The variational and diffusion quantum Monte Carlo methods are used to calculate the correlation energy of the paramagnetic three-dimensional homogeneous electron gas at intermediate to high density. Ground-state energies in finite cells are determined using Slater-Jastrow-backflow trial wave functions, and finite-size errors are removed using twist-averaged boundary conditions and extrapolation of the energy per particle to the thermodynamic limit of infinite system size. Our correlation energies in the thermodynamic limit are more accurate than previous results. The present diffusion quantum Monte Carlo energies together with our recently reported [Phys. Rev. B 105, 245135 (2022)] results at low density, are used to parametrize the correlation energy of the electron gas using a functional form that satisfies the exact asymptotic behavior at high density.

Zero thermal expansion (ZTE) is one of the most fascinating phenomena in condensed-matter physics due to its strong correlation essence and great application prospect. However, the origin of ZTE remains elusive and it becomes an overwhelming challenge to realize the controllable design for which magnetic interaction plays a key role. In this work, with the help of neutron powder diffraction analysis, a noncoplanar $\left[\frac{1}{2},\frac{1}{2},\frac{1}{2}\right]$ antiferromagnetic (AFM) phase is experimentally obtained in the antiperovskite system ${\mathrm{Mn}}_3{\mathrm{Sn}}_{0.5}{\mathrm{Zn}}_{0.5}{\mathrm{C}}_x$. It shows ZTE behavior in a particularly wide temperature range from 10 to 162 K with linear thermal expansion coefficient 9.3 × ${10}^{-7}{\mathrm{K}}^{-1}$. Herein, the theoretical spin model is combined with the experimental results to well understand the strong spin-lattice correlation between AFM ordering and ZTE behavior. The ZTE in the noncoplanar antiferromagnetic ordered system is attributed to the fierce competition between the nearest AFM direct exchange and ferromagnetic superexchange interaction, which is effectively tuned by C occupation. Our work not only paves the way toward understanding the physical origin of ZTE, but it also provides a feasible strategy for the ZTE design, which is also of great significance for promoting the study of a strong correlation system.

While the dominant magnetic interaction in ${\mathrm{La}}_2{\mathrm{CuO}}_4$ is superexchange between nearest-neighbor Cu moments, the pinning of the spin direction depends on weak anisotropic effects associated with spin-orbit coupling. The symmetry of the octahedral tilt pattern allows an out-of-plane canting of the Cu spins, which is compensated by an opposite canting in nearest-neighbor layers. A strong magnetic field applied perpendicular to the planes can alter the spin canting pattern to induce a weak ferromagnetic phase. In light of recent evidence that the lattice symmetry is lower than originally assumed, we take another look at the nature of the field-induced spin-rotation transition. Comparing low-temperature neutron diffraction intensities for several magnetic Bragg peaks measured in fields of 0 and 14 T, we find that a better fit is provided by a model in which spins rotate within both neighboring planes but by different amounts, resulting in a noncollinear configuration. This model allows a more consistent relationship between lattice symmetry and spin orientation at all Cu sites.

We probe the magnetic order in single crystals of $\mathrm{Tb}{\mathrm{Rh}}_6{\mathrm{Ge}}_4$ using electrical transport, magnetization, and thermodynamic measurements. $\mathrm{Tb}{\mathrm{Rh}}_6{\mathrm{Ge}}_4$ crystallizes in the noncentrosymmetric tetragonal $\mathrm{Li}{\mathrm{Co}}_6{\mathrm{P}}_4$-type structure, where the Tb ions form a triangular lattice in the basal plane and chains along the $c$ axis. This compound undergoes a second-order antiferromagnetic transition at $T_N=12.7$ K, which is followed by an additional transition at $T_M=2.8$ K. When fields are applied along the easy $c$ axis, multiple metamagnetic transitions are observed, where there are plateaus at 1/9 and 1/3 of the saturation magnetization. We map the field-temperature phase diagram revealing complex magnetism, where antiferromagnetic coupling within the basal plane may lead to significant magnetic frustration.

We study the coupled-top model with three large spins located on a triangle. Depending on the coupling strength, there exist three phases: disordered paramagnetic phase, ferromagnetic phase, and frustrated antiferromagnetic phase, which can be distinguished by the mean-field approach. The paramagnetic-ferromagnetic phase transition is accompanied by the breaking of the global $Z_2$ symmetry, whereas the paramagnetic-antiferromagnetic phase transition is accompanied by the breaking of both the global $Z_2$ symmetry and the translational symmetry. Exact analytical results of higher-order quantum effects beyond the mean-field contribution, such as the excitation energy, quantum fluctuation, and von Neumann entropy, can be achieved by the Holstein-Primakoff transformation and symplectic transformation in the thermodynamic limit. Near the quantum critical point, the energy gap closes, along with the divergence of the quantum fluctuation in certain quadrature and von Neumann entropy. Particular attention should be paid to the antiferromagnetic phase, where geometric frustration takes effect. The critical behaviors in the antiferromagnetic phase are quite different from those in the paramagnetic and ferromagnetic phases, which highlight the importance of geometric frustration. The triangular coupled-top model provides a simple and feasible platform to study the quantum phase transition and the novel critical behaviors induced by geometric frustration.

We have studied electric and thermal transport properties in two-dimensional van der Waals ferromagnetic ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$. The low-temperature longitudinal resistivity measured in the $ab$ plane is contributed by the impurity scattering, the quantum correction, and the electron-electron interaction. Meanwhile, the low-temperature specific heat consists of linear and cubic temperature terms, corresponding to contributions of electrons and phonons, respectively. Therefore, the heavy-fermion state in ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ can be described by Landau's Fermi liquid theory. The Kadowaki-Woods ratio in ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ is five times larger and smaller than the values of transition metals and heavy-fermion compounds, respectively. Moreover, the thermal conductivity measured along the $c$ axis increases monotonically with temperature, exhibiting a phonon glass electron crystal behavior, due to the dominant role of boundary scattering of phonons. The $T^{1.35}$ dependence of the lattice thermal conductivity observed at low temperatures arises from a combined effect of the highly anisotropic dispersion and strong impurity scattering of phonons.

The gradual ferromagnetic spin reorientation in hexagonal close packed cobalt (hcp-Co) phase between $230{}^{\circ }\mathrm{C}$ and $330{}^{\circ }\mathrm{C}$ reported for a Co single crystal [Bertaut et al., Solid State Commun. 1, 81 (1963)] suggests that this phase could not have a hexagonal symmetry. This hypothesis is verified positively by synchrotron radiation diffraction and neutron diffraction on polycrystalline powder cobalt. The analysis of diffraction data has been done by using a specific set of Bragg peaks, which are not sensitive to the stacking faults present in abundance in hcp-Co. The crystal structure of the hcp-type ordered areas of cobalt is described by the monoclinic symmetry with the magnetic space group $C{2}^{\prime }/m^{\prime }$. In this monoclinic crystal structure the former hexagonal [001] axis is no longer perpendicular to the hexagonal layers. The hexagonal [001] and [010] axes make an angle equal $\alpha \approx$ 90.10(1)${}^{\circ }$, while the angle between in-plane [100] and [010] axes equals $\gamma \approx$ 120.11(1)${}^{\circ }$. The monoclinic symmetry provides an approximate description of the crystal structure of the stacking faulted hcp-Co areas coexisting with fcc-Co areas.

Iron $\alpha \leftrightarrow \epsilon , \alpha \to \gamma$, and $\gamma \to \epsilon$ transformations have been characterized in diamond anvil cells under hydrostatic compression conditions. In situ x-ray diffraction of single or oligocrystals and ex situ SEM-EBSD measurements have been analyzed with multigrain techniques. The mechanisms of $\alpha \leftrightarrow \epsilon$ transitions are martensitic, following Burgers paths which requires a high plastic activity. A memory effect of the reversion exists in the vast majority of the sample: the starting orientation of $\alpha \text{−}\mathrm{Fe}$ single crystal is recovered. Small grains of $\alpha \text{−}\mathrm{Fe}$ exhibit a new orientation compatible with Burgers path, possibly associated with twinning in $\epsilon \text{−}\mathrm{Fe}$. Close to the $\alpha \text{−}\gamma \text{−}\epsilon \text{−}\mathrm{Fe}$ triple point (8.7 GPa, 750 K), the $\alpha \to \gamma$ transformation occurs via diffusion and reconstruction of $\gamma \text{−}\mathrm{Fe}$, and $\gamma \to \epsilon$ transformation is martensitic but involves no plasticity. As a result, the microstructures in $\epsilon \text{−}\mathrm{Fe}$ produced by a direct $\alpha \to \epsilon$ transformation and by $\alpha \to \gamma \to \epsilon$ transitions path are very different.

We present the results of muon spin relaxation ($\mu \mathrm{SR}$), neutron powder diffration (NPD), and inelastic neutron scattering (INS) investigations on polycrystalline ${\mathrm{Pr}}_2{\mathrm{Pd}}_3{\mathrm{Ge}}_5$. The polycrystalline ${\mathrm{Pr}}_2{\mathrm{Pd}}_3{\mathrm{Ge}}_5$ is known to exhibit two antiferromagnetic transitions near $T_{\mathrm{N}1}=8.3$ K and $T_{\mathrm{N}2}=7.5$ K which is confirmed by the heat capacity measurements on the present sample. In the magnetically ordered state the NPD data show clear evidence for magnetic Bragg peaks, which for $T<T_{\mathrm{N}2}$ could be indexed with a propagation vector k = (1, 0, 0), and with k = (1, 0, 0.07) for $T_{\mathrm{N}2}<T<T_{\mathrm{N}1}$. We have determined the magnetic structure and found a canted antiferromagnetic structure of ordered ${\mathrm{Pr}}^{3+}$ moments. At 7.6 K we find an amplitude modulated incommensurate antiferromagnetic arrangement of ordered moments with a maximum ordered moment of 1.64(3) ${\mu }_{\mathrm{B}}$/Pr lying in the $ab$ plane tilted at about ${26}^{\circ }$ from the $b$ axis. At 1.8 K the antiferromagnetic structure is found to be commensurate with an ordered moment of 2.80(6) ${\mu }_{\mathrm{B}}$/Pr lying in the $ab$ plane tilted at about ${28}^{\circ }$ from the $b$ axis. Our zero-field $\mu \mathrm{SR}$ spectra at 1.5 K and at shorter time scale (below 0.5 $\mu \mathrm{s}$) reveal two oscillatory frequencies further supporting a long-range-ordered magnetic ground state. We have calculated the muon sites using the density functional theory calculation and present the results of internal field calculations at the muon stopping sites, which are in good agreement with the experimental observations. In the paramagnetic state, the INS data show three well defined CEF excitations near 8.0, 12.3, and 18.1 meV arising from the crystal electric field (CEF) split $J=4$ ground state of ${\mathrm{Pr}}^{3+}$. The CEF level scheme is deduced by analyzing the INS data by a model based on the CEF model.

In type-II superconductors exposed to magnetic fields between upper and lower critical values, $H_{c1}$ and $H_{c2}$, penetrating magnetic flux forms a lattice of vortices whose motion can induce dissipation. Consequently, the magnetization $M$ of superconductors is typically progressively weakened with increasing magnetic field $B\propto n_v$ (for vortex density $n_v$). However, some materials exhibit a nonmonotonic $M\left(B\right)$, presenting a maximum in $M$ at what is known as the second magnetization peak. This phenomenon appears in most classes of superconductors, including low-$T_c$ materials, iron-based, and cuprates, complicating pinpointing its origin and garnering intense interest. Here we report on vortex dynamics in optimally doped and overdoped ${\mathrm{HgBa}}_2{\mathrm{CuO}}_{4+x}$ crystals, with a focus on a regime in which plastic deformations of the vortex lattice govern magnetic properties. Specifically, we find that both crystals exhibit conspicuous second magnetization peaks and, from measurements of the field- and temperature-dependent vortex creep rates, identify and characterize phase boundaries between elastic and plastic vortex dynamics, as well as multiple previously unreported transitions within the plastic flow regime. We find that the second magnetization peak coincides with the elastic-to-plastic crossover for a very small range of high fields and a sharp crossover within the plastic flow regime for a wider range of lower fields. Moreover, we find evidence that this transition in the plastic flow regime is due to a dimensional crossover, specifically, a transition from three to two-dimensional plastic dynamics.

Tantalum diselenide ($\mathrm{Ta}{\mathrm{Se}}_2$) has emerged as a promising platform to investigate the interplay between two intriguing quantum electronic states in materials: the charge density wave order (CDW) and superconductivity. In this work, we report the ability to tune these quantum electronic states by intercalating Pt into $2H-\mathrm{Ta}{\mathrm{Se}}_2$. By introducing 20% of Pt into $2H-\mathrm{Ta}{\mathrm{Se}}_2$, we demonstrate that the structural phase changes from the $2H$ to the $4H_b$ phase of $\mathrm{Ta}{\mathrm{Se}}_2$ with Pt atoms intercalated within the van der Waals spacing. According to the Fermi surface of the $4H_b$ phase, a Lifshitz transition occurred, destroying the Fermi-surface nesting found in the $2H$ phase. This can be attributed to the structural phase transformation and the influence of donated electrons from Pt, thus tuning the Van Hove singularities into the Fermi-level vicinity, suppressing the CDW state, and enhancing the superconducting temperature $\left(T_c\right)$ to $\sim 2.7$ K. The resulting superconducting properties of the $4H_b-\mathrm{P}{\mathrm{t}}_{0.2}\mathrm{Ta}{\mathrm{Se}}_2$ are consistent with those of a BCS type-II superconductor, with a superconducting gap of 3.0 meV. Our results provide insights into the role of electron doping and structural phase changes in fine-tuning quantum electronic-state phenomena in materials. These findings could have significant implications in designing superconducting materials with tailored properties for practical applications.

We present a recipe for an electronic two-dimensional (2D) higher order topological insulator (HOTI) on a triangular lattice that can be realized in a large family of materials. The essential ingredient is mirror symmetry breaking, which allows for a finite quadrupole moment and trivial ${\mathbb{Z}}_2$ index. The competition between spin-orbit coupling and the symmetry-breaking terms gives rise to four topologically distinct phases; the HOTI phase appears when symmetry breaking dominates, including in the absence of spin-orbit coupling. We identify triangular monolayer adsorbate systems on the (111) surface of zincblende/diamond type substrates as ideal material platforms and predict the HOTI phase for $X=(\mathrm{Al},\mathrm{B},\mathrm{Ga})$ on SiC.

Understanding the electronic transport properties of iron under high temperatures and pressures is essential for constraining geophysical processes. The difficulty of reliably measuring these properties under conditions prevalent in the Earth's core calls for first-principles methods that can support diagnostics. We present results on the electrical conductivity obtained by simulating the microscopic Ohm's law using time-dependent density functional theory and place them in the context of recent experimental measurements.

We study many-body localization (MBL) transition in disordered Floquet systems using a polynomially filtered exact diagonalization (POLFED) algorithm. We focus on disordered kicked Ising model and quantitatively demonstrate that finite-size effects at the MBL transition are less severe than in the random field XXZ spin chains widely studied in the context of MBL. Our conclusions extend also to other disordered Floquet models, indicating smaller finite-size effects than those observed in the usually considered disordered autonomous spin chains. We observe consistent signatures of the transition to MBL phase for several indicators of ergodicity breaking in the kicked Ising model. Moreover, we show that an assumption of a power-law divergence of the correlation length at the MBL transition yields a critical exponent $\nu \approx 2$, consistent with the Harris criterion for one-dimensional disordered systems.

Photocatalytic water splitting is a promising strategy for large-scale clean energy production. However, efficient and low-cost solid-state photocatalysts are still lacking. We present here first-principles calculations for investigating the suitability of an epitaxial layer of strontium germanate on a Si(100) single crystal as a photocathode. Conduction and valence band offsets at the interface between these two semiconductors were determined using state-of-the-art approximations of density functional theory for the accurate prediction of band alignments. The resulting band lineup is also confirmed by inspection of the spatially resolved density of states. It is concluded that the conduction band offset of the investigated heterostructure is favorable for photocathodic functionality.

Features of the spin dynamics in ensembles of interacting (FH-chem) and weakly interacting (FH-coated) magnetic ultrasmall ($\langle d\rangle \sim 2$ nm) ferrihydrite nanoparticles have been explored. The dc and ac magnetic susceptibilities $[{\chi }^{\prime }\left(T\right)$ and ${\chi }^{\prime \prime }\left(T\right)]$ of the investigated samples have been thoroughly measured in a weak magnetic field (2 Oe) around the temperatures of superparamagnetic blocking of the nanoparticle magnetic moments (19 and 50.4 K for FH-coated and FH-chem, respectively, according to the dc magnetization data). It has been shown that the magnetic interactions between nanoparticles induce the formation of the cluster spin-glass state below the superparamagnetic blocking temperature ($T_g=18$ and 49.5 K for FH-coated and FH-chem, respectively). It has been found that coating of nanoparticles increases the critical scaling index from $z\nu =5.9$ (FH-chem) to $z\nu =8.0$ (FH-coated). This indicates a general slowdown of the dynamics of correlated spins, which is also expressed as an increase in relaxation time ${\tau }_0$ after switching on the interparticle interactions. We attribute this phenomenon to a consequence of a change in the volume of correlated spins with the increasing size of a cluster of interacting nanoparticles. It has been demonstrated using the simulated ${\chi }^{\prime \prime }\left(T\right)$ dependence that the dissipation of the magnetic energy occurs in two independent stages. The first stage is directly related to the blocking of the nanoparticle magnetic moments, while the second stage reflects the spin-glass behavior of surface spins and depends strongly on the intensity of the interparticle interactions.

The heterostructures constructed with superconductor and ferromagnet (S/F) have attracted intensive attention because of their remarkable properties such as spin-triplet pairing at the interface due to the magnetic proximity effect (MPE). Recently, the heteroepitaxial thin films formed by rock-salt rare earth monoxides LaO and EuO were realized in experiments [Kaminaga et al., Chem. Lett. 48, 1244 (2019)], in which LaO is a conventional superconductor with the superconducting $T_c\sim 5$ K and EuO is a ferromagnetic insulator with a Curie temperature of 69 K. To elucidate the MPE in the LaO/EuO heterostructure, we have studied its electronic and magnetic properties based on first-principles calculations. The spin splitting of the surface bands as well as the nonzero local magnetic moments on La atoms confirm the existence of MPE. In addition, the electron gases accumulated at the interface and on top of the EuO layer are also spin-polarized. Interestingly, we find that the spin polarization spreads throughout the LaO layers, in which the electron gases in the interstitial regions play an important role. Furthermore, we demonstrate that the net magnetic moment of the LaO layers in the LaO/EuO heterostructure can be effectively modulated by means of an external electric field. These results not only deepen the understanding of the MPE in the LaO/EuO heterostructures, but also suggest that LaO/EuO can serve as a promising platform for studying the Majorana bound states and may apply in the voltage-controlled superconducting switch.

We study electronic correlation effects in the three-band Hubbard model in presence of Hund's and spin-orbit couplings using slave-spin mean-field theory. We consider three different regimes of hopping parameter values for the model on a square lattice. For orbital diagonal and isotropic hopping, we show that spin-orbit coupling (SOC), in general, enhances electronic correlations via the reduction of orbital degeneracy. In presence of Hund's coupling $J$, SOC tends to oppose the effect of $J$ on electronic correlations. Considering symmetry allowed anisotropic hopping, we find that the quasiparticle weights become orbital selective in presence of interaction. The effect of $J$ is particularly interesting for the band filling of two particles per site. Here, the Janus-faced effect of $J$ on correlation is obtained only in the narrower band, whereas electronic correlation in the wider band get reduced by $J$ for all values of Hubbard repulsion $U$. For model parameters corresponding to ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$, interestingly, we find that the mass renormalizations in the bands become anomalous in presence of strong $U$ and $J$. The effective mass enhancement in the wider band becomes greater compared to that in the narrower band. We show that it originates in the peculiar electronic band structure of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$, in which the spinon Fermi surface topology changes in a particular way in the presence of interactions.

Topological phonon polaritons (TPhPs) are promising optical modes relevant in long-range radiative heat transfer, information processing, and infrared sensing, whose topological protection is expected to enable their robust existence and transport. In this work we show that TPhPs can be supported in one-dimensional bichromatic silicon carbide nanoparticle (NP) chains, and demonstrate that they can considerably enhance radiative heat transfer for an array much longer than the wavelength of radiation. By introducing incommensurate or commensurate modulations on the interparticle distances, the NP chain can be regarded as an extension of the off-diagonal Aubry-André-Harper model. By calculating the eigenstate spectra with respect to the modulation phase that creates a synthetic dimension, we demonstrate that under this type of modulation the chain supports nontrivial topological modes localized over the boundaries since the present system inherits the topological property of two-dimensional integer quantum Hall systems. In this circumstance the gap-labeling theorem and corresponding Chern number can be used to characterize the features of band gaps and topological edge modes. Based on many-body radiative heat transfer theory for a set of dipoles, we theoretically show the presence of topological gaps and midgap TPhPs can substantially enhance radiative heat transfer for an array much longer than the wavelength of radiation. We show how the modulation phase that acts as the synthetic dimension can tailor the radiative heat transfer rate by inducing or annihilating topological modes. We also discuss the role of dissipation in the enhancement of radiative heat transfer. We further present a theoretical analysis based on eigenvalue decomposition to quantitatively reveal the role of TPhPs. These findings therefore provide a fascinating route for tailoring near-field radiative heat transfer based on the concept of topological physics.