The magnetic structure of high-pressure quadruple perovskite $\mathrm{Ca}{\mathrm{Mn}}_3{\mathrm{V}}_4{\mathrm{O}}_{12}$ was investigated using neutron powder diffraction data. Below $T_N=54\mathrm{K}$, the $S=\frac{5}{2} {\mathrm{Mn}}^{2+}$ spins adopt a ${120}^{\circ }$ arrangement in kagome layers formed of second nearest neighbor $A^{\prime }$ sites. The ${\mathrm{V}}^{4+}$ electrons are itinerant and do not mediate the magnetic interactions as evidenced by the insensitivity of the magnetic structure to the valence of the vanadium cations in $A{\mathrm{Mn}}_3{\mathrm{V}}_4{\mathrm{O}}_{12}$ ($A={\mathrm{La}}^{3+}, {\mathrm{Ca}}^{2+}$).

We study a nonlinear spin dynamics of a ferromagnetic ring in a vortex state induced by the spin-polarized current. We also suggest using the ferromagnetic ring as a free layer of a coreless vortex spin-transfer nano-oscillator. The calculated working frequency is about several GHz, which is much higher than the gyromode frequency of the disk-based vortex oscillator. The response of the vortex-state ring to the spin-polarized current has hysteretic behavior with the reasonable values of the thresholds' current densities: ignition threshold is about ${10}^8\text{A}{\text{cm}}^{-2}$ and elimination current to maintain the oscillations has much lower values of about ${10}^6\text{A}{\text{cm}}^{-2}$. The output signal can be extracted with the help of the inverse spin-Hall effect or by the giant magnetoresistance. The output electromotive force averaged over all sample vanishes and we suggest using a ferromagnetic ring or disk in a vortex state as a giant magnetoresistance analyzer. For an inverse spin-Hall analyzer we advise using two heavy metals with different signs of spin-Hall angle. The ring-based spin-transfer nano-oscillator (STNO) is supposed to increase the areas of practical application of the STNOs.

Due to its complex magnetic structure, fcc Fe grown on a Cu(100) substrate has been studied for decades. Many experimental measurements have gradually confirmed that fcc $\mathrm{Fe}|\mathrm{Cu}$(100) films have a noncollinear magnetic configuration. In contrast, current theoretical calculations have found that collinear magnetic configurations are always more stable than noncollinear magnetic configurations. To clarify this discrepancy, we set up $\mathrm{Fe}|\mathrm{Cu}$(100) films and ${\left[{\mathrm{Fe}}_7\right|{\mathrm{Cu}}_7]}_n$ superlattice and carry out first-principles calculations to study the magnetic ground states therein. We find that the exchange interactions along the normal direction of the thin film exhibit long-range RKKY-like behavior. Using these exchange interactions, we construct an effective Hamiltonian, with which the noncollinear magnetic ground states were found. Moreover, Monte Carlo simulations confirm these noncollinear magnetic ground states to be stable at a finite temperature. Thus, our results catch the physical origin of the noncollinear magnetic ground states in fcc Fe-based films and reveal that even the collinear exchange coupling may induce noncollinear magnetic states.

We study the square-lattice extended Hubbard model with on-site $U$ and nearest-neighbor $V$ interactions by exact diagonalization. We show that nonequilibrium quench dynamics can help determine the equilibrium phase transition boundaries, which agree with the calculations of the fidelity metric, dynamical structure factor, and correlation function. At half filling, the phase diagrams in the strong-coupling regime include spin density wave and $d_{x^2-y^2}$-wave superconductivity at large positive $U$, charge density wave (extended $s^{*}$-wave superconductivity) at large positive (negative) $V$, and $s$-wave superconductivity at large negative $U$ with vanishing $V$. The energies of different particle sectors also help determine the phase separation region. With carrier doping, charge fluctuation results in a strong competition between different orders, making it more difficult to identify the leading instability on finite-size clusters. Nevertheless, the more exotic $p$-wave superconducting pairing is found to be enhanced when the system is heavily overdoped by $37.5\%–50\%$ holes, especially in the interaction parameter range relevant to the cuprate superconductors.

Adding a dopant to an antiferromagnetic spin background disturbs the magnetic order and leads to the formation of a quasiparticle coined the magnetic polaron, which plays a central role in understanding strongly correlated materials. Recently, remarkably detailed insights into the spatial properties of such polarons have been obtained using atoms in optical lattices. Motivated by this we develop a nonperturbative scheme for calculating the wave function of the magnetic polaron in a bilayer antiferromagnet using the self-consistent Born approximation. The scheme includes an infinite number of spin waves, which is crucial for an accurate description of the most interesting regime of strong correlations. Utilizing the developed wave function, we explore the spatial structure of the polaron dressing cloud consisting of magnetically frustrated spins surrounding the hole. Mimicking the nonmonotonic behavior of the antiferromagnetic order, we find that the dressing cloud first decreases and then increases in size with increasing interlayer hopping. The increase reflects the decrease in the magnetic order as a quantum phase transition to a disordered state is approached for large interlayer hopping. We, furthermore, find that the symmetry of the ground state dressing cloud changes as the interlayer coupling increases. Our results should be experimentally accessible using quantum simulation with optical lattices.

We construct a recursive second-quantized formula for Moore-Read Pfaffian states. We demonstrate the utility of such second-quantized presentations by directly proving the existence of frustration-free parent Hamiltonians, without appealing to polynomial clustering properties. Furthermore, we show how this formalism is connected to the existence of a nonlocal order parameter for Moore-Read states, and we provide proof that the latter exhibit off-diagonal long-range order (ODLRO) in these quantities. We also develop a similar second-quantized presentation for the fermionic anti- and PH-Pfaffian states, as well as $f$- and higher wave paired composite fermion states, and we discuss ODLRO in most cases.

The Benalcazar-Bernevig-Hughes (BBH) model [W. A. Benalcazar, B. A. Bernevig, and T. L. Hughes, Science 357, 61 (2017)], featuring a bulk quadrupole moment, edge dipole moments, and corner states, is a paradigm of both higher-order topological insulators and topological multipole insulators. In this work, we generalize the BBH model to arbitrary dimensions by utilizing the Clifford algebra. For the generalized BBH model, the analytical solution of corner states can be directly constructed in a unified way. Based on the solution of corner states and chiral symmetry analysis, we develop a general boundary projection method to extract the boundary Hamiltonians, which turns out to be the BBH models of lower dimension and reveals the dimensional hierarchy.

The two-particle self-consistent approach (TPSC) is a method for the one-band Hubbard model that can be both numerically efficient and reliable. However, TPSC fails to yield physical results deep in the renormalized classical regime of the bidimensional Hubbard model where the spin correlation length becomes exponentially large. We address the limitations of TPSC with improved approaches that we call TPSC+ and TPSC+SFM (spin fluctuation mediated). In this work, we show that these improved methods satisfy the Mermin-Wagner theorem and the Pauli principle. We also show that they are valid in the renormalized classical regime of the two-dimensional Hubbard model, where they recover a generalized Stoner criterion at zero temperature in the antiferromagnetic phase. We discuss some limitations of the TPSC+ approach with regards to the violation of the $f$-sum rule and conservation laws, which are solved within the TPSC+SFM framework. Finally, we benchmark the TPSC+ and TPSC+SFM approaches for the one-band Hubbard model in two dimensions and show how they have an overall better agreement with available diagrammatic Monte Carlo results than the original TPSC approach.

Persistent spin texture (PST) can maintain a uniform spin configuration in the momentum space, resulting in a spatially periodic mode known as a persistent spin helix (PSH). The PSH is robust against spin-independent scattering and renders an extremely long spin lifetime, which can improve the performance of potential spintronic devices. Here, $T\text{−}XY$ ($X\ne Y=\mathrm{P}$, As, Sb, and Bi) monolayers with dynamical, mechanical, and thermal stabilities are predicted to intrinsically possess PST. Due to the $C_{2\upsilon }$ point-group symmetry, a unidirectional spin configuration is preserved in the out-of-plane direction for both conduction and valence bands around the high-symmetry $\mathrm{\Gamma }$ point. That is, the expectation value of the spin $S$ only has the out-of-plane component $S_z$. The application of an out-of-plane external electric field can induce in-plane components $S_x$ and $S_y$, thus offering a promising platform for the on-off logical functionality of spin devices. Our work reveals an alternative family of $T$-phase two-dimensional (2D) materials, which could provide promising applications in spintronic devices.

Transport property under metallic ferroaxial ordering in an external magnetic field is theoretically investigated. After presenting the relation between the magnetoconductivity tensor and ferroaxial moment from the symmetry viewpoint, we analyze the behavior of the unconventional Hall effect and magnetoconductivity for a general five $d$-orbital tight-binding model under the point group $C_{4\mathrm{h}}$, where the ferroaxial moment is activated. We show that the crystalline electric field that arises from the symmetry reduction from $D_{4\mathrm{h}}$ to $C_{4\mathrm{h}}$ is essential for the ferroaxial-related magnetotransport, while the relativistic spin–orbit coupling is not required. We also compare the unconventional Hall effect driven by the ferroaxial moment with the conventional Hall effect, the latter of which does not require the ferroaxial moment. The present results provide characteristic transport properties in the ferroaxial systems, which can be observed in various candidate materials like ${\mathrm{Ca}}_5{\mathrm{Ir}}_3{\mathrm{O}}_{12}$.

We study the motion of holes in a mixed-dimensional setup of an antiferromagnetic ladder, featuring nearest-neighbor hopping $t$ along the ladders and Ising-type spin interactions along, $J_{\parallel }$, and across, $J_{\perp }$, the ladder. We determine exact solutions for the low-energy one- and two-hole eigenstates. The presence of the trans-leg spin coupling, $J_{\perp }$, leads to a linear confining potential between the holes. As a result, holes on separate legs feature a superlinear binding energy scaling as ${(J_{\perp }/t)}^{2/3}$ in the strongly correlated regime of $J_{\perp },J_{\parallel }\le t$. This behavior is linked to an emergent length scale $\lambda \propto {(t/J_{\perp })}^{1/3}$, stemming from the linear confining potential, and which describes how the size of the two-hole molecular state diverges for $J_{\perp },J_{\parallel }\ll t$. On the contrary, holes on the same leg unbind at sufficiently low spin couplings. This is a consequence of the altered short-range boundary condition for holes on the same leg, yielding an effective Pauli repulsion between them, limiting their kinetic energy and making binding unfavorable. Finally, we determine the exact nonequilibrium quench dynamics following the sudden immersion of initially localized nearest-neighbor holes. The dynamics is characterized by a crossover from an initial ballistic quantum walk to an aperiodic oscillatory motion around a finite average distance between the holes due to the confining potential between them. In the strongly correlated regime of low spin couplings, $J_{\perp },J_{\parallel }\le t$, we find this asymptotic distance to diverge as $t/J_{\perp }$, showing a much stronger scaling than the eigenstates. The predicted results should be amenable to state-of-the-art quantum simulation experiments using currently implemented experimental techniques.

We investigate the finite-frequency optical response of systems described at low energies by Dirac-Weyl Hamiltonians with higher pseudospin $\mathcal{S}$ values. In particular, we examine the situation where a tilting term is applied in the Hamiltonian, which results in tilting of the Dirac electronic band structure. We calculate and discuss the optical conductivity for the cases $\mathcal{S}=1$, 3/2, and 2, in both two and three dimensions in order to demonstrate the expected signatures in the optical response. We examine both undertilted (type I) and overtilted (type II) as well as the critically tilted case (type III). Along with the well-known case of $\mathcal{S}=1/2$, a pattern emerges for any $\mathcal{S}$. We note that in situations with multiple nested cones, such as happens for $\mathcal{S}>1$, the possibility of having one cone being type I while the other is type II allows for more rich variations in the optical signature, which we will label as type-IV behavior. We also comment on the presence of optical sum rules in the presence of tilting. Finally, we discuss tilting in the $\alpha -{\mathrm{T}}_3$ model in two dimensions, which is a hybrid of the $\mathcal{S}=1/2$ (honeycomb lattice) and $\mathcal{S}=1$ (dice or ${\mathrm{T}}_3$ lattice) model with a variable Berry phase. We contrast this model's conductivity with that of $\mathcal{S}=3/2$ and $\mathcal{S}=2$ as the resultant optical response has some similarities, although there are clear distinguishing features between these cases.

Non-Hermiticity is a common property of a multitude of nonconservative physical systems that exchange energy with the surrounding environment. It brings about altogether new behaviors such as the non-Hermitian skin effect and the appearance of exceptional points, which have no counterparts in Hermitian systems. Despite intensive research activities on non-Hermitian physics, some fundamental issues, such as what the topological zero modes (i.e., the edge states with a degenerate zero eigenvalue that generally occur in the thermodynamic limit) will truly take when the lattice size becomes finite and whether they are definitely attributed to the formation of exceptional points, are still unclear, at least on an analytical level. Here we wish to address these open questions within the framework of the one-dimensional non-Hermitian Su-Schrieffer-Heeger model involving gain and loss. By virtue of this model under the open boundary condition, we obtain analytically the asymptotic solutions of topological edge states along with their explicit energy formulas that are universal for arbitrary lattice size. We also figure out the parameter conditions defining the domain of zero modes as well as the analytical criteria discriminating their localization characteristics, all exhibiting consistency with numerical results. We reveal that the zero modes sitting on either end of the chain are generated from exceptional points, but those sitting on both ends are indeed from diabolic points. In addition, we demonstrate that the skin modes caused by the non-Hermitian skin effect may possess higher-order exceptional points under certain parameter conditions. We anticipate that these analytical results will help illuminate the elusive non-Hermitian topology and may facilitate the experimental studies of some intriguing topological phenomena related to edge states.

We report anisotropic magnetodielectric coupling in layered van der Waals antiferromagnetic ${\mathrm{FePS}}_3$ (Néel temperature $T_N\sim$ 120 K) with perpendicular anisotropy. Above $T_N$, while the dielectric response function along the $c$ axis shows frequency-dependent relaxations, in-plane data is frequency independent and reveals a deviation from phonon-anharmonicity in the ordered state, thereby implying a connection to spin-phonon coupling known to be indicative of onset of magnetic ordering. At low temperature (below 40 K), atypical anomaly in the dielectric constant is corroborated with temperature-dependent dc and ac susceptibility. The magnetodielectric response across this anomaly differs significantly for both in-plane and out-of-plane cases. We have explained this in terms of preferential orientation of magnetic antiferromagnetic zigzag alignment, implied by the in-plane structural anisotropy as confirmed by ab initio calculations. Controlling the relative strength of magnetodielectric coupling with magnetic anisotropy opens a strategy for tracking subtle modifications of structures, such as in-plane anisotropy, with potential applications for spintronic technologies.

Electron-phonon interactions play a key role in many branches of solid-state physics. Here, our focus is on the transport properties of one-dimensional systems, and we apply efficient real-time matrix-product state methods to compute the optical and thermal conductivities of Holstein chains at finite temperatures and filling. We validate our approach by comparison with analytical results applicable to single polarons valid in the small polaron limit. Our work provides a systematic study of contributions to the thermal conductivity at finite frequencies and elucidates differences in the spectrum compared to the optical conductivity, covering both the Luttinger-liquid and charge-density-wave regimes. Finally, we demonstrate that our approach is capable of extracting the DC conductivities as well. Beyond this first application, several future extensions seem feasible, such as the inclusion of dispersive phonons, different types of local electron-phonon coupling, and a systematic study of drag effects in this electron-phonon coupled system.

A strong linear-in-$k$ Rashba spin-orbit coupling (SOC) has been discovered theoretically for holes in semiconductor nanowires originating from direct dipolar coupling to the external electric field. Such direct Rashba SOC effect not only overcomes the major drawback of the hole Rashba SOC for its leading order being cubic-in-$k$ but also renders its strength orders of magnitude stronger than the corresponding electron counterpart. Here, the direct hole Rashba SOC effect has been experimentally observed through the circular photogalvanic effect (CPGE) by conducting the experimental measurement of a helicity-dependent photocurrent in the $p$-type $\mathrm{Ga}{\mathrm{As}}_{1-x}{\mathrm{Sb}}_x$ semiconducting nanowires upon application of an external gate voltage at room temperature. We have observed that the CPGE current undergoes a transition from rapid increase to saturation as the gate voltage varies. This finding is consistent with the predicted common feature of the direct Rashba SOC of holes in semiconductor nanowires, providing clear evidence for the theoretical concept.

This work shows an alternative approach to extract the pyroelectric coefficient directly from the response of the crystal structure to temperature variations. The approach uses crystal structure parameters determined at different temperatures and Born effective charges calculated by density functional theory to evaluate the spontaneous polarization. On this basis, the pyroelectric coefficient is calculated using the first derivative of the polarization with respect to temperature. In this work, we utilize laboratory single-crystal x-ray diffraction in a temperature range from 80 to 400 $\mathrm{K}$ to demonstrate this approach on the standard pyroelectric materials lithium niobate and lithium tantalate. The accuracy of the presented method for the spontaneous polarization is on par with reported experimental data and relative errors are below $7\%$. Our determined pyroelectric coefficients have larger errors, but are within the range of reported literature values. The outlined semitheoretical method is recommended when electrical characterization under temperature change is not feasible, e.g., when the preparation of large area contacts is problematic or only small sample volumes are available ($<100$ $\mu {\mathrm{m}}^3$).

Monitored quantum circuits exhibit entanglement transitions at certain measurement rates. Such a transition separates phases characterized by how much information an observer can learn from the measurement outcomes. We study SU(2)-symmetric monitored quantum circuits, using exact numerics and a mapping onto an effective statistical-mechanics model. Due to the symmetry's non-Abelian nature, measuring qubit pairs allows for nontrivial entanglement scaling even in the measurement-only limit. We find a transition between a volume-law entangled phase and a critical phase whose diffusive purification dynamics emerge from the non-Abelian symmetry. Additionally, we identify a “spin-sharpening transition.” Across the transition, the rate at which measurements reveal information about the total spin quantum number changes parametrically with system size.

Magnetic topological materials exhibiting unique topological quantum physics due to the combination of spintronics and topology have aroused the interest of researchers. We propose $P{6}_{3}22$-type ${\mathrm{BaNiIO}}_6$—a dynamically stable material with two fully spin-polarized hourglass charge-three (C-3) Weyl points (WPs) and six fully spin-polarized charge-one (C-1) WPs around the Fermi level—with the help of first-principles calculations and symmetry analysis. C-3 WPs have been theoretically proposed for more than a decade. However, they have only been reported in nonmagnetic phonon systems rather than in magnetic electronic systems. $P{6}_{3}22$-type ${\mathrm{BaNiIO}}_6$ shows 100% spin polarization and belongs to the group of half-metals due to the metallic states and the semiconducting states for the bands in spin-up and spin-down directions, respectively. The half-metallic state and the spin-polarized C-3 and C-1 WPs are robust to uniform strains (from $-5$ to 5%) and on-site Hubbard-Coulomb interactions (from 0 to 6 eV). Furthermore, unique surface arcs connected the projections of two spin-polarized C-3 WPs and six spin-polarized C-1 WPs, leading to fully spin-polarized sextuple-helicoid surface arcs on the (001) surface of $P{6}_{3}22$-type ${\mathrm{BaNiIO}}_6$. Undoubtedly, $P{6}_{3}22$-type ${\mathrm{BaNiIO}}_6$, with fully spin-polarized C-3 and C-1 WPs and fully spin-polarized sextuple-helicoid surface arcs, is a promising candidate for applications in spintronic and topological physics.

Multihydrogen lanthanum hydrides have shown the highest critical temperature $T_c$ at 250–260 K under pressures of 170–200 GPa. However, such high pressure is a great challenge for sample preparation and practical applications. To address this challenge, we propose a design strategy for ambient-pressure superconductors that involves constructing few-hydrogen metal-bonded perovskite hydrides, such as the Al-based superconductor ${\mathrm{Al}}_4\mathrm{H}$, with better ductility than the well-known multihydrogen, cuprate, and Fe-based superconductors. Based on the Migdal-Eliashberg theory, we predict that the structurally stable ${\mathrm{Al}}_4\mathrm{H}$ has a favorable $T_c$ of up to 54 K under ambient pressure.