Superconductivity provides a canonical example of a quantum phase of matter. When superconducting islands are connected by Josephson junctions in a lattice, the low-temperature state of the system can map to the celebrated XY model and its associated universality classes. This has been used to experimentally implement realizations of Mott insulator and Berezinskii-Kosterlitz-Thouless transitions to vortex dynamics analogous to those in type-II superconductors. When an external magnetic field is added, the effective spins of the XY model become frustrated, leading to the formation of topological defects (vortices). Here, we observe the many-body dynamics of such an array, including frustration, via its coupling to a superconducting microwave cavity. We take the design of the transmon qubit, but replace the single junction between two antenna pads with the complete array. This allows us to probe the system at 10 mK with minimal self-heating by using weak coherent states at the single (microwave) photon level to probe the resonance frequency of the cavity. We observe signatures of an ordered vortex lattice at rational flux fillings of the array.

A multiscale approach including density functional theory (DFT) and atomistic kinetic Monte Carlo (AKMC) simulations is applied to investigate the diffusion of interstitial oxygen atoms in bcc Fe under the influence of substitutional foreign atoms (Al, Si, P, S, Ti, Cr, Mn, Ni, Y, Mo, and W). The substitutional atoms can be assumed to be immobile since their diffusion coefficient is much smaller than that of oxygen. First, jumps of oxygen in pure bcc Fe between first-, second-, and third-neighbor octahedral interstitial sites are investigated. It is found that the first-neighbor jump is most relevant, with the tetrahedral site as the saddle point. The second-neighbor jump consists of two consecutive first-neighbor jumps. The barrier for a direct third-neighbor jump is too high to be significant for the diffusion process. In the presence of substitutional atoms the most important migration paths are first-neighbor jumps between modified octahedral sites with modified tetrahedral sites as saddle points. Calculations show that Si, P, Ni, Mo, and W cause some modifications of the migration barriers of oxygen and their interaction with O is mainly repulsive. Al, Cr, and Mn have a significant influence on the barriers and they exhibit strong attractive interactions with O. The most important modification of the barriers is found for S, Ti, and Y where deep attractive states exist. Based on the migration energies obtained by DFT, AKMC simulations on a rigid lattice are employed to determine the diffusion coefficient of oxygen in a dilute iron alloy containing the different substitutional atoms. It is found that Si, P, Ni, Mo, and W have almost no influence on the diffusivity of O. The presence of Al, Cr, Mn, S, Ti, and Y causes a significant reduction of the mobility of oxygen. In these cases the temperature dependence of the oxygen diffusion coefficient shows considerable deviations from an Arrhenius law. These phenomena are discussed in detail by considering the occupation time for the different states. The present findings on the strong dependence on the kind of substitutional atoms change the picture of oxygen diffusion in dilute iron alloys substantially.

Magnetic domain walls are pinned strongly by abrupt changes in magnetic anisotropy. When driven into oscillation by a spin-polarized current, locally pinned domain walls can be exploited as tunable sources of short-wavelength spin waves. Here, we develop an analytical framework and discrete Heisenberg model to describe the static and dynamic properties of pinned domain walls with a head-to-tail magnetic structure. We focus on magnetic domain walls that are pinned by ${90}^{\circ }$ rotations of uniaxial magnetic anisotropy. Our model captures the domain wall response to a spin-transfer torque that is exerted by an electric current. Model predictions of the domain wall resonance frequency and its evolution with magnetic anisotropy strength and external magnetic field are compared to micromagnetic simulations.

Resonant elastic x-ray scattering (REXS) at the Eu $M_5$ edge reveals an antiferromagnetic structure in layered ${\mathrm{EuCd}}_2{\mathrm{Sb}}_2$ at temperatures below $T_{\mathrm{N}}=7.4$ K with a magnetic propagation vector of $(0,0,1/2)$ and spins in the basal plane. Magnetotransport and REXS measurements with an in-plane magnetic field show that features in the magnetoresistance are correlated with changes in the magnetic structure induced by the field. Ab initio electronic structure calculations predict that the observed spin structure gives rise to a gapped Dirac point close to the Fermi level with a gap of $\mathrm{\Delta }E\sim 0.01$ eV. The results of this study indicate that the Eu spins are coupled to conduction electron states near the Dirac point.

We theoretically investigate the Cooper-pair symmetry that can be realized in hole-doped monolayer ${\mathrm{MoS}}_2$ by solving linearized BCS gap equations in the three-orbital attractive Hubbard-like model in the presence of the atomic spin-orbit coupling. In hole-doped monolayer ${\mathrm{MoS}}_2$, both spin-orbit coupling and the multiorbital effects are more prominent than those of an electron-doped system. Near the valence band edge, the Fermi surfaces are composed of three different types of hole pockets; namely, one consists mainly of the almost spin degenerate $|d_{z^2}\rangle$ orbital near the $\mathrm{\Gamma }$ point, and the others are the spin-split upper and lower bands near the $\mathrm{K}$ and ${\mathrm{K}}^{\prime }$ points arising from the $|d_{x^2-y^2}\rangle$ and $|d_{xy}\rangle$ orbitals. The number of relevant Fermi pockets increases with the increase of the doping. At very low doping, the upper split bands of $|d_{x^2-y^2}\rangle$ and $|d_{xy}\rangle$ are concerned, yielding extremely low $T_{\mathrm{c}}$ due to the small density of states of the split bands. For further doping, the conventional spin-singlet state (SS) appears in the $\mathrm{\Gamma }$ pocket, which has a mixture of the spin-triplet, orbital-singlet (ST-OS) and spin-singlet, orbital-triplet (SS-OT) states in the $\mathrm{K}$ and ${\mathrm{K}}^{\prime }$ pockets. The ratio of the mixture depends on the relative strength of the interactions and the sign of the exchange interactions. Moderately strong ferromagnetic exchange interactions even lead to the pairing state with the dominant ST-OS state over the conventional SS one. With these observations, we expect that the fascinating pairing with relatively high $T_{\mathrm{c}}$ emerges at high doping that involves all three Fermi pockets.

The diamagnetic susceptibility of a superconductor is directly related to its superfluid density. Mutual inductance is a highly sensitive method for characterizing thin films, however, in traditional mutual inductance measurements, the measured response is a nontrivial average over the area of the mutual inductance coils, which are typically of millimeter size. Here we measure localized, isolated features in the diamagnetic susceptibility of Nb superconducting thin films with lithographically defined through holes, $\delta$-doped ${\mathrm{SrTiO}}_3$, and the two-dimensional electron system at the interface between ${\mathrm{LaAlO}}_3$ and ${\mathrm{SrTiO}}_3$, using scanning superconducting quantum interference device susceptometry, with spatial resolution as fine as $0.7\mu \mathrm{m}$. We show that these features can be modeled as locally suppressed superfluid density, with a single parameter that characterizes the strength of each feature. This method provides a systematic means of finding and quantifying submicron defects in two-dimensional superconductors.

The interplay of spin-orbit coupling and vibronic coupling on the heavy $d^1$ site of cubic double perovskites is investigated by ab initio calculations. The stabilization energy of spin-orbital-lattice entangled states is found to be comparable to or larger than the exchange interactions, suggesting the presence of Jahn-Teller dynamics in the systems. In ${\mathrm{Ba}}_2{\mathrm{YMoO}}_6$, the pseudo-Jahn-Teller coupling enhances the mixing of the ground and excited spin-orbit multiplet states, which results in strong temperature dependence of effective magnetic moments. The entanglement of the spin and lattice degrees of freedom induces a strong magnetoelastic response. This multiferroic effect is at the origin of the recently reported breaking of local point symmetry accompanying the development of magnetic ordering in ${\mathrm{Ba}}_2{\mathrm{NaOsO}}_6$.

We explore the electronic and the optical properties of monolayer ${\mathrm{TiS}}_3$, which shows in-plane anisotropy and is composed of a chain-like structure along one of the lattice directions. Together with its robust direct band gap, which changes very slightly with stacking order and with the thickness of the sample, the anisotropic physical properties of ${\mathrm{TiS}}_3$ make the material very attractive for various device applications. In this study, we present a detailed investigation on the effect of the crystal anisotropy on the excitons and the trions of the ${\mathrm{TiS}}_3$ monolayer. We use many-body perturbation theory to calculate the absorption spectrum of anisotropic ${\mathrm{TiS}}_3$ monolayer by solving the Bethe-Salpeter equation. In parallel, we implement and use a Wannier-Mott model for the excitons that takes into account the anisotropic effective masses and Coulomb screening, which are obtained from ab initio calculations. This model is then extended for the investigation of trion states of monolayer ${\mathrm{TiS}}_3$. Our calculations indicate that the absorption spectrum of monolayer ${\mathrm{TiS}}_3$ drastically depends on the polarization of the incoming light, which excites different excitons with distinct binding energies. In addition, the binding energies of positively and the negatively charged trions are observed to be distinct and they exhibit an anisotropic probability density distribution.

We study transient effects in a setup where the quantum dot is abruptly sandwiched between the metallic and superconducting leads. Focusing on the proximity-induced electron pairing manifested by the in-gap bound states, we determine characteristic timescales needed for these quasiparticles to develop. In particular, we derive analytic expressions for (i) charge occupancy of the quantum dot, (ii) amplitude of the induced electron pairing, and (iii) the transient currents under equilibrium and nonequilibrium conditions. We also investigate the correlation effects within the Hartree-Fock-Bogolubov approximation, revealing a competition between the Coulomb interactions and electron pairing.

We present a spatially resolved angle-resolved photoemission spectroscopy (ARPES) study on the Y-based high-$T_c$ cuprate superconductor ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ to disentangle surface electronic inhomogeneity. Two surface terminations consisting of either a CuO or BaO layer are identified through a chemical-states-specified core-level intensity distribution. This enables us to perform termination-selective ARPES measurements that uncover the different charge fillings and electronic configurations depending on the surface termination. By combining the real-space and electronic information, we propose a simple model to explain the termination-dependent surface electronic reconstruction. Our results demonstrate a significant importance of the spatially resolved ARPES in order to obtain intriguing electronic information, particularly from surface-inhomogeneous systems.

A method for finding dispersion in chains of plasmonic particles of arbitrary shape is proposed. Our approach is based on analytic continuation via polylogarithms and is basically a generalization of the method known for spherical nanoparticle chains. As an example, we consider an axial chain of split-ring resonators. Three distinct solutions are distinguished, namely, two plasmons and a nonexponential wave. Dispersion relations, decay profiles, and spectra of excitation by a point source are obtained and compared with that in a spherical nanoparticle chain. The nuances of implementing the method are discussed.

Orbital tomography has recently been established as a technique to reconstruct molecular orbitals directly from photoemission data using iterative phase retrieval algorithms. In this work, we present a detailed description of steps for processing of the photoemission data followed by an improved iterative phase retrieval procedure and the interpretation of reconstructed two-dimensional orbital distributions. We address the issue of background subtraction by suggesting a signal restoration routine based on the maximization of mutual information algorithm and solve the problem of finding the geometrical center in the reconstruction by using a tight-centered object support in a two-step phase retrieval procedure. The proposed image processing and improved phase retrieval procedures are used to reconstruct the highest occupied molecular orbital of pentacene on Ag(110), using photoemission data only. The results of the reconstruction agree well with the density functional theory simulation, modified to comply with the experimental conditions. By comparison with photoelectron holography, we show that the reconstructed two-dimensional orbital distribution can be interpreted as a superposition of the in-focus orbital distribution evaluated at the $z=0$ plane and out-of-focus distributions evaluated at other $z=\mathrm{const}$ planes. Three-dimensional molecular orbital distributions could thus be reconstructed directly from two-dimensional photoemission data, provided the axial resolution of the imaging system is high enough.

Nonreciprocal charge transport phenomena are studied theoretically for two-dimensional noncentrosymmetric superconductors under an external magnetic field $B$. Rashba superconductors, surface superconductivity on the surface of three-dimensional topological insulators, and transition-metal dichalcogenides such as ${\mathrm{MoS}}_2$ are representative systems, and the current-voltage $I-V$ characteristics, i.e., $V=V\left(I\right)$, for each of them is analyzed. $V\left(I\right)$ can be expanded with respect to the current $I$ as $V\left(I\right)={\sum }_{j=1,\infty }{a}_j(B,T)I^j$, and the $(B,T)$ dependence of $a_j$ depends on the mechanism of the charge transport. Our analysis is based on the time-dependent Ginzburg-Landau theory, which contains up to third-order terms in the momentum of the order parameter. Above the mean field superconducting transition temperature $T_0$, the fluctuation of the superconducting order parameter gives the additional conductivity, i.e., paraconductivity. With the extension of paraconductivity to the nonlinear response, we obtain the nonreciprocal charge transport. On the other hand, below $T_0$, the vortices determine the Kosterlitz-Thouless transition and also the resistivity. The nonreciprocal resistivity is analyzed from the dynamics of vortices in this temperature region. Based on these results, we propose the experiments to identify the mechanism of the nonreciprocal transport with the realistic estimates for the order of magnitude of the coefficients $a_j(B,T)$ for each case.

In this paper, we investigated the effects of annealing on the physical properties of $\mathrm{Ba}{\left(\mathrm{F}{\mathrm{e}}_{1-x}\mathrm{C}{\mathrm{o}}_x\right)}_2\mathrm{A}{\mathrm{s}}_2$ and $\mathrm{BaF}{\mathrm{e}}_2{\left(\mathrm{A}{\mathrm{s}}_{1-x}{\mathrm{P}}_x\right)}_2$ single crystals systematically. In both systems, the effects of annealing on the phase transition temperatures and the critical current density $J_{\mathrm{c}}$ are contrasting; the superconducting and magnetostructural transition temperatures $T_{\mathrm{c}}$ and $T_{\mathrm{sN}}$, respectively, increased for all doping levels after annealing, whereas the critical current density $J_{\mathrm{c}}$ only increased around the optimally doped region while it decreased in the other regions. These facts indicate that the changes in $T_{\mathrm{c}}$ and $J_{\mathrm{c}}$ caused by annealing are governed by different mechanisms and that the mechanism for $J_{\mathrm{c}}$ varies depending on the doping level. The results demonstrate that the enhancement of $T_{\mathrm{c}}$ and $T_{\mathrm{sN}}$ as well as the decrease of $J_{\mathrm{c}}$ can be attributed to the reduction of disorder, while the enhancement of $J_{\mathrm{c}}$ is associated with the enhanced pinning arising from the antiferromagnetic-orthorhombic phase mixed into the superconducting phase.

Effects of 3 MeV ${\mathrm{H}}^{+}$ (proton) irradiation on superconductivity in ${\mathrm{BaFe}}_2{\left({\mathrm{As}}_{0.67}{\mathrm{P}}_{0.33}\right)}_2$ was investigated through in situ resistivity measurements and magnetotransport measurements. The suppression of $T_{\mathrm{c}}$ by ${\mathrm{H}}^{+}$ irradiation is more moderate in comparison with electron irradiation, yet more effective than that of irradiation of heavier ${\mathrm{He}}^{+}$ ions. Surprisingly, the $B$-linear magnetoresistance (MR) in the pristine crystal crosses over to an anomalous negative MR after the irradiation. We discuss that the negative MR is most likely to emanate from sparse magnetic impurities. The appearance of a paramagnetic signal in magnetization measurements supports the existence of magnetic impurities in the sample. Although the estimated concentration of local magnetic moments suggests that the concentration of magnetic impurities is dilute, thereby signifying that irradiation-induced defects are dominantly nonmagnetic, the role of magnetic scattering cannot be completely neglected. Hence, ${\mathrm{H}}^{+}$ irradiation in this system contains magnetic-scattering centers, which are pair breakers for both the $s_{++}$- and the $s_{\pm }$-gap structures, indicating that the suppression of $T_{\mathrm{c}}$ is a consequence of both magnetic and nonmagnetic scatterings. This result opens up the possibility for the scenario of the slow but steady suppression of $T_{\mathrm{c}}$ emanating from the $s_{++}$-gap symmetry with pair breaking due to dilute magnetic scatterers.

We present a single-crystal diffuse neutron scattering study on the quantum spin ice candidate ${\mathrm{Nd}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$ pyrochlore in magnetic fields along the $\left(110\right)$ direction. Two-dimensional scattering sheets perpendicular to the $\left(1\overline{1}0\right)$ direction were observed, evidencing field-induced one-dimensional correlations and disorder. The pyrochlore lattice is completely separated into orthogonal sets of chains, which is in strong contrast to classical spin ice and surprising for an “all-in-all-out” (AIAO) ordered magnet with a non-Ising Hamiltonian. Our mean-field and Monte Carlo simulations reveal that the $\left(110\right)$ field induces a transition from the AIAO order to a “two-in-two-out” disordered state with interactions between the two sets of chains canceled out, resulting in disorder and quantum spin-$\frac{1}{2} XYZ$ chains.

We investigate the dynamics of two Jordan Wigner solvable models; namely, the one-dimensional chain of hard-core bosons and the one-dimensional transverse field Ising model under coin-toss-like aperiodically driven staggered on-site potential and the transverse field, respectively. It is demonstrated that both the models heat up to the infinite temperature ensemble for a minimal aperiodicity in driving. Consequently, in the case of the hard-core bosons chain, we show that the initial current generated by the application of a twist vanishes in the asymptotic limit for any driving frequency. For the transverse Ising chain, we establish that the system not only reaches the diagonal ensemble but the entanglement entropy also attains the thermal value in the asymptotic limit following initial ballistic growth. All these findings, contrasted with that of the perfectly periodic situation, are analytically established in the asymptotic limit within an exact disorder matrix formalism developed using the uncorrelated binary nature of the coin-toss aperiodicity.

A spin-1/2 $XY$ chain model of magnetoelectrics on a zigzag chain is considered rigorously. The magnetoelectric coupling is described within the Katsura-Nagaosa-Balatsky mechanism. In the zigzag geometry it leads to the staggered Dzyaloshinskii-Moriya interaction. Using nonuniform spin rotations, the model is reduced to a dimerized $XY$ chain and solved exactly using the Jordan-Wigner transformation. We analyze the ground-state phase diagram of the model and the zero- and finite-temperature magnetoelectric effects and obtain the magnetization and polarization curves versus magnetic and electric fields, as well as the parameters of anisotropic dielectric and magnetoelectric response. It is also shown that the electric field may enhance the magnetocaloric effect in the model.

We have investigated the microwave nonreciprocity for a noncentrosymmetric antiferromagnet ${\mathrm{Ba}}_2{\mathrm{MnGe}}_2{\mathrm{O}}_7$. The magnon modes expected by the conventional spin wave theory for staggered antiferromagnets are certainly observed. The magnitudes of exchange interaction and magnetic anisotropy are obtained by the comparison with the theory. The microwave nonreciprocity is identified for one of these modes. The relative magnitude of microwave nonreciprocity can be explained with the use of spin wave theory and Kubo formula.