We present an accurate local density functional for electronic-structure calculations within the density functional theory (DFT). The functional is derived by analyzing the structure of the standard perturbative expansion of the correlation energy of the interacting uniform electron gas. Then, the expansion is partially resummed and reorganized as a self-consistent series in powers of a renormalized electron-electron interaction vertex based on the screened frequency-momentum-dependent dielectric matrix given by the well-known random-phase approximation. First, we demonstrate that the range of $r_s$, where this reorganized and renormalized series converges, contains and is significantly larger than the average range realized in real crystalline materials. Using a combination of analytical, numerical, and stochastic integration techniques we are able to calculate all the diagrams which have contribution up to the same leading order. We benchmarked the functional using the quantum espresso implementation of the DFT applied to the same list of materials, selected previously by other authors, in its entirety without any modification of the list. We find that for ground-state properties in general, such as equilibrium atomic distances and bulk moduli, the functional presented here is more accurate than the currently available most popular one.

Phonon localization is a phenomenon that influences numerous material properties in condensed matter physics. Anderson localization brings rise to localized atomic-scale phonon interferences in disordered lattices with an influence limited to high-frequency phonons having wavelengths comparable to the size of a randomly perturbed unit cell. Here we computationally expose a form of phonon localization induced by augmenting a crystalline material with intrinsic phonon nanoresonators with feature sizes that can be smaller or larger than the phonon wavelengths but must be relatively small compared to the phonon mean free paths. This mechanism is deterministic and takes place within numerous discrete narrow-frequency bands spread throughout the full spectrum with central frequencies controlled by design. For demonstration, we run molecular dynamics simulations of all-silicon nanopillared membranes at room temperature and apply to the underlying thermalized environment narrowband wave packets as an excitation at precisely the frequencies where resonant hybridizations are evident in the anharmonic phonon band structure. Upon comparison to other frequency ranges where the nanostructure does not exhibit local resonances, significant intrinsic spatial phonon localization along the direction of transport is explicitly observed. Furthermore, the energy exchange with external sources is minimized at the resonant frequencies. We conclude by making a direct comparison with Anderson localization highlighting the superiority of the resonant phonons across both sides of the interference frequency limit.

We use kinetic theory and the thermodynamic Bethe ansatz to derive the hydrodynamics of spin transport in the Haldane-Shastry chain. We obtain analytical expressions for relaxation from weak-domain-wall initial conditions and corresponding predictions for the spin Drude weight. We corroborate the latter against an exact microscopic calculation at infinite temperature and Luttinger-liquid expectations at zero temperature. We further obtain an analytical expression for the long-wavelength dynamics of the longitudinal spin structure factor at all fillings and temperatures. We show that the latter interpolates between an empirically exact expression that we have found at infinite temperature and the long-wavelength limit of the Haldane-Zirnbauer formula at zero temperature.

The layered molecular conductors $\kappa \text{−}{\left(\mathrm{BEDT}\text{−}\mathrm{TTF}\right)}_{2}X$ are a perfect experimental platform for studying the physics of the Mott transition and related exotic electronic states. In these materials, the subtle balance between various instabilities of the normal metallic state can be efficiently changed by applying a very moderate external pressure or by subtle chemical modifications, e.g., by a replacement of the insulating anion $X^{-}$, frequently referred to as “chemical pressure.” A crucially important but still unsettled issue is an exact understanding of the influence of physical and chemical pressure on the electronic structure. To elucidate this issue, we study, in a broad pressure range, magnetic quantum oscillations in two $\kappa$ salts, the ambient-pressure antiferromagnetic insulator with $X=\mathrm{Cu}\left[\mathrm{N}{\left(\mathrm{CN}\right)}_2\right]\mathrm{Cl}$ and the ambient-pressure superconductor with $X=\mathrm{Cu}{\left(\mathrm{NCS}\right)}_2$. The data obtained provide quantitative information on important parameters governing the Mott physics, including the electronic correlation strength ratio $U/t$ and the spin frustration ratio $t^{\prime }/t$. This allows us to directly evaluate the effects of physical and chemical pressure in the present materials. Our analysis reveals significant weakening of both the electronic correlation strength and the magnetic ordering instability under pressure. On the other hand, the anion replacement is found to considerably change the frustration parameter $t^{\prime }/t$ while leaving the correlation strength virtually unaffected.

It is shown that if the atomic screening function is described in the Thomas-Fermi approximation, the corresponding continuous potential for planar channeling to a good accuracy reduces to a truncated Coulomb potential. The sum of two displaced Coulomb potentials also accurately approximates interplanar static continuous potentials for Si, Ge, W crystals in orientation (110), as well as the thermal potential of a Ge crystal in orientation (111), not too close to atomic planes. Such a possibility can be used to facilitate the description of channeled and quasichanneled particle motions. We illustrate this by calculating classical particle channeling periods, quantum energy levels, and the probability of tunneling of a negatively charged particle through a single atomic plane. Simple scaling laws in dependencies of those quantities on the atomic number $Z$ result this case.

Wurtzite LaN (wz-LaN) is a semiconducting nitride that has piezoelectric and ferroelectric properties, making it promising for applications in electronics, either as a binary compound or in alloys such as LaAlN. The prospects for wz-LaN in devices are influenced by the properties of point defects and impurities; here, we use first-principles density functional theory with a hybrid functional to calculate their formation energies, as well as their atomic and electronic structures. Among native point defects, we find that nitrogen-related defects, both vacancies ($V_{\mathrm{N}}^{+}$) and interstitials (${\mathrm{N}}_i^{-}$), are energetically most favorable under most relevant chemical potentials and positions of the Fermi level; $V_{\mathrm{N}}^0$ may additionally be observed under N-poor conditions, and ${\mathrm{N}}_i^0$ may be prominent under N-rich conditions. We also investigate the incorporation of oxygen and hydrogen, which will likely be present as unintentional impurities. We find that the ${\mathrm{O}}_{\mathrm{N}}^{+}$ substitutional species readily forms, but oxygen will not lead to $n$-type conductivity due to formation of $DX$ centers and compensation by interstitial defects. Similarly, substitutional ${\mathrm{H}}_{\mathrm{N}}$ and interstitial ${\mathrm{H}}_i$ can compensate both $p$- and $n$-type dopants. Our results provide detailed, microscopic guidance for the development of electronic devices based on wz-LaN.

It is commonly believed that time reversal symmetry breaking perturbations such as magnetic field or scattering on magnetic impurities destruct superconductivity and suppress the critical temperature of the superconducting phase transition. However, in recent experimental studies, significant enhancement of superconducting critical temperature by parallel magnetic field was found for several thin superconducting systems [H. J. Gardner et al., Nat. Phys. 7, 895 (2011); T. Asaba et al., Sci. Rep. 8, 6520 (2018)]. Here we present a possible explanation of the observed phenomenon showing that combination of interfacial spin-orbit interaction and external magnetic field can cause the increase of the superconducting critical temperature of thin superconducting film in a wide range of magnetic fields. We use the Ginzburg-Landau formalism, taking into account Lifshitz invariant originated from Rashba spin-orbit interaction, which is also responsible for the superconducting diode effect. We also calculate the modification of the Little-Parks oscillations of the critical temperature of hollow superconducting cylinder at the presence of Rashba interfacial spin-orbit interaction.

Higher-order topological phases (HOTPs) host exotic topological states that go beyond the traditional bulk-boundary correspondence. Up to now, there is still a lack of experimentally measurable momentum-space topological characterization for the HOTPs, which is not conducive to revealing the essential properties of these topological states and also restricts their detection in quantum simulation systems. Here, we propose a concept of polarized topological charges to characterize chiral-symmetric HOTPs in momentum space, which further facilitates a feasible experimental scheme to detect the HOTPs in ${}^{87}\mathrm{Rb}$ cold atomic system. Remarkably, our characterization theory not only shows that the second-order (third-order) topological phases are determined by a quarter (negative eighth) of the total polarized topological charges, but also reveals that the higher-order topological phase transitions are identified by the creation or annihilation of polarized topological charges. Particularly, these polarized topological charges can be measured by pseudospin structures of the systems. Due to theoretical simplicity and observational intuitiveness, this work shall advance the broad studies of the HOTPs in both theory and experiment.

Recent low-temperature electron transport experiments in high-quality graphene rely on a technique of doped graphene leads, where the coupling between the graphene flake and its metallic contacts is increased by locally tuning graphene to high doping near the contacts. While this technique is widely used and has demonstrated its usefulness numerous times, little is known about the actual transport properties of the doped graphene leads. Here, we present an experiment probing those properties in the quantum Hall regime at low temperature and high magnetic field, showing that electronic phase coherence and transport chirality are preserved, despite the significant charge equilibration occurring at the edges of the leads. Our work yields a finer understanding of the properties of the doped graphene leads, allowing for improvements of the contact quality that can be applied to other two-dimensional materials.

Recently, spinless $PT$ (product of spatial and temporal inversion operations) symmetric systems have been shown to display multigap band topology for the real-valued Hamiltonians that goes beyond conventional topological classification, e.g., that by Chern number for Weyl points. The $3\times 3$ low-energy models around triply degenerate points [denoted as real triple points (RTPs) in this work] can be made real-valued by choosing a suitable basis in such systems with a minimal number of bands for multigap topology. Interestingly, RTPs have been shown to occur ubiquitously as the Nambu-Goldstone (NG) mode for acoustic phonons, and be characterized by Euler number as a topological invariant even though the Chern number vanishes due to the $PT$ symmetry. Here, combining symmetry analysis, $k·p$ models, and first-principles calculations, we perform a comprehensive study of RTPs realizable in phonon spectra. We provide $k·p$ models around RTPs by NG mode and symmetry-protected RTPs pinned at high-symmetry points (HSPs) in the 1651 magnetic space groups containing $PT$ symmetry. On the other hand, we list the numbers of occurrences of RTPs and other coexisting topological phonons at HSPs in the 15478 materials from the Inorganic Crystal Structure Database. In addition, based on the computed force constants from the Phonon Database at Kyoto University, we catalog 386 materials with at least one RTP owning a nonvanishing Euler number. We take ${\mathrm{KMgF}}_3$ in space group 221 to demonstrate the resulting link nodal structure by external strain. The complete lists of RTPs, effective models, coexisting different types of topological phonons, and predicted materials are believed to promote future studies on multigap band topology and related thermal transport of phonons.

The enhanced coherence thermal transport in complex materials poses challenges in achieving ultralow lattice thermal conductivity in crystalline materials. In this work, based on a global structure search, we find a stable quasi-one-dimensional crystal, $q\text{−}1\mathrm{D} \mathrm{Bi}{\mathrm{I}}_3$, with a simple unit cell containing eight atoms. Using the Wigner thermal transport theory and machine-learning potential, we derive Pearson correlation coefficient matrices based on the calculations of over one million coherent modes, and find that the phonon coherent thermal conductivity is mainly correlated with the generalized group velocity, the frequency interval of coherent phonon modes, and the generalized coherent lifetime. Especially, the unique geometry and hierarchical bonding features of $q\text{−}1\mathrm{D} \mathrm{Bi}{\mathrm{I}}_3$ induce significant anharmonicity, while the small number of atoms in the unit cell reduces the Wigner time limit for the wavelike tunneling of phonons, suppressing the coherence thermal transport. Thus, the synergistic effect of enhanced phonon scattering and reduced phonon coherence leads to an ultralow lattice thermal conductivity of 0.088 (0.099)$\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ in the $x\left(y\right)$ direction. Our work demonstrates the significance of suppressing phonon coherence for achieving ultralow lattice thermal conductivity of crystal materials.

Se-doped $\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_3$ is a commercial $n$-type thermoelectric material near room temperature, which is valued for its high ZT and low lattice thermal conductivity. Nowadays, this material has attracted widespread interest as a candidate for advancing sustainable energy solutions. However, the understanding of the origins of this low lattice thermal conductivity remains inadequate. We present a temperature-dependent Raman spectroscopy study exploring the effects of Se atom substitution on phonon behavior and anharmonicity in the Se-doped $\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_3$ system, and discuss their influence on the low lattice thermal conductivity. Our analysis of the temperature-dependent Raman shift and linewidth of Raman peaks reveals significant third-order anharmonicity across all observed phonon modes. Conversely, tiny fourth and higher-order anharmonicity occurs only in the out-of-plane $A_{1\mathrm{g}}$ vibration modes, regardless of the Se substitution level. Furthermore, as the Se substitution exceeds one-third, Se begins to replace the Te1 site in $\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_3$, which significantly broadens the linewidth of the $E_{\mathrm{g}}^2$ mode. This broadening indicates a rapid reduction in the lifetime of $E_{\mathrm{g}}^2$ mode owing to increased alloy scattering. These findings provide direct evidence of phonon anharmonicity in Se-doped $\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_3$, highlighting its crucial role in reducing lattice thermal conductivity. Our experimental results suggest that appropriate concentration of substituted material and specific site substitution can enhance phonon scattering processes, leading to improved thermoelectric performance.

Antiferromagnetic compounds chromium sesquioxide ($\mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_3$) and dioxomolybdenum selenite present linear magnetoelectric effects. Anti-inversion symmetry in the corresponding magnetic crystal classes dictate the makeup of magnetic Bragg diffraction patterns. Copper axial and polar magnetic multipoles contribute to resonant x-ray and magnetic neutron amplitudes in a symmetry informed analysis of monoclinic $\mathrm{C}{\mathrm{u}}_2\left(\mathrm{Mo}{\mathrm{O}}_4\right)\left(\mathrm{Se}{\mathrm{O}}_3\right)$ presented with a view to steering future diffraction experiments. The compound might be viewed as a low-dimensional quantum magnet on account of its crystal structure and the quantum nature of the Cu spin ($S$ = 1/2).

Studying the magnetic ground states of frustrated antiferromagnets provides unique insight into the stability of quantum spin liquids, even if the anticipated state is not realized toward T = 0. Particularly relevant are structural modifications setting in at temperatures where the magnetic correlations come into play. Here, we explore the lattice dynamics of Y-kapellasite $\left[{\mathrm{Y}}_3\mathrm{C}{\mathrm{u}}_9{\left(\mathrm{OH}\right)}_{19}\mathrm{C}{\mathrm{l}}_8\right]$ single crystals by infrared spectroscopy in combination with ab initio calculations. We observe significant changes in the phonon spectra at $T_s=32$ K that gradually evolve down to low temperatures. The increase in the number of phonon modes provides evidence for a lowering of symmetry, and we discuss several possibilities of crystal structure modifications. Our analysis also reveals that the structural variation involves exclusively H and O atoms, while the other atoms remain rather unaffected. An 8% redshift of the lowest-lying phonon mode upon cooling indicates strong magnetoelastic effects upon decoupling $\mathrm{Cu}\text{−}6f$ hexagons through the lattice vibrations.