Quantum entanglement and its main quantitative measures, the entanglement entropy and entanglement negativity, play a central role in many-body physics. An interesting twist arises when the system considered has symmetries leading to conserved quantities: Recent studies introduced a way to define, represent in field theory, calculate for $1+1\mathrm{D}$ conformal systems, and measure, the contribution of individual charge sectors to the entanglement measures between different parts of a system in its ground state. In this paper, we apply these ideas to the time evolution of the charge-resolved contributions to the entanglement entropy and negativity after a local quantum quench. We employ conformal field-theory techniques and find that the known dependence of the total entanglement on time after a quench $S_A\sim ln\left(t\right)$, results from $\sim \sqrt{ln\left(t\right)}$ significant charge sectors, each of which contributes $\sim \sqrt{ln\left(t\right)}$ to the entropy. We compare our calculations to numerical results obtained by the time-dependent density matrix renormalization-group algorithm and exact solution in the noninteracting limit, finding good agreement between all these methods.

The interaction between superconductivity and magnetism in heavy fermion compounds has remained a challenge ever since the discovery of unconventional superconductivity in such systems. The heavy fermion $\mathrm{Ce}T\mathrm{In}{}_5$ ($T$ = Co,Rh,Ir) family offers a good platform to study the relationship between superconductivity and magnetism, whose ground state can be easily tuned by chemical doping, making the ambient-pressure experimental techniques like angle-resolved photoemission spectroscopy possible to address this old but engaging question. By Cd doping, the superconducting state of ${\mathrm{CeCoIn}}_5$ can be smoothly tuned to an antiferromagnetic ground state, which can be reversed by applying pressure. Here we present an electronic structure study of $\mathrm{CeCo}(\mathrm{In}{}_{0.85}\mathrm{Cd}{}_{0.15}{)}_5$ with an antiferromagnetic ground state and the results are compared with ${\mathrm{CeCoIn}}_5$. We found that the hybridization strength between the $f$ electrons and conduction electrons in ${\mathrm{CeCoIn}}_5$ has been suppressed by Cd doping, but still the Fermi surface includes a significant contribution from the Ce $f$ electrons. Our results find that the electronic tuning effect by Cd doping arises from the change in the hybridization strength between the Ce $f$ electrons and conduction electrons caused by the Cd dopant, and the subtle interplay between itinerancy and localization of the $f$ electrons determines the ground state.

We consider an electron gas, both in two (2D) and three (3D) dimensions, interacting with quenched impurities and phonons within leading order finite-temperature many-body perturbation theories, calculating the electron self-energies, spectral functions, and momentum distribution functions at finite temperatures. The resultant spectral function is in general highly non-Lorentzian, indicating that the system is not a Fermi liquid in the usual sense. The calculated momentum distribution function cannot be approximated by a Fermi function at any temperature, providing a rather simple example of a non-Fermi liquid with well-understood properties.

Polaritons in metals, semimetals, semiconductors, and polar insulators can allow for extreme confinement of electromagnetic energy, providing many promising opportunities for enhancing typically weak light-matter interactions such as multipolar radiation, multiphoton spontaneous emission, Raman scattering, and material nonlinearities. These extremely confined polaritons are quasielectrostatic in nature, with most of their energy residing in the electric field. As a result, these “electric” polaritons are far from optimized for enhancing emission of a magnetic nature, such as spin relaxation, which is typically many orders of magnitude slower than corresponding electric decays. Here, we take concepts of “electric” polaritons into magnetic materials, and propose using surface magnon polaritons in negative magnetic permeability materials to strongly enhance spin relaxation in nearby emitters. Specifically, we provide quantitative examples with ${\mathrm{MnF}}_2$ and ${\mathrm{FeF}}_2$, enhancing spin transitions in the THz spectral range. We find that these magnetic polaritons in 100-nm thin films can be confined to lengths over 10 000 times smaller than the wavelength of a photon at the same frequency, allowing for a surprising 12 orders of magnitude enhancement in magnetic dipole transitions. This takes THz spin-flip transitions, which normally occur at timescales on the order of a year, and forces them to occur at sub-ms timescales. Our results suggest an interesting platform for polaritonics at THz frequencies, and more broadly, a way to use polaritons to control light-matter interactions.

We studied the effect of inserting 0.5-nm-thick spacer layers (Ti, V, Cr, Mo, W) at the Pt/Co interface on the spin-orbit torques, the Hall effect, magnetoresistance, saturation magnetization, and magnetic anisotropy. We find that the dampinglike spin-orbit torque decreases substantially for all samples with a spacer layer compared to the reference Pt/Co bilayer, consistently with the opposite sign of the atomic spin-orbit coupling constant of the spacer elements relative to Pt. The reduction of the dampinglike torque is monotonic with atomic number for the isoelectronic $3d,4d$, and $5d$ elements, with the exception of V that has a stronger effect than Cr. The fieldlike spin-orbit torque almost vanishes for all spacer layers irrespective of their composition, suggesting that this torque predominantly originates at the Pt/Co interface. The anomalous Hall effect, magnetoresistance, and saturation magnetization are also all reduced substantially, whereas the sheet resistance is increased in the presence of the spacer layer. Finally, we evidence a correlation between the amplitude of the spin-orbit torques, the spin-Hall-like magnetoresistance, and the perpendicular magnetic anisotropy. These results highlight the significant influence of ultrathin spacer layers on the magnetotransport properties of heavy-metal/ferromagnetic systems.

Rare-earth delafossites were recently proposed as promising candidates for the realization of an effective $S=1/2$ quantum spin liquid (QSL) on the triangular lattice. In contrast to the most actively studied triangular-lattice antiferromagnet ${\mathrm{YbMgGaO}}_4$, which is known for considerable structural disorder due to site intermixing, ${\mathrm{NaYbS}}_2$ delafossite realizes structurally ideal triangular layers. We present detailed muon spin rotation ($\mu \mathrm{SR}$) studies on this regular (undistorted) triangular Yb sublattice based system with an effective spin $J_{\mathrm{eff}}=1/2$ in the temperature range 0.05–40 K. Zero-field and longitudinal-field $\mu \mathrm{SR}$ studies confirm the absence of any long-range magnetic order state down to 0.05 K ($\sim J/80$). Current $\mu \mathrm{SR}$ results, together with the so far available bulk characterization data, suggest that ${\mathrm{NaYbS}}_2$ is an ideal candidate to identify the QSL ground state.

Molecular dynamics simulations and methods of importance sampling are used to study the heat transport of low-dimensional carbon lattices. For both carbon nanotubes and graphene sheets, heat transport is found to be anomalous, violating Fourier's law of conduction with a system size dependent thermal conductivity and concomitant nonlinear temperature profiles. For carbon nanotubes, the thermal conductivity is found to increase as the square root of the length of the nanotube, while for graphene sheets the thermal conductivity is found to increase as the logarithm of the length of the sheet over the system sizes considered. The particular length dependence and nonlinear temperature profiles place carbon lattices into a universality class with nonlinear lattice models, and suggest that heat transport through carbon nanostructures is better described by a Levy walk rather than simple diffusion.

We study the emergence of bosonic pairs in a system of two coupled one-dimensional fermionic chains subject to a gauge flux (two-leg flux ladder), with both attractive and repulsive interaction. In the presence of strong attractive nearest-neighbor interaction and repulsive next-to-nearest-neighbor interaction, the system crosses into a regime in which fermions form tightly bound pairs, which behave as bosonic entities. By means of numerical simulations based on the density-matrix-renormalization-group (DMRG) method, we show in particular that in the strongly paired regime, the gauge flux induces a quantum phase transition of the Ising type from vortex density wave (VDW) to a charge density wave (CDW), characteristic of bosonic systems.

Bismuth iron garnet (BIG), i.e., ${\mathrm{Bi}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}$, is a strong ferrimagnet that also possesses outstanding magneto-optical properties such as the largest known Faraday rotation. These properties are related with the distribution of magnetic moments on octahedral and tetrahedral sites, the presence of spin gaps in the density of state, and a strong spin-orbit coupling. In this work, first-principles ab initio calculations are performed to study the structural, electronic, and magnetic properties of BIG using density functional theory with “$\mathrm{Hubbard}+U$” $\left(\mathrm{DFT}+U\right)$ correction including spin-orbit coupling and hse06 hybrid functional. We found that the presence of spin gaps in the electronic structure results from the interplay between exchange and correlation effects and the crystal field strengths for tetrahedral and octahedral iron sublattices. The $\mathrm{DFT}+U$ treatment tends to close the spin gaps for larger $U$ due to overlocalization effects, notably in the octahedral site. On the other hand, the hybrid functional confirms the occurrences of three spin gaps in the iron states of the conduction band as expected from optical measurements. A strong exchange splitting at the top of the valence bands associated with a lone-pair type mixture of O $p$ and Bi $s,p$ states is also obtained. Similar exchange splitting was not previously observed for other iron based garnets, such as for yttrium iron garnet. It follows that hole doping, as obtained by Ca substitution at Bi sites, results in a full spin polarized density at the Fermi energy. This work helps to shed more light on the theoretical comprehension of the properties of BIG and opens the route towards the use of advanced many body calculations to predict the magneto-optical coupling effects in BIG in a direct comparison with the experimental measurements.

We present a theory of nonradiative recombination (NRR) with an emphasis on the so far little-explored dynamic effect in the process. We show that it can significantly enhance the NRR rate over that of a static midgap level as suggested by the Shockley-Read-Hall theory, whereby offering an alternative explanation to the long-lasting discrepancy between theory and experiment for semiconductors. As an illustration, we show that dynamic NRR can take place at the $DX$ center in Si-doped GaAs which, combined with a modified ABC model at high carrier-density limit, makes it possible to verify the theory directly by experiment.

We present a detailed analysis and comparison of four models describing the extension of the electron-energy loss function from the optical limit of q→0 into the (q,ω) plane to obtain the bulk and surface terms of differential inverse inelastic mean free paths. We found that the best model that describes accurately and times efficiently the calculation of the energy loss function of free-electron-like materials is the combination of the Penn algorithm [Phys. Rev. B 35, 482 (1987)] with the Ritchie-Howie method [Philos. Mag. 36, 463 (1977)]. Applying this model in our reverse Monte Carlo method, we determined, with high-precision, electron-energy loss functions of silicon and germanium based on the theoretical analysis of the high-energy resolution reflected electron energy loss spectroscopy (REELS) spectra, measured at 3, 4, and 5 keV incident electron energies. The refractive index $n$, the extinction coefficient $k$, and the complex dielectric function ($\varepsilon ={\varepsilon }_1+i{\varepsilon }_2$) were calculated from the obtained energy loss function in a wide energy loss range of 0–200 eV. The accuracy of the obtained results is justified with various sum rules. We found that the calculated optical data of Si and Ge fulfill the sum rules with an average accuracy of 0.11% or even better. Therefore, the use of these optical data in materials science and surface analysis is highly recommended for further applications.

Beenakker noticed that the peculiar band structure of Dirac fermions in two-dimensional (2D) solids allows for the specular Andreev reflection in these systems, which has no analogue in other 2D electron systems. An interesting deformation of the Dirac equation in the solid state is to tilt it, which has now been realized in materials. In this paper we report another peculiar feature of the Andreev reflection in tilted 2D Dirac cone systems. The tilt deformation of the Dirac equation is characterized by two parameters $\mathit{\zeta }=\zeta (cos\theta ,sin\theta )$. We show that when the tilt parameter is tuned to its “horizon value” $\zeta =1$, irrespective of the incidence angle of electrons, the Andreev reflected hole is always reflected perpendicular to the interface. Furthermore, at $\zeta =1$, if the tilt direction is perpendicular to the interface, the conductance will be energy independent for all subgap energies. For generic tilt $\mathit{\zeta }$, the tilt dependence of the conductance line shape can be used to extract information about the direction and magnitude of the tilt.

We report the auxiliary coherent potential approximation (ACPA) for calculating the phonon dispersion of three-dimensional alloys with both mass and force-constant disorders. To obtain the average spectra function of disordered alloys, the average coherent scattering structure factors are derived from the auxiliary coherent medium in single-site approximation. We provide an analytical proof of the sum rule in the auxiliary coherent medium, which ensures the analyticity of physical properties. To demonstrate the accuracy and applicability of the ACPA method, we apply the ACPA to calculate phonon dispersion of several alloys, including CuPd CuAu, PdFe, and NiPt with different disorder concentrations. We find the ACPA phonon dispersion results agree very well with the itinerant coherent potential approximation calculations and experimental measurements. The approximate separable force-constant model used in the ACPA can very well represent the first-principles disordered force constants, presenting minor or even negligible influence on the phonon dispersion of the alloy. The ACPA model features easy implementation and high computational efficiency, providing an effective method for simulating vibrational properties of realistic alloys.

Using first-principles electronic structure calculations (local density approximation), we present second-moment calculations of the temperature dependence of the vibrational normal mode frequencies in Si up to 1500 K . The method is based on simple ensemble averages of displacements and forces and is easy to implement. These efficient calculations incorporate all interactions nonperturbatively, implicitly including all high order force constants, in contrast to typical perturbative approaches. Also in this work, we propose and apply to our classical calculations an estimated quantum correction that could be used for classical approaches other than the moments method. We compare our results to available experiments, including recent inelastic neutron scattering data and conclude that the second-moment gives the frequency shift to within a factor of 2 in contrast to quasiharmonic approaches that fail by an order of magnitude to predict the anharmonic shift. Noting the relative simplicity and speed of the calculations, we conclude that the second-moment approximation reasonably accounts for anharmonicity in a system that has been very closely studied experimentally and may reliably be applied in an exploratory way to more complex systems. We suggest that further improvement on the results could be obtained by incorporating the fourth moment, which can be implemented with little additional cost.

We explore the dynamics of spiral spin waves in permalloy nanoelements with variable aspect ratio of geometric dimensions, and their potential use as improved spin wave emitters with no or little biasing field required. Numerical results show that above a certain thickness, propagating spiral waves can be obtained in circular and square shaped elements in a flux closure state. VNA-FMR experiments on 20-nm (thin) and 80-nm (thick) samples confirm two type of spectra corresponding to different dispersions for thinner and thicker elements. We show that, for the thicker films, the vortex core region acts as a source of large amplitude spiral spin waves, which dominate over other modes. In case of the thinner elements, these modes are critically damped. For different shapes of the patch, we show that a rich collection of confined propagating modes can also be excited, modifying the final wave front and enriching the potential of the nanodot as a spin wave emitter. We give an explanation for the intense spiral modes from the perspective of a balance of dipolar and exchange energies in the sample.

By means of an accurate path-integral Monte Carlo, we investigate a two-dimensional ensemble of particles interacting via a Lifshitz-Petrich-Gaussian potential. In particular, analyzing structures described by a commensurate ratio between the two wave numbers that mark the pattern, the Lifshitz-Petrich-Gaussian boson model may display a stable and well-defined stripe phase lacking any global phase coherence but featuring a superfluid signal along the stripe direction only. Upon increasing quantum fluctuations and quantum-mechanical exchange of bosons, the double-degeneration of the negative minima in the Fourier transform of the potential is removed at the expense of a density modulation peculiar to a cluster triangular crystal. We also show that this last structure possess all features adhering to the definition of a supersolid phase.

We performed high-pressure Raman and resistance measurements on a two-dimensional monoclinic semiconductor GeAs. We discovered a superconductivity that emerges after the insulator-metal transition above 10 GPa, which is related to the structural transition. Our results indicate that the semiconducting monoclinic phase and rocksalt structure phase coexist above 10 GPa and structural transformation to the rocksalt phase is completed above $17\sim 18\mathrm{GPa}$. The maximum superconducting transition temperature $T_c$ is about 8 K close to the structural transition boundary, and the $T_c$ is gradually decreasing at higher pressures. Upon pressure release, the nonpolar rocksalt structure transforms to a polar tetragonal superconducting phase. Our first-principles calculations indicate that the relatively high $T_c$ in the rocksalt phase is mainly due to the enhancement of the electron-phonon coupling. These results show that superconductivity in this material strongly depends on its structure, achieving maximum $T_c$ in a higher-symmetry phase.

Bismuth iodide ${\mathrm{Bi}}_4{\mathrm{I}}_4$ exhibits intricate crystal structures and topological insulating states that are highly susceptible to influence by environments, making its physical properties highly tunable by external conditions. In this work, we study the evolution of structural and electronic properties of ${\mathrm{Bi}}_4{\mathrm{I}}_4$ at high pressure using an advanced structure search method in conjunction with first-principles calculations. Our results indicate that the most stable ambient-pressure monoclinic $\alpha -{\mathrm{Bi}}_4{\mathrm{I}}_4$ phase in $C2/m$ symmetry transforms to a trigonal $P31c$ structure ($\varepsilon -{\mathrm{Bi}}_4{\mathrm{I}}_4$) at 8.4 GPa, then to a tetragonal $P4/mmm$ structure ($\zeta -{\mathrm{Bi}}_4{\mathrm{I}}_4$) above 16.6 GPa. In contrast to the semiconducting nature of ambient-pressure ${\mathrm{Bi}}_4{\mathrm{I}}_4$, the two high-pressure phases are metallic, in agreement with reported electrical measurements. The $\varepsilon -{\mathrm{Bi}}_4{\mathrm{I}}_4$ phase exhibits distinct ionic states of ${\mathrm{I}}^{\delta -}$ and (${\mathrm{Bi}}_4{\mathrm{I}}_3{)}^{\delta +}$ ($\delta =0.4123$ e), driven by a pressure-induced volume reduction. We show that both $\varepsilon$- and $\zeta -{\mathrm{Bi}}_4{\mathrm{I}}_4$ are superconductors, and the emergence of pressure-induced superconductivity might be intimately linked to the underlying structural phase transitions.

We study the Josephson current in two types of lateral junctions with spin-orbit coupling and an exchange field. The first system (type 1 junction) consists of superconductors with heavy metal interlayers linked by a ferromagnetic bridge, such that the spin-orbit coupling is finite only at the superconductor/heavy metal interface. In the second type (type 2) of system we assume that the spin-orbit coupling is finite in the bridge region. The length of both junctions is larger than the magnetic decay length such that the Josephson current is carried uniquely by the long-range triplet component of the condensate. The latter is generated by the spin-orbit coupling via two mechanisms, spin precession and inhomogeneous spin relaxation. We show that the current can be controlled by rotating the magnetization of the bridge or by tuning the strength of the spin-orbit coupling in type 2 junctions and also discuss how the ground state of the junction can be tuned from a 0 to a $\pi$ phase difference between the superconducting electrodes. In leading order in the spin-orbit coupling, the spin precession dominates the behavior of the triplet component and both junctions behave similarly. However, when spin relaxation effects are included the type 2 junction offers a wider parameter range in which 0-$\pi$ transitions take place.

By converting conventional spin-singlet Cooper pairs to polarized spin-triplet pairs, it is possible to sustain long-ranged spin-polarized supercurrents flowing through strong ferromagnets. Obtaining such a conversion via spin-orbit interactions, rather than magnetic inhomogeneities, has recently been explored in the literature. A challenging aspect with regard to experimental detection has been that in order for Rashba spin-orbit interactions, present, e.g., at interfaces due to inversion symmetry breaking, to generate such long-ranged supercurrents, an out-of-plane component of the magnetization is required. This limits the choice of materials and can induce vortices in the superconducting region complicating the interpretation of measurements. Therefore, it would be desirable to identify a way in which Rashba spin-orbit interactions can induce long-ranged supercurrents for purely in-plane rotations of the magnetization. Here, we show that this is possible in a lateral Josephson junction where two superconducting electrodes are placed in contact with a ferromagnetic film via two thin, heavy normal metals. The magnitude of the supercurrent in such a setup becomes tunable by the in-plane magnetization angle when using only a single magnetic layer. These results could provide a new and simpler way to generate controllable spin-polarized supercurrents than previous experiments which utilized complicated magnetically textured Josephson junctions.