Statistical Mechanics
Monte Carlo study of the superfluid phase of $^4$He
Massimo Boninsegni
Detailed numerical results obtained with state-of-the-art
Quantum Monte Carlo (QMC) simulations are presented for the superfluid phase of $^4$He at saturated vapor pressure. The aim of this contribution is that of providing reliable, up-to-date estimates for this archetypal superfluid, reflecting the methodological progress that has taken place over the past two decades. We simulate a system comprising 2,048 helium atoms, i.e., an order of magnitude greater in size than those for which results currently regarded as standard references were originally obtained. We offer revised estimates for energetic and structural properties, as well as for the ground state condensate fraction.
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Mesoscale and Nanoscale Physics
Suppressing spin qubit decoherence during shuttling via confinement modulation
Daniel Q. L. Nguyen, Maximilian Rimbach-Russ and Stefano Bosco
Reliable long-range
qubit shuttling is a powerful tool for scalable
quantum computing architectures. We investigate strategies to improve the coherence of moving
spin qubits by performing continuous dynamical decoupling by modulating their confinement potential. Specifically, we introduce temporal and spatial breathing shuttling protocols that leverage
spin-orbit interactions in hole-
spin systems to electrically drive the
qubit while moving. This enables efficient dressed-state shuttling, where the
spin is continuously rotated during transport, suppressing the effect of low-frequency noise. Using the filter function formalism, we identify driving regimes that efficiently mitigate both global and local
magnetic and electric noise sources. We find that confinement-modulated shuttling can significantly enhance coherence during transport, while revealing distinct limitations depending on the correlation length of the noise. Applying our framework to germanium hole-
spin qubits, we show that these protocols provide a practical route toward noise-resilient long-range coherent
quantum links.
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Materials Science
Coordination Engineering of Dual-Atom Catalysts for Overall Water Splitting: Mechanistic Insights from Constant-Potential First-Principles and Machine Learning
Jiahang Li, Suhang Li, Chong Yan et al. (+4 more)
The rational design of bifunctional electrocatalysts for the hydrogen
evolution reaction (HER) and oxygen
evolution reaction (OER) is essential for achieving efficient and cost-effective overall water splitting. Atomically dispersed transition-metal catalysts, including single-atom catalysts and dual-atom catalysts (DACs), have emerged as a prominent class of heterogeneous catalysts, in which coordination engineering plays a decisive role in tuning catalytic performance. Herein, we explore coordination-engineered bifunctional overall water splitting electrocatalysts using
graphene-supported DACs (TM1TM2-C6-xNx) as model systems. By tuning C/N coordination and dual-metal combinations (Fe, Co, Ni, and Cu), a library of 228 structures was constructed. A three-step screening strategy, combining constant-charge and constant-potential density functional theory with kinetic analysis of
proton-coupled electron transfer (PCET), identifies 24 highly active candidates (TM1TM2 = CoNi, CoCu and Co2) with mixed C/N coordination for OER. These catalysts exhibit overpotentials comparable to that of IrO2 and low PCET barriers (lower than 0.40 eV), among which 22 also show high HER activity. Machine learning reveals clear coordination-dependent structure-performance relationships. Such bifunctionality arises from coordination engineering that enables the simultaneous optimization of OER intermediate adsorption and the hydrogen binding strength for HER. This work establishes coordination engineering as an effective strategy for designing high-performance bifunctional dual-atom electrocatalysts for overall water splitting.
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All authors Jiahang Li, Suhang Li, Chong Yan, Jiajun Yu, Qinzhuang Liu, Ruo-Ya Wang, Dongwei Ma
Superconductivity
Superconducting diode effect in correlated electron systems by nonreciprocal magnetism
Kyohei Nakamura and Youichi Yanase
The superconducting diode effect (SDE), characterized by a nonreciprocal critical current in
superconductors, has recently been observed in strongly correlated electron systems and near
quantum criticality, pointing to unconventional mechanisms beyond weak-coupling theories. Here we investigate the SDE in the Rashba-Zeeman-Hubbard model, which captures $d$-wave superconductivity in an
antiferromagnetic quantum critical regime, using the Dyson-Gor'kov equation with the fluctuation exchange approximation. We show that electron correlations suppress the conventional intrinsic SDE arising from depairing currents. More importantly, a supercurrent nonreciprocally induces
antiferromagnetic order, which fundamentally governs the critical current and enables perfect diode efficiency. Our results reveal a previously unrecognized correlation-driven mechanism of the SDE and establish strongly correlated
superconductors as a platform for superconducting diode physics.
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Materials Science
Coordination-Induced Tuning of Ligand-Centered Red Emission in a cis-[Cd(Tz)2(py)2] Complex for Light-Emitting Diodes
Samara M. da Silva, R. F. Silva, A. Nonato et al. (+6 more)
Organic–inorganic complexes are promising materials for light-emitting applications. Here, we report a new organometallic complex, cis-[Cd(Tz)$_2$(py)$_2$], featuring a distorted octahedral Cd(II) coordination environment. IR and Raman spectroscopy reveal pronounced coordination-induced changes, particularly in the Raman response of the triazene moiety, indicating electronic and structural perturbation upon Cd(II) complexation. Hirshfeld surface analysis shows that the
crystal packing is mainly governed by H$\cdots$H, O$\cdots$H/H$\cdots$O, and C$\cdots$H/H$\cdots$C contacts, whereas $\pi$–$\pi$ stacking interactions contribute modestly. Solid-state UV–Vis spectroscopy reveals broad absorption from $\sim$700 to 200 nm and a direct optical band gap of 1.83 eV, indicating
semiconductor-like behavior. Photoluminescence measurements show a broad emission band at 500–850 nm with enhanced red contribution upon coordination. The emission is mainly assigned to ligand-centered transitions ($\pi \rightarrow \pi^*$ and $n \rightarrow \pi^*$), consistent with the $d^{10}$ configuration of Cd(II), which suppresses metal-centered and charge-transfer processes. The CIE chromaticity coordinates confirm warm emission, highlighting the potential of cis-[Cd(Tz)$_2$(py)$_2$] for red-emitting optoelectronic applications.
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All authors Samara M. da Silva, R. F. Silva, A. Nonato, Paulo Villis, Rodrigo S. Corrêa, L. C. Gómez-Aguirre, C.W.A. Paschoal, Pedro I. S. Maia, Benedicto A. V. Lima
Quantum Gases
Atomic Interferometry with Spin-Orbit-Coupled Spin-1 Condensates
Renfei Zheng, Junying Wu, Josep Cabedo et al. (+4 more)
We propose and analyze a
quantum interferometry scheme based on a Raman-dressed Bose gas with
spin-orbit coupling. In this system, the atom-light coupling mixes
spin and momentum degrees of freedom, giving rise, in the low-energy regime, to an effective spinor condensate whose
spin-mixing interaction can be tuned independently of the atomic density. This controllability enables a separation between state preparation and phase imprinting, and provides a natural route to echo-type protocols based on effective time reversal. Within this framework, critical regimes of the effective spinor
Hamiltonian can be used to generate
entanglement and enhance interferometric sensitivity beyond the standard
quantum limit. In addition, the
spin-momentum locking of the dressed modes gives access to spatial density modulations that provide an alternative readout of the interferometric phase. In particular, phase information can be extracted from the displacement of
spin-orbit-induced density stripes even when conventional
spin observables are insensitive within the effective spinor description. Our results identify Raman-dressed spinor gases as a flexible platform for nonlinear atomic interferometry, combining controllable
spin-mixing dynamics with spatially resolved phase readout.
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All authors Renfei Zheng, Junying Wu, Josep Cabedo, Alessio Celi, Zhihao Lan, Weiping Zhang, Lu Zhou
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Suppressing Plasmonic Heating in Aqueous Environments with Hexagonal Boron Nitride
Martina Russo, Roland van der Vegt, Bohai Liu et al. (+5 more)
Optical heating of plasmonic nanostructures is a critical challenge in nanoscale systems. Although plasmonic effects enable enhanced optical functionalities, the associated temperature rise can degrade performance in heat-sensitive applications such as biosensing, nanophotonics, and microelectronics. Conventional cooling strategies fail at these scales due to limited heat transport and high interfacial thermal resistance, motivating the integration of advanced materials for thermal management. Here, we investigate hexagonal boron nitride (hBN) thin flakes as heat spreaders to mitigate plasmonic heating of gold nanospheres immobilized on hBN deposited on glass and surrounded by water. Using finite-element simulations, we quantify the influence of hBN thickness, in-plane thermal conductivity, and interfacial thermal conductance on cooling efficiency. Complementary experiments employ cross-grating wavefront microscopy (CGM) for nanothermometry to map the temperature around optically heated gold nanoparticles and quantify the cooling effect of hBN. We extend the application of CGM for rapid, non-invasive, and all-optical characterization of non-absorbing 2D materials. Our results reveal a strong thickness dependence, where heat dissipation in thin flakes is limited by the heat capacity of hBN and in thick flakes by interfacial thermal conductance. Including hBN, we obtain a reduction in temperature rise by up to 60% compared to glass. In addition, the presence of two main heat dissipation pathways emerges: a direct one from the nanoparticle to the hBN and an indirect one from the particle via water to the hBN. This combined simulation-experiment framework offers a versatile approach to improve thermal management in plasmonic systems and beyond, establishing design guidelines for integrating 2D materials into thermally sensitive platforms such as biosensors and integrated
circuits.
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All authors Martina Russo, Roland van der Vegt, Bohai Liu, Sam Beijers, Sara Salera, Guillaume Baffou, Klaas-Jan Tielrooij, Peter Zijlstra
Superconductivity
Long range proximity effects in planar structures involving the halfmetal ferromagnet La0.7Sr0.3MnO3 and Pt interlayers
Junxiang Yao, Julian van Doorn, Mariona Cabero et al. (+1 more)
Over the last decade, there has been steady research on superconducting junctions with a ferromagnet as the weak link, and where triplet correlations can transport supercurrents over a substantial distances. Of particular interest are halfmetallic ferromagnets, in which only one
spin band is present, so that, presumably, the induced supercurrent is fully
spin-polarized. We have earlier reported on a study of triplet transport in planar La0.7Sr0.3MnO3(LSMO) nanostrip Josephson junctions with NbTi superconducting contacts, where we found high values for the supercurrents, and large junction lengths (up to 1.3 {\mu}m). Here, we extend that work by studying the dependence of the critical current Ic on the length of the nanostrip between the contacts and the width of the strip. All junctions show strong supercurrents, but we do not observe simple systematics. Apparently, the fabrication process does not allow sufficient control over some of its parameters. To gain more insight in the mechanism for triplet generation at the LSMO/NbTi interface, we also studied the effect of Pt as an interlayer between the LSMO and the NbTi. For this, we etched a NbTi/Pt electrode structure on a full film of LSMO. The results are highly promising, showing sharp superconducting transitions and zero-resistance states being reached at an electrode distance of 2 {\mu}m, with indications that larger distances should be feasible.
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All authors Junxiang Yao, Julian van Doorn, Mariona Cabero, Jan Aarts
Materials Science · Cross-listed from physics.app-ph
High-pressure magnetic transition in iron observed via diamond quantum sensing
Kouki Yamamoto, Kenshin Uriu, Ryotaro Suda et al. (+5 more)
Diamond
quantum sensors offer high precision and spatial resolution as
magnetic probes, making them promising for a wide range of applications. While diamond anvil
cells (DACs) can generate extremely high pressures, techniques for magnetometry under such conditions remain limited. By fabricating an ensemble of NV centers directly on the anvil diamond surface, we enable precise
magnetic measurements under high pressure. In this work, we employ this NV ensemble to image the stray
magnetic field of iron up to 30 GPa, enabling the observation of the
magnetic transition ($\alpha$-$\varepsilon$ transition) in iron.
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All authors Kouki Yamamoto, Kenshin Uriu, Ryotaro Suda, Misaki Sasaki, Mari Einaga, Katsuya Shimizu, Kento Sasaki, Kensuke Kobayashi
Other Condensed Matter · Cross-listed from physics.optics
Plasmon Induced Delocalized Second-Harmonic Generation Towards Buried-Interface Spectroscopy
Alan R. Bowman, Sergejs Boroviks, Omer Can Karaman et al. (+3 more)
Second-harmonic generation microscopy is a powerful technique capable of probing local
crystal symmetries and electric fields at interfaces. However, it often suffers from weak signal strength and is difficult to understand in multilayer systems where many materials can give competing signal contributions. In this work we present direct observation of delocalized, surface plasmon polariton-mediated second-harmonic generation on gold monocrystalline surfaces and structures. We generate second-harmonic light up to 35 um from the excitation spot and, excitingly, we obtain signal from atomically flat surfaces without a fundamental excitation beam present in the same region. We reveal that this process arises from the interaction of two counter-propagating surface plasmon polaritons, which we believe to be the first observation of this process at the microscale. This signal has the same polarisation dependence as localised second-harmonic generation and is emitted in a collimated beam travelling perpendicular to the sample surface. In part due to local electric field enhancements, we were able to observe these signals on a CMOS camera with 1 s exposure and no gain using an industrial-grade pulsed
laser. Our results enable wide area multilayer samples to be probed using a single excitation beam, with applications including in energy, catalysis and single particle surface sensing.
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All authors Alan R. Bowman, Sergejs Boroviks, Omer Can Karaman, Laura M. Herz, Olivier J.F. Martin, Giulia Tagliabue
Quantum Gases
Quantum corrections to the Josephson dynamics: a population-imbalance approach
Oliver Hideg, Sofia Salvatore and Luca Salasnich
We investigate
quantum corrections to the Josephson dynamics of two weakly coupled Bose-Einstein condensates using the population imbalance as the sole dynamical variable. Starting from the two-variable action, we derive the imbalance-only Lagrangian with a position-dependent mass and quantize it via symmetric operator ordering. The leading
quantum corrections to the classical potential and mass are computed via the one-loop
quantum effective action, using a covariant background-field method that fully accounts for the coordinate dependence of the mass. This yields explicit expressions for the effective potential and the effective mass, from which we derive the
quantum-corrected Josephson frequency. Numerical comparison with exact diagonalization of the two-site Bose-Hubbard model shows that the imbalance-only formulation outperforms the complementary phase-only approach in the regime of weak interactions, which is the natural domain of validity of the population-imbalance description.
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Strongly Correlated Electrons
Dynamical magnetotropic susceptibility as a new probe of Kitaev materials and beyond
João C. Inácio, J. Schwab, G. Rakhmanova et al. (+8 more)
The magnetotropic susceptibility, $k(\omega)$, probes ultra-low-frequency uniform ($\boldsymbol{q}=0$)
spin and charge fluctuations in a
crystal mounted on an oscillating cantilever: its real part shifts the oscillation frequency, while its imaginary part characterises the induced damping. We derive $k(\omega)$ within linear response theory for a generic correlated-electron
Hamiltonian, showing that its real part is sensitive to
magnetic anisotropy and its imaginary part encodes the uniform dynamical
spin susceptibility, even for
spin-symmetric
insulators, while in metals it reveals eddy-current damping conditions. Using auxiliary-field
quantum Monte Carlo, we compute $k(\omega)$ for microscopic models of $\alpha$-RuCl$_3$, finding that the low-temperature $k(\omega=0)/T$ scaling with $B/T$ is a signature of dominant Kitaev coupling, robust to optical
phonons, while the dynamical response shows local-moment-like features. We highlight applications to Kondo destruction
quantum criticality, relevant to strange
metallicity and unconventional superconductivity.
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All authors João C. Inácio, J. Schwab, G. Rakhmanova, S. Safari, V. Zambra, H. Nasir, S. Khim, S. Paschen, K. A. Modic, Fakher F. Assaad, Toshihiro Sato
Statistical Mechanics
Fixed points and crossovers for the hysteresis scaling of dynamic mean-field models
Jiapeng Yang and Fan Zhong
Phase transitions are divided into first-order phase transitions and continuous ones in current classification. While the latter shows striking phenomena of scaling and universality, the former is generically characterized by discontinuous jumps in extensive variables and pronounced hysteresis. Recent studies have demonstrated universal scaling behavior controlled by a cubic fixed point in first-order phase transitions. However, more recent investigations into the hysteresis in a dynamic mean-field quartic model driven through its first-order phase transitions have revealed new scaling exponents for different driving rates. Here, we discover a new exponent for large driving rates arising surprisingly from critical phenomena and show that, depending on the magnitude of the driving rates and on the absence or presence of noise, the same mean-field model remarkably exhibits several universality classes with definite universal scaling exponents governed by their corresponding fixed points through a systematic scaling analysis based on renormalization group theory. The theories and their various crossovers between different fixed points along with complete universal scaling of full curve collapse are verified by numerical results. This further confirms universal scaling in first-order phase transitions.
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Quantum Gases
Exact Analytical Vortex Solution for a Two-Dimensional Quantum Gas with LHY Correction
Ibrar, Mahammad Ahmed Hussain and Ayan Khan
In this investigation, we provide an exact analytical
vortex solution for a Bose
liquid in two dimensions with beyond mean-field correction (BMF). Analytical solutions in two-dimensional systems with BMF corrections are rarely found in the literature. The present result provides a clear framework for understanding
vortex structures in low-dimensional
quantum fluids and serves as a reliable
benchmark for future theoretical and experimental studies.
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Materials Science
An Unsupervised Machine Learning-based Framework for Wafer Scale Variability Analysis and Performance Prediction of Ferroelectric Hf0.5Zr0.5O2 Thin Film Capacitors
Anika Anu and Sayani Majumdar
Fabrication process-induced performance variability remains a formidable barrier in the high-volume manufacturing of
semiconductor chips. With skyrocketing Artificial Intelligence (AI) workload, demand for non-volatile and computational
memories is growing exponentially. As embedded non-volatile
memory, ferroelectric Hf0.5Zr0.5O2 emerged as a strong candidate due to their CMOS back-end-of-line (BEOL) compatibility, scalability and high performance. However, their sensitive crystallization kinetics leads to significant device-to-device (D2D) non-uniformity leading to unpredictability of performance over wafer scale. In this work, we demonstrate unsupervised machine learning can analyze intra-die D2D variations and predict performance of "unseen" dies efficiently. We present a framework utilizing Principal Component Analysis (PCA) and K-Means clustering to analyze D2D performance variations in HZO capacitors and building on data from multiple dies, we move beyond traditional descriptive statistics to a predictive "Virtual Metrology" approach that separates performance categories, defined by key parameters like remanent polarization (Pr) and coercive voltage (Vc). The analysis further extends to comparing uniformity across different dies across the wafer showing the proposed methodology can accurately predict device performance on untested dies with a low Mean Absolute Percentage Error (MAPE) in the range of 5-10%, suggesting a robust path for accelerated yield improvement and reduced metrology overhead.
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Disordered Systems and Neural Networks
Even–odd classification of reentrant topology in a Su–Schrieffer–Heeger chain with integer-power quasiperiodic hopping
Yusheng Niu, Hui Liu and Zhihao Xu
We investigate reentrant
topology in a one-dimensional Su–Schrieffer–Heeger chain with integer-power quasiperiodically modulated intracell hopping. The modulation is controlled by a positive integer exponent $n$ and a tunable parameter $\beta$, which interpolates between a smooth integer-power quasiperiodic profile and a sign-function limit. Combining the zero-mode inverse-localization-length criterion with a real-space topological indicator, we determine the phase diagrams in the $\beta\to0$, $\beta\to\infty$, and finite-$\beta$ regimes. We find an even–odd classification of reentrant topological windows governed by the dc component and support of the full modulation profile. For positive modulation strength, odd powers yield a zero-mean sign-changing profile and can induce reentrance from the clean trivial regime $|t_1|>1$, whereas even powers yield a positive-mean non-negative profile and allow reentrance only from the negative clean trivial regime $t_1<-1$. Although even-power profiles contain sign-changing fluctuations after subtracting their positive average, the full modulation profile remains non-negative. This even–odd structure of the full modulation profile provides a control knob for topological Anderson-like reentrant phases. We further discuss the associated bulk localization properties and show that the phase diagrams are robust against moderate hopping fluctuations, suggesting a feasible realization in electrical
circuits.
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Strongly Correlated Electrons
Incommensurate Magnetic Ordered Phase with Enhanced Low-Temperature Magnetic Specific Heat in SmAu$_3$Al$_7$
Ryuji Higashinaka, Takuma Iwami, Kohsuke Saitou et al. (+12 more)
Neutron scattering and
muon spin rotation ($\mu$SR) measurements on single-
crystal SmAu$_3$Al$_7$ reveal magnetically ordered states associated with successive transitions at $T_{\rm N}$ = 2.8 K and $T^*$ = 0.9 K.
Magnetic Bragg peaks appear below $T_{\rm N}$ with an incommensurate (IC) propagation vector ${\bf q}$ = (0.30, 0, 1.33). $\mu$SR detects spontaneous internal fields below $T_{\rm N}$, and the spectral shape is consistent with the IC
magnetic ordering. No anomalies are observed at $T^*$, indicating that the
magnetic structure remains essentially unchanged below and above $T^*$. The
magnetic order is revealed to be a spatially homogeneous long-range ordered state, rather than a partially disordered state proposed in earlier studies. The possible connection between the IC
magnetic order and the enhanced low-temperature
magnetic specific heat is discussed.
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All authors Ryuji Higashinaka, Takuma Iwami, Kohsuke Saitou, Takashi U. Ito, Chihiro Tabata, Koji Kaneko, Takashi Ohhara, Ryoji Kiyanagi, Akiko Nakao, Jumpei G. Nakamura, Wataru Higemoto, Akihiro Koda, Shinsaku Kambe, Yuji Aoki, Tatsuma D. Matsuda
Materials Science
Magnetic Behavior of Ferro-, Antiferro-, and Ferrimagnetic Systems in the Griffiths Phase: A Theoretical Study
Sumanta Mukherjee
In this report, we provide a theoretical framework for the
magnetic behavior of the Griffiths phase, which, along with three-dimensional
spin-1/2 Ising
ferromagnetic systems, can be extended to
antiferromagnetic as well as ferrimagnetic systems. We find that the
magnetic behavior in the Griffiths phase of three-dimensional
antiferromagnetic and ferrimagnetic systems is more unusual than that of conventional
ferromagnetic systems. However, this study offers a possible framework for the identification of Griffiths phase behavior in three-dimensional
antiferromagnetic and ferrimagnetic systems.
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Strongly Correlated Electrons
Induced discommensurations in the lock-in transition of charge-density waves
Katsuhiko Inagaki and Satoshi Tanda
We studied McMillan's free energy of the lock-in transition in charge-density waves. The wave profiles near the critical value were obtained by numerical annealing. First, we demonstrated that our method reproduces the previous studies. The obtained wave profiles include discommensurations near the critical value. Then, we calculated possible wave profiles in the commensurate state. We found that discommensurations are able to be excited in the commensurate state, leading the system to turn into an incommensurate state. We proposed that these wave profiles result from topological invariants. Moreover, excitation of the discommensurations is favorable for the direction to the original wavelength of the incommensurate state. This is attributed to the nature of McMillan's free energy. The current-induced incommensurations, which we discovered with the diffraction study of $o$-TaS$_3$ et al., J. Phys. Soc. Jpn. 77, 093708 (2008)], is consistent with this study.
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Strongly Correlated Electrons
Electrical detection of spin-flip transition in metal/\ce{Na_5Co_{15.5}Te_6O_{36}} heterostructure
Hirotsugu Tagami, Takuya Kawada and Yuki Shiomi
We report on the longitudinal magnetoresistance (MR) in thin metal films on an Ising-type
antiferromagnetic insulator, \ce{Na_5Co_{15.5}Te_6O_{36}} (\ce{NCTO}). Steep changes in the MR spectra with hysteresis were observed at
spin-flip transitions driven by
magnetic fields applied along the easy axis of the \ce{NCTO}
crystal. The MR jumps almost follow step-like changes in magnetization at the
spin-flip transition. At very low temperatures where \ce{Co} moments are partially frozen, the MR anomalies exhibit a tunnel-magnetoresistance-like shape. The observed MR anomalies at the
spin-flip transition are attributed to strain effects via magnetostriction upon the
magnetic-structure change of the \ce{Co} nets in \ce{NCTO}, because similar MR jumps are observed in \ce{Pt/NCTO}, \ce{Pt/SiO_x/NCTO}, and \ce{Cu/NCTO}
heterostructures. Interestingly, we found that the high-field slopes of the MR spectra show opposite signs between \ce{Pt/NCTO} and \ce{Cu/NCTO} at low temperatures. Because similar MR spectra are observed for \ce{Pt/SiO_x/NCTO} in which the interface
magnetic interaction is negligible, the weak antilocalization due to the strong
spin-orbit interaction of the Pt films is likely to contribute to the low-temperature MR.
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Soft Condensed Matter
Pre-charging polymer surfaces enhances droplet mobility and electrification
Shuaijia Chen, Kenta Morita, Dumindu Dassanayaka et al. (+4 more)
Surface-bound electric charge on
polymer materials can strongly influence droplet behaviour and solid-
liquid charge transfer, but the mechanisms and the means to control these effects remain unclear. In this work, we systematically controlled the surface charge on
polymer surfaces, including polytetrafluoroethylene (PTFE) and Nylon-66, by first neutralising the surfaces with an anti-static ion blower and then applying charge using an ion gun. We find that droplets pick up pre-deposited surface ions during the first wetting of the surface, and that the transferred charge directly correlates with the deposited charge encountered by the wetted area for moderate deposited densities (|{\sigma}_d |<40 {\mu}C/m2) independent of material properties. We also demonstrate that the deposited charge reduces contact angle and increases contact-line mobility in a manner consistent with an increase in effective solid surface energy. For higher surface charge densities, we observe instabilities such as droplet splitting or detachment. This work demonstrates an effective approach to control solid-
liquid electrification, enabling amplification or suppression of surface charge and the directed manipulation of fluid motion on surfaces.
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All authors Shuaijia Chen, Kenta Morita, Dumindu Dassanayaka, Hans-Jürgen Butt, Peter C. Sherrell, Amanda V. Ellis, Joseph D. Berry
Superconductivity
Signatures of time-reversal-symmetry breaking in multiband 2H-TaS2 revealed by zero-field Josephson nonreciprocity
Daniel Margineda, David Caldevilla-Asenjo, Yuriy Yerin et al. (+7 more)
Superconductors that spontaneously break time-reversal
symmetry host complex order parameters and are widely regarded as a hallmark of unconventional superconductivity. Whether such
symmetry breaking can also arise in
superconductors with nominally isotropic
spin-singlet pairing remains an open question. Here we report a zero-field Josephson diode effect in noncentrosymmetric 2H-TaS2/2H-NbSe2 van der Waals junctions. The diode efficiency shows no systematic correlation with supercurrent amplitude, TaS2 thickness, or normal-state resistance, arguing against simple extrinsic, purely interfacial, or transparency-driven mechanisms. Time-reversal-symmetric scenarios are further tested using
symmetry-controlled and molecule-intercalated control devices, in which the nonreciprocal response is absent or strongly reduced. Normal-state
Hall transport in TaS2 exhibits a nonlinear response consistent with multiband correlated electronic states. Within a Josephson framework, our modelling shows that interband scattering acts as a phase-locking mechanism generating an intrinsic anomalous phase difference and a nonsinusoidal asymmetric current-phase relation, leading to finite zero-field rectification. Together, zero-field Josephson nonreciprocity and nonlinear
Hall transport provide complementary evidence for a multiband superconducting phase structure in 2H-TaS2, consistent with intrinsic time-reversal-
symmetry breaking.
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All authors Daniel Margineda, David Caldevilla-Asenjo, Yuriy Yerin, Covadonga Álvarez-García, Andrei Mazanik, Maxim Ilyn, Celia Rogero, Luis E. Hueso, F. Sebastian Bergeret, Marco Gobbi
Materials Science
An Advanced Epitaxial Strategy Enabling Vertical GaN Devices on Silicon Wafers
Fumio Kawamura, Takeyoshi Onuma and Kazutaka Mitsuishi
While vertical GaN-on-silicon architectures promise a transformative leap in cost-effective power electronics and high-resolution micro-LEDs, their deployment remains bottlenecked by the high electrical resistance of conventional epitaxial buffer layers. Here, a universal and straightforward sputtering-based strategy is presented to realize high quality GaN epitaxial films on Si(111) substrates characterized by exceptionally low vertical resistance, ohmic behavior, and robust thermal stability. This technique centers on the in-situ formation of a sub nanometer (0.5 nm) silicide-based template via rapid thermal annealing method demonstrating unprecedented versatility across 25 different metallic species. Scanning transmission electron microscopy (STEM) reveals that a unique amorphous like interlayer (AL-IL) effectively accommodates
lattice mismatch and relaxes epitaxial strain. These AL-IL templates further serve as high performance platforms for metalorganic chemical vapor deposition (MOCVD) overgrowth, successfully bridging the gap between scalable, low-cost fabrication and device-grade vertical performance.
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Mesoscale and Nanoscale Physics
Thermodynamic Charge Partition in Accumulation-Layer Heterostructures
Elmar Böckenhoff
We develop a thermodynamic description of accumulation-layer
heterostructures in which the induced sheet density is partitioned between the near-interface accumulation-layer charge and a complementary screening charge in the surrounding structure. Treating this partition as the central state variable yields a complete Helmholtz free energy, a corrected locked-branch chemical potential, and a shifted release potential that separates energetic path selection from
geometric capacitance. The physical path is selected spectrally: compressible segments remain fully screened, whereas incompressible segments evolve along a locked branch until release is triggered by the relevant gap. Differential capacitance, tunnel current and plateau width then emerge as different projections of the same coupled thermodynamic structure. A canonical two-stage self-consistent Poisson–Schrödinger reduction supplies universal master functions for the isolated accumulation layer and master surfaces for its finite-buffer extension, making the theory calculable across density and geometry. Comparison with magnetocapacitance and magnetotunneling data supports a picture in which nearby extended charge refills the accumulation layer and the effective screening depth grows with
magnetic field.
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Disordered Systems and Neural Networks · Cross-listed from cs.CL
Escaping Mode Collapse in LLM Generation via Geometric Regulation
Xin Du and Kumiko Tanaka-Ishii
Mode collapse is a persistent challenge in generative modeling and appears in autoregressive text generation as behaviors ranging from explicit looping to gradual loss of diversity and premature trajectory convergence. We take a dynamical-systems view and reinterpret mode collapse as reduced state-space accessibility caused by *
geometric collapse*: during generation, the model's internal trajectory becomes confined to a low-dimensional region of its representation space. This implies mode collapse is not purely a
token-level phenomenon and cannot be reliably solved by symbolic constraints or probability-only decoding heuristics. Guided by this perspective, we propose *Reinforced Mode Regulation* (RMR), a lightweight, online state-space intervention that regulates dominant self-reinforcing directions in the
Transformer value cache (implemented as low-rank damping). Across multiple large
language models, RMR substantially reduces mode collapse and enables stable generation at extremely low
entropy rates (down to 0.8 nats/step), whereas standard decoding typically collapses near 2.0 nats/step.
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Materials Science
Kinetically Arrested Twin-Domain State in Formamidinium Lead Iodide
Xia Liang, Milos Dubajic, Zezhu Zeng et al. (+4 more)
Hybrid lead halide perovskites exhibit a delicate interplay between average crystallographic
symmetry, local structural disorder and A-site orientational dynamics, giving rise to unusual vibrational and electronic behaviour. Here, we combine large-scale molecular dynamics with a density-functional-theory-accurate machine learning force field to resolve the structural dynamics of perovskites across mesoscopic length scales. In formamidinium lead iodide FAPbI$_{3}$, we identify a high-temperature $\alpha$ phase with dynamic local order and correlated tilt nanodomains, an ordered $\gamma$ phase with long-range $a^{+}a^{+}a^{+}$ tilt coherence, and, below $\sim$100 K, a history-dependent $\gamma'$ state consisting of locally $\gamma$-like nanoscale regions separated by sharp twin-like boundaries. This low-temperature disordered state is not a distinct bulk polymorph, but a kinetically arrested metastable twin-domain network selected by the interplay between shallow tilt energetics and slowing FA reorientation. This picture provides a consistent explanation for the low-temperature diffuse scattering features observed experimentally, and accounts for the broadened low-energy vibrational response found in the simulations. Furthermore, this unique structural landscape imprints a spatially varying electronic disorder that directly impacts macroscopic optoelectronic properties, evidenced by an anomalous increase in the Urbach energy at low temperatures. Our results reconcile the debated low-temperature behaviour of FAPbI$_{3}$ in terms of competition between ordered and arrested structural states, and show more broadly that in hybrid perovskites the organic cation can actively select the macroscopic structural and electronic response through its reorientation kinetics, placing thermal history on equal footing with composition as a determinant of structural and optoelectronic properties.
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All authors Xia Liang, Milos Dubajic, Zezhu Zeng, Yang Lu, Johan Klarbring, Samuel D. Stranks, Aron Walsh
Soft Condensed Matter
Machine learning evaluation of structural descriptors for supercooled water
Kohei Yoshikawa, Kokoro Shikata, Kang Kim et al. (+1 more)
The anomalous behavior of
liquid water is widely associated with a
liquid-
liquid phase transition between high- and low-density states in the supercooled regime. At the microscopic level, tetrahedral hydrogen-bond networks govern these properties, motivating structural descriptors that characterize local molecular environments. These structural descriptors quantify features such as tetrahedral order, local density, and the separation between the first and second coordination shells; however, they have largely been proposed independently, with limited systematic comparison. Here we evaluate 16 previously proposed descriptors using a neural-network-based temperature classification framework, enabling an objective assessment of their ability to distinguish temperature-dependent structural changes in supercooled water. We further apply an explainable artificial intelligence method that identifies the structural features responsible for the model predictions. This approach reveals how different descriptors encode local structural information and establishes a data-driven framework for benchmarking structural descriptors in
liquid water.
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All authors Kohei Yoshikawa, Kokoro Shikata, Kang Kim, Nobuyuki Matubayasi
Statistical Mechanics · Cross-listed from cs.LG
Trees to Flows and Back: Unifying Decision Trees and Diffusion Models
Sai Niranjan Ramachandran and Suvrit Sra
Decision trees and
diffusion models are ostensibly disparate model classes, one discrete and hierarchical, the other continuous and dynamic. This work unifies the two by establishing a crisp mathematical correspondence between hierarchical decision trees and
diffusion processes in appropriate limiting regimes. Our unification reveals a shared optimization principle: Global Trajectory Score Matching (GTSM), for which gradient boosting (in an idealized version) is asymptotically optimal. We underscore the conceptual value of our work through two key practical instantiations: \treeflow, which achieves competitive generation quality on tabular data with higher fidelity and a 2\times computational speedup, and \dsmtree, a novel
distillation method that transfers hierarchical decision logic into neural networks, matching teacher performance within 2% on many
benchmarks.
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Mesoscale and Nanoscale Physics
Investigation of nonlocal transport associated with the orbital Hall effect in Ti
Keitaro Takashina, Naoki Yano, Asahi Oe et al. (+3 more)
We investigate nonlocal transport in single-layer Ti
Hall bars to explore signatures of orbital-current transport driven by the orbital
Hall effect. Despite the negligible
spin Hall effect in Ti, we observe a finite nonlocal resistance in the single-layer Ti
Hall bar and study its dependence on the central channel width. Finite-element simulations show that the measured signal contains a sizable Ohmic bypass contribution. However, the bypass contribution is strongly suppressed at small channel widths and cannot fully account for the observed nonlocal resistance even when variations in the Ti resistivity are taken into account. Our results therefore suggest an additional nonlocal contribution distinct from the Ohmic bypass background, which may be associated with orbital transport driven by the orbital
Hall effect in Ti.
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All authors Keitaro Takashina, Naoki Yano, Asahi Oe, Mari Taniguchi, Shuto Kimura, Kazuya Ando
Mesoscale and Nanoscale Physics
Polarization-controlled effective Rabi dynamics in driven Graphene: A Floquet-Magnus approach
V. G. Ibarra-Sierra, J. L. Cardoso, C. Flores-Valente et al. (+2 more)
Polarization ellipticity $\beta$ and the relative angle $\Delta$ between electron momentum and driving field act as independent control parameters for coherent dynamics in periodically driven Dirac systems. In this work, we analyze the dynamics of resonantly driven Dirac electrons in
graphene under elliptically polarized electromagnetic radiation using the Floquet-Magnus expansion. Working in the interaction picture and applying a rotating-wave-type transformation, we derive an effective two-level
Hamiltonian that governs the macromotion at resonance ($\omega = \Omega/2$). The resulting quasienergy splitting depends nontrivially on $\beta$ and $\Delta$ through interference between the Bessel harmonics $J_0(\zeta)$ and $J_2(\zeta)$. Circular polarization ($\beta = \pm 1$) restores rotational
symmetry and yields a $\Delta$-independent effective Rabi frequency, whereas elliptical and linear polarizations produce anisotropic responses with a $\pi$-periodic angular modulation. Beyond spectral properties, we identify a polarization-induced phase that acts as an effective initial Floquet kick, shifting the effective initial conditions and producing measurable shifts in the timing of occupation oscillations, whose sign depends on both helicity and relative orientation. Through an explicit
Fourier decomposition of the time-
evolution operator, we separate macromotion from micromotion contributions and validate the zeroth-order Magnus approximation via numerical simulations, achieving root-mean-square errors of $\sim 1\%$ over 100 driving periods in the weak-field regime. These results establish polarization ellipticity and relative orientation as tunable and experimentally accessible knobs for
quantum control in two-dimensional Dirac materials, with direct implications for time-resolved spectroscopy.
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All authors V. G. Ibarra-Sierra, J. L. Cardoso, C. Flores-Valente, A. Kunold, J. C. Sandoval-Santana