We report on the existence of cluster spin-glass behavior and magnetocaloric properties of potassium-ion-intercalated copper hexacyanoferrate open framework material ${\mathrm{K}}_{2x/3}\mathrm{Cu}{\left[\mathrm{Fe}{\left(\mathrm{CN}\right)}_6\right]}_{2/3}·n{\mathrm{H}}_2\mathrm{O}(x=0$ and 0.3) synthesized using a coprecipitate method. The structural properties are investigated using room-temperature powder x-ray and neutron diffraction measurements. The results derived from the fitted x-ray and neutron diffraction data using the Rietveld refinement method reveal that both compounds are in pure single-nanocrystalline phase with face-centered cubic crystal structure of space group $Fm\text{−}3m$. The room-temperature Mössbauer spectroscopy reveals the presence of a low-spin (LS) state of ${\mathrm{Fe}}^{\mathrm{III}}$ for compound $x=0$, whereas for compound $x=0.3$, LS states of ${\mathrm{Fe}}^{\mathrm{II}}$ and ${\mathrm{Fe}}^{\mathrm{III}}$ are evident. The chemical and Mössbauer studies reveal stoichiometries of compounds as ${\mathrm{Cu}}^{\mathrm{II}}{\left[{\mathrm{Fe}}^{\mathrm{III}}{\left(\mathrm{CN}\right)}_6\right]}_{2/3}·3.75{\mathrm{H}}_2\mathrm{O}\left(x=0\right)$ compound (1) and ${\mathrm{K}}_{0.2}{\mathrm{Cu}}^{\mathrm{II}}{\left[{\mathrm{Fe}}_{0.3}^{\mathrm{II}}{\mathrm{Fe}}_{0.7}^{\mathrm{III}}{\left(\mathrm{CN}\right)}_6\right]}_{2/3}·{\mathrm{H}}_2\mathrm{O}\left(x=0.3\right)$. The dc magnetization measurement shows a magnetic phase transition from a paramagnetic to a ferromagneticlike state below the magnetic ordering temperatures of $\sim 18.6$ and $\sim 16.3$ K for the compounds (1) and (2), respectively. The positive value of Curie constants obtained from the fitting of the Curie-Weiss law in the paramagnetic region confirms the presence of ferromagnetic interaction in both compounds. The spin-only effective paramagnetic moments are found to be $\sim 2.3$ and $\sim 1.9{\mu }_{\mathrm{B}}/\mathrm{f}.\mathrm{u}.$ for compounds (1), and (2), respectively. The analysis of ac susceptibility measurements as a function of frequency shows that the spin dynamics follows the Vogel-Fulcher and the power law. The best fitted values of ${\tau }_o=4.037\times {10}^{-7}$ s and $3.5\times {10}^{-6}$ s for compounds (1) and (2), respectively, confirm a cluster spin-glass behavior of both compounds. A neutron depolarization study further validates the cluster spin-glass nature of both compounds. The magnetocaloric effect for both the compounds is further investigated and found to be higher for compound (1) than compound (2). The maximum magnetic entropy change—$\mathrm{\Delta }{S}_M$ under a magnetic field of 50 kOe is found to be $\sim 6.61$ and $2.95\mathrm{J}\mathrm{k}{\mathrm{g}}^{-1}{\mathrm{K}}^{-1}$ for compounds (1) and (2), respectively. The relative cooling power is found to be $78.3\mathrm{J}\mathrm{k}{\mathrm{g}}^{-1}$ for compound (1) and $40\mathrm{J}\mathrm{k}{\mathrm{g}}^{-1}$ for compound (2).

We argue that classical pyrochlore Heisenberg antiferromagnets with small further-neighbor couplings can order in a state where pairs of sublattices form antiparallel spirals. The spiral ordering wave vectors of the two pairs are in general different from each other and are constrained by which sublattices are being paired. This sublattice pairing state generally breaks inversion and most rotation symmetries. Its existence depends on the antiferromagnetic nearest-neighbor coupling which favors the spins on each tetrahedron to sum to zero. To substantiate our argument, we extend the nematic bond theory, a diagrammatic large-$N_s$ method, to non-Bravais lattices, and we demonstrate that the predicted state is indeed realized at low temperatures in a large region of exchange coupling space. We also carry out a spin wave calculation which suggests that the sublattice pairing state is coplanar.

We study the ordered phases of the $S=1/2$ fcc Heisenberg antiferromagnet, with first- and second-neighbor interactions, using perturbative series expansions at zero temperature. From calculations of ground-state energies we determine the regions of stability of semiclassical AF1, AF2, and AF3 phases. For the pure nearest-neighbor case our results suggest that AF1 is favored over AF3, a result in disagreement with linear spin-wave theory, but in agreement with other more recent work. We also investigate the two possible AF2 phases and locate the crossover between AF3 and AF2 at $J_2/J_1\sim 0.535$.

The stress relaxation dynamics of a ${\mathrm{La}}_{60}{\mathrm{Ni}}_{15}{\mathrm{Al}}_{25}$ metallic glass were studied in ribbon and bulk samples. In both tensile and single cantilever testing modes, it is observed that the stress decay of deep glass is mediated by the β relaxation, which contributes about 5% to the total stress. The characteristic time of stress relaxation near the glass transition coincides with that of the α relaxation, indicating that the two-step stress decay may correspond directly to the two dynamic relaxations. A possible atomic mechanism involving both relaxation and deformation is proposed based on the evolution of shear transition zone, which enables reconstruction of the two-step deformation theoretically. The present experimental and theoretical protocol further provides a strategy to detect the β relaxation associated phenomena at room temperature and even lower, circumventing interference from physical aging or the α relaxation. These findings clarify the elusive roles of relaxation modes in the nonelastic deformation of amorphous matters and reveal the interrelationships between them.

The nanocrystalline ${\mathrm{La}}_{0.67-x}{\mathrm{Bi}}_x{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3$ ($x$ = 0.0, 0.1) samples were synthesized using a citrate complex method. The synthesized samples crystallizes in single phase and orthorhombic crystal structure with Pbnm space group. The nanocrystalline ${\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3$ (LCMO) exhibits significant second-order paramagnetic (PM) to ferromagnetic (FM) phase transition, whereas weak second-order phase transition (SOPT) was observed for ${\mathrm{La}}_{0.57}{\mathrm{Bi}}_{0.1}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3$ (LBCMO). Magnetic entropy and Landau analysis have been used for the confirmation of order of transition in the vicinity of transition temperature ($T_c$). The Griffiths phase (GP), which was determined by the temperature-dependent inverse susceptibility (${\chi }^{-1}$) data, demonstrated a strong influence on La-site chemical substitution. Dimeron model is used to explain GP behavior for the samples. Temperature-dependent resistivity [$\rho$($T$)] also suggests the existence of dimeron formation above metal-insulator transition temperature ($T>T_{MI}$). A an unusual magnetic state also have been observed within the nonlinear region of Arrott plots for $T>T_c$. Using information on the intrinsic magnetic field, the critical behavior of the LBCMO sample was examined close to its Curie temperature. The critical exponents $\beta , \gamma$, and $\delta$ are 0.3108, 1.02, and 4.2, respectively. The observed critical behavior is not following any universality class.

Using resonant inelastic x-ray scattering, we measure the paramagnon dispersion and damping of undoped, antiferromagnetic ${\mathrm{Ca}}_2{\mathrm{CuO}}_2{\mathrm{Cl}}_2$ as well as doped, superconducting ${\mathrm{Na}}_x{\mathrm{Ca}}_{2\text{−}x}{\mathrm{CuO}}_2{\mathrm{Cl}}_2$. Our estimation of the spin-exchange parameter and width of the paramagnon peak at the zone boundary $X=(0.5,0)$ confirms that no simple relation can be drawn between these parameters and the critical temperature $T_{\mathrm{c}}$. Consistently with other cuprate compounds, we show that upon doping there is a slight softening at (0.25,0) but not at the zone boundary $X$. In combination with these measurements we perform calculations of the dynamical spin structure factor of the one-band Hubbard model using cluster dynamical mean-field theory. The calculations are in excellent agreement with the experiment in the undoped case, both in terms of energy position and width. While the increase in width is also captured upon doping, the dynamical spin structure factor shows a sizable softening at $X$, which provides insightful information on the length-scale of the spin fluctuations in doped cuprates.

We report the systematic investigation of the magnetoresistance and Hall resistivity of the kagome superconductor ${\mathrm{RbV}}_3{\mathrm{Sb}}_5$ single crystals. The crystals show pronounced quantum oscillations with multifrequency. Analysis of oscillations reveals the existence of three bands that have two-dimensional character and host light effective quasiparticle mass and nontrivial Berry phase. In addition, we observed a giant anomalous Hall conductivity (AHC) that reaches up to $3.3\times {10}^3{\mathrm{\Omega }}^{-1}\mathrm{c}{\mathrm{m}}^{-1}$ in ${\mathrm{RbV}}_3{\mathrm{Sb}}_5$. The temperature dependence of AHC reveals an origin that correlated with the charge-density wave order. The anomalous Hall ratio $\left(\sim 1\%\right)$ shows weak temperature dependence below 30 K. These results will shed information on the nature of correlated topological physics in kagome material ${\mathrm{RbV}}_3{\mathrm{Sb}}_5$.

We study the effects of tunneling between a Weyl semimetal (WSM) and a simple parabolic band. When coupled to the nonmagnetic parabolic band, the interface between the two exhibits two main phenomena. First, the WSM's chiral arc state lowers in energy, and second, a previously extended WSM state becomes localized to the interface and is lowered in energy. Together these surface bound states create a new closed orbit in momentum space, and a noticeable spin-dependent asymmetry in the interface spectrum in the vicinity of the Weyl nodes appears. We study these effects with a lattice model that we solve numerically on a finite sample and analytically using an Ansatz on an infinite sample. Our Ansatz agrees very well with the numerical simulation as it accurately describes the behavior of the chiral state, from its energy asymmetry to the spin rotation at the interface. We find that the tunneling effectively increases the Fermi arc length, allowing for the presence of interface states beyond the bare Weyl nodes. These additional states may carry current along the interface, and their contribution can be detected in the conductance. In addition to conductivity, the effect of tunneling between the WSM and the metal can be seen in quantum oscillation experiments, which we briefly address.

We introduce a homogenization approach to characterize the dynamical response of a generic dispersive space-time crystal in the long-wavelength limit. The theory is applied to dispersive space-time platforms with a traveling-wave modulation. It is shown that for long wavelengths the effective response may be described by a frequency-dependent permittivity. Due to the active nature of space-time systems, the permittivity is not bound by the same constraints as in standard time-invariant metamaterials. In particular, we find that dispersive space-time crystals can exhibit rather peculiar physics, such as an anomalous (“non-Foster”) permittivity dispersion with a negative stored energy density, alternate between gain and loss regimes, and present multiple resonances in the quasistatic regime. Furthermore, it is verified with numerical simulations that the effective theory captures faithfully the exact dispersion of the first few photonic bands.

Through in situ photoemission spectroscopy (PES), we investigated the changes in the electronic structure of Cr-doped $\mathrm{V}{\mathrm{O}}_2$ films coherently grown on $\mathrm{Ti}{\mathrm{O}}_2$ (001) substrates. The electronic phase diagram of ${\mathrm{Cr}}_x{\mathrm{V}}_{1-x}{\mathrm{O}}_2$ is drawn by a combination of electric and spectroscopic measurements. The phase diagram is similar to that of bulk ${\mathrm{Cr}}_x{\mathrm{V}}_{1-x}{\mathrm{O}}_2$, while the temperature of metal-insulator transition $\left(T_{\mathrm{MIT}}\right)$ is significantly suppressed by the epitaxial strain effect. In the range $x=0-0.04$, where $T_{\mathrm{MIT}}$ remains unchanged as a function of $x$, the PES spectra show a dramatic change across $T_{\mathrm{MIT}}$, demonstrating the characteristic spectral changes associated with the Peierls phenomenon. In contrast, for $x>0.04$, the $T_{\mathrm{MIT}}$ linearly increases, and the metal-insulator transition (MIT) may disappear at $x=0.08-0.12$. The PES spectra at $x=0.08$ exhibit pseudogap behavior near the Fermi level, whereas the characteristic temperature-induced change remains almost intact, suggesting the existence of local V-V dimerization. The suppression of V-V dimerization with increasing $x$ was confirmed by polarization-dependent x-ray absorption spectroscopy. These spectroscopic investigations reveal that the energy gap and V $3d$ states are essentially unchanged with $0\le x\le 0.08$ despite the suppression of V-V dimerization. The invariance of the energy gap with respect to $x$ suggests that the MIT in ${\mathrm{Cr}}_x{\mathrm{V}}_{1-x}{\mathrm{O}}_2$ arises primarily from the strong electron correlations, namely, the Peierls-assisted Mott transition. Meanwhile, the pseudogap at $x=0.08$ eventually evolves to a full gap (Mott gap) at $x=0.12$, which is consistent with the disappearance of the temperature-dependent MIT in the electronic phase diagram. These results demonstrate that a Mott insulating phase without V-V dimerization is stabilized at $x>0.08$ as a result of the superiority of Mott instability over the Peierls one.

In a recent experiment [Trishin et al., Phys. Rev. Lett. 127, 236801 (2021)], rich physics was observed for Fe atoms on ${\mathrm{MoS}}_2\text{/}\mathrm{Au}\text{(}111\text{)}$, characterized by three different behaviors depending on the spectral density of the substrate ${\rho }_c$: one dominated by single-ion anisotropy, one by the Kondo effect, and an intermediate one. Based on symmetry and previous works, we show that the appropriate model to describe the system is the anisotropic two-channel spin-1 Kondo model, which has an underlying topological quantum phase transition (TQPT) between an ordinary Fermi liquid (FL) and a topological one with a nontrivial value of the Luttinger integral. Solving the model with the numerical renormalization group, we show that the different behaviors can be explained in a unified fashion as a function of ${\rho }_c$ and correspond to both FLs and an intermediate regime close to the TQPT in the topological phase. Further experiments should confirm this transition.

We introduce superlattices made of ferroelectric halide perovskites as a class of functional materials possessing large Rashba effect and phase transition from normal insulator (NI) to topological insulator (TI) induced by an electric field. Using first-principles methods, in $\mathrm{CsPb}{\mathrm{I}}_3/\mathrm{CsSi}{\mathrm{I}}_3$ and $\mathrm{CsSn}{\mathrm{I}}_3/\mathrm{CsSi}{\mathrm{I}}_3$ superlattices, we found a nonmonotonic Rashba parameter with respect to the magnitude of polarization and large maximal Rashba effect at a critical polarization, where the phase transition from NI to TI occurs when changing the polarization. This phase transition and the large maximal Rashba effect are related to band-gap engineering under an electric field. In contrast to traditional nonpolar TIs, in these ferroelectric TIs, the energy level of the Dirac point and the spin texture of surface states are largely tunable by changing polarization or strain. Our results thus highlight the interplay among ferroelectricity, Rashba effect, and topological order in a single material, which is promising toward electronic and spintronic applications.

We present a low-scaling diagrammatic Monte Carlo approach to molecular correlation energies. Using combinatorial graph theory to encode many-body Hugenholtz diagrams, we sample the Møller-Plesset ($\mathrm{MP}n$) perturbation series, obtaining accurate correlation energies up to $n=5$, with quadratic scaling in the number of basis functions. Our technique reduces the computational complexity of the molecular many-fermion correlation problem, opening up the possibility of low-scaling, accurate stochastic computations for a wide class of many-body systems described by Hugenholtz diagrams.

The symmetry of a domain wall in ferroelastic ${\mathrm{WO}}_3$ is analyzed by angle-resolved polarized Raman spectroscopy. We find that a low-energy Raman mode at $46\mathrm{c}{\mathrm{m}}^{-1}$ is largely enhanced within the confined region of the domain wall, whose width is presumed to be $\sim 25\mathrm{nm}$ from diffusive x-ray scattering. The wall effect on the enhancement of the Raman signal per unit area is estimated to be three times larger than the contribution of the domains. The light-polarization-dependent Raman intensity at the wall is characterized by the symmetric $A_{1g}$ Raman tensor that is attributed to the prototypic quasitetragonal phase imposed by the ferroelastic compatibility relationship.

Owing to the same symmetry and very close lattice constants, diamond and cubic boron nitride (cBN) possess very similar physical properties, such as being superhard and brittle at ambient conditions. Here, the generalized stacking fault energy (GSFE) of different slip systems for diamond and cBN were calculated from first principles. The results show the perfect dislocation in diamond on the {100} plane dominates, while it is the {111} plane for cBN. This distinct difference originated from the saddle-shaped GSFE curve in diamond compared to the Gaussian line shape in cBN. Interestingly, the {111} slip plane of cBN remains unchanged under normal compression, while in diamond there is a transition from a {100} to {111} slip plane at a critical normal stress. This study provides an atomistic understanding of the experimental findings of room-temperature plasticity in diamond.

Understanding and predicting the anharmonic lattice dynamics of complex strongly anharmonic crystals has long been a significant challenge in condensed matter physics and materials physics. Here, we study the underlying physical principles of the ultralow glasslike ${\kappa }_{\mathrm{L}}$ in tetragonal $\alpha \text{−}{\mathrm{CsCu}}_5{\mathrm{Se}}_3$ by combining self-consistent phonon theory and the unified thermal transport theory of crystal and glass in the framework of the Peierls-Boltzmann transport equation and first-principles anharmonic lattice dynamics. We consider the impacts of both phonon broadening by three-phonon (3ph) interaction and phonon frequency anharmonic renormalization by quartic anharmonicity on the contributions from the particlelike phonon wave packet and wavelike phonon channel transport. The strong anharmonic renormalization leads to continuous temperature-induced hardening of the acoustic modes and low-lying optical modes, which is mainly associated with the tetrahedrally coordinated rattlinglike vibrations of the Cu3 atoms. This hardening effect reduces the phonon linewidths in the low-energy area via decreasing the available 3ph scattering phase space, thus partially counteracting the decreased impact on ${\kappa }_{\mathrm{L}}$ by increasing the phonon population and yielding a weak temperature-dependent ${\kappa }_{\mathrm{L}}$. Furthermore, the strong phonon broadening results in the coherent thermal transport channel that stems from the coherent coupling between different vibration eigenstates. Upon heating, the off-diagonal terms in the heat-flux operator become quite significant and dominate the phonon thermal transport process, suggesting the qualitative breakdown of the traditional phonon gas model in complex disordered crystals. In this paper, we provide the physical microscopic mechanisms of the glasslike ${\kappa }_{\mathrm{L}}$ in complex host-guest systems and highlight the influence of the lattice anharmonicity on thermal conductivity.

We predict unidirectional magnetoresistance effects arising in a bilayer composed of a nonmagnetic metal and a ferromagnetic insulator, whereby both longitudinal and transverse resistances vary when the direction of the applied electric field is reversed or the magnetization of the ferromagnetic layer is rotated. In the presence of spin-orbit coupling, an electron wave incident on the interface of the bilayer undergoes a spin rotation and a momentum-dependent phase shift. Quantum interference between the incident and reflected waves furnishes the electron with an additional velocity that is even in the in-plane component of the electron's wave vector, giving rise to quadratic magnetotransport that is rooted in the wave nature of electrons. The corresponding unidirectional magnetoresistances exhibit decay lengths at the scale of the Fermi wavelength—distinctive signatures of the quantum nonlinear magnetotransport effect.

Elastically strained ferromagnetic objects have been studied by coupled micromagnetic-mechanical numerical simulations. Both temporal evolution of the magnetization and modal frequency analysis of ferromagnetic thin films and arrays of nanostructures are presented. For this purpose, we have numerically coupled the micromagnetic equations (including magnetoelastic effects) to the ones of solid mechanics by including periodic boundary conditions. Our approach has been evaluated first on an elastically strained thin film and validated by performing in situ ferromagnetic resonance experiments. We have undertaken simulations on nanostructured arrays (modulated arrays of nanowires) and show that the heterogeneity of the strain fields and magnetic mode profiles of those strained nanostructures induce significative disparities in the magnetic mode energies, allowing applications to be foreseen where one could control in a differentiated way the spin-wave energies as a function of the applied elastic strains.

Confinement is a ubiquitous phenomenon in which constituent particles are bound together into a new quasiparticle. In condensed matter physics, magnon bound states can be regarded as a confinement of magnons, and an oscillating deconfinement crossover of two-magnon bound states scattered by a two-magnon continuum was revealed in the one-dimensional (1D) ferromagnetic chain by the spin entanglement entropy (SEE) analysis. Now, we extend the study to the two-dimensional (2D) and three-dimensional (3D) cases. Although the interactions between magnons in high dimensions are not as effective as in one dimension, two-magnon bound states can still survive around the corners of the Brillouin zone (BZ). In 2D or 3D square lattices, the bound states reduce their dimensionality to be 1D bound states at the BZ edges, which are bound only along the direction parallel to the BZ edge. This is verified by examining the relation between the magnon separation $d$ and the intercept $D$ of the SEE, which is found to satisfy the 1D relation $D=lnd+1$, but in 2D and 3D lattices. Meanwhile, the 2D bound states satisfy $D=2lnd+1.3$ in both 2D and 3D lattices. Unlike those in the 1D chain, some bound states will enter the continuum directly rather than cling to its bottom. We find that these immersed bound states are neither preserved nor deconfined completely when just meeting the continuum in finite-size systems, which is similar to what occurs in the 1D chain. Their SEE and magnon separation oscillate with respect to the system size. Therefore, these bound states undergo the oscillating deconfinement crossover in the continuum.

We study the Andreev reflections and the quantum transport in the proximitized graphene/superconductor junction. The proximitized graphene possesses the pseudospin staggered potential and the intrinsic spin-orbit coupling induced by substrate, which are responsible for the spin-valley dependent double Andreev reflections and the anomalous transport properties in the junction. The pure specular Andreev reflection can happen in the superconducting gap for the $K\uparrow$ and $K^{\prime }\downarrow$ electrons, while the pure retro-Andreev reflection happens for the $K\downarrow$ and $K^{\prime }\uparrow$ electrons. The coexisting two types of Andreev reflections related to the fixed spin-valley indices strongly depend on the chemical potential of the proximitized graphene. The condition of the emergence of the specific type of Andreev reflection for the electrons with the fixed spin-valley index is clarified. The spin-valley dependent Andreev reflections bring about the peculiar conductance spectra of the junction, which can help determine the values of the pseudospin staggered potential and the intrinsic spin-orbit coupling induced in graphene. Hence our research results not only provide an experimental method to detect the induced potential and coupling in graphene but also establish the foundation of the superconductor electronics based on the spin-valley indices.