Soft Condensed Matter
Density-Selected Topological Pathways in the Melting of Single-Particle-Thick Stripes
José Rafael Bordin
The melting of stripe-forming systems involves changes in connectivity that are not fully captured by conventional structural and orientational descriptors. We investigate a two-dimensional model with competing interactions whose low-temperature phase consists of one-particle-thick stripes. Molecular dynamics simulations along seven heating isochores are analyzed using thermodynamic, orientational, dynamical, and graph-based observables. Heating produces a multistage reconstruction in which the loss of stripe
alignment and the reorganization of filament connectivity occur over distinct temperature ranges. Density controls whether the disordered filaments fragment into finite
polymer-like clusters or remain joined in a dynamically fluid, system-spanning network. The topological observables distinguish these outcomes, which are not resolved by the thermodynamic and orientational responses alone. Thus, the same ordered stripe microphase can melt into topologically distinct fluids selected by density.
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Soft Condensed Matter
Magnetic active matter across scales
Francisca Guzmán-Lastra, Margaret Rosenberg, Marco Musacchio et al. (+2 more)
Magnetic interactions provide a versatile and powerful tool for controlling and organizing active matter, where individual units continuously consume energy to drive autonomous motion. These interactions arise naturally in biological systems, such as magnetotactic bacteria, and can be engineered into synthetic platforms, including colloidal microswimmers,
magnetic nanoparticles, and macroscopic granular
robots. This review focuses on active, self-propelled particles that carry an intrinsic
magnetic dipole moment, powered by their own energy consumption rather than driven by external fields; here, the dipole moment mediates interactions and self-organization, not propulsion. We survey experimental and theoretical studies across all length scales, showing how dipolar interactions shape single-particle dynamics, collective behavior, and self-organization. We discuss models incorporating pairwise dipolar forces and confinement, and examine emergent phenomena such as chaining, swarming, and tunable pattern formation. We close by outlining challenges and opportunities in the design, control, and application of
magnetic active systems, from programmable materials and biomedical actuation to nonequilibrium physics.
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All authors Francisca Guzmán-Lastra, Margaret Rosenberg, Marco Musacchio, Lorenzo Caprini, Hartmut Löwen
Mesoscale and Nanoscale Physics
Quantum Anomalous Hall Effect in $d^{10}$ Oxide Monolayers
Zeyu Li, Xudong Zhu, Yulei Han et al. (+1 more)
Quantum anomalous
Hall effect (QAHE) arises from the interplay between
magnetic order and
spin-orbit coupling, which opens up a topologically nontrivial band gap to host
chiral edge states in the absence of
magnetic field. So far,
magnetic order of QAHE usually originates from partially filled transition-metal $d$ orbitals or correlation-driven moiré bands. Here, we propose an experimentally accessible family of two-dimensional
oxides, M$_2$DO$_6$ (M = Zn, Cd; D = Se, Te), that can realize QAHE from the half-filled O-$2p$ orbital induced spontaneous ferromagnetism. In M$_2$DO$_6$ monolayers,
spin-polarized Dirac points appear at K/K$^{\prime}$ valleys and along $\Gamma$-K/$\Gamma$-K$^{\prime}$ lines. $C_3$ rotational
symmetry then generates eight
symmetry-related crossings in the first Brillouin zone. Upon gap opening by
spin-orbit coupling, each massive Dirac point contributes half Chern number, resulting in a high-Chern-number QAHE phase with $\mathcal{C}=4$. We establish cation deintercalation as a general strategy to activate O-$2p$ ferromagnetism in
oxides. Our finding provides a route to realize QAHE from O-$2p$ ferromagnetism and offers design principles applicable to oxygen-based
magnetic topology platforms beyond conventional $d$-electron systems.
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All authors Zeyu Li, Xudong Zhu, Yulei Han, Zhenhua Qiao
Soft Condensed Matter
Effect of Weak Non-Conservative Dynamics on Pattern Formation in Scalar Active Matter
Sameer Kumar
Biological systems such as bacteria and
cells undergo growth or degradation, resulting in weak violations of mass conservation. We investigate how such weak non-conservative dynamics affect phase separation in scalar active matter by incorporating a reaction term into a minimal continuum model. Through numerical simulations and linear stability analysis, we show that even weak non-conservative reactions arrest coarsening and stabilize nonequilibrium microphase-separated states. With increasing activity, the system undergoes a morphological transition from interconnected labyrinthine patterns to worm-like structures and eventually to isolated droplets. Quantitative analysis of the correlation function and static structure factor reveals a well-defined steady-state characteristic length. Qualitative analysis of the resulting phases shows that the non-conservative reaction primarily promotes microphase separation and enhances local hexagonal ordering, while activity predominantly controls the domain morphology. Our results demonstrate that weak violations of mass conservation fundamentally alter the nonlinear coarsening dynamics of active phase separation and provide a minimal framework for understanding pattern formation in related systems.
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Materials Science
Optically Tunable Threshold Switching and Thermally Activated Transport in Planar Ag/MAPbI$_3$ Thin Single-Crystal Devices
Ofelia Durante, Valeria Demontis, Sebastiano De Stefano et al. (+14 more)
Halide perovskites have enabled major advances in optoelectronics, extending well beyond photovoltaics. Their mixed ionic-electronic conduction, once regarded as detrimental to device stability, is increasingly viewed as a functional degree of freedom for
memory and neuromorphic-inspired devices, especially when coupled to external stimuli such as light. Specifically, single
crystals are attractive models because they suppress grain-boundary effects and microstructural disorder that can mask intrinsic transport and interfacial mechanisms in polycrystalline films. Here, we report the growth of thin methylammonium lead iodide (MAPbI$_3$) single
crystals by a space-confined method and their integration into planar two-terminal devices with directly deposited Ag contacts. At room temperature, the devices exhibit ultra-low dark currents ($10^{-13}-10^{-12}$ A) and negligible hysteresis in the dark. Under illumination, the current increases due to photogeneration and the I-V characteristics develop a pronounced polarity-dependent hysteresis and a threshold-like transition between two conductance states. Temperature-dependent dark measurements (300-400 K) show thermionically activated, contact-influenced transport and a weakly varying normalized hysteresis metric. Together with the back-to-back Schottky-diode analysis and control devices using more inert contact materials, these results support a transport model in which Ag/perovskite interfaces play a central role and the hysteretic response is influenced by coupled interfacial and ionic processes.
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All authors Ofelia Durante, Valeria Demontis, Sebastiano De Stefano, Selene Matta, Adolfo Mazzotti, Daniela Marongiu, Emanuele Meloni, Elisa Pili, Fang Liu, Nicola Sestu, Angelica Simbula, Mauro Carta, Michele Saba, Andrea Mura, Massimiliano Di Ventra, Giovanni Bongiovanni, Antonio Di Bartolomeo
Soft Condensed Matter
Lipid Controlled Non-Monotonic Assembly and Rheology of an Egg Yolk Protein at Water-Soybean Oil Interface
Nancy Jaglan, Rumal Singh and Sajal K Ghosh
An essential component of food items like mayonnaise and salad dressing is hen egg yolk. Phosvitin (PVT) is a phosphoprotein, which exists in the granules of this hen egg yolk which stabilizes the food emulsion by preventing phase separation. To understand, how this
protein is adsorbed at the interface of water and edible oil in the presence and absence of lipids is essential for improved control in food production. To monitor the kinetics of this adsorption, the dynamic interfacial tension has been determined in the current investigation. The drop in interfacial tension over time indicates the adsorption of
protein at interface which is enhanced on increasing the concentration of
protein in water phase. However, at higher concentration, the positive activation energy hinders the adsorption process resulting a saturated interfacial tension. The dilation rheology of the macromolecular film at this oil-water interface shows the elastic nature of the film to be greater than the viscous nature, indicating the formation of a soft gel film. At low concentration, the zwitterionic lipid, 1-palmitoyl-2-oleoyl-sn-glycero 3-phosphocholine (POPC), promotes this
protein adsorption at the interface. Interestingly, at high concentration, the lipid overtakes the interface removing the
protein from there. The lipid-
protein composite film again shows the nature of a soft gel. The non-monotonic effects of lipids on assembly of
protein at the water-edible oil interface is an important observation to optimize the composition of relevant food products.
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Statistical Mechanics · Cross-listed from math-ph
Confinement transitions in half-space constrained Riesz gases
Sung-Soo Byun, Yong-Woo Lee and Eui Yoo
We study a Riesz gas with interaction parameter $s \in (d-3,d)$ in an arbitrary spatial dimension $d$, confined to a half-space by a hard wall. We prove that the
equilibrium measure exhibits a dichotomy according to the interaction range. For $s \in (d-2,d)$, corresponding to the weakly long-ranged regime, the
equilibrium measure always retains a non-trivial bulk component and thus is never completely confined to the wall. In contrast, for $s \in (d-3,d-2]$, corresponding to the strongly long-ranged regime, a confinement transition occurs: there exists a critical wall position beyond which the
equilibrium measure is supported entirely on the wall. Our
theorem generalises recent results established for the Coulomb gas, corresponding to the case $s=d-2$.
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Materials Science
Data-Efficient Adaptation of DPA-4 Force Fields to DFT+U Energetics: A Case Study in NiO
Fengyu Xie, Peiheng Jiang and Zhicheng Zhong
Foundation machine-learned force fields (MLFFs) are often pretrained on broad materials
datasets whose electronic-structure conventions may not reproduce the phase energetics required for a specific correlated material. Using NiO as a case study, we examine whether incorrect source-level phase energetics can be corrected efficiently through target-level fine-tuning. Along a common structural interpolation, non-
spin-polarized PBE and
ferromagnetic PBE+U predict opposite energetic orderings of the octahedral Oct and square-planar Sqr phases. Pretrained DPA-4 models adapt rapidly to the NiO PBE+U surface, reaching energy and force root-mean-square errors (RMSEs) of approximately 0.5 meV/atom and 30 meV/Å, respectively, with approximately 170 PBE+U labels. Crucially, models previously fine-tuned to the opposing no-U surface recover the qualitative PBE+U phase ordering with nearly the same target-data efficiency as models fine-tuned directly from their respective pretrained initializations. Our results show that incorrect source-level phase energetics can be reversed through target-level fine-tuning, and suggest a practical multi-fidelity strategy in which pretraining prioritizes broad, consistent, and affordable data, while compact target-level
datasets impose energetics through application-specific fine-tuning.
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Materials Science
Lithography-free patterning of SrTiO$_3$-based two-dimensional electron gases using direct atomic layer processing
Anshu Gupta, Karolis Parfeniukas, Amit Chanda et al. (+5 more)
We present a scalable and lithography-free strategy for the realization of a two-dimensional electron gas (2DEG) in TiO$_2$-patterned SrTiO$_3$ (100) via Al deposition using magnetron sputtering. A 15 nm thick TiO$_2$ layer, deposited by direct atomic layer processing, is employed to spatially define the conducting regions, enabling direct transport measurements without post-growth microfabrication. Upon Al deposition, an insulating AlO$_x$ overlayer is formed, and the region lacking the TiO$_2$ pattern leads to the creation of oxygen vacancies in SrTiO$_3$. These oxygen vacancies act as electron donors, populating the Ti 3$d$ conduction bands and giving rise to a confined 2DEG at the interface. Magneto-transport measurements reveal a sheet carrier density on the order of $\approx5-7\times10^{13}$ cm$^{-2}$, comparable to values typically achieved in pulsed
laser deposition-grown SrTiO$_3$-based
heterostructures, along with effective electrostatic tunability. This work demonstrates a simple, cost-effective, and industry-compatible route for engineering
oxide 2DEGs, providing a versatile platform for scalable device fabrication and interfacial transport studies.
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All authors Anshu Gupta, Karolis Parfeniukas, Amit Chanda, Thor Hvid-Olsen, Mira Baraket, Maksym Plakhotnyuk, Kasper S. Pedersen, Felix Trier
Quantum Gases · Cross-listed from quant-ph
Antibunching Enhancement via Non-Markovianity in a Hybrid Optical-Microwave Cross-Cavity
Shiying Gu, Jun-Qi Li and Liping Guo
Unconventional
photon blockade (UPB) provides an attractive route for generating antibunched light through
quantum interference without requiring strong nonlinear coupling. In conventional Markovian systems, irreversible dissipation progressively destroys the phase coherence, even limiting the achievable single-
photon purity. Here we propose a scheme for imposing non-Markovian effects on a microwave cavity where a Er$^{3+}$:Y$_2$SiO$_5$
crystal loaded into a hybrid optical-microwave system. Based on the time-convolutionless non-Markovian framework, we derive the time-dependent non-Markovian decay rate and the renormalized microwave drive in the weak-coupling regime. We show that the second-order correlation function is significantly suppressed, even to the order of $10^{-7}$, since the backflow of environmental information enhances
photon blocking. In addition, this structured reservoir engineering not only provides an additional degree of freedom, but also further optimizes the blockade via optical detuning. Importantly, the delayed second-order correlation exhibits a broadened antibunching profile, thereby relaxing the timing requirements for single-
photon synchronization. Our results demonstrate that environmental non-Markovianity can be transformed from a source of decoherence into a controllable
quantum resource, opening new opportunities for high-purity single-
photon generation.
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Materials Science · Cross-listed from physics.optics
Aggregation-engineered loss-tolerant strong coupling in metallic microcavities
Andrea Betti, Eleonora Cara, Giulia Serrano et al. (+7 more)
Room-temperature strong coupling in organic microcavities is usually achieved by combining high-quality optical resonators with highly ordered excitonic media, a requirement that limits scalability and processing flexibility. Here we show that this constraint can be relaxed by using molecular aggregation as a design parameter rather than treating it as a parasitic effect. We realize solution-processed Rhodamine 6G-poly(vinyl alcohol) films embedded in low-quality-factor silver Fabry-Perot microcavities and demonstrate clear angle-resolved anticrossing with coupling energies up to 324 meV despite the large optical losses of the metallic mirrors. A two-
exciton coupled-oscillator model shows that the relative weight of these species controls the collective coupling strength and can be tuned through dye loading and
spin-coating conditions. In contrast, angle-resolved photoluminescence is dominated by a broad, red-shifted lower-polariton emission, consistent with relaxation through excimer-like states formed in densely packed molecular domains. These results identify molecular aggregation as a practical design lever for loss-tolerant strong coupling in wet-processed metallic cavities and suggest that ground-state aggregates and excited-state excimer-like species play distinct roles in polariton formation and emission.
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All authors Andrea Betti, Eleonora Cara, Giulia Serrano, Lorenzo Poggini, Alessia Valzelli, Natascia De Leo, Paolo Bartolini, Andrea Taschin, Renato Torre, Alice Boschetti
Strongly Correlated Electrons
Spin nematic liquid crystal and scalar spin chirality in tetragonal lattice YbMnBi$_2$
Yaofeng Xie, Sijie Xu, Yu Pan et al. (+22 more)
A
spin nematic order, analogous to the nematic
liquid crystal, characterizes the spontaneous breaking of
spin-space rotational
symmetry while preserving time-reversal ($T$)
symmetry. In contrast, scalar
spin chirality (SSC), a composite three-
spin order, breaks $T$
symmetry and is known to induce an anomalous
Hall effect (AHE). Although a
spin nematic phase has been suggested in frustrated magnets and the square-
lattice iridate, how it might affect magnetotransport properties is unknown. Here we use polarized
neutron scattering to show that tetragonal $A$MnBi$_2$ ($A$ = Ca, Yb) is a strictly $c$-axis-aligned collinear antiferromagnet (C-type), with $T_N \approx 270$ K and 290 K, respectively. On cooling from 450 K to $T_N$, low-energy
spin excitations in YbMnBi$_2$ spontaneously change from isotropic to anisotropic in
spin space within the tetragonal plane, forming a dynamic
spin nematic phase around 400 K due to heavy Yb-induced
spin-orbit coupling, before gapping out below $T_N$. Similar measurements on CaMnBi$_2$ reveal isotropic paramagnetic scattering without a
spin nematic phase above $T_N$. Under an in-plane
magnetic field, the Yb$^{3+}$ moments may interact with the dynamic
spin nematic phase to induce nonzero SSC, giving rise to AHE and an anomalous Nernst effect (ANE) in YbMnBi$_2$ that are absent in CaMnBi$_2$ above $T_N$. A
symmetry-based Ginzburg-Landau analysis shows that coupling terms between the nematic order and SSC are allowed under an external
magnetic field, which could explain the rapid increase of AHE with field in YbMnBi$_2$. Our results provide compelling evidence for dynamic SSC-induced AHE and ANE in the paramagnetic phase of a compensated collinear antiferromagnet, opening a new avenue for the physics of composite
spin orders and room-temperature spintronics without
magnetic order.
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All authors Yaofeng Xie, Sijie Xu, Yu Pan, Taekoo Oh, Tingjun Zhang, Masaaki Matsuda, Zhaoyu Liu, Zehao Wang, Yiheng Wang, Siyu Pan, Avishek Maity, Sylwia Pawledzio, Xiaoping Wang, Songxue Chi, Feng Ye, Yiqing Hao, Huibo Cao, Barry L. Winn, Melissa K. Graves-Brook, Shuai Wu, Fan Li, Xiaoyuan Zhou, Claudia Felser, Naoto Nagaosa, Pengcheng Dai
Materials Science
Advancing in situ hydrogen embrittlement studies through an integrated charging cell for SEM micromechanical testing
Lavakumar Bathini, Guillaume Kermouche, Sergio Sao-Joao et al. (+2 more)
A comprehensive understanding of hydrogen-deformation interactions at the microscale is essential for revealing hydrogen embrittlement mechanisms. In situ micromechanics with simultaneous hydrogen (H-) charging has therefore gained traction in recent times. In the present study, we aim to address the drawbacks of current in situ H-charging setups by developing a more robust 3-electrode-based back-side charging system for a scanning electron microscope to perform various micromechanical tests. The development of the novel setup is discussed and demonstrated through micropillar compression of an Fe-25Cr single
crystal (110) during H-charging. H has increased the yield strength and the apparent strain-hardening rate. H activates multiple slip systems and enhances dislocation density and
entanglement, leading to pronounced forest hardening as revealed by electron microscopy. Estimation of activation volume from strain-rate jump tests indicates that the deformation is controlled by the solute drag effect on kink mobility and dislocation forest hardening.
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All authors Lavakumar Bathini, Guillaume Kermouche, Sergio Sao-Joao, Frédéric Christien, Szilvia Kalácska
Strongly Correlated Electrons
Light-induced effective magnetic fields in Landau quantized graphene
Hiroki Ueda, Alexej Pashkin, Ece Uykur et al. (+6 more)
Ultrafast magnetism triggered by circularly polarized radiation underpins ultrafast
spin control, relevant to future technologies, e.g., opto-spintronics and magnonics. The dynamics are often complicated and intertwined among correlated subsystems, such as electrons,
spins,
phonons, plasmons,
topology, and
lattice, due to many-body
quantum coupling at ultrafast timescales. Here, we demonstrate light-induced effective
magnetic fields generated by selective excitation between non-equidistant Landau quantized states in
graphene, a prototypical Dirac material, using circularly polarized pulses. By magnetically tuning the Landau-level transition resonance away from other low-energy excitations, we obtain a clean electrostatically controllable platform and identify the microscopic origin of the light-induced
magnetic signals, independent of sublattice coupling. Because different Landau levels carry distinct optical
Hall conductivities, direct modification of their occupancies via optical excitations creates transient Faraday rotation signals with dispersive
magnetic-field dependence, mirroring the static magneto-optical lineshape. The induced effective
magnetic field normalized by the pump electric field exceeds typical reported values for the inverse Faraday effect of electronic origin. Our results establish a clear microscopic picture of the inverse Faraday effect of electronic origin, which can trigger hierarchical dynamics among correlated sublattices once Landau-level transitions are magnetically tuned to coincide with other low-energy excitations in Dirac systems and related materials.
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All authors Hiroki Ueda, Alexej Pashkin, Ece Uykur, Kryštof Kašša, Filip Chudoba, Jan Kunc, Manfred Helm, Milan Orlita, Stephan Winnerl
Mesoscale and Nanoscale Physics
Magnetic noise of a dark exciton Bose-Einstein condensate
Pieter M. Gunnink
Excitons provide a promising platform for the realization of solid-state Bose-Einstein condensation (BEC), offering
quantum coherence, strongly correlated electron-hole physics, and superfluidity. Yet, its unambiguous experimental identification remains challenging. In particular, $S_z= \pm 1$ triplet
excitons are excellent candidates to realize an
exciton BEC, because of their intrinsically limited recombination rate and thus long lifetimes. However, since their optical detection is inherently forbidden, experimental signatures remain elusive. In this work, we demonstrate that the
magnetic nature of a $S_z= \pm 1$ triplet
exciton BEC gives rise to stray
magnetic field noise, that can be measured using nitrogen-vacancy (NV) center magnetometry. Using an external
magnetic field to tune the system from an
antiferromagnetic to a
ferromagnetic ordering, the longitudinal
spin sound mode of the BEC softens, bringing the mode into the characteristic gigahertz frequency range of the NV
spin relaxation rate and thus allowing direct detection. Furthermore, we demonstrate an unconventional UV scaling at small distances $d$ from the sample, owing to the cubic corrections to the sound mode dispersion and damping rate in the form of Beliaev damping. Through this approach, we establish that the
spin component of
exciton BECs offers new approaches to detect
exciton BECs.
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Materials Science
Deep-Learning-Accelerated Dopant Selection for High-k HfO2 Dielectrics: A Disorder-Resolved Study of Y, Si and Al
Zunair Masroor, Bonwook Gu, Wonjoong Kim et al. (+3 more)
Hafnium
oxide (HfO2) is the cornerstone high-k dielectric in modern silicon technology. Since the constraints of silicon device fabrication rule out replacing the material itself, dopant incorporation is the principal means available to engineer its band gap and dielectric constant within existing process flows. However, dopant selection is still largely empirical due to the coupled interplay among thermodynamic stability, electronic insulation, and dielectric response. Here, we present a high-throughput computational framework integrating special quasi-random structures (SQS), machine-learning potentials (SevenNet), and graph neural networks (ALIGNN) to systematically evaluate doped-HfO2 compositions across three dopants (Al, Si, Y) and two technologically relevant polymorphs (monoclinic and orthorhombic). Our analysis uncovers a fundamental design principle: formation energy, band gap, and dielectric constant are decoupled parameters requiring application-specific prioritization rather than simultaneous optimization. Yttrium achieves the lowest formation energy (-3.763 eV/atom) and favors orthorhombic phase stabilization at process-compatible thermal budgets; silicon preserves near-pristine band gaps (around 5.72 eV) critical for suppressing leakage in gate dielectric applications; and aluminum enables concentration-tunable band gap widening (5.6-5.9 eV) suited for voltage scaling. Validation against experimental literature and density functional theory (DFT) confirms quantitative accuracy (0.02 eV band gap error for Si-doping, mean absolute error less than 0.001 eV/atom formation energy). This framework provides rational, property-decoupled guidance for dopant engineering in HfO2-based dielectrics and related high-k
oxide systems.
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All authors Zunair Masroor, Bonwook Gu, Wonjoong Kim, Trinh Ngoc Le, Summal Zoha, Han-Bo-Ram Lee
Superconductivity
Thickness-Driven Superconductor-Insulator Transition in (Cu,C)-1234 and Proximity-Induced Superconductivity Recovery in (Cu,C)-1234/YBCO Heterostructure
Zhihang Xu, Detian Yang, Ping Zhu et al. (+4 more)
Superconducting proximity effect and related thickness-driven property
evolution remain an important issue in understanding high temperature
superconductors. Among proximity systems,
superconductor-
superconductor (S-S') is special for the existence of intrinsic superconductivity in both materials. Such platform allows the different superconducting orders to compete, couple and reconstruct at the interface. In this paper, (Cu,C)-1234/YBCO
heterostructure grown on LAO (001) with fixed thickness of bottom YBCO layer as 150 nm and varied thickness of top (Cu,C)-1234 layer as 188nm, 87 nm, 18nm and estimated 1.2 nm were fabricated and component films were preserved. Electrical transport characterization indicated that as the thickness decrease the (Cu,C)-1234 film degrades and underwent the
superconductor-
insulator transition (SIT) from thicker to less than 18 nm. In contrast, superconductivity is re-established in transport measurements when the insulating (Cu,C)-1234 layer is coupled to superconducting YBCO As the (Cu,C)-1234 thickness is further reduced to approximately 1.2 nm, the recovered superconductivity is strongly suppressed. The observed thickness dependence is consistent with a scenario in which interfacial coupling restores superconductivity over a finite thickness range before increasing disorder and dimensional confinement dominate in the two-dimensional limit. This work establishes a promising platform for investigating interfacial coupling between cuprate
superconductors and provides new insight into the superconducting proximity effect in high-temperature superconducting
heterostructures.
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All authors Zhihang Xu, Detian Yang, Ping Zhu, Ruoxian Sun, Xiaoyang Cai, Yanqun Guo, Chuanbing Cai
Disordered Systems and Neural Networks
Logarithmically Correlated Landscapes and Localization in Non-Hermitian Quasicrystals
Xianqi Tong, Qifeng Ding and Xiaosen Yang
We study a one-dimensional Hatano-Nelson ring whose nonreciprocal hopping is quasiperiodically modulated through zero. A gauge transformation maps every eigenstate onto a single spatial envelope, whose logarithm becomes a deterministic, logarithmically correlated field once the hopping vanishes along the quasiperiodic orbit. We derive an exact
Fourier representation and prove that the landscape variance grows logarithmically with system size, with a stiffness set by the modulation power and the arithmetic of the incommensurate frequency. The extended phase terminates at an algebraic boundary given by Jensen's formula. Inside the singular regime, localization requires the stiffness to exceed a critical threshold: above it, the wavefunction weight concentrates on the few highest landscape peaks and the state is localized; below it, the weight spreads over too many competing peaks and the state is a critical multifractal. The extreme-value statistics are anomalous: peak gaps grow as a power of the logarithm of rank, with an exponent that encodes the continued-fraction type of the frequency, distinct from the Anderson, Aubry-André, and random-gauge universality classes. The stiffness adds across channels in multiband
lattices, and all signatures survive percent-level component disorder, placing the mechanism within reach of nonreciprocal topolectrical
circuits.
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Materials Science
First-principles cumulant approach to the vibronic structure of spin defects
Jinsoo Park, Yu Jin, Arpan Kundu et al. (+2 more)
Color centers in wide-band-gap
semiconductors are leading platforms for solid-state
quantum technologies, yet a quantitative description of their vibronic structure has remained elusive due to the complexity of multi-
phonon processes in localized defect states. Here we present a first-principles Green's function framework based on the retarded cumulant ansatz (RCA) to describe electron-
phonon interactions in
spin defects; our approach goes beyond the adiabatic and lowest-order perturbation theory approximations underlying widely used approaches. Applied to the negatively charged nitrogen-vacancy (NV$^-$) center in diamond, our method reveals that multi-
phonon satellites persist over a 400 meV energy window even at zero temperature, driven by
quantum zero-point fluctuations. We demonstrate that accurate spectral functions require mode-, momentum-,
spin-, and orbital-resolved electron-
phonon matrix elements sampled across the full Brillouin zone, to account for hybridized and propagating
phonon channels. We find that the vibronic structure of the NV$^-$ center exhibits strong
spin and orbital anisotropy, with different orbitals coupling to qualitatively distinct parts of the
phonon spectrum, and
spin-selective coupling affecting both sideband positions and intensities.
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All authors Jinsoo Park, Yu Jin, Arpan Kundu, Jorge O. Sofo, Giulia Galli
Quantum Gases
Fluctuation Spectra and Response Function of Coupled Atomic and Molecular BECs
Avinaba Mukherjee and Raka Dasgupta
We investigate out-of-
equilibrium properties of atomic molecular Bose Einstein condensates coupled through a Feshbach resonance, with the Feshbach coupling and detuning subject to Gaussian white noise. Using a bosonic Josephson junction framework and a Bloch sphere description, we examine the interplay of detuning, coherence, and noise governing the system dynamics. Coupling and detuning noise produce distinct fluctuation spectra, featuring both Feshbach resonant and symmetric off resonant peaks. We characterize the dispersive and absorptive response of the atom dimer system under periodic driving. The atom molecule hybridization at the Feshbach resonance maximizes the linewidth and minimizes both the effective temperature and the phase difference between the driving field and the system. This leads to an optimized power utilization and quality factor.
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Mesoscale and Nanoscale Physics
Spin lifetime anisotropy in graphene induced by the SiO2 interface
Aron W. Cummings, Chunhao Guo, Andrew Grieder et al. (+5 more)
Understanding how common dielectric substrates influence the
spin transport properties of
graphene is essential for advancing
graphene-based spintronic technologies. Here we use a comprehensive set of numerical simulations to reveal how a SiO$_2$ substrate modifies the
spin texture and governs
spin relaxation in
graphene. Using first-principles density
matrix dynamics simulations, as well as tight-binding (TB) transport simulations, we quantify the effects of electron-
phonon scattering,
impurity scattering, and electrostatic disorder on the
spin relaxation process. We find that a 2D SiO$_2$ substrate induces a predominantly Rashba-type helical
spin texture in
graphene, leading to a
spin lifetime anisotropy of 1/2. Meanwhile, bulk SiO$_2$ breaks in-plane
symmetry in
graphene, leading to anisotropic in-plane and out-of-plane components in the
spin texture, which we capture with a newly-developed TB model of
graphene. Transport simulations under realistic disorder conditions reveal a
spin lifetime anisotropy between 0.5 and 1, similar to what is seen in measurements of
graphene spin valves on a SiO$_2$ substrate. Our results reveal a more complex picture of
spin relaxation at the ubiquitous
graphene/SiO$_2$ interface, beyond the standard Rashba model, providing critical insight for interpreting experiments and guiding substrate engineering for
graphene spintronics.
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All authors Aron W. Cummings, Chunhao Guo, Andrew Grieder, Shihao Tu, Mayank Gupta, Junqing Xu, Juan Marmolejo-Tejada, Yuan Ping
Superconductivity
Acoustic Plasmon Resonance: Breaking the Anderson Stiffness Paradigm in Quasi-Two-Dimensional Superconducting Films
V. M. Kovalev and A. V. Chaplik
Recent experiments on superconducting films have revealed an acoustic plasmon mode that depends critically on the superconducting transition, directly challenging the long-standing Anderson-
Higgs paradigm regarding the stiffness of the
plasma spectrum in
superconductors. In this Letter, we provide a microscopic theoretical framework that explains this behavior and establishes the physical conditions under which classical Anderson-
Higgs constraints are bypassed. We demonstrate that in films of finite thickness, the transverse redistribution of normal and superfluid charge densities enables a unique coupling mechanism to electromagnetic radiation - a feature fundamentally absent in the conventional Carlson-Goldman scenario. Our theory predicts an acoustic mode whose dispersion, temperature scaling, and dependence on film thickness are in remarkable agreement with recent experimental observations. By delineating the regime of this acoustic response, we reconcile the observed electromagnetic activity of collective excitations with the fundamental principles of superconductivity.
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Mesoscale and Nanoscale Physics
Realization of Arbitrary Gauge Fields via Symmetry-Protected Zero Modes
J. X. Dai, Bingbing Wang, Jiangzi Chen et al. (+2 more)
Gauge fields are fundamental to modern physics, but prescribed gauge configurations are often difficult to implement in artificial systems. Here, we present a general scheme for realizing arbitrary static $\mathrm{O}(N)$
lattice gauge configurations using
symmetry-protected zero modes of sublattice-imbalanced bipartite units. The target $\mathrm{O}(N)$ link on each bond is encoded in the connectivity and strengths of positive microscopic couplings. By decoupling the zero-mode
manifold from the remaining modes, the target gauge
Hamiltonian forms an exact spectral block of the microscopic tight-binding model rather than a perturbative approximation. We experimentally demonstrate this framework in acoustic
crystals through a $\mathbb{Z}_2$ quadrupole topological
insulator, an $\mathrm{SO}(2)$ Hofstadter model, and an $\mathrm{SO}(3)$ non-Abelian topological
insulator. Our results provide a general and accessible route to gauge-field physics in artificial systems.
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All authors J. X. Dai, Bingbing Wang, Jiangzi Chen, Y. X. Zhao, Haoran Xue
Materials Science · Cross-listed from stat.AP
Process-fracture mapping of a DLP-printed photopolymer using Bayesian active learning and surrogate-based sensitivity analysis
Ethan Blackwell, Yogesh C. Chandrashekar, Guoqiang Li et al. (+1 more)
Digital light processing (DLP) enables rapid fabrication of
polymer structures, but fracture performance depends on multiple interacting processing variables, making exhaustive experimental characterization impractical. This work presents a data-efficient framework for process-fracture mapping of a DLP-printed photopolymer using
Bayesian active learning and digital image correlation (DIC)-assisted Mode I fracture experiments. Four processing parameters were considered: layer angle, UV exposure time, layer height, and print temperature. Fracture resistance was quantified by the critical J-integral, $J_c$, obtained from three-point-bending tests with DIC-based evaluation of crack-mouth opening displacement and hinge-point kinematics. Beginning with two randomly selected conditions, Gaussian process regression (GPR) and a modified upper confidence bound (UCB)-style acquisition function selected 26 additional experiments, yielding 28 processing conditions with three replicates each. The final GPR surrogate reproduced the training data with $R^2=0.99$ and achieved leave-one-out cross-validation performance of $R^2=0.63$ and Pearson $r=0.81$. Surrogate-based sensitivity analysis quantified parameter effects and global contributions. One-at-a-time response curves revealed nonlinear conditional trends, while global Sobol analysis identified UV exposure time as the dominant processing variable, with first-order and total-order indices of 0.6780 and 0.7581, respectively. Based on total-order influence, the parameters ranked as UV exposure time, layer angle, print temperature, and layer height. The first-order Sobol indices summed to 0.8058, indicating non-negligible interaction and higher-order effects. These results demonstrate that
Bayesian-active-learning-guided experimentation can efficiently recover process-fracture relationships and parameter interactions from a sparse experimental campaign.
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All authors Ethan Blackwell, Yogesh C. Chandrashekar, Guoqiang Li, Kshitiz Upadhyay
Materials Science
Magnetoelastic coupling descriptor for high-throughput ab initio search of magnetocaloric materials
Debajit Chakraborty, Kirill D. Belashchenko and Aleksander L. Wysocki
We use Landau theory of phase transitions to design a magnetoelastic coupling descriptor that can identify
magnetic materials on the brink of a first-order transition, where a strong magnetocaloric effect (MCE) can arise. The descriptor can be computed from electronic structure calculations and requires structural optimization in the paramagnetic state, which we model using special quasi-random collinear
spin configurations. We first evaluate the descriptor for a set of known magnetocaloric materials and identify compounds in which the MCE is driven by magnetoelastic coupling. We then apply the descriptor in a high-throughput ab initio screening of
magnetic L1$_2$ compounds. This search identifies the L1$_2$ cubic phases of Mn$_3$Ge and Mn$_3$Sb as materials with strong magnetoelastic coupling and potential for a large magnetocaloric response.
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Disordered Systems and Neural Networks
Unifying Physical Backpropagation
Cyrill Bösch, Yigithan Gediz, Clara C. Wanjura et al. (+1 more)
Physical computing systems exploit device dynamics for computation, but their gradient-based optimization is challenging: backpropagation through a digital twin suffers from a model-reality gap. On-device gradient computation could resolve this issue, and a handful of theoretical and experimental studies have proposed ways to achieve it. Yet a unifying theory identifying when a physical system can compute the gradient of its own performance has been missing. Here we develop such a unification based on the adjoint method: we identify sufficient conditions under which the adjoint field required for formally exact gradients can be generated on the same hardware that performs the computation. Linear and nonlinear systems obey fundamentally different conditions: for linear systems, damping or gain is admissible provided reciprocity is preserved. For nonlinear trajectory systems, the sufficient conditions are reciprocity of the linearized system and the existence of a time-reversal mirror. Algorithmically, the nonlinear case requires infinitesimal nudging, whereas linear systems admit a finite-amplitude experiment. We recover (
quantum)
Equilibrium Propagation,
Hamiltonian echo backpropagation, fully forward mode training and in situ gradient methods in integrated-photonic and free-space-optical systems. Finally, we show that reciprocity is a special case of more general intertwining conditions. For linear systems, these permit exact on-device gradients in a class of non-Hermitian, non-reciprocal systems. For nonlinear trajectories, they combine with generalized time-reversal mirrors to cover, e.g., PT-symmetric equations. The framework also includes time-dependent parameters and Onsager-reciprocal dynamics, providing a unified basis for formally exact physical learning.
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All authors Cyrill Bösch, Yigithan Gediz, Clara C. Wanjura, Hakan E. Türeci
Mesoscale and Nanoscale Physics
Spatially Resolving the Pre-Thermal Anatomy of a Driven Bosonic Fluid
Shantam Ravan, Aaron Müller, Johannes Cremer et al. (+5 more)
Understanding how coherently driven
quantum many-body systems redistribute energy prior to thermal
equilibrium remains a central challenge in many-body physics. Here, we utilize nitrogen-vacancy (NV) magnetometry to perform micron-scale spatial imaging of room-temperature
magnon dynamics in a yttrium iron garnet (YIG) thin film. We resolve a hierarchy of discrete parametric scattering events that serve as deterministic stepping stones toward thermalization. By applying a two-tone wave-mixing protocol, we first isolate the elementary four-
magnon interaction and extract its coupling strength via the spatial growth of the scattering product. We then drive the system with an intense single-frequency excitation near
ferromagnetic resonance, revealing that
magnon-
magnon interactions trigger a spontaneous, multi-generation scattering cascade. We demonstrate that in each generation, the dominant scattering channels correspond to one of the out-scattered
magnons being in the slow
magnon regime, reminiscent of the enhancement of optical nonlinearities in slow light systems. We capture this dynamics quantitatively using a near field magnonics framework and extract the cascade order and nonlinear coefficients directly from power-dependent frequency shifts. By revealing the multi-stage dynamical process through which monochromatic injected
magnons evolve toward
equilibrium, our work establishes spatially resolved magnonics as a powerful platform for visualizing non-
equilibrium many-body kinetics.
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All authors Shantam Ravan, Aaron Müller, Johannes Cremer, Jonathan Curtis, Daniel Fernandez, Ronald Walsworth, Eugene Demler, Amir Yacoby
Mesoscale and Nanoscale Physics
Dynamics of the spontaneous emission factor in multiple quantum well nanowire lasers
Parya Reyhanian, Christopher G Poulton, Arti Agrawal et al. (+1 more)
The spontaneous emission factor - often known as the e̱ta} factor - is an important quantity in the description of
quantum well
lasers, influencing both the threshold power as well as the general shape of the light in-light out (L-L) curve. Past work on modelling multiple
quantum well (MQW) nanowire
laser devices has typically assumed that the e̱ta} factor is a constant parameter that can either be estimated or fit in a post-hoc manner. However, the e̱ta} factor can be derived from the transitions between valence and conduction bands in
semiconductor quantum wells, together with knowledge of the cavity modes. Here we investigate the dynamic nature of the e̱ta} factor for MQW nanowire
lasers, and show how it can be computed. We also examine the dependence of the spontaneous emission rate and spontaneous emission factor e̱ta} on the charge carrier density,
quantum well thickness, and composition, and discuss the impact on
laser threshold and operation.
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All authors Parya Reyhanian, Christopher G Poulton, Arti Agrawal, Charlene J. Lobo