars, their direct visualization in quantum systems remains an open field4-10. Here we demonstrate that, by using an in situ graphene quantum dot (GQD) creation and a wavefunction mapping technique11,12, quantum scars are imaged for Dirac electrons with nanometre spatial resolution and millielectronvolt energy resolution with a scanning tunnelling microscope. Specifically, we find enhanced probability densities in the form of lemniscate ∞-shaped and streak-like patterns within our stadium-shaped GQDs. Both features show equal energy interval recurrence, consistent with predictions for relativistic quantum scars13,14. By combining classical and quantum simulations, we demonstrate that the observed patterns correspond to two unstable periodic orbits that exist in our stadium-shaped GQD, thus proving that they are both quantum scars. In addition to providing unequivocal visual evidence of quantum scarring, our work offers insight into the quantum-classical correspondence in relativistic chaotic quantum systems and paves the way to experimental investigation of other recently proposed scarring species such as perturbation-induced scars15-17, chiral scars18,19 and antiscarring20.

Materials such as graphene and topological insulators host massless Dirac fermions that enable the study of relativistic quantum phenomena. Single quantum dots and coupled quantum dots formed with massless Dirac fermions can be viewed as artificial relativistic atoms and molecules, respectively. Such structures offer a unique testbed to study atomic and molecular physics in the ultrarelativistic regime (particle speed close to the speed of light). Here we use a scanning tunnelling microscope to create and probe single and coupled electrostatically defined graphene quantum dots to unravel the magnetic-field responses of artificial relativistic nanostructures. We observe a giant orbital Zeeman splitting and orbital magnetic moment up to ~70 meV T–1 and ~600μB (μB, Bohr magneton) in single graphene quantum dots. For coupled graphene quantum dots, Aharonov–Bohm oscillations and a strong Van Vleck paramagnetic shift of ~20 meV T–2 are observed. Our findings provide fundamental insights into relativistic quantum dot states, which can be potentially leveraged for use in quantum information science. Electrostatically defined quantum dots in graphene constitute a testbed to study atomic and molecular physics in the ultrarelativistic regime—when the particle speed is close to the speed of light. Magnetic-field-dependent tunnelling spectroscopy experiments now reveal giant orbital magnetic moments and paramagnetic shifts in single and double quantum dots due to their relativistic nature.

The effect of random competing single-ion anisotropies in antiferromagnets was studied using epitaxial Mn$_x$Ni$_{1-x}$F$_2$ antiferromagnetic thin film alloys grown via molecular beam epitaxy. The crystal structure of this material is tetragonal for all values of $x$, and the Mn sites have a magnetic easy axis single-ion anisotropy while the Ni sites have an easy plane anisotropy perpendicular to the Mn easy axis. Crystallographic and magnetization measurements demonstrated that the thin film alloys were homogeneously mixed and did not phase-separate into their constituent parts. Pure MnF$_2$ thin films epitaxially grown on MgF$_2$ exhibited compressive strain along all three crystallographic axes which resulted in piezomagnetic effects. The piezomagnetism disappeared if the film was grown on a (MnNi)F$_2$ graded buffer layer. A mean-field theory fit to the transition temperature as a function of the Mn concentration $x$, which takes into account piezomagnetic effects, gave a magnetic exchange constant between Mn and Ni ions of $J_{\text{MnNi}} = 0.305 \pm 0.003$~meV. Mean-field theory calculations also predicted the existence of an oblique antiferromagnetic phase in the Mn$_x$Ni$_{1-x}$F$_2$ alloy which agreed with the experimental data. A magnetic phase diagram for Mn$_x$Ni$_{1-x}$F$_2$ thin film alloys was constructed and showed evidence for the existence of two unique magnetic phases, in addition to the ordinary antiferromagnetic and paramagnetic phases: an oblique antiferromagnetic phase, and an emergent magnetic phase proposed to be either a magnetic glassy phase or a helical phase. The phase diagram is quantitatively different from that of Fe$_x$Ni$_{1-x}$F$_2$ because of the much larger single-ion anisotropy of Fe$^{2+}$ compared to Mn$^{2+}$.

Photoinduced structural dynamics of rare-earth nickelate thin films, NdNiO3 and SmNiO3, grown on (001) oriented SrTiO3 were studied using time-resolved x-ray diffraction. The evolution of the (002) Bragg peak was tracked following laser excitation. The recovery pathways were found to be strongly dependent on laser fluence for NdNiO3 and distinct for the two rare-earth nickelates. The recovery of the (002) peak shifts was modeled using a one-dimensional thermal diffusion model which showed that the recovery processes are nonthermal at high fluences. For NdNiO3, the timescales for the recovery of the (002) peak shift were found to be closely related to Ni magnetism recovery, potentially indicating magnetostructural coupling. Moreover, the evolution of integrated intensity and full width at half maximum points towards the presence of a structural phase separation during recovery. Our studies highlight structural recovery pathways in nickelates by comparing the distinct responses of the photoinduced metal-insulator transition in NdNiO3 and SmNiO3.

Half-metallic Heusler alloys are receiving significant attention for spintronic applications utilizing magnetic tunnel junctions and requiring large spin polarization. Co2MnSi (CMS) is one of the most promising candidates for this purpose. Here, we report the magnetization dynamics of a thin, epitaxial CMS film in a magnetic CoFe/CMS bilayer structure sputtered on an MgO substrate. The magnetic precession frequency response of the CoFe/CMS bilayer shows a fourfold symmetry with respect to the azimuthal applied field angle, reflecting the crystal symmetry of the CMS layer and not the underlying CoFe film. Moreover, the effective Gilbert damping parameter exhibits inhomogeneous broadening at lower applied magnetic fields. At large fields, however, the azimuthal angle dependence disappears, and the intrinsic Gilbert damping is observed. This study provides insight into the dynamics of a magnetic bilayer structure that forms an integral element in spintronic applications.

A spontaneous ferromagnetic moment can be induced in Bi$_{2}$Te$_{3}$ thin films below a temperature T $\approx$ 16 K by the introduction of Mn dopants. We demonstrate that films grown via molecular beam epitaxy with the stoichiometry Mn$_{0.14}$Bi$_{1.86}$Te$_3$ maintain the crystal structure of pure Bi$_{2}$Te$_{3}$. The van der Waals nature of inter-layer forces in the Mn$_{0.14}$Bi$_{1.86}$Te$_3$ crystal causes lattice mismatch with the underlayer to have a limited effect on the resulting crystal structure, as we demonstrate by thin film growth on tetragonal MgF$_{2}$ (110) and NiF$_{2}$ (110). Electronic transport and magnetic moment measurements show that the ferromagnetic moment of the Mn$_{0.14}$Bi$_{1.86}$Te$_3$ thin films is enhanced as the Fermi level moves from the bulk conduction band and towards the bulk band gap, suggesting that electronic surface states play an important role in mediating the ferromagnetic order. Ferromagnetic Mn$_{0.14}$Bi$_{1.86}$Te$_3$/antiferromagnetic NiF$_{2}$ bilayers show evidence that the ferromagnetic moment of the Mn$_{0.14}$Bi$_{1.86}$Te$_3$ film is suppressed, suggesting the existence of an interface effect between the two magnetic layers.

The different magnetic behaviors of LaCoO$_3$ films grown on LaAlO$_3$ and SrTiO$_3$ are related to the Co-O-Co bond angles and the constraints imposed on the Co-O bond lengths by the substrate geometries. Long-range magnetic order occurs below T ~ 90 K when the Co-O-Co bond angle is greater than 163 degrees, consistent with the behavior of bulk and nanoparticles forms of LaCoO$_3$. A LaAlO$_3$ substrate prevents magnetic long-range order at low temperatures near the film-substrate interface and collinear antiferromagnetic sublattices away from the interface. At low temperatures, the antiferromagnetically ordered sublattices are non-collinear in films grown on SrTiO$_3$ substrates, leading to a significant net moment.

The effect of random competing single-ion anisotropies in antiferromagnets was studied using epitaxial MnxNi1-xF2 antiferromagnetic thin film alloys grown via molecular beam epitaxy. The crystal structure of this material is tetragonal for all values of x, and the Mn sites have a magnetic easy-axis single-ion anisotropy while the Ni sites have an easy-plane anisotropy perpendicular to the Mn easy axis. Crystallographic and magnetization measurements demonstrated that the thin film alloys were homogeneously mixed and did not phase separate into their constituent parts. Pure MnF2 thin films epitaxially grown on MgF2 exhibited compressive strain along all three crystallographic axes which resulted in piezomagnetic effects. The piezomagnetism disappeared if the film was grown on a (MnNi)F-2 graded buffer layer. A mean-field theory fit to the transition temperature as a function of the Mn concentration x, which takes into account piezomagnetic effects, gave a magnetic exchange constant between Mn and Ni ions of J(MnNi) = 0.305 +/- 0.003 meV. Mean-field theory calculations also predicted the existence of an oblique antiferromagnetic phase in the MnxNi1-xF2 alloy which agreed with the experimental data. A magnetic phase diagram for MnxNi1-xF2 thin film alloys was constructed and showed evidence for the existence of two unique magnetic phases, in addition to the ordinary antiferromagnetic and paramagnetic phases: an oblique antiferromagnetic phase, and an emergent magnetic phase proposed to be either a magnetic glassy phase or a helical phase. The phase diagram is quantitatively different from that of FexNi1-xF2 because of the much larger single-ion anisotropy of Fe2+ compared to Mn2+.

At present, there is no first-principles understanding of how to connect a planet’s bulk composition to its initial atmospheric properties. Since terrestrial exoplanets likely form their atmospheres through outgassing, a novel step towards building such a theory is to assay meteorites, the left-over building blocks of planets, by heating them to measure their outgassed volatiles. Our Solar System presents a wide variety of meteorite types, including carbonaceous chondrites which are believed to be representative of the bulk material in the solar nebula during planet formation. In addition, carbonaceous chondrites contain the highest proportions of volatiles relative to other remnant materials from terrestrial planet formation that can be directly studied in the laboratory. Although planet formation alters planetesimals through thermal and differentiation processes, carbonaceous chondrite-like material was likely an important source of volatiles for the Solar System’s terrestrial planets, making these meteorites well-suited for studying early terrestrial exoplanet atmospheres. To inform the initial chemical composition of terrestrial planet atmospheres, we present the results of our outgassing experiments in which we heated carbonaceous (CM, CO, CV) chondrite samples to 1200 ℃ and measured the abundances of released volatiles (e.g., H 2 O, CO, CO 2 , H 2 , H 2 S) as a function of temperature and time. Our experimental set-up consists of a residual gas analyzer, a type of mass spectrometer particularly sensitive to trace amounts of gas, connected to a furnace to heat samples at specified rates. We also perform complementary bulk element analysis on the samples before and after the heating experiments using inductively coupled plasma mass spectrometry to monitor outgassing of heavier elements (e.g., Na, Mg, P, S, K, Ca, Cr, Mn, Fe, Co, Ni, Zn). We compare these experimental results to thermochemical equilibrium models of outgassing from the same types of chondrites and determine how these experiments will improve the atmospheric models. This work presents an experimental framework utilizing chondritic meteorites that takes an important step forward in connecting terrestrial planet interiors and early atmospheres. Ultimately, our results provide a set of experimentally-determined initial conditions for outgassed atmospheric compositions and enable better assumptions to be made in terrestrial exoplanets’ initial atmospheres.

Atmosphere. Taylor Duncan, Xinting Yu, Maggie Thompson, Kyle Kim, Myriam Telus, Toyanath Joshi, David Lederman. Department of Earth and Planetary Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (tamdunca@ucsc.edu). Department of Astronomy and Astrophysics, University of California Santa Cruz, CA 95064. Department of Physics, University of California Santa Cruz, Santa Cruz, CA 95064.