This study explores, through first-principles calculations, the structural stability, electronic properties, and potential applications of nanofoam structures consisting of graphenelike nanoribbons of C, B, and N atoms with edges covalently connected by triple junctions. Among the stoichiometries considered, pristine BN structures are the most stable, with formation energies per atom 26% smaller than those of the corresponding pristine carbon foams, on average. Remarkably, one of the BN foam structures was found to be more stable than the planar hexagonal boron nitride (h-BN) structure. The least stable foam structures are those with B, C, and N atoms, as expected due to the existence of “wrong” C-B and C-N bonds. Interestingly, these B-C-N foams are more stable in all structures considered when carbon atoms are located at the triple junction regions. A variety of electronic properties are found among the foams investigated. Interestingly, one of the boron nitride foams is both ferromagnetic and metallic. These findings provide valuable insights into the design and optimization of lightweight nanoporous materials for use in aerospace, energy storage, and electronics devices.

Spin-phonon coupling and its efficacy in inducing multiple topological phase transitions in a frustrated kagome antiferromagnet have been rare in literature. To this end, we study the ramifications of invoking optical phonons in such a system via two different coupling mechanisms, namely, a local and a nonlocal one, which are distinct in their microscopic origin. In case of the local spin-phonon coupling, a single phonon mode affects the magnetic interactions, whereas in the nonlocal case, two neighboring phonon modes are involved in the energy renormalization, and it would be worthwhile to compare and contrast between the two. To tackle these phonons, we propose an analytic approach involving a canonical spin-Peierls transformation applied to magnons. The formalism renders a hybridization between the magnons and the phonon modes, yielding magnon-polaron quasiparticles. In both the coupling regimes, validations for the topological signatures are systematically derived from the bulk and edge spectral properties of the magnon-polaron bands that are characterized by their corresponding Chern numbers. Thereafter, we investigate transitions from one topological phase to another solely via tuning the spin-phonon coupling strength. Moreover, these transitions significantly impact the behavior of the thermal Hall conductivity that aids in discerning distinct topological phases. Additionally, the explicit dependencies on the temperature and the external magnetic field are explored in inducing topological phase transitions associated with the magnon-polaron bands. Thus, our work serves as an ideal platform to probe the interplay of frustrated magnetism and polaronic physics.

In this work we develop a theoretical framework for the control of corner modes in higher-order topological insulators (HOTIs) featuring long-range hoppings and diverse geometries, enabling precise tunability of their spatial positions. First, we demonstrate that the locations of corner states can be finely tuned by varying long-range hoppings in a circular HOTI, as revealed by a detailed edge theory analysis and the condition of vanishing Dirac mass. Moreover, we show that long-range hoppings in different directions (e.g., $x$ and $y$) have distinct effects on the positioning of corner states. Second, we investigate HOTIs with various polygonal geometries and find that the presence and location of corner modes depend sensitively on the shape. In particular, a corner hosts a localized mode if the Dirac masses of its two adjacent edges have opposite signs, while no corner mode emerges if the masses share the same sign. Our findings offer a versatile approach for the controlled manipulation of corner modes in HOTIs, opening avenues for the design and implementation of higher-order topological materials.

As a novel magnetism that combines features of ferromagnetism and antiferromagnetism, altermagnetism is attracting great attention due to its special energy band structure and potential application prospects. The NiAs-type metallic CrSb was proposed to be a new altermagnet, which has been experimentally verified by spin-resolved angle-resolved photoemission spectroscopy. In this work, we show the magnetic, electrical, and thermoelectric properties of CrSb single crystals. It is found that the thermoelectricity exhibits an anomalous Nernst effect (ANE) with the value of $|S_{zy}^A|\sim 0.3\mu \mathrm{V}/\mathrm{K}$, which is comparable to the value in the ferromagnetic metals. In addition, first-principles calculation shows that the experimental results are qualitatively consistent with the characteristics of an altermagnet and support the observation of ANE. This work not only provides a splendid bulk platform to study altermagnet physics, but also indicates that ANE is a highly effective method to study alternating spin-splitting band structure near the Fermi level and will greatly intrigue the research interest of ANE in altermagnets.

The universality class of the Mott metal-insulator transition in electronic systems strongly coupled to the lattice degrees of freedom has been the subject of recent debate. While transport scaling exponents as well as a critical slowing down of resistance fluctuations point towards Ising-type criticality, a strong involvement of the lattice elasticity suggests a mean-field scenario instead. We investigate the low-frequency resistance noise in the model system $\kappa \text{−}{\left(\mathrm{ET}\right)}_2\mathrm{Cu}\left[\mathrm{N}{\left(\mathrm{CN}\right)}_2\right]\mathrm{Cl}\left(\kappa \text{−}\mathrm{Cl}\right)$—selected because it is known to exhibit critical elasticity—tuned to the Mott end point by hydrostatic pressure. Contrary to previous reports for the related, deuterated $\kappa$-Br compound, we do not find any indication of a critical slowing down, but observe a strong and anisotropic change of the relative resistance noise level in the metallic compared to the insulating phase. We speculate within the framework of isostructural criticality that a critical slowing down might emerge in the presence of structural disorder.

We characterize site-controlled $\mathrm{I}{\mathrm{n}}_{0.25}\mathrm{G}{\mathrm{a}}_{0.75}\mathrm{As}$ quantum dots in (111)B GaAs pyramidal recesses as a platform for spin qubit implementation. By combining scanning confocal cryomicroscopy, magnetophotoluminescence studies, and resonant excitation, we identify and isolate a positively charged exciton with a hole spin in its ground state. Application of a strong 5-T magnetic field parallel to the growth axis induces a fourfold splitting of the energy levels of the positively charged exciton, creating an optically addressable double-Λ (Lambda) system. We combine weak above-band and resonant excitation to demonstrate spin-pumping and high-fidelity spin initialization through all four optical transitions and study the system behavior as a function of the resonant driving strength, showing the existence of a robust spin that can be optically pumped and initialized. These results demonstrate the potential of these quantum dots for precise spin manipulation and their relevance for future quantum hardware.

We investigate here structural (at local and global levels) and transport properties for $X_2\mathrm{MnAl}$ ($X=$ Co and Ti). Additionally, the magnetic properties were also studied for ${\mathrm{Ti}}_2\mathrm{MnAl}$. Our x-ray diffraction results show that both the compounds stabilize in B2 disordered phase with cubic structure of $Pm\overline{3}m$ space group. Further, the structural configuration of the above disordered phase for both the compounds was identified using combined studies of x-ray absorption spectroscopy and multiple scattering calculations at the transition metal $K$ edges. Upon such identification, in the case of ${\mathrm{Co}}_2{\mathrm{Mn}}_{1-y}{\mathrm{Cr}}_y\mathrm{Al}$ ($y=$ 0, 0.05, 0.1, 0.2) with change in $y$, we are able to establish a better connection quantitatively between the inverse of Mn-Co bonds and peak in the temperature-dependent resistivity. This highlights the crucial importance of a detailed understanding of the nature of B2 disorder. In the case of $y=0$, in the temperature range of study, the resistivity is driven by the functional form associated with (a) three-dimensional enhanced electron-electron Coulomb interaction scattering mechanism and (b) an unconventional one-magnon process. For ${\mathrm{Ti}}_2\mathrm{MnAl}$, the transport shows metallic glasslike behavior at high temperature, while at low temperature it follows both the Cote-Meisel's model and quantum correction model. In this compound, the magnetic studies suggest the formation of superparamagnetic clusters in the paramagnetic matrix at low temperatures. Our density functional theory results are in line with the transport and magnetic properties. In literature, the spin polarization percentage ($P$) for $X=$ Co in B2 disordered phase is $76\%$. However, the present results emphasize the fact that in B2 disordered phase, the value of $P$ can range from $90\%$ to $71\%$ depending on the structural configuration introduced by swapping of the atomic positions of Mn and Al. For the compound under study, the value of percentage spin polarization obtained ranges between $82\%$ to $85\%$. In addition, we also identify the origin of the difference in the shape of the Mn $3d$ density of states for both the alloys. Our results for $X=$ Co alloy highlights the importance of identifying the specific structural configuration associated with a particular disorder category especially in the estimation of $T_c$ and $P$ and for $X=$ Ti, the physical properties can be tuned by varying the position of $E_F$ and thereby its utilization in device applications.

The bosonic Kitaev chain is known to have extraordinary properties distinct from its fermionic counterpart. For example, it exhibits the non-Hermitian skin effect—its eigenmodes are exponentially localized to the edges of the chain—even when the system is Hermitian. Such non-Hermitian effects originate from the fact that the dynamics of bosonic quadratic Hamiltonians is governed by a non-Hermitian matrix. In the topological phase of the model, the modes conspire to lead to phase-dependent and directional exponential amplification of a classical drive. In this work, we study the robustness of this topological amplification to on-site dissipations. We examine the effect of uniform and nonuniform losses under various configurations. We find a remarkable resilience to dissipation in some configurations, while in others the dissipation causes a topological phase transition which eliminates the exponential amplification. In particular, when the dissipation is placed on every other site, the system remains topological and the exponential amplification persists even for very large loss rates which exceed the system's non-Hermitian gap. On the other hand, we find that dividing the chain into unit cells of an odd number of sites and placing dissipation on the first site leads to a topological phase transition at a certain critical value of the dissipation. Our work thus provides insights into the robustness against losses of the topological amplification of non-Hermitian systems and sets explicit limits on the bosonic Kitaev chain's ability to act as a multimode quantum sensor in realistic lossy scenarios.

While germanium (Ge) has long been an important player in microelectronics, strain-engineered Ge heterostructures have recently gained increased attention owing to the intriguing possibility of using strain to change the relative positions of the conduction band valleys and, as a result, go from an indirect to a direct gap material. Time-resolved pump-probe spectroscopy is an excellent tool to provide insight into the fundamental interactions and microscopic dynamics of electrons, holes, phonons, and impurities. In this study, using complementary techniques of single-color time-resolved differential reflectivity and two-color time-resolved differential transmission, we gained insights into the effects of interfacial strain on carrier dynamics in several different Ge-based heterostructures. Our structures include high-quality Ge films interfaced with InGaAs and AlAs grown on semi-insulating GaAs as the substrate. In contrast to traditional microwave photoconductivity decay ($\mu -\mathrm{PCD}$) measurements, which typically have a time resolution on the ns scale, we probe samples on a 100 fs scale and can measure decay times approximately three orders of magnitude faster than previous $\mu -\mathrm{PCD}$ measurements. Therefore, our results are sensitive to the effects of both carrier recombination as well as electron intervalley and hole interband scattering.

We report the appearance of nontrivial zero-energy corner modes in the form of topological defects (trimers) in a carefully designed 2D crystalline topological insulator. The proposed scenario is developed via an unconventional stacking of 1D topological atomic chains with crystalline mirror symmetry along the diagonal $(y=x)$ line. Our analysis shows that by systematically varying the hopping parameters $t$ (intrachain), $v$ (within the unit cell) and $w$ (between unit cells), the system exhibits more than one distinct nontrivial second-order topological phase. These phases are distinguished by their zero-energy corner modes. In one of these phases, the system supports four zero modes. Two of them reside on the trimers, and the rest reside on isolated sites situated at the corners along the diagonal line. However, in the second case, the zero modes on the isolated sites persist at the corners while the zero modes on the trimers vanish. A critical look at the phase evolution of the Bloch states helps investigate the topology of these phases by using winding numbers. Our work also shows the bulk-corner correspondence that exists between the invariants and the zero modes at the corners. With four zero modes at the corners and a winding number of 2, we conclude that the system has transformed into a second-order topological insulator via tuning of the hopping amplitudes.

Density functional theory is used to study the effect of compressive and tensile biaxial strain on ${\mathrm{Mn}}_3\mathrm{GaN}$. ${\mathrm{Mn}}_3\mathrm{GaN}$ is a noncollinear antiferromagnetic antiperovskite with a similar structure to that of an ideal cubic oxide perovskite, but with cations at the octahedral sites while the anion, nitrogen, is found at the B site. The present study explores the response of ${\mathrm{Mn}}_3\mathrm{GaN}$ to (001) strain, considering biaxial strain levels ranging from $-5$% to 5%. It is found that the electron structure is insensitive to tensile strain. The study supports previous results in that a spin-canted antiferromagnetic order emerges due to tensile strain, inducing net magnetization. Compressive strain collapses the noncollinear antiferromagnetic spin structure and induces a ferrimagnetic order at $-2$% strain. Notably, in contrast with oxide perovskites, ${\mathrm{Mn}}_3\mathrm{GaN}$ does not respond to strain by octahedral tilt, but rather by intraband redistributions of charge between Mn $d$ states. Despite the similar structure to oxide perovskites, the bonds between the B-site anion and octahedral site cations in ${\mathrm{Mn}}_3\mathrm{GaN}$ bonds are less rigid, such that strain is instead accommodated by a change in bond length rather than a change in bond angles.

${\mathrm{Na}}_3{\mathrm{Co}}_2{\mathrm{SbO}}_6$ is a promising candidate to realize the Kitaev spin liquid phase since the large Kitaev spin exchange interaction is tunable via the change in electronic structure, such as the trigonal crystal field splitting (${\mathrm{\Delta }}_{\text{TCF}}$). Here, we show that the uncorrelated electronic structure of ${\mathrm{Na}}_3{\mathrm{Co}}_2{\mathrm{SbO}}_6$ is rather insensitive to the strain effect due to the low crystal symmetry accompanied by oxygen displacements and the presence of Sb $s$ orbitals. Using density functional theory plus dynamical mean field theory, we find that the correlated electronic structure of ${\mathrm{Na}}_3{\mathrm{Co}}_2{\mathrm{SbO}}_6$ is an orbital-selective Mott insulating state where the trigonal $a_{1g}$ orbital is insulating due to the nearly full occupation, while other $d$ orbitals behave as typical Mott insulators, resulting in the effective tunability of ${\mathrm{\Delta }}_{\text{TCF}}$ under the strain effect. The sign change of ${\mathrm{\Delta }}_{\text{TCF}}$ can occur as the in-plane tensile strain is applied, and the Kitaev spin liquid phase could possibly be realized due to the strongly suppressed ${\mathrm{\Delta }}_{\text{TCF}}$ under tensile strain. Our results show that the local Co-site symmetry and dynamical correlation effects will play an important role in engineering the novel magnetic phase in this and related materials.

We theoretically show that the continuous magnetic translational invariance within the Hilbert (sub)space of a single Landau level (LL) can persist even in the presence of a superlattice electrostatic potential modulation, while such invariance is broken in the full real-space Hilbert space. This is due to the interplay of the superlattice constant and the fundamental length scale of the quantum Hall fluids. In particular for the lowest LL (LLL), when the spacing of superlattice is below the magnetic length, continuous magnetic translational symmetry is very robust. For the fractional quantum Hall phases, the continuous translational symmetry is preserved when the superlattice spacing is below the corresponding fundamental lengths which we can now quantitatively define, which is different from the length scale from the quantum metric. Moreover, our analysis implies that the dynamics of the anyonic excitations can be robust against the short wavelength part of the disorder potentials, and we discuss the related experimental ramifications.

Density-functional theory based molecular-dynamics simulations were used to investigate high-pressure chemical reactions in liquid mixtures of ${\mathrm{CO}}_2$ with several elements (Si, Mn, and Fe) at high temperatures of 2000–3000 K. Our ab initio simulations indicate that these reactant elements can reduce ${\mathrm{CO}}_2$ to C at high pressures (20 GPa) leading to the formation of C-C chains, with Si by far the most effective carbon-reducing agent. A combined chemical analysis using Bader charge analysis and crystal orbital Hamilton population (COHP) on simulation snapshots shows that significant charge transfer from the reducing element to the C atoms creates instability in the C-O covalent bonds. COHP analysis further shows that Mn/Fe-O and Mn/Fe-C bonding interactions are weaker compared to the Si counterparts. These results further our understanding of the redox chemistry of ${\mathrm{CO}}_2$ at conditions relevant to planetary mantle interiors and demonstrate the effectiveness of high pressure in the reduction of ${\mathrm{CO}}_2$ directly to solid carbon.

We study localization properties in disordered two-dimensional altermagnets, an emerging class of material s characterized by momentum-dependent alternating spin polarization and zero net magnetization, in the presence of Rashba spin-orbit coupling. Through large-scale numerical calculations of localization length and finite-size conductance, we map out the phase diagram and identify two distinct disorder-driven transitions: a diffusive metal-insulator transition and a marginal metal-insulator transition. Finite-size scaling analysis reveals that the critical behavior of the diffusive metal-insulator transition deviates from the conventional Anderson scenario, with the critical exponent showing strong sensitivity to the strength of the altermagnetic interaction. Meanwhile, the marginal metal-insulator transition exhibits key signatures of the Berezinskii-Kosterlitz-Thouless (BKT) universality class. Our results highlight the interplay of disorder, spin-orbit coupling, and spin-dependent band topology in altermagnets, and demonstrate that these materials are a promising platform for exploring unconventional quantum phase transitions without net magnetization or an anomalous Hall effect.

Noncentrosymmetric magnetic Weyl semimetals provide a platform for investigating the interplay among magnetism, inversion symmetry breaking, and topologically nontrivial Weyl fermions. The Weyl-mediated Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction may be related to the magnetic orders observed in rare-earth magnetic Weyl semimetals. Previous studies of RKKY interaction between magnetic impurities in Weyl semimetals found Heisenberg, Ising-like, and Dzyaloshinskii-Moriya (DM) types of interactions. However, different range functions are obtained in the literature. In this work, we calculate the Weyl-mediated RKKY interaction by using the divergence-free imaginary-time formalism and obtain exact analytical results at finite temperature. The discrepancies among zero-temperature range functions in the literature are resolved. At nonzero temperature, the interaction strength decays exponentially in the long distance limit. But in the short distance limit, the DM interaction shows a thermal enhancement, an effect persists up to higher temperature for shorter distance. This provides a mechanism stabilizing the helical order observed in rare-earth magnetic Weyl semimetals.

${\mathrm{EuAl}}_4$ exhibits a complex phase diagram, including the development of a charge density wave (CDW) below $T_{\mathrm{CDW}}=145\mathrm{K}$. Below $T_N=15.4\mathrm{K}$, a series of antiferromagnetically (AFM) ordered phases appear, while nontrivial topological phases, like skyrmion lattices, are stabilized under an applied magnetic field. The symmetries of the variously ordered phases are a major issue concerning the understanding of the stabilization of the ordered phases as well as concerning the interplay between the various types of order. ${\mathrm{EuAl}}_4$ at room temperature has tetragonal symmetry with space group $I4/mmm$. The CDW phase has an incommensurately modulated crystal structure described by the modulation wave vector $\mathbf{q}\approx 0.17{\mathbf{c}}^{*}$. On the basis of various experiments, including elastic and inelastic x-ray scattering, and second-harmonic generation, it has been proposed that the symmetry of the CDW phase of ${\mathrm{EuAl}}_4$ could be centrosymmetric orthorhombic, noncentrosymmetric orthorhombic or noncentrosymmetric tetragonal. Here, we report temperature-dependent, single-crystal x-ray diffraction experiments that show that the CDW is a transverse CDW with phason disorder, and with noncentrosymmetric symmetry according to the orthorhombic superspace group $F222\left(00\sigma \right)00s$. Essential for this finding is the availability of a sufficient number of second-order ($2\mathbf{q}$) satellite reflections in the x-ray diffraction data set. The broken inversion symmetry implies that skyrmions might form due to Dzyaloshinskii-Moriya (DM) interactions, instead of a more exotic mechanism as it is required for centrosymmetric structures.

We consider the quantum-state-diffusion dynamics of the XXZ-staggered spin chain, also focusing on its noninteracting XX-staggered limit, and of the Sachdev-Ye-Kitaev (SYK) model. We describe the process through quantum trajectories and evaluate the nonstabilizerness (also known as “magic”) along the trajectories, quantified by the stabilizer Rényi entropy (SRE). In the absence of measurements, we find that the SYK model is the only one in which the time-averaged SRE saturates the random state bound and has a scaling with the system size that is well described by the theoretical prediction for quantum chaotic systems. In the presence of measurements, we numerically find that the steady-state SRE versus the coupling strength to the environment is well fitted by a generalized Lorentzian function. The scaling of the fitting parameters with the system size suggests that the steady-state SRE linearly increases with the system size in all the considered cases and displays no measurement-induced quantum transition, as confirmed by the curves of the steady-state SRE versus the system size.

The unique spatial arrangement of Li atoms in Li-rich compounds induces properties on Li-rich compounds, including interstitial quasiatoms, superconductivity, and superionic states. However, the dependence of increasing Li concentration on electron-phonon coupling (EPC) and superionic behavior at high pressure remains inadequately understood. Here, we systematically investigate the crystal structure of the $\mathrm{L}{\mathrm{i}}_x\mathrm{Sn}$ ($x$ = 1–8) compound at 0–150 GPa using structure prediction and first-principles calculations. Band calculations reveal that the $P6/mmm$ phases of $\mathrm{L}{\mathrm{i}}_x\mathrm{Sn}$ ($x$ = 1–7) commonly exhibits Dirac points, van Hove singularities, and flat bands. Superconducting critical temperatures ($T_{\mathrm{c}}$) were also investigated, with LiSn exhibiting a $T_{\mathrm{c}}$ of 9.3 K at 0 GPa. We further analyzed the relationship between superconductivity and EPC strength, phonon softening, linewidth, and density of states. Deep learning molecular dynamics simulations of LiSn, ${\mathrm{Li}}_2\mathrm{Sn}, {\mathrm{Li}}_3\mathrm{Sn}$, and ${\mathrm{Li}}_4\mathrm{Sn}$ demonstrate that when the Li concentration exceeds twice that of Sn, Li atoms undergo melting while Sn remains solid, indicating the emergence of a superionic state. Among them, ${\mathrm{Li}}_3\mathrm{Sn}$ exhibits the highest melting temperature of 1013 K. These findings enrich the crystal structure of Li-Sn compounds and provide a theoretical basis for constructing superconductors with a Kagome lattice and superionic states.

Over the past two decades, the overlap matrix approach has been developed to compute quantum entanglement in free-fermion systems, particularly to calculate entanglement entropy and entanglement negativity. This method involves the use of partial trace and partial transpose operations within the overlap matrix framework. However, in previous studies, only the conventional partial transpose in fermionic systems has been considered, which does not account for fermionic anticommutation relations. Although the concept of a fermionic partial transpose was introduced by Shapourian et al. [Phys. Rev. B 95, 165101 (2017)], it has not yet been systematically incorporated into the overlap matrix framework. In this paper, we introduce the fermionic partial transpose into the overlap matrix approach, provide a systematic analysis of the validity of partial trace and partial transpose operations, and derive an explicit formula for calculating entanglement negativity in bipartite systems. Additionally, we numerically compute the logarithmic negativity of two lattice models to verify the Gioev-Klich-Widom scaling law. For tripartite geometries, we uncover limitations of the overlap matrix method and demonstrate that the previously reported logarithmic negativity result for a homogeneous one-dimensional chain in a disjoint interval geometry exceeds its theoretical upper bound.