A combined study of non-Hermitian physics and strong correlations can yield numerous intriguing effects. Authors of a previous study on the non-Hermitian Kondo model in the ultracold atoms reported the reversion of the renormalization group (RG) flow. In this paper, we investigate the non-Hermitian Kondo effect in the system with a specific form of density of states $\rho \left(\omega \right)\sim {\left|\omega \right|}^r(r>0)$, known as the pseudogap system. We find that, for $r<\frac{1}{2}$, our results from the perturbative RG are consistent with those of the Hermitian pseudogap Kondo effect. For $r=\frac{1}{2}$, a fixed point with the reversion property emerges in the RG flow. For $r>\frac{1}{2}$, an unstable fixed point appears in the complex plane of the parameter space. Furthermore, through the large-$N$ expansion, we validate the RG results for $r<\frac{1}{2}$, finding that the self-consistent equations have nontrivial solutions in a specific region of the complex plane of the parameter space.

We investigate a one-dimensional correlated-hopping model of spinless fermions with an East constraint. We first analytically unravel the complete fragmentation structure of this model by labeling each fragment by a unique root configuration and utilizing the transfer matrix method. We show that the growth of the size of each fragment of the model follows the widely studied Dyck sequence and is therefore analytically tractable with the help of Catalan triangles. While the eigenstate thermalization hypothesis (ETH) does not hold within the full Hilbert space which exhibits Poisson statistics of the energy level spacing, an examination of various quantities restricted to the largest fragments shows that a weaker version of the subspace-restricted thermalization holds. This weaker violation of the ETH within the largest fragments is supported by the presence of subspace-restricted quantum many-body scars due to quantum fragmentation. Our analysis further reveals that the filling fraction at which the model has the largest fragment shifts with increasing system sizes from half-filling due to the distinct fragmentation structure. Next, we show that the inclusion of a nearest-neighbor density-density interaction with strength $V$ induces a spectral transition within the largest fragment from a weakly ETH-violating phase containing scars to a statistical bubble localized phase as $V$ increases. In particular, the $V\to \infty$ limit produces an integrable model. We find that the addition of finite-$V$ stabilizes the ground state near half-filling while keeping intact the fragmentation structure of the East model. However, this behavior abruptly changes exactly at $V=\infty$ due to the emergence of a distinct fragmentation structure; we analytically explore this in a comprehensive manner. The infinite-$V$ model has many interesting properties, among which the appearance of the ground state and the largest fragment at two different filling fractions is specially noteworthy. Finally, we propose an experimental setup to realize the infinite-$V$ model as a particular limit of a special kind of $t\text{−}V$ model with an on-site potential.

Bulk transition metal dichalcogenides (TMDs) provide a prominent platform for self-hybrid light-matter interactions, owing to their strong oscillator strength and large modal overlap. Recently the Brillouin zone folding-induced quasibound states in the continuum (BZF-qBICs) have been attracting significant attention because of their sustainable high quality (Q) factor in momentum space and robustness against disorder. However, studies on strong self-hybrid coupling based on BZF-qBICs are rarely reported. Here, we propose a simple design of a metasurface with holes punched into a standalone bulk TMD flake and demonstrate the strong self-hybrid coupling between the BZF-qBIC resonances and the intrinsic exciton in bulk ${\mathrm{WS}}_2$. We show that the BZF-qBICs induced by periodically perturbing the radius of air holes exhibit a folded band structure and reduced radiation channels, leading to tunable high Q factors. We further demonstrate that introducing relative displacements to the perturbed holes to break the in-plane symmetry enables an intriguing transition from electric quadrupole to toroidal dipole dominated BZF-qBICs, with the latter exhibiting robust polarization independence in the associated metasurface. This polarization-independent BZF-qBIC is used to realize self-hybrid coupling with the intrinsic excitons with a large Rabi splitting over 190 meV. Moreover, the coupling strength of the hybrid system can be further modulated by tuning the perturbation factor associated with the radius of the holes. Our findings propose a strategy for self-hybrid strongly coupled platforms, which may serve as a catalyst for the innovation of high-performance optoelectronic devices.

We have investigated the dynamical polarizability, plasmon dispersion relations, and dephasing in semi-Dirac energy bands. These structures demonstrate zero band gap and a half-linear, half-parabolic low-energy spectrum. We have performed rigorous numerical calculations and discovered some unusual plasmonic and collective properties in these materials. The obtained plasmon dispersion relations are strongly anisotropic and exhibit mixed features associated with both a two-dimensional electron gas and graphene in each specified direction. Such gapless energy dispersions lead to an isolated region for undamped or weakly Landau damped plasmon modes within a limited frequency-wave vector region. With finite tilting, we find two peaks in the polarization function. One plasmon mode is undamped while the other is strongly Landau damped. This feature can be utilized as an indicator for specifying a unique tilted plasmon spectrum from semi-Dirac bands. Additionally, we have presented our calculated density of states for tilted semi-Dirac bands and demonstrated how it could be employed in developing a qualitative model for generating a plasmon spectrum of these materials.

We examine the insulator-to-metal transition taking place in ${\mathrm{NaOsO}}_3$, a Slater insulator, under pressure. While an antiferromagnetic metallic phase is absent in Slater's picture, we find a robust phase present with a high ordering temperature. This is traced to the negative charge transfer energy regime to which the system belongs. The band gap is found to have a weak pressure dependence, an order of magnitude smaller than other known materials. This follows from the unusual $d$ filling to which Os corresponds, with the antiferromagnetism favoring the insulating state. Consequently, the pressure-dependent bond length decrease and the bond angle variations compete in minimizing the changes in the effective hopping between the Os sites, leading to a “persistent insulating” state.

Recent observations of an 80 K superconductor in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ under high pressure have attracted significant attention. Recent experiments indicate that ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ may be in the charge transfer regime, challenging the previous models based purely on the Ni $d_{x^2-y^2}$ and $d_{z^2}$ orbitals. In this study, we propose a low energy model that incorporates doped holes in the oxygen $p$ orbitals. Given that the parent nickel state is in the $3d^8$ configuration with a spin-one moment, doped hole only screens it down to spin-half, in contrast to the Zhang-Rice singlet in cuprate. We dub the single hole state as the Zhang-Rice doublet and build an effective model which includes three spin-one states $\left(d^8\right)$ and two Zhang-Rice doublet states $\left(d^{8}L\right)$. At moderate pressure around 20 GPa, the dominated oxygen orbital is an in-plane Wannier orbital with the same lattice symmetry as the $d_{x^2-y^2}$ orbital. The resulting model reduces to the bilayer type II t-J model previously proposed in the Mott-Hubbard regime. Notably, the hopping between the in-plane $p$ orbitals of the two layers is still suppressed. Density matrix renormalization group simulation reveals a pairing dome with the optimal hole doping level at $x=0.4–0.5$, distinct from the hole doped cuprate where optimal doping occurs around $x=0.19$. Further increasing pressure initially raises the critical temperature $\left(T_c\right)$ until reaching an optimal pressure beyond which the $p_z$ orbital of oxygen becomes favorable and superconductivity is diminished. This shift from in-plane $p$ orbital to $p_z$ orbital may elucidate the experimentally observed superconducting dome with varying pressure. As an extension, we also suggest a trilayer version of the type II t-J model as the minimal model for pressured ${\mathrm{La}}_4{\mathrm{Ni}}_3{\mathrm{O}}_{10}$, which is distinct from the models in the Mott-Hubbard regime.

Symmetry breaking is a fundamental concept in condensed matter physics, driving various quantum phenomena. Layered transition metal dichalcogenides (TMDs) serve as an excellent platform for investigating electronic instabilities and emergent phases. Using first-principles calculations, we reveal a striking transformation in ${\mathrm{TiSe}}_2$ and ${\mathrm{ZrSe}}_2$ induced by Li intercalation. Specifically, ${\mathrm{TiSe}}_2$ transitions from a charge density wave state to a ferromagnetic phase, while ${\mathrm{ZrSe}}_2$ evolves from a semiconductor to a superconducting state. In ${\mathrm{LiTiSe}}_2$, the localization of Ti $3d$ orbitals creates overlapping van Hove singularities near the Fermi level, stabilizing a Stoner-type ferromagnetic phase via exchange interactions that break spin-rotational symmetry. In contrast, superconductivity in ${\mathrm{LiZrSe}}_2$ arises from enhanced electron-phonon coupling, facilitated by delocalized Zr $4d$ orbitals and Zr-Zr bond-stretching phonon modes, leading to Cooper pair condensation and the breaking of U(1) gauge symmetry. These findings highlight how variations in $d$-orbital localization and interatomic interactions govern distinct quantum phases, demonstrating the transformative potential of intercalation for tuning electronic properties and accessing unique quantum states in layered TMDs.

We applied synchrotron x-ray diffraction in a diamond-anvil cell at 48–51 GPa, alongside first-principles theoretical calculations, to study the crystal structure of solid atomic iodine at high pressure. We report the synthesis of two phases of atomic iodine at 48–51 GPa via laser heating of iodine (I) in nitrogen $\left({\mathrm{N}}_2\right)$ or neon (Ne) media. Unlike the familiar monatomic $I4/mmm$ structure, which consists of crystallographically equivalent atoms, a previously unobserved $Pm\overline{3}n$ structure determined by single-crystal and powder x-ray diffraction is of an inclusion type, featuring two distinct types of atoms: a central, detached atom and peripheral atoms that form linear chains. Additionally, we observe crystallization of the familiar high-pressure fcc structure, albeit at much lower pressures compared to cold-compressed iodine. The discovery of the $Pm\overline{3}n$ structure in iodine marks an important step in understanding the pressure-induced phase transition sequence in halogens.

This paper endeavors to expand the exploration of prospective superconductivity within the $P6/mmm\text{−}{\mathrm{MgB}}_2$ structural framework by substituting Mg atoms with a random selection of two distinct cations from a pool of 24 candidates. Employing a high-throughput screening methodology to scrutinize zone-center electron-phonon couplings, we found an inverse relationship between thermodynamic stability and electron-phonon coupling strength in the resulting ternary metal borides. Notably, within the ${\mathrm{MgNiB}}_4$ system, we demonstrated that electron-phonon superconductivity is stronger in less dynamically stable configurations. The qualitative reasons for the emerging instabilities when electron-phonon coupling becomes strong are discussed. This insight indicates that the quest for superior superconducting materials should concentrate on the intricate balance between electronic and phononic characteristics in structures that are on the brink of instability.

The spin Seebeck effect (SSE) is a phenomenon of thermoelectric generation that occurs within a device consisting of a bilayer of a metal and a ferromagnet. When ferrimagnetic ${\mathrm{Tb}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$ (TbIG) is substituted for the ferromagnet, the effect goes to zero at low temperatures, yet it increases to positive values with the application of a magnetic field. This is opposite to the expectation that the SSE should be suppressed by a magnetic field due to the increase in the magnon gap. In this paper, the crystal-field excitations (CFE) in TbIG are calculated within a mean-field theory exploiting the Stevens parameters of terbium gallium garnet, ${\mathrm{Tb}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ (TGG), from the neutron-scattering experimental literature. Like TGG, the primitive cell of TbIG hosts 12 Tb sites with six inequivalent magnetic sublattices, but due to the net [111]-molecular field from the tetrahedral and octahedral Fe ions, these can be classified into two distinct groups, the $\mathbf{C}$ and the ${\mathbf{C}}^{\prime }$ sites, which account for the “double-umbrella” magnetic structure. We show that when an external magnetic field is applied along the [111] direction of the crystal, the lowest CFE of the $\mathbf{C}$ sublattices decreases. As a consequence of the magnetic field dependence of the lowest CFE, we find that at low temperatures, the SSE in TbIG can be enhanced by an applied magnetic field.

We study the effect of the magnon-magnon interaction on the nonlinear magnon transport. The magnon-magnon interaction induces nonreciprocal magnon decay when the time-reversal symmetry is broken and leads to nonlinear thermal responses of magnons. We construct a theoretical framework to study the nonlinear thermal responses due to the nonreciprocal magnon decay by using the imaginary Dyson equation and quantum kinetic theory, which is then applied to models of one-dimensional (1D) antiferromagnets and 2D honeycomb ferromagnets with Dzyaloshinskii-Moriya interactions. An order estimate shows that the nonlinear thermal response from the present mechanism is feasible for experimental measurement.

Quenched randomness strongly affects properties of magnetic materials. Two-dimensional (2D) random singlet (RS) states emerge in the random $J\text{−}Q$ model by destroying valence bond solid order with spatial randomness. We examine the 2D RS states in a magnetic field with quantum Monte Carlo simulations. The magnetization and susceptibilities show power-law scaling with magnetic field at low temperature. Moreover, they show one-parameter scaling behavior with $B/T$, and the scaling functions are remarkably consistent with a phenomenological model of random spin pairs with a singular distribution of interactions. These universal scaling functions can be used to diagnose 2D RS states in experiments.

We demonstrate that the magnetization in magnetic semiconductors exhibits nutational motion when subjected to an external magnetic field. This behavior originates from the splitting of the conduction-electron band which induces anisotropic, distance-dependent exchange coupling between localized spins. To investigate this phenomenon, we examine a general system that includes both charge and spin degrees of freedom, characteristic of a magnetic semiconductor. This system is composed of two subsystems: (1) a gas of noninteracting conduction electrons and (2) a ferromagnetic array of localized spins, coupled through the Vonsovskii ($\mathit{sd}$) local interaction. The entire system is subject to external electrical and magnetic disturbances. Through the Feynman-Schwinger formalism, we integrate out the faster (Grassmann) charge degrees of freedom associated with the conduction electrons to obtain the effective Hamiltonian for the localized spins in the form of an XXZ spin model. We then provide general analytical formulas for the corresponding anisotropic exchange couplings, expressed in both Fourier and direct spaces, as functions of the effective field that induces conduction-band splitting. As a practical application of this general formalism, we investigate the dynamics of the net magnetic moment within the effective spin model. We demonstrate, analytically and numerically, that the anisotropy of the distance-dependent exchange coupling induces nutational magnetization oscillations at significantly higher frequencies than the typical precession, which is also modified accordingly. Analytical expressions for the modified precession and low-lying nonuniform modes have been derived and compared with the numerical solution of the system of coupled Landau-Lifshitz equations for the localized spins. Our results indicate that the frequency of the nutation modes decreases while their amplitude increases as the band-splitting field intensifies. Moreover, we show that the leading correction to the localized spin gyromagnetic factor $g_S$, due to the polarization of conduction electrons in an external magnetic field, is linear in the $\mathit{sd}$ coupling. We hope this study will motivate further research into nutational phenomena in magnetic semiconductors, possibly resulting in improvements in the accurate control of magnetization dynamics within spin-based electronic devices.

Interplay between spin-orbit coupling and magnetic frustration can give rise to unique quantum phases with unusual excitations. Here, we report a comprehensive analysis of $\mathrm{YbNb}{\mathrm{O}}_4$, where $\mathrm{Y}{\mathrm{b}}^{3+}$ ions form a stretched diamond sublattice within the monoclinic crystal structure. Our bulk experimental investigations exclude the presence of magnetic ordering and spin freezing. Additionally, a low-energy effective spin-1/2 state is noted at lower temperatures. Our muon spin relaxation (μSR) measurements reveal the absence of static internal field. However, a critical slowing down of spins is observed below 2 K due to the development of strong magnetic correlations. The longitudinal field μSR investigations further suggest the strongly fluctuating nature of the spins and confirms the correlated dynamical ground state in $\mathrm{YbNb}{\mathrm{O}}_4$ down to 300 mK. Our studies suggest that the titled system can be a potential candidate for hosting a spin liquid state.

We explore the electronic and magnetic properties of ${\mathrm{NH}}_4^{+}$-intercalated vanadium pentoxide (${\mathrm{NH}}_4^{+}\text{−}{\mathrm{V}}_2{\mathrm{O}}_5$), a material that has been identified as a promising cathode for aqueous zinc-ion batteries. Density functional theory (DFT) calculations incorporating the Hubbard $U$ correction reveal that ${\mathrm{NH}}_4^{+}\text{−}{\mathrm{V}}_2{\mathrm{O}}_5$ is an antiferromagnetic insulator with an energy gap of 1.97 eV. The introduction of ${\mathrm{NH}}_4^{+}$ ions into the ${\mathrm{V}}_2{\mathrm{O}}_5$ structure results in significant structural distortions, leading to the formation of magnetic vanadium ions (${\mathrm{V}}^{4+}$, $3d^1$) and nonmagnetic ions (${\mathrm{V}}^{5+}$, $3d^0$). The magnetic vanadium ions are organized into chains with antiferromagnetic order along the $a$ axis. Our findings indicate that ${\mathrm{NH}}_4^{+}\text{−}{\mathrm{V}}_2{\mathrm{O}}_5$ exhibits strong electron correlation effects and negligible interchain magnetic interactions, rendering it a promising candidate for a one-dimensional magnetic van der Waals system. This work provides insights into the electronic and magnetic behaviors of ${\mathrm{NH}}_4^{+}\text{−}{\mathrm{V}}_2{\mathrm{O}}_5$, with implications for its potential applications in energy storage technologies.

Magnetic superconductors manifest a fascinating interplay between their magnetic and superconducting properties. This becomes evident, for example, in the significant enhancement of the upper critical field observed in uranium-based superconductors, or the destruction of superconductivity well below the superconducting transition temperature $T_c$ in cobalt-doped ${\mathrm{NbSe}}_2$. In this work, we argue that the Kondo interaction plays a pivotal role in governing these behaviors. By employing a periodic Anderson model, we study the Kondo effect in superconductors with either singlet or triplet pairing. In the regime of small impurity energies and high doping concentrations, we find the emergence of a Kondo resistive region below $T_c$. While a magnetic field suppresses singlet superconductivity, it stabilizes triplet pairing through the screening of magnetic impurities, inducing reentrant superconductivity at high fields. Moreover, introducing an antisymmetric spin-orbital coupling suppresses triplet superconductivity. This framework provides a unified picture to understand the observation of Kondo effect in ${\mathrm{NbSe}}_2$ as well as the phase diagrams in Kondo superconductors such as ${\mathrm{UTe}}_2$ and URhGe.

It is shown that even a weak out-of-plane attraction, $V\to 0$, can form real-space pairs in the body-centered tetragonal lattice despite the presence of a Hubbard repulsion and a fully developed three-dimensional kinetic energy. In the hole channel, the pairs have $d$ orbital symmetry, which, following Bogoliubov's argument, translates into a $d$-symmetric macroscopic superconducting order parameter. The findings help us to understand key features of ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ and further support the real-space mechanism of superconductivity in cuprates. The rules of real-space superconductivity are formulated at the end.

We investigate the dynamical deconfinement transition driven by excitations in a long-range Ising model. At low temperatures, spatially separated pairs of domain wall kinks are bound by the confining potential and exhibit uncorrelated Bloch oscillations in time. This picture is analogous to bound mesons in quark confinement. As the temperature increases, the meson picture breaks down as the domain wall kinks in proximity interact and disperse, leading to an extended deconfined regime. In this paper, we characterize the deconfinement transition with signatures observed in the average density of domain wall kinks and nonequilibrium changes in its fluctuation. Our findings provide insights into the mechanisms of confinement and deconfinement in long-range spin models, thus opening avenues for further exploration and experimental verification.