The interplay of the electron exchange interaction and spin-orbit coupling results in spontaneous supercurrents near magnetic insulator islands, which are placed on the top of a two-dimensional (2D) superconductor, and whose magnetization is parallel to 2D electron gas. It is shown that in contrast to the well-studied situation, where such an effect involves only topologically trivial spatial variations of the superconducting order parameter, one should take into account supercurrent vortices. The latter are spontaneously generated around the island's boundary of an arbitrary shape, and they result in screening of the Zeeman field. This problem has been considered for electrons subject to a strong Rashba spin-orbit coupling, including Dirac systems as well. In the latter case, vortices can carry Majorana zero modes.

Recent synthesis of ${\mathrm{Li}}_{2x}{\mathrm{BC}}_3$, pseudoisostructural to ${\mathrm{MgB}}_2$, has been reported, with control of doping level by concentration $x$ of Li. Density-functional calculations based on the virtual crystal approximation confirm metalization over a wide range of Li concentration but predict regions of structural instability. The electron-phonon coupling strength and superconducting critical temperature $T_c$ around $x=0.5$ is found to be comparable to that in ${\mathrm{MgB}}_2$, but of different character, accounting for the unexpected result that a stronger bond-stretch mode and a higher B–C ${\mathrm{E}}_g$ mode frequency results in little increase in $T_c$. The B–C honeycomb layer contributes strong $\sigma$-bonding ($p_x,p_y$) cylinders similar to ${\mathrm{MgB}}_2$,while the corresponding C–C states lie well below the Fermi level and are dead” for coupling. However, the $\pi$-bonding ($p_z$) states on the B–C/C–C layer provide a large Fermi-level density of states and weak coupling that moderates the coupling strength and thereby $T_c$.

The angstrom-scale coherence length describing the superfluid wave function of ${}^4\mathrm{He}$ at low temperatures has prevented its preparation in a truly one-dimensional geometry. Mesoporous ordered silica-based structures, such as the molecular sieve MCM-41, offer a promising avenue towards physical confinement, but the minimal pore diameters that can be chemically synthesized have proven to be too large to reach the quasi-one-dimensional limit. We present an active nano-engineering approach to this problem by preplating MCM-41 with a single, well controlled layer of Ar gas before filling the pores with helium. The structure inside the pore is investigated via experimental adsorption isotherms and neutron scattering measurements that are in agreement with large scale quantum Monte Carlo simulations. The results demonstrate angstrom and Kelvin scale tunability of the effective confinement potential experienced by ${}^4\mathrm{He}$ atoms inside the MCM-41, with the Ar layer reducing the diameter of the confining media into a regime where a number of solid layers surround a one-dimensional quantum liquid.

Semiclassical neutral atom theory is an important constraint of the state-of-the-art development of exchange-correlation functionals for solid-state physics. Based on this theory, we construct a screened range-separated hybrid functional for strongly bound bulk solids, which also satisfies the accurate linear response of the local density approximation. The constructed functional shows remarkable performance and is competitive with other popular screened hybrids. Our comprehensive assessment of the constructed screened hybrid for the general purpose solid-state structural properties, structural phase transition, prototypical ferroelectric properties, band gaps, and optical absorption spectra is showing its accuracy for the diverse nature of solid-state properties. Moreover, when applied to general purpose chemical applications, the constructed functional is also reasonably accurate and competitive. Accurate screened hybrids based on semiclassical neutral atom theory are appealing for various solid-state and material science applications and are also attractive for the development of the dielectric-dependent hybrids for interfaces and surfaces.

We present a detailed quasinormal mode analysis of gold bowtie nanoantennas and also highlight the important role of the substrate and the onset of multimode behavior. In particular, we show that the directional radiatiave $\beta$ factor is dominated by emission into high index substrates and explain how the $\beta$ factors and non-radiative quenching depend on the underlying mode properties. We also study the generalized Purcell factors and explore the role of gap size and substrate in detail. These rich modal features are essential to understand for future applications such as sensing, lasing, and quantum information processing, for example in the design of efficient single photon emitters.

We report a combined scanning tunneling microscopy and x-ray magnetic circular dichroism study to investigate the structural properties and magnetic behavior of a Co ultrathin film composed of dimer nanolines. These Co nanolines, ∼6 nm in length, are grown on a Si nanotemplate composed of nanoribbons self-organized on Ag(110). The first two Co layers present a weak magnetic response while upper Co layers exhibit an enhanced magnetization. Orbital and spin moments are experimentally determined. We show that an in-plane magnetization is favored and the magnetic anisotropy energy associated with the directions parallel and perpendicular to the nanolines are measured. The Co ultrathin film is shown to behave as a superparamagnetic system composed of one-dimensional segments containing each ∼170 ferromagnetically coupled Co atoms, with a blocking temperature estimated to be between 20 and 40 K. Our set of experiments allows for a comprehensive description of the magnetic behavior of the Co nanoline ultrathin film grown on a functionalized metallic substrate.

We introduce an adiabatic transfer protocol for spin states in large quantum dot arrays that is based on time-dependent modulation of the Heisenberg exchange interaction in the presence of a magnetic field gradient. We refer to this protocol as spin-CTAP (coherent transport by adiabatic passage) in analogy to a related protocol developed for charge-state transfer in quantum dot arrays. The insensitivity of this adiabatic protocol to pulse imperfections has potential advantages for reading out extended spin qubit arrays. When the static exchange interaction varies across the array, a quantum-controlled version of spin-CTAP is possible, where the transfer process is conditional on the spin states in the middle of the array. This conditional operation can be used to generate $N$-qubit entangled GHZ states. Using a realistic noise model, we analyze the robustness of the spin-CTAP operations and find that high-fidelity ($>95\%$) spin eigenstate transfer and GHZ state preparation is feasible in current devices.

One-dimensional (1D) quantum wires, which are functionalized by magnetic ad-atoms, can host ballistic helical transport. Helicity protects transport from an undesirable influence of material imperfections, and it makes the magnetically doped wire a very promising element for nanoelectronics and spintronics. However, fabricating purely 1D conductors is experimentally very challenging and not always feasible. In this paper, we show that the protected helical transport can exist even in quasi-1D wires. We model the quasi-1D magnetically doped wire as two coupled dense 1D Kondo chains. Each chain consists of itinerant electrons interacting with localized quantum magnetic moments—Kondo impurities. We have analyzed the regimes of weak, intermediate, and strong interchain coupling, and we found conditions necessary for the origin of the aforementioned protected transport. Our results may pave the way for experimental realizations of helical states in magnetically doped wires.

The topological properties of a material's electronic structure are encoded in its Berry curvature, a quantity which is intimately related to the transverse electrical conductivity. In transition metal dichalcogenides with broken inversion symmetry, the nonzero Berry curvature results in a valley Hall effect. In this Rapid Communication we identify a previously unrecognized consequence of Berry curvature in these materials: an electric-field-induced change in the electrons' charge density orientation. We use first-principles calculations to show that measurements of the electric-field-induced change in the charge density or local density of states in ${\mathrm{MoS}}_2$ can be used to measure its energy-dependent valley and orbital Hall conductivity.

We study finite-temperature properties of the Kondo effect in a carbon nanotube (CNT) quantum dot using the Wilson numerical renormalization group (NRG). In the absence of magnetic fields, four degenerate energy levels of the CNT consisting of spin and orbital degrees of freedom give rise to the SU(4) Kondo effect. We revisit the universal scaling behavior of the SU(4) conductance for quarter- and half-filling in a wide temperature range. We find that the filling dependence of the universal scaling behavior at low temperatures $T$ can be explained clearly with an extended Fermi-liquid theory. This theory clarifies that a $T^2$ coefficient of conductance becomes zero at quarter-filling, whereas the coefficient at half-filling is finite. We also study a field-induced crossover from the SU(4) to SU(2) Kondo state observed at the half-filled CNT dot. The crossover is caused by the matching of the spin and orbital Zeeman splittings, which lock two levels among the four at the Fermi level even in magnetic fields $B$. We find that the conductance shows the SU(4) scaling behavior at ${\mu }_{B}B<k_B{T}_K^{\mathrm{SU}\left(4\right)}$ and it exhibits the SU(2) universality at ${\mu }_{B}B\gg k_B{T}_K^{\mathrm{SU}\left(4\right)}$, where $T_K^{\mathrm{SU}\left(4\right)}$ is the SU(4) Kondo temperature. To clarify how the excited states evolve along the SU(4) to SU(2) crossover, we also calculate the spectral function. The results show that the Kondo resonance width of the two states locked at the Fermi level becomes sharper with increasing fields. The spectral peaks of the other two levels moving away from the Fermi level merge with atomic limit peaks for ${\mu }_{B}B\gtrsim k_B{T}_K^{\mathrm{SU}\left(4\right)}$.

In order to simulate open quantum systems, many approaches (such as Hamiltonian-based solvers in dynamical mean-field theory) aim for a reproduction of a desired environment spectral density in terms of a discrete set of bath states, mimicking the open system as a larger closed problem. Existing strategies to find a compressed representation of the environment for this purpose can be numerically demanding, or lack the compactness and systematic improvability required for an accurate description of the system propagator. We propose a method in which bath orbitals are constructed explicitly by an algebraic construction based on the Schmidt decomposition of response functions, efficiently and systematically compressing the description of the full environment. These resulting bath orbitals are designed to directly reproduce the system Green's function, not hybridization, which allows for consideration of the relevant system energy scales. This results in an accurate and efficient truncation of the environment, with applications in a wide range of numerical simulations of open quantum systems.

We demonstrate a giant enhancement of the transverse magneto-optical Kerr effect. In contrast to conventional magnetoplasmonic structures, we exploit surface plasmon resonances (SPRs) excited along the surface of a ferromagnetic substrate on which a uniaxial $\varepsilon$-near-zero (ENZ) metamaterial is grown. In this design, bulky prism couplers are not required and SPR sensors can be produced in integrated, miniaturized systems. We also obtained the analytical expression for the ENZ-SPR phase-matching condition, which can be used for the straightforward design of plasmonic and magnetoplasmonic devices.

In this paper, we predict two-dimensional transition metal boride $\mathrm{Ti}{\mathrm{B}}_2{\mathrm{C}}_2$ and $\mathrm{Hf}{\mathrm{B}}_2{\mathrm{C}}_2$ nanosheets, which exhibit favorable mechanical and thermal properties. Young's moduli of $\mathrm{Ti}{\mathrm{B}}_2{\mathrm{C}}_2$ and $\mathrm{Hf}{\mathrm{B}}_2{\mathrm{C}}_2$ are 137.8 and 128.9 N/m, respectively. Both nanosheets could sustain up to 500 K based on our ab initio molecular dynamics results. In addition, both nanosheets are semimetallic, exhibiting 12 Dirac cones in the first Brillouin zone, six pairs of which form compensated electron-hole pockets. Under different types of external strains, both $\mathrm{Ti}{\mathrm{B}}_2{\mathrm{C}}_2$ and $\mathrm{Hf}{\mathrm{B}}_2{\mathrm{C}}_2$ are robust, and the Dirac cones could be tuned to be anisotropic. We propose that the multiple Dirac cones are induced by a combination of the $p-d$ electron-counting rule and bilayer stacking; to verify our opinion, we also predicted and proved that $T{\mathrm{B}}_2{\mathrm{Si}}_2$ ($T$ = Ti, Zr, Hf) are mechanical stable two-dimensional nanosheets with multiple Dirac cones based on phonon and electronic band structure calculations.

We investigate the impacts of combination of fermion-fermion interactions and impurity scatterings on the low-energy stabilities of two-dimensional asymmetric materials with a quadratic band-crossing point by virtue of the renormalization group that allows us to treat distinct sorts of physical ingredients on the same footing. The coupled flow evolutions of all interaction parameters which carry the central physical information are derived by taking into account one-loop corrections. Several intriguing results are manifestly extracted from these entangled evolutions. At first, we realize that the quadratic band touching structure is particularly robust once the fermionic couplings flow toward the Gaussian fixed point. Otherwise, it can either be stable or broken down against the impurity scattering in the vicinity of nontrivial fixed points. In addition, we figure out two parameters $\eta$ and $\lambda$ that measure rotational and particle-hole asymmetries are closely energy dependent and exhibit considerably abundant behaviors depending upon the fates of fermion-fermion couplings and different types of impurities. Incidentally, as both $\eta$ and $\lambda$ can be remarkably increased or heavily reduced in the low-energy regime, an asymmetric system under certain restricted conditions exhibits an interesting phenomenon in which transitions either from rotational or particle-hole asymmetry to symmetric situation would be activated.

The Talbot effect has been known in linear optics since the 19th century and has found various technological applications. In this paper, with the help of micromagnetic simulations, we demonstrate the self-imaging phenomenon for spin waves in a thin, out-of-plane and in-plane magnetized ferromagnetic film whose propagation is described by the Landau-Lifshitz nonlinear equation. We show that the main features of the obtained Talbot carpets for spin waves can be described, to a large extent, by the approximate analytical formulas yielded by the general analysis of the wave phenomena. Our results indicate a route to a feasible experimental realization of the Talbot effect at low and high frequencies and offer interesting effects and possible applications in magnonics.

For noncollinear antiferromagnetic metals, magnon spectra display nontrivial multiband structure in which both direction and magnitude of the angular momenta of magnons are momentum dependent. We study the roles of these magnons on the spin transport properties by taking into account the momentum and angular momentum transfer between conduction electrons and magnons. We have calculated spin conductivity tensor by using the coupled Boltzmann equations for the electron spin and magnon, and we show that the unpolarized electron current driven by an electric field can efficiently induce a magnon spin current. The temperature dependence of the magnon spin conductivity is also calculated.

We carried out inelastic neutron scattering to study the spin-orbit (SO) exciton in a single crystal sample of ${\mathrm{CoTiO}}_3$ as a function of temperature. ${\mathrm{CoTiO}}_3$ is a honeycomb magnet with dominant $XY$-type magnetic interaction and an $A$-type antiferromagnetic order below $T_N\approx 38$ K. We found that the SO exciton becomes softer but acquires a larger bandwidth in the paramagnetic phase, compared to that in the magnetically ordered phase. Moreover, an additional mode is only observed in the intermediate temperature range, as the sample is warmed up above the lowest accessible temperature below $T_N$. Such an unusual temperature dependence observed in this material suggests that its ground states (an $S_{\mathrm{eff}}=\frac{1}{2}$ doublet) and excited states multiplets are strongly coupled and therefore cannot be treated independently, as often done in a pseudospin model. Our observations can be explained by a multilevel theory within random phase approximation that explicitly takes into account both the ground and excited multiplets. The success of our theory, originally developed for the rare-earth systems, highlights the similarity between magnetic excitations in $f$- and $d$-electron systems with strong spin-orbit coupling.

We study numerically the thermodynamic properties of the spin nematic phases in a magnetic field in the spin-1 bilinear-biquadratic model. When the field is applied, the phase transition temperature initially goes up and then decreases rapidly toward zero, which is detected by the peak shift in the specific heat. The underlying mechanism of the reentrant behavior is the entropic effect. In a weak field the high temperature paramagnetic phase rapidly loses its entropy while the ferroquadrupolar nematic phase remains robust by modifying the shape of the ferroquadrupolar moment. This feature serves as a fingerprint of generic ferroquadrupolar phases, while it is not observed for the case of antiferroquadrupoles.