We explore the electrical and magnetic properties of a fractal assembly of Josephson junctions with transparent interfaces. For this purpose, we employ an $\mathrm{Mg}/\mathrm{MgO}/\mathrm{Mg}{\mathrm{B}}_2$ nanocomposite with ∼16 vol. % of $\mathrm{Mg}{\mathrm{B}}_2$ nanograins, which are distributed in a fractal manner in the normal matrix. Irrespective of the low volume fraction of $\mathrm{Mg}{\mathrm{B}}_2$ nanograins, the nanocomposite behaves as a bulk-like superconductor, i.e., zero resistivity, perfect diamagnetism, and strong vortex pinning. Thus, a global Josephson phase coherence is achieved in the nanocomposite. The lower ($H_{\mathrm{c}1\mathrm{J}}$) and higher ($H_{\mathrm{c}2\mathrm{J}}$) critical fields of the Josephson network are exceptionally high ($H_{\mathrm{c}1\mathrm{J}}=96\mathrm{Oe}$ and $H_{\mathrm{c}2\mathrm{J}}=83.5\mathrm{kOe}$) as compared to those reported previously for granular superconductors. This will give an example of robust macroscopic superconducting coherence derived from long-range proximity coupling among fractally distributed superconducting nanograins through quantum interference of Andreev quasiparticles. Transverse-field muon spin rotation measurements reveal that the mean internal field in the superconducting mixed state increases with decreasing temperature below which the Josephson phase coherence sets in, opposite to the diamagnetic response observed in magnetization measurements. This unusual behavior implies a highly disordered and fluctuating nature of the Josephson vortices in the present superconducting nanocomposite.

Carbon phosphide (CP) monolayer, a hybrid of graphene and phosphorene that simultaneously preserves their high electrical mobility, finite band gap, and air stability, has been successfully synthesized in a recent experiment. In this work, we study the electronic and transport properties of CP nanoribbons in $\alpha$-phase with different edge configurations using first-principle density functional theory simulation. We find that the electronic properties of the CP nanoribbon exhibit contrasting behaviors depending on the edge termination configurations. In the presence of hydrogen edge passivation, the nanoribbon mimics black phosphorus nanoribbons with field-effect-tunable band gap. Conversely, for a bare edge terminated by a phosphorus atom, the nanoribbon becomes graphene-like, exhibiting large spin splitting in the ferromagnetic state and can be tuned into a half metal under an external transverse electric field in the antiferromagnetic state. Intriguingly, when the external transverse electric field exceeds a critical value, the charge transport channel becomes strongly localized to only one edge, and the edge localization can be tuned by an external electric field. Leveraging on the unusual spin-resolved transport properties of the CP nanoribbon, we demonstrate the operation of a bipolar spin filter with exceptional spin polarization efficiency approaching 100%. Our findings reveal the potential of the CP nanoribbon as a spintronic material that fuses the strengths of both graphene and phosphorene.

Magneto-optical materials represent a type of materials that intrinsically or extrinsically lack time-reversal symmetry and exhibit the nonreciprocal magneto-optical effects, which have been extended to two-dimensional layered materials recently. However, the corresponding magneto-optical investigations have thus far been limited to two-dimensional layered inorganic materials. Here we theoretically report the generation and manipulation of the magneto-optical effects in two-dimensional layered organic materials. It is found that monolayer hexagonal organometallic lattice intrinsically supports the nonzero Faraday rotation angle due to the joint contributions from spin-orbit coupling as well as its inherent ferromagnetism. In addition, its evolutions of the band structures and Berry curvatures induced by an external electric field grant us the controllable magneto-optical effects. The nontrivial magneto-optical effects of two-dimensional layered organic materials, in conjunction with their electric-field control, considerably endow the available organic magneto-optical candidates beyond what are currently used in the present magneto-optical fields.

Systems with multistable equilibrium states are of tremendous importance in information science to conceive logic gates. Here we predict that simple phase-transition oscillators driven by near-field heat exchanges have a bistable thermomechanical behavior around their critical temperature, opening the way to a possible Boolean treatment of information from heat flux at microscale.

We demonstrate an algebraic construction of frequency-dependent bath orbitals which can be used in a robust and rigorously self-consistent DMFT-like embedding method, here called $\omega$-DMFT, suitable for use with Hamiltonian-based impurity solvers. These bath orbitals are designed to exactly reproduce the hybridization of the impurity to its environment, while allowing for a systematic expansion of this bath space as impurity interactions couple frequency points. In this way, the difficult nonlinear fit of bath parameters necessary for many Hamiltonian-formulation impurity solvers in DMFT is avoided, while the introduction of frequency dependence in this bath space is shown to allow for more compact bath sizes. This has significant potential use with a number of new, emerging Hamiltonian solvers which allow for the embedding of large impurity spaces within a DMFT framework. We present results of the $\omega$-DMFT approach for the Hubbard model on the Bethe lattice, a one-dimensional chain, and the two-dimensional square lattice, which show excellent agreement with standard DMFT results, with fewer bath orbitals and more compact support for the hybridization representation in the key impurity model of the method.

We investigate the short-time evolution of the half filled one-dimensional extended Hubbard model in the strong-coupling regime, driven by a transient laser pump. Combining twisted boundary conditions with the time-dependent Lanczos technique, we obtain snapshots of the single-particle spectral function with high momentum resolution. The analysis of the oscillations of the spectral function shows that its characteristic frequencies are consistent with the magnitudes of the optical gap. Furthermore, we examine the time-evolving spectral structure in the charge-density-wave phase in detail and find that one of the bands in the single-particle spectrum originates from the photoinduced bond-order background.

The strongly coupled electron liquid provides a unique opportunity to study the complex interplay of strong coupling with quantum degeneracy effects and thermal excitations. To this end, we carry out extensive ab initio path integral Monte Carlo (PIMC) simulations to compute the static structure factor, interaction energy, density response function, and the corresponding static local field correction in the range of $20\le r_s\le 100$ and $0.5\le \theta \le 4$. We subsequently compare these data to several dielectric approximations and find that different schemes are capable to reproduce different features of the PIMC results at certain parameters. Moreover, we provide a comprehensive data table of interaction energies and compare those to two recent parametrizations of the exchange-correlation free energy, where they are available. Finally, we briefly touch upon the possibility of a charge-density wave. The present study is complementary to previous investigations of the uniform electron gas in the warm dense matter regime and, thus, further completes our current picture of this fundamental model system at finite temperature. All PIMC data are available online.

Degeneracy points and exceptional points embedded in the energy band are distinct because of their topological features. We report a hybrid exceptional point formed through merging two ordinary exceptional points with opposite chiralities that were created from the type-III Dirac points emerging from a flat band. The hybrid exceptional point is induced by the destructive interference at the proper match between the non-Hermiticity and the synthetic magnetic flux. The degeneracy points and different types of exceptional points are distinguishable by their topological features of the global geometric phase accompanied by the scaling exponent of phase rigidity. Our findings not only pave the way for creating, moving, and merging exceptional points but also shed light on future investigations of non-Hermitian topological phases.

It has long been controversial whether or not electrochromism with the color change due to applied voltage is caused by small polarons. Recently, the coloration efficiency of Ca-doped $\mathrm{BiFe}{\mathrm{O}}_3$ (CBFO) was reported to be more prominent over a wider energy range than that of a conventional oxide. However, only an interpretation based on oxygen vacancy (${\mathrm{V}}_{\mathrm{O}}$), which cannot account for the wide energy dependence of absorption, has been attempted. Here, we show that using first-principles hybrid-functional calculations, hole-trap centers in CBFO can be produced by a variety of small hole polarons and bipolarons around substitutional Ca ($\mathrm{C}{\mathrm{a}}_{\mathrm{Bi}}$) and ultimately play a significant role of color change. The polaron formation is attributed to the fact that up to two excess holes are trapped to enhance the Bi–O $sp\sigma$ bond. It is consistent with the experimental results that under the electroforming condition, electrochromism occurs well in the $p$-type region when CBFO is separated into two discrete regions relatively rich in ${\mathrm{V}}_{\mathrm{O}}$ ($n$ type) and $\mathrm{C}{\mathrm{a}}_{\mathrm{Bi}}$ ($p$ type). We, therefore, propose that identifying the diversity of the carrier-trap polarons provides a crucial clue to a deeper understanding of the origin of electrochromism.

Many-body localized systems in which interactions and disorder come together defy the expectations of quantum statistical mechanics: In contrast to ergodic systems, they do not thermalize when undergoing nonequilibrium dynamics. What is less clear, however, is how topological features interplay with many-body localized phases as well as the nature of the transition between a topological and a trivial state within the latter. In this paper, we numerically address these questions using a combination of extensive tensor network calculations, specifically density matrix renormalization-group-X, as well as exact diagonalization, leading to a comprehensive characterization of Hamiltonian spectra and eigenstate entanglement properties.

Metastable face-centered-cubic $\mathrm{F}{\mathrm{e}}_{78}\mathrm{N}{\mathrm{i}}_{22}$ thin films are excellent candidates for focused ion beam direct writing of magnonic structures due to their favorable magnetic properties after ion-beam-induced transformation. The focused ion beam transforms the originally nonmagnetic fcc phase into the ferromagnetic bcc phase with additional control over the direction of uniaxial magnetic in-plane anisotropy and saturation magnetization. Local magnetic anisotropy direction control eliminates the need for external magnetic fields, paving the way towards complex magnonic circuits with waveguides pointing in different directions. In the present study, we show that the magnetocrystalline anisotropy in transformed areas is strong enough to stabilize the magnetization in the direction perpendicular to the long axis of narrow waveguides. Therefore, it is possible to propagate spin waves in these waveguides in the favorable Damon-Eshbach geometry without the presence of any external magnetic field. Phase-resolved microfocused Brillouin light scattering yields the dispersion relation of these waveguides in zero as well as in nonzero external magnetic fields.

We present an $S=1/2$ antiferromagnetic (AF) honeycomb lattice composed of a verdazyl-based complex $\left[\mathrm{Zn}{\left(\mathrm{hfac}\right)}_2\right][o$-Py-V-(4-${\mathrm{F})}_2]$. Ab initio molecular orbital calculations indicate that two AF interactions and a ferromagnetic interaction lead to the formation of a honeycomb lattice. We explain the magnetic susceptibility, magnetization curve, and magnetic specific heat based on the $S$ = 1/2 Heisenberg AF honeycomb lattice using the quantum Monte Carlo method. Further, by considering the distortion effect on the magnetic behavior, we confirm that the dimer-like lattice distortion in the present compound is small enough not to affect the intrinsic two-dimensional properties of the honeycomb lattice. Our numerical study on the distorted honeycomb lattice reveals a quantum phase transition from a disordered dimer phase to an AF ordered phase at a critical distortion ratio.

We study the current-voltage characteristic of narrow superconducting strips in the gapless regime near the critical temperature in the framework of the Ginzburg-Landau model. Our focus is on its instabilities occurring at high current biases. The latter are consequences of dynamical states with periodic phase-slip events in space and time. We analyze their structure and derive the value of the reentrance current at the onset of the instability of the normal state. It is expressed in terms of the kinetic coefficient of the time-dependent Ginzburg-Landau equation and calculated numerically.

Ni-Mn based ternary Heusler compounds have drawn attention lately as significant magnetocaloric effects in some of them have been observed. Substitution of Ni and Mn by other $3d$-transition metals in controlled quantity has turned out to be successful in enhancing the effect and bring the operational temperatures closer to room temperature. Using density functional theory calculations, in this work, we have systematically explored the roles of various factors such as site occupancies, magnetic interactions, and compositions associated with the constituents of Mn-excess ${\mathrm{Ni}}_2\mathrm{MnSb}$ Heusler compounds upon substitution of Ni and/or Mn by $3d$-transition metals Fe, Co, and Cu. Our calculations unveiled the physics behind the variations of physical properties associated with the magnetocaloric effects, and thus interpreted the available experimental results successfully. The work also provided important information on the compounds and the composition ranges where significant magnetocaloric effects may be realized, and further experimental investigations need to be done.

Time-resolved x-ray diffraction was used to examine the phase evolution of polycrystalline Mg shocked along the principal Hugoniot to states that span multiple phase boundaries into the liquid. The diffraction data indicate that the hcp-bcc phase boundary lies above 27 GPa, with the hcp-bcc transition occurring within nanoseconds of loading. Experiments at 55 GPa reveal a mixture of bcc and liquid, indicating incipient melt occurring 10–15 GPa lower than previously reported, with complete melting observed at 63 GPa.

By recasting the definition of the dielectric constants in terms of currents, as well as using atomistic simulations and analytical derivations, we show that the dielectric permittivity can be negative at an ultrashort timescale, under perfect screening conditions and for very different materials and switching mechanisms, in line with recent experiments and modelings. In particular, we found that this effect can be due to a previously overlooked phenomenon of postswitching polarization oscillations. We also derived practical analytical formulas that can be experimentally checked.

Heterostructures made of strongly correlated oxides host various fundamentally interesting and potentially useful emergent phenomena. ${\left(\mathrm{LaMn}{\mathrm{O}}_3\right)}_n/{{\left(\mathrm{SrMn}{\mathrm{O}}_3\right)}_n}_{-1}$ superlattices that consist of an $A$-type antiferromagnetic insulator $\mathrm{LaMn}{\mathrm{O}}_3$ and a $G$-type antiferromagnetic insulator $\mathrm{SrMn}{\mathrm{O}}_3$ were investigated in this work. Several very intriguing effects were observed in such superlattices that include (1) the coexistence of a strong exchange bias effect and a giant vertical magnetization shift in superlattices with intermediate periods, (2) an insulator-to-metal transition associated with a change in the superlattice thickness, and (3) a large nontrivial negative magnetoresistance around the insulator-to-metal transition. To understand these phenomena, microscopic preferential orbital occupancy in different superlattices was studied through measurements of x-ray linear dichroism at Mn $L$ edges. This study facilitated the construction of a spin configuration model that takes into account the competition between interfacial ferromagnetism and underlying canted antiferromagnetism in the superlattices and can successfully explain the observed novel magnetic and transport properties. The phase transition and giant vertical magnetization shift phenomena observed in this work offer additional degrees of freedom for applications of antiferromagnetic insulator manganite-based superlattices, enabling novel device concepts.

We experimentally demonstrate coherent control of the nonlinear response of optical second harmonic generation in resonant nanostructures beyond the weak-field regime. Contrary to common perception, we show that maximizing the intensity of the pulse does not yield the strongest nonlinear power-law response. We show this effect emerges from the temporally asymmetric photoinduced response in a resonant mediated noninstantaneous interaction. We develop a novel theoretical approach which captures the photoinduced nonlinearities in resonant nanostructures beyond the two photon description and give an intuitive picture to the observed noninstantaneous phenomena.

The layered transition metal dichalcogenides have emerged as valuable platforms to study the challenging problem of metal-insulator transition in two dimensions. It was demonstrated that multilayer $\mathrm{Mo}{\mathrm{S}}_2$ exhibits clearly distinctive metallic and insulating behaviors in conductivity in response to both temperature and the electric field. Here, we report on the scaling analyses of conductivity for the electric field in addition to the temperature, which is performed with the consideration of electron-electron interactions for multilayer $\mathrm{Mo}{\mathrm{S}}_2$. Based on the analysis of hot electron effects in the electric field, we find that scaling for the electric field is relevant for the metallic phase in the high-field regime, enabling one to extract the dynamical critical exponent $z$ close to 1. This result supports that the metal-insulator transition in multilayer $\mathrm{Mo}{\mathrm{S}}_2$ is a true quantum critical phenomenon, in which strong interactions induce the transition.