Papers

Integrating epitaxial thin films of ferroelectric PbTiO3 and paraelectric SrTiO3 into artificially layered periodic superlattices provides a unique platform for tuning strain, depolarization, and interfacial/surface energies, thereby accessing a rich phase diagram of topological polar structures (skyrmions, vortices, merons, or sinusoidal waves) and superstructures (polar supercrystals). Here we show that the 3D arrangement of polar vortices in a supercrystal suppresses thermal conductivity (k) of PTO/STO superlattices (SLs). The temperature dependence of k reflects the evolution of the polar superstructure, as determined by X-ray diffraction and transmission electron microscopy. The comparison with other SLs suggests that the 3D arrangement is crucial for controlling thermal conductivity beyond the usual interfacial scattering. Moreover, we observed an unexpected reduction in thermal conductivity with increasing superlattice thickness, a phenomenon reminiscent of phonon-wave Anderson localization. Our results show that complex polar superstructures can be useful active elements for modulating heat transport in technologies where control over heat dissipation is critical.

Magnetophonon resistance oscillations (MPR) associated with the resonant scattering of electrons by optical phonons at temperatures of 77-240 K, as well as resonant scattering of electrons by acoustic phonons (PIRO) at temperatures of 10-25 K, were investigated in the same samples featuring a GaAs quantum well and AlAs/GaAs superlattice barriers doped with Si. The study of MPR demonstrated that resonant electron scattering occurs on bulk longitudinal optical phonons and does not depend on the dimensionality of the system or inter-subband transitions in systems with two subbands of size quantization. However, the amplitude of the oscillation with number $N=1$ in two-dimensional structures depends on the interplay of scattering mechanisms, which, in turn, is influenced by the structure of the system. As for PIRO, in samples with two size quantization subbands, resonant electron scattering by longitudinal acoustic phonons is observed against the background of inter-subband transitions (MISO), leading to their interference.

We construct a measure that exhibits two aspects of a new type of universality and dramatically simplifies the integration of tensors $T_{a_1,a_2,\ldots,a_D} \in \mathbb{C}$ ($a_1,\ldots,a_D=1,\ldots,N$) at large $N$. In contrast to matrix integration, in which matrix traces canonically yield the integrand, tensors need additional information (equivalent to a $D$-coloured graph $B$) to contract their indices and form a tensor trace $B(T)$. We show that, whenever each $B_1,\ldots, B_n$ can be obtained by a recursive construction known as melonicity, then the leading order in $N$ of the integral of $ {B_1}(T) {B_2}(T) \cdots {B_n}(T) $ is independent of the – often intricate – combinatorics of the traces $B_i$, but also, to our surprise, independent of $D$ as far as $D\geq 3$. Instead, at large $N$, these integrals are some functions (indexed by $n$) of the number of vertices $2p_i$ of $B_i$ which we call melonic polynomials. Melonic traces cumulants with respect to any ('interacting') measure \[ \exp\Big\{-N^{D-1} \sum_{i=1}^m g_i {B_i}(T)\Big\} \mathrm{d}\mu_0(T) \quad (g_1,\ldots,g_m \in \mathbb{R}, \mathrm{d}\mu_0(T) =\text{the tensor Gaussian}) \] with each $B_i$ melonic, can be computed with our universal measure that replaces each $B_i$ by a canonical trace depending only on $p_i$. We prove that any two melonic tensor models are indistinguishable at large-$N$, independently of the number of tensor indices (first universality aspect), and of the fine-grainedness of their interactions (second universality), being a sufficient condition that the couplings (the parameters $g_i$ above) agree and their respective traces are monomials with the same degree in $T$.

We use whispering-gallery-mode analysis to characterise the microwave dielectric properties of single-crystal TeO$_2$ at cryogenic temperatures and compare its loss performance with other low-loss dielectric materials. Finite-element modelling is combined with measurements at room temperature, 4 K, and 20 mK to develop accurate cryogenic simulations and extract the anisotropic dielectric permittivities, giving $\varepsilon_\parallel=25.75\pm0.08$ and $\varepsilon_\perp=20.90\pm0.07$. Loss measurements reveal quality factors as high as $9\times10^6$ and minimum loss tangents approaching $3\times10^{-8}$, placing TeO$_2$ among promising low-loss dielectrics for cryogenic microwave applications. Electron-spin-resonance spectroscopy further indicates a clean spin environment, while identifying distinct spin systems consistent with the known properties of the crystal.

Ternary and quaternary amorphous oxide semiconductors have many properties that make them promising candidates for use in electronic applications like display, memory, and back end of line logic. However, finding the right material for a given application and optimizing its properties, deposition, and integration, requires a thorough understanding of the physics and chemistry at play. When properly carried out, first principles computations can play a crucial role in enhancing this understanding. In this work, we highlight several pitfalls often observed in research applying these computations, with the Zn-Sn-O system as an example. We show that a proper understanding of the fundamental differences between the physics of the crystalline and amorphous or disordered phases is crucial, as is a proper statistical sampling of structural models. For the Zn-Sn-O system we conclude that from a performance point of view, mobility and initial threshold voltage, it is a promising material class. However, our computed results show that a similar sensitivity to hydrogen induced doping may be present as in IGZO.

Temperature is one of the central concepts of thermodynamics, yet its meaning far from equilibrium remains unclear. The problem is especially challenging in isolated quantum many-body systems, whose states evolve unitarily, may remain far from equilibrium, and retain energy coherence, a genuinely quantum feature with no direct classical counterpart. Specifically, energy fluctuations in a nonstationary quantum state have two distinct origins. Part of these fluctuations comes from uncertainty in the energy populations and has the usual thermodynamic meaning. The rest comes from quantum coherence between energy sectors and is responsible for the state's time dependence. We propose that, even away from equilibrium, temperature identifies the state within the family of regular states sharing the same energy-coherence structure. The resulting inverse temperature is obtained from a principle of minimum discrimination information, which selects the least distinguishable state compatible with the prescribed energy and coherence structure. This replaces the usual maximum-entropy principle, which, applied naively, can yield a biased estimator of the inverse temperature. We also lay the groundwork for an extension of the construction to subsystems and show that, although the inverse temperature of a subsystem is not determined by its reduced state alone, under an alignment assumption, its instantaneous rate of change is a local quantity for sufficiently large subsystems.

All glasses, including organic semiconductor glasses, are non-equilibrium materials whose properties will change with time. This physical aging process is poorly understood for organic semiconductors, hindering the rational design of highly durable devices. In this study, we investigated the volume and enthalpy recovery processes in both thin films and bulk glasses of N,N'-Bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD). Our results revealed that volume recovery kinetics exhibit negligible dependence on film thickness for liquid-cooled TPD films between 400 nm and 100 nm. Additionally, the volume recovery process in TPD films was strongly coupled to the enthalpy recovery observed in bulk TPD glasses during annealing near the glass transition temperature. Remarkably, TPD films prepared by physical vapor deposition at room temperature demonstrated exceptional resistance to physical aging, with an aging rate approximately one order of magnitude lower than that of their liquid-cooled counterparts. These results not only enhance our understanding of the non-equilibrium dynamics in amorphous systems but also offer valuable insights for the design of next-generation organic devices with significantly improved stability and durability.

Conformal field theory provides universal predictions for Loschmidt amplitudes following quenches from product states to critical Hamiltonians. Building on this observation, we develop a route to extracting conformal data from real-time dynamics without preparing critical low-energy states. After analytic continuation, the Loschmidt amplitude is described by a boundary-CFT partition function on a strip, whose transverse transfer matrix encodes both the boundary operator spectrum and the central charge. Local space-time perturbations of the amplitude are governed by equilibrium correlation functions, and therefore provide access to critical exponents. In parallel, generalized temporal entropies exhibit scaling with time analogous to the equilibrium scaling of spatial entanglement entropy. We show that the low-lying boundary spectrum can be reconstructed from the system-size dependence of finite-chain Loschmidt echoes, whose damped oscillations encode differences of boundary scaling dimensions. Finally, we propose a finite-size scaling protocol that can extract these quantities from simulations or experiments on state-of-the-art quantum platforms.

We calculate the valley-resolved Hall viscosity for Lorentz-invariant integer quantum Hall phases in Semenoff-semiconducting graphene-like systems at zero temperature. The Kubo formalism based discussion reported in Phys. Rev. B 100, 115421 (2019) revealed the divergence of single valley viscous Hall contributions for this case with only a valley-summed Hall viscosity being finite and therefore well-defined. Our approach to the Hall viscosity calculation is based on an equivalent Green function formulation within Wigner-Weyl calculus. We find that the previously identified divergence may be regularized in a way compatible with both valley-summed Hall viscosity and (non)local Hall conductivity. Together with the local Hall conductivity and its first nonlocal correction, reported as well in Phys. Rev. B 100, 115421 (2019), we extend the empirical relativistic Hoyos-Son formula to individual valleys. Both the original Hoyos-Son formula for Galilean invariant fluids and its relativistic extension to Dirac materials are found to be structurally identical for integer quantum Hall phases and expressible in terms of local electric and viscous Hall responses. In addition we evaluate the valley(-difference) Hall viscosity for biased Bernal bilayer graphene in the chiral fermion low energy approximation using the same regularization prescription. Prospects of measuring valley Hall viscosity in nonlocal transport for mono- and bilayer graphene- and group-VI TMD-based devices are discussed.

The bosonic Kitaev chain (BKC) model is a deceptively simple looking quadratic pairing Hamiltonian. Despite being purely Hermitian, it exhibits a number of striking non-Hermitian topological phenomena, including skin effects. We show here how symmetries play a key role in this model, and how identifying these allows one to develop generalized BKC-like models. We emphasize the surprising fact that any quadratic bosonic pairing Hamiltonian with a sublattice (chiral) symmetry necessarily has a dynamical matrix with an effective time reversal symmetry. This symmetry is unrelated to physical time-reversal, but enables non-trivial topological invariants. We also discuss how this symmetry is unrelated to another key property of the BKC, the decoupling of quadrature dynamics. This feature can instead be connected to a distinct symmetry, namely an effective particle-hole symmetry of the dynamical matrix. We discuss non-trivial generalized BKC models that only keep one of these two effective symmetries intact. We also provide a classification of all translationally-invariant 1D pairing Hamiltonians, and show connections between the BKC and a well-studied non-Hermitian fermionic system, the symplectic Hatano-Nelson model.

The identification of molecules that combine long spin coherence times and efficient spin-optical interfaces, ideally at room temperature, is pivotal towards the development of molecular quantum technology. By means of advanced first-principles methods, we here unravel the electronic structure for triangulene (1), its aza-cation derivative (2), and the crystal of 2,6,10-tri-tert-butyl-4,8,12-trimesityl-triangulene (3), and show that these organic diradicals possess a triplet ground state well separated from the first singlet excited state approaching 0.5 eV, closely resembling solid-state defects like nitrogen vacancy centers. In addition, we compute spin decoherence times due to the interaction with phonons and surrounding nuclear spins, showing that a deuterated molecule of 3 in a nuclear spin-free environment would support $T_2 = 0.21$ ms at 10 K. Importantly, we show that the engineering of specific low-energy vibrations could significantly improve $T_2$ toward the limit imposed by the molecular core spin relaxation, here estimated to be as long as $T_1=27$ ms at 300 K for 2. Finally, we compute two-phonon contributions to inter-system crossing at 300 K for2 as a luminescent prototype, and find that it is highly spin-selective, supporting the possibility to engineer optical read out and spin initialization. These results advance a unified first-principles theoretical foundation of spin decoherence and spin-selective excited-state processes and point to novel chemical design strategies for optically addressable, highly coherent molecular qubits.

The effective dynamics of a colloidal particle immersed in a complex medium at equilibrium is usually described in terms of a linear overdamped Langevin equation, possibly with memory. However, numerical simulations and experiments have shown that this linear model fails, suggesting that the effective dynamics of the probe is actually nonlinear. Focusing on the case in which the medium is described by a fluctuating and correlated Gaussian field, linearly coupled to the colloid, we derive this effective dynamics and discuss its various consequences, including those on the stochastic thermodynamics of a driven particle. When the field is generated by the particle itself, with negligible fluctuations, the resulting self-chemotactic dynamics turns out to display anomalous diffusion and run-and-tumble motion in low spatial dimension, which we characterise analytically.

Poly(amidoamine) (PAMAM) dendrimers are promising candidates for nucleic acid delivery; however, biocompatibility and transfection efficiency remain a challenge. Here, we investigated how the composition of short peptide tails conjugated to generation 2 PAMAM (G2) dendrimers influence DNA association and condensation across a range of pH values. Using a combination of potentiometric titrations, DNA precipitation assays, and coarse-grained molecular simulations with charge regulation, we show that the ionization of G2 dendrimers is strongly affected by both pH and proximity to DNA. Although charge regulation enhances dendrimer protonation and strengthens DNA association at low pH, DNA condensation by unmodified G2 remains largely insensitive to pH within the studied range. In contrast, conjugation of a single peptide tail introduces a pronounced pH dependence to DNA condensation. Histidine-containing conjugates exhibit the strongest response, with condensation efficiency decreasing markedly as the pH increases. Simulations reveal that the interaction strength between conjugates and DNA depends on both peptide composition and pH and that histidine-containing peptide tails become nearly neutral at physiological pH, contributing little to DNA binding. While single-conjugate simulations explain the trends in DNA association, they do not fully account for the observed condensation behavior, highlighting the importance of collective effects involving multiple conjugates. Overall, peptide conjugation transforms G2 PAMAM dendrimers from relatively pH-insensitive DNA condensing agents into pH-responsive DNA-binding systems. These findings provide molecular-level insight into the interplay between charge regulation, peptide composition, and DNA condensation.

2D van der Waals (vdW) magnets provide new opportunities for spin-orbit torque magnetoresistive random-access memory (SOT-MRAM) due to their unique properties. Electrically manipulating the magnetization of vdW magnets is key to realizing 2D SOT-MRAM, whereas conventional spin Hall materials such as heavy metals and topological insulators suffer from limitations in torque efficiency and energy consumption. Although recent studies show that the orbital Hall conductivity in light metals greatly exceeds the spin Hall conductivity, direct experimental demonstrations that the orbital Hall effect (OHE) can induce more energy-efficient SOT switching than the spin Hall effect in vdW magnets remain scarce. Here, we utilize Cr as the orbital current source to efficiently manipulate the magnetization of the vdW ferromagnet Fe3GaTe2 at room temperature. In the Fe3GaTe2/Pt (1.5 nm)/Cr (4.5 nm) trilayer structure, the orbital current originating from Cr is converted into the spin current via Pt, which then exerts a torque on Fe3GaTe2. Compared with control samples using 6 nm Pt as the spin current source, the switching current density in OHE-based devices is reduced by 3.9 times, resulting in a 52% reduction in power consumption. This work presents the promising potential of harnessing orbital currents to realize energy-efficient 2D SOT-MRAM.

Amorphous indium oxide (a-In$_2$O$_3$) is a high-electron-mobility semiconductor of central importance in thin-film transistors and a promising photoanode for solar-driven water oxidation. Despite sustained experimental and computational investigations, the structural motifs underlying its unusual transport properties and the existence of O-O peroxide-like bonds within its network have remained unresolved. Here we develop a MACE-based machine-learned interatomic potential trained on first-principles molecular dynamics trajectories and use it to generate and analyze amorphous structures containing up to 5120 atoms, two orders of magnitude larger than those adopted in typical ab initio studies. We find X-ray structure factors in excellent quantitative agreement with experiment and we confirm that In$_2$O$_3$ is a poor glass former, with the likely presence of quasi-crystalline regions in amorphous samples. Our large-scale structural analysis reveals extended chains of edge-sharing InO$_k$ polyhedra providing a concrete structural basis for the high electron mobility of a-In$_2$O$_3$. Our results strongly support the formation of O-O peroxide-like bonds in the amorphous network, with a mean length of 1.5 Å. We show that these bonds introduce localized in-gap states near the conduction band minimum, acting as a source of intrinsic n-type self-doping and enhancing sub-gap optical absorption. These effects are detectable via a distinct Raman feature near 850 cm$^{-1}$ that is absent in the IR spectrum. Overall, our results establish a comprehensive structure-property picture of a-In$_2$O$_3$, provide directly testable experimental predictions, and suggest that controlled amorphization is a viable strategy for improving the photoelectrochemical activity of a-In$_2$O$_3$.

Self-attention neural networks provide powerful variational wavefunctions that surpass the expressivity of traditional variational ansatze. This expressivity, however, comes with increased computational complexity, raising a pressing question about scalability – can such wavefunctions retain their accuracy at large system sizes? We apply self-attention wavefunctions to the two-dimensional homogeneous electron gas for up to N=169 particles, obtaining energies systematically lower than state-of-the-art DMC. Direct access to the ground state wavefunction further lets us recover the full collective-mode dispersion of the liquid phase, from the small-q plasmon branch to a roton-like minimum near q=2k_F. Observables at N=91 and N=169 are in near-perfect agreement, indicating convergence to the thermodynamic limit.

We investigate how irreducible multipartite entanglement, a long-range correlation by nature, can emerge from short-range dynamics far from equilibrium. Focusing on the Markov gap as a probe of irreducible tripartite entanglement (IrTE) in free-fermion chains, we uncover qualitatively distinct dynamical behaviors: the Markov gap grows either quasi-linearly or in staircase-like jumps depending on the initial state. We also propose attainable upper and lower bounds for the onset time of IrTE based on the Lieb-Robinson bound. Strikingly, the Markov gap saturates to a volume-law value on a timescale $t\sim\! L^2$, much slower than the ballistic spreading of bipartite correlations. To understand what information about the wavefunctions is revealed by the Markov gap calculation, we introduce the concept of essential tripartite fermion (ETF) and an associated tripartite null matrix. The value of Markov gap closely tracks the number of small singular values of this tripartite null matrix, yielding a transparent, operational physical interpretation of the measure. We further demonstrate that several dynamical signatures persist in the interacting XXZ chain.

Accurate evaluation of Gibbs free energies is essential for constructing pressure-temperature phase diagrams. Conventional methods based on the quasi-harmonic approximation (QHA) require phonon spectra at many volume points and are therefore expensive in general. Here we develop an efficient method based on the interpolation of a few ab initio data points for Gibbs free energy evaluation under volume compression. Phonon spectra are calculated only at selected volumes. An effective Gruneisen parameter derived from the zero-point energy (ZPE) reconstructs the static-ZPE branch, while piecewise mode-resolved Gruneisen slopes reconstruct the finite-temperature vibrational branches on the target volume grids. The method is validated against QHA benchmarks for diamond (C), Al, Si, Ge, rutile TiO2, beta-PtO2, and Ta2O5 polymorphs. For simple benchmark systems (C, Al, Si, Ge, rutile TiO2, and beta-PtO2), the Gibbs free energy mean absolute errors (MAEs) relative to the QHA benchmarks remain below 0.53 meV/atom, with a six-system average of 0.148 meV/atom, while the number of explicit phonon volume points is reduced from about 20-21 to 3 in the lowest-cost implementation. For the more complex Ta2O5 polymorphs, the reconstructed free energies reproduce the main phase-stability topology despite larger phase-dependent errors. With reference to the QHA workflows, the interpolation method in this work achieves speedups of 5.911-9.023 times and remains reliable for moderate compression ranges where phonon frequencies vary smoothly with volume.

We investigate the space-time evolution of the magnetization induced in a 2D ferromagnetic island by a short pulse of a rotating electric field. The field generates elastic twists that act on the magnetization via the Barnett effect: magnetization by rotation. Analytical studies are conducted within classical electrodynamics of continuous media and continuous elastic theory, while numerical studies are performed using discretized Landau-Lifshitz spin dynamics on the atomic lattice. The effect is studied for typical parameters of magnetic oxides at various field frequencies and amplitudes, and for various strengths of magnetic anisotropy, exchange, and damping. The possibility of reversing the island magnetization with an electric-field pulse is demonstrated.

We study the critical properties of random quantum circuits with a $U(1)$ symmetry subject to local projective measurements that explicitly break this symmetry. We find that, at the measurement-induced phase transition, symmetry-breaking measurements act as a relevant perturbation at large scales, leading to the same universal critical properties as the corresponding monitored random circuit with non-symmetric unitary dynamics. In particular, we consider monitored $U(1)$-symmetric Haar-random circuits in the limit of large local Hilbert-space dimension, where the trajectory-averaged entanglement entropy can be exactly obtained in terms of a classical statistical mechanics model. In this model, the charge associated with the conservation law follows a symmetric simple exclusion process, in which symmetry-breaking measurements correspond to disordered defects that create and destroy charges. We prove that the charge correlation length remains finite for any measurement rate, ruling out a charge-sharpening transition, in contrast to the case of symmetry-preserving measurements. We further support our predictions at finite local Hilbert-space dimension through numerical finite-size scaling analyses of the entanglement transition in monitored $U(1)$-symmetric Haar and stabilizer random circuits.

We use a gate-defined Josephson junction (JJ) device made from twisted-layer graphene for studying vortex dynamics in two dimensions. The JJ sensor signals the presence of individual vortices in the superconducting leads nearby the junction through shifts in the Fraunhofer interference pattern of the magnetic-field-dependent critical current $I_c(B)$ across the junction. Rapid vortex fluctuations manifest as telegraph-type noise in time traces of the junction voltage $V(t)$. Measurements of $I_c(B)$ and $V(t)$ are interpreted in terms of multi-vortex processes where fast vortex fluctuations in the leads are modulated by quasi-stationary vortices trapped in the leads. The different timescales associated with these processes allow for their disentangling and quantitative analysis. Tracking the temperature dependence of the vortex-dynamical rates between $T = 7$ mK and $T = 120$ mK, we find that the creep type vortex motion is thermally activated above $T \approx 100$ mK, while the saturation of rates below $T \approx 80$ mK is suggestive of a sharp transition to macroscopic quantum tunneling of vortices.

We develop a general framework for the statistics of mixed-dimensional excitations subject to intertwined conservation laws, extending the familiar Fermi statistics with conserved particle number. We define statistics microscopically through a hopping-operator algebra: a local operator subalgebra (LOsA) generated by operators that locally move or deform excitations while preserving the conservation law. Nontrivial statistics arise when this subalgebra is nontrivial. We first focus on LOsAs that encode pointed conservation laws. These give rise to invertible excitations, whose fusion rules are exactly those of the symmetry defects of a higher group $\cG$. For such $\cG$-conserved excitations in $d$-dimensional space, we show that the corresponding LOsA – and hence the statistics it defines – is classified by a cohomology class $[\omega] \in H^{d+2}(B\cG;\R/\Z)$, where changing $[\omega]$ by a coboundary corresponds merely to a rephasing of the local operators. We further provide a holographic realization: excitations with this prescribed conservation law and statistics live on the boundary of a $\cG$ higher-group gauge theory in $(d+1)$-dimensional space, twisted by $[\omega]$. More generally, non-pointed conservation laws and the associated statistics of non-invertible excitations are defined by a pair: a LOsA together with its excitation-complex representation. This is equivalent to the pair consisting of a LOsA and its Hilbert-space representation, which is the data defining a generalized symmetry. Consequently, non-pointed conservation laws and their statistics in $d$-dimensional space are classified by fusion $d$-categories, just as generalized symmetries are. The higher-group results above are the fully-pointed special cases of this more general classification.

We show that geometric curvature, encoded in the folding angle between two corner-sharing triangles on a kagome lattice, provides a continuous tuning knob for topological magnon phase. Starting from an extended spin Hamiltonian with exchange, Dzyaloshinskii-Moriya (DM) interaction, and a higher-order bow-tie coupling of scalar chiralities, we derive the chirality-mediated hopping amplitude, which depends on the folding and spin canting of the bow-tie triangles. At small folding and canting angles, the bow-tie coupling surpasses DM, establishing a curvature-dominated regime. These results establish curvature as an intrinsic geometric control parameter for topological magnonics and reveal a direct analogy with chirality-induced spin selectivity in molecular systems, pointing to a unified mechanism for chirality driven transport across scales. The mechanism is particularly relevant for chiral crystals where the DM interaction is weak or forbidden by symmetry, as in systems with a six-fold screw axis.

Renormalization provides a framework for relating microscopic models of physical systems to effective descriptions at larger length scales. This procedure is studied for the boundary states of non-chiral two-dimensional topologically ordered models. The initial data consist of renormalization fixed points built from representations of finite-dimensional $C^*$-Hopf algebras, which are then perturbed by uniform on-site noise quantum channels and repeatedly coarse-grained. The resulting flows admit an intrinsic algebraic description in terms of completely positive maps on the $C^*$-Hopf algebra or, equivalently, positive linear functionals on its enveloping $C^*$-Hopf algebra. Their iteration is governed by convolution powers, and convergent trajectories yield new matrix product density operator fixed points, described by finite $*$-quantum hypergroups. This provides a concrete physical interpretation of such structures. For finite group algebras and their duals, we provide explicit classifications via Goursat's lemma for groups. Finally, we formulate and prove a quantum generalization of Goursat's lemma for finite-dimensional $C^*$-Hopf algebras, a result of independent interest, which gives an explicit structural description of all convergent renormalization trajectories.

Despite enormous expenditures in the research field, the electron-doped side of nickelate superconductors remains uncharted territory. Substituting the trivalent rare-earth cations by a tetravalent one hitherto failed. Here, we demonstrate by first-principles calculations a disorder-free route to electron dope Ruddlesden-Popper nickelates. When intercalating wide-band-gap insulating layers such as La$X$O$_3$ ($X$=Al, Ga, Sc) into La$_2$NiO$_4$, the extra (LaO)$^+$ layers act as electron donors, releasing carriers into the Ni-3$d$ orbitals. This electron doping puts La$_2$NiO$_4$:La$_2$AlO$_4$ naturally in the optimal region for $d_{x^2-y^2}$-wave superconductivity with T$_c$ exceeding 50 K. The same concept also allows us to electron dope La$_3$Ni$_2$O$_7$, the superconductor in the limelight.

Nanofluids, which are composed of insoluble, stable, and well-dispersed solid particles of nanoscale and/or subnanometer sizes suspended in a base liquid, are the next generation of liquids of today. The purpose of this paper is to investigate the one dimensional and three dimensional angle dependent radial distribution functions RDF and ARDF of polymeric nanofluids made up of nonrigid (soft) nanoparticles and a polymer melt (base fluid) using the molecular dynamics simulation approach and to search the shape stabilities by using these results. For this purpose, we use the nanoparticles of three different sizes: 28, 42, and 56 particles. We research them both within the base fluid and without this polymeric medium for instability analysis. We found that the nanoparticles with 28 atoms show the shape instability inside the base fluid when we increase the system temperature from T=1.2 to T=1.8 and hence, the structure of two concentric spherical shell of the nanoparticle breaks down and as a result the empty vacuum between these inner and the outer shells disappears. In contrast to this findings, the nanoparticles with 42 and 56 atoms show the shape stability inside the base fluid by preserving their concentric shell structures when we rise the system temperature and decrease the affinity between the nanoparticles and the base liquid medium.

Light carries angular momentum, but the microscopic pathways that transform it into magnetization remain elusive. Here we establish that crystal-field excitations, historically viewed primarily as equilibrium spectroscopic fingerprints of localized 4$f$ electrons, constitute an active microscopic route through which circularly-polarized terahertz (THz) light creates magnetic polarization. Using wavelength-selective ultrafast Faraday spectroscopy on the paramagnetic insulator CeF$_3$, we show that resonant excitation of localized 4$f$ crystal-field transitions generates a helicity-dependent magnetization that survives for up to about 100 ps. Most strikingly, while the optical helicity is held fixed, the THz-driven response reverses sign as the excitation wavelength is tuned across the crystal-field resonance. The resulting dispersive spectral response follows the crystal-field excitation spectrum rather than that of optical phonons, and is captured by resonant electronic theory of the inverse Faraday effect. Our results identify crystal-field excitations as a previously unrecognized dynamical reservoir for optical angular momentum and broaden the microscopic pathways through which THz light can create and manipulate magnetic states.

In recent years, crystal generation models have enabled the design of massive numbers of candidate materials. However, the lack of dynamical stability among generated structures has become a major bottleneck preventing their translation into practical materials discovery. To address this challenge, we propose PhononScore, a phonon-aware scoring function for crystal generation. Unlike computationally expensive explicit phonon calculations, PhononScore predicts a unified stability score from crystal structures, enabling ranking of candidate materials dynamical stability with second-level computational cost. We construct a multi-fidelity phonon dataset containing 157,463 crystal structures. On the PhononBench benchmark, PhononScore improves the average dynamical stability rate of candidate pools generated by nine crystal generation models from 30.7% to 83.7%, achieving a 2.72-fold enrichment of stable structures, while the average stability rate of the Top-10 candidates reaches 97.5%. On a high-fidelity DFT-PBE phonon benchmark, the DFT-finetuned PhononScore-DFT increases the Top-100 stability rate to 93.0% and achieves 5-6-fold enrichment of dynamically stable structures under an extremely imbalanced hard-screening scenario. As a materials-screening tool analogous to scoring functions in drug discovery, PhononScore can serve directly as a dynamical-stability feedback signal for crystal generation, active learning, and reinforcement learning, enabling second-level stability-aware reranking without explicit phonon calculations and providing a unified and efficient dynamical stability evaluator for high-throughput materials discovery, active learning, reinforcement learning, and closed-loop inverse design. The online PhononScore platform is available at: http://phononbench.cn/phononscore/

In monolayer transition metal dichalcogenides, exciton valley relaxation is typically attributed to the Dyakonov-Perel (DP) mechanism, where frequent intravalley scattering with phonons or defects suppresses the intervalley exchange-induced precession and the role of intervalley scattering is considered secondary. Employing a first-principles nonequilibrium exciton Green's function (NEGF) approach with the generalized Kadanoff-Baym ansatz (GKBA), which treats exchange-driven precession and exciton-phonon scattering on an equal footing across the full Brillouin zone, we demonstrate that even in the small momentum regime most favorable to DP physics, realistic exciton-phonon scattering is too weak to induce the motional narrowing that defines the DP regime. Upon accounting for excitons across the entire Brillouin zone, large momentum intervalley scattering becomes the dominant pathway for valley relaxation, shortening the depolarization by a factor of 3-4 relative to intravalley-only models. We find that valley depolarization and decoherence time are approximately 50 fs at 300 K and lengthen to 130 fs at 10 K. By comparing our results with a Lindblad-type collision framework, we explicitly demonstrate the role of non-Markovian effects and reveal that the Markovian Lindblad framework is highly basis dependent. In the valley-pseudospin basis underlying prior analyses, the Lindblad approach artificially amplifies scattering-induced equilibration, biasing the dynamics toward a DP interpretation. Our study provides a comprehensive picture of valley relaxation, and establishes the exciton density matrix approach derived from NEGF+GKBA as a powerful tool for investigating ultrafast exciton dynamics.

We interpret the strange metal (SM) properties of slightly overdoped cuprates in terms of the recently proposed Shrinking Fermi Liquid theory. This is based on the pervading presence in the cuprate phase diagram of charge density fluctuations (CDF), which have been identified and characterized in RIXS. These fluctuations are abundant and have a low energy due to the proximity of the charge density wave quantum critical point hidden under the superconducting dome of cuprates, but have a short range and non-critical character with a finite energy M/\gamma ~10 meV as measured above Tc. Here M~ \xi^-2 is determined by the short correlation length \xi, while \gamma encodes the Landau damping ruling the lifetime of the charge fluctuations. Besides these low energy CDF, cuprates also display phonons and a broad continuum of particle-hole excitations, mostly due to spin paramagnons arising from their strongly correlated character. With these experimentally characterized ingredients we show that above Tc the SM properties in transport are well described in terms of fermionic Landau quasiparticles scattering with CDF and phonons. The optical properties can instead be interpreted by the combined effect of low energy CDF determining the temperature dependence, and of the paramagnon continuum determining a linear in frequency scattering rate. Remarkably, the combined effect of these simple ingredients also induces \omega/T scaling properties for frequencies larger than M/\gamma. When superconductivity is suppressed by strong magnetic fields the SM properties extend down to a few Kelvin. By assuming that the CDF dissipation parameter \gamma grows logarithmically by lowering T, we account for all anomalous transport and thermodynamic properties of cuprates (specific heat, Seebeck, heat transport, resistivity, and magnetoresistance) thereby providing a consistent scenario for the SM phase of cuprates.