Glassy freezing dynamics was investigated in ${\mathrm{BaZr}}_{0.5}{\mathrm{Ti}}_{0.5}{\mathrm{O}}_3$ (BZT50) ceramic samples by means of dielectric spectroscopy in the frequency range 0.001 Hz–1 MHz at temperatures $10<T<300$ K. From measurements of the quasistatic dielectric polarization in bias electric fields up to $\sim 28$ kV/cm it has been found that a ferroelectric state cannot be induced, in contrast to the case of typical relaxors. This suggests that—at least for the above field amplitudes—BZT50 effectively behaves as a dipolar glass, which can be characterized by a negative value of the static third order nonlinear permittivity. The relaxation spectrum has been analyzed by means of the frequency-temperature plot, which shows that the longest relaxation time obeys the Vogel-Fulcher relation $\tau ={\tau }_0\exp [E_0/(T-T_0)]$ with the freezing temperature of 48.1 K, whereas the corresponding value for the shortest relaxation time is $\sim 0$ K, implying an Arrhenius type behavior. By applying a standard expression for the static linear permittivity of dipolar glasses and/or relaxors the value of the Edwards-Anderson order parameter $q\left(T\right)$ has been evaluated. It is further shown that $q\left(T\right)$ can be described by the spherical random bond-random field model of relaxors.

Amorphous solids yield in strain-controlled protocols at a critical value of the strain. For larger strains the stress and energy display a generic complex serrated signal with elastic segments punctuated by sharp energy and stress plastic drops having a wide range of magnitudes. Here we provide a theory of the scaling properties of such serrated signals taking into account the system-size dependence. We show that the statistics are not homogeneous: they separate sharply to a regime of “small” and “large” drops, each endowed with its own scaling properties. A scaling theory is first derived solely by data analysis, showing a somewhat complex picture. But after considering the physical interpretation one discovers that the scaling behavior and the scaling exponents are in fact very simple and universal.

The superconducting and magnetic properties of single crystalline (${\mathrm{Li}}_{0.84}{\mathrm{Fe}}_{0.16}$)${\mathrm{OHFe}}_{0.98}\mathrm{Se}$ with the transition temperature $T_c\simeq 40$ K were studied by means of muon-spin rotation ($\mu \mathrm{SR}$). The zero-field and field-shift $\mu \mathrm{SR}$ experiments confirm the homogeneity of the sample and the antiferromagnetic ordering within the (${\mathrm{Li}}_{0.84}{\mathrm{Fe}}_{0.16}$)OH layers below $T_m\simeq 10$ K. The temperature dependence of the in-plane component of the magnetic penetration depth (${\lambda }_{ab}$) was found to be consistent with gap opening within the superconducting FeSe planes, and it is well described within either the single $s\text{−}\mathrm{wave}$ gap or two $s\text{−}\mathrm{wave}$ gaps scenario. The opening of an additional small superconducting gap within the insulating (${\mathrm{Li}}_{1-x}{\mathrm{Fe}}_x$)OH layers was detected from the temperature evolution of the out-of plane component of the magnetic penetration ${\lambda }_c^{-2}\left(T\right)$. The superconductivity in (${\mathrm{Li}}_{0.84}{\mathrm{Fe}}_{0.16}$)OH is most probably induced by the proximity to the superconducting FeSe layers.

We study layered systems and heterostructures of $s$-wave superconductors by means of a suitable generalization of dynamical mean-field theory. In order to reduce the computational effort, we consider an embedding scheme in which a relatively small number of active layers is embedded in an effective potential accounting for the effect of the rest of the system. We introduce a feedback of the active layers on the embedding potential that improves on previous approaches and essentially eliminates the effects of the finiteness of the active slab allowing for cheap computation of very large systems. We extend the method to the superconducting state, and we benchmark the approach by means of simple paradigmatic examples showing some examples on how an interface affects the superconducting properties. As examples, we show that superconductivity can penetrate from an intermediate coupling superconductor into a weaker coupling one for around ten layers, and that the first two layers of a system with repulsive interaction can turn superconducting by proximity effects even when charge redistribution is inhibited.

Detailed structural and magnetotransport properties of monophosphate tungsten bronze ${\text{K}}_x\left({\text{PO}}_2\right){}_4\left({\text{WO}}_3\right){}_8$ single crystals are reported. Both galvanomagnetic and thermal properties are shown to be consistent with a charge density wave electronic transition due to hidden nesting of the quasi-1D portion of the Fermi surface. We also observe the enhancement of electronic anisotropy due to reconstruction of the Fermi surface at the Peierls transition. The resistivity presents a thermal hysteresis suggesting a first-order nature characteristic of a strong-coupling scenario. However, other measurements such as the change of carrier density demonstrate a second-order Peierls scenario with weak-coupling features. We suggest that the structural transition driven by the residual strain in the K-P-O environment is responsible for the resistivity hysteresis and modifies the Fermi surface which then helps the rise to the second-order Peierls instability.

The emission of an electron pair upon single-photon absorption requires a finite electron-electron interaction. Therefore, double photoemission is a particularly sensitive tool to study the electron correlation in matter. This is supported by a recent theoretical work which predicts that the pair intensity is a direct reflection of the correlation strength. In order to explore the validity of this statement, we performed a study on a variety of materials. Among them are noble metals, transition metals, and insulators. The latter include transition metal oxides such as CoO and NiO which are also termed highly correlated. We find an increased pair emission rate of NiO and CoO compared to the metals which reach a factor of 10. We also discovered that an increase of the coincidence intensity is accompanied by an increase in the singles count rate. This demonstrates that the electron pair emission is an efficient process at surfaces contributing up to $15\%$ to the single-electron emission in double photoemission. We performed also electron pair emission studies upon primary electron impact and find similar intensity relations.

We have made ${}^{53}\mathrm{Cr}$ NMR measurements on polycrystalline and single-crystalline film samples to study the local electronic state of a half-metallic ferromagnet ${\mathrm{CrO}}_2$ which has the rutile structure with one crystallographically equivalent Cr site. We observe two kinds of ${}^{53}\mathrm{Cr}$ NMR spectra in the ferromagnetic state of both the samples. An analysis on the hyperfine field shows the presence of two Cr sites with different orbital occupancies, suggesting that a local orbital order takes place with breaking the local symmetry in the rutile structure. This may be ascribed to the negative charge transfer between chromium and oxygen ions.

Oxygen vacancy $\left(V_{\mathrm{O}}\right)$ is a common native point defect that plays crucial roles in determining the physical and chemical properties of metal oxides such as ZnO. However, fundamental understanding of $V_{\mathrm{O}}$ is still very sparse. Specifically, whether $V_{\mathrm{O}}$ is mainly responsible for the $n$-type conductivity in ZnO has been still unsettled in the past 50 years. Here, we report on a study of oxygen self-diffusion by conceiving and growing oxygen-isotope ZnO heterostructures with delicately controlled chemical potential and Fermi level. The diffusion process is found to be predominantly mediated by $V_{\mathrm{O}}$. We further demonstrate that, in contrast to the general belief of their neutral attribute, the oxygen vacancies in ZnO are actually $+2$ charged and thus responsible for the unintentional $n$-type conductivity as well as the nonstoichiometry of ZnO. The methodology can be extended to study oxygen-related point defects and their energetics in other technologically important oxide materials.

We reexamine the effect of long-range Coulomb interactions on the quasiparticle velocity in graphene. Using a nonperturbative functional renormalization group approach with partial bosonization in the forward scattering channel and momentum transfer cutoff scheme, we calculate the quasiparticle velocity, $v\left(k\right)$, and the quasiparticle residue, $Z$, with frequency-dependent polarization. One of our most striking results is that $v\left(k\right)\propto ln[C_k\left(\alpha \right)/k]$ where the momentum- and interaction-dependent cutoff scale $C_k\left(\alpha \right)$ vanishes logarithmically for $k\to 0$. Here $k$ is measured with respect to one of the charge neutrality (Dirac) points and $\alpha =2.2$ is the strength of dimensionless bare interaction. Moreover, we also demonstrate that the so-obtained multilogarithmic singularity is reconcilable with the perturbative expansion of $v\left(k\right)$ in powers of the bare interaction.

We analyze the nature of the single-particle states, away from the Dirac point in the presence of long-range charge impurities in a tight-binding model for electrons on a two-dimensional honeycomb lattice which is of direct relevance for graphene. For a disorder potential $V\left(\vec{r}\right)=V_{0}exp(-|\vec{r}-{\vec{r}}_{\mathrm{imp}}{|}^2/{\xi }^2)$, we demonstrate that not only the Dirac state but all the single-particle states remain extended for weak-enough disorder. Based on our numerical calculations of inverse participation ratio, dc conductivity, diffusion coefficient, and the localization length from time evolution dynamics of the wave packet, we show that the threshold $V_{\mathrm{th}}$ required to localize a single-particle state of energy $E\left(\vec{k}\right)$ is minimum for the states near the band edge and is maximum for states near the band center, implying a mobility edge starting from the band edge for weak disorder and moving towards the band center as the disorder strength increases. This can be explained in terms of the low-energy Hamiltonian at any point $\vec{k}$ which has the same nature as that at the Dirac point. From the nature of the eigenfunctions, it follows that a weak long-range impurity will cause weak antilocalization effects, which can be suppressed, giving localization if the strength of impurities is sufficiently large to cause intervalley scattering. The intervalley spacing $2|\vec{k}|$ increases as one moves in from the band edge towards the band center, which is reflected in the behavior of $V_{\mathrm{th}}$ and the mobility edge.

We show that electromagnetic plane waves can be fully “teleported” through thin, nearly fully reflective sheets, assisted by a pair of parity-time-symmetric lossy and active sheets in front and behind the screen. The proposed structure is able to almost perfectly absorb incident waves over a wide range of frequency and incidence angles, while waves having a specific frequency and incidence angle are replicated behind the structure in synchronization with the input signal. It is shown that the proposed structure can be designed to teleport waves at any desired frequency and incidence angle. Furthermore, we generalize the proposed concept to the case of teleportation of electromagnetic waves over electrically long distances, enabling full absorption at one surface and the synthesis of the same signal at another point located electrically far away from the first surface. The physical principle behind this selective teleportation is discussed, and similarities and differences with tunneling and cloaking concepts based on $\mathcal{PT}$ symmetry are investigated. From the application point of view, the proposed structure works as an extremely selective filter, both in frequency and spatial domains.

By using angle-resolved photoemission spectroscopy combined with first-principles calculations, we reveal that the topmost unit cell of ZrSnTe crystal hosts two-dimensional (2D) electronic bands of the topological insulator (TI) state, although such a TI state is defined with a curved Fermi level instead of a global band gap. Furthermore, we find that by modifying the dangling bonds on the surface through hydrogenation, this 2D band structure can be manipulated so that the expected global energy gap is most likely to be realized. This facilitates the practical applications of 2D TI in heterostructural devices and those with surface decoration and coverage. Since ZrSnTe belongs to a large family of compounds having the similar crystal and band structures, our findings shed light on identifying more 2D TI candidates and superconductor-TI heterojunctions supporting topological superconductors.

The influence of partial coherence on the image reconstruction in ptychography is analyzed, and a simple method is proposed to reconstruct a clear image for the weakly scattering object with partially coherent illumination. It is demonstrated numerically and experimentally that by illuminating a weakly scattering object with a divergent radiation beam, and doing the reconstruction only from the bright-field diffraction data, the mathematical ambiguity and corresponding reconstruction errors related to the partial coherency can be remarkably suppressed, thus clear reconstructed images can be generated even under seriously incoherent illumination.

Topological insulators are characterized by an inverted band structure in the bulk and metallic surface states on the surface. In LaBi, a semimetal with a band inversion equivalent to a topological insulator, we observe surface-state-like behavior in the magnetoresistance. The electrons responsible for this pseudo-two-dimensional transport, however, originate from the bulk states rather topological surface states, which is witnessed by the angle-dependent quantum oscillations of the magnetoresistance and ab initio calculations. As a consequence, the magnetoresistance exhibits strong anisotropy with large amplitude $(\sim {10}^5\%)$.

Varying the quantum-well width in an HgTe/CdTe heterostructure allows for realizing normal and inverted semiconducting band structures, making it a prototypical system to study two-dimensional (2D) topological-insulator behavior. We have calculated the zero-temperature thermodynamic density of states $D_{\mathrm{T}}$ for the electron-doped situation in both regimes, treating interactions within the Hartree-Fock approximation. A distinctively different behavior for the density dependence of $D_{\mathrm{T}}$ is revealed in the inverted and normal cases, making it possible to detect the system's topological phase through measurement of macroscopic observables, such as the quantum capacitance or electronic compressibility. Our results establish the 2D electron system in HgTe quantum wells as unique in terms of its collective electronic properties.

We suggest that all-photodesigned metamaterials, subwavelength custom patterns of photoexcited carriers on a semiconductor, can display an exotic extrinsic electromagnetic chirality in the terahertz (THz) frequency range. We consider a photoinduced pattern exhibiting one-dimensional geometrical chirality, i.e., its mirror image cannot be superposed onto itself by translations without rotations, and in the long wavelength limit we evaluate its bianisotropic response. The photoinduced extrinsic chirality turns out to be fully reconfigurable by recasting the optical illumination which supports the photoexcited carriers. The all-photodesigning technique represents a feasible, easy, and powerful method for achieving effective matter functionalization and, combined with the chiral asymmetry, it could be the platform for a new generation of reconfigurable devices for THz wave polarization manipulation.

First-principles calculations on monolayer 8-Pmmn borophene are reported to reveal unprecedented electronic properties in a two-dimensional material. Based on a Born effective charge analysis, 8-Pmmn borophene is the first single-element-based monolayered material exhibiting two sublattices with substantial ionic features. The observed Dirac cones are actually formed by the $p_z$ orbitals of one of the inequivalent sublattices composed of uniquely four atoms, yielding an underlying hexagonal network topologically equivalent to distorted graphene. A significant physical outcome of this effect includes the possibility of converting metallic 8-Pmmn borophene into an indirect band gap semiconductor by means of external shear stress. The stability of the strained structures are supported by a phonon frequency analysis. The Dirac cones are sensitive to the formation of vacancies only in the inequivalent sublattice electronically active at the Fermi level.

Inducing topological transitions by a time-periodic perturbation offers a route to controlling the properties of materials. Here, we show that the adiabatic preparation of a nontrivial state involves a selective population of edge states, due to exponentially small gaps preventing adiabaticity. We illustrate this by studying graphenelike ribbons with hopping's phases of slowly increasing amplitude, as, e.g., for a circularly polarized laser slowly turned on. The induced currents have large periodic oscillations, but flow solely at the edges upon time averaging, and can be controlled by focusing the laser on either edge. The bulk undergoes a nonequilibrium topological transition, as signaled by a local Hall conductivity, the Chern marker introduced by Bianco and Resta in equilibrium. The breakdown of this adiabatic picture in the presence of intraband resonances is discussed.

Motivated by recent experiments on the quantum-spin-liquid candidate material ${\mathrm{LiZn}}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$, we study a single-band extended Hubbard model on an anisotropic kagome lattice with the $\frac{1}{6}$ electron filling. Due to the partial filling of the lattice, the intersite repulsive interaction is necessary to generate Mott insulators, where electrons are localized in clusters rather than at lattice sites. It is shown that these cluster Mott insulators are generally U(1) quantum spin liquids with spinon Fermi surfaces. The nature of charge excitations in cluster Mott insulators can be quite different from conventional Mott insulator and we show that there exists a cluster Mott insulator where charge fluctuations around the hexagonal cluster induce a plaquette charge order (PCO). The spinon excitation spectrum in this spin-liquid cluster Mott insulator is reconstructed due to the PCO so that only $\frac{1}{3}$ of the total spinon excitations are magnetically active. Based on these results, we propose that the two Curie-Weiss regimes of the spin susceptibility in ${\mathrm{LiZn}}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$ may be explained by finite-temperature properties of the cluster Mott insulator with the PCO as well as fractionalized spinon excitations. Existing and possible future experiments on ${\mathrm{LiZn}}_2{\mathrm{Mo}}_3{\mathrm{O}}_8$, and other Mo-based cluster magnets are discussed in light of these theoretical predictions.