Papers

Many subcellular condensates continuously produce biopolymers. Coupling Flory-Huggins thermodynamics to two-fluid viscoelasticity, we probe the diffusion of such source-driven polymeric droplets, and identify a universal structural compressive rim at their diffusion front. Integrating analytical scaling laws, numerical simulations, and experimental data, we show that this framework captures key structural and dynamic characteristics of the nucleolus, demonstrating the role of polymer diffusion in non-equilibrium biological transport.

Scalable quantum photonic technologies require deterministic sources of entangled photons that are compatible with established semiconductor manufacturing platforms. While self-assembled III–V semiconductor quantum dots are among the most promising sources of on-demand entanglement generation, their integration with silicon-based architectures remains a central challenge. Here, we demonstrate energy–time entanglement from a single InGaAs/GaAs quantum dot monolithically grown on a silicon substrate. Under coherent two-photon excitation, we achieve coherent control of the biexciton–exciton cascade, evidenced by Rabi oscillations and dressed-state formation. Using a four-channel Franson interferometer, we observe phase-dependent two-photon interference with visibilities up to $(64.0 \pm 7.0)\%$ for an 80 ps integration window (and $(49.4 \pm 1.9)\%$ for a 1600 ps window), approaching the threshold for Bell inequality violation at short time scales. These results establish monolithically integrated III–V-on-silicon quantum dots as promising sources of energy–time entangled photons for scalable quantum photonic technologies.

We theoretically investigate the linear and second-order nonlinear optical responses of valley-polarized bilayer graphene under uniaxial strain. Employing a low-energy effective Hamiltonian that incorporates trigonal warping and strain-induced anisotropy, we calculate the optical susceptibilities within the quantum kinetic formalism. We show that, while the second-order response vanishes in valley-balanced bilayer graphene owing to the cancellation of contributions from opposite valleys, a finite valley polarization lifts this cancellation and enables a net second-harmonic generation (SHG) signal. Uniaxial strain substantially modifies the nonlinear response by distorting the low-energy electronic structure and altering the pseudospin texture, producing a highly anisotropic SHG spectrum. Pronounced resonant enhancements occur at photon energies $\hbar\omega \approx E_f$ and $\hbar\omega \approx 2E_f$, associated with two-photon and one-photon interband resonances, respectively. Remarkably, changing the sign of the strain parameter reverses the direction of the induced second-harmonic current, providing a mechanically controlled switching mechanism for nonlinear optical transport. These results establish strain engineering as an effective route for manipulating valley-dependent nonlinear optical phenomena in bilayer graphene and suggest new opportunities for tunable mid-infrared photonic and valley-optoelectronic applications.

Garnet-type lithium lanthanum zirconium oxide Li$_7$La$_3$Zr$_2$O$_{12}$ (LLZO) is a favorable solid electrolyte for all-solid-state Li-ion batteries due to its wide electrochemical stability, compatible ionic conductivity, and good safety. However, further improvement in ionic conductivity is required for its practical applications. In this work, titanium (Ti) is doped into LLZO to enhance its Li-ion transport properties and structural stability. The series Li$_7$La$_3$Zr$_{2-x}$Ti$_x$O$_{12}$ has been successfully synthesized using conventional solid-state reaction method. The content of Ti has been varied from 0 to 0.20 atoms per formula unit (a.p.f.u). The conducting cubic phase has been confirmed by the X-ray diffraction technique (XRD). Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) have been used for structural analysis, and elemental distribution. Density measurements have been carried out for all the samples. Electrochemical impedance spectroscopy revealed that the high ionic conductivity of $8.08\times 10^{-5}$ Scm$^{-1}$ is offered by the Li$_7$La$_3$Zr$_{1.9}$Ti$_{0.1}$O$_{12}$ sample, which has the lowest activation energy of 0.37 eV. The DC polarization analysis verified that the main contribution to conductivity in the 0.10 Ti sample comes from ions. A one order of magnitude increase in room temperature ionic conductivity is observed for the 0.10 Ti sample, making it a strong candidate for solid electrolyte applications.

Periodically driven quantum systems offer remarkable flexibility in tailoring effective Hamiltonians and synthetic band structures. However, such driving also induces heating and dynamical instabilities that limit the coherence and lifetime of many-body states. Here, we demonstrate that these instabilities can be suppressed by employing multi-tone driving schemes. Using a Bose-Einstein condensate of cesium atoms in an optical lattice, we experimentally explore two approaches: pulsed driving composed of odd harmonics and two-tone driving with tunable amplitude and relative phase. We show that both methods allow independent control of the effective tunneling amplitude and Peierls phase factor, while significantly reducing phonon excitation and the resulting rapid decay of the condensate. Numerical simulations and theoretical modeling based on Bogoliubov-de Gennes equations confirm the suppression of unstable modes under optimized driving conditions. Our results establish multifrequency drives as powerful tools for stabilizing driven many-body systems and pave the way toward robust Floquet engineering with interactions.

We study the critical dynamics of the quantum random-field Ising model using the nonperturbative functional renormalization group (NP-FRG). The static critical behavior is found to be controlled by the zero-temperature fixed point of the classical random-field Ising model, where both thermal and quantum fluctuations are dangerously irrelevant. Considering a family of quantum dynamical universality classes defined by a bare dynamical kernel $F_\Lambda(\omega)\sim |\omega|^\sigma$, we show how this fluctuationless fixed point nevertheless controls the quantum dynamics by computing the full Matsubara-frequency dependence of the running dynamical kernel $F_k(\omega)$. This is essential at zero temperature: a naive treatment of the dynamical kernel flow leads to a divergence at a finite length scale, resulting in apparent localization. In contrast, keeping the full frequency dependence of the dynamical kernel and choosing a regulator adapted to its running scale yields a controlled flow. The resulting dynamics is of activated form, with a relaxation time given by $\ln \tau \sim \xi^\Psi$. The exponent $\Psi$ is determined by the static RFIM fixed-point exponents and by $\sigma$. At finite temperature, the flow crosses over to the classical thermally activated scaling of the random-field Ising model. These results provide a quantitative field-theoretic realization of the heuristic activation scenario proposed earlier for the quantum random-field model and establish a framework for analyzing the dynamics of other disordered quantum systems that may exhibit similar tentative localization-like singularities.

Machine learning models are increasingly trained as regressors and then deployed as generators, from language models to learned simulators. In this setting, accuracy on held-out data says little about the distribution a model produces when it is sampled. We study this problem where the correct distribution is fixed by first principles, in machine learning interatomic potentials (MLIPs) trained by minimizing the mean squared error (MSE) on density functional theory (DFT) energies and forces, then used to run molecular simulations. The MSE never constrains the Boltzmann distribution that the potential defines, so an MLIP can match held-out DFT data and still drift, when sampled, into spurious minima that corrupt its thermodynamics. Building on the variational principle of statistical physics, we introduce Contrastive Regularized MSE (CRMSE), a post-training step in which the potential acts as its own energy-based model and learns to reproduce the distribution it generates, without any new DFT data. On molecules from the MD17 benchmark, CRMSE restores physical sampling and recovers DFT free-energy profiles, while keeping energy and force errors within chemical accuracy. Our results suggest that a model meant to be sampled must be trained on the distribution it produces, not only for pointwise accuracy.

Quantum tunneling is fundamental to diverse phenomena and underpins a wide range of modern technologies. In the study of superconducting quantum computation and high-temperature superconducting materials, tunneling on multi-particle scale is central. Recently, several cold atom experiments successfully simulated the tunneling process in a many-particle ensemble. However, the many-body nature remains largely unexplored. Here, we observe the universal scaling of many-body effects in quantum tunneling process, using a hexagonal-triangular quantum simulator with independent control of barrier, temperature and interaction. In the weak-interaction regime, the critical tunneling coefficient scales parabolically with temperature under various conditions, in contrast to the linear scaling of single-particle tunneling. By further increasing the interactions beyond the mean-field regime, the scaling exponent decreases, consistent with quantum field theory predictions. Our results address the fundamental question of how many-body effects renormalize quantum tunneling, with direct implications for correlated quantum matter and devices.

We employ large-scale Dissipative Particle Dynamics simulations to investigate dilute solutions of linear polymers and unknotted, non-concatenated ring polymers in explicit solvent. By systematically varying solvent quality, we examine the interplay between hydrodynamic interactions, chain architecture, and intermolecular association. Under good solvent conditions, both linear and ring polymers remain expanded and well dispersed, displaying center-of-mass dynamics consistent with normal diffusion. In poor solvents, attractive polymer-polymer interactions drive the formation of irregular aggregates characterized by partial chain collapse, substantial interpenetration, and slower dynamics. Despite their different topologies, the two polymer architectures exhibit remarkably similar structural and dynamical responses across the solvent conditions considered. These results indicate that solvent quality largely determines the organization and transport properties of dilute polymer solutions, whereas topological effects remain comparatively weak in the investigated regime.

The dynamic magnetic pair-density function (DymPDF) $D_{\rm M}(r, E)$ is obtained via the Fourier transform of the dynamic magnetic structure factor, $S_{\rm M}(Q, E)$, which is measured using nonpolarized inelastic neutron scattering. While there is a long history of magnetic excitation studies with $S_{\rm M}(Q, E)$, there are no reports on $D_{\rm M}(r, E)$. In this study, we examine simple magnet models and representative magnet examples, such as FeTiO$_{3}$ and YBa$_{2}$Cu$_{3}$O$_{6}$, to investigate the real-space dynamics of $D_{\rm M}(r, E)$. We derive the $D_{\rm M}(r, E)$ equations for simple magnet models in a low energy limit. By comparing these equations to the simulations, we demonstrate the characteristic energy dependence of real-space local magnon modes, including the transition of the magnon mode from acoustic to optical. Our novel analysis reveals the local magnon modes accompanied by a sign change in each spin-pair correlation at a given energy in nanoscale real space even under non-periodic conditions. This method is unique for studying local magnetic dynamics.

We study $N$ non-interacting Brownian particles in an external potential under simultaneous stochastic resetting to the origin. Although they do not interact directly, common resets generate strong dynamically emergent correlations (DEC). We analyze how confinement modifies these correlations and the nonequilibrium stationary state for $V(x)=\kappa |x|^\alpha$, $\alpha\geq0$, focusing mainly on two analytically tractable cases: harmonic confinement (HC), $\alpha=2$, and box confinement (BC), $\alpha\to\infty$. In both cases the stationary state is controlled by the competition between confinement and resetting lengths. We derive exact results for the stationary joint distribution, density, correlations, extreme value statistics (EVS), and gap statistics. While the density behaves similarly in HC and BC, the normalized correlation coefficient differs sharply. In BC it is non-monotonic and overshoots the unconfined value, as hard walls suppress decorrelating trajectories. In HC it instead increases monotonically toward the unconfined limit. For general $\alpha$, the behavior is monotonic for $0<\alpha<\alpha_c=1+\sqrt{5}$ and non-monotonic for $\alpha>\alpha_c$. The difference between HC and BC is also visible in edge observables. In HC, the maximum scales as $M_1=O(\sqrt{\ln N})$ and has a limiting distribution with bounded support and a shape transition controlled by the ratio of the two length scales. In BC, the maximum is at distance $O(1/N)$ from the boundary, as in equilibrium, but its fluctuations have a broad power-law tail with logarithmic corrections. The first gap shows a similar contrast: BC gives a smaller typical gap but stronger anomalous fluctuations than HC. Finally, we extend the EVS analysis to general $\alpha$ and identify, via simulations and scaling arguments, three universality classes: $0\leq\alpha\leq1$, $1<\alpha<\infty$, and the singular limit $\alpha\to\infty$.

Skyrmion stability is commonly assumed to scale with skyrmion size or exchange stiffness within micromagnetic models. Here, we demonstrate that long-range exchange frustration can break this paradigm, enhancing the collapse energy barrier without increasing skyrmion size or magnetic energy scale. By mapping the continuum model onto a spin-lattice Hamiltonian, we find that skyrmions with identical micromagnetic parameters can exhibit significantly different energy barriers, depending on their underlying atomistic exchange interactions. We attribute this behavior to saddle point textures, whose pronounced noncollinearity captures long-range frustration beyond the micromagnetic approximation. We further develop an exchange optimization framework to predict that long-range frustration can double the energy barrier in physically realistic conditions, possibly valid for ultrathin films or van der Waals magnets. These results hold across different lattice symmetries, revealing an intrinsic limitation of micromagnetics and establishing long-range frustration engineering as a promising route toward highly stable nanoscale skyrmions.

Many biological machines function through controlled conformational transitions, yet designing synthetic nanostructures with prescribed dynamical behavior remains a major challenge. Here, we develop a modular inverse-design framework for bistable nanostructures whose function is controlled by an energy profile along a geometric reaction coordinate. Inspired by proteins with rigid domains connected by flexible hinges, we introduce a hinge-arm paradigm in which a small bistable hinge controls the energetics of a conformational transition, while rigid arms map this transition onto the separation between external binding sites. Specifically, we ask which features of a target energy profile can be programmed under different design constraints. We find that the energy barriers and the binding-site separations in the two metastable states can be readily designed, while controlling the location of the transition state or the full shape of the energy profile requires additional design freedom. Using a differentiable design framework, we find that some optimized solutions are numerically inexact but still display the functional behavior for which the target profile was selected, emphasizing the importance of function-based evaluation criteria. These results establish a practical hierarchy of designability for bistable nanostructures and provide a route toward synthetic nanomachines that couple conformational transitions to target behavior.

In light of the increasing supply chain concerns regarding silver for solar cell metallization, the replacement of the silver contacts by copper is desirable. As copper diffuses readily in silicon, deposition of an additional diffusion barrier to protect the respective absorber material stacks is required. We investigate multifunctional layers of transparent conductive oxides (TCOs) from the In-Zn-O system to serve as front electrode and Cu diffusion barrier coating, focusing on purely amorphous layers without grain boundaries to impede copper diffusion. We employ a 2D combinatorial approach to simultaneously screen the Zn/(In+Zn) ratio and the oxygen content in a single materials library deposited by magnetron sputtering without intentional substrate heating. Cu diffusion barrier performance was evaluated by depositing Cu on top of intentionally ultrathin In-Zn-O libraries of 7 nm on silicon wafers and annealing them at temperatures of 200-450{\deg}C. Both the formation of copper silicides, as well as the silicon photoluminescence signal were monitored. The first was detected only after the crystallization of the In-Zn-O films and required annealing temperatures of 450{\deg}C and above. Even for extended dwell times of 20 h at a relevant process temperature of 200{\deg}C, we find no evidence of Cu ingress for most of our fabricated In-Zn-O compositions, whereas Si/Cu stacks without In-Zn-O barriers showed a reduction of their photo-luminescence intensity already after less than 1 h. These results suggest thin amorphous In-Zn-O films with an optimal Zn/(In+Zn) ratio of ~0.12 and intermediate oxygen deficiency as effective transparent conductive Cu diffusion barriers for solar cell applications.

Quasiperiodic systems usually interpolate between extended, critical, and localized states as the quasiperiodic modulation is increased. Here we show that the magnetic Qi-Wu-Zhang Chern-insulator model realizes a distinct full-spectrum transition in which localization is avoided. For an irrational magnetic flux, the two-dimensional model reduces to a spinor quasiperiodic chain with a matrix onsite modulation controlled by the hopping amplitude $t_x$. When $|m+2|>t_y$, increasing $t_x$ produces the conventional extended-critical-localized sequence with a critical line at $t_x=t_y$. In contrast, when $|m+2|\le t_y$, the system changes from an extended phase to a critical phase at $t_x=|m+2|$ and remains critical even for stronger quasiperiodic modulation. Finite-size scaling of the average inverse participation ratio gives $\overline{\mathrm{IPR}}\sim q^{-\alpha}$ with $0<\alpha<1$ throughout this persistent critical regime. A dual transformation exchanging $t_x$ and $t_y$, together with a Lyapunov-exponent analysis, explains the phase diagram. Wave-packet dynamics further distinguish ballistic, anomalous-diffusive, and localized regimes. These results identify magnetic Chern-insulator systems as a natural platform for robust criticality and anomalous quantum transport.

We consider a family of continuous-time Markov chains with finite strongly connected transition graph and rates $\left(r_N\right)_{N>0}$ depending on a parameter $N$, so that, when $N$ is large, transitions may happen on different time scales. Under suitable general assumptions on the asymptotic behavior of the rates, we give a recursive characterization of the limiting invariant measure. The recursion is encoded in a forest structure equivalent to the one recently developed in the analysis of dynamical aspects of metastability \cite{BL,LX}. Our proof is based on a combinatorial representation of the invariant measure, given by the Markov chain tree theorem. Basic steps are the reduction of the chain by a trace process, the introduction of an effective dynamics, and a careful analysis of the set of relevant arborescences in the expansion. In particular we use a factorization of fast arborescences. As a byproduct we obtain properties of the arborescences of generalized star-delta reductions of weighted digraphs.

We study scattering in noninteracting multi-terminal quantum wire junctions and show that junctions with dihedral symmetry can exhibit exact zero-reflection points for $N \ge 4$ terminals. By analyzing the scattering matrix, we identify these reflectionless points in the $(E,t')$ parameter space, where $E$ is the incident particle energy and $t'$ is the junction hopping amplitude. These points exhibit an even-odd dependence on $N$ and converge asymptotically to a common limiting value in the large-$N$ limit. We show that the reflectionless points are characterized by an integer winding number associated with the phase of the reflection amplitude, providing a topological description for their stability against weak on-site disorder. We also consider junctions with broken time-reversal symmetry and find that a magnetic flux can induce additional reflectionless points, including for the $N = 3$ case. For a four-terminal junction threaded by a $\pi$-flux, we identify a unique parameter regime in which the reflection amplitude vanishes over the entire energy band. Finally, we discuss experimental signatures through the behavior of Friedel oscillations and examine the stability of these reflectionless points in the presence of weak interactions.

Spin point groups classify magnetic phases in the weak spin-orbit coupling regime and characterize the static properties of altermagnetic phases, but their dynamical consequences remain largely unexplored. Here, we derive selection rules for high-harmonic generation of charge and spin currents by extending dynamical symmetry to include spin point group operations. Since spin currents transform under both real and spin space operations, whereas charge currents transform only under real space operations, spin current selection rules can reveal magnetic information that is inaccessible to charge current harmonics. In a minimal altermagnetic model, an axis-aligned linearly polarized drive is non-diagnostic for distinguishing ferromagnetic and altermagnetic phases, although the antiferromagnetic phase is distinguished by the absence of the corresponding spin-current harmonics. A diagonal linearly polarized drive distinguishes the three spin-point-group phases within the weak-coupling spin-group description, whereas a single-helicity circularly polarized drive provides a sharper spin-current-harmonic criterion for distinguishing them from magnetic-point-group mimics. These results establish spin current harmonics as a dynamical probe of spin group symmetry. Finite spin-orbit coupling lifts these zeros only perturbatively: the forbidden harmonics acquire amplitudes analytic in the coupling strength, so that the fingerprint becomes a small same-order helicity contrast, below $3\times10^{-2}$ at low orders for couplings up to $10^{-2}$ of the hopping in our model.

Recent Scanning Tunneling Microscopy (STM) experiments measuring the superconducting gap features in thin films of superconducting bilayer nickelates La2PrNi2O7 at ambient pressure and compressive strain paved the way to study the Cooper-pairing models and the band-selective identification of the gap features in these systems. Here, using the realistic two-orbital bilayer model and the continuum Green's function formalism, we theoretically analyze orbital and band-selective local density of states as well as the corresponding STM spectra. We find that the multiorbital character and the spatial dependence of the Wannier functions leads to the spectra developing characteristic features depending on the position of the scanning tunneling microscope's tip. This allows for a band-resolved analysis of the superconducting coherence peaks and scattering momenta. We identify a clear path for experimental measurements to not only identify the debated incipiency of the gamma-band, but also identification of the coherence peaks' band origins via distance dependent measurements of the local density of states and its corrections through impurity scattering.

We have studied spin-related transport in a polycrystalline NiCo2O4 (NCO) film on a MgAl2O4/Si(001) substrate, motivated by potential applications of the theoretical half-metallicity of NCO to Si-based high-performance spin-transport devices. Our approach is to systematically measure and analyze the temperature dependence of the film's resistivity ($\rho-T$) with various in-plane currents (100 nA$-$1 mA) and temperatures (4$-$290 K). With increasing current, the $\rho-T$ curve changes drastically from semiconducting ($d\rho/dT<0$) to non-monotonic and eventually toward metallic ($d\rho/dT>0$). A distinctive feature is that the single NCO film exhibits a $\rho-T$ characteristic of polycrystalline defective NCO at 100 nA, whereas it exhibits a $\rho-T$ characteristic of epitaxial less-defective NCO over a wide temperature range at 1 mA. This current-induced evolution of $\rho-T$ reflects the enhancement of the Curie temperature of defective regions near grain boundaries, accompanied by enhanced spin alignment there. We proposed a spin-related transport model that extends conventional hopping conduction models by incorporating the temperature- and current-dependent degree of spin alignment, as well as its spatial dependence inherent to polycrystalline NCO. This model comprehensively explains the interplay between the spin-alignment profile and transport mechanism. The analysis reveals that spin injection from grain bodies to grain boundaries enhances the spin alignment there and strengthens double-exchange interactions, facilitating conduction. This phenomenon strongly depends on both temperature and current. Our findings provide evidence of spin-polarized electrons inside the grain bodies, highlighting the potential of our polycrystalline NCO film as an efficient spin source. The present model is further supported by current$-$voltage and magnetoresistance features.

Rare-earth quantum materials provide a promising platform for emergent phenomena ranging from quantum spin liquids with long-range entanglement to topological magnetic textures. However, the strong spin-orbit coupling that stabilizes their low-energy pseudospin degrees of freedom also tends to generate strongly anisotropic exchange interactions, complicating the realization of quasi-isotropic Heisenberg magnetism. Here we investigate the microscopic origin of superexchange in $\mathrm{Ce}^{3+}$- and $\mathrm{Yb}^{3+}$-based insulators with edge-sharing octahedral geometry. Using degenerate perturbation theory for a multiorbital Hubbard model, we show that isotropic exchange originates predominantly from virtual hopping within the ground-state Kramers doublet, whereas anisotropic interactions arise primarily from processes involving excited multiplets. This leads to a simple orbital design principle: quasi-isotropic exchange is promoted when the ground-state doublet has a strong maximal-angular-momentum character with respect to the quantization axis perpendicular to the superexchange plane spanned by rare-earth and ligand ions. We demonstrate this mechanism for both ideal and distorted geometries and show that it is broadly consistent with experimentally studied Yb-based insulators. Our results establish a practical framework for engineering quasi-isotropic interactions in rare-earth quantum materials.

Motivated by the quest for active quantum matter, we investigate the dynamics of an impurity immersed in a quantum gas – a polaron – whose coupling to the surrounding medium is periodically modulated in time, alternating in sign. By integrating out the bath degrees of freedom, we derive an effective velocity-dependent drag force acting on the impurity. Above a critical modulation frequency, the corresponding drag coefficient becomes negative at low velocities, signaling the onset of self-propulsion. In the classical limit, we characterize this transition as a function of the modulation frequency and the bath chemical potential. We then compute the leading-order quantum corrections to the impurity dynamics and show that, while the transition remains robust, it can be suppressed by sufficiently precise measurements of the impurity position.

We investigate the emergence of topological superconductivity at the two-dimensional heterostructure interface between a $p$-wave magnet (pWM) and an $s$-wave superconductor. By analyzing nodal gap closings, we identify seven distinct nodal topological phases, each characterized by the presence of Majorana zero-energy flat bands and quantized zero-bias conductance peaks. We demonstrate that the effective $p$-wave nature of the system gives rise to spin-triplet pairing correlations with even-frequency, odd-parity and odd-frequency, even-parity symmetries. Notably, the introduction of inter-orbital hopping induces an exotic orbital-singlet term characterized by simultaneous odd-parity and odd-frequency. Furthermore, we explore the transition from static phases to Floquet topological regimes through periodic driving. These driven phases host both zero and $\pi$ Majorana flat bands, with transport signatures governed by the Floquet sum rule. Most significantly, we show that periodic driving fundamentally reshapes the topological and superconducting landscape by generating multiple nodal points that support higher winding numbers and multiple Majorana flat bands, while the emergent Floquet degree of freedom doubles the number of symmetry-allowed Cooper-pair correlations. The first class of correlations is hosted by the even-Floquet sectors and has a direct counterpart in the static limit. In contrast, the second is a distinct Floquet-generated class that confines to the odd-Floquet sectors, representing a fundamentally nonequilibrium pairing channel that cannot exist in static systems. Finally, we demonstrate the robustness of these topological modes against strong disorder, confirming their potential for stable fault-tolerant applications.

Shallow strained Ge quantum wells have gained recent attention for realizing scalable, high-performance hybrid superconductor/semiconductor-based qubits. Epitaxial superconducting contacts can improve the quality and consistency of the superconductor/semiconductor interface. The growth of Ge quantum wells by molecular beam epitaxy is then motivating due to the relative ease of integration with epitaxial superconductor growth. However, the performance of Ge quantum wells grown by molecular beam epitaxy (MBE) has been limited. To improve the properties of MBE-grown Ge quantum wells, the growth conditions were systematically optimized. Thick buffer layers are utilized to eliminate certain defects, and an optimal growth temperature is found. A peak hole mobility of 105,000 cm\textsuperscript{2}/Vs at 2 K is obtained in a 22-nm deep Ge quantum well, demonstrating that the Ge quantum wells grown in this study represent the highest mobilities for shallow MBE-grown samples. Mobility modeling indicates that the increase in mobility due to growth temperature optimization are likely due to a reduction in interface roughness scattering, and further improvements in mobility are expected through improved surface passivation.

The relationship between plastic deformation accommodation structures and residual elastic strain fields in deformed metals is poorly understood at the intragranular scale, largely because no experimental technique has provided simultaneous, three-dimensional, bulk-sensitive access to both fields at the length scale of dislocation boundaries. Here we use dark-field X-ray microscopy (DFXM) to map intragranular misorientation and residual elastic strain simultaneously in three dimensions within a grain of 50% cold-rolled Fe 3%Si alloy. We resolve geometrically necessary boundaries (GNBs) and incidental dislocation boundary (IDB) cell structures in the bulk non-destructively. Correlating the elastic strain field with the segmented plastically deformed substructure reveals that GNBs act as the primary carriers and distributors of long range residual elastic strain. GNBs separate subdomains of distinct mean d-spacing, across the grain volume. The plastic misorientation associated with IDBs and dislocation cells develops within GNB-delimited subdomains that carry comparatively similar values of elastic strain. This supports a mechanistic picture in which GNBs accommodate nearly all the long-range residual elastic strain in the deformed state, while plastic slip propagates into GNB interiors to organize into IDB cells with similar strain levels. The three-dimensional misorientation and strain gradients quantified here provide direct experimental input for recovery and recrystallization modelling in ferritic steels, such as electrical steels.

This study presents a systematic investigation of Mn$_{1-x}$Pb$_{x}$(Bi$_{1-y}$Sb$_{y}$)$_{2}$Te$_{4}$ crystals over a wide range of concentrations (x = 10-60%, y = 5-60%). It was found that the value of the bulk band gap is determined exclusively by the Pb concentration and it closes at Pb 40-50 %, which corresponds to a topological phase transition. The position of the Dirac point is determined by the Pb/Sb ratio, rather than the absolute Sb content. The magnetic properties depend on the dilution of the Mn sublattice by Pb and are weakly sensitive to Sb. We show that the simultaneous substitution of Mn and Bi allows independent control of the topological phase and the position of the Fermi level.

We present a free-space plasmonic modulator based on a single heavily-doped semiconductor layer. We investigate its ability to modulate both the linear and nonlinear response at mid-infrared frequencies slightly below the plasma frequency of the semiconductor. We demonstrate electric control of the linear transmittance and reflectance, and of the efficiency of third-harmonic generation with a field-effect gate structure. We discuss further performance optimization of the device in terms of modulation speed and depth towards a fast modulator with very simple active material requirements. Our results establish a viable route toward practical plasmonic modulators and mixers operating in the mid-infrared atmospheric window available for free-space communications at wavelengths between 8 and 12 um.

Fully compensated ferrimagnets (fFIMs) have attracted interest due to their compensated moments and nonrelativistic spin splitting across the Brillouin zone. Known fFIMs, however, are mostly restricted to complex three-dimensional (3D) systems or require external fields in two-dimensional (2D) heterostructures, leaving intrinsic fFIM monolayers unexplored. We identify a hidden-phase MnSe monolayer, derived from the (001) planes of wurtzite, as an intrinsic fFIM featuring inequivalent sublattices not linked by any symmetry. It is a unipolar magnetic semiconductor (UMS) with perpendicular magnetic anisotropy (528.60 * 10^-3 eV per unit cell) and simultaneously exhibits ferroelectricity (polarization 4.63 * 10^-10 C/m) and ferroelasticity (signal 61%), with barriers of 7.6 * 10^-3 and 0.10 eV/f.u., respectively, establishing a single-phase triferroic system. The ground fFIM UMS characteristics are robust against strain up to 3%. The In2Se3/MnSe heterostructure enables nonvolatile electrical control between semiconducting and metallic states. Constructed tunnel junctions exhibit giant tunneling magnetoresistance (2.98 * 10^5%), electroresistance (6.97 * 10^14%), elastoresistance (7.95 * 10^4%), and near-perfect spin filtering (~100%). Collectively, this spontaneous 2D fFIM with coexisting triferroic orders provides a promising platform for ultrahigh-density, low-power, and miniaturized memory devices.

Achieving continuous control over macroscopic thermal expansion remains a fundamental challenge in solid-state physics. Using classical and path-integral molecular dynamics alongside lattice dynamics at near-ab initio accuracy, we report an entropy-driven thermal-expansion crossover from positive (PTE) to negative thermal expansion (NTE) in alkoxy-functionalized MOF-5, an archetypal metal-organic framework (MOF). We demonstrate that this non-linear response is continuously tunable via the alkoxy side-chain length, quantified by the number of carbon atoms $n$ grafted onto the archetypal cubic MOF-5 framework: systems with short chains ($n \le 2$) exhibit monotonic NTE, whereas longer chains ($n \ge 3$) trigger a pronounced PTE-to-NTE crossover. At low temperatures, thermal activation of longer side chains opens additional conformational states and generates steric pressure inside the pore, driving positive expansion through a gain in side-chain conformational entropy. Conversely, at elevated temperatures, the side chains enhance transverse linker fluctuations and strengthen the string-tension mechanism associated with low-frequency framework modes, causing structural contraction favored by framework vibrational entropy. Finally, by varying the concentration of side-chain-functionalized linkers, the thermal expansion coefficient can be continuously regulated to realize negative, near-zero, and positive thermal expansion within selected temperature windows. These results establish side-chain engineering as a practical route for programming macroscopic thermodynamic responses in MOFs.

We establish a coordinate-free differential geometric framework for anomalous transport in topological bands using the Hodge-de Rham decomposition of the Brillouin zone. Standard formulations face mathematical singularities (Dirac strings) when using the quantum Berry connection in bands with non-zero Chern numbers. Applying this decomposition to the Berry curvature 2-form isolates the quantized topological monopole flux from a globally smooth geometric 1-form proxy potential, $\mathcal{A}$. Substituting this regularized potential into semiclassical transport integrals yields distinct analytical advantages. For linear transverse transport, our cohomological decomposition enables an exact geometric derivation of Haldane's insight via the co-area formula, partitioning the response into a continuous Fermi sea topological background and a localized Fermi surface geometric line integral. For non-linear transport, this globally smooth proxy unifies the geometric description, reproducing the high numerical stability of scalar integration-by-parts techniques directly from its exact sector, accommodating arbitrary Chern numbers. By enforcing the continuous Coulomb-Hodge gauge ($\delta \mathcal{A} = 0$) alongside vanishing harmonic holonomies over fundamental 1-cycles ($\oint_{\gamma_i} \mathcal{A} = 0$), we map the Hodge potential $\mathcal{A}$ to the Maximally Localized Wannier Function (MLWF) gauge in trivial bands, providing a non-singular computational proxy for topologically obstructed bands. Finally, we analytically demonstrate that solving the Hodge Laplacian for $\mathcal{A}$ zeroes the macroscopic Brillouin zone average (uniform $\mathbf{R}=0$ zero-mode) topological divergence, yielding a mathematically consistent covariant formulation that matches the algorithmic robustness of standard methods against discrete $\mathbf{k}$-grid noise.