Materials Science
Modification of Surface Properties in Ruthenium Thin Films through Nitrogen Ion Irradiation
Anmol Sharma, Arnab Tripathy, Rajeev Gupta et al. (+8 more)
Surface modification is an important strategy for tailoring the physical and chemical properties of materials for advanced technological applications. In thin films, changes in surface structure, roughness, and composition can strongly influence their functional behavior. In this work, we studied the effect of N+-ion irradiation at 20 keV energy on Ru thin films of two different thicknesses, 100 Å and 1000 Å, over a fluence range of ~1014 to 1017 ions/cm2. The main objective of this study is to investigate the
evolution of the structural and wettability properties of Ru thin films of different thicknesses under increasing ion fluence. Overall, the results reveal that increasing ion fluence promotes surface roughening in both film thicknesses, which is correlated with an increase in contact angle. This indicates a clear transition from hydrophilic to hydrophobic behaviour, with the highest contact angle of ~95.54{\deg} observed at a fluence of 1017 ions/cm2. TRIM simulations reveal that for the 100 Å film, the projected ion range exceeds the film thickness, allowing interaction with the bottom substrate, whereas in the 1000 Å film, ion penetration remains largely confined within the Ru layer. GIXRD confirms fluence-dependent structural modification, including peak broadening with preferred orientation changes from Ru (101) to (002). Overall, this study demonstrates that N+-ion irradiation serves as an effective route for tuning both the surface morphology and wettability of Ru thin films, enabling controlled enhancement of hydrophobicity.
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All authors Anmol Sharma, Arnab Tripathy, Rajeev Gupta, Raj Kumar, Harsh Vardhan, Ratnesh Kumar Pandey, Atul Thakur, Shalendra Kumar, Ranjeet Kumar Brajpuriya, Vishakha Kaushik, Sachin Pathak
Materials Science · Cross-listed from cond-mat.mes-hall
Laser-induced metastable (anti-)skyrmion states with higher-order topological charge
Tim Titze, Marcel Möller, Timo Schmidt et al. (+6 more)
Ultrafast creation and manipulation of topologically non-trivial
spin objects promises significant potential for spintronic applications. Here, we demonstrate
laser-induced nucleation of skyrmions and antiskyrmions with topological charge up to $|Q|=3$ from the saturated magnetization state of a Co/Ni-multilayer which does not intrinsically host a skyrmionic ground state. The resulting configuration of
spin objects thus constitutes a metastable, thermodynamically hidden
magnetic state. We control the number and type of
spin objects by the excitation fluence and the external out-of-plane
magnetic field.
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All authors Tim Titze, Marcel Möller, Timo Schmidt, Mariam Hassan, Sabri Koraltan, Stefan Mathias, Manfred Albrecht, Claus Ropers, Daniel Steil
Materials Science · Cross-listed from cond-mat.str-el
2D Weak Localization in Trilayer Ruddelsden-Popper Nickelates
Hyo-Bin Ahn, Xinglong Chen, Yu Zhang et al. (+5 more)
Ruddlesden-Popper (RP) nickelates superconduct when pressure suppresses intertwined charge- and
spin-density waves. Here, we employ measurements of
quantum corrections to magnetoconductivity as a probe of the dimensionality, phase coherence, and scattering mechanisms of the underlying single
crystal trilayer RP nickelate Pr4Ni3O10 and La4Ni3O10. We observe signatures of 2D Weak Localization (WL), implying that the in-plane electron transport is in the
quantum diffusive regime, while the out-of-plane transport is incoherent, and the electronic ground state is a quasi-2D disordered Fermi
liquid. Application of pressure up to 3 GPa continuously suppresses signatures of WL, potentially signaling a 2D/3D dimensional crossover and an eventual pressure-driven transition into a
superconductor.
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All authors Hyo-Bin Ahn, Xinglong Chen, Yu Zhang, Hong Zheng, Michael R. Norman, J. F. Mitchell, Daniel Phelan, Ulrich Welp
Materials Science
Mesoscale Crystallographic Helicity in Confined Tellurium Quantum Wires
Moniruzzaman Jamal, I K M Reaz Rahman, Ke Ma et al. (+7 more)
Helical order can facilitate
symmetry breaking and emergent physical responses in crystalline materials, yet how intrinsic chirality manifests beyond atomic length scales remains poorly understood. Here, the direct observation and quantitative characterization of long-range crystallographic helicity in template-grown tellurium (Te)
quantum wires on amorphous substrates are reported. Four-dimensional scanning transmission electron microscopy (4D-STEM) enables quantitative mapping of crystallographic orientation with nanometer-scale spatial resolution. The resulting orientation maps establish continuous mesoscale
lattice twisting, providing direct evidence of long-range crystallographic helicity. Correlated orientation and strain mapping reveal pronounced lateral strain heterogeneity, with compressive strain concentrated within the wire interior. Systematic analysis across multiple wires suggests that higher twist rates are generally associated with weaker lateral compressive strain, narrower wires, and better atomic chain - template axis
alignment. Complementary first-principles calculations on finite Te nanorods further suggest that twisting is intrinsically accessible in
nucleus-scale Te clusters and strain can bias the preferred torsional state. Together, these results support a growth-incorporated, strain-biased picture in which nanoscale confinement and anisotropic strain facilitate torsional relaxation and stabilize mesoscale helicity in Te nanostructures highlighting strain and confinement as potential routes for engineering chiral
lattice states in van der Waals nanostructures.
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All authors Moniruzzaman Jamal, I K M Reaz Rahman, Ke Ma, Juhyeok Lee, Karen C. Bustillo, Mark Asta, Matthew P. Sherburne, Daryl C. Chrzan, Ali Javey, Mary Scott
Materials Science
Reliable training of neural hyperelastic models via full-field data
Konrad Friedrichs, Franz Dammaß, Karl A. Kalina et al. (+1 more)
We present a systematic investigation of the robustness and limitations of
equilibrium gap-based calibrations for hyperelastic physics-augmented neural networks (PANNs), where we consider the special case of isotropic and polyconvex PANNs. In full-field parameterizations, it is commonly assumed that the displacement field is captured with sufficient spatial resolution for an accurate evaluation of the deformation field, and that the specimen is thin enough for plane stress to hold to a good approximation. Since these assumptions are never ideally satisfied in real experiments, we investigate, using synthetically generated data, how severely an under-resolved surface measurement and a non-negligible specimen thickness can affect the model parameterization. Furthermore, we perform calibration on real experimental data for a set of inhomogeneous specimen geometries. We show that the coverage of the admissible deformation states during calibration governs the ability of a model to generalize to unseen geometries and load cases; this ability can be improved further by appropriate combinations of specimens. Accurately depicting the material behavior underlying this rich data, however, requires a sufficiently flexible constitutive model, for which PANNs are well suited. Yet a rich coverage of deformation states alone is not sufficient: unless the calibration data comprise biaxial-tension-like states, models that include the second deformation invariant extrapolate unphysically towards equi-biaxial tension, whereas restricting the PANN to the first invariant remains reliable.
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All authors Konrad Friedrichs, Franz Dammaß, Karl A. Kalina, Markus Kästner
Materials Science
Assessing the magnetic states and the accuracy of first-principles Hubbard corrections for the battery cathode Li$_x$CoO$_2$ ($x=0,1$)
Valentina Sanella, Cristiano Malica, Alberto Carta et al. (+4 more)
Li$_x$CoO$_2$ is a prototypical layered cathode material for Li-ion batteries, yet its accurate description from first principles remains challenging because of self-interaction errors, weak interlayer interactions, and a complex
magnetic energy landscape. Here, we present a systematic investigation of the structural, electronic,
magnetic, and electrochemical properties of Li$_x$CoO$_2$ ($x=0,1$) using density-functional theory augmented with self-consistent Hubbard corrections and long-range van der Waals interactions, together with a systematic exploration of possible
magnetic states. The on-site interactions on Co-$3d$ and O-$2p$ states, as well as inter-site Co-O interactions, are determined from first principles using linear-response theory in the framework of density-functional perturbation theory, with Löwdin-orthogonalized atomic orbitals employed as Hubbard projectors. For LiCoO$_2$, the inclusion of Hubbard corrections provides an accurate description of the structural properties, while the electronic structure is very sensitive to the choice of Hubbard projectors. In particular, frontier Wannier-function projectors substantially improve the description of the occupied electronic states compared with localized atomic orbitals. For CoO$_2$, we demonstrate that a systematic exploration of the
magnetic energy landscape is essential to identify the lowest-energy low-
spin ground state. However, the resulting Hubbard-corrected electronic structure is insulating, consistent with the prediction of the HSE06 hybrid functional, but in contrast to the experimentally observed metallic behavior. Structural relaxation further drives the system toward a different metallic solution with an electronic configuration inconsistent with low-
spin Co$^{4+}$ character. Despite these limitations, the calculated intercalation voltages agree well with experiment, with deviations as small as 2%.
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All authors Valentina Sanella, Cristiano Malica, Alberto Carta, Maria Andolfatto, Nicola Marzari, Livia Giordano, Iurii Timrov
Materials Science · Cross-listed from cond-mat.mes-hall
Density-matrix quantum kinetics of spin-mode crossover and ac Edelstein response in spin–orbit-coupled chiral metals
Shuntaro Sumita and Yusuke Kato
To clarify
spin relaxation and precession across the weak-to-strong SOC crossover in chiral conductors, we formulate a density-
matrix quantum kinetic theory for a three-dimensional isotropic chiral metal with hedgehog SOC and nonmagnetic impurity scattering. The formulation retains interband coherence, and its collision integral conserves charge, energy, and
spin during impurity scattering. We identify three
spin modes that evolve continuously from a long-lived D'yakonov–Perel' relaxation mode and two strongly damped precessional modes at weak SOC to one relaxational and two coherent precessional modes at strong SOC. A closed multipole decomposition maps the
spin dynamics onto an effective Bloch equation, providing a unified interpretation of relaxation and precession across the crossover. We further derive the ac Edelstein susceptibility and the reciprocal current response to a time-dependent Zeeman field, show that their poles coincide with the
spin modes, and verify Onsager reciprocity. The theory thus provides a unified analytic description of
spin relaxation, precession, and
spin–charge conversion across the weak-to-strong SOC crossover.
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Materials Science · Cross-listed from cond-mat.str-el
Spin splitting without symmetry: a nearly compensated ferrimagnet and the origin of altermagnetism
Joo Yull Rhee
The
spin splitting of collinear altermagnets is usually attributed to the
crystal symmetry relating the opposite-
spin sublattices — a rotation or mirror in place of the translation or inversion of a conventional antiferromagnet. We show that this
symmetry organizes the splitting but does not produce it; its origin is the anisotropic arrangement of the
magnetic orbitals and their ligands, which also fixes the
symmetry itself. Two results establish this. A triclinic ($P1$) \ce{Mn} oxide, a fully compensated ferrimagnet whose two inequivalent sublattices are related by no
symmetry, is
spin split throughout the Brillouin zone; repositioning the same ligands, atom for atom, to restore an inversion centre relating the two metal sites collapses the splitting to a residual two orders of magnitude smaller, so the splitting follows from the arrangement rather than the
symmetry.
Symmetry, we show formally, can only ever reverse or forbid a splitting that already exists: it cannot create one between sublattices an arrangement has left electronically identical, nor where the underlying orbitals carry no anisotropy to arrange in the first place. Organizing the analysis through an operation-resolved
symmetry hierarchy and reading the
crystal classes as a single axis, the enforced nodal planes fall from two to one to zero across the orthorhombic, monoclinic, and triclinic classes while the arrangement-generated splitting persists to the base. The altermagnet and the fully compensated ferrimagnet are thus the two ends of one axis — the same splitting, organized by
symmetry at one end and unorganized at the other — and the search for compensated
spin-split magnets is a search over orbital arrangements rather than
symmetry labels.
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Materials Science
Ultrastrong Au-Te bonding drives disorder in monolayer ZrTe$_5$ on gold
Konrád Kandrai, Zoltán Tajkov, Péter Kun et al. (+3 more)
Monolayer ZrTe$_5$ is predicted to host a large-gap
quantum spin Hall phase, motivating efforts to isolate single layers of the material. Gold-assisted exfoliation produces clean monolayers of many chalcogen-terminated van der Waals
crystals, but the strong Te-Au bond may compete with the bonding network of the ZrTe$_5$ layer itself. Across tens of samples, low-temperature scanning tunneling microscopy on gold-exfoliated flakes shows a disordered monolayer surface in the overwhelming majority of cases, while thicker flakes preserve the characteristic quasi-one-dimensional chain structure. Ab initio calculations of the ZrTe$_5$/Au(111) interface reproduce this asymmetry and resolve its mechanism: the Te atoms facing the gold chemisorb, rupturing the weak zigzag Te-Te bonds that cross-link the ZrTe$_3$ chains, turning the discrete bond-length spectrum of the
crystal into a continuous one, while the chains persist as distorted units. Charge analysis shows the signature of covalent Te-Au bonding with a modest transfer that hole-dopes the monolayer; in the bilayer, the distortion and the doping stay confined to the layer contacting the gold, and the chemisorption and disorder each preclude the predicted
quantum spin Hall phase. The same quasi-covalent Te-Au bond may perturb the contact layer of other gold-exfoliated Te-terminated
crystals, particularly those with weakly connected intralayer networks.
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All authors Konrád Kandrai, Zoltán Tajkov, Péter Kun, Levente Tapasztó, János Koltai, Péter Nemes-Incze
Materials Science
Agent-authored deposition recipes for X-ray multilayer mirrors: schema-bound LLM control of a magnetron sputtering system with reflectivity-verified outcomes
Oleksiy V. Penkov, Haoyu Fu, Yueying Zhan et al. (+2 more)
Periodic multilayer mirrors for X-rays require a layer period controlled to about 0.1 nm, set by deposition rates held in the laboratory's own notebook. A supervising model session gave a large
language model
agent a target multilayer specification and calibration constants derived from a laboratory archive. The
agent authored recipes in the magnetron sputtering system's native recipe
language and submitted them through a Model Context Protocol bridge of 17 tools in three tiers, with enforcement in the control application. The target was a 30-bilayer Ru/C multilayer with a period of 6.85 nm, a pair chosen because each period is fitted as two layers. The
agent could read and write only its own working project, so it could alter neither the calibration record nor the measurements that scored it. We scored mirrors by X-ray reflectivity and fixed the 3% acceptance threshold on relative period difference before deposition. Across four scored depositions, the relative period difference fell from 20% on the calibration as given to 2.26% after one measured-feedback iteration and 0.79% after a second. We identified sixteen failure modes of the
agent-facing interface. The result is bounded to the period, pair, and chamber observed.
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All authors Oleksiy V. Penkov, Haoyu Fu, Yueying Zhan, Pengyuan Wu, Jiong Jin
Materials Science · Cross-listed from physics.optics
Interplay between growth conditions and formation of localized light emitters in epitaxial AlN thin films
Meysam Saeedi, Duc V. Dinh, Andrey N. Anisimov et al. (+3 more)
AlN is a promising material for integrated
quantum photonics due to its broad transparency window, its compatibility with CMOS technology, and the possibility to host localized light emitters acting as single
photon sources. However, little is understood yet about the microscopic nature and formation mechanisms of these light emitters. In this contribution, we demonstrate that their formation efficiency depends significantly on the growth conditions of the AlN thin film. We reveal that localized light emitters with distinct zero-
phonon lines in the 600–800~nm range can be efficiently formed in epitaxial AlN thin films grown under N-rich conditions by exposing the AlN to a post-growth treatment consisting in a
proton irradiation followed by an annealing process. In contrast, the density of light emitters formed in AlN grown under Al-rich conditions remains low, even after the thin films have been exposed to the post-growth treatment. These results open a pathway toward a better understanding of the microscopic nature of these light emission centers, as well as their engineered integration as
quantum light sources in AlN-based optomechanical platforms.
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All authors Meysam Saeedi, Duc V. Dinh, Andrey N. Anisimov, Mingyun Yuan, Georgy V. Astakhov, Alberto Hernández-Mínguez
Materials Science
Crack propagation threshold in single-crystal silicon: a cleavage plane-crackons model
Faming Gao
Experiments revealed the discontinuities in the dependence of the crack speeds on the crack driving force. Despite great efforts, until now, previous theoretical methods, such as linear elastic fracture mechanics and molecular dynamics calculations, failed to elucidate the issue of speed gap. Herein, the cleavage plane-crackons model for crack propagation has been proposed. The normalized crack propagation speed of silicon is proportional to the one-fourth power of the
quantum numbers. This motion equation is consistent with experimental results of silicon. It clarifies the underlying mechanism of the long-standing issue of the speed gap. The relationship between
quantum numbers and the roughness of the surface of the cracks has been established. The critical
quantum number for the onset of unstable crack propagation in single-
crystal silicon has been determined. The correspondence between the critical
quantum number and fracture toughness has been discovered. This methodology lead to insights into the underlying mechanism of the fracture processes. It is not limited to silicon and can be extended to other crystalline material to understand and predict the fracture behaviors.
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Materials Science · Cross-listed from cond-mat.mes-hall
In-plane anomalous and third-harmonic Hall response in an easy-plane trigonal magnet
Arnab Das and Soumik Mukhopadhyay
We report the emergence of an in-plane anomalous Hall effect (IPAHE) and a pronounced third-harmonic Hall response in an easy-plane trigonal
magnetic system achieved via tuning of
magnetic anisotropy. Angle-dependent Hall measurements reveal a clear departure from conventional sinusoidal behavior, revealing a strong sin(3{\theta}) component at elevated fields, which increases as the
magnetic anisotropy is reduced, accompanied by a finite in-plane Hall signal. Consistently, the observed nonlinear Hall signal exhibits a cubic field dependence, indicative of a leading third-order contribution to the transverse conductivity. The enhancement of the third harmonic reflects the
evolution toward coherent in-plane magnetization and
symmetry-governed nonlinear transport. These observations support an intrinsic,
symmetry-controlled transport mechanism enabled by reduced
magnetic anisotropy and establish a direct link between anisotropy,
crystal symmetry, and higher-order Hall response.
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Materials Science
Inferring Dislocation Microstructures from X-ray Diffraction via Cross-Modal Contrastive Learning
Benjamin Udofia, Nicolas Bertin and Markus Stricker
Understanding and inferring dislocation microstructures from diffraction patterns remains an open challenge in materials characterization, as diffraction measurements provide only indirect information about the underlying dislocation structure. In this work, a cross-modal learning framework is developed to enable the prediction of 3D dislocation structures directly from diffraction data. Dislocation density fields generated from discrete dislocation dynamics simulations are paired with corresponding virtual X-ray diffraction patterns and embedded into a shared 2D latent space using contrastive learning. The
alignment between structural and diffraction representations of dislocation structures is evaluated directly in the learned latent space using correlations between corresponding latent features. To estimate the role of
dataset size for this approach, farthest point sampling is employed to construct representative and diverse training subsets of varying sizes. The results show strong cross-modal
alignment and that model performance improves rapidly with increasing
dataset size. Near-saturation is achieved with approximately 500 representative observations from a
dataset of 10,000 observations, enabling accurate prediction of dislocation density fields from previously unseen diffraction data of the same distribution. Qualitative comparisons confirm that the predicted structures capture the dominant spatial features of the underlying dislocation microstructures. These findings demonstrate an efficient approach for learning structure-diffraction relationships and highlight the potential for inferring structural characteristics of dislocation networks directly from diffraction patterns, providing a pathway toward diffraction-based structural analysis and future extension to experimental data.
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Materials Science · Cross-listed from cond-mat.mes-hall
Fluctuation-induced antiparallel spin polarization near the boundaries of chiral metals
Kosuke Yoshimi, Yusuke Kato, Yuta Suzuki et al. (+4 more)
The
spin response of chiral conductors to nonequilibrium electrical fluctuations remains largely unexplored. We develop a low-frequency semiclassical Boltzmann theory coupled to Gauss's law for a chiral metal with
spin-orbit coupling of hedgehog type, treating impurity scattering beyond the conventional relaxation-time approximation. We first determine the quadratic response to a local ac current and its frequency dependence, and then show that zero-mean stationary current fluctuation and electric-field fluctuation near boundaries generate finite time-averaged
spin polarizations in the two boundary regions of the chiral metal. The polarizations are normal to the boundaries and antiparallel: for one chirality they point inward at both boundaries, and for the other they point outward. Within this model, the dominant contribution arises from the linear Edelstein effect driven by a quadratic effective electric field localized near each boundary. This picture may provide a qualitative explanation for CISS-related
spin polarization reported in the absence of an applied bias. More broadly, we expect other externally maintained
stochastic drives to induce
spin polarization through the same mechanism.
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All authors Kosuke Yoshimi, Yusuke Kato, Yuta Suzuki, Shuntaro Sumita, Takuro Sato, Hiroshi M. Yamamoto, Yoshihiko Togawa
Materials Science
Direct observation of reversible ionic polarization at a buried solid-state battery interface
Giovanni Ceccio, Romana Miksova, Jiri Vacik et al. (+5 more)
Electric fields control ionic distributions at solid-solid interfaces. However, whether buried interfaces possess an intrinsic ionic reversibility has remained experimentally unresolved. Here, we directly observe reversible ionic polarization at the buried amorphous LiCoO2/Li1.5Al0.5Ge1.5P3O12 electrolyte interface. By combining the Elastic Recoil Detection Analysis (ERDA) method, utilizing time-of-flight (ToF) measurements and nanometer-scale resolution, with the
Neutron Depth Profiling (NDP) method for the absolute quantification of lithium, we show that an applied bias of +-1 V results in a reversible redistribution of approximately 9.3% of lithium in the interface region, while conserving its total content. Upon polarity reversal, the lithium redistribution is completely reversed, indicating reversible interfacial ionic polarization rather than irreversible lithium loss or permanent interphase formation. These results demonstrate that buried interfaces in solidelectrolyte systems can behave as electrically reconfigurable ionic regions with an intrinsic reversible freedom for ion motion, thereby providing direct microscopic insight into the physics of space-charge formation and low-voltage interfacial response in solid-state electrochemical systems.
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All authors Giovanni Ceccio, Romana Miksova, Jiri Vacik, Zoltan Szaraz, Josef Dobrovodsky, Pavlina Zavadilová, Pavol Noga, Ivan Mastronardo
Materials Science · Cross-listed from cond-mat.supr-con
Universal transverse diode effects in superconducting unconventional magnet hybrids
Pei-Hao Fu, Luca Chirolli and Jorge Cayao
We demonstrate that superconducting unconventional magnet junctions harbor transverse
spin and charge diode effects with perfect rectification efficiencies. This nonreciprocal transverse transport is governed by the interplay of mirror reflections and
spin rotation with respect to the Néel vector, a mechanism that is universally applicable to all unconventional magnets. Interestingly, the transverse
spin diode features pure
spin currents, while the charge diode yields
spin-polarized charge currents, both exhibiting highly controllable rectification functionalities at vanishing net magnetization. Our results position superconducting unconventional magnets at the forefront of orthogonal engineering in next-generation transverse superconducting spintronics.
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Materials Science
Enhancing Conformality in Atomic Layer Deposition through Low Growth Per Cycle
Christine Gonsalves, Jorge A. Velasco, Ahmed Othman et al. (+2 more)
Atomic layer deposition (ALD) is a key enabling technology for advanced microelectronics as it enables the growth of functional thin films on complex three-dimensional substrates with unmatched atomic-scale precision. Conformal film growth in high-aspect-ratio (HAR) structures is limited by slow
diffusion of reactant molecules into deep, narrow features. This work elucidates an approach to grow conformal films faster by investigating the relationship between the ALD growth per cycle (GPC) and the film penetration depth in HAR structures through modeling and experiments.
Diffusion-reaction simulations reveal, under Knudsen
diffusion conditions, an inverse square root relationship between the film penetration depth and GPC. The prediction is validated experimentally with a model zinc oxide ALD process on rectangular lateral HAR structures, using an inhibitor molecule to decrease the GPC. While ALD is traditionally optimized for "high GPC," this work shows that "low GPC" may increase efficiency when conformality is key.
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All authors Christine Gonsalves, Jorge A. Velasco, Ahmed Othman, Ville Miikkulainen, Riikka L. Puurunen
Materials Science
Enhanced anomalous Nernst effect in Pr-doped kagome and honeycomb magnet LaCo$_5$
Zheng Li, Yueyang Wu, Tianhao Li et al. (+7 more)
In this work, we report the successful synthesis of La$_{1-x}$Pr$_x$Co$_5$ ($x = 0.09, 0.21, 0.45$) single
crystals.
Magnetic field-dependent magnetization measurements reveal that Pr substitution induces negligible changes in the
magnetic properties of LaCo$_5$, with the ferromagnetic ordering predominantly governed by the Co sublattices. Remarkably, the doped systems exhibit significant enhancements in the anomalous Nernst effect. At 300~K, the anomalous Nernst thermopower $S^A_{yx}$ reaches 6.5~$\mathrm{\mu V/K}$ in La$_{0.55}$Pr$_{0.45}$Co$_5$, corresponding to a $\sim$ 40 % enhancement compared to the parent compound. This significant improvement can be predominantly attributed to Pr-doping-induced Fermi level modification, which directly leads to a redistribution of Berry
curvature across the Fermi surface. This work highlights the effectiveness of Pr doping in boosting the anomalous Nernst effect of La$_{1-x}$Pr$_x$Co$_5$, offering a practical strategy to design advanced materials for room-temperature energy-harvesting technologies and high-efficiency thermal sensing devices.
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All authors Zheng Li, Yueyang Wu, Tianhao Li, Jun-jian Mi, Shu-Xiang Li, Jiang Ma, Qian Tao, Xiaofeng Xu, Sheng Xu, Zhu-An Xu
Materials Science
Mechanical control of competing magnetic order in crystalline MnPtGa membranes
R Rawat, F Fei, T Samanta et al. (+5 more)
MnPtGa hosts competing
magnetic states, including ferromagnetic, canted antiferromagnetic, and
spin density wave (SDW) order in the centrosymmetric $P6_3/mmc$ structure, while a related inversion-broken structure supports chiral skyrmions. Controlling this competition motivates materials platforms that enable tunable strain and
symmetry breaking, together with probes of SDW order compatible with ultrathin samples. Here, we demonstrate single crystalline MnPtGa membranes grown by molecular beam epitaxy on
graphene/Ge(111) and released by mechanical exfoliation. X-ray and electron diffraction confirm high crystalline quality. SQUID magnetometry reveals a 140 K anomaly in the zero-field-cooled $dM/dT$ that persists after exfoliation, while time-resolved reflectivity shows a coincident peak in the electronic relaxation time consistent with a quasiparticle
phonon bottleneck associated with a putative SDW gap. Intentional rippling suppresses the $\sim 140$ K
magnetic anomaly, demonstrating mechanical control of the low-temperature state. These results establish MnPtGa membranes as a platform for detecting and strain-tuning competing
magnetic orders.
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All authors R Rawat, F Fei, T Samanta, Z LaDuca, K Su, M Arnold, J Xiao, J K Kawasaki
Materials Science
Observation of topological surface phonons in diamond with nonlinear optics
Qi Wang, Xinyi Liu, Xinyue Sheng et al. (+8 more)
Topological
quantum states in electronic systems have profoundly transformed the understanding of phases of matter. Recent theories predict novel vibrational topological
quantum states, i.e., topological
phonons in various solids. However, this paradigm is yet to be established due to the lack of convincing experimental verification of topological surface
phonons—a hallmark signature of topological
phonon states. Here, we report the discovery of topological surface
phonons in diamond using sum-frequency spectroscopy—a nonlinear optical spectroscopy capable of probing surface
phonons with high sensitivity. Diamond, known for exceptional hardness and thermal transport, is unveiled as a
phonon topological semimetal hosting topological nodal-lines and nexus triple points in the bulk. With consistent theory and experiments, we uncover the resultant topological surface
phonons on diamond (111) and (100) surfaces. Moreover, by chemically modifying these surfaces, we reveal the disorder effect on topological surface
phonons. These findings pave the way for bridging two fundamental domains:
quantum topology and
lattice dynamics, besides having important implications on diamond-based devices and functional interfaces.
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All authors Qi Wang, Xinyi Liu, Xinyue Sheng, Zhi-Kang Lin, Xiaowei Lu, Xiaosheng Yang, Peining Li, Yizhou Liu, Chang-Hui Li, Wei-Tao Liu, Jian-Hua Jiang
Materials Science
Revealing Hidden Inversion Symmetry Breaking in ZrTe$_5$ via Phonon-Assisted Heterodyne Amplification
S. J. Li, J. H. Huang, H. Y. Wu et al. (+13 more)
ZrTe$_5$ is a sensitive topological material where small perturbations can alter its electronic structure. Its
equilibrium crystal structure has been widely regarded as centrosymmetric, while recent experiments have raised the possibility of inversion-
symmetry breaking. Here we probe this hidden
symmetry lowering using nonlinear optical spectroscopy. Although conventional second-harmonic generation does not resolve an
equilibrium symmetry-breaking signal, terahertz-field-induced second-harmonic generation (TFISH) reveals it through
phonon-assisted heterodyne amplification. A coherently driven infrared-active
phonon acts as a local oscillator for the vanishingly weak second-order susceptibility $\chi^{(2)}$, converting an otherwise undetectable
symmetry-breaking response into a
phonon-frequency modulation of the TFISH signal. The field-linear scaling of this modulation demonstrates $\chi^{(2)}$ is an
equilibrium susceptibility rather than a response induced by the THz field. Polarization- and temperature-dependent measurements identify a bulk polar distortion along the crystallographic $a$ axis that persists to room temperature, while the $c$ axis remains nonpolar. These results provide direct optical evidence for
equilibrium inversion-
symmetry breaking in bulk ZrTe$_5$ and establish a structural constraint for understanding its electronic and topological properties.
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All authors S. J. Li, J. H. Huang, H. Y. Wu, S. P. Zheng, C. J. Kong, B. Xu, H. Wang, T. Dong, L. Yue, D. Wu, Y. Wan, Z. L. Li, X. B. Wang, S. J. Zhang, N. L. Wang, Y. T. Li
Materials Science
Irreducible sub-nm$^2$ ferroelectric domains by 2D-flat polar band in perovskite superlattices
Pawan Kumar and Jun Hee Lee
Flat polar
phonon bands in ferroelectrics have been envisioned to realize irreducibly small domains for achieving the highest
memory density. However, such bands are extremely rare, with only a one-dimensional flat polar band discovered in ferroelectric hafnia, which gives rise to irreducibly narrow, line-type domains with a half-unit-
cell width of 2.7 Angstrom. Here, we report the discovery of a two-dimensional flat polar band in the ferroelectric (BaTiO$_3$)$_1$/(BaXO$_3$)$_1$ superlattice (X = Zr, Sn), which generates extremely localized, noninteracting dipoles within its quarter-unit-
cell area that form quasi-degenerate states of irreducible sub-nm$^2$ ferroelectric domains. The estimated ferroelectric domain density, exceeding 300 Tbit/cm$^2$ (assuming one bit per domain) represents a record high among the known ferroelectrics, with independently switchable dipoles at low voltages. The ferroelectric phase hosting two-dimensional flat bands constitutes a competing ground state across superlattice stacking directions and thus can be experimentally realized in both freestanding structures and epitaxial growth on MgO substrates. This discovery opens unprecedented opportunities to explore multidimensional flat polar bands in ferroelectrics and to engineer ultra-dense and low-power
memory devices.
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Materials Science
Deterministic patterning and alignment of tellurium quantum wires using nanoscale templates
I K M Reaz Rahman, Scott Dhuey, Moniruzzaman Jamal et al. (+14 more)
Tellurium (Te) is an intriguing one-dimensional (1D)
semiconductor that has recently attracted considerable interest as a p-type channel material. However, scalable synthesis methods have lacked control over the orientation and patterning of the Te atomic chains, thus limiting its practical use. Guided by theory, we overcome this challenge using nanowire-shaped templates to achieve oriented, single-
crystal growth of Te on amorphous substrates. Strong
alignment of Te atomic chains is achieved as template widths are reduced to sub-20 nm. This high structural order, confirmed by 4D scanning transmission electron microscopy, enables the observation of pristine
quantum transport phenomena for deterministically patterned Te. Field-effect transistors exhibit well-defined conductance plateaus at 77 K due to population of individual 1D subbands. Furthermore, Coulomb blockade emerges at 1.7 K, with the Te channel acting as a gate-tunable
quantum dot. This synthesis approach provides a scalable pathway for integration of Te-based
quantum materials for future electronic and
quantum technologies.
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All authors I K M Reaz Rahman, Scott Dhuey, Moniruzzaman Jamal, Taehoon Kim, Naoki Higashitarumizu, Selven Virasawmy, Aidar Kemelbay, Genki Ohkatsu, Aditya Nirmale, Inha Kim, Hyong Min Kim, Karen C. Bustillo, Joel W. Ager III, Daryl C. Chrzan, Mary Scott, Yutaka Majima, Ali Javey
Materials Science
$Ab$ $initio$ Study of Substitutional Defects in Li$_{3}$OCl Solid Electrolyte for Li-ion Batteries
Carson D. Ziemke, Naveed Naemi, Ha M. Nguyen et al. (+7 more)
Improving ion transport in solid electrolytes and cathode coatings remains a key challenge for all-solid-state Li-ion batteries because their room-temperature ionic conductivity is still substantially lower than that of
liquid electrolytes. In our previous combined experimental and theoretical study, we showed that thermal
neutron irradiation enables defect engineering in LiBO$_2$ through the transmutation of $^6$Li and $^{10}$B, generating
lattice vacancies that enhance ionic conductivity. Here, we examine whether this approach can be extended to Li$_3$OCl, a representative antiperovskite solid electrolyte. Using density functional theory, we investigate substitutional defects at Li sites involving B, He, and H, associated with B doping and the
neutron-capture reactions $^{6}\mathrm{Li}+n\rightarrow\,^{3}\mathrm{H}+\alpha$ and $^{10}\mathrm{B}+n\rightarrow\,^{7}\mathrm{Li}+\alpha+\gamma$. We evaluate defect formation energetics, the resulting structural distortions, and compare these substitutional defects with other mono-, di-, and trication substitutions at Li sites. Our results show that substitutional defects associated with
neutron irradiation provide a feasible route to tune the defect chemistry of antiperovskite solid electrolytes and support
neutron-driven defect engineering as a strategy for developing advanced materials for high-performance all-solid-state Li-ion batteries.
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All authors Carson D. Ziemke, Naveed Naemi, Ha M. Nguyen, Anthony Dorhauer, Carlos Garcia, Narendirakumar Narayanan, Yangchuan Xin, John Gahl, Thomas W. Heitmann, Carlos Wexler