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Physics Condensed Matter

cond-mat Watch Condensed Matter

Wednesday 4 March

Mesoscale and Nanoscale Physics

Imaging asymmetric Coulomb blockade phenomena across metallic nanoislands

Junho Bang, Byeongin Lee, Hankyu Lee et al. (+2 more)

Coulomb blockade (CB) arises in nanoscale systems with ultra-small capacitance, where discrete charging effects dictate electron transport, enabling wide-ranging applications based on single-electron transistors. Despite established electrostatic control of charge states in quantum dots and nanoislands, a rigorous quantitative link between junction parameters and the CB spectrum remains elusive. Here, using scanning tunneling spectroscopy, we investigate the spatial variation of CB in indium nanoislands on semiconducting black phosphorus. We observe spatially dispersive charging resonances whose trajectories exhibit a finite shift of the symmetry axis in bias as well as a pronounced asymmetric curvature. By comparing the experimental results with calculations based on orthodox theory, we show that these features originate from work function differences in the junctions, underscoring the importance of junction-specific electrostatics in nanoscale charge transport.
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All authors Junho Bang, Byeongin Lee, Hankyu Lee, Jian-Feng Ge, Doohee Cho

Strongly Correlated Electrons

Skyrmion generation via Laguerre-Gaussian beam irradiation in frustrated magnets

Reivienne Jei Laxamana and Satoru Hayami

Since its discovery, the study of magnetic skyrmions has been on the rise. In this paper, we discuss our investigations on the light-induced mechanisms for skyrmion generation in a centrosymmetric triangular magnetic lattice with competing $J_1$-$J_3$ interactions, and easy-axis anisotropy. We solve the stochastic Landau-Lifshitz-Gilbert equation for the lattice spin dynamics under Laguerre-Gaussian beam irradiation. Numerical results show that skyrmions are nucleated in two thermodynamic regions, each favoring different phases: the ferromagnetic phase and the skyrmion-lattice phase. In the ferromagnetic region, isolated skyrmions are generated mainly through stochastic thermal nucleation. In this regime, higher temperatures and larger beam widths are required to overcome the nucleation barrier. In contrast, in the skyrmion-lattice region, skyrmion nucleation occurs via thermal annealing, where the system relaxes toward its true ground state. These findings establish a comprehensive theoretical framework for optimizing optical control to generating light-induced skyrmionic textures in frustrated magnets.
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Materials Science

Ultralow and Tunable Thermal Conductivity of Parylene C for Thermal Insulation in Advanced Packaging

Yicheng Wei, Han Xu, Xingqiang Zhang et al. (+2 more)

Parylene C thin films have significant applications in advanced packaging of microelectronics. Their thermal properties are critical for thermal management of electronic devices. However, a unified understanding of the tunable structure and the corresponding thermal conductivity is still missing. This study investigated parylene C thin films of varying thickness and post-annealing temperatures grown via thermal chemical vapor deposition. The ultralow thermal conductivity of as-deposited parylene C measured by time domain thermoreflectance (TDTR) is 0.10 W/m-K. The thermal conductivity can be tuned by post-annealing. Significant increase in thermal conductivity is observed in the annealed samples (0.18 W/m-K) which induces melting and recrystallization. The results of XRD and polarized Raman spectroscopy show that the enhanced thermal conductivity is due to improved crystalline quality and the change in chain orientations. The measured thermal conductivities of the as-deposited and annealed films are much lower than the values predicted by the Cahill minimum thermal conductivity model, which can be explained by the diffuson-mediated minimum thermal conductivity model. Parylene C is found to possess the lowest thermal conductivity among dense low-k materials. Our work provides guidance for the structural design of ultra-low thermal conductivity polymers and corresponding thermal design of electronics.
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All authors Yicheng Wei, Han Xu, Xingqiang Zhang, Wei Wang, Zhe Cheng

Mesoscale and Nanoscale Physics

Non-reciprocity and exchange-spring delay of domain-wall Walker breakdown in magnetic nanowires with azimuthal magnetization

Lucía Gómez-Cruz, Laura Álvaro-Gómez, Claudia Fernández-González et al. (+13 more)

Domain-wall (DW) motion is a crucial process involved in magnetization reversal, be it under magnetic field or spin-polarized current stimulus. In most cases the DW speed does not exceed $\approx$100m/s and collapses above a given threshold of the stimulus, an effect known as Walker breakdown. A few specific material properties have been identified to delay the breakdown of speed by increasing the energy barrier preventing internal precession. We show that in a 3D nanomagnetic system, here with vortex-state domains, the topology of the magnetization distribution may intrinsically and robustly delay the Walker breakdown due to an exchange-spring effect. However, in contrast to situations in lower dimension, the motion remains steady-state. In addition, curvature induces a major non-reciprocal effect, delaying or not the Walker breakdown depending on the sequence of chiralities of the azimuthal domains on both sides of the DW, independent of its direction of motion.
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All authors Lucía Gómez-Cruz, Laura Álvaro-Gómez, Claudia Fernández-González, Sandra Ruiz-Gómez, Christophe Thirion, Giuseppe Curci, Lucia Aballe, Eva Pereiro, Rachid Belkhou, Eduardo Martinez, Victor Raposo, Jean-Christophe Toussaint, Daria Gusakova, Aurélien Masseboeuf, Olivier Fruchart, Lucas Pérez

Materials Science

Insights into hydrogen-induced vacancy stability and creep in chemically complex alloys

Prashant Singh, Yash Pachaury, Aaron Anthony Kohnert et al. (+2 more)

Hydrogen (H) content modifies the creep response of Fe-based alloys by altering thermodynamics of point-defects; here we identify the electronic-structure mechanism underlying this effect. Using spin-polarized first-principles calculations combined with a cluster dynamics formulation, we establish a general framework linking H-assisted vacancy stabilization to diffusion-mediated creep in BCC Fe, FCC Fe, and chemically complex FCC Fe-Cr-Ni alloys. H-vacancy binding analysis shows that H-stabilized vacancies form at low hydrogen content in BCC Fe but require much higher chemical potentials in FCC Fe and Fe-Cr-Ni alloys due to broader d-bands, electronic screening, and chemical disorder. Consequently, plastic deformation mediated by diffusive processes is expected to be far more strongly impacted in BCC Fe than in FCC alloys. These electronic-controlled trends determine steady-state vacancy populations and provide a symmetry-resolved microscopic basis for H-assisted creep in ferritic and austenitic steels.
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All authors Prashant Singh, Yash Pachaury, Aaron Anthony Kohnert, Laurent Capolungo, Duane D. Johnson

Mesoscale and Nanoscale Physics

Multimode cavity magnonics in mumax+: from coherent to dissipative coupling in ferromagnets and antiferromagnets

Gyuyoung Park, OukJae Lee and Biswanath Bhoi

Coherent coupling between microwave cavity photons and magnon excitations enables quantum transduction, magnon-mediated entanglement, and magnon number-resolved detection. Micromagnetic simulation of photon-magnon coupling typically requires either modifying the core solver or implementing a full electromagnetic solver. Here we present a two-tier cavity magnonics extension for mumax+, a GPU-accelerated open-source micromagnetic framework. The first tier consists of CUDA kernels that integrate N cavity-mode ODEs simultaneously with the LLG equation inside the GPU-based RK45 adaptive time-stepper, eliminating per-step GPU-CPU transfers; spatially resolved mode profiles enter both the coupling and the feedback, enabling selective addressing of non-uniform spin-wave modes. The second tier is a lightweight Python co-simulation class that reproduces the same uniform-mode physics through operator-split RK4 integration without recompilation. We validate the implementation with eight benchmark simulations: (i) magnon-polariton anticrossing spectra, (ii) vacuum Rabi oscillations, (iii) the cooperativity phase diagram spanning weak-to-strong coupling regimes, (iv) cavity mode-profile-dependent coupling selection rules, (v) multi-mode polariton hybridization with magnon-mediated cavity-cavity energy transfer, (vi) mode-selective coupling via spatial overlap engineering, (vii) antiferromagnetic magnon-cavity coupling with Neel-vector spectroscopy, and (viii) abnormal anticrossing from dissipative photon-magnon coupling, demonstrating the transition from level repulsion to level attraction.
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Strongly Correlated Electrons

NMR evidence of spin supersolid and Pomeranchuk effect behaviors in the triangular-lattice antiferromagnet Rb$_2$Ni$_2$(SeO$_3$)$_3$

Ying Chen, Zhanlong Wu, Xuejuan Gui et al. (+15 more)

We performed $^{85}$Rb nuclear magnetic resonance (NMR) measurements on the $S$ = 1 bilayer triangular-lattice antiferromagnet Rb$_2$Ni$_2$(SeO$_3$)$_3$ in magnetic fields up to 26 T. In the field range from 3 T to 26 T, the NMR spectral lines split and their respective spectral weight ratios reveal the existence of the magnetic up-up-down (UUD) phase, although the 1/3-plateau phase is only reached at fields above 16 T. Two distinct gapless regimes are further identified: one at low fields and low temperatures, and the other at high fields and high temperatures, consistent with the spin supersolid Y and V phases. Notably, the UUD-V phase boundary exhibits a negative slope in $dT/dH$, where the supersolid phase is located at temperatures above the solid phase due to strong low-energy spin fluctuations.
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All authors Ying Chen, Zhanlong Wu, Xuejuan Gui, Guijing Duan, Shuo Li, Xiaoyu Xu, Kefan Du, Xinyu Shi, Rui Bian, Xiaohui Bo, Guochen Liu, Jun Luo, Jie Yang, Yi Cui, Rui Zhou, Jinchen Wang, Rong Yu, Weiqiang Yu

Strongly Correlated Electrons

Contribution of remote bands to orbital magnetization in twisted bilayer graphene

Pinzhuo Li, Kun Jiang, Ziqiang Wang et al. (+2 more)

Motivated by recent theoretical and experimental works on orbital magnetization $M_{\mathrm{orb}}$ for the interacting system, we develop a gauge-invariant framework to compute $M_{\mathrm{orb}}$ for correlated phases of magic-angle twisted bilayer graphene within self-consistent Hartree-Fock approximation. Based on the projector formulation of the theory of orbital magnetization, we evaluate both $M_{\mathrm{orb}}$ and the self-rotation contribution $m_{\mathrm{SR}}$ directly from the Hartree-Fock Hamiltonian. We demonstrate that, in contrast to topological invariants such as the Chern number, both $M_{\mathrm{orb}}$ and $m_{\mathrm{SR}}$ obtain substantial contributions from remote bands and thus require careful convergence with respect to the number of included remote bands. Applying this approach to correlated phases at integer fillings, we obtain converged $M_{\mathrm{orb}}$ and $m_{\mathrm{SR}}$ for time reversal symmetry broken Chern insulating states at $\nu=\pm3$ and for competing correlated phases at other integer fillings. Our results establish a systematic and controlled approach for evaluating orbital magnetization in correlated moiré systems and clarify the crucial role of remote bands in determining their magnetic response.
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All authors Pinzhuo Li, Kun Jiang, Ziqiang Wang, Jian Kang, Yi Zhang

Mesoscale and Nanoscale Physics

Coulomb interaction unlocks Majorana-mediated electron teleportation between Quantum dots

Sirui Yu, Hong Mao, Jinshuang Jin et al. (+1 more)

We investigate quantum transport in a hybrid system composed of two quantum dots (QDs) coupled through a pair of spatially separated Majorana zero modes (MZMs) with negligible coupling energy. We focus on nonlocal correlations mediated by the MZMs, particularly the role of Coulomb interaction U between the QDs and the Majorana wire. Using the numerically exact fermionic dissipation equation of motion (DEOM) method, we compute both the transient current and the current-current cross-correlation noise spectrum. In the non-interacting case (U=0), destructive interference between the degenerate normal tunneling and anomalous tunneling channels suppresses electron teleportation between the dots. Introducing a finite Coulomb interaction $U$ lifts this channel degeneracy, enabling strong nonlocal correlations and inter-dot electron teleportation. This effect manifests as a robust signal in the cross-correlation noise spectrum, which is significantly stronger than that induced by a finite Majorana coupling energy $\varepsilon_{M}$. Our findings propose Coulomb interaction as an efficient and experimentally accessible control parameter for generating and detecting Majorana-mediated nonlocal transport in the topologically relevant long-wire limit ($\varepsilon_{M}\rightarrow0$).
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All authors Sirui Yu, Hong Mao, Jinshuang Jin, Chui-Ping Yang

Strongly Correlated Electrons

X-ray magnetic circular dichroism evidence of intrinsic $d$-wave altermagnetism in rutile-structure NiF$_2$

Zezhong Li, Kosuke Sakurai, Yiu-Fung Chiu et al. (+13 more)

We present the x-ray magnetic circular dichroism (XMCD) at the Ni $L_{2,3}$-edge as an evidence of the $d$-wave altermagnetism in rutile-structure NiF$_2$. Sizable XMCD signal is observed in excellent agreement with theoretical simulations. Owing to a considerable net magnetization due to spin canting, the XMCD spectrum consists of an altermagnetic signal as well as a non-negligible ferromagnetic contribution. We verify experimentally that the XMCD spectrum can be written as a sum of contributions from altermagnetism and weak ferromagnetism. Two experimental methods to isolate the ferromagnetic contribution are shown to yield essentially the same result. These are dependence of XMCD on applied magnetic fields below the Néel temperature and the XMCD measured in applied field above the Néel temperature. Our results demonstrate the utility of XMCD as a probe for altermagnetic materials with the coexisting weak ferromagnetism induced by the relativistic spin-orbit coupling.
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All authors Zezhong Li, Kosuke Sakurai, Yiu-Fung Chiu, Dirk Backes, Dharmalingam Prabhakaran, Mizuki Furo, Choongjae Won, Wenliang Zhang, Sang-Wook Cheong, Andrew Boothroyd, Mirian Garcia-Fernandez, Sahil Tippireddy, Jan Kuneš, Stefano Agrestini, Atsushi Hariki, Ke-Jin Zhou

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

A Photonic Tautochrone: Spatiotemporal Beam Focusing for Enhanced Nonlinear Response

W. Verstraelen, S. Zanotti, N. W. E. Seet et al. (+6 more)

We propose to implement an optical analogue of the tautochrone property of the cycloid to allow the focusing of ultrashort pulses inside photonic systems. This allows to enhance nonlinear effects, resulting in orders of magnitude increase of nonlinearity-induced phase shifts, while employing low irradiances. Building upon the optical-mechanical analogy, we show how to produce optical limiters for temporal light pulses, and how to implement temporal bistability and even multistability with large numbers of states. Finally, we move this concept to the quantum realm and predict a tautochrone quantum blockade regime with a stronger antibunching.
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All authors W. Verstraelen, S. Zanotti, N. W. E. Seet, J. Zhao, D. Sanvitto, J. Zuñiga-Perez, K. Dini, Y. G. Rubo, T. C. H. Liew

Materials Science

Nonvolatile Control of Nonlinear Hall and Circular Photogalvanic Effects via Berry Curvature Dipole in Multiferroic Monolayer CrNBr2

Wenzhe Zhou, Dehe Zhang, Guibo Zheng et al. (+2 more)

The Berry curvature dipole induced by symmetry breaking play a pivotal role in electronic transport properties and nonlinear responses, such as the nonlinear Hall effect and circular photogalvanic effect. The study of the Berry curvature dipole, often explored in time-reversal symmetric systems, but it should not be limited to such materials. Here, we predicted that the ferroelectricity in monolayer CrNBr2 produces Berry curvature dipole, leading to the nonlinear Hall effect and circular photogalvanic current. The linear anomalous Hall effect and circularly polarized optical absorption, governed by spin-orbit coupling, are independent of ferroelectric polarization and exhibit extremely small conductance. In contrast, multiferroic monolayer CrNBr2 achieves a large nonlinear Hall conductivity and circular photogalvanic current, despite its suppression at high temperatures from phonon scattering. The coupling between the ferroelectric polarization and the Berry curvature dipoles allows for nonvolatile switching of these effects, presenting substantial promise for nanoelectronic and optoelectronic devices.
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All authors Wenzhe Zhou, Dehe Zhang, Guibo Zheng, Yinheng Li, Fangping Ouyang

Materials Science

Plasmonic polaron in self-intercalated 1T-TiS2

Byoung Ki Choi, Woojin Choi, Zhiyu Tao et al. (+24 more)

Electron-boson coupling is central to a comprehensive understanding of the diverse physical phenomena emerging from many-body interactions. Yet less attention has been paid to how plasmons, collective bosonic modes of electron density oscillation, interact with conduction electrons and how external parameters can tune this interaction. Here, we present a clear display of composite quasiparticles stemming from electron-plasmon coupling, known as the plasmonic polaron, in self-intercalated 1T-TiS2, by using angle-resolved photoemission spectroscopy (ARPES), high-resolution electron energy loss spectroscopy (HR-EELS) and first-principles calculations. The single particle spectral function exhibits a distinctive plasmon-loss satellite with the same characteristic energy scale determined by HR-EELS measurements. The bosonic energy scale of plasmonic polaron is tunable by controlling charge carrier density and temperature, distinguishing itself from conventional polarons arising from electron-phonon interactions. Furthermore, we find that the dielectric screening strongly affects the formation of the plasmonic polaron states. Our findings provide direct spectroscopic evidence of plasmonic polarons and establish self-intercalated layered materials as a promising platform for studying, controlling, and harnessing plasmonic interactions in quantum materials.
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All authors Byoung Ki Choi, Woojin Choi, Zhiyu Tao, Ji-Eun Lee, Sae Hee Ryu, Seungrok Mun, Hyobeom Lee, Kyoungree Park, Seha Lee, Hayoon Im, Yong Zhong, Hyejin Ryu, Min Jae Kim, Sue Hyeon Hwang, Xuetao Zhu, Jiandong Guo, Jong Mok Ok, Jaekwang Lee, Haeyong Kang, Sungkyun Park, Jonathan D. Denlinger, Heung-Sik Kim, Aaron Bostwick, Zhi-Xun Shen, Choongyu Hwang, Sung-Kwan Mo, Jinwoong Hwang

Statistical Mechanics · Cross-listed from physics.plasm-ph

Effect of magnetic drift on the stability structure of the ambipolar condition

Keiji Fujita and Shinsuke Satake

In non-axisymmetric plasmas, the ambipolar condition may have multiple roots. In such cases, the evolution of the ambipolar electric field can be described by the dynamics in a bistable potential, where the relative depth of the potential wells primarily determines the realized root. In this study, we show that the inclusion of the magnetic drift in the orbit model can significantly modify the potential landscape and affect root selection. This effect provides a possible explanation for discrepancies between simulation results obtained using different orbit models, as well as between simulations and experimental observations of ambipolar radial electric field profiles. Further, the analysis suggests that the ambipolar electric field may be more susceptible to fluctuations than previously expected, indicating the potential relevance of noise-induced state transitions.
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Strongly Correlated Electrons

Magnetic Signature of Chiral Phonons Revealed by Neutron Spectroscopy in Ferrimagnetic Fe$_{1.75}$Zn$_{0.25}$Mo$_3$O$_8$

Song Bao, Junbo Liao, Zhentao Huang et al. (+13 more)

Lattice vibrations can carry angular momentum and magnetic moments under broken inversion or time-reversal symmetry, forming so-called chiral phonons. While such excitations have been explored in nonmagnetic systems via optical probes, their direct detection in magnetic materials and coupling to spin excitations remain largely unexplored. Here, using neutron spectroscopy, sensitive to both nuclear and magnetic scattering, we reveal the magnetic signature of chiral phonons in ferrimagnetic Fe$_{1.75}$Zn$_{0.25}$Mo$_3$O$_8$ with Curie temperature $T_{\rm C}\sim49$ K. Below $T_{\rm C}$, we observe enhanced magnetic scattering of phonons at small momenta, arising from strong magnon-phonon coupling. In addition, out-of-plane intensity modulation, phonon mode splitting, and field-induced Zeeman shifts are observed, all closely associated with the ferrimagnetic order. These features vanish above $T_{\rm C}$, where phonon spectra are dominated by nuclear scattering. These observations demonstrate the existence of chiral phonons carrying substantial magnetic moments that directly contribute to magnetic scattering, and establish neutron spectroscopy as a powerful, momentum-resolved probe of their magnetic character.
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All authors Song Bao, Junbo Liao, Zhentao Huang, Yanyan Shangguan, Zhen Ma, Bo Zhang, Shufan Cheng, Hao Xu, Zihang Song, Shuai Dong, Maofeng Wu, Ryoichi Kajimoto, Mitsutaka Nakamura, Tom Fennell, Dmitry Khalyavin, Jinsheng Wen

Statistical Mechanics

Adding noise and scaling forces to speed up the Langevin clock

Prithviraj Basak, Stephen Whitelam and John Bechhoefer

Using experiments on a colloidal particle trapped in an optical tweezer, we confirm a recent proposal to increase the effective mobility or clock rate of systems described by Langevin dynamics, by simultaneously scaling deterministic forces and adding external noise. A corollary, which we also confirm experimentally, is that a system driven out of equilibrium by a time-dependent protocol can remain closer to thermal equilibrium. As an application, we demonstrate more precise recovery of free-energy differences from nonequilibrium work relations. Langevin clock rescaling provides a general strategy for accelerating calculations in the emerging field of thermodynamic computing, which uses stochastic devices governed by Langevin dynamics to do low-energy calculations.
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Mesoscale and Nanoscale Physics

Impact of the out-of-plane conductivity on spin transport evaluation in a van der Waals material

Ryoya Nakamura, Futo Tokuda, Yoshinobu Ono et al. (+5 more)

Layered materials are promising candidates for spintronic applications due to their unique electronic structures and spin transport properties. However, the strong anisotropic conductivity inherent in these materials complicates the quantitative evaluation of spin Hall conductivity and spin diffusion length. In this work, we present a comprehensive study of spin transport in a transition metal dichalcogenide PtTe$_2$ by combining a three-dimensional finite element model with nonlocal spin valve structures. We developed a theoretical model that treats an anisotropic spin diffusion in the same way as the conventional isotropic model, enabling the extraction of spin diffusion lengths along both the in-plane and out-of-plane directions. Our analysis revealed that the conventional isotropic assumption tends to overestimate some values, particularly for the out-of-plane spin diffusion length and spin Hall conductivity. These findings provide new insight into anisotropic spin diffusion and spin-charge conversions in layered materials and emphasize the importance of accounting for anisotropic conductivity in the design of spintronic devices.
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All authors Ryoya Nakamura, Futo Tokuda, Yoshinobu Ono, Nan Jiang, Hideaki Sakai, Masayuki Ochi, Hiroaki Ishizuka, Yasuhiro Niimi

Quantum Gases

Dynamical Superfluid and Bose-Insulator Phases in Quantized Polariton Lattices

Sanjib Ghosh

We demonstrate that Hilbert-space quantization in polariton lattices-manifested as multiple quantized energy levels in strongly confined sites-provides an unconventional route to realizing and manipulating different quantum phases. We show that nonlinear interactions transfer population into excited on-site quantum levels, which acts as an intrinsic dynamical channel controlling quantum coherence across the lattice. While weak nonlinearity confines polaritons to the lowest mode, yielding a robust superfluid phase with broken U(1) symmetry, strong nonlinearity induces phase diffusion through inter-level mixing. This dynamically generated fluctuations suppress global phase coherence and drives the system into a dynamical Bose-insulating phase. The changes between these phases occurs either as a nonequilibrium phase transition or a sharp crossover.
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Mesoscale and Nanoscale Physics

Symmetry selection rules for the intrinsic nonlinear thermal Hall effect in altermagnets: Role of quantum metric and $C_{2}$ rotational symmetry

Gunn Kim

We establish symmetry-based selection rules for the intrinsic nonlinear thermal Hall effect driven by the quantum metric in altermagnets. We show that a nonvanishing nonlinear thermal Hall conductivity $\kappa_{xyy}$ requires three conditions: (i) a nontrivial quantum metric, (ii) breaking of mirror symmetry $M_{x}$, and (iii) breaking of twofold rotational symmetry $C_{2}$. Using tight-binding models on a square lattice, we demonstrate that $d$-wave altermagnets naturally break $C_{2}$ through parity-mixing orbital hybridizations, while $g$-wave systems preserve $C_{2}$, forcing the response to vanish identically. Step-by-step Taylor expansions and explicit unitary matrix proofs establish these results. Our framework provides predictive power for material selection and lays the groundwork for nonlinear spin-caloritronic devices.
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Tuesday 3 March

Materials Science · Cross-listed from physics.class-ph

Universal Displacements in Linear Strain-Gradient Elasticity

Dimitris Sfyris and Arash Yavari

We study universal displacement fields in three-dimensional linear strain-gradient elasticity within the Toupin-Mindlin first strain-gradient theory. Building on the approach of Yavari (2020), we derive, for each material symmetry class, the universality PDEs obtained by requiring the equilibrium equations (in the absence of body forces) to hold for any material in that class, and we determine the complete set of universal displacements. Using the full symmetry classification together with compact matrix representations of the elasticity tensors, we provide explicit characterizations for all 48 strain-gradient symmetry classes, including centrosymmetric and chiral classes. For several high-symmetry classes, the strain-gradient universality PDEs impose no additional restrictions beyond the classical ones, so the universal displacement families coincide with those of classical linear elasticity (for example, the isotropic classes SO(3) and O(3)). For lower symmetry classes, the strain-gradient universality PDEs can be stricter than their classical counterparts, so the universal displacements form proper subsets of the classical universal displacement families due to additional higher-order differential conditions.
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Mesoscale and Nanoscale Physics

Analysis of an all-to-all connected star array of transmon qubits

Ricardo A. Pinto

We analyzed quantum $XX$ and $ZZ$ coupling and state transfer in an all-to-all connected star array of capacitively coupled superconducting transmon qubits. It is shown that in a highly-connected system like this a variety of different $ZZ$ couplings arise that correspond to the different ways qubits can interact with each other, opening different channels for unwanted qubit crosstalk and thus qubit operation errors. We studied the dependence of both the $XX$ and the $ZZ$ coupling on qubit detuning that controls qubit-qubit interaction. The $XX$ coupling, quantified by the error state occupation probability, shows a $\Delta\omega^{-2}$ decay with qubit detuning $\Delta\omega$. On the other hand, all $ZZ$ coupling frequencies show spikes at values in the lower detuning region that correspond to resonances between qubit states and states out of the computational basis, after which all couplings quickly decay to zero as qubit detuning further increases. This allows to define an operational region where near-zero qubit coupling can be achieved. We derive equations for the couplings as a function of qubit detuning that agree with numerical results solving the Schrödinger equation.
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Materials Science · Cross-listed from physics.chem-ph

Absolute Primary Nanothermometry Using Individual Stark Sublevels of Rare-Earth-doped Crystals

Allison R. Pessoa, Thomas Possmayer, Jefferson A. O. Galindo et al. (+4 more)

We present two independent optical methods for absolute primary thermometry using rare-earth-doped nanoparticles. Both approaches rely exclusively on the internal energy levels and population dynamics of the dopant ions, eliminating the need for external temperature references. We experimentally demonstrate the concepts by using Y$_2$O$_3$: Yb$^{3+}$/Er$^{3+}$ nanoparticles, exploiting Boltzmann distribution between individual Stark sublevels of the Er$^{3+}$ ions, emitting in the green spectral region ($\sim$550 nm) and in the near-infrared spectral region ($\sim$1600 nm). Our strategy establishes rare-earth-based luminescence thermometers as genuine absolute primary probes, conceptually comparable to Johnson noise and acoustic gas thermometers, but with the fundamental advantage of possibly being employed at the nanoscale, potentially down to the single-ion limit, with optical readout and over wide temperature ranges.
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All authors Allison R. Pessoa, Thomas Possmayer, Jefferson A. O. Galindo, Luiz F. dos Santos, Rogéria R. Gonçalves, Leonardo de S. Menezes, Anderson M. Amaral

Materials Science

A Pathway Selection Process for Dynamically Self-Organizing Systems

J. A. Sekhar

Self-organization creates new order and shifts sub-boundaries while reorganizing energy and entropy within a control volume. This article examines pathway selection and tests whether maximizing the entropy generation rate can forecast process pathways. All entropy-generating processes distribute internal energy through temperature changes or structural responses, thereby creating new patterns or causing volume changes. Rapid self-organization, such as a supercooled liquid metal transforming into a solid, is a quasi-adiabatic process that tends to approach equilibrium or a steady state with respect to parameters like temperature. This is one of the main examples studied. Entropy generation is linked to internal energy redistribution, either as work performed (called stored work) or as thermal energy stored within a system. A system's resilience during and after self-organization is reflected in the emergence of measurable engineering properties. In the examples studied, the entropy generation rate is maximized throughout the process, regardless of the work needed to create new boundaries. Self-organization is a dissipative process, linked to pattern formation. The article discusses various patterns and shapes in physical systems, including grain size and morphology during thermo-mechanical deformation of crystalline solids, solid-liquid transformations, atmospheric effects, fluid-flow eddies, and patterned flight in birds that conserve energy within the framework of entropy-rate maximization. Morphological boundary limits are examined in terms of the ratio of the energy dissipation rate to the entropy generation rate for several examples. Processes can continue beyond an identifiable self-organizing phase, albeit with different time constants, thereby maintaining continuity and connectivity by maximizing the entropy-generation rate.
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Mesoscale and Nanoscale Physics

Graphene Zero-Bias Sub-Terahertz Turnkey Detector with Above 43 GHz Bandwidth

E.I. Titova, A. Titchenko, M. Titova et al. (+16 more)

High-frequency terahertz (THz) detectors are vital for next-generation high-speed wireless communication systems. Graphene, with its high carrier mobility, broadband absorption, and weak electron-phonon coupling, offers great promise for ultra-fast THz photothermoelectric devices. Although graphene-based detectors in the infrared range have shown bandwidths above 500 GHz, extending their operation to the THz range is difficult because long-wavelength radiation does not efficiently couple to the small graphene area. To overcome this issue, THz antennas are often employed; however, their use typically limits system performance to only a few gigahertz due to parasitic effects. In this work, we present an antenna-coupled sub-THz graphene detector with a bandwidth exceeding 43 GHz. We optimized the detector design to minimize losses, match the antenna impedance to the 1 kOhm graphene channel, and maintain zero-bias operation. Importantly, we introduce a compact, turnkey packaged solution. Our results provide a practical route toward high-speed and low-power graphene THz detectors suitable for real-world communication and imaging applications.
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All authors E.I. Titova, A. Titchenko, M. Titova, K. Shein, A. Kuksov, A. Sobolev, S. Zhukov, K. Kapralov, E. Zhukova, Ya. Gershtein, M. Kashchenko, A. Shabanov, M. Kravtsov, L. Elesin, K. S. Novoselov, G. Goltsman, D. A. Svintsov, I. Gayduchenko, D. A. Bandurin

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

Finite-Size Effects in Nonlocal Metasurfaces

Tom Hoekstra, Sander A. Mann and Jorik van de Groep

Metasurfaces leveraging nonlocal resonances enable narrowband spectral control and strong near-fields, with applications spanning augmented reality, biosensing, and nonlinear optics. However, the large spa- tial extent of these modes also poses new challenges: finite-size effects often deteriorate the performance of practical, footprint-limited devices. Here, we develop a spatiotemporal coupled-mode theory model that intuitively and quantitatively captures how finite size affects the scattering response of nonlocal metasurfaces. This reveals that, when the modal propagation length becomes constrained by the phys- ical interaction length, the scattered field shows strong interference fringes and linewidth broadening. We derive an expression for the quality factor that incorporates an additional edge-loss channel, demon- strating that the stored energy and effective lifetime scale exponentially with the interaction length. We validate these predictions experimentally using position- and momentum-resolved spectroscopy on a 30-micron-wide metasurface. Overall, this work formalizes the impact of finite size on the scattering re- sponse of nonlocal photonic systems, and provides handles on how to minimize the impact of finite-size effects in metasurface design.
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Strongly Correlated Electrons

Coupled-cluster approach to vibronic effects in resonant inelastic x-ray scattering of quantum materials: Application to a $5d^1$ rhenium oxide

Teruki Matsuzaki, Liviu F. Chibotaru, Maristella Alessio et al. (+1 more)

First-principles analysis of the spectroscopic signatures of correlated quantum materials poses significant challenges due to the interplay between spin-orbit and vibronic couplings, as well as the need to describe both dynamic and static electron correlation to reach decent accuracy. In this work, we apply the equation-of-motion coupled-cluster (EOM-CC) method to derive the spin-orbit-lattice entangled vibronic states and predict the Re $L_3$ edge resonant inelastic x-ray scattering (RIXS) spectra of Ba$_2$MgReO$_6$. The EOM-CC yields interaction parameters in close agreement with those extracted from RIXS spectra, with errors of less than 5%. In particular, the EOM-CC method allowed us to determine the weak vibronic coupling to the $T_{2g}$ vibrations, which is difficult to address experimentally. The simulated spectra indicate that vibronic coupling to the $T_{2g}$ modes gives rise to a shoulder on the elastic peak. Going beyond the conventional treatment, which focuses solely on $E_g$ modes, we show that vibronic couplings to both $T_{2g}$ and $E_g$ modes are required to account for the fine structure of the RIXS spectra. This work demonstrates that the EOM-CC method is a powerful tool for accurately predicting the complex local states at metal sites and spectroscopic signatures of correlated insulating materials.
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All authors Teruki Matsuzaki, Liviu F. Chibotaru, Maristella Alessio, Naoya Iwahara

Disordered Systems and Neural Networks

Statistics of Thermal Avalanches in Driven Amorphous Systems

Zhiyu Cao and Peter G. Wolynes

Within the framework of the random first-order transition theory of glasses, we discuss the statistics of thermal avalanches, the large scale rearrangements in driven amorphous systems near their instability. Stringy excitations yield nonPoisson waiting time statistics. Embedding these statistics in a generalized Master equation captures the nonMarkovian, aging dynamics of avalanche clusters. We apply this framework to analyze nonequilibrium signatures of thermal avalanches, auto correlation functions and effective temperatures, under both quasi static shear and stochastic shaking protocols. We use full counting statistics to derive the complete distribution of both the avalanche magnitudes and avalanche counts, uncovering the intermediate time behavior.
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Materials Science

Predicting Spin-Crossover Behavior in Metal-Organic Frameworks from Limited and Noisy Data Using Quantile Active Learning

Ashna Jose, Emilie Devijver, Martin Uhrin et al. (+2 more)

Spin-crossover (SCO) metal-organic frameworks (MOFs) hold great promise for sensing, spintronics, and gas-related applications, however, only a small number of SCO-active examples are known among the thousands of MOFs already synthesized. Computational screening enhanced by machine learning offers a powerful route to uncover these hidden candidates much more rapidly than trial-and-error experiments. However, progress is limited by the computational complexity of obtaining accurate adiabatic energy differences, as these typically require separate geometry optimizations for both spin states, a process that is technically challenging, prone to convergence failures, and difficult to automate at scale. To mitigate these issues, we introduce a data-efficient strategy based on Quantile Regression Tree-based Active Learning, designed to navigate large chemical spaces while remaining robust to noisy and scarce labels obtained from unrelaxed geometries. After actively selecting a 200-sized subset of representative MOFs for electronic-structure evaluation, a Random Forest regressor trained on this data accurately identifies SCO-relevant candidates despite label noise, recovering 82% of true positives with only two false negatives. Applying the model to the unlabeled dataset yields a new collection of high-confidence SCO MOFs, which we denote pSCO-105. This work shows that spin crossover can be reliably identified from limited and imperfect data through smart training-set selection, enabling accelerated screening of SCO MOFs.
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All authors Ashna Jose, Emilie Devijver, Martin Uhrin, Noel Jakse, Roberta Poloni

Materials Science

Probing Interface-Driven Mechanisms of Non-Classical Light in van der Waals Heterostructures

Bárbara L. T. Rosa, Lara Greten, Raphaela de Oliveira et al. (+7 more)

Single-photon emitters in two-dimensional semiconductors offer a versatile platform for integrated quantum photonics, yet their performance is strongly influenced by local dielectric environments and substrate-induced disorder. Here, we examine SPEs in monolayer WSe$_2$ incorporated into hBN/WSe$_2$/Clinochlore van der Waals heterostructures and assess how interface-mediated dielectric modulation governs their optical and quantum characteristics. Low-temperature micro-photoluminescence reveals narrow emission lines (100 - 300 $\mu$eV) and robust non-classical behavior, with $g^{(2)}(0) = 0.13 \pm 0.02$ on SiO$_2$ and $0.54 \pm 0.02$ for emitters directly coupled to Clinochlore. Magneto-optical measurements yield effective g-factors near -8, consistent with defect states hybridized with dark excitons. WSe$_2$ on Clinochlore exhibits up to a fivefold enhancement in emission intensity, attributed to coupling with Fe-related substrate states that introduce resonant absorption near 1.75 eV. Kelvin probe force microscopy confirms strong dielectric contrast across thin and thick Clinochlore regions. Time-resolved photoluminescence shows that emitters on SiO$_2$ display a single $\approx 4$ ns lifetime, whereas those on Clinochlore exhibit biexponential dynamics with sub-nanosecond and tens-of-nanoseconds decay components. A phenomenological model incorporating coupling to bright and dark Fe-related states in Clinochlore accounts for modified excitation pathways. These results establish interface dielectric engineering in vdW heterostructures as an effective strategy for tailoring the radiative dynamics and brightness of quantum emitters in atomically thin materials.
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All authors Bárbara L. T. Rosa, Lara Greten, Raphaela de Oliveira, César Ribahi, Aris Koulas-Simos, Chirag C. Palekar, Yara Gobato, Ingrid D. Barcelos, Andreas Knorr, Stephan Reitzenstein

Materials Science

Strain effects on $n$-type doping in AlN

Haochen Wang and Chris G. Van de Walle

Controllable doping in AlN and its alloys is essential for deep-ultraviolet light sources. Ionization energies for donors in AlN ($\mathrm{Si_{Al}}$, $\mathrm{S_N}$, $\mathrm{Se_N}$) are high. We report first-principles calculations demonstrating that strain engineering can result in a reduction in ionization energies. The donor levels for $\mathrm{S_N}$ and $\mathrm{Se_N}$ shift closer to the conduction-band minimum (CBM) under in-plane tensile strains, driven by a downward shift of the CBM. The most widely used donor, $\mathrm{Si_{Al}}$, forms a $DX$ center in AlN. We find that a 2.5% in-plane tensile strain (which would be induced by pseudomorphic growth on GaN in experiment) shifts the ($+/-$) transition level from 271 meV to 98 meV below the CBM, which would enhance the electron concentration by three orders of magnitude. These results demonstrate that strain engineering offers an effective route to enhance doping levels in AlN.
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