Mesoscale and Nanoscale Physics
Advances in momentum-resolved EELS of phonons, excitons and plasmons in 2D materials and their heterostructures
Cana Elgvin, Fredrik S. Hage, Khairi F. Elyas et al. (+4 more)
Functional nanomaterials, including 2D materials and their
heterostructures are expected to impact fields ranging from catalysis, optoelectronics to nanophotonics. To realize their potential, novel experimental approaches need to be developed to characterize the combined materials and their components. Techniques using fast electrons, such as electron energy-loss spectroscopy (EELS), probe phenomena over an unrivaled energy range with high resolution. In addition, momentum-resolved EELS simultaneously records energy and momentum transfer to the sample and thus generates two-dimensional data sets for each beam position. This allows excitations that occur at large momentum transfer to be resolved, including those outside of the light cone and beyond the first Brillouin zone, all whilst retaining nanometer sized spatial selectivity. Such capabilities are particularly important when probing
phonons, plasmons,
excitons and their coupling in 2D materials and their
heterostructures.
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All authors Cana Elgvin, Fredrik S. Hage, Khairi F. Elyas, Katja Höflich, Øystein Prytz, Christoph T. Koch, Hannah C. Nerl
Materials Science
Room temperature optical control of spin states in organic diradicals
Rituparno Chowdhury, Alistair Inglis, Lucy E. Walker et al. (+13 more)
We report a family of luminescent alternant diradicals which, at room temperature, support a ground-state
spin-triplet, near-unity photoluminescence
quantum yields, and optical
spin addressability. These diradicals comprise trityl groups meta-linked via pyridyl or phenyl groups, enabling optically bright triplet-to-triplet and singlet-to-singlet transitions. At room temperature, we observe optically detected
magnetic resonance in these systems at zero
magnetic field and a strong magneto-photoluminescence (10% modulation at 2 mT applied
magnetic field). Distinct photoluminescence bands (at 630 nm and 700 nm) show opposite-sign
spin-optical responses, arising from
spin-selective intersystem crossing between triplet and singlet
manifolds. These bright, all-organic diradicals offer a new set of chemically tunable materials for room temperature
spin-optical interfaces, paving the way for application as
quantum sensors.
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All authors Rituparno Chowdhury, Alistair Inglis, Lucy E. Walker, Petri Murto, Chiara Delpiano-Cordeiro, Colin Morrison, Naitik A. Panjwani, Yao Fu, Yan Sun, Wei Zhou, Peter J. Skabara, Akshay Rao, Alexei Chepelianskii, Hugo Bronstein, Sam L. Bayliss, Richard H. Friend
Materials Science · Cross-listed from physics.chem-ph
Understanding How Synthetic Impurities Affect Glyphosate Solubility and Crystal Growth Using Free Energy Calculations and Molecular Dynamics Simulations
Alejandro Castro, Ignacio Sanchez-Burgos, Nuria H. Espejo et al. (+3 more)
Glyphosate, the most widely used herbicide worldwide, crystallizes through complex intermolecular interactions that are strongly influenced by synthesis-derived
impurities. Understanding this process at the molecular scale is critical for optimizing production, ensuring product quality, and assessing environmental impact. Here, we employ direct coexistence molecular dynamics simulations and free energy calculations to elucidate how glycine-a prevalent synthesis byproduct-modulates glyphosate solubility and
crystal growth in aqueous solutions. Our simulations identify two major mechanisms by which glycine hinders crystallization. First, direct coexistence simulations show that glycine preferentially adsorbs at
crystal surfaces, hindering glyphosate attachment and slowing growth. Second, free energy calculations demonstrate that glycine enhances glyphosate solubility, reducing the supersaturation driving force to incorporate into the
crystal phase. Experimental measurements corroborate our predictions, confirming both enhanced solubility and reduced crystallization kinetics in glycine-bearing systems. These findings establish that glycine-typically considered an inert
impurity-actively disrupts glyphosate crystallization by promoting its dissolution. More broadly, this integrated computational-experimental approach highlights the power of molecular simulations to disentangle
impurity effects, interfacial phenomena, and solution thermodynamics in crystallization, providing molecular-level insights for optimizing industrial protocols and predicting agrochemical behavior under relevant environmental conditions.
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All authors Alejandro Castro, Ignacio Sanchez-Burgos, Nuria H. Espejo, Adiran Garaizar, Giovanni Maria Maggioni, Jorge R. Espinosa
Superconductivity
Homogeneous and inhomogeneous phases in a numerical model of a time-reversal-breaking superconductor
Pedro L. Contreras E
In this manuscript, we find an inhomogeneous stripes phase in a numerical model for an unconventional
superconductor with time-reversal-breaking
symmetry and triplet odd pairing. We contrast a robust well known homogeneous phase with dilute disorder characterized by a
unitary resonance and a tiny gap that resembles an s-wave
superconductor, with a new inhomogeneous phase with extremely dilute disorder and real frequency stripes. This phase has only two ultra-small frequency collision values at the edges of the
unitary resonance, indicating the displacement of the s-wave tiny gap to the outer edges of the resonance. We perform a statistical analysis of the real frequency density and encounter a lack of spectral stability, characterized by a sequence of vertical frequency stripes. Experimentalists can verify this finding by looking for an unstable phase in extremely clean samples of candidates for triplet
superconductors.
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Materials Science
Deep prior-based denoising for state-of-the-art scientific imaging and metrology
Yuichi Yokoyama, Kohei Yamagami, Yuta Sumiya et al. (+2 more)
Deep learning has revolutionized computer
vision, yet a major gap persists between complex, data-hungry deep learning models and the practical demands of state-of-the-art scientific measurements. To fundamentally bridge this gap, we propose deep prior-based denoising, a robust deep learning model that requires no training data. We demonstrate its effectiveness by removing grid artifacts in angle-resolved photoemission spectroscopy (ARPES), a long-standing and critical data analysis challenge in materials science. Our results demonstrate that deep prior-based denoising yields clearer ARPES images in a fraction of the time required by conventional, experiment-based denoising methods. This ultra-efficient approach to ARPES will enable high-speed, high-resolution three-dimensional band structure mapping in momentum space, thereby dramatically accelerating our understanding of microscopic electronic structures of materials. Beyond ARPES, deep prior-based denoising represents a versatile tool that could become a new standard in any advanced scientific measurement fields where data acquisition is limited.
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All authors Yuichi Yokoyama, Kohei Yamagami, Yuta Sumiya, Hayaru Shouno, Masaichiro Mizumaki
Materials Science
Are diffusion models ready for materials discovery in unexplored chemical space?
Sanghyun Kim, Gihyeon Jeon, Seungwoo Hwang et al. (+4 more)
While
diffusion models are attracting increasing
attention for the design of novel materials, their ability to generate low-energy structures in unexplored chemical spaces has not been systematically assessed. Here, we evaluate the performance of two
diffusion models, MatterGen and DiffCSP, against three databases: a ternary
oxide set (constructed by a genetic
algorithm), a ternary nitride set (constructed by template informatics), and the GNoME database (constructed by a combination of both). We find that
diffusion models generally perform stably in well-sampled chemical spaces (
oxides and nitrides), but are less effective in uncommon ones (GNoME), which contains many compositions involving rare-earth elements and unconventional stoichiometry. Finally, we assess their size-extrapolation capability and observe a significant drop in performance when the number of atoms exceeds the trained range. This is attributed to the limitations imposed by periodic boundary conditions, which we refer to as the curse of periodicity. This study paves the way for future developments in materials design by highlighting both the strength and the limitations of
diffusion models.
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All authors Sanghyun Kim, Gihyeon Jeon, Seungwoo Hwang, Jiho Lee, Jisu Jung, Seungwu Han, Sungwoo Kang
Quantum Gases · Cross-listed from physics.atom-ph
Acousto-optic lens for 3D shuttling of atoms in a neutral atom quantum computer
Zhichao Guo, Rik A.H. van Herk, Edgar J.D. Vredenbregt et al. (+1 more)
We present a novel acousto-optic lens (AOL) design for neutral atom
quantum computing. This approach enhances atom rearrangement in optical tweezer arrays and addresses the speed limitations imposed by the cylindrical
lensing effect of acousto-optic deflectors (AODs). By combining a double-pass AOD configuration for dynamic focal tuning with a standard pair of crossed AODs for transverse beam steering, our design enables the generation of arbitrary focal point trajectories. This configuration enables shuttling of atoms in 3D space, thereby helping to realise fully connected two-
qubit gates and mid-
circuit measurements. We detail the optical implementation, characterize its performance, and discuss its applications in scalable
quantum computing architectures.
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All authors Zhichao Guo, Rik A.H. van Herk, Edgar J.D. Vredenbregt, Servaas J.J.M.F. Kokkelmans
Mesoscale and Nanoscale Physics
Non-Hermitian Bethe-Salpeter Equation for Open Systems: Emergence of Exceptional Points in Excitonic Spectra from First Principles
Zhenlin Zhang, Wei Hu, Enrico Perfetto et al. (+1 more)
In open
quantum systems hosting
excitons, dissipation mechanisms critically shape the excitonic dynamics, band-structure and topological properties. A microscopic understanding of
excitons in such non-Hermitian settings demands a first-principles generalization of the Bethe-Salpeter equation (BSE). Building on a recently introduced nonequilibrium Green's function formalism compatible with Lindbladian dynamics, we derive a non-Hermitian BSE from diagrammatic perturbation theory on the Keldysh contour, and obtain a microscopic excitonic
Hamiltonian that incorporates dissipation while preserving causality. We apply the formalism to valley
excitons in transition metal dichalcogenides coupled to structured
photon baths. We uncover a rich landscape of exceptional points in momentum space, forming either discrete sets or continuous
manifolds, depending on bath structure. The exceptional points give rise to nonanalytic valley-polarization, unusual polarization pattern in photoluminescence, and nontrivial topological signatures. Our results establish a first-principles framework for predicting and controlling excitonic behavior in open
quantum materials, showing how engineered environments can be leveraged to induce and manipulate non-Hermitian and topological properties.
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All authors Zhenlin Zhang, Wei Hu, Enrico Perfetto, Gianluca Stefanucci
Strongly Correlated Electrons
Superconductivity in the repulsive Hubbard model on different geometries induced by density-assisted hopping
Franco T. Lisandrini, Edmond Orignac, Roberta Citro et al. (+2 more)
We study the effect of density-assisted hopping on different dimerized
lattice geometries, such as
bilayers and ladder structures. We show analytically that the density-assisted hopping induces an attractive interaction in the lower (bonding) band of the dimer structure and a repulsion in the upper (anti-bonding) band. Overcoming the onsite repulsion, this can lead to the appearance of superconductivity with a pairing structure more complex than s-wave pairing. Combining numerical and analytical methods such as the
matrix product states ansatz, bosonization and perturbative calculations we map out the phase diagram of the two-leg ladder system and identify its superconducting phase. We characterize the transition from the non-density-assisted repulsive regime to the
spin-gapped superconducting regime as a Berezinskii-Kosterlitz-Thouless transition.
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All authors Franco T. Lisandrini, Edmond Orignac, Roberta Citro, Ameneh Sheikhan, Corinna Kollath
Materials Science
Magnetically Assisted Separation of Weakly Magnetic Metal Ions in Porous Media.Part 1: Experiments
Alwell Nwachukwu, Muhammad Garba, Jamel Ali et al. (+3 more)
We report experiments on the magnetophoresis of paramagnetic (MnCl2) and diamagnetic (ZnCl2) metal ions in porous media under the influence of a non-uniform
magnetic field generated by a permanent magnet. Experiments were carried out in a range of initial ion concentrations (1-100 mM), porous media particle sizes (63 um and 500 um), and varying mixture ratios of metal ion concentrations. For single-ion magnetophoresis, paramagnetic MnCl2 migrated toward the magnet surface, with an enrichment of approximately 2-4 percent near regions of high
magnetic field. Conversely, diamagnetic ZnCl2 moved away from regions of highest
magnetic field gradients, with depletion levels of 0.5-1.8 percent relative to the initial concentration. Our results demonstrate that magnetophoresis is directly proportional to porous media particle size, increasing with larger particle sizes, a trend attributed to the reduced drag forces experienced by the ions in media with larger particles. Interestingly, in binary mixtures, both MnCl2 and ZnCl2 migrated toward regions of highest
magnetic field, contrary to their individual behaviors. The magnetophoretic effect of MnCl2 was diminished with increasing concentrations of ZnCl2, indicating interactions between the two ions. These findings suggest that both metal ions undergo field-induced cluster formation, with cluster sizes in the micrometer range, in both single and binary ion systems. In binary mixtures, the two ions appear to interact, potentially forming mixed clusters containing both MnCl2 and ZnCl2.
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All authors Alwell Nwachukwu, Muhammad Garba, Jamel Ali, Theo Siegrist, Munir Humayun, Hadi Mohammadigoushki
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Multiplexed back focal plane imaging with on-chip integrated microlens array
Magdalena Furman, Marcin Muszyński, Przemysław Oliwa et al. (+7 more)
On-chip optical architectures that enable angle-resolved spectroscopy are essential for advancing photonic platforms towards low-volume, scalable, and cryo-compatible devices. Here, we introduce spatially resolved momentum-space imaging using arrays of 3D-printed microlenses directly integrated onto
semiconductor optical microcavities. Each microlens functions as an independent optical element with a high numerical aperture (approx. 0.95), enabling parallel back focal plane imaging across, in our implementation, 64 distinct locations. This approach eliminates the need for bulky microscope objectives while maintaining broad wavevector access, even under cryogenic conditions. We demonstrate its versatility across various cavity systems, including dielectric planar resonators, GaAs-based polariton microcavities, and CdTe platforms supporting nonequilibrium Bose-Einstein condensation of
exciton-polaritons. The microlenses not only enhance collection efficiency but also enable tightly focused excitation, yielding an order of magnitude reduction in condensation thresholds compared with conventional setups. Our results establish 3D-printed microlens arrays as a compact, versatile, integrated platform for next-generation angle-resolved spectroscopy in nanophotonics and
quantum materials.
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All authors Magdalena Furman, Marcin Muszyński, Przemysław Oliwa, Łukasz Zinkiewicz, Aleksander Bogucki, Jacek Szczytko, Piotr Wasylczyk, Wojciech Pacuski, Mateusz Król, Barbara Piętka
Materials Science
Configurational Entropy-Driven Phase Stability and Thermal Transport in Rock-Salt High-Entropy Oxides
Ashutosh Kumar, Adrien Moll, Jitendra Kumar et al. (+3 more)
High-
entropy oxides (HEOs) offer a unique platform for exploring the thermodynamic interaction between configurational
entropy and enthalpy in stabilizing complex solid solutions. In this study, a series of rock-salt structured
oxides with varying configurational
entropy, ranging from binary to multi-cation systems, to elucidate the competing roles of enthalpy and
entropy in phase stabilization is investigated. Compositions including (Ni$_{0.8}$Cu$_{0.2}$)O to(NiCuZnCoMg)$_{0.9}$A$_{0.1}$O (A = Li, Na, K) were synthesized and their stuctural, microstructural and thermal properties have been discussed. X-ray diffraction combined with thermal cycling confirms that even a medium configurational
entropy ($\sim$ 0.95R) can induce single-phase behavior stabilized by configurational
entropy ($\Delta S_{conf}$), challenging the traditional threshold of $1.5\,R$. High-resolution TEM and EDS mapping reveal nanocrytalline features and homogeneous elemental distribution respectively, while XPS analysis confirms divalent oxidation states. A strong coupling between high configurational
entropy with thermal conductivity ($\kappa$) has been observed. First, a sharp decrease in $\kappa$ with increasing $\Delta S_{conf}$ is seen and then decomposed samples (while cooling) show high $\kappa$, demonstrating the role of $\Delta S_{conf}$ on $\kappa$. Furthermore, Li-doped compositions exhibit improved thermoelectric performance, with a maximum figure of merit ($zT$) of $\sim$0.15 at 1173K\, driven by low thermal conductivity and favorable carrier transport. The results highlight that configurational
entropy, even at intermediate values, plays a significant role in stabilizing disordered single-phase
oxides and tailoring
phonon transport.
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All authors Ashutosh Kumar, Adrien Moll, Jitendra Kumar, Diana Dragoe, David Bérardan, Nita Dragoe
Disordered Systems and Neural Networks · Cross-listed from nlin.AO
Triadic percolation on multilayer networks
Hanlin Sun, Filippo Radicchi and Ginestra Bianconi
Triadic interactions are special types of higher-order interactions that occur when regulator nodes modulate the interactions between other two or more nodes. In presence of triadic interactions, a percolation process occurring on a single-layer network becomes a fully-fledged dynamical system, characterized by period-doubling and a route to chaos. Here, we generalize the model to multilayer networks and name it as the multilayer triadic percolation (MTP) model. We find a much richer dynamical behavior of the MTP model than its single-layer counterpart. MTP displays a Neimark-Sacker bifurcation, leading to oscillations of arbitrarily large period or pseudo-periodic oscillations. Moreover, MTP admits period-two oscillations without negative regulatory interactions, whereas single-layer systems only display discontinuous hybrid transitions. This comprehensive model offers new insights on the importance of regulatory interactions in real-world systems such as
brain networks,
climate, and ecological systems.
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Materials Science
Rostyslav O. Serha, Carsten Dubs and Andrii V. Chumak
Quantum magnonics studies the
quantum properties of
magnons, the quanta of
spin waves, and their application in
quantum information processing. Progress in this field depends on identifying
magnetic materials with characteristics tailored to the diverse requirements of magnonics and
quantum magnonics. For single-
magnon excitation, its control, hybrid coupling, and
entanglement, the most critical property is the ability to support long
magnon lifetimes. This perspective reviews established and emerging
magnetic materials, including
ferromagnetic metals, Heusler compounds, antiferromagnets, altermagnets, organic and 2D van der Waals magnets, hexaferrites, europium chalcogenides, and in particular yttrium iron garnet (YIG), highlighting their key characteristics. YIG remains the
benchmark, with bulk
crystals supporting sub-microsecond Kittel-mode lifetimes and ultra-pure spheres achieving $\sim18\,\mu$s for dipolar-exchange
magnons at millikelvin temperatures. However, thin YIG films on gadolinium gallium garnet (GGG) substrates suffer from severe lifetime reduction due to substrate-induced losses. In contrast, YIG films on a new
lattice matched, diamagnetic alternative, yttrium scandium gallium/aluminum garnet (YSGAG), overcomes these limitations and preserves low
magnetic damping down to millikelvin temperatures. These advances provide a practical pathway toward ultralong-living
magnons in thin films, enabling scalable
quantum magnonics with coherent transport, strong
magnon-
photon,
magnon-
qubit coupling, and integrated
quantum networks.
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Materials Science
A Room-Temperature Ferrotoroidic Material Exhibiting Magnetic Semiconductor Properties with Superhigh Hole Mobility
Jianyuan Qi, Shijie Xiong, Beining Ma et al. (+1 more)
The design and fabrication of room-temperature ferrotoroidic materials and
magnetic semiconductors are recognized worldwide as a great challenge, and of both theoretical and practical importance in the field of condensed matter physics and information storage. Reported herein are ferrotoroidic
crystal powder and film formed by supramolecular self-assembly based on uranyl and cyclodextrin, with the Curie temperature above room temperature. Experimental measurements and calculations demonstrate spontaneous
vortex-like
alignment of
magnetic moments and furthermore a macroscopic long-range arrangement in the
crystal, which breaks simultaneously space-inversion and time-reversal
symmetries, exhibiting strong superexchange,
spin-orbit coupling as well as anomalous
Hall effect (AHE). The electrical measurements show the film with a superhigh carrier mobility of 3200 cm2*V-1*s-1 and a
Hall resistivity as high as 0.32 mV*A-1*cm at room temperature. This work is expected to pave greatly the applied research on new-generation magnetoresistive random access
memory (MRAM), especially as flexible material.
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All authors Jianyuan Qi, Shijie Xiong, Beining Ma, Xinghai Shen
Mesoscale and Nanoscale Physics
Clarification of Floquet–Enhanced Thermal Emission Through the Nonequilibrium Green's Function Formalism
Yuhua Ren, Hui Pan and Jian-Sheng Wang
Floquet engineering offers a powerful route to enhance emission in time-modulated media. Here, we investigate the influence of time-modulated permittivity in silicon carbide on its intensity spectrum. We consider both the nonequilibrium Green's function approach and the macroscopic
quantum electrodynamics approach, and establish their formal compatibility by deriving the Lippmann-Schwinger equation in both cases. To analyze spectral features, we propose several methods for decomposing the electric field into positive- and negative-frequency components, along with the criteria required for physical consistency. Our analytical and numerical results show that, when defined appropriately, the intensity spectrum avoids divergence, though the resulting enhancement remains modest. These findings provide a unified theoretical foundation for modeling time-dependent media, and reinforce the utility of Floquet engineering as a versatile platform for tailoring emission dynamics.
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Strongly Correlated Electrons
Field-induced magnetic phases in the Kitaev candidate Na$_3$Co$_2$SbO$_6$
Kranthi Kumar Bestha, Manaswini Sahoo Niccolò Francini, Robert Kluge et al. (+13 more)
We report a rich anisotropic
magnetic phase diagram of Na$_3$Co$_2$SbO$_6$, a previously proposed cobaltate Kitaev candidate, based on field- and temperature-dependent magnetization, specific heat, and magnetocaloric effect studies. At low temperatures, our experiments uncover a low-lying $j_{\textrm{eff}} = \frac{1}{2}$ state with an
antiferromagnetic ground state and pronounced in-plane versus out-of-plane anisotropy. The experimentally identified
magnetic phases are theoretically characterized through classical Monte Carlo simulations within an extended Kitaev-Heisenberg model with additional ring exchange interactions. The resulting phase diagram reveals a variety of exotic field-induced
magnetic phases, including double-$\textbf{q}$, $\frac{1}{3}$-AFM, zigzag, and
vortex phases.
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All authors Kranthi Kumar Bestha, Manaswini Sahoo Niccolò Francini, Robert Kluge, Ryan Morrow, Andrey Maljuk, Sabine Wurmehl, Sven Luther, Yurii Skourski, Hannes Kühne, Swarnamayee Mishra, Jochen Geck, Manuel Brando, Bernd Büchner, Laura T. Corredor, Lukas Janssen, Anja U. B. Wolter
Strongly Correlated Electrons
Cubic magnetic anisotropy in $B$20 magnets: Interplay of anisotropy and magnetic order in Fe$_{1-x}$Co$_{x}$Si
G. Gödecke, A. O. Leonov, J. Grefe et al. (+2 more)
The metallic systems MnSi and Fe$_{1-x}$Co$_{x}$Si are known to feature a generic
magnetic phase diagram primarily determined by the isotropic exchange and Dzyaloshinskii-Moriya interactions. However, additional weaker anisotropies, lowest in the hierarchy of energy scales, play a crucial role: they determine the relative order of phases in the phase diagram and may even enable skyrmion stability far below the ordering temperature. Among cubic B20 helimagnets, the
insulator Cu$_2$OSeO$_3$ is currently the only known example exhibiting a low-temperature, anisotropy-induced skyrmion pocket. In this manuscript, we present a systematic study of cubic magnetocrystalline anisotropy by means of angle-resolved SQUID magnetization measurements in MnSi and Fe$_{1-x}$Co$_{x}$Si ($0.08 \leq x \leq 0.70$) single
crystals and provide quantitative values of the anisotropy constants. For Fe$_{1-x}$Co$_{x}$Si, the cubic anisotropy is found to be strongly dependent on the Co concentration $x$. In particular, for low Co concentrations ($x \sim 0.10$), the anisotropy is sufficiently strong to stabilize a low-temperature skyrmion
lattice, in agreement with theoretical predictions. This finding suggests that Fe$_{1-x}$Co$_{x}$Si may represent the first
chiral metallic system to exhibit a low-temperature skyrmion phase controllably stabilized by cubic anisotropy for specific directions of the
magnetic field.
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All authors G. Gödecke, A. O. Leonov, J. Grefe, S. Süllow, D. Menzel
Strongly Correlated Electrons
Consistent gauge theories for the slave particle representation of the strongly correlated $t$-$J$ model
Xi Luo, Tao Shi, Yue Yu et al. (+1 more)
We aim to clarify the confusion and inconsistency in our recent works [1,2], and to address the incompleteness therein. In order to avoid the ill-defined nature of the free propagator of the gauge field in the ordered states of the $t$-$J$ model, we adopted a gauge fixing that was not of the Becchi-Rouet-Stora-Tyutin (BRST) exact form in our previous work [2]. This led to the situation where Dirac's second-class constraints, namely, the slave particle number constraint and the Ioffe-Larkin current constraint, were not rigorously obeyed. Here we show that a consistent gauge fixing condition that enforces the exact constraints is BRST-exact in our theory. An example is the Lorenz gauge. On the other hand, we prove that although the free propagator of the gauge field in the Lorenz gauge is ill-defined, the full propagator is still well-defined. This implies that the strongly correlated $t$-$J$ model can be exactly mapped to a perturbatively controllable theory within the slave particle representation.
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All authors Xi Luo, Tao Shi, Yue Yu, Long Liang
Materials Science
Strained Donor-Bound Excitons in $^{28}$Si
David A. Vogl, Noah L. Braitsch, Başak Ç. Özcan et al. (+3 more)
We present a comprehensive experimental study of the neutral donor to donor-bound
exciton transition (D$^0$$\rightarrow\,$D$^0$X) in isotopically enriched $^{28}$Si, focusing on the group-V donors P, As, and Sb under finely tuned uniaxial stress along the [100] and [110]
crystal axes and
magnetic fields from 3.5 mT to 1.7 T. From these measurements, donor-specific deformation potentials are extracted. The uniaxial electron deformation potential $\Xi_\mathrm{u}$ is found to be significantly larger than values reported for other states or transitions in silicon and shows a clear dependence on the donor species, indicating an increased sensitivity of the D$^0$X state to strain and central-
cell effects. We also observe a
magnetic field dependence of the hole shear deformation potential $d$, suggesting a more complex strain coupling mechanism than captured by standard theory. Diamagnetic shift parameters determined from Zeeman spectra show good agreement with earlier measurements. Our results provide a refined parameter set critical for the design of silicon
quantum devices based on D$^0$X transitions.
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All authors David A. Vogl, Noah L. Braitsch, Başak Ç. Özcan, Niklas S. Vart, M. L. W. Thewalt, Martin S. Brandt
Mesoscale and Nanoscale Physics
Quantum-Limited Acoustoelectric Amplification in a Piezoelectric-2DEG Heterostructure
Eric Chatterjee, Daniel Soh and Matt Eichenfield
We provide a
quantum mechanical description of
phonon amplification in a
heterostructure consisting of a two-dimensional electron gas (2DEG) stacked on top of a piezoelectric material. An applied drift voltage effectively creates a population inversion in the momentum states of the 2DEG electrons, giving rise to spontaneous emission of
phonons. Once an acoustic wave is launched, the pumped electrons release
phonons via stimulated emission, returning to depleted ground states before being pumped back to the excited states. We show that whereas efficient amplification using a 1D electron gas requires the acoustic wavelength to roughly equal the average electron-electron spacing, a 2DEG enables efficient amplification for any wavelength greater than the average electron-electron spacing. We derive the imaginary and real parts of the 2DEG first-order acoustic susceptibility as functions of electronic drift velocity in specific limits and derive the gain per unit length for the signal and the
quantum noise, with the gain matching the classical result in the short-electronic-lifetime (low-mobility) regime. Moreover, we analyze the gain clamping due to pump depletion and calculate the maximum achievable intensity. Our results provide a framework for designing novel acoustic devices including a
quantum phononic
laser and phase-insensitive
quantum phononic amplifiers.
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Mesoscale and Nanoscale Physics
Tunable Chern Insulator States with Coexisting Magnonic and Electronic Topology in 2D Honeycomb Kitaev Ferromagnets
Haozhou Cai, Zhiming Xu, Jian Wu et al. (+1 more)
The coexistence of topological
magnons and electrons in
magnetic materials presents a compelling route toward developing low-dissipation, multifunctional spintronic devices. However, material systems enabling their simultaneous realization and control remain largely unexplored. Here, we propose the coexistence and concurrent tunability of magnonic and electronic Chern
insulator phases in Kitaev magnets and use MnBr$_{3}$ monolayer as a prototype. We find the significant Kitaev interaction in MnBr$_{3}$ induces the magnonic Chern
insulator phase, manifesting as the
magnon thermal
Hall effect. Concurrently, MnBr$_{3}$ exhibits the
quantum anomalous
Hall effect driven by its electronic Chern
insulator phase. Crucially, we demonstrate that these dual topological phases can be simultaneously controlled by reorienting the in-plane
spins with an external
magnetic field. Our findings not only deepen the fundamental understanding of
spin excitations in Kitaev magnets but also provide a promising platform for exploring the interplay between electronic and magnonic
topology.
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All authors Haozhou Cai, Zhiming Xu, Jian Wu, Weiyi Pan
Superconductivity
Quantum fluctuation-induced first-order breaking of time-reversal symmetry in unconventional superconductors
Yin Shi
Spontaneous time-reversal
symmetry breaking in
superconductors with competing non-degenerate pairing channels is an exotic
quantum phase transition that could give rise to robust topological superconductivity and unusual magnetism. It is proposed mostly in two-dimensional systems and is signaled by a nonzero relative phase between the two superconducting order parameters, hence it should particularly be prone to order-parameter phase fluctuations. Nevertheless, the existing understanding of it is still at the mean-field level. Here, we illustrate the non-negligible effects of the phase fluctuations on such
quantum phase transitions using the hole-doped square-
lattice $t$-$J$ model as an example. We derive the phase fluctuation-corrected free energy and show that under the
quantum phase fluctuations, the time-reversal asymmetric $s+id$ phase region splits off a dome featuring a first-order border with the $d$ phase, indicating the possibility of a phase separation into the time-reversal symmetric and asymmetric phases. The phase fluctuations also narrow the range of the $s+id$ phase considerably. We further discuss the implications of our findings for recent experiments on disorder-induced first-order
quantum breakdown of superconductivity and promising high-temperature topological superconductivity in twisted cuprate Josephson junctions.
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Materials Science
$\beta$-Ga$_2$O$_3$(001) surface reconstructions from first principles and experiment
Konstantin Lion, Piero Mazzolini, Kingsley Egbo et al. (+4 more)
We present a comprehensive investigation of reconstructions on $\beta$-Ga$_2$O$_3$(001) combining first-principles calculations with experimental observations. Using ab initio atomistic thermodynamics and replica-exchange grand-canonical molecular dynamics simulations, we explore the configurational space of possible reconstructions under varying chemical potentials of oxygen and gallium. Our calculations reveal several stable surface reconstructions, most notably a previously unreported 1$\times$2 reconstruction consisting of paired GaO$_4$ tetrahedra that exhibits remarkable stability across a wide range of experimental growth conditions. In this reconstruction, two Ga atoms share one oxygen bond and are separated by a distance of 2.64 Å along the [010] direction. High-angle annular dark-field scanning transmission electron microscopy imaging of homoepitaxially grown (001) layers is consistent with the predicted structure. Additional investigations of possible indium substitution at the surface sites, which can occur during metal-exchange catalysis growth, reveal a cooperative effect in In incorporation, with distinct stability regions for In-substituted structures under O-rich conditions. Our findings provide an understanding for controlling surface properties during epitaxial growth of $\beta$-Ga$_2$O$_3$(001).
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All authors Konstantin Lion, Piero Mazzolini, Kingsley Egbo, Toni Markurt, Oliver Bierwagen, Martin Albrecht, Claudia Draxl
Strongly Correlated Electrons · Cross-listed from quant-ph
Partial Self-Correction in Layer Codes
Dominic J. Williamson
The storage of large-scale
quantum information at finite temperature requires an autonomous and reliable
quantum hard drive, also known as a self-correcting
quantum memory. It is a long-standing open problem to find a self-correcting
quantum memory in three dimensions. The recently introduced Layer Codes achieve the best possible scaling of code parameters and logical energy barrier in three dimensions, these are tantalizing features for the purposes of self-correction. In this work we show that a family of Layer Codes, based on good
Quantum Tanner Codes, exhibit partial self-correction. Their
memory time grows exponentially with linear system size, up to a length scale that is exponential in the inverse temperature. At this length scale, the
memory time scales as a double exponential of inverse temperature. To establish this result we introduce a concatenated matching decoder that combines three rounds of parallelized minimum-weight perfect-matching with a decoder for good
Quantum Tanner Codes. We show that our decoder corrects errors up to a constant fraction of the energy barrier, and a constant fraction of the code distance, for a family of Layer Codes. Our results position Layer Codes as the leading candidate for a partially self-correcting
memory in three dimensions. While they fall short of achieving strict self-correction in the thermodynamic limit, our work highlights the potential of these local codes in three dimensions, with fast distance and logical
qubit growth, fast decoders, and a long
memory time over a wide range of parameters.
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Materials Science
Quasiparticle effects and strong excitonic features in exfoliable 1D semiconducting materials
Simone Grillo, Chiara Cignarella, Friedhelm Bechstedt et al. (+5 more)
We report a comprehensive first-principles study of the electronic and optical properties of recently identified exfoliable one-dimensional semiconducting materials, focusing on chalcogenide-based atomic chains derived from van der Waals-bonded bulk
crystals. Specifically, we investigate covalently bonded S3 and Te3 chains, and polar-bonded As2S3 and Bi2Te3 chains, using a fully first-principles approach that combines density-functional theory (DFT), density-functional perturbation theory (DFPT), and many-body perturbation theory within the GW approximation and Bethe-Salpeter equation (BSE). Our vibrational analysis shows that freestanding isolated wires remain dynamically stable, with the zone-center optical
phonon modes leading to infrared activity. The main finding of this study is the presence of very strong
exciton binding energies (1-3 eV), which make these novel 1D materials ideal platforms for room-temperature excitonic applications. Interestingly, the
exciton character remains Wannier-Mott-like, as indicated by average electron-hole separations larger than the
lattice constant. Notably, the optical gaps of these materials span a wide range - from infrared (0.8 eV, Bi2Te3), through visible spectrum (yellow: 2.17 eV, Te3; blue: 2.71 eV, As2S3), up to ultraviolet (4.07 eV, S3) - highlighting their versatility for broadband optoelectronic applications. Our results offer a detailed, many-body perspective on the optoelectronic behavior of these low-dimensional materials and underscore their potential for applications in next-generation nanoscale optoelectronic devices.
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All authors Simone Grillo, Chiara Cignarella, Friedhelm Bechstedt, Paola Gori, Maurizia Palummo, Davide Campi, Nicola Marzari, Olivia Pulci
Statistical Mechanics
An exactly solvable asymmetric simple inclusion process
Arvind Ayyer and Samarth Misra
We study a generalization of the asymmetric simple inclusion process (ASIP) on a periodic one-dimensional
lattice, where the integers in the particles rates are deformed to their $t$-analogues. We call this the $(q, t, \theta)$~ASIP, where $q$ is the asymmetric hopping parameter and $\theta$ is the
diffusion parameter. We show that this process is a misanthrope process, and consequently the steady state is independent of $q$. We compute the steady state, the one-point correlation and the current in the steady state. In particular, we show that the single-site occupation probabilities follow a beta-binomial distribution at $t=1$. We compute the two-dimensional phase diagram in various regimes of the parameters $(t, \theta)$ and perform simulations to justify the results. We also show that a modified form of the steady state weights at $t \neq 1$ satisfy curious palindromic and antipalindromic
symmetries. Lastly, we define an enriched process at $t=1$ and $\theta$ an integer which projects onto the $(q, 1, \theta)$~ASIP and whose steady state is uniform, which may be of independent interest.
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Superconductivity
Altermagnetism and Superconductivity: A Short Historical Review
Zhao Liu, Hui Hu and Xia-Ji Liu
This review is organized into three parts. In the first part, we explore the deep interconnections among three seemingly unrelated concepts in condensed matter physics: electronic
liquid crystal phases, multipole expansions, and altermagnetism. At the heart of these phenomena lies a shared foundation:
spin-momentum locking in the nonrelativistic regime. Originally proposed in the context of electronic
liquid crystal phases, nonrelativistic
spin-momentum locking was later elegantly incorporated into the formalism of multipole expansions. This framework can be further extended across multiple atomic sites, making it particularly effective for describing altermagnets, which host localized
magnetic moments with anisotropic magnetization densities distributed over sublattices. In the second part, we examine superconducting phenomena associated with altermagnetism from three complementary perspectives. First, we investigate superconductivity associated with nonrelativistic
spin-momentum locked
Fermi surfaces, the unifying theme of the first part, highlighting a rich variety of unconventional superconducting states. These include finite-momentum pairing, $d$-wave and
spin-triplet superconductivity, and topological Bogoliubov
Fermi surfaces, among others. We then review superconductivity emerging from either static altermagnetic order or altermagnetic fluctuations. Finally, we discuss the possible competition and intertwining between altermagnetic order and superconductivity, illustrated using the repulsive Hubbard model. Additional related topics are addressed in the concluding part. Overall, this work offers both an accessible introduction to the newly identified
magnetic order known as altermagnetism and a conceptual guide for researchers aiming to harness the ensuing unconventional superconductivity in the development of future
quantum technologies.
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Strongly Correlated Electrons
Nematic Fluctuations and Electronic Correlations in Heavily Hole-Doped Ba$_{1-x}$K$_x$Fe$_2$As$_2$ Probed by Elastoresistance
Franz Eckelt, Steffen Sykora, Xiaochen Hong et al. (+6 more)
This work investigates nematic fluctuations and electronic correlations in the hole-doped iron pnictide
superconductor Ba$_{1-x}$K$_x$Fe$_2$As$_2$ by means of longitudinal and transverse elastoresistance measurements over a wide doping range ($0.63 < x < 0.98$). For this purpose, the orbital character of the electronic response was revealed by decomposition of the elastoresistance into the $A_{1g}$ and $B_{2g}$
symmetry channels. It was shown that at lower doping levels nematic fluctuations in the $B_{2g}$ channel dominate, while for $x > 0.68$ the $A_{1g}$ channel becomes dominant and reaches a pronounced maximum at $x \approx 0.8$ which indicates strong orbital-selective electronic correlations. Despite the dominance of the $A_{1g}$ signal at high doping, a weak contribution in the $B_{2g}$ channel persists, which can be interpreted as a remnant of nematic fluctuations. Model calculations based on a five-orbital tight-binding
Hamiltonian with interactions attribute the observed enhancement in the $A_{1g}$ channel to an orbital-selective Kondo-like resonance, predominantly involving the $d_{xy}$ orbital. We discuss our results in relation to the
evolution of the Sommerfeld coefficient reported in the literature and a reported change of the superconducting order parameter. All this indicates that for $x > 0.68$ qualitatively new physics emerges. Our findings suggest that electronic correlations in the strongly hole-doped regime play an important role in superconductivity, while the detectable weak nematic fluctuations may also be of relevance.
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All authors Franz Eckelt, Steffen Sykora, Xiaochen Hong, Vilmos Koscis, Vadim Grinenko, Bernd Büchner, Kunihiro Kihou, Chu-Ho Lee, Christian Hess
Mesoscale and Nanoscale Physics
Chern insulators and topological flat bands in cavity-embedded kagome systems
Hikaru Goto, Ryo Okugawa and Takami Tohyama
We investigate topological band structures of a kagome system coupled to a circularly polarized cavity mode, using a model based on a muffin-tin potential and
quantum light-matter interaction. We show that Chern insulating phases emerge in the cavity-embedded kagome system due to the light-matter interaction that breaks time-reversal
symmetry. We also find that a nearly flat band can be topologically nontrivial with a nonzero Chern number. By varying the light-matter interaction, we also reveal that topological phase transitions occur between different Chern insulating phases in the ultrastrong coupling regime. The phase transitions change the sign of the Chern number, switching the direction of the edge current. We demonstrate the existence of topological edge modes in the cavity-embedded kagome Chern
insulators by constructing a low-energy effective tight-binding model.
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