Materials Science · Cross-listed from physics.geo-ph
Unstable Slip in Fault Gouge Driven by Temperature and Water
Li Wang, Jie Meng, Dongpo Wang et al. (+2 more)
Microscale granular sliding within fault gouge is fundamental to earthquake nucleation, yet the mechanism by which temperature affects friction through interfacial water remains poorly understood. Here, large-scale molecular dynamics simulations were conducted on a hydrophilic quartz-water-quartz interface over 300-500 K to quantify temperature-dependent changes in frictional strength, real contact area, and water-layer structure. Results show that both the friction coefficient and friction force decrease monotonically with increasing temperature, following near-linear relationships of $\mu \propto T^{-1}$ and $F_t \propto A$, indicating that frictional weakening is primarily governed by temperature-driven contact restructuring. Structural analyses further show that heating progressively disrupts the hydrogen-bond network in the first adsorption layer, reduces adsorption-layer density, and weakens radial distribution peaks, demonstrating a transition of interfacial water from an ordered, strongly adsorbed state to a more diffuse, weakly bound configuration with delayering and quasi-phase-transition behavior. This interfacial reconstruction weakens intergranular bridging and structural cohesion, promoting a shift from structural locking to water-mediated lubrication. These results suggest that frictional stability under coupled temperature-water conditions is strongly controlled by the thermal
evolution of interfacial water structure.
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All authors Li Wang, Jie Meng, Dongpo Wang, Gongji Zhang, Helge Hellevang
Materials Science
UniMatSim: A High-Throughput Materials Simulation Automation Framework Based on Universal Machine Learning Potentials
Yanjin Xiang, Yihan Nie, Yunzhi Gao et al. (+2 more)
Universal machine learning interatomic potentials (UMLIPs) offer accuracy close to first-principles calculations at a fraction of the cost, showing significant potential for large-scale material simulations. However, the fragmented UMLIPs ecosystem lacks unified interface standards and integration frameworks, hindering their automated deployment in high-throughput workflows. To address this, we present UniMatSim, a modular Python framework. It systematically integrates various UMLIPs (e.g., CHGNet, M3GNet, MACE) and automates workflows from structural optimization to stability verification. The framework enables seamless model switching via abstracted interfaces, incorporates task orchestration, and provides standardized modules for key properties (elasticity,
phonons, molecular dynamics), including automated handling for low-dimensional materials. As a test case, using the 2D Lieb
lattice system, we constructed a multi-stage high-throughput screening workflow covering structural optimization, elastic stability, and
phonon spectrum calculations. Starting from 1,176 candidate compositions, a four-model consensus pipeline yields 393 stable structures. These are refined by
magnetic-state screening and DFT band-structure calculations to 59 Lieb-
lattice candidates with staggered-
magnetic-band characteristics. Results show UniMatSim significantly improves computational efficiency and reproducibility, providing a reliable infrastructure for data-driven materials discovery and design.
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All authors Yanjin Xiang, Yihan Nie, Yunzhi Gao, Haidi Wang, Wei Hu
Materials Science
Intrinsic Even-Odd Thickness-Driven Anomalous Hall in Epitaxial MnBi2Te4 Thin Films
Debarghya Mallick, Simon Kim, An-Hsi Chen et al. (+12 more)
We demonstrate precise control of magnetism in MnBi2Te4 thin films through careful synthesis by molecular beam epitaxy, achieving minimal defects and accurate layer thickness control. By optimizing Mn-Bi-Te ratios and growth temperatures, we minimize detrimental self-doping effects and accurately target integer-layer films. X-ray diffraction and reflectivity provide quantitative measures of film quality and thickness. When these macroscale probes of structure and thickness are integrated with magnetotransport measurements, a striking even-odd layer dependence of the anomalous
Hall effect is revealed. Odd-layer films exhibit a large hysteresis up to the Néel temperature (~25K), consistent with non-compensated antiferromagnetism, while even-layer films show minimal response, as expected for an antiferromagnet. The sign of the anomalous
Hall effect exhibits a sign reversal for intrinsic magnetism versus magnetism associated with defects. This work identifies critical factors for inducing pure, non-compensated ferromagnetism and reveals the character of the intrinsic anomalous
Hall effect in MnBi2Te4, which together is a step towards realizing the zero-field
quantum anomalous
Hall effect in topological materials.
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All authors Debarghya Mallick, Simon Kim, An-Hsi Chen, Gabriel A. Vázquez-Lizardi, Alessandro R. Mazza, T. Zac Ward, Gyula Eres, Yue Cao, Debangshu Mukherjee, Hu Miao, Liang Wu, Christopher Nelson, Danielle Reifsnyder Hickey, Robert G. Moore, Matthew Brahlek
Materials Science · Cross-listed from cond-mat.supr-con
Pseudo Point Nodal Superconducting Gap in Spin-Triplet UTe$_2$
S. Hosoi, K. Imamura, M. M. Bordelon et al. (+7 more)
The unconventional
superconductor UTe$_2$ represents a rare example of
spin-triplet pairing with potentially topologically protected
quantum states. However, conflicting reports on its gap structure, particularly regarding point nodes, have hindered understanding of the order parameter
symmetry and topological properties. Here we report high-resolution thermal conductivity measurements on high-quality UTe$_2$ single
crystals down to ~50 mK that resolve the gap anisotropy through bulk directional transport. The $b$-axis thermal conductivity $\kappa_b/T$ exhibits negligible residual conductivity as $T \to 0$, and its temperature dependence is consistent with a small superconducting energy gap along the $b$-axis. Under
magnetic fields, the residual $\kappa_b/T$ shows only weak field-induced enhancement. Remarkably, a threshold field emerges at low fields for $H \parallel a$, characterized by a kink that signals a change in quasiparticle transport normal to the field. Below the threshold, $\kappa_b/T$ remains isotropic for all field orientations, whereas strong anisotropy between transport along and normal to the field develops above it. These signatures strongly suggest that UTe$_2$ exhibits a fully gapped state with a pseudo point-nodal structure, where gap minima approach but never reach zero. We estimate the minimal gap $\Delta_{min}/\Delta_0 \sim 0.1$ along the $b$-axis, where $\Delta_0$ is the characteristic superconducting gap. This unusual gap structure provides crucial insights into the pairing mechanism and
topology of this
spin-triplet
superconductor and excludes non-
unitary mixing of pairing
symmetries.
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All authors S. Hosoi, K. Imamura, M. M. Bordelon, E. D. Bauer, S. M. Thomas, F. Ronning, P. F. S. Rosa, R. Movshovich, I. Vekhter, Y. Matsuda
Materials Science
Switchable circular dichroism and ionic migration dominated charge transport in a chiral spin crossover polymer
M Zaid Zaz, Sartaz Sakib, Wai Kiat Chin et al. (+6 more)
We demonstrate thermally switchable chiroptical activity in a
chiral spin crossover (SCO) material, where circular dichroism is significant in the low
spin state but quenched in the high-
spin state for both enantiomers. With magnetometry we establish a cooperative transition with hysteresis near room temperature. Fe L3,2 edge Xray absorption directly links the quenching of chirality to a reorganization of Fe 3d electronic structure that accompanies the
spin state transition. Moreover, electrical measurements show pronounced I(V) hysteresis and cycling dependent C(V) behavior, indicating transport in this
chiral SCO material is dominated by ionic migration rather than mobile electrons or holes.
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All authors M Zaid Zaz, Sartaz Sakib, Wai Kiat Chin, Peace Adegbite, Gauthami Viswan, Alpha T Ndaiye, Andrew J Yost, Rebecca Y Lai, Peter A Dowben
Materials Science
Exceptional Optical Phonon Coherence in Enriched Cubic Boron Arsenide via Suppression of Three-Phonon Scattering
Tong Lin, Fengjiao Pan, Gaihua Ye et al. (+8 more)
Cubic boron arsenide (BAs) is a promising
semiconductor for next-generation electronics due to its outstanding ambipolar mobility and thermal conductivity, the latter of which is attributed to the suppression of three-
phonon scattering. However, precisely accounting for different high-order anharmonic scattering processes is challenging from both theory and experiment, so that questions remain open regarding the ultimate limit of
phonon lifetime and thermal conductivity in BAs. Here we show that this gap nearly eliminates three-
phonon scattering for zone-center optical
phonons in a wide temperature range, leading to a record-high, isotope purity-limited
phonon coherence with a quality factor above $3.7\times 10^3$ for >98% enriched $^{11}$BAs below 100 K. We discriminate three decoherence mechanisms by their temperature-dependent contribution to the damping rate using high-resolution Raman and
Fourier transform infrared spectroscopy. For the as-synthesized
crystals, we find that defect scattering has negligible contributions to the linewidth of optical
phonons in comparison to isotope scattering. These results provide critical insights into the intrinsic and extrinsic scattering mechanisms of optical
phonons in BAs, motivating further studies to quantify anharmonic effects and realize superior
phonon transport.
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All authors Tong Lin, Fengjiao Pan, Gaihua Ye, Sanjna Sukumaran, Cynthia Nnokwe, Ange Benise Niyikiza, William A. Smith, Stephen B. Bayne, Rui He, Zhifeng Ren, Hanyu Zhu
Materials Science · Cross-listed from cond-mat.str-el
Moiré in $\Gamma$-valley square lattice: Copper- and iron-based superconductor simulation in a single device
Toshikaze Kariyado, Yusuf Wicaksono, Ashvin Vishwanath et al. (+2 more)
Novel superconducting phases have been found in various moiré
heterostructures based on hexagonal
lattices. However, the archetypal high-temperature
superconductors (cuprates, iron-based and nickelate families) all share a square
lattice foundation. These materials host a rich landscape of correlated phenomena, such as charge and
spin stripes, pseudogap behavior, and unconventional
metallicity, which continue to challenge our fundamental understanding of strongly correlated electrons. In this work, we investigate the possibility of simulating the effective models governing these high-$T_c$
superconductors using twisted homobilayers of $\Gamma$-valley square-
lattice systems. We develop a universal theoretical framework and carry out a detailed analysis of a promising candidate material ZnF$_2$. We find that the first moiré band realizes a single-orbital square-
lattice Hubbard model, widely believed to capture cuprate physics, while the second and third moiré bands map to a $p_x,p_y$ two-orbital square-
lattice Hubbard model, which shares common physics to the minimal $d_{xz}, d_{yz}$ models proposed for iron pnictides. Our study combines continuum
Hamiltonian modeling, first-principle calculations, and Hartree-Fock mean field theory. The latter focuses on the quarter-filling regime of the two-orbital model and in particular leads to, among others, a stable antiferro-orbital,
ferromagnetic insulating phase. These results highlight $\Gamma$-valley square-
lattice moiré systems as a new and important generation of van der Waals
heterostructures to realize interesting strongly correlated phases of matter.
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All authors Toshikaze Kariyado, Yusuf Wicaksono, Ashvin Vishwanath, Pavel Volkov, Zhu-Xi Luo
Materials Science · Cross-listed from physics.class-ph
Nonlinear potential field in contact electrification
Benjamin J. Kulbago and James Chen
The cause of electron transfer in contact electrification is one of the most hotly debated physical problems today. In this study, the electron transfer is hypothesized to be partly driven by the surface dipole induced potential during contact. This phenomena is demonstrated by a combination of atomistic field theory (AFT) and molecular dynamics (MD) simulation. A representative contact system of carbon and silicon dioxide was chosen for its excellent tribo-tunneling power output performance. The results reveal the existence of a nonlinear potential field as well as the existence of a separation dependent potential barrier at the contact interface. Possible scenarios of triboelectric charge transfer are discussed in light of these results. These results are critical to the fundamental understanding of contact electrification.
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Materials Science · Cross-listed from cs.LG
Neural Field Thermal Tomography: A Differentiable Physics Framework for Non-Destructive Evaluation
Tao Zhong, Yixun Hu, Dongzhe Zheng et al. (+2 more)
Inverse problems for stiff
parabolic partial differential equations (PDEs), such as the inverse heat conduction problem (IHCP), are severely ill-posed: the forward map rapidly damps high-frequency interior structure before it reaches the boundary. Soft-constrained physics-informed neural networks (PINNs), which embed the PDE as a residual penalty, suffer from gradient pathology in this regime and tend to fit boundary measurements while leaving the interior field essentially untouched. We propose Neural Field Thermal
Tomography (NeFTY), a hard-constrained neural field framework for label-free three-dimensional inverse heat conduction. NeFTY represents the unknown diffusivity as a continuous coordinate-based neural network, and at every optimization step passes the candidate field through a differentiable implicit-Euler heat solver with harmonic-mean interface flux, so that the governing PDE holds exactly on the discretization rather than as a soft penalty. Adjoint gradients propagate the surface reconstruction error back to the network weights at solver-level
memory cost, making test-time inversion tractable on a single GPU. Across synthetic 3D
benchmarks, NeFTY substantially outperforms soft-constrained PINN variants and a voxel-grid baseline on label-free volumetric recovery, and it transfers to real thermography data, surpassing classical signal-processing baselines in both defect
segmentation and depth estimation. Additional details at https://cab-lab-princeton.github.io/nefty/
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All authors Tao Zhong, Yixun Hu, Dongzhe Zheng, Aditya Sood, Christine Allen-Blanchette
Materials Science · Cross-listed from cond-mat.str-el
Dzyaloshinskii-Moriya-driven instabilities in square-kagome quantum antiferromagnets
Leonid S. Taran, Arnaud Ralko, Fedor V. Temnikov et al. (+3 more)
Decorated square-kagome
quantum antiferromagnets provide a natural setting in which strong frustration,
lattice decoration, and
spin-orbit-induced anisotropy compete on comparable energy scales. Here we show that in Na$_6$Cu$_7$BiO$_4$(PO$_4$)$_4$Cl$_3$ the coupling ($J_{10}$) which links the decorating Cu(3) sites to the square-kagome backbone, stabilizes the gapped
quantum-paramagnetic regime, while
symmetry-allowed Dzyaloshinskii-Moriya (DM) interactions systematically suppress the minimum spinon gap $\Delta_{\mathrm{spinon}}$ and drive the system toward
magnetic condensation. To establish this, we combine ab initio calculation of the DM vectors with a generalized Schwinger-
boson self-consistent mean-field theory that treats singlet and triplet hopping/pairing channels on equal footing. As a
benchmark, the isotropic square-kagome Heisenberg model exhibits four competing low-energy saddle points distinguished by their Wilson-loop fluxes and by characteristic static and dynamical structure-factor fingerprints. A minimal DM perturbation does not qualitatively reshape this competing landscape, but already enhances the tendency towards order. For the realistic decorated
Hamiltonian, finite-size scaling of $\Delta_{\mathrm{spinon}}$ together with momentum-resolved structure factors identifies $J_{10}$ (exchange with decorating Cu) as the control parameter of the gapped regime and shows that the full
symmetry-allowed DM pattern shifts the system further toward condensation. Our results place Na$_6$Cu$_7$BiO$_4$(PO$_4$)$_4$Cl$_3$ in close proximity to a
magnetic instability and provide experimentally testable predictions for anisotropy-enhanced soft modes in decorated square-kagome materials.
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All authors Leonid S. Taran, Arnaud Ralko, Fedor V. Temnikov, Vladimir V. Mazurenko, Sergey V. Streltsov, Yasir Iqbal
Materials Science
Island Sliding Barriers: A first-principles metric for determining remote epitaxy viability
Quinn T. Campbell, Manny Xavier de Jesus Lopez, Anthony Rice et al. (+6 more)
Remote epitaxy, where a 2D van der Waals material (usually
graphene) is inserted on top of the substrate before film epitaxy, has emerged as a promising path for growing electronics with lower defect rates and less stringent
lattice matching requirements. The exact mechanism behind remote epitaxy has not been definitively shown, however, and it is not obvious when examining a new substrate-film pair whether they would be compatible with the remote epitaxy process. In this paper, we use first principles calculations to test several different mechanisms for determining whether a given substrate-film pair will successfully be grown with remote epitaxy. We find that previously calculated metrics such as electrostatic potential do not hold sufficient explanatory power. We find that the sliding barrier of small islands on the surface when the atomic positions are allowed to optimize provides the most rigorous criteria for whether a given substrate-film pair is remote epitaxy active. This indicates that remote epitaxy is likely a phenomenon related to the kinetics and ease of island migration on the
graphene surface.
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All authors Quinn T. Campbell, Manny Xavier de Jesus Lopez, Anthony Rice, Timothy J. Ruggles, Taisuke Ohta, Caitlin McCowan, Sadhvikas Addamane, Scott W. Schmucker, Justine Koepke
Materials Science · Cross-listed from cond-mat.mes-hall
Microscopic screening theory for excitons in two-dimensional materials: A bridge between effective models and ab initio descriptions
P. Ninhos, A. J. Uría-Álvarez, C. Tserkezis et al. (+2 more)
We present a computational approach for
exciton calculations in two-dimensional (2D) materials within the Bethe-Salpeter equation (BSE) framework, employing an atomistic description with point-like orbitals. Unlike widespread efficient calculations that rely on classical or effective interaction models, such as the Rytova-Keldysh model, our method incorporates
quantum screened interactions. By explicitly computing the 2D dielectric function at the random-phase approximation level, we capture screening effects beyond such approximations with an accuracy akin to first-principles methods. Consequently, we can realistically estimate excitonic binding energies with a bearable computational cost. A detailed account of the various convergence parameters sheds light on a possible cause of the large dispersion of binding energies reported in the literature using first-principles GW/BSE implementations. This work thus provides an alternative pathway towards efficient and faithful dielectric screening and
exciton computations in low-dimensional materials.
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All authors P. Ninhos, A. J. Uría-Álvarez, C. Tserkezis, N. A. Mortensen, J. J. Palacios
Materials Science · Cross-listed from cond-mat.supr-con
Ab-initio superfluid weight and superconducting penetration depth
Kaja H. Hiorth, Martin Gutierrez-Amigo, Théo Cavignac et al. (+3 more)
Machine learning and high-throughput screening approaches to
superconductor discovery require physically meaningful descriptors that capture essential physics while remaining computationally tractable. The superfluid weight is an ideal descriptor as it is a prerequisite for superconductivity, determines the
magnetic penetration depth and the Berezinskii-Kosterlitz-Thouless transition temperature in two-dimensional materials, may limit the critical temperature in unconventional
superconductors through phase coherence, and reveals
quantum geometric contributions to supercurrent transport. We develop a computationally efficient framework for calculating the zero-temperature, mean-field superfluid weight for uniform pairing from density functional theory band structures and Bloch wavefunctions. We separately evaluate the conventional contribution from band
curvature and the
geometric contribution from
quantum geometry. To validate the method, we calculate London penetration depths for a few conventional
superconductors (Al, Pb, Nb, MgB$_2$, LuRu$_3$B$_2$ and YRu$_3$B$_2$) and find good agreement with experiment after accounting for nonlocal corrections, strong-coupling effects, and sample quality. The conventional contribution dominates by orders of magnitude in these wide-band materials, as expected. This framework provides a foundation for large-scale screening of superconducting candidates and exploring
quantum geometric effects in unconventional
superconductors.
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All authors Kaja H. Hiorth, Martin Gutierrez-Amigo, Théo Cavignac, Kristjan Haule, Miguel A.L. Marques, Päivi Törmä
Materials Science
Importance of nonlinear long-range electron-phonon interaction for the carrier mobility of anharmonic halide perovskites
Matthew Houtput, Ingvar Zappacosta, William Wenborn et al. (+4 more)
The interaction between the electrons and the
lattice vibrations in a solid is responsible for various important effects, such as formation of polarons, temperature dependent bandgaps,
phonon-limited carrier transport, and conventional superconductivity. Most works assume a linear electron-
phonon interaction, where the electron only interacts with one
phonon at a time. However, the validity of this assumption has not been verified in polar anharmonic materials, where large ionic displacements may invalidate the assumption of linear interaction. Here, we show that nonlinear electron-
phonon interactions contribute significantly to the finite-temperature electron mobility of the inorganic lead halide perovskite CsPbI$_3$. The effect of nonlinear interaction is taken into account using the recently derived expression for the long-range part of the one-electron-two-
phonon matrix element. We calculate the electron mobility from first principles within the self-energy relaxation-time approximation, treating the electron-
phonon coupling in the long-range approximation. Despite these approximations, the calculated mobilities are in good agreement with the available experimental data, while enabling us to isolate and quantify the contribution of nonlinear electron-
phonon interactions relative to the conventional linear coupling. We find that the one-electron-two-
phonon interaction modifies the temperature dependence of the mobility in CsPbI$_3$ and reduces its room-temperature value by about 10%. This sizeable contribution results from the combined effects of strong
lattice anharmonicity and large thermal
phonon populations, the latter being enhanced by the low
phonon frequencies associated with the heavy constituent atoms. These results show when nonlinear electron-
phonon interactions become relevant, and indicate they should be considered for finite-temperature properties of halide perovskites.
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All authors Matthew Houtput, Ingvar Zappacosta, William Wenborn, Serghei Klimin, Samuel Poncé, Jacques Tempere, Cesare Franchini
Materials Science · Cross-listed from physics.chem-ph
Nuclear Quantum Effects in Multi-Step Condensed Matter Chemistry: A Path Integral Molecular Dynamics Study of Thermal Decomposition
Jalen Macatangay and Alejandro Strachan
Nuclear quantum effects (NQEs) are often central to a predictive understanding of chemical reactions and rates. While their incorporation in gas-phase reactions is well established, studies involving condensed matter often neglect or approximate such effects. To clarify the role of NQEs in multi-step, multi-molecular reactions in a molecular
crystal, we compare atomistic simulations of the thermal decomposition of the energetic material TATB using path integral molecular dynamics (PIMD), the more approximate
quantum thermal bath (QTB), and classical MD (ClMD). PIMD samples the
quantum canonical distribution by representing each atom as a string of beads (replicas), while QTB uses a frequency-dependent thermostat to reproduce the Bose-Einstein distribution. We find that PIMD results in faster chemical decomposition of the TATB
crystal compared to ClMD, as the initial steps involve hydrogen transfer processes. Interestingly, some of the subsequent reactions (e.g. the formation of N2) occur on identical timescales. The PIMD simulations also predict a reduction in overall activation energy by ~8% as compared to the classical result. As observed in model systems and simple unimolecular gas-phase reactions, the QTB significantly overestimates
quantum acceleration of chemical reactions and the reduction in activation energy. A comparison of the kinetic energy operator in PIMD and the centroid dynamics provides insight into the physics behind the differences between the QTB and PIMD results.
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Materials Science · Cross-listed from cs.CE
An Atlas of Extreme Properties in Cubic Symmetric Metamaterials
Sahar Choukir, Nirosh Manohara and Chandra Veer Singh
Current research on three-dimensional metamaterial has largely focused on conventional strut, plate, and shell-based
lattice designs. Although these designs offer several advantages, they possess inherent limitations that can restrict their performance in certain applications, motivating the exploration of alternative structural
topologies. Here, we present a large-scale,
symmetry guided framework for the generation and analysis of architected metamaterials based on all 36 cubic space groups. Using a voxel-based representation, we construct a database of approximately 1.95 million periodic unit
cells spanning a broad range of relative densities and topological complexity. This
dataset reveals a rich elastic property landscape shaped by crystallographic
symmetry, including rare pentamode designs with high bulk to shear ratios such as $K/G \approx 166$ , isotropic-auxetic architectures with Poisson's ratio as low as $\nu=-0.76$, and structures achieving up to 93% of the Hashin-Shtrikman upper bound on stiffness. Complementing the
dataset, we develop a three-dimensional convolutional neural network surrogate model trained and evaluated on the full database to predict strain-energy density values under uniaxial, shear, and hydrostatic loading. Together, this work establishes a comprehensive atlas of cubic symmetric metamaterials and provides a pre-trained model for the accelerated discovery and design of 3D architected materials with extreme mechanical properties.
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Materials Science
Sliding Ferroelectricity Driven Spin-Layertronics in Altermagnetic Multilayers
Rui Peng, Guangxu Su, Yangyang Fan et al. (+3 more)
The synergy of ferroicity with altermagnetism offers a novel platform for designing multifunctional altermagnetic-spintronic device technology. In this work, we propose a mechanism to achieve nonvolatile electrical manipulation of
spin and layer degrees of freedom in an altermagnetic
bilayer via sliding ferroelectricity. Using first-principles calculations, we show that an interlayer translation can induce a switchable out-of-plane ferroelectric polarization in
bilayer CuF2, which directly couples to and reverses the d-wave altermagnetic
spin splitting. Notably, the altermangetic
spin splitting is layer-locked, the sliding ferroelectricity-driven switching thus embodying a nonvolatile
spin-layertronics functionality that couples
spin-polarized transport and layer degree of freedom in a single platform. We show that in quadrilayer CuF2, four polarization states are identified which may offer multi-state logic device applications. These findings establish sliding ferroelectricity as a versatile tool for designing voltage-controlled, high-speed and energy-efficient
spin-layertronic devices based on altermagnets.
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All authors Rui Peng, Guangxu Su, Yangyang Fan, Jiaan Li, Fanxin Liu, Yee Sin Ang
Materials Science · Cross-listed from physics.optics
Fast Programming of In-Plane Hyperbolic Phonon Polariton Optics Through van der Waals Crystals using the Phase-Change Material In3SbTe2
Lina Jäckering, Umberto Saldarelli, Aaron Moos et al. (+8 more)
The high directionality of
hyperbolic phonon polaritons (HPhPs) has opened radically new ways to route and steer the flow of energy at the nanoscale. However, launching HPhPs requires fabricating efficient and precisely aligned polariton launching structures, which remains time-consuming and expensive with conventional nanofabrication approaches. Recently, using optical
laser pulses, polariton launching structures have been programmed into the plasmonic phase-change material In3SbTe2. Here, we leverage this approach to reconfigure HPhPs by programming a variety of launching and confining nanostructures through {\alpha}-MoO3 flakes deposited onto In3SbTe2. Importantly, optical programming after flake deposition enables
alignment of launching stripes to the [001]-axis of the flake, essential to control the directional polariton propagation. We showcase these capabilities in a variety of structures: i) an optically programmed disk, showing similar tuning ranges and confinement as focusing by gold disks; and ii) a cavity for in-plane HPhPs created by reconfiguring the single disk to a double disk structure, tailoring the confinement by simply reprogramming the disk distance. Our fabrication scheme offers fast turn-around times, flexible
alignment and the opportunity to reconfigure the structures. Thus, it is a fast, efficient and versatile way to tailor propagation and confinement of highly directional polaritons on demand.
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All authors Lina Jäckering, Umberto Saldarelli, Aaron Moos, Lukas Conrads, Enrique Terán-García, Christian Lanza, Aitana Tarazaga Martín-Luengo, Gonzalo Álvarez-Pérez, Pablo Alonso-González, Matthias Wuttig, Thomas Taubner
Materials Science
Helium-Cooled Cryogenic STEM Imaging and Ptychography for Atomic-Scale Study of Low-Temperature Phases
Noah Schnitzer, Mariana Palos, Geri Topore et al. (+7 more)
Much of the exotic functionality of
prime interest in
quantum materials emerges from structural and electronic ground states that can only be accessed at cryogenic temperatures. Understanding device operation therefore requires structural characterization under the same low-temperature conditions at which these functional phases exist, as room-temperature measurements often probe a different structural state. Achieving atomic-resolution in scanning transmission electron microscopy imaging and particularly 4D-STEM electron ptychography at
liquid helium temperature has remained extremely challenging because even small amounts of drift, vibration, and thermal instability associated with the cryogen can disrupt the stringent stability requirements of atomic-resolution STEM. In this work we demonstrate atomic-resolution STEM and multislice electron ptychography at temperatures as low as 20 K using a commercial helium cooled holder. We find that rapid scans and a multi-stage registration workflow are critical to reducing artifacts associated with cryogenic instability for atomic-resolution imaging, while for ptychography scan position correction including compensation for coupling between probe aberrations and position refinement is necessary for successful reconstructions. Together these results establish a pathway for reliable atomic-resolution STEM and ptychography at low temperature, enabling direct visualization of structural ground states relevant to
quantum technology.
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All authors Noah Schnitzer, Mariana Palos, Geri Topore, Nishkarsh Agarwal, Maya Gates, Yaqi Li, Robert Hovden, Ismail El Baggari, Suk Hyun Sung, Michele Shelly Conroy
Materials Science
Ab initio informed electronic stopping models for light ion propagation in metals
Evgeniia Ponomareva, Artur Tamm and Andrea E. Sand
Understanding ion-matter interactions at the atomistic level is key to advancing materials for the
semiconductor industry, space systems, and
nuclear fusion technologies. However, most atomistic frameworks still rely on simplified descriptions of how ions transfer energy to the electronic subsystem, overlooking the sensitivity of this process to the actual ion path. Existing electron-ion interaction models, such as the tensorial unified two-temperature model, were developed to study self-irradiation scenarios, but their suitability for light-ion irradiation remains unexplored. Here, we propose that for light projectiles, stepping back from the tensorial formulation toward a simpler, local model of electronic stopping provides a more efficient and physically transparent trajectory-dependent description. We parameterize and validate both models for hydrogen and helium in tungsten using ab initio electronic stopping data and large-scale ion range simulations, benchmarked against existing experimental data. This provides a consistent framework for including nonadiabatic electronic stopping in atomistic simulations of light-ion energy dissipation.
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Materials Science
Magnetic criticality and magnetocaloric response in MnBi$_2$Te$_4$ and MnBi$_4$Te$_7$
Nazma Firdosh, Shreyashi Sinha and Sujit Manna
MnBi$_2$Te$_4$ and MnBi$_4$Te$_7$ are
antiferromagnetic topological
insulators belonging to the MnBi$_{2n}$Te$_{3n+1}$ series, where structural layering provides a natural route to tune
magnetic interaction in van der Waals magnets. Despite extensive interest in their topological properties, how the insertion of Bi$_2$Te$_3$ quintuple layers modifies
magnetic critical fluctuations near the
antiferromagnetic transition remains unresolved. Here, we combine scanning tunneling microscopy (STM), critical scaling analysis, and magnetocaloric measurements to directly correlate real-space structures with
magnetic criticality. STM reveals atomically flat septuple-layer terraces in MnBi$_2$Te$_4$ whereas MnBi$_4$Te$_7$ displays coexisting septuple and quintuple layer terminations reflecting its alternating stacking sequence. MnBi$_2$Te$_4$ exhibits robust three-dimensional Ising-like critical behavior together with a distinct low-temperature first-order transition. In contrast, MnBi$_4$Te$_7$ displays crossover-dominated criticality arising from weakened interlayer exchange and competing
magnetic phases. Correspondingly, the magnetocaloric response differs significantly between the two compounds. MnBi$_2$Te$_4$ shows dual-type magnetocaloric behavior with a sharp field-induced sign reversal of the isothermal
magnetic entropy change ($-\Delta S_M$). It exhibits both inverse ($-\Delta S_M < 0$) and conventional ($-\Delta S_M > 0$) magnetocaloric effects. In contrast, MnBi$_4$Te$_7$ shows only conventional magnetocaloric response with a broad positive
entropy peak. These results establish structural layering as a key parameter governing
magnetic critical fluctuations and magnetocaloric behavior in MnBi$_{2n}$Te$_{3n+1}$ topological magnets.
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Materials Science
Engineering Magnetic Anisotropy in Permalloy Films via Atomic Force Nanolithography
Abhishek Naik, Cyril Delforge, Nicolas Lejeune et al. (+5 more)
Atomic force nanolithography provides a precise method for sculpting
magnetic thin films, enabling controlled engineering of
magnetic anisotropy in soft ferromagnets at the microscale. We demonstrate that nanoscale groove arrays patterned into permalloy (Ni80Fe20) films induce a robust in-plane uniaxial anisotropy, with the easy axis aligned along the groove direction. The anisotropy field is shown to increase with decreasing groove period and increasing engraving depth, offering continuous tunability of
magnetic hardness within a single fabrication step. Artificially engraved microstructures further allow domain configurations and domain-wall trajectories to be directed along predefined pathways, exemplified by the creation of a chessboard-like
magnetic landscape. Owing to its adaptability to diverse
ferromagnetic materials and arbitrary corrugation geometries, this approach provides a versatile platform for tailoring in-plane
magnetic anisotropy. Concrete applications are demonstrated in the design of magnonic elements and anisotropic magnetoresistance sensors.
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All authors Abhishek Naik, Cyril Delforge, Nicolas Lejeune, Daniel Stoffels, Joris Van de Vondel, Kristiaan Temst, Alejandro V. Silhanek, Emile Fourneau
Materials Science · Cross-listed from cond-mat.str-el
Electronic Structure and Resonant Circular Dichroism of La$_{0.7}$Sr$_{0.3}$MnO$_3$ from Soft X-ray Angle-Resolved Photoemission
Øyvind Finnseth, Damian Brzozowski, Anders Christian Mathisen et al. (+12 more)
Coupling between
spin, orbital, charge, and
lattice degrees of freedom in transition-metal
oxides produces a variety of electronic and
magnetic phenomena of importance for future technologies. Here, we explore the electronic band structure of a (111)-oriented La0.7Sr0.3MnO3 thin film through soft X-ray angle-resolved photoemission spectroscopy (ARPES). The measurements agree with the electronic band structure calculated with density functional theory using Hubbard U correction. Furthermore, we probe the circular dichroism in ARPES, and observe a pronounced momentum- resolved
magnetic circular dichroism in resonant photoemission from the Mn L-edge. The approach combines the momentum- and
spin-selectivity of ARPES and X-ray
magnetic circular dichroism, respectively, which could provide a useful approach for the study of unconventional magnetism.
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All authors Øyvind Finnseth, Damian Brzozowski, Anders Christian Mathisen, Stefanie Suzanne Brinkman, Xin Liang Tan, Fabian Gohler, Benjamin A. D. Williamson, Kristoffer Eggestad, Meng-Jie Huang, Jens Buck, Moritz Hoesch, Kai Rossnagel, Sverre M. Selbach, Hendrik Bentmann, Ingrid Hallsteinsen
Materials Science · Cross-listed from cond-mat.str-el
Non-Collinear and Non-Coplanar Magnetic Orders in 1/1 Periodic Approximant to the Icosahedral Quasicrystal
Shinji Watanabe and Tatsuya Iwasaki
Ground-state properties of rare-earth based 1/1 periodic approximants of icosahedral quasicrystal are clarified theoretically on the basis of an effective model for magnetism taking into account uniaxial anisotropy arising from crystalline electric field. By performing numerically-exact calculation on the 1/1 approximant
crystal with a
lattice constant $a$=14.725 Å, we have determined the ground-state phase diagram for
ferromagnetic interactions. The result shows that eight kinds of noncollinear and noncoplanar
magnetic structures are stabilized, whose
magnetic space groups are identified as $I_{\rm P}m'\bar{3}'$, $C2'/m'$ and $R\bar{3}$. We have clarified the degeneracy of each ground state, which is expected to be reflected in the numbers of the domains. By analyzing each state, the
magnetic as well as topological properties are revealed. Our results are shown to explain the measured
magnetic structures in the 1/1 approximants and the effective model is discussed to be useful for understanding the
magnetic structures and their topological properties in broad range of rare-earth based 1/1 approximants.
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Materials Science
Dielectric Tensor of CrSBr from Spectroscopic Imaging Ellipsometry
Pierre-Maurice Piel, Sebastian Schaper, Aleksandra Łopion et al. (+4 more)
Chromium sulfur bromide (CrSBr) is a
magnetic van der Waals
semiconductor with a direct bandgap and pronounced anisotropy in its electronic, optical,
spin and
lattice degrees of freedom. Here, we employ spectroscopic imaging ellipsometry (SIE) and Mueller-
matrix analysis to determine the full dielectric tensor of paramagnetic CrSBr thin films. Our measurements reveal optical anisotropy, characterized by three distinct diagonal components of the dielectric tensor. The in-plane elements are dominated by prominent excitonic resonances polarized along the two main crystallographic axes. Two main excitonic bands (A and B
excitons) centered around 1.3eV and 1.7eV, respectively, are identified; the A-
exciton polarized along the b-crystallographic direction, whereas the B-
exciton appears to consist of two nearly degenerate contributions polarized along two orthogonal in-plane
crystal axes. These results provide fundamental insight into anisotropic light-matter interactions in CrSBr, relevant for future
spin-optoelectronic and photonic applications.
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All authors Pierre-Maurice Piel, Sebastian Schaper, Aleksandra Łopion, Jakob Henz, Aljoscha Soll, Zdenek Sofer, Ursula Wurstbauer