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Physics Condensed Matter Materials Science

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Friday 26 June

Materials Science

Single-Crystalline Al/Ge Heterostructure with an Atomically Sharp Commensurate Interface

Jian-Huan Wang, Ding-Ming Huang, Han Gao et al. (+3 more)

A key challenge in developing Al/Ge heterostructures for quantum applications is Al-Ge interdiffusion. This process is facilitated by grain boundaries in polycrystalline films, which degrades interface quality and impairs device performance and reliability. Here, we present epitaxial growth of single-crystalline Al(111) on Ge(111) by molecular beam epitaxy, achieving an atomically flat and sharp interface. At the interface, a commensurate 7-Al-lattice/5-Ge-lattice epitaxial relationship is observed, which dramatically reduces the intrinsic lattice mismatch from 28.4% to about 0.1%. Interestingly, this well-ordered interface does not form below a critical thickness of 0.3 nm. Instead, Al initially nucleates as random clusters, which then transform into two-dimensional (2D) islands and, as Al deposition further increases, eventually develop into a continuous film. By optimizing the growth parameters, we have achieved an ultra-flat Al film with a surface root-mean-square roughness of about 0.16 nm and an ultra-thin continuous film with thickness of only 2 nm. These epitaxially grown Al-Ge heterostructures, with their atomically flat surfaces and sharp interfaces, provide a promising platform for studying topological quantum states.
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All authors Jian-Huan Wang, Ding-Ming Huang, Han Gao, Yuan Yao, H. Q. Xu, Jian-Jun Zhang

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

Confined exciton polaron in MoS$_2$ on twisted-hBN

Garima Gupta, Mayank Chhaperwal, Pankaj Kumar et al. (+5 more)

The simple electrostatic picture of a trion is that of an excess charge inducing an exciton polarization and binding closer (farther) to the hole (electron) side of it. Trion formation can be forbidden when such spontaneous rearrangement of charges is not allowed by the application of external perturbation, such as electric field. Here we test this hypothesis experimentally using a non-monotonic electric field. We realize this scenario by imprinting the ferroelectric domains at the AA-stacked twisted-hBN (t-hBN) interface onto a monolayer of MoS2 placed over it. The spatially varying in-plane electric field around the domain wall serves the dual purpose of (a) confining and polarizing the 2D exciton in the domain wall, and (b) depleting the free charge carriers from the domain wall. We observe a large quantized exciton splitting confirming strong exciton confinement in the domain wall. Forced by the confining potential, the electron side of the polarized exciton lies closer to the domain with accumulated free electrons, which should ideally prevent any trion formation. Contrary to the laid hypothesis, we observe signatures of quantized charged exciton emission, with an inter-level splitting that mimics the level-splitting of the quantized excitons. This paradox is explained using the many-body picture of exciton polaron, where a conduction band hole attractively binds the polarized exciton and the electron Fermi sea. The results provide a definitive way to unambiguously discern exciton polaron from trion.
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All authors Garima Gupta, Mayank Chhaperwal, Pankaj Kumar, Pushkar Dasika, Kenji Watanabe, Takashi Taniguchi, Archana Raja, Kausik Majumdar

Materials Science

Three-dimensional visualization of threading dislocation in GaN by polarized-light microscopy

Yukari Ishikawa, Kisara Matsumoto, Kazuki Ohnishi et al. (+1 more)

We demonstrate high-throughput three-dimensional imaging of threading dislocations in ammonothermal GaN wafers using polarized-light microscopy with collimated LED illumination. Threading dislocations exhibited focal-depth-dependent in-plane shifts, enabling visualization of their three-dimensional inclination behavior over large areas. Synchrotron radiation X-ray topography indicated that dislocations with identical in-plane Burgers vector components tended to exhibit similar trace geometries and inclination directions. The threading dislocations were found to be tilted by approximately 3.3{\deg} from the c-axis in directions perpendicular to their Burgers vectors, indicating climb-mediated motion associated with strain relaxation during crystal growth. These results demonstrate a simple nondestructive approach for large-area three-dimensional characterization of dislocations in GaN wafers.
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All authors Yukari Ishikawa, Kisara Matsumoto, Kazuki Ohnishi, Yongzhao Yao

Materials Science · Cross-listed from quant-ph

Fault tolerant computation of the static structure factor and finite size effects

Rishabh Bhardwaj, Alexander Reed Muñoz, Travis E. Jones et al. (+1 more)

Fault-tolerant quantum algorithms offer a promising pathway for estimating the ground-state energies of periodic materials that are beyond the practical reach of classical electronic-structure methods. A remaining challenge is finite-size mitigation: quantum algorithms evaluate a finite supercell or finite Brillouin-zone mesh, while materials properties are defined in the thermodynamic limit. In this work we develop a quantum post-processing strategy for the leading two-body finite-size correction. After one-body shell effects are reduced by twist averaging, the dominant residual error is controlled by long-wavelength density fluctuations, which are encoded in the small-momentum static structure factor $S(q)$. We formulate the corresponding operator in a Bloch-orbital basis, construct its block encoding through the density operator, and estimate its ground-state expectation value using an amplified Hadamard test. We also introduce adaptive global and local binary search procedures for identifying the infrared fitting window used to reconstruct the two-body finite size error correction. The resulting cost remains subleading relative to the main ground-state energy estimation routine: the structure-factor correction has leading $\tilde{O}(N_bN_k)^3$ dependence on the Bloch-orbital basis size, avoids the large plane-wave prefactor of full Hamiltonian simulation, and requires only $\tilde{O}(N_bN_k)$ logical qubits. This provides a fault-tolerant alternative to down-sampling, replacing repeated energy calculations on larger cells with targeted measurements of the infrared density correlations that control the finite-size effects.
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All authors Rishabh Bhardwaj, Alexander Reed Muñoz, Travis E. Jones, John Golden

Materials Science

Vacancy-mediated nitrogen diffusion and aggregation via high-fluence electron beam irradiation in HPHT synthesized diamond crystal

Chikara Shinei, Yuta Masuyama, Jun Chen et al. (+5 more)

The negatively charged nitrogen vacancy (NV-) center in diamond is a promising point defect for highly sensitive quantum sensing. The formation of high-density NV- centers is essential for improving sensitivity. We performed room-temperature electron beam irradiation (EBI) and annealing on nitrogen-doped high-pressure high-temperature diamond crystals, aiming to convert all substitutional nitrogen into NV structures by increasing EBI fluence. While the Ns0 to NV0 and NV- conversion process dominated at low EBI fluences, in a high-fluence region, NV0 and NV- center and Ns0 and Ns+ concentrations decreased with increasing EBI fluence, indicating the formation of unknown nitrogen-related defects such as the H3 center, which is a nitrogen and vacancy aggregation defect. Although H3 centers were observed at high EBI fluence, their annealing temperature of 1375 +- 25 {\deg}C was lower than the typically reported temperatures over 1600 {\deg}C. We attribute this low-temperature formation to vacancy-mediated nitrogen diffusion and aggregation.
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All authors Chikara Shinei, Yuta Masuyama, Jun Chen, Hiroshi. Abe, Masashi Miyakawa, Takashi Taniguchi, Takeshi Ohshima, Tokuyuki Teraji

Materials Science

Amorphous Fe-Sn nanofilms for anomalous-Nernst heat-flux sensing

Kenji Tanabe, Ko Mibu, Atsushi Tsukazaki et al. (+1 more)

Amorphous magnetic films are promising for anomalous-Nernst heat-flux sensing because their low thermal conductivity can enhance the temperature gradient generated by an applied heat flux. However, amorphization often degrades electronic transport and thermoelectric properties, making it challenging to obtain a large anomalous Nernst response in structurally disordered films. Here, we demonstrate nanometer-thick amorphous Fe-Sn films as high-sensitivity anomalous-Nernst heat-flux sensing materials. By systematically controlling composition and thickness, we find that amorphous Fe-Sn nanofilms combine a large anomalous Nernst response with low thermal conductivity, resulting in a heat-flux sensitivity of 0.37 um/A. This value exceeds the sensitivities reported for both amorphous magnetic thin films and representative crystalline topological magnets. X-ray diffraction and Mossbauer spectroscopy show that the optimized films lack long-range crystallinity while retaining local Fe-Sn environments, suggesting that short-range atomic order contributes to the anomalous Nernst response in the amorphous matrix. The sensitivity is also reproduced on flexible polymer substrates, indicating compatibility with mechanically compliant device architectures. These results establish amorphous Fe-Sn nanofilms as a platform for anomalous-Nernst heat-flux sensing and provide a materials design route based on local-structure control and thermal-conductivity reduction.
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All authors Kenji Tanabe, Ko Mibu, Atsushi Tsukazaki, Kohei Fujiwara

Materials Science

Defying Diamagnetism: Anomalous Redshift and Robust Chiral Spin Mixing in 2D Perovskites under High Magnetic Fields up to 50 T

D. Y. Park, S. Park, Yongmin Kim et al. (+4 more)

We report circularly polarized magneto-photoluminescence (MPL) measurements on the enantiomeric pair of two-dimensional chiral perovskites R- and S-(C4H9NH3)2PbI4 in pulsed magnetic fields up to 50 T at 4.2 K. The R-form exhibits strong preferential emission into the RC channel (I_RC/I_LC = 10:1), with the S-form showing the opposite sense, robust against the applied field. Three key observations are reported: (i) an anomalous redshift of all exciton transition energies with increasing field-contrasting with the normal diamagnetic blueshift of achiral perovskites-with a non-monotonic initial blueshift to 7.6 T in the dominant RC channel of the R-form; (ii) complete invariance of PL peak positions upon reversal of the field direction, consistent with Rashba-induced mixing of the bright exciton with a nearby m_x = 0 dark state; and (iii) field-induced increase in PL intensity and narrowing of the linewidth, attributed to suppression of disorder scattering as the cyclotron orbit contracts. These results are interpreted in the framework of Rashba spin-splitting and polaron formation in the chiral two-dimensional perovskite lattice.
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All authors D. Y. Park, S. Park, Yongmin Kim, N. Myoung, Z. Yang, Y. Kohama, Y. H. Matsuda

Materials Science

CoTAR: Topology and Atomic State Reconstruction in Condensed Phases

Hodaka Mori, Yu Miyazaki and Takechika Kikkawa

Universal machine learning interatomic potentials (uMLIPs) enable condensed-phase molecular dynamics (MD) simulations with near-first-principles accuracy, but their lack of explicit molecular topology limits bond-aware analysis and reconnection to classical force fields. Here, we present CoTAR, a hybrid graph neural network (GNN)–hidden Markov model (HMM) framework that reconstructs molecular topology, formal charges, and unpaired electrons from atomic species, coordinates, and total charge by combining message passing on a proximity graph with a van der Waals prior, chemical constraints, and temporal smoothing. Across 128 nonreactive, topology-preserving condensed-phase systems, CoTAR achieved a bond-order-weighted F1 score of 0.906 on classical-MD data; for uMLIP trajectories, few-shot fine-tuning improved the valid-snapshot rate from 38.6% to 84.7%. The reconstructed topologies also supported downstream classical MD simulations, and HMM smoothing improved system-level MD simulation feasibility from 83.6% to 85.9%, indicating that CoTAR provides a practical framework for bond-aware analysis of condensed-phase uMLIP trajectories.
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Materials Science

Entropy engineering of BF-BT-based high-entropy ceramics for ultra-high energy storage performance

Yitao Jiao, Zhenhao Fan, Dawei Wang et al. (+1 more)

Dielectric capacitors are promising for pulsed power applications, but the energy storage performance of lead-free bulk ceramics is often limited by low breakdown strength and large ferroelectric hysteresis. Herein, a high entropy perovskite oxide BaTi0.2Zr0.2Sn0.2Hf0.2Nb0.1Sc0.1O3 was introduced into the BF-BT matrix to develop lead free high entropy ferroelectric ceramics. Multicomponent B-site substitution induces lattice distortion, enhanced pseudocubic characteristics, relaxor behavior, and grain refinement. These effects suppress polarization hysteresis and electrical conduction, resulting in a significant increase in breakdown strength. A maximum breakdown strength of 840 kV/cm1 and a recoverable energy density of 10.55 J/cm3 were achieved. Entropy-induced microstructural heterogeneity promotes a more uniform electric-field distribution and delays dielectric breakdown. This work demonstrates entropy engineering as an effective route to achieving high breakdown strength and superior energy-storage performance in lead-free ferroelectric ceramics.
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All authors Yitao Jiao, Zhenhao Fan, Dawei Wang, Hai-Feng Li

Materials Science

Emergence of millimeter-wave resonances in self-assembled ferroelectric metamaterials

Florian Bergmann, Peter Meisenheimer, Aiden Ross et al. (+26 more)

Resonators are a key component in modern communications and computing. As demand and technological advances push component requirements into the terahertz regime, there is significant research devoted to the search for resonances at these frequencies. While uniform solid-state materials usually do not intrinsically feature resonances in this frequency range, self-assembled periodic arrays of ferroelectric nanodomains may provide an engineering route to design millimeter-wave properties. Here, we utilize prototypical dielectric-ferroelectric SrTiO3/PbTiO3 superlattices to robustly design periodic ferroelectric nano-scale domains. Phase field simulations predict an emergent domain breathing mode in complex polar textures and state-of-the-art millimeter-wave characterization shows evidence for such emergent resonances up to hundreds of GHz. Complex polar textures in these superlattices lead to emergent piezoelectric properties that also result in millimeter-wave resonances, which are predicted by second principles methods and confirmed by direct measurement. The principles investigated in this work suggest a new modality for ferroelectrics in the design of millimeter-wave electronics.
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All authors Florian Bergmann, Peter Meisenheimer, Aiden Ross, Marvin Schewe, Fernando Gómez-Ortiz, Kaiwen Yang, Xinyan Li, Thomas J. Lee, Pushpendra Gupta, Liam G.Connolloy, Tzu-Hsuan Hsu, Jack Kramer, Bryan T. Bosworth, Nicholas R. Jungwirth, Eric J. Marksz, Aaron Hagerstrom, Tomasz Karpisz, Arundhati Ghosal, Lane W. Martin, Yimo Han, Angela C. Stelson, Christian J. Long, Ruochen Lu, Lucas Caretta, Javier Junquera, Jason J. Gorman, Long-Qing Chen, Ramamoorthy Ramesh, Nathan D. Orloff

Thursday 25 June

Materials Science

Thermal Corrections and Analysis on the Phase Stability of CsPbCl3 and Cs2AgSbCl6 during In-Situ Thermal Treatment

Ethan R. Cronk, Wenjun Xiang, Rachel Fister et al. (+4 more)

Cesium lead chloride (CsPbCl3) is a well known and principal model for inorganic perovskite halide optoelectronic research. The many available techniques including high temperature stability testing have been used to investigate the increasing interest in inorganic perovskites as primary layers in solar cell applications. Due to the nature of high temperature testing, the characterization technique, reproducibility, and the true sample temperature are vital in determining relative stability. By choosing CsPbCl3 in the investigation of the structural stability of perovskites at high temperatures, it acts as a baseline to create and verify a methodology that accurately probes sample temperature, phase transitions, and decomposition onsets. Therefore, we present a methodological approach to investigate the thermal interactions and stability of CsPbCl3 as a parent single perovskite halide based on ligand-assisted re-precipitation synthesis techniques. Where we use our approach to inform and probe thermal interactions in other cesium/chlorine compounds like Cs2AgSbCl6. By analyzing the stoichiometry and initial phases through investigations of the crystalline structure and particle morphology, we calculated temperature conversions using a control substrate and refinements to best estimate changing structure parameters. Using in-situ temperature dependent X-ray diffraction, we were able to effectively probe the phase transitions and decomposition temperatures of the investigated halide powders. Creating a process that can confirm known high temperature structural phenomena of model perovskite halides while verifying our true sample temperature. Which allowed for further testing on the thermal kinetics of on the double perovskite structure Cs2AgSbCl6 and will continue to allow us to test other perovskites and perovskite families of interest in modern high temperature perovskite halide research.
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All authors Ethan R. Cronk, Wenjun Xiang, Rachel Fister, Biswajit Ball, Feng Yan, Liping Yu, Nicholas S. Bingham

Materials Science

PtyRANNOSAUR: Ptychography with Robust Artificial Neural Networks Optimized for Sub-Angstrom Accuracy and Ultrafast Reconstruction

Kieran Loehr, Rahim Raja, Xiaochuan Ding et al. (+5 more)

We present PtyRANNOSAUR, a data-driven neural network code that reconstructs atomic resolution electron ptychography data in seconds, 10-100x faster than standard methods. PtyRANNOSAUR uses convolutional autoencoders to map 4D-scanning transmission electron microscopy data to 2D phase images. Each model is trained on a large database of crystal structures and is tailored for a range of experimental parameters, such as accelerating voltage, convergence angle, defocus, and sample thickness. This approach yields high quality reconstructions without requiring any fine-tuning of hyperparameters. In addition, the code handles spatial partial coherence, multiple scattering, and scan position errors, which are critical for state-of-the-art electron ptychography reconstructions. By testing PtyRANNOSAUR on experimental and simulated data, we show that the neural networks accurately reconstruct atomic structures of a broad range of materials systems and can achieve high resolutions of $<0.5$ Å, comparable to the best iterative reconstructions of the same data. These advances enable near-live, state-of-the-art electron ptychography reconstructions.
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All authors Kieran Loehr, Rahim Raja, Xiaochuan Ding, Jeffrey Huang, Gillian Nolan, Sang hyun Bae, Bryan K. Clark, Pinshane Y. Huang

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

Multiphoton Fingerprints of Altermagnetic Spin Splittings

Sayed Ali Akbar Ghorashi and Andrew M. Rappe

We systematically investigate multiphoton absorption as a polarization-resolved nonlinear optical probe of planar altermagnets (ALMs). We show that the angular harmonic of the altermagnetic spin splitting fixes the lowest optical absorption at which a symmetry-selective response appears: two-photon absorption for $d$-wave order, four-photon absorption for $g$-wave order, and six-photon absorption for $i$-wave order. In each case, there exists a polarization channel locked to the symmetry harmonic of the altermagnetic texture in which the direct $n$-photon contribution to the transition matrix element is absent. This changes the frequency scaling of the absorption rate relative to other polarization channels and provides a direct optical fingerprint of the underlying altermagnetic harmonic. Our results establish a hierarchy of nonlinear spectroscopic signatures that distinguishes $d$-, $g$-, and $i$-wave altermagnetic spin splittings beyond linear response.
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Materials Science

A BRAVE Alloy Design Campaign (Bayesian Risk-aware Alloy discoVery and Exploration)

Mrinalini Mulukutla, Danial Khatamsaz, Trevor Hastings et al. (+23 more)

In constrained alloy optimization, the compositions with the highest performance potential often reside at the boundary of phase stability – where the risk of experimental failure is also highest. This work demonstrates this principle through a risk-aware Bayesian optimization campaign on single-phase FCC high-entropy alloys in the Al-V-Cr-Mn-Fe-Co-Ni-Cu system. A learned feasibility classifier, integrated directly into the multi-objective acquisition function, probabilistically penalizes candidates likely to produce failed experiments while preserving access to high-performing boundary compositions. From approximately 27,000 CALPHAD-screened candidates, 48 alloys were synthesized over three closed-loop iterations targeting five objectives (yield strength, UTS/YS ratio, strain at UTS, dynamic-to-quasi-static hardness ratio, and simulated depth of penetration), exploring 0.12% of the feasible space. Two compositional regimes emerged: a V-rich, Ni-rich high-strength regime (UTS up to ${\sim}1480$~MPa at 50% elongation) and a Mn-containing high-ductility regime (UTS/YS up to 4.20 at $>$50% elongation). Among feasible alloys, vanadium simultaneously drives yield strength ($r = 0.84$) and sigma-phase formation ($r = 0.54$ with infeasibility); at V = 24~at.%, the three strongest alloys and three sigma failures share the same compositional point. Additionally, the strongest performing alloys cluster in a narrow region of compositional space (V $\geq$ 20 at.%, Ni $\geq$ 36 at.%), representing ${\sim}100$ of $27,074$ feasible candidates – a probability of $P \approx 6.5 \times 10^{-6}$ under random sampling. This dual role – consistent with the KKT prediction that constrained optima lie on active constraint boundaries – required feasibility-aware acquisition to access; hard filtering would have excluded this region entirely.
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All authors Mrinalini Mulukutla, Danial Khatamsaz, Trevor Hastings, Wenle Xu, Daniel Salas, Joydeep Kundu, Vasanth C. Shunmugasamy, Daniel Lewis, Jacob Hempel, Clinton Strosser, Alexandra Salinas, Brent Vela, Nicolas Flores, Sina Hossein Zadeh, Ali Rachidi, David Elbert, Brady Butler, James Paramore, Dimitris Lagoudas, Justin Wilkerson, George Pharr, Douglas Allaire, Vahid Attari, Ibrahim Karaman, Ankit Srivastava, Raymundo Arróyave

Materials Science

Mapping the Growth of Two-Dimensional $\pi$-Conjugated Polymers on Au(111): Organometallic Intermediates and Edge Terminations

Simon W. Briesenick, Wyatt A. Behn, Manuel González Lastre et al. (+6 more)

Kagome lattices provide an exciting space for the exploration of graphene-like $\pi$-conjugated molecular systems with flat bands. Using heterotriangulene-derived precursors, along with an on-surface Ullmann coupling process, makes growing polymers with Kagome lattices accessible and straightforward. Here, we use scanning tunneling microscopy alongside high-resolution atomic force microscopy to examine the evolution of tribromotrioxaazatriangulene on Au(111) into ordered, covalent films. Using density functional theory and scanning probe methods, we find previously unreported organometallic intermediate states involving Au adatoms incorporated within the growing polymer lattice. We also find that a majority of polymer edges remain brominated up to 250 $^{\circ}$C and a large number of edges bonded to Au adatoms coordinated to an adjacent bromine atom. These observations suggest that residual bromine could play a role in stabilizing the polymer edges to Au adatoms and thereby influence the growth pathways that lead to ordered Kagome polymer lattices.
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All authors Simon W. Briesenick, Wyatt A. Behn, Manuel González Lastre, Chang Wan Kang, Pablo Pou, Ekaterina D. Ulyanov, Rubén Pérez, Dmytro F. Perepichka, Peter Grutter

Materials Science

Ultrafast non-thermal suppression of ferroelectricity by carrier screening in LiNbO3

Man Tou Wong, Zhuquan Zhang, Zi-Jie Liu et al. (+1 more)

Ferroelectric materials are key to energy-efficient electronics, memory, and optical applications. While charge carriers typically screen and suppress ferroelectricity, their role under nonequilibrium conditions remains elusive. Here, we use femtosecond laser pulses to liberate trapped carriers in LiNbO3 and track the response using time-resolved second-harmonic generation and stimulated Raman scattering. Even dilute photoexcited carriers induce a rapid yet enduring suppression of polarization and Raman susceptibility. Fluence- and temperature-dependent analyses confirm the suppression is non-thermal and arises from transient carrier screening. These findings reveal an efficient, reversible, and symmetry-preserving mechanism to modulate ferroelectricity on ultrafast timescales, offering a new route to control ferroic and competing quantum phases.
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All authors Man Tou Wong, Zhuquan Zhang, Zi-Jie Liu, Keith A. Nelson

Materials Science

3D Imaging of Complex Skyrmion and Hopf Topologies in an Extended Sample

I. Binnie, H. Fang, B. Shearer et al. (+16 more)

Spin textures are key for emergent magnetic phenomena such as topological protection and underpin novel spintronic device paradigms based on racetrack memory, logic gates, and neuromorphic computing. Using a coherent diffractive imaging technique called vector ptycho-tomography, in combination with algorithms that are robust to noise, we image the 3D magnetic texture of skyrmion and Hopf topologies with no prior assumptions about the sample. This directly reveals experimentally for the first time an extended 3D skyrmion lattice, including the domain wall shape, topological charge, helicity, and Hopf index. Our findings demonstrate experimentally that dipole stabilized skyrmions in Fe/Gd multilayers exhibit barrel-shaped skyrmion tubes with a twisted helicity, transitioning from N$\'e$el-type winding at the surfaces to both clockwise and counterclockwise Bloch-type winding in the bulk, that can also be described as fractional hopfions. We image a lattice of 24 skyrmions with topological charge 1, average depth-dependent domain wall width of 23 to 40 nm, depth-dependent twisted helicity from $\pm$155$\deg$ to $\pm$30$\deg$, and fractional Hopf index of $\pm$0.3. Over 10 TB of data were analyzed to yield a fully-resolved 3D reconstruction over a >0.4 $\mu$m$^3$ volume, with high fidelity down to the Nyquist limit of 8 nm. This method fills a key gap in the current landscape of magnetic imaging by enabling high-resolution, element-specific 3D reconstructions of full-field extended spin textures - offering a new route for exploring the topological complexity of magnetic materials in three dimensions.
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All authors I. Binnie, H. Fang, B. Shearer, A. Grafov, N. Jenkins, Y. Shao, C. O'Leary, Y. Liao, T. Feggeler, A. Oh, S. Yazdi, J. Zou, B. Wang, E-E. Cating, S. A. Montoya, D. Shapiro, J. Miao, H. C. Kapteyn, M. M. Murnane

Materials Science

Investigation on the temperature dependence of substrate-induced in-plane uniaxial magnetic anisotropy in Ni thin films grown on 128{\deg} Y-cut LiNbO3

Kalani Perera, Morton Greenslit, Luke Doucette et al. (+2 more)

We report the temperature dependence of the substrate-induced magnetic anisotropy in continuous Ni thin films deposited at room temperature using magnetron sputtering on a 128{\deg} Y-cut LiNbO3 substrate. Ultrathin films exhibit a pronounced temperature dependence in magnetization, with as-grown films showing isotropic behavior and an unconventional hysteresis branch crossing at relatively low temperatures, whereas no branch crossing is observed in annealed films over the investigated temperature range, indicating suppression of the underlying mechanism. Temperature-dependent magnetization measurements show that post-deposition annealing establishes uniaxial anisotropy with well-defined easy and hard axes, whose strength evolves with temperature due to the nature of residual strain governed by both lattice mismatch and coefficient of thermal expansion (CTE) mismatch between the Ni film and the 128{\deg} Y-cut substrate, independent of film thickness for both 5 nm and 100 nm films. The emergence of this anisotropy following annealing indicates enhanced magnetoelastic coupling at the film-substrate interface, as the magnetic response begins to follow the anisotropic strain imposed by lattice mismatch and CTE mismatch.
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All authors Kalani Perera, Morton Greenslit, Luke Doucette, Mauricio Pereira da Cunha, Nicholas S Bingham

Materials Science · Cross-listed from cond-mat.soft

Organic Semiconductor Alignment via Confinement in Vapor-Guided Droplets

Robert Malinowski, Alessandro Rossi, Lewis M. Cowen et al. (+8 more)

Organic semiconductors are lightweight, solution-processable materials with strong potential for printed and flexible electronics, from deformable displays to wearable sensors. Despite significant advances in materials synthesis and manufacturing, controlling molecular and mesoscale alignment during deposition remains a central challenge, as film morphology critically governs charge transport and device performance. Here, we demonstrate that flows developing within the intrinsically confined volume of microliter vapor-guided droplets can be harnessed to produce highly aligned organic semiconductor films. As droplets move in response to an external vapor source, internal flows align organic semiconducting nanowires within the droplet prior to deposition, yielding films with pronounced directional order. Organic field-effect transistors fabricated with this approach exhibit approximately 40% enhancement in saturation current relative to spin-coated controls. Beyond improved device performance, the contactless and compact nature of our method enables the deposition and alignment of organic semiconductors on curved and flexible surfaces. More broadly, vapor-guided droplets offer a scalable framework for the confinement-induced alignment of functional soft materials, with potential for integration into existing additive manufacturing platforms for flexible electronics and beyond.
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All authors Robert Malinowski, Alessandro Rossi, Lewis M. Cowen, Peter A. Gilhooly-Finn, Michael A. Parkes, Ming-Hao Chang, Yu-Cheng Chiu, Ioannis Papakonstantinou, Matthew O. Blunt, Bob C. Schroeder, Giorgio Volpe

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

Finite temperature precursors of Mottness in the Fermi Hubbard model

Sayantan Roy, Abhisek Samanta and Nandini Trivedi

We investigate finite-temperature precursors of Mottness in the repulsive Hubbard model above the spin-ordering temperature, using numerically exact determinant quantum Monte Carlo. We show that the finite-temperature crossover is accompanied by a pronounced suppression of charge fluctuations, despite the presence of a gapless single-particle spectra, demonstrating that Mottness first emerges via two-particle response in an anomalous metallic regime, before appearing in single-particle spectral functions. We further show that a gap formation in the density of states occurs through momentum-resolved redistribution of spectral weight across the Brillouin zone, that begins at the onset of anomalous metallic regime, rather than through gap formation in single-particle spectral functions at individual momenta. Upon doping, the anomalous-metallic regime generates transport and spectroscopic signatures characteristic of doped Mott insulators. This shows that the transport and spectroscopic anomalies of the doped Hubbard model do not require the presence of a fully formed Mott insulator at half-filling, but instead originate from the strong charge-response renormalization and spectral-weight redistribution that develop within the precursor anomalous metallic regime at half-filling.
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Materials Science · Cross-listed from quant-ph

From Approximate Floquet Engineering to Full Floquet Theory: Coherent Control of Chiral Spin Systems in Spintronics

Andrea Simion, Claudiu Filip and Coriolan Tiusan

Coherent control of interacting spin systems under time-periodic driving is a central challenge in spin-based quantum technologies. Here we demonstrate the applicability of a full Floquet-space formalism, adapted from Nuclear Magnetic Resonance (NMR) methodologies, to model the dynamics of driven coupled electron spins in the presence of a static magnetic field B0 and a transverse oscillating field B1. The framework explicitly includes isotropic exchange coupling J and the chiral Dzyaloshinskii-Moriya antisymmetric exchange interaction (DMI), and its numerical convergence is systematically validated with respect to Fourier-space truncation. In the non-interacting limit, the expected driven-spin dynamics is recovered, with the oscillation periodicity governed by B1. Exchange coupling alone does not modify the collective spin expectation values under the chosen initial condition, consistent with symmetry considerations. In contrast, increasing DMI generates a finite Sy component, suppresses Sz, and produces tilted, elliptical Bloch-sphere trajectories, reflecting the emergence of chiral spin-spin correlations. These effects are pronounced for open boundary conditions, while remaining nearly negligible in the periodic boundary case. When exchange coupling and DMI coexist, the dynamics becomes strongly perturbed and multi-frequency in nature. Together, these results demonstrate that full Floquet-space modeling provides a robust and predictive framework for analyzing and engineering coherent dynamics in driven interacting spin systems beyond simple coherent-rotation regimes.
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Materials Science · Cross-listed from cond-mat.mes-hall

Phase-Shifted Planar Hall and Magnetoresistive Responses in Weyl Semimetals

Sandip Bera and Sudhansu S. Mandal

The planar Hall resistivity and magnetoresistivity of Weyl semimetals are conventionally expected to exhibit $\sin 2\phi$ and $\cos2\phi$ angular dependences, respectively, where $\phi$ is the angle between electric and magnetic fields. However, experiments reveal shifted extrema in the planar Hall signal and sign reversals in magnetoresistivity at $\phi < \pi/4$. Here, using a diagrammatic Kubo-formula approach, we identify an intrinsic quadratic magnetic-field contribution to the planar transport response that is absent in conventional semiclassical description. This contribution introduces an additional term proportional to $\cos 2 \phi$ and $\sin 2\phi$, respectively, in transverse and longitudinal conductivities. Consequently, both planar Hall and magnetoresistive responses acquire a phase-shifted form $\sin 2(\phi+\phi_r)$ and $\cos 2(\phi+\phi_r)$, respectively. The same phase shift extracted independently from longitudinal and transverse responses quantitatively describes available experimental data. Our results establish a microscopic origin of the anomalous angular dependence observed in Weyl semimetals.
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Materials Science

Connection between the GKSL master equation and the Landauer formula

Misa Nozaki and Takatoshi Fujita

We derive a current formula within the Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) master equation formalism for a non-interacting system, and identify the conditions under which it reduces to the Landauer formula.

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

Magnetoresistance in chiral systems driven by inter-band spin-orbit coupling

Misa Nozaki and Takatoshi Fujita

Chiral-induced spin selectivity (CISS), in which electrons transmitted through nonmagnetic chiral materials exhibit strong spin-dependent transport, has attracted growing interest for spintronic applications. However, a quantitative understanding of CISS remains elusive, partly because most previous studies rely on single-band models. In this work, we theoretically investigate multi-band effects on magnetoresistance (MR)-CISS, which is typically observed in experiments using magnetic conductive atomic force microscopy. To evaluate the spin polarization in MR-CISS, we simulate the nonequilibrium steady-state current using the Gorini-Kossakowski-Sudarshan-Lindblad master equation. We find that spin polarization exceeding 25% can be achieved for realistic inter-band spin-orbit coupling strengths in the presence of on-site Coulomb interactions. These findings highlight the crucial role of inter-band spin-orbit coupling in the mechanism of CISS.
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Materials Science · Cross-listed from cond-mat.mes-hall

Low-energy model for doped graphene nanoribbons

J. Ferrer, A. García-Fuente, Y. Yang et al. (+2 more)

We analyse in this article the many-body behavior of free-standing doped graphene nanoribbons where the chemical potential lies inside the bulk single-particle bands. We perform an exact mapping from both an extended and an on-site Hubbard model of the ribbons to a Kanamori model, which includes ferromagnetic exchange and pair-hopping interactions. We determine the resulting Coulomb matrix elements analytically, and identify their scaling behavior as a function of ribbon width and length. We propose a low-energy version of the Kanamori Hamiltonian to address the response of the ribbons to external fields, with a view to their use as transport channels in nanoelectronics. We find that the model and the proposed ribbon parameters can produce open-shell, high-spin many-body states that can lead to shell- and spin-blockade responses.
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All authors J. Ferrer, A. García-Fuente, Y. Yang, S. Volosheniuk, H.S.J. van der Zant

Materials Science · Cross-listed from physics.optics

In-plane vector-field imaging of propagating surface phonon polaritons

Richarda Niemann, Dorothée S. Mader, Gonzalo Alvarez-Pérez et al. (+9 more)

Polariton interferometry through optical near-field microscopy has become a powerful tool in nanophotonics, enabling direct spatial access to the propagation characteristics of strongly confined, evanescent polariton modes. Scattering-type near-field optical microscopy has matured as the prime tool for such studies, yet mostly the out-of-plane components of the optical near fields are probed, owing to the elongated geometry of the nanotip. Here, we demonstrate a complementary far-field nonlinear microscopy approach which allows to selectively probe in-plane polariton field components. Accessing the full vector field is interesting when studying complex mode patterns such as hyperbolic polaritons or skyrmions, where the in-plane field components are typically only inferred from the out-of-plane component but not measured directly. To this end, we use nonlinear infrared-visible wide-field sum-frequency generation microscopy, where the short visible wavelength of the nonlinear signal provides the high spatial resolution to access evanescent modes in the infrared. The symmetry selection rules of the nonlinear process further enable polarization-selective imaging of both in-plane polariton field components through spatial interferometry. The concept is demonstrated experimentally using surface phonon polaritons at the AlN-air interface launched by a gold antenna. A simple, semi-analytical model reproduces the peculiar propagation patterns. Hyperspectral imaging with a tunable narrowband laser further gives access to the polariton dispersion. The wide-field methodology holds high promise for in-depth and high-throughput studies of infrared nanophotonic structures.
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All authors Richarda Niemann, Dorothée S. Mader, Gonzalo Alvarez-Pérez, Ana I. F. Tresguerres-Mata, Aitana Tarazaga Martín-Luengo, Stefan Partel, Joshua D. Caldwell, Niclas S. Mueller, Martin Wolf, Javier Martín-Sánchez, Pablo Alonso-González, Alexander Paarmann

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

Coexistence of static order and spin dynamics in an S = 5/2 frustrated triangular antiferromagnet

U. Jena, B. Sana, Satish Kumar et al. (+6 more)

Frustrated triangular-lattice antiferromagnets in the classical high-spin limit provide a paradigmatic setting in which the interplay of competing exchange interactions, anisotropy, and collective degrees of freedom can lead to unconventional low-energy excitations, anomalous criticality, and persistent dynamical responses. Here, we present comprehensive thermodynamic, $\mu$SR, and neutron diffraction experiments, along with first-principles calculations, on a triangular-lattice antiferromagnet, MnSnB$_2$O$_6$, where Mn$^{2+}$ ($S=5/2$) moments form a nearly perfect 2D triangular network without any anti-site disorder. The Curie-Weiss fit to the magnetic susceptibility yields a moderate Curie-Weiss temperature of $-12$ K, indicating dominant antiferromagnetic interactions between Mn$^{2+}$ moments, which is supported by first-principles calculations. Specific-heat measurements reveal the onset of long-range magnetic order at $T_{\rm N}\approx 1$ K, which is ascribed to intraplane exchange interactions. The specific heat exhibits pronounced short-range correlations above $T_{\rm N}$ and an unconventional power-law behavior, $C\propto T^{1.37}$, deep in the ordered state, suggesting the presence of non-trivial low-energy excitations. Zero-field $\mu$SR experiments down to 50~mK confirm the presence of magnetic ordering below $T_{\rm N}$, in agreement with thermodynamic and neutron diffraction experiments. The $\mu$SR measurements detect persistent spin dynamics coexisting with static magnetic order. The temperature evolution of the order parameter down to 50~mK from neutron diffraction suggests that the ordered state is consistent with a 3D Ising-like antiferromagnet. This family of archetypal frustrated magnets offers a promising venue for the experimental realization of emergent phenomena governed by competing exchange interactions and exotic low-energy excitations.
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All authors U. Jena, B. Sana, Satish Kumar, M. Pregelj, A. Bandyopadhyay, P. Manuel, J. S. Lord, D. T. Adroja, P. Khuntia

Materials Science

HF Etching and Silanization: Evidence for the Role of Surface Hydroxyl Groups in Silicon Nitride Resonator Loss

Ariane Giesriegl, Nicola Cavalleri, Robert West et al. (+4 more)

Silicon nitride $SiN_x$ nanomechanical resonators are central to sensing, quantum technologies, and fundamental physics experiments due to their exceptional mechanical quality factors (Q). However, as resonator thickness approaches the nano-scale, surface-related dissipation limits performance. Here, we investigate the role of surface chemistry in low-stress Si-rich SiNx membranes through a combination of hydrofluoric acid (HF) etching and trimethylchlorosilane (TMCS) silanization, correlated with surface characterization and mechanical measurements. Preliminary analysis by TEM-EELS, XPS, RBS/ERDA, and XRR reveals a native oxide surface layer (1-2 nm). Surface modification by HF and TMCS was subsequently evaluated using XPS, photothermal FTIR, contact-angle measurements, and intrinsic quality factor ($Q_{int}$) characterization. While HF etching effectively removes the native oxide and TMCS introduces hydrophobic $Si-(CH_3)_3$ termination, neither oxide thickness nor surface energy correlates with mechanical dissipation. TMCS treatments produce the largest enhancements, increasing $Q_{int}$ by up to 50%, whereas HF etching alone yields lower gains of 20-25%. These findings suggest surface hydroxyl groups as a key contributor to energy loss in $SiN_x$ resonators and demonstrate that chemical functionalization can substantially suppress surface dissipation.
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All authors Ariane Giesriegl, Nicola Cavalleri, Robert West, Antonius Armanious, Markus Sauer, Thomas Schachinger, Silvan Schmid

Materials Science

A Hybrid Quantum Mechanics Machine Learning Forcefield (QM/ML) Framework for Accurate Solute-Dislocation Interaction Simulations

Junting Zhang, Colleen Reynolds, Ryan S. Stroud et al. (+4 more)

Solute-dislocation interactions play a central role in controlling microstructural evolution and mechanical behaviour of structural materials, yet conventional atomistic modelling approaches struggle to combine the chemical accuracy with computational scalability. In the nuclear industry, these challenges become particularly acute, as experiments reveal strong correlations between solute segregation and irradiation-induced dislocation loops. However, theoretical insight remains limited because density functional theory (DFT) simulations are prohibitively expensive at relevant length scales, while traditional semi-empirical interatomic potentials lack the chemical fidelity required for predictive solute-defect calculations. Here, we introduce a hybrid quantum-mechanics/machine-learning (QM/ML) simulation framework that couples DFT with neural-network machine learning interatomic potentials (MLIPs), enabling accurate atomistic dislocation simulations at reduced computational cost. We demonstrate the QM/ML framework's capability by reproducing the experimentally observed Sn and Fe segregation to dislocation loops in Zr and investigating magnetically complex solute-dislocation interactions in steel. These results establish the approach as a transferable, high-fidelity tool for modelling irradiation-induced defect structures and benchmarking emerging MLIPs.
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All authors Junting Zhang, Colleen Reynolds, Ryan S. Stroud, Jana Smutna, Daniel J. M. King, Andrew P. Horsfield, Mark R. Wenman

Materials Science

Giant and Broadband Circular Dichroism from Particle-Hole Symmetry Breaking in Weyl Semimetals

Xiangyu Jiang, Zeping Shi, Yuhan Du et al. (+14 more)

Circular dichroism originates from symmetry breaking of material structure, leading to differential absorption of left- and right-circularly polarized light. However, circular dichroism in most materials is inherently weak and spectrally narrow, especially in the mid-to-far infrared. Here, we uncover giant infrared circular dichroism in the magnetic-field-forced Weyl semimetal Mn(Bi,Sb)2Te4, driven by extreme particle-hole symmetry breaking. Helicity-resolved magneto-infrared spectroscopy reveals circular dichroism exceeding 3000 mdeg (~130 mdeg/nm) with above-degree response extending over the 6-13 {\mu}m spectral range. The optical resonances are enhanced by a strong band nesting effect intrinsic to the Landau levels of type-II Weyl dispersion. A symmetry-based kp model reproduces these magneto-infrared responses and demonstrates that magnetization-induced asymmetric spin-orbit coupling generates particle-hole symmetry breaking, suppressing spin-up, parity-even wavefunction components in the valence Landau band and thereby producing pronounced optical helicity selectivity. Our findings establish particle-hole symmetry breaking as an effective route toward helicity-resolved optical control in quantum materials.
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All authors Xiangyu Jiang, Zeping Shi, Yuhan Du, Haonan Chen, Jiayu Wang, Wenbin Wu, Guangyi Wang, Congming Hao, Mingfan Yao, Mingsen Zhou, Xin Chen, Chenyao Xu, Zhongbo Yan, Cheng Zhang, Hai-Zhou Lu, Junhao Chu, Xiang Yuan