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Physics Condensed Matter Materials Science

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Tuesday 3 March

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

Fingerprint of $T_c$ advancement in Li-doped Bi-2223 superconductors prepared by cationic molecular mixing within Pechini sol-gel synthesis

N.K. Man, Huu T. Do, Nguyen V. Tu et al. (+1 more)

Trilayered Bi-2223 superconductor features the highest critical temperature $T_c$ among the bismuth-based cuprate collection and symbolizes an ideal prototype for studying intrinsic superconducting properties. The previous solid-state reaction method substantiated the growth of the high-quality Bi-2223 compounds but was accompanied by excessively laborious time and effort in terms of multiple grinding, pressing, as well as calcining stages, %causing risk of constituent loss, so finding a less tedious synthesis path is imperative. Here, we present an advanced sol-gel synthesis for assembling the multicomponent complexity of Bi1.4Pb0.6Sr2Ca2(Cu1-xLix)3O10 superconductors (Li-doped Bi-2223), with $x$ = 0.0–0.20, utilizing metallic cationic molecular mixing within the chemical Pechini polyesterization route followed by single-step pyrolysis and sintering stages. Although monovalent cations such as Li$^+$ pose limitations in establishing a perplex crosslinking network or chelating mechanism in the Pechini method, they represent a unique probe to elucidate the major chemical process during polymerization. We observe that a 5 molar~% Li-doped sample pronounces the highest $T_c$ = 111.4 K among the series of samples, as confirmed by both ac susceptibility and dc resistivity measurements, and is equivalent to the value obtained by our preceding solid state fabrication. In addition, we showcase a rare observation of layer-by-layer crystalline phase growth under microstructure probe. Through analyzing the reliable ac susceptibility data at low magnetic fields in a wide range of frequency, we provide the quantum flux formation and flux creep mechanism by Anderson-Müller's model and Cole-Cole plot.
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All authors N.K. Man, Huu T. Do, Nguyen V. Tu, Nguyen V. Quy

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

All-Electrostatic Valley Filtering by Barrier Rotation in Tilted Dirac/Weyl Semimetals

Can Yesilyurt

Charge carriers in Dirac/Weyl semimetals with tilted anisotropic energy dispersion exhibit valley-dependent refraction and reflection at electrostatic barrier interfaces. Here, we show that an angled barrier interface provides a purely electrostatic route to valley filtering, producing finite valley-polarized conductance. We develop a generalized transfer-matrix formalism for the tilted, anisotropic Dirac Hamiltonian, extend it to treat electrostatic barriers at arbitrary angles, and calculate the transmission in the rotated-barrier frame. We also present simulated valley-resolved trajectories in a finite device geometry, demonstrating that one valley is selectively transmitted, while the other is predominantly reflected by the angled barrier, without invoking real or pseudomagnetic fields.
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Materials Science · Cross-listed from physics.flu-dyn

Phase-field investigation of non-isothermal solidification coupled with melt flow dynamics

Timileyin David Oyedeji, Aaron Brunk, Yangyiwei Yang et al. (+3 more)

Solidification, coupled with melt flow, plays a critical role in determining the microstructure and properties of materials in several manufacturing processes. Phase-field models coupled with the Navier-Stokes equations are widely used to model and simulate these dynamics. However, most existing models neglect essential thermodynamic couplings, particularly the capillary (Korteweg) stress in the momentum equation. This stress, which arises from the coupling between the phase field and the melt flow, accounts for thermal capillary effects during non-isothermal solidification. Neglecting it leads to models inconsistent with non-equilibrium thermodynamics and incapable of capturing capillarity-driven melt flow. In this work, we present a thermodynamically consistent, non-isothermal phase-field model for solidification coupled with melt flow, incorporating cross-coupling terms and explicitly including the Korteweg stress in the momentum equation. Model validation is performed for solidification-only cases, followed by simulations of dendritic growth under melt flow. The results show that thermal capillary effects induce flow near the interface, influencing dendrite tip velocity and morphology. Simulations under forced convection further demonstrate asymmetric dendrite growth due to the imposed flow field. Additionally, we numerically demonstrate the influence of viscosity interpolation schemes on enforcing the no-slip boundary condition in phase-field models with melt flow.
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All authors Timileyin David Oyedeji, Aaron Brunk, Yangyiwei Yang, Herbert Egger, Holger Marschall, Bai-Xiang Xu

Materials Science

Intrinsic Electric Field Driven High Sensitive Photodetection in Alloy TMDC MoSSe

Chumki Nayak, Suvadip Masanta, Shubhadip Moulick et al. (+7 more)

Alloying offers an effective way to improve the functionality of transition metal dichalcogenides (TMDCs) in both fundamental research and optoelectronic applications, as it allows for engineering their electronic and optical properties. This study investigates the optoelectronic properties of CVD-synthesized alloy MoSSe, which exhibits an inherent out-of-plane dipole moment, arising from asymmetry in S and Se atoms on either side of the Mo layer, as confirmed by piezoelectric force microscopy, polarization-resolved second harmonic generation studies and theoretical first-principles calculations. Time-resolved photoluminescence measurements reveal an extended exciton radiative recombination lifetime in MoSSe, attributed to electron-hole wavefunction separation by the dipole moment, which improves photodetection by facilitating enhanced electron-hole separation before recombination. The device demonstrates significant responsivity over broad spectral range. By employing the photogating effect, the device response can be switched from slow to fast modes. These findings are further supported by illumination intensity-dependent photoluminescence and Raman measurements, underscoring the potential of polar TMDCs in future optoelectronic devices.
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All authors Chumki Nayak, Suvadip Masanta, Shubhadip Moulick, Manotosh Pramanik, Atanu Kabiraj, Satchidananda Rath, Sukanya Ghosh, Atindra Nath Pal, Bipul Pal, Achintya Singha

Materials Science

Dual-wavelength control of charge accumulation in rubrene microcrystals with anisotropic conductivity

Moha Naeimi, Ingo Barke and Sylvia Speller

Previously, a novel type of rubrene microcrystals was reported, forming two distinct sectors – diamond- and triangular-shaped – that exhibit pronounced contrasts in photoluminescence (PL) spectra and exciton dynamics. In the present work, their internal electronic structure is investigated using time-of-flight photoemission electron spectroscopy (TOF-PES), revealing that the two sector's different charging characteristics arising from anisotropic conductivities. Upon photoemission via a one-photon photoemission (1PPE) process excited by 6.2 eV (200 nm) photons, the diamond-shaped sectors accumulate significant charge, whereas the triangular sectors remain essentially uncharged. The charge accumulation in the diamond sectors can be neutralized by additional sub-threshold illumination, which generates charge carriers through internal photoeffect. The dynamics and energetics of the observed band shifting is described quantitatively by a model combining surface capacitance and drift-diffusion. These crystalline systems enable the creation of built-in charge landscapes that can be manipulated both spatially and temporally.
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Materials Science

Thermodynamic and transport properties of high-quality single crystals of the altermagnet CrSb

Shubhankar Paul, Atsutoshi Ikeda, Giordano Mattoni et al. (+2 more)

Altermagnetism (AM) is an emerging magnetic order unifying essential characteristics of ferromagnetic and antiferromagnetic states. The CrSb has attracted significant interest owing to its large altermagnetic spin-splitting energy. In this paper, we present the growth details of high-quality single crystals of CrSb using the self-flux method and investigate their physical properties. We obtained large (001) oriented hexagonal crystals, up to 2~$\times$~2.5~$\times$~1~mm$^3$ in size with residual resistivity ratio $\sim$ 11. A pronounced positive magnetoresistance of up to 80% is observed at 3.5 K. Most strikingly, the room temperature specific heat value exceeds the Dulong-Petit limit, being attributed to a broad magnon contribution from the altermagnetic order of CrSb. The specific heat fit reveals a magnon energy gap $\sim$ 16 $\pm$ 1 meV. Further, ac susceptibility measurements demonstrate the absence of superconductivity down to 0.1 K. These findings underscore CrSb as a viable altermagnet for room temperature magnonic and spintronic applications.
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All authors Shubhankar Paul, Atsutoshi Ikeda, Giordano Mattoni, Shingo Yonezawa, Chanchal Sow

Materials Science

HERB: a unified framework for the evaluation of Hydrogen Embrittlement mechanisms driven by the Rice-Beltz concept

Kai Zhao

The multiscale picture of hydrogen embrittlement (HE) mechanisms has been under controversy for a long time. Here I report a thermomechanically-consistent HERB framework driven by the Rice-Beltz concept meanwhile incorporating the hydrogen transport near the crack-tip and void growth within the plastic zone. Triggered solely by dislocation emission from the crack tip, the HERB theory unifies multiple HE mechanisms, such as HEDE, HELP, NVC and HESIV within a single framework. Specifically, a generalized model for predicting the hydrogen-informed dislocation emission is established by incorporating the Rice-Beltz model with the transition state theory. Accounting for the dynamic variation of the trapping energy of spherical inclusions, hydrogen transport is modeled in the dislocation free zone in front of the crack tip. Semi-analytical expressions of the density of geometrically necessary dislocations are obtained by incorporating the Hutchinson-Rice-Rosengren solution with the conventional theory of mechanism-based strain gradient plasticity model. By exploring the feasibility of stochastic analysis, the present theory demonstrates that the hydrogen-informed void dynamics is dominated by the dislocation density between the limits of Lifshitz-Allen-Cahn and Lifshitz-Slyozov-Wagner laws, even though individual events remain unpredictable. These insights fundamentally reshape hydrogen/dislocation interactions across multiple scales, including the core width, short-range and long-range levels.
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Materials Science

Unlocking the Potential of Ni2+ and Ni2+-Cr3+ Synergy for Bifunctional Pressure and Temperature Optical Sensing

M. Szymczak and L. Marciniak

Reliable simultaneous optical sensing of pressure and temperature under extreme and dynamically fluctuating conditions remains a major challenge due to intrinsic cross-sensitivity between these two thermodynamic parameters. Multimodal systems enabling simultaneous yet fully decoupled monitoring of both parameters are therefore highly sought after. Here, we demonstrate that the synergistic interplay between Cr3+ and Ni2+ luminescence provides a platform for bifunctional temperature-pressure sensing with independent readout channels. Two complementary detection strategies were systematically investigated: ratiometric approach based on luminescence intensity ratio and kinetic approaches exploiting emission decay dynamics. Among the kinetic strategies, a time-gated dual-ion lifetime concept - introduced here for the first time for luminescence manometry - enables pressure readout with record-high relative sensitivity reaching 148.33% GPa-1 while exhibiting complete immunity to temperature fluctuations. Conversely, temperature sensing is achieved via time-gated single-ion Ni2+ luminescence, ensuring high thermometric performance with negligible pressure-induced interference. Importantly, this work study, for the first time, the potential of Ni2+ ions for application in near-infrared luminescence manometry. The unique combination of ultrahigh sensitivity, multimodal readout capability, and possibility of near-infrared operation positions the Ni2+-Cr3+ luminescence synergy as a benchmark platform for next-generation bifunctional optical sensors, enabling reliable operation in complex, dynamically evolving, and optically demanding environments.
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Materials Science · Cross-listed from physics.ins-det

Capacitively Coupled GaAs p-i-n/Substrate Photodetector with Ohmic Contacts on Lightly Doped n-GaAs for Hard X-Ray Imaging

V.G. Harutyunyan, S.D. Zilio, M. Colja et al. (+5 more)

In this work, we present a capacitively coupled GaAs p +-i-n/substrate photodetector (CC-GaAs PIN/S PD), which also represents a preliminary step toward 3D detection (x, y, time) of high-energy X-ray pulses. Although the final 3D detector will be based on a separate absorption and multiplication avalanche photodiode (SAM APD) design, the present device exhibits characteristics that offer valuable insights into the performance expected once a multiplication layer is incorporated into the final device. In particular, we present a fabrication strategy that employs multi-step annealing in the low-temperature range of 280 330C to achieve Cr/Au ohmic contacts on lightly doped n-GaAs, which is also required for the photodetector architecture. Simultaneously, the same contact preparation process was applied to p + GaAs. Furthermore, the fabricated CC-GaAs PIN/S PD includes an additional contact designed to reduce leakage current by applying the same bias as that of the anode. Measurements performed using an 80 MHz laser demonstrated the photodetector's ability to detect pulses corresponding to 10^6 electrons per pulse.
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All authors V.G. Harutyunyan, S.D. Zilio, M. Colja, M. Cautero, G. Cautero, L. Sbuelz, D. Curcio, G. Biasiol

Materials Science

Nanocrystalline structure and strain in magnesium under extreme dynamic compression

Daria A. Komkova, Alexey Yu. Volkov and Evgeny F. Talantsev

The study of materials behavior under extreme conditions is fundamental to science and modern technology. Fast ramp compression is a unique method for exploring materials behavior and phase transformations under extreme conditions. One unexplored feature of this method is the nanoscale structure of the material under dynamic compression. This leaves a gap in understanding the details of phase transformations under fast ramp compression. Here, we made a first step in the exploration by applying the Williamson-Hall (WH) analysis to X-ray diffraction data (XRD) measured in magnesium subjected to fast ramp compression at four pressures. We found that at $P = 309 GPa$ magnesium in bcc-like phase has an average crystalline size $D = (2.2 \pm 0.7) nm$ and microstrain $\varepsilon = (-0.011 \pm 0.007)$. At $P = 409 GPa$, magnesium demonstrates $D = (4.5 \pm 3) nm$ with $\varepsilon = (-0.003 \pm 0.007)$. At $P = 563 GPa$, Fmmm magnesium has crystalline size $D = (2.6 \pm 0.5) nm$ with microstrain $\varepsilon = (-0.004 \pm 0.004)$. At $P = 959 GPa$, we revealed that sh-magnesium exhibits average size of $D > 12 nm$ and relatively high value of microstrain $\varepsilon = (0.011 \pm 0.002)$. In the result, we report the first microstructural evolution insights of magnesium under fast ramp compression.
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Materials Science

Decoupling Intrinsic Molecular Efficacy from Platform Effects: An Interpretable Machine Learning Framework for Unbiased Perovskite Passivator Discovery

Jing Zhang, Ziyuan Li, Shan Gao et al. (+3 more)

Rational design of interface passivators for perovskite solar cells is hindered by the entanglement of intrinsic molecular efficacy with extrinsic platform-dependent performance - a confounding factor that obscures true chemical advances. Here, we present a generalizable, interpretable machine learning framework that decouples these effects via an asymptotic saturation model, enabling unbiased discovery of molecules with genuine intrinsic gains. Trained on a curated dataset of 240 experimental entries, our model identifies hydrogen bond acceptor strength and electrostatic potential difference as key descriptors. Guided by these insights, we screened >121 million PubChem compounds using a hierarchical strategy integrating diversity clustering and uncertainty quantification. Five dual-functional candidates (e.g., TDZ-S, TZC-F) are identified, exhibiting superior predicted efficacy (surpassing experimental benchmarks) and high confidence. First-principles calculations confirm strong chemisorption (Eads<-1.7 eV), net electron donation, and optimized interfacial energetics. Crucially, our closed-loop "data-interpretation-screening-verification" pipeline establishes a transferable paradigm for rational materials design, extendable to other optoelectronic interfaces beyond perovskites.
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All authors Jing Zhang, Ziyuan Li, Shan Gao, Zhen Zhu, Jing Wang, Xiangmei Duan

Materials Science

One-Dimensional Metallic Polymeric Nitrogen

Kewei Ding, Junyi Miao, Ying Liu et al. (+7 more)

The pressure-induced metallic states of light elements attract significant attention, because of potential applications as high-temperature superconductor and high-energy-density material, especially for hydrogen and nitrogen1-10. Several semiconducting polymeric nitrogen phases with three- or two-dimensional sp3-bonded networks were synthesized6-10, but its metallic form remains unobserved. Here, we report the synthesis of a metallic polymeric nitrogen with one-dimensional feature (1D-PN) at 130-140 GPa and above 3000 K. Synchrotron XRD and Raman spectroscopy, supported by DFT calculations, reveal that it adopts an infinite arm-chair like chain with sp2-hybridized pi-bonds. Simulations predict a superconducting transition at 21.19 K under 113 GPa, higher than that reported in high-pressure experiments for non-metallic elements. At ambient pressure, this phase acquiring an energy density of as high as 8.78 kJ/g is not only kinetically stable but also thermodynamically more stable than cubic gauche nitrogen. This multifunctional property profile positions 1D-PN as a disruptive candidate for both electronic and energetic applications.
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All authors Kewei Ding, Junyi Miao, Ying Liu, Anxin Yu, Cheng Lu, Wenrui Zhang, Yanchun Li, Haipeng Su, Zhongxue Ge, Xianlong Wang

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

Metal-insulator transition and thermal scales in $d$-wave altermagnet

Santhosh Kannan, Jainam Savla and Madhuparna Karmakar

We present the first finite-temperature study of a strongly correlated $d$-wave altermagnet across the Mott insulator-metal transition using a non-perturbative numerical approach. We map out the thermal phase diagram and provide quantitative estimates of the transition scales in an interacting altermagnet. We show that altermagnetism-induced geometric frustration stabilizes a finite-temperature correlated magnetic metal and enhances the magnetic transition scale across regimes of interaction. These results establish the finite-temperature landscape of correlated altermagnets and clarify the role of strong electronic interactions in this phase.
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Materials Science

Manipulating Charge Distribution in Moiré Superlattices by Light

Ruiping Guo, Haowei Chen, Wenhui Duan et al. (+2 more)

In ordinary solids, nonlinear optical responses are typically studied in terms of unit-cell averages due to the angström-scale lattice constants. In contrast, moiré superlattices, characterized by a large length scale, unlock an often-overlooked degree of freedom: intra-supercell spatial variations of local observables. Here, we formulate the second-order direct current (DC) charge response in a spatially resolved manner, showing that even uniform optical illumination can drive a static, spatially non-uniform charge redistribution within a supercell. This effect is ubiquitous and cannot be forbidden by any crystalline symmetries. Furthermore, we identify a dominant contribution arising from diverging analytical response coefficients, which leads to linear-in-time growth of the redistribution in the absence of relaxation. This growth is driven by the convergence or divergence of local DC photocurrents. Applying our theory to twisted bilayer MoTe$_2$, we demonstrate strong, highly tunable charge modulation controlled by light intensity and frequency, opening a route to in situ, all-optical control of moiré-periodic electrostatic potentials. Our work underscores the importance of intra-cell degrees of freedom, which enable a qualitatively richer class of nonlinear optical responses in moiré superlattices.
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All authors Ruiping Guo, Haowei Chen, Wenhui Duan, Yong Xu, Chong Wang

Materials Science

Unusual magnetic and charge transport properties in In-Substituted Half-Metallic Kagome Ferromagnet Co3Sn2S2

Karan Singh, Subhadip Pradhan, K. Mukherjee et al. (+3 more)

The kagome ferromagnet Co3Sn2S2 has been studied extensively for its unusual topology of electronic bands, origin of ferromagnetism and strong coupling between magnetism and charge transport. To understand the role of nonmagnetic element Sn, we have investigated magnetic, transport, and electronic structure of the isostructural compound Co3SnInS2, where all the Sn (divalent) atoms in the Co3Sn Kagome layer are replaced by In (trivalent) atoms. We find long-range ferromagnetic order is nearly quenched in Co3SnInS2. The system exhibits predominantly antiferromagnetic correlations with only a very small net magnetic moment and turns ferromagnetic in the presence of an external magnetic field. Transport measurements show a semiconducting behaviour at low temperatures. Magnetoresistance shows a nonmonotonic field dependence, changing from negative to positive with increasing magnetic field. An anomalous Hall effect is observed, but its magnitude is significantly reduced compared to Co3Sn2S2 where the topological character of the Fermi surface plays a dominant role. These results indicate that substitution of Sn by In in the Co3Sn plane not only suppresses the topological electronic features of the transport electrons but drives the system away from the ferromagnetic Half-metallicity to an almost nonmagnetic semiconducting state with unusual paramagnetic response. Electronic structure calculations are consistent with some of these observations.
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All authors Karan Singh, Subhadip Pradhan, K. Mukherjee, Ashis Kumar Nandy, Subhendra D. Mahanti, D. Topwal

Materials Science

Fragmenting Diffusion Pathways Confers Extraordinary Radiation Resistance in Refractory Multicomponent Alloys

Bin Xing, Bijun Xie, Wanjuan Zou et al. (+11 more)

The accumulation and growth of vacancy clusters under irradiation is a pivotal degradation mode for structural materials in extreme environments. Even tungsten undergoes rapid defect coarsening compromising its integrity. Here we show a tungsten multicomponent alloy that effectively fragments the vacancy diffusion network, kinetically trapping defects within localized domains. This effect originates from a broad spectrum of migration barriers and substantial vacancy-jump heterogeneity, which drives the interconnectivity of diffusion paths below the percolation threshold. Starving clusters of the necessary vacancy supply, irradiation experiments and atomic-scale defect characterizations confirm negligible defect growth as radiation doses increase by four orders of magnitude. These results provide a fundamental paradigm for percolation-engineered kinetics, offering a predictive pathway for tailoring defect diffusion and discovering inherently radiation-tolerant materials.
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All authors Bin Xing, Bijun Xie, Wanjuan Zou, Eric Lang, Evgeniy Boltynjuk, Hangman Chen, Michael P Short, George Tynan, Timothy J Rupert, Jason Trelewicz, Horst Hahn, Blas P Uberuaga, Khalid Hattar, Penghui Cao

Materials Science

A hierarchy of thermodynamics learning frameworks for inelastic constitutive modeling

Reese E. Jones and Jan N. Fuhg

Recent advances in physics-augmented neural networks have enabled thermodynamically consistent data-driven constitutive modeling of complex inelastic materials. Most existing approaches, however, implicitly adopt a specific thermodynamic framework and embed structural assumptions such as normality, dual dissipation potentials, or other structure from manually constructed models directly into the learning architecture. Consequently, differences in predictive performance may arise not only from data or network design, but also from the underlying theoretical assumptions. In this work, we present a unified comparison of several thermodynamically consistent inelastic modeling frameworks from a machine learning perspective. We consider internal-variable formulations with dissipation potential, generalized standard materials, and metriplectic structures, and we analyze their structural assumptions, admissible dependencies, convexity requirements, and implications for dissipation and evolution. Each framework is implemented within a common neural potential architecture based on invariant representations and neural ordinary differential equations. This unified setting ensures that performance differences can be attributed to thermodynamic structure rather than architectural variation. The models are trained and evaluated on three representative inelastic datasets generated from high-fidelity representative volume element simulations: an elastoplastic alloy, a viscoelastic composite, and a rate-dependent crystal plasticity polycrystal. By isolating the role of thermodynamic structure, we assess how restrictions such as duality, normality, operator-based evolution, and convexity influence learnability, expressiveness, stability, and generalization.
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Materials Science

First-principles insights into the atomic structure of carbon-nitrogen-oxygen complex color centers in silicon

Péter Udvarhelyi

Spin-active color centers are the basis of solid-state defect systems utilized in quantum technologies. Although silicon is an emerging host material for quantum defects, there is an urgent need to characterize color centers with a non-zero electron-spin ground state in this platform, in addition to the prominent T-center. In this work, we carry out first-principles calculations to identify the possible atomic structures originating the experimentally observed N-line series in silicon. We propose that the core structure of the N1 center consists of a neighboring carbon and nitrogen interstitial pair. Furthermore, we predict that more complex defects involving self-interstitial and interstitial oxygen atoms are feasible candidates for the further lines in the series. As all of these color centers are isoelectronic to the T-center, they provide a family of alternative spin qubits with emission near the low-energy telecommunication bands.
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Materials Science

Exploring stable long-lifetime plasmon excitations in the Lieb lattice

Andrii Iurov, Liubov Zhemchuzhna, Godfrey Gumbs et al. (+1 more)

The subject of the present paper is a thorough numerical investigation of plasmon expectations, their dispersions and damping within a Lieb lattice. The Lieb lattice is known for its unique low-energy band structure which consists of a bandgap as well as a flat band intersecting the conduction band at its lowest point. In contrast to previously studied dice lattice, the location of the current flat band exhibits reduced and broken symmetries, which give rise to interesting electronic and optical properties of this new material. In this work, we have investigated the conditions for observing a well-defined and stable plasmon mode within a wide frequency range. Specifically, we have considered a free-standing layer with various doping levels, as well as different types of monolayers of the Lieb lattice interacting with a surface-plasmon mode localized on top of a semi-infinite conductor. In particular, we have observed and described fully long-living plasmon modes with unusual energy dispersions. Additionally, we have carried out a detailed investigation on the static screening associated with the Lieb lattice. Our study has further revealed that these predicted features seem to be quite different from those of pseudospin-1 materials but resemble those of graphene instead.
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All authors Andrii Iurov, Liubov Zhemchuzhna, Godfrey Gumbs, Danhong Huang

Materials Science

Room-temperature magnetic p-n junctions for charge-and-spin diodes

Yuzhang Jiao, Yutong Wang, Xiangning Du et al. (+11 more)

Non-magnetic p-n junctions have been fundamental components in the silicon era, serving as the backbone for nearly all Si-based semiconductor devices, including transistors. To tackle challenges such as scaling limitations, excessive latency, and high-power consumption in Si-based electronics, we develop magnetic p-n junctions composed of a p-type amorphous magnetic semiconductor (p-AMS) and n-type Si. These charge-and-spin junctions exhibit typical diode characteristics for charge current, along with distinctive spin diode features. By manipulating spin-polarized space charges, we observed a giant magnetic enhancement of approximately 24.36% at a breakdown current of 5 mA, and an impressive 29-fold increase in magnetic moments for p-AMS. The observed spin behavior is attributed to space charge effects or carrier depletion in the p-AMS with extended hole states.
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All authors Yuzhang Jiao, Yutong Wang, Xiangning Du, You Ba, Yingqi Zhang, Zhiwei Tang, Xiangrong Wang, Tiantian Chai, Xiaoke Mu, Cheng Song, Kefu Yao, Zhengjun Zhang, Yonggang Zhao, Na Chen

Materials Science · Cross-listed from physics.optics

High-Stress Si3N4 Reflective Membranes Monolithically Integrated with Cavity Bragg Mirrors

Megha Khokhar, Lucas Norder, Paolo M. Sberna et al. (+1 more)

High-stress silicon nitride (Si3N4) membranes represent the state-of-the-art for cavity optomechanics, combining ultralow dissipation, optical transparency, and full compatibility with wafer-scale nanofabrication. Yet their integration into high-finesse optical cavities has remained difficult, typically requiring bonding or alignment-sensitive assembly that limits scalability and long-term stability. Here, we introduce a monolithic, wafer-level integration strategy that directly suspends high-stress Si3N4 photonic-crystal membranes above thermally compatible SiN/SiO2 distributed Bragg reflectors (DBRs) capable of withstanding the high temperatures required for stoichiometric Si3N4 growth. A defect-free amorphous-silicon sacrificial layer and stiction-free plasma undercut yield vertically coupled cavities with sub-micron spacing-forming self-aligned resonators within seconds of release. Owing to the intrinsic tensile stress, the suspended membranes exhibit atomic-scale sagging, ensuring near-ideal cavity parallelism and long-term stability. Optical reflectivity measurements reveal cavity finesse exceeding 800 with nanoscale gaps between mirrors. Mechanical ringdown measurements show Q > 10^5, indicating that DBR integration preserves the low-dissipation character of high-stress Si3N4. This demonstrates that the integration process preserves the material's exceptional dissipation dilution, supporting straightforward extension to high-Q nanomechanical architectures reported in the literature. The resulting Si3N4-DBR platform unites optical and mechanical coherence with high fabrication yield and design flexibility, enabling scalable optomechanical devices for precision sensing and quantum photonics.
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All authors Megha Khokhar, Lucas Norder, Paolo M. Sberna, Richard A. Norte

Monday 2 March

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

PolyMon: A Unified Framework for Polymer Property Prediction

Gaopeng Ren, Yijie Yang, Jiajun Zhou et al. (+1 more)

Accurate prediction of polymer properties is essential for materials design, but remains challenging due to data scarcity, diverse polymer representations, and the lack of systematic evaluation across modelling choices. Here, we present PolyMon, a unified and accessible framework that integrates multiple polymer representations, machine learning methods, and training strategies within a single, accessible platform. PolyMon supports various descriptors and graph construction strategies for polymer representations, and includes a wide range of models, from tabular models to graph neural networks, along with flexible training strategies including multi-fidelity learning, {\Delta}-learning, active learning, and ensemble learning. Using five key polymer properties as benchmarks, we perform systematic evaluations to assess how representations and models affect predictive performance. These case studies further illustrate how different training strategies can be applied within a consistent workflow to leverage limited data and incorporate physical model derived information. Overall, PolyMon provides a comprehensive and extensible foundation for benchmarking and advancing machine learning-based polymer property prediction. The code is available at github.com/fate1997/polymon.
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All authors Gaopeng Ren, Yijie Yang, Jiajun Zhou, Kim E. Jelfs

Materials Science

TritonDFT: Automating DFT with a Multi-Agent Framework

Zhengding Hu, Kuntal Talit, Zhen Wang et al. (+8 more)

Density Functional Theory (DFT) is a cornerstone of materials science, yet executing DFT in practice requires coordinating a complex, multi-step workflow. Existing tools and LLM-based solutions automate parts of the steps, but lack support for full workflow automation, diverse task adaptation, and accuracy-cost trade-off optimization in DFT configuration. To this end, we present TritonDFT, a multi-agent framework that enables efficient and accurate DFT execution through an expert-curated, extensible workflow design, Pareto-aware parameter inference, and multi-source knowledge augmentation. We further introduce DFTBench, a benchmark for evaluating the agent's multi-dimensional capabilities, spanning science expertise, trade0off optimization, HPC knowledge, and cost efficiency. TritonDFT provides an open user interface for real-world usage. Our website is at https://www.tritondft.com. Our source code and benchmark suite are available at https://github.com/Leo9660/TritonDFT.git.
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All authors Zhengding Hu, Kuntal Talit, Zhen Wang, Haseeb Ahmad, Yichen Lin, Prabhleen Kaur, Christopher Lane, Elizabeth A. Peterson, Zhiting Hu, Elizabeth A. Nowadnick, Yufei Ding

Materials Science

Precursor-Dependent Energetics as a Predictive Principle for Polymorph Selection in Thin Films

Hyeon Woo Kim, Han Uk Lee, Rohan Mishra et al. (+1 more)

Vapor deposition allows for the synthesis of metastable polymorphs with unique properties, yet polymorph selection remains largely empirical due to the lack of predictive guidelines bridging thermodynamics, kinetics, and synthesis conditions. Here, we show that precursor chemistry can control metastable polymorph selection by modulating the reaction driving force governing nucleation. By integrating first-principles reaction energetics and substrate interactions into classical nucleation theory, we establish a quantitative framework that connects precursor-dependent reaction energetics to polymorph accessibility during vapor deposition. Using Ga2O3 as a model system, we demonstrate that highly reactive precursors with large reaction driving forces kinetically stabilize the metastable {\alpha} phase, whereas low-driving-force precursors permit thermodynamic relaxation to the stable e̱ta} phase. Furthermore, precursor flow rates amplify supersaturation, expanding the kinetic window for stabilizing the elusive ąppa} phase. The predictive capability of this approach is further validated in the TiO2 system, where precursor-dependent reaction energetics correctly capture the competitive nucleation between rutile and anatase. These results establish precursor chemistry as a tunable chemical lever for controlling nucleation kinetics and provide a predictive design principle for metastable polymorph synthesis in vapor deposition.
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All authors Hyeon Woo Kim, Han Uk Lee, Rohan Mishra, Sung Beom Cho

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

Electrically-controllable superconducting memory effect in UTe2

Zheyu Wu, Hanyi Chen, Mengmeng Long et al. (+13 more)

If a computer could be assembled from superconducting components, the energy efficiency would far surpass that of conventional electronics. Historic research efforts towards this goal yielded pivotal breakthroughs in the development and discovery of scanning tunnelling microscopy and high temperature superconductivity. Although recent strides have been taken in advancing superconducting diode and switching technologies, harnessing read/writeable memory functionality in superconducting platforms has remained challenging. Here we show that bulk single crystal specimens of the triplet superconductor candidate uranium ditelluride (UTe$_2$) possess such properties. Upon applying a magnetic field to access an intermediate regime straddling two distinct superconducting phases, we find that direct current pulses can push the material in and out of a metastable state possessing an enhanced critical current $J_c$. This switching is controllable by the strength and duration of the stimuli, with the system `remembering' whether it is in the high or low $J_c$ state for extended periods. We interpret this to be due to competition between two distinct vortex species, which can be perturbatively pushed into a non-equilibrium high-disorder configuration with stronger pinning forces and thus higher $J_c$. Rather than requiring proximate magnetic or semiconducting interfaces, this memory functionality appears to be an intrinsic property of UTe$_2$ rooted in the superconducting order itself. Our findings underscore the rich complexity of quantum vortex matter, and demonstrate the viability of engineering a new class of superconducting memory elements with ultralow-power switching.
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All authors Zheyu Wu, Hanyi Chen, Mengmeng Long, Daniel Shaffer, Dmitry V. Chichinadze, Andrej Cabala, Theodore I. Weinberger, Alexander J. Hickey, Jinxu Pu, Dave Graf, Vladimir Sechovsky, Michal Valiska, Gang Li, Rui Zhou, F. Malte Grosche, Alexander G. Eaton

Materials Science

Strain-induced structural transitions in (111)-oriented (LaMnO$_3$)$_{2n}|$(SrMnO$_3$)$_n$ superlattices

Imran Ahamed, Shivalika Sharma, Fabrizio Cossu et al. (+1 more)

By means of first-principles electronic structure calculations, we hereby investigate the structural transitions induced by epitaxial strain in (111)-oriented (LaMnO$_3$)$_{2n}|$(SrMnO$_3$)$_n$ superlattices, with $n=2,4,6$. All superlattices in the explored range of strain are shown to prefer a half-metallic ferromagnetic order where the local magnetic moments are coupled to volume-breathing distortions. More in detail, our results reveal that thickness plays a crucial role in the response to epitaxial strain, which is particularly evident in the resulting tilt pattern of the oxygen octahedra. The thinnest superlattice, for $n=2$, always adopts the $a^-a^-a^-$ tilt pattern and the competing $a^-a^-c^+$ tilt pattern can be stabilized as a metastable state only in presence of compressive strain. Instead, the superlattice with $n=4$ favours the $a^-a^-c^+$ tilt pattern at equilibrium conditions, but the in-phase rotations around the third pseudocubic axis are so fragile that the $a^-a^-a^-$ pattern is recovered under a tiny amount of either compressive or tensile strain. The superlattice with $n=6$ exhibits a more nuanced behaviour: compressive strain drives a transition from $a^-a^-c^+$ to $a^-a^-a^-$, whereas tensile strain preserves the $a^-a^-c^+$ tilt pattern and significantly accentuates the structural differences between the two inequivalent sublattices within this symmetry. In fact, the Jahn-Teller distortions are quenched in one of the sublattices, leading to enhanced volume-breathing distortions and corresponding enhanced charge and spin oscillations. This suggests that Hund's physics may be more relevant in this regime of tensile strain, maximizing the interplay between strong electronic correlations and structural effects.
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All authors Imran Ahamed, Shivalika Sharma, Fabrizio Cossu, Igor Di Marco

Materials Science

Thermal conductivity and tunable thermal anisotropy of magnetic CrSBr monolayer

Marta Loletti, Alejandro Molina-Sánchez, Juan Sebastián Reparaz et al. (+2 more)

We present first-principles calculations of the thermal conductivity, ${\bm \kappa}$, of monolayer CrSBr, a van der Waals magnetic 2D material. We find a considerable thermal anisotropy, with a ratio $\kappa_{xx}/\kappa_{yy}$ of around 1.8. The anisotropy stems from a combined effect of phonon velocities and lifetimes and can be tuned by controlling the flake size by suppressing long mean path phonons.
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All authors Marta Loletti, Alejandro Molina-Sánchez, Juan Sebastián Reparaz, Xavier Cartoixà, Riccardo Rurali

Materials Science

The contribution of nitrogen Frenkel-pair formation to the high-temperature heat capacity of uranium mononitride

Mohamed AbdulHameed and Benjamin Beeler

The high-temperature heat capacity of uranium mononitride (UN) remains uncertain due to conflicting measurements and models above ~1700 K. To assess whether intrinsic defect formation contributes to the observed superlinear behavior of $C_P(T)$, we perform large-scale molecular dynamics simulations using two interatomic potentials to quantify nitrogen diffusion and Frenkel-pair populations from 1800–2600 K. Both models show increasing anion mobility, but the Tseplyaev potential yields substantially larger Frenkel concentrations, producing a defect heat-capacity contribution of up to ~10 J/(mol-K). This defect-driven term is consistent with the curvature seen in historical correlations and recent ab initio results, suggesting that nitrogen sublattice disorder provides a plausible intrinsic mechanism for the high-temperature heat capacity of UN.
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Materials Science

Charge, Bonding, and Optical Properties of the B$_7$Ca$_2$ Cluster: An Alkaline-Earth Dimer Stabilized by a Single Boron Ring

Peter Ludwig Rodríguez-Kessler

The charge, bonding, and optical properties of the calcium-doped boron cluster B$_7$Ca$_2$ have been systematically investigated using density functional theory calculations. Extensive global basin-hopping searches identify a single-ring B$_7$ geometry stabilized by two calcium atoms symmetrically located on opposite sides of the boron ring as the global minimum. Electronic structure analysis reveals pronounced charge redistribution and strong Ca–B interactions that promote electron delocalization over the boron framework. Hirshfeld charge analysis indicates substantial electron donation from the electropositive calcium atoms to the electron-deficient B$_7$ ring, leading to effective electronic stabilization without the involvement of transition-metal $d$ orbitals. Optical absorption spectra further reflect the delocalized nature of the frontier electronic states. Real-space bonding analyses based on the electron localization function (ELF), Interaction Region Indicator (IRI), and the Laplacian of the electron density reveal a multicenter bonding pattern dominated by electron delocalization within the boron ring, with calcium acting primarily as an electrostatic and charge-donating stabilizer rather than forming localized two-center Ca–B bonds. These results establish B$_7$Ca$_2$ as a prototypical example of an alkaline-earth-metal-stabilized boron ring and highlight the ability of non-transition metals to stabilize aromatic boron clusters through charge transfer and multicenter bonding.
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Materials Science · Cross-listed from physics.optics

Electric Field Resolved Image Formation in a Widefield Optical Microscope

Arjun Ashoka, Juhwan Lim, Akshay Rao et al. (+1 more)

Visualizing the spatiotemporal evolution of the electric field of light is fundamental to optics, from designing photonic devices to developing next-generation microscopes. However, we lack the experimental tools to directly access the electric field of light in the sample plane of an optical microscope. Here, we introduce an all-optical imaging modality that resolves the electric field of light in the plane of a traditional widefield transmission optical microscope with 100-attosecond temporal and 200-nanometer spatial resolution. With this we demonstrate the delayed buildup of scattering contrast and pulse broadening through and around a thick MoTe2 flake - dynamics inaccessible via standard simulations. We showcase our technique's versatility by additionally resolving the full in-plane vector electric field lines during photoexcitation as the optical pulse propagates through and around the MoTe2 flake.
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All authors Arjun Ashoka, Juhwan Lim, Akshay Rao, Dmitry A. Zimin