Materials Science
GRADAR: orientation-map-driven detection and ranking of grains for targeted two-beam electron channeling contrast imaging
Johan Ewald Westraadt
Electron channeling contrast imaging (ECCI) resolves individual dislocations in bulk samples, but only when the imaged grain is held in a two-beam diffraction condition to well under half a degree. In a polycrystal it must be re-established grain by grain, and every published workflow we are aware of chooses the grain first and solves the stage for that orientation. This paper treats the inverse problem: nominate one reflection family and a stage envelope, and determine which grains of an EBSD-mapped polycrystal can reach that family's two-beam condition, a question posed in 2019 and open since. At fixed tilt $t$, stage rotation sweeps the incident beam around a cone of half-angle $t$ in each grain's
crystal frame, and a family with Bragg angle $\theta_B$ is reachable exactly when one of its plane normals lies within $(t + \theta_B)$ of the specimen surface. On a measured 163-grain austenitic stainless steel map at 20 kV, {111} reachability rises from 38.7% at 7 deg tilt to 77.3% at 15 deg; {220} and {311} already reach 79.8% and 91.4% at 7 deg. Ranking survivors by predicted darkness alone is wrong: same-family candidates are equivalent with respect to their own band at exact Bragg incidence, and the darkest tend to lie closest to rival-band Bragg conditions. GRADAR therefore ranks darkest-clean, gating every candidate on a minimum clearance from all rivals, and returns a dial-ready stage move per selected grain. Because the beam moves only ~0.12 deg per degree of stage rotation at 7 deg tilt, an ordinary rotation stage sets the selected condition to better than 0.1 deg. The predicted sweep is checked against the AstroECP
dataset's published silicon precession series: simulated and measured traces agree at r = 0.84, and the measured intensity is dark at all 16 predicted two-beam edges. Per-grain polycrystal validation is deferred to a companion study.
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Materials Science · Cross-listed from cond-mat.supr-con
Emergence of Double-Dome Superconductivity in the Pressurized Dirac Semimetal BaMg2Bi2
Qi Wang, Juefei Wu, Cuiying Pei et al. (+3 more)
Dirac semimetal BaMg2Bi2 is reported to be a unique topological material that manifests surface superconductivity that coexistswith bulk band
topology at ambient pressure. Here, we present a comprehensive investigation of high-pressure superconductingproperties in BaMg2Bi2 single
crystal. Significantly, a pressure-driven double-dome superconducting behavior was revealed, withthe superconducting transition temperature Tc approaching the maximum values of 6.67 K at 4.5 GPa and 7.22 K at 10.4 GPafor the first and second superconducting domes, respectively. The combination of high-pressure X-ray diffraction, Hall resistivitymeasurements, and theoretical calculations demonstrates that, the first superconducting regime is closely related to the pressure-modulated Lifshitz transition, whereas the second superconducting phase emerges concurrently with a structural transition fromthe ambient-pressure P3m1 phase to a high-pressure Pnma phase.
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All authors Qi Wang, Juefei Wu, Cuiying Pei, Yi Zhao, Yiyan Wang, Yanpeng Qi
Materials Science · Cross-listed from cond-mat.supr-con
Superconducting ternary compounds Li-X-B (X=Mo, W) within the mild pressure range: First-principles predictions
Bangshuai Zhu, Juefei Wu, Dexi Shao et al. (+6 more)
Among the superconducting hydrides under high pressure, a number of studies concentrate on the ternary compounds to explore unique
superconductors, which are capable of reducing the stable pressure and maintain superconductivity. In this work, to verify our proposed strategy of ternary composition lines (TCLs) to explore ternary compounds, we combined the first-principles calculations and
crystal structure predictions to study the ternary compounds Li-X-B (X=Mo, W) under high pressure. After calculations along five and four TCLs in Li-W-B and Li-Mo-B, respectively, five Li-W-B compounds and four Li-Mo-B compounds were predicted. The compositions of LiWB4, Li4MoB2 and LiMo2B2 could be thermodynamically stable under high pressure, and Li2WB6 is around 0.02 eV/atom above the convex hull at 0 GPa, which has potential for synthesizing. Both of the predicted Li2WB6 P6/mmm and Li2WB4 R-3m are superconducting and their Tc are around 11 K, which are similar to the Tc of WB2 P6/mmm around 100 GPa. An anomalous increase of Tc was found in Li4MoB2 C2/m upon compression. We carried out full ternary search (FTS) to evaluate the validity of the TCLs strategy in Li-W-B system at 0 GPa. Our results are helpful for understanding the phase diagram of Li-X-B (X=Mo, W) under high pressure and the introducing of Li atoms provide candidate structures to reduce the measured stable pressure from ~100 GPa in WB2 P6/mmm to 0 GPa. Meanwhile, we preliminary validate the strategy of TCLs in structure predictions and we expect to improve this strategy in the future, shedding light on the studies of ternary compounds.
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All authors Bangshuai Zhu, Juefei Wu, Dexi Shao, Junjie Wang, Yu Han, Cuiying Pei, Qi Wang, Jian Sun, Yanpeng Qi
Materials Science · Cross-listed from cond-mat.supr-con
Cryogenic focused-ion-beam microstructuring enabling quantitative $c$-axis transport measurements in Tl$_2$Ba$_2$CuO$_{6+\delta}$
Ayanesh Maiti, Carsten Putzke, Linus Holeschovsky et al. (+10 more)
Absolute transport measurements in correlated
quantum materials are often limited by disorder, inhomogeneity,
geometric uncertainty, and small
crystal size. Focused ion beam (FIB) technology offers a route to overcome many of these limitations by enabling transport devices with precisely defined geometry to be fabricated from lamellae extracted from carefully selected regions of a
crystal, but its application to cuprate
superconductors has been hindered by ion-beam-induced damage. Here we study the clean overdoped cuprate Tl2201 and show that conventional FIB processing causes thermally driven oxygen loss, while cryogenic FIB microstructuring largely suppresses this degradation and preserves the
crystal structure from the bulk to the atomic scale. Microstructured devices quantitatively reproduce established in-plane resistivity and Hall carrier density measurements without rescaling. Applying this approach to $c$-axis transport, we obtain absolute $\rho_c(T)$ values approximately three times larger than previously reported, bringing the transport anisotropy into quantitative agreement with the known Fermi surface geometry within an isotropic relaxation-time approximation. These results resolve a long-standing discrepancy between transport and
quantum oscillation measurements in overdoped Tl2201 and establish cryogenic FIB microstructuring as a route to reliable quantitative transport measurements in
quantum materials where disorder, inhomogeneity, geometry, or small
crystal size have previously limited experimental accuracy.
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All authors Ayanesh Maiti, Carsten Putzke, Linus Holeschovsky, Roemer D. H. Hinlopen, Chunyu Guo, Dorothee Herrmann, Seunghyun Khim, Berit H. Goodge, Andre W. Tyler, Michele S. Conroy, Andreas W. Rost, Andrew P. Mackenzie, Philip J. W. Moll
Materials Science · Cross-listed from cond-mat.supr-con
Pressure-induced concurrent amorphization and superconductivity in topological material NbNiTe5
Lingxiao Zhao, Yi Zhao, Bangshuai Zhu et al. (+6 more)
We have systematically studied the structural and electronic properties of a topological material NbNiTe5 under high pressure. The
evolution of the normal state resistance shows a non-monotonic trend from 0.7 GPa to 5.1 GPa, in accordance with the second-order transition along the inter-layer direction observed in X-ray diffraction and Raman spectra. At around 10 GPa, the sample starts amorphization, which is concurrent with the emergence of superconductivity. Upon further compression, the structural disorder enhances and the superconducting transition becomes clearer, suggesting that the superconductivity is modulated by the degree of disorder in NbNiTe5 under high pressure. Within 45.7 GPa, the superconducting transition temperature (Tc) slowly rises from 0.6 K at 9.5 GPa to 1.4 K at 45.7 GPa. Our findings extend the family of transition metal chalcogenide
superconductors and shed new light on understanding superconductivity in disordered systems.
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All authors Lingxiao Zhao, Yi Zhao, Bangshuai Zhu, Qi Wang, Cuiying Pei, Juefei Wu, Jin-Ke Bao, Wen-He Jiao, Yanpeng Qi
Materials Science · Cross-listed from cond-mat.mes-hall
Optical switching of magnetic order in few-layer CrSBr
Lukas Husel, Julian Trapp, Moritz Würf et al. (+7 more)
Manipulating magnetism with light is crucial for both fundamental understanding and technological advancements of information storage devices. The layered antiferromagnet CrSBr, part of the recently emerging class of two-dimensional van der Waals magnets, offers a unique path towards optical control of magnetism via magneto-
excitons, which allow optical readout of the
spin alignment and also provide a strong absorption channel. Here, we use
exciton absorption and photoluminescence to demonstrate optical switching of the
magnetic order in bi- and trilayer CrSBr. Using a continuous-wave
laser with a power as low as a few microwatts at near-critical external
magnetic fields, we demonstrate both local and remote switching of the
magnetic configuration in extended lateral domains and further employ this mechanism to deterministically prepare the zero-field
magnetic configuration. Our results establish optical switching as a useful means of controlling magnetism in CrSBr, with potential applications in magneto-optoelectronic devices.
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All authors Lukas Husel, Julian Trapp, Moritz Würf, Anna Rupp, Tim Wedl, Kenji Watanabe, Takashi Taniguchi, Iva Plutnarova, Zdenek Sofer, Alexander Högele
Materials Science
Synthesis and structural validation of close-to-stoichiometric NiTe$_2$ single crystals
T. Tirasutt, L. H. Tjeng and A. C. Komarek
We report the synthesis of stoichiometric NiTe$_{2}$ single
crystals via chemical vapor transport together with precise structural characterization. A combined analysis using powder and single
crystal X-ray diffraction (XRD) was performed to determine
lattice parameters and structural details. High-resolution single
crystal XRD reveals no evidence of interstitial nickel, confirming a close-to-stoichiometric composition. This work establishes a reliable
benchmark for the
crystal structure of stoichiometric NiTe$_{2}$, offering a reference for future studies on its physical properties.
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Materials Science · Cross-listed from physics.optics
Gallium phosphide on insulator for nanophotonics and quantum technologies
Tobias Bucher, Otto Arnold, Muyi Yang et al. (+7 more)
Gallium phosphide is a promising material platform for visible and near-infrared photonics and
quantum technologies owing to its high refractive index, low optical absorption, and strong second-order nonlinearity. Here, we demonstrate the fabrication of GaP-on-
insulator substrates by ion slicing. The splitting depth and exfoliation behavior of bulk GaP are tailored by controlling the He$^{+}$ ion implantation energy and fluence, enabling thin-film transfer onto amorphous substrates by anodic bonding and
plasma-enhanced direct wafer bonding. Channeling Rutherford backscattering spectrometry and X-ray diffraction confirm that the transferred layers retain their single-crystalline structure, while implantation-induced disorder and optical absorption are substantially reduced by annealing at 500 {\deg}C and subsequent polishing. The annealed films exhibit linear optical properties approaching those of bulk GaP. In addition, a (110)-oriented GaP thin film shows the characteristic polarization dependence expected from the zinc-blende second-order nonlinear susceptibility tensor, demonstrating a near-pristine second-order nonlinear response. This flexible fabrication approach enables the integration of high-quality single-crystalline GaP with variable orientation for free-space and integrated nanophotonics as well as nonlinear and
quantum optical devices.
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All authors Tobias Bucher, Otto Arnold, Muyi Yang, Zifei Zhang, Katsuya Tanaka, Annkathrin Köhler, Berit Marx-Glowna, Duk-Yong Choi, Isabelle Staude, Carsten Ronning
Materials Science · Cross-listed from cond-mat.soft
Equilibrium gigahertz acoustics reveals long-range confinement in liquids
Ievgeniia Chaban and Thomas Pezeril
Understanding how the mechanical properties of
liquids confined within nanometer-scale gaps differ from bulk behavior is central to biophysics, lubrication, catalysis, electrochemistry, and surface science. Yet the characterization of ultrathin confined
liquids remains challenging, as many existing approaches rely on destructive or intrusive contact-based techniques, mostly measuring the
liquid flow in the low frequency regime. Here, we present a non-invasive, all-optical technique based on ultrafast
laser ultrasonics that probes confined
liquids at
equilibrium in the gigahertz frequency range. The method measures the phase and amplitude of time-domain Brillouin scattering signals transmitted through
liquid layers whose thickness is varied step by step with subnanometer effective sampling. Supported by numerical modeling of acoustic propagation and optical detection, these signals allow us to extract the thickness-dependent acoustic velocity and attenuation of confined
liquids. We show that nanometric confinement modifies the GHz acoustic response of glycerol, the
liquid crystal 8CB, and a butyl-based ionic
liquid over unexpectedly long spatial scales. These effects extend from a few nanometers to several tens of nanometers and reveal bound interfacial layers, acoustic stiffening, and enhanced solid-like behavior under confinement. Our results open a route to probing
liquid confinement in a scarcely explored regime: dynamically measured at gigahertz frequencies, yet sufficiently weakly perturbative to preserve the
equilibrium confined state.
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Materials Science · Cross-listed from cond-mat.str-el
Long and short time linear response of metals: a geometric approach
Nishchhal Verma and Raquel Queiroz
The time-dependent
quantum geometric tensor, which captures dipole fluctuations of bound electrons, is essential for understanding the electronic properties of
insulators,
superconductors, and flat bands. It is often considered subleading for low-energy descriptions of metals that are dominated by intra-band processes. Here, we revisit this perspective and highlight scenarios where the
quantum geometry of the wavefunctions close to the Fermi surface plays a significant role. We compute the time-dependent
quantum geometric tensor for metals, explain its divergence, and contrast it against singular
geometric tensors of Dirac and Weyl semi-metals. We identify the ratio of Drude to total spectral weight, $D/\mathcal{S}_1$, as a
lattice-scale probe of bound versus itinerant charge, and quantify it in the kagome metal, where the two van Hove fillings respond differently despite identical Fermi surfaces.
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Materials Science
Second-Harmonic Imaging of Magnetic Domains in Thin Film Hematite
Holger Mirkes, Johannes Schmuck, Katharina Müller et al. (+7 more)
Hematite is an antiferromagnetic oxide and candidate altermagnetic
insulator whose Néel order reorients from an easy-axis to an easy-plane phase at the Morin transition. Interpreting altermagnetic transport and
symmetry sensitive optical responses requires knowledge of the Néel vector orientation relative to the
crystal axes and of the domain structure within the probed device. Here, we show that polarization-resolved second-harmonic generation (SHG) microscopy resolves
magnetic symmetry and domains in epitaxial (0001)-oriented hematite films. Across the Morin temperature, the SHG polarization anisotropy evolves from an approximately sixfold pattern consistent with the easy-axis orientation to pronounced twofold patterns consistent with the easy-plane orientation. A
symmetry analysis based on
magnetic-dipole and electric-quadrupole contributions reproduces this
evolution. Importantly, the interference between SHG amplitudes that are odd and even under reversal of the
magnetic order renders opposite Néel-vector orientations optically distinguishable. Consistently, opposite directions of an applied in-plane
magnetic field produce distinct SHG responses in our experiments. Using this
magnetic contrast, we image micrometer-scale domains, their reorganization across the Morin transition, and their reconfiguration under
magnetic and thermal cycling, including a remanent change after cycling through the
spin-flop transition. These results establish SHG microscopy as a local probe of
magnetic symmetry, Néel-vector orientation, and domain
evolution in hematite films.
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All authors Holger Mirkes, Johannes Schmuck, Katharina Müller, János Papp, Paul Seifert, Matthias Althammer, Hans Huebl, Stephan Geprägs, Alexander W. Holleitner, Christoph Kastl
Materials Science · Cross-listed from physics.optics
Direct Wafer Bonding of Crystal-Ion-Sliced GaP Thin Films for Photonic Applications
Hossein Esfandiar, Emanuel Glück, Fabian Ganss et al. (+11 more)
Gallium phosphide (GaP) is a promising material platform for integrated photonics because of its high refractive index, broad optical transparency, and strong second-order nonlinear response. Here, we demonstrate GaP-on-
insulator thin films fabricated by
crystal ion slicing and direct wafer bonding, using fused silica and SiO$_2$/Si/Si thermally oxidized silicon substrates as representative platforms. Unlike GaP thin-film platforms that rely on heteroepitaxial growth or sacrificial-layer release, the presented approach enables the flexible integration of crystalline GaP thin films, independent of both donor and target substrates. Following post-transfer annealing, the films exhibit near-bulk crystalline quality with low residual strain, smooth surfaces suitable for nanophotonic fabrication, and homogeneous bonding interfaces. Furthermore, annealing restores the linear optical dispersion (n and k) approaching that of epitaxially grown GaP with estimated plane wave absorption loss of 0.9 dB/cm at 1550 nm in the telecom C-band. The demonstrated approach establishes a scalable pathway toward high-quality GaP thin-film photonics compatible with versatile heterogeneous integration and back-end-of-line CMOS processing.
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All authors Hossein Esfandiar, Emanuel Glück, Fabian Ganss, Ulrich Kentsch, Dennis Arslan, Jana Paeschke, Sebastian Ritter, Andreas Ihring, Muyi Yang, Isabelle Staude, Stefan Facsko, Falk Eilenberger, Carolin Rothhardt, Sebastian W. Schmitt
Materials Science
Polaron-mediated metal-insulator transition and proton conduction in hydrogenated nickelate perovskites
Hang Ma, Tianxing Ma and Ying Liang
Nickel-based perovskites, owing to their spontaneous hydrogen uptake and the dramatic increase in resistivity upon hydrogenation, have emerged as promising candidates for
proton-conducting fuel
cell electrolytes. However, the mechanism of the hydrogen-induced metal-
insulator transition (MIT) in rare-earth nickelates remains under debate, particularly regarding whether the doped electrons occupy Ni e$_g$ states or O 2p ligand hole states. Here, we reveal a comprehensive MIT mechanism using first-principles calculations on NdNiO$_3$: the electrons introduced by hydrogen doping occupy the O 2p ligand hole states of the Ni-O hybridized d$_8$L configuration, promoting electron-polaron formation. The resulting electron polarons, together with
proton polarons, weaken the Ni-O hybridization and thereby drive the originally itinerant Ni e$_g$ electrons toward localization. This generates a local d8 (t$_{2g}$$^6$e$_g$$^2$) electronic configuration, leading to a Mott transition. In addition, we also find that compared with NdNiO$_3$, SmNiO$_3$ with a smaller A-site ionic radius more readily absorbs hydrogen but exhibits weaker
proton diffusion capability. Hydrogenation promotes
proton permeation along the [001] direction via the intraoctahedral transfer, whereas the overall
proton diffusivity is reduced. These results provide guidance for experimental screening of strongly correlated oxides as electrolyte materials and offer theoretical insights for enhancing
proton conductivity in rare-earth nickelates.
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Materials Science
Ab initio High-Pressure Phase Diagrams of Al-Mg Alloys in the Low Solute Concentration Limit
Shambhu Bhandari Sharma, Shailesh Mehta and Dario Alfè
Binary
alloy phase diagrams at high pressure are essential for understanding solidification and chemical partitioning in both engineered materials and planetary interiors, yet their experimental determination becomes increasingly challenging under extreme conditions. We apply a fully ab initio approach [J. Chem. Phys. 162, 184502 (2025)], based on density-functional theory, to compute the dilute-limit phase diagram of the Al-Mg system from ambient conditions up to 150 GPa. As a first step, we calculate the melting curves of pure fcc Al and pure hcp/bcc Mg, including the hcp-bcc phase boundary and triple point of Mg, all of which agree closely with available experimental data. The binary phase diagram is then constructed at both compositional extremes. On the Al-rich side, Mg consistently favours the
liquid throughout the entire pressure range, with this preference strengthening monotonically under compression. On the Mg-rich side, Al partitions preferentially into the
liquid at ambient pressure but undergoes a complete reversal above ~60 GPa, becoming solid-favouring as the Mg host transitions from hcp to bcc. This pressure-driven reversal inverts the
topology of the Mg-rich coexistence field from a conventional downward-sloping to an upward-sloping phase boundary, and has direct implications for models of planetary differentiation and interior chemical stratification.
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Materials Science · Cross-listed from physics.class-ph
Solving the Dissipation Inequality not as a constitutive restriction
Maximiliano Larrain Silva and Amit Acharya
A solution procedure is formulated and solved for treating the nonlinear Dissipation Inequality as a constraint equation within continuum mechanics, and allowing for incomplete knowledge of constitutive behavior. The scheme is demonstrated in the context of the rate-dependent, elastoplastic response of a bar, resulting in a nonlinear problem of constrained optimization. Both closed form and computational results are developed. The computational solutions utilize a sequence of convex optimization problems, and are shown to be accurate. In the example considered, the approach is shown to automatically correct an (intentionally) faulty constitutive specification, resulting in the solution to be in accord with the fundamental postulates of continuum mechanics.
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Materials Science · Cross-listed from cond-mat.mes-hall
Charge Tunable Optical Nonlinearity of Moiré Exciton-Polaritons
Zhijie Li, Kok Wee Song, Jens-Christian Drawer et al. (+16 more)
Transition metal dichalcogenides represent a versatile platform to study strong light-matter interactions based on
excitons and electrons in ordered
lattices. Twist-engineering of moiré structures further enables the manipulation of the polaritonic nonlinearities via engineering the
exciton landscape on the nanoscale. In this work, we demonstrate in-situ control of the optical saturation-based nonlinearity of moiré
exciton-polaritons by phase space restriction via charge doping. Strong
exciton-
photon coupling is established in a gate-controllable MoTe$_2$-MoSe$_2$ heterobilayer, embedded in a spectrally-tunable open cavity. A small gate voltage can effectively lower the necessary polariton density by one order of magnitude to achieve a similar nonlinear saturation effect as in the charge-neutral case. Our microscopic description successfully explains the observed phenomena in the framework of Pauli blocking for the moiré superlattices with charge preoccupation.
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All authors Zhijie Li, Kok Wee Song, Jens-Christian Drawer, Vita Solovyeva, Martin Esmann, Niklas Nilius, Muhammad Sufyan Ramzan, Caterina Cocchi, Falk Eilenberger, Takashi Taniguchi, Kenji Watanabe, Atanu Patra, Subhamoy Sahoo, Simon Betzold, Sven Höfling, Alexander Högele, Oleksandr Kyriienko, Christian Schneider, Bo Han
Materials Science · Cross-listed from cond-mat.mes-hall
Band topology and symmetry-driven magneto-optical response in two-dimensional d-wave altermagnets with staggered spin-orbit coupling
Meysam Bagheri Tagani Carmine Autieri and Wojciech Brzezicki
Altermagnets combine compensated collinear
magnetic order with momentum-dependent
spin splitting, providing a route to transverse electronic and optical responses without a net ferromagnetic moment. We develop a strictly periodic four-band tight-binding model for a two-dimensional d-wave altermagnet and distinguish the roles of three
spin orbit coupling (SOC) channels: uniform Rashba SOC, a sublattice-staggered Rashba interaction, and bond-staggered SOC. In the absence of SOC, the d-wave kinetic anisotropy produces
spin-polarized Dirac points on orthogonal Brillouin-zone boundaries, related by the altermagnetic fourfold
spin-group
symmetry. Uniform Rashba SOC mixes the
spin sectors and shifts these nodes but preserves the antiunitary
symmetry that forbids an integrated Hall response. The sublattice-staggered Rashba term breaks this
symmetry and activates transverse optical response, whereas the bond-staggered SOC provides the mass that gaps the boundary nodes. Their combined action generates strong Berry-
curvature hot spots and, within a narrow parameter window, an isolated lower two-band
manifold with Chern number C=-2. For the representative parameters considered here it is possible to stabilize a Chern
insulator phase. Using covariant-velocity Kubo calculations, we show that large optical Hall conductivity and circular dichroism extend well beyond the nonzero-Chern region and are controlled by SOC-induced avoided crossings and
symmetry breaking. We further find that carrier doping strongly modifies the resonant and dc Hall responses through Pauli blocking and the occupation of Berry-
curvature hot spots, enabling gate-controlled sign reversals. These results identify the complementary roles of distinct interfacial SOC mechanisms in producing
topology and tunable magneto-optical activity in compensated two-dimensional magnets.
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Materials Science · Cross-listed from math.DG
The Primitive and Diamond surfaces locally minimize the variance of Gauss curvature
Hao Chen
We prove that the Schwarz' Primitive (P) and Diamond (D) surfaces are local minimizers of the variance of Gaussian
curvature among local deformations within the moduli space of triply periodic minimal surfaces of genus 3 (TPMSg3s). Our approach interprets the branch values of the Gauss map as a configuration of eight points on the sphere and expresses the variance of Gaussian
curvature as the product of two integrals involving exponentials of Green's functions. We then show that the Hessian of this functional is positive definite at the cubic configuration when restricted to antipodal deformations, thereby establishing the local minimality of the P and D surfaces. Along the other deformation directions, the Hessian is positive definite except for a two-dimensional eigenspace with slightly negative
eigenvalues, leaving promising hope that the Gyroid is also a local minimizer.
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Materials Science
Transient Ferromagnetism in Ultrafast Phase Transitions in Perovskites under XUV Irradiation: A Comparative Study of SrTiO3 and KTaO3
Aldo Artimez Pena and Nikita Medvedev
We study ultrafast structural and electronic responses of strontium titanate and potassium tantalate to intense femtosecond irradiation using the XTANT3 multiscale code. It is found that at threshold doses of 0.7 eVatom in STO and 0.9 eVatom in KTO, a superionic state thermally forms with selective melting of the oxygen subsystem while metallic sublattices remain ordered. This state persists up to 1.6 eVatom STO and 1.5 eVatom KTO, above which complete disorder occurs. Analysis of the transient electronic density of states suggests that the B site d orbitals govern the divergent behaviour of the two materials: the compact Ti 3d orbitals in STO produce a narrow conduction band and large intraatomic exchange parameter, driving a transient ferromagnetic instability on 1 ps timescales, whereas the more spatially extended Ta 5d orbitals in KTO yield a broader conduction band and smaller exchange parameter, keeping KTO paramagnetic. These results suggest d orbital spatial extent as a structural parameter that influences phase transition sequences, and
magnetic response under extreme electronic excitation, with implications for the ultrafast optical control of electronic and
magnetic properties in perovskite based optoelectronic devices. Landau Devonshire analysis shows that irradiation at 0.3 eVatom transiently deepens the polar potential well in unstrained and strained STO and KTO, with the effect amplified approximately 2 fold in strained STO and 6 fold in strained KTO with respect to the unstrained cases.
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Materials Science · Cross-listed from quant-ph
Characterizing the nitrogen-vacancy center singlet transition and its phonon sideband for absorption-based room-temperature magnetometry
Tobias Probst, Florian Schall, Sebastian Heuft et al. (+9 more)
Magnetometry with nitrogen-vacancy (NV) centers in diamond has shown great promise in recent years. In particular, absorption-based magnetometry techniques, employing a cavity to enhance the absorption length, can improve the contrast and sensitivity compared to conventional techniques based on reading out the NV$^-$ triplet fluorescence. The absorption techniques rely on
magnetic-field-dependent absorption at the NV$^-$ singlet zero
phonon line at 1042$\,$nm and its
phonon sideband. In a cavity-enhanced spectroscopy approach, we study pump-
laser- and microwave-induced cavity signal changes at room temperature over a spectral range of 680-1050$\,$nm. Through normalization, we eliminate the cavity-enhancement effect and provide quasi-single-pass values for the absorption and optically detected
magnetic resonance (ODMR) contrast. The highest contrast is found at 1042$\,$nm, but multiple points of high contrast are found at the peaks of the
phonon sideband. Additionally, cavity-enhanced ODMR contrasts in the range of 50-80$\,\%$ are presented. We further measure the broadband singlet absorption cross section at room temperature with a novel method through microwave-induced signal changes. This method is insensitive to pump-
laser-induced signal changes by other defects and quantifies the room-temperature absorption strength of the singlet transition and its entire
phonon sideband. We determine the absorption cross section at 1042$\,$nm to be $\sigma^{\,\bigstar}_{1042}=(0.89\pm0.14)\cdot 10^{-21}\,\text{m}^2$ or $\sigma^{\,\blacktriangle}_{1042}=(2.9\pm0.5)\cdot 10^{-21}\,\text{m}^2$. depending on the employed 532$\,$nm NV$^-$ absorption cross section.
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All authors Tobias Probst, Florian Schall, Sebastian Heuft, Janina J. Schindler, Lukas Lindner, Sven Mägdefessel, Rüdiger Quay, Philipp Reineck, Alexander M. Zaitsev, Takeshi Ohshima, Matthias Weidemüller, Jan Jeske
Materials Science · Cross-listed from cond-mat.mes-hall
Resolving High-Energy States of Interlayer Excitons in MoSe$_2$/WSe$_2$ Heterostructures
Chirag Chandrakant Palekar, Paulo E. Faria Junior, Tobias Manthei et al. (+8 more)
High-energy states of interlayer
excitons (IXs) in van der Waals
heterostructures remain largely unexplored despite their importance for understanding many-body interactions and nonlinear optical phenomena. Here, we use photoluminescence excitation (PLE) spectroscopy to resolve a Rydberg-like series of excited IX states in MoSe$_2$/WSe$_2$
heterostructures. We observe multiple PLE resonances below the intralayer
exciton energies, which we assign to the 2s-, 3s-, and 4s-like states of the IXs. These resonances are consistently observed across
heterostructures with different twist angles, indicating that the high-energy state spectrum is only weakly affected by the twist angle. Wannier-
exciton calculations incorporating screened Coulomb interactions reproduce the overall energy scale and qualitative trends of the measured Rydberg-like series, supporting the assignment of the observed resonances. Our findings demonstrate that PLE provides direct experimental access to the previously unexplored high-energy IX states in van der Waals
heterostructures.
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All authors Chirag Chandrakant Palekar, Paulo E. Faria Junior, Tobias Manthei, Maximilian Nagel, Bhabani Sankar Sahoo, Shachi Machchhar, Imad Limame, Martin Podhorský, Jaroslav Fabian, Bárbara Rosa, Stephan Reitzenstein
Materials Science
Exciton-induced magnons carrying orbital angular momentum in CrI3
Martin Pavelka, Vishal Shokeen, Ruslan Chulkov et al. (+15 more)
Magnons are collective
spin excitations that contain and transport
spin angular momentum in
magnetic materials. It has been suggested that they can also carry orbital angular momentum in analogy to the electronic motion around the
nucleus. We explore the real-space
topology of
magnon wave-packets emanating from atomic-like
excitons in the ferromagnetic
insulator CrI3 and demonstrate the existence of orbital angular momentum in such wave-packets. We reveal that orbital angular momentum of
magnons is nearly equal to their
spin angular momentum and compensates the latter. This illustrates the existence of an unexplored internal angular momentum balance and demonstrates that the magnetization can be quenched without the need of angular momentum exchange with the
lattice.
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All authors Martin Pavelka, Vishal Shokeen, Ruslan Chulkov, Soma Dutta, David Muradas Belinchón, Ulrich Noumbe, Mahmoud Abdel-Hafiez, M. Venkata Kamalakar, Mathias Augustin, Vitaliy Goryashko, Torstein Hegstad, Johan H. Mentink, Jamal Berakdar, Oscar Grånäs, Anders Bergman, Olle Eriksson, Anna Delin, Hermann A. Durr
Materials Science
Resonantly-enhanced Raman response in graphene-capped bismuthene on SiC
Lukas Gehrig, Cedric Schmitt, Erica Fragomeni et al. (+15 more)
Two-dimensional
quantum spin Hall
insulators based on atomic monolayers offer a promising route toward dissipationless electronics, yet their practical use is often limited by environmental instability. Encapsulating the system with a
graphene capping layer has been shown to be a reliable method to prevent oxidation and degradation. However, the confirmation of a successful encapsulation still relies on ultra-high
vacuum techniques, that considerably slow the process. Here, we present an ex situ, rapid, nondestructive and spatially resolved Raman characterization of
graphene-capped bismuthene, a honeycomb monolayer of Bi on SiC. A pronounced Raman scattering peak at around 122 cm-1 is identified as the E2g
phonon of bismuthene, via a comparison with density functional perturbation theory calculations. We use excitation-energy and polarization-dependent Raman measurements to enable an unambiguous assignment of the spectral features. Tuning the excitation energy close to the excitonic transition in pristine bismuthene, we observe a strong enhancement of the Raman response and the emergence of additional scattering peaks. In this regime, higher-order
phonon features, as well as interfacial modes between bismuthene and the SiC substrate, become visible, suggesting the involvement of resonant scattering processes. Our results establish Raman micro-spectroscopy as a versatile tool for probing
graphene-protected
quantum materials, providing access to
lattice dynamics and interlayer coupling.
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All authors Lukas Gehrig, Cedric Schmitt, Erica Fragomeni, Simone Sotgiu, Stefan Enzner, Tommaso Venanzi, Bing Liu, Kilian Strauß, Jonas Erhardt, Martin Kamp, Elena Stellino, Paolo Postorino, Jörg Schäfer, Simon Moser, Christoph Stampfer, Giorgio Sangiovanni, Ralph Claessen, Leonetta Baldassarre
Materials Science
Machine Learning Assisted Design of Complex and High Entropy Alloys by Hybrid HiPIMS/Pulsed-DC PVD Process for Low Carbon Energy Applications in Extreme Environments
Paul Foulquier, Ryma Haddad, Ali Mahmoud et al. (+4 more)
Complex and high
entropy alloys are attracting much
attention currently thanks to their mechanical and corrosion resistance properties in harsh environments, in particular needed for carbon-free energy applications. However, their elaboration in bulk and in thin film form in a trial-and-error approach is impractical due to their complexity and the cocktail effect. The recent development of artificial intelligence brings a new possibility for their elaboration and adjustment of their properties. Firstly, we present an overview of Materials and data science research. Then we describe how DIADEM - French initiative for Materials and Data science convergence - tackles the development of innovative coatings for carbon-free energy applications (nuclear, high temperature electrolysis, ...) thanks to the development of a nationwide network of synthesis and characterization platforms - the DIADEM discovery hub. We describe in particular DIADEM-2D, an AI-driven Hybrid HiPIMS/Pulsed-DC PVD process using 4 cathodes in confocal combinatorial configuration. We present the high
entropy alloy determination using data from the literature for corrosion resistance in molten salt media and nuclear accidental conditions. An element-independent model gathering deposition parameters and coating properties has been implemented allowing the design of protective coatings with a particular composition. We demonstrate the feasibility of this process and its accuracy.
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All authors Paul Foulquier, Ryma Haddad, Ali Mahmoud, Eric Monsifrot, Fanny Balbaud-Celerier, Jean-Philippe Poli, Frederic Schuster
Materials Science
Dual-Mode Exciton Coupling in Epitaxially Registered Organic-Inorganic 2D Heterocrystals
Eunbeen Jeon, Kihyun Lee, Jieun Yeon et al. (+5 more)
Two-dimensional (2D) heterocrystals comprising molecules and
semiconductors can serve as an ideal platform for studying interfacial
excitons and for future optoelectronic applications, yet the energy and charge flow across these atomically sharp interfaces remain unclear. In this work, we investigated PTCDA-MoS2 as a prototypical 2D organic-inorganic
heterostructure and revealed dual-mode
exciton coupling between the constituent
crystals. Monolayer-resolved PTCDA molecular
crystals were grown on monolayer MoS2 via physical vapor assembly, and their crystallographic details, including the stacking angle, were determined by electron diffraction. Upon the formation of the
heterostructures, PTCDA's photoluminescence was completely quenched because of organic-to-inorganic hole transfer, whereas that of MoS2 increased markedly with PTCDA thickness. Using differential reflectance and photoluminescence excitation spectroscopy, we found that the enhancement arises from two distinct mechanisms. Ground-state charge transfer injects holes into MoS2, which suppresses negative trion formation and enhances the radiative recombination of neutral
excitons. In addition, resonant energy transfer, enabled by spectral overlap between PTCDA and MoS2, diverts excitation energy from PTCDA to MoS2. Our findings reconcile previously proposed mechanisms and establish a unified framework in which charge and energy transfer cooperate to govern
exciton coupling at organic-inorganic interfaces.
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All authors Eunbeen Jeon, Kihyun Lee, Jieun Yeon, Juseung Oh, Kenji Watanabe, Takashi Taniguchi, Kwanpyo Kim, Sunmin Ryu
Materials Science
Machine-Learning-Accelerated Metallene Stabilization from High-Throughput Sandwich Modeling
Mohammad Bagheri and Pekka Koskinen
Metallenes have appealing properties, but stabilizing them in a monolayer phase poses challenges for their synthesis. A recent experiment showed that the van der Waals squeezing method can stabilize certain metallenes in a MoS2 sandwich. This pioneering work motivates systematic studies, but such studies are experimentally impractical, while first-principles modeling remains prohibitive. Here, armed with universal machine-learning interatomic potentials, we constructed 1620 metallene sandwich
heterostructures containing 6 different sandwich layers and 45 metals. We performed
phonon calculations, which revealed 1208 dynamically stable structures. We found that transition-metal dichalcogenides, particularly MoSe2, are highly effective in stabilizing metallenes. Specifically, buckled hexagonal and honeycomb
crystal lattices exhibit the greatest stability. We further evaluated the thermal stability of selected
heterostructures with density-functional theory molecular dynamics simulations at room temperature. By uncovering the physical and chemical factors governing the stabilization of metallenes, our results provide systematic insights to guide and accelerate synthesis for future applications.
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Materials Science
Physics-Informed Neural Networks for Sparse Strain-Field Reconstruction in 4D-STEM
Roberto dos Reis, Gabriel T. dos Santos, Yukun Liu et al. (+2 more)
Quantitative strain mapping using four-dimensional scanning transmission electron microscopy (4D-STEM) typically requires densely sampled scans that can damage beam-sensitive specimens. We develop a physics-informed neural network (PINN) for sparse 4D-STEM strain reconstruction that embeds elastic
equilibrium and Saint-Venant compatibility in the training loss through automatic differentiation. The architecture combines a coordinate-based implicit representation, sine activations with stable second derivatives, frozen residual-scale normalization, an exponential physics-weight ramp, and residual-based adaptive collocation. We apply a sine-activated residual network to an experimental $180\times400$-pixel strain map of domain-structured PbGeSnSe$_{1.5}$Te$_{1.5}$. Across $1$-$75%$ sampling ($720$-$54{,}000$ probe positions), $R^2$ for $\varepsilon_{xx}$ reaches $0.80$ at $10%$ sampling and saturates near $0.86$ by $25%$; the chevron strain-band morphology is recovered from $10%$ of probe positions. At $10%$ sampling, the PINN reduces mean absolute error by approximately $26%$ relative to compressed sensing and $22%$ relative to Gaussian-process regression. An ablation against an equal-capacity data-only SIREN shows that the PDE prior improves accuracy at extreme sparsity and consistently improves physical self-consistency, but biases the reconstruction when data are abundant. Monte Carlo dropout and mean-field variational inference provide per-pixel epistemic uncertainty maps correlated with reconstruction error. With an appropriate constitutive model, the framework is adaptable to strain mapping across diverse material systems.
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All authors Roberto dos Reis, Gabriel T. dos Santos, Yukun Liu, Xiaobing Hu, Vinayak P. Dravid