Materials Science · Cross-listed from physics.app-ph
Non-reciprocal heat transfer advances flexible thermoelectric devices
Jinwen Yang, Wenmei Luo, Hongbin Xu et al. (+5 more)
Complex heat dissipation assemblies, inferior performance, and limited flexibility are the primary constraints impeding the wide application and commercialization of conventional flexible thermoelectric devices in wearable electronics and other high-end cooling scenarios. In this work, we report a non-conventional design for flexible thermoelectric devices which can reduce the temperature to -7.03 at room temperature without external heat sink, achieving a cooling temperature drop of 29.25. The design is based on non-reciprocal heat transfer, integrated with thermally conductive composites and screen-printing technologies. This approach takes advantage of directional heat flow, thereby eliminating the need for complex heat sink networks, which extend the applications of flexible thermoelectric devices from personal thermal management to more broader fields such as home healthcare and emergency first aid.
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All authors Jinwen Yang, Wenmei Luo, Hongbin Xu, Fuqing Duan, Yafei Ding, Jie Chen, Guimei Zhu, Baowen Li
Materials Science
Anomalous bulk dealloying below the parting limit
Weiyue Zhou, Hooman Gholamzadeh, Lei Ding et al. (+9 more)
Dealloying has been extensively studied both as a corrosion degradation mechanism in structural materials, including those used in
nuclear, aerospace, or marine environments, and as a versatile method to fabricate porous materials for catalysts and other functional applications. Classical dealloying theory in aqueous environments predicts a critical reactive-element concentration (parting limit) for continuous selective dissolution at temperatures where bulk
diffusion does not dominate; this threshold is commonly reported around 50~60 at.%. Yet recent studies show that molten salt environments can generate extensive bulk dealloying below this threshold. Despite the importance of this anomalous dealloying behavior in many energy systems and electrochemical applications, its fundamental origin remains elusive. Here, we address this critical gap, revealing a grain boundary (GB)-assisted bulk dealloying mechanism. Using three-dimensional (3D) reconstruction of the dealloyed regions correlated with crystallographic and elemental analyses, we directly map the 3D GB-void architecture and reveal that
diffusion-induced recrystallization (DIR) generates a high-density GB network, which then promotes molten-salt infiltration and can drive bulk dealloying far-below the conventionally reported parting limit, producing a distinctive morphology reminiscent of discontinuous precipitation (DP). Understanding this dynamic GB-void interplay is crucial for the prediction and control of dealloying in complex electrochemical environments.
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All authors Weiyue Zhou, Hooman Gholamzadeh, Lei Ding, Kevin Daub, Mehdi Mosayebi, Travis Casagrande, Yingxin Zhu, Miaomiao Jin, Mark R. Daymond, Yang Yang, Michael P. Short, Suraj Y. Persaud
Materials Science
Dominant-pair free energies predict phase selection in high-entropy alloys
Dennis Boakye and Chuang Deng
Phase selection in multicomponent
alloys is governed by the competition between entropic stabilization of disordered solutions and enthalpic driving forces for chemical ordering. However, widely used parametric criteria reduce it to a single scalar, carrying no explicit free energy for any competing ordered phase. Herein, we develop a thermodynamic framework based on the semi-empirical macroscopic atom model and the Dinsdale
lattice stability database to fill this gap. We show that a dominant-pair mechanism, in which the Al-transition-metal interaction family dominates the ordering enthalpy, enables the complex multicomponent B2-ordering problem to be reduced to an effective pseudo-binary system with an analytically evaluated Bragg-Williams free energy. Combined with a minimum-free-energy classifier, the framework predicts the lowest-energy phase as a function of composition and temperature. This provides continuous phase stability maps rather than the single-value predictions of conventional descriptors. Demonstrated on high-
entropy alloys using a
dataset of 269 experimentally characterized samples, the model outperforms widely used phase-selection criteria in the class-balanced macro-F1 metric and achieves 77.9% on the well-posed three-class task, outperforming the valence electron concentration criterion. The model is general by construction and computationally efficient for predicting phase stability in multicomponent
alloys over a broad range of compositions and temperatures.
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Materials Science
Structure-Dependent Chemical Order Modification in Strained Alloy Nanoparticles
Yue Wang, Zibo Chen, Evropi Toulkeridou et al. (+2 more)
Alloy nanoparticles (nanoalloys) exhibit tuneable physicochemical properties that depend sensitively on their atomic arrangement, making control over chemical ordering a central challenge in nanomaterials design. While most theoretical studies consider nanoalloys in
vacuum, practical systems are typically supported, where strong cluster-substrate interactions can introduce significant
lattice strain. Here, we investigate strain as a control parameter for chemical ordering in bimetallic nanoalloys using atomistic molecular dynamics and Monte Carlo simulations. By imposing controlled tensile and compressive strain through an implicit anchored interface, we systematically probe the response of NiPt nanoparticles with distinct structural motifs. For truncated octahedral particles, we find that chemical ordering and segregation behaviour remain remarkably robust even under large strains, indicating that intrinsic thermodynamic preferences dominate. In contrast, icosahedral nanoparticles exhibit pronounced strain-induced chemical redistribution, with a significant increase in surface Ni concentration under tensile strain. This behaviour is attributed to the combined effects of intrinsic
geometric frustration and a high fraction of undercoordinated sites in icosahedral structures. Our results demonstrate that strain can selectively modulate chemical ordering in nanoalloys in a structure-dependent manner, establishing a general framework for understanding strain-induced chemical ordering in nanoalloys.
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All authors Yue Wang, Zibo Chen, Evropi Toulkeridou, Joseph Kioseoglou, Panagiotis Grammatikopoulos
Materials Science
Topological Hall plateau in quasi-2D kagome magnet YMn$_6$Sn$_6$
Sambit Jena, Nastaran Salehi, Manuel Pereiro Lopez et al. (+5 more)
We examine the impact of the Dzyaloshinskii–Moriya interaction (DMI) in kagome magnets and show that a predominantly planar DMI together with
ferromagnetic exchange stabilizes a disordered skyrmion phase in quasi-two-dimensional (2D) YMn$_6$Sn$_6$. Within an {\it{ab initio}} framework combining density functional theory and
spin-dynamics simulations, we generate realistic
spin textures of disordered skyrmion and find that this phase persists for $B_{\rm ext} \leq 0.5$~T, with a decreasing skyrmion size as
magnetic field increases. We demonstrate the emergence of topological
Hall plateau in the range $-0.5 \leq B_{\mathrm{ext}} \leq 0.5$~T, driven by nearly uniform scalar
spin chirality and the resulting constant real-space Berry
curvature. This response is anti-symmetric with
magnetic field while magnitude and sign of these plateau are determined by a complex interplay between Hund's coupling strength and chemical potential signifying the role of Dirac points and van Hove singularities. In addition, we reveal topological
magnon excitations in the disordered skyrmion phase of quasi-2D YMn$_6$Sn$_6$.
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All authors Sambit Jena, Nastaran Salehi, Manuel Pereiro Lopez, Olle Eriksson, Narayan Mohanta, Karthik V Raman, Tanay Nag, Banasree Sadhukhan
Materials Science · Cross-listed from cond-mat.mes-hall
Untangling 3D atomic reconstruction in twisted bilayer 2D crystals via dark field transmission electron microscopy
Pankaj Kumar, Michel Bosman, Nikolai Lavrentev et al. (+4 more)
Reconstruction of the atomic
crystal structure in twisted 2D materials has been demonstrated to be responsible for multiple exciting phenomena in van der Waals
heterostructures, from the appearance of flat bands in twisted
bilayer graphene to Wigner crystallization in transition metal dichalcogenides (TMDs). However, there are still no experimental methods for accessing the 3D atomic distributions nor models that describe the exact atomic shifts in such reconstructed structures, which significantly impedes the development of the field. Dark field (DF) transmission electron microscopy (TEM) has been conventionally employed to visualize the local in-plane atomic displacements. Here we expand this method to obtain a full description of the reconstructed atomic systems and demonstrate the quantitative relations between the local stacking and the intensity in the DF image. We show how local 3D atomic displacements and the interlayer distance can be extracted from a DF image.
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All authors Pankaj Kumar, Michel Bosman, Nikolai Lavrentev, He Zheng, Ding Peng, Kostya S. Novoselov, Tatiana Latychevskaia
Materials Science
What enables GaOx as hole transport layer for a 16 percent 1.0 eV CuInSe2 Bottom Cells with VOC above 550 mV?
Francesco Lodola, Zhuangyi Zhou, Boaz Koren et al. (+10 more)
Among the highly efficient photovoltaic technologies, that do not rely on epitaxy, only chalcopyrites have a bandgap tunable down to 1.00 eV, the ideal for tandem applications. This is obtained with a pure CuInSe2 absorber without Ga. GaOx has been shown to be an efficient hole transport layer that prevents recombination at the metallic back contact. On the other hand, GaOx has proven detrimental, when it forms on In containing transparent back contacts in bifacial
solar cells. Here, we investigate the conditions that make the GaOx layer conductive. We employ a GaOx hole transport layer that is formed through ion exchange during co-evaporation of the low band gap absorber layer. We find that no additional Cu is needed, and that Na is not necessary for a conductive GaOx. Nor did we find a systematic influence of oxygen flow during the sputtering process of the
oxide layer. The GaOx layer is partly crystalline. The optimized passivating hole transport layer enables a CuInSe2 bottom
solar cell, without any addition of Ag or heavy alkalis, with an active area efficiency above 16% and a record-certified open-
circuit voltage VOC of 552meV
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All authors Francesco Lodola, Zhuangyi Zhou, Boaz Koren, Saeed Bayat, Alessandro Magon, Yucheng Hu, Adrian-Marie Philippe, Michele Melchiorre, Hasan Arif Yetkin, Gunnar Kusch, Nathalie Valle, Rachel A. Oliver, Susanne Siebentritt
Materials Science
Proximity-Induced Skyrmion Stabilization at the Cu2OSeO3/Bi2Se3 Interface
Sina Mehboodi, Victor Ukleev, Chen Luo et al. (+7 more)
We investigate proximity-induced
magnetic interactions at the interface between the topological
insulator Bi2Se3 and the
chiral magnetic insulator Cu2OSeO3, with particular focus on the low temperature skyrmion phase. Broadband
ferromagnetic resonance spectroscopy reveals enhanced stability of noncollinear
spin textures in the Cu2OSeO3/Bi2Se3
heterostructure compared with bare Cu2OSeO3. In addition to an extra resonance mode in the tilted conical phase that is absent in bare Cu2OSeO3, field cycling resolves two counterclockwise skyrmion resonance branches separated by approximately 238 MHz, consistent with the coexistence of a bulk skyrmion
lattice and an interfacial skyrmion phase stabilized by proximity-induced exchange coupling and enhanced interfacial Dzyaloshinskii-Moriya interactions. The finite frequency separation indicates that the two skyrmion phases occupy distinct
magnetic energy landscapes while retaining similar resonance character. Resonant elastic x-ray scattering measurements further confirm that the interfacial skyrmion phase spans a broader
magnetic-field range than the bulk phase, demonstrating enhanced stability and ordering of topological
spin textures at the interface. These findings establish interface engineering as a promising route for extending the stability regime of skyrmion and tilted-conical phases in topological-
magnetic heterostructures.
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All authors Sina Mehboodi, Victor Ukleev, Chen Luo, Radu-Marius Abrudan, Jie Xiao, Ronny Golnak, Florin Radu, Matthias Kronseder, Christian H. Back, Aisha Aqeel
Materials Science
Giant perpendicular Edelstein polarization in 2D compensated magnets via bichromatic Floquet driving
Mohsen Yarmohammadi, Daegeun Jo, Marco Berritta et al. (+3 more)
While unconventional $p$-wave magnets can generate nonrelativistic Edelstein polarizations,
spin-group
symmetries strictly forbid these responses in unconventional magnets with higher-order harmonics, such as $d$-wave altermagnets. Here, we demonstrate that combining Rashba
spin-orbit coupling with bichromatic Floquet driving activates
giant perpendicular Edelstein polarizations (PEPs) across 2D altermagnets and broader classes of unconventional
spin-polarized magnets – a feat monochromatic driving cannot achieve. By dynamically breaking two-fold rotational
symmetry, the two-frequency drive (including bilinear, bicircular, and circular-linear configurations) induces a stray-field-free in-plane Zeeman-like field that generates orbitally dominated PEPs (0.5–1.5 $\mu_{\rm B}$). This massive response is governed by universal selection rules tied to the system's
magnetic parity and the second beam's harmonics. These emergent PEPs provide a powerful mechanism for perpendicular
memory writing.
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All authors Mohsen Yarmohammadi, Daegeun Jo, Marco Berritta, Libor Šmejkal, James K. Freericks, Peter M. Oppeneer
Materials Science · Cross-listed from cond-mat.soft
Optimal interactions for addressable self-assembly
Tighe McAsey, Sushrut Tadwalkar, Ali Fele-Paranj et al. (+1 more)
Addressable self-assembly asks that each building block assemble into a particular location in a target structure. Although particles may all be distinct, achieving high yield is a challenge because of monomer depletion: more target structures can nucleate than there are building blocks for, so they form partial fragments which cannot complete growth. We ask how to design the interactions between building blocks to achieve the highest yield in a given time. Using reaction equations describing all the intermediate steps of assembly, combined with numerical optimization, we show that the optimal interactions are such that (i) all bonds are either very strong or very weak, and (ii) the strong bonds form a spanning tree of the target structure. We then prove that when interactions form a spanning tree, monomer depletion cannot occur: assembly can always proceed downhill in energy space, with no kinetic traps. This result is a combinatorial property of the underlying interaction graph, and does not depend on the particular model for the kinetics. It suggests a robust design principle: create a network of strong interactions that has no loops, and make all other interactions much weaker. We validate this principle in numerical simulations of larger structures, and we further show that spanning trees that are more compact have typically better yield. Our results suggest a new framework for understanding monomer depletion and addressable self-assembly, which may be applied to DNA nanotechnology and which may give insight into the assembly pathways of certain multiprotein complexes.
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All authors Tighe McAsey, Sushrut Tadwalkar, Ali Fele-Paranj, Miranda Holmes-Cerfon
Materials Science
A technical report on the surface-energy and morphology-based screening for electrode/electrolyte interface compatibility in SOFC/ReSOC materials
Guido Violano and Luciano Afferrante
The performance and durability of solid
oxide fuel
cells and reversible solid
oxide cells are strongly affected by the electrode-electrolyte interface, where charge transfer, ionic transport, adhesion, morphology and thermomechanical stability interact. Early-stage compatibility screening is usually based on electrochemical or compositional criteria, whereas surface-related descriptors are rarely included in a unified framework. This work proposes a surface-based methodology to assess the expected compatibility of candidate electrode-electrolyte pairings. Contact-angle measurements with water and glycerol are used to determine total, dispersive and polar surface free energy components through the Owens-Wendt-Rabel-Kaelble method. Confocal topography is used to extract ISO 25178 roughness parameters, including average roughness, peak-to-valley height, valley depth, skewness, kurtosis and surface slope. A compatibility
matrix is constructed by combining energetic affinity and morphological suitability, with emphasis on the electrolyte surface, since the electrode is deposited directly onto the electrolyte substrate. The results indicate that the most promising interfaces are not necessarily those with the highest surface free energy, but those combining high adhesion work, low interfacial energy and a substrate morphology suitable for continuous electrode deposition. The proposed approach provides a rational pre-electrochemical screening tool to prioritize electrode-electrolyte combinations for subsequent validation by electrochemical impedance spectroscopy, area specific resistance, electrical contact resistance, microstructural analysis and durability testing. Although it does not replace electrochemical characterization, it offers a physically grounded way to connect surface chemistry, topography and interface formation in solid
oxide cell materials.
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Materials Science · Cross-listed from cond-mat.soft
Nonlinear diffusion and compressive rims in source-driven biopolymer condensates
Avraham Moriel and Howard A. Stone
Many subcellular condensates continuously produce biopolymers. Coupling Flory-Huggins thermodynamics to two-fluid viscoelasticity, we probe the
diffusion of such source-driven polymeric droplets, and identify a universal structural compressive rim at their
diffusion front. Integrating analytical scaling laws, numerical simulations, and experimental data, we show that this framework captures key structural and dynamic characteristics of the nucleolus, demonstrating the role of
polymer diffusion in non-
equilibrium biological transport.
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Materials Science
Optimizing Ti substitution for the enhanced densification, ionic conductivity, and microstructure of garnet-type Li$_7$La$_3$Zr$_2$O$_{12}$ solid electrolytes
Neha, A. V. Deshpande, Muktai Aote et al. (+1 more)
Garnet-type lithium lanthanum zirconium
oxide Li$_7$La$_3$Zr$_2$O$_{12}$ (LLZO) is a favorable solid electrolyte for all-solid-state Li-ion batteries due to its wide electrochemical stability, compatible ionic conductivity, and good safety. However, further improvement in ionic conductivity is required for its practical applications. In this work, titanium (Ti) is doped into LLZO to enhance its Li-ion transport properties and structural stability. The series Li$_7$La$_3$Zr$_{2-x}$Ti$_x$O$_{12}$ has been successfully synthesized using conventional solid-state reaction method. The content of Ti has been varied from 0 to 0.20 atoms per formula unit (a.p.f.u). The conducting cubic phase has been confirmed by the X-ray diffraction technique (XRD). Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) have been used for structural analysis, and elemental distribution. Density measurements have been carried out for all the samples. Electrochemical impedance spectroscopy revealed that the high ionic conductivity of $8.08\times 10^{-5}$ Scm$^{-1}$ is offered by the Li$_7$La$_3$Zr$_{1.9}$Ti$_{0.1}$O$_{12}$ sample, which has the lowest activation energy of 0.37 eV. The DC polarization analysis verified that the main contribution to conductivity in the 0.10 Ti sample comes from ions. A one order of magnitude increase in room temperature ionic conductivity is observed for the 0.10 Ti sample, making it a strong candidate for solid electrolyte applications.
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All authors Neha, A. V. Deshpande, Muktai Aote, Abhishek Pradhan
Materials Science · Cross-listed from physics.chem-ph
Contrastive Regularization of Machine Learning Potentials
Dimitrios Tzivrailis, Georgios Sotiropoulos, Alberto Rosso et al. (+1 more)
Machine learning interatomic potentials are trained to predict energies and forces but built to be sampled: their purpose is to drive molecular simulations whose observables average over the
equilibrium distribution the potential defines. They exemplify a broader AI problem – learned regressors deployed as generators – where pointwise accuracy does not guarantee a correct distribution. We show that potentials trained by standard Mean Squared Error (MSE) minimization on Density Functional Theory (DFT) data can reach chemical accuracy on held-out data, yet still fail as samplers: their trajectories drift into spurious low-energy minima and return thermodynamic observables that depart sharply from the reference. To correct this, we introduce Contrastive Regularized MSE (CRMSE), a post-training step that augments the MSE with a contrastive term derived from the Kullback–Leibler divergence between the potential's implicit Boltzmann distribution and the target. The network serves as its own energy-based model: persistent Langevin chains expose the configurations it drifts into and raise their energy, adding no new ab initio data. On the ethanol and aspirin molecules of the MD17
dataset, CRMSE confines the sampler to the physical basin and recovers the energy distribution, interatomic-distance distributions, and dihedral free-energy profiles to near-quantitative agreement with DFT, while preserving force accuracy and keeping energy errors within chemical accuracy; it remains effective when the training set is sharply reduced. That MSE training fails this way on MD17 – one of the most widely used
benchmarks – while a minimal contrastive correction repairs it suggests that reliable sampling depends less on data volume than on training the model against the distribution it produces: distribution-level training is not a refinement of regression accuracy, but a distinct requirement.
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All authors Dimitrios Tzivrailis, Georgios Sotiropoulos, Alberto Rosso, Eiji Kawasaki
Materials Science · Cross-listed from cond-mat.str-el
Local magnon modes studied by dynamic magnetic pair-density function analysis
Shin-ichi Shamoto, Yukio Yasui, Kazuki Iida et al. (+4 more)
The dynamic
magnetic pair-density function (DymPDF) $D_{\rm M}(r, E)$ is obtained via the
Fourier transform of the dynamic
magnetic structure factor, $S_{\rm M}(Q, E)$, which is measured using nonpolarized inelastic
neutron scattering. While there is a long history of
magnetic excitation studies with $S_{\rm M}(Q, E)$, there are no reports on $D_{\rm M}(r, E)$. In this study, we examine simple magnet models and representative magnet examples, such as FeTiO$_{3}$ and YBa$_{2}$Cu$_{3}$O$_{6}$, to investigate the real-space dynamics of $D_{\rm M}(r, E)$. We derive the $D_{\rm M}(r, E)$ equations for simple magnet models in a low energy limit. By comparing these equations to the simulations, we demonstrate the characteristic energy dependence of real-space local
magnon modes, including the transition of the
magnon mode from acoustic to optical. Our novel analysis reveals the local
magnon modes accompanied by a sign change in each
spin-pair correlation at a given energy in nanoscale real space even under non-periodic conditions. This method is unique for studying local
magnetic dynamics.
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All authors Shin-ichi Shamoto, Yukio Yasui, Kazuki Iida, Yasuhiro Inamura, Motoyuki Ishikado, Mitsutaka Nakamura, Lieh-Jeng Chang
Materials Science
Accelerated development of amorphous InZnO thin films as transparent conductive Cu diffusion barriers
Stefanie Frick, Reyu Sakakibara, Manuel Kober-Czerny et al. (+4 more)
In light of the increasing supply chain concerns regarding silver for
solar cell metallization, the replacement of the silver contacts by copper is desirable. As copper diffuses readily in silicon, deposition of an additional
diffusion barrier to protect the respective absorber material stacks is required. We investigate multifunctional layers of transparent conductive
oxides (TCOs) from the In-Zn-O system to serve as front electrode and Cu
diffusion barrier coating, focusing on purely amorphous layers without grain boundaries to impede copper
diffusion. We employ a 2D combinatorial approach to simultaneously screen the Zn/(In+Zn) ratio and the oxygen content in a single materials library deposited by magnetron sputtering without intentional substrate heating. Cu
diffusion barrier performance was evaluated by depositing Cu on top of intentionally ultrathin In-Zn-O libraries of 7 nm on silicon wafers and annealing them at temperatures of 200-450{\deg}C. Both the formation of copper silicides, as well as the silicon photoluminescence signal were monitored. The first was detected only after the crystallization of the In-Zn-O films and required annealing temperatures of 450{\deg}C and above. Even for extended dwell times of 20 h at a relevant process temperature of 200{\deg}C, we find no evidence of Cu ingress for most of our fabricated In-Zn-O compositions, whereas Si/Cu stacks without In-Zn-O barriers showed a reduction of their photo-luminescence intensity already after less than 1 h. These results suggest thin amorphous In-Zn-O films with an optimal Zn/(In+Zn) ratio of ~0.12 and intermediate oxygen deficiency as effective transparent conductive Cu
diffusion barriers for
solar cell applications.
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All authors Stefanie Frick, Reyu Sakakibara, Manuel Kober-Czerny, Arnold Müller, Miloš Baljozović, Franz-Josef Haug, Sebastian Siol
Materials Science
Spin-related transport in a polycrystalline NiCo2O4 film: Drastic current-induced change in resistivity-temperature characteristics via spin injection
Shiho Sugiyama, Masaaki Tanaka and Ryosho Nakane
We have studied
spin-related transport in a polycrystalline NiCo2O4 (NCO) film on a MgAl2O4/Si(001) substrate, motivated by potential applications of the theoretical half-
metallicity of NCO to Si-based high-performance
spin-transport devices. Our approach is to systematically measure and analyze the temperature dependence of the film's resistivity ($\rho-T$) with various in-plane currents (100 nA$-$1 mA) and temperatures (4$-$290 K). With increasing current, the $\rho-T$ curve changes drastically from semiconducting ($d\rho/dT<0$) to non-monotonic and eventually toward metallic ($d\rho/dT>0$). A distinctive feature is that the single NCO film exhibits a $\rho-T$ characteristic of polycrystalline defective NCO at 100 nA, whereas it exhibits a $\rho-T$ characteristic of epitaxial less-defective NCO over a wide temperature range at 1 mA. This current-induced
evolution of $\rho-T$ reflects the enhancement of the Curie temperature of defective regions near grain boundaries, accompanied by enhanced
spin alignment there. We proposed a
spin-related transport model that extends conventional hopping conduction models by incorporating the temperature- and current-dependent degree of
spin alignment, as well as its spatial dependence inherent to polycrystalline NCO. This model comprehensively explains the interplay between the
spin-
alignment profile and transport mechanism. The analysis reveals that
spin injection from grain bodies to grain boundaries enhances the
spin alignment there and strengthens double-exchange interactions, facilitating conduction. This phenomenon strongly depends on both temperature and current. Our findings provide evidence of
spin-polarized electrons inside the grain bodies, highlighting the potential of our polycrystalline NCO film as an efficient
spin source. The present model is further supported by current$-$voltage and magnetoresistance features.
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Materials Science · Cross-listed from cond-mat.str-el
Design Principles for Quasi-Isotropic Exchange in Rare-Earth Quantum Magnets
Kotaro Shimizu, Esteban Agustin Ghioldi, Filip Ronning et al. (+1 more)
Rare-earth
quantum materials provide a promising platform for emergent phenomena ranging from
quantum spin liquids with long-range
entanglement to topological
magnetic textures. However, the strong
spin-orbit coupling that stabilizes their low-energy pseudospin degrees of freedom also tends to generate strongly anisotropic exchange interactions, complicating the realization of quasi-isotropic Heisenberg magnetism. Here we investigate the microscopic origin of superexchange in $\mathrm{Ce}^{3+}$- and $\mathrm{Yb}^{3+}$-based
insulators with edge-sharing octahedral geometry. Using degenerate perturbation theory for a multiorbital Hubbard model, we show that isotropic exchange originates predominantly from virtual hopping within the ground-state Kramers doublet, whereas anisotropic interactions arise primarily from processes involving excited multiplets. This leads to a simple orbital design principle: quasi-isotropic exchange is promoted when the ground-state doublet has a strong maximal-angular-momentum character with respect to the quantization axis perpendicular to the superexchange plane spanned by rare-earth and ligand ions. We demonstrate this mechanism for both ideal and distorted geometries and show that it is broadly consistent with experimentally studied Yb-based
insulators. Our results establish a practical framework for engineering quasi-isotropic interactions in rare-earth
quantum materials.
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All authors Kotaro Shimizu, Esteban Agustin Ghioldi, Filip Ronning, Cristian D. Batista
Materials Science
Growth optimization of shallow Ge quantum wells grown by molecular beam epitaxy
J.T. Dong, J.P. Thompson, R. Card et al. (+2 more)
Shallow strained Ge
quantum wells have gained recent
attention for realizing scalable, high-performance hybrid
superconductor/
semiconductor-based
qubits. Epitaxial superconducting contacts can improve the quality and consistency of the
superconductor/
semiconductor interface. The growth of Ge
quantum wells by molecular beam epitaxy is then motivating due to the relative ease of integration with epitaxial
superconductor growth. However, the performance of Ge
quantum wells grown by molecular beam epitaxy (MBE) has been limited. To improve the properties of MBE-grown Ge
quantum wells, the growth conditions were systematically optimized. Thick buffer layers are utilized to eliminate certain defects, and an optimal growth temperature is found. A peak hole mobility of 105,000 cm\textsuperscript{2}/Vs at 2 K is obtained in a 22-nm deep Ge
quantum well, demonstrating that the Ge
quantum wells grown in this study represent the highest mobilities for shallow MBE-grown samples. Mobility modeling indicates that the increase in mobility due to growth temperature optimization are likely due to a reduction in interface roughness scattering, and further improvements in mobility are expected through improved surface passivation.
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All authors J.T. Dong, J.P. Thompson, R. Card, K. Sardashti, C.J.K. Richardson
Materials Science
Geometrically necessary boundaries accommodate the residual elastic strain in cold-rolled Fe-3%Si
Aditya Shukla, Nikolas Mavrikakis and Can Yildirim
The relationship between plastic deformation accommodation structures and residual elastic strain fields in deformed metals is poorly understood at the intragranular scale, largely because no experimental technique has provided simultaneous, three-dimensional, bulk-sensitive access to both fields at the length scale of dislocation boundaries. Here we use dark-field X-ray microscopy (DFXM) to map intragranular misorientation and residual elastic strain simultaneously in three dimensions within a grain of 50% cold-rolled Fe 3%Si
alloy. We resolve geometrically necessary boundaries (GNBs) and incidental dislocation boundary (IDB)
cell structures in the bulk non-destructively. Correlating the elastic strain field with the segmented plastically deformed substructure reveals that GNBs act as the primary carriers and distributors of long range residual elastic strain. GNBs separate subdomains of distinct mean d-spacing, across the grain volume. The plastic misorientation associated with IDBs and dislocation
cells develops within GNB-delimited subdomains that carry comparatively similar values of elastic strain. This supports a mechanistic picture in which GNBs accommodate nearly all the long-range residual elastic strain in the deformed state, while plastic slip propagates into GNB interiors to organize into IDB
cells with similar strain levels. The three-dimensional misorientation and strain gradients quantified here provide direct experimental input for recovery and recrystallization modelling in ferritic steels, such as electrical steels.
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Materials Science
Tuning topological phase and Dirac point position via Pb and Sb substitution in Mn$_{1-x}$Pb$_{x}$(Bi$_{1-y}$Sb$_{y}$)$_{2}$Te$_{4}$
T. P. Makarova, D. A. Estyunin, V. A. Golyashov et al. (+7 more)
This study presents a systematic investigation of Mn$_{1-x}$Pb$_{x}$(Bi$_{1-y}$Sb$_{y}$)$_{2}$Te$_{4}$
crystals over a wide range of concentrations (x = 10-60%, y = 5-60%). It was found that the value of the bulk band gap is determined exclusively by the Pb concentration and it closes at Pb 40-50 %, which corresponds to a topological phase transition. The position of the Dirac point is determined by the Pb/Sb ratio, rather than the absolute Sb content. The
magnetic properties depend on the dilution of the Mn sublattice by Pb and are weakly sensitive to Sb. We show that the simultaneous substitution of Mn and Bi allows independent control of the topological phase and the position of the
Fermi level.
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All authors T. P. Makarova, D. A. Estyunin, V. A. Golyashov, K. A. Kokh, O. E. Tereshchenko, A. S. Frolov, S. Ideta, Y. Kumar, K. Shimada, A. M. Shikin