It has been demonstrated experimentally that friction forces between a two-dimensional (2D) material and an amorphous substrate are sufficient to stabilize tensile and compressive strains on the order of 1% within the 2D material. Here, a simple atomic-scale model is used to explore the friction between a 2D material and an idealized substrate. The atomic-scale model shows that the observed strains can be sustained by bonds with strengths on the order of van der Waals bonds. The model also reveals interesting atomic-scale structures at the interface that include vortices, antivortices, and other more complicated structures.

Motivated by recent advances in ultracold atomic gas experiments, we investigate a two-terminal mesoscopic system in which two-body loss occurs locally at the center of a one-dimensional chain. By means of the self-consistent Born approximation in the Keldysh formalism, we uncover mesoscopic current formulas that are experimentally relevant and applicable to the weak dissipation regime. Although these formulas are analogous to those for systems with one-body loss, it turns out that the channel transmittance and loss probability depend on the nonequilibrium occupation at the lossy site. We demonstrate that this occupation dependence leads to a weaker suppression of currents in the presence of two-body loss compared to one-body loss.

The intertwining of electron-hole correlation and nontrivial topology is known to give rise to exotic topological excitonic insulators. Here, we show that the involvement of quantum geometry can characterize more exotic excitonic phases exhibiting physical properties that are not influenced by their topology but by geometry. Starting from a topological band insulator and gradually reducing the band gap, many-body interaction can initially generate a $p+ip$-wave and then an $s$-wave excitonic insulator. Interestingly, they bear the same Chern number but exhibit completely different spin textures and magneto-optical Kerr responses, reflecting the intricate geometric distinctions in their wave functions. We also propose to enhance the correlation effect via Floquet engineering, which provides a systematic way to realize these topological excitonic insulators and their phase transitions in the nonequilibrium steady states. Our results demonstrate correlated phenomena characterized by quantum geometry, beyond the conventional topological classifications.

Charge density wave (CDW) resulting from a periodic distortion in the lattice creates orders beyond the original lattice. In $2{H\text{−}\mathrm{NbSe}}_2$, one of the layered transition metal dichalcogenides, the $3\times 3$ charge order appears in two-dimensional (2D) layers. Although CDW can be observed by different techniques, the spatial distribution within a 2D layer has never been systematically visualized. Here, by using scanning tunneling microscopy and density functional theory, we monitored the evolution of CDW along the $c$ axis and found a strong relation with the orbital charges. The results show that the appearance of the CDW varies while tuning the tunneling current and undergoes a transition from Se orbital charges to Nb orbital charges. The calculation of orbital charge distributions shows that both CDW intensity modulation and the transition are strongly intertwined with the distribution of Se $4p$ orbitals and Nb $4d$ orbitals.

Several recent experiments have challenged the premise that cuprate high-temperature superconductors approach conventional Landau-BCS behavior in the high-doping limit. We argue, based on an analysis of their superconducting spectra, that anomalous properties seen in the most-studied overdoped cuprates require a pairing interaction that is strongly inhomogeneous on nm length scales. This is consistent with recent proposals that the “strange-metal” phase above $T_c$ in the same doping range arises from a spatially random interaction. We show, via mean-field Bogoliubov-de Gennes (BdG) calculations and time-dependent Ginzburg-Landau (TDGL) simulations, that key features of the observed tunneling spectra are reproduced when both inhomogeneity and thermal phase fluctuations are accounted for. In accord with experiments, BdG calculations find that low-$T$ spectra are highly inhomogeneous and exhibit a low-energy spectral shoulder and broad coherence peaks. However, the spectral gap in this approach becomes homogeneous at high $T$, in contrast to experiments. This is resolved when thermal fluctuations are included within TDGL; in this case, global phase coherence is lost at the superconducting $T_c$ via a broadened BKT transition, while robust phase-coherent superconducting islands persist well above $T_c$. The local spectrum remains inhomogeneous at $T_c$, and the gap is found to fill instead of close with increasing temperature.

Exploring ferromagnetic moments in magnetoelectric materials is of both fundamental and technological importance. It enables the control of the correlated state using an uncompensated moment. However, its material realization is challenging owing to its exclusive microscopic mechanisms. Here, we report a nearly isotropic ferromagnetic moment in the magnetoelectric antiferromagnet ${\mathrm{Co}}_4{\mathrm{Ta}}_2{\mathrm{O}}_9$, by performing dc and ac magnetic susceptibility, magnetization, and neutron diffraction measurements on identical single crystals. Combined with the group theory analysis, we demonstrate a $P1$ magnetic space group. This implies that physical activities can occur along any crystallographic direction, which explains the unusual magnetoelectric property of ${\mathrm{Co}}_4{\mathrm{Ta}}_2{\mathrm{O}}_9$. The ground state is classified as the M-type altermagnet based on the magnetic point group. Our study provides essential information to resolve the debate on the magnetic ground state and understand the magnetoelectric properties of the related compound with the prospect of observing and examining the $P1$ magnetic space group or ferromagnet in ferroelectrics.

We have revisited the nonconserved (or model A) critical dynamics of the two-dimensional Ising model through numerical simulations of its lattice and continuum formulations—Glauber dynamics and the time-dependent Ginzburg-Landau (TDGL) equation, respectively—to analyze them with current tools from surface kinetic roughening. Our study examines two critical quenches, one from an ordered and other one from a disordered initial state, for both of which we assess the dynamic scaling ansatz, the critical exponent values, and the fluctuation field statistics that occur. Notably, the dynamic scaling ansatz followed by the system strongly depends on the initial condition: A critical quench from the ordered phase follows Family-Vicsek (FV) scaling, while a critical quench from the disordered phase shows an initial overgrowth regime with intrinsic anomalous roughening, followed by relaxation to equilibrium. This behavior is explained in terms of the dynamical instability of the stochastic Ginzburg-Landau equation at the critical temperature, whereby the linearly unstable term is eventually stabilized by nonlinear interactions. For both quenches, we have determined the occurrence of probability distribution functions for the field fluctuations, which are time independent along the nonequilibrium dynamics when suitably normalized by the time-dependent fluctuation amplitude. Additionally, we have developed a related interface model for a field that scales as the space integral of the TDGL field (integral GL model). Numerical simulations of this model reveal either FV or faceted anomalous roughening, depending on the critical quenched performed, as well as an emergent symmetry in the fluctuation statistics for a critical quench from the ordered phase.

This report investigates the role of orbital degrees of freedom in ${\mathrm{CrVO}}_4$, focusing on orbital-driven spin-exchange interactions and spin-phonon coupling through both experiments and first-principles calculations. Combining synchrotron radiation x-ray powder diffraction, Raman spectroscopy, and x-ray absorption fine structure measurements, a significant correlation between magnetic transition and structural modification was identified, revealing spin-lattice coupling at the transition ($T_N$). This coupling is linked to conventional magnetoelastic interactions, even active above $T_N$, supported by both experimental and theoretical findings. The calculations revealed crystal field splitting and orbital nondegeneracy resulting from charge transfer in the $3d^3$ system of ${\mathrm{CrVO}}_4$ due to octahedral symmetry breaking. The study discusses the detailed mechanism of orbital-resolved spin-exchange interactions, leading to one-dimensional A-type antiferromagnetic ordering. Notably, no significant orbital-selective spin-phonon coupling was observed at approximately 200 K ($4T_N$) in ${\mathrm{CrVO}}_4$, in contrast to earlier studies [A. P. Roy et al., Phys. Rev. Lett. 132, 026701 (2024)]. These findings advance the understanding of the fundamental physics in ${\mathrm{CrVO}}_4$ and significantly contribute to the field of spin-orbital-lattice physics in transition metal oxides.

Nitrogen-vacancy (NV) centers in diamond and superconducting qubits are two promising solid-state quantum systems for quantum science and technology, but the realization of controlled interfaces between individual solid-state spins and superconducting qubits remains fundamentally challenging. Here, we propose and analyze a hybrid quantum system consisting of a magnetic skyrmion, an NV center, and a superconducting qubit, where the solid-state qubits are both positioned in proximity to the skyrmion structure in a thin magnetic disk. We show that it is experimentally feasible to achieve strong (coherent or dissipative) coupling between the NV center and the superconducting qubit by using the quantized gyration mode of the skyrmion as an intermediary. This allows coherent information transfer and nonreciprocal responses between the NV center and the superconducting qubit at the single quantum level with high controllability. The proposed platform provides a scalable pathway for implementing quantum protocols that synergistically exploit the complementary advantages of spin-based quantum memories, microwave-frequency superconducting circuits, and topologically protected magnetic excitations.

Simultaneous breaking of time reversal and inversion symmetries in multiferroics couples ferroelectricity to magnetism and is a source of unusual physical phenomena that can be used in next-generation electronic devices. A notable example is ${\mathrm{DyFeO}}_3$, which under applied magnetic fields exhibits a giant linear magnetoelectric response and a large spontaneous electric polarization induced by coexisting orders of Fe and Dy subsystems. Here, we use high-resolution neutron diffraction to show that at zero field ${\mathrm{DyFeO}}_3$ hosts an incommensurate magnetic soliton lattice formed by spatially ordered Dy domain walls with an average domain size of 231(8) Å. The long-ranged interaction between the domain walls is mediated by magnons propagating through the Fe subsystem and is analogous to the Yukawa force in particle physics. An applied magnetic field destroys the long-ranged incommensurate order, unlocks the linear magnetoelectric response, and stabilizes the ferroelectric state. The magnetic domain walls are electrically charged and the soliton array dimerizes when both electric and magnetic fields are applied. Numerical simulations with experimental parameters suggest that the generic competition between the ferroelectric and incommensurate states can be effectively controlled by an applied electric field.

We report the observation of multiple quantum-well (MQW) polaritons in organic-inorganic metal halide two-dimensional (2D) perovskite films with precisely controlled well-layer numbers. Using the Langmuir-Blodgett method, we fabricated high-quality MQW structures that eliminate well-width fluctuations, enabling the study of MQW polaritons in the low layer number region. Optical reflection spectroscopy and transfer matrix calculations reveal that spectral changes with increasing well numbers originate from MQW-polariton effects, successfully demonstrating the correspondence between spectral structures and MQW-polariton modes. We identify the superradiant regime, where a single radiant mode dominates, followed by the sequential emergence of higher-order radiant modes. These findings provide crucial insights into the evolution of MQW polaritons toward three-dimensional polaritons and contribute to fundamental studies of ultimate 2D systems. Furthermore, our results offer valuable knowledge for the development of perovskite-based optical devices.

A 20-nm-wide (100)-oriented HgTe quantum well (QW) hosts a two-dimensional (2D) semimetal comprising both electrons and holes. In this study, we report that in addition to the previously observed quadratic temperature dependence of resistance, the system also displays an unexpected linear temperature dependence within specific top-gate voltage ranges. To account for this behavior, we extend the existing theoretical framework for temperature-dependent resistance in HgTe QW-based 2D semimetals with a focus on electron-hole scattering at low temperatures. Using the Boltzmann transport equation, we investigate the role of electron-hole interactions in this 2D semimetal. Our calculations reproduce a resistivity temperature dependence that aligns closely with experimental data. These findings establish this system as a robust platform for exploring interaction-limited transport regimes in a two-component plasma, particularly in the presence of disorder.

Exchange-only (EO) qubits, implemented in triple-quantum-dot systems, offer a compelling platform for scalable semiconductor-based quantum computing by enabling universal control through purely exchange interactions. While high-fidelity single- and two-qubit gates have been demonstrated, the synthesis of efficient multiqubit operations—such as the Toffoli gate—remains a key bottleneck. Conventional gate decompositions into elementary operations lead to prohibitively long and error-prone pulse sequences, limiting practical deployment. In this work, we introduce a gradient-based optimization algorithm, Jenga-Krotov (JK), tailored to discover compact, high-fidelity EO gate sequences. Applying JK to the Toffoli gate, we reduce the number of required exchange unitaries from 216 (in direct decomposition) to 92, and compress the time steps required from 162 to 50, all while maintaining target fidelity. Under realistic noise, the accumulated gate error from our optimized sequence is an order of magnitude lower than that of conventional approaches. We have also applied the JK algorithm to other multiqubit gates and algorithm. For the Fredkin gate, it reduces the number of time steps from 200 to 104 and the number of exchange unitaries from 276 to 172. For the quantum Fourier transform, it compresses the sequence from 180 to 80 time steps and from 237 to 202 exchange unitaries. These results demonstrate that the JK algorithm is a general and scalable strategy for multiqubit gate synthesis in EO architectures, potentially facilitating realization of multiqubit algorithms on semiconductor platforms.

We study a class of bifurcations generically occurring in dynamical systems with nonmutual couplings ranging from models of coupled neurons to predator-prey systems and nonlinear oscillators. In these bifurcations, extended attractors such as limit cycles, limit tori, and strange attractors merge and split in a similar way as fixed points in a pitchfork bifurcation. We show that this merging and splitting coincide with the coalescence of covariant Lyapunov vectors with vanishing Lyapunov exponents, a feature that generalizes the exceptional points that can exist in families of non-Hermitian matrices or operators. We distinguish two classes of bifurcations associated with generalized exceptional points, corresponding respectively to continuous and discontinuous behaviors of the covariant Lyapunov vectors at the transition depending on the presence of a ${\mathbb{Z}}_2$ symmetry. We outline some physical consequences of this class of theories exhibiting generalized exceptional points, including nonreciprocal responses, the destruction of isochrons, and anomalous noise effects. In particular, we show that the effective diffusion coefficient on the attractor can stay finite or even diverge when the noise strength vanishes. We illustrate our results with concrete examples from neuroscience, ecology, and physics.