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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Wednesday 15 October

Materials Science · Cross-listed from cond-mat.dis-nn

Symmetry Transitions Beyond the Nanoscale in Pressurized Silica Glass

Zhen Zhang, Zhencheng Xie and Walter Kob

Silica is the paradigmatic network glass-former and understanding its response to pressure is essential for comprehending the mechanical properties of silica-based materials and the behavior of silicate melts in the Earth's interior. While pressure-induced changes in the short-range structure - particularly the breakdown of tetrahedral symmetry - have been well documented, structural transformations on larger length scales, important for many material properties, remain poorly understood. Here, we numerically investigate the three-dimensional structure of silica glass as a function of compression up to $P \approx 100$~GPa. Using a novel many-body correlation function, we reveal a complex medium-range order: While for $P \lesssim 10$~GPa, one finds tetrahedral, octahedral, and cubic symmetries, the structure at higher $P$s exhibits alternating cubic and octahedral particle arrangements. The $P$-dependence of the corresponding structural correlation length displays two distinct maxima, which permits to rationalize the anomalous compressibility of silica. The identified complex structural organization on intermediate range scales is the result of a pressure-and scale-dependent interplay between directional bonding, packing efficiency, and network stiffness. Since these competing effects are common in network glass-formers, the identified three-dimensional medium-range order, and hence the physical properties of the glass, are expected to be universal features of such materials under extreme conditions.
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Materials Science

Thermal and Electrical Properties of (Cr,Mo,Ta,V,W)C High-Entropy Carbide Ceramics

Ali Sarikhani, Steven M. Smith, Suzana Filipovic et al. (+2 more)

The synthesis and characterization, along with the resulting properties, of fully dense \((\mathrm{Cr, Mo, Ta, V, W})\mathrm{C}\) high-entropy carbide ceramics were studied. The ceramics were synthesized from metal oxide and carbon powders by carbothermal reduction, followed by spark plasma sintering at various temperatures for densification. Increasing the densification temperature resulted in grain growth and an increase in the lattice parameter. Thermal diffusivity increased linearly with testing temperature, resulting in thermal conductivity values ranging from approximately \(7~\mathrm{W\,m^{-1}\,K^{-1}}\) at room temperature to \(12~\mathrm{W\,m^{-1}\,K^{-1}}\) at \(200~^\circ\mathrm{C}\). Measured heat capacity values matched theoretical estimates made using the Neumann–Kopp rule. Room-temperature electrical resistivity decreased from \(137\) to \(120~\mu\Omega\cdot\mathrm{cm}\) as the excess carbon decreased from \(5.4\) to \(0.1~\mathrm{vol\%}\), suggesting an enhanced electronic contribution to thermal conductivity as excess carbon decreased. All specimens exhibited a Vickers hardness of approximately \(29~\mathrm{GPa}\) under a \(0.49~\mathrm{N}\) load. These results underscore the tunability of this high-entropy carbide system.
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All authors Ali Sarikhani, Steven M. Smith, Suzana Filipovic, William G. Fahrenholtz, Gregory E. Hilmas

Materials Science

Melting phase relation of seifertite and pyrite-type SiO2 determined by machine learning potentials

Doyoon Park, Xin Deng and Jie Deng

Silica (SiO2) is fundamental to both industrial technology and planetary science, yet the phase relations of its high-pressure polymorphs remain poorly constrained. Here, we develop two machine learning potentials (MLPs) for SiO2 that faithfully represent the SCAN and PBEsol exchange-correlation functionals over a wide temperature (1000-10000 K) and pressure (100-400 GPa) range using deep neural networks. With large-scale two-phase simulations powered by these potentials, we determine the melting curves of seifertite and pyrite-type SiO2 and infer the solid-solid phase boundary between these two phases. The SCAN functional, which captures intermediate-range van der Waals interactions, reproduces structural and thermodynamic properties with high fidelity, predicting melting temperatures 6-10 % higher and a seifertite to pyrite-type transition pressure 22 % higher than the PBEsol. The strongly negative Clapeyron slope (-6.1 MPa/K) of this transition suggests that mantle convection could be highly layered in super-Earth exoplanets, potentially affecting their long-term thermal evolution and habitability.
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Materials Science

Energetic Origins of Competing Deformation Modes in Metastable Titanium Alloys

Ganlin Chen, Deepak V Pillai, Yufeng Zheng et al. (+1 more)

Metastable alloys, such as $\beta$-phase titanium (Ti) alloys with a body-centered cubic (BCC) lattice, can exhibit exceptional mechanical properties through the interplay of multiple deformation mechanisms – diffusionless phase transformations, deformation twinning, and conventional dislocation slip. However, understanding how these mechanisms compete or cooperate across a wide range of metastable alloys and loading conditions remains a fundamental challenge. Here, we employ molecular dynamics (MD) simulations to investigate the nucleation behavior of competing deformation modes in metastable $\beta$-Ti alloys as a function of temperature, composition, and loading conditions. We reveal that twinning pathways emerge through reversible transformations between the $\beta$ phase and the orthorhombic $\alpha"$ phase, in agreement with crystallographic theories. Quantitative analyses demonstrate that the dominant deformation mechanisms and preferred twinning-plane orientations are governed by two key energetic parameters: the free energy barrier for homogeneous $\beta \leftrightarrow \alpha"$ transformations and the misfit strain energy along specific phase boundaries. These energetic quantities vary systematically with thermodynamic and mechanical conditions, thereby rationalizing the deformation mode transitions observed in both simulations and experiments. These energetic metrics offer a physically grounded and computationally tractable basis for designing next-generation metastable alloys.
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All authors Ganlin Chen, Deepak V Pillai, Yufeng Zheng, Liang Qi

Materials Science

Large-gap quantum anomalous Hall insulator in two-dimensional pentagonal TiN$_8$ monolayer

Zheng Wang, Linda Sophie Reitz, Beichen Ruan et al. (+4 more)

Discovering the quantum anomalous Hall (QAH) effect in two-dimensional magnets is a central goal of topological condensed matter physics, yet candidate materials combining a sizable gap with a well-defined Chern number remain scarce. We report a new material platform that realizes emergent magnetism and nontrivial band topology within the largely overlooked family of two-dimensional MN$_8$ monolayers. Through first-principles calculations, we reveal that these systems exhibit out-of-plane magnetic ground states and nontrivial topological features driven by the localized $d$-orbitals of the embedded transition metals. Remarkably, we identify TiN$_8$ as a quantum anomalous Hall insulator characterized by a Chern number of $C=-1$ with a large topological gap of 223 meV. As a companion system, MoN$_8$ is predicted to be a rare high-Chern-number QAH insulator, with a Chern number of $C=2$, although its much smaller gap of 12 meV renders it more fragile. These findings establish the penta-MN$_8$ family as a versatile and promising platform to realize exotic topological quantum states. This work not only broadens the material landscape for magnetic topological insulators but also lays a solid theoretical foundation for the development of next-generation spintronic and quantum computing devices.
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All authors Zheng Wang, Linda Sophie Reitz, Beichen Ruan, Zhuoheng Li, Shu-Shen Lyu, Richard Dronskowski, Kaixuan Chen

Materials Science

Reciprocal Space Attention for Learning Long-Range Interactions

Hariharan Ramasubramanian, Alvaro Vazquez-Mayagoitia, Ganesh Sivaraman et al. (+1 more)

Machine learning interatomic potentials (MLIPs) have revolutionized the modeling of materials and molecules by directly fitting to ab initio data. However, while these models excel at capturing local and semi-local interactions, they often prove insufficient when an explicit and efficient treatment of long-range interactions is required. To address this limitation, we introduce Reciprocal-Space Attention (RSA), a framework designed to capture long-range interactions in the Fourier domain. RSA can be integrated with any existing local or semi-local MLIP framework. The central contribution of this work is the mapping of a linear-scaling attention mechanism into Fourier space, enabling the explicit modeling of long-range interactions such as electrostatics and dispersion without relying on predefined charges or other empirical assumptions. We demonstrate the effectiveness of our method as a long-range correction to the MACE backbone across diverse benchmarks, including dimer binding curves, dispersion-dominated layered phosphorene exfoliation, and the molecular dipole density of bulk water. Our results show that RSA consistently captures long-range physics across a broad range of chemical and materials systems. The code and datasets for this work is available at https://github.com/rfhari/reciprocal_space_attention
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All authors Hariharan Ramasubramanian, Alvaro Vazquez-Mayagoitia, Ganesh Sivaraman, Atul C. Thakur

Tuesday 14 October

Materials Science · Cross-listed from physics.ins-det

Frequency domain laser ultrasound microscopy for nanometric layer thickness imaging with GHz elastic plate resonances

Martin Ryzy, Guqi Yan, István Veres et al. (+6 more)

Nanometric layer thickness imaging is crucial for fundamental research and characterization of micro fabricated devices. Here, we assess the potential of a non-contact opto-acoustic frequency domain laser ultrasound (FreDomLUS) microscopy technique for imaging nanometric thickness variations via GHz zero-group velocity (ZGV) elastic plate resonances. The method exploits the ZGV's lateral energy confinement that leads to sharp resonance peaks which can be effectively probed with the FreDomLUS technique at GHz acoustic frequencies. For demonstration purposes we introduced sub-10 nm height variation patterns in the topmost layer of solidly mounted bulk-acoustic wave resonators with a design frequency of around 1.7 GHz. They are raster-scanned to retrieve ZGV-frequencies from local acoustic spectra as a contrast quantity for imaging. We show how to retrieve quantitative height information by numerically calibrating the factor which inversely relates ZGV frequency change with the layer thickness change. Height variations in stacks with nominal thickness changes of 8 nm, 4 nm, and 1 nm can be resolved and indicate sub-nanometer depth resolution capabilities. The lateral resolution is studied by measuring the method's step edge function and it is found to be in the micrometer range. Atomic force microscopy imaging is used to validate the results.
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All authors Martin Ryzy, Guqi Yan, István Veres, Thomas Berer, Ivan Alić, Clemens Grünsteidl, Georg Watzl, Georg Gramse, Susanne Kreuzer

Materials Science · Cross-listed from physics.ins-det

Frequency domain laser ultrasound for inertial confinement fusion target wall thickness measurements

Martin Ryzy, Guqi Yan, Clemens Grünsteidl et al. (+4 more)

In inertial confinement fusion experiments hollow, spherical mm-sized capsules are used as a container for nuclear fuel. To achieve maximum implosion efficiency, a perfect capsule geometry is required. This paper presents a wall thickness measurement method based on zero-group velocity guided elastic wave resonances. They are measured with a non-destructive, contactless frequency domain laser ultrasound microscopy system. Wall thickness measurements along the equator of a high-density carbon capsule with a diameter of around 2 mm and a wall thickness of around 80 $\unicode{x00B5}$m excellently agree with infrared interferometry reference measurements. In addition, the multi-resonant nature of a spherical shell is studied by complementing experimental observations with plate dispersion calculations and finite element wave propagation simulations. The presented method is scalable and can be applied to a broad range of target materials, including metals, or metal-doped targets.
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All authors Martin Ryzy, Guqi Yan, Clemens Grünsteidl, Georg Watzl, Kevin Sequoia, Pavel Lapa, Haibo Huang

Materials Science

Emergent domain topology in the multiferroic hexagonal manganites

Aaron Merlin Müller, Lukas Heckendorn, Manfred Fiebig et al. (+1 more)

Emergent topological phenomena in multiferroic materials arise from the intricate coupling between structural, electric, and magnetic order parameters. Hexagonal manganites provide a paradigmatic platform for such studies. These compounds exhibit a strongly coupled distortive-improper ferroelectric order, arising from trimerizing lattice distortions, and a 120{\deg} noncollinear antiferromagnetic spin structure. While their two-dimensional domain topology has been extensively studied, the full three-dimensional multiferroic domain architecture has remained largely unexplored, mainly due to the experimental challenges of probing bulk structures beyond surfaces. Here, we employ a Landau free-energy framework combined with large-scale phase-field simulations to reveal the intricate three-dimensional multiferroic domain network of hexagonal manganites. We demonstrate that the coupling between the structural and antiferromagnetic order parameters gives rise to a rich variety of three-dimensional topological features. In particular, these features give rise to an attraction between different types of domain walls. Moreover, we identify bifurcations of vortex-like lines at domain-wall intersections, a phenomenon that can exist only in three dimensions and fundamentally alters the topology of the domain network. Our results provide a comprehensive theoretical basis for understanding three-dimensional domain interactions in multiferroics and highlight the essential role of dimensionality in coupling improper ferroelectricity, magnetism, and topology in hexagonal manganites.
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All authors Aaron Merlin Müller, Lukas Heckendorn, Manfred Fiebig, Thomas Lottermoser

Materials Science

Photostriction-Driven Phase Transition in Layered Chiral NbOX$_2$ Crystals: Electrical-Field-Controlled Enantiomer Selectivity

Jorge Cardenas-Gamboa, Martin Gutierrez-Amigo, Aritz Leonardo et al. (+5 more)

Chiral crystals offer an unique platform for controlling structural handedness through external stimuli. However, the ability to select between structural enantiomers remains challenging, both theoretically and experimentally. In this work, we demonstrate a two-step pathway for enantiomer selectivity in layered chiral NbOX$_2$ (X = Cl, Br, I) crystals based on photostriction-driven phase transitions. Ab-initio simulations reveal that optical excitation is capable of inducing a structural phase transition in NbOX$_2$ from the monoclinic ($C2$) ground state to the higher-symmetry ($C2/m$) structure. In the resulting transient high-symmetry state, an applied electric field breaks the residual inversion-symmetry degeneracy, selectively stabilizing one enantiomeric final state configuration over the other. Our results establish a combined optical-electrical control scheme for chiral materials, enabling reversible and non-contact enantiomer selection with potential applications in ultrafast switching, optoelectronics, and chiral information storage.
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All authors Jorge Cardenas-Gamboa, Martin Gutierrez-Amigo, Aritz Leonardo, Gregory A. Fiete, Juan L. Mañes, Jeroen van den Brink, Claudia Felser, Maia G. Vergniory

Materials Science · Cross-listed from cond-mat.mes-hall

Dynamical breaking of inversion symmetry, strong second harmonic generation, and ferroelectricity with nonlinear phonons

Egor I. Kiselev

We show how crystalline inversion symmetry can be dynamically broken by optical phonons with generic, hardening Kerr-like non-linearities. The symmetry-broken state is reached through a parametric instability that can be accessed by driving close to half the phonon resonance. After the onset of the instability, the system settles to a steady state with inversion-symmetry breaking phonon trajectories and strong second harmonic generation. The time averaged positions of the atoms are displaced relative to equilibrium, resulting in a ferroelectric rectification of the driving signal.
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Materials Science · Cross-listed from cond-mat.soft

Time is length in self-similar logarithmic aging of physically cross-linked semiflexible polymer networks

Patrick Ilg, Clarisse Luap and Martin Kröger

Physical aging in polymers is a fundamental yet poorly understood phenomenon, as diverse macromolecular systems exhibit remarkably similar slow dynamics. Through molecular dynamics simulations of physically crosslinked networks composed of semiflexible polymers, we identify a previously unexplored class of self-similar aging. The network undergoes ultra-slow coarsening characterized by a logarithmically growing mesh size, $L(t)\sim \ln t$, which governs the spatial organization, cohesive and bending energies, and the aging dynamics of the system. This single time-dependent length scale defines an internal clock, giving rise to spatio- temporal self-similarity of both structure and dynamics - offering a perspective on aging in soft and disordered materials.
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Materials Science

Emergent spin Hall quantization and high-order van Hove singularities in square-octagonal MA$_2$Z$_4$

Rahul Verma, Yash Vardhan, Hsin Lin et al. (+1 more)

Quantum spin Hall (QSH) insulators are versatile platforms for exploring exotic quantum phases, especially when combined with high-order van Hove singularities (VHSs) that enhance electron correlations. However, perfect spin Hall quantization is often hindered by spin mixing from strong spin-orbit coupling, and the emergence of such VHSs is highly sensitive to material-specific electronic structures. Here, we predict a class of seven-layered square-octagonal MA$_2$Z$_4$ (M = Mo/W, A = Si/Ge, Z = Pnictogen) isomers that host a robust, large-gap QSH phase with nearly quantized spin Hall conductivity and intrinsic high-order VHSs. Topological and symmetry analyses reveal that compounds with Z = P, As, and Sb are $\mathbb{Z}_2$ nontrivial with spin Chern number $C_s = 1$ and support $S_z$-polarized edge states, while those with Z = N are trivial insulators. The QSH phase features an $S_z$-conserving spin Hamiltonian consistent with an emergent spin $\mathrm{U}(1)$ quasi-symmetry, yielding spin Hall conductivity $\sim 2e^2/h$. Notably, MA$_2$(As, Sb)$_4$ compounds exhibit quasi-flat bands near the Fermi level in the inverted regime, with WSi$_2$Sb$_4$ additionally hosting four high-order VHSs at generic momentum points. These results position square-octagonal MA$_2$Z$_4$ materials as robust QSH insulators for realizing quantized spin Hall conductivity and correlated topological phases, including fractionalized states and possibly non-Abelian anyons.
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All authors Rahul Verma, Yash Vardhan, Hsin Lin, Bahadur Singh

Materials Science · Cross-listed from cond-mat.str-el

Exotic Surface Stripe Orders in Correlated Kagome Metal CsCr3Sb5

Yunxing Li, Peigen Li, Taimin Miao et al. (+20 more)

The newly discovered kagome superconductor CsCr3Sb5 exhibits distinct features with flat bands and unique magnetism, providing a compelling platform for exploring novel quantum states of correlated electron systems. Emergent charge order in this material is a key for understanding unconventional superconductivity, but it remains unexplored at the atomic scale and the underlying physics is elusive. Here, we identify and unreported stripe orders on the surface which are distinct from the bulk and investigate the underlying bulk electronic properties using a combination of scanning tunneling microscopy (STM), angle-resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations. Specifically, a mixture of 2a0 * a0 and 3a0 * a0 stripe order is found on Cs-terminated surface while 4a0 * root3a0 stripe order is found on the Sb-terminated surface. The electronic spectra exhibit strongly correlated features resembling that of high temperature superconductors, with kagome flat bands lying about 330 meV above EF, suggesting that the electron correlations arise from Coulomb interactions and Hund's coupling. Moreover, a distinct electron-boson coupling mode is observed at approximately 100 meV. These findings provide new insights into the interplay between surface and bulk charge orders in this strongly correlated kagome system.
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All authors Yunxing Li, Peigen Li, Taimin Miao, Rui Xu, Yongqing Cai, Neng Cai, Bo Liang, Han Gao, Hanbo Xiao, Yongzhen Jiang, Jiefeng Cao, Fangyuan Zhu, Hongkun Wang, Jincheng Xie, Jingcheng Li, Zhongkai Liu, Chaoyu Chen, Yunwei Zhang, X. J. Zhou, Dingyong Zhong, Huichao Wang, Jianwei Huang, Donghui Guo

Materials Science · Cross-listed from quant-ph

Many-body post-processing of density functional calculations using the variational quantum eigensolver for Bader charge analysis

Erik Schultheis, Alexander Rehn and Gabriel Breuil

Quantum chemistry and condensed matter physics are among the most promising applications of quantum computers. Further, estimating properties of a material is crucial to evaluate its industrial applications. To investigate charge distributions of weakly and strongly correlated systems we calculate Bader charges for various periodic systems by solving many-body Hamiltonians using the variational quantum eigensolver. The Hamiltonians are computed from Kohn-Sham orbitals obtained from a prior DFT calculation. We first demonstrate the accuracy of our method on various doped MgH2 supercells. Further, we show that our approach, compared to standard DFT, significantly improves the Bader charge values for strongly correlated transition metal oxides, where we take DFT+U results as a reference. The computational framework behind our many-body calculations, called Dopyqo, is made openly available as a software package.
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Materials Science · Cross-listed from physics.med-ph

Scalable covalently functionalized black phosphorus hybrids for broadspectrum virucidal activity

Na Xing, Jasmin Er, Ricardo M. Vidal et al. (+14 more)

At the onset of viral outbreaks, broad-spectrum antiviral materials are crucial before specific therapeutics become available. We report scalable, biodegradable black phosphorus (BP) hybrids that provide mutation-resilient virucidal protection. BP sheets, produced via an optimized mechanochemical process, are covalently functionalized with 2-azido-4,6-dichloro- 1,3,5-triazine to form P=N bonds. Fucoidan, a sulfated polysaccharide with intrinsic antiviral activity, and hydrophobic chains are then incorporated to achieve irreversible viral deactivation. The material exhibits strong antiviral inhibition and complete virucidal activity against multiple viruses, including recent severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) variants. It maintains high biocompatibility, remains effective against viral mutations, and is shelf stable for at least five month. The combination of biodegradability, scalable synthesis, and synergistic antiviral and virucidal mechanisms establishes BP-conjugates as a new class of highly efficient antivirals. They offer a broad spectrum antiviral solutions that could bridge the gap between antiviral medicines and general antiseptics.
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All authors Na Xing, Jasmin Er, Ricardo M. Vidal, Sandhya Khadka, Robert Schusterbauer, Maik Rosentreter, Ranen Etouki, Rameez Ahmed, Taylor Page, Philip Nickl, Obida Bawadkji, Anja Wiesner, Joerg Radnik, Vasile-Dan Hodoroaba, Kai Ludwig, Jakob Trimpert, Ievgen S. Donskyi

Materials Science

Two-Dimensional Altermagnetic Iron Oxyhalides: Real Chern Topology and Valley-Spin-Lattice Coupling

Yong-Kun Wang, Si Li and Shengyuan A. Yang

Altermagnets, a novel class of collinear magnetic materials, exhibit unique spin-split band structures, yet topological insulating states in intrinsic altermagnetic systems are rare. Here, we identify monolayer Fe$_2X_2$O ($X$ = Cl, Br, I) as a new family of 2D altermagnetic real Chern insulators. These materials display robust $d$-wave altermagnetic ordering, semiconducting band gaps, and nontrivial real Chern numbers per spin channel, yielding spin-polarized topological corner modes. They also feature spin-polarized valleys with strong altermagnetism-valley-spin-lattice coupling, enabling valley-selective excitation via linear dichroism and strain-induced valley polarization. In multiferroic Fe$_2$Cl$_2$O, magnetism coexists with ferroelasticity, and an applied strain can switch the Néel vector. These findings position 2D iron oxyhalides as a promising platform for exploring altermagnetism and magnetic topological states for spintronics and valleytronics.
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Materials Science

Impact of Oxygen Vibrations on Raman Intensity Variation in the Catalyst Fe$_2$(MoO$_4$)$_3$

Young-Joon Song and Roser Valentí

Iron molybdate (Fe$_2$(MoO$_4$)$_3$) is a widely used commercial catalyst for oxidative dehydrogenation. Recently, the possibility that bulk oxygen atoms participate in catalytic reactions has been proposed based on the experimentally observed significant reduction in Raman intensity during the catalytic process, which implies the formation of oxygen defects. In this work, we performed density functional theory (DFT) calculations to elucidate the microscopic mechanism of the experimentally observed Raman intensity variation. Our phonon analysis reveals that oxygen-dominated vibrational modes, with a small contribution from Mo, occur near 782cm$^{-1}$– the same frequency region where the Raman intensity reduction was measured. To make the calculations computationally feasible for this large system, we introduced an effective frozen-phonon approach to indirectly account for the effects of a very small concentration of defects on the Raman intensity. Our results suggest that oxygen vibrations are primarily responsible for the decrease in the calculated Raman intensity. Moreover, structural relaxation of Fe$_2$(MoO$_4$)$_3$ containing an oxygen vacancy indicates that oxygen diffusion from the bulk to the surface may occur very rapidly, such that the local symmetry remains effectively unchanged. This interpretation is in line with the absence of measurable peak shifts or broadening in the experimental Raman spectra.
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Materials Science

Formation of C-centers in Si-based systems by light ion irradiation

Carolina Crosta, Riccardo Nardin, Patrick Daoust et al. (+8 more)

Atomic-scale crystal defects in Si are quantum-light sources offering tantalizing integration with existing photonic technologies. Yet, the controlled creation of near-infrared color centers for long- haul quantum communication and information still remains a challenge. In this work, we utilize light ions, such as H+ and He+, to gently generate quantum emitters in a crystalline Si matrix. Temperature-dependent photoluminescence measurements demonstrate the presence of optically-active defects, whose fluorescence matches the primary telecom window around 1550 nm. In addition, time-resolved investigations unveil long-lived excitonic states in the {\mu}s regime, thus confirming the formation of interstitial oxygen-carbon complexes, termed C-centers. Finally, we explored controlled ion irradiation strategies to seamlessly generate C-centers also in Ge-on-Si heterostructures, which offer an advanced technological platform for the future realization of integrated quantum photonics. This analysis, informed by practical color center synthesis and proof-of-principle experiments in epitaxial architectures, indicates intriguing prospects and profitable strategies to advance the burgeoning field of light-based quantum technologies.
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All authors Carolina Crosta, Riccardo Nardin, Patrick Daoust, Stefano Achilli, Ian Colombo, Matteo Campostrini, Emiliano Bonera, Jacopo Pedrini, Oussama Moutanabbir, Valentino Rigato, Fabio Pezzoli

Materials Science

Escape-Induced Temporally Correlated Noise Driven Universality Crossover

Mrinal Manna, Sourav Mukherjee, Soumen Giri et al. (+11 more)

Universal behavior in far-from-equilibrium systems is driven by interactions between transport processes and noise structure. The Kardar-Parisi-Zhang (KPZ) framework predicts that extensions incorporating conserved currents or temporally correlated noise give rise to distinct growth morphologies and universality classes, yet direct experimental realization has remained elusive. Here, we report atomically resolved Sn thin-film growth on Sb-doped MnBi$_2$Te$_4$, revealing a sharp dynamical crossover between two fundamentally different regimes. Early stage growth follows conserved KPZ scaling, forming two-dimensional islands and stanene layers. Beyond a critical deposition time, temporally correlated noise dominates, driving the nucleation of $\alpha$ -Sn clusters, their evolution into faceted grains, and coexistence with faceted $\beta$-Sn. Molecular dynamics simulation and Auger electron spectroscopy show adatom escape as the microscopic origin of temporally correlated noise, providing a microscopic mechanism for the universality crossover. These findings establish, for the first time, that temporal noise correlations can fundamentally alter the scaling class of a growing interface, linking atomistic kinetics to emergent universal behavior.
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All authors Mrinal Manna, Sourav Mukherjee, Soumen Giri, Pramod Bhakuni, Sajal Barman, Arnab Kumar Pariari, Anil Gome, Markus Hucker, V. Raghavendra Reddy, Anupam Roy, Sudipta Roy Barman, Smarajit Karmakar, Chandana Mondal, Rajib Batabyal

Materials Science

Anharmonic Effects in Ge2Sb2Te5 and Consequences on Thermodynamic Stability

Owain T. Beynon and Adham Hashibon

Chalcogenides are an important class of phase change material (PCMs) due to their application in digital memory solutions. Owing to their ability to reversibly cycle between crystalline and amorphous states, their use as phase change random access memory (PCRAM) is of interest, and of the many chalcogenide materials Ge2Sb2Te5 (GST) is a promising candidate owing to its stability and low crystallization temperature. GST possesses two stable crystalline polymorphs, cubic and hexagonal. Studies show that phenomena such as heat transport and thermal lattice expansion drive the phase-change nature of these materials. These phenomena are not incorporated in the harmonic approximation, which is a popular model for describing vibrations in solids. Through ab initio density functional theory (DFT), we computationally investigate the anharmonic behaviour of pristine hexagonal GST, i.e. without vacancies or defects, while considering the various stacking models that exist and inclusion of van der Waals (vdW) interactions in our modelling. We present the vibrational analysis of different stacking models in GST; Petrov and Kooi-De Hosson (KDH) models and the quantification anharmonic behaviour. Our calculations find that the KDH model is the most stable stacking sequence, being 88 meV more stable than the Petrov model when considering anharmonicity, where this difference is underestimated using a purely harmonic framework (65 meV). These results demonstrate the importance of incorporating anharmonic and dispersion effects when modelling GST, especially in the choice of stacking models, along with implications for phenomena relating to phase-change behaviour.
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Materials Science

Two-Dimensional Na2LiAlP2 Crystal for High-Performance Field-Effect Transistors

Run-Jie Peng, Xing-Yu Wang, Jun-Hui Yuan et al. (+4 more)

High-performance, low-power transistors are core components of advanced integrated circuits, and the ultimate limitation of Moore's law has made the search for new alternative pathways an urgent priority. Two-dimensional (2D) materials have become the most promising exploration target due to their exceptional electronic properties and scalability. In this work, we conducted device transport research on the previously proposed 2D quaternary semiconductor Na2LiAlP2 using the non-equilibrium Green's function method. The results demonstrate that even with a channel length of 5 nm, Na2LiAlP2 still exhibits excellent n-type transistor characteristics, fully meeting and surpassing the technical specifications outlined in the International Roadmap for Devices and Systems (IRDS). Encouragingly, the device can easily achieve the required on-state current of 900 {\mu}A/{\mu}m under low operating voltages of 0.1 V and 0.2 V. Moreover, at 0.1 V operating voltage, the device's subthreshold swing breaks through the theoretical limit of 60 mV/dec, reaching an astonishing value 30.33 mV/dec. Additionally, its p-type transistor performance also stands out with a subthreshold swing of ~50 mV/dec when the channel length is 7 nm. Our research not only showcases the exceptional transistor properties of Na2LiAlP2 but also further expands the research scope of 2D high-performance transistors.
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All authors Run-Jie Peng, Xing-Yu Wang, Jun-Hui Yuan, Nian-Nian Yu, Kan-Hao Xue, Jiafu Wang, Pan Zhang

Materials Science · Cross-listed from cond-mat.supr-con

Possible high-Tc superconductivity at 45 K in the Ge-doped cluster Mott insulator GaNb4Se8

Ji-Hai Yuan, Ya-Dong Gu, Yun-Qing Shi et al. (+8 more)

The Ge-doped GaNb4Se8 polycrystalline samples were synthesized by solid-state reaction method. Zero resistance transitions were observed in one batch of samples with the highest onset superconducting Tc at 45 K. This discovery may demonstrate a new class of Nb-based high-Tc superconductors arising from doped Mott insulators.
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All authors Ji-Hai Yuan, Ya-Dong Gu, Yun-Qing Shi, Hao-Yu He, Qing-Song Liu, Jun-Kun Yi, Le-Wei Chen, Zheng-Xin Lin, Jia-Sheng Liu, Meng Wang, Zhi-An Ren

Materials Science

Self-attention enabled quantum path analysis of high-harmonic generation in solids

Cong Zhao and Xiaozhou Zou

High-harmonic generation (HHG) in solids provides a powerful platform to probe ultrafast electron dynamics and interband–intraband coupling. However, disentangling the complex many-body contributions in the HHG spectrum remains challenging. Here we introduce a machine-learning approach based on a Transformer encoder to analyze and reconstruct HHG signals computed from a one-dimensional Kronig–Penney model. The self-attention mechanism inherently highlights correlations between temporal dipole dynamics and high-frequency spectral components, allowing us to identify signatures of nonadiabatic band coupling that are otherwise obscured in standard Fourier analysis. By combining attention maps with Gabor time–frequency analysis, we extract and amplify weak coupling channels that contribute to even-order harmonics and anomalous spectral features. Our results demonstrate that multi-head self-attention acts as a selective filter for strong-coupling events in the time domain, enabling a physics-informed interpretation of high-dimensional quantum dynamics. This work establishes Transformer-based attention as a versatile tool for solid-state strong-field physics, opening new possibilities for interpretable machine learning in attosecond spectroscopy and nonlinear photonics.
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Materials Science

Defect Passivation and Förster-Type Energy Exchange in H2Pc-TMD Organic-Inorganic Heterostructures

Šimun Mandić, Ana Senkić and Nataša Vujičić

Organic - inorganic heterostructures (HS) combine the strong light absorption and exciton generation capabilities of organic molecules with the unique excitonic properties of layered transition metal dichalcogenides (TMDs), where the interfacial band alignment dictates the optical response. In this work, we investigate the influence of H2Pc molecules on CVD-grown MoS2 and WS2 monolayers using correlative microscopy techniques - Kelvin probe force microscopy (KPFM), photoluminescence (PL), and Raman spectroscopy. Comprehensive analysis of both electronic and optical properties provides detailed insights into the energy band alignment in these two HS. Despite their similar band alignments, the heterostructures exhibit strikingly different optical signatures. In the case of H2Pc/MoS2 HS, the effect of defect healing is more pronounced, while for the H2Pc/WS2 HS, strong indications of Förster energy transfer are observed. These findings highlight the critical role of transition dipole moment in addition to spectral overlap between donor emission and acceptor absorption in the design of optoelectronic devices.
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Materials Science · Cross-listed from cs.LG

Continuous SUN (Stable, Unique, and Novel) Metric for Generative Modeling of Inorganic Crystals

Masahiro Negishi, Hyunsoo Park, Kinga O. Mastej et al. (+1 more)

To address pressing scientific challenges such as climate change, increasingly sophisticated generative models are being developed to efficiently sample the large chemical space of potential functional materials. The proliferation of these models has necessitated the establishment of rigorous evaluation metrics. While uniqueness (U), novelty (N), and stability (S) of samples serve as standard metrics, their current formulations show several limitations. U and N rely on binary comparisons of crystals, rendering them dependent on heuristic thresholds, incapable of quantifying the degree of similarity, sensitive to atomic coordinate perturbations, and not invariant to sample permutation. Similarly, the binary assessment of S risks a premature exclusion of marginally unstable yet potentially novel candidates. These limitations are addressed by making the aforementioned metrics continuous. Furthermore, we integrate them into a unified metric “continuous SUN" (cSUN), which offers a smoother score distribution and greater tunability than the conventional binary SUN metric. Experimental results demonstrate that our continuous metrics provide granular insights into sample distributions and facilitate the identification of the most promising candidates. Finally, the use of cSUN as a reward signal in reinforcement learning is explored, showing that its adjustable weighting scheme effectively mitigates reward hacking and avoids local minima.
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All authors Masahiro Negishi, Hyunsoo Park, Kinga O. Mastej, Aron Walsh

Materials Science

Controlling Magnetism in the 2D van der Waals Antiferromagnet CrPS$_4$ via Ion Intercalation

Alberto M. Ruiz, Diego López-Alcalá, Gonzalo Rivero-Carracedo et al. (+2 more)

Two-dimensional van der Waals (vdW) magnetic materials are versatile platforms for tailoring electronic and magnetic properties, in which the insertion of chemical species into their interlayer gaps offers a powerful route to engineer magnetism. Here, we focus on the A-type antiferromagnetic semiconductor CrPS$_4$ (T$_N$ = 38 K) and investigate its electronic and magnetic properties upon intercalation of lithium (Li$^+$) and organic tetrabutylammonium (TBA$^+$) ions using first-principles calculations. Our results show that Li$^+$ incorporation induces a semiconductor-to-metal transition in CrPS$_4$ and selectively modifies its magnetic behaviour: switching from out-of-plane to in-plane antiferromagnetism, followed by an in-plane ferromagnetic ground state at higher intercalation levels. This is accompanied by a continuous increase of the ordering temperature, reaching a fivefold enhancement for Li$_{0.5}$CrPS$_4$. Similarly, TBA$^+$ intercalation expands the vdW gap, decoupling CrPS$_4$ layers and stabilising in-plane ferromagnetism with a T$_C$ above 100 K. Furthermore, it also modifies magnon propagation, leading to enhanced group velocities and a more isotropic magnon transport. This work highlights intercalation as a powerful and versatile approach for controlling magnetic behaviour and spin dynamics, paving the way for the design of tunable 2D layered magnetic materials for spintronic and magnonic applications.
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All authors Alberto M. Ruiz, Diego López-Alcalá, Gonzalo Rivero-Carracedo, Andrei Shumilin, José J. Baldoví

Materials Science

Two-Dimensional Altermagnetism in Epitaxial CrSb Ultrathin Films

Keren Li, Yuzhong Hu, Yue Li et al. (+12 more)

Altermagnets constitute an emerging class of collinear magnets that exhibit zero net magnetization yet host spin-split electronic bands arising from non-relativistic spin-space-group symmetries. Realization of altermagnetism in the two-dimensional (2D) limit remains an outstanding challenge because dimensional reduction suppresses kZ dispersion and destabilizes the symmetry operations essential for spin compensation. Here, we investigate ultrathin CrSb films grown epitaxially on Bi2Te3 substrate and uncover the evolution of altermagnetism in the 2D limit. Scanning tunneling microscopy (STM), quasiparticle interference (QPI), angle-resolved photoemission spectroscopy (ARPES), and density functional theory (DFT) calculations show that interfacial symmetry breaking in the one-unit-cell (1 UC) limit gives rise to localized electronic states and uncompensated magnetic moments. These interfacial effects become weakened from 7/4 UC, accompanied by the recovery of a bulk-like coordination environment and the emergence of altermagnetic electronic characteristics. Our results show that the essential altermagnetic electronic structure of CrSb survives at a thickness of only ~1.05 nm, demonstrating the robustness of altermagnetism in the 2D limit and opening opportunities for integrating stray-field-free spin order into low dimensional spintronic architectures.
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All authors Keren Li, Yuzhong Hu, Yue Li, Ruohang Xu, Shaozhong Ma, Heping Li, Kun Liu, Chen Liu, Lu Cao, Jincheng Zhuang, Yee Sin Ang, Jiaou Wang, Haifeng Feng, Weichang Hao, Yi Du

Materials Science

DiffCrysGen: A Generative Diffusion Model for Accelerated Design of Inorganic Crystalline Materials

Sourav Mal, Nehad Ahmed, Junaid Jami et al. (+2 more)

Efficient exploration of the vast chemical space is a fundamental challenge in materials design and discovery, particularly for designing functional inorganic crystalline materials with targeted properties. Diffusion-based generative models have emerged as a powerful route, but most existing approaches require domain-specific constraints and separate diffusion processes for atom types, atomic positions, and lattice parameters, adding complexity and limiting efficiency. Here, we present DiffCrysGen, a fully data-driven, score-based diffusion model that generates complete crystal structures in a single, end-to-end diffusion process. This unified framework simplifies the model architecture and accelerates sampling by two to three orders of magnitude compared to existing methods without compromising chemical and structural diversity of the generated materials. In order to demonstrate the efficacy of DiffCrysGen in generating valid and useful materials, using density functional theory (DFT), we validate a number of newly generated rare earth-free magnetic materials that are energetically and dynamically stable, and are potentially synthesizable. These include ferromagnets with high saturation magnetization and large magnetocrystalline anisotropy, as also metallic antiferromagnets. These results establish DiffCrysGen as a general platform for accelerated design of functional materials.
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All authors Sourav Mal, Nehad Ahmed, Junaid Jami, Subhankar Mishra, Prasenjit Sen

Materials Science

Room temperature control of axial and basal antiferromagnetic anisotropies using strain

Jack Harrison, Junxiong Hu, Charles Godfrey et al. (+6 more)

Antiferromagnetic materials are promising platforms for the development of ultra-fast spintronics and magnonics due to their robust magnetism, high-frequency relativistic dynamics, low-loss transport, and the ability to support topological textures. However, achieving deterministic control over antiferromagnetic order in thin films is a major challenge, due to the formation of multi-domain states stabilised by competing magnetic and destressing interactions. Thus, the successful implementation of antiferromagnetic materials necessitates careful engineering of their anisotropy. Here, we demonstrate strain-based robust control over multiple antiferromagnetic anisotropies and nanoscale domains in the promising spintronic candidate a-Fe2O3, at room temperature. By applying isotropic and anisotropic in-plane strains across a broad temperature-strain phase space, we systematically tune the interplay between magneto-crystalline and magneto-elastic interactions. We discover that strain-driven control steers the system towards an aligned antiferromagnetic state, whilst preserving topological spin textures, such as merons, antimerons and bimerons. We directly map the nanoscale antiferromagnetic order using linear dichroic scanning transmission X-ray microscopy integrated with in situ strain and temperature control. A Landau model and micromagnetic simulations reveal how strain reshapes the magnetic energy landscape. These findings suggest that strain could serve as a versatile control mechanism to reconfigure equilibrium or dynamic antiferromagnetic states on demand in a-Fe2O3, paving the way for next-generation spintronic and magnonic devices.
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All authors Jack Harrison, Junxiong Hu, Charles Godfrey, Jheng-Cyuan Lin, Tim A Butcher, Jörg Raabe, Simone Finizio, Hariom Jani, Paolo G Radaelli