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Physics Condensed Matter

cond-mat Watch Condensed Matter

Friday 9 October

Materials Science

Evolution and breakdown of chiral anomaly in Weyl semiconductor tellurium

Zhifeng Xue, Jiaji Zhao, Yi Ji et al. (+16 more)

Chiral anomaly in topological materials manifests as negative longitudinal magnetoresistance, yet the tunability and evolution of this effect remain elusive. Here we show that doped tellurium serves as a versatile platform to realize a giant negative longitudinal magnetoresistance that is highly tunable via the Fermi level and magnetic field. By moving the Fermi level towards the Weyl point, we observe a pronounced enhancement of negative magnetoresistance, which arises from chiral anomaly and robustly persists up to ambient temperature. Beyond the quantum limit, the system exhibits positive linear magnetoconductance, serving as a compelling transport signature of the chiral anomaly in the lowest Landau level. Notably, in the extreme quantum limit at cryogenic temperatures, the magnetoresistance undergoes a dramatic reversal from negative to positive. This reversal points to a potential field-induced phase transition into a collective electronic state driven by enhanced electron-electron interactions. Our findings provide valuable insights into the unconventional chiral transport and emergent correlated quantum states under extreme magnetic fields.
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All authors Zhifeng Xue, Jiaji Zhao, Yi Ji, Fuyang Chen, Nannan Tang, Gangjian Jin, Bing Shen, Bin Wang, Yang Wang, Mingxi Chi, Jin-Zhu Zhao, Ruiqiang Wang, Qizhong Zhu, He Wang, Huakun Zuo, Donghui Guo, Dingyong Zhong, Mingxun Deng, Huichao Wang

Statistical Mechanics · Cross-listed from quant-ph

When irrelevance governs: dissipation-regression scaling in open quantum criticality

Fan Zhong

The real-time dynamics of quantum phase transitions in open systems coupled to finite-temperature environments sits at the heart of contemporary condensed-matter and quantum-information science. Here, invoking a Schwinger-Keldysh formalism, we uncover that, within the coherence-dominated regime of critical real-time evolution, a dissipative coupling deemed naively irrelevant determines, counterintuitively, the longest timescale that holds sway. Possessing a well-defined temporal scaling dimension, it engenders a novel dissipation-regression scaling that systematically reproduces the unusual Kibble-Zurek scaling and relaxation observed in recent numerical studies. By contrast, dissipation-dominated dynamics behaves qualitatively differently. There, furthermore, we show that the discretized and diagonalized formulations of the same open quantum Ising chain realize distinct universality classes.
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Mesoscale and Nanoscale Physics

Parity-Anomalous Hall Response of Chiral Lifshitz Fermions

Yanmiao Han, Rundong Zhao and Yu-Hao Wan

The parity anomaly of a single massless Dirac fermion is manifested as a half-quantized Hall response once the required parity-breaking regularization is supplied. We study the corresponding response for two-dimensional chiral Lifshitz fermions. For a node with low-energy coupling (qx +iqy)^N, the Fermi-loop winding number W = N gives an anomalous Hall response {\sigma}xy^anom = (W/2)e^2/h. We examine this mechanism in chiral multilayer Haldane models tuned to a valley-selective critical line, where a single gapless chiral Lifshitz fermion remains at the K valley. For the AB, ABC, and ABCA stacks, the projected pseudospin textures give W = 2, 3, 4, while Kubo calculations yield {\sigma}xy = (1, 3/2, 2)e^2/h; integrated equilibrium boundary currents reproduce the same W/2 sequence. Six-terminal simulations with dephasing further show that the Hall conductivity is quantized at W/2 while the longitudinal conductivity remains finite. These results identify gapless chiral Lifshitz fermions as a higher-order, winding-controlled generalization of the parity-anomalous Hall response, distinct from a quantum anomalous Hall insulating state even when W/2 is an integer.
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Strongly Correlated Electrons

Odd-Parity Crystalline Electric Field and Multipoles in Icosahedral Quasicrystal and Approximant: Magnetic Toroidal and Electric Dipoles in Ce-Based Systems

Shinji Watanabe, Syunta Furuya and Mitsuaki Kawamura

Quasicrystals (QCs) lack periodic arrangement of atoms but possess unique structural order distinct from periodic crystals and random systems. The electronic property is far from complete understanding. Here we have formulated not only even-parity but also odd-parity crystalline electric field (CEF) in the Ce-based icosahedral QC and approximant crystal (AC) on the basis of the point charge model. Under the odd-parity CEF due to local-inversion symmetry breaking at the Ce site, the hybrid wavefunction of 4f and 5d states at Ce is shown to give rise to the odd-parity multipoles such as electric dipole and magnetic toroidal (MT) dipole. We have found that the vortex order in the 1/1 AC where the magnetic moments on each icosahedron swirl is characterized by the cluster-type MT moment. The ferroic alignment of the cluster MT moments in the vortex order gives rise to the electro-magnetic effect. The cluster-MT moment is shown to be resonated with the MT dipole moments in each icosahedron by tuning the 4f energy level and 5d energy level so as to approach. We have revealed a noncollinear magnetic structure is stabilized in the ground state of the icosahedral QC cluster, behind which there exists underlying mechanism to prefer the ferroic interaction for the net MT dipole moments between the icosahedrons. We point out that the 4f and 5d energy levels can be made approach at the valence transition or the valence crossover, which is ubiquitous in the rare-earth based ACs and QCs.
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Strongly Correlated Electrons

Real-Time Relaxation Dynamics of Dark Excitons in Mirror-Symmetric Monolayers

Rishabh Saraswat, Mantasha Ansari, Rekha Verma et al. (+1 more)

Symmetry governs which exciton-phonon (exc-ph) scattering channels can exist, but not which a relaxing exciton actually uses. Combining group theory with ab initio many-body perturbation theory, we derive the mirror parity $\sigma_h$, of finite-momentum excitons in planar $D_{3h}$ monolayers, and form exact exc-ph selection rules that hold across the whole Brillouin zone. The parity of the lowest exciton band changes across a closed contour. The even phonons connect states of the same parity, while odd phonons connect states of opposite parity. We use these rules to compute exciton linewidths and we solve the real-time Boltzmann transport equation for monolayer GaN as the test case and benchmark it against monolayer hBN.
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All authors Rishabh Saraswat, Mantasha Ansari, Rekha Verma, Sitangshu Bhattacharya

Soft Condensed Matter

Ionic liquid/PDMS coated nanostructured ZnO surfaces for superior antibacterial activity

Anushika Rohilla, Ajit Seth, Mayank Bharadwaj et al. (+2 more)

The development of nanostructured antibacterial surfaces has gained significant attention due to the urgent need to combat bacterial colonization and biofouling across food, healthcare, and marine sectors. Among functional metal oxides, zinc oxide (ZnO) nanostructures are particularly promising owing to their rich morphology, favourable physicochemical attributes, and intrinsic bactericidal properties. Here, we utilize a green, eco-friendly Hot Water Treatment (HWT) method to fabricate dense ZnO nanorod arrays on zinc substrates. To overcome the practical limitations and challenges of conventional antibacterial coatings, such as poor operational stability, cytotoxicity, and the risk of antimicrobial resistance, we developed a durable hybrid coating composed of an imidazolium-based ionic liquid stabilized with polydimethylsiloxane. The resulting hybrid-coated nanostructured surfaces exhibit superior antibacterial efficacy against Escherichia coli through a combination of topography-induced mechanical strain and membrane disruption.
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All authors Anushika Rohilla, Ajit Seth, Mayank Bharadwaj, Rumal Singh, Sajal K Ghosh

Materials Science

High-Throughput Discovery of Chiral Carbon-Boron Semimetals with Weyl Topology and Phonon-Mediated Superconductivity

Lizhou Yang, Wenneng Zhao, Ye Yang et al. (+9 more)

Chiral crystals provide a natural platform for unconventional topological fermions, while light-element carbon–boron frameworks are promising for phonon-mediated superconductivity owing to strong covalent bonding and high phonon frequencies. Here, we combine Wyckoff-position-based structure generation with high-throughput first-principles calculations to search for C–B crystals in selected hexagonal chiral space groups. Starting from 972 generated $\mathrm{C}_m\mathrm{B}_n$ structures ($m,n=1\text{--}4$), successive filters based on energetic stability, dynamical stability, electronic metallicity, topological band features, and thermal stability identify six stable candidates: $(\mathrm{C}_3\mathrm{B}_2)_8$, $(\mathrm{C}\mathrm{B}_2)_3$, $(\mathrm{C}\mathrm{B}_4)_6$, $(\mathrm{C}_3\mathrm{B}_2)_6$, $(\mathrm{C}_2\mathrm{B}_3)_6$, and $(\mathrm{C}\mathrm{B}_2)_6$. These materials host diverse topological semimetal states near the Fermi level, including charge-one, charge-two, and charge-three Weyl points, nodal rings, and nodal-surface states. Notably, $(\mathrm{C}_3\mathrm{B}_2)_8$ exhibits screw-symmetry-protected charge-three Weyl points and strong electron–phonon coupling, yielding a McMillan transition temperature of $31.1\,\mathrm{K}$ for the Coulomb pseudopotential parameter $\mu^* = 0.10$. In addition, $(\mathrm{C}\mathrm{B}_2)_3$ hosts multiple charge-one Weyl points and pronounced anisotropic multiband superconductivity revealed by fully anisotropic Eliashberg calculations. These results extend the materials scope of topological semimetals with phonon-mediated superconductivity to chemically designed chiral light-element structures.
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All authors Lizhou Yang, Wenneng Zhao, Ye Yang, Weiwei Chen, YongKeat Chan, Chen-Hao Lv, Qing-Bo Liu, Yujia Xiang, Xinming Qin, Zedong Li. Weiyi Wang, Jinlong Yang, Wei Hu

Mesoscale and Nanoscale Physics

Vacuum-field-mediated Landau-level reconstruction in a cavity-coupled two-dimensional electron gas

Zi-Heng Zhu and Yu Chen

We study a two-dimensional electron gas in the integer quantum Hall regime coupled to a single spatially modulated cavity mode in the static off-resonant limit. Retaining both paramagnetic and diamagnetic contributions on equal footing, we derive a gauge complete single-particle Hamiltonian in which virtual photon exchange generates a periodic kinetic renormalization and a diamagnetic scalar potential. Both terms transfer momentum by $2k_0$ and displace guiding centers by $\Delta X=2k_0\ell_B^2$, forming a finite-$k_0$ momentum ladder. Diagonalizing the strip Hamiltonian, we find that the ladder reconstructs the Landau-level band structure and redistributes, rather than multiplies, the associated chiral edge states. Occupied-subspace Chern numbers remain $C_\nu=\nu$ for $\nu=1,2,3$ throughout $0\le\lambda_{\mathrm{cav}}\le 0.5$, while the bulk gaps decrease without closing. Strip Kubo responses show cavity-induced displacements of the Hall-step energies; at finite width the plateau heights are noninteger and approach the integers as $L_x$ increases. The ladder is spectrally resolved at $k_0\ell_B=0.5$ and collapses at $k_0\ell_B=0.1$. These results isolate a spatially local, finite-$k_0$ momentum ladder as a clean-system mechanism by which a structured vacuum field reconstructs quantum Hall spectra and strip transport without changing the integer topology, complementary to cavity-mediated all-to-all hopping.
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Statistical Mechanics · Cross-listed from quant-ph

An Instability of the Quantum Markov Length

David C. Newsom and Michael Levin

The Markov length, the length scale governing the exponential decay of conditional mutual information (CMI) in a quantum many-body state, has proven useful for characterizing mixed-state phases of matter. Nevertheless, we show that a state's Markov length is not generally stable under weak local channels. The failure of stability occurs already at a pure product state. We demonstrate this explicitly in a one-dimensional fermionic chain, where a fine-tuned depth-two circuit of nearest-neighbor Gaussian channels maps the vacuum to a state whose CMI decays algebraically and whose Markov length is therefore infinite, even when the channels are taken arbitrarily close to the identity. The algebraic decay is rooted in the nonanalyticity of the von Neumann entropy at rank-deficient density operators. We exhibit an analogous instability on an ordinary qubit chain. More generally, we show that the Markov length is unstable in any translation-invariant state with even a single rank-deficient reduced density operator. These results pose a challenge to recent definitions of mixed-state phase equivalence based on the Markov length.
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Materials Science

Symmetry-Enforced Topology and Van Hove Saddle Points in Hexagonal TiAs

Azizur Rahman, Shashi B Mishra, Sheraz Khan et al. (+8 more)

We report the first successful growth of stoichiometric hexagonal TiAs single crystals (space group $P6_3/mmc$) using chemical vapor transport and investigate their vibrational, electronic, topological, and magnetotransport properties. Polarized Raman spectroscopy identifies all four Raman-active phonon modes ($A_{1g} + E_{1g} + 2E_{2g}$), consistent with the hexagonal crystal symmetry. First-principles calculations reveal nontrivial band topology characterized by a symmetry indicator $\mathbb{Z}_4 = 2$ and a strong topological index $\nu_0 = 1$, together with symmetry-protected fourfold band degeneracies at the nonsymmorphic Brillouin-zone boundary. The Fermi surface exhibits an orbital-dependent crossover from quasi-two-dimensional cylindrical sheets to a corrugated three-dimensional structure along $k_z$. A Van Hove saddle point approximately 0.5 eV below the Fermi level along $\Gamma\text{--}K$ is associated with a neck-disrupting Lifshitz transition and enhanced density of states. Magnetotransport measurements reveal a pronounced twofold angular magnetoresistance, consistent with anisotropic Fermi-surface geometry and open cyclotron orbits. Hall measurements indicate uncompensated, hole-dominated transport, accounting for the absence of extreme magnetoresistance and contributing to the field-orientation-dependent Hall response. These results establish hexagonal TiAs as a platform for exploring the interplay of nonsymmorphic band topology, Van Hove singularities, and anisotropic electronic transport in transition-metal monopnictides.
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All authors Azizur Rahman, Shashi B Mishra, Sheraz Khan, Khushnood Shah, Xun Ma, Xiaoyang Lin, Tomasz Sobol, Lei Zhang, Weisheng Zhao, Min Zhang, Zahir Muhammad

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

Alter-excitons in Altermagnets: Symmetry, Splitting and Dispersion

Yuanfan Xiong, Liangyu Wang, Xuan Wu et al. (+2 more)

Magnetism provides a fertile platform for discovering emergent quantum phenomena governed by symmetry. Recent developments of spin-space-group (SSG) theory have revealed altermagnets as a distinct class of nonrelativistic collinear magnets with unconventional spin-dependent electronic structures. Here, we demonstrate that altermagnetic symmetry imposes fundamentally different constraints on electronic and excitonic excitations. Although the quasiparticle and two-body Hamiltonians possess identical SSG symmetries, we find that symmetry-protected degeneracies present in the electronic band structure can be intrinsically lifted in the exciton spectrum at specific momenta. This splitting arises solely from the many-body nature of excitons and does not require spin-orbit coupling or noncollinear magnetic order. Combining symmetry analysis with many-body perturbation theory, we predict a novel class of spin-split excitonic quasiparticles, termed alter-excitons, and reveal their characteristic dispersions in altermagnetic systems. Our results establish excitons as a sensitive probe of hidden spin-space symmetries and uncover a new route toward symmetry-engineered many-body phenomena in collinear magnets.
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All authors Yuanfan Xiong, Liangyu Wang, Xuan Wu, Wei Hu, Jinlong Yang

Materials Science

Room-temperature ferroelectric p-wave magnet

Kaiwen Shen, Nicoly Hembeck, Warlley H. Campos et al. (+16 more)

P -wave magnets exhibit odd-parity spin polarization in momentum space while retaining zero net magnetization, offering a promising route toward nonrelativistic spintronics. Previously reported p-wave magnets based on combined time-reversal and lattice-translation symmetry, Tt, have thus far exhibited ordering temperatures below the liquid-nitrogen range. Here, we demonstrate a distinct route to a pristine p-wave magnetism that does not require T t symmetry, and instead is based on incommensurate spin-spiral order. Specifically, the cycloidal magnetic structure of the multiferroic BiFeO3 (BFO) intrinsically realizes p-wave magnetism coexisting with ferroelectric polarization at room temperature. Combining symmetry analysis, density-functional-theory calculations, and circular photogalvanic-effect (CPGE) measurements, we find a large nonrelativistic spin splitting of approximately 100 meV associated with the cycloidal order. The resulting p-wave spin polarization gives rise to a characteristic CPGE response whose sign can be reversibly switched by electrically controlling the cycloid chirality. Our results establish ferroelectric BiFeO3 as a room-temperature platform for electrically switchable p-wave magnetism and provide a route toward voltage-controlled spintronic devices based on parity-breaking magnetic order.
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All authors Kaiwen Shen, Nicoly Hembeck, Warlley H. Campos, Jianting Dong, Bin Li, Yuhang Li, Gui Wang, Jan Priessnitz, Yifan Gao, Yingfen Wei, Hao Jiang, Xumeng Zhang, Ming Wang, Jia Zhang, Wu Shi, Qi Liu, Libor Šmejkal, Xianzhe Chen, Ming Liu

Strongly Correlated Electrons

Ground-State Phase Diagram of the Effective Model with Antiferromagnetic Nearest-Neighbor and Ferromagnetic Next-Nearest-Neighbor Interactions in 1/1 Periodic Approximants to Icosahedral Quasicrystals

Shinji Watanabe

By performing complete enumeration of all configurations of magnetic moments, we have determined the ground-state phase diagram of the effective model with antiferromagnetic nearest-neighbor interactions $J_1$ and ferromagnetic next-nearest-neighbor interactions $J_2$ on the 1/1 periodic approximant to icosahedral quasicrystal. Depending on the ratio of $J_2/J_1$ and the magnetic anisotropy arising from the crystalline electric field, various non-collinear ferrimagnetic orders and antiferromagnetic orders are shown to be stabilized, whose magnetic space groups are identified as $R\bar{3}$, $C2'/m'$, $Pm'm'2$ and $I_{\rm P}m'\bar{3}'$. We have revealed the topological as well as magnetic property of each ground state with degeneracy, which is useful to understand experimental observations of magnetic structures and domains in the rare-earth-based 1/1 approximants.
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Thursday 8 October

Strongly Correlated Electrons · Cross-listed from quant-ph

Analog quantum simulation of Shastry-Sutherland Ising materials

Vahagn Mkhitaryan, Milan Kornjača, Mao Lin et al. (+17 more)

Frustrated magnets host rich emergent behavior because competing interactions generate dense manifolds of low-energy states. The Ising Shastry-Sutherland model is a paradigmatic setting, motivated experimentally by Ising-like rare-earth tetraborides such as TmB$_4$ and ErB$_4$, whose field-induced magnetization plateaus have motivated extensive microscopic modeling. Yet how tunable quantum fluctuations reorganize this material-motivated phase diagram remains largely unexplored. Here, we realize a transverse- and longitudinal-field Ising model on the Shastry-Sutherland lattice using a programmable Rydberg-atom array. We map its quantum phase diagram using density matrix renormalization group calculations and probe corresponding signatures experimentally in arrays containing more than 110 atoms. Beyond the established classical phases, the calculations identify two regimes absent in the classical limit and stabilized at finite transverse field: a $2/5$ filling plateau whose finite stability region emerges from a classically degenerate phase boundary and a symmetry-preserving quantum-dimer regime replacing classically selected collinear order. Experiments on finite open arrays reveal signatures consistent with these regimes across three boundary-pinning conditions, with the resulting response maps agreeing qualitatively with the calculated phase diagram. Our results establish programmable Rydberg-atom arrays as tools for exploring frustrated, material-motivated Hamiltonians and motivate searches for new, quantum-driven magnetization plateaus and quantum-dimer behavior in ErB$_4$ under a transverse field or in strain-tuned TmB$_4$.
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All authors Vahagn Mkhitaryan, Milan Kornjača, Mao Lin, Alexander Schuckert, Majd Hamdan, Sergio H. Cantú, Ammar Ali, Tommaso Macrí, Nathan Gemelke, Alexander Keesling, Peter Komar, Travis S.Humble, Alexei Bylinski, Pedro L. S. Lopes, Fangli Liu, Alexandra Boltasseva, Mikhail D. Lukin, Arnab Banerjee, Vladimir M. Shalaev, Sheng-Tao Wang

Materials Science

Drude, Where's My Charge? End-to-End Learning of Polarizable Drude Force Fields for Polymer Electrolytes

Artur Lyssenko, KyuJung Jun and Rafael Gomez-Bombarelli

Molecular dynamics simulations of solid polymer electrolytes require force fields that are fast enough to converge ion transport over hundreds of nanoseconds, yet accurately describe the ion-polymer interactions that govern it. Fixed-charge force fields meet the first requirement but neglect electronic polarization, an effect often approximated by scaling ionic charges using empirically chosen factors. Here we present AutoDrude, a differentiable framework that parametrizes polarizable Drude force fields directly from DFT energies, forces, and dipoles, with no empirical tuning and at only 1.20 times the cost of a fixed-charge simulation. For PEO-LiTFSI, the dipole-constrained (hard-constraint) AutoDrude model reproduces the experimental ionic conductivity as accurately as the best charge-scaled model (17% versus 16% mean absolute percentage error). We compare the polarizable forcefield to fixed charge ones models by fitting a fixed charge model. Unlike the charge-scaled models tested here, however, AutoDrude also reproduces the dilute-limit cation transference number, its increase with salt concentration, and the absence of Li-TFSI contact ion pairs at low concentration. A penalty-based (soft-constraint) variant yields a closer fit to the DFT reference yet underestimates the conductivity by up to an order of magnitude, demonstrating that closer agreement with DFT training data alone does not guarantee accurate ion transport. These results indicate that although charge scaling can reproduce ionic conductivity the explicit inclusion of polarization is necessary to capture the concentration dependence of cation transport in PEO-LiTFSI.
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Strongly Correlated Electrons

Quadratic XY-anisotropy correction to the spontaneous staggered magnetization of the gapped XYZ spin-$1/2$ chain

Felipe Taha Sant'Ana

The staggered order parameter of the gapped XYZ spin-$1/2$ chain follows from the eight-vertex solution, but in elliptic variables that fix the Hamiltonian couplings only implicitly. We derive a closed form for the coefficient governing the leading quadratic response of the spontaneous staggered magnetization to the XY anisotropy at fixed longitudinal anisotropy in the gapped antiferromagnetic regime. Starting from the Baxter–Kelland–Jimbo–Miwa–Nakayashiki polarization formula, we show that at fixed longitudinal anisotropy both the modular nome and the crossing-parameter variable of the formula move with the XY anisotropy, and that the motion of the crossing-parameter variable reverses the sign of the expansion at fixed elliptic variables. The coefficient is a rational term plus a Lambert series. It is strictly negative and bounded above by a rational function of the longitudinal anisotropy, to which it is asymptotic in the Ising limit. At the isotropic point it diverges as the inverse five-halves power of the distance to that point, and since the Lambert sum has an asymptotic expansion with exponentially small remainder, the subleading terms of the divergence also follow in closed form. When the XY anisotropy vanishes as the five-fourths power of the distance to the isotropic point, the ratio of the perturbed to the unperturbed order parameter tends to a Gaussian in the scaling variable, and the quadratic truncation is controlled when that variable is small. A fourth-order perturbative calculation in the spin chain, with no input from the eight-vertex solution, reproduces the leading strong-coupling behaviour, and infinite-DMRG calculations at four anisotropies in the gapped regime are consistent with the closed form.
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Materials Science

Realizing Two-Dimensional Altermagnets with 100% Spin Polarization along the [110] Direction in Ambidentate-Ligand Based Square Organometallic Lattices

Qing-Bo Liu, Xin-Yi Chen, Xiangyang Li et al. (+2 more)

Altermagnetism, as a novel magnetic paradigm, not only possesses a zero net magnetic moment, but also exhibits a substantial nonrelativistic spin-splitting effect. Currently, developing a simple and experimentally feasible method for designing altermagnets is eagerly pursued. Moreover, achieving 100% spin polarization along certain directions in valence or conduction bands for altermagnets remains challenging. To address these issues, based on a tight-binding model, we propose a viable chemical strategy for constructing organometallic altermagnets by using ambidentate ligands. Furthermore, in these organometallic altermagnets, direction-dependent 100% spin polarization along the [110] direction in band edges can be induced via the coexistence of altermagnetically spin-split dispersive and flat bands, where the flat band suppresses electron transport in one spin channel and the dispersive band enables conduction in the other spin channel. Then, via first-principles calculations, a screening of 90 two-dimensional ambidentate-ligand based square organometallic lattices leads to the identification of three altermagnetic materials, namely Fe(taz)2Cl2 (taz = 1,2,4- triazine), Co(app)2Cl2, and Fe(app)2Cl2 (app = 1,4-azaphosphinine), all of which possess 100% spin polarization along the [110] direction in valence bands, as well as notable piezomagnetic behavior. This study paves the way for achieving direction-dependent fully spin-polarization in altermagnetic materials.
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All authors Qing-Bo Liu, Xin-Yi Chen, Xiangyang Li, Xingxing Li, Jinlong Yang

Materials Science

Dynamic Chemical Changes of Ti3C2Tx MXenes in Halide Perovskite Precursor Environments

Kirill Sobolev, Nagaprasad Reddy Samala, Mariela J. Pavan et al. (+8 more)

The integration of two-dimensional Ti3C2Tx MXenes into Halide Perovskite (HaP) optoelectronics has shown immense potential for enhancing device performance, yet the fundamental chemical interactions within the precursor ink (a critical stage determining the final material state) remain largely unexplored. This study presents a comprehensive investigation into the chemical stability and surface evolution of Ti3C2Tx MXenes when exposed to the individual and combined components of a model methylammonium lead iodide (MAPbI3) solution. By combining detailed X-ray Photoelectron Spectroscopy (XPS) analysis with Density Functional Theory (DFT) calculations, we decouple the complex interactions between MXenes and the ink constituents. We demonstrate that elemental iodine (I2) and polyiodides (In-) act as aggressive oxidizers, triggering rapid degradation and dissolution of the MXene flakes. Conversely, lead iodide (PbI2) induces a slower oxidation process driven by the strong adsorption of Pb2+ ions onto oxygen terminated sites. In stark contrast, methylammonium iodide (MAI) exhibits a stabilizing effect: it adsorbs onto the MXene surface via hydrogen bonding, effectively passivating the flakes and retarding degradation. In addition, our results reveal that the sequence of precursor addition governs the MXene surface state, requiring extra caution, but also enabling further tunability. These findings provide a critical view on how MXene integration with materials, in general, and HaP in particular, should be perceived, providing a fundamental for their rational engineering.
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All authors Kirill Sobolev, Nagaprasad Reddy Samala, Mariela J. Pavan, Sharon Hazan, Vladimir Ezersky, Shakked Schwartz, Omer Bartov, Adi Yakir, Michal Leskes, Tamar Goldzak Mizrachi, Yevgeny Rakita

Mesoscale and Nanoscale Physics

Nonlocal Josephson coupling and current redistribution in a large-area graphene multiterminal Josephson junction

Luojia Zhang, Kushagra Aggarwal, Jay D. Sau et al. (+4 more)

Multiterminal Josephson junctions (MTJJs) extend conventional two-terminal Josephson physics to devices defined by multiple superconducting phases, where rich phenomena have been predicted. However, in conventional MTJJs, superconducting transport is often dominated by local coupling between neighboring leads, obscuring physics that goes beyond simple connectivity. Here, we realize a multiterminal Josephson network in a graphene Hall bar geometry with micron-scale dimensions, enabling substantial nonlocal coupling between distant terminals. Our key observation is a pronounced negative differential longitudinal resistance (NDLR) in the four-probe response near switching currents, while no such feature appears in two-terminal measurements. We reproduce the NDLR response with a network containing the interplay between two distinct forms of nonlocality: nonlocal Josephson coupling, which determines the switching sequence of the superconducting network, and nonlocal normal-state conductance, which redistributes current after different regions switch. Our results highlight the potential of the emergent NDLR for characterizing superconductor–semiconductor hybrid systems and for nonlinear circuits. Further, this Josephson Hall bar geometry provides a platform for exploring the interplay between mesoscopic superconductivity and many-body ground states in graphene-based heterostructures.
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All authors Luojia Zhang, Kushagra Aggarwal, Jay D. Sau, Ethan G. Arnault, Kenji Watanabe, Takashi Taniguchi, Valla Fatemi

Materials Science

Corrugated Niobene: Stability, Mechanical and Electronic Properties from First-Principles Calculations

Willian O. Santos, José A. S. Laranjeira, Kleuton A. L. Lima et al. (+2 more)

The growing diversity of two-dimensional (2D) materials has expanded opportunities in electronics, energy technologies, catalysis, and optical applications. Within this landscape, understanding how corrugated architectures accommodate metallic bonding and influence the stability and properties of monoelemental niobium sheets remains an open research direction. Here, we propose a corrugated niobene nanosheet, denoted c-Nb, and investigate its structural, energetic, vibrational, mechanical, electronic, and optical properties using density functional theory simulations. The optimized structure adopts a centrosymmetric P-3m1 symmetry, with six atoms per primitive cell and a geometrical thickness of 4.279 Angstrom. Its cohesive energy of -6.03 eV/atom indicates strong binding relative to isolated atoms, although bulk BCC Nb remains energetically favored by 2.49 eV/atom. The absence of imaginary phonon frequencies along the investigated high-symmetry path and the positive-definite in-plane stiffness matrix support dynamical and mechanical structural stability. Despite its pronounced corrugation, the nanosheet exhibits isotropic in-plane elasticity, with Young's and shear moduli of 43.66 N/m and 13.66 N/m, respectively, and a Poisson's ratio of 0.598. Electronic states near the Fermi level are dominated by Nb 4d orbitals, establishing multiband metallicity. These findings identify a corrugated structural candidate that combines strong cohesion, elastic compliance, and metallic electronic behavior, extending the structural diversity of monoelemental 2D metals and providing a basis for further exploration of niobium nanosheets in electronic and ultraviolet-responsive systems.
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All authors Willian O. Santos, José A. S. Laranjeira, Kleuton A. L. Lima, Douglas S. Galvão, David L. Azevedo

Materials Science

The quantum geometry of the chemical bond

Gabrielle Carrel, Nishchhal Verma, Fatmagül Katmer et al. (+2 more)

Electronic properties of materials depend both on band energies and quantum geometry of electronic states. We relate bonding indices to the quantum geometric tensor (QGT), showing how chemical bonding dictates the momentum-space texture of bands, bridging chemical and physical descriptions of solids. We show the QGT decomposed into the three center bond index, weighted by their oriented area. Resolving these contributions by orbital pair reveals the donor–acceptor character that distinguish ionic, covalent, hypervalent, and metavalent bonding. We identify the bonding pattern for topology in materials: noncollinear three center bonds, which are the source of Berry curvature in solids. Bond fluctuation can be directly linked to electromagnetic response by resolving their energy spectrum, opening a quantitative route towards the design of physical properties of materials from bonding motifs.
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All authors Gabrielle Carrel, Nishchhal Verma, Fatmagül Katmer, Leslie M. Schoop, Raquel Queiroz

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

Predictive Synthesis of MOFs and COFs

Bin Feng, Reid A. Coyle, Shyam Chand Pal et al. (+3 more)

Predictive synthesis concerns the prospective modeling of how a targeted structure can be realized. The synthesis of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) intrinsically involves a multidimensional space of interdependent variables, posing a challenge for bench chemists to parameterize and predict. In this Perspective, we discuss the evolution from chemical-intuition-driven experimentation toward the integration of artificial intelligence (AI) and machine learning (ML) in the laboratory. By virtue of prior knowledge, uncertainty, and experimental failure in determining what should be attempted next, we envision predictive synthesis progressing from static recipe recommendation toward real-time control and transferable principles of framework formation. In this context, the significance lies in transforming trial-and-error practice into a means of measurable chemical reasoning, thereby accelerating crystalline materials discovery and advancing synthetic chemistry.
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All authors Bin Feng, Reid A. Coyle, Shyam Chand Pal, Peter Walther, Saeun Park, Zhiling Zheng

Strongly Correlated Electrons

Homogeneous to multi-scale inhomogeneous complex magnetism in Ba3LnRu2O9 (Ln = Gd, Ho), Revealed by muSR and Machine-Learned Muon-Site Calculations

S. Ghosh, K. Sharma, E. Kushwaha et al. (+7 more)

We report a comprehensive muon spin rotation and relaxation (muSR) study of the hexagonal 6H-perovskites Ba3LnRu2O9 (Ln = Gd, Ho) to investigate the role of rare-earth anisotropy in the magnetic ground state of 4d-4f coupled systems. Ba3HoRu2O9 exhibits two successive magnetic orderings at TN1 = 46 K and TN2 = 10 K, leading to a complex magnetic ground state, whereas Ba3GdRu2O9, with Gd3+ (L = 0) S-state ions, shows primarily single magnetic ordering at TN = 14.5 K. Zero-field (ZF) and longitudinal-field (LF) muSR measurements reveal markedly different magnetic behavior despite their structural similarity. Ba3HoRu2O9 displays a multi-scale inhomogeneous magnetic state characterized by two-component exponential relaxation, broad local-field distributions, incomplete LF decoupling, and persistent spin dynamics. The muSR results identify two characteristic magnetic energy scales near 46 and 10 K, associated with correlated Ru-Ho interactions and quasistatic magnetic ordering, respectively. Redfield analysis further demonstrates strong local magnetic fields and distributed spin fluctuation timescales, confirming magnetic inhomogeneity. Machine-learning-assisted muon-site and dipolar-field calculations show that the broad field distribution naturally arises from muons sensing distinct coexisting magnetic domains at different structural sites. In contrast, Ba3GdRu2O9 exhibits a comparatively homogeneous antiferromagnetic ground state below 14.5 K, with Gaussian relaxation consistent with a narrow static field distribution. These results establish that the rare-earth ion in Ba3LnRu2O9 is a powerful tuning parameter, driving the ground state from homogeneous to complex, multi-scale inhomogeneous behavior through competing 4d-4f magnetic interactions.
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All authors S. Ghosh, K. Sharma, E. Kushwaha, M. Kumar, G. Roy, A. Pandey, F. L. Pratt, S. Cottrell, D. T. Adroja, T. Basu

Mesoscale and Nanoscale Physics

Electron binding by charge disorder surrounding gapped bilayer graphene

Jude McClay, Angelika Knothe, Igor Rozhansky et al. (+1 more)

Bilayer graphene (BLG) is a unique electronic material offering electrostatic tunability of its band gap. Here, we study how charge disorder in the dielectric environment modifies band-edge states by binding electrons and holes to Coulomb centres, taking into account the in- and out-of-plane dielectric response of Bernal bilayers. We apply this framework to (a) hBN-encapsulated medium-size-gap BLG used for gate-defined quantum dots, and (b) BLG under double n/p ionic gating. In hBN/BLG/hBN, we find that single remote charges produce only weakly bound states, with binding energies generally small compared with the BLG gap. Under ionic gating, we find that the bound states are too large to be trapped by individual ions – localisation arises from fluctuations in the ion density, whose magnitude is limited by Coulomb charging energy at the freezing temperature $T_f$ of the ionic configuration. Thus, in both regimes, charge disorder does not produce deep midgap states, with the bound states remaining closer to the conduction and valence band edges.
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All authors Jude McClay, Angelika Knothe, Igor Rozhansky, Vladimir Fal'ko

Strongly Correlated Electrons

Improving the lower bound on the Laughlin gap: An SDP search

Qiang Gao

A recent preprint by OpenAI resolved the spherical fermionic Laughlin spectral-gap conjecture for the full $V_1$ interaction by a Fock-space inequality: $H_Q^2\ge \gamma H_Q$ on the lowest-Landau-level Fock space for all large flux $Q$ and every $\gamma$ below $0.0461673\ldots$, so that the gap above the Laughlin state at filling $1/3$ is at least $1/25$. That proof, with its original constant, has also been formalized in Lean. We show that the same argument supports a much larger constant. Two sharper estimates, a product-twirl bound for the three-body tail and a staircase price for the four-body allowance, raise the constant above $0.0601$ without changing the original certificate. Treating the auxiliary operators as the variables of a semidefinite program (SDP) and enlarging the finite set of orbital modes on which they act then gives $H_Q^2\ge\gamma H_Q$ for every $\gamma<\gamma_*=0.2190037845063196\ldots$, certified by exact rational arithmetic. Consequently the gap above the Laughlin state is at least $1/5$ for all sufficiently large spheres, and the untruncated planar $V_1$ Hamiltonian has positive spectrum bounded below by $\gamma_*$, uniformly in particle number and angular momentum. A heuristic extrapolation of the SDP optima suggests that auxiliary operators of the present form can give at most about $0.222$, while exact diagonalization of finite systems places the true gap near $0.4$. A larger family of auxiliary operators could push the bound further towards the true gap, and the SDP formulation makes such families easy to test. The proof of the improvement and the SDP search were completed by the AI model Claude Opus 5.5 (Anthropic) under the author's direction.
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Statistical Mechanics

Spectral optimization of spherical lattices and applications to classical and quantum interacting spin systems

Jonas Völler, Grigorios Makris, Fabian Hassler et al. (+1 more)

We develop an optimization algorithm for spherical lattice discretizations based on the spectrum of the discretized Laplace operator. Starting from refined icosahedral lattices, we minimize the splitting of the $(2\ell+1)$, $\ell=0,1,2,\dots$, continuum multiplets expected from $\mathrm{SO}(3)$ symmetry via gradient descent. This approach simultaneously produces lattices based on triangles with nearly uniform circumradii and perimeters. Although the optimization uses only the free-particle spectrum, we show that the resulting lattices carry over to interacting models. On the optimized lattices, rotational symmetry is restored for the critical Ising and Potts models and primary scaling dimensions are accurately reproduced for the three-dimensional Ising conformal field theory, when appropriate geometry-dependent interaction strengths are used. Higher-angular-momentum descendant states reveal weak residual symmetry breaking beyond the sectors protected by the underlying icosahedral symmetry.
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All authors Jonas Völler, Grigorios Makris, Fabian Hassler, Stefan Wessel

Statistical Mechanics · Cross-listed from hep-th

Tropical QFT and the sine-Gordon model

Michael Borinsky, Jury Radkovski and Suriyah Rajalingam Kannagi

A tropical quantum field theory is an exactly solvable deformation limit of an ordinary QFT, governed by a non-linear partial differential equation. We use the integrable two-dimensional sine-Gordon theory as a testbench to compare the exact features of an undeformed model with its tropical counterpart. We classify scale-invariant tropical QFTs in $D=2$ and leverage functional renormalization group methods to demonstrate that all scale-invariant theories with periodic effective actions are infrared fixed points of flows originating from sine-Gordon Lagrangians. For the tropical sine-Gordon model, we compute the $\beta$-functions exactly, solve the renormalized theory both via a convergent expansion and numerically for all admissible couplings, and illustrate the complete renormalization group flow from the Gaussian to the IR fixed point. Finally, we study the large-order behaviour of the loop expansion and relate it to the Hamilton-Jacobi equation, whose solutions we interpret as tropical instantons.
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Mesoscale and Nanoscale Physics

Entropy Production in Mesoscopic Electronic Transport Beyond Weak-Coupling

Ivana R. A. C. Lucena, Caio H. Lewenkopf and Alexandre R. Rocha

We investigate the full statistics of entropy production in coherent mesoscopic conductors beyond the weak-coupling regime. Using the inside-outside perspective and the Landauer-Büttiker scattering framework, we relate entropy production to the full counting statistics of particle transport and show that the corresponding cumulant-generating function satisfies the fluctuation symmetry independently of the coupling strength. We obtain closed analytical expressions for the cumulant-generating function in the weak- and strong-coupling limits, enabling a detailed characterization of entropy production distributions and higher-order cumulants. These cumulants reveal distinct signatures of resonant transport and coherent fermionic partitioning. While coupling-induced broadening substantially modifies the transport statistics, the fluctuation symmetry imposed by microscopic reversibility remains preserved in the long-time limit.
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Strongly Correlated Electrons

Search for free non-Abelian anyons in paired composite-fermion states

Mytraya Gattu and J. K. Jain

The even-denominator fractional quantum Hall (FQH) states, understood as topological superconductors of composite fermions, are predicted to support elementary quasiparticles (QPs) or quasiholes (QHs) obeying non-Abelian braid statistics. Using the microscopic framework of parton theory, we investigate many experimentally observed paired composite-fermion states and find that their elementary QPs and QHs in general bind to form Abelian molecules, thus obscuring non-Abelian braid statistics. An exception is the $\nu=1/2$ state in wide quantum wells, where our calculations show free QPs or QHs; we thus identify this state as an especially promising candidate for realizing and studying non-Abelian braid statistics. We also indicate how the study of such bound states can help reveal the topological structure of the state.
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Statistical Mechanics

Entropic-ordered superfluid

Isabella Zane and Andrew Lucas

We present a minimal classical lattice model of superfluidity at arbitrarily high temperatures, using a modified three-dimensional XY model with “soft" rotors. The global U(1) symmetry is spontaneously broken above a positive critical temperature due to entropic order. We study hydrodynamics in this high-temperature regime and verify consistency with the fluctuation-dissipation theorem, explaining how the large noise variance at very high temperatures is not sufficient to destroy superfluidity or the long lifetime of Goldstone modes.
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