Mesoscale and Nanoscale Physics
Spontaneous Running Waves and Self-Oscillatory Transport in Dirac Fluids
Prayoga Liong, Aliaksandr Melnichenka, Anton Bukhtatyi et al. (+2 more)
We predict hydrodynamic Turing instability of current-carrying Dirac electron fluids that drives spontaneous self-oscillatory transport. The instability arises near charge neutrality, where carrier kinetics make current dissipation strongly density dependent. Above a critical drift velocity, a uniform electronic flow becomes unstable and undergoes a dynamical transition to a state with coupled spatial modulation and temporal oscillations–an electronic analogue of Kapitsa roll waves in viscous films. The transition exhibits two clear signatures: a nonanalytic, second-order-like onset in the time-averaged current and narrow-band electromagnetic emission at a tunable washboard frequency $f=u/\lambda$. Although reminiscent of sliding charge-density waves, the mechanism is intrinsic and disorder independent. Owing to the small effective mass of Dirac carriers, hydrodynamic time scales translate into emission frequencies in the tens to hundreds of gigahertz range, establishing Dirac materials as a platform for high-frequency self-oscillatory electron hydrodynamics.
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All authors Prayoga Liong, Aliaksandr Melnichenka, Anton Bukhtatyi, Albert Bilous, Leonid Levitov
Mesoscale and Nanoscale Physics
Current-Induced Modulation of Spin-Wave Propagation in a Y-Junction via Transverse Spin-Transfer Torque
Lorenzo Gnoatto, Rai M. Menezes, Artim L. Bassant et al. (+3 more)
We report the transverse control of
spin-wave propagation in the configuration where the
spin-wave wavevector k is perpendicular to the charge-current density J. Building on theoretical predictions of
spin-wave refraction by nonuniform
spin-polarized currents, and guided by micromagnetic simulations used to optimize the device geometry and current distribution, we experimentally explore a Y-shaped Permalloy structure in which a locally injected current perturbs the
spin-wave dispersion. Measurements reveal current-dependent amplitude differences between the two output branches, providing initial experimental indications consistent with transverse,
spin-transfer-torque-driven deflection. Although the magnitude of the effect is modest and accompanied by significant uncertainties, the observed trends qualitatively follow expectations from the simulations. These results demonstrate the feasibility of influencing
spin-wave routing through local current injection and establish a proof-of-concept basis for current-controlled manipulation of
spin-wave propagation in reconfigurable magnonic
circuits.
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All authors Lorenzo Gnoatto, Rai M. Menezes, Artim L. Bassant, Rembert A. Duine, Milorad V. Milosevic, Reinoud Lavrijsen
Disordered Systems and Neural Networks
Unified Description of Learning Dynamics in the Soft Committee Machine from Finite to Ultra-Wide Regimes
Assem Afanah and Bernd Rosenow
We study the learning dynamics of the soft committee machine (SCM) with Rectified Linear Unit (ReLU) activation using a statistical-mechanics approach within the annealed approximation. The SCM consists of a student network with $N$ input units and $K$ hidden units trained to reproduce the output of a teacher network with $M$ hidden units. We introduce a reduced set of macroscopic order parameters that yields a unified description valid from the conventional regime $K \ll N$ to the ultra-wide limit $K \ge N$. The control parameter $\alpha$, proportional to the ratio of training samples to adjustable weights, serves as an effective measure of
dataset size. For small $\gamma = M/N$, we recover a continuous phase transition at $\alpha_{c} \approx 2\pi$ from an unspecialized, permutation-symmetric state to a specialized state in which student units align with the teacher. For finite $\gamma$, the transition disappears and the generalization error decreases smoothly with
dataset size, reaching a low plateau when $\gamma=1$. In the asymptotic limit $\alpha \to \infty$, the error scales as $\varepsilon_{g} \propto 1/\alpha$, independent of $\gamma$ and $K$. The results highlight the central role of network dimensions in SCM learning and provide a framework extendable to other activations and quenched analyses.
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Mesoscale and Nanoscale Physics
Spectroscopy of Wigner crystal polarons in an atomically thin semiconductor
L. Wang, F. Menzel, F. Pichler et al. (+5 more)
Strongly interacting electrons in two-dimensional systems can spontaneously break translational
symmetry, forming a periodic Wigner
crystal. Although these
crystals have been realized in several platforms, experimental studies of their collective many-body excitations in the absence of a
magnetic field remain an outstanding challenge. Here, we access this regime optically by uncovering Wigner
crystal polarons: novel light-matter excitations arising from the dressing of
excitons by collective excitations of the Wigner
crystal. These hybrid quasiparticles manifest as new optical resonances in cryogenic reflectance spectra of a charge-tunable WSe$_2$ monolayer, appearing concurrently with previously identified
exciton umklapp transitions. In contrast to the latter, the energies of Wigner
crystal polarons are governed not only by the electronic
lattice constant but also by their hybridization with attractive
exciton-polarons, whose strength is controlled by electronic interactions. These novel many-body excitations provide an optical interface to the
spin state of the Wigner
crystal, which as we demonstrate, can be controlled both magnetically and optically. Our work establishes layered materials as a unique platform for exploring dynamical
impurity dressing by strongly correlated electronic orders.
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All authors L. Wang, F. Menzel, F. Pichler, P. Knüppel, K. Watanabe, T. Taniguchi, M. Knap, T. Smoleński
Materials Science
Predictive Inorganic Synthesis based on Machine Learning using Small Data sets: a case study of Hydrodynamic Diameter-controlled Cu Nanoparticles
Brent Motmans, Digvijay Ghogare, Thijs G.I. van Wijk et al. (+6 more)
Cu NPs have a broad applicability, yet their synthesis is sensitive to subtle changes in reaction parameters. This sensitivity, combined with the time- and resource-intensive nature of experimental optimization, poses a major challenge in achieving reproducible and size-controlled synthesis. While ML shows promise in materials research, its application is often limited by scarcity of large high-quality experimental data sets. This study explores ML to predict the DLS-derived hydrodynamic diameter of Cu NPs using a small data set of 25 syntheses. Latin Hypercube Sampling is used to efficiently cover the parameter space while creating the experimental data set. Ensemble regression models successfully predict hydrodynamic diameters with good predictive performance given the limited
dataset. Since quantitative regression requires a unique DLS-derived hydrodynamic diameter, the regression model is restricted to mono-modal DLS distributions, while a complementary classification model identifies synthesis conditions for which quantitative prediction is applicable. Using equivalent out-of-sample validation, the ML and DoE models showed comparable generalization. The final ensemble model achieved an R2=0.74 compared to 0.60 for the DoE model, while retaining the complete synthesis parameter space, making it better suited for synthesis guidance. Additionally, classification models using both random forests and LLMs are evaluated to distinguish between large and small particles. These classification models exhibited only modest predictive performance, indicating that this small
dataset is insufficient to fully exploit the capabilities of complex LLMs. Overall, this study demonstrates that carefully curated small data sets, paired with robust classical ML, can effectively support the synthesis of Cu NPs and highlights that for lab-scale studies, complex models like LLMs may offer limited benefits.
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All authors Brent Motmans, Digvijay Ghogare, Thijs G.I. van Wijk, Joren Van Herck, Saba Heidarian, Pieter De Meyer, Berend Smit, An Hardy, Danny E.P. Vanpoucke
Statistical Mechanics · Cross-listed from hep-lat
Critical coupling in $\phi_2^4$ theory
Stephan Durr and Tolga S. H. Kiel
We consider $\phi^4$ theory with $\phi(x)\in\mathbb{R}$ in two Euclidean dimensions. We determine for a variety of self-couplings $\hat{\lambda}$ the (negative) critical bare mass $\hat{\mu}_{0\mathrm{c}}^2(\hat{\lambda})$ where the
lattice-regularized system changes from the symmetric to the broken phase. Based on these data, the transition to infinite volume and a universal scheme with the renormalized parameter $\hat{\mu}_\mathrm{c}^2(\hat{\lambda})$ is made. Finally, $f_\mathrm{c}=\lim_{\hat{\lambda}\to0}\hat{\lambda}/\hat{\mu}_\mathrm{c}^2(\hat{\lambda})$ is determined, with a judicious choice of the parameterizations considered. Our final result reads $f_\mathrm{c}=11.1097(20)_\mathrm{stat}(09)_\mathrm{sys}=11.1097(22)_\mathrm{tot}$.
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Mesoscale and Nanoscale Physics
Quartic energy band engineering in artificial semiconductor honeycomb lattices
Emre Okcu, Emre Mesudiyeli, Hâldun Sevinçli et al. (+1 more)
Artificially engineered
lattices provide a flexible platform for reproducing and extending the electronic behavior of atomic-scale materials. Artificial
graphene systems, in particular, mimic
graphene-like linear dispersion with tunable Dirac cones and offer a route to realizing more exotic band structures. Here we examine the emergence of quartic energy dispersion in artificial
graphene heterostructures using analytical modeling and numerical solutions of the effective
Hamiltonian. We identify three distinct quartic band types: Mexican-hat-shaped (MHS), purely quartic, and non-MHS quartic bands, and determine the conditions under which each arises. We find that a staggered honeycomb
lattice supports all three classes of quartic dispersion, whereas its planar counterpart yields only purely quartic and non-MHS forms. These results demonstrate the feasibility of engineering quartic band edges in artificial
lattices and clarify how
lattice geometry can be used to tailor their characteristics.
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All authors Emre Okcu, Emre Mesudiyeli, Hâldun Sevinçli, A. Devrim Güçlü
Statistical Mechanics · Cross-listed from quant-ph
Replica Keldysh field theory of quantum-jump processes: General formalism and application to imbalanced and inefficient fermion counting
Felix Kloiber-Tollinger and Lukas M. Sieberer
Measurement-induced phase transitions have largely been explored for projective or continuous measurements of Hermitian observables, assuming perfect detection without information loss. Yet such transitions also arise in more general settings, including
quantum-jump processes with non-Hermitian jump operators, and under inefficient detection. A theoretical framework for treating these broader scenarios has been missing. Here we develop a comprehensive replica Keldysh field theory for general
quantum-jump processes in both bosonic and fermionic systems. Our formalism provides a unified description of pure-state
quantum trajectories under efficient detection and mixed-state dynamics emerging from inefficient monitoring, with deterministic Lindbladian
evolution appearing as a limiting case. It thus establishes a direct connection between phase transitions in nonequilibrium steady states of driven open
quantum matter and in measurement-induced dynamics. As an application, we study imbalanced and inefficient
fermion counting in a one-dimensional
lattice system: monitored gain and loss of
fermions occurring at different rates, with a fraction of gain and loss jumps undetected. For imbalanced but efficient counting, we recover the qualitative picture of the balanced case:
entanglement obeys an area law for any nonzero jump rate, with an extended
quantum-critical regime emerging between two parametrically separated length scales. Inefficient detection introduces a finite correlation length beyond which
entanglement, as quantified by the fermionic logarithmic negativity, obeys an area law, while the subsystem
entropy shows volume-law scaling. Numerical simulations support our analytical findings. Our results offer a general and versatile theoretical foundation for studying measurement-induced phenomena across a wide class of monitored and open
quantum systems.
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Quantum Gases
C. Morin, C. Lagoin, T. Gupta et al. (+5 more)
In condensed-matter physics, long-range correlations introduce
quantum states of matter that challenge intuition. For example, supersolids combine density order that manifests as
symmetry-breaking spatial arrangement, and frictionless superfluid flow. However, supersolids have proven to only exist under very stringent conditions, with evidence limited to a few spontaneously fragmented superfluids observed in the weakly-interacting regime. Here, we demonstrate a framework to realize crystalline supersolids in the strong interaction regime, by confining dipolar
bosons in a
lattice with long-range hopping. We show that dipolar
excitons realize this
lattice model. At fractional
lattice fillings of one quarter, one third and one half we observe mesoscopic
quantum crystals across around 100 sites that spontaneously break the
lattice translational
symmetry. At the same time, coherent long-range hopping induces off-diagonal long-range order such that the
exciton solids are superfluids. Our numerical methods quantitatively confirm that supersolidity builds up in the ground-state of the
lattice Hamiltonian.
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All authors C. Morin, C. Lagoin, T. Gupta, N. Reinic, K. Baldwin, L. Pfeiffer, G. Pupillo, F. Dubin
Statistical Mechanics · Cross-listed from hep-th
Timelike Entanglement Entropy and Renormalization Group Flow Irreversibility
Dimitrios Giataganas
We study
holographic $c$-
theorems based on timelike
entanglement entropy and show that timelike $c$-functions capture irreversible renormalization group (RG) flow. We demonstrate that timelike $c$-functions are applicable to both relativistic and nonrelativistic
quantum matter in nematic phases with broken rotational
symmetry, and that they remain monotonic along
holographic anisotropic RG flows under explicit
geometric conditions, thereby passing some of the most stringent consistency tests. We derive the exact flow of the composite timelike $c$-function in general homogeneous anisotropic geometries and establish the $c$-
theorem for adiabatic flows. Across all classes of scaling backgrounds examined, consistent with the null energy condition and thermodynamic stability, the monotonicity condition universally reduces to a constraint on a running
geometric effective dimension. We further construct a second $c$-function purely from the imaginary part of the timelike
entanglement entropy and prove its monotonicity under the local effective-dimension condition, without requiring adiabaticity. For Poincaré-invariant flows, this condition follows directly from the null energy condition. Moreover, we identify a
geometric upper bound on the rate of change of the timelike $c$-functions, which constrains how rapidly effective degrees of freedom can be coarse-grained. Our results suggest that capturing RG irreversibility in nonrelativistic flows requires observables that are intrinsically sensitive to the temporal direction. The applicability of
holographic $c$-
theorems is thus extended to highly nontrivial RG flows and points toward a new information-theoretic diagnostic of
holographic RG dynamics.
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Materials Science
Solid Oxide Electrolysis Cells: Bridging Materials Development and Process System Engineering for Gigawatt-Scale Applications
Matthias Riegraf, Marc Riedel, Soren Hojgaard Jensen et al. (+3 more)
High-temperature solid
oxide electrolysis
cells (SOECs) are a potential core power-to-X (P2X) technology due to their unparalleled system efficiencies, that can exceed 85 % when excess heat from exothermic downstream processes is available. Recent advancements in materials,
cell and stack design have enabled the deployment of megawatt (MW) scale demonstration plants and gigawatt (GW) scale manufacturing capacities. Consequently, key challenges to industrial-scale adoption scale now increasingly lie at the system level. Unlike previous SOEC reviews focused on materials and stack-level innovations, this work uniquely addresses emerging interdisciplinary system-level challenges and highlights the need for a paradigm shift. Several key insights are identified. Pressurized operation plays a crucial role in enhancing SOEC system performance and enabling better process integration. The dynamic capabilities of SOECs are better than often assumed and can further be improved via advanced operating strategies and modularization. Balance-of-plant (BoP) component costs rival stack capital expenditure, emphasizing the need for cost reductions through economies of scale via mass production and cross-industry synergies. Co-electrolysis remains at a lower technology readiness level and lacks MW scale demonstration. Furthermore, demonstrated integration with downstream processes across entire P2X chains remains scarce. Future research and development strategies are proposed, offering a roadmap to overcome these challenges and accelerate SOEC commercialization.
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All authors Matthias Riegraf, Marc Riedel, Soren Hojgaard Jensen, Srikanth Santhanam, S. Asif Ansar, Marc Heddrich
Materials Science
Probing formation and epitaxy of ultrathin Titanium Silicide using low and medium energy ion scattering
Philipp M. Wolf, Eduardo Pitthan, Zhen Zhang et al. (+3 more)
Titanium silicide is a key contact material in advanced three-dimensional
semiconductor device architectures. Here, we examine the formation of ultrathin Ti-silicide on Si(100) using a combination of non-destructive in-situ and ex-situ ion scattering techniques capable of resolving composition and structure at the nanoscale. In-situ Time-of-Flight Low-Energy Ion Scattering (ToF-LEIS) indicates intermixing after annealing at 350 {\deg}C, with further compositional changes after annealing at 500 {\deg}C, including the emergence of a Si terminating layer at the surface. Consecutive ex-situ Time-of-Flight Medium-Energy Ion Scattering (ToF-MEIS) reveals a Ti-rich polycrystalline surface layer and a Si-rich interface layer exhibiting strong ordering along the Si [100] axis. High-Resolution Transmission Electron Microscopy (HR-TEM) images confirm these findings, revealing a $\approx$1.5 nm thick epitaxial silicide layer at the interface. The presence of an epitaxial interface is particularly promising for minimizing contact resistivity in ultrathin contact layers, where interfacial order can dominate electronic performance. In addition, both ToF-MEIS and HR-TEM unveil significant variations in the thickness of the silicide layer, with a substantial interface roughness but no translation of this roughness to the surface.
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All authors Philipp M. Wolf, Eduardo Pitthan, Zhen Zhang, Tuan T. Tran, Radek Holeňák, Daniel Primetzhofer
Strongly Correlated Electrons
Hyperfine coupling in singlet ground state magnets
Peter Thalmeier
The influence of hyperfine coupling to
nuclear spins and of their quadrupolar splitting on the induced moment order in singlet ground state magnets is investigated. The latter are found among non-Kramers f electron compounds. Without coupling to the
nuclear spins these magnets have a
quantum critical point (QCP) separating paramagnetic and induced moment regime. The hyperfine interaction suppresses the QCP and leads to a gradual crossover between induced electronic and
nuclear hyperfine coupling dominated
magnetic order. It is shown how the critical temperature depends on the electronic and
nuclear control parameters including the
nuclear spin size and its possible
nuclear quadrupole splitting. In particular the dependence of the specific heat on the control parameters and applied field is investigated for ferro- and
antiferromagnetic order. It is shown that the three peak structure in the electronic induced moment regime gradually changes to a two-peak structure in the hyperfine coupling dominated
nuclear moment order regime or for increasing field strength. Most importantly the possibility of a reentrance behaviour of
magnetic order or likewise nonmonotonic critical fields due to hyperfine coupling influence is demonstrated. Finally the systematic
evolution of the phase diagram under the influence of
nuclear quadrupole coupling is clarified.
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Materials Science
Atomic forces from correlation energy functionals based on the adiabatic-connection fluctuation-dissipation theorem
Damian Contant and Maria Hellgren
We extend the capabilities of correlation energy functionals based on the adiabatic-connection fluctuation-dissipation
theorem by implementing the analytical atomic forces within the random phase approximation (RPA), in the context of plane waves and pseudopotentials. Forces are calculated at self-consistency through the optimized effective potential method and the Hellmann-Feynman
theorem. In addition, non-self-consistent RPA forces, starting from the PBE generalized gradient approximation, are evaluated using density functional perturbation theory. In both cases, we find forces of excellent numerical quality. Furthermore, for most molecules and solids studied, self-consistency is found to have a negligible impact on the computed geometries and vibrational frequencies. The RPA is shown to systematically improve over PBE and, by including the exact-exchange kernel within RPA + exchange (RPAx), through finite-difference total energy calculations, we obtain an accuracy comparable to advanced wavefunction methods. Finally, we estimate the anharmonic shift and provide accurate theoretical references based on RPA and RPAx for the zone-center optical
phonon of diamond, silicon, and germanium.
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Strongly Correlated Electrons
Fractional Chern insulator with higher Chern number in optical lattice
Ying-Xing Ding, Wen-Tong Li, Li-Min Zhang et al. (+4 more)
Fractional Chern
insulators arise in topologically nontrivial flat bands, characterized by an integer Chern number C that corresponds to the number of dissipationless edge states in the non-interacting regime. Higher Chern numbers can replicate the physics of higher Landau levels and often confer enhanced topological robustness. However, realizing correlated fractional phases with higher Chern numbers in such flat band systems remains challenging. Here, we propose an interlayer coupling scheme to generate higher Chern numbers in a flat-band system, where the interlayer coupling transforms two C = 1 bands in a
bilayer checkerboard
lattice into a single flat band with C = 2 by lifting their degeneracy and merging their topological indices. Exact diagonalization calculation reveals that this engineered band hosts two fractional Chern
insulator states with C = 2/3 and 2/5, respectively. An experimental setup is proposed to simulate these states using cold alkaline-earth-like atoms in an effective
bilayer optical
lattice. Our work provides a general and widely applicable strategy for constructing higher Chern number flat bands, opening a pathway to explore exotic fractional
quantum phases.
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All authors Ying-Xing Ding, Wen-Tong Li, Li-Min Zhang, Yu-Biao Wu, Duanlu Zhou, Lin Zhuang, Wu-Ming Liu
Disordered Systems and Neural Networks · Cross-listed from hep-ph
Learning holographic QCD with unflavored meson spectra
Mathew Thomas Arun and Ritik Pal
We develop a data-driven neural network framework to reconstruct the five-dimensional background geometry, the dilaton potential, and the
chiral-
symmetry-breaking scalar potential of
holographic QCD from
hadron mass spectra. Framed as an inverse problem, the model is trained using a discretized form of the Schrödinger-like equation, which resembles a linear moose in “deconstructed" 5 dimensions with Dirichlet boundary conditions, in contrast to the AdS/DL with “emergent" space-time. Using the masses of the unflavored
mesons $\rho$, $a_1$, $a_2$, and $f_0$ and their excitations as training data, the model learns confining effective potentials and computes a dilaton profile that satisfies the null energy condition. The network predicts that the dilaton's IR behavior will be much steeper than its quadratic form. Moreover, the
symmetry-breaking bulk potential of the scalar field, $V(X) \sim k_1 X^3+k_2 X^4$, was computed, and the parameters $k_1$ and $k_2$ predicted to be $\sim -4$ and $\sim 9$ respectively. The deep-learned parameters, metric, and the dilaton profile were then used to predict the pion mass and its spectrum with good accuracy. A Python code, along with the trained models, is provided to facilitate further studies\footnote{Available at Github, https://github.com/rp-winter/NN-AdS-QCD
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Strongly Correlated Electrons
Moiré-modulated $\Gamma$ valley in twisted bilayer and twisted double-bilayer MoTe$_2$
Wanying Chen, Hongyun Zhang, Jinxi Lu et al. (+18 more)
Twisted MoTe$_2$ hosts intriguing correlated
quantum phenomena including the fractional
quantum anomalous
Hall effect in twisted
bilayer (t-BL) MoTe$_2$ near 3.7$^\circ$, which is sensitive to the twist angle and moiré superlattices. Here, we directly visualize the twist-angle-modulated electronic structure of t-BL and twisted double-
bilayer (t-DBL) near this critical angle. We find that the moiré superlattice not only modifies the relative energy between $\Gamma$ and K valleys in t-BL MoTe$_2$, but also strongly reconstructs the $\Gamma$ valley for both t-BL and t-DBL. Specifically, the deep $p_z$-derived band at $\Gamma$ exhibits a distinct splitting that systematically varies with increasing twist angle. Theoretical analysis suggests that this modulation arises from the twist-angle-dependent
lattice relaxation, especially interfacial corrugations. Our work directly visualizes the moiré-modulated electronic structure and provides key spectroscopic information of
lattice relaxation and interlayer interactions underlying the physics of twisted MoTe$_2$.
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All authors Wanying Chen, Hongyun Zhang, Jinxi Lu, Yu Gu, Qiyun Xu, Fei Wang, Xuanxi Cai, Jiansong Li, Jiayong Xiao, Rui Chen, Kenji Watanabe, Takashi Taniguchi, Jose Avila, Pavel Dudin, Matthew D. Watson, Pu Yu, Shengwei Jiang, Wenhui Duan, Tingxin Li, Chong Wang, Shuyun Zhou
Superconductivity
Charge order in the Pr substituted YBa$_2$Cu$_3$O$_7$ from high-field Hall effect measurements
C. M. Duffy, M. Altangerel, S. Badoux et al. (+8 more)
The mechanism of doping in the composite Pr$_x$Y$_{1-x}$Ba$_2$Cu$_3$O$_{7-\delta}$ (Pr-YBCO) system is distinct from that of pure YBCO, offering a means to explore the requirements for the numerous electronic orders appearing in the phase diagram. One such example is the ubiquitous 2D charge order and concomitant
Fermi surface reconstruction in underdoped YBCO. Here, using magnetotransport and
Hall effect measurements, we find signatures of a
Fermi surface reconstruction similar to that in pure YBCO indicating the presence of 2D charge order in Pr-YBCO. Additionally, we find that the phase diagrams of Pr-YBCO and YBCO are decidedly symmetric despite the additional disorder in the former and the distinction between hole depletion through Pr substitution and through O reduction. This indicates that while the mechanism of doping differs, the amount of charge carriers in the planes is the most important factor governing the electronic orders in these systems.
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All authors C. M. Duffy, M. Altangerel, S. Badoux, D. Vignolles, T. Oustric, C. M. Moir, Keke Feng, A. Frano, M. B. Maple, L. Taillefer, C. Proust
Strongly Correlated Electrons
Interfacial Strain Modulated Correlated Plasmons in La1.85Sr0.15CuO4 and Their Role in High-temperature Superconductivity
Xiongfang Liu, Shengwei Zeng, Xun Liu et al. (+9 more)
High-temperature superconductivity in cuprate materials remains a major challenge in physics due to the complexity of their strongly correlated electronic states. Interfacial strain is a powerful lever for tuning electronic correlations in complex
oxides, offering new pathways to control emergent
quantum phases. Here, we report the discovery of interfacial strain modulated correlated plasmons observed exclusively in superconducting La1.85Sr0.15CuO4 (LSCO) through spectroscopic ellipsometry. This form of plasmons is absent in the non-superconducting LSCO counterparts. Detailed analysis reveals that these correlated plasmons, arising from the collective excitations within Mott-correlated bands, are driven by long-range electronic correlations in the Cu-O planes. Furthermore, long-range electronic correlations, intricately modulated by interfacial strain, may play a crucial role in the emergence of superconductivity and in tuning the transition temperature. Dynamical cluster approximation (DCA) with
quantum Monte Carlo (QMC) calculations of the extended Hubbard model suggest that long-range Coulomb interactions play an important role in LSCO, showing good agreement with our experimental findings. The collective evidence from both the experimental results and theoretical findings provides new insights into the nature of collective excitations and their pivotal role in the emergence of high-temperature superconductivity.
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All authors Xiongfang Liu, Shengwei Zeng, Xun Liu, Kun Han, Difan Zhou, Chi Sin Tang, Ping Yang, Mark B. H. Breese, Chuanbing Cai, Ariando Ariando, Mi Jiang, Xinmao Yin
Soft Condensed Matter
A single-chain nanoparticle-based mean-field theory for associative polymers
Marco Cappa, Stefano Chiani, Francesco Sciortino et al. (+1 more)
Associative
polymers are a class of
polymers containing attractive stickers that can reversibly bind to each other. Their fully-bonded state gives rise, in dilute conditions, to a fluid phase of so-called single-chain nanoparticles (SCNPs). These constructs have been used in a wide range of applications, from the design of new materials (e.g. biomolecular condensates) to drug-delivery vectors. The thermodynamic properties of SCNPs sensitively depend on the number of different sticker types, since numerical simulations show that a continuous transition to a network of chains upon increase of
polymer concentration in the single sticker-type case can be replaced by an abrupt network formation (via a first-order phase transition) in the multiple sticker-type case. We present here a theory that, using the SCNP fluid as the reference system, quantifies the free energy change associated with transferring an intra-molecular bond to an inter-molecular bond, elucidating the impact on the phase separation process of the sticker
topology. Despite its simplicity, the theory highlights which microscopic assumptions (loop statistics, chain-level excluded volume) are most relevant for accurately capturing the thermodynamics of these systems. Our results match available numerical predictions obtained via coarse grained simulations of these systems, highlighting in particular the sensitivity of the phase behaviour on the sequence of the stickers along the chain.
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All authors Marco Cappa, Stefano Chiani, Francesco Sciortino, Lorenzo Rovigatti
Soft Condensed Matter
Machine Learning-based Optimal Control for Colloidal Self-Assembly
Andres Lizano-Villalobos, Fangyuan Ma, Wentao Tang et al. (+2 more)
Achieving precise control of colloidal self-assembly into specific patterns remains a longstanding challenge due to the complex process dynamics. Recently, machine learning-based state representation and reinforcement learning-based control strategies have started to accumulate popularity in the field, showing great potential in achieving an automatable and generalizable approach to producing patterned colloidal assembly. In this work, we adopted a machine learning-based optimal control framework, combining unsupervised learning and graph convolutional neural work for state observation with deep reinforcement learning-based optimal control policy calculation, to provide a data-driven control approach that can potentially be generalized to other many-body self-assembly systems. With Brownian dynamics simulations, we demonstrated its superior performance as compared to traditional order parameter-based state description, and its efficacy in obtaining ordered 2-dimensional spherical colloidal self-assembly in an electric field-mediated system with an actual success rate of 97%.
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All authors Andres Lizano-Villalobos, Fangyuan Ma, Wentao Tang, Wei Sun, Xun Tang
Materials Science
Interplay of Crystallization and Amorphous Spinodal Decomposition during Thermal Annealing of Organic Photoactive Layers
Maxime Siber, Olivier J. J. Ronsin, Gitti L. Frey et al. (+1 more)
Tailoring the nanomorphology of organic photoactive layers through a specialized chain of processing steps is an imperative challenge on the path towards reliable and performant organic electronic manufacturing. This hurdle generally proves delicate to be overcome, as organic materials can be subject to many different phase transformation phenomena that are able to interfere with each other and produce a wide variety of morphological configurations with distinct structural, mechanical, and optoelectronic properties. A typical combination of such mechanisms, which the present systems are often prone to, and which is complex to investigate experimentally at the nanoscale, is the phase separation resulting from the interplay between amorphous demixing and crystallization. In this work, an in-house Phase-Field modeling framework is employed to simulate and, consequently, explain the phenomenological behavior of a photoactive bulk heterojunction during a thermal annealing treatment. The model predictions are validated against available electron microscopy imaging of the nanostructural
evolution during the process. It is demonstrated that the simulations can successfully provide a detailed comprehension of
crystal nucleation and growth shaped by amorphous spinodal decomposition, so as to yield valuable insights for physically-based morphology control. In addition, this study shows the relevance of extensive thermodynamic and kinetic characterizations of organic
semiconductor mixtures (e.g., phase diagram assessments, surface tension measurements, composition-dependent molecular diffusivity evaluations) for the associated field of research.
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All authors Maxime Siber, Olivier J. J. Ronsin, Gitti L. Frey, Jens Harting
Materials Science
Orbital-related gyrotropic responses in Cu$_2$WSe$_4$ and chirality indicator
Kazuki Nakazawa, Terufumi Yamaguchi and Ai Yamakage
In recent years, counterparts of phenomena studied in spintronics have been actively explored in the orbital sector. The relationship between orbital degrees of freedom and
crystal chirality has also been intensively investigated, although the distinction from gyrotropic properties has not been fully clarified. In this work, we investigate
spin and orbital Edelstein effects as well as the nonlinear responses in the ternary transition-metal chalcogenide Cu$_2$WSe$_4$, which has a gyrotropic but achiral
crystal structure. We find that in the Edelstein effect, magnetization is dominated by the orbital contribution rather than the
spin contribution. On the other hand, both the nonlinear
chiral thermoelectric (NCTE)
Hall effect–a response to the cross product of the electric field and the temperature gradient–and the nonlinear
Hall effect–conventional second-order response to the electric field–are found to be dominated by the Berry
curvature dipole. We further find that
spin-orbit coupling plays only a minor role in these effects, whereas the orbital degrees of freedom are essential. Finally, we demonstrate that the orbital
magnetic-moment contributions to both the Edelstein effect and the NCTE
Hall effect are closely linked to chirality, and we discuss the possibility of using them as a chirality indicator.
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Quantum Gases
Repulsive fermions and shell effects on the surface of a sphere
Lorenzo Frigato, Andrea Bardin and Luca Salasnich
In recent years, ultracold atomic gases confined in curved geometries have attracted considerable theoretical interest. This is motivated by recent realizations of bubble traps in microgravity conditions, which open the possibility of investigating
quantum many-body physics beyond the conventional flat-space paradigm. The theoretical interest up to now was mainly focused on Bose gases and their phenomenology, and has left the study of
Fermi gases behind. In this paper, we investigate a two-component repulsive
Fermi gas constrained to the surface of a sphere at finite temperature. We first analyze the non-interacting case, showing how the intrinsic geometrical features of the spherical surface give rise to a shell structure and modify the low-temperature thermodynamics compared to the flat two-dimensional gas. Repulsive interactions are then considered through an effective path-integral approach within a Hartree-Fock mean-field approximation, enabling us to derive the grand canonical potential and to regularize the associated Matsubara summation. We then investigate the stability of the
spin-balanced state and obtain the finite-temperature Stoner criterion for
fermions on a sphere, highlighting the interplay between the repulsive interactions and shell effects.
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Materials Science
Magnetic behavior and phase diagram of epitaxial Er3Fe5O12 thin films across the compensation temperature
Satakshi Pandey, Antoine Barbier, Anne Forget et al. (+6 more)
Rare-earth iron garnet (RE3Fe5O12) films are promising insulating ferrimagnets. They can show low
magnetic damping, perpendicular
magnetic anisotropy, and ultrafast
spin dynamics, which makes them ideal for
spin transport applications. In this work, we investigate the interaction between the
magnetic sublattices in Er3Fe5O12 thin films grown by pulsed
laser deposition on a Gd3Ga5O12 substrate. Structural and
magnetic characterization reveals high-quality single-
crystal growth, with compensation temperature close to the reported bulk value (~80 K).
Magnetic phase diagrams based on element-specific measurements map out the regions where ferrimagnetic, canted, and aligned phases are stable across the compensation temperature. The micromagnetic dynamics resulting from perpendicular
magnetic pulse perturbation of an in-plane magnetized layer was investigated at room temperature and reveals complex configurations. These results are a key feature for modulating magnetization dynamics through the compensation phenomenon, which is essential for
spin-based devices operating in a low-temperature regime.
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All authors Satakshi Pandey, Antoine Barbier, Anne Forget, Brice Sarpi, Francesco Maccherozzi, Roberto Sant, Nicholas B. Brookes, Jean-Baptiste Moussy, Pamella Vasconcelos Borges Pinho
Materials Science
Tight-binding and density-functional study of the Raman tensor in two-dimensional massive Dirac fermion systems
Selçuk Parlak, Abhishek Kumar, Runhan Li et al. (+2 more)
Recently, two unusual features were theoretically predicted for the Raman response of out-of-plane
phonons in
magnetic two-dimensional materials hosting massive Dirac
fermions. First, the phase difference between certain Raman tensor elements was found to be quantized to $\pm \pi/2$, sensitive only to the sign of the Dirac
fermion mass. Second, a selection rule was identified in the Raman intensity under circularly polarized light, which generalizes the well-known optical valley selection rule. These predictions were based on a low-energy effective model in the continuum approximation. Here, we test the robustness of those results for more realistic theoretical approaches. First, we calculate the Raman tensor for an electronic tight-binding model on a honeycomb
lattice with broken time-reversal and inversion
symmetries. Second, we compute the Raman tensor from density-functional theory for a monolayer of
ferromagnetic 2H-RuCl$_2$. Both calculations corroborate the analytical results found in the continuum model, thereby theoretically confirming the peculiar behavior of the Raman tensor for two dimensional massive Dirac
fermion systems.
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All authors Selçuk Parlak, Abhishek Kumar, Runhan Li, Maia G. Vergniory, Ion Garate
Materials Science
Extending the Flory-Huggins Theory for Crystalline Multicomponent Mixtures
Maxime Siber, Olivier J. J. Ronsin and Jens Harting
The Flory-Huggins theory is a well-established
lattice model that is commonly used to study the mixing of distinct chemical species. It can successfully predict phase separation phenomena in blends of incompatible materials. However, it is limited to amorphous mixtures, excluding systems where the phase segregation is shaped by the concurrent crystallization of one or several blend components. A generalization of the Flory-Huggins formalism is thus necessary to capture the coupling and the interplay of crystallization with amorphous demixing mechanisms, such as spinodal decomposition. This work therefore revolves around the derivation of a free energy model for multicomponent mixtures that encompasses the physics of both processes. It is detailed which concepts from the original Flory-Huggins theory are required to apprehend the presented developments and how the current framework is built upon them. Furthermore, additional discussion points address chemical potential calculations and selected examples of binary and ternary phase diagrams, thereby highlighting the variety of blend behaviors that can be represented.
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Quantum Gases
Finite-temperature quantum rotor approach for ultracold bosons in optical lattices
M. Rodríguez Martín and T. A. Zaleski
Interacting
bosons in optical
lattices directly expose
quantum phases in a clean, highly controllable environment. This requires engineering systems with very low
entropies, but the resulting temperature–interaction ratios $T/U$ of present experiments remain well above the domain where zero-temperature theories are expected to be reliable. The
quantum-rotor approach (QRA), while analytically powerful and extremely flexible, inherits ground-state phase correlations and therefore breaks down once thermal winding of the phase field becomes significant. Here we construct a finite-temperature extension of QRA by (i) performing resummation of winding-number contributions for temperatures $k_{B}T/U\lesssim 0.2$ and (ii) developing an auxiliary-variable expansion that remains accurate toward the classical limit. The resulting closed expression for the phase correlator is inserted into the standard spherical-approximation QRA without sacrificing the method's flexibility with respect to
lattice geometry and dimensionality. The approach reproduces the shrinkage of Mott lobes from $T=0$ up to $k_{B}T/U\simeq 0.2$ in quantitative agreement with theoretical predictions and with in-situ imaging experiments. This finite-T QRA thus supplies an analytic, computationally light tool for strongly correlated
lattice bosons and sets the stage for amplitude-fluctuation upgrades required at higher temperatures.
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Soft Condensed Matter
Explosive dispersal of non-motile microbes through metabolic buoyancy
Jimreeves David and Shashi Thutupalli
For non-motile microorganisms, spatial expansion in quiescent fluids is presumed to be limited by
diffusion. We report that microbial colonies can explosively circumvent this constraint through a self-amplifying physical process. As non-motile yeast and bacteria metabolize dense nutrients into lighter waste within their fluid environment, they generate buoyancy-driven Rayleigh-Bénard convection, an ubiquitous fluid-dynamical phenomenon that organizes material on scales from chemical reactors to planetary atmospheres. This robust, self-generated flow fragments and disperses cellular aggregates, which seed new growth sites, enhancing total metabolic activity and further strengthening the convective flow in an autocatalytic cycle. The resulting expansion follows accelerating power-law kinetics, quantitatively captured by a physical theory linking metabolic flux to flow velocity, and produces fractal patterns through a flow-focusing instability we term Circulation-Driven Aggregation, the hydrodynamic analogue of
Diffusion-Limited Aggregation. This `metabolic fireworks' mechanism establishes a canonical instance of proliferating active matter, where cellular metabolic activity self-organizes a physical transport engine–a living Rayleigh-Bénard convection–providing a fundamental, physics-based dispersal strategy.
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Superconductivity
On the Properties of Elemental and High-Tc Superconductors in an Applied Magnetic Field in a Unified Framework
G.P. Malik and V.S. Varma
The unified approach based on the Generalized BCS equations incorporating chemical potential employed to deal with the critical temperature, gap(s) and coherence length(s) of any
superconductor (SC) in an earlier paper is shown here to be also applicable when the SC is in an applied field. Presented herein are the calculated values of the following parameters related to its penetration depth and critical current density: the interaction parameter governing the formation of Cooper pairs (CPs), the number of occupied Landau levels, the number density of charge carriers, the critical velocity of CPs, and the values of chemical potential at T = Tc and zero. Our study is found to corroborate the finding reported by Rasolt and Tesanovic [Revs. Mod. Phys., 64, 709 (1992)] that in some systems the effective electron-electron interaction is enhanced with increasing
magnetic field and sheds new light on the finding reported by Audouard et al. [Euro. Phys. Lett., 109, 27003 (2015)] that the properties of a
superconductor in
magnetic fields are controlled by a single band despite the multiband nature of the
Fermi surface. The SCs dealt with are Cd, Zn, Al, In, Hg, MgB2, YBCO, Bi-2212 Bi-2223, Tl-2212, Tl-2223 and compressed H3S and LaH10.
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