Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Transition Dipole Rotation Beyond the Condon Approximation in Single hBN Quantum Emitters
Serkan Paçal, Chanaprom Cholsuk, Mouli Hazra et al. (+4 more)
The design of polarization-encoded
quantum interfaces relies on the assumption that solid-state emitters possess static transition dipoles defined by the host
lattice symmetry. Here, we demonstrate that the transition dipole moment of single hexagonal boron nitride
quantum emitters is not a static property but rotates as a function of
photon energy. Through high-resolution energy-resolved spectroscopy, we reveal a continuous rotation of the emission dipole orientation reaching up to $40^{\circ}$ across the vibronic
manifold at room temperature, driven by coupling to the
phonon bath. This spectral rotation is effectively suppressed at cryogenic temperatures (6 K), where the acoustic
phonon population is negligible, identifying thermally activated
lattice vibrations as the primary driver of the reorientation. First-principles calculations on two representative defects spanning weak and strong electron-
phonon coupling regimes confirm that
phonon-displaced geometries produce a systematic deviation of the transition dipole orientation from the zero-
phonon line, with the magnitude scaling with vibronic coupling strength. The experimental observations and calculations demonstrate that single
quantum emitters can operate beyond the Condon approximation, with the transition dipole acquiring a dependence on the instantaneous
nuclear configuration. Our results identify a fundamental limit for polarization fidelity in solid-state
quantum networks and connect solid-state single-emitter physics to a class of effects previously accessible only in ensemble measurements in molecular and biological spectroscopy.
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All authors Serkan Paçal, Chanaprom Cholsuk, Mouli Hazra, Çağlar Samaner, Özgür Çak{\i}r, Tobias Vogl, Serkan Ateş
Mesoscale and Nanoscale Physics
$\mathbb Z_{2q}$ parafermionic hinge states in a three-dimensional array of coupled nanowires
Sarthak Girdhar, Viktoriia Pinchenkova, Even Thingstad et al. (+1 more)
We construct a model of a three-dimensional helical second-order topological
superconductor formed by an array of weakly coupled Rashba nanowires. We identify the parameter regime in which there are energy gaps in both the bulk and surface energy spectra, while a pair of helical $\mathbb{Z}_{2q}$ parafermionic modes (with $q$ being an odd integer) remains gapless along a closed path of one-dimensional hinges. The precise trajectory of these hinge modes is dictated by the hierarchy of interwire couplings and the boundary termination of the sample. In the noninteracting limit $q= 1$, the system hosts gapless Majorana hinge modes.
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All authors Sarthak Girdhar, Viktoriia Pinchenkova, Even Thingstad, Jelena Klinovaja
Materials Science · Cross-listed from cs.CE
Improved Implementation of Approximate Full Mass Matrix Inverse Methods into Material Point Method Simulations
John A. Nairn
Approximate full mass
matrix methods for the material point method, known as FMPM(k) of order k, can improve the calculation of grid velocities from grid momentum. It can be implemented in any MPM code by inserting a new calculation task whenever grid velocities are needed. The implementation recommended in this paper only needs these calculations once per time step just before when updating particle positions and velocities. FMPM implementation issues arise, however, when its methods are mixed with other MPM feature that rely on lumped mass calculations. Some common lumped-mass MPM features are grid-based, velocity boundary condition, multimaterial contact calculations, crack contact calculations, and imperfect interfaces. This paper first derives a revised FMPM(k) implementation that both simplifies and clarifies the "FMPM Loop" that can be added to MPM codes. Next, that loop is modified to allow FMPM(k) to work well even in simulations that need other MPM features that previously caused conflicts. Two other FMPM(k) issues are apparent loss of stability at very higher order k and inherent computational cost. These issues are discussed in an analysis of temporal stability as a function of order k and in consideration of options to improve efficiency.
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Materials Science
Symmetry-protected four double-Weyl fermions and their topological phase transitions in nonmagnetic crystals
Yun-Yun Bai, Ke-Xin Pang and Yan Gao
Realizing Weyl semimetals (WSMs) with the minimal number of Weyl points (WPs) fundamentally simplifies extracting intrinsic topological responses. While a minimum of four conventional ($|C|=1$) WPs in nonmagnetic
crystals is well-established, the exact
symmetry requirements and material realization for the unique configuration of four unconventional double-Weyl points (DWPs, $|C|=2$) remain unresolved. Here, we establish rigorous crystalline
symmetry constraints restricting the existence of exactly four
symmetry-protected DWPs to merely 28 space groups in both nonmagnetic spinless and spinful systems. Guided by this classification, we identify an $sp$$^2$–$sp$$^3$ hybridized
chiral carbon allotrope, THRLN-C$_{32}$, as an ideal candidate hosting precisely this four-DWP configuration near the
Fermi level. These $C_4$-protected DWPs project extended or closed-loop
Fermi arcs onto the surface Brillouin zone, providing unambiguous spectroscopic signatures. Furthermore, external strain drives profound topological phase transitions encapsulated in a unified
evolution landscape: the pristine four-DWP state dissociates into two exotic three-terminal Weyl complexes, degenerates into eight conventional $|C|=1$ WPs, or collapses into a trivial
insulator. This work provides a definitive theoretical framework for minimal double-WSMs in nonmagnetic spinful systems and introduces an optimal material platform for investigating strain-tunable topological
quantum phenomena.
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Strongly Correlated Electrons · Cross-listed from hep-th
Exotic theta terms in 2+1d fractonic field theory
Yuki Furukawa
In this work, we study exotic theta terms in the 2+1d $\phi$-theory, which provides a continuum description of the XY-plaquette model. The $\phi$-theory can be viewed as a fractonic analogue of the 1+1d compact
boson and exhibits momentum and winding subsystem
symmetries. In this theory, discontinuous field configurations play a crucial role. Although such configurations spoil the naive
topology of the field, they induce nontrivial backreactions that give rise to new topological terms. We study two types of theta terms, which we call the bulk theta term and the foliated theta term. The foliated theta term is constructed by coupling winding currents on neighboring leaves of a foliation. Remarkably, the corresponding theta angle can vary spatially without affecting the classical equations of motion. Both theta terms lead to generalized Witten effects, in which
vortex operators carrying winding subsystem charge acquire momentum subsystem charge. In the case of the foliated theta angle, the Witten effect exhibits a more intricate structure:
vortex operators acquire a quadrupolar momentum charge. We demonstrate these features using
lattice realizations based on the modified Villain formulation.
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Statistical Mechanics · Cross-listed from hep-th
Groenewold-Moyal twists, integrable spin-chains and AdS/CFT
Riccardo Borsato and Miguel García Fernández
We take the first steps to address via integrability the spectral problem of AdS/CFT dual pairs deformed by Groenewold-Moyal twists. In particular, we start by considering a twisted
spin-chain that couples, through a Groenewold-Moyal twist deformation, two $\mathfrak{sl}(2)$-invariant
spin-chains. We interpret this deformed
spin-chain as a deformation of a subsector of the $AdS_3/CFT_2$
spin-chain, but the construction shares qualitative features also with the corresponding deformation of the $AdS_5/CFT_4$
spin-chain, for example. As in similar types of deformations, we show that there exists a certain basis in which the
spin-chain
Hamiltonian takes a Jordan-block form. At the same time, by working in the basis of eigenstates of the generators used to construct the Groenewold-Moyal twist, the
Hamiltonian appears to be diagonalisable and with a deformed spectrum. Employing the method of the Baxter equation, we write down the energy of the ground state and of excited states in a perturbation of the deformation parameter. We then consider the string-theory side of the duality, where the twist is realised as a deformation of AdS of the type of Maldacena-Russo-Hashimoto-Itzhaki. We construct a deformation of the usual BMN classical solution, and in the large-$J$ limit we match the leading $\mathcal O(J^{-3})$ term of the energy of the
spin-chain groundstate with a conserved charge of the string classical solution. Differently from the undeformed setup as well as similar kinds of deformations, we find that the general expression of this charge of the string sigma-model is non-local, and that it does not correspond to a standard isometry. Nevertheless, it can be computed from the monodromy
matrix and it is part of the tower of conserved charges provided by integrability.
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Quantum Gases · Cross-listed from physics.atom-ph
Two-dimensional shelving spectroscopy of ultraviolet ground state transitions in dysprosium
Kevin S. H. Ng, Paul Uerlings, Fiona Hellstern et al. (+5 more)
The open inner-shell electronic structure of lanthanides with large
magnetic moments gives rise to a rich spectrum of transitions available for
laser cooling, trapping, and coherent control. Despite this, the large number of ultraviolet (UV) transitions below 400nm have so far been rarely utilized in dipolar atom experiments. Here, we investigate multiple UV ground state transitions in dysprosium. Several of these UV excited states have the largest decay strengths to the ultralong-lived, low-lying first excited state which are comparable to the most commonly used strongest transitions found in dipolar atoms. Using two-dimensional shelving spectroscopy which improves detection sensitivity and provides a straightforward way to determine the hyperfine-isotope structure and excited state total angular momentum $J$, we measure isotope shifts, hyperfine coefficients, and create King plots to determine their electronic nature. Such knowledge of these UV transitions which analogously exist in other
magnetic atoms is important for optically populating the first excited state and can be used towards creating an optical clock, high resolution imaging in
quantum gas microscopy, and probing lanthanide
nuclei with enhanced Schiff moments in search of physics beyond the standard model.
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All authors Kevin S. H. Ng, Paul Uerlings, Fiona Hellstern, Jens Hertkorn, Luis Weiß, Stephan Welte, Tilman Pfau, Ralf Klemt
Other Condensed Matter
Spin-Valley Relaxation of Rydberg Excitons
V. Jindal, K. Mourzidis, M. Semina et al. (+8 more)
Rydberg
excitons, characterized by large spatial extension and reduced electron-hole overlap, must have a
spin-valley dynamics different from that of ground state
excitons. Here we report a direct measurement of
spin relaxation of Rydberg
excitons in high-quality WSe2 monolayer using continuous-wave and time-resolved optical orientation experiments. Excited excitonic states exhibit exceptionally large photoluminescence circular polarization, approaching 90% for the 3s state. Time-resolved measurements reveal a strong increase of the
spin relaxation time with the principal
quantum number, from ~2 ps for the 1s
exciton to ~75 ps for the 3s
exciton. A microscopic model based on electron-hole exchange-driven
spin relaxation quantitatively reproduces the observed trend, demonstrating that Rydberg
excitons enable tunable
spin-valley dynamics in two-dimensional
semiconductors.
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All authors V. Jindal, K. Mourzidis, M. Semina, D. Lagarde, A. Balocchi, P. Renucci, T. Boulier, T. Taniguchi, K. Watanabe, M. Glazov, X. Marie
Materials Science
Physics-Informed 3D Atomic Reconstruction and Dynamics of Free-Standing Graphene from Single Low-Dose TEM Images
Xiaojun Zhang, Shih-Wei Hung, Yawei Wu et al. (+4 more)
Resolving the three-dimensional (3D) atomic geometry of free-standing
graphene in real time is essential for understanding how intrinsic rippling governs its electronic properties. However, the low electron doses required to mitigate radiation damage impose severe signal-to-noise constraints that limit conventional reconstruction methods. Here, we present a physics-informed computational framework that reconstructs 3D atomic coordinates of single-layer
graphene from individual low-dose transmission electron microscopy (TEM) frames (8x10^3 e-/Ang^2, 1 ms temporal resolution). The approach combines simulated annealing optimisation with molecular dynamics regularisation, achieving sub-angstrom out-of-plane accuracy (sigma_z < 0.45 Ang), validated against ground-truth simulations. A Kullback-Leibler divergence-based calibration aligns the forward model with experimental image statistics, reducing systematic bias. Applied to high-speed time-series data, the framework enables simultaneous extraction of real-time ripple dynamics, strain tensors, surface
curvature, bond-length distributions, and density functional theory (DFT)-derived electron localisation functions (ELF). We establish quantitative relationships linking local geometry, strain, and bond-length variations to electron localisation, demonstrating that sub-angstrom structural fluctuations drive spatially localised, millisecond-scale electronic modulation. A critical dose threshold is identified below which structural information becomes irrecoverable, providing practical guidance for experimental design. The framework is broadly applicable to beam-sensitive two-dimensional materials.
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All authors Xiaojun Zhang, Shih-Wei Hung, Yawei Wu, Jyh-Pin Chou, Angus I. Kirkland, Roar Kilaas, Fu-Rong Chen
Materials Science
Determining the Free-Carrier Fraction in 2D Perovskites using Power Dependent Photoluminescence
Antonella Cutrupi, Marc Melendez Schofield, Raquel Utrera-Melero et al. (+4 more)
Determining the nature of the optical excited state (
excitons or free carriers) in nanostructured materials is crucial for device design, as optoelectronic and photovoltaic technologies require different considerations regarding the optimized excited state dynamics. Power-dependent photoluminescence is widely used to distinguish between
excitons and free carriers, but the classical power-law analysis oversimplifies the underlying physics when the exponent lies between the linear (pure
excitons) and quadratic (pure free carriers) limits. In this work, we present a complete study enabling a direct and quantitative analysis of the free-carrier fraction based on power-dependent peak photoluminescence and placing its analysis in the context of the Saha-equation. We study Ruddlesden-Popper perovskites with varying thickness as a model system, as they cover a wide range of
exciton binding energies and the full range of free carrier fractions. Our results agree with previously reported values for the
exciton binding energies in these materials, confirming the reliability of this approach and providing a simple and effective tool for probing the nature of optically excited states in
semiconductors with intermediate
exciton binding energies. We demonstrate that our method allows probing spatial variations in the fraction of free charges near grain boundaries or edges at micrometer spatial resolution. Finally, our results highlight the importance of performing optical characterization under excitation densities relevant to realistic operating conditions, as higher fluences can artificially enhance
exciton formation and distort excited-state interpretation under
solar-fluence conditions.
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All authors Antonella Cutrupi, Marc Melendez Schofield, Raquel Utrera-Melero, Michel Frising, Enrique Arevalo Rodriguez, Upasana Das, Ferry Prins
Materials Science
Programmable Photocatalysis via Symmetry-Defined Periodic Potentials
Qun Yang, Di Luo and Prineha Narang
Photocatalysis in atomically thin
semiconductors is often limited by rapid electron-hole recombination, making it difficult to translate favorable band structures into efficient chemical function. Here we propose
symmetry-defined periodic potentials as a strategy for photocatalysis: instead of modifying the chemistry of the active layer, one engineers a long-wavelength electrostatic landscape that spatially separates photoexcited electrons and holes. Applied to monolayer InSe, we show that experimentally accessible moiré patterns, such as those generated by twisted hBN, produce miniband formation, band-gap renormalization, and robust carrier separation. Using commensurate BN/InSe local registries, we further show that the moiré control layer transfers a measurable electrostatic modulation to InSe, providing the microscopic link between continuum potential engineering and the local surface environment. The key result is that the periodic potential strongly reorganizes carrier distribution while only weakly perturbing adsorption trends, thereby identifying a practically useful regime in which charge separation can be engineered without demanding major changes to the underlying surface chemistry. These results position periodic potentials as a broadly applicable design principle for photocatalysis and other light-driven interfacial phenomena in two-dimensional materials.
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Statistical Mechanics
Critical scaling and supercritical coarsening in Active Model B+
Abir Bhowmick and P. K. Mohanty
We study critical dynamics and phase-ordering kinetics in Active Model B (AMB) and its minimal extension, Active Model B$+$ (AMB$+$), using deterministic simulations in two dimensions. At criticality $r_c=0$, both models display identical mean-field scaling despite nonequilibrium currents, with order-parameter decay with time as $m(t)\sim t^{-\alpha}$, with $\alpha=\frac14$, and dynamical exponent being $z=4$. A generalized equal-area construction yields the binodal densities and phase diagram of AMB$+$. For supercritical quenches, domain size grows as $L(t)\sim t^{1/3}(1+c/\ln t)$, revealing logarithmic corrections to the classic $t^{1/3}$ growth-law; moreover it is consistent with the functional renormalization group predictions for marginal activity in $d=2$. While the logarithmic corrections are quite prominent in AMB, in AMB$+$ they are suppressed as the active current acts against the formation of macro-clusters; the growth is eventually arrested when a long-lived microphase-separated state appears.
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Mesoscale and Nanoscale Physics
Atomic-Scale Detection of Néel Vector Switching in the Single-Layer A-type Antiferromagnet Cr2S3-2D
Affan Safeer, Calisa Dias, Mahdi Ghorbani-Asl et al. (+9 more)
The detection of Néel vector switching in a single-layer A-type antiferromagnet marks an important step toward functional two-dimensional spintronics. Here, Cr$_2$S$_3$-2D, grown on
graphene on Ir(110), is established as a first single-layer A-type antiferromagnet.
Spin-polarized scanning tunneling microscopy reveals hysteresis loops with a large switching field and a pronounced dependence on island size. X-ray
magnetic circular dichroism at the Cr L$_{2,3}$ edges exhibits a tiny signal with a linear
magnetic field dependence, consistent with a nearly compensated
antiferromagnetic ground state and a Néel temperature of about 160 K. Quantitative analysis of the island-size dependence of the switching field, together with first principles calculations, indicates a slight imbalance between the
magnetic moments of the two Cr planes of Cr$_2$S$_3$-2D when supported on a substrate. This imbalance results in a net magnetization for the A-type antiferromagnet, which enables the 180$^\circ$ rotation of the Néel vector. Moreover, Cr$_2$S$_3$-2D retains its
magnetic properties after several days of exposure to air.
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All authors Affan Safeer, Calisa Dias, Mahdi Ghorbani-Asl, Abdallah Karaka, Pradyumna Bawankule, Weibin Li, Pierluigi Gargiani, Wouter Jolie, Arkady V. Krasheninnikov, Amilcar Bedoya-Pinto, Thomas Michely, Jeison Fischer
Disordered Systems and Neural Networks · Cross-listed from cs.IT
The Random Subsequence Model and Uniform Codes for the Deletion Channel
Ryan Jeong and Francisco Pernice
We introduce the Random Subsequence Model, a
spin glass model on pairs of random strings $(X,Y) \in \{0,1\}^N \times \{0,1\}^M$ whose partition function counts subsequence
embeddings of $Y$ into $X$. We study two variants: the null model, where $X$ and $Y$ are independent and uniform, and the planted model, where $X$ is uniform and $Y$ is a uniformly-random length-$M$ subsequence of $X$. We connect the Random Subsequence Model to longstanding problems in various fields, including the best rate achievable by uniformly-random codes in the deletion channel, the longest common subsequence problem between two random strings, and models of directed
polymers in statistical physics. In the regime where $N,M\to\infty$ at a fixed ratio $\alpha = M/N \in (0,1)$, we exhibit strict asymptotic separations between the null annealed free energy and the quenched free energies of the null and planted models at all values of the density parameter $\alpha$. This suggests that these models are in a
spin glass phase at zero temperature throughout the entire dense regime. As a consequence, we show that uniformly-random codes achieve a positive rate in the deletion channel for all deletion probabilities $p\in [0,1),$ settling multiple
conjectures of the second author, Isik and Weissman (2024) and proving the first such positive rate result for the regime $p \geq 1/2$. We also give an exact analytic formula for the annealed free energy of the planted model for all values of the density parameter. This implies a corresponding analytic upper bound on the best rate achievable by uniformly-random codes in the deletion channel, complementing the lower bound from our first result. Our upper and lower bounds for the capacity of the deletion channel under uniform codes are far closer to each other than the best known upper and lower bounds for the capacity of the deletion channel.
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Soft Condensed Matter · Cross-listed from physics.flu-dyn
Viscous Bending Mitigates the Spontaneous Meandering of Rivulets in Hele-Shaw Cells
Grégoire Le Lay and Adrian Daerr
We investigate the spontaneous meandering of slender rivulets in Hele-Shaw
cells and identify the physical mechanism that selects the most unstable wavenumber, a quantity that has remained elusive even since the identification of the instability threshold [Daerr et al., Phys. Rev. Lett. 106, 184501 (2011)]. Earlier criteria did not distinguish between wavelengths and thus predicted an undiscriminated amplification of arbitrarily short perturbations. By incorporating viscous bending into the depth-averaged Navier-Stokes equations, we show that this effect is responsible for the selection of a fastest-growing mode, answering a question that has remained open for 15 years. We answer the open question of whether the meandering instability is absolute or convective. Our analysis also provides a simpler alternative derivation of the instability criterion, based on a low-viscosity assumption, and finally it yields a new physical interpretation of the mechanism: the destabilization arises directly from friction effects, instead of being caused by inertial forces. Together, these results complete the linear-stability picture of rivulet meandering in confined geometries, and establish viscous bending as a key parameter governing wavelength selection. They lay the groundwork for future exploration of the nonlinear features of the spontaneous meandering instability.
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Materials Science
Magnetoelastic Transport-Path Reconstruction and Giant Magnetotransport Responses in a Two-Dimensional Antiferromagnet
Liu Yang, Ming Li, Shui-Sen Zhang et al. (+8 more)
Nonvolatile magnetotransport responses in a single
magnetic material have generally not been expected to exhibit a large ON/OFF ratio, because they are usually tied to
spin-orbit coupling and therefore remain relatively weak. Here we show, contrary to this expectation, that
giant nonvolatile magnetotransport can arise in a single
magnetic material through magnetoelastic reconstruction of nonrelativistic real-space transport paths. Using the two-dimensional antiferromagnet FePS$_{3}$ as a representative system, first-principles
quantum transport calculations reveal that charge transport is strongly tied to its quasi-one-dimensional zigzag sublattice chains and, under suitable doping, can even become confined to them. Moreover, strain lifts the degeneracy among
symmetry-related zigzag variants and thus reorients these transport paths through magnetoelastic coupling. As a result, both the longitudinal and transverse conductivities change dramatically, yielding a
giant magnetoelastic magnetoresistance of up to $10^{4}$% and an energy-independent
Hall ratio that far exceeds the spontaneous
Hall ratios found in conventional magnets. These results establish a route to exploiting
symmetry-related
magnetic variants and their associated transport paths for reconfigurable, high-performance spintronic devices with large nonvolatile readout contrast.
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All authors Liu Yang, Ming Li, Shui-Sen Zhang, Hang Zhou, Yi-Dong Liu, Xiao-Yan Guo, Wen-Jian Lu, Yu-Ping Sun, Evgeny Y. Tsymbal, Kaiyou Wang, Ding-Fu Shao
Materials Science
Fe3O4 nano-octahedra and SnO2 nanorods modifying low-Pd amount electrocatalysts for alkaline direct ethanol fuel cells
Tuani C. Gentil, Lanna E.B. Lucchetti, João Paulo C. Moura et al. (+7 more)
This work describes the ethanol oxidation reaction (EOR) in alkaline medium using low-palladium nanoparticle electrocatalysts modified by Fe3O4 nano-octahedra and SnO2 nanorods. Operation studies on an alkaline direct ethanol fuel
cell (ADEFC) were conducted using the developed electrocatalysts, and stability studies were performed using the advanced scanning flow
cell (SFC) technique coupled to inductively coupled
plasma mass spectrometry (online SFC-ICP-MS). The EOR was catalyzed by single (Pd/C and commercial Pd/C Alfa Aesar) and by synthesized binary and ternary electrocatalysts, in which Fe3O4 and SnO2 nanostructures partially replaced the high-cost noble metal. The PdFe3O4/C was identified as the most promising synthesized material in the electrochemical studies, exhibiting the highest mass activity (1426 mA mg-1 Pd) by cyclic voltammetry (CV), followed by the binary PdSnO2/C (1135 mA mg-1 Pd), and by the ternary (1074 mA mg-1 Pd). This enhancement was attributed to the bifunctional mechanism enabled by Fe3O4 and SnO2, therefore reducing poisoning and improving the EOR. Moreover, the operating results revealed that PdFe3O4/C showed the highest power density among the synthesized materials (31 mW cm-2 at 70 C), even with an approximately 45 percent reduction in Pd content compared to the commercial catalyst. XPS results showed that the Pd 3d5/2 and 3d3/2 peaks for PdFe3O4/C, PdSnO2/C, and PdFe3O4SnO2/C were shifted by approximately 0.5 eV to higher binding energies compared to Pd/C, indicating a loss of electron density in Pd due to strong metal-
oxide interactions.
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All authors Tuani C. Gentil, Lanna E.B. Lucchetti, João Paulo C. Moura, Júlio César M. Silva, Maria Minichov, Valentín Briega-Martos, Aline B. Trench, Bruno L. Batista, Serhiy Cherevko, Mauro C. Santos
Quantum Gases · Cross-listed from physics.atom-ph
Defect-free arrays at the thousand-atom scale in a 4-K cryogenic environment
Desiree Lim, Hadriel Mamann, Grégoire Pichard et al. (+18 more)
We report on a cryogenic platform at 4 K incorporating high numerical aperture optics for the generation of large-scale tweezers arrays, and compatible with Rydberg-state manipulation. We achieve trapping lifetimes of around 5000 s, significantly extending the available experimental time for the preparation of large-scale arrays. By combining two trapping
lasers at different wavelengths and by minimizing other atom losses during the rearrangement and imaging processes, we demonstrate the preparation of defect-free arrays with up to 1024 atoms. Our cryogenic design opens exciting prospects for analog and digital
quantum computing.
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All authors Desiree Lim, Hadriel Mamann, Grégoire Pichard, Lilian Bourachot, Arvid Lindberg, Clotilde Hamot, Hugo Le Bars, Florian Fasola, Siddhy Tan, Gwennolé Cournez, Sylvain Dutartre, Thierry Cartry, Sylvain Lemettre, Richard Hostein, Julien Paris, Franck Ferreyrol, Andréa Collardey, Adrien Signoles, Thierry Lahaye, Corentin Monmeyran, Bruno Ximenez
Materials Science
Photo-Assisted Pd-Nb2O5/Carbon Nanocomposites for Enhanced Ethanol Electro-Oxidation Kinetics and CO Tolerance in Alkaline Media
João V. T. Neves, Stephanie S. Aristides-Barros, Aline B. Trench et al. (+4 more)
Pd-based anodes for alcohol oxidation suffer from surface poisoning and sluggish kinetics. Here, we developed Pd-Nb2O5/C nanocomposites to improve ethanol electrooxidation kinetics and CO tolerance in alkaline media. Orthorhombic Nb2O5 prepared by the Pechini route was combined with fcc Pd nanoparticles via polyol reduction, yielding Pd(x)-Nb2O5(y)/C nanocomposites with x:y = 100:0, 70:30, 50:50, 30:70, 0:100. Rietveld-refined X-ray diffraction confirmed phase purity and showed similar Pd crystallite sizes (4.46 nm for Pd/C and 4.92-5.08 nm for Nb2O5-containing catalysts). Transmission and scanning electron microscopies coupled with energy-dispersive X-ray spectroscopy reveal uniformly dispersed Pd nanoparticles on Nb2O5 and carbon. UV-Vis diffuse reflectance indicated a band gap of 3.10 eV, and chopped-light photocurrent measurements confirm the strong ultraviolet responsiveness of Nb2O5. X-ray photoelectron spectroscopy reveals that Pd(0.5)Nb2O5(0.5)/C had the highest Pd0 content (58.99%). Electrochemical testing demonstrates that, relative to Pd/C, optimized Pd(0.5)Nb2O5(0.5)/C reduces the ethanol oxidation onset potential by up to 160 mV, increases poisoning tolerance by a factor of five at a fixed potential, and raises the current density from 1.59 to 1.76 mA cm-2. Under light irradiation, the current density increases from 1.07 to 2.10 mA cm-2, accompanied by improved stability and extended durability, attributed to light-induced electron-hole generation and enhanced OH- adsorption. These results highlight the synergistic contribution of
oxide-metal interactions and photoactivation to ethanol oxidation and provide insights for designing efficient catalysts for alkaline fuel
cells. s
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All authors João V. T. Neves, Stephanie S. Aristides-Barros, Aline B. Trench, Ivani M. Costa, Mauro C. Santos, Giancarlo R. Salazar-Banda, Katlin I. B. Eguiluz
Materials Science
Excitons in WSe2 time-resolved ARPES: particle or oscillation?
Kai Wu, Michele Puppin and Andrea Marini
The time-resolved angle-resolved photoemission spectra of WSe$_2$, a paradigmatic transition metal dichalcogenide, are dominated by a transient signal that, after being initially observed in the gap at the K valley, scatters, on an ultra-fast time scale of $\sim$ 30 fs, to the $\Sigma$ valley. In this work we question the common interpretation of the experimental dynamics in terms of a massive bound electron-hole
exciton that scatters with
phonons and behaves as a quasi-particle. By using a combined theoretical and experimental investigation, we demonstrate that the observed dynamics can be interpreted as the photo-induced transition from direct to indirect excitonic-insulating order. The features that appear in the experimental spectrum correspond to single-particle levels renormalized by the excitonic spontaneous polarization.
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Materials Science
Machine learning Hamiltonian enables scalable and accurate defect calculations: The case of oxygen vacancies in amorphous SiO$_2$
Zhenxing Dai, Zhong Yang, Mingjue Ni et al. (+4 more)
Point defects critically influence the properties of materials and devices, yet density functional theory (DFT) remains computationally demanding for defect supercell calculations. Machine learning interatomic potentials (MLIPs) offer high efficiency but require extensive
datasets. MLIPs trained only on defect configurations in small supercells exhibit systematic energy errors in larger supercells, demonstrating limited transferability. Here, we present a machine learning
Hamiltonian (MLH) model-based method for calculating total energies and atomic forces in defect supercells with linear-scaling computational cost, enabling efficient structural relaxation and accurate formation energy predictions. We take oxygen vacancies in amorphous SiO$_2$ as an example and train the MLH model on defect configurations in 95-atom supercells, with the training data derived from 120 self-consistent field calculations and 12 structural relaxations. The MLH model enables efficient structural relaxations for host (defect-free) and defect systems in larger supercells, avoiding the systematic energy errors observed in MLIPs. The cancellation of energy errors between host and defect systems yields accurate formation energy predictions, with deviations from DFT below 50 meV. The proposed method holds significant potential for defect simulations in complex materials.
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All authors Zhenxing Dai, Zhong Yang, Mingjue Ni, Menglin Huang, Hongjun Xiang, Xin-Gao Gong, Shiyou Chen
Quantum Gases
In-situ Observation of Magnetostriction Crossover in a Strongly Dipolar Two-Dimensional Bose Gas
Yifei He, Xin-Yuan Gao, Haoting Zhen et al. (+3 more)
Magnetostriction, the anisotropic spatial deformation, is a hallmark of dipolar gases with strong long-range interactions, yet it poses a challenge for in-situ characterization. Here, we observe a magnetostriction crossover from the strongly anisotropic superfluid phase to the nearly isotropic normal phase using in-situ imaging of quasi-two-dimensional 166Er gases. Then, we develop a quasi-2D Hartree-Fock-mean-field framework that provides a robust tool for interaction-aware thermometry, enabling the determination of temperature and chemical potential across all dipole orientations from a single fit. We further demonstrate that the low-density wings effectively obey a local-density equation of state. Finally, we reveals the crossover from the isotropic thermal wings to the anisotropic coherent core in a single in-situ image, providing a pathway for future accurate studies of strongly dipolar superfluidity and thermodynamics in 2D.
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All authors Yifei He, Xin-Yuan Gao, Haoting Zhen, Mithilesh K. Parit, Yangqian Yan, Gyu-Boong Jo
Superconductivity
Perpendicular electric field induced competing $s^\pm$- and $d$-wave pairings in La$_3$Ni$_2$O$_7$ thin film
Yongping Wei, Xun Liu, Fan Yang et al. (+1 more)
Inspired by the possibility that superconducting properties may be altered by applying a perpendicular electric field in the Ruddlesden-Popper (RP)
bilayer nickelate La$_3$Ni$_2$O$_7$ thin film, we investigated the imbalanced two-orbital
bilayer Hubbard model with a layer potential bias using dynamical cluster
quantum Monte Carlo calculations. Focusing on the pairing
symmetry evolution with the potential bias between layers for the undoped, hole-doped, and electron-doped regimes, we found that the $s^\pm$-wave pairing, originating from the $d_{z^2}$ orbital at high temperature regime as well as $d_{x^2-y^2}$ orbital at lower temperatures, is suppressed by the potential bias; while a possible pairing
symmetry transition from $s^\pm$-wave to $d$-wave pairing occurs, driven by the interlayer orbital mismatch and the transfer of electrons into the $d_{x^2-y^2}$ orbitals. Our large-scale many-body calculations align with the previous expectation from weak-coupling methods and provide further insight into the superconducting mechanism in RP nickelates.
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All authors Yongping Wei, Xun Liu, Fan Yang, Mi Jiang
Mesoscale and Nanoscale Physics
Coexistence of Ferromagnetic and Overscreened Kondo Effects in a Single Molecule
Elia Turco, Nils Krane, Hongyan Chen et al. (+5 more)
The quest for
quantum ground states beyond the
Fermi-
liquid paradigm remains a central challenge in many-body physics. The
ferromagnetic Kondo effect is an intriguing variant of the Kondo effect in which an asymptotically free
spin gives rise to singular
Fermi-
liquid behavior. Despite its theoretical importance, this regime has eluded experimental observation owing to subtle spectroscopic signatures, small energy scales, and
symmetry constraints in nanostructures. Here, we demonstrate the coexistence of
ferromagnetic and overscreened Kondo effects within a molecular
spin system—a triangulene dimer comprising
spin-1 and
spin-1/2 units adsorbed on a metal surface. Low-temperature scanning tunneling spectroscopy reveals signatures of singular
Fermi-
liquid behavior, supported by many-body calculations. The molecular design provides control over
spin configuration and coupling asymmetry, allowing distinct regimes within the same platform. Our results establish a strategy for realizing non-
Fermi-
liquid physics at the atomic scale and demonstrate that
ferromagnetic Kondo behavior can be deliberately engineered in molecular systems.
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All authors Elia Turco, Nils Krane, Hongyan Chen, Simon Gerber, Wulf Wulfhekel, Roman Fasel, Pascal Ruffieux, David Jacob
Mesoscale and Nanoscale Physics
Revisiting quadratic band crossing: from interaction-driven instability to intrinsic topology
Yadong Jiang, Linghao Huang, Zhaochen Liu et al. (+2 more)
The realization of robust
quantum anomalous
Hall (QAH) phases at elevated temperatures remains a central challenge in condensed matter physics. While quadratic band crossing points (QBCP) provide a promising route towards QAH states, existing proposals are largely confined to idealized models or hindered by interaction-driven competing orders. Here, we demonstrate that these limitations are not intrinsic to QBCP but arise from their specific implementation. We propose a general mechanism where band inversion between a
symmetry-protected orbital doublet (e.g. $d_{xz},d_{yz}$) and an isolated orbital (e.g. $d_{z^2}$)-generically generates a QBCP with opposite
curvature. This crossing is directly gapped at the single-particle level by intrinsic atomic
spin-orbit coupling, while the underlying band inversion naturally shields the resulting topological gap against other interaction-driven instabilities. We further suggest monolayer compounds $MNX_2$ ($M$= Ni, Pd, Pt; $N$= Nb, Ta; $X$= S, Se, Te) as a realistic material class that intrinsically realizes this mechanism. These findings provide a concrete pathway toward robust QAH phases in correlated materials.
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All authors Yadong Jiang, Linghao Huang, Zhaochen Liu, Huan Wang, Jing Wang
Disordered Systems and Neural Networks · Cross-listed from math-ph
Existence of a Phase Transition in the One-Dimensional Ising Spin Glass Model with Long-Range Interactions on the Nishimori Line
Manaka Okuyama and Masayuki Ohzeki
Dyson [Commun. Math. Phys. 12, 91 (1969)] rigorously proved the existence of a phase transition in the one-dimensional Ising model with long-range interactions of the form $r^{-\alpha}$ for $1 < \alpha < 2$. In the present study, we extend this result to the Ising
spin glass model with Gaussian disorder on the Nishimori line. Following Dyson's method, we first prove the existence of long-range order at finite low temperatures in the Dyson hierarchical Ising
spin glass model on the Nishimori line, with power-law-like interactions $J(r) \sim r^{-\alpha}$ for $1 < \alpha < 3/2$. The key ingredients of the proof are the interpolation method developed in the rigorous analysis of mean-field
spin glass models, the Gibbs–Bogoliubov inequality on the Nishimori line, and the Tsirelson–Ibragimov–Sudakov inequality (Gaussian concentration inequality). We then use the Griffiths inequality on the Nishimori line to rigorously establish the existence of a phase transition in the one-dimensional Ising
spin glass model with long-range interactions on the Nishimori line for $1 < \alpha < 3/2$. For $3/2 \le \alpha \le 2 $, the existence of a phase transition remains an open problem.
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Strongly Correlated Electrons
Magnetic order and excitations in the magnetically intercalated van der Waals material Cr$_{\frac{1}{4}}$NbSe$_2$
Ryota Yamaoka, Hiraku Saito, Yuki Settai et al. (+10 more)
Cr$_{\frac{1}{4}}$NbSe$_2$ is a triangular
lattice magnet in which
magnetic Cr$^{3+}$ ions are intercalated to form triangular
lattices between NbSe$_2$ van der Waals layers stacked along the c axis. By unpolarized and polarized
neutron scattering experiments, we have revealed that the
magnetic ground state of this system is a 120$^{\circ}$-type
antiferromagnetic order characterized by the
magnetic propagation wave vector of $q=(\frac{1}{3}, \frac{1}{3}, 0)$. We also performed inelastic
neutron scattering measurements using co-aligned single
crystals, and determined dispersion relations of
magnetic excitations at low temperatures. Comparing the observed spectra with calculations based on the linear
spin-wave theory, we revealed that the out-of-plane
ferromagnetic interaction is fairly strong as compared to the in-plane nearest neighbor
antiferromagnetic interaction. Although the
crystal structure of this system is composed of two-dimensional van der Waals layers, the
magnetic order has a three dimensional character, which would be attributed to long-range
magnetic interactions mediated by conduction electrons.
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All authors Ryota Yamaoka, Hiraku Saito, Yuki Settai, Xiang Huang, Daisuke Nishio-Hamane, Shingo Takahashi, Daichi Ueta, Tatsuro Oda, Hodaka Kikuchi, Tao Hong, Masaki Nakano, Shinichiro Seki, Taro Nakajima
Materials Science
Photoexcited Hole States at the SrTiO3(001) Surface Imaged with Noncontact AFM
Igor Sokolovic, Florian Ellinger, Aji Alexander et al. (+8 more)
The behaviour of excess charges in ionic
lattices, such as the formation of polarons and charge trapping at defect sites, influences the physical and chemical properties of materials and translates into applications in electronics, optics, photovoltaics, and catalysis. Here we show that the bulk-terminated SrTiO3(001) surface accumulates photoexcited charges and keeps the associated photovoltage for many days at cryogenic temperatures. A combination of scanning tunneling microscopy, atomic force microscopy (STM/AFM) and Kelvin probe force microscopy (KPFM) was used to measure this photovoltage and to localize the photoexcited charges with atomic precision down to the single-quasiparticle limit. Density functional theory (DFT) shows that holes favor localization at oxygen 2p orbitals adjacent to Sr vacancies, creating long-lived trapped states. The methodology presented here provides guidelines for imaging of charges trapped in the
crystal lattice using noncontact AFM.
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All authors Igor Sokolovic, Florian Ellinger, Aji Alexander, Dominik Wrana, Llorenc Albons, Sreehari Sreekumar, Michael Schmid, Ulrike Diebold, Michele Reticcioli, Cesare Franchini, Martin Setvin
Materials Science
Ferroelectric Band Twinning from Pair-State Symmetry
Shibo Fang, Jianhua Wang, Zhenzhou Guo et al. (+7 more)
Ferroelectric switching provides a nonvolatile way to control electronic structures, but a general
symmetry rule connecting the full Bloch bands of two switchable polarization states is still lacking. Here, we introduce ferroelectric band twinning, a pair-state relation in which the bands of two opposite-polarization states are mapped onto each other by a non-inversion state-exchange
symmetry. Using dichromatic groups, we derive the band-twinning rule and identify 11 ferroelectric band-twinning point-group classes. Screening the Ferroelectric Materials Database yields 16 candidate compounds, of which the two
lattice-metric-preserving candidates, bulk gamma-Ag3SI and BaAl2O4, are selected for first-principles validation. For gamma-Ag3SI, we further show that the same pair-state
symmetry controls the transformation of shift-current tensor components under polarization reversal. These results establish ferroelectric band twinning as a general
symmetry framework for nonvolatile control of momentum-dependent electronic structures in ferroelectrics.
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All authors Shibo Fang, Jianhua Wang, Zhenzhou Guo, Jialing Gong, Haiyu Meng, Ruixiang Fei, Wenhong Wang, Xiaotian Wang, Zhenxiang Cheng, Yee Sin Ang
Materials Science
Towards viable H$_2$ storage in Ca decorated low-dimensional materials with insights from reference quantum Monte Carlo
Yasmine S. Al-Hamdani, Dario Alfè and Andrea Zen
Hydrogen technology is set to be a key energy alternative for mitigating pollution and reducing CO$_2$ emissions. However, the current storage mechanism of hydrogen molecules in carbon fibre tanks detracts from the fuel economy of hydrogen in mobile applications, necessitating the development of alternative storage mechanisms. Adsorbing hydrogen in its molecular form (H$_2$) at typical operating conditions of
proton exchange membranes can potentially meet storage requirements. However, H$_2$ is the smallest molecule with only two electrons and therefore it has very limited propensity to physisorb in a material within the binding energy window of $-0.2$ to $-0.4$ eV that is suitable for storage. Calcium atom decorators on
graphene have previously shown promise for tunable H$_2$ binding, but the system is thermodynamically unstable toward the formation of calcium hydride. Moreover, the absolute adsorption of H$_2$ is challenging to predict accurately and is typically overestimated with van der Waals inclusive density functional approximations. In this work, we perform state-of-the-art fixed-node
diffusion Monte Carlo alongside a selection of density functional approximations for two strategies of anchoring Ca: (i) Ca on boron doped
graphene and (ii) Ca inside carbon nanotubes. We predict reliable Ca and H$_2$ binding energies, and establish that Ca is anchored inside carbon nanotubes and on boron doped
graphene, while boosting the H$_2$ adsorption energy. Importantly, the H$_2$ adsorption energy is found to be improved by the anchoring strategies, with the energy inside a Ca decorated carbon nanotube reaching the viable storage window. The reference DMC binding energies provide much-needed
benchmarks for developing data-driven methods and guiding experiment in the systematic design of hydrogen storage materials.
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