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Physics Condensed Matter Materials Science

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Friday 21 November

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

Building 3D superconductor-based Josephson junctions using a via transfer approach

Cequn Li, Le Yi, Kalana D. Halanayake et al. (+8 more)

The coupling of superconductivity to unconventional materials may lead to novel quantum states and potential applications. Controlling the quality of the superconductor-normal metal interface is of crucial importance to the understanding and engineering of the superconducting proximity effect. In many cases, conventional lithography-based deposition methods introduce undesirable effects. Using the concept of via contact and dry transfer, we have constructed smooth, van der Waals-like contact between 3D superconducting NbN/Pd and graphene with low contact resistance of approximately 130 $\Omega \cdot \mu m$. Gate-tunable supercurrent, Fraunhofer pattern, and Andreev reflections are observed, the properties of which can be understood using an induced superconducting gap $\Delta$' in this planar contact geometry. We discuss potential mechanisms impacting the magnitude of $\Delta$' and suggest ways of further increasing the proximity coupling. This gentle, lithography-free contacting method can be applied to air- and damage-sensitive surfaces to engineer novel superconducting heterostructures.
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All authors Cequn Li, Le Yi, Kalana D. Halanayake, Jessica L. Thompson, Yingdong Guan, Kenji Watanabe, Takashi Taniguchi, Zhiqiang Mao, Danielle Reifsnyder Hickey, Morteza Kayyalha, Jun Zhu

Materials Science

Altermagnetic Flatband-Driven Fermi Surface Geometry for Giant Tunneling Magnetoresistance

Xingyue Yang, Shibo Fang, Zongmeng Yang et al. (+3 more)

Altermagnetism, characterized by zero net magnetization and symmetry-protected spin-split band structures, has recently emerged as a promising platform for spintronics. In altermagnetic tunnel junctions (AMTJs), the suppression of tunneling in the antiparallel configuration relies on the mismatch between spin-polarized conduction channels in momentum space. However, ideal nonoverlapping spin-polarized Fermi surfaces are rarely found in bulk altermagnets. Motivated by the critical influence of Fermi surface geometry on tunneling magnetoresistance (TMR), we investigate three experimentally synthesized altermagnets – bulk $\mathrm{V_2Te_2O}$, $\mathrm{RbV_2Te_2O}$, and $\mathrm{KV_2Se_2O}$ – to elucidate how flatband-driven Fermi surfaces minimize spin-channel overlap and boost AMTJ performance. Notably, $\mathrm{RbV_2Te_2O}$ and $\mathrm{KV_2Se_2O}$ host flat altermagnetic Fermi sheets, which confine spin degeneracy to minimal arc-like or nodal-like regions. Such Fermi surface geometry drastically reduces spin overlap, resulting in an unprecedented intrinsic TMR well over $10^3\%$ in the $\mathrm{KV_2Se_2O}$-based AMTJ. Incorporating an insulating barrier further enhances the TMR to $\sim10^6\%$, surpassing most conventional MTJs. These results not only establish $\mathrm{KV_2Se_2O}$ as a compelling candidate AMTJ material, but also highlight the critical role of flatband Fermi surface geometry in achieving high-performance altermagnetic-spintronic device technology.
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All authors Xingyue Yang, Shibo Fang, Zongmeng Yang, Pin Ho, Jing Lu, Yee Sin Ang

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

Coexistence of unconventional spin-orbit torque and in-plane Hall effect in a single ferromagnetic layer

Jiaxin Chen, Hongsheng Zheng, Hongliang Chen et al. (+18 more)

The symmetry of a material fundamentally governs its spin transport properties. While unconventional spin transport phenomena have been predominantly explored in low-symmetry systems (e.g., $C_{1v}$ symmetry), high-symmetry crystals–which constitute the majority of industry-compatible materials–are generally expected to exhibit only conventional spin-transport behavior. Here, we report the coexistence of two unconventional spin transport effects, the crystal spin-orbit torque (CSOT) and the crystal in-plane Hall effect (CIHE), in a CoPt single ferromagnetic layer with $C_{3v}$ symmetry. Leveraging the CSOT, we achieve nearly 100% field-free perpendicular magnetization switching in a 6 nm CoPt layer at room temperature. Simultaneously, the CIHE observed in this material exhibits nearly identical dependencies on both current angle and growth temperature as the CSOT. Symmetry analysis confirms that both effects share a common physical origin. Our work not only establishes CoPt as a high-performance spin-orbit material, but also demonstrates that unconventional spin transport can be realized in high-symmetry systems, thereby opening a broad pathway for their application in practical spintronics.
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All authors Jiaxin Chen, Hongsheng Zheng, Hongliang Chen, Qia Shen, Chang Pan, Zhenyi Zheng, Hemian Yi, Dandan Guan, Xiaoxue Liu, Yaoyi Li, Shiyong Wang, Hao Zheng, Canhua Liu, Jinfeng Jia, Jingsheng Chen, Ruidan Zhong, Lei Wang, Xuepeng Qiu, Yumeng Yang, Aurélien Manchon, Liang Liu

Materials Science · Cross-listed from physics.acc-ph

A Short Introduction to Metal Forming

Charbel Moussa and Pierre Montmitonnet

The present paper is a short introduction to metal forming. The paper highlights the different disciplines that should be considered when analyzing metal forming. Hence, mechanical flow, heat flow, mechanical and thermal contact, and microstructure evolution are presented within the perspective of metal forming. For every aspect, well-established knowledge is presented in addition to scientific open questions on which active research is still done.
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Materials Science · Cross-listed from physics.app-ph

Ferroelectric Nematic Liquid Crystals as Charge Boosters for Triboelectric Nanogenerators

Jia-Yao Ye, Susanta Chakraborty, Karthick Subramani et al. (+3 more)

Driven by growing demand for clean energy, triboelectric nanogenerators (TENGs) have emerged as promising self-powered systems, yet achieving high charge density remains a critical challenge. In polymer dielectrics, triboelectricity can be further amplified by incorporating high-dielectric and polar materials for functional adaptability. Conventional dielectrics, including liquid crystals (LCs), offer limited improvement for triboelectrification, whereas the breakthrough ferroelectric nematic liquid crystals (NF-LCs), with giant spontaneous polarization and high dielectric constant, act as highly effective charge boosters. Here, we introduce NF-LC (DIO) as a functional filler in a PVDF-based TENG. Increasing DIO content progressively grows the electroactive phase and effective polarization in PVDF and defines a marked improvement in TENGs electrical performances through favourable dipolar alignment and strengthened charge-trap effects. The optimized composite film achieves an impressive open-circuit voltage of 1.1 kV, short-circuit current of 50 micro Amp, and power density of 110 W/m2 - seven times higher than pure PVDF. The device exhibits excellent charge-storage capability, powers over 500 LEDs without power management. This work establishes NF-LC-based TENGs as a new platform for high-performance self-powered energy harvesting, linking soft matter physics with applied energy technology.
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All authors Jia-Yao Ye, Susanta Chakraborty, Karthick Subramani, Xing-Zhou Tang, Yan-Nan Xie, Bing-Xiang Li

Materials Science

Ferroelectric Switchable Topological Magnon Hall Effect in Type-I Multiferroics

Quanchao Du, Jinlian Lu, Xueqing Wan et al. (+2 more)

Electric control of magnetism at room temperature is crucial for developing next-generation, low-power spintronic devices. However, the intrinsic incompatibility between ferroelectricity and magnetism in crystal symmetry, along with the absence of strong magnetoelectric coupling mechanisms, continues to pose major challenges. In this work, we propose a general theoretical framework for magnon manipulation based on ferroelectric polarization switching in two-dimensional multiferroics. Taking monolayer multiferroics $\mbox{Ti}_{2}\mbox{F}_{3}$ as an example, our calculations demonstrate that ferroelectric switching can significantly modulate spin exchanges, thereby enabling nonvolatile and reversible electric control of the magnons. More importantly, the ferroelectric polarization reversal leads to a sign change in the Berry curvature, ensuring effective control over the valley Hall and nonlinear Hall response of magnons. This study provides a new way for realizing low-power and electrically controllable magnonic devices.
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All authors Quanchao Du, Jinlian Lu, Xueqing Wan, Zhenlong Zhang, Zhijun Jiang

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

Single-Defect Spectroscopy via Random Telegraph Noise in Graphene-Contacted ReS$_2$-hBN Heterostructures

Shubhrasish Mukherjee, Gaurab Samanta, Shubhadip Moulick et al. (+5 more)

Defect spectroscopy in two-dimensional (2D) field-effect transistors (FETs) requires device architectures that suppress contact and disorder artifacts while preserving intrinsic carrier dynamics. Here, we demonstrate ReS$_2$-hBN FETs with few-layer graphene (FLG) van der Waals contacts that form nearly barrier-free interfaces, enabling intrinsic transport in ReS$_2$, an anisotropic, low-symmetry TMDC rarely exhibiting disorder-free behavior. The clean ReS$_2$-FLG platform allows direct observation of random telegraph noise (RTN) even in micron-scale channels, manifested as discrete two-level current fluctuations between 90-150 K arising from stochastic trapping at localized hBN defect sites. With increasing temperature, the RTN evolves into a 1/f spectrum as multiple traps activate. Statistical analysis of RTN amplitudes and capture-emission kinetics identifies substitutional carbon-related centers in hBN as dominant defects. These findings establish a generalizable approach for probing dielectric-origin defect dynamics in intrinsically conducting, low-symmetry 2D semiconductors.
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All authors Shubhrasish Mukherjee, Gaurab Samanta, Shubhadip Moulick, Ruta Kulkarni, Kenji Watanabe, Takashi Taniguchi, Arumugum Thamizhavel, Atindra Nath Pal

Materials Science

Effect of temperature and excitation power on down-conversion process in Tb3+/Yb3+-activated silica-hafnia glass-ceramic films

S. E. Amrani, M. Sun, S. Valdueza-Felip et al. (+4 more)

Transparent glass ceramics, when activated by rare earth ions, are excellent photonic materials. Regarding photonic glass-ceramics based on silicates, hafnia and silica in a binary system has proved to be an excellent matrix to incorporate rare earth ions in the hafnia nanocrystals, resulting in important luminescence enhancement and, consequently, allowing a large spectrum of critical applications. Here we will focus on the downconversion mechanism driven by the couple Tb3+/Yb3+, largely exploited in photovoltaic systems. The research presented here has been performed on 70SiO2-30HfO2 silica-hafnia glass-ceramic films activated with 19 % rare earth ions: [Tb + Yb]/[Si + Hf] = 19 %. Two main results will be discussed: (a) the intensity and the broadening of the Yb3+ emission band at 975 nm were found to be temperature-dependent, as shown in the figure; (b) the energy transfer mechanism Tb3+ >> Yb3+ will be discussed, referring to the mechanisms that have been proposed in the literature. In relation to the latter topic, the power dependence spectra for the luminescence of Yb3+: 2F5/2 >> 2F7/2 will be discussed.
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All authors S. E. Amrani, M. Sun, S. Valdueza-Felip, F. B. Naranjo, M. R. Britel, M. Ferrari, A. Bouajaj

Materials Science

New insights into the magnetism of DyCo$_{5}$

Alena Vishina, Konstantin Skokov, Hiroki Tsuchiura et al. (+5 more)

In this work, we present the first magnetization measurements of DyCo$_5$ single crystals in magnetic fields up to 14 T, spanning a temperature range up to 600 K. Our investigation reveals several unique features, including a significant magnetization anisotropy and an observed minimum in spontaneous magnetization near the compensation point, phenomena not previously reported. This work also uncovers the complex magnetic behavior of DyCo$_5$, with a pronounced interplay between the Dy and Co sublattices, each exhibiting distinct temperature-dependent magnetic properties. The combination of dynamical mean-field theory (DMFT), atomistic spin-dynamics (ASD) simulations, and the Effective Spin Model (ESM) for rare-earth compounds successfully explains the experimental data across both low and high temperatures. Our theoretical approach not only explains the observed magnetic anisotropy and the behavior near the compensation temperature but also successfully reproduces key experimental features such as the saturation behavior at high fields and the evolution of the magnetic moment at different temperatures.
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All authors Alena Vishina, Konstantin Skokov, Hiroki Tsuchiura, Patrik Thunström, Alex Aubert, Oliver Gutfleisch, Olle Eriksson, Heike C. Herper

Materials Science

Low-to-mid Al content ($x\sim$ 0-0.56) Al$_x$In$_{1-x}$N layers deposited on Si(100) by radio-frequency sputtering

R. Blasco, S. Valdueza-Felip, D. Montero et al. (+3 more)

Radio-frequency (RF) sputtering is a low-cost technique for the deposition of large-area single-phase AlInN on silicon layers with application in photovoltaic devices. Here, the effect of the Al mole fraction x from 0 to 0.56 on the structural, morphological, electrical, and optical properties of $n$ Al$_x$In$_{1-x}$N layers deposited at 550 $^\circ$C on p-Si(100) by RF sputtering is studied. X-ray diffraction data show a wurtzite structure oriented along the c-axis in all samples, where the full width at half maximum of the rocking curve around the InN (0002) diffraction peak decreases from $\sim 9^\circ$ to $\sim 3^\circ$ while incorporating Al to the AlInN layer. The rootmean-square surface roughness, estimated from atomic force microscopy, evolves from 20 nm for InN to 1.5 nm for Al$_{0.56}$In$_{0.44}$N. Low-temperature photoluminescence spectra show a blueshift of the emission energy from 1.59 eV (779 nm) for InN to 1.82 eV (681 nm) for Al$_{0.35}$In$_{0.65}$N according to the Al content rise. Hall effect measurements of Al$_x$In$_{1-x}$N ($0<x <0.35$) on sapphire samples grown simultaneously point to a residual n-type carrier concentration in the 1021 cm$^{-3}$ range. The developed n-AlInN/p-Si junctions present promising material properties to explore their performance operating as solar cell devices.
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All authors R. Blasco, S. Valdueza-Felip, D. Montero, M. Sun, J. Olea, F. B. Naranjo

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

Giant Nonlinear Photon-Drag Currents in Moiré Bilayers

Zhuocheng Lu, Zhuang Qian, Zhichao Guo et al. (+4 more)

The bulk photovoltaic effect provides a fundamental pathway for direct light-to-current conversion in quantum materials. However, these nonlinear currents are often strictly constrained or forbidden by crystal symmetries, hindering their exploration in a broader range of materials. While the nonlinear photon-drag effect leverages finite photon momentum to circumvent these constraints, its investigation has been largely confined to toy models, lacking a robust numerical framework for realistic materials. Here, we develop a unified microscopic theory of nonlinear photon-drag currents formulated within a geometric-loop framework, providing both a transparent quantum-geometric interpretation and numerical tractability. Applying this formalism to twisted bilayer graphene (TBG), we demonstrate that a finite, in-plane photon momentum can trigger massive nonlinear responses, rivaling the giant photovoltaic currents reported in typical 2D materials. These currents exhibit high tunability via photon wavevector, twist angle, and light polarization. Our work not only provides a generalized framework for momentum-dependent light-matter interactions but also establishes the nonlinear photon-drag effect as a potent mechanism for unlocking unprecedented optoelectronic functionalities beyond the limitations of the conventional bulk photovoltaic effect.
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All authors Zhuocheng Lu, Zhuang Qian, Zhichao Guo, Likun Shi, Shi Liu, Hua Wang, Kai Chang

Materials Science

Energy-Dependent Magnetic Modifications in HOPG via Microbeam Scanning

Ram Kumar, Aditya H. Kelkar, Neeraj Shukla et al. (+2 more)

Medium-energy ion irradiation is a promising technique for inducing magnetism in materials with partially filled d or f electron bands. This approach enables precise control over the density and spatial distribution of irradiation-induced defects, which play a crucial role in modifying the electronic and magnetic properties of the system. The primary objective of this experiment was to investigate the influence of ion energy variation on the magnetic properties of highly oriented pyrolytic graphite (HOPG). To achieve this, HOPG samples were irradiated with protons 1-3 MeV and carbon ions 600 keV - 2 MeV. A significant change in the magnetic moment was observed with respect to the irradiation energy for both ion species. The effect of energy variation was analyzed using a vibrating sample magnetometer (VSM) and SRIM simulations. The results demonstrate that ion-beam-induced magnetic ordering strongly depends on both the ion species and the beam energy. Magnetic measurements were performed with varying irradiation energies, showing that carbon ion irradiation produces a higher degree of magnetic ordering compared to proton irradiation at the same dose. The maximum magnetization was obtained at 1.2 MeV carbon ion irradiation. SRIM simulations confirm that carbon ions create a greater number of lattice defects than proton ions, which correlates with the enhanced magnetic response.
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All authors Ram Kumar, Aditya H. Kelkar, Neeraj Shukla, Paras Poswal, Sheshmani Singh

Materials Science

Accelerated Materials Discovery through Cost-Aware Bayesian Optimization of Real-World Indentation Workflows

Vivek Chawla, Stephen Puplampu, Haochen Zhu et al. (+3 more)

Accelerating the discovery of mechanical properties in combinatorial materials requires autonomous experimentation that accounts for both instrument behavior and experimental cost. Here, an automated nanoindentation (AE-NI) framework is developed and validated for adaptive mechanical mapping of combinatorial thin-film libraries. The method integrates heteroskedastic Gaussian-process modeling with cost-aware Bayesian optimization to dynamically select indentation locations and hold times, minimizing total testing time while preserving measurement accuracy. A detailed emulator and cost model capture the intrinsic penalties associated with lateral motion, drift stabilization, and reconfiguration-factors often neglected in conventional active-learning approaches. To prevent kernel-length-scale collapse caused by disparate time scales, a hierarchical meta-testing workflow combining local grid and global exploration is introduced. Implementation of the workflow is shown on a experimental Ta-Ti-Hf-Zr thin-film library. The proposed framework achieves nearly a thirty-fold improvement in property-mapping efficiency relative to grid-based indentation, demonstrating that incorporating cost and drift models into probabilistic planning substantially improves performance. This study establishes a generalizable strategy for optimizing experimental workflows in autonomous materials characterization and can be extended to other high-precision, drift-limited instruments.
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All authors Vivek Chawla, Stephen Puplampu, Haochen Zhu, Philip D. Rack, Dayakar Penumadu, Sergei Kalinin

Materials Science · Cross-listed from physics.optics

Broadband telecom single-photon emissions from InAs/InP quantum dots grown by MOVPE droplet epitaxy

Shichen Zhang, Li Liu, Kai Guo et al. (+6 more)

The development of quantum materials for single-photon emission is crucial for the advancement of quantum information technology. Although significant advancement has been witnessed in recent years for single photon sources in near infrared band ({\lambda}~700-1000 nm), several challenges have yet to be addressed for ideal single photon emission at the telecommunication band. In this study, we present a droplet-epitaxy strategy for O-band to C-band single-photon source based semiconductor quantum dots (QDs) using metal-organic vapor-phase epitaxy (MOVPE). Via investigating the growth conditions of the epitaxial process, we have successfully synthesized InAs/InP QDs with narrow emission lines spanning a broad spectral range of {\lambda}~1200-1600 nm. The morphological and optical properties of the samples were characterized using atomic force microscopy and micro photoluminescence spectroscopy. The recorded single-photon purity of a plain QD structure reaches (g(2)(0) = 0.16), with a radiative recombination lifetime as short as 1.5 ns. This work provides a crucial platform for future research on integrated microcavity enhancement techniques and coupled QDs with other quantum photonics in the telecom bands, offering significant prospects for quantum network applications.
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All authors Shichen Zhang, Li Liu, Kai Guo, Xingli Mu, Yuanfei Gao, Junqi Liu, Fengqi Liu, Quanyong Lu, Zhiliang Yuan

Thursday 20 November

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

Floquet-engineered Valley Topology with Anisotropic Response in 1T'-WSe$_2$ and Janus WSeTe monolayers

Zhe Li, Haijun Cao, Lijuan Li et al. (+3 more)

Valley topology has emerged as a key concept for realizing new classes of quantum states. Here, we investigate Floquet-engineered topological phase transitions in anisotropic 1T'-WSe$_2$ and its Janus derivative WSeTe monolayers, which exhibit valley-degenerate and valley-polarized characteristics, respectively. In 1T'-WSe$_2$, a single topological-phase-transition (TPT) occurs from the quantum-spin-Hall state (QSH) to the quantum anomalous Hall (QAH) state, involving one spin channel at both valleys simultaneously. In contrast, Janus WSeTe undergoes a two-stage Floquet-driven TPT that occurs within a single valley and sequentially involves two spin components. The intermediate phase manifests as a valley-polarized QAH (vp-QAH) state with a finite valley Chern number, while the final phase evolves into a high-Chern-number QAH state with distinct valley gaps. Furthermore, an in-plane anisotropic response of the TPTs is predicted under oblique light incidence, reflecting the intrinsic low-symmetry nature of the lattice. These findings provide a comprehensive understanding of Floquet-engineered valley-based topological properties and offer guidance for designing light-controllable valleytronic and topological devices.
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All authors Zhe Li, Haijun Cao, Lijuan Li, Huixia Fu, Mengxue Guan, Sheng Meng

Materials Science

Magnetic Properties of the Quasi-1D Magnesium Lanthanide Borates Mg$Ln$B$_5$O$_{10}$

Lachlan G. M. Rooney, Siân E. Dutton and Nicola D. Kelly

Lanthanide borates are widely studied for their optical and magnetic properties. A wide variety of structures are known with 3, 2, 1 and 0 dimensional connectivity of lanthanide ions. Here, we explore Mg$Ln$B$_5$O$_{10}$, with a quasi-1D arrangement of the $Ln$ ions. Polycrystalline samples of Mg$Ln$B$_5$O$_{10}$ ($Ln$ = La, Pr, Nd, Sm–Er) were synthesised with high purity via a sol-gel method. Powder X-ray diffraction data confirmed the reported monoclinic space group ($P2_1/c$). The magnetic $Ln^{3+}$ ions in Mg$Ln$B$_5$O$_{10}$ form relatively isolated zig-zag chains parallel to the $b$ axis. Magnetic susceptibility and isothermal magnetisation were measured: all samples except $Ln=$ (Eu, Sm) fit the Curie-Weiss Law in isothermal magnetisation at high temperatures, in broad agreement with theoretical expectations. $Ln =$ (Nd, Tb, Dy, Ho) exhibit signatures characteristic of Ising spin saturation, implying single ion anisotropy, while Gd exhibits characteristics of Heisenberg spins. Estimation of magnetic interactions suggests that Mg$Ln$B$_5$O$_{10}$ are candidate materials for quasi-1D magnetism. The magnetocaloric entropy change was also calculated, with MgGdB$_5$O$_{10}$ showing promise for application to solid-state refrigeration at liquid helium temperatures.
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Materials Science

A Constraint-Modulated Rate Law for Glass-Forming Systems: Viscosity Evidence and Dielectric Transfer in Salol

Debra S. Gavant and Christian E. Precker

The viscosity of a glass-forming liquid can increase by more than 14 decades as structural mobility diminishes upon cooling. Continuous Present Actualization (CPA) treats physical change as an ongoing process under the physical conditions currently in force. CPA plus constraint (CPA+C) tests the material hypothesis that relational constraints modulate the observable rate of structural reconfiguration. The bounded function $C(T)$ supplies an operational temperature modulation for this proposed influence. The five-parameter law is compared with the VFT, MYEGA, and Avramov–Milchev equations using source-verified data. For 35 published salol viscosity symbols spanning 14.15 decades, CPA+C is favored over the nearest comparator by 47.72 Akaike information criterion (AIC) units and reduces the leave-one-symbol-out root-mean-square prediction error from 0.398 to 0.207. It is selected in all 1,000 symbol-level bootstrap resamples under AIC, its small-sample correction (AICc), and the Bayesian information criterion (BIC). For 60 source-verified B$_2$O$_3$ viscosity measurements, CPA+C has a 57.39-unit AIC advantage over the nearest comparator. Salol provides the prospectively identified cross-observable test. The viscosity fit fixes both temperature coordinates and the complete temperature dependence of the viscosity-derived modulation before the dielectric comparison; only dielectric-specific coefficients are fitted. This fixed-geometry model improves on a denominator-matched control by 16.32 AIC units, with AIC preference across all 1,000 propagated viscosity geometries. The viscosity-derived modulation therefore retains predictive information for molecular reorientation in the same liquid. Together, the salol and B$_2$O$_3$ viscosity results and the salol transfer establish a reproducible constraint-modulated rate signature consistent with progressive narrowing of configurational access.
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2511.16791 · 20 Nov · 18 pages, 6 figures. Substantially revised and expanded. Salol now uses 35 published symbols as inferential units; B2O3 was source-verified; earlier OTP comparisons are no longer primary evidence. Independently validated salol dielectric and viscosity-to-dielectric transfer analyses added. Data/code: https://doi.org/10.5281/zenodo.22306850

Abstract PDF $LIQD ×2$BAYS ×1

Materials Science

Light-Induced Lattice Coherence and Emission Enhancement in PTM-Passivated CsSnI3 Perovskites

Thomas Y. Adams, Bruce Barrios, Michael Ziegenfus et al. (+2 more)

Metal halide perovskites continue to lead in optoelectronic applications, but the toxicity of lead has driven efforts to identify environmentally benign alternatives. Cesium tin iodide is one such, with a direct bandgap and near-infrared emission, though its performance is limited by instability. We show that phthalimide (PTM) passivation during single crystal growth enhances optical output and ambient stability. Under continuous excitation, PTM-passivated microscale crystals show up to a nearly one order of magnitude increase in photoluminescence (PL) quantum yield, accompanied by reversible sharpening of a low-frequency Raman mode associated with Cs rattling. This reveals dynamic, light-induced lattice reordering that passivates trap states and enhances radiative recombination. Mechanical grinding yields nanocrystals with redshifted, narrowed PL, consistent with a relaxed polymorph and reduced inhomogeneous broadening. Despite increased surface area, PTM remains effective in preserving near-infrared emission in nanocrystals as well. Power-dependent PL reveals distinct carrier dynamics, where microcrystals show redshift due to bandgap renormalization, while nanocrystals show blueshift and elevated carrier temperatures (300 to 1900 K), consistent with hot-carrier recombination. Extended illumination reveals reversible optical changes, including PL modulation, reflecting dynamic light-matter interactions and evolving defect landscapes. These results identify PTM-passivated Cesium tin iodide as an ideal platform for probing morphology-dependent carrier relaxation and light-induced vibrational coherence in lead-free perovskites.
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All authors Thomas Y. Adams, Bruce Barrios, Michael Ziegenfus, Hui Cai, Sayantani Ghosh

Materials Science

Tungsten doping-induced phase transition in CVD-grown MoS2 bilayers

Ana Senkić, Rachael Keneipp, Petra Ivatović et al. (+5 more)

Controlling the crystal phase of two-dimensional (2D) transition metal dichalcogenides (TMDs) is essential for tailoring their optical and electronic properties. While phase transitions in monolayer TMDs and semiconductor-to-metal conversions have been widely studied, structural transitions between semiconducting polytypes - particularly in bilayer (2L) systems - remain underexplored. Here, we demonstrate a W doping-induced phase transition from non-centrosymmetric AA stacking to centrosymmetric AB' in 2L MoS2 synthesized by chemical vapor deposition (CVD). Using polarization-resolved second harmonic generation (SHG) and low-frequency Raman spectroscopy, we identify a phase transition correlated with increasing tungsten (W) concentration. The dilute W-doped 2L system exhibits a vanishing SHG signal and a stiffening of the layer-breathing (LB) vibrational mode, in contrast to undoped samples with strong SHG and a softer LB mode. Aberration corrected scanning transmission electron microscopy (AC-STEM) demonstrates the spatial distribution of W concentration and associated structural changes. These findings highlight W-doping as an effective strategy for inducing phase transitions in 2L TMDs, opening new possibilities for engineered heterostructures, phase-controlled device applications or as a source of single photon emitters.
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All authors Ana Senkić, Rachael Keneipp, Petra Ivatović, Namrata Pradeep, Vincent Meunier, Marko Kralj, Marija Drndić, Nataša Vujičić

Materials Science

Landau-Lifshitz-Bloch simulations of the magnetocaloric effect in continuous ferromagnetic-paramagnetic transitions

Luis M. Moreno-Ramírez, Luis Sánchez-Tejerina, Óscar Alejos et al. (+2 more)

The usefulness of modeling magnetocaloric materials expands from the understanding of their behavior to the prediction of new materials, playing a fundamental role in the optimization of their performance. In contrast with other areas of magnetic materials research, micromagnetic simulations of magnetocaloric materials are scarce due to the difficulty of modeling the material in the vicinity of the transition. To solve this limitation, we propose the use of micromagnetic simulations based on the Landau-Lifshitz-Bloch equation to study the magnetocaloric effect of a ferromagnetic material around its Curie transition. Following our proposed methodology, we obtain reliable isothermal entropy change curves for both monocrystalline and polycrystalline configurations, where we consider different anisotropic contributions. The robustness of the method was evaluated, yielding results that agreed with previous experimental and theoretical observations. Our study shows that micromagnetic simulations are a powerful tool for analyzing magnetocaloric materials with complex microstructures.
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All authors Luis M. Moreno-Ramírez, Luis Sánchez-Tejerina, Óscar Alejos, Victorino Franco, Víctor Raposo

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

Strained hyperbolic Dirac fermions: Zero modes, flat bands, and competing orders

Christopher A. Leong and Bitan Roy

Starting from the nearest-neighbor tight-binding model on {10,3} and {14,3} hyperbolic lattices that, for a uniform hopping amplitude, gives rise to emergent Dirac fermions on a curved space with a constant negative curvature, displaying a vanishing density of states, we propose spatially modulated hopping pattern therein that preserve the underlying 5- and 7-fold rotational symmetries, respectively, and effectively couples fermions to time-reversal symmetric axial magnetic fields. Such strain-induced axial fields produce a flat band near zero-energy, triggering nucleation of a charge density-wave, featuring a staggered pattern of fermionic density between two sublattices, and the Haldane phase fostering intra-sublattice circulating currents with a net zero magnetic flux for weak nearest- and next-nearest-neighbor Coulomb repulsions, respectively. Sufficiently weak on-site Hubbard repulsion destabilizes such flat bands toward the formation of a magnetic phase that simultaneously supports antiferromagnetic and ferromagnetic orders in the whole system. While the magnetization in the bulk and boundary cancel each other, the Neél order is of the same sign everywhere, thereby yielding a global antiferromagnet. Throughout, we draw parallels between these findings and the well-studied qualitatively similar results on a 3-fold rotational symmetric strained honeycomb lattice, thereby unifying the phenomenon of axial magnetic catalysis for Dirac fermions, encompassing the ones living on the Euclidean plane. Finally, we show that with a specific class of non-Hermiticity, manifesting via an imbalance in the hopping amplitudes between two sublattices in the opposite directions, magnitudes of all these orders can be boosted substantially when all the eigenvalues in the noninteracting systems are real, staging a non-Hermitian amplification of axial magnetic catalysis.
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Materials Science

Revealing Phonon Bridge Effect for Amorphous vs Crystalline Metal-Silicide Layers at Si/Ti Interfaces by a Machine Learning Potential

Mayur Singh, Lokanath Patra, Chengyang Zhang et al. (+4 more)

Metal-semiconductor interfaces play a central role in micro and nano-electronic devices as heat dissipation or temperature drop across these interfaces can significantly affect device performance. Prediction of accurate thermal boundary resistance (TBR) across these interfaces, considering realistic structures and their correlation with underlying thermal transport, remains challenging. In this work we develop a unified Neuroevolution Potential (NEP) for the Si-Ti system that accurately reproduces energies, forces, and phonon properties of bulk Si, Ti, and TiSi2 and extends naturally to interfacial environments to analyze interfacial transport. An important development over current machine-learned interatomic potentials is the capability to model complex structures at metal-semiconductor interfaces, as the NEP enables large scale non-equilibrium molecular dynamics simulations of epitaxial Si/Ti interfaces to elucidate the effect of amorphous or crystalline silicide interfacial layers. Simulated TBRs show excellent agreement with our time-domain thermoreflectance (TDTR) measurements. Spectral analyses reveal that amorphous TiSi2 interfacial layer helps in efficient interfacial transport when the thickness is less than 1.5 nm compared to the crystalline TiSi2 layer, but this trend reverses when the interfacial layer thickness increases beyond 1.5 nm. Comparison of TBRs at Si/TiSi2 interface for different crystalline phases of TiSi2 establishes that C54 phase has reduced TBR compared to C49 phase, which is correlated with the difference in their phonon density of states (PDOS) overlap with Si. These results provide atomistic insight into the role of crystalline versus amorphous silicides in interfacial heat transport and demonstrate a transferable machine-learned potential for studying heat dissipation in advanced semiconductor devices.
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All authors Mayur Singh, Lokanath Patra, Chengyang Zhang, Greg MacDougall, Suman Datta, David Cahill, Satish Kumar

Materials Science

Li-P-S Electrolyte Materials as a Benchmark for Machine-Learned Interatomic Potentials

Natascia L. Fragapane and Volker L. Deringer

With the growing availability of machine-learned interatomic potential (MLIP) models for materials simulations, there is an increasing demand for robust, automated, and chemically insightful benchmarking methodologies. In response, we here introduce LiPS-25, a curated benchmark dataset for a canonical series of solid-state electrolyte materials from the Li2S-P2S5 pseudo-binary compositional line, including crystalline and amorphous configurations. Together with the dataset, we present a suite of performance tests that range from conventional numerical error metrics to physically motivated evaluation tasks. With a focus on graph-based MLIP architectures, we run numerical experiments that assess (i) the effect of hyperparameters and (ii) the fine-tuning behavior of selected pre-trained ("foundational") MLIP models. Beyond the Li-P-S solid-state electrolytes, we expect that such benchmarks and their code implementations can be readily adapted to other material systems.
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Materials Science

Leveraging the Bi$_2$O$_3$–Fe$_2$O$_3$ Phase Diagram to Tailor BiFeO$_3$ Structure and Dielectric Response

Subir Majumder, Paul Ben Ishai and Gilad Orr

Advancing the functional performance of bismuth ferrite (BiFeO$_3$) requires precise control over phase stability and microstructure, challenges often complicated by secondary phase formation within the Bi$_2$O$_3$-Fe$_2$O$_3$ system. In this work, we employ a phase-diagram-guided synthesis strategy to clarify the processing-structure-property relationships governing BiFeO$_3$ ceramics. Based on previous reports and our experimental observations, a refined Bi$_2$O$_3$-Fe$_2$O$_3$ phase diagram was constructed identifing the onset of liquid-phase formation near 835$^\circ$C in Bi-rich compositions. Solid-state synthesis using non-stoichiometric precursor ratios (55$\colon$45 and 70$\colon$30 Bi$_2$O$_3$ $\colon$ Fe$_2$O$_3$) reveals that the 55$\colon$45 composition sintered at 775$^\circ$C favours phase-pure rhombohedral $R3c$ BiFeO$_3$ with suppressed sillenite- and mullite-type impurities, lattice contraction, and improved grain uniformity. These structural refinements result in near-Debye dielectric relaxation and a four-orders-of-magnitude enhancement in electrical conductivity relative to lower-temperature or Bi-rich conditions. This work demonstrates the effectiveness of phase-diagram control as a scalable route to tuning dielectric response in BFO-based multiferroics and provides a foundation for processing optimization in complex oxide ceramics.
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Materials Science · Cross-listed from physics.ed-ph

Efficient and affordable thermoelectric measurement setup using Arduino and LabVIEW for education and research

Alex J. Oh, Colby J. Stoddard, Craig Queenan et al. (+1 more)

Thermoelectric materials can convert thermal energy into electricity, making them promising candidates for harvesting waste heat, an increasingly important challenge in the energy-intensive modern world. The search for improved thermoelectric materials is therefore an active area of research in materials physics. Despite their fundamental and practical significance, thermoelectric properties - such as the Seebeck coefficient and power factor - are rarely explored in student labs due to the complexity in measurement schemes and requirement for sophisticated equipment. In this work, we present a user-friendly, low-cost and efficient thermoelectric measurement system built with Arduino and LabVIEW, which can simultaneously measure Seebeck coefficients and power factors as a function of temperature. This was made possible by improving the resolution of Arduino over ~1000 times with amplifiers and noise reduction schemes. With a total cost of only ~$100 and simple measurement protocols, this setup is well suited not only for student labs but also for efficient thermoelectric research.
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All authors Alex J. Oh, Colby J. Stoddard, Craig Queenan, Seongshik Oh

Materials Science

The Plastic Origin of van der Waals material GaGeTe

Qiao Wang and Ping-An Hu

Plastic inorganic semiconductors are promising candidates for high performance stable flexible electronics. Germanium based chalcogenide materials are well known for excellent semiconducting properties, specifically superior carrier mobility. However, these materials typically exhibit inherent brittleness, which in germanium tellurides originates from the intrinsic half bond nature of the metavalent Ge Te bond. Here, we report an ultra high plasticity germanium based chalcogenide of GaGeTe. Bulk GaGeTe can sustain a large engineering strain up to 7.5% without fracture. Through a comprehensive multi scale investigation ranging from macroscopic characterization to atomic resolution scanning transmission electron microscopy, we reveal that the exceptional plasticity is due to a synergistic effect of interlayer gliding and intralayer lattice distortion. DFT calculations further elucidate the chemical origin. The existence of Ga atoms avoids the formation of brittle metavalent Ge Te bonds. Instead, a robust honeycomb lattice formed by strong Ga Te, Ge Ge, and Ga Ge bonds preserves high bond strength under large tensile strains in simulations, thereby underpinning the macroscopic plastic behavior. This systematic study on the origin of the plasticity in GaGeTe introduces bond engineering as a potential approach for constructing plastic inorganic semiconductors.
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Materials Science

Linear magneto-birefringence as a probe of altermagnetism

V. Sunko and J. Orenstein

Altermagnets are a class of collinear magnets that exhibit non-relativistic spin splitting (NRSS) of electronic bands in the absence of net magnetization. Their potential to generate large spin polarization without spin-orbit coupling has created strong interest in probes that access the underlying order parameter directly. In this Perspective, we show that linear magneto-birefringence (LMB) provides a natural and broadly applicable route to detecting altermagnetic order. Building on the correspondence between the momentum-space structure of NRSS and the ferroic ordering of magnetic multipoles in real space, we demonstrate how $d$-wave and $g$-wave NRSS textures yield distinct LMB responses. We present a symmetry-based framework that identifies the optical geometries and field configurations required to isolate specific multipole components, enabling domain imaging and providing benchmarks for theoretical models of LMB.
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Materials Science

Quantifying Phase Transformations in Alloying Anodes via In-Situ Liquid Cell Hard X-ray Spectroscopy and Cryogenic Microscopy

Neil Mulcahy, Syeda Ramin Jannat, Yaqi Li et al. (+7 more)

Understanding electrochemical phenomena at complex liquid solid interfaces requires linking real time structural dynamics with atomic scale interfacial chemistry. Here, we integrate operando synchrotron X-ray fluorescence and diffraction with high resolution cryogenic electron and ion multi model microscopy to provide a mechanistic understanding of Pt based alloying anodes across length scales. We directly observe the initial lithiation driven formation of Li2Pt and its evolution to a stable LiPt intermetallic phase during extended cycling via a solid solution type reaction mechanism. Simultaneously, the solid electrolyte interphase transitions from an unstable carbonate rich to a stable LiF dominated composition, confirmed by cryogenic scanning transmission electron microscopy and electron energy loss spectroscopy. Crucially, cryogenic atom probe tomography reveals spatially distinct compositional regimes within the alloy anode, including lithium flux limited, heterogeneous interfacial zone and a diffusion controlled, homogeneous LiPt alloy bulk. This nanoscale compositional gradient rationalises the emergent solid solution reaction mechanism and highlights how kinetic limitations and interface dynamics govern alloy formation and electrochemical stability. Our findings demonstrate a broadly applicable correlative framework bridging operando structural dynamics with near atomic resolution interfacial chemistry, advancing the rational design of durable alloy electrodes for next generation energy storage.
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All authors Neil Mulcahy, Syeda Ramin Jannat, Yaqi Li, Tigran Simonian, Mariana Palos, James O. Douglas, Jessica M. Walker, Baptiste Gault, Mary P. Ryan, Michele Shelly Conroy

Materials Science · Cross-listed from cs.DB

From Patents to Dataset: Scraping for Oxide Glass Compositions and Properties

Gustavo Laranja Thomaello, Thomaz Yeiden Busnardo Aguena, Eric Trevelato Costa et al. (+4 more)

In this work, we present web scraping techniques to extract in- formation from patent tables, clean and structure them for future use in predictive machine learning models to develop new glasses. We extracted compositions and three properties relevant to the development of new glasses and structured them into a database to be used together with information from other available datasets. We also analyzed the consistency of the information obtained and what it adds to the existing databases. The extracted liquidus temperatures comprise 5,696 compositions; the second subset includes 4,298 refractive indexes and, finally, 1,771 compositions with Abbe numbers. The extraction performed here increases the available information by approximately 10.4% for liquidus temperature, 6.6% for refractive index, and 4.9% for Abbe number. The impact extends beyond quantity: the newly extracted data introduce compositions with property values that are more diverse than those in existing databases, thereby expanding the accessible compositional and property space for glass modeling applications. We emphasize that the compositions of the new database contain relatively more titanium, magnesium, zirconium, niobium, iron, tin, and yttrium oxides than those of the existing bases.
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All authors Gustavo Laranja Thomaello, Thomaz Yeiden Busnardo Aguena, Eric Trevelato Costa, Rafael Baságlia Rosante, Thiago Rodrigo Ramos, Daiane Aparecida Zuanetti, Edgar Dutra Zanotto

Materials Science

Quasiparticle states of hexagonal BN: A van der Waals density functional study

Raul Quintero-Monsebaiz and Per Hyldgaard

We compute and track the impact of truly nonlocal-correlation effects on the quasi-particle (QP) band-structure of hexagonal boron-nitride (h-BN) systems. To that end, we start with the consistent-exchange vdW-DF-cx version [PRB 89, 035412 (2014)] of the van der Waals density functional (vdW-DF) method [JPCM 39, 390001 (2020)] for exchange-correlation (XC) functional design and enforce piece-wise linearity in the energy changes with partial charging, using the Koopmans-integer (KI) DFT framework [JCTC 19, 7079 (2023)]. Our approach and results (denoted KI-CX) extends present-standard use of KI DFT (denoted KI-PBE as it is based on the semilocal PBE [PRL 77, 3865 (1996)] XC functional) to capture, for example, the impact of the interlayer coupling on the QPs. We contrast KI-CX and KI-PBE results for the QP band-structure and compare with both $GW$ calculations and experimental observations of the (direct and indirect) QP gaps. We find that KI-CX brings improvements in the h-BN QP energy description and generally agrees with $GW$ studies.
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