The interplay of electronic interactions and frustration in crystalline systems leads to a panoply of correlated phases, including exotic Mott insulators with nontrivial patterns of entanglement. Disorder introduces additional quantum interference effects that can drive localization phenomena. Quasicrystals, which are neither disordered nor perfectly crystalline, are interesting playgrounds for studying the effects of interaction, frustration, and quantum interference. Here we consider a solvable example of a quantum spin liquid on a tricoordinated quasicrystal. We extend Kitaev's original construction for the spin model to our quasicrystalline setting and perform a large-scale flux sampling to find the ground-state configuration in terms of the emergent Majorana fermions and flux excitations. This reveals a fully gapped and time-reversal-symmetric quantum spin liquid, regardless of the exchange anisotropies, accompanied by a tendency toward nontrivial (de)localization at the edge and the bulk. The advent of moiré materials and a variety of quantum simulators provide a new platform to bring phases of quasicrystalline quantum matter to life in a controlled fashion.

Ultrahigh magnetic field up to 300 T obtained by explosive flux compression has been applied to study the interplay of two qualitatively different magnetic subsystems in $\mathrm{G}{\mathrm{d}}_2\mathrm{BaNi}{\mathrm{O}}_5$, i.e., the S $=1$ nickel chain system with the spin-singlet gapped ground state and S $=7/2$ gadolinium system forming a distorted triangular lattice, which orders at $T_{\mathrm{N}}=55$ K. The measurements show that the magnetization of the Gd subsystem rapidly saturates at $\sim 14{\mu }_{\mathrm{B}}$/f.u. This is followed by the further increase of magnetization at the critical field $H_{\mathrm{C}1}=90\pm 20$ T, where the Haldane gap starts to close. Theoretical classical and quantum Monte Carlo calculations demonstrate that $H_{\mathrm{C}1}$ is strongly affected by the staggered field of Gd spins, which effectively increases the Haldane gap by a frustrating exchange interaction, and show that the full magnetization saturation of both Gd and Ni subsystems is expected at the critical field $H_{\mathrm{C}2}\sim 800$ T.

Using the model of four sublattices, the Landau-Ginzburg-Devonshire-Kittel phenomenological approach and the Stephenson-Highland ionic adsorption model for the description of coupled polar and antipolar long-range orders in ferroics, we analytically calculated the phase diagrams and polar properties of $\mathrm{B}{\mathrm{i}}_{1-x}\mathrm{S}{\mathrm{m}}_x\mathrm{Fe}{\mathrm{O}}_3$ nanoparticles covered by surface ions with dependence on their size, surface ions density, samarium content $x$, and temperature. The size effects and ferroionic coupling govern the appearance and stability conditions of the long-range ordered ferroelectric, reentrant ferrielectric, and antiferroelectric phases in $\mathrm{B}{\mathrm{i}}_{1-x}\mathrm{S}{\mathrm{m}}_x\mathrm{Fe}{\mathrm{O}}_3$ nanoparticles. Calculated phase diagrams are in qualitative agreement with the x-ray diffraction phase analysis, electron paramagnetic resonance, infrared spectroscopy, and electrophysical measurements of $\mathrm{B}{\mathrm{i}}_{1-x}\mathrm{S}{\mathrm{m}}_x\mathrm{Fe}{\mathrm{O}}_3$ nanopowders sintered by the solution combustion method. The combined theoretical-experimental approach allows us to explain the influence of the ferroionic coupling and size effects in $\mathrm{B}{\mathrm{i}}_{1-x}\mathrm{S}{\mathrm{m}}_x\mathrm{Fe}{\mathrm{O}}_3$ nanoparticles on their polar properties.

Light-induced mechanical deformations in single-domain ${\mathrm{PbTiO}}_3/{\mathrm{SrTiO}}_3$ superlattices were simulated using first-principle calculations. By varying thickness or the chemical fraction of ${\mathrm{PbTiO}}_3$, we discover that these heterostructures' photostrictive behavior can be tuned quantitatively and qualitatively. Additionally, we present simple analytical models to explain the calculated deformations and predict a critical ${\mathrm{PbTiO}}_3$ fraction with no photostriction. Our results present two pathways for tuning the photostrictive behavior of ${\mathrm{PbTiO}}_3/{\mathrm{SrTiO}}_3$ superlattices, which could be utilized for innovative optomechanical applications.

We use resonant inelastic x-ray scattering (RIXS) to compare the doping dependence of magnetic excitations of an infinite-layer nickelate to those of a prototypical superconducting cuprate. The polarization analysis of RIXS spectra establishes the dominant spin-flip nature of the midinfrared peak in both cases. Hole doping leads to opposite behavior of the magnetic energy in the two materials. By fitting the data with an original Hubbard-based model for dynamic susceptibility, we find that $t$ is comparable in the two materials while $U$ is about twice larger in the nickelate. This finding accounts for the smaller magnetic bandwidth of nickelates and for its decrease upon doping.

The advent of unique high-entropy oxides has sparked substantial research interest due to their exceptional functional properties, which often surpass the mere sum of their constituent elements' characteristics. This paper introduces a complex high-entropy spinel oxide with composition (${\mathrm{Ni}}_{0.2}{\mathrm{Mg}}_{0.2}{\mathrm{Co}}_{0.2}{\mathrm{Cu}}_{0.2}{\mathrm{Zn}}_{0.2})\left({\mathrm{Mn}}_{0.66}{\mathrm{Fe}}_{0.66}{\mathrm{Cr}}_{0.66}\right){\mathrm{O}}_4$. We performed comprehensive structural (x-ray and neutron diffraction), microstructural, magnetic, and local electronic structure investigations on this material. Despite the material's high degree of disorder, detailed magnetization measurements and low-temperature neutron powder diffraction studies reveal long-range ferrimagnetic ordering beginning at 293 K. The sample exhibits a high saturation magnetization of 766 emu/$\mathrm{cm}{}^3$ (at 50 K), a low coercivity ($H_C$) of 100 Oe (50 K), a high transition temperature ($T_C$) around room temperature, and high resistivity value of 4000 ohm-cm at room temperature, indicating its potential for high-density memory devices. The magnetic structure is determined using a collinear-type ferrimagnetic model with a propagation vector k = 0,0,0. Various analytical techniques, including modified Arrott plots, Kouvel-Fischer analysis, and critical isotherm analysis, are employed to investigate the phase transitions and magnetic properties of this complex system. Our results indicate a second-order phase transition. Remarkably, despite the complex structure and significant disorder, the critical exponents obtained are consistent with the mean field model. The high entropy leads to a remarkably homogeneous distribution of multiple cations, validating the approximation of average local magnetic environments and supporting the mean field theory.

Recent investigations into layered and clathratelike binary polyborides drive us to explore the crystal structures and associated properties of Ac-B compounds through first-principles calculations in combination with crystal structure prediction techniques. Electron transfer from Ac to B gives rise to the emergence of $s{p}^3$-hybridized B frameworks with centered Ac atoms, namely Ac at ${\mathrm{B}}_{24}$ cages in ${\mathrm{AcB}}_6$, Ac at ${\mathrm{B}}_{26}$ cages in ${\mathrm{AcB}}_8$, and Ac at semiclosed ${\mathrm{B}}_{24}$ units in ${\mathrm{AcB}}_{12}$. Research unveils that three B-based compounds can stabilize at ambient pressure and exhibit inherent incompressibility with Vickers hardness of $22\sim 38\mathrm{GPa}$. Intriguingly, the rigid ${\mathrm{AcB}}_8$ and ${\mathrm{AcB}}_{12}$ are identified as ambient-pressure superconductors with superconducting transition temperatures ($T_c\mathrm{s}$) of 27 and 8 K, respectively. In particular, based on the Migdal-Eliashberg theory, the ambient-pressure superconductivity of clathratelike ${\mathrm{AcB}}_8$ is characterized as single gap and anisotropic, originating from the coupling of $\mathrm{B}\text{−}2p$ orbitals states with all phonon modes. Our work not only provides significant guidance for studying anisotropic superconductivity in other clathratelike polyborides but also lays the foundation for seeking and designing superconducting materials with superior hardness in rare-metal borides.

We address the key question of representation of chiral topological quantum states in $2+1$ dimensions (i.e., with nonzero chiral central charge) by projected entangled pair states (PEPS). A noted result (due to Wahl et al. [Phys. Rev. Lett. 111, 236805 (2013)], and Dubail and Read [Phys. Rev. B 92, 205307 (2015)] says that this is possible for noninteracting fermions, but the answer is as yet unknown for interacting systems. Characteristic counting of degeneracies of low-lying states in the entanglement spectrum (ES) at fixed transverse momentum of bipartitioned long cylinders (“Li-Haldane counting”) provides often-used supporting evidence for chirality. However, nonchiral PEPS (with zero chiral central charge), yet with strong breaking of time-reversal and reflection symmetries, with invariance under the product of these two operations (i.e., “apparently” chiral states), are known whose low-lying ES exhibits the same Li-Haldane counting as a chiral state in certain topological sectors [Kurečić et al., Phys. Rev. B 99, 045116 (2019); Arildsen et al., Phys. Rev. B 108, 245150 (2023)]. In this work, we identify a distinct indicator and hallmark of chirality in the ES of PEPS with global $\mathrm{SU}\left(3\right)$ symmetry: the splittings of conjugate irreps. We prove that in the ES of the chiral states conjugate irreps are exactly degenerate because the operators that would split them [related to the cubic Casimir invariant of $\mathrm{SU}\left(3\right)$] are forbidden. By contrast, in the ES of nonchiral states, conjugate splittings are demonstrably nonvanishing. Such a diagnostic provides an unambiguous and powerful tool to distinguish chiral and nonchiral topological states in $2+1$ dimensions via their entanglement spectra.

We consider the effect of spin-orbit coupling on a two-dimensional Kondo Lattice model, in which conduction electrons are antiferromagnetically coupled to a Yao-Lee spin liquid. When a Rashba spin-orbit interaction and a nearest-neighbor Kondo interaction is introduced, the low-energy Majorana bands become gapped and develop Chern numbers, protecting unidirectionally propagating Majorana edge modes. Our model describes a chiral topological superconductor with fractionalized charge-$e$ order parameter and spontaneously broken time-reversal symmetry, which may be of interest for certain heavy fermion superconductors, such as ${\mathrm{UTe}}_2$.

The use of soft-X-ray spectroscopy to probe changes in the ground-state due to vibronic excitations is studied. The changes in $L$-edge X-ray absorption on divalent cobalt in the presence of a vibrating Jahn-Teller distortion are calculated. For linear dichroism, a strong dependence on the distortion is obtained reflecting the change in the local quadrupole moment due to the changes in the $xy$ versus $yz/zx$ hole densities during the oscillation. In the presence of a magnetic moment, significant variations in the circular dichroic signal are obtained related to the quenching and unquenching of the orbital angular momentum.

We consider a multilayered metamaterial composed of anisotropic layers with in-plane anisotropy axes periodically rotated with respect to each other. Due to the breaking of inversion symmetry, the structure develops an effective chirality. We derive the effective chirality tensor of the metamaterial describing both normal and oblique incidence scenarios. We also identify the arrangement of the layers maximizing chiral response for the fixed lattice period, wavelength, and anisotropy of the layers.

Recent experiments on pentalayer rhombohedral graphene moiré superlattices have observed the quantum anomalous Hall effect at a moiré filling factor of $\nu =1$ and various fractional values. These phenomena are attributed to a flat Chern band induced by electron-electron interactions. In this study, we demonstrate that at $\nu =2$, many-body effects can lead to the emergence of quantum spin Hall and quantum valley Hall states, in addition to the quantum anomalous Hall state, even in the absence of spin-orbit coupling or valley-dependent potentials. These three topological states can be selectively induced by the application and manipulation of a magnetic field. Furthermore, we show that at $\nu =3$ and 4, the ground state can be a combination of topologically trivial and nontrivial states, unlike the cases of $\nu =1$ and 2. This contrasts with the conventional quantum Hall effect in graphene where the ground state at filling factor $\nu$ is given as the particle-hole counterpart at $4-\nu$.

We investigate the Hatsugai-Kohmoto (HK) model on a square lattice, which describes both a Mott insulator at half-filling and a non-Fermi liquid phase on doping. Through the solution of this exactly solvable model with the inclusion of pairing interactions, we demonstrate the emergence of strong pair-density-wave (PDW) fluctuations associated with center-of-mass momentum $\mathbf{Q}=(\pi ,\pi )$ at finite temperatures for low dopings up to a critical doping and intermediate $U$ interaction. Furthermore, we also confirm that a superconducting instability appears in the model within a wide regime of interaction $U$ and doping parameter $x$. In view of the fact that it has been recently put forward that the metal-insulator transition of the HK model belongs to the same universality class as the Mott transition of the paradigmatic Hubbard model [Huang et al., Nat. Phys. 18, 511 (2022)], our work may thus shed light on an interesting scenario regarding the emergence of a fluctuating PDW phase on doping a Mott insulator, which has been argued to be relevant for understanding the physics of the cuprate superconductors in the underdoped regime.

Diamondlike semiconductors (DLSs) with abundant and eco-friendly constituents are highly valued in energy technology. Those with innately low thermal conduction are uncommon yet helpful for thermoelectric (TE) applications. We present the impact of lattice and electron dynamics on the TE performance of a ternary DLS ${\mathrm{Cu}}_2{\mathrm{SiSe}}_3$. The structural and mechanical analyses uncover the ionic-covalent bonding and ductile nature of ${\mathrm{Cu}}_2{\mathrm{SiSe}}_3$. Interestingly, the ${\mathrm{CuSe}}_3$ and ${\mathrm{SiSe}}_3$ tetrahedral geometries have been identified to contribute independently to the valence and conduction band edges, respectively, offering an opportunity to engineer the band structure. The bonds with different chemical natures within these geometries suggest the possibility of anharmonicity. With a band gap value of ∼1.42 eV, the valence band is featured with band anisotropy, providing a large Seebeck coefficient. The relatively weaker interaction between Cu-Se and their considerable vibration belonging to the <100 $\mathrm{c}{\mathrm{m}}^{-1}$ region decides most of the thermal conduction. On accounting for quartic anharmonicity-based phonon renormalization along with three- and four-phonon scattering, a lower value of average lattice thermal conductivity ${\kappa }_l^{\mathrm{avg}}\sim 2.02\left(0.99\right)\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ at 300 (700) K is noticed, with particlelike contribution ${\kappa }_p^{\mathrm{avg}}\sim 1.9\left(0.83\right)\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ and wavelike contribution ${\kappa }_c^{\mathrm{avg}}\sim 0.12\left(0.16\right)\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$. Ionized impurity-scattering-dominated band edges give an overall hole lifetime of ∼52 fs at room temperature, and at the higher temperature of 700 K, higher mobility is maintained at ∼26.0 $\mathrm{c}{\mathrm{m}}^2{\mathrm{V}}^{-1}{\mathrm{s}}^{-1}$ with $\sim {10}^{19}\mathrm{c}{\mathrm{m}}^{-3}$ doping of carriers. A higher power factor for $p$-type ${\mathrm{Cu}}_2{\mathrm{SiSe}}_3$ is related to the high density of states effective mass and band geometry near the valence band edge. Average ZT ∼ 0.37 at 300 K and >1.0 for the intermediate temperature range (500–700 K) is reported within ${10}^{19}\text{–}{10}^{20}\mathrm{c}{\mathrm{m}}^{-3}$ carrier doping. These excellent $p$-type TE signatures would provide an avenue to flexible ternary DLSs as a green energy solution.

We develop a microscopic theory of the spin Seebeck effect (SSE) at the interface of a bilayer system of a ferromagnetic insulator and graphene. We compare the tunneling spin current at the interface because of the SSE and the spin pumping (SP), where the SSE and SP are induced by the temperature gradient and the microwave irradiation, respectively. We demonstrate that the thermally driven SSE exhibits a quantum oscillation pattern similar to that predicted in coherently driven SP. Additionally, we show a peak shift of the quantum oscillation owing to the contribution of thermally excited magnons with higher frequencies, which becomes particularly pronounced at higher temperatures.

Edge reconstruction of gate-tunable compressible quantum Hall fluids in the filling fraction range 1/3 to 2/3 is studied by measuring transmitted conductance of two individually excited fractional $e^2/3h$ edge modes of bulk 2/3 fractional quantum Hall fluid. Our findings reveal that the measured transmitted conductance deviates from the fully equilibrated value for the filling fraction range 1/3–2/3 of the gate-tunable compressible quantum Hall fluids at higher magnetic fields. This observation suggests that at the boundary of the compressible fluid, a reconstructed $e^2/3h$ fractional edge mode is present and the mode does not completely equilibrate with the inner dissipative bulk region. Consequently, this outer reconstructed edge mode supports adiabatic charge transport, allowing nonequilibrated current transport through the compressible region. These studies open new avenues for achieving robust fractional edge modes even in compressible quantum Hall fluids under strong magnetic fields, enhancing our understanding of edge state dynamics in these complex systems.

The interlayer magnetic transition (IMT) between atomic-thin magnets has received significant attention for its potential in spintronic applications. A perspective of understanding and tuning magnetic transition is based on the band-coupling model (BCM), which has the advantages of being transparent and intuitive. In the current work, first we apply the BCM to the IMT of $3d^1$ two-dimensional (2D) magnets with electron correction and interlayer band coupling (IBC). Detailed analyses show a scenario that the IBC favors interlayer ferromagnetic (antiferromagnetic) order if the IBC induces (does not induce) band crossing; this conclusion is robust to the different energy orders caused by the competition between crystal-field splitting and spin splitting. Then, we verify the above scenario for a real material (bilayer H-phase ${\mathrm{VSe}}_2$) by density-functional theory calculations and interlayer orbital-hybridization analysis. Finally, we argue that our proposed mechanism of IMT could be applicable to more van der Waals 2D magnets with IBC, and the mechanism is not limited to 2D semiconductors but may also apply to 2D metals. Our current work paves an avenue for tuning IMTs in 2D layered magnets.

Rashba spin-orbit coupling (RSOC) facilitates spin manipulation without relying on an external magnetic field, opening up exciting possibilities for advanced spintronic devices. In this paper, we examine the effects of crystal momentum $\left(k\right)$ nonlinearity and anisotropy on the conventional Rashba effect, with a particular focus on their impact on the spin Hall conductivity (SHC) in a newly predicted family of 2D Janus materials, ${\mathrm{W}}_2\mathrm{CO}X$ $(X=\mathrm{S}, \mathrm{Se}, \mathrm{Te})$. Using first-principles density functional theory calculations, we confirm the dynamical and mechanical stability of the studied 2D materials. Strikingly, this materials family exhibits pronounced nonlinear Rashba spin splitting at the $\mathrm{\Gamma }$ point of Brillouin zone near the Fermi level, which cannot be adequately described by the linear-$k$ Rashba model. Therefore, third-order momentum contributions $\left(k^3\right)$ must be incorporated into the Rashba Hamiltonian. Our analysis reveals that among the studied systems, ${\mathrm{W}}_2\mathrm{COS}$ exhibits the highest $k^3$ contribution of $-45.9 \mathrm{eV} {\AA }^3$, despite having the lowest linear Rashba constant. A detailed analysis of electronic structure reveals topologically nontrivial behavior in these 2D materials, yielding sizable SHC that is primarily governed by the nonlinear Rashba effect. Notably, these materials also exhibit large spin Hall angle (0.018–2.5 at ${\mathrm{E}}_F$), which is comparable to that of in bulk topological insulators like ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ and ${\mathrm{Bi}}_2{\mathrm{Te}}_3$, and surpassing those in narrow bandgap bulk semiconductors GeTe and SnTe, as well as heavy metals such as Pt. Sizable SHC, large spin Hall angles, and the ability to tune SHC via electric fields without altering the topological properties, rooted in the crystal field splitting, underscore the potential of these materials for spintronic applications.

Second-order Raman spectra of monolayer ${\mathrm{MoSe}}_2$ are observed by using circularly polarized light for four laser energies, which are resonant with the C exciton. Helicity-dependent Raman spectra show that the overtone mode of a helicity-changing mode observed at $560–610{\mathrm{cm}}^{-1}$ is a helicity-conserved mode, while the combinational mode of helicity-changing modes is still a helicity-changing mode. We discuss the selection rule of helicity-dependent double resonance Raman spectra by using first-principles density functional calculations and Raman tensor analysis, in which overtone and combinational modes give exactly opposite helicity-dependent behaviors after the decomposition to the $\mathrm{\Gamma }$ point.

The generation of on-demand out-of-plane spin polarization (${\mathit{\sigma }}_z$) promises an efficient field-free switching of perpendicular nanomagnet has been limited mostly in the single crystal materials. For a direct technological application, it is desired to have an out-of-plane spin current generation from polycrystalline sputtered films rather than expensive single crystalline films. Here, we report the observation of out-of-plane and in-plane torques generated by the $\widehat{z}$ and $\widehat{x}$ spin polarization in the polycrystalline antiferromagnet ${\mathrm{IrMn}}_3$/permalloy (Py) heterostructure. A comparatively high value of out-of-plane spin torque ratio of 0.024 has been observed with a large out-of-plane spin Hall conductivity of $\approx 2.82\times {10}^4\left(\frac{\hslash }{2e}\right){\left(\mathrm{\Omega }\mathrm{m}\right)}^{-1}$. Additionally, we have investigated the underline mechanism and the fundamental role of $\widehat{z}$ spins in the context of external field-free magnetization switching of a perpendicular magnetic anisotropy (PMA) material. Our findings provide a new perspective on generation and detection of out-of-plane spin polarization in antiferromagnet material and manipulate the magnetization for the development of the next generation high-density, low-power consumption, logic device applications.