It has been more than fifty years already since the first ever density functional theory (DFT) simulation of a jellium surface demonstrated that uniform electric fields and external point charges induce equivalent electrostatics in the limit of linear response. During the years that followed, improved jellium models and computational resources allowed including strong electric fields to explore the problem beyond linear response. Nowadays, most DFT simulations of metallic surfaces are routinely conducted using finite slabs with periodic boundary conditions (PBCs) and the pseudopotential method to account explicitly for the ionic lattice. Surprisingly, there is apparently no record of dedicated studies that jointly discuss how the electrostatic response of metallic slabs in strong electric fields is affected by the PBCs, the net charge, the number of atomic layers, the surface orientation, and the adopted exchange-correlation potential. To investigate these points, we carry out detailed DFT simulations for the low-index facets of Li, Al, and Ag of neutral and charged slabs for varying ranges of external fields. Using key response parameters, we quantify and compare the electrostatics of slabs within and beyond the linear response regime and find that neutral and charged slabs exhibit equivalent responses for equivalent external perturbations. This analysis also offers a numerical demonstration that the electrostatic equivalence for the original jellium model also applies to slabs of finite size in PBCs. Our findings do not only invite the revision of some standard approximations to characterize the electrostatic response of metallic slabs but also aim to support the development of semiclassical, DFT-based methods for metallic interfaces using PBCs.

This study utilizes spatially resolved low-temperature scanning tunneling microscopy and spectroscopy to investigate cobalt oxide nanoislands on Au(111) single-crystal surfaces. The electronic structure of bilayer, trilayer, and multilayer islands is measured, and the findings are correlated with structural variations across the islands, at oxygen defect lines on the islands, and at the island step edges. Of particular importance is the identification of electronic features below the Fermi level unique to certain island edges that are well-known to exhibit increased chemical reactivity. The results advance the understanding of the electronic properties of surface-supported cobalt oxide nanostructures, which are known to be important for catalytic applications. Furthermore, on the trilayer island structures a distinct peak in the density of states at the Fermi level is measured that adds to theoretical predictions of superconductivity in ${\mathrm{CoO}}_2$ layers.

We study photoassisted transport for the edge states of a two-dimensional electron gas in the fractional quantum Hall regime, pinched by a single quantum point contact. We provide a general expression of the photoassisted current using a Keldysh-Floquet approach, when the AC drive is applied either directly to the edge states, or when it modulates the tunneling amplitude at the quantum point contact. Strikingly, for a simple cosine modulation of the tunneling amplitude, the phase shift of the second harmonic of the photoassisted current is directly related to the scaling dimension of the quasiparticle operators describing the fractional excitations. As the scaling dimension is intimately related to the statistics, our proposal of a gate modulation of the backscattered current provides a diagnosis of the statistics of Laughlin quasiparticles using a simple quantum point contact geometry.

We study the direct laser drive of infrared-active phonons that are quadratically coupled to a spinless fermion chain. Feedback is incorporated by phonon dressing of the electronic dispersion, which enables effective nonlinearities in the phonon dynamics. We uncover a first-order phase transition in the phononic steady state in which hysteretic effects allow either large or small phonon occupation depending on the drive protocol. We discuss the implications of these findings for probing phase transitions in real driven materials.

We report a systematic quantitative evaluation of parametric amplification gain of magnetization dynamics in an yttrium iron garnet $\left({\mathrm{Y}}_3{\mathrm{Fe}}_5{\mathrm{O}}_{12}\right)$ thin disk via ac spin pumping and the inverse spin Hall effect. We demonstrate its signature phase dependence where amplification and attenuation occur every $\frac{\pi }{2}$ phase shift of the input signal. The results also show the pump-power dependence of the gain that is explained well by our theoretical model. Finally, the optimal conditions for amplification are investigated by measuring the magnetic field dependence, where we find the highest gain of 11.4 dB.

We present a neutron diffraction study of ${\mathrm{NaYbO}}_2$, a candidate quantum spin-liquid (QSL) compound hosting a geometrically frustrated triangular lattice of magnetic ${\mathrm{Yb}}^{3+}$ ions. We observe diffuse magnetic scattering that persists to at least 20 K, demonstrating the presence of short-range magnetic correlations in this system up to a relatively high-energy scale. Using a reverse Monte Carlo and magnetic pair distribution function analysis, we confirm the predominant antiferromagnetic nature of these correlations and show that the diffuse scattering data can be well described by noninteracting layers of Heisenberg or XY spins on the triangular lattice. We rule out Ising spins and short-range-ordered stripe or ${120}^{\circ }$ phases as candidate ground states of ${\mathrm{NaYbO}}_2$. These results are consistent with a possible QSL ground state in ${\mathrm{NaYbO}}_2$ and showcase the benefit of a combined reciprocal- and real-space analysis of materials with short-range magnetic correlations.

Generating and tailoring photocurrent in topological materials has immense importance in fundamental studies and technological front. Present work introduces a universal method to generate ultrafast photocurrent in both inversion-symmetric and inversion-broken Weyl semimetals with degenerate Weyl nodes at the Fermi level. Our approach harnesses the asymmetric electronic population in the conduction band induced by an intense single-color circularly polarized laser pulse. It has been found that the induced photocurrent can be tailored by manipulating helicity and ellipticity of the employed laser. Moreover, our approach generates photocurrent in realistic situations when the Weyl nodes are positioned at different energies and have finite tilt along a certain direction. Present work adds a new dimension on practical applications of Weyl semimetals for optoelectronics and photonics-based quantum technologies.

The orthovanadate system $R\mathrm{V}{\mathrm{O}}_3$ ($R=\mathrm{rare}$-earth and Y) is known to exhibit multiple orbital, magnetic, and structural transitions depending on the size of the rare-earth ions. $\mathrm{LaV}{\mathrm{O}}_3$ is reported to exhibit a $G$-type orbital ordered ($G$-OO) phase and magnetization reversal below the antiferromagnetic transition. From high angular-resolution synchrotron x-ray powder diffraction measurements, we report the observation of the $C$-OO phase, hitherto unknown in $\mathrm{LaV}{\mathrm{O}}_3$, and its coexistence with the $G$-OO phase below $T_{\mathrm{OO}}^1$ ($\sim 135$ and 125 K) in ambient-pressure (AP) and high-pressure (HP) synthesized $\mathrm{LaV}{\mathrm{O}}_3$, respectively. At $T_{\mathrm{OO}}^2\sim 20$ K, HP-$\mathrm{LaV}{\mathrm{O}}_3$ shows an orbital flipping transition from $G$- to $C$-OO, which results in an increase of the $C$-OO phase fraction. At 6 K, the $C$-OO phase becomes predominant ($\sim 61\%$) in HP-$\mathrm{LaV}{\mathrm{O}}_3$, whereas it is $\sim 41\%$ in AP-$\mathrm{LaV}{\mathrm{O}}_3$. We suggest that the different magnetic structures associated with coexisting orbital ordered phases should be responsible for the magnetization reversal phenomenon in $\mathrm{LaV}{\mathrm{O}}_3$.

We review all symmetry-allowed spin-singlet and spin-triplet superconducting order parameters in graphene ($s$-wave, $d$-wave, $p$-wave, and $f$-wave) generated by generic on-site, nearest-neighbor, and next-nearest-neighbor pairing interactions in a tight-binding model. For each pairing channel, we calculate both the band structure and the dependence of the density of states on energy, chemical potential, and pairing strength. In particular, we distinguish between nodal superconducting states and fully gapped states and study the dependence of gap closing points on the chemical potential and the superconducting pairing strength. We further investigate the difference between mono-, bi-, and trilayer ABC and ABA graphene, including accounting for the effects of trigonal warping.

We study the emergence of electronic edge states in superconducting monolayer, bilayer, and trilayer graphene for both spin-singlet and spin-triplet superconducting order parameters. We focus mostly on the gapped chiral $p+i{p}^{\prime }$- and $d+i{d}^{\prime }$-wave superconducting states that show a nonzero Chern number and a corresponding number of edge states. For the $p+i{p}^{\prime }$-wave state, we observe a rich phase diagram for the Chern number when tuning the chemical potential and the superconducting order parameter amplitude, which depends strongly on the number of layers and their stacking and is also modified by trigonal warping. At small parameter values, compared to hopping energy, we observe a region whose Chern number is unique to rhombohedrally stacked graphene and is independent of the number of layers. Our results can be understood in relation not only to the superconducting order parameter winding as expected but also to the normal state band structure. This observation establishes the importance of the normal state characteristics for understanding the topology in superconducting graphene systems.

We consider the most energetically favorable symmetry-allowed spin-singlet and spin-triplet superconducting pairing symmetries in monolayer and few-layer graphene and for each calculate the energy spectrum in the presence of a scalar or magnetic impurity. We find that two doubly degenerate subgap states exist for scalar impurities for all types of pairing, except for the spin-singlet $s$-wave state. For magnetic impurities, two or four subgap states may form depending on the order parameter symmetry. We find that the spin polarization of these states allows one to distinguish between spin-singlet and -triplet pairing; for example, only the spin-triplet states show opposite-energy subgap states with the same spin. We also calculate the quasiparticle interference patterns associated with the subgap states and find that they exhibit features that could distinguish between different types of pairing symmetries, especially a breaking of rotational symmetry for nodal states, which is stronger for the spin-singlet $d_{xy}$ and $d_{x^2-y^2}$ states than for the spin-triplet $p_x$ and $p_y$ states.

We numerically studied the vortex dynamics at zero temperature in superfluid ${}^4\mathrm{He}$ confined between two parallel rough solid boundaries, one of which oscillates in a shear mode. This study was motivated by the experimental work by Barquist et al. [Phys. Rev. B 101, 174513 (2020); Phys. Rev. B 106, 094502 (2022)] which employed a microelectromechanical systems (MEMS) oscillator operating in superfluid ${}^4\mathrm{He}$ at a near-zero temperature. Their experiments suggest that the motion of the MEMS oscillator is damped by quantized vortices. In our study, we postulated that this damping effect was closely associated with vortex pinning phenomena and developed pinning models. Our primary objective is to understand the vortex dynamics in the presence of pinning and to provide insight into the experimental observations regarding the damping mechanism. We confirmed that Kelvin waves were excited in the pinned vortices when the oscillation frequency of the solid boundary matched with the mode frequency of the Kelvin wave. Additionally, we examined the formation and evolution of vortex tangles between the boundaries. The vortex tangle was suppressed in the presence of pinning, while the absence of pinning allowed to form well-developed vortex tangle resulting in turbulence. Finally, by evaluating the tension of pinned vortices we extracted the damping force acting on the solid boundaries.

In this paper, we explore the localization features of wave functions in a family of mosaic quasiperiodic chains obtained by continuously interpolating between two limits: the mosaic Aubry-André (AA) model, known for its exact mobility edges with extended states in the band-center region, and localized ones in the band-edge regions for a large enough modulation amplitude, and the mosaic Fibonacci chain, which exhibits its multifractal nature for all the states except for the extended one with $E=0$ for an arbitrary finite modulation amplitude. We discover that the mosaic AA limit for the states in the band-edge regions evolves into multifractal ones through a cascade of delocalization transitions. This cascade shows lobes of lower fractal dimension values separated by maxima of fractal dimension. In contrast, the states in the band-center region (except for the $E=0$ state) display an anomalous cascading process, where it emerges lobes of higher fractal dimension values are separated by the regions with lower fractal dimensions. Our findings offer insight into understanding the multifractality of quasiperiodic chains.

The inverse Rashba-Edelstein effect (IREE) in a two-dimensional electron gas (2DEG) induced by spin pumping from an adjacent ferromagnetic insulator (FI) is investigated theoretically. In particular, spin and current densities in the 2DEG in which both Rashba and Dresselhaus spin-orbit interactions coexist are formulated, and their dependencies on ferromagnetic resonance frequency and orientation of the spin in the FI are clarified. It is shown that spin density diverges when the ratio between the Rashba and Dresselhaus spin-orbit interactions approaches unity, while current density stays finite there. These results can be applied for evaluating spin splitting on the Fermi surface in a 2DEG and designing spintronic devices using IREE.

We present a noteworthy finding of high-temperature ferroelectric order in a fairly unexplored ${\mathrm{Gd}}_2{\mathrm{MnFeO}}_6$ compound, characterized by a disordered double-perovskite structure. This material exhibits a remarkable cryogenic refrigerant capacity alongside the ferroelectric order, making it a rare occurrence. Notably, the refrigerant capacity of this Gd-based double perovskite surpasses that of all previously reported counterparts. Around 92 K ($T_{FE}$), we observe the presence of ferroelectric order, which is significantly higher in temperature compared to the magnetic order at 4 K ($T_N$). The involvement of dominant short-range magnetic order below $T_{FE}$ ($\gg T_N$) leads to a notable magnetoelectric consequence. Raman studies further support our findings, revealing a steplike octahedral distortion of $(\mathrm{Mn}/\mathrm{Fe}){\mathrm{O}}_6$ at $T_{FE}$. This distortion aligns with a structural transition to a polar $Pna{2}_1$ structure at $T_{FE}$, consequently inducing the ferroelectric order. The high-temperature ferroelectric order associated with the linear magnetoelectric coupling and promising magnetic refrigeration capacity are in tune with the strong magnetic frustration and significant Jahn-Teller effect in ${\mathrm{Gd}}_2{\mathrm{MnFeO}}_6$.

The effective spin-1/2 antiferromagnetic Heisenberg-Ising chain materials, $A{\mathrm{Co}}_2{\mathrm{V}}_2{\mathrm{O}}_8, A=\mathrm{Sr},\mathrm{Ba}$, are a rich source of exotic fundamental phenomena and have been investigated for their model magnetic properties both in zero and nonzero magnetic fields. Here we investigate a new member of the family, namely, ${\mathrm{PbCo}}_2{\mathrm{V}}_2{\mathrm{O}}_8$. We synthesize powder and single-crystal samples of ${\mathrm{PbCo}}_2{\mathrm{V}}_2{\mathrm{O}}_8$ and determine its magnetic structure using neutron diffraction. Furthermore, the magnetic field/temperature phase diagrams for a magnetic field applied along the c, a, and [110] crystallographic directions in the tetragonal unit cell are determined via magnetization and heat capacity measurements. A complex series of phases and quantum phase transitions are discovered that strongly depend on both the magnitude and direction of the field. Our results show that ${\mathrm{PbCo}}_2{\mathrm{V}}_2{\mathrm{O}}_8$ is an effective spin-1/2 antiferromagnetic Heisenberg-Ising chain with properties that are, in general, comparable to those of ${\mathrm{SrCo}}_2{\mathrm{V}}_2{\mathrm{O}}_8$ and ${\mathrm{BaCo}}_2{\mathrm{V}}_2{\mathrm{O}}_8$. One interesting departure from the results of these related compounds is, however, the discovery of a new field-induced phase for the field direction $H\parallel \left[110\right]$.

Spin-accumulation and spin-current profiles are calculated for a disordered Pt film subjected to an in-plane electric current within the nonequilibrium Green's function approach. In the bulklike region of the sample, this approach captures the intrinsic spin Hall effect found in other calculations. Near the surfaces, the results reveal qualitative differences with the results of the widely used spin-diffusion model, even when the boundary conditions are modified to try to account for them. One difference is that the effective spin-diffusion length for transverse spin transport is significantly different from its longitudinal counterpart and is instead similar to the mean-free path. This feature may be generic for spin currents generated via the intrinsic spin Hall mechanism because of the differences in transport mechanisms compared to longitudinal spin transport. Orbital accumulation in the Pt film is only significant in the immediate vicinity of the surfaces and has a small component penetrating into the bulk only in the presence of spin-orbit coupling, as a secondary effect induced by the spin accumulation.

Quantum critical phenomena influence the finite temperature behavior of condensed matter systems through quantum critical fans whose extents are determined by the exponents of the zero temperature criticality. Here we emphasize the aspects of quantum critical lines, as discussed previously, and study an exactly solved model involving a transverse field Ising model with added three-spin interaction. This model has three critical lines. We compute the spin-spin correlation function and extract the correlation length, and identify the crossovers: quantum critical to quantum disordered, or renormalized classical regimes. We construct the quantum critical fans along one of the critical lines. In addition, we also construct finite temperature dynamic structure factors. We hope this model will become experimentally realizable in the future, and our results could stimulate studies in many similar models.

The photoluminescence emission spectrum at low temperature of the ${\mathrm{TiO}}_2$ anatase shows a broad band around 2.3 eV that has been largely attributed to self-trapped excitons. In this paper, time-resolved experiments conducted at low temperature on a thin layer and a single crystal give insights into the carrier dynamics inside ${\mathrm{TiO}}_2$. The decay of the photoluminescence with time can be described by a single power law from the picoseconds time range up to the milliseconds time range. The decay rate increases with increasing temperature. We propose to interpret these observations by a collision mechanism between self-trapped excitons that diffuse via hopping processes. These excitons, which are stabilized by the indirect band gap of anatase ${\mathrm{TiO}}_2$, can be ionized at higher temperatures and lead thus to an acceleration of the observed dynamics.