A single crystal of ${\mathrm{UPd}}_2{\mathrm{Si}}_2$ was studied in wide ranges of temperature and magnetic field strength with the main goal of revealing the existence of a Lifshitz point in its magnetic phase diagram. The experiments showed that the boundaries between paramagnetic, modulated antiferromagnetic, and uniform antiferromagnetic phases do not meet up to 14 T.

A single crystal of ${\mathrm{UPd}}_2{\mathrm{Si}}_2$ was studied in wide ranges of temperature, magnetic field strength, and hydrostatic pressure with the main aim of revealing the existence of a Lifshitz point in its magnetic phase diagram. The experiments showed that up to 14 T and 7 GPa, the boundaries between paramagnetic, modulated, and uniform magnetic phases do not meet. The application of external pressure leads to stabilization of the antiferromagnetic phase. Simultaneously, the triple point in the $H\text{−}T$ phase diagram, where the ferrimagnetic phase emerges, is shifted to higher fields. This finding is discussed with respect to two different magnetic phase diagrams of ${\mathrm{UPd}}_2{\mathrm{Si}}_2$ reported in the literature.

A general free bosonic system with a pairing term is described by a bosonic Bogoliubov-de Gennes (BdG) Hamiltonian. The representation is given by a pseudo-Hermitian matrix, which is crucially different from the Hermitian representation of a fermionic BdG Hamiltonian. In fermionic BdG systems, a topological invariant of the whole particle (hole) bands can be nontrivial, which characterizes the Andreev bound states (ABS), including Majorana fermions. In bosonic cases, on the other hand, the corresponding topological invariant is thought to be trivial, owing to the stability condition of the bosonic ground state. In this paper, we consider a two-dimensional model that realizes a bosonic analogy of the ABS at the boundaries. The boundary states of this model are located outside the bulk bands and are characterized by a nontrivial Berry phase (or polarization) of the hole band. Furthermore, we investigate the zero-energy flat-band limit in which the Bloch Hamiltonian is defective, where the particle and hole states are identical to each other. In this limit, the Berry phase is ${\mathbb{Z}}_2$ quantized thanks to an emergent parity-time symmetry induced by the defective nature. This is an example of a topological invariant that uses the defective nature as a projection structure. Thus, boundary states in our model are essentially different from Hermitian topological modes and their variants. We also discuss the entanglement entropy of the system with bosonic Andreev bound states, motivated by the relationship between our model and the continuous variable surface codes.

We analyze the quantum limit of sensitivity in four-dimensional scanning transmission electron microscopy (4D-STEM), which has emerged as a favored technique for imaging the structure of a wide variety of materials, including biological and other radiation-sensitive materials. 4D-STEM is an indirect (computational) imaging technique, which uses a scanning beam and records the scattering distribution in momentum (diffraction) space for each beam position. We find that, in measuring a sample's electrostatic potential, the quantum Fisher information from 4D-STEM can match that from real-space phase-contrast imaging. Near-optimum quantum Fisher information is achieved using a delocalized speckled probe. However, owing to the detection in the diffraction plane, 4D-STEM ultimately enables only about half of the quantum limit, whereas Zernike phase-contrast imaging enables the quantum limit for all spatial frequencies admitted by the optical system. On the other hand, 4D-STEM can yield information on spatial frequencies well beyond those accessible by phase-contrast TEM. Our conclusions extend to analogous imaging modalities using coherent scalar visible light and x rays.

Materials with strong spin-orbit coupling and low crystalline symmetry are promising for generating large unconventional spin-orbit torques (SOTs), such as in-plane fieldlike (FL) torques and out-of-plane dampinglike (DL) torques, which can effectively manipulate and deterministically switch an out-of-plane magnetization without the need for additional external in-plane magnetic fields. Here, we report SOTs generated by magnetron-sputtered $1T^{\prime }{\mathrm{MoTe}}_2$/Permalloy (Py; ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$)/MgO heterostructures using both spin-torque ferromagnetic resonance (ST-FMR) and second harmonic Hall measurements. We observed unconventional FL and DL torques in our samples due to spins polarized normal to the interface of ${\mathrm{MoTe}}_2$ and Py layers, and studied the influence of crystallographic order and ${\mathrm{MoTe}}_2$ layer thickness on the SOTs. By comparing the Raman spectra of $1T^{\prime }{\mathrm{MoTe}}_2$ samples prepared in different ways, we found a tensile strain in sputtered ${\mathrm{MoTe}}_2$ films, which might further enhance the generation of unconventional torques by reducing the symmetry of $1T^{\prime }{\mathrm{MoTe}}_2$.

Transition metal phosphorous trichalcogenides represent a class of van der Waals magnetic materials ideal for exploring two-dimensional magnetism. This study investigates the spin-orbital states of ${\mathrm{FePS}}_3$ and ${\mathrm{FePSe}}_3$ monolayers and the origin of their Ising zigzag antiferromagnetism (AFM), using density functional calculations, crystal field level diagrams, superexchange analyses, and parallel tempering Monte Carlo (PTMC) simulations. Our calculations show that under the trigonal elongation of the ${\mathrm{FeS}}_6$ (${\mathrm{FeSe}}_6$) octahedra, the $e_g^{\pi }$ doublet of the Fe $3d$ crystal field levels lies lower than the $a_{1g}$ singlet by about 108 meV (123 meV), which is much larger than the strength of Fe $3d$ spin-orbit coupling (SOC). Then, the half-filled minority-spin $e_g^{\pi }$ doublet of the high-spin ${\mathrm{Fe}}^{2+}$ ions ($d^{5\uparrow ,1\downarrow }$) splits by the SOC into the lower $L_{z+}$ and higher $L_{z-}$ states. The spin-orbital ground state $d^{5\uparrow }{L}_{z+}^{1\downarrow }$ formally with $S_z=2$ and $L_z=1$ gives the large $z$-axis spin/orbital moments of $3.51/0.76{\mu }_{\mathrm{B}}$ ($3.41/0.67{\mu }_{\mathrm{B}}$) for ${\mathrm{FePS}}_3$ (${\mathrm{FePSe}}_3$) monolayer, and both the moments are reduced by the strong (stronger) Fe $3d$ hybridizations with S $3p$ (Se $4p$) states. As a result, ${\mathrm{FePS}}_3$ (${\mathrm{FePSe}}_3$) monolayer has a huge perpendicular single-ion anisotropy (SIA) energy of 19.4 meV (14.9 meV), giving an Ising-type magnetism. Moreover, via the maximally localized Wannier functions, we find that the first-nearest-neighboring (1NN) Fe-Fe pair has large hopping parameters in-between some specific orbitals, and so does the third-nearest-neighboring (3NN) Fe-Fe pair. In contrast, the second-nearest-neighboring (2NN) Fe-Fe pair has much smaller hopping parameters and the fourth-nearest-neighboring Fe-Fe pair has negligibly small ones. Then, a combination of those hopping parameters and the superexchange picture can readily explain the computed strong 1NN ferromagnetic coupling and the strong 3NN antiferromagnetic one but the relatively much smaller 2NN antiferromagnetic coupling. Furthermore, our PTMC simulations give $T_{\mathrm{N}}$ of 119 K for ${\mathrm{FePS}}_3$ monolayer and well reproduce its experimental Ising zigzag AFM, and also predict for ${\mathrm{FePSe}}_3$ monolayer the same magnetic structure with a close or even higher $T_{\mathrm{N}}$.

A major focus of current research on superconducting superhydrides is to achieve superconductivity at lower pressures, especially ambient pressure. Here we present the prediction of a class of high-temperature ternary hydrogen-rich superconductors, which are metastable at mild pressure and dynamically stable at ambient pressure using crystal structure searching. Our findings reveal the existence of a hexagonal $\mathrm{ThSi}{\mathrm{H}}_7$ compound with a superconducting $T_{\mathrm{c}}$ of 61.5 K at ambient pressure, as estimated by electron-phonon coupling calculations. Interestingly, the H sites in $\mathrm{ThSi}{\mathrm{H}}_7$ materialize a breathing kagome network, equivalent to a triangular lattice of trimer plaquettes, which is entirely different from previously known hydrogen clathrate structures. By substituting Th with lanthanide elements, we discovered that $\mathrm{LaSi}{\mathrm{H}}_7$ and $\mathrm{CeSi}{\mathrm{H}}_7$ are also dynamically stable at 0 GPa, while $\mathrm{PrSi}{\mathrm{H}}_7$ and $\mathrm{NdSi}{\mathrm{H}}_7$ are dynamically stable at 10 and 15 GPa with high $T_{\mathrm{c}}$ values of 63.9 and 65.9 K, respectively. Our results provide a system for superconducting hydrides and open a promising avenue for studying ambient pressure high-temperature superconductors.

In this study, we explore the precise physical quantities in the thermodynamic limit of the one-dimensional Hubbard model with nonparallel boundary magnetic fields based on the off-diagonal Bethe ansatz solution. A particular emphasis is placed on the half-filling condition to investigate the distinct patterns of Bethe roots in the reduced Bethe ansatz equations for different boundary parameters. The ground state of the system can be divided into five regions according to the distribution of Bethe roots. By analyzing these patterns, we calculate the densities of states, ground-state energy density, and surface energy. The results reveal the existence of stable-boundary bound states, which are dependent on specific constraints regarding the boundary magnetic fields.

Lattice thermal conductivity (${\kappa }_{\mathrm{L}}$) is a crucial characteristic of crystalline solids with significant implications for thermal management, energy conversion, and thermal barrier coating. The advancement of computational tools based on density functional theory (DFT) has enabled the effective utilization of phonon quasiparticle-based approaches to unravel the underlying physics of various crystalline systems. While the higher order of anharmonicity is commonly used for explaining extraordinary heat transfer behaviors in crystals, the impact of exchange-correlation (XC) functionals in DFT on describing anharmonicity has been largely overlooked. The XC functional is essential for determining the accuracy of DFT in describing interactions among electrons/ions in solids and molecules. However, most XC functionals in solid-state physics are primarily focused on computing the properties that only require small atomic displacements from the equilibrium (within the harmonic approximation), such as harmonic phonons and elastic constants, while anharmonicity involves larger atomic displacements. Therefore, it is more challenging for XC functionals to accurately describe atomic interactions at the anharmonicity level. In this study, we systematically investigate the room-temperature ${\kappa }_{\mathrm{L}}$ of 16 binary compounds with rocksalt and zinc-blende structures using various XC functionals such as local density approximation (LDA), Perdew-Burke-Ernzerhof (PBE), revised PBE for solid and surface (PBEsol), optimized B86b functional (optB86b), revised Tao-Perdew-Staroverov-Scuseria (revTPSS), strongly constrained and appropriately normed functional (SCAN), regularized SCAN (rSCAN), and regularized-restored SCAN (${\mathrm{r}}^2\mathrm{SCAN}$) in combination with different perturbation orders, including phonon within harmonic approximation (HA) plus three-phonon scattering ($\mathrm{HA}+3\mathrm{ph}$), phonon calculated using self-consistent phonon theory (SCPH) plus three-phonon scattering (SCPH $+$ 3ph), and SCPH phonon plus three- and four-phonon scattering (SCPH $+$ 3,4ph). Our results show that the XC functional exhibits strong entanglement with perturbation order and the mean relative absolute error (MRAE) of the computed ${\kappa }_{\mathrm{L}}$ is strongly influenced by both the XC functional and perturbation order, leading to error cancellation or amplification. The minimal (maximal) MRAE is achieved with revTPSS (rSCAN) at the HA $+$ 3ph level, SCAN (${\mathrm{r}}^2\mathrm{SCAN}$) at the SCPH $+$ 3ph level, and PBEsol (rSCAN) at the SCPH $+$ 3,4ph level. Among these functionals, PBEsol exhibits the highest accuracy at the highest perturbation order. The SCAN-related functionals demonstrate moderate accuracy but are suffer from numerical instability and high computational costs. Furthermore, the different impacts of quartic anharmonicity on ${\kappa }_{\mathrm{L}}$ in rocksalt and zinc-blende structures are identified by all XC functionals, attributed to the distinct lattice anharmonicity in these two structures. These findings serve as a valuable reference for selecting appropriate functionals for describing anharmonic phonons and offer insights into high-order force constant calculations that could facilitate the development of more accurate XC functionals for solid materials.

We present a comprehensive Fermi liquid description for thermoelectric transport and current noise, applicable to multilevel quantum dots (QD) and magnetic alloys (MA) without electron-hole or time-reversal symmetry. Our formulation for the low-energy transport is based on an Anderson model with $N$ discrete impurity levels, and is asymptotically exact at low energies, up to the next-leading order terms in power expansions with respect to temperature $T$ and bias voltage $eV$. The expansion coefficients can be expressed in terms of the Fermi liquid parameters, which include the three-body correlation functions defined with respect to the equilibrium ground state in addition to the linear susceptibilities and the occupation number $N_d^{}$ of impurity electrons. We apply this formulation to the $\mathrm{SU}\left(N\right)$ symmetric QD and MA, and calculate the correlation functions for $N=4$ and 6, using numerical renormalization group approach. The three-body correlations are shown to be determined by a single parameter over a wide range of electron fillings $1\lesssim N_d^{}\lesssim N-1$ for strong Coulomb interactions $U$, and they also exhibit the plateau structures due to the $\mathrm{SU}\left(N\right)$ Kondo effects at integer values of $N_d^{}$. We find that the Lorenz number $L=\kappa /\left(T\sigma \right)$ for QD and MA, defined as the ratio of the thermal conductivity $\kappa$ to the electrical conductivity $\sigma$, deviates from the universal Wiedemann-Franz value ${\pi }^2/\left(3e^2\right)$ as the temperature increases from $T=0$, showing the $T^2$ dependence, the coefficient for which depends on the three-body correlations away from half filling. Furthermore, we find that the current noise for the SU(4) quantum dots and that for SU(6) show a pronounced difference at the quarter $N_d^{}/N=1/4$ and $3/4$ fillings. In particular, the linear noise for $N=4$ exhibits a flat peak while the peak for $N=6$ shows a round shape, reflecting the fact that, at these filling points, the $\mathrm{SU}\left(N\right)$ Kondo effects occur for $N\equiv 0$ (mod 4), whereas the intermediate-valence fluctuations occur for $N\equiv 2$ (mod 4). We also demonstrate the role of three-body correlations on the nonlinear current noise and the other transport coefficients.

Bulk-boundary correspondence (BBC) of symmetry-protected topological (SPT) phases relates the nontrivial topological invariant of the bulk to the number of topologically protected boundary states. Recently, a finer classification of SPT phases in Hermitian systems has been discovered, known as subsymmetry-protected topological (sub-SPT) phases [Wang et al., Nat. Phys. 19, 992 (2023)]. In sub-SPT phases, a fraction of the boundary states is protected by the subsymmetry of the system, even when the full symmetry is broken. While the conventional topological invariant derived from the Bloch band is not applicable to describe the BBC in these systems, we propose to use the non-Bloch topological band theory to describe the BBC of sub-SPT phases. Using the concept of the generalized Brillouin zone (GBZ), where Bloch momenta are generalized to take complex values, we show that the non-Bloch band theory naturally gives rise to a non-Bloch topological invariant, establishing the BBC in both SPT and sub-SPT phases. In a one-dimensional system, we define the winding number, whose physical meaning corresponds to the reflection amplitude in the scattering matrix. Furthermore, the non-Bloch topological invariant characterizes the hidden intrinsic topology of the GBZ under translation symmetry-breaking boundary conditions. The topological phase transitions are characterized by the generalized momenta touching the GBZ, which accompanies the emergence of diabolic or band-touching points. Additionally, we discuss the BBCs in the presence of local or global full-symmetry or subsymmetry-breaking deformations.

We predict the formation of intravalley and intervalley controllable trions in buckled two-dimensional (2D) materials such as silicene, germanene, and stanene monolayers in an external electric field. A study is performed within the framework of a nonrelativistic potential model using the method of hyperspherical harmonics (HH). We solve the three-body Schrödinger equation with the Rytova-Keldysh potential by expanding the wave functions of a trion in terms of the HH. A resultant system of coupled differential equations is solved numerically. Controllable ground-state energies of intravalley and intervalley trions by the external electric field are presented. The dependencies of the binding energy (BE) of trions in silicene, germanene, and stanene as a function of the electric field are qualitatively similar. BEs of trions formed by $A$ and $B$ excitons have a non-negligible difference that increases slightly as the electric field increases. It is demonstrated that trion BEs can be controlled by the external electric field, and the dielectric environment has a significant effect on the trion BE. The capability to control the BE and compactness of trions in buckled 2D materials by an external electric field suggests a possible trions crystallization in Xenes.

We present an all-electron, four-component relativistic implementation of electric field gradients (EFGs) at the nuclei using Gaussian-type orbitals and periodic boundary conditions. This allows us to include relativistic effects variationally, which is important for compounds containing heavy elements and for a property dependent on the electronic structure close to the nuclei. The all-electron approach ensures an accurate treatment of both core and valence orbitals, as both are important in the evaluation of EFGs. Computational efficiency is achieved through the use of a recent implementation of density fitting in combination with quaternion algebra and restricted kinetic balance. We use the relativistic approach to calculate the EFGs in different arsenic, antimony, and bismuth halides and oxyhalides, and explore the importance of relativistic effects on EFGs in solids and compare these with results obtained for molecular species. Our calculations contribute to establishing a reliable estimate for the nuclear quadrupole moment of ${}^{209}\mathrm{Bi}$, for which our best estimate is $-428\left(17\right)$ mb, in excellent agreement both with molecular data and a recent reevaluation of the nuclear quadrupole moment obtained from atomic data and ab initio calculations. Our results suggest that there is a need to revisit the experimental data for the EFGs of several bismuth oxyhalides.

Recent experiments show that doping a small amount of fluorinated pseudohalides $\left({\mathrm{BF}}_4\right)$ into ${\mathrm{CH}}_3{\mathrm{NH}}_3{\mathrm{PbI}}_3$ $\left({\mathrm{MAPbI}}_3\right)$ can enhance the performance of wide-band-gap (WBG) perovskite solar cells. Using time-domain density functional theory and ab initio nonadiabatic molecular dynamics we demonstrate that ${\mathrm{BF}}_4$-doped WBG perovskites not only maintain the high defect tolerance but also exhibit greatly improved thermodynamic stability due to enhanced dissociation energy and reduced thermal atomic fluctuation. The strengthened hydrogen bond network introduces increased lattice rigidity, confined inner space, and the reorientated dipole direction of methylammonium molecules, which synergistically suppress the ion migration in ${\mathrm{BF}}_4$-doped ${\mathrm{MAPbI}}_3$ perovskite. Notably, the charge carrier lifetime experiences an order-of-magnitude improvement after ${\mathrm{BF}}_4$ doping, which is mainly attributed to the weakened nonadiabatic coupling. This work provides valuable insights into the effect of fluorinated pseudohalides doped in perovskite materials and suggests a promising approach to enhancing the stability and efficiency of WBG perovskite solar cells.

We numerically investigate the guiding center structure factors of several states in the Read-Rezayi family. Using exact diagonalizations on the torus and density matrix renormalization group on an infinite cylinder, we test a conjecture proposed in Can et al. [Phys. Rev. Lett. 113, 046803 (2014)] for the $\nu =\frac{3}{5}$ and $\nu =\frac{4}{6}$ Read-Rezayi states. Furthermore, we discuss the strong finite-size effects present in numerically accessible wavefunctions, and provide a simple recipe to minimize them on manifolds where non-Abelian theories have topological degeneracies.

In a growing number of materials, phonons have been found to generate a thermal Hall effect, but the underlying mechanism remains unclear. Inspired by previous studies that revealed the importance of ${\mathrm{Tb}}^{3+}$ ions in generating the thermal Hall effect in a family of pyrochlores, we investigated the role of ${\mathrm{Tm}}^{3+}$ ions in ${\mathrm{TmVO}}_4$, a paramagnetic insulator with a different crystal structure. We observe a negative thermal Hall conductivity in ${\mathrm{TmVO}}_4$ with a magnitude such that the Hall angle, $|{\kappa }_{xy}/{\kappa }_{xx}|$, is approximately $1\times {10}^{-3}$ at $H$ = 15 T and $T$ = 20 K, typical for a phonon-generated thermal Hall effect. In contrast to the negligible ${\kappa }_{xy}$ found in the nonmagnetic pyrochlore analog (where the ${\mathrm{Tb}}^{3+}$ ions are replaced with ${\mathrm{Y}}^{3+}$), we observe a negative ${\kappa }_{xy}$ in ${\mathrm{YVO}}_4$ with a Hall angle of magnitude comparable to that of ${\mathrm{TmVO}}_4$. This shows that the ${\mathrm{Tm}}^{3+}$ ions are not essential for the thermal Hall effect in this family of materials. Interestingly, at an intermediate Y concentration of $x=0.3$ in ${\mathrm{Tm}}_{1-x}{\mathrm{Y}}_x{\mathrm{VO}}_4, {\kappa }_{xy}$ was found to have a positive sign, pointing to the importance of impurities in the thermal Hall effect of phonons.

With the successive confirmation of two-dimensional (2D) ferroelectricity and ferromagnetism and the proposal of ferrovalley, the coexistence of multiple ferroic orders in single-phase materials has attracted extensive attention. Here we demonstrate the coexistence and coupling effects of these three ferroic orders in conventional valley material systems by combining first-principles calculations and the symmetry analysis method. We show that, in 2D ferromagnets lacking inversion symmetry, spin-orbit coupling causes spin direction-dependent ferroelectricity through the $p\text{−}d$ hybridization mechanism. The magnitude of spin-induced polarization can be significantly improved by increasing the atomic number of the anion, and the Janus monolayer exhibit an additional in-plane polarization component with respect to its parent structure when the spin deviates from being in plane. Ferrovalley and the resulting anomalous Hall effect depend on the out-of-plane spin component. This work contributes to the design of 2D room-temperature multiferroics with intrinsic magnetoelectric coupling.

It has long been an ultimate goal to introduce chemical doping at the atomic level to precisely tune properties of materials. Two-dimensional materials have a natural advantage due to their high surface to volume ratio, but achieving this goal experimentally remains a huge challenge. Here, we demonstrate the ability to introduce chemical doping in graphene with atomic-level precision by controlling chemical adsorption of individual Se atoms, which are extracted from the ${\mathrm{WSe}}_2$ that is underneath, at the interface of the $\text{graphene}/{\mathrm{WSe}}_2$ heterostructures. Our scanning tunneling microscopy (STM) measurements, combined with first-principles calculations, reveal that individual Se atoms can chemisorb on three possible positions in graphene, which generate distinct pseudospin-mediated atomic-scale vortices in graphene. Furthermore, the chemisorbed positions of individual Se atoms can be manipulated by the STM tip, which enables us to achieve atomic-scale control of quantum interference of the pseudospin-mediated vortices in graphene. This result offers the promise of controlling properties of materials with atomic-level precision through chemical doping.

Aluminum nitride is a technologically important wide band-gap semiconductor which has been shown to host bright quantum emitters. We use photon emission correlation spectroscopy (PECS), time-resolved photoluminescence (TRPL), and state-population dynamic simulations to probe the dynamics of emission under continuous wave (CW) and pulsed optical excitation. We infer that there are at least four dark shelving states, which govern the TRPL, bunching, and saturation of the optical transition. We study in detail the emission dynamics of two quantum emitters (QEs) with differing power-dependent shelving processes, hypothesized to result from charge ionization and recombination. These results demonstrate that photon bunching caused by shelving the system in a dark state inherently limits the saturation rate of the photon source. In emitters where increasing optical power deshelves the dark states, we observe an increased photon emission intensity.