Materials Science
Noise Estimation and Suppression in Quantitative EMCD Measurements
Hitoshi Makino, Bernd Rellinghaus, Sebastian Schneider et al. (+2 more)
Quantitative electron
magnetic circular dichroism (EMCD) in transmission electron microscopy (TEM) enables the measurement of
magnetic moments with elemental and atomic site sensitivity, but its practical application is fundamentally limited by noise. This study presents a comprehensive methodology for noise estimation and suppression in EMCD measurements, demonstrated on Ti-doped barium hexaferrite lamellae. By employing a classical three-beam geometry and long-term acquisition of electron energy-loss spectra, we systematically analyze the signal-to-noise ratio (SNR) across individual energy channels using bootstrap statistics. A robust energy
alignment procedure based on the neighboring Ba-M4,5 edges with an adequate energy upsampling is introduced to minimize systematic errors from energy misalignment. The impact of detector noise, particularly from CMOS-based EELS cameras, is evaluated through variance-to-mean analysis and described by the noise amplification coefficients, revealing that detector-amplified shot noise is the dominant noise source. We recommend a stricter SNR threshold for reliable EMCD detection and quantification, ensuring that critical spectral features such as the Fe-L2,3 peaks meet the requirements for quantitative analysis. The approach also provides a framework for determining the minimum electron dose necessary for valid measurements and can be generalized to scintillator-based or direct electron detectors. This work advances the reliability of EMCD as a quantitative tool for
magnetic characterization at the nanoscale with unknown
magnetic structures. The proposed procedures lay the groundwork for improved error handling and SNR optimization in future EMCD studies.
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All authors Hitoshi Makino, Bernd Rellinghaus, Sebastian Schneider, Axel Lubk, Darius Pohl
Other Condensed Matter
Strong quantum interaction between excitons bound by cavity photon exchange
Miguel S. Oliveira and Cristiano Ciuti
We theoretically predict the interaction between polaritonic excitations arising from the coupling of a cavity
photon mode with bound to continuum intersubband transitions in a doped
quantum well. The resulting
exciton bound by
photon exchange, recently demonstrated experimentally, exhibits a binding energy that can be continuously tuned by varying the cavity frequency. We show that polariton-polariton interactions, originating from both Coulomb interactions and Pauli blocking, can be dramatically enhanced by reducing the
exciton binding energy, thereby increasing the effective Bohr radius along the growth direction. This regime is reminiscent of Rydberg atoms, where weak binding leads to strong
quantum interactions. Our predictions indicate that this physics can give rise to
giant quantum optical nonlinearities in the mid and far infrared, a spectral region that remains largely unexplored in
quantum optics and offers exciting opportunities for both fundamental studies and applications.
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Quantum Gases
Thermal effects on density-modulated phases in a dipolar Bose–Einstein condensate
Changjian Yu, Jinbin Li and Kui-Tian Xi
Density-modulated phases in dipolar Bose–Einstein condensates arise from the competition between contact repulsion, long-range dipole–dipole interactions, and beyond-mean-field fluctuations. We examine finite-temperature stationary states of a harmonically trapped dipolar Bose gas using a temperature-dependent extended Gross–Pitaevskii equation within the local-density approximation. In this framework, the thermal correction shifts some structural boundaries toward larger scattering lengths and changes the parameter region in which connected density-modulated states are obtained. The density contrast changes sharply at $T = 0$, whereas at finite temperature it varies more gradually, consistent with a smooth crossover-like
evolution in the finite trapped system. We also use Leggett's bound to estimate a
geometric upper limit on the possible superfluid response for representative density profiles. These results suggest that finite-temperature corrections can reshape pattern formation in dipolar
quantum gases.
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Materials Science
Anomalous enhancement of magnetism by nonmagnetic doping in the honeycomb-lattice antiferromagnet ErOCl
Yanzhen Cai, Mingtai Xie, Jing Kang et al. (+8 more)
Tuning
magnetic anisotropy through chemical doping is a powerful strategy for designing functional materials with enhanced
magnetic properties. Here, we report an enhanced Er^3+
magnetic moment resulting from nonmagnetic Lu^3+ substitution in the honeycomb-
lattice antiferromagnet ErOCl. Unlike the Curie-Weiss type divergence typically observed in diluted
magnetic systems, our findings reveal a distinct enhancement of magnetization per Er^3+ ion under high
magnetic fields, suggesting an unconventional mechanism. Structural analysis reveals that Lu^3+ doping leads to a pronounced contraction of the c axis, which is attributed to chemical pressure effects, while preserving the layered SmSI-type
crystal structure with space group R-3m. High-resolution Raman spectroscopy reveals a systematic blueshift of the first and seventh crystalline electric field (CEF) excitations, indicating an increase in the axial CEF parameter B_2^0. This modification enhances the
magnetic anisotropy along the c axis, leading to a significant increase in magnetization at low temperatures and under high
magnetic fields, contrary to conventional expectations for
magnetic dilution. Our work not only clarifies the intimate connection between magnetism and CEF in rare-earth compounds, but more importantly, it reveals a physical pathway to effectively tune
magnetic anisotropy via anisotropic
lattice distortion induced by chemical pressure.
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All authors Yanzhen Cai, Mingtai Xie, Jing Kang, Weizhen Zhuo, Wei Ren, Xijing Dai, Anmin Zhang, Jianting Ji, Feng Jin, Zheng Zhang, Qingming Zhang
Superconductivity
Charge stripe and superconductivity tuned by interlayer interaction in a sign-problem-free bilayer extended Hubbard model
Runyu Ma, Zenghui Fan, Hongxin Liu et al. (+2 more)
Competing orders represent a central challenge in understanding strongly correlated systems. In this work, we employ projector
quantum Monte Carlo simulations to study a sign-problem-free
bilayer extended Hubbard model. In this model, a charge stripe phase, characterized by a peak at momentum $k_x=2\pi\delta$ is induced by highly anisotropic interlayer
spin-exchange coupling $J_z$, and strongly suppressed upon introducing the
spin-flip term $J_\bot$; in contrast, \(J_\perp\) favors the emergence of interlayer pairing superconductivity. We further demonstrate that the anisotropy of the interlayer
spin-exchange directly governs the competition between these two phases, while the on-site interaction \(U\) plays a complex role in tuning both the charge stripe and superconductivity. Our work identifies the key factors driving charge stripe formation, highlights the sensitivity of both the charge stripe and superconducting phases to interaction parameters, and thereby provides valuable insights into competing orders in strongly correlated systems.
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All authors Runyu Ma, Zenghui Fan, Hongxin Liu, Tianxing Ma, Hai-Qing Lin
Superconductivity
Skyrmion-vortex pairing and vortex-drag induced Skyrmion Hall effect
Shantonu Mukherjee
An interaction between
ferromagnetic and superconducting orders, to be realized in a two dimensional
ferromagnetic superconductor, is proposed obeying necessary
symmetry principles. This interaction allows us to formulate a duality, similar to the
Boson-
vortex duality in 2+1 dimensional superfluid. In the dual theory the Skyrmion and the
vortex excitations interact with each other via an emergent gauge field. The static interaction potential is attractive for a Skyrmion and a
vortex with opposite topological charges. This interaction can lead to formation of bound pairs of the mentioned topological excitations. Furthermore, we argue that such pairing implies that a Magnus force acting on the
vortex induces a transverse,
Hall-like drift motion of the Skyrmion, which we term the
vortex-drag induced Skyrmion
Hall effect. Possible experimental manifestations of this effect are also discussed.
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Disordered Systems and Neural Networks · Cross-listed from hep-lat
Dirac spectrum in the chirally symmetric phase of a gauge theory. II
Matteo Giordano
I discuss the consequences of the constraints imposed on the Dirac spectrum by the restoration of
chiral symmetry in the
chiral limit of gauge theories with two light
fermion flavors, with particular
attention to the fate of the anomalous $\mathrm{U}(1)_A$
symmetry. Under general, physically motivated assumptions on the spectral density and on the two-point
eigenvalue correlation function, I show that effective $\mathrm{U}(1)_A$ breaking in the symmetric phase requires specific spectral features, including a spectral density effectively behaving as $m^2\delta(\lambda)$ in the
chiral limit, a two-point function singular at zero, and delocalized near-zero modes, besides an instanton gas-like behavior of the topological charge distribution. I then discuss a $\mathrm{U}(1)_A$-breaking scenario characterized by a power-law divergent spectral peak tending to $O(m^4)/|\lambda|$ in the
chiral limit and by a near-zero mobility edge, and argue that the mixing of the approximate zero modes associated with a dilute gas of topological objects provides a concrete physical mechanism producing the required spectral features, and so a viable mechanism for effective $\mathrm{U}(1)_A$ breaking in the symmetric phase of a gauge theory.
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Strongly Correlated Electrons
Pseudo-Goldstone mode in altermagnetic $\alpha$-MnTe: high-field electron spin resonance studies
K. Yu. Povarov, J. Wosnitza, S. Rößler et al. (+3 more)
We report multi-frequency electron
spin resonance spectroscopy studies of $\alpha$-MnTe in
magnetic fields up to $16$ T, applied along the easy anisotropy axis. At temperatures below $T_\mathrm{N} = 310$ K, we observe a single resonance line corresponding to the pseudo-Goldstone mode of the
antiferromagnetic resonance (AFMR). This mode exhibits the isotropic behavior with $g_\mathrm{eff}=2.01$, consistent with a complete quench of the orbital angular momenta for Mn$^{2+}$ ions. At low temperatures, the resonance mode is remarkably narrow ($\sim50$ mT for the full width at the half-maximum at $5$ K). The AFMR mode exhibits substantial broadening with increasing temperature, which can be understood in terms of the
magnon-
magnon scattering
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All authors K. Yu. Povarov, J. Wosnitza, S. Rößler, M. Schmidt, A. A. Tsirlin, S. A. Zvyagin
Strongly Correlated Electrons · Cross-listed from math-ph
A Remarkable Application of Zassenhaus Formula to Strongly Correlated Electron Systems
Louis Jourdan and Patrick Cassam-Chenaï
We show that the Zassenhaus decomposition for the exponential of the sum of two non-commuting operators, simplifies drastically when these operators satisfy a simple condition, called the no-mixed adjoint property. An important application to a
Unitary Coupled Cluster method for strongly correlated electron systems is presented. This ansatz requires no Trotterization and is exact on a
quantum computer with a finite number of Givens gate equals to the number of free parameters. The formulas obtained in this work also shed light on why and when optimization after Trotterization gives exact solutions in disentangled forms of
unitary coupled cluster.
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Strongly Correlated Electrons
Ultrafast recovery dynamics of dimer stripes in IrTe2
M. Rumo, G. Kremer, M. Heber et al. (+10 more)
The transition metal dichalcogenide IrTe2 displays a remarkable series of first-order phase transitions below room temperature, involving
lattice displacements as large as 20 percents of the initial bond length. This is nowadays understood as the result of strong electron-
phonon coupling leading to the formation of local multicentre dimers that arrange themselves into one-dimensional stripes. In this work, we study the out-of-
equilibrium dynamics of these dimers and track the time
evolution of their population following an infrared photoexcitation using free-electron lased-based time-resolved X-ray photoemission spectroscopy. First, we observe that the dissolution of dimers is driven by the transfer of energy from the electronic subsystem to the
lattice subsystem, in agreement with previous studies. Second, we observe a surprisingly fast relaxation of the dimer population on the timescale of a few picoseconds. By comparing our results to published ultrafast electron diffraction and angle-resolved photoemission spectroscopy data, we reveal that the long-range order needs tens of picoseconds to recover, while the local dimer distortion recovers on a short timescale of a few picoseconds.
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All authors M. Rumo, G. Kremer, M. Heber, N. Wind, C. W. Nicholson, K. Y. Ma, G. Brenner, F. Pressacco, M. Scholz, K.Rossnagel, F. O. von Rohr, D. Kutnyakhov, C. Monney
Soft Condensed Matter
Morphology, Polarization Patterns, Compression, and Entropy Production in Phase-Separating Active Dumbbell Systems
Lucio Mauro Carenza, Claudio Basilio Caporusso, Pasquale Digregorio et al. (+3 more)
Polar patterns and topological defects are ubiquitous in active matter. In this paper, we study a paradigmatic polar active dumbbell system through numerical simulations, to clarify how polar patterns and defects emerge and shape
evolution. We focus on the interplay between these patterns and morphology, domain growth, irreversibility, and compressibility, tuned by dumbbell
rigidity and interaction strength. Our results show that, when separated through MIPS, dumbbells with softer interactions can slide one relative to each other and compress more easily, producing blurred hexatic patterns, polarization patterns extended across entire hexatically varied domains, and stronger compression effects. Analysis of isolated domains reveals the consistent presence of inward-pointing topological defects that drive cluster compression and generate non-trivial density profiles, whose magnitude and extension are ruled by the
rigidity of the pairwise potential. Investigation of
entropy production reveals instead that clusters hosting an aster (spiral) defect are characterized by a flat (increasing)
entropy profile mirroring the underlying polarization structure, thus suggesting an alternative avenue to distinguish topological defects on thermodynamical grounds. Overall, our study highlights how interaction strength and defect-compression interplay affect cluster
evolution in particle-based active models, and also provides connections with recent studies of continuum polar active field models.
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All authors Lucio Mauro Carenza, Claudio Basilio Caporusso, Pasquale Digregorio, Antonio Suma, Giuseppe Gonnella, Massimiliano Semeraro
Materials Science
Molecular Dynamics Study of Irradiation-Induced Defect and Dislocation Evolution in Strained Nickel
Maciej Wilczynski, Mark Fedorov, Tymofii Khvan et al. (+2 more)
Molecular dynamics (MD) simulations were performed to investigate the influence of mechanical strain on irradiation-induced defect and dislocation
evolution in nickel single
crystals subjected to cumulative overlapping 5 keV collision cascades at 300 K. The simulations reveal that tensile strain modifies the dynamics of defect generation and recovery, promoting stress-assisted defect mobility and enhancing defect survival compared to the unstrained case. The heat spike duration and intensity decrease systematically with increasing strain, indicating faster energy dissipation and altered defect recombination behavior under applied stress. Analysis of the dislocation structure shows that Shockley-type partial dislocations dominate the microstructural response, while Hirth and other dislocation types remain comparatively minor. Both the total and Shockley dislocation densities reach a saturation value of $~10^{16}m^{-2}$ , marking the establishment of a steady-state microstructure governed by the balance between dislocation accumulation and recovery. The
evolution of the total dislocation density with strain is successfully described by the Kocks-Mecking model, demonstrating its applicability to strain-dependent irradiation effects in metallic systems
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All authors Maciej Wilczynski, Mark Fedorov, Tymofii Khvan, F. Javier Dominguez-Gutierrez, and Jacek Jagielski
Other Condensed Matter · Cross-listed from physics.chem-ph
Regularised density-potential inversion for periodic systems: application to exact exchange in one dimension
Oliver M. Bohle, Maryam Lotfigolian, Andre Laestadius et al. (+1 more)
A detailed convex analysis-based formulation of density-functional theory for periodic systems in arbitrary dimensions is presented. The electron-electron interaction is taken to be of Yukawa type, harmonising with underlying function spaces for densities and wave functions. Moreau–Yosida regularisation of the underlying non-interacting density functionals is then considered, allowing us to recast the Hohenberg–Kohn mapping in a form that is insensitive to perturbations (non-expansiveness) and lends itself to numerical implementation. The general theory is exemplified with a numerical Hartree–Fock implementation for one-dimensional systems. We discuss in particular the challenge of self-consistent field optimisation in calculations related to the regularised noninteracting Hohenberg–Kohn map. The implementation is used to demonstrate that it is practically feasible to recover local Kohn–Sham potentials reproducing the effects of exact exchange within this scheme, which provides a proof-of-principle for recovering the exchange-correlation potential at more accurate levels of theory. Error analysis is performed for the regularised inverse Kohn–Sham
algorithm by quantifying, both theoretically and numerically, how perturbations of the input ground-state density propagate through the regularised density-to-potential map.
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All authors Oliver M. Bohle, Maryam Lotfigolian, Andre Laestadius, Erik I. Tellgren
Materials Science
Energy evolution in nanocrystalline iron driven by collision cascades
Ivan Tolkachev, Daniel R. Mason, Max Boleininger et al. (+2 more)
Nanocrystalline materials are promising candidates for future fusion reactor applications, due to their high density of grain boundaries which may serve as sinks for irradiation induced defects. We use molecular dynamics to simulate collision cascades in nanocrystalline iron and compare these to collision cascades in initially defect free single
crystals. We create nanocrystalline samples via Voronoi tessellation of initially randomly placed grain seeds and via severe plastic shearing. An irradiation induced annealing is observed whereby after ~ 2 displacements per atom (dpa), irradiation drives all simulation
cells to a single crystalline state. Irradiation-induced defects that distort the
lattice generate elastic strain, so we use excess potential energy as a measure of defect content. At low doses, the Voronoi samples feature a few large, low energy grains, whereas the sheared samples show many small, high energy grains due to the high defect and grain boundary content caused by severe deformation. As dose increases beyond 1 dpa however, all nanocrystalline samples converge to a similar behaviour. Excess potential energy mirrors this trend, plateauing above ~ 4 dpa. We hypothesise that the initially pristine
cells will also reach a similar plateau after 5 dpa, which is seemingly confirmed by running a single instance of each
cell type to 10 dpa. A model is developed to explain the energy
evolution.
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All authors Ivan Tolkachev, Daniel R. Mason, Max Boleininger, Pui-Wai Ma, Felix Hofmann
Strongly Correlated Electrons
Non-equilibrium correlation effects in spin transport through the 2D ferromagnet Fe$_4$GeTe$_2$
Declan Nell, Stefano Sanvito and Andrea Droghetti
Understanding non-
equilibrium spin transport through 2D ferromagnets is a theoretical challenge, as correlations produce a complex electronic structure with coexisting itinerant and localized electrons. We have developed a fully non-
equilibrium ab initio method, combining density functional theory, dynamical mean-field theory, and non-
equilibrium Green's functions to investigate the transport in Fe$_4$GeTe$_2$, a prototypical high-temperature 2D ferromagnet. We show that, while
spin transport remains essentially single-particle under moderate bias, inelastic
spin-dependent scattering of carriers with particle-hole excitations drives a distinctive hot-correlated electron regime beyond a critical voltage. This regime is marked by incoherent features in both the electronic spectrum and the conductance, which are experimentally accessible. Our results demonstrates that material-specific many-body non-
equilibrium methods are essential for a complete understanding of
spin transport in 2D ferromagnets.
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Quantum Gases
Impurity-controlled vortex mobility and pair-breaking in fermionic superfluid rings
Buğra Tüzemen, Andrea Barresi, Gabriel Wlazłowski et al. (+2 more)
Using time-dependent density functional theory, we study how density and size of
impurities govern dissipation of persistent currents of fermionic superfluid rings in the BCS regime. The critical winding number for
vortex emission increases with
impurity density, but this enhancement is
impurity size-dependent and capped by the pair-breaking threshold. Below this
vortex-emission threshold, the winding number remains constant while flow energy dissipates through
impurity-enhanced pair-breaking. Above the threshold,
vortex-
impurity interactions produce distinct mobility regimes-deflected trajectories, individual pinning, collective pinning, and inter-site hopping, controlled by the
impurity size and density, which determine the dominant dissipation channel. These findings provide design principles for ultracold-atom experiments and insights into
vortex-pinning dynamics in
neutron-
star crusts and
superconductors.
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All authors Buğra Tüzemen, Andrea Barresi, Gabriel Wlazłowski, Piotr Magierski, Klejdja Xhani
Materials Science
Observation of hexagonal close-packed water ice at conditions in ice giant planetary interiors
Alexis Forestier, Gunnar Weck, Sandra Ninet et al. (+4 more)
Using synchrotron x-ray diffraction in
laser-heated diamond anvil
cells, we report the observation of an hexagonal close-packed (hcp) phase of water ice at high pressure and temperature conditions. Above 200 GPa and 1800 K, the hcp phase becomes dominant upon entering the superionic regime, as evidenced by anomalous thermal expansion. Observations are consistent with the hcp phase becoming thermodynamically more stable than the face-centered cubic (fcc) phase via a martensitic transition extending across the 130 - 200 GPa pressure range, within the superionic regime. Hcp ice is also observed to emerge from stacking disorder developing within the fcc oxygen
lattice upon cooling, during its reversion to the bcc phase. The presence of an fcc-hcp martensitic transition in the superionic regime of warm dense ice may have implications for planetary models of Uranus and Neptune.
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All authors Alexis Forestier, Gunnar Weck, Sandra Ninet, Gaston Garbarino, Mohamed Mezouar, Frédéric Datchi, Paul Loubeyre
Mesoscale and Nanoscale Physics
Bounds on Lorentz-violating parameters in magnetically confined 2D systems: A phenomenological approach
Edilberto O. Silva
We present a unified, SI-consistent framework to constrain minimal SME coefficients $a_\mu$ and $b_\mu$ using magnetically confined two-dimensional electron systems under a uniform
magnetic field. Working in the nonrelativistic (Schrödinger–Pauli) limit with effective mass, we derive the radial problem for cylindrical geometries and identify how spatial components ($\mathbf a,\mathbf b$) reshape the effective potential, via $1/r$ and $r$ terms or
spin-selective offsets, while scalar components ($a_0,b_0$) act through a global energy shift and a
spin-momentum coupling. Phenomenological upper bounds follow from requiring LV-induced shifts to lie below typical spectroscopic resolutions: $|a_0|\lesssim\delta E$, $|b_z|\lesssim\delta E/\hbar$, and compact expressions for $|a_\varphi|$ and $|b_0|$ that expose their dependence on device scales ($r_0$, $B_0$, $\mu$, $m$). Dimensional analysis clarifies that, in this regime, spatial $a_i$ carry momentum dimension and $b_i$ carry inverse-time/length dimensions, ensuring gauge-independent, unit-consistent reporting. Finite-difference
eigenvalue calculations validate the scaling laws and illustrate spectral signatures across realistic parameter sets. The results show that scalar sectors (notably $a_0$) are tightly constrained by state-of-the-art $\mu$eV-resolution probes, while spatial and axial sectors benefit from
spin- and $m$-resolved spectroscopy and
geometric leverage, providing a reproducible pathway to test Lorentz
symmetry in condensed-matter platforms.
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Mesoscale and Nanoscale Physics
Phase-Rotated Altermagnets as Chern Valves for Topological Transport
Carlos Caro and Francisco Gamez
Motivated by the emerging control of Berry-
curvature textures in altermagnets, we explore a two-terminal configuration where a topological-
insulator film is interfaced with two altermagnetic electrodes whose crystalline phases can be rotated independently. The proximity coupling imprints each momentum-dependent of the altermagnet
spin texture onto the Dirac surface states, giving rise to an angular mass whose sign follows the
lattice orientation. Adjusting the phase of one electrode redefines this mass pattern, thereby tuning the number and spatial distribution of
chiral edge channels. This results in discrete conductance steps and a reversible inversion of the thermoelectric coefficient-achieved without external
magnetic fields or net magnetization. A compact Dirac model captures both the quantized switching and its resilience to moderate disorder. Overall, this
symmetry-driven mechanism provides a practical and low-dissipation route to programmable topological transport via
lattice rotation.
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Mesoscale and Nanoscale Physics
Viscous AC current-driven nanomotors
Vladimir U. Nazarov, Tchavdar N. Todorov and E. K. U. Gross
The recent discovery that electrons in nano-scale conductors can act like a highly viscous
liquid has triggered a surge of research activities investigating consequences of this surprising fact. Here we demonstrate that the electronic viscosity has an enormous influence on the operation of a prototypical AC-current-driven nano-motor. The design of this prototype consists of a diatomic molecule immersed in an otherwise homogeneous electron
liquid which carries an AC current. The motion of the diatomic is determined by a subtle balance between the current-induced forces and electronic friction. By ab-initio time-dependent density-functional simulations we demonstrate that the diatomic performs a continuous rotation provided the amplitude and frequency of the imposed AC current lie within certain islands of stability. Outside these islands the
nuclear motion is either chaotic or comes to a stand-still. The proposed design of the nano-motor is the conceptually simplest realization of the idea of an molecular waterwheel sandwiched between conducting leads
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Superconductivity
Quantum geometric magnetic monopole and two-phase superconductivity in CeRh$_2$As$_2$
Kosuke Nogaki and Youichi Yanase
Recent angle-resolved photoemission spectroscopy (ARPES) and density functional theory plus Hubbard $U$ (DFT+$U$) studies revealed that a heavy-
fermion superconductor CeRh$_2$As$_2$ exhibits van Hove singularities and the Dirac point near the
Fermi level $E_{\mathrm F}$, which are key signatures of strong-correlation effects and
quantum geometry. We have constructed a two-dimensional 12-orbital Dirac-Anderson model as an effective model for CeRh$_2$As$_2$. The band structure and
Fermi-surface
topology of the Dirac-Anderson model agree well with the ARPES data and the DFT+$U$ calculations. We show that the
quantum geometry strongly favors
magnetic-monopole fluctuations because of the Dirac point at the $M$ point. By solving the linearized Éliashberg equation, we demonstrate that the $B_{1u}$ and $B_{2g}$ representations,
spin-triplet states originating from the Dirac point, exhibit the leading superconducting instabilities. By comparing the random-phase approximation and the fluctuation-exchange approximation, we further demonstrate that strong-correlation effects mitigate the influence of
quantum geometry. The phase diagram of CeRh$_2$As$_2$ under pressure is discussed in connection with the theoretical results.
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Strongly Correlated Electrons
Soft and hard x-ray orbital-resolved photoemission study of a strongly correlated Cd-Ce quasicrystal approximant
Goro Nozue, Hidenori Fujiwara, Satoru Hamamoto et al. (+15 more)
We have investigated the orbital-dependent electronic states of Cd6Ce, a prototype of strongly correlated rare-earth-based Tsai-type quasicrystals and approximants (ACs) by soft and hard x-ray photoemission spectroscopy. Our results reveal that the 4f orbitals are predominantly hybridized with the valence-band electrons far from the
Fermi level (EF), in sharp contrast to the hybridization with conduction electrons at EF seen for the intermetallic Ce-based compounds. This anomalous hybridization should be taken into account in discussing the unresolved
magnetic ground state in Cd6Ce. These findings suggest that Cd-based ACs, some of which show the multi-step
magnetic transitions, could provide a new platform for investigating novel
magnetic properties that cannot be understood within the conventional framework of hybridization at EF.
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All authors Goro Nozue, Hidenori Fujiwara, Satoru Hamamoto, Miwa Tsutsumi, Akane Ose, Takayuki Kiss, Atsushi Higashiya, Atsushi Yamasaki, Yuina Kanai-Nakata, Shin Imada, Masaki Oura, Kenji Tamasaku, Makina Yabashi, Tetsuya Ishikawa, Farid Labib, Shintaro Suzuki, Ryuji Tamura, Akira Sekiyama
Superconductivity
Signatures of superconducting pairing driven by electron-electron interactions in moiré WSe$_2$/WSe$_2$ homobilayer modelled by Hubbard Hamiltonian
Andrzej Biborski and Michał Zegrodnik
Strong evidence of unconventional superconductivity has been very recently reported experimentally in twisted transition metal dichalcogenide
bilayer and gathered a significant amount of interest. Here we consider the Hubbard model on a triangular
lattice describing the hole-doped moiré superlattice emerging in WSe$_{2}$/WSe$_{2}$ twisted homobilayer in the moderately correlated regime. By applying the Density
Matrix Renormalization Group, we diagonalize the
spin-valley-polarized
Hamiltonian and show signatures of coexisting singlet and triplet pairings in the range of hole dopings and displacement fields reported in the experiments. In this view, we show that the superconductivity in the WSe$_{2}$/WSe$_{2}$ twisted homobilayer is likely to be induced by electronic correlations and has a mixed-
symmetry character. These predictions can shed light on the nature of the superconducting state observed in the twisted homobilayer of WSe$_{2}$/WSe$_{2}$. We also identify the emerging superconducting orders, which are $d_{xy}(d_{x^2-y^2} \pm id_{xy} )$ and $p_y(p_{x}\mp ip_{y})$ for the singlet and triplet channels in the cylinder of width three(four), respectively.
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Superconductivity
V. M. Gordeeva, Yanmeng Lei, Xiyin Ye et al. (+4 more)
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All authors V. M. Gordeeva, Yanmeng Lei, Xiyin Ye, G. A. Bobkov, A. M. Bobkov, Tao Yu, I. V. Bobkova
Mesoscale and Nanoscale Physics
Identifying geometric third-order nonlinear transport in disordered materials
Zhen-Hao Gong, Zhi-Hao Wei, Hai-Zhou Lu et al. (+1 more)
In nonlinear transport, the
quantum-
geometric effects can generate higher-harmonic voltages in response to a driving current, which has defined a fast-moving field of intense interest. However, in realistic materials where disorder scattering also contributes to nonlinear transport, identifying the
geometric mechanisms remains a challenge. In particular, a theoretical framework for data analysis is still lacking for nonlinear transport at any order. Here, we develop a mechanism-resolved and
symmetry-guided framework for identifying mechanisms of third-order nonlinear transport in disordered materials. We find a total of 20 mechanisms of third-order nonlinear transport, by treating
quantum-
geometric and disorder-mediated mechanisms on an equal footing. More importantly, we propose a protocol of data analysis that combines
symmetry diagnosis of
magnetic point groups and scaling law of relation between the third-order nonlinear
Hall conductivity and linear longitudinal conductivity. We identify characteristic fingerprints in the scaling-law weights, which allow the mechanisms to be quantitatively distinguished in experiments. We have applied the protocol to identify the
geometric mechanisms in materials with and without time-reversal
symmetry, including 2D materials, topological materials, and altermagnets. The theory can be generalized to arbitrary orders of nonlinear transport, further promoting nonlinear transport as a probe of
geometric effects and phase transitions in
quantum materials.
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All authors Zhen-Hao Gong, Zhi-Hao Wei, Hai-Zhou Lu, X. C. Xie
Materials Science
Unlocking Dynamic Luminescent Mapping of pH with Sustainable Lignin-Derived Carbon Dots with Multimodal Readout Capacity
Maja Szymczak, Jan Hočevar, Jernej Iskra et al. (+4 more)
In this work, we demonstrate the use of CQDs synthesized from lignin - currently one of the most abundant and underutilized by-products of paper and pulp production - for advanced pH monitoring applications. The presented approach integrates green chemistry principles with an operator-friendly, low-cost, and practical solution for spatial and temporal pH measurement. CQDs functionalized with m-aminophenylboronic acid enable highly sensitive and reversible pH readouts through two complementary mechanisms: ratiometric monitoring of emission band intensities, and direct visual observation of colorimetric changes reflected in the CIE1931 chromaticity coordinates. The system achieves maximal sensitivities of 137 percent per pH unit and 49.5 percent per pH unit, respectively, while simultaneously maintaining high measurement resolution and full reproducibility of the readouts, placing it among the most effective CQD-based pH sensors reported to date. Here, we demonstrate the capability of 2D luminescent imaging of pH distributions, allowing for both spatially resolved and time-resolved monitoring. Employing just an excitation source, a digital camera or smartphone, and RGB channel analysis, the setup eliminates the necessity for specialized filters or sophisticated instrumentation. The combination of
multimodal readout strategies with the capacity for large-area visualization establishes lignin-derived CQDs as a sustainable and practical platform for pH sensing. By simultaneously addressing the challenges of waste valorization and the demand for innovative sensing technologies, this solution fulfills the requirements of both environmentally responsible material design and next-generation pH sensor development.
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All authors Maja Szymczak, Jan Hočevar, Jernej Iskra, Darja Lisjak, Jelena Papan Djaniš, Lukasz Marciniak, Karolina Elzbieciak-Piecka
Statistical Mechanics
Evaluating the Performance of Direct Higher-Order Formulations in Combinatorial Optimization Problems
Kazuki Ikeuchi, Yoshiki Matsuda and Shu Tanaka
Ising machines, including
quantum annealing machines, are promising next-generation computers for combinatorial optimization problems. However, due to hardware limitations, most Ising-type hardware can only solve objective functions expressed in linear or quadratic terms of binary variables. Therefore, problems with higher-order terms require an order-reduction process, which increases the number of variables and constraints and may degrade solution quality. In this study, we evaluate the effectiveness of directly solving such problems without order reduction by using a high-performance simulated annealing-based optimization solver capable of handling
polynomial unconstrained binary optimization (PUBO) formulations. We compare its performance against a conventional quadratic unconstrained binary optimization (QUBO) solver on the same hardware platform. As
benchmarks, we use the low autocorrelation binary sequence (LABS) problem and the vehicle routing problem with distance balancing, both of which naturally include higher-order interactions. Results show that the PUBO solver consistently achieves superior solution quality and stability compared to its QUBO counterpart, while maintaining comparable computational time and requiring no order-reduction compilation indicating potential advantages of directly handling higher-order terms in practical optimization problems.
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Materials Science · Cross-listed from math-ph
Peierls Instability in Hexagonal Lattices
David Gontier, Thaddeus Roussigné and Éric Séré
We investigate a conventional tight-binding model for
graphene, where distortion of the honeycomb
lattice is allowed, but penalized by a quadratic energy. We prove that the optimal 3-periodic
lattice configuration has Kekulé O-type
symmetry, and that for a sufficiently small elasticity parameter, the minimizer is not translation-invariant. Conversely, we prove that for a large elasticity parameter the translation-invariant configuration is the unique minimizer.
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Materials Science
Edge Magnetism in Colloidal MoS2 Triangular Nanoflakes
Surender Kumar, Stefan Velja, Muhammad Sufyan Ramzan et al. (+1 more)
The control of localized
magnetic domains at the nanoscale holds great promise for next-generation spintronic applications. Colloidal transition metal dichalcogenides nanostructures are experimentally accessible and chemically tunable platforms for spintronics, deserving dedicated research to assess their potential. Here, we investigate from first principles free-standing triangular MoS2 nanoflakes with sulfur-terminated, hydrogen-passivated edges, to probe intrinsic
spin behavior at varying side lengths. We find a critical edge length of approximately 1.5 nm separating nonmagnetic nanoflakes from larger ones with a
magnetic ground state emerging from several, energetically competing
spin configurations. In these systems, the
magnetic activity is not uniformly distributed along the edges but localized on specific "
magnetic islands" around molybdenum edge atoms. The localization of
magnetic moments is robust even in non-equilateral nanoflake geometries, highlighting their intrinsic stability regardless of the (high)
symmetry of the hosting structure. These findings establish that the S-terminated, H-passivated triangular MoS2 nanoflakes are a stable and experimentally accessible platform via colloidal synthesis for low-dimensional, next-generation spintronic devices.
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All authors Surender Kumar, Stefan Velja, Muhammad Sufyan Ramzan, Caterina Cocchi
Soft Condensed Matter
Vector Nematodynamics with Symmetry-driven Energy Exchange
L. M. Pismen
We review inadequacy of existing nematodynamic theories and suggest a novel way of establishing relations between nematic orientation and flow based on the local
symmetry between simultaneous rotation of nematic
alignment and flow, which establishes energy exchange between the the two without reducing the problem to near-
equilibrium conditions and invoking Onsager's relations. This approach, applied in the framework of the vector-based theory with a variable modulus, involves antisymmetric interactions between nematic
alignment and flow and avoids spurious instabilities in the absence of an active inputs.
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