Materials Science
Latent Heat and Raman Spectrum Change on Phase Transition of Water Including Calcium Chloride
Dongha Kim and Changyoun Lee
This study investigates how Raman O-H stretching signatures may be able to track latent-heat-related energetics during water's phase transitions. Prior work on latent heat and Raman analysis of phase change is reviewed to establish theoretical approach. Building on a framework that links O-H frequency shifts to hydrogen-bond strength, we relate
entropy/enthalpy variations to temperature-dependent changes in peak position and integrated intensity. Experiments on pure water and impurity-doped samples, specifically CaCl$_2$, were performed under controlled temperatures, and spectra were deconvoluted and integrated over defined bands. The Raman metrics exhibit reproducible temperature dependence that captures the transition window, while CaCl$_2$ induces systematic shifts and measurable modifications in the apparent latent-heat signature. These results highlight Raman spectroscopy as a quantitative probe of thermodynamic
evolution and impurity effects in water and related systems.
Read the full abstract ▾
Materials Science · Cross-listed from cond-mat.soft
Soap Films Amplify the Air-Water Interface but Neither Produce Detectable H2O2 Nor Enhance Reduction of Gold Ions
Muzzamil Ahmad Eatoo, Yash K. Mohature, Francisco P. Tome et al. (+4 more)
Soap films afford gentle production of air-water interfaces and underlie numerous practical applications. Recently these interfaces have been shown to exhibit unexpected redox capability, wherein Triton X soap films formed with water or HAuCl4 solutions (i) oxidize water up to 1.67 mM H2O2 and (ii) reduce aqueous Au3+ ions into gold nanoparticles, without external energy or catalyst. These reports tend to align with the broader claims of the redox nature of the air-water interface, which has been intensely debated. Here, we re-examine these claims via complementary application of a broad range of techniques, including NMR spectroscopy, fluorescence, colorimetric, TEM, DLS, ICP-OES. Experimental results reveal no evidence for H2O2 formation despite repeated formation of over 300 cycles of soap films, were probed via NMR spectroscopy and other analytical methods. Next, we interrogated soap films for their ability to spontaneously reduce Au3+ ions. TEM and time-resolved DLS revealed that the formation of Au nanoparticles was already formed spontaneous in bulk solutions, and casting soap films (300 cycles) had no measurable effect on particle size or density. This observation was confirmed via complementary quantitative ICP-OES. Our investigations showed that Au nanoparticles formation in bulk HAuCl4 solution without or with triton soap was accompanied by H2O2 generation, and we provide mechanistic insights into these processes. Collectively, these results demonstrate that amplification of the air-water interfacial area through soap-film formation is insufficient, by itself, to induce detectable H2O2 generation or enhance Au-ion reduction. More broadly, our findings highlight the need to distinguish reactions that are driven by purely air-water interfacial effects from those that originate from bulk-solution chemistry and at the solid-water interface
Read the full abstract ▾
All authors Muzzamil Ahmad Eatoo, Yash K. Mohature, Francisco P. Tome, Lisa Oki Exposito, Sirisha Kamireddy, Najeh Kharbatia, Himanshu Mishra
Materials Science
Thermodynamic origins of multimode spinodal decomposition in multicomponent alloys
Pravan Omprakash
In a binary
alloy, spinodal decomposition has one composition direction in which the free energy can fall. A multicomponent
alloy has more directions available, yet its elements usually separate together in a single, pseudobinary mode. Why does this happen, and what would allow two independent directions to become unstable? We examine these questions using binary interaction parameters and the composition-constrained
curvature of the regular-solution free energy. Across equimolar BCC quaternaries, one unstable mode is the most common outcome at 500 K, while 15.2% have at least two. The tendency of unlike elements to mix helps explain the preference for one mode. We then show how particular arrangements of interactions, including a balanced repulsive triangle and an attractive-repulsive pair, guarantee two downhill directions. When those directions have similar strengths, simplified phase-field models produce a broad texture of locally different solid solutions rather than two chemical blocks. A phase-specific screen identifies five provisional
alloys with nearly balanced modes, with Cu-In-Ir-Ti providing an example of this possibility. Thus, we establish a theoretical framework for engineering microstructures via spinodal decomposition derived from basic binary interaction tendencies.
Read the full abstract ▾
Materials Science · Cross-listed from cond-mat.str-el
Causality violations in cluster GW+DMFT: Exact Lehmann moments and the necessity of non-local vertex corrections
Michael O. Atambo
The $GW$ approximation is known to violate causality, yielding self-energies with unphysical poles in the upper half of the complex frequency plane. The combined $GW$+DMFT approach attempts to cure this by injecting the exact local self-energy. Using exact diagonalization on minimal Hubbard clusters, we rigorously
benchmark the analytic structure of the $GW$ and $GW$+DMFT self-energies. We demonstrate a “dimer anomaly”: on the two-site dimer, inversion
symmetry forces the non-local self-energy to be purely real, masking the causality violation. Moving to the non-bipartite three-site Hubbard ring, where hopping frustration yields a finite imaginary part in the non-local self-energy, we prove that both $GW$ and $GW$+DMFT violate the Matsubara causality condition. By analytically evaluating the exact Lehmann moments, we derive a closed-form expression for the high-frequency tail of the self-energy, $C = U^2\,\mathrm{Var}(d)\,I$, and show that standard methods fail to capture the exact equal-time two-particle correlators required to enforce it. The equal-time correlators that govern this tail are precisely those encoded in the high-frequency asymptotics of the fully irreducible vertex $\Lambda$; nevertheless, our intermediate-frequency analysis demonstrates that the local-only truncation of $\Lambda$ in $GW$+DMFT leaves non-local RPA resonances uncorrected. The two diagnostics are logically independent: $GW$+DMFT satisfies the necessary high-frequency condition $C\succeq0$ yet still violates the Matsubara sign condition at finite frequencies. Taking the interpolation-free real-axis evaluation of the exact self-energy as the primary causality certificate, with rational continuation as supporting evidence, we establish a rigorous
benchmark demonstrating that local self-energy corrections are insufficient to guarantee a causal analytic structure on frustrated clusters.
Read the full abstract ▾
Materials Science · Cross-listed from cond-mat.mes-hall
Three-Dimensional Shankar Skyrmions in Frustrated Antiferromagnets
Vladyslav M. Kuchkin, Ricardo Rama-Eiroa, Carlos Saji et al. (+2 more)
We formulate a continuum theory for three-dimensional (3D) Shankar skyrmions in frustrated chiral antiferromagnets (AFs) and derive the conditions for metastable finite-size $\pi_3(SO(3))$
solitons. A Derrick–Hobart scaling analysis shows that exchange, Dzyaloshinskii–Moriya interaction (DMI), anisotropy, and frustration can balance to set a finite
equilibrium size. We identify two microscopic routes to this common topological and stabilization framework: intrinsic rotation-frame order in noncollinear AFs and an $\mathbb{S}^3$ extension of an amplitude-softened Néel field. In the latter, the smooth four-component texture projects onto a Néel field containing a spatially separated pair of oppositely charged Bloch points. Numerical minimization yields metastable monopole textures, while the effective dynamics identifies coherent breathing oscillations as their characteristic finite-frequency collective mode. Our results provide a microscopic framework for the statics and dynamics of Shankar skyrmions and identify frustrated chiral AFs as promising hosts of 3D non-Abelian topological textures.
Read the full abstract ▾
All authors Vladyslav M. Kuchkin, Ricardo Rama-Eiroa, Carlos Saji, Alvaro S. Nunez, Roberto E. Troncoso
Materials Science
Enabling Domain-Specific Atomistic Models: A Machine Learning Potential for the Solid Acid Family
Jonas Hänseroth, Rose Asuka Baroness von Stackelberg and Christian Dreßler
Machine-learned interatomic potentials trained across the periodic table have made atomistic simulation broadly accessible, and specializing them to a single compound class is widely expected to improve accuracy. Yet examples remain scarce, and fewer still surpass universal models in speed or reach a higher level of electronic-structure theory. Here we present a potential that is universal within the class of water-free solid-state hydrogen-bond network mediated
proton conductors rather than across chemistry and a database of 4.4 million first-principles configurations spanning 55 materials. It surpasses leading general-purpose potentials across this domain, recovering measured activation energies and the ordering of anion rotational dynamics that those models miss; agreement on static structure does not imply agreement on transport. Accuracy falls for compositions far from the training set but stays competitive for close structural relatives, and a higher level of electronic-structure theory is reached with a few hundred additional configurations per material. We further introduce a compact variant carrying a fifth of the parameters, faster still and yet more accurate than every general-purpose model tested. It sustains more than a quarter of a million atoms on a single graphics processor, placing grain boundaries and the transition into the highly conducting phase within reach, and making a
quantum treatment of the
protons affordable. Reference accuracy and accessible system size thus become largely independent, offering a template for other compound classes.
Read the full abstract ▾
Materials Science
Single-particle detection of the Néel transition in LaCrO$_3$ microcrystals via widefield nitrogen-vacancy center magnetic imaging
Carson O. Patterson, Ethan Q. Williams, Eden Tzanetopoulos et al. (+6 more)
Rare-earth orthochromites exhibit rich, chemically tunable
magnetic behavior, making them attractive for temperature sensing and temperature-dependent switching applications. Realizing this potential requires understanding how synthesis conditions and particle morphology influence the underlying Cr$^{3+}$
magnetic ordering. Orthochromite magnetism has traditionally been characterized by ensemble techniques such as
neutron diffraction and SQUID magnetometry, which report only averaged
magnetic properties and cannot access particle-level information. Here we use widefield nitrogen-vacancy (NV) magnetometry to image the stray
magnetic fields of individual LaCrO$_3$ microcrystals produced via molten salt synthesis, resolving the antiferromagnetic Néel transition in single particles. Of the 18 particles measured between 278 and 298 K, five show a clear onset of magnetization near the ensemble Néel temperature, four show no measurable
magnetic signal, and nine display temperature-independent signatures consistent with localized
magnetic impurities undetected by ensemble measurements. Below the Néel temperature, particle magnetization remains fixed under a rotating in-plane field, consistent with canted antiferromagnetic ordering rather than paramagnetism, while repeated thermal cycling shows that the
magnetic field pattern varies between cooldowns with certain features recurring at the same locations, consistent with micron-scale structurally pinned antiferromagnetic domains in which the sign of the weak ferromagnetic moment is set independently each time they pass through the Néel transition. These results establish single-particle NV magnetometry as a sensitive probe of
magnetic ordering and domain structure in individual microcrystals, a key step toward correlating individual particle morphology and defect structure with
magnetic ordering in orthochromites.
Read the full abstract ▾
All authors Carson O. Patterson, Ethan Q. Williams, Eden Tzanetopoulos, Benjamin C. Li, Rachel T. Smith, Matthew Chang, Hideyuki Watanabe, Daniel R. Gamelin, Kai-Mei C. Fu
Materials Science
Results of Classical and Nonclassical theories of nucleation for ordering transition in barium titanate
V. Sobolev and T. Liebsch
Results of classical and nonclassical approach to nucleation at the ordering phase transition in barium titanate are presented. A nonclassical nucleation model is applied to the first-order paraelectric cubic phase to ferroelectric tetragonal phase transition in barium titanate is considered.
Read the full abstract ▾
Materials Science
Stress-based structure optimization for a range-separated hybrid van der Waals density functional
Per Hyldgaard, Yunqi Shao, Raul Quintero-Monsebaiz et al. (+1 more)
Complex matter, often partly soft and pliable, is the generic form of material systems. We must therefore generally call on density functional theory (DFT) to first predict the atomic structure before we can use it to also characterize (expected) properties. A recent range-separated hybrid (RSH) van Waals density functional (vdW-DF), `vdW-DF2-ahbr' (abbreviated AHBR) [PRX 12, 041003 (2022)], shows promise as a high-accuracy predictor of both binding energies and structure, from molecules to solids. However, the present implementation in
Quantum Espresso (QE) does not, in our experience, support robust stress-based unit-
cell optimization of RSHs. Here we document and illustrate work enabling practical AHBR-based complex-matter discovery: We port the AHBR XC functional to the Vienna Ab Initio Simulation Package (VASP) where use of stress-based DFT optimization is already stable also for RSHs. We test the implementation by comparing high-accuracy AHBR-QE and AHBR-VASP predictions of non-covalent molecular interactions and for structure and cohesion of simple bulk structures. We also illustrate and test the use of the new AHBR-VASP implementation to predict and understand (atomic and anti-ferromagnetic) structure in distorted-rocksalt metal monoxides. Finally, we illustrate use for complex-soft-matter discovery by predicting motifs for layer stacking in the C2N covalent-organic framework (COF) system [Nat. Commun. 6, 6486 (2015)].
Read the full abstract ▾
All authors Per Hyldgaard, Yunqi Shao, Raul Quintero-Monsebaiz, Lars Öhrström
Materials Science
Ab initio calculated diamagnetic and paramagnetic susceptibility of carbonate minerals
Jaroslav Hamrle, Matěj Machek, Vladimír K. Kusbach et al. (+1 more)
The anisotropy of
magnetic susceptibility (AMS) is a widely used tool to infer rock fabrics, yet quantitative interpretation is limited by sparse single-
crystal magnetic properties for rock-forming minerals and by the difficulty of separating intrinsic diamagnetism from impurity-related magnetism. Here we use density-functional theory (DFT) combined with perturbation theory to compute the diamagnetic susceptibility and AMS of calcite-group carbonates (calcite, magnesite, and dolomite) and to quantify the additional paramagnetic contribution from transition-metal doping. For pure calcite, the calculated susceptibility and its anisotropy are in good agreement with published single-
crystal measurements, validating the ab initio approach for diamagnetic phases. We provide improved intrinsic diamagnetic reference values for magnesite and dolomite, for which experimental susceptibilities are commonly affected by
magnetic impurities. To address impurity effects explicitly, we model Fe and Mn substitution in calcite using supercells. The computed
spin moments reproduce expected high-
spin states (Fe$^{2+}$, $S=2$; Mn$^{2+}$, $S=5/2$) and yield a susceptibility anisotropy per Fe concentration that matches the experimental slope. The strong anisotropy is primarily governed by an orbital contribution tied to the crystallographic $c$-axis rather than by
spin-orbit coupling, highlighting orbital magnetisation as a key but numerically challenging ingredient for modelling of paramagnetic AMS in carbonates.
Read the full abstract ▾
All authors Jaroslav Hamrle, Matěj Machek, Vladimír K. Kusbach, Zuzana Roxerová
Materials Science
Energy-Efficient Non-Volatile Photonic Switching via Composition-Engineered Sn-Doped GST
Xingyu Zhang, Daniel Vaz, Chi-Yi Kao et al. (+5 more)
Integrated phase-change photonics allows non-volatile optical switching with no static power draw, but the electrical energy needed to reversibly switch the material's state limits practical scaling. Efforts to improve energy efficiency have mostly focused on device optimization, such as redesigning the integrated microheater or waveguide. Here, we take a different, materials-centered approach by alloying Sn to Ge$_2$Sb$_2$Te$_5$ (GST) without altering the device structure or CMOS compatibility. We explore Sn concentrations ranging from 0 at.% to 20 at.% on waveguide-integrated PN and PIN heaters and observe a reduction in both the amorphization and crystallization energies in the 5–10 at.% range. At higher Sn content this trend reverses and the switching energy increases, which is suggestive of phase segregation when combined with TEM compositional analysis. A 10 at.% Sn device continues to switch over 1000 cycles, with observable degradation in the extinction ratio from 4.5 $\pm$ 0.3 dB to 2.4 $\pm$ 0.3 dB. Post-cycling imaging shows PCM migration and void formation which we believe can be further improved by enhanced encapsulation. Overall, Sn alloying offers a route to lower programming energy in integrated phase-change photonics without negatively affecting the switching speed relative to un-doped GST.
Read the full abstract ▾
All authors Xingyu Zhang, Daniel Vaz, Chi-Yi Kao, Marcus Tamura, Xiong Feng, Carlos A. Rios Ocampo, Bhavin J. Shastri, Nathan Youngblood
Materials Science
Accidental accuracy and formal consistency in $GW$+BSE: Exact benchmarks and regime-dependent error cancellation
Michael O. Atambo
Standard many-body perturbation theory for optical excitations combines the $GW$ approximation for quasiparticle energies with the Bethe-Salpeter equation (BSE) for the electron-hole response. Formally, the BSE kernel must equal the functional derivative of the self-energy, $K=\delta\Sigma/\delta G$. In routine practice, however, the kernel is built from a statically screened direct interaction and a bare exchange interaction, which breaks this consistency. Using exact diagonalization of the extended Hubbard dimer, we construct a controlled
benchmark that isolates the price of this inconsistency. We show that the internally inconsistent practical $GW$+BSE construction frequently yields accurate optical gaps through accidental cancellation between an underestimated $GW$ gap and an oversized bare-exchange kernel, and we map the regions of parameter space where this accidental accuracy occurs. Upon switching on the nearest-neighbor interaction and binding the
exciton, the practical construction remains the accurate one throughout the weak-binding regime, with cancellation optima at parts in $10^{3}$, while the frozen-$W$ construction fails at every binding strength. Beyond a binding threshold both static constructions deteriorate, showing that deeply bound
excitons require physics beyond any static kernel. Accidental accuracy is therefore a property of the weak-binding regime, and the systematic failure of the frozen-$W$ derivative kernel within the explored parameter space traces to its overscreening of the exchange channel. The accuracy of the practical kernel is an accidental cancellation of two independent errors, an underestimated quasiparticle gap and an oversized exchange term, not a hidden consistency. These results provide a controlled taxonomy of approximation failure in $GW$+BSE and a precise diagnostic for when standard workflows can be trusted.
Read the full abstract ▾
Materials Science
How Thermodynamically Accessible are Quaternary Mixed-Metal Chalcohalides?
Pascal Henkel, G. Krishnamurthy Grandhi, Jarno Laakso et al. (+6 more)
Quaternary mixed-metal chalcohalides (MMCHs) are a promising mixed-anion
semiconductor family, but their thermodynamic accessibility remains largely unexplored. We combine density functional theory with the Alexandria Materials Database to carry out a rapid and reliable evaluation of the thermodynamic accessibility of 54 M(II)$_2$M(III)Ch$_2$X$_3$ compounds. All evaluated MMCHs are predicted to be thermodynamically unstable, but a considerable fraction of MMCHs lie within computational uncertainty of the convex hull. Their predicted decomposition follows five distinct reaction pathways, most commonly into M(III)$_2$Ch$_3$, M(II)X$_2$, and M(II)Ch. Solution processing of six Sn-based MMCHs supports our analysis. Notably, this includes the first synthesis of the previously unreported Sn$_2$InS$_2$Br$_3$ in a multiphase film. Our approach identifies convex hull proximity and competing phase formation as key constraints on MMCH synthetic accessibility during solution processing, thereby guiding future MMCH exploration.
Read the full abstract ▾
All authors Pascal Henkel, G. Krishnamurthy Grandhi, Jarno Laakso, David Rovira Ferrer, Edgardo Saucedo, Jingrui Li, Paola Vivo, Miguel A. L. Marques, Patrick Rinke
Materials Science
3/8 charge-density wave instability in the kagome metal CsV$_3$Sb$_5$
Luca Buiarelli, Hyeonseo H. Park, Ethan T. Ritz et al. (+2 more)
The kagome metal CsV$_3$Sb$_5$ exhibits charge density wave (CDW) and superconducting transitions, both of which are substantially affected by pressure. Recent x-ray diffraction experiments identify a new charge-ordered phase at a pressure coinciding with the dip of the superconducting dome. This CDW phase displays a distinctive wavevector $\mathbf{Q} = (3/8, 0, 1/2)$ and monoclinic
symmetry, in contrast to the $2\times2\times 2$ and $2\times2\times 4$ orders reported at ambient pressure. In this letter, we show that density functional perturbation theory (DFPT) calculations on a fine reciprocal-space grid predict the leading
lattice instability of CsV$_3$Sb$_5$ to be at this wavevector. Finite-displacement calculations reveal that while anharmonic effects stabilize the conventional $L_2^-$ CDW at ambient pressure, the competing $3/8$ instability becomes energetically favorable above $\sim$1 GPa, consistent with experimental observations. Interestingly, the nesting function displays a peak at the same wavevector. A Landau free energy analysis explains the emergence of the monoclinic distortion observed in x-ray diffraction, in addition to several bond-ordering patterns that may be relevant to the observed trends in the superconducting $T_c$.
Read the full abstract ▾
All authors Luca Buiarelli, Hyeonseo H. Park, Ethan T. Ritz, Rafael M. Fernandes, Turan Birol
Materials Science · Cross-listed from cond-mat.mes-hall
Rundong Ma, Konstantin Davydov, Liuxin Gu et al. (+9 more)
Interlayer
excitons in transition metal dichalcogenide (TMD)
heterostructures exhibit long lifetimes and long-range transport, making them promising for excitonic devices and
quantum many-body phases, such as Bose-Einstein condensates. Achieving these goals requires a precise understanding of
spin-allowed bright and nominally
spin-forbidden dark
excitons, because the lowest-energy
exciton species governs population, transport, and condensation. Despite substantial progress, unambiguously distinguishing singlet and triplet interlayer
excitons has been challenging, as moiré
excitons in these
heterostructures can mimic their optical signatures. Here, we report the direct spectroscopic identification of bright (singlet) and dark (triplet) interlayer
excitons in high-quality, dual-gated WSe$_2$/hBN/WSe$_2$ homobilayers. Electric-field-dependent photoluminescence and reflectance reveal two momentum-direct interlayer transitions with distinct
spin configurations. The interlayer dark
excitons obey selection rules that differ from those of bright
excitons. Strikingly, interlayer dark
excitons retain strong valley polarization, even with their ultralong lifetime exceeding microseconds. Finally, we demonstrate twist-angle control, wherein twist-induced electron-hole momentum mismatch modulates interlayer
exciton emission. These results provide critical insights into the electronic and excitonic structure of TMD
heterostructures, opening new avenues for excitonic many-body physics and optoelectronic devices.
Read the full abstract ▾
All authors Rundong Ma, Konstantin Davydov, Liuxin Gu, Lifu Zhang, Hassan Alnatah, Beini Gao, Ruihao Ni, Suji Park, Houk Jang, Takashi Taniguchi, Kenji Watanabe, You Zhou
Materials Science
Irreducible Weyl Semimetals
Ke-Xin Pang and Yan Gao
A key objective in Weyl-semimetal (WSM) research is to identify phases built from minimal configurations of Weyl points (WPs), which provide the simplest settings for investigating the intrinsic physics of chiral topological charges. Pang et al. [Phys. Rev. Res. 8, 033304 (2026)] recently established that crystallographically realizable WSMs can be decomposed into linear combinations of 16 minimal "irreducible Weyl molecules" (IWMs). A fundamental question remains unresolved: which of these non-decomposable configurations can themselves form standalone crystalline phases? Here we introduce irreducible Weyl semimetals (IWSMs), in which two bands crossing near the Fermi level form an elementary
symmetry-compatible complex whose complete Weyl-node configuration is charge neutral and crystallographically indivisible. Combining all 1651
magnetic space groups with Weyl-orbit multiplicities and band-compatibility relations, we classify IWSMs formed by crystalline-
symmetry-protected twofold WPs. Only ten of the sixteen primitive inventories admit one-copy realizations, comprising four Pair, four Split, and two Mixed charge-node architectures. Remarkably, this classification uncovers five unconventional and previously unrecognized topological phases: the charge-three Pair IWSM {3, -3}; the Split IWSMs {3, -1, -1, -1}, and {4, -1, -1, -1, -1}; and the Mixed IWSMs {3, 1, -2, -2} and {3, 3, -2, -2, -2}. For all ten classes,
symmetry-constrained
lattice models verify the complete node inventories, Chern charges, and surface chiral-flow incidence. Our results establish crystalline irreducibility as a phase-level organizing principle beyond individual Weyl nodes and provide a
symmetry-resolved framework for identifying minimal Weyl complexes in electronic, phononic, and photonic systems.
Read the full abstract ▾
Materials Science
Disentangling octahedral distortion and symmetry breaking in the ordered double perovskite SrLaCoNbO$_6$
Ajay Kumar, Clemens Ulrich, Yaroslav Mudryk et al. (+1 more)
We report a comprehensive high temperature structural investigation of the B-site ordered double perovskite SrLaCoNbO$_6$ using combined Raman spectroscopy and x-ray diffraction (XRD) over the range 25–900~$^\circ$C. Two distinct temperature-driven anomalies are identified at $T_\mathrm{OD} = 300\pm 25~^\circ$C and $T_\mathrm{PT} = 750\pm 25~^\circ$C through pronounced renormalizations in the
phonon frequency and linewidth, accompanied by the
evolution and suppression of characteristic XRD reflections. The low-temperature anomaly at $T_\mathrm{OD}$ is associated with an isostructural octahedral distortion within the monoclinic $P2_1/n$ phase. At $T_\mathrm{OD}$, the radial and angular distortion parameters of the CoO$_6$ and NbO$_6$ octahedra decrease to near-zero values before reversing upon further heating due to an inversion of the in-plane Co–O and Nb–O bond-length hierarchy. The high-temperature anomaly at $T_\mathrm{PT}$ corresponds to a
symmetry-breaking structural phase transition from $P2_1/n$ to the monoclinic $I2/m$ phase, confirmed by group-theoretical analysis and Rietveld refinement. These results demonstrate that integrating temperature-dependent Raman spectroscopy with laboratory-based XRD, complemented by quantitative octahedral distortion analysis, provides a robust approach to disentangle isostructural octahedral distortions from
symmetry-breaking phase transitions in complex double perovskite oxides without recourse to synchrotron or
neutron diffraction facilities.
Read the full abstract ▾
All authors Ajay Kumar, Clemens Ulrich, Yaroslav Mudryk, Rajendra S. Dhaka
Materials Science
Electronic Coupling and Charge-Transfer Landscape of Graphene on Ge(001)/Si(001): Multiscale Analysis Assisted by Machine Learning
Pawel Dabrowski, Przemysław Przybysz, Maciej Rogala et al. (+11 more)
Understanding and controlling charge transfer at
graphene-
semiconductor interfaces is essential for the integration of two-dimensional materials into silicon-compatible technologies. Here, we combine ultraviolet photoelectron spectroscopy (UPS), Kelvin probe force microscopy (KPFM), angle-resolved photoemission spectroscopy (ARPES), scanning tunneling spectroscopy (STS) and density functional theory (DFT) to resolve work-function modulation and electronic coupling in
graphene grown on Ge(001)/Si(001). UPS and KPFM reveal a spatially non-uniform work-function landscape correlated with the nanofaceted morphology of the substrate. ARPES and DFT calculations for the pristine interface consistently indicate n-type doping and electron transfer from Ge to
graphene. In contrast, modeling of the oxidized interface predicts a reversal to p-type doping, providing a plausible explanation for the different doping polarities reported in the literature. Machine-learning-assisted classification of the STS data resolves distinct local electronic regimes, ranging from nearly free-standing
graphene on nanofacet tops to more strongly coupled inter-facet regions and nanoribbon-like regions with distinct local electronic responses. By identifying the mechanisms governing local
graphene-substrate interactions and charge transfer, our study provides guidelines for tailoring the synthesis process and minimizing defect formation during delamination. These insights support the production of high-quality
graphene layers for electronic devices and for transfer as protective coatings for air-sensitive materials.
Read the full abstract ▾
All authors Pawel Dabrowski, Przemysław Przybysz, Maciej Rogala, Iaroslav Lutsyk, Paweł Krukowski, Witold Kozłowski, Michał Piskorski, Piotr Milczarski, Iwona Pasternak, Jakub Sitek, Marek Kopciuszyński, Ryszard Zdyb, Jagoda Sławińska, Pawel J. Kowalczyk
Materials Science · Cross-listed from cond-mat.mes-hall
Multiscale modelling of nanoscaled FETs based on 2D ferroelectric materials
Alejandro Toral-Lopez, Michele Virgilio, Gianluca Fiori et al. (+1 more)
Ferroelectric materials are highly attractive for low-power, high-speed electronics and emerging neuromorphic computing architectures. However, the severe physical scaling limits of conventional bulk (3D) ferroelectrics at the nanoscale have shifted
attention towards two-dimensional (2D) ferroelectric monolayers. Accurate device-level performance predictions are essential to accelerate the experimental testing and screening of these novel materials. In this work, we present a multiscale simulation framework that bridges first-principles density functional theory with Non-
Equilibrium Green's Function (NEGF) transport calculations. Using a 2D Indium Phosphide monolayer as a case study, our approach leverages a continuously interpolated, polarization-dependent
Hamiltonian embedded within a self-consistent Poisson-NEGF solver. The model captures the dynamic interplay between ion movement and electronic transport, naturally reproducing macroscopic hysteresis loops and
memory windows without empirical parameters. This predictive pipeline provides a computationally efficient tool to evaluate and optimize next-generation 2D ferroelectric field-effect transistors.
Read the full abstract ▾
All authors Alejandro Toral-Lopez, Michele Virgilio, Gianluca Fiori, Damiano Marian
Materials Science
Hierarchical Fourier Phase Projection for Local Electronic Observables
Tao Hu, Weiqing Zhou, Zhichang Fu et al. (+2 more)
Large-scale electronic-structure calculations require efficient access to local observables without explicitly constructing all occupied orbitals. We develop hierarchical
Fourier phase projection (HPP), which organizes
Fourier probes into a reusable spatial hierarchy that progressively removes short-range aliasing while exploiting density-
matrix locality. The method provides systematic refinement from low-cost local estimates to the projection-exact limit of the chosen numerical occupation operator, without discarding previously evaluated responses. Tests using frozen Kohn–Sham
Hamiltonians for semiconducting and metallic systems demonstrate controllable convergence of electron densities and nonlocal pseudopotential forces, weak size dependence of the probing resolution required for a fixed local accuracy, and near-linear growth of the direct computational cost at fixed probing workload. Inter-level changes further provide practical information for terminating the refinement at finite accuracy. HPP connects electronic locality, observable accuracy, and computational effort within a single hierarchical framework, providing a scalable route to local quantities in large-scale electronic-structure calculations.
Read the full abstract ▾
All authors Tao Hu, Weiqing Zhou, Zhichang Fu, Yechen Chen, Shengjun Yuan
Materials Science
From Chemical Complexity to Tunable Magnetic Ordering in Highly Disordered High-Entropy Spinel Oxides
Neha Sharma, Sushanta Mandal, Nikita Sharma et al. (+10 more)
High-
entropy stabilization chemistry is redefining materials design by transforming configurational disorder, arising from the deliberate incorporation of multiple principal cations, into a thermodynamic advantage that promotes phase stability and enables emergent functionalities. In this work, we investigate the
evolution of
magnetic ordering in spinel-type high
entropy oxides by systematically varying the cation composition of the B site within a fixed high-
entropy A-site
matrix, (Ni$_{0.2}$Mg$_{0.2}$Co$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$)B$_2$O$_4$. Upon introducing multicomponent B-site configurations, we uncover a strikingly linear dependence of the
magnetic transition temperature (T$_C$) on the T$_C$s of the corresponding single B-site high-
entropy systems. Remarkably, this trend persists even in highly complex (Ni$_{0.2}$Mg$_{0.2}$Co$_{0.2}$Cu$_{0.2}$Zn$_{0.2}$)(Cr$_{0.2}$Mn$_{0.2}$Fe$_{0.2}$Ga$_{0.2}$X$_{0.2}$)$_2$O$_4$, X = Al and Ti. Despite the material's extremely high degree of disorder, absence of a dominant
magnetic ion or a straightforward superexchange pathway, detailed magnetization measurements, low-temperature X-ray
magnetic circular dichroism, and
neutron powder diffraction studies reveal robust long-range ferrimagnetic ordering. These results reveal an emergent predictability in ferrimagnetic high-
entropy spinel oxides, where, despite extreme configurational disorder and competing interactions, robust ferrimagnetic order can arise from, rather than be hindered by, extreme configurational disorder. This establishes a pathway for predictively tuning
magnetic transition temperatures in high-
entropy oxides beyond conventional ordered systems.
Read the full abstract ▾
All authors Neha Sharma, Sushanta Mandal, Nikita Sharma, Amritpal, Sangeeta Thakur, Viktor Ukleev, Chen Luo, Florin Radu, S. D. Kaushik, Tirthankar Chakraborty, Sanjoy Kr. Mahatha, Denis Pelloquin, Sourav Marik
Materials Science
Nonrelativistic and Relativistic Contributions to Spin-Momentum Locking and Spin Photogalvanic Effect in an Altermagnetic Multiferroic
Giuseppe Cuono, Subhadeep Bandyopadhyay, Amar Fakhredine et al. (+6 more)
Altermagnetic multiferroics provide a platform where non-relativistic
spin-momentum locking (SML) coexists with relativistic
spin textures, yet disentangling their different origins remains challenging. Here, using first-principles density-functional-theory calculations and
symmetry analysis of the multipolar expansion of the
spin polarization, we investigate the altermagnetic multiferroic BaCuF4. Its dominant non-relativistic altermagnetic d-wave SML originates primarily from a CuF6 octahedral rotation coupled to the polar distortion and can therefore be reversed by ferroelectric switching. We show that
spin-orbit coupling generates additional
spin multipoles and, depending on the Neel-vector orientation, induces
spin canting and weak ferromagnetism. By exploiting the group-subgroup relations between
spin groups and
magnetic space groups, we then distinguish non-relativistic altermagnetic, canting-associated, and purely relativistic contributions to the SML. We further show that this hierarchy is encoded in the nonlinear
spin-photogalvanic response, whose
spin projection selectively probes contributions of different origins. These results establish a direct connection between the microscopic
spin texture and nonlinear
spin transport in altermagnetic multiferroics.
Read the full abstract ▾
All authors Giuseppe Cuono, Subhadeep Bandyopadhyay, Amar Fakhredine, Mathews Benny, Xujia Gong, Paolo Barone, Andrea Droghetti, Carmine Autieri, Silvia Picozzi
Materials Science
Pronounced Site Preference in Cr-Doped Mn-Based M-Type Hexaferrites and Its Chemical Origins
Dylan Correll, Susheng Tan, Evan Wang et al. (+1 more)
Cation distribution plays a critical role in determining the properties of crystalline oxides. Understanding the chemical factors that govern cation distribution is therefore essential for the rational design of cation-ordered materials, particularly frustrated magnets in which structural disorder can strongly affect the
magnetic ground state. Here, we investigate the origin and
evolution of cation distribution in the extensively studied M-type hexaferrite structure using the first Mn-based M-type hexaferrite, KSb3Mn9O19, as a model system. A systematic Cr3+-doped series, KSb3(Mn1-xCrx)9O19, was examined using powder and single-
crystal X-ray diffraction, electron microscopy, and energy-dispersive X-ray spectroscopy. Cr3+ exhibits a pronounced preference for the Mn Kagome sublattice, accompanied by the
evolution of Mn vacancies and Mn3+/Sb3+ disorder on neighboring sites. Analysis of the local coordination environments and their
evolution with Cr content suggests that
crystal-field effects, chemical bonding, and local structural strain collectively govern this site selectivity. The
magnetic properties of the Cr-doped compounds show similar behaviors as the undoped parent compound, other than the doping-induced
spin-glass state at the highest Cr concentration, supported by heat capacity measurements. These results establish a chemical picture of cation site distribution and selection in M-type hexaferrites and demonstrate how substitution at one crystallographic site can induce coupled redistribution and disorder across neighboring sublattices. Moreover, this work establishes local coordination chemistry as a route toward understanding and ultimately controlling cation distribution in complex oxides, providing chemical design principles for structurally well-defined frustrated
magnetic materials.
Read the full abstract ▾
All authors Dylan Correll, Susheng Tan, Evan Wang, Xin Gui
Materials Science
Chemical-Disorder-Induced Non-metallic Transport in Thermodynamically Metallic Mo4TGa16Ge (T = Co, Rh or Ir)
Chaoguo Wang, Jiaqi Tian and Xin Gui
Flat-band electronic states can be highly sensitive to chemical perturbations, offering opportunities to access a broader range of electronic behaviors beyond that of parent materials. Here, we report the discovery of a new series of compounds, Mo4TGa16Ge (T = Co, Rh, or Ir), derived from the strongly correlated flat-band
superconductor, Mo4PtGa17, via nominally preserving the total valence electron counts. All three materials crystallize in a noncentrosymmetric cubic space group, F-43m, with Ge selectively occupying one of the Ga sites in the parent compound. Although the total electron count remains the same, Mo4TGa16Ge exhibits significantly distinct properties from Mo4PtGa17. Theoretical calculations predict metallic electronic structures with narrow, dominant Mo-d states at the Fermi energy, while low-temperature heat capacity results demonstrate finite Sommerfeld coefficients. However, electrical transport measurements show predominantly non-metallic behaviors with small observed activation energies, excluding the possibilities of conventional semiconducting behaviors. Combining chemical bonding analysis, electronic structure and compositional determination from X-ray crystallography and spectroscopy, we propose that the coexistence of the non-metallic transport features and the thermodynamically metallic behaviors can be attributed to the high sensitivity of the narrow-band materials to chemical disorders. Thus, the discovery and investigation of Mo4TGa16Ge provide a chemically tunable platform for studying disorder-controlled transport in flat-band intermetallics.
Read the full abstract ▾
Materials Science
Switching Anomalous Hall and Nernst Responses by Nonmagnetic N Occupation at Fixed Noncoplanar Mn Antiferromagnetic Order
Xin Liu, Jiyuan Xu, Li Ma et al. (+4 more)
Nonmagnetic atomic occupation can control anomalous transverse transport by modifying
magnetic symmetry without changing the underlying
magnetic order. We demonstrate this effect using controlled $\gamma$-Mn, Mn$_4$N, and MnN reference states with the same
lattice constant and identical noncoplanar all-in-all-out Mn
magnetic configurations, while varying only the occupation of the N sublattice. The anomalous Hall and anomalous Nernst responses exhibit a pronounced zero–finite–zero
evolution across the series despite the unchanged Mn
spin order. In $\gamma$-Mn and MnN, the high
magnetic symmetry enforces complete cancellation of the Brillouin-zone-integrated Berry
curvature. In Mn$_4$N, N occupation lowers the
magnetic symmetry while preserving inversion and breaking the relevant twofold rotational
symmetries, thereby lifting the cancellation constraint and permitting an uncompensated Berry-
curvature contribution along the [111] direction. The resulting finite anomalous Hall conductivity reaches $-126$~S/cm near the Fermi level. These results establish nonmagnetic sublattice occupation as a
symmetry-control parameter for Berry-
curvature-driven transport in compensated antiferromagnets, independent of changes in the
magnetic order.
Read the full abstract ▾
All authors Xin Liu, Jiyuan Xu, Li Ma, Guoke Li, Dewei Zhao, Congmian Zhen, Denglu Hou
Materials Science · Cross-listed from cond-mat.soft
A Bioinspired Magnetothermally Triggered Capsule for Rapid Microrobot Release
Mengfan Zhang, Zike Chen, Zhihao Lv et al. (+3 more)
Capsules are attractive platforms for microrobot delivery, combining structural simplicity with protected delivery and rapid release remains challenging. Inspired by the latched spring mechanism of Impatiens balsamina seed dispersal, a magnetothermally triggered capsule integrates a phase-change hydrogel latch, a monostable cover that serves as an elastic spring, and a payload-carrying base. Mechanical analysis guides the cover design to avoid bistability after assembly and premature hydrogel latch rupture before triggering. During transport, the hydrogel constrains the inverted cover. Under an alternating
magnetic field, Fe3O4-mediated heating softens the hydrogel and induces cohesive failure, releasing stored energy to drive capsule opening and microrobot ejection. The capsule opens within 50 ms after hydrogel softening and ejects microrobots at an estimated initial velocity of 1.0 m/s. Demonstrations on a three-dimensional platform and ex vivo porcine stomach establish protected delivery, target-site opening, and post-release actuation.
Read the full abstract ▾
All authors Mengfan Zhang, Zike Chen, Zhihao Lv, Zheng Jia, Rui Xiao, Guoyong Mao
Materials Science · Cross-listed from physics.chem-ph
What Does a Semilocal Machine-Learning Correction Actually Learn? Size-Dependent Errors across Four Parent Functionals
Abhishek Bhattacharjee, Kishan Kumar Mohanta, Subrata Jana et al. (+1 more)
Machine-learning (ML) corrections to density functional approximations (DFAs) offer a route to improving electronic-structure predictions while retaining the efficiency of semilocal functionals. An important question is whether such corrections learn transferable improvements or instead compensate for errors specific to the parent functional. Here, we address this question by applying the semilocal ML correction of Wang et al. [J.~Chem.~Phys.~158, 154107 (2023)] to PBE, B3LYP, SCAN, and r$^2$SCAN, while keeping the network architecture, loss function, training set, and optimization protocol unchanged. We find that the learned correction develops a systematic size-dependent contribution to atomization energies for all four parents, with $|r|\geq0.9999$ along the $n$-alkane series, where r is the Pearson coefficient of the linear fit. Its magnitude and sign depend systematically on the parent: the correction partially compensates the size-dependent errors of PBE and B3LYP, but introduces substantial size-dependent contributions for SCAN and r$^2$SCAN, whose parent errors show little size dependence. In contrast, ionization potentials, electron affinities, and isomerization energies are largely unaffected. Spatial decomposition further reveals distinct origins of this extensive contribution, with bonding regions dominating for B3LYP, SCAN, and r$^2$SCAN and core regions dominating for PBE. These results show that the global-energy ML correction is strongly dependent on the error structure of its parent DFA, highlighting size-dependent error accumulation as a critical consideration in the assessment and development of ML-enhanced density functionals.
Read the full abstract ▾
All authors Abhishek Bhattacharjee, Kishan Kumar Mohanta, Subrata Jana, Prasanjit Samal
Materials Science
Screening of Coulomb Interactions in MoS2 Nanoribbons: Enhanced Coulomb interactions, Antiscreening, and Edge Magnetism
A. Montaghemi, H. Hadipour, A. Khademi et al. (+1 more)
MoS2 has attracted significant
attention for its promising applications in optoelectronics, owing to the remarkable stability of its
excitons and trions. These quasiparticles have large binding energies that arise from the MoS2 moderate band gap and the unconventional screening of Coulomb interactions in low dimensions. Here, we investigate the screening of long-range Coulomb interactions in the 1H and 1T' phases of MoS2 across different dimensionalities, with particular emphasis on nanoribbons. Our analysis is based on first-principles calculations combined with the constrained random-phase approximation. This work presents a comparative study of MoS2, h-BN, black phosphorene, and
graphene nanoribbons, with emphasis on the role of Coulomb interactions in shaping their electronic and
magnetic properties. In one-dimensional nanoribbons,
quantum confinement leads to a substantial enhancement of Coulomb interactions relative to 2D MoS2. Calculations show that the Hubbard U increases from 2.6 eV in the 2D system to nearly 3.5 eV in the semiconducting nanoribbons. In these systems, the Coulomb interaction is long-ranged, with its tail extending over more than 100 A, nearly twice of that in the 2D structure. The presence of asymmetric edge states involving d and p orbitals in non-hydrogen-passivated zigzag MoS2 nanoribbons, in contrast to phosphorene, h-BN, and
graphene nanoribbons, results in a finite net magnetization.
Read the full abstract ▾
All authors A. Montaghemi, H. Hadipour, A. Khademi, A. Yazdani