Recently, it was realized that liquid viscosity has a lower bound which is nearly constant for all liquids and is governed by fundamental physical constants. This was supported by experimental data in noble and molecular liquids. Here, we perform large-scale molecular dynamics simulations to ascertain this bound in two other important liquid types: the ionic molten salt system LiF and metallic Pb. We find that these ionic and metallic systems similarly have lower viscosity bounds corresponding to the minimum of kinematic viscosity of $\sim {10}^{-7}{\mathrm{m}}^2/\mathrm{s}$. We show that this agrees with experimental data in other systems with different structures and bonding types, including noble, molecular, metallic, and covalent liquids. This expands the universality of viscosity bounds into the main system types known.

Altermagnets are compensated magnets with unconventional $d$-, $g$-, and $i$-wave spin order in reciprocal space. So far the search for new altermagnetic candidates has been focused on materials in which the magnetic unit cell is identical to the nonmagnetic one, i.e., magnetic structures with zero propagation vector. Here, we substantially broaden the family of altermagnetic candidates by predicting supercell altermagnets. Their magnetic unit cell is constructed by enlarging the nonmagnetic primitive unit cell, resulting in a nonzero propagation vector for the magnetic structure. This connection of the magnetic configuration to the ordering of sublattices gives an extra degree of freedom to supercell altermagnets, which can allow for the control over the order parameter spatial orientation. We identify realistic candidates ${\mathrm{MnSe}}_2$ with a $d$-wave order, and ${\mathrm{RbCoBr}}_3, {\mathrm{CsCoCr}}_3$, and ${\mathrm{BaMnO}}_3$ with $g$-wave order. We demonstrate the reorientation of the order parameter in ${\mathrm{MnSe}}_2$, which has two different magnetic configurations, whose energy difference is only 5 meV, opening the possibility of controlling the orientation of the altermagnetic order parameter by external perturbations.

Recent excitement in the quantum spin ice (QSI) community has come from the experimental discovery of pseudospin-$\frac{1}{2}$ breathing pyrochlores, including ${\mathrm{Ba}}_3{\mathrm{Yb}}_2{\mathrm{Zn}}_5{\mathrm{O}}_{11}$, in which inversion symmetry is broken by the “up” and “down” tetrahedra taking different physical sizes. We show here that the often-neglected $J_{z\pm }$ coupling between Kramers ions, in combination with the breathing nature of the lattice, can produce an imaginary ring flip term. This can lead to an unconventional “$U{\left(1\right)}_{\pi /2}$ phase”, corresponding to a maximally dense packing of visons on the lattice. The coherent, emergent QED dynamics of conventional QSI persist in this phase, in a manner reminiscent of fragmentation in spinon crystals. We characterize the excitations of the system within the enlarged QSI phase diagram, showing that the imaginary ring flip acts both as a chemical potential for visons and as an effective three-photon vertex akin to strong light-matter coupling. The coupling causes a structured high-energy continuum to emerge above the photon dispersion, which is naturally interpreted as three photon up-conversion in a nonlinear optical crystal.

We investigate quench dynamics of spin ice after removal of a strong magnetic field along the $\left[100\right]$ crystal direction, using Monte Carlo simulations and theoretical arguments. We show how the early time relaxation of the magnetization can be understood in terms of nucleation and growth of strings of flipped spins, in agreement with an effective stochastic model that we introduce and solve analytically. We demonstrate a crossover at longer times to a regime dominated by approximately isotropic clusters, which we characterize in terms of their morphology, and present evidence for a percolation transition as a function of magnetization.

In the realm of non-Hermitian physics and noise-control engineering, exceptional points (EPs), where two or more discrete eigenvalues and the corresponding eigenvectors coalesce, have garnered significant attention. Here, we present an integrated approach that fuses intrinsic loss through loss-factor modulation with extra airflow loss via the rainbow-trapping effect to reach the EP in a loss-only system. Moreover, by introducing the hierarchical concept with graded dimension and scaling effect, the asymmetric hierarchical acoustic metamaterials achieve efficient broadband sound absorption with absorption coefficients exceeding 0.7 over 400 Hz at low frequencies within the deep-subwavelength scale. This is evidenced through both numerical simulations and experimental results, showcasing near-total reflection from one side and high absorption from the other. This study presents a loss-induced hierarchical design approach for manipulating acoustic waves, offering insights for advancements in acoustic metamaterials and noise-control applications.

The classical $J_1-J_2$ Ising model on the square lattice is a minimal model of frustrated magnetism whose phase boundaries have remained under scrutiny for decades. Signs of first-order phase transitions have appeared in some studies, but strong evidence remains lacking. The current consensus, based upon the numerical data and theoretical arguments in [S. Jin et al., Phys. Rev. Lett. 108, 045702 (2012)], is that first-order phase transitions are ruled out in the region $g=J_2/\left|J_1\right|\gtrsim 0.67$. We point out a loophole in the basis for this consensus, and we find strong evidence that the phase boundary is instead weak first order at $0.67\lesssim g<\infty$ such that it asymptotically becomes second order when $g\to \infty$. We also find strong evidence that the phase boundary is first order in the region $0.5<g\lesssim 0.67$. We establish these results with adiabatic evolution of matrix product states directly in the thermodynamic limit, and with the theory of finite-entanglement scaling. We also find suggestive evidence that when $g\to 0.5^{+}$, the phase boundary becomes of an anomalous first-order type wherein the correlation length is very large in one of the coexisting phases but very small in the other.

The discovery of hydrogen-rich high $T_c$ superconducting materials, such as ${\mathrm{H}}_3\mathrm{S}$ and ${\mathrm{LaH}}_{10}$ under the ultrahigh pressures of more than one million atmospheres is constantly refreshing the record of superconducting critical temperature, ushering the era of room temperature superconductivity. Herein, we investigate the role of the hydrogen bond in the superconductivity of the superhydrides of oxygen, as the hydrogen bond reflects an electronic structure of oxygen in terms of the polarity of the lone pair of electrons. In an extensive exploration of the structures and superconductivity in oxygen hydrides, we predict a high $T_c$ superconducting transition in $Im\text{−}3m$ phase of ${\mathrm{H}}_3\mathrm{O}$ with first-principles calculations combined with swarm-structure search. A high $T_c$ of 301.5 K is obtained, as the $Im\text{−}3m$ phase of ${\mathrm{H}}_3\mathrm{O}$ is dynamically stabilized at the pressure as high as 670 GPa. It is found that a significant contribution to superconduction arises from the oxygen $s$-state electrons. With increasing the pressure, the orbital hybridization brings the essential rise of the coordination unsaturation that is favorable for the emergence of the superconductivity, whereas the superhydride compound reaches the stability at a much higher pressure than that for the isoelectric compounds of the sulfur, selenium, and tellurium due to the difficulty in orbital hybridization for the larger energy-level spacing in oxygen. Considering the difference in the hydrogen bond, we also investigate the isotope effect and obtain $T_c$ values up to 247 K for ${\mathrm{D}}_3\mathrm{O}$. Our work deepens the understanding of the relationship between superconductivity and coordination unsaturation in the presence of the strong hydrogen bond and can be instructive for the design of superconducting materials under pressurization.

We show that one-dimensional topological superconductivity can be placed in the context of phenomena associated with strongly correlated electron systems. Here we propose a system consisting of a one-dimensional chain of strongly correlated fermions placed on a superconducting (SC) substrate that exhibits a spin-singlet extended $s$-wave pairing. Strong electron correlation is shown to transform an extended $s$-wave SC into a topological SC that hosts Majorana fermions. In contrast to the approaches based on mean-field treatments, no Zeeman or exchange magnetic field is needed to produce such an effect.

In this study, we derive the expressions of transmission and reflection for the quasi-one-dimensional spin-wave system in the presence of anomalous quadratic interactions due to the Holstein-Primakoff transformation, which are the generalization of Fisher-Lee formula in electronic systems. We employ the Green's function technique to calculate the coherent transport in nanowires with two terminals by considering the exchange randomness and spin dilution. The quantized magnon transmission is modified by both types of disorder, leading to reduced mean-free paths which could be relevant for the implementation of unconventional logic gates. In the linear response regime, the longitudinal thermal conductance divided by temperature shows a broad peak corresponding to a maximum release of entropy, implying the development of spin-correlations. This behavior resembles that of longitudinal and transverse thermal conductivity revealed in the Kitaev model within the framework of quantum spin liquids. These results provide insights into the mechanisms of magnon transport in quasi-one-dimensional spin-wave systems, paving the way for further research on anisotropic magnets and their potential applications in novel computational devices.

All-dielectric optical nanoantennas from high-refractive-index materials are becoming a promising way for efficient manipulation of light at the nanoscale. Here we propose an all-dielectric nanostructure based on bulk transition metal dichalcogenides (TMDs) with very simple geometry, a single-element nanodisk with an off-centered hole sited on glass substrate. We demonstrate that such TMD-based nanostructures can be utilized as a high-performance controllable directional nanoantenna due to its aspect of high refractive index in visible range. Owing to the off-centered hole, scattering spectrum of the nanodisk presents an extra Mie resonance, which is dominated by electric and magnetic dipole of Mie resonance. The interference between them leads to a transverse Kerker effect with an efficient unidirectional sides scattering around the Mie resonance. Importantly, we further investigate the intrinsic coupling between the TMD excitons and Mie resonance, as well as the influence of the coupling on the unidirectional side scattering of the system. We show that unidirectional side scattering occurs for both newly formed polariton states as a direct consequence of self-hybridized exciton-Mie interaction. Their directivities are strongly dependent on the directional feature of the Mie resonance, which can be effectively controlled by size of the nanodisk and the position of off-centered hole. Our results may provide exciting possibility for efficient light manipulations and are expected to open new pathways for the design of novel nanophotonic devices.

The quest for functional materials for the next generation of electronics plays a pivotal role in the postsilicon era, and two-dimensional layered semiconductors are at the core of this extensive research. In this work, we demonstrate that some members of the ${MA}_2{Z}_4$ family are candidates for high-efficiency optoelectronics. Through first-principles calculations, we find that the intrinsic electron mobility of ${MA}_2{\mathrm{N}}_4$ (where $M$ = {Mo, W} and $A$ = {Si, Ge}) layer materials reaches up to ${10}^3{\mathrm{cm}}^2/\mathrm{V}\mathrm{s}$ at liquid nitrogen temperature, and decreases as the temperature rises due to the enhanced electron-phonon scattering. Interestingly, the charge transport in these materials takes place purely along the intercalated transition metal nitride layer, so the surface adsorptions (impurities) or substrate interactions have nearly no effect on the carrier mobility due to the $A$-N bilayer protection, and the high electron mobility does not depend on the thickness of the sample. These features are distinct from other two-dimensional (2D) materials, such as silicene, black phosphorus, and indium selenide, and the 2D ${MA}_2{Z}_4$ family of materials are proposed as an outstanding candidate for field effect transistors and further studies.

The obstruction to constructing localized degrees of freedom is a signature of several interesting condensed matter phases. We introduce a localization renormalization procedure that harnesses this property and apply our method to distinguish between topological and trivial phases in quantum Hall and Chern insulators. By iteratively removing a fraction of maximally localized orthogonal basis states, we find that the localization length in the residual Hilbert space exhibits a power-law divergence as the fraction of remaining states approaches zero, with an exponent of $\nu =0.5$. In sharp contrast, the localization length converges to a system-size-independent constant in the trivial phase. We verify this scaling using a variety of algorithms to truncate the Hilbert space and show that it corresponds to a statistically self-similar expansion of the real-space projector. This result is in accord with a renormalization group picture and motivates the use of localization renormalization as a versatile numerical diagnostic for quantum Hall systems.

The optical dielectric function of ${\mathrm{ZnGeN}}_2$ is calculated from the interband transitions using the energy bands calculated in the quasiparticle self-consistent ($\mathrm{QS})G\widehat{W}$ method using two different levels of approximation: the independent particle approximation and the Bethe-Salpeter equation (BSE) approach. The first allows us to relate peaks in ${\varepsilon }_2\left(\omega \right)$ to specific bands and k points but does not include electron-hole interaction effects. The second includes electron-hole interaction or excitonic effects. The corresponding changes in the shape of ${\varepsilon }_2\left(\omega \right)$ are found to be similar to those in GaN. The screened Coulomb interaction $\widehat{W}$ is here calculated including electron-hole interactions in the polarization function and gives a band structure already going beyond the random phase approximation. The static dielectric constants including only electronic screening, commonly referred to as ${\varepsilon }^{\infty }$, were calculated separately by extrapolating the wave-vector-dependent macroscopic ${\varepsilon }_M(\mathbf{q},\omega =0)$ for $\mathbf{q}\to 0$. Below the quasiparticle gap, we find three bound excitons optically active for different polarization. The convergence of these bound excitons with respect to the density of the k mesh used in the BSE is studied and found to require a fine mesh. It is also found that these bound excitons originate from only the lowest conduction band and the top three valence bands. To incorporate the lattice screening, we include a scaling factor ${({\varepsilon }^{\infty }/{\varepsilon }^0)}^2$, which allows us to obtain exciton binding energies of the correct order of magnitude similar to those in GaN. The excitons are related to each of the threefold split valence bands and the splittings of the latter are also studied as a function of strain. Finally, a relation between the anisotropic effective masses and the valence-band splitting is pointed out and explained.

The finite temperature version of the Vashishta-Singwi (VS) dielectric scheme for the paramagnetic warm dense uniform electron fluid is revisited correcting for an earlier thermodynamic derivative error. The VS scheme handles quantum mechanical effects at the level of the random phase approximation and treats correlations via the density expansion of a generalized Singwi-Tosi-Land-Sjölander (STLS) closure that inserts a parameter determined by enforcing the compressibility sum rule. Systematic comparison with quasiexact results, based on quantum Monte Carlo simulations, reveals a structural superiority of the VS scheme towards strong coupling and a thermodynamic superiority of the STLS scheme courtesy of a favorable cancellation of errors. Guidelines are provided for the construction of dielectric schemes that are expected to be more accurate but computationally costly.

The topology of non-Hermitian systems is fundamentally changed by the non-Hermitian skin effect, which leads to the generalized bulk-boundary correspondence. Based on the non-Bloch band theory, we get insight into the interplay between the non-Hermiticity and the second-order topological superconductors in two spatial dimensions. We investigate that the non-Hermiticity drives both the bulk states and topological edge modes to accumulate toward opposite corners of the system depending on the particle and hole degrees of freedom protected by the particle-hole symmetry. Furthermore, the degeneracy of the Majorana corner modes can be broken in terms of both the eigenenergies and the eigenstates. Through an edge theory analysis, we elucidate the impact of non-Hermiticity and enable the extension of higher-order topological superconductors to the realm of non-Hermitian systems. We show that the $Z_2$ skin effect and $Z_2$ skin-topological modes reveal the universal characteristics of non-Hermitian second-order topological superconductors, and the generalized bulk-boundary correspondence is further enriched by the particle-hole symmetry.

A theory of weak localization in graphene with Rashba splitting of the energy spectrum is developed. Anomalous magnetoresistance caused by weak localization is calculated accounting for inter- and intravalley, and spin-orbit and spin-valley scattering processes. It is shown that the anomalous magnetoresistance is described by an expression different from the traditional Hikami-Larkin-Nagaoka formula. The reason is that the effect of Rashba splitting gives rise to the spin-orbit vector potential which is not reduced to a spin dephasing only. The developed theory can be applied to heterostructures of graphene with transition metal dichalcogenides.

The $8\text{−}\mathrm{eV}$ first nuclear excited state in ${}^{229}\mathrm{Th}$ is a candidate for implementing a nuclear clock. Doping ${}^{229}\mathrm{Th}$ into ionic crystals such as ${\mathrm{CaF}}_2$ is expected to suppress nonradiative decay, enabling nuclear spectroscopy and the realization of a solid-state optical clock. Yet, the inherent radioactivity of ${}^{229}\mathrm{Th}$ prohibits the growth of high-quality single crystals with high ${}^{229}\mathrm{Th}$ concentration; radiolysis causes fluoride loss, increasing absorption at $8\mathrm{eV}$. These radioactively doped crystals are thus a unique material for which a deeper analysis of the physical effects of radioactivity on growth, crystal structure, and electronic properties is presented. Following the analysis, we overcome the increase in absorption at $8\mathrm{eV}$ by annealing ${}^{229}\mathrm{Th}$-doped ${\mathrm{CaF}}_2$ at $1250{}^{\circ }\mathrm{C}$ in ${\mathrm{CF}}_4$. This technique allows to adjust the fluoride content without crystal melting, preserving its single-crystal structure. Superionic state annealing ensures rapid fluoride distribution, creating fully transparent and radiation-hard crystals. This approach enables control over the charge state of dopants, which can be used in deep-UV optics, laser crystals, scintillators, and nuclear clocks.

Non-Hermitian lattices with nonreciprocal couplings under open boundary conditions are known to possess linear modes exponentially localized on one edge of the chain. This phenomenon, dubbed non-Hermitian skin effect, induces all input waves in the linearized limit of the system to unidirectionally propagate toward the system's preferred boundary. Here we investigate the fate of the non-Hermitian skin effect in the presence of Kerr-type nonlinearity within the well-established Hatano-Nelson lattice model. Our method is to probe the presence of nonlinear stationary modes which are localized at the favored edge, when the Hatano-Nelson model deviates from the linear regime. Based on perturbation theory, we show that families of nonlinear skin modes emerge from the linear ones at any nonreciprocal strength. Our findings reveal that, in the case of focusing nonlinearity, these families of nonlinear skin modes tend to exhibit enhanced localization, bridging the gap between weakly nonlinear modes and the highly nonlinear states (discrete solitons) when approaching the anti-continuum limit with vanishing coupling. Conversely, for defocusing nonlinearity, these nonlinear skin modes tend to become more extended than their linear counterpart. To assess the stability of these solutions, we conduct a linear stability analysis across the entire spectrum of obtained nonlinear modes and also explore representative examples of their evolution dynamics.