Statistical Mechanics
Macroscopic Thermodynamic Framework for the Mpemba Effect
Yun-Qian Lin, Z. C. Tu and Yu-Han Ma
The counterintuitive Mpemba effect, wherein a hotter system cools faster, critically lacks a general macroscopic theory. Here, starting from linear irreversible thermodynamics, we formulate a generalized Newton's cooling law, $\mathrm{d}T/\mathrm{d}t = -[\gamma_0 + \mathcal{M}Q(t)](T-T_r)$, for a system at temperature $T$ relaxing in a thermal reservoir at $T_r$, where the bare relaxation rate $\gamma_0$ is modified by an initial-state
memory term, $Q(t) \propto T(0)-T_r$. Arising from the interplay between heat flux and structural
evolution, the coefficient $\mathcal{M}$ governs anomalous relaxation behaviors, where $\mathcal{M} > 0$ ($\mathcal{M} < 0$) induces the (inverse) Mpemba effect. This universal thermodynamic framework maps out phase diagram to provide general criteria for the Mpemba effect in complex systems, offering a macroscopic picture that bridges disparate microscopic approaches.
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Statistical Mechanics
Pareto fronts and trade-off relations from exact multi-objective optimization of thermal machines
José A. Almanza-Marrero, Édgar Roldán and Gonzalo Manzano
Thermal machines are physical systems that, when fueled by input energy, perform output tasks such as heat pumping or the production of work. Their performance is characterized with several, often competing quantities, such as power, efficiency, energy waste, and resilience to environmental noise. Multi-objective optimization provides a key tool to investigate the characterization of the best thermal machines operating in the irreversible linear-response regime. Here, we derive exact analytical parameterizations for the optimal (Pareto) fronts associated with any given choice of relative weights assigned to their mean extracted power $P$, efficiency $\eta$,
entropy production $\Sigma$ and the amplitude of power fluctuations $\sigma^2_P$. The geometry of the front of endoreversible machines is universal: two-, three-, and four-objective trade-offs follow analytical formulae that do not depend on the value of any physical parameter of the machine. We show that such universal thermodynamic Pareto fronts also set quantitative fundamental limits for the performance of non-endoreversible machines. Furthermore, we demonstrate that our results apply to existing experimental data from different physical systems also beyond the linear regime, ranging from atomic to macroscopic scales, including single-atom engines, colloidal systems, macroscopic engines and power plants.
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Mesoscale and Nanoscale Physics
Theory of x-ray scattering from optically pumped excitons in atomically thin semiconductors
Joris Sturm, Andrei Benediktovitch, Nina Rohringer et al. (+1 more)
We propose a framework to explore the internal charge distribution of mesoscopic quasiparticles by inelastic x-ray scattering, while also accounting for the conventional scattering from electrons. Specifically, we investigate a new contribution of intrinsic and optically pumped
excitons (bound electron-hole pairs) to the x-ray scattering spectrum of transition metal dichalcogenides (TMDCs). The optical excitation leads to the creation of Wannier
exciton populations, adding new quasi-elastic processes beyond the conventional electronic features to the x-ray scattering spectra. Differential spectra (with and without optical pumping) can be used to isolate and identify the internal charge distribution of the optically pumped
excitons in the scattering response, potentially offering insights into many-body interactions and quasi-particle dynamics in 2D systems.
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All authors Joris Sturm, Andrei Benediktovitch, Nina Rohringer, Andreas Knorr
Mesoscale and Nanoscale Physics
Anatomy of the modern theory of orbital magnetism from first-principles: term-by-term analysis in the gauge-covariant formalism
Hojun Lee, Insu Baek, Mirco Sastges et al. (+3 more)
We present an in-depth analysis of the orbital magnetism by means of the so-called modern theory based on the Berry phase across distinct classes of materials-d transition metals, sp metals, and transition metal dichalcogenides-highlighting the microscopic nature of band structure characteristics. We adopt a gauge-covariant formulation of the modern theory proposed in [Lopez et al. Phys. Rev. B 85, 014435 (2012)], which enables the calculation of orbital magnetism in a controlled manner in any chosen gauge of Wannier functions and gives the total contribution as a gauge-invariant measurable. This captures consistently the contributions due to the anomalous position, velocity, and orbital angular momentum of Wannier basis, as well as the contributions due to
Hamiltonian such that their sum is gauge-invariant. For d transition metals, we find that the atom-centered approximation captures the majority of the total contribution given by modern theory, which we attribute to localized nature of d electrons. However, 5d metals tend to exhibit larger deviation between the two methods than 3d metals do, as 5d electrons are more delocalized than 3d electrons. On the other hand, sp metals exhibit a strong deviation between the two methods, where large kinetic energy of sp electrons is important. Finally, in 1H-MoS2, we find that the valley orbital moment far exceeds the atomic limit of d electrons due to coherent hybridization between valence and conduction bands in direct band gaps. Our work elucidates the interplay of the chemical nature of electronic orbitals and the effect of band structures in a consistent manner and highlights the role of Berry phase in orbital magnetism. The results suggest a promising direction of orbitronics beyond controlling atomic orbitals, in which the orbital magnetism can be greatly enhanced by exploiting Berry phase.
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All authors Hojun Lee, Insu Baek, Mirco Sastges, Yuriy Mokrousov, Hyun-Woo Lee, Dongwook Go
Strongly Correlated Electrons · Cross-listed from quant-ph
Structure and Classification of Matrix Product Quantum Channels
Giorgio Stucchi, J. Ignacio Cirac, Rahul Trivedi et al. (+1 more)
We develop a framework for
Matrix Product
Quantum Channels (MPQCs), a one-dimensional tensor-network description of completely positive, trace-preserving maps. We focus on translation-invariant channels, generated by a single repeated tensor, that admit a local purification. We show that their purifying isometry can always be implemented by a constant-depth brickwork
quantum circuit, implying that such channels generate only short-range correlations when applied on product states. In contrast to the
unitary setting, where one-dimensional
quantum cellular automata (in one-to-one correspondence with
matrix product
unitaries) carry a nontrivial index, we prove that all locally purified channels belong to a single phase, that is, they can be continuously deformed into one another. We then extend the framework to a broader class of translation-invariant channels capable of generating long-range
entanglement and show that these remain deterministically implementable in constant depth using two rounds of measurements and feedforward.
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All authors Giorgio Stucchi, J. Ignacio Cirac, Rahul Trivedi, Georgios Styliaris
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Anisotropic propagation of GHz surface and bulk acoustic waves in gallium arsenide studied by random scattering
T.A. Steenbergen, M.M. Wohlfarth, P.E. Veefkind et al. (+2 more)
Understanding the complex anisotropic acoustic propagation in
crystals is crucial for optimizing the performance of surface and bulk acoustic wave devices. Here, we investigate the anisotropy and coupling of GHz acoustic modes in (001)-cut gallium arsenide through theory and experiment. We first numerically calculate the angle-dependent phase velocities for surface and bulk modes, and we provide a code which can easily be adapted to different material systems. We validate our theoretical model experimentally by exciting surface modes with an interdigital transducer, and achieve omnidirectional acoustic propagation through random scattering of the acoustic waves. We measure the complex acoustic field with a scanning optical interferometer, and extract the angle-dependent velocities of surface and bulk modes using
Fourier domain analysis. Our method could be used for the optimization of GHz-range classical and
quantum acoustic devices by identifying surface and bulk modes.
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All authors T.A. Steenbergen, M.M. Wohlfarth, P.E. Veefkind, M. Fisicaro, W. Löffler
Statistical Mechanics
Starvation suppression in dense scale-free metabolic networks: Dynamical mean-field analysis of catalytic reaction networks
Kota Mitsumoto and Shuji Ishihara
Cellular metabolic networks exhibit scale-free
topologies with power-law degree distributions across diverse organisms. Although such
topologies are often linked to mutational robustness and evolutionary advantage, their role in metabolic dynamics remains unclear. Using dynamical mean-field theory, we derive an exact solution for an intracellular catalytic reaction model on dense random networks with arbitrary degree distributions. We show that the metabolic-starvation transition observed under nutrient-poor conditions for homogeneous degree distributions disappears when the out-degree distribution is scale-free. We also show a power-law in-degree distribution of the underlying catalytic reaction network gives rise to a power-law distribution of biomolecular abundances with the same exponent. Large-scale numerical simulations validate these predictions. Our results provide a theoretical framework linking network
topology and metabolic dynamics.
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Materials Science
First-principle study of the influence of hydroxyapatite on magnesium surfaces
Anthony Veit Berg, Ablai Forster, Tim Hansson et al. (+3 more)
Hydroxyapatite (HA) on a magnesium (Mg) surface is studied using density functional theory, to help understand the effect of HA coating and alloying in the surfaces of Mg-based biodegradable implants. We determine the adsorption energies and structural changes of a single layer of HA on pure Mg(0001) and on sparsely calcium (Ca) or zinc (Zn) doped Mg(0001) and find that both Zn and Ca doping improves the adsorption, except in a few positions of HA relative to the dopant position. All adsorption configurations, whether with pure or doped Mg surfaces, show deformation of the surface and HA layer. For Ca doping, we found that for a certain adsorption configuration, the dopant Ca atom moves out of the Mg surface and into the HA layer, leaving behind a Mg vacancy in the top layer of the Mg surface. Plots of electron density changes show that electrons accumulate around the Ca dopant and the neighboring Mg atoms, while in Zn doping this is less pronounced. Overall, our results demonstrate that the dopant choice and relative position of HA influence the interaction between HA and Mg-surfaces, and affect both adsorption energies and atomic and electronic structures.
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All authors Anthony Veit Berg, Ablai Forster, Tim Hansson, Alexandra J. Jernstedt, Emmy Salminen, Elsebeth Schröder
Soft Condensed Matter
Amorphous Silicates – Time-Current Superposition and the Dynamics of Plastic Flow in the Glassy State
Matthieu Bourguignon, Gustavo A. Rosales-Sosa, Yoshinari Kato et al. (+4 more)
Electron irradiation enables quantitative control over the plastic flow dynamics of silicate glasses, even far below the glass transition temperature. Through stress-relaxation experiments spanning ambient to near-glass-transition temperatures, we uncover a time-current equivalence that grants direct access to steady-state plastic flow over five decades in strain rate. This equivalence allows reconstruction of the intrinsic plastic-flow curve and quantitative assessment of the roles of network connectivity and temperature. Notably, the observed temperature dependence reveals a striking discrepancy with existing theoretical frameworks, highlighting the need for a comprehensive model of plastic flow dynamics in the glassy state.
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All authors Matthieu Bourguignon, Gustavo A. Rosales-Sosa, Yoshinari Kato, Sergio Sao-Joao, Morgan Rusinowicz, Guillaume Kermouche, Etienne Barthel
Mesoscale and Nanoscale Physics
Ellipticity-Controlled Bright-Dark Coherence Transition in Monolayer WSe2
Kang Lan, Xiangji Cai, Zhongxiao Man et al. (+4 more)
The generation of
exciton valley coherence typically requires linearly polarized (LP) light as an external coherent drive, whereas circularly polarized (CP) light fails to induce coherence. Here, we develop a unified, microscopically-grounded open-
quantum-system framework within a five-level model incorporating bright-dark
exciton interactions in monolayer WSe2, and demonstrate that the polarization ellipticity of the excitation field provides selective control over distinct
exciton species contributing to valley coherence. Specifically, LP and CP excitations generate bright and dark coherence, respectively, with continuous ellipticity tuning enabling controlled transitions between these states. We further reveal dual
magnetic advantages for manipulating dark coherence even in the absence of initial coherence: (i) an out-of-plane
magnetic field suppresses coherence decay and (ii) an in-plane field enables its optical readout, with quantitatively realistic field strengths. These findings provide a powerful mechanism for accessing hidden dark states via ellipticity-driven coherence transfer, and establish a new pathway for harnessing bright-dark valley-coherence transitions in future
quantum control.
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All authors Kang Lan, Xiangji Cai, Zhongxiao Man, Shijie Xie, Ning Hao, Ping Zhang, Jiyong Fu
Mesoscale and Nanoscale Physics
Increasing valley splitting in Si/SiGe by practically achievable heterostructure profiles
Lukas Cvitkovich, Peter Stano, Dominique Bougeard et al. (+2 more)
Silicon
spin qubits are marred by the valley degeneracy of the conduction band. In a nanodevice, the degeneracy is lifted by interfaces and
alloy disorder, but the resulting valley splitting is small, of order 100 $\mu$eV in Si/SiGe
quantum wells. Substantial efforts were invested both in theory and experiments to overcome the valley issue. Unfortunately, the existing recipes either rely on atomistic details of the interface that are beyond experimental control, or demand
heterostructure profiles beyond current state-of-the-art
heterostructure epitaxy. We revisit the valley splitting induced by non-trivial Ge profiles and advocate a novel view of the intervalley coupling as backscattering on point-like
impurities realized by
crystal planes containing Ge atoms. This perspective reveals that enhancing the backscattering amplitude, which sets the valley splitting, requires constructive interference of multiple scatterers. % We arrive at a remarkable prediction that the Ge content along the
heterostructure growth direction does not have to have any specific periodicity, including the practically unreachable $2\pi/(2k_0)$ period, to significantly increase the valley splitting. Numerical evidence from tight-binding simulations and intuitive physical interpretations corroborate this statement. We devise profiles that seem within the capabilities of current MBE growth techniques and boost the valley splitting beyond the 1\,meV scale.
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All authors Lukas Cvitkovich, Peter Stano, Dominique Bougeard, Yann-Michel Niquet, Daniel Loss
Strongly Correlated Electrons
Spin subdiffusion in perturbed infinite-U Hubbard chain
Jakub Rękas, Marcin Mierzejewski, Zala Lenarčič et al. (+1 more)
The $t$-model represents the Hubbard model in the limit $U \to \infty$ and is one of the basic models of strongly correlated electrons. On a one-dimensional chain, the model is integrable, and the charge dynamics corresponds to that of free spinless
fermions. However, the sequence of
spins is frozen, leading to the
Hilbert space fragmentation and nontrivial
spin dynamics. We consider integrable and perturbed models with perturbations that break integrability while preserving fragmentation, and show that they exhibit various types of
spin dynamics, from ballistic transport to anomalous
diffusion in the integrable case, and from
diffusion to subdiffusion in the perturbed case. Due to fragmentation, in all cases considered,
spin transport is mediated by charge transport, with a particular magnetization dependence, most notably leading to subdiffusion in the grandcanonical average of the perturbed model, with a mechanism distinct from subdiffusion in disordered or dipole-conserving models.
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All authors Jakub Rękas, Marcin Mierzejewski, Zala Lenarčič, Peter Prelovšek
Mesoscale and Nanoscale Physics
Magnon-Driven Anomalous Hall Effect in Altermagnets
Zheng Liu, Yang Gao and Qian Niu
We propose a
magnon-driven anomalous
Hall effect in altermagnets, arising from the coupling between coherently excited
chiral magnons and
chiral electronic motion. Using density-
matrix perturbation theory and
symmetry analysis, we show that the resulting
Hall conductivity is solely determined by the chiralithy of the Néel-order precession, in sharp contrast to the anomalous
Hall effect from the
equilibrium Néel order. It then has distinct
symmetry requirements from the latter and can exist even when the latter is forbidden by
symmetry. The
magnon-driven anomalous
Hall effect is exemplified in a minimal
lattice model with the same
symmetry of the altermagnet CrSb, which hosts no static anomalous
Hall effect. Our results reveal a direct interplay between
chiral magnons and
chiral electronic motion, paving the way of probing
magnon chirality and to control electronic chirality through
magnons.
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Mesoscale and Nanoscale Physics
Twist-Tuned Magnonic Nanocavity Mode in a Trilayer Moiré Superlattice
Tianyu Yang, Gianluca Gubbiotti, Marco Madami et al. (+2 more)
The concept of moiré superlattices has recently been introduced into the field of magnonics, enabling unprecedented control over
spin-wave propagation and confinement in nanoscale magnonic devices. In this work, we report a numerical investigation on the nanocavity in a trilayer
magnetic moiré superlattice structure consisting of antidot
lattices. By tuning the middle layer twist angle, high tunability of the magnonic band structure can be achieved with characteristic flat bands and the corresponding nanocavity mode formation in outer layers. At an optimal twist angle of 3 deg, excitation at the flat band frequency yields nanocavity mode with linewidth of 175 nm. In contrast to its
bilayer counterpart, the trilayer magnonic moiré superlattice exhibits antiphase nanocavity modes in the outer layers while showing no nanocavity formation in the middle layer. Our study indicates that the switching and distribution of the nanocavity modes can be governed by tuning the middle layer twist angle with a strong
magnon intensity confinement. The trilayer magnonic moiré structure holds a distinct advantage in tunability, which opens up new avenues for the design of future moiré magnonic devices.
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All authors Tianyu Yang, Gianluca Gubbiotti, Marco Madami, Haiming Yu, Jilei Chen
Soft Condensed Matter
Modelling the passive and active response of skeletal muscles within the adapted Voigt representation framework
Sara Galasso and Giulio G. Giusteri
We present a constitutive model for the passive and active response of skeletal muscles. At variance with more classical approaches, the model is developed exploiting adapted Voigt representations of strain and stress tensors within the context of nonlinear Cauchy elasticity. This framework allows us to identify non-trivial stress-strain relations in a rather direct way from experimental data, enhancing the mechanical interpretability of the material functions that describe the tissue response and obtaining additional insight on the distinct role of the contractile fibres and of the surrounding extracellular
matrix. We propose a two-material model, with an additive splitting of the stress contributions, in which only one component depends on an activation parameter. The constitutive model for the passive behaviour satisfactorily predicts the nonlinear stress response to elongation at different relative orientations with respect to the fibre direction and highlights the dominant role of the extracellular
matrix. The activation model, essentially determined by the mechanics of the contractile fibres, captures well the isometric stress response of tetanised tissue through the prescription of an along-fibre active strain that also depends on the
matrix deformation.
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Mesoscale and Nanoscale Physics
Flying qubits Surfing on Plasmons
D.C. Glattli and P. Roulleau
The rapid emergence of flying
qubits in
graphene and other low-dimensional conductors is pushing
quantum electronics into an ultrafast regime where conventional transport theories no longer apply. In these systems, single-electron wave packets propagate coherently over micrometer scales while interacting with collective charge excitations on comparable time scales. Yet existing theoretical frameworks describe either fermionic single-particle dynamics or bosonic plasmonic modes, without reconciling the two. Here we introduce a unified theory of dynamical
quantum transport that bridges this long-standing divide. Starting from a gauge-invariant scattering approach, we show how a time-dependent single-electron excitation self-consistently generates a propagating internal potential that behaves as a collective plasmonic mode. Electrons propagate at the
Fermi velocity while simultaneously 'surfing' on this self-induced plasmon wave, whose velocity is renormalized by Coulomb interactions and screening. This dynamical mean-field framework captures
photon-assisted transport, charge relaxation, and edge magnetoplasmon dynamics within a single description and remains valid far beyond the low-frequency limit. By unifying single-electron and plasmonic pictures, our results provide a timely foundation for the interpretation and control of flying-
qubit experiments in
graphene at gigahertz/terahertz frequencies.
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Soft Condensed Matter
Effects of Divalent Cations on Diffusion Dynamics of Biological Water Confined between Lipid Membranes
Minho Lee, Jinwon Park, Ji-Hyun Kim et al. (+2 more)
Biological water is an ionic solution containing both monovalent and divalent ions. However, the effects of divalent ions on the dynamics of biological water remain largely unknown. Here, we investigate how the transport dynamics of water molecules nanoconfined between lipid membranes depends on the concentration of calcium (Ca2+) and magnesium (Mg2+) ions by using molecular dynamics simulations and the generalized transport equation for biological water. We find that the
diffusion coefficient of biological water monotonically increases with Ca2+ ion concentration but exhibits a largely opposite, non-monotonic dependence on Mg2+ concentration. The deviation of the water molecules' displacement distribution from the Gaussian also shows distinct dependence on the concentrations of Mg2+ and Ca2+. These contrasting behaviors originate from the different hydration radii of these divalent ions and their distinct effects on the interfacial structure and dynamics of biological water. The relaxation of the lateral displacement distribution of water molecules toward a Gaussian is determined by the time-correlation function of
diffusion coefficient fluctuations, whose relaxation time increases with salt concentrations. The primary source of the lateral
diffusion coefficient fluctuation is thermal motion of water molecules in the longitudinal direction, along which microscopic environments surrounding a water molecule, including the functional groups of lipid membrane and ion concentrations, drastically change.
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All authors Minho Lee, Jinwon Park, Ji-Hyun Kim, Minhaeng Cho, Jaeyoung Sung
Mesoscale and Nanoscale Physics
Commensurate moiré superlattices in anisotropically strained twisted bilayer graphene
Ayan Mondal, Cristina Joseph and Bheema Lingam Chittari
We investigate how anisotropic strain reorganizes commensurate moiré superlattices and electronic structure in twisted
bilayer graphene (TBG) across a finite range of reference twist angles. Motivated by experiments showing robust moiré phenomenology under angular disorder and heterostrain (Kapfer et al., Science 381,677 (2023)), we construct commensurate strained supercells generated by a general anisotropic deformation of the top
graphene layer of TBG. The results show that anisotropic strain does not generically destroy the electronic structure of nearby pristine moiré systems; rather, its effect depends sensitively on whether the strained commensurate geometry remains two dimensional or crosses over toward a quasi one dimensional regime. This provides a
geometric perspective on the persistence of moiré electronic features over a finite window of twist angle and heterostrain. Within this framework, the allowed strained configurations naturally separate into tilted two dimensional moiré patterns and quasi one dimensional stripe like patterns. We find that several such strained two dimensional solutions occur near a given pristine twist angle, and that nearby solutions retain triangular like AA-region localization, comparable low energy bandwidths, and a low field Hofstadter spectrum close to the unstrained system. In contrast, quasi one dimensional strained configurations show stronger dimensional reduction, reduced Dirac point multiplicity, stripe like spatial localization, and stronger Hofstadter splitting.
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Mesoscale and Nanoscale Physics
Helicity-Selective Phonon Absorption and Phonon-Induced Spin Torque from Interfacial Spin-Lattice Coupling
Gyungchoon Go and Se Kwon Kim
In
magnetic heterostructures with broken inversion
symmetry, the Rashba effect gives rise to a gradient-free interaction between
magnons and
phonons, which we term interfacial
spin-
lattice coupling. Here, we investigate the dynamic consequences of this interfacial coupling in
ferromagnetic heterostructures. By expressing the interaction in terms of circular variables for magnetization and
lattice displacement, we reveal a direct interface-induced helicity-helicity coupling hat does not rely on
lattice deformation gradients. Consequently, it leads to helicity-dependent
phonon absorption, enabling in-plane acoustic waves to exert a
spin torque on the magnetization, which becomes dominant in thin
magnetic films. Our findings highlight the crucial, yet overlooked, role of inversion-asymmetric interfaces in angular-momentum conversion between
spin and
lattice, opening up possibilities for efficient
phonon-driven
magnetic devices that are enabled by interface engineering.
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Materials Science
Influence of oxygen ion implantation on magnetic microstructure in Pt/Co/Pt multilayers with perpendicular magnetic anisotropy
Anmol Sharma, Mukul Gupta, Prasanta Karmakar et al. (+7 more)
The interaction of oxygen with cobalt and cobalt-based
alloys has been a very important topic in the field of spintronics as it leads to enhanced orbital anisotropy and interfacial Dzyaloshinskii-Moriya interaction (DMI), which are crucial in the context of applications such as
magnetic tunnel junctions (MTJs) based data storage and domain wall (DW) motion. To understand the complex and interesting relationship between oxygen and
ferromagnetic (FM)/heavy metal (HM) interfaces, we studied controlled oxygen ion implantation in a cobalt layer located in a Pt/Co 1.2 /Pt (nm) multilayer with a specific structure. At high implantation fluence, the perpendicular anisotropy was lost, as verified by in-plane hysteresis measurements. Under low
magnetic field conditions, the DW dynamics of Co/Pt multilayers were analyzed, highlighting key parameters such as DW velocity, roughness amplitude, and roughness exponent. After O+-ion implantation, the DW velocity increased by more than 50 times, rising from 5 um/s to 300 um/s compared with the as-deposited multilayer. The fundamental cause of this improvement is the structural and
magnetic changes brought by the implantation, which successfully lower the energy barriers preventing DW movements. The results show how oxygen implantation can be used to precisely tailor the
ferromagnetic interfaces, leading to promised improvements in the functionality of next-generation spintronic devices.
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All authors Anmol Sharma, Mukul Gupta, Prasanta Karmakar, V. Raghavendra Reddy, Vivek K. Malik, Andrei Gloskovskii, Ranjeet Kumar Brajpuriya, Ajay Gupta, Vishakha Kaushik, Sachin Pathak
Strongly Correlated Electrons
Coherent canted ferrimagnetism and higher-order anisotropy in the nodal-line magnetic semiconductor Mn3Si2Te6
Chang-woo Cho, Beomtak Kang, Ildo Choi et al. (+9 more)
The interplay between
magnetic order and electronic
topology in van der Waals materials enables extreme responses to external stimuli. The nodal-line
semiconductor Mn3Si2Te6 exemplifies this, exhibiting colossal angular magnetoresistance (CAMR) where resistivity changes by orders of magnitude upon rotating the
magnetic field. While this phenomenon implies a profound coupling between
spin orientation and charge transport, the microscopic
magnetic potentials driving
spin orientations remain elusive. Here, we combine thermodynamic torque magnetometry and electron
spin resonance spectroscopy to reconstruct the
magnetic anisotropy energy that controls magnetization rotation in Mn3Si2Te6. We show that low-temperature ground state is a coherent canted ferrimagnet stabilized by competing second- (K1) and fourth-order (K2)
magnetic anisotropy. Crucially, torque requires a substantial
symmetry-allowed sixth-order term (K3), which provides near-plane stiffness and sustains canting at high fields. Using the resulting anisotropy parameters, we compute the non-linear relation between field angle {\theta}_H and magnetization angle {\theta}_M and reparameterize CAMR in terms of {\theta}_M, providing a concrete
magnetic basis for how sharp angular transport features can emerge near the in-plane configuration.
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All authors Chang-woo Cho, Beomtak Kang, Ildo Choi, Jitae Gwak, Jisung Lee, Seung-Young Park, Seyoung Kwon, Sungkyun Park, Joonyoung Choi, Younjung Jo, Benjamin A. Piot, Jun Sung Kim
Materials Science · Cross-listed from physics.optics
Mid-infrared reconfiguration of population flow in lanthanide nanocrystals
Xinyang Yu, Yin Huang, Karin Yamamura et al. (+15 more)
Converting mid-infrared (MIR) radiation to visible or near-infrared wavelengths is essential for imaging and sensing, yet achieving sensitive, low-power, and scalable detection remains challenging. Lanthanide nanocrystals provide an alternative through ratiometric luminescence but are typically constrained by Boltzmann statistics, which tie population distributions to
lattice temperature and limit signal contrast. Here we show that MIR irradiation rebalances dissipative relaxation pathways, driving lanthanide emitters into a non-Boltzmann steady state that enables non-thermal control of population distributions. This allows emission behaviors inaccessible under thermal
equilibrium. We exploit this regime to achieve linear MIR detection with respect to MIR power across 6.8 to 8.6 micrometers. The ratiometric response is intrinsically independent of the pump power, enabling operation at an ultralow excitation power of 10 uW, several orders of magnitude lower than conventional approaches. Using standard silicon photodetectors, we then demonstrate room-temperature MIR imaging with detection limits approaching 4 nW um-2. Our results establish lanthanide nanoparticles as an efficient platform for MIR conversion and sensing in nanophotonic systems.
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All authors Xinyang Yu, Yin Huang, Karin Yamamura, Chenyi Wang, Lei Ding, Mehran Kianinia, Yang Yu, Jiyun Kim, Baolei Liu, Xiaoxue Xu, Otto Cranwell Schaeper, Yue Bian, Lan Fu, Guochen Bao, Qian Peter Su, Fan Wang, Igor Aharonovich, Chaohao Chen
Strongly Correlated Electrons
Magnetic anisotropy from interligand hopping in strongly correlated insulators: application to the magnon spectrum of CrI$_3$
Evgenii Barts, Paolo Barone and Maxim Mostovoy
Spin-orbit coupling (SOC) gives rise to complex
magnetic states such as
spin liquids, skyrmion
crystals, and topological
spin-wave excitations. We consider exchange interactions in multi-orbital Mott
insulators where SOC is strong on ligand ions. SOC on the ligands enables electron hopping accompanied by
spin flips and fluctuations in the orbital state of the ligand hole. These processes generate anisotropic exchange interactions and greatly increase the number of possible exchange paths. The number grows further with the inclusion of hopping between ligands, which mediates interactions between more distant
spins. We propose an effective method to calculate exchange interactions at arbitrary separations between
spins. Applying it to monolayer CrI$_3$, we obtain anisotropic interactions between nearest-neighbor and next-nearest-neighbor Cr
spins, as well as single-ion anisotropy induced by long-range hopping. In this material,
magnetic anisotropy stabilizes long-range
ferromagnetic order and opens a
magnon gap at the Dirac points, which defines a nontrivial
magnon band
topology. Using Hubbard model parameters from first-principles calculations, the resulting spectrum agrees well with the
spin-wave dispersion observed experimentally in bulk CrI$_3$, except that the calculated Dirac gap is much smaller.
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Strongly Correlated Electrons
Continuous crossover between high-pressure ice phases VII and X driven by monopole screening: a model study
Sena Watanabe, Yukitoshi Motome and Haruki Watanabe
The
proton-disordered molecular phase of water ice (ice-VII) and its ultrahigh-pressure non-molecular phase (ice-X) share identical macroscopic
crystal symmetry (space group $Pn\bar{3}m$). This raises a fundamental thermodynamic question: are they distinct phases separated by a singularity, or are they adiabatically connected via a continuous crossover? To resolve this paradox, we investigate the finite-temperature phase diagram of high-pressure ices VII and X, as well as VIII, the
proton-ordered phase that emerges at lower temperatures, using an effective classical
spin-$1$ Blume-Capel model on the pyrochlore
lattice. Through Monte Carlo simulations, we demonstrate that within this model, the transformation between the states corresponding to ice-VII and ice-X lacks a thermodynamic singularity, as characterized by non-divergent and non-coinciding peaks in the specific heat and susceptibility associated with the $S^z=0$ occupation. We attribute this continuous crossover behavior to the topological fragility of the hydrogen-bond network: the thermal proliferation of point-like monopole excitations (violations of the ice rules) induces Debye-Hückel screening of the emergent gauge field, destroying the topological Coulomb phase at any finite temperature. In contrast, the destruction of the
proton-ordered ice-VIII phase involves spontaneous
symmetry breaking and remains a first-order phase transition. Our findings provide a microscopic rationale that reconciles the macroscopic crystallographic
symmetries of dense ice with its underlying topological properties.
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Materials Science
Realizing giant valley polarization effect based on monolayer altermagnets
Weifeng Xie, Libo Wang, Xiong Xu et al. (+4 more)
Stable and remarkable valley polarization effect is the key to utilizing valley degree of freedom in valleytronic devices. According to first-principles calculations and
symmetry analysis, we reveal that valley polarization effect in monolayer V2Se2O altermagnet is correlated with the net
magnetic moment between
magnetic V atoms under uniaxial strain, thereby proposing two strategies for achieving
giant valley polarization effect. Firstly, substituting one V atom in V2Se2O with Cr to construct a ferrimagnetic monolayer VCrSe2O enhances the net
magnetic moment between
magnetic atoms, thereby realizing a
giant valley polarization effect. Applying uniaxial strain along either the a-axis or b-axis significantly increases the value of valley polarization, which exhibits a nearly linear relationship with the net
magnetic moments between the
magnetic atoms. Secondly, constructing a van der Waals
heterostructure composed of V2Se2O and {\alpha}-SnO monolayers breaks mirror
symmetry, thereby inducing a net
magnetic moment, which in turn causes a remarkable valley polarization effect. Compressing the interlayer distance of the
heterostructure can increase the net
magnetic moment between V atoms, then enhancing the value of valley polarization to nearly 400 meV. This work reveals that valley polarization in monolayer altermagnet is correlated with the net
magnetic moment between
magnetic atoms. Finally, we propose two strategies to achieve
giant valley polarization based on monolayer altermagnets, providing theoretical guidance for the potential applications of ferrimagnetic monolayers and altermagnet-based
heterostructures in valleytronics.
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All authors Weifeng Xie, Libo Wang, Xiong Xu, Yunliang Yue, Huayan Xia, Longhui He, Hui Wang
Soft Condensed Matter
Discontinuous change of viscosity in a sheared granular gas with velocity-dependent restitution
Makoto R. Kikuchi, Yuria Kobayashi and Satoshi Takada
We investigate the rheology of a sheared granular gas composed of hard spheres with a velocity-dependent restitution coefficient. Using kinetic theory, we derive the shear viscosity and show that it exhibits an S-shaped dependence on the shear rate when the restitution coefficient switches between two values depending on the collision velocity. As a result, a discontinuous change of viscosity emerges between low- and high-shear regimes, both characterized by Bagnold-type scaling. While the phenomenology resembles the Wyart-Cates scenario for dense suspensions, the present transition arises purely from kinetic effects without frictional contacts or jamming.
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Soft Condensed Matter
The effect of interactions on elastic cavitation
Ali Saeedi, S Chockalingam and Mrityunjay Kothari
Cavitation refers to the sudden, unstable expansion of a defect or cavity within a material in response to applied loads, when the loads reach a critical threshold. It is widely recognized as a common failure nucleation mechanism in soft and biological materials. For an isolated cavity in the bulk of an incompressible neo-Hookean solid loaded by remote hydrostatic tension, the classical cavitation pressure is well established as $2.5 \mu$, where $\mu$ is the shear modulus. However, in realistic settings the cavitation threshold is influenced by interaction of the cavity with nearby interfaces and other cavities. Interface interaction effects are particularly relevant in multi-material systems and additively manufactured structures, where defects frequently occur near material boundaries. Meanwhile, cavity-cavity interactions become important in materials exhibiting finite porosity, such as foams, porous solids, and phase-separating
polymers. Here, we characterize the effect of interactions on cavitation pressure for (i) a nearby rigid interface and (ii) a neighboring identical cavity. For cavities near a rigid interface, our analysis shows that the cavitation pressure increases as the initial cavity-interface distance decreases, starting from the bulk value for a distant cavity and approaching the cavitation pressure value for a defect situated at an interface ($\approx3.5\mu$) as the cavity approaches the interface boundary. In contrast, interacting cavities exhibit a non-monotonic dependence of the cavitation pressure on the initial inter-cavity distance $d$: the threshold approaches the bulk value of $2.5\mu$ for distant cavities and reaches a maximum of $\sim2.67\mu$ at $d\sim3.8R$, where $R$ is the initial cavity radius.
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Strongly Correlated Electrons
Non-collinear ferromagnetism in the Kondo lattice Ce$_5$CoGe$_2$
Jinyu Wu, Jiawen Zhang, Toni Shiroka et al. (+7 more)
The dense Kondo
lattice Ce$_5$CoGe$_2$ exhibits superconductivity once the
magnetic ordering is suppressed by pressure. Here the ambient pressure
magnetic state is investigated via magnetization, heat capacity, powder
neutron diffraction, and
muon spin relaxation ($\mu$SR) measurements.
Neutron diffraction results reveal a noncollinear
ferromagnetic structure, where the four inequivalent Ce sites exhibit different
magnetic moments. Point-charge model calculations of the crystalline-electric field (CEF) ground states corroborate different moments between the sites, and suggest sizeable components of the moments along different directions, consistent with the non-collinear structure. Analysis of the Dzyaloshinskii-Moriya (DM) interaction for the bonds connecting Ce atoms demonstrates that most of these bonds exhibit a nonzero DM vector, suggesting that competition between intersite
magnetic exchange interactions, CEF driven single-ion anisotropy, the Kondo effect and the DM interaction may drive the non-collinear ferromagnetism.
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All authors Jinyu Wu, Jiawen Zhang, Toni Shiroka, Shams Sohel Islam, Mingyi Wang, Yongjun Zhang, Devashibhai T. Adroja, Yu Liu, Huiqiu Yuan, Michael Smidman