Mesoscale and Nanoscale Physics
Quantum transport in Cooper pair splitters using hierarchical equations of motion
Riya Baruah, Neill Lambert, Franco Nori et al. (+1 more)
We investigate charge transport in Cooper pair splitters beyond the weak-coupling and Markovian limits. To this end, we employ hierarchical equations of motion (HEOM), which can capture the combined effects of strong coupling to the leads, nonperturbative interactions, and finite voltage and temperature differences. Within this framework, we compute the electric currents as functions of the level positions of a Cooper pair splitter for various voltage and temperature configurations. In the large-bias regime, our results reduce to analytical expressions obtained from a Markovian Lindblad equation. However, recent experiments were conducted with finite voltage or temperature differences, where a Markovian description may not suffice. In this regime, HEOM yield quantitative agreement with the measured currents. We can also account for an experimentally observed thermoelectric effect in Cooper pair splitters. Our results show that HEOM provide a useful framework for describing nonequilibrium
quantum transport in Cooper pair splitters and related hybrid devices.
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All authors Riya Baruah, Neill Lambert, Franco Nori, Christian Flindt
Soft Condensed Matter
Identifying the signatures of residual activity in harmonically bound active Brownian dynamics
Sanatan Halder and Manas Khan
A confined self-propelled particle exhibits a range of intriguing dynamical phenomena dictated by the interplay between the intrinsic activity of the particle and the imposed confinement. This competition manifests as a crossover in the steady-state position distribution of a harmonically bound active Brownian particle (HBABP) from Boltzmann-like to bimodal, commonly recognized as the passive and active regimes, respectively, upon variations in activity and confinement strength. We present a comprehensive analysis of the resultant dynamics of an HBABP employing analytical calculations and numerical simulations, examining the variations in the position distribution, residual or resultant velocity, mean square displacement, power spectral density, and effective harmonic confinement at varying activities in the characteristic regimes across the crossover. These analyses provide a reliable identification of the signature of residual or remnant activity in ABP dynamics after being impeded by the harmonic confinement. Our results show that the resultant HBABP dynamics in the regime with a Boltzmann-like position distribution is dominated by residual activity, and the motion in the other regime, with a bimodal position distribution, is similar to that of a harmonically bound Brownian particle–devoid of residual activity–at a displaced position, where the activity is balanced by the restoring force field.
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Statistical Mechanics
An Experimental Scheme for Testing Molecular Rectification with Only Micrometer-Scale Fabrication Requirements
Jiantang Jiang
In our previous work, we proposed a theoretical model capable of inducing sustained directed transport without consuming information or external energy. However, the experimental verification schemes proposed previously were technically challenging, and the model has therefore not yet been experimentally tested. In this work, we propose a greatly simplified experimental design. By introducing hydrophilic functional groups onto the tip of a gold needle through surface modification and pressing the needle against one of two
liquid-vapor interfaces, the compressed interface is maintained at a higher ionic concentration than the other interface, thereby sustaining a concentration difference between them. This design reduces the fabrication requirement from the nanometer scale to the micrometer scale, substantially lowering experimental complexity and facilitating experimental examination of the proposed mechanism.
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Materials Science · Cross-listed from physics.app-ph
Universal scaling of electrochemical information transfer at solid-liquid interfaces
Eikichi Kimura, Ashutosh Rathi, Saki Tsuchiya et al. (+6 more)
Electrochemical potentials at solid-
liquid interfaces govern diverse chemical and energy conversion processes; however, the extent to which their electrochemical influence extends into the solid remains unclear. Here, we show that the maximum accessible electrochemical information is governed by a single dimensionless screening parameter $u$, defined as the ratio of the effective electrostatic separation between the interface and probe to the electrostatic propagation length in the solid. The maximum Fisher information follows a universal inverse-square scaling with this parameter. This relation identifies electrostatic screening as a fundamental constraint on information transfer across solid-
liquid interfaces and provides quantitative design principles for interfacial electrochemical sensing.
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All authors Eikichi Kimura, Ashutosh Rathi, Saki Tsuchiya, El Mustapha Mansouri, Sara Mandić, Kristi Kanya Saikia, Keisuke Oshimi, Masazumi Fujiwara, Keigo Arai
Materials Science
From Amorphous to Amorphous-Crystalline Mixed-Phase Boron Nitride: Evolution of the Thermal and Elastic Properties
Jiaqi Yang, Thomas Souvignet, Onurcan Kaya et al. (+11 more)
Amorphous boron nitride (aBN) is a promising dielectric and protective coating, yet its nanoscale heat dissipation and elastic response remain poorly quantified. Here we synthesize a variety of BN thin films by borazine-based chemical vapor deposition (800-1000 C) and study the temperature-driven structural transition from fully amorphous networks to mixed amorphous-crystalline films with embedded BN nanocrystallites.Frequency-domain thermoreflectance data show an ultralow, thickness-dependent cross-plane thermal conductivity for aBN (kout < 0.5 W m-1 K-1 for 10-40 nm), which increases systematically with crystalline order up to 1.5 W m-1 K-1. Micro-Brillouin light scattering and finite-element modelling reveal a concomitant stiffening, with Young's modulus rising from 7.5 +/- 0.7 GPa (800 C) to 53 +/- 5 GPa (1000 C). Green-Kubo molecular dynamics simulations rationalize these trends via bonding
topology and vibrational transport, and highlight how oxygen, hydrogen and carbon
impurities and composition provide practical knobs to further tune the thermal and mechanical responses in BN films for improving nano-electronics, interconnects and coating applications.
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All authors Jiaqi Yang, Thomas Souvignet, Onurcan Kaya, Peng Xiao, Emigdio Chavez-Angel, Daniel Capolat Palomar, Zuzanna Ewa Kaczmarska, Bartlomiej Graczykowski, Javier Rodriguez Viejo, Clivia M. Sotomayor Torres, Catherine Marichy, Catherine Journet, Stephan Roche, Marianna Sledzinska
Strongly Correlated Electrons
GHz non-reciprocal optical conductivity in hematite ($\alpha$-$\text{Fe}_2\text{O}_3$)
Peng Rao, Johannes Gröbmeyer, P. Peter Stavropoulos et al. (+5 more)
We study the non-reciprocal properties of the iron
oxide $\alpha$-Fe$_2$O$_3$ (hematite) in the canted easy-plane
antiferromagnetic phase, specifically in the GHz to THz frequency range. First, using the the microscopic
spin Hamiltonian, we obtain the correct classical ground state where the canting is induced by the Dzyaloshinskii-Moriya interactions (DMI). The
magnon spectrum is simulated using linear
spin wave theory. We then compute the polarizability and the sub-gap optical conductivities using linear response. We find that the conductivity tensor contains frequency peaks at the zero momentum
magnon gaps of order $0.1~$meV which can be tuned by the DMI and on-site anisotropic
spin interactions. Furthermore, we show that the canting-induced net
magnetic moment $\mathbf{m}$ represents a measure for the effective time-reversal-
symmetry breaking and non-reciprocity of the system: a finite $\mathbf{m}$ results in a non-zero
Hall conductivity. Finally, we discuss the prospective application of hematite in non-reciprocal circulator design, by computing the non-reciprocal circulator transmission amplitude using the conductivities as input.
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All authors Peng Rao, Johannes Gröbmeyer, P. Peter Stavropoulos, Alexander Mook, Matthias Althammer, Hans Huebl, Alexander Holleitner, Johannes Knolle
Materials Science
Mechanical mapping of thin elastic films and living cells with spherical tip atomic force microscopy probes at large indentations
Gabriel Gomila, Mauricio Cano, Beatriz Cantero et al. (+7 more)
An analytical model to quantify large indentation force curves acquired on elastic thin films and living
cells with spherical tip Atomic Force Microscopy (AFM) probes is presented. The model accounts for the bottom effect in the whole indentation range and overcomes the limitations of Sneddon's and Hertz's contact models, which are valid for semi-infinite thick samples, and of paraboloid tip models with bottom effect correction (BEC) that are applicable to spherical tips only for relatively small indentations. The model is experimentally validated with force volume measurements on polyacrylamide (PAA) hydrogel thin films, where an excellent agreement is obtained. The accurate correction of the bottom effect demonstrates that the intrinsic Young's modulus of PAA thin films increases for thickness below a critical value (~15 um). The model also shows excellent agreement with force curves acquired on live macrophages, providing accurate Young's modulus values for these very soft
cells (E~200 Pa). Young's modulus values extracted with the proposed model significantly differ from those obtained from Sneddon's or paraboloid models with BEC, whose values deviate by 100% and -25%, respectively. Results show the potential of the proposed model for analysing force curve measurements with spherical tips at large indentations on thin film elastic materials and living
cells at the micro and nanoscale.
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All authors Gabriel Gomila, Mauricio Cano, Beatriz Cantero, Sophie Strawbridge, Lara Aiassa, Loris Rizzello, Giuseppe Battaglia, Eleni Dalaka, Jordi Comelles, Annalisa Calò
Mesoscale and Nanoscale Physics
Levitated nano-trampoline resonators for magnetic field sensing
Xianfeng Chen, Nirmala Raj, Matthew R. Chua et al. (+7 more)
Levitated systems and high-$Q$ membrane nanomechanical resonators have achieved exceptional sensitivity in precision sensing, but functionalizing such resonators for practical applications without degrading their low dissipation remains challenging. Here, we combine diamagnetic levitation with a high-$Q$ nanomechanical resonator to realize a high-precision magnetometer for sensing weak oscillating
magnetic fields. A macroscopic diamagnetically levitated graphite plate acts as a free-floating proof mass that couples strongly to
magnetic fields, converting them into mechanical motion that is resonantly amplified by a low-dissipation nano-trampoline resonator. Operating at room temperature and without
magnetic shielding, we achieve a peak
magnetic-field sensitivity of $4.5\, \mathrm{pT}/\sqrt{\mathrm{Hz}}$ using a resonator with a mechanical quality factor of $Q=6\times10^{6}$ at $443\, \mathrm{kHz}$. The system sensitivity is limited by thermomechanical noise. With further improvements in mechanical $Q$, this hybrid levitated platform offers a pathway toward femtotesla-level AC
magnetic-field sensing, establishing diamagnetically levitated nanomechanical resonators as a new class of high-sensitivity magnetometers at room temperature.
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All authors Xianfeng Chen, Nirmala Raj, Matthew R. Chua, Yi Fan Chen, Chenyue Gu, Minxing Xu, Young-Wook Cho, Syed M. Assad, Lu Ding, Ping Koy Lam
Soft Condensed Matter
Geometric Renormalization and a Chirality Threshold in Recursively Coiled Filaments
Hiroyuki Shima
Repeated coiling creates a filament hierarchy. We formulate helicalization as an iterated map acting on an arbitrary rod compliance, rather than homogenizing one prescribed construction. A marginal Jordan mode yields an outer-radius inverse-square stiffness class, while pitch disorder creates a Lyapunov threshold between amplified and screened extension–twist response. An exact finite-level rate distinguishes representative amplified and screened cases by level three; direct three-dimensional beam calculations validate the response through level four and convergence through level five.
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Mesoscale and Nanoscale Physics
Fractional parametric resonance in spintronic diodes
Andrea Grimaldi, Denys Slobodianiuk, Eleonora Raimondo et al. (+7 more)
Parametric pumping is a powerful tool for the excitation, amplification, and processing of oscillations and waves of different nature. In general, parametric resonance can occur when the pumping frequency $f_p$ and eigenfrequency of a linear mode (or wave) $f_0$ satisfy the relation $f_p$=2$f_0$/n (n=1,2,3,...). While such parametric resonance is well known in mechanical, superconductive, and
quantum systems, in
magnetic and spintronic systems only the lowest (n=1) parametric resonance at double the
spin wave mode frequency $f_p$=2$f_0$ was thoroughly studied and explored. Here, using a theoretical analysis based on both micromagnetic simulations and an analytical model, we show the emergence of resonances at fractional frequencies $f_p$=2$f_0$/n (with n>10) in spintronic diodes driven by the simultaneous action of ac
spin-transfer torque (STT, current densities < $10^6$ A/cm2) and voltage-controlled
magnetic anisotropy (VCMA, effective anisotropy fields < 50 mT). The analytical model shows that parametric magnetization dynamics is irreducible to the standard Mathieu model of a parametric oscillator and demonstrates the crucial role of VCMA-driven mode frequency modulation: together with parametric coupling, it results in higher-order odd (n=3,5,7,...) fractional resonances, observed above certain VCMA pumping threshold, while simultaneous action with linear STT drive produces thresholdless even (n=4,6,8,...) resonances. This higher-order parametric dynamics is not restricted to VCMA pumping and opens new directions for the application of spintronic diodes for nonlinear signal processing and electromagnetic energy harvesting.
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All authors Andrea Grimaldi, Denys Slobodianiuk, Eleonora Raimondo, Raghav Sharma, Anna Giordano, Mario Carpentieri, Hyunsoo Yang, Riccardo Tomasello, Roman Verba, Giovanni Finocchio
Materials Science
Accelerating grain boundary modelling and simulation by automated pre-evaluation of the irreducible macroscopic representation
Wei Wan
A major challenge in the modelling and simulation of grain boundaries (GBs) is the conflict between the system size and computation capability, which inherently restricts the computationally accessible boundary characters. We present an
algorithm to find the irreducible macroscopic representation of any given coincident-site-
lattice GB character in the cubic
lattice, and thus determine the irreducible size of its supercell. The
algorithm is compared with the conventional orthogonal supercell and a published calculation method to assess its merits in saving computational resources. This supercell size parameter can be used to predict which GB character is relatively special across the vast 5D space, as those GBs possess small structural units are likely to exhibit particular structure-property relationships that are worthy of
attention. The prediction is confirmed by examining the energy and mobility trends of aluminum mixed GBs obtained from the atomistic simulations.
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Materials Science
Quantitative Analysis of Composition and Contamination of Atomically Thin Materials by Recoil-Projectile Coincidence in Ion Transmission
Carolin Frank, Kevin Vomschee, Tuan Thien Tran et al. (+6 more)
Surface contamination strongly affects the intrinsic properties of nanoscale materials, making its reliable identification and quantification crucial for both accurate experimental interpretation and nanofabrication. Although scanning transmission electron microscopy can resolve contaminants at atomic resolution within nanometer-scale regions, it cannot easily provide a quantitative, large-area contamination measure. Here, we introduce a minimally destructive
recoil-projectile coincidence method for ion transmission experiments that enables element-specific identification and quantification of surface contaminants with isotopic resolution. We demonstrate this approach by comparing self-supporting
graphene samples prepared using either a polymethylmethacrylate (PMMA)-based or a PMMA-free transfer process. Carbon and hydrogen are identified as the dominant surface contaminants. PMMA-free transferred
graphene exhibits the lowest native contamination levels. Following in-situ thermal annealing at 400 {\deg}C for 1 h, the measured carbon areal density approaches the value expected for atomically clean single-layer
graphene within the experimental uncertainty, while hydrogen coverage is strongly reduced. Unlike PMMA-transferred
graphene, which rapidly recontaminates after annealing, PMMA-free transferred
graphene remains nearly contamination-free for at least 140 min under ultra-high
vacuum conditions ($p_{\mathrm{base}} = 2 \times 10^{-8}$ mbar). Beyond
graphene, the presented method establishes a quantitative characterization platform for ultrathin materials, enabling studies of surface cleanliness, adsorption, implantation and surface interaction dynamics in such systems.
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All authors Carolin Frank, Kevin Vomschee, Tuan Thien Tran, Barbara Maria Mayer, Radek Holeňák, Yossarian Liebsch, E. Harriet Åhlgren, Marika Schleberger, Daniel Primetzhofer
Mesoscale and Nanoscale Physics
Phenomenological geometric ordering in fractional quantum Hall systems
M. A. Hidalgo
The fractional
quantum Hall effect (FQHE) is conventionally understood in terms of strongly correlated many-body states and emergent quasiparticles with fractional charge. Here, we propose a complementary phenomenological framework in which
impurity-induced
geometric correlations within a Landau level contribute to the organization and stability of fractional
quantum Hall states. The model considers a two-dimensional electron gas coupled to a correlated distribution of ionized
impurities located at a finite distance from the electronic layer.
Impurity-induced overlap between displaced Landau orbitals generates coherent guiding-center correlations and an effective splitting of the Landau-level degeneracy into fractional sublevels. Within this framework, the resulting energy spectrum reproduces the principal odd-denominator fractional sequences through the interplay between guiding-center quantization and
impurity-induced orbital coherence. An explicit expression for the correlation energy is obtained in terms of the
magnetic length,
impurity spacing, and
impurity-layer separation, providing a direct connection between the proposed mechanism and experimentally controllable
heterostructure parameters. The model naturally incorporates the integer
quantum Hall regime as the limiting case of vanishing correlation-induced splitting. Within this
geometric picture, effective fractional factors emerge from collective orbital coherence and correlation-modified guiding-center dynamics rather than being uniquely associated with independent fractionally charged quasiparticles. Although the model does not attempt to derive topological order, anyonic statistics, or many-body incompressibility, it suggests that
impurity-induced geometry and guiding-center coherence may provide an additional contribution to the emergence, stability, and experimental visibility of fractional
quantum Hall states.
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Disordered Systems and Neural Networks
Multiplicity of Stable Attractors in Disordered Neural Models
Raffaele Marino, Roberto Livi and Antonio Politi
We show how large-deviation statistics allows one to obtain reliable estimates of the multiplicity of stable fixed-points in a model of neural ordinary differential equations previously employed in computational tasks. The result is obtained by developing a suitable perturbative method in the amplitude of the disorder. It turns out that for not-too-large coupling strengths there are no qualitative differences between the symmetric case, when the dynamics is a purely gradient
evolution, and the asymmetric case, when limit cycles and chaos can, in principle, arise. The selection of this specific model is dictated by pedagogical reasons, but we are confident that the approach can be extended to other many-degree-of-freedom dynamical models characterized by different classes of random coupling
matrices.
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Superconductivity
Structural stability, electronic structure, and magnetism of the $d^9$ double infinite-layer La$_3$Ni$_2$O$_5$F under chemical pressure and epitaxial strain
K. Madani, Q. N. Meier and A. Cano
Nickelate materials exhibit rich electronic properties that can be engineered toward cuprate-like regimes through topotactic and mixed-anion chemistry. Using first-principles calculations, we investigate the newly synthesized double infinite-layer oxyfluoride La$_3$Ni$_2$O$_5$F and its
evolution under chemical pressure and epitaxial strain. The calculated
phonon spectrum confirms the dynamical stability of the reported double infinite-layer
crystal structure. Further, we find a highly two-dimensional cuprate-like
Fermi surface dominated by Ni-$d_{x^2-y^2}$ states, with a moderate rare-earth-derived self-doping yielding an effective $\sim d^{1.2}_{x^2-y^2}$ filling. These electronic features remain remarkably robust under both chemical pressure and epitaxial strain.
Spin-polarized calculations further reveal an extended
manifold of nearly degenerate
magnetic configurations with different in-plane and out-of-plane
spin arrangements. Compressive strain further enhances this
magnetic frustration while leaving the underlying electronic structure largely unchanged. Our results thus identify La$_3$Ni$_2$O$_5$F as a promising cuprate analogue and establish
lattice engineering as an effective strategy for fine tuning its electronic and
magnetic properties.
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Materials Science · Cross-listed from physics.bio-ph
Hair is a functionally graded composite, not a uniform fiber
Andrew K. Schulz, Svetlana Griego, Vesna Srot et al. (+11 more)
Hair provides mammals with diverse benefits, including protection, thermoregulation, and enhanced sensory perception. Unlike tendons and teeth, which are biomineralized, hair is hypothesized to accomplish its structure-function relationship purely through keratin, a fibrous
protein that provides structural integrity. Recent research showed that mechanical properties can vary substantially both within and across hair types: the whiskers of Asian elephant (Elephas maximus) exhibit a two-order-of-magnitude material stiffness reduction from base to tip, whereas elephant body hairs are nearly homogenous. Here, we demonstrate that three hierarchical structures vary significantly along the body hairs and whiskers of domestic cat (Felis catus): the layered outer keratin wall, 250-nm-diameter melanosome-like granules in the cortex, and calcium enrichment of these granules. As occasionally described for human hair, the oblong granules are arranged in longitudinal channels, potentially reinforcing the cortex; their prevalence correlates with local mechanical properties along the hair's length. Prolonged chemical treatment of body hairs removes calcium from the granules while breaking down the outer cuticle and internal cortex, hardening bases and splitting tips. Though previously assumed uniform, morphology, composition, and elemental enrichment can change along hairs, producing composite structures with functional gradients.
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All authors Andrew K. Schulz, Svetlana Griego, Vesna Srot, Giulia Ballardini, Natalia Gonzalez-Vazquez, Devin Sheehan, Felicitas Predel, Cem Balda Dayan, Deepti S. Philip, Helena Vrencev, Jelena Lazovic, Peter A. van Aken, Gunther Richter, Katherine J. Kuchenbecker
Soft Condensed Matter
Materializing split, mixed, and three-body interactions using rotor-based mechanical hysterons
Oche T. Ali, Faten A. Al Ardat, Jack Feider et al. (+4 more)
Interacting hysteretic
spins are an appealing model for cyclically-driven athermal disordered matter. Because they provide a basis for storing and processing information from their environment, such models are also being pursued as a framework for intelligent matter. Recent proof-of-concept designs have begun to demonstrate the strong, controlled, pairwise interactions that are necessary for this endeavor. But, it is not yet clear what are the limits—practically or fundamentally—on such interactions. Here we build rotor-based mechanical hysterons that extend the generality of their interactions in three ways: (i) splitting the interaction strength based on the hysteron state, (ii) building a non-reciprocal interaction of mixed sign, and (iii) incorporating tunable three-body effects. We access these effects within a simple, replicable design platform, and we rationalize our results. Our work expands the space of behaviors for designed structures that compute on mechanical inputs.
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All authors Oche T. Ali, Faten A. Al Ardat, Jack Feider, Harry Maakestad, Alex Walk, Zachariah S. Schrecengost, Joseph D. Paulsen
Statistical Mechanics
Inertial Asynchronous Computation
Doruk Efe Gökmen, Michel Fruchart, Dmitrii Zendrikov et al. (+3 more)
Computation is the controlled
evolution of a state. Asynchronous evolutions, where all parts of the state change in their own time without stopping each other, put this control in jeopardy. It is in fact a mystery how natural processes perform asynchronous computations using many units with no global orchestration. Here we demonstrate how collective computational abilities can emerge in asynchronous many-body systems. The key insight is to split the physical "hardware" underlying the computation into two asymmetrically coupled parts, analogous to position and momentum in a harmonic oscillator. The resulting inertia nudges the
evolution of the state so that the asynchronous computation proceeds in the right order. By treating our inertial asynchronous computer as a nonequilibrium material, we map out its phase diagram numerically and analytically using a framework we dub loop dynamical mean-field theory. We experimentally demonstrate our approach using analog spiking neuromorphic chips designed to mimic actual
neurons in the
brain. In addition, we construct software that can run on asynchronous hardware: we denoise movies whose clean versions were never seen during training, an instantiation of the generalization transition underlying modern machine learning. Our results point to a general strategy for reliable, decentralized computation in energy-constrained settings from dynamics self-assembly to
cell differentiation.
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All authors Doruk Efe Gökmen, Michel Fruchart, Dmitrii Zendrikov, Giacomo Indiveri, Giulio Biroli, Vincenzo Vitelli
Materials Science
Switchable Altermagnetism via Spin-Induced Improper Polarization
Zhihao Dai, Michele Reticcioli, Wei Ren et al. (+2 more)
Enabling reversible
spin-splitting switching in stray-field-free altermagnets is promising for spintronic applications, but currently limited to a narrow class of polar materials. We propose a broader approach based on
spin-induced improper polarization in nonpolar dual-sublattice magnets. We demonstrate this mechanism in DyFeO3, where the product of nonpolar Fe and Dy
spin modes transforms as an induced polar mode. Density functional theory shows that the relative Dy–Fe
spin alignment selects the polarization, while the Fe sublattice controls nonrelativistic
spin splitting, thus enabling reversible switching. These results establish
spin-induced improper polarization as a route to switchable altermagnetism in nonpolar bulk systems.
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All authors Zhihao Dai, Michele Reticcioli, Wei Ren, Hongjun Xiang, Alessandro Stroppa
Materials Science
Ferrimagnetic Skyrmions in a Tetragonal Mn1.9Co0.1Sb Single Crystal at Room Temperature
Huanhuan Zhang, YaJiao Ke, Weiwei Wang et al. (+10 more)
The development of room temperature small-sized ferrimagnetic skyrmion materials is significant for topological spintronic device applications. As a room temperature ferrimagnetic material, the tetragonal Mn1.9Co0.1Sb
crystal exhibits multiple phase transitions, including
spin reorientation transitions. However, the
magnetic spin textures and their
evolution mechanisms during
magnetic phase transitions in Mn1.9Co0.1Sb
crystals remain unexplored. Using Lorentz transmission electron microscopy, we discovered and verified dipolar skyrmion behavior and its
magnetic evolution at room temperature. We established a stable phase diagram of
magnetic textures as functions of temperature and
magnetic field, while also investigating the
evolution mechanisms of
spin textures across multiple temperature-induced
magnetic phase transitions. Through micromagnetic simulations, a ferrimagnetic configuration with in-plane
ferromagnetic coupling and interlayer
antiferromagnetic arrangement was established, which stands in contrast to synthetic ferrimagnetic/
antiferromagnetic systems that exhibit interlayer
antiferromagnetic coupling via the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. We determined that the intrinsic frequency of ferrimagnetic skyrmions can reach the THz regime due to strong interlayer antiparallel exchange interactions. These findings highlight the diversity of room temperature ferrimagnetic skyrmion regulation behaviors in Mn1.9Co0.1Sb and their dynamic
evolution characteristics, opening new avenues for developing novel spintronic devices with enhanced functionalities capable of operating under ambient conditions.
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All authors Huanhuan Zhang, YaJiao Ke, Weiwei Wang, Lingyao Kong, Lin Chen, Sheng Qiu, Jialiang Jiang, Yongsen Zhang, Youhong Peng, Yaodong Wu, Mingliang Tian, Haifeng Du, Jin Tang
Materials Science
Enhanced Curie temperature and room-temperature 50-nm skyrmions achieved in hexagonal ferromagnet Mn5Ge3+x synthesized via a high-pressure method
Yongsen Zhang, Wei Liu, Meng Shi et al. (+14 more)
The development of new high-temperature ultrasmall-size skyrmion materials holds immense significance for the promising applications of topological spintronic devices. In this study, we demonstrate that a high-pressure synthesis technique can significantly elevate the Curie temperature of Mn5Ge3+x
crystals, from 294 K to 350 K. This enhancement is attributed to the combined effects of
lattice contraction and increased Ge content, the conclusion supported by Density Functional Theory calculations. Additionally, our real-space
magnetic imaging reveals the stability of dipolar skyrmions with diameters of approximately 50 nm at room temperature. Our micromagnetic simulations closely replicate the diverse experimental topological
magnetic textures observed. Furthermore, magnetotransport measurements indicate the potential for the electrical distinction between various topological
magnetic textures in skyrmion-based devices. We also report deterministic manipulations on single dipolar skyrmions in confined nanostructures by using in-plane currents. The observation, electrical manipulation, and electrical detection of room-temperature ultrasmall topological
magnetic textures underscore the potential of Mn5Ge3+x as a promising platform for spintronic device applications.
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All authors Yongsen Zhang, Wei Liu, Meng Shi, Shuisen Zhang, Sheng Qiu, Yaodong Wu, Jialiang Jiang, Huanhuan Zhang, Hui Han, Kang Wang, Dingfu Shao, Zhenfa Zi, Chao Ma, Haifeng Du, Mingliang Tian, Shouguo Wang, Jin Tang
Mesoscale and Nanoscale Physics
Current-induced creation and dynamics of embedded magnetic skyrmion bags
Yaodong Wu, Jialiang Jiang, Lingyao Kong et al. (+5 more)
Magnetic skyrmion bags-
vortex-like structures hosting multiple skyrmions with tunable topological charge (Q)-hold significant promise for next-generation spintronic computing. However, while their creation using
magnetic fields has been demonstrated, their direct electrical generation remains an outstanding challenge. Here, we report the direct current-induced formation and manipulation of embedded skyrmion bags in a FeGe nanoplate under zero
magnetic field. Using in-situ Lorentz transmission electron microscopy, we capture the transformation of a distorted helical ground state into embedded skyrmion bags with diverse configurations, driven by nanosecond current pulses. Theoretical analysis indicates that this process is driven by the
spin-transfer-torque-induced fracture of the helical state. Furthermore, we demonstrate electrically-induced transitions between skyrmion bags of different Q, leading to the stabilization of complex three-dimensional topological structures, including experimental signatures of
magnetic monopoles and bobbers. Our work establishes a foundation for all-electrical control of high-Q topological
spin textures and topological defects, paving the way for their application in functional spintronic devices.
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All authors Yaodong Wu, Jialiang Jiang, Lingyao Kong, Meng Shi, Shouguo Wang, Mingliang Tian, Haifeng Du, Jin Tang
Strongly Correlated Electrons
Orbital Embedding and the Physical Definition of Quantum Geometry
Chang-geun Oh and Shuichi Murakami
The
Quantum Geometric Tensor, encompassing the
quantum metric and Berry
curvature, is a central concept in modern condensed matter physics. However, its standard calculation via $k$-derivatives of the Bloch projector conceals a fundamental ambiguity regarding the choice of unit-
cell convention, specifically in the treatment of intra-
cell orbital positions (i.e., with or without the orbital position $e^{ikx_\alpha}$). We resolve this inconsistency by introducing a convention-independent physical QGT defined via a covariant derivative that explicitly incorporates the full position operator. We demonstrate that this formulation is uniquely mandated by the microscopic derivation of the physical current via the Peierls substitution. Notably, we uncover a leading-order failure in standard $k \cdot p$ effective theories for systems with bond-ordered gaps, identifying a need for caution in their application. Finally, we propose
geometric engineering as a new design paradigm, enabling the independent tuning of
geometric responses without altering the energy dispersion.
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Materials Science
Crystallization of pristine cubic ice from liquid at ambient pressure
Chenwei Zheng, Paul F. Henry, Aasim I. Shaffi et al. (+11 more)
The phase diagram of frozen water is famously rich: to date, over twenty crystalline polymorphs have been identified. Of the low-pressure 'ice I' family, hexagonal (Ih) is the principal form on Earth, while cubic (Ic) is much more elusive. Fundamental questions remain open as to whether cubic ice Ic can form directly from the
liquid state, its thermodynamic stability and natural occurrence. Here we show that pristine cubic ice Ic can be formed at atmospheric pressure simply by cooling an aqueous solution confined within mesoporous silica. Using primarily
neutron scattering, we show unambiguously that under these conditions, cubic ice Ic forms reproducibly and is the only thermodynamically stable crystalline phase of water. The discovery that cubic ice Ic is directly accessible from the
liquid state, and stable at atmospheric pressure, strongly suggests that this polymorph plays a much more significant role in natural and synthetic processes than previously thought.
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All authors Chenwei Zheng, Paul F. Henry, Aasim I. Shaffi, Sanghamitra Mukhopadhyay, Miroslava Novoveska, Milz L. Beaumont, Yidan Wang, Camilla Di Mino, Tom F. Headen, Marta Falkowska, Christopher A. Howard, Adam J. Clancy, Christoph G. Salzmann, Neal T. Skipper