arXiv subjects

Sheng Ran

Publications and source records attributed to Sheng Ran.

At least 19 recordsLinked to original sources

arXiv2026

SeriesXRD: automated reflection tracking and phase identification in high-pressure X-ray diffraction series

High-pressure synchrotron X-ray diffraction increasingly produces hundreds to thousands of detector frames in a single experiment, while separating, assigning, and tracking weak reflections across an entire series often remain manual. This bottleneck is particularly severe for micron- and nanoscale samples in diamond-anvil cells, where scattering from the anvils, gasket, pressure medium, and pressure markers can dominate the sample signal. We present SeriesXRD, an open-source workflow that analyzes diffraction as a series rather than as independent patterns. The program suppresses azimuthally localized diamond scattering, subtracts background, fits and tracks reflections between frames, matches known phases using pressure-dependent lattice parameters, subtracts confidently assigned contributions, and groups persistent unexplained reflections for follow-up as candidate sample-associated or unknown-phase features. We demonstrate the method on 1288 frames collected from an approximately 30-nm-thick layered UOTe flake in a diamond-anvil cell over 3.5-50.7 GPa. The dataset is strongly background dominated, with detectable UOTe diffraction in only approximately 4% of the frames. SeriesXRD recovered the sample-associated reflections identified in the original manual analysis while reducing the corresponding phase-assignment and residual-analysis workflow from more than two months of researcher time to an overnight automated run. Across the full series, 17,143 peaks were fitted, 14,395 passed quality criteria, and 90% of accepted peaks were assigned to known background or reference phases. SeriesXRD therefore converts large, background-dominated diffraction series into a tractable set of phase assignments and coherent unexplained reflections while retaining a traceable record of each decision.

cond-mat.mtrl-sci↗

arXiv2026

Quantum noise spectroscopy of superconducting dynamics in a cuprate thin film

Characterizing the low-energy dynamics of quantum materials is crucial for understanding strongly correlated electronic states, yet remains experimentally challenging, particularly in two-dimensional systems. Here, we leverage nitrogen-vacancy (NV) centers in diamond as a non-invasive quantum sensor to study thin-film Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (BSCCO), revealing several distinct dynamical phenomena across the superconducting phase diagram. At zero magnetic field and low temperatures, NV depolarization ($T_1$) spectroscopy captures GHz-scale noise from nodal quasiparticle excitations, consistent with Bardeen--Cooper--Schrieffer (BCS) mean-field theory. Near the critical temperature $T_c \approx 90$ K, supercurrent-fluctuation-induced noise sharply reduces $T_1$. By analyzing the temperature scaling of $T_1$, we observe clear deviations from mean-field prediction, reflecting the importance of order parameter fluctuations and enabling the determination of critical exponents. Under a small magnetic field, a broad and asymmetric reduction of $T_1$ unveils a liquid-like phase of mobile vortices. NV decoherence ($T_2$) spectroscopy further probes MHz-scale noise and reveals complex vortex-solid fluctuations well below $T_c$. Our results establish quantum noise spectroscopy as a non-invasive probe of superconducting dynamics over frequency and length scales complementary to existing techniques.

cond-mat.supr-con↗

arXiv2026

A Chiral Superlattice Route to Spin-Split Topological Antiferromagnetism

The interplay between chirality and magnetism is a profound topic, spanning particle physics, condensed matter, chemistry and origin of life. In this paper, we study this interplay in the new antiferromagnet (AFM) UOTe, and we report a chiral superlattice route to spin-split topological phenomena from collinear antiferromagnetism. Pristine UOTe is a collinear AFM without Berry curvature or spin-split bands. However, we identify the spontaneous formation of a chiral superlattice in UOTe, which can be viewed as frozen chiral phonons at finite wave vector. When electrons move through the chiral superlattice, their orbital Bloch wavefunction and quantum geometry are modulated by the strong chiral superlattice potential, generating large Berry curvature in the chiral superlattice, which we detect by the nonlinear Hall effect. At 150 K, the chiral superlattice induced Berry curvature couples to the collinear AFM order, generating a giant anomalous Hall angle ~0.14 abruptly near $T_N$ that is among the largest in bulk magnets. Moreover, our spin Hanle precession measurement shows that the chiral superlattice also generates spin-polarized current from the collinear AFM, a long-standing goal in spintronics. We shed light on the supermodulation formation mechanism based on chemical ion size and physical interlayer-intralayer energy competitions, using which we propose a design principle to discover similar bond-mismatch superlattices, providing a chiral superlattice pathway through real space engineering of quantum geometry.

cond-mat.mes-hall↗

arXiv2026

Crystal Structure Based Graph Neural Network And LLM Multi-Modal Approach for Material Magnetic Ordering Prediction

AI/ML models are useful for the prediction of materials' properties. Recently, there has been great progress in developing Neural Network models to predict the properties of solids, molecules, and crystals, avoiding expensive and time-consuming laboratory testing. This study presents a novel AI/ML-based multi-modal approach to predict material magnetic ordering using material crystal structure information as input to a Graph Neural Network model (GNN) and semantic text descriptions of the material's properties and structure as input to a Large Language Model (LLM), before performing information fusion of the GNN and LLM outputs to predict material magnetic ordering in four classes (Non-magnetic, Ferromagnetic, Antiferromagnetic, Ferrimagnetic). The model is trained, validated, and tested on a dataset which is a combination of Materials Project dataset, Magndata dataset, and a set of uranium compounds with magnetic ordering determined in laboratory testing, with an 80/10/10 (training/validation/testing) data split. The proposed GNN and LLM multi-modal approach achieves better overall accuracy than both the standalone GNN and LLM approaches with three fusion strategies.

cond-mat.mtrl-sci↗

arXiv2026

Hexagonal Stacking Maximizes Proton Configurational Entropy among Ice-I Polytypes

Ice I admits cubic, hexagonal, and mixed layer stackings, but rigorous comparisons of its proton configurational entropy have focused on the two ideal endmembers. We identify every cyclic uniform-registry ice-I stacking with a word in a nonnegative layer-transfer operator and its transpose. Applying the Schatten-Hölder inequality to every even-length word proves that alternating hexagonal stacking maximizes the ice-rule configuration count at each common finite cross-section. Consequently, hexagonal ice maximizes the thermodynamic configuration constant among all periodic uniform-registry ice-I polytypes. We also construct rigorous lower and upper bounds without finite-size extrapolation. Restricting Nagle's positive even-subgraph expansion to disjoint blocks gives the lower bound; Finner's hypergraph Hölder inequality and rational Collatz-Wielandt certificates for two-replica prism operators give the upper bounds. The resulting configuration constant $w$, whose logarithm is the entropy per molecule in units of Boltzmann's constant, satisfies $1.503360 \le w \le 1.540196$, with the sharper cubic-ice ceiling $w \le 1.527699$. The same bracket controls lower and upper configuration growth rates of fixed aperiodic stackings along the specified prism-tileable exhaustions. These results establish hexagonal stacking as a possibly nonunique maximizer; equality of the cubic and hexagonal entropy constants remains unresolved.

cond-mat.stat-mech↗

arXiv2026

A d-Electron Heavy-Fermion-Like Superconductor with Frustration-Induced Flat Bands

Heavy-fermion superconductors are mostly associated with f-electron materials with Kondo lattices, while known d-electron heavy-fermion-like systems are often linked to orbital-selective local moments, Hund-metal physics, or a charge-density-wave mechanism. Here we report Mo4PtGa17, a noncentrosymmetric itinerant d-electron superconductor with a geometrically frustrated breathing-pyrochlore Mo lattice. Thermodynamic, transport and NMR measurements reveal heavy-fermion-like behavior superconductivity and dominant ferromagnetic spin fluctuations near a ferromagnetic instability. Theoretical calculations identify nearly flat bands, van Hove singularities and Kramers nodal lines near the Fermi energy, derived intrinsically from Mo-4d states and are robust against on-site electronic correlations. These results suggest that the geometrically frustrated lattice in Mo4PtGa17 generates an intriguing electronic structure that enhances the density of states, spin susceptibility and quasiparticle mass. Mo4PtGa17 therefore identifies a unique route to heavy-fermion-like superconductivity in d-electron materials through geometrical frustration, different from the previously reported systems.

cond-mat.str-el↗

arXiv2026

Field-rigid Ising antiferromagnetism with giant spin-flip fields in Van der Waals UOTe

Van der Waals antiferromagnets provide a route to thickness-controlled magnetic order, but few combine high-temperature Ising order with conducting, correlated, and topological electronic structure. Here we show that UOTe realizes this combination. Magnetic susceptibility reveals a strongly anisotropic paramagnetic response, while neutron diffraction establishes c-axis antiferromagnetic order below $T_N \simeq 150$ K with an order-parameter exponent $β= 0.14$, close to the two-dimensional Ising value. Torque magnetometry further shows that the ordered state remains well described by a uniaxial antiferromagnet below the high-field transition. Pulsed-field magnetization up to 73 T shows that the ordered state survives to very large fields applied along the c axis before entering a broad metamagnetic regime that begins near 50 T, and remains unsaturated at the highest measured field. Angle-dependent proximity detector oscillator measurements show that the metamagnetic instability is set by the field component along the ordered moment direction, providing direct evidence for Ising-like field rigidity. UOTe therefore establishes a field-rigid Ising antiferromagnet with giant spin-flip fields in a compensated Van der Waals metal, where high-temperature c-axis order, quasi-two-dimensional magnetic criticality, Kondo-associated uranium 5f hybridization, metallic transport, and symmetry-enabled topology coexist in a single material.

cond-mat.str-el↗

arXiv2026

Endogenous Regime Switching Driven by Scalar-Irreducible Learning Dynamics

Achieving endogenous regime switching is crucial for the emergence of autonomous intelligence, yet remains a central challenge for existing machine learning frameworks, where such transitions are typically externally imposed. In this work, we introduce a classification that distinguishes scalar-reducible dynamics, which can be expressed as gradient flows driven by a scalar objective, from scalar-irreducible dynamics that cannot be reduced to such a form. While most existing machine learning systems operate within the scalar-reducible class, we demonstrate that scalar-irreducible dynamics naturally enable internally generated regime switching through feedback between fast dynamical variables and slow structural adaptation. Using a minimal dynamical model, we illustrate how this mechanism produces sustained endogenous regime transitions without external scheduling. Our results suggest a new dynamical paradigm for regime exploration and provide a potential route toward autonomous learning systems whose adaptive behavior is organized internally rather than externally prescribed.

cs.LG↗

arXiv2026

Signature of Unconventional Superconductivity in the High Temperature Normal State Resistivity

Unconventional superconductivity remains one of the central unsolved problems in quantum materials, and revealing its connection to the normal state is widely believed to be key to uncovering the pairing mechanism. Previous efforts have largely focused on the temperature range immediately above the superconducting transition, where specific scattering channels-such as strange-metal transport-have been identified as sharing a possible microscopic origin with superconductivity. Here, using machine learning, we demonstrate a strong correlation between normal-state resistivity and superconductivity in Fe-based superconductors. Remarkably, the predictive information reside in a wide window of 150-300 K, far above $T_c$ of this family. We further show that the signatures of superconductivity are distributed across multiple scattering channels, which requires further theoretical investigation.

cond-mat.supr-con↗

arXiv2026

Scaling Breakdown as a Signature of Spinon-Gauge Interaction in the Quantum Spin Liquid YbZn$_2$GaO$_5$

Scaling behavior in magnetization has been reported in a wide range of quantum spin liquid (QSL) candidates and is often interpreted as evidence for scale-free spin liquid physics. Here we present a comprehensive scaling analysis of high-field magnetization measurements on the QSL material YbZn$_2$GaO$_5$. Between 5 K and 70 K, $M(H)$ displays scale invariance resembling that of a zero-field quantum critical point. Below 3 K, we observe a breakdown of this scale invariance that cannot be recovered by simply changing the critical exponents. This temperature coincides with the onset of enhanced spin correlations observed in $μ$SR measurements. Moreover, the form of the deviation from scaling is consistent with collective spinon excitations coupled via emergent gauge interactions. These results indicate that the breakdown of scaling reflects the emergence of intrinsic low-energy excitations upon entering the QSL regime. Our work clarifies that magnetic scaling is associated with quantum critical fluctuations rather than with the spin liquid phase itself, and establishes magnetization scaling as a sensitive thermodynamic probe of emergent energy scales in QSL systems.

cond-mat.str-el↗

arXiv2026

Limited coincidence between ultrahigh-field superconductivity and line of metamagnetic endpoints in UTe$_2$

The field-dependent magnetization of UTe$_2$ was measured through the metamagnetic transition at a variety of field angles, tracking how the step in magnetization evolves with fields tilted away from the $b$ axis. For fields oriented within the $ab$ plane, jumps in both $M_a$ and $M_b$ vanish approximately 18° away from the $b$ axis. From contactless conductivity measurements, we find that the halo-like high-field superconducting region extends to the $ab$ plane, where it exists only within a very narrow ($<$1°) angular range near the termination of the metamagnetic phase boundary and extends beyond the highest measured field of 73 T. As the field orientation tilts towards the $c$ axis, the superconducting and metamagnetic phase boundaries no longer coincide and exhibit distinct trends.

cond-mat.supr-con↗

arXiv2026

Kondo driven suppression of charge density wave in Van der Waals material UTe$_3$

Competing electronic instabilities lie at the heart of emergent phenomena in quantum materials. In low-dimensional metals, Fermi-surface nesting can drive charge density wave (CDW) formation through a Peierls-like mechanism, while in strongly correlated systems, Kondo hybridization reconstructs the electronic structure by entangling localized moments with itinerant electrons. How these two fundamentally different instabilities interact$-$whether they coexist, compete, or mutually exclude each other$-$remains an open question. Here, we present suppression of charge density wave via the Kondo interaction in van der Waals material UTe$_3$. The angle-resolved photoemission spectroscopy (ARPES) data reveals Fermi surface nesting under similar conditions as seen in RETe$_3$ compounds. Despite that, no CDW is found in UTe$_3$ after an extensive search. We demonstrate that strong hybridization between U 5$f$ electrons and Te $p$ states reconstructs the low-energy electronic structure, removes the instability, and preempts CDW formation. Our results reveal a rare example where Kondo hybridization preempts density wave formation, offering a new route to controlling ordering phenomena in correlated 2D materials.

cond-mat.str-el↗

arXiv2026

Kondo Reshapes Multiple Orders in a $5f$ van der Waals Material

Electron interactions can drive magnetism, superconductivity, and topology. However, the realization of these phases remains limited in van der Waals materials, and the full landscape of strong correlations remains uncharted in any context. While interactions between conduction electrons and localized spins yield a well-known competition between heavy fermions (Kondo hybridization) and magnetic order (RKKY exchange), such spin-driven competition represents only part of the correlated electron phase diagram. Here we demonstrate that a heavy-fermion state can also compete with charge order, such as the charge density wave (CDW) state typical in the van der Waals $4f$ rare-earth tritellurides (RTe$_3$). We exploit the spatially-extended $5f$ orbitals of $β$-UTe$_3$ to enhance Kondo hybridization compared to its isostructural RTe$_3$ cousins. Our scanning tunneling spectroscopy on $β$-UTe$_3$ shows Fano resonances characteristic of the heavy fermion state, while our quasiparticle interference imaging reveals the disappearance of Fermi-level nesting and the appearance of flat bands. We extend the tritelluride tight-binding model to include Kondo coupling and quantify the Fermi surface reconstruction. Consistent with the destruction of nesting, we observe no CDW in $β$-UTe$_3$. Our expansion of the Kondo phase diagram beyond spin-mediated competition opens new possibilities for proximity-induced phase engineering in correlated van der Waals heterostructures.

cond-mat.str-el↗

arXiv2026

Learning Beyond Optimization: Stress-Gated Dynamical Regime Regulation in Autonomous Systems

Despite their apparent diversity, modern machine learning methods can be reduced to a remarkably simple core principle: learning is achieved by continuously optimizing parameters to minimize or maximize a scalar objective function. This paradigm has been extraordinarily successful for well-defined tasks where goals are fixed and evaluation criteria are explicit. However, if artificial systems are to move toward true autonomy-operating over long horizons and across evolving contexts-objectives may become ill-defined, shifting, or entirely absent. In such settings, a fundamental question emerges: in the absence of an explicit objective function, how can a system determine whether its ongoing internal dynamics are productive or pathological? And how should it regulate structural change without external supervision? In this work, we propose a dynamical framework for learning without an explicit objective. Instead of minimizing external error signals, the system evaluates the intrinsic health of its own internal dynamics and regulates structural plasticity accordingly. We introduce a two-timescale architecture that separates fast state evolution from slow structural adaptation, coupled through an internally generated stress variable that accumulates evidence of persistent dynamical dysfunction. Structural modification is then triggered not continuously, but as a state-dependent event. Through a minimal toy model, we demonstrate that this stress-regulated mechanism produces temporally segmented, self-organized learning episodes without reliance on externally defined goals. Our results suggest a possible route toward autonomous learning systems capable of self-assessment and internally regulated structural reorganization.

cs.LG↗

arXiv2026

Layer-dependent antiferromagnetic Chern and axion insulating states in UOTe

Magnetic topological insulators have received significant interest due to their dissipationless edge states, which promise advances in energy-efficient electronic transport. However, the magnetic topological insulator state has typically been found in ferromagnets (FMs) that suffer from low magnetic ordering temperatures and stray fields. Identifying an antiferromagnetic topological insulator that exhibits the quantum anomalous Hall effect (QAHE) with a relatively high Néel temperature has been a longstanding challenge. Here, we focus on the recently discovered van der Waals (vdW) antiferromagnet (AFM) UOTe, which not only features a high Néel temperature ($\sim$150K) but also exhibits intriguing Kondo interaction and topological characteristics. Our systematic analysis of the layer-dependent topological phases based on \textit{ab} initio computations predicts the two-layer UOTe film to be an ideal 2D AFM Chern insulator in which the Hall conductivity is quantized with a fully compensated spin magnetization. By applying an in-plane strain or electric field, we show how the itinerancy of U-5f electrons can be manipulated to trigger a transition between the nontrivial ($C = 1$) and trivial ($C = 0$) phases. Interestingly, the 3-layer UOTe film is found to have zero charge conductance but it hosts a quantized spin Hall conductivity (SHC) with finite magneto-electric coupling, suggesting the presence of an axion insulator-like state. The unique magnetic structure of UOTe supports a layer-tunable topology in which films with an odd number of layers are axion-like insulators, while films with an even number of layers are Chern insulators, and the bulk material is a Dirac semimetal. Our study offers a new intrinsic AFM materials platform for realizing correlated topological phases for next-generation spintronics applications and fundamental science studies.

cond-mat.mtrl-sci↗

arXiv2026

Visualizing the low-energy electronic structure of the triplet superconductor UTe$_2$ through quasiparticle interference

The identification, control and theoretical modelling of spin-triplet superconductors (STC) remain a central theme in quantum materials research. Intrinsic STC are rare but offer rich condensate properties and unique surface properties allowing insights into the nature of the spin-triplet order, and promising applications in quantum technologies. Owing to interactions, the order parameter in STCs can often be intertwined with other symmetry breaking orders like charge/spin density waves (CDW/SDW) or pair density waves (PDW) complicating their phase diagrams. UTe2 stands out as the only known odd-parity, STC that harbors such intertwined orders on the surface and possible topological surface states composed of Majorana fermions. While the (0-11) facet is the most heavily studied, the fermiology of this surface that gives rise to such exotic phenomena is still lacking and continues to be an area of active interest. Here, we employ low-temperature spectroscopic imaging to reveal the Fermi surface of UTe2 through quasiparticle interference. We find scattering originating from the uranium-derived bands that play a major role in the formation of the CDW and the PDW phases. Tunneling spectroscopy further reveals spectral signatures of the CDW gap, corroborating its onset temperature. Suppressing the CDW with a magnetic field, highlights the presence of small, circular Fermi pockets that disperse strongly near the Fermi energy. We discuss the nature of the interference patterns and the origin of the small Fermi pockets in the context of the calculated band structure and the unconventional CDW phase.

cond-mat.supr-con↗

arXiv2026

Enhancement of antiferromagnetic spin fluctuations in UTe$_2$ under pressure revealed by $^{125}$Te NMR

Characterizing magnetic fluctuations is one of the keys to understanding the origin of superconductivity in the spin-triplet superconductor UTe$_2$ which exhibits two superconducting (SC) phases (SC1 and SC2) under pressure: SC1 where a superconducting transition temperature of $T_{\rm c}$ decreases with pressure while $T_{\rm c}$ of SC2 rises with pressure. Previously, D. Ambika et al. [Phys. Rev. B 105, L220403 (2022)] have reported the possible coexistence of ferromagnetic (FM) and antiferromagnetic (AFM) spin fluctuations in UTe$_2$ under pressure from their nuclear magnetic resonance (NMR) measurements. To delve the relationship between the magnetic fluctuations and the two SC phases, we have carried out detailed $^{125}$Te NMR measurements on a single crystal of UTe$_2$ with $T_{\rm c}$ = 1.6 K at various pressures ranging from 0 to 2.05 GPa. By comparing the temperature $T$ dependence of nuclear spin-lattice relaxation rates divided by temperature 1/$T_1T$ with that of the Knight shift $K$ for magnetic fields along the $a$, $b$, and $c$ directions, we evidence the enhancement of AFM spin fluctuations with increasing pressure. Based on the results, we suggest that FM spin fluctuations are more favorable for SC1 and AFM spin fluctuations are crucial for SC2. Our findings will inspire further study on this material to understand the peculiar SC phases in detail.

cond-mat.supr-con↗

arXiv2025

Visualizing Pair-breaking Scattering Interference in Bulk FeSe

Spatially periodic modulations of the superconducting gap have been recently reported in diverse materials and are often attributed to pair density wave order. An alternative mechanism, termed pair-breaking scattering interference (PBSI), was proposed to produce gap modulations without finite-momentum pairing. Here we investigate signatures of PBSI in bulk FeSe using scanning tunneling microscopy with superconductive tips, enabling enhanced energy resolution and Josephson tunneling. Subsurface magnetic scatterers with Yu-Shiba-Rusinov states are identified in FeSe, around which we observe particle-hole symmetric gap modulations accompanied by spatial modulation of the Josephson current. Those modulations have wavevectors consistent with intra-pocket PBSI. We further demonstrate that phase-referenced quasiparticle interference imaging offers an independent and direct probe of PBSI beyond gap mapping. These results establish PBSI as a viable origin of gap modulations in superconductors lacking preexisting charge/spin density wave orders, and motivate further investigation of the intriguing gap modulation phenomenology.

cond-mat.supr-con↗