Showing 1–50 of 589 results for author: Zhang, F

Tuning Carrier Type and Density in Highly Conductive and Infrared-Transparent (Bi1-xSbx)2Te3 films

Authors: Xiangren Zeng, Shenjin Zhang, Zhiheng Li, Weiyue Ma, Renjie Xie, Yanwei Cao, Fengguang Liu, Fengfeng Zhang, Haichao Zhao, Xiong Yao

Abstract: Infrared transparent conductors have long been sought due to their broad optoelectronic applications in the infrared wavelength range. However, the search for ideal materials has been limited by the inherent trade-off between electrical conductance and optical transmittance. Band engineering offers an effective approach to modulate carrier type and density, enabling concurrent tuning of both condu… ▽ More Infrared transparent conductors have long been sought due to their broad optoelectronic applications in the infrared wavelength range. However, the search for ideal materials has been limited by the inherent trade-off between electrical conductance and optical transmittance. Band engineering offers an effective approach to modulate carrier type and density, enabling concurrent tuning of both conductance and transmittance. In this work, we present a band engineering strategy that enables effective tuning of both infrared transmittance and electrical conductance in topological insulator (Bi1-xSbx)2Te3, bridging the gap and paving the way for applying topological insulators to infrared photoelectric devices. More importantly, with the combination of high carrier mobility and a large optical dielectric constant as suggested by previous report, Sb2Te3 achieves a high electrical conductance (~1000 S/cm) and outstanding infrared transmittance (92.3%) in the wavelength range of 8~13 um, demonstrating strong potential as an infrared transparent conductor. Our findings reveal that concurrent enhancement of both carrier mobility and optical dielectric constant is key to overcoming the conductance-transmittance trade-off. This work provides valuable insight for the exploration of high-performance infrared transparent conducting materials. △ Less

Submitted 17 December, 2025; originally announced December 2025.

Journal ref: ACS Appl. Electron. Mater. (2025)

Evaluating Large Language Models in Scientific Discovery

Authors: Zhangde Song, Jieyu Lu, Yuanqi Du, Botao Yu, Thomas M. Pruyn, Yue Huang, Kehan Guo, Xiuzhe Luo, Yuanhao Qu, Yi Qu, Yinkai Wang, Haorui Wang, Jeff Guo, Jingru Gan, Parshin Shojaee, Di Luo, Andres M Bran, Gen Li, Qiyuan Zhao, Shao-Xiong Lennon Luo, Yuxuan Zhang, Xiang Zou, Wanru Zhao, Yifan F. Zhang, Wucheng Zhang , et al. (31 additional authors not shown)

Abstract: Large language models (LLMs) are increasingly applied to scientific research, yet prevailing science benchmarks probe decontextualized knowledge and overlook the iterative reasoning, hypothesis generation, and observation interpretation that drive scientific discovery. We introduce a scenario-grounded benchmark that evaluates LLMs across biology, chemistry, materials, and physics, where domain exp… ▽ More Large language models (LLMs) are increasingly applied to scientific research, yet prevailing science benchmarks probe decontextualized knowledge and overlook the iterative reasoning, hypothesis generation, and observation interpretation that drive scientific discovery. We introduce a scenario-grounded benchmark that evaluates LLMs across biology, chemistry, materials, and physics, where domain experts define research projects of genuine interest and decompose them into modular research scenarios from which vetted questions are sampled. The framework assesses models at two levels: (i) question-level accuracy on scenario-tied items and (ii) project-level performance, where models must propose testable hypotheses, design simulations or experiments, and interpret results. Applying this two-phase scientific discovery evaluation (SDE) framework to state-of-the-art LLMs reveals a consistent performance gap relative to general science benchmarks, diminishing return of scaling up model sizes and reasoning, and systematic weaknesses shared across top-tier models from different providers. Large performance variation in research scenarios leads to changing choices of the best performing model on scientific discovery projects evaluated, suggesting all current LLMs are distant to general scientific "superintelligence". Nevertheless, LLMs already demonstrate promise in a great variety of scientific discovery projects, including cases where constituent scenario scores are low, highlighting the role of guided exploration and serendipity in discovery. This SDE framework offers a reproducible benchmark for discovery-relevant evaluation of LLMs and charts practical paths to advance their development toward scientific discovery. △ Less

Submitted 17 December, 2025; originally announced December 2025.

Discriminating Gap Symmetries of Superconducting La$_3$Ni$_2$O$_7$

Authors: Zhan Wang, Yuxin Wang, Kun Jiang, Jiangping Hu, Fu-Chun Zhang

Abstract: The discovery of high-T$_c$ superconductor in Ruddlesden-Popper nickelate materials represented by La$_3$Ni$_2$O$_7$ has opened new directions in the quest for unconventional superconductivity. A central unresolved issue concerns the pairing symmetry of the superconducting order. In this paper, we model the superconducting order of La$_3$Ni$_2$O$_7$ using the established Fermi surface structure to… ▽ More The discovery of high-T$_c$ superconductor in Ruddlesden-Popper nickelate materials represented by La$_3$Ni$_2$O$_7$ has opened new directions in the quest for unconventional superconductivity. A central unresolved issue concerns the pairing symmetry of the superconducting order. In this paper, we model the superconducting order of La$_3$Ni$_2$O$_7$ using the established Fermi surface structure together with phenomenological pairing functions belonging to $s_\pm$ and $d$-wave symmetry classes, which are the leading possibilities in the current debate. We compute several experimentally accessible observables-including tunneling density of states, point contact spectroscopy, superfluid density, and Raman spectroscopy-each of which exhibits distinct characteristics for different gap symmetries. These quantities provide a concrete and experimentally testable route for identifying the pairing symmetry of La$_3$Ni$_2$O$_7$ and for clarifying the microscopic nature of nickelate superconductivity. △ Less

Submitted 14 December, 2025; originally announced December 2025.

Comments: 10+3 pages, 4 figures

Yamaji effect and quantum oscillation in Yang-Rice-Zhang model of underdoped cuprates

Authors: Yicheng Zhong, Fu-Chun Zhang, Kun Jiang

Abstract: Recent experiments have revealed signatures of small Fermi pockets in the pseudogap phase of cuprate superconductors, most notably the Yamaji effect observed in $\mathrm{HgBa}_2\mathrm{CuO}_{4+δ}$. The Yang-Rice-Zhang (YRZ) model provides a successful phenomenological description of the pseudogap state and naturally predicts such small pockets. In this work, we use a microscopic framework to calcu… ▽ More Recent experiments have revealed signatures of small Fermi pockets in the pseudogap phase of cuprate superconductors, most notably the Yamaji effect observed in $\mathrm{HgBa}_2\mathrm{CuO}_{4+δ}$. The Yang-Rice-Zhang (YRZ) model provides a successful phenomenological description of the pseudogap state and naturally predicts such small pockets. In this work, we use a microscopic framework to calculate angle-dependent magnetoresistance and quantum oscillation within the YRZ model. Our calculations simultaneously reproduce the experimentally observed Yamaji oscillations and the Shubnikov-de Haas oscillation corresponding to a pocket area of about $p/8$, with $p$ the hole density. By further testing the effect of Green's-function zeros, we confirm that isolated zeros leave the oscillation period unchanged, whereas an extended zero segment suppresses and modifies the oscillation. Our findings demonstrate that the YRZ model captures essential features of the pseudogap regime and provides a general quantum approach that can be applied to more complex electronic structures. △ Less

Submitted 11 December, 2025; originally announced December 2025.

Comments: 5 pages, 4 figures with appendix

Protein Diffusion and Stokes-Einstein Deviation in Supercooled Cryoprotectant Solutions

Authors: Maddalena Bin, Anita Girelli, Mariia Filianina, Mario Reiser, Sharon Berkowicz, Milla Åhlfeldt, Michelle Dargasz, Sonja Timmermann, Jaqueline Savelkouls, Takeshi Kawasaki, Shinji Saito, Federico Zontone, Yuriy Chushkin, Fajun Zhang, Frank Schreiber, Michael Paulus, Christian Gutt, Fivos Perakis

Abstract: Vitrification during cryopreservation requires a detailed understanding of the dynamic behavior of biological solutions. We investigate ferritin diffusion in glycerol-water mixtures at supercooled temperatures using X-ray Photon Correlation Spectroscopy (XPCS). Diffusion coefficients were measured from ambient conditions to $T = 210$ K and analyzed using the Vogel-Fulcher-Tammann (VFT) relation, y… ▽ More Vitrification during cryopreservation requires a detailed understanding of the dynamic behavior of biological solutions. We investigate ferritin diffusion in glycerol-water mixtures at supercooled temperatures using X-ray Photon Correlation Spectroscopy (XPCS). Diffusion coefficients were measured from ambient conditions to $T = 210$ K and analyzed using the Vogel-Fulcher-Tammann (VFT) relation, yielding an arrest temperature of $T_0 = 85 \pm 11$ K for ferritin ($R_{\rm h} = 7.3$ nm), markedly lower than $T_0 = 122 \pm 4$ K for larger nanoparticles ($R_{\rm h} = 50$ nm). Below $T \approx 230$ K, ferritin diffusion exceeds the Stokes-Einstein prediction by up to a factor of 2.7, revealing nanoscale deviations from bulk viscosity. A fluctuating-friction model quantitatively links this enhancement to local friction heterogeneity, with fluctuations increasing upon cooling and reaching $\sim 80\%$ of the mean friction at $T=210$ K. These results establish a molecular-scale connection between protein diffusion and solvent dynamical heterogeneity in cryoprotected solutions. △ Less

Submitted 2 December, 2025; originally announced December 2025.

Expansion of Momentum Space and Full 2$π$ Solid Angle Photoelectron Collection in Laser-Based Angle-Resolved Photoemission Spectroscopy by Applying Sample Bias

Authors: Taimin Miao, Yu Xu, Bo Liang, Wenpei Zhu, Neng Cai, Mingkai Xu, Di Wu, Hongze Gu, Wenjin Mao, Shenjin Zhang, Fengfeng Zhang, Feng Yang, Zhimin Wang, Qinjun Peng, Zuyan Xu, Zhihai Zhu, Xintong Li, Hanqing Mao, Lin Zhao, Guodong Liu, X. J. Zhou

Abstract: Angle-resolved photoemission spectroscopy (ARPES) directly probes the energy and momentum of electrons in quantum materials, but conventional setups capture only a small fraction of the full 2$π$ solid angle. This limitation is acute in laser-based ARPES, where the low photon energy restricts momentum space despite ultrahigh resolution. Here we present systematic studies of bias ARPES, where apply… ▽ More Angle-resolved photoemission spectroscopy (ARPES) directly probes the energy and momentum of electrons in quantum materials, but conventional setups capture only a small fraction of the full 2$π$ solid angle. This limitation is acute in laser-based ARPES, where the low photon energy restricts momentum space despite ultrahigh resolution. Here we present systematic studies of bias ARPES, where applying a sample bias expands the accessible momentum range and enables full 2$π$ solid angle collection in two dimension using our 6.994 eV laser source. An analytical conversion relation is established and validated to accurately map the detector angle to the emission angle and the electron momentum in two dimensions. A precise approach is developed to determine the sample work function which is critical in the angle-momentum conversion of the bias ARPES experiments. Energy and angular resolutions are preserved under biases up to 100 V, and minimizing beam size is shown to be crucial. The technique is effective both near normal and off-normal geometries, allowing flexible Brillouin zone access with lower biases. Bias ARPES thus elevates laser ARPES to a new level, extending momentum coverage while retaining high resolution, and is applicable across a broad photon-energy range. △ Less

Submitted 24 November, 2025; originally announced November 2025.

Electric-Field-Dependent Thermal Conductivity in Fresh and Aged Bulk Single Crystalline $\mathrm{BaTiO_3}$

Authors: Fanghao Zhang, Guanchun Rui, Yujie Quan, Shantal Adajian, Matthew Delmont, Q. M. Zhang, Bolin Liao

Abstract: Active thermal management requires advances in thermal switching materials, whose thermal conductivity responds to external stimuli. The electric field, as one of the most convenient and effective stimuli, has shown great potential in tuning the thermal conductivity of ferroelectric materials. While previous studies on electric-field-induced ferroelectric thermal switching have primarily focused o… ▽ More Active thermal management requires advances in thermal switching materials, whose thermal conductivity responds to external stimuli. The electric field, as one of the most convenient and effective stimuli, has shown great potential in tuning the thermal conductivity of ferroelectric materials. While previous studies on electric-field-induced ferroelectric thermal switching have primarily focused on thin films and bulk solid solutions with strong extrinsic interface and defect scatterings, bulk single crystals, which can offer clear insights into intrinsic thermal switching mechanisms, have received comparatively less attention. Here, we demonstrate electric-field-induced thermal switching in bulk single-crystalline $\mathrm{BaTiO_3}$ (BTO) at room temperature and elucidate the critical role of domain evolution and aging in governing heat transport. Using a customized steady-state platform with in-situ electric fields up to $\pm$10 kV/cm, we observe a modulation of thermal conductivity up to 35% in fresh BTO driven by polarization reorientation and domain restructuring. First-principles finite-temperature lattice-dynamics calculations confirm that the switching behavior primarily originates from anisotropic phonon transport associated with domain configuration rather than strain-induced changes in phonon velocities. We further reveal that both ambient aging and controlled thermal aging can enhance the switching contrast through the formation and alignment of defect dipoles that modulate phonon-defect scattering. These results establish defect-domain interactions as a powerful design parameter for ferroelectric thermal switches and demonstrate a versatile experimental platform for exploring field-tunable heat transport and phase behavior in bulk functional materials. △ Less

Submitted 18 November, 2025; originally announced November 2025.

(Dis-)appearance of liquid-liquid phase transitions in a heterogeneous activated patchy particle model and experiment

Authors: Furio Surfaro, Peixuan Liang, Hadra Banks, Fajun Zhang, Frank Schreiber, Martin Oettel

Abstract: The ion-activated patchy particle model is an important theoretical framework to investigate the phase behaviour of globular proteins in the presence of multivalent ions. In this work, we study and highlight the influence of patch heterogeneity on the extension, appearance and disappearance of the liquid-liquid coexistence region of the phase diagram. We demonstrate that within this model the bind… ▽ More The ion-activated patchy particle model is an important theoretical framework to investigate the phase behaviour of globular proteins in the presence of multivalent ions. In this work, we study and highlight the influence of patch heterogeneity on the extension, appearance and disappearance of the liquid-liquid coexistence region of the phase diagram. We demonstrate that within this model the binding energy between salt ions and patches of different type is a key factor in determining the phase behavior. Specifically, we show under which conditions liquid-liquid phase separation (LLPS) in these systems can appear or disappear for varying binding energy and ion-mediated attraction energy between ion-occupied and unoccupied patches. In particular we address the influence of the patch type dependence of these energies on the (dis)appearance of LLPS. These results rationalize our new results on ion-dependent liquid-liquid phase separation in solutions of bovine serum albumine with trivalent cations. In comparison with models with non-activated patches, where the gas-liquid transition disappears when the number of patches approaches two, we find the complementary mechanism that ions may shift the attractions from stronger to weaker patches (with an accompanying disappearance of the transition), if their binding energy to the patches changes. The results have implications for the understanding of charge-driven LLPS in biological systems and its suppression. △ Less

Submitted 11 November, 2025; originally announced November 2025.

Comments: 13 pages, submitted to JCP

Phase diagrams of S=1/2 bilayer Models of SU(2) symmetric antiferromagnets

Authors: Fan Zhang, Nisheeta Desai, Wenan Guo, Ribhu K. Kaul

Abstract: We study the $T=0$ phase diagrams of models of bilayers of $S=1/2$ square lattices antiferromagnets with SU(2) Heisenberg symmetry that have 2, 4, and 6 spin exchanges. We study two families of bilayer models with distinct internal symmetries and, hence, different phase diagram topologies. A traditional bilayer model in which the interlayer interaction is Heisenberg so that the two layers can exch… ▽ More We study the $T=0$ phase diagrams of models of bilayers of $S=1/2$ square lattices antiferromagnets with SU(2) Heisenberg symmetry that have 2, 4, and 6 spin exchanges. We study two families of bilayer models with distinct internal symmetries and, hence, different phase diagram topologies. A traditional bilayer model in which the interlayer interaction is Heisenberg so that the two layers can exchange spin (and energy) with each other, making it possible to achieve a simple dimerized valence bond liquid-like state. The resulting phase diagram is rich with Néel, valence bond solid and simple dimer phases, and both first-order and continuous transitions, which we demonstrate are consistent with the conventional Landau theory of order parameters. In the second family of models in which the layers can exchange only energy but no spin (reminiscent of the Ashkin-Teller coupling), the simple dimer state cannot occur. The phase diagrams reveal a number of phase transitions that are accessed for the first time. We find that the phase transition between Néel and VBS is first order in both the spin-spin and energy-energy coupled models, although they have strikingly distinct finite-size scaling behavior and that the transition from VBS to dimer in the spin-spin coupling model deviates from the expected scenario of an XY model with dangerously irrelevant four-fold anisotropy. △ Less

Submitted 19 November, 2025; v1 submitted 6 November, 2025; originally announced November 2025.

Comments: 10 pages, 5 figures

Stability of mixed-state phases under weak decoherence

Authors: Yifan F. Zhang, Sarang Gopalakrishnan

Abstract: We prove that the Gibbs states of classical, and commuting-Pauli, Hamiltonians are stable under weak local decoherence: i.e., we show that the effect of the decoherence can be locally reversed. In particular, our conclusions apply to finite-temperature equilibrium critical points and ordered low-temperature phases. In these systems the unconditional spatio-temporal correlations are long-range, and… ▽ More We prove that the Gibbs states of classical, and commuting-Pauli, Hamiltonians are stable under weak local decoherence: i.e., we show that the effect of the decoherence can be locally reversed. In particular, our conclusions apply to finite-temperature equilibrium critical points and ordered low-temperature phases. In these systems the unconditional spatio-temporal correlations are long-range, and local (e.g., Metropolis) dynamics exhibits critical slowing down. Nevertheless, our results imply the existence of local "decoders" that undo the decoherence, when the decoherence strength is below a critical value. An implication of these results is that thermally stable quantum memories have a threshold against decoherence that remains nonzero as one approaches the critical temperature. Analogously, in diffusion models, stability of data distributions implies the existence of computationally-efficent local denoisers in the late-time generation dynamics. △ Less

Submitted 3 November, 2025; originally announced November 2025.

Comments: 25 pages, 3 figures

COFAP: A Universal Framework for COFs Adsorption Prediction through Designed Multi-Modal Extraction and Cross-Modal Synergy

Authors: Zihan Li, Mingyang Wan, Mingyu Gao, Zhongshan Chen, Xiangke Wang, Feifan Zhang

Abstract: Covalent organic frameworks (COFs) are promising adsorbents for gas adsorption and separation, while identifying the optimal structures among their vast design space requires efficient high-throughput screening. Conventional machine-learning predictors rely heavily on specific gas-related features. However, these features are time-consuming and limit scalability, leading to inefficiency and labor-… ▽ More Covalent organic frameworks (COFs) are promising adsorbents for gas adsorption and separation, while identifying the optimal structures among their vast design space requires efficient high-throughput screening. Conventional machine-learning predictors rely heavily on specific gas-related features. However, these features are time-consuming and limit scalability, leading to inefficiency and labor-intensive processes. Herein, a universal COFs adsorption prediction framework (COFAP) is proposed, which can extract multi-modal structural and chemical features through deep learning, and fuse these complementary features via cross-modal attention mechanism. Without Henry coefficients or adsorption heat, COFAP sets a new SOTA by outperforming previous approaches on hypoCOFs dataset. Based on COFAP, we also found that high-performing COFs for separation concentrate within a narrow range of pore size and surface area. A weight-adjustable prioritization scheme is also developed to enable flexible, application-specific ranking of candidate COFs for researchers. Superior efficiency and accuracy render COFAP directly deployable in crystalline porous materials. △ Less

Submitted 3 November, 2025; originally announced November 2025.

Inter-orbital spin-triplet superconductivity from altermagnetic fluctuations

Authors: Chen Lu, Chuang Li, Chao Cao, Huiqiu Yuan, Fu-Chun Zhang, Lun-Hui Hu

Abstract: Altermagnetic (AM) fluctuations are a new class of collinear spin fluctuations whose role in mediating superconductivity faces a fundamental tension: their $Γ$-point peak favors intra-orbital spin-triplet pairing, while their spin compensation favors inter-orbital singlets. Here, we demonstrate that inversion-symmetry-broken AM fluctuations generically resolve this competition in favor of spin-tri… ▽ More Altermagnetic (AM) fluctuations are a new class of collinear spin fluctuations whose role in mediating superconductivity faces a fundamental tension: their $Γ$-point peak favors intra-orbital spin-triplet pairing, while their spin compensation favors inter-orbital singlets. Here, we demonstrate that inversion-symmetry-broken AM fluctuations generically resolve this competition in favor of spin-triplet pairing. As a proof of concept, we study a minimal two-orbital model with two van Hove singularities. The broken inversion symmetry induces momentum-orbital locking: the same orbital dominates at opposite momenta, enhancing the triplet channel. Crucially, a subdominant fluctuation channel arising from inter-van-Hove nesting provides an internal Josephson coupling that locks the phase difference between triplet pairs on different orbitals. We find this coupling changes sign ($+$ to $-$) upon a crossover from AM-dominant to ferromagnetic-dominant fluctuations. The resulting $π$-phase difference manifests as a $τ_z$-type order parameter, $c_{k,1\uparrow}c_{-k,1\uparrow} - c_{k,2\uparrow}c_{-k,2\uparrow}$. Although intra-orbital in the original basis, its orbital-nontrivial character, as manifested by its equivalence to inter-orbital pairing under rotation, defines a general \textit{inter-orbital spin-triplet superconductivity}. This state is distinct from the $τ_0$-triplet pairing mediated by ferromagnetic fluctuations, as evidenced by the canceled intra-orbital supercurrent in a Josephson junction between them. △ Less

Submitted 21 October, 2025; originally announced October 2025.

Comments: 5 pages, 5 figures. Comments are welcome

Magnetic Field-Enhanced Graphene Superconductivity with Record Pauli-Limit Violation

Authors: Jixiang Yang, Omid Sharifi Sedeh, Chiho Yoon, Shenyong Ye, Henok Weldeyesus, Armel Cotten, Tonghang Han, Zhengguang Lu, Zach Hadjri, Junseok Seo, Lihan Shi, Emily Aitken, Prayoga P Liong, Zhenghan Wu, Mingchi Xu, Christian Scheller, Mingyang Zheng, Rasul Gazizulin, Kenji Watanabe, Takashi Taniguchi, Dominique Laroche, Mingda Li, Fan Zhang, Dominik M. Zumbühl, Long Ju

Abstract: Spin-polarized superconductors offer a rare platform for studying electronic correlations, but few candidate systems have been experimentally confirmed to date. Here, we report the observation of a spin-polarized superconducting state, denoted SC5, in WSe2-proximitized rhombohedral trilayer graphene. At in-plane magnetic field B|| = 0 T, SC5 has a critical temperature of 68 mK and an out-of-plane… ▽ More Spin-polarized superconductors offer a rare platform for studying electronic correlations, but few candidate systems have been experimentally confirmed to date. Here, we report the observation of a spin-polarized superconducting state, denoted SC5, in WSe2-proximitized rhombohedral trilayer graphene. At in-plane magnetic field B|| = 0 T, SC5 has a critical temperature of 68 mK and an out-of-plane critical magnetic field of only 12 mT. Surprisingly, these values are significantly enhanced as B|| increases, and the superconductivity persists to B|| = 8.8 T. This value corresponds to a record-high Pauli-limit violation ratio of at least 80 among all superconductors, while the true critical field is beyond the limit of our instrument. We conclude that SC5 experiences a canting crossover from Ising-type to spin-polarized superconductor with increased B||. △ Less

Submitted 21 November, 2025; v1 submitted 12 October, 2025; originally announced October 2025.

Comments: 18 pages, 4 figures

Classically Sampling Noisy Quantum Circuits in Quasi-Polynomial Time under Approximate Markovianity

Authors: Yifan F. Zhang, Su-un Lee, Liang Jiang, Sarang Gopalakrishnan

Abstract: While quantum computing can accomplish tasks that are classically intractable, the presence of noise may destroy this advantage in the absence of fault tolerance. In this work, we present a classical algorithm that runs in $n^{\rm{polylog}(n)}$ time for simulating quantum circuits under local depolarizing noise, thereby ruling out their quantum advantage in these settings. Our algorithm leverages… ▽ More While quantum computing can accomplish tasks that are classically intractable, the presence of noise may destroy this advantage in the absence of fault tolerance. In this work, we present a classical algorithm that runs in $n^{\rm{polylog}(n)}$ time for simulating quantum circuits under local depolarizing noise, thereby ruling out their quantum advantage in these settings. Our algorithm leverages a property called approximate Markovianity to sequentially sample from the measurement outcome distribution of noisy circuits. We establish approximate Markovianity in a broad range of circuits: (1) we prove that it holds for any circuit when the noise rate exceeds a constant threshold, and (2) we provide strong analytical and numerical evidence that it holds for random quantum circuits subject to any constant noise rate. These regimes include previously known classically simulable cases as well as new ones, such as shallow random circuits without anticoncentration, where prior algorithms fail. Taken together, our results significantly extend the boundary of classical simulability and suggest that noise generically enforces approximate Markovianity and classical simulability, thereby highlighting the limitation of noisy quantum circuits in demonstrating quantum advantage. △ Less

Submitted 7 October, 2025; originally announced October 2025.

Comments: 32 pages, 7 figures + X inline figures

Semiconductor Meta-Graphene and Valleytronics

Authors: Praveen Pai, Aron W. Cummings, Alexander Cerjan, Wei Pan, Fan Zhang, Catalin D. Spataru

Abstract: Nano-patterned semiconductor interfaces offer a versatile platform for creating quantum metamaterials and exploring novel electronic phenomena. In this study, we illustrate this concept using artificial graphene--a metamaterial featuring distinctive properties including Dirac and saddle points. We demonstrate that introducing additional nano-patterning can open a Dirac band gap, giving rise to wha… ▽ More Nano-patterned semiconductor interfaces offer a versatile platform for creating quantum metamaterials and exploring novel electronic phenomena. In this study, we illustrate this concept using artificial graphene--a metamaterial featuring distinctive properties including Dirac and saddle points. We demonstrate that introducing additional nano-patterning can open a Dirac band gap, giving rise to what we term artificial hexagonal boron nitride (AhBN). The calculated valley Chern number of AhBN indicates the presence of topological valley Hall states confined to Dirac-gap domain walls. A key question is whether these one-dimensional edge states are topologically protected against disorder, given their vulnerability to Anderson localization. To this end, we perform band structure and electronic transport simulations under experimentally relevant disorder, including charge puddles and geometric imperfections. Our results reveal the resilience of the domain wall states against typical experimental disorder, particularly while the AhBN band gap remains open. The localization length along the domain wall can reach several microns--several times longer than the bulk electron mean free path--even though the number of bulk transport channels is greater. To enhance the effectiveness of the low-dissipation domain wall channel, we propose ribbon geometries with a large length-to-width ratio. These findings underscore both the potential and challenges of AhBN for low-energy, power-efficient microelectronic applications. △ Less

Submitted 6 October, 2025; originally announced October 2025.

Beyond Belief Propagation: Cluster-Corrected Tensor Network Contraction with Exponential Convergence

Authors: Siddhant Midha, Yifan F. Zhang

Abstract: Tensor network contraction on arbitrary graphs is a fundamental computational challenge with applications ranging from quantum simulation to error correction. While belief propagation (BP) provides a powerful approximation algorithm for this task, its accuracy limitations are poorly understood and systematic improvements remain elusive. Here, we develop a rigorous theoretical framework for BP in t… ▽ More Tensor network contraction on arbitrary graphs is a fundamental computational challenge with applications ranging from quantum simulation to error correction. While belief propagation (BP) provides a powerful approximation algorithm for this task, its accuracy limitations are poorly understood and systematic improvements remain elusive. Here, we develop a rigorous theoretical framework for BP in tensor networks, leveraging insights from statistical mechanics to devise a \emph{cluster expansion} that systematically improves the BP approximation. We prove that the cluster expansion converges exponentially fast if an object called the \emph{loop contribution} decays sufficiently fast with the loop size, giving a rigorous error bound on BP. We also provide a simple and efficient algorithm to compute the cluster expansion to arbitrary order. We demonstrate the efficacy of our method on the two-dimensional Ising model, where we find that our method significantly improves upon BP and existing corrective algorithms such as loop series expansion. Our work opens the door to a systematic theory of BP for tensor networks and its applications in decoding classical and quantum error-correcting codes and simulating quantum systems. △ Less

Submitted 26 October, 2025; v1 submitted 2 October, 2025; originally announced October 2025.

Comments: Added discussion about related and concurrent works. 12+13 pages, 5+2 figures

Ab initio calculation of atomic solid hydrogen phases based on Gutzwiller many-body wave functions

Authors: Zhuo Ye, Jun Liu, Yong-Xin Yao, Feng Zhang, Kai-Ming Ho, Cai-Zhuang Wang

Abstract: We apply two ab initio many-body methods based on Gutzwiller wave functions, i.e., correlation matrix renormalization theory (CMRT) and Gutzwiller conjugate gradient minimization (GCGM), to the study of crystalline phases of atomic hydrogen. Both methods avoid empirical Hubbard U parameters and are free from double-counting issues. CMRT employs a Gutzwiller-type approximation that enables efficien… ▽ More We apply two ab initio many-body methods based on Gutzwiller wave functions, i.e., correlation matrix renormalization theory (CMRT) and Gutzwiller conjugate gradient minimization (GCGM), to the study of crystalline phases of atomic hydrogen. Both methods avoid empirical Hubbard U parameters and are free from double-counting issues. CMRT employs a Gutzwiller-type approximation that enables efficient calculations, while GCGM goes beyond this approximation to achieve higher accuracy at higher computational cost. By benchmarking against available quantum Monte Carlo results, we demonstrate that while both methods are more accurate than the widely used density-functional theory (DFT), GCGM systematically captures additional correlation energy missing in CMRT, leading to significantly improved total energy predictions. We also show that by including the correlation energy $E_c$ from LDA in the CMRT calculation, CMRT+$E_c$ produces energy in better agreement with the QMC results in these hydrogen lattice systems. △ Less

Submitted 3 October, 2025; v1 submitted 2 October, 2025; originally announced October 2025.

Comments: 22 pages, 4 figures

exaPD: A highly parallelizable workflow for multi-element phase diagram (PD) construction

Authors: Feng Zhang, Zhuo Ye, Maxim Moraru, Ying Wai Li, Weiyi Xia, Yongxin Yao, Ryan Richard, Cai-Zhuang Wang

Abstract: Phase diagrams (PDs) illustrate the relative stability of competing phases under varying conditions, serving as critical tools for synthesizing complex materials. Reliable phase diagrams rely on precise free energy calculations, which are computationally intensive. We introduce exaPD, a user-friendly workflow that enables simultaneous sampling of multiple phases across a fine mesh of temperature a… ▽ More Phase diagrams (PDs) illustrate the relative stability of competing phases under varying conditions, serving as critical tools for synthesizing complex materials. Reliable phase diagrams rely on precise free energy calculations, which are computationally intensive. We introduce exaPD, a user-friendly workflow that enables simultaneous sampling of multiple phases across a fine mesh of temperature and composition for free energy calculations. The package employs standard molecular dynamics (MD) and Monte Carlo (MC) sampling techniques, as implemented in the LAMMPS package. Various interatomic potentials are supported, including the neural network potentials with near {\it ab initio} accuracy. A global controller, built with Parsl, manages the MD/MC jobs to achieve massive parallelization with near ideal scalability. The resulting free energies of both liquid and solid phases, including solid solutions, are integrated into CALPHAD modeling using the PYCALPHAD package for constructing the phase diagram. △ Less

Submitted 1 October, 2025; originally announced October 2025.

Robust Majorana Platform Driven by a Meissner-Induced Anisotropic Doppler Shift

Authors: Xiao-Hong Pan, Si-Qi Yu, Li Chen, Fu-Chun Zhang, Xin Liu

Abstract: The realization of robust Majorana zero modes (MZMs), a cornerstone for fault-tolerant quantum computing, is hindered by the challenge of creating a platform that simultaneously offers a large topological gap, high tunability, and resilience to disorder. A system unifying these properties has remained elusive. Here, we propose and validate a novel platform that harnesses the Meissner effect in a t… ▽ More The realization of robust Majorana zero modes (MZMs), a cornerstone for fault-tolerant quantum computing, is hindered by the challenge of creating a platform that simultaneously offers a large topological gap, high tunability, and resilience to disorder. A system unifying these properties has remained elusive. Here, we propose and validate a novel platform that harnesses the Meissner effect in a topological insulator (TI) nanowire partially covered by a superconducting (SC) layer. Under an external magnetic field, Meissner screening currents in the SC induce a spatially varying Doppler shift on the TI surface. This effect generates a highly anisotropic effective g-factor, which selectively drives a topological phase transition localized on the nanowire's bottom surface. This mechanism is crucial as it spatially separates the topological phase from the SC/TI interface, permitting strong proximity-induced superconductivity while preventing detrimental band renormalization at the interface from closing the topological gap. Furthermore, by confining the topological superconducting phase to the gate-tunable bottom surface, our platform fully leverages the intrinsic disorder resilience of the TI's topologically protected surface states. Through a combination of supercurrent simulations, self-consistent Schrödinger-Poisson calculations, and large-scale tight-binding computations, we validate the platform's robustness. Our work establishes a practical pathway toward Meissner-mediated topological superconductivity for realizing robust MZMs in SC/TI hybrid systems. △ Less

Submitted 29 September, 2025; originally announced September 2025.

Comments: 9 pages, 5 figures

Competing $s$-wave pairing in overdoped $t$-$J$ model

Authors: Wayne Zheng, Tao Cheng, Zheng-Yuan Yue, Fu-Chun Zhang, Wei-Qiang Chen, Zheng-Cheng Gu

Abstract: The $d$-wave pairing symmetry has long been considered a defining feature of high-temperature superconductivity in cuprates. In this work, we reveal that $s$-wave pairing states exhibit variational energies comparable to the $d$-wave state in a square $t$-$J$ model, particularly at high doping levels ($δ\gtrsim 15\%$) by using the state-of-the-art tensor network simulation. This surprising result… ▽ More The $d$-wave pairing symmetry has long been considered a defining feature of high-temperature superconductivity in cuprates. In this work, we reveal that $s$-wave pairing states exhibit variational energies comparable to the $d$-wave state in a square $t$-$J$ model, particularly at high doping levels ($δ\gtrsim 15\%$) by using the state-of-the-art tensor network simulation. This surprising result suggests that $s$-wave pairing may play an important role in the cuprate phase diagram, especially for the overdoped region. Our findings provide a potential resolution to discrepancies in recent Josephson tunneling experiments on twisted bilayer cuprates and offer new insights into the evolution of pairing symmetry with doping. △ Less

Submitted 26 September, 2025; originally announced September 2025.

Comments: 8 pages, 7 figures

Spin-Polarized Josephson Supercurrent in Nodeless Altermagnets

Authors: Chuang Li, Jin-Xing Hou, Fu-Chun Zhang, Song-Bo Zhang, Lun-Hui Hu

Abstract: Long-range propagation of equal-spin triplet Cooper pairs typically occurs in ferromagnet/$s$-wave superconductor junctions, where net magnetization plays a crucial role. Here, we propose a fundamentally different scenario in which Josephson supercurrents mediated exclusively by spin-triplet pairings emerge in systems with \textit{zero} net magnetization. We identify collinear altermagnets, partic… ▽ More Long-range propagation of equal-spin triplet Cooper pairs typically occurs in ferromagnet/$s$-wave superconductor junctions, where net magnetization plays a crucial role. Here, we propose a fundamentally different scenario in which Josephson supercurrents mediated exclusively by spin-triplet pairings emerge in systems with \textit{zero} net magnetization. We identify collinear altermagnets, particularly a subclass termed nodeless altermagnets, as ideal platforms to realize this phenomenon. These materials host spin-split Fermi surfaces that do not intersect altermagnetic nodal lines and support maximal spin-valley polarization, yielding fully spin-polarized electronic states at each valley. Consequently, Josephson junctions based on nodeless altermagnets sustain supercurrents solely through spin-polarized triplet pairing correlations, simultaneously contributed by spin-up Cooper pairs from one valley and spin-down Cooper pairs from the other. Furthermore, controlling the relative local inversion-symmetry breaking at the two interfaces enables a robust 0--$π$ transition without fine tuning, while adjusting the junction orientation allows a crossover between pure triplet and mixed singlet-triplet states. Our work thus establishes nodeless altermagnets as a unique platform for altermagnetic superconductors with magnetization-free spin-polarized supercurrents. △ Less

Submitted 17 September, 2025; originally announced September 2025.

Direct Observation of d-Wave Superconducting Gap Symmetry in Pressurized La3Ni2O7-delta Single Crystals

Authors: Zi-Yu Cao, Di Peng, Seokmin Choi, Fujun Lan, Lan Yu, Enkang Zhang, Zhenfang Xing, Yuxin Liu, Feiyang Zhang, Tao Luo, Lixing Chen, Vuong Thi Anh Hong, Seung-Yeop Paek, Harim Jang, Jinghong Xie, Huayu Liu, Hongbo Lou, Zhidan Zeng, Yang Ding, Jun Zhao, Cailong Liu, Tuson Park, Qiaoshi Zeng, Ho-kwang Mao

Abstract: The recent discovery of superconductivity in pressure-stabilized bulk La3Ni2O7-delta, with a critical temperature (Tc) exceeding 77 K, has opened a new frontier in high-temperature superconductivity research beyond cuprates. Yet, the superconducting gap amplitude and symmetry, the key parameters to characterize a superconductor, remain elusive due to the overwhelming challenges of gap studies unde… ▽ More The recent discovery of superconductivity in pressure-stabilized bulk La3Ni2O7-delta, with a critical temperature (Tc) exceeding 77 K, has opened a new frontier in high-temperature superconductivity research beyond cuprates. Yet, the superconducting gap amplitude and symmetry, the key parameters to characterize a superconductor, remain elusive due to the overwhelming challenges of gap studies under high pressure. Here, we introduce in situ directional point-contact spectroscopy conducted under truly hydrostatic pressure, enabling the direct mapping of the superconducting gap in pressurized La3Ni2O7-delta single crystals. Depending on the junction orientation, differential conductance (dI/dV) spectra exhibit distinct V-shaped quasiparticle features and a sharp zero-bias peak, indicating a predominant d-wave-like pairing symmetry. Measurement of the c-axis gap amplitude Delta yields a gap-to-Tc ratio of 2Delta/kBTc = 4.2(5), positioning La3Ni2O7-delta firmly among unconventional, nodal high-Tc superconductors. These findings set stringent constraints on theoretical models for nickelate superconductors and establish a robust spectroscopic approach for understanding superconductors under extreme pressures. △ Less

Submitted 15 September, 2025; originally announced September 2025.

Comments: 20 pages, 4 figures, 4 supplementary figures

Quantum Theory of Exciton Magnetic Moment: Interaction and Topological Effects

Authors: Gurjyot Sethi, Jiawei Ruan, Fang Zhang, Weichen Tang, Chen Hu, Mit Naik, Steven G. Louie

Abstract: Combining magnetometry with optical spectroscopy has uncovered novel quantum phenomena and is emerging as a platform for quantum information science. Yet, the theory of magnetic response of excitons, correlated electron-hole pairs in semiconductors, remains incomplete due to insufficient treatment of electron-hole interaction and topological effects. In biased bilayer graphene, for instance, theor… ▽ More Combining magnetometry with optical spectroscopy has uncovered novel quantum phenomena and is emerging as a platform for quantum information science. Yet, the theory of magnetic response of excitons, correlated electron-hole pairs in semiconductors, remains incomplete due to insufficient treatment of electron-hole interaction and topological effects. In biased bilayer graphene, for instance, theoretical predictions of valley g-factor for p-excitons deviate from experiment by nearly an order of magnitude. Here, we develop a quantum theory of exciton orbital magnetic moment that reveals several conceptually new terms absent in prior theories, including an unforeseen contribution from exciton band quantum geometry. Our ab initio calculations yield results in excellent agreement with measurements, establishing the importance of a full theory including interaction and topological effects for the magnetic response of excitons. △ Less

Submitted 19 September, 2025; v1 submitted 8 September, 2025; originally announced September 2025.

Depletion-Induced Interactions Modulate Nanoscale Protein Diffusion in Polymeric Crowder Solutions

Authors: Michelle Dargasz, Nimmi Das Anthuparambil, Sebastian Retzbach, Anita Girelli, Sonja Timmermann, Johannes Möller, Wonhyuk Jo, Aliaksandr Lenonau, Agha Mohammad Raza, Maddalena Bin, Jaqueline Savelkouls, Iason Andronis, Frederik Unger, Felix Brausse, Jörg Hallmann, Ulrike Boesenberg, Jan-Etienne Pudell, Angel Rodriguez-Fernandez, James Wrigley, Roman Shayduk, Mohamed Youssef, Alexey Zozulya, Anders Madsen, Felix Lehmkühler, Fivos Perakis , et al. (4 additional authors not shown)

Abstract: Macromolecular crowding plays a crucial role in modulating protein dynamics in cellular and in vitro environments. Polymeric crowders such as dextran and Ficoll are known to induce entropic forces, including depletion interactions, that promote structural organization, but the nanoscale consequences for protein dynamics remain less well understood. Here, we employ megahertz X-ray photon correlatio… ▽ More Macromolecular crowding plays a crucial role in modulating protein dynamics in cellular and in vitro environments. Polymeric crowders such as dextran and Ficoll are known to induce entropic forces, including depletion interactions, that promote structural organization, but the nanoscale consequences for protein dynamics remain less well understood. Here, we employ megahertz X-ray photon correlation spectroscopy (MHz-XPCS) at the European XFEL to probe the dynamics of the protein ferritin in solutions containing sucrose, dextran, and Ficoll. We find that depletion-driven short-range attractions combined with long-range repulsions give rise to intermediate-range order (IRO) once the polysaccharide overlap concentration $c^*$ is exceeded. These IRO features fluctuate on microsecond to millisecond timescales, strongly modulating the collective dynamics of ferritin. The magnitude of these effects depends sensitively on crowder type, concentration, and molecular weight. Normalizing the crowder concentration by $c^*$ reveals scaling behavior in ferritin self-diffusion with a crossover near 2$c^*$, marking a transition from depletion-enhanced mobility to viscosity-dominated slowing. Our results demonstrate that bulk properties alone cannot account for protein dynamics in crowded solutions, underscoring the need to include polymer-specific interactions and depletion theory in models of crowded environments. △ Less

Submitted 9 September, 2025; v1 submitted 4 September, 2025; originally announced September 2025.

Quantum Geometry Induced Kekulé Superconductivity in Haldane phases

Authors: Yafis Barlas, Fan Zhang, Enrico Rossi

Abstract: Chiral two-dimensional electron gases, which capture the electronic properties of graphene and rhombohedral graphene systems, exhibit singular momentum-space vortices and are susceptible to interaction-induced topological Haldane phases. Here, we investigate pairing interactions in these inversion-symmetric Haldane phases of chiral two-dimensional electron gases. We demonstrate that the nontrivial… ▽ More Chiral two-dimensional electron gases, which capture the electronic properties of graphene and rhombohedral graphene systems, exhibit singular momentum-space vortices and are susceptible to interaction-induced topological Haldane phases. Here, we investigate pairing interactions in these inversion-symmetric Haldane phases of chiral two-dimensional electron gases. We demonstrate that the nontrivial band topology of the Haldane phases enhances intra-valley (${\bf Q} = \pm 2 {\bf K_D}$) pair susceptibility relative to inter-valley (${\bf Q} = 0$) pair susceptibility, favoring the emergence of a lattice-scale pair-density wave order. When longitudinal acoustic phonons mediate the pairing interaction, the system supports a chiral Kekulè superconducting order. Our findings are relevant to superconductivity in rhombohedral graphene and Kagome metals. △ Less

Submitted 24 December, 2025; v1 submitted 29 August, 2025; originally announced August 2025.

Comments: 8 pages

Doping Evolution of Nodal Electron Dynamics in Trilayer Cuprate Superconductor Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+δ}$ Revealed by Laser-Based Angle-Resolved Photoemission Spectroscopy

Authors: Hao Chen, Jumin Shi, Xiangyu Luo, Yinghao Li, Yiwen Chen, Chaohui Yin, Yingjie Shu, Jiuxiang Zhang, Taimin Miao, Bo Liang, Wenpei Zhu, Neng Cai, Xiaolin Ren, Chengtian Lin, Shenjin Zhang, Zhimin Wang, Fengfeng Zhang, Feng Yang, Qinjun Peng, Zuyan Xu, Guodong Liu, Hanqing Mao, Xintong Li, Lin Zhao, X. J. Zhou

Abstract: The doping evolution of the nodal electron dynamics in the trilayer cuprate superconductor Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+δ}$ (Bi2223) is investigated using high-resolution laser-based angle-resolved photoemission spectroscopy (ARPES). Bi2223 single crystals with different doping levels are prepared by controlled annealing which cover the underdoped, optimally-doped and overdoped regions. The elec… ▽ More The doping evolution of the nodal electron dynamics in the trilayer cuprate superconductor Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+δ}$ (Bi2223) is investigated using high-resolution laser-based angle-resolved photoemission spectroscopy (ARPES). Bi2223 single crystals with different doping levels are prepared by controlled annealing which cover the underdoped, optimally-doped and overdoped regions. The electronic phase diagram of Bi2223 is established which describes the T$_\mathrm{c}$ dependence on the sample doping level. The doping dependence of the nodal Fermi momentum for the outer (OP) and inner (IP) CuO$_2$ planes is determined. Charge distribution imbalance between the OP and IP CuO$_2$ planes is quantified, showing enhanced disparity with increasing doping. Nodal band dispersions demonstrate a prominent kink at $\sim$94$\,$meV in the IP band, attributed to the unique Cu coordination in the IP plane, while a weaker $\sim$60$\,$meV kink is observed in the OP band. The nodal Fermi velocity of both OP and IP bands is nearly constant at $\sim$1.62$\,$eVÅ independent of doping. These results provide important information to understand the origin of high T$_\mathrm{c}$ and superconductivity mechanism in high temperature cuprate superconductors. △ Less

Submitted 13 August, 2025; originally announced August 2025.

Comments: 18 pages, 4 figures

Journal ref: Chinese Physics B 34, 077404 (2025)

Cavity-Mediated Gas-Liquid Transition

Authors: Fan Zhang, Haowei Li, Wei Yi

Abstract: We study the gas-liquid transition in a binary Bose-Einstein condensate, where the two Zeeman-shifted hyperfine spin components are coupled by cavity-assisted Raman processes. Below a critical Zeeman field, the cavity becomes superradiant for an infinitesimally small pumping strength, where the enhanced superradiance is facilitated by the simultaneous formation of quantum droplet, a self-bound liq… ▽ More We study the gas-liquid transition in a binary Bose-Einstein condensate, where the two Zeeman-shifted hyperfine spin components are coupled by cavity-assisted Raman processes. Below a critical Zeeman field, the cavity becomes superradiant for an infinitesimally small pumping strength, where the enhanced superradiance is facilitated by the simultaneous formation of quantum droplet, a self-bound liquid phase stabilized by quantum fluctuations. Above the critical Zeeman field, the gas-liquid transition only takes place at a finite pumping strength after the system becomes superradiant. As the back action of the gas-liquid transition, the superradiant cavity field undergoes an abrupt jump at the first-order transition point. Furthermore, as a result of the fixed density ratio of the quantum droplet, the cavity field exhibits a linear scaling with the pumping strength in the liquid phase. These features serve as prominent signals for the cavity-mediated gas-liquid transition and coexistence, which derive from the interplay of Zeeman field, cavity-assisted spin mixing, and quantum fluctuations. △ Less

Submitted 22 June, 2025; v1 submitted 10 June, 2025; originally announced June 2025.

A pipeline for Megahertz X-ray Photon Correlation Spectroscopy on soft matter samples at the MID instrument of European XFEL

Authors: Aliaksandr Leonau, Felix Brausse, James Wrigley, Mads B. Jakobsen, Amir Tosson, Michelle Dargasz, Nimmi Das Anthuparambil, Felix Lehmkühler, Anita Girelli, Maddalena Bin, Fivos Perakis, Sebastian Retzbach, Fajun Zhang, Frank Schreiber, Matheus Teodoro, Cammille Carinan, Robert Rosca, Fabio Dall Antonia, Wonhyuk Jo, Ulrike Boesenberg, Angel Rodriguez-Fernandez, Roman Shayduk, Jörg Hallmann, Alexey Zozulya, Jan-Etienne Pudell , et al. (5 additional authors not shown)

Abstract: In this paper we present the experimental protocol and data processing framework for Megahertz X-ray Photon Correlation Spectroscopy (MHz-XPCS) experiments on soft matter samples, implemented at the Materials Imaging and Dynamics (MID) instrument of the European X-ray Free-Electron Laser (EuXFEL). Due to the introduction of a standard configuration and the implementation of a highly automated data… ▽ More In this paper we present the experimental protocol and data processing framework for Megahertz X-ray Photon Correlation Spectroscopy (MHz-XPCS) experiments on soft matter samples, implemented at the Materials Imaging and Dynamics (MID) instrument of the European X-ray Free-Electron Laser (EuXFEL). Due to the introduction of a standard configuration and the implementation of a highly automated data processing pipeline, MHz-XPCS measurements can now be conducted and analyzed with minimal user intervention. A key challenge lies in managing the extremely large data volumes generated by the Adaptive Gain Integrating Pixel Detector (AGIPD) - often reaching several petabytes within a single experiment. We describe the technical implementation, discuss the hardware requirements related to effective parallel data processing, and propose strategies to enhance data quality, in particular related to data reduction strategies and an improvement of the signal-to-noise ratio. Finally, we address strategies for making the processed data FAIR (Findable, Accessible, Interoperable, Reusable), in alignment with the goals of the DAPHNE4NFDI project. △ Less

Submitted 10 June, 2025; originally announced June 2025.

Lithography defined semiconductor moires with anomalous in-gap quantum Hall states

Authors: Wei Pan, D. Bruce Burckel, Catalin D. Spataru, Keshab R. Sapkota, Aaron J. Muhowski, Samuel D. Hawkins, John F. Klem, Layla S. Smith, Doyle A. Temple, Zachery A. Enderson, Zhigang Jiang, Komalavalli Thirunavukkuarasu, Li Xiang, Mykhaylo Ozerov, Dmitry Smirnov, Chang Niu, Peide D. Ye, Praveen Pai, Fan Zhang

Abstract: Quantum materials and phenomena have attracted great interest for their potential applications in next-generation microelectronics and quantum-information technologies. In one especially interesting class of quantum materials, moire superlattices (MSL) formed by twisted bilayers of 2D materials, a wide range of novel phenomena are observed. However, there exist daunting challenges such as reproduc… ▽ More Quantum materials and phenomena have attracted great interest for their potential applications in next-generation microelectronics and quantum-information technologies. In one especially interesting class of quantum materials, moire superlattices (MSL) formed by twisted bilayers of 2D materials, a wide range of novel phenomena are observed. However, there exist daunting challenges such as reproducibility and scalability of utilizing 2D MSLs for microelectronics and quantum technologies due to their exfoliate-tear-stack method. Here, we propose lithography defined semiconductor moires superlattices, in which three fundamental parameters, electron-electron interaction, spin-orbit coupling, and band topology, are designable. We experimentally investigate quantum transport properties in a moire specimen made in an InAs quantum well. Strong anomalous in-gap states are observed within the same integer quantum Hall state. Our work opens up new horizons for studying 2D quantum-materials phenomena in semiconductors featuring superior industry-level quality and state-of-the-art technologies, and they may potentially enable new quantum information and microelectronics technologies. △ Less

Submitted 6 June, 2025; originally announced June 2025.

Comments: published by Nano Letters

Unusual Electron-Phonon Interactions in Highly Anisotropic Two-Dimensional $Ta_2$$Ni_3$$Te_5$

Authors: Fei Wang, Qiaohui Zhou, Hong Tang, Fan Zhang, Yanxing Li, Ana M Sanchez, Keyuan Bai, Sidra Younus, Chih-Kang Shih, Adrienn Ruzsinszky, Xin Lu, Jiang Wei

Abstract: Electron-phonon interactions (EPIs) represent a fundamental cornerstone of condensed matter physics, commanding persistent attention due to their pivotal role in driving novel quantum phenomena within low-dimensional materials. Here, we unveil unusual anisotropic electron-phonon coupling behaviors in quasi-one-dimensional $Ta_2$$Ni_3$$Te_5$ nano-flakes through a powerful combination of angle-resol… ▽ More Electron-phonon interactions (EPIs) represent a fundamental cornerstone of condensed matter physics, commanding persistent attention due to their pivotal role in driving novel quantum phenomena within low-dimensional materials. Here, we unveil unusual anisotropic electron-phonon coupling behaviors in quasi-one-dimensional $Ta_2$$Ni_3$$Te_5$ nano-flakes through a powerful combination of angle-resolved polarized Raman spectroscopy and density functional perturbation theory (DFPT). High-resolution transmission electron microscopy and scanning tunneling microscopy directly visualize the pronounced quasi-one-dimensional atomic chains within the crystal structure, establishing a structural foundation for the observed anisotropic interactions. Our Raman investigations reveal remarkable polarization-dependent responses in $A_g$ phonon modes that deviate significantly from conventional behavior, which our theoretical analyses attribute to complex anisotropic electron-photon and electron-phonon interactions. Temperature-dependent Raman measurements further uncover an intriguing phonon decay mechanism involving both three- and four-phonon processes, with the latter showing significant contributions in some modes - a possible manifestation of strong anisotropic electron-phonon interactions. Beyond revealing $Ta_2$$Ni_3$$Te_5$ as an exceptional platform for exploring anisotropic EPIs, this work demonstrates that integrating angle-resolved polarized Raman spectroscopy with DFPT calculations offers a powerful methodology for investigating electron-phonon interactions in emerging low-dimensional quantum materials. △ Less

Submitted 19 July, 2025; v1 submitted 6 June, 2025; originally announced June 2025.

Floquet Möbius topological insulators

Authors: Longwen Zhou, Fan Zhang, Jiaxin Pan

Abstract: Möbius topological insulators have dispersive edge bands with Möbius twists in momentum space, which are protected by the combination of chiral and $Z_2$-projective translational symmetries. In this work, we reveal a unique type of Möbius topological insulator, whose edge bands could twist around the quasienergy $π$ of a periodically driven system and are thus of Floquet origin. By applying time-p… ▽ More Möbius topological insulators have dispersive edge bands with Möbius twists in momentum space, which are protected by the combination of chiral and $Z_2$-projective translational symmetries. In this work, we reveal a unique type of Möbius topological insulator, whose edge bands could twist around the quasienergy $π$ of a periodically driven system and are thus of Floquet origin. By applying time-periodic quenches to an experimentally realized Möbius insulator model, we obtain interconnected Möbius edge bands around zero and $π$ quasienergies, which can coexist with a gapped or gapless bulk. These Möbius bands are topologically characterized by a pair of generalized winding numbers, which are integer-quantized due to an emergent chiral symmetry at a high-symmetry point in momentum space. Numerical investigations of the quasienergy and entanglement spectra provide consistent evidence for the presence of such Möbius topological phases. A protocol based on the adiabatic switching of edge-band populations is further introduced to dynamically characterize the topology of Floquet Möbius edge bands. Our findings thus extend the scope of Möbius topological phases to nonequilibrium settings and unveil a unique class of Möbius-twisted topological edge states without static counterparts. △ Less

Submitted 31 August, 2025; v1 submitted 2 June, 2025; originally announced June 2025.

Comments: 19 pages, 10 figures

Journal ref: Phys. Rev. B 112, 134302 (2025)

Quantum-Classical Embedding via Ghost Gutzwiller Approximation for Enhanced Simulations of Correlated Electron Systems

Authors: I-Chi Chen, Aleksei Khindanov, Carlos Salazar, Humberto Munoz Barona, Feng Zhang, Cai-Zhuang Wang, Thomas Iadecola, Nicola Lanatà, Yong-Xin Yao

Abstract: Simulating correlated materials on present-day quantum hardware remains challenging due to limited quantum resources. Quantum embedding methods offer a promising route by reducing computational complexity through the mapping of bulk systems onto effective impurity models, allowing more feasible simulations on pre- and early-fault-tolerant quantum devices. This work develops a quantum-classical emb… ▽ More Simulating correlated materials on present-day quantum hardware remains challenging due to limited quantum resources. Quantum embedding methods offer a promising route by reducing computational complexity through the mapping of bulk systems onto effective impurity models, allowing more feasible simulations on pre- and early-fault-tolerant quantum devices. This work develops a quantum-classical embedding framework based on the ghost Gutzwiller approximation to enable quantum-enhanced simulations of ground-state properties and spectral functions of correlated electron systems. Circuit complexity is analyzed using an adaptive variational quantum algorithm on a statevector simulator, applied to the infinite-dimensional Hubbard model with increasing ghost mode numbers from 3 to 5, resulting in circuit depths growing from 16 to 104. Noise effects are examined using a realistic error model, revealing significant impact on the spectral weight of the Hubbard bands. To mitigate these effects, the Iceberg quantum error detection code is employed, achieving up to 40% error reduction in simulations. Finally, the accuracy of the density matrix estimation is benchmarked on IBM and Quantinuum quantum hardware, featuring distinct qubit-connectivity and employing multiple levels of error mitigation techniques. △ Less

Submitted 1 June, 2025; originally announced June 2025.

Comments: 15 pages, 5 figures

Softness and Hydrodynamic Interactions Regulate Lipoprotein Transport in Crowded Yolk Environments

Authors: Nimmi Das Anthuparambil, Michelle Dargasz, Sonja Timmermann, Anita Girelli, Sebastian Retzbach, Johannes Möller, Wonhyuk Jo, Agha Mohammad Raza, Aliaksandr Leonau, James Wrigley, Frederik Unger, Maddalena Bin, Prince Prabhu Rajaiah, Iason Andronis, William Chèvremont, Jörg Hallmann, Angel Rodriguez-Fernandez, Jan-Etienne Pudell, Felix Brausse, Ulrike Boesenberg, Mohamed Youssef, Roman Shayduk, Rustam Rysov, Anders Madsen, Felix Lehmkühler , et al. (5 additional authors not shown)

Abstract: Low-density lipoproteins (LDLs) serve as nutrient reservoirs in egg yolk for embryonic development and as promising drug carriers. Both roles critically depend on their mobility in densely crowded biological environments. Under these crowded conditions, diffusion is hindered by transient confinement within dynamic cages formed by neighboring particles, driven by solvent-mediated hydrodynamic inter… ▽ More Low-density lipoproteins (LDLs) serve as nutrient reservoirs in egg yolk for embryonic development and as promising drug carriers. Both roles critically depend on their mobility in densely crowded biological environments. Under these crowded conditions, diffusion is hindered by transient confinement within dynamic cages formed by neighboring particles, driven by solvent-mediated hydrodynamic interactions and memory effects -- phenomena that have remained challenging to characterize computationally and experimentally. Here, we employ megahertz X-ray photon correlation spectroscopy to directly probe the cage dynamics of LDLs in yolk-plasma across various concentrations. We find that LDLs undergo anomalous diffusion, experiencing $\approx$ 100-fold reduction in self-diffusion at high concentrations compared to dilute solutions. This drastic slowing-down is attributed to a combination of hydrodynamic interactions, direct particle-particle interactions, and the inherent softness of LDL particles. Despite reduced dynamics, yolk-plasma remains as a liquid, yet sluggish, balancing dense packing, structural stability, and fluidity essential for controlled lipid release during embryogenesis. △ Less

Submitted 28 May, 2025; originally announced May 2025.

Comments: 59 pages

Thermal conductivity of boron arsenide above 2100 watts per meter per Kelvin at room temperature

Authors: Ange Benise Niyikiza, Zeyu Xiang, Fanghao Zhang, Fengjiao Pan, Chunhua Li, David Broido, Ying Peng, Bolin Liao, Zhifeng Ren

Abstract: Boron arsenide (BAs) single crystals had been previously reported to have thermal conductivity of 1500 W/mK at room temperature. Now we achieved thermal conductivity above 2100 W/mK at room temperature in BAs crystals due to much lower concentration of impurities Si, C, and O grown from purified arsenic. We also observed a T-1.8 dependence of the thermal conductivity, suggesting a more significant… ▽ More Boron arsenide (BAs) single crystals had been previously reported to have thermal conductivity of 1500 W/mK at room temperature. Now we achieved thermal conductivity above 2100 W/mK at room temperature in BAs crystals due to much lower concentration of impurities Si, C, and O grown from purified arsenic. We also observed a T-1.8 dependence of the thermal conductivity, suggesting a more significant contribution from four-phonon scatterings than suggested by previous theory. We found that our experimental result can be fit with a modified theoretical calculation by tuning down the three-phonon scattering for phonons in the 4-8 THz range, although current phonon transport theory cannot provide a physical explanation. Such an advance will not only attract more effort on growing BAs single crystals and studying their practical applications but also stimulate theoretical work to predict more materials with possibly even higher thermal conductivities. △ Less

Submitted 20 May, 2025; originally announced May 2025.

Comments: The latest research on boron arsenide

High Chern Number Quantum Anomalous Hall States in Haldane-Graphene Multilayers

Authors: Yuejiu Zhao, Long Zhang, Fu-Chun Zhang

Abstract: We consider a rhombohedral-stacked $N$-layer graphene coupled to a monolayer of Haldane model. We show that high order Dirac points in multilayer graphene can be gapped out by topological proximity effect of the Haldane model layer, leading to total Chern number $|C|=N+1$ quantum anomalous Hall states. This provides a new way to construct high Chern number quantum anomalous Hall states in realisti… ▽ More We consider a rhombohedral-stacked $N$-layer graphene coupled to a monolayer of Haldane model. We show that high order Dirac points in multilayer graphene can be gapped out by topological proximity effect of the Haldane model layer, leading to total Chern number $|C|=N+1$ quantum anomalous Hall states. This provides a new way to construct high Chern number quantum anomalous Hall states in realistic crystalline graphene systems. △ Less

Submitted 24 December, 2025; v1 submitted 14 May, 2025; originally announced May 2025.

Comments: 6 pages, 4 figures

Journal ref: Phys. Rev. B 112, 235166(2025)

Vortex States and Coherence Lengths in Flat-Band Superconductors

Authors: Chuang Li, Fu-Chun Zhang, Lun-Hui Hu

Abstract: Superconductivity in flat-band systems, governed by quantum metric of Bloch states rather than the BCS framework, exhibits unique phenomena due to the vanishing electron group velocity. Here, we propose the vortex states and vortex size as direct probes to explore the quantum geometry effects in flat-band superconductors. We show that flat-band vortex bound states are sharply localized near the vo… ▽ More Superconductivity in flat-band systems, governed by quantum metric of Bloch states rather than the BCS framework, exhibits unique phenomena due to the vanishing electron group velocity. Here, we propose the vortex states and vortex size as direct probes to explore the quantum geometry effects in flat-band superconductors. We show that flat-band vortex bound states are sharply localized near the vortex core, and the energy gap between the lowest two bound states is on the order of the bulk superconducting gap. Both the spatial spread and energy scales of bound states are controlled by the flat-band's quantum metric length. Moreover, the vortex size at zero temperature, set by the quantum metric length, is atomic in scale and independent of interaction strength. Near $T_c$, the vortex size corresponds to the Ginzburg-Landau coherence length, diverges as $ξ\sim \sqrt{T_c/(T_c-T)}ξ_0$, where $ξ_0$ depends linearly on the quantum metric length. Thus, the quantum metric serves as the lower bound for vortex state spread and vortex size. We also introduce perturbations to make the flat band dispersive, and distinguish flat-band vortices from BCS-like vortices. Our results establish vortices as universal probes of quantum geometry in flat-band superconductors. △ Less

Submitted 3 May, 2025; originally announced May 2025.

Superior electrochemical performance of zinc-ion batteries with fine-grained and textured zinc anode produced by high-pressure torsion

Authors: Xinxin Hu, Shivam Dangwal, Xucheng Wang, Fan Zhang, Haijuan Kong, Jun Li, Kaveh Edalati

Abstract: Zinc-ion batteries are promising alternatives to lithium-ion batteries, offering advantages in safety, cost, and environmental impact. However, their performance is often limited by the functioning of the zinc anode. This study employs severe plastic deformation via the high-pressure torsion (HPT) method to enhance the electrochemical performance of zinc anodes. HPT reduced the grain size from >10… ▽ More Zinc-ion batteries are promising alternatives to lithium-ion batteries, offering advantages in safety, cost, and environmental impact. However, their performance is often limited by the functioning of the zinc anode. This study employs severe plastic deformation via the high-pressure torsion (HPT) method to enhance the electrochemical performance of zinc anodes. HPT reduced the grain size from >1000 μm to 20 μm and introduced a (002) basal texture. The battery assembled with HPT-processed zinc demonstrated improved cycling stability, rate performance, and specific discharge capacity (>500 mAh/g at 0.5 A/g after 50 cycles), particularly at high current densities. This performance enhancement was attributed to grain-boundary and texture effects on improved ion transfer (confirmed by electrochemical impedance spectroscopy), fast redox reaction kinetics (confirmed by cyclic voltammetry), and reduced corrosion (confirmed by microscopy and potentiodynamic polarization test). This study highlights the potential of severely deformed materials with textured fine grains for advanced rechargeable battery technologies. △ Less

Submitted 27 March, 2025; originally announced March 2025.

Isoperimetric Inequalities in Quantum Geometry

Authors: Praveen Pai, Fan Zhang

Abstract: We reveal strong and weak inequalities relating two fundamental macroscopic quantum geometric quantities, the quantum distance and Berry phase, for closed paths in the Hilbert space of wavefunctions. We recount the role of quantum geometry in various quantum problems and show that our findings place new bounds on important physical quantities. We reveal strong and weak inequalities relating two fundamental macroscopic quantum geometric quantities, the quantum distance and Berry phase, for closed paths in the Hilbert space of wavefunctions. We recount the role of quantum geometry in various quantum problems and show that our findings place new bounds on important physical quantities. △ Less

Submitted 20 March, 2025; originally announced March 2025.

Comments: 6 pages, 2 figures

High-throughput Discovery of Anti-gap Semiconductors

Authors: Zeyu Xiang, Fanghao Zhang, Bolin Liao

Abstract: Conventional semiconductors typically have bonding states near the valence band maximum (VBM) and antibonding states near the conduction band minimum (CBM). Semiconductors with the opposite electronic configuration, namely an antibonding VBM and a bonding CBM, are here termed ``anti-gap semiconductors". They have been theoretically proposed to exhibit excellent optoelectronic properties because of… ▽ More Conventional semiconductors typically have bonding states near the valence band maximum (VBM) and antibonding states near the conduction band minimum (CBM). Semiconductors with the opposite electronic configuration, namely an antibonding VBM and a bonding CBM, are here termed ``anti-gap semiconductors". They have been theoretically proposed to exhibit excellent optoelectronic properties because of their strong tolerance to defects. However, no anti-gap semiconductors have been identified so far, despite a known list of semiconductors with an antibonding VBM. Here, we use high-throughput computation to identify over 100 anti-gap semiconductors. From this group, we analyze the transition metal dichalcogenide MX$_2$ (M=Hf, Zr; X=S, Se) family in detail. In addition to verifying their defect tolerance for both electrons and holes using first-principles simulations, we also discovered that photoexcitation of charge carriers can lead to significant lattice stiffening and increased thermal conductivity in anti-gap semiconductors, which can be potentially used as photo-driven thermal switches. Our work analyzes the formation of the anti-gap electronic structure and showcases their unusual photoinduced lattice dynamics that can have a potential impact on their photophysical applications. △ Less

Submitted 19 March, 2025; originally announced March 2025.

Ab initio study of exciton insulator phase: Emergent $\textit{p}$-wave spin textures from spontaneous excitonic condensation

Authors: Fang Zhang, Jiawei Ruan, Gurjyot Sethi, Chen Hu, Steven G. Louie

Abstract: An excitonic insulator$^{1,2}$ (EI) is a correlated many-body state of electron-hole pairs, potentially leading to high-temperature condensate and superfluidity$^{3-7}$. Despite ever-growing experiments suggesting possible EI states in various materials, direct proofs remain elusive and debated. Here we address the problem by introducing an ab initio methodology, enabling the parameter-free determ… ▽ More An excitonic insulator$^{1,2}$ (EI) is a correlated many-body state of electron-hole pairs, potentially leading to high-temperature condensate and superfluidity$^{3-7}$. Despite ever-growing experiments suggesting possible EI states in various materials, direct proofs remain elusive and debated. Here we address the problem by introducing an ab initio methodology, enabling the parameter-free determination of electron-hole pairing order parameter and single-particle excitations within a Bardeen-Cooper-Schrieffer (BCS)-type formalism. Our calculations on monolayer 1T'-MoS$_{2}$$^{8,9}$ reveals that it is an unconventional EI with a transition temperature ~900K, breaking spontaneously the crystal's inversion, rotation, and mirror symmetries, while maintaining odd parity and unitarity. We identify several telltale spectroscopic signatures emergent in this EI phase that distinguish it from the band insulator (BI) phase, exemplified with a giant $\textbf{k}$-dependent $\textit{p}$-wave spin texture. △ Less

Submitted 14 March, 2025; originally announced March 2025.

Comments: 20 pages, 4 figures

The Role of Hydrogen and Oxygen Interstitial Defects in Crystalline Si cells: Mechanism of Device Degradation in Humid Environment

Authors: Bo Li, Feifei Zhang, Yu Pang, Jinyu Hu, Huiyan Zhao, Guocai Liu, Chao He, Xingtao An

Abstract: The efficiency of silicon solar cells gradually decreases in various environments, with humidity being a key factor contributing to this decline through moisture-induced degradation (MID) involving multiple mechanisms including encapsulant hydrolysis and metal ion migration. Among these mechanisms, the role of water-derived hydrogen and oxygen interstitial defects represents an underexplored yet f… ▽ More The efficiency of silicon solar cells gradually decreases in various environments, with humidity being a key factor contributing to this decline through moisture-induced degradation (MID) involving multiple mechanisms including encapsulant hydrolysis and metal ion migration. Among these mechanisms, the role of water-derived hydrogen and oxygen interstitial defects represents an underexplored yet fundamental degradation pathway. This study employs density functional theory and quantum transport theory to investigate hydrogen and oxygen interstitial defects as a novel perspective for understanding MID mechanisms. Results reveal that neutral hydrogen interstitials at bond-center sites exhibit low diffusion barriers (0.96 eV) and act as deep-level recombination centers, while oxygen interstitials face higher diffusion barriers (2.2 eV) with limited trapping capability. Device simulations demonstrate that hydrogen defects cause substantially more pronounced photovoltaic current degradation through enhanced non-radiative recombination. Critically, under humid conditions, hydrogen from water molecules readily penetrates silicon lattices forming active recombination centers, while oxygen incorporation remains kinetically limited with negligible impact. This interstitial defect perspective provides novel understanding of MID mechanisms, explaining why moisture exposure primarily degrades silicon solar cells through hydrogen rather than oxygen incorporation, offering fundamental insights for developing targeted mitigation strategies. △ Less

Submitted 15 November, 2025; v1 submitted 14 March, 2025; originally announced March 2025.

Comments: 23 pages, 5 figures

MSC Class: 82D37

A full breakthrough in vacuum ultraviolet nonlinear optical performance of NH4B4O6F

Authors: Fangfang Zhang, Zilong Chen, Chen Cui, Zhihua Yang, Miriding Mutailipu, Fuming Li, Xueling Hou, Xifa Long, Shilie Pan

Abstract: The lack of suitable vacuum ultraviolet (VUV) nonlinear optical (NLO) crystals has hindered the development of compact, high-power VUV sources via second harmonic generation (SHG). Here, we report on the development of the fluorooxoborate crystal NH4B4O6F (ABF) as a promising material for VUV light generation. For the first time, devices with specific phase-matching angles were constructed, achiev… ▽ More The lack of suitable vacuum ultraviolet (VUV) nonlinear optical (NLO) crystals has hindered the development of compact, high-power VUV sources via second harmonic generation (SHG). Here, we report on the development of the fluorooxoborate crystal NH4B4O6F (ABF) as a promising material for VUV light generation. For the first time, devices with specific phase-matching angles were constructed, achieving a record 158.9 nm VUV light through phase-matching SHG and a maximum nanosecond pulse energy of 4.8 mJ at 177.3 nm with a conversion efficiency of 5.9 %. The enhanced NLO performance is attributed to optimized arrangements of fluorine-based units creating asymmetric sublattices. This work marks a significant milestone in the field of NLO materials, facilitating the future applications of compact, high-power VUV lasers utilizing ABF. △ Less

Submitted 6 March, 2025; originally announced March 2025.

Quarter Metal Superconductivity

Authors: Chiho Yoon, Tianyi Xu, Yafis Barlas, Fan Zhang

Abstract: We investigate the recently discovered multiple superconducting states in rhombohedral graphene quarter metal. We demonstrate that one of these states features a single-spin, single-valley, single-band, single-Fermi-pocket parent state and is most likely a chiral topological pair-density wave, marked by a threefold symmetry that may not be spontaneously broken, unpaired Majorana zero modes at edge… ▽ More We investigate the recently discovered multiple superconducting states in rhombohedral graphene quarter metal. We demonstrate that one of these states features a single-spin, single-valley, single-band, single-Fermi-pocket parent state and is most likely a chiral topological pair-density wave, marked by a threefold symmetry that may not be spontaneously broken, unpaired Majorana zero modes at edges, vortices, and dislocations, and an anomalous intrinsic superconducting diode effect. △ Less

Submitted 24 February, 2025; originally announced February 2025.

Comments: 7+2 pages, 3+3 figures

Robust Super-Moiré in Large Angle Single-Twist Bilayers

Authors: Yanxing Li, Chuqiao Shi, Fan Zhang, Xiaohui Liu, Yuan Xue, Viet-Anh Ha, Qiang Gao, Chengye Dong, Yu-chuan Lin, Luke N Holtzman, Nicolas Morales-Durán, Hyunsue Kim, Yi Jiang, Madisen Holbrook, James Hone, Katayun Barmak, Joshua Robinson, Xiaoqin Li, Feliciano Giustino, Eslam Khalaf, Yimo Han, Chih-Kang Shih

Abstract: Forming long wavelength moiré superlattices (MSL) at small-angle twist van der Waals (vdW) bilayers has been a key approach to creating moiré flat bands. The small-angle twist, however, leads to strong lattice reconstruction, causing domain walls and moiré disorders, which pose considerable challenges in engineering such platforms. At large twist angles, the rigid lattices render a more robust, bu… ▽ More Forming long wavelength moiré superlattices (MSL) at small-angle twist van der Waals (vdW) bilayers has been a key approach to creating moiré flat bands. The small-angle twist, however, leads to strong lattice reconstruction, causing domain walls and moiré disorders, which pose considerable challenges in engineering such platforms. At large twist angles, the rigid lattices render a more robust, but shorter wavelength MSL, making it difficult to engineer flat bands. Here, we depict a novel approach to tailoring robust super-moiré (SM) structures that combines the advantages of both small-twist and large-twist transition metal dichalcogenides (TMDs) bilayers using only a single twist angle near a commensurate angle. Structurally, we unveil the spontaneous formation of a periodic arrangement of three inequivalent commensurate moiré (CM) stacking, where the angle deviation from the commensurate angle can tune the periodicity. Electronically, we reveal a large set of van Hove singularities (VHSs) that indicate strong band hybridization, leading to flat bands near the valence band maximum. Our study paves the way for a new platform of robust SM bilayers with structural rigidity and controllable wavelength, extending the investigation of the interplay among band topology, quantum geometry, and moiré superconductivity to the large twist angle regime. △ Less

Submitted 24 February, 2025; v1 submitted 17 February, 2025; originally announced February 2025.

Efficiently charting the space of mixed vacancy-ordered perovskites by machine-learning encoded atomic-site information

Authors: Fan Zhang, Li Fu, Weiwei Gao, Peihong Zhang, Jijun Zhao

Abstract: Vacancy-ordered double perovskites (VODPs) are promising alternatives to three-dimensional lead halide perovskites for optoelectronic and photovoltaic applications. Mixing these materials creates a vast compositional space, allowing for highly tunable electronic and optical properties. However, the extensive chemical landscape poses significant challenges in efficiently screening candidates with t… ▽ More Vacancy-ordered double perovskites (VODPs) are promising alternatives to three-dimensional lead halide perovskites for optoelectronic and photovoltaic applications. Mixing these materials creates a vast compositional space, allowing for highly tunable electronic and optical properties. However, the extensive chemical landscape poses significant challenges in efficiently screening candidates with target properties. In this study, we illustrate the diversity of electronic and optical characteristics as well as the nonlinear mixing effects on electronic structures within mixed VODPs. For mixed systems with limited local environment options, the information regarding atomic-site occupation in-principle determines both structural configurations and all essential properties. Building upon this concept, we have developed a model that integrates a data-augmentation scheme with a transformer-inspired graph neural network (GNN), which encodes atomic-site information from mixed systems. This approach enables us to accurately predict band gaps and formation energies for test samples, achieving Root Mean Square Errors (RMSE) of 21 meV and 3.9 meV/atom, respectively. Trained with datasets that include (up to) ternary mixed systems and supercells with less than 72 atoms, our model can be generalized to medium- and high-entropy mixed VODPs (with 4 to 6 principal mixing elements) and large supercells containing more than 200 atoms. Furthermore, our model successfully reproduces experimentally observed bandgap bowing in Sn-based mixed VODPs and reveals an unconventional mixing effect that can result in smaller band gaps compared to those found in pristine systems. △ Less

Submitted 24 January, 2025; originally announced January 2025.

Comments: 22 pages, 9 figures

Guided modes in graphene waveguides

Authors: Fan-Ming Zhang, Ying He, Xi Chen

Abstract: By analogy of optical waveguides, we investigate the guided modes in graphene waveguides, which is made of symmetric quantum well. The unique properties of the graphene waveguide are discussed based on the two different dispersion relations, which correspond to classical motion and Klein tunneling, respectively. It is shown that the third-order mode is absent in the classical motion, while the fun… ▽ More By analogy of optical waveguides, we investigate the guided modes in graphene waveguides, which is made of symmetric quantum well. The unique properties of the graphene waveguide are discussed based on the two different dispersion relations, which correspond to classical motion and Klein tunneling, respectively. It is shown that the third-order mode is absent in the classical motion, while the fundamental mode is absent in the Klein tunneling case. We hope these phenomena can lead to the potential applications in graphene-based quantum devices. △ Less

Submitted 14 January, 2025; originally announced January 2025.

Comments: 4 pages, 4 figures

Journal ref: Appl. Phys. Lett. 94, 212105 (2009)

Anisotropic and tunable vortex topology in multiband iron-based superconductors

Authors: Si-Qi Yu, Wei Cheng, Chuang Li, Xiao-Hong Pan, Gang Xu, Fu-Chun Zhang, Xin Liu

Abstract: Building on the multiband nature of iron-based superconductors (FeSCs), we have uncovered pronounced anisotropy in Majorana vortex topology arising from the interaction between vortex orientation and multiple electronic topologies. This anisotropy manifests in two distinct vortex configurations: the z-vortex and x-vortex, oriented perpendicular and parallel to the Dirac axis (z-axis for FeSCs), re… ▽ More Building on the multiband nature of iron-based superconductors (FeSCs), we have uncovered pronounced anisotropy in Majorana vortex topology arising from the interaction between vortex orientation and multiple electronic topologies. This anisotropy manifests in two distinct vortex configurations: the z-vortex and x-vortex, oriented perpendicular and parallel to the Dirac axis (z-axis for FeSCs), respectively. The x-vortex exhibits a unique duality, displaying two distinct topological phase diagrams. One is strikingly simple, comprising only trivial and topological superconducting phases, and remains resilient to multiband entanglement. The other mirrors the z-vortex's complex diagram, featuring alternating trivial, topological crystalline and topological superconducting phases. Crucially, the former is exclusive to the x-vortex and supports unpaired Majorana vortices across a wide parameter range, even with Dirac nodes in electronic bands. Notably, uniaxial strain can modulate these x-vortex phases, enabling the x-vortex to support both stable Majorana vortices and rich exotic physics in a controllable manner. Moreover, we propose that the x-vortex offers promising advantages for developing iron-based superconducting quantum devices. Our findings introduce a novel paradigm in vortex topology within multiband superconducting systems, highlighting the x-vortex as a promising platform for exploring Majorana physics and advancing iron-based superconducting quantum technology. △ Less

Submitted 30 December, 2024; v1 submitted 26 December, 2024; originally announced December 2024.

Comments: 7 pages + 4 figures

Self-doped Molecular Mott Insulator for Bilayer High-Temperature Superconducting La3Ni2O7

Authors: Zhan Wang, Heng-Jia Zhang, Kun Jiang, Fu-Chun Zhang

Abstract: The bilayer structure of recently discovered high-temperature superconducting nickelates La$_3$Ni$_2$O$_7$ provides a new platform for investigating correlation and superconductivity. Starting from a bilayer Hubbard model, we show that there is a molecular Mott insulator limit formed by the bonding band owing to Hubbard interaction $U$ and large interlayer coupling. This molecular Mott insulator b… ▽ More The bilayer structure of recently discovered high-temperature superconducting nickelates La$_3$Ni$_2$O$_7$ provides a new platform for investigating correlation and superconductivity. Starting from a bilayer Hubbard model, we show that there is a molecular Mott insulator limit formed by the bonding band owing to Hubbard interaction $U$ and large interlayer coupling. This molecular Mott insulator becomes self-doped due to electrons transferred to the antibonding bands at a weaker interlayer coupling strength. The self-doped molecular Mott insulator is similar to the doped Mott insulator studied in cuprates. We propose La$_3$Ni$_2$O$_7$ to be a self-doped molecular Mott insulator, whose molecular Mott limit is formed by two nearly degenerate antisymmetric $d_{x^2-y^2}$ and $d_{z^2}$ orbitals. Partial occupation of higher energy symmetric $d_{x^2-y^2}$ orbital leads to self-doping, which may be responsible for high-temperature superconductivity in La$_3$Ni$_2$O$_7$. The effects of Hund's coupling $J_H$ on the low-energy spectra are also studied via exact diagonalization. The proposed low-energy theory for La$_3$Ni$_2$O$_7$ is found to be valid in a wide range of $U$ and $J_H$. △ Less

Submitted 28 May, 2025; v1 submitted 24 December, 2024; originally announced December 2024.

Comments: 8+5 pages, 5+1 figures

Journal ref: National Science Review 12, nwaf353 (2025)

Intrinsic pinning of FeSe$_1$$_-$$_x$S$_x$ single crystals probed by torque magnetometry

Authors: Nan Zhou, Yue Sun, Q. Hou, T. Sakakibara, X. Z. Xing, C. Q. Xu, C. Y. Xi, Z. S. Wang, Y. F. Zhang, Y. Q. Pan, B. Chen, X. Luo, Y. P. Sun, Xiaofeng Xu, T. Tamegai, Mingxiang Xu, Zhixiang Shi

Abstract: Intrinsic pinning is caused by natural pinning centers that occur because of the modulation of the order parameter or weak superconducting layers. Early work has shown that intrinsic pinning generates a high pinning force and critical current density in some layered oxide superconductors. Studying the intrinsic pinning of superconductors is crucial for both fundamental studies and potential applic… ▽ More Intrinsic pinning is caused by natural pinning centers that occur because of the modulation of the order parameter or weak superconducting layers. Early work has shown that intrinsic pinning generates a high pinning force and critical current density in some layered oxide superconductors. Studying the intrinsic pinning of superconductors is crucial for both fundamental studies and potential applications. Herein, we use torque magnetometry to study angle-resolved in-plane and out-of-plane magnetic torque for a series of high-quality FeSe$_1$$_-$$_x$S$_x$ single crystals. A fourfold torque signal was observed when the magnetic field was within the \textit{ab} plane. We interpret that this fourfold in-plane irreversible torque is from the intrinsic pinning due to combined effects of gap nodes/minimum and twin domains. Additionally, we attributed the observed out-of-plane torque peaks to intrinsic pinning due to the layered structure. △ Less

Submitted 6 December, 2024; originally announced December 2024.

Comments: 10 pages, 7 figures

Journal ref: Materials Today Physics 37 (2023) 101195

Multiple magnetic orders discovered in the superconducting state of EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$

Authors: Nan Zhou, Yue Sun, Ivan S. Veshchunov, S. Kittaka, X. L. Shen, H. M. Ma, W. Wei, Y. Q. Pan, M. Cheng, Y. F. Zhang, Y. Kono, Yuping Sun, T. Tamegai, Xuan Luo, Zhixiang Shi, Toshiro Sakakibara

Abstract: The interplay between superconductivity and magnetism is an important subject in condensed matter physics. EuFe$_{2}$As$_{2}$-based iron pnictides could offer an interesting plateau to study their relationship that has attracted considerable attention. So far, two magnetic phase transitions were observed in EuFe$_{2}$As$_{2}$-based crystal, which were deemed to originate from the itinerant Fe mome… ▽ More The interplay between superconductivity and magnetism is an important subject in condensed matter physics. EuFe$_{2}$As$_{2}$-based iron pnictides could offer an interesting plateau to study their relationship that has attracted considerable attention. So far, two magnetic phase transitions were observed in EuFe$_{2}$As$_{2}$-based crystal, which were deemed to originate from the itinerant Fe moments ($\sim$ 190 K) and the localized Eu$^{2+}$ moments ($\sim$ 19 K), respectively. Here, we systematically studied the heat capacity for the EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ crystals with \textit{x} = 0.21 (optimally doped) and \textit{x} = 0.29 (overdoped). We have found two new magnetic orders in the superconducting state (ranging from 0.4 to 1.2 K) in the optimally doped crystal. As more P was introduced into the As site, one of the magnetic orders becomes absent in the overdoped crystal. Additionally, we observed strong field and orientation dependence in heat capacity. The present findings in EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ have detected the new low-temperature magnetic orders, which may originate from the localized Eu$^{2+}$ spins order or the spin reorientation. △ Less

Submitted 6 December, 2024; originally announced December 2024.

Comments: 14 pages, 12 figures

Journal ref: New J. Phys. 26 (2024) 093008