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Physics Condensed Matter

cond-mat Watch Condensed Matter

Saturday 1 November

Materials Science

Altermagnetism and Anomalous Transport in Ag$^{2+}$ Fluorides: KAgF$_3$ and K$_2$AgF$_4$

Xiao Nan Chen, Sining Zhang, Zhengxuan Wang et al. (+2 more)

Compounds containing Ag$^{2+}$ ion with 4d$^9$ configuration will cause significant Jahn-Teller distortions and orbital ordering. Such orbital order is closely related to the magnetic coupling, according to Goodenough-Kanamori Ruels. Our first-principles calculations reveal that the ground state of KAgF$_3$ exhibits collinear A-type antiferromagnetic (A-AFM) ordering accompanied by C-type orbital ordering. In contrast, K$_2$AgF$_4$ adopts a collinear intralayer antiferromagnetic configuration coupled with ferromagnetic orbital ordering. The A-AFM KAgF$_3$ presents distinct altermagnetic responses, including: (i) prominent anomalous transport effects, such as anomalous Hall conductivity (AHC), anomalous Nernst conductivity (ANC), and thermal anomalous Hall conductivity (TAHC); and (ii) strong magneto-optical responses, manifested through pronounced Kerr and Faraday effects. On the other hand, K$_2$AgF$_4$ behaves as a conventional collinear antiferromagnet preserving $\mathcal{PT}$ symmetry, hence precluding the emergence of an anomalous Hall response.
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All authors Xiao Nan Chen, Sining Zhang, Zhengxuan Wang, Minping Zhang, Guangtao Wang

Materials Science

Applicability of Electrical Conductivity Ratio Method to Complicated Band Structure and the Carrier Scattering Mechanisms of SnSe

Pan Ren, Junling Gao, Guiying Xu et al. (+7 more)

The electrical conductivity ratio (ECR) method can be used to analyze carrier scattering mechanism (CSM) without the need of magenetic transport measurements. In this work, the applicability of the ECR method in the analysis of complex energy band structures is discussed. Combined with the thermoelectric properties of SnSe, the feasibility using ECR method of ideal single band transport model to study the CSM of semiconductor materials with complicated band structure is studied. The results indicate that ECR method is not only applicable to idea band structure as reported before but also to the complicated band structure. The analysis results of the CSM of single crystal SnSe by ECR method using ideal single-band model agree with the carrier mobility temperature dependence in the nonphase transition temperature range. The CSM along three direction of single crystal SnSe are different because of its anisotropic crystal structure. The difference between dislocation scattering (DS) and charged impurity scattering (CIS) is that DS is always accompanied by polar optical phonon scattering (POP), such as the CSM of SnSe along b axis direction. The difference between CIS and DS can be more easily distinguished by the ECR method than the carrier mobility temperature dependent method. DS and POP might be one of the approaches to improve thermoelectric property because the scattering factor for DS or POP is larger than that of acoustic phonon scattering (APS) and alloy scattering (AS). For polycrystalline SnSe, the carrier scattering mechanisms varies with the crystal structure and the temperature. This indicates that the ECR method can better reflect the variation of carrier scattering mechanisms with temperature compared to the carrier mobility temperature dependence method.
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All authors Pan Ren, Junling Gao, Guiying Xu, Bohang Nan, Tao Guo, Quanxin Yang, Fanchen Meng, Myles McKenna, Jian He, Sitong Niu

Statistical Mechanics

Short-time dynamics in phase-ordering kinetics

Leila Moueddene and Malte Henkel

Short-time dynamics in the $2D$ Blume-Capel model, with a non-conserved order-parameter and short-ranged interactions, is analysed. For non-equilibrium dynamics, both at a critical point in the $2D$ Ising universality class and at the tricritical point, we reproduce the values $\Theta=0.190({5})$ and $\Theta=-0.542({5})$, respectively, of the critical initial slip exponent. These agree with more early estimates and with the Janssen-Schaub-Schmittmann scaling relation. In phase-ordering kinetics, after a quench into the ordered phase, we establish the validity of short-time dynamics. In the $2D$ Ising universality class, we find $\Theta=0.39({1})$ in agreement with the scaling relation $\lambda=d-2\Theta$.
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Materials Science

Atomic-Scale Roughness of Freestanding Oxide Membranes Revealed by Electron Ptychography

Huaicheng Yuan, Yu-Chen Liu, Li-Shu Wang et al. (+3 more)

Freestanding oxide films offer significant potential for integrating exotic quantum functionalities with semiconductor technologies. However, their performance is critically limited by surface roughness and interfacial imperfection caused by dangling bonds, which disrupt coherent interactions and suppress quantum phenomena at heterointerfaces. To address the challenge of structural characterization of surfaces and interfaces, we develop a metrological approach achieving atomic-scale precision in mapping the topography of both free surfaces and buried interfaces within ultrathin oxide heterostructures leveraging three-dimensional structures reconstructed from multislice electron ptychography. This method also allows for counting the number of atoms, even including light elements such as oxygen, along the electron trajectory in electron microscopy, leading to the identification of surface termination in oxide films. The planar-view of measurement geometry, allowing for large field-of-view imaging, provides remarkably rich information and high statistics about the atomic-scale structural inhomogeneities in freestanding membranes. This quantitative analysis provides unprecedented capabilities for correlating structural imperfection with quantum device performance, offering critical insights for engineering robust heterointerfaces in next-generation oxide electronics.
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All authors Huaicheng Yuan, Yu-Chen Liu, Li-Shu Wang, Zehao Dong, Jan-Chi Yang, Zhen Chen

Statistical Mechanics

Exact Solution and Correlation Functions of Generalized Double Ising Chains

Pavel Khrapov and Stepan Shchurenkov

In this paper the exact solution and correlation functions for a double-chain Ising model with multi-spin interactions and symmetric Hamiltonian density are obtained. The study employs the transfer matrix method to derive fundamental thermodynamic characteristics of the system. The main results include exact expressions for the partition function, free energy, internal energy, specific heat capacity, magnetization, susceptibility, and entropy in a strip of finite length and in the thermodynamic limit. The work provides explicit formulas for the eigenvalues and shows structure of eigenvectors of the transfer matrix. The expression for magnetization in the thermodynamic limit using components of normalized eigenvector corresponding to the maximum eigenvalue is obtained. A detailed analysis is conducted for a special case of interactions involving all kinds of two- and four-spin interactions. This gives the simplified formula for free energy, it is calculated using the root of quadratic equation. Using special relation between parameters the solution for gonihedric model on the plane is obtained. The research reveals properties of the system, including specific features of ground states and phase diagram characteristics. Particular attention is given to the behavior of physical quantities near frustration points and the investigation of spin correlation functions. Plots of physical characteristics, including inverse correlation length, illustrating the obtained results are constructed.
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Quantum Gases

Connected correlations in cold atom experiments

Thomas Chalopin, Igor Ferrier-Barbut, Thierry Lahaye et al. (+2 more)

The recent development of single-atom-resolved probes has made full counting statistics measurements accessible in quantum gas experiments. This capability provides access to high-order moments of physical observables, from which cumulants, or equivalently connected correlations, can be precisely determined. Through a selection of recent cold atom experiments, this article illustrates the significance of connected correlations in characterizing ensembles of interacting quantum particles. First, non-zero connected correlations of order n > 2 unambiguously identify non-Gaussian quantum states. Second, connected correlations of order n identify clusters made of n elements whose statistical properties are irreducible to combinations of smaller clusters. The ability to identify such multi-particle clusters offers a an interesting perspective on strongly correlated quantum states of matter at the microscopic scale.
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All authors Thomas Chalopin, Igor Ferrier-Barbut, Thierry Lahaye, Antoine Browaeys, David Clément

Soft Condensed Matter

Phase separation dynamics and active turbulence in a binary fluid mixture

Sohail Ahmed, Zixiang Lin and Zijie Qu

Active matter, encompassing natural systems, converts surrounding energy to sustain autonomous motion, exhibiting unique non-equilibrium behaviors such as active turbulence and phase separation. In this study, we develop a continuum two-fluid model for a binary mixture of an active nematic and a passive Newtonian fluid, coupling Cahn-Hilliard dynamics for phase separation with Beris-Edwards nematohydrodynamics and two distinct momentum equations connected by viscous drag. A phase field-based lattice Boltzmann method is used to investigate the existence of active turbulence and phase separation in the binary mixture. We find that active stress enhances velocity and vorticity differences between phases, and that increased active concentration promotes stronger inter-fluid coupling. Activity not only amplifies turbulent fluctuations but also arrests domain coarsening, leading to a finite characteristic length scale that decreases with increasing activity. Key parameters, like active parameter, tumbling parameter and Frank elastic constant, affect the characteristic scale of flow. These results highlight the role of relative motion and drag-mediated momentum transfer in active binary mixtures, providing a framework for studying systems such as bacterial suspensions in polymeric fluids or active emulsions.
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Materials Science

Alternative treatment of relativistic effects in linear augmented plane wave (LAPW) method: application to Ac, Th, ThO2 and UO2

A. V. Nikolaev, U. N. Kurelchuk and E. V. Tkalya

We examine the influence of the relativistic effects within the linear augmented plane wave method (LAPW) for solids and propose a few alternative ways to accurately take them into account: (1) we introduce new radial dependencies for LAPW (Bloch-type) basis functions, based on two actual radial solutions of the Dirac equation for j=l-1/2 and j=l+1/2 states. The proposed radial 6p functions receive more weight from the Dirac p-1/2 solution and, due to this, can on average correctly describe completely filled $6p$ bands even without the additional p-1/2 local atomic function, as is done in the LAPW+p-1/2 method; (2) the canonical LAPW matrix elements for the spherically symmetric component of the potential, assuming non-relativistic radial wave functions, should be corrected; (3) we argue that for a realistic spin-orbit (SO) energy splitting of the semicore 6p-states the spin-orbit interaction constant zeta(p) should be calculated with the 6p-3/2 radial component, because the value of zeta(p) obtained with the canonical mixing of the 6p-1/2 and 6p-3/2 components overestimates the SO splitting. Different ways of taking into account relativistic effects can change the equilibrium lattice constant up to 0.15 A and the elastic modulus up to 26 GPa. We find that in the full treatment of the spin-orbit coupling UO2 has a small gap of forbidden states (0.2-0.4 eV) at the Fermi level, which persists for all k-vectors and, therefore, UO2 should be classified as a semimetal. We also discuss the peculiarities of the electron band structure of actinium, which result in an overestimation of its lattice constant.
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Materials Science

Elastic and Strain–Tunable Electronic and Optical Properties of La2AlGaO6 Hybrid Perovskite: A First-Principles Study

Chaithanya Purushottam Bhat, Jyoti Dagar, Ashwin K. Godbole et al. (+1 more)

Perovskite materials, known for their structural versatility and multifunctional properties, continue to draw interest for advanced electronic and optoelectronic applications. In this study, we investigate the elastic and strain–engineered mechanical, electronic properties and optical properties of the orthorhombic La2AlGaO6 (LAGO) hybrid perovskite using first–principles quantum mechanical calculations based on density functional theory (DFT). Structural optimizations were performed using both the local density approximation (LDA) and the generalized gradient approximation (GGA). The mechanical stability of LAGO was confirmed through the Born–Huang criteria, and key elastic constants (C11, C12, C33, C44, and C66) were evaluated. These constants were further used to derive mechanical parameters such as Young's modulus, bulk modulus, shear modulus, Poisson's ratio, Cauchy's pressure, and anisotropic factor, offering insights into the material's ductility, hardness, and elastic anisotropy. Crucially, we explored the influence of biaxial strain on the electronic band structure, DOS/PDOS, and Fermi energy, revealing significant band gap modulation under compressive and tensile strain, and hence, varying the optical properties. The coupling between elastic response and electronic structure highlights LAGO's potential for tunable device applications, where mechanical stimuli can be employed to tailor its electronic functionality.
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All authors Chaithanya Purushottam Bhat, Jyoti Dagar, Ashwin K. Godbole, Debashis Bandyopadhyay

Superconductivity

Cu-spin Correlation in the Electron-overdoped High-Tc Cuprate Thin Films of La_2-x_Ce_x_CuO_4_ Probed by Low-energy Muons

S.E. Park, Y. Kawai, A. Suter et al. (+7 more)

We investigated the Cu-spin correlation in the overdoped regime of the electron-doped high-Tc cuprate thin films of La_2-x_Ce_x_CuO_4_, changing the reduction condition from muon spin relaxation using low-energy muons. The Cu-spin correlation developed at low temperatures for optimally reduced films with x=0.13 as well as x=0.17 where the superconductivity was almost suppressed. These results are contrary to those observed in the hole-doped high-Tc cuprates where the development of the antiferromagnetic Cu-spin correlation disappears together with the suppression of superconductivity. The Cu-spin correlation developed at low temperatures in x=0.17 may be understood in terms of antiferromagnetism, but it may be related to a ferromagnetic order recently suggested in the nonsuperconducting heavily overdoped La$_2-x_Ce_x_CuO_4_ with x~0.18.
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All authors S.E. Park, Y. Kawai, A. Suter, H. Okabe, J. G. Nakamura, H. Kuwahara, Z. Salman, T. Prokscha, R. Kadono, T. Adachi

Materials Science

Narrow magneto-optical transitions in Erbium implanted silicon carbide-on-insulator

Alexey Lyasota, Joshua Bader, Shao Qi Lim et al. (+5 more)

Solid state spin photon interfaces operating in the near telecom and telecom bands are a key resource for long distance quantum communication and scalable quantum networks. However, their optical transitions often suffer from spectral diffusion that hampers the generation of coherent spin photon entanglement. Here we demonstrate narrow magneto-optical transitions of erbium dopants implanted into thin film silicon carbide (SiC)-on-insulator, a viable platform for industrially scalable quantum networks. Using high-resolution resonant spectroscopy and spectral hole burning at cryogenic temperatures, we reveal sub megahertz homogeneous linewidths and identify two lattice sites that best stabilise the emitters. We further characterise their optical lifetimes and magneto-optical response, establishing erbium doped SiC-on-insulator as a robust and scalable platform for on-chip quantum networks.
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All authors Alexey Lyasota, Joshua Bader, Shao Qi Lim, Brett C. Johnson, Jeffrey C. McCallum, Qing Li, Sven Rogge, Stefania Castelletto

Strongly Correlated Electrons

Absence of magnetic order and magnetic fluctuations in RuO$_{2}$

Jiabin Song, Chao Mu, Shilin Zhu et al. (+5 more)

A novel magnetic class blending ferromagnetism and antiferromagnetism, termed altermagnetism, has gained significant attention for its staggered order in coordinate and momentum spaces, time-reversal symmetry-breaking phenomena, and promising applications in spintronics. Ruthenium dioxide (RuO$_{2}$) has been considered a candidate material for altermagnetism, yet the presence of magnetic moments on Ru atoms remains a subject of debate. In this study, we systematically investigated the magnetic properties of RuO$_{2}$ powder using nuclear quadrupole resonance (NQR) measurements. The NQR spectra show that there is no internal magnetic field. Furthermore, the temperature independence of spin-lattice relaxation rate, $1/T_1T$, proves that there are no magnetic fluctuations. Our results unambiguously demonstrate that Ru atoms in RuO$_{2}$ possess neither static magnetic moments nor fluctuating magnetic moments, and thus RuO$_{2}$ does not possess the magnetic characteristics essential for altermagnetism.
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All authors Jiabin Song, Chao Mu, Shilin Zhu, Xuebo Zhou, Wei Wu, Yun-ze Long, Jianlin Luo, Zheng Li

Strongly Correlated Electrons · Cross-listed from hep-th

Conformal Bootstrap with Duality-Inspired Fusion Rule

Yu Nakayama and Toshiki Onagi

We present a systematic exploration of conformal field theories (CFTs) constrained by duality-inspired fusion rules using the conformal bootstrap. We classify the operator spectrum into three sectors: $[\sigma]$, $[\epsilon]$, and $[1]$. The $[\sigma]$ sector consists of all $\mathbb{Z}_{2}$-odd operators. The $\mathbb{Z}_{2}$-even operators are further divided into the $[\epsilon]$ sector, which contains only the operators that change sign under duality, and the $[1]$ sector, which encompasses all remaining operators. We impose a selection rule motivated by Kramers-Wannier duality, specifically forbidding the appearance of the $[\epsilon]$ sector in the $[\epsilon] \times [\epsilon]$ operator product expansion. By applying this constraint to the lowest-lying relevant scalars, we derive bounds on their conformal dimensions $(\Delta_\sigma, \Delta_\epsilon)$ in dimensions $d=2$ through $d=7$. Our bounds correctly allow the $d=2$ Ising model while excluding the $d=3$ Ising model, demonstrating the effectiveness of the imposed condition. Furthermore, we observe a distinct feature in $d=2$ corresponding to the $\mathcal{M}(8,7)$ minimal model and find non-trivial constraints in $d=3$ ($\Delta_\sigma \gtrsim 0.85$), relevant for theories like QED$_3$. This work opens a new avenue for non-perturbatively probing the landscape of CFTs constrained by fusion rules.
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Soft Condensed Matter

Physics-informed digital twin and onboard control of a brainbot for intelligent active matter

Isa Mammadli, Prajol Shrestha, Jayant Pande et al. (+6 more)

Establishing adaptive particles that sense their state, anticipate their evolution, and compute control inputs onboard has been a major challenge in non-equilibrium physics. We address this challenge by realizing an autonomous brainbot, building on a recently developed programmable bristlebot. First, we construct a physics-informed digital twin of the device, based on a kinematic model that reproduces measured trajectory statistics and generates long, statistically faithful synthetic trajectories. The kinematics forms the foundation for implementing onboard model predictive control (MPC), enabling autonomous trajectory tracking, demonstrated by accurate execution of a non-trivial target path. This provides a proof of principle for a brainbot that senses its state, predicts its evolution, and computes control inputs onboard, unlike conventional active particles with fixed motility, thereby transforming the brainbot into an agentic physical entity. By integrating physical modeling, data-driven parameter identification, and control into a unified framework, our approach provides a scalable platform for machine-learning-enabled multi-agent studies and lays the groundwork for intelligent, adaptive active matter.
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All authors Isa Mammadli, Prajol Shrestha, Jayant Pande, Filip Novkoski, Siddhant Mohapatra, Martial Noirhomme, Andreas Maier, Nicolas Vandewalle, Ana-Suncana Smith

Strongly Correlated Electrons

Low-Frequency Noise and Resistive Switching in $\beta$-Na$_{0.33}$V$_2$O$_5$

Nitin Kumar, Nicholas Jerla, John Ponis et al. (+2 more)

The interplay between charge ordering and its manifestation in macroscopic electrical transport in low-dimensional materials is crucial for understanding resistive switching mechanisms. In this study, we investigate the electronic transport and switching behavior of single-crystalline $\beta$-Na$_{0.33}$V$_2$O$_5$, focusing on low-frequency resistance noise dynamics of charge-order-driven resistive switching. Using electrical transport, low frequency noise spectroscopy, and X-ray diffraction, we probe electron dynamics across the Na-ion-ordering (IO) and charge-ordering (CO) transitions. Near room temperature, the weak temperature dependence of the noise spectral density points to a dominance of nearest-neighbor polaron hopping. Below IO transition temperature (\( T_{IO} \sim 240 \, \text{K} \)), structural analysis reveals that Na-ions adopt a zig-zag occupancy pattern, breaking the two-fold rotational symmetry and influencing the electronic ground state. Subsequently, a sharp drop in resistance noise below the CO transition temperature (\( T_{CO} \sim 125 \, \text{K} \)) indicates the emergence of correlated electron behavior. Furthermore, application of sufficient electric field leads to the destabilization of the CO state, and a transition to a high-conducting state. The material exhibits distinct resistive switching between 35~K and 110~K, with a resistance change spanning two orders of magnitude, primarily driven by electronic mechanisms rather than Joule heating. These findings provide new insights into charge-order-induced switching and electronic correlations in quasi-one-dimensional systems, with potential applications in cryogenic memory and neuromorphic computing devices owing to the low noise levels in their stable resistive states.
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All authors Nitin Kumar, Nicholas Jerla, John Ponis, Sarbajit Banerjee, G. Sambandamurthy

Mesoscale and Nanoscale Physics · Cross-listed from physics.optics

Direct Observation and Optical Manipulation of Exciton-polariton Parametric Scattering Lasing in Temporal

Junxing Dong, Si Shen, Jingzhuo Wang et al. (+7 more)

The hybrid light-matter character of exciton-polaritons gives rise to distinct polariton parametric scattering (PPS) process, which holds promise for frontier applications in polaritonic quantum devices. However, the stable excitation and coherent optical manipulation of PPS remain challenging due to scattering bottlenecks and rapid dephasing effect in polariton many-body systems. In this study, we first report the direct observation and optical amplification of non-degenerate intermode PPS lasing at room temperature (RT). The specific polariton branch of strong-coupled nanobelt planar microcavity is resonantly excited by a near-infrared (NIR) femtosecond laser via two-photon absorption (TPA) scheme, and the non-degenerate signal- and idler-states are stimulated. Angle-resolved dispersion patterns clearly reveal the evolution of the pump-, signal-, and idler-states under different excitation powers. Based on our self-constructed ultrafast femtosecond resonant optical trigger set-up, a selective enhancement and modulation of the signal-state is realized. Furthermore, the dynamic measurements of nonlinear signal-state enhancement process demonstrate a sub-picosecond response time (0.4ps), confirming its potential for ultrafast optical manipulation. Our work establishes a platform for exploring TPA-driven PPS laser and provides a novel optical modulation route for polariton-based optoelectronic devices.
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All authors Junxing Dong, Si Shen, Jingzhuo Wang, Lisheng Wang, Yifan Zhang, Huashan Li, Xianghu Wang, Wei Gao, Yongzheng Fang, Hai Zhu

Statistical Mechanics · Cross-listed from hep-th

Transmission Coefficients from Phantom Currents

Yuma Furuta, Yuya Kusuki and Toshiki Onagi

A representative quantity that characterizes the dynamics of conformal interfaces is the transmission coefficient, which is defined through correlation functions of the stress tensor. Typically, this coefficient is complicated and highly dependent on its details. In this work, we introduce a new perspective based on the notion of a “phantom current”. We have shown that a spin-2 phantom current arising from the folding trick completely determines the transmission coefficient. In particular, when there is a single phantom current, the transmission coefficient is uniquely fixed by its conformal dimension. As a result, our framework provides a unified explanation of known results in minimal models and the free boson, while also yielding concrete predictions for previously unexplored interfaces.
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Mesoscale and Nanoscale Physics

Quasiperiodicity-induced bulk localization with self similarity in non-Hermitian systems

Yu-Peng Wang, Chuo-Kai Chang, Ryo Okugawa et al. (+1 more)

We analyze the localization behavior in a non-Hermitian system subject to a quasiperiodic onsite potential. We characterize localization transitions using multiple quantitative indicators, including inverse participation ratio (IPR), eigenstate fractal dimension (EFD), extended eigenstate ratio (EER), and spectral survival ratio. Despite the breaking of self-dual symmetry due to non-Hermiticity, our results reveal the existence of a critical potential strength, with its value increasing linearly with the nearest-neighbor antisymmetric hopping term. On the other hand, the inclusion of longer-range hopping not only enriches the topological properties but also gives rise to novel localization phenomena. In particular, it induces the emergence of mobility edges, as evidenced by both IPR and EFD, along with distinct features in the spectrum fractal dimension, which we extract using the box-counting method applied to the complex energy spectrum. Additionally, we uncover self-similar structures in various quantities, such as EER and complex eigenvalue ratio, as the potential strength varies. These findings highlight important aspects of localization and fractal phenomena in non-Hermitian quasiperiodic systems.
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All authors Yu-Peng Wang, Chuo-Kai Chang, Ryo Okugawa, Chen-Hsuan Hsu

Materials Science

Impact of Oxygen Plasma Surface Treatment on Photoresist Adhesion in BaTiO3-Based Photonic Device Fabrication

Weiyou Kong, Weijia Kong, Lukas Chrostowski et al. (+1 more)

Oxygen-plasma pre-cleans are routine before fabrication, but on BaTiO3 thin films we observed catastrophic photoresist lift-off during mild rinsing and sonication. To explain the failure, we combined optical microscopy, EDS, and XPS. EDS showed no meaningful bulk stoichiometry change, whereas XPS revealed a nanometer-scale, plasma-induced shift in surface chemistry: hydroxylation and carbonate formation consistent with a BaCO3-rich interphase at the resist/BaTiO3 boundary. This chemically weak interphase, recreated upon each plasma step and removable by simple solvent cleaning, provides the mechanism for delamination. The key takeaway for practitioners is process guidance: avoid uncritical O2-plasma use on BTO; if cleaning is required, use alternative chemistries (e.g., UV-ozone) or carefully tuned plasma windows that preserve adhesion. More broadly, the study illustrates how lightweight analytics at the surface (correlative microscopy + surface spectroscopy) can pinpoint the root cause of yield-limiting defects in oxide photonics and translate directly into higher-reliability process recipes.
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All authors Weiyou Kong, Weijia Kong, Lukas Chrostowski, Xin Xin

Quantum Gases · Cross-listed from physics.atom-ph

Universality in Ionic Three-body Systems Near an Ion-atom Feshbach Resonance

Jacek Gȩbala, Michał Tomza and José P. D'Incao

We calculate bound and scattering properties of a system of two neutral atoms and an ion near an atom-ion Feshbach resonance. Our results indicate that long-range atom-ion interactions lead to significant deviations from universal behavior derived from contact or van der Waals potentials. We find that ionic systems display an overall suppression of inelastic transitions leading to recombination rates and lifetimes of Efimov state orders of magnitude smaller with respect to those for neutral atoms. We further characterize the dense spectra of triatomic molecular ions with extended lifetimes. Our results provide a deeper insight on the universality and structure of three-body ionic systems and establishing them as a promising platform for exploring novel few- and many-body phenomena with long-range interactions.
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Friday 31 October

Mesoscale and Nanoscale Physics

Resolving the phase of a Dirac topological state via interferometric photoemission

Shiri Gvishi, Ittai Sidilkover, Yun Yen et al. (+10 more)

The electronic wavefunction is at the heart of physical phenomena, defining the frontiers of quantum materials research. While the amplitude of the electron wavefunction in crystals can be measured with state-of-the-art probes in unprecedented resolution, its phase has remained largely inaccessible, obscuring rich electronic information. Here we develop a quantum-path electron interferometer based on time- and angle-resolved photoemission spectroscopy, that enables the reconstruction of phase information associated with electronic states, as encoded in the photoemission transition amplitudes - with energy and momentum resolution. We demonstrate the scheme by resolving the phase along the Dirac electronic band of a prototypical topological insulator and observe a resonance-associated phase jump as well as a momentum and phase synchronized inversion revealing the helicity of the Dirac cone. We show the interferometer can be optically controlled by the polarization of the absorbed light, allowing a differential measurement of the phase - a crucial component for extracting phase information from an interferogram. This photo-electron-interferometer provides direct experimental access to the phase of electronic transition amplitudes. Its implementation relies on experimentally accessible conditions - such as the presence of a suitable intermediate state and polarization-selective coupling - and can therefore be extended to a wide class of materials.
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All authors Shiri Gvishi, Ittai Sidilkover, Yun Yen, Shaked Rosenstein, Nir Hen Levin, Adi Perelmuter, Omer Pasternak, Costel R. Rotundu, Ido Biran, Semën Gorfman, Naaman Amer, Michael Sentef, Hadas Soifer

Soft Condensed Matter

AI-Driven Design of poly(ethylene terephthalate)-replacement copolymers

Chiho Kim, Wei Xiong, Akhlak Mahmood et al. (+2 more)

Poly(ethylene terephthalate) (PET), a widely used thermoplastic in packaging, textiles, and engineering applications, is valued for its strength, clarity, and chemical resistance. Increasing environmental impact concerns and regulatory pressures drive the search for alternatives with comparable or superior performance. We present an AI-driven polymer design pipeline employing virtual forward synthesis (VFS) to generate PET-replacement copolymers. Inspired by the esterification route of PET synthesis, we systematically combined a down-selected set of Toxic Substances Control Act (TSCA)-listed monomers to create 12,100 PET-like polymers. Machine learning models predicted glass transition temperature (Tg), band gap, and tendency to crystallize, for all designs. Multi-objective screening identified 1,108 candidates predicted to match or exceed PET in $T_{\rm g}$ and band gap, including the “rediscovery” of other known commercial PET-alternate polymers (e.g., PETG, Tritan, Ecozen) that provide retrospective validation of our design pipeline, demonstrating a capability to rapidly design experimentally feasible polymers at a scale. Furthermore, selected, entirely new (previously unknown) candidates designed here have been synthesized and characterized, providing a definitive validation of the design framework.
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All authors Chiho Kim, Wei Xiong, Akhlak Mahmood, Rampi Ramprasad, Huan Tran

Mesoscale and Nanoscale Physics

Dynamics of excitons in CdSe nanoplatelets

Gerard Czajkowski

We show how to calculate the linear and nonlinear optical functions of CdSe nanoplatelets, taking into account the effect of a dielectric confinement on excitonic states. We consider both stationary and non-stationary excitation regime. We obtain obtain analytical expressions for the absorption coefficient, the exciton resonance energy and binding energy of nanoplatelets. The impact of plate geometry (thickness, lateral dimension) on the spectrum is discussed. In the nonlinear case we analyze the impact of temperature. For the short-pulse excitation the time dependence of the spectra is considered. The results are compared with the available experimental data.
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Mesoscale and Nanoscale Physics · Cross-listed from physics.chem-ph

Resolving the Marcus-Rehm-Weller Paradox in Electron Transfer

Ethan Abraham

Marcus theory famously predicts that electron-transfer rates decrease once the thermodynamic driving force exceeds the reorganization energy. Yet many systems instead exhibit Rehm-Weller kinetics characterized by rate saturation rather than decrease. Here we show that these apparently contradictory phenomenologies emerge as opposite physical limits of the same two-state quantum Hamiltonian. In the normal region, the model recovers both Marcus and Rehm-Weller behavior. In the inverted region, however, it predicts Marcus's decreasing rate in the nonadiabatic limit but Rehm-Weller saturation in the adiabatic limit. Using physically realistic reorganization energies and electronic coupling values, we show that Rehm-Weller's data can be quantitatively reproduced within a microscopic quantum model without invoking phenomenological corrections.
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Materials Science · Cross-listed from physics.ins-det

Quantifying the Full Damage Profile of Focused Ion Beams via 4D-STEM Precession Electron Diffraction and PSNR Metrics

M.G. Masteghin, Z.P. Aslam, A.P. Brown et al. (+4 more)

Focused ion beams (FIBs) are widely used in nanofabrication for applications such as circuit repair, ultra-thin lamella preparation, strain engineering, and quantum device prototyping. Although the lateral spread of the ion beam is often overlooked, it becomes critical in precision tasks such as impurity placement in host substrates, where accurate knowledge of the ion-matter interaction profile is essential. Existing techniques typically characterise only the beam core, where most ions land, thus underestimating the full extent of the point spread function (PSF). In this work, we use four-dimensional scanning transmission electron microscopy (4D-STEM) to resolve the ion beam tail at defect densities equivalent to $<$0.1 ions nm$^{-2}$. Convergent beam electron diffraction (CBED) patterns were collected in calibration regions with known ion fluence and compared to patterns acquired around static dwell spots exposed to a 30 keV Ga$^{+}$ beam for 1-10 s. Cross-correlation using peak signal-to-noise ratio (PSNR) revealed that 4D-STEM datasets are ultra-sensitive for defect quantification and more robust against scanning artefacts than conventional dark-field imaging. This approach is complementary to image resolution methods enabling a comprehensive profiling of ion-induced damage even at low-dose regimes, offering a more accurate representation of FIB performance and supporting application tailoring beyond the conventional resolution metrics focused solely on the beam core.
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All authors M.G. Masteghin, Z.P. Aslam, A.P. Brown, M.J. Whiting, S.K. Clowes, R.P. Webb, D.C. Cox

Soft Condensed Matter · Cross-listed from physics.bio-ph

Confinement inhibits surficial attachment and induces collective behaviors in bacterial colonies

Vincent Hickl, Gabriel Gmünder, René M. Rossi et al. (+4 more)

Bacterial colonies are a well-known example of living active matter, exhibiting collective behaviors such as nematic alignment and collective motion that play an important role in the spread of microbial infections. While the underlying mechanics of these behaviors have been described in model systems, many open questions remain about how microbial self-organization adapts to the variety of different environments bacteria encounter in natural and clinical settings. Here, using novel imaging and computational analysis techniques, the effects of confinement to 2D on the collective behaviors of pathogenic bacteria are described. Biofilm-forming Pseudomonas aeruginosa are grown on different substrates, either open to the surrounding fluid or confined to a single monolayer between two surfaces. Orientational ordering in the colony, cell morphologies, and trajectories are measured using single-cell segmentation and tracking. Surprisingly, confinement inhibits permanent attachment and induces twitching motility, giving rise to multiple coexisting collective behaviors. This effect is shown to be independent of the confining material and the presence of liquid medium. The nematic alignment and degree of correlation in the cells' trajectories determines how effectively bacteria can invade the space between two surfaces and the 3D structure of the colony after several days. Confinement causes the formation of dynamic cell layers driven by collective motion as well as collective verticalization leading to the formation of densely packed crystalline structures exhibiting long-range order. These results demonstrate the remarkable breadth of collective behaviors exhibited by bacteria in different environments, which must be considered to better understand bacterial colonization of surfaces.
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All authors Vincent Hickl, Gabriel Gmünder, René M. Rossi, Antonia Neels, Qun Ren, Katharina Maniura-Weber, Bruno F. B. Silva

Materials Science

Temperature-driven polarization rotation and triclinic phase at morphotropic phase boundary of Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals

Alexei A. Bokov, Haiyan Guo and Zuo-Guang Ye

Information about the crystal structures in the range of morphotropic phase boundary of ferroelectric perovskite solid solutions is important for understanding their intricate properties which result in wide opportunities for practical applications. However, for the (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 solid solution system this information is contradictory. Different composition-temperature phase diagrams have been reported for this system in literature based on the investigations of single crystals and ceramics using various experimental techniques. In this work we apply polarized light microscopy (PLM), X-ray diffraction (XRD) and dielectric spectroscopy to study the crystal structure and phase transitions in the 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 single crystal. We confirm the monoclinic MB symmetry (space group Cm) of the room-temperature phase. According to PLM, it transforms with increasing temperature into a triclinic (Tr) phase rather than the previously reported monoclinic MC or tetragonal phase. XRD data are consistent with the presence of Tr phase. The Tr phase transforms to the monoclinic MC (Pm) phase and then to the cubic phase. Ergodic relaxor behavior is observed above the Curie temperature. The unit cell in the MC phase is pseudotetragonal with the lattice parameters a = b < c and small monoclinic angle. In the MB phase the direction of spontaneous polarization is temperature independent and close to the <111> pseudocubic direction. In the Tr and MC phases it changes with temperature so that near the Curie point it is close to [001] axis. No significant anomalies in the dielectric properties or changes in the domain structure are observed at the MB to Tr and Tr to MC phase transitions. The domain structure changes dramatically when the temperature varies within the Tr phase, causing a sharp change in birefringence.
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Materials Science

Ambient-Induced Selenium Segregation and Nanoparticle Formation in 2H-HfSe2: An Experimental and Theoretical Study

Stefany P. Carvalho, Guilherme S. L. Fabris, Ana Carolina F. de Brito et al. (+7 more)

We investigate the air-induced degradation of few-layer hafnium diselenide (HfSe$_2$) through combined experimental and theoretical approaches. AFM and SEM reveal the formation of selenium-rich spherical features upon ambient exposure, while EDS confirms Se segregation. Ab initio molecular dynamics simulations show that Se atoms migrate to flake edges and that O/O$_2$ exposure leads to selective Hf oxidation, breaking Se–Hf bonds and expelling Se atoms. No stable Se–O bonds are observed, indicating structural reorganization rather than oxidation. These findings emphasize the material's instability in air and the importance of encapsulation for preserving HfSe$_2$ in practical applications. Scanning tunneling spectroscopy confirms the semiconducting character of the nanoparticles, with an electronic bandgap compatible with that of elemental Se. These results highlight the critical role of lattice defects and oxidation dynamics in the degradation process and underscore the need for encapsulation strategies to preserve the integrity of HfSe$_2$-based devices.
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All authors Stefany P. Carvalho, Guilherme S. L. Fabris, Ana Carolina F. de Brito, Raphael B. de Oliveira, Wesley Kardex C. de Oliveira, Catalina Ruano-Merchan, Carlos A. R. Costa, Luiz F. Zagonel, Douglas Galvao, Ingrid D. Barcelos

Strongly Correlated Electrons

I. Magnetic, thermal and transport properties of YbCu$_{5-x}$Zn$_x$ alloys

I. Čurlik, F. Akbar, S. Gabani et al. (+2 more)

Within the family of cubic YbCu$_4$X compounds ($X$ = Ni, Au and Zn), we have investigated the YbCu$_{5-x}$Zn$_x$ ($1\geq x \geq 0.7$) alloys by means of structural, magnetic, thermal and transport measurements. In the $\tau 1-$ YbCu$_{5-x}$Zn$_x$ (cubic AuBe$_5$ type, $0.7 \leq x \leq 1.5$) structural phase, Yb ion is in its Yb$^{3+}$ magnetic configuration. However, by increasing Zn content the unit cell grows faster than a reference computed as a Cu by Zn atoms substitution, which indicates a shift of Yb ions towards the larger Yb$^{2+}$ configuration. The magnetic behavior confirms such tendency with a clear decrease of the saturation magnetization and effective moment between $x=0.7$ and $x=1$. The specific heat at low temperature shows a logarithmic dependence characteristic for a non-fermi-liquid behavior. The characteristic energies of all studied parameters, including magneto resistivity, show notably low values as an indication that these alloys are close to a quantum critical point, which is approached from the non-magnetic side as the Zn content decreases.
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All authors I. Čurlik, F. Akbar, S. Gabani, M. Giovannini, J. G. Sereni

Soft Condensed Matter

Emergent clusters in strongly confined systems

Pamud Akalanka Bethmage, Ryker Fish, Brennan Sprinkle et al. (+1 more)

Driven suspensions, where energy is input at a particle scale, are a framework for understanding general principles of out-of-equilibrium organization. A large number of simple interacting units can give rise to non-trivial structure and hierarchy. Rotationally driven colloidal particles are a particularly nice model system for exploring this pattern formation, as the dominant interaction between the particles is hydrodynamic. Here, we use experiments and large-scale simulations to explore how strong confinement alters dynamics and emergent structure at the particle scale in these driven suspensions. Surprisingly, we find that large-scale (many times the particle size) density fluctuations emerge as a result of confinement, and that these density fluctuations sensitively depend on the degree of confinement. We extract a characteristic length scale for these fluctuations, demonstrating that the simulations quantitatively reproduce the experimental pattern. Moreover, we show that these density fluctuations are a result of the large-scale recirculating flow generated by the rotating particles inside a sealed chamber. This surprising result shows that even when system boundaries are far away, they can cause qualitative changes to mesoscale structure and ordering.
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All authors Pamud Akalanka Bethmage, Ryker Fish, Brennan Sprinkle, Michelle M. Driscoll