We have theoretically and experimentally investigated the dispersion of the cavity-magnon-polariton (CMP) in a one-dimensional (1D) configuration, created by inserting a low damping magnetic insulator into a high-quality 1D microwave cavity. By simplifying the full-wave simulation based on the transfer matrix approach in the long wavelength limit, an analytic approximation of the CMP dispersion has been obtained. The resultant coupling strength of the CMP shows different dependence on the sample thickness as well as the permittivity of the sample, determined by the parity of the cavity modes. These scaling effects of the cavity and material parameters are confirmed by experimental data. Our work provides a detailed understanding of the 1D CMP, which could help to engineer a coupled magnon-photon system.

The metamagnetic transition in FeRh thin films has been investigated via temperature-dependent x-ray-absorption fine-structure spectroscopy in order to gain correlations between magnetization and local electronic and geometric structures. According to the Fe and Rh $K$-edge x-ray-absorption near-edge structure (XANES), strong hybridization between Fe and Rh was revealed to exist. This Fe-Rh hybridization was observed to decrease during the phase transition from the antiferromagnetic (AFM) to ferromagnetic (FM) phases from the systematic change in the Fe $K$-edge XANES. In addition, only the Debye-Waller factor of the Fe-Fe pair in the AFM phase was observed to be considerably enhanced when compared with that in the FM phase, which was ascribed to local structural fluctuation inherent in the AFM phase. By considering the different features of the exchange interactions in Fe-Rh and Fe-Fe, this anomalous behavior is interpreted as being consistent with the recent theoretical study proposing the local fluctuations of spin and structure. Therefore, we consider that the local spin and Fe-Fe distance fluctuations play an important role in driving the metamagnetic transition, whereas the Fe-Rh hybridization correlates with the static stability of each magnetic phase.

Using different techniques, and Fermi-liquid relationships, we calculate the variation with the applied magnetic field (up to second order) of the zero-temperature equilibrium conductance through a quantum dot described by the impurity Anderson model. We focus on the strong-coupling limit $U\gg \mathrm{\Delta }$, where $U$ is the Coulomb repulsion and $\mathrm{\Delta }$ is half the resonant-level width, and consider several values of the dot level energy $E_d$, ranging from the Kondo regime ${\epsilon }_F-E_d\gg \mathrm{\Delta }$ to the intermediate-valence regime ${\epsilon }_F-E_d\sim \mathrm{\Delta }$, where ${\epsilon }_F$ is the Fermi energy. We have mainly used the density-matrix renormalization group (DMRG) and the numerical renormalization group (NRG) combined with renormalized perturbation theory (RPT). Results for the dot occupancy and magnetic susceptibility from the DMRG and $\mathrm{NRG}+\mathrm{RPT}$ are compared with the corresponding Bethe ansatz results for $U\to \infty$, showing an excellent agreement once $E_d$ is renormalized by a constant Haldane shift. For $U<3\mathrm{\Delta }$ a simple perturbative approach in $U$ agrees very well with the other methods. The conductance decreases with the applied magnetic field for dot occupancies $n_d\sim 1$ and increases for $n_d\sim 0.5$ or $n_d\sim 1.5$ regardless of the value of $U$. We also relate the energy scale for the magnetic-field dependence of the conductance with the width of the low-energy peak in the spectral density of the dot.

Candidates for correlated topological insulators, originated from the spin-orbit coupling as well as the Hubbard-type correlation, are expected in the (111) bilayer of perovskite-structural transition-metal oxides. Based on the first-principles calculation and tight-binding model, the electronic structure of a ${\text{LaMnO}}_3$ (111) bilayer sandwiched in ${\text{LaScO}}_3$ barriers has been investigated. For the ideal undistorted perovskite structure, the Fermi energy of ${\text{LaMnO}}_3$ (111) bilayer just stays at the Dirac point, rendering a semimetal (graphenelike) which is also a half metal [different from graphene or the previously studied ${\text{LaNiO}}_3$ (111) bilayer]. The Dirac cone can be opened by the spin-orbit coupling, giving rise to nontrivial topological bands corresponding to the (quantized) anomalous Hall effect. For the realistic orthorhombic distorted lattice, the Dirac point moves with increasing Hubbard repulsion (or equivalent Jahn-Teller distortion). Finally, a Mott gap opens, establishing a phase boundary between the Mott insulator and topological magnetic insulator. Our calculation finds that the gap opened by spin-orbit coupling is much smaller in the orthorhombic distorted lattice ($\sim 1.7$ meV) than the undistorted one ($\sim 11$ meV). Therefore, to suppress the lattice distortion can be helpful to enhance the robustness of the topological phase in perovskite (111) bilayers.

We have investigated the lattice distortion coupled to the Co $3d$-spin-state ordering in thin films of perovskite ${\mathrm{LaCoO}}_3$ with various epitaxial strains by measurements of the magnetization, x-ray diffraction, and optical spectra. In the system with tensile strain about 0.5%, a lattice distortion characterized by the modulation vector $q=(1/6,1/6,1/6)$ emerges at 40 K, followed by a ferromagnetic ordering at 24 K. Alternatively, in systems with tensile strain exceeding 1%, the lattice distortion characterized by $q=(1/4,1/4,1/4)$ emerges at 120 K or higher, and subsequently the ferromagnetic or ferrimagnetic ordering occurs around 90 K. The evolution of infrared phonon spectra and resonant x-ray scattering at the Co $K$ edge suggests that the population change in the Co $3d$ spin state causes the strain-induced switching of spin-state ordering as well as of magnetic ordering in this canonical spin-state crossover system.

In this work we consider whether nonsymmorphic symmetries such as a glide plane can protect the existence of topological crystalline insulators and superconductors in three dimensions. In analogy to time-reversal symmetric insulators, we show that the presence of a glide gives rise to a quantized magnetoelectric polarizability, which we compute explicitly through the Chern-Simons 3-form of the bulk wave functions for a glide-symmetric model. Our approach provides a measurable property for this insulator and naturally explains the connection with mirror-symmetry-protected insulators and the recently proposed ${\mathbb{Z}}_2$ index for this phase. More generally, we prove that the magnetoelectric polarizability becomes quantized with any orientation-reversing space group symmetry. We also construct analogous examples of glide-protected topological crystalline superconductors in classes $\mathrm{D}$ and $\mathrm{C}$ and discuss how bulk invariants are related to quantized surface thermal Hall and spin Hall responses.

We study dc conductivity of a Weyl semimetal with uniaxial anisotropy (Fermi velocity ratio $\xi =v_{\perp }/v_{\parallel }\ne 1$) considering the scattering of charge carriers by a wide class of impurity potentials, both short- and long-range. We obtain the ratio of transverse and longitudinal (with respect to the anisotropy axis) conductivities as a function of both $\xi$ and temperature. We find that the transverse and longitudinal conductivities exhibit different temperature dependence in the case of short-range disorder. For general long-range disorder, the temperature dependence ($\sim T^4$) of the conductivity turns out to be insensitive of the anisotropy in the limits of strong $(\xi \gg$ and $\ll 1)$ and weak $\left(\xi \approx 1\right)$ anisotropy.

Sulfurization reaction energies of 24 metal sulfide ($M$-S) systems including $M=$ Li, Na, K, Mg, Ca, Sr, Ba, Zn, Al, Ti, Mn, Fe, Co, Ni, Cu, Mo, Rh, Pd, Ir, Pt, La, Ce, Th, and U are evaluated using generalized gradient approximation (GGA) and $\mathrm{GGA}+U$ calculations. Our results indicate that unlike metal oxides and halides, GGA reaction energy predictions can be improved consistently only if separate energy corrections are used for S in sulfide anion (${\mathrm{S}}^{2-}$) and disulfide anion (${\mathrm{S}}_2^{2-}$) because of the existence of covalent ${}^{-}\mathrm{S}–{\mathrm{S}}^{-}$ bonds in the latter anion. Enumerating all possible sulfurization reactions between pairs of $d$- and $f$-block metal sulfides within each $M$-S system, we predict effective $U$ values for $\mathrm{GGA}+U$ thermochemistry and confidence intervals for these $U$ values. We find that applying $U$ on the $d$ or $f$ orbitals of these nonsimple metal ions consistently improves GGA reaction energy predictions for most of these systems, except for the reactions where the reaction energy is insensitive to $U$ applied to the metal $M$, and only the S anions perform the redox activity (i.e., change the nominal oxidation state). We show that $\mathrm{GGA}+U$ calculations with the predicted $U$ values and anion-dependent systematic energy corrections provide a significant improvement over standard, uncorrected GGA in predicting cell voltages of a variety of $M$-S based battery systems including $\mathrm{Li}/{\mathrm{FeS}}_2$, $\mathrm{Li}/{\mathrm{TiS}}_2$, $\mathrm{Li}/{\mathrm{Mo}}_6{\mathrm{S}}_8$, and $\mathrm{Mg}/{\mathrm{Mo}}_6{\mathrm{S}}_8$.

Advances in theory are needed to match recent progress in measurements of coupled semiconductor resonators supporting terahertz plasmons. Here, we present a field-based model of plasmonic resonators that comprise gated and ungated two-dimensional electron systems. The model is compared to experimental measurements of a representative system, in which the interaction between the gated and ungated modes leads to a rich spectrum of hybridized resonances. A theoretical framework is thus established for the analysis and design of gated low-dimensional systems used as plasmonic resonators, underlining their potential application in the manipulation of terahertz frequency range signals.

We calculate the spin transport of hydrogenated graphene using the Landauer-Büttiker formalism with a spin-dependent tight-binding Hamiltonian. Hydrogen adatoms are a common defect and they carry a finite magnetic moment, which makes it important to understand their influence on spin transport for graphene-based spin devices. Our tight-binding model accurately reproduces the density-functional theory band structure and atom-projected density of states. The advantages of using the Landauer-Büttiker formalism are that it simultaneously gives information on sheet resistance and localization length as well as spin relaxation length. Furthermore, the transport can be computed very efficiently using this method by employing the recursive Green's function technique. Here, we study hydrogen adatoms on graphene with randomly aligned magnetic moments, where interference effects are explicitly included. We show that a 5 ppm hydrogen defect density is sufficient to reduce the spin relaxation length to $2\mu \mathrm{m}$ and that the inverse spin relaxation length and sheet resistance scale nearly linearly with the impurity concentration. Moreover, the spin relaxation mechanism in hydrogenated graphene is Markovian only near the charge neutrality point or in the highly dilute impurity limit.

We show theoretically that an open-dissipative polariton condensate confined within a trapping potential and driven by an incoherent pumping scheme gives rise to bistability between odd and even modes of the potential. Switching from one state to the other can be controlled via incoherent pulsing which becomes an important step towards construction of low-powered optoelectronic devices. The origin of the effect comes from modulational instability between odd and even states of the trapping potential governed by the nonlinear polariton-polariton interactions.

We use one single, few-picosecond-long, variably polarized laser pulse to deterministically write any selected spin state of a quantum dot confined dark exciton whose life and coherence time are six and five orders of magnitude longer than the laser pulse duration, respectively. The pulse is tuned to an absorption resonance of an excited dark exciton state, which acquires nonnegligible oscillator strength due to residual mixing with bright exciton states. We obtain a high-fidelity one-to-one mapping from any point on the Poincaré sphere of the pulse polarization to a corresponding point on the Bloch sphere of the spin of the deterministically photogenerated dark exciton.

The fluorescence spectrum of a strongly pumped two-level system is characterized by the Mollow triplet that has been observed in a variety of systems, ranging from atoms to quantum dots and superconducting qubits. We theoretically studied the fluorescence of a strongly pumped intersubband transition in a quantum well. Our results show that the many-electron nature of such a system leads to a modification of the usual Mollow theory. In particular, the intensity of the central peak in the fluorescence spectrum becomes a function of the electron coherence, allowing access to the coherence time of a two-dimensional electron gas through a fluorescence intensity measurement.

The prospect of a Dirac half metal, a material which is characterized by a band structure with a gap in one spin channel but a Dirac cone in the other, is of both fundamental interest and a natural candidate for use in spin-polarized current applications. However, while the possibility of such a material has been reported based on model calculations [H. Ishizuka and Y. Motome, Phys. Rev. Lett. 109, 237207 (2012)], it remains unclear what material system might realize such an exotic state. Using first-principles calculations, we show that the experimentally accessible Mn-intercalated epitaxial graphene on SiC(0001) transits to a Dirac half metal when the coverage is $>1/3$ monolayer. This transition results from an orbital-selective breaking of quasi-two-dimensional inversion symmetry, leading to symmetry breaking in a single spin channel which is robust against randomness in the distribution of Mn intercalates. Furthermore, the inclusion of spin-orbit interaction naturally drives the system into the quantum anomalous Hall (QAH) state. Our results thus not only demonstrate the practicality of realizing the Dirac half metal beyond a toy model, but also open up an avenue to the realization of the QAH effect.

Traditionally, efforts to achieve perfect absorption have required the use of complicated metamaterial-based structures as well as relying on destructive interference to eliminate back reflections. Here, we have demonstrated both theoretically and experimentally that such perfect absorption can be achieved using a naturally occurring material, hexagonal boron nitride (hBN) due to its high optical anisotropy without the requirement of interference effects to absorb the incident field. This effect was observed for $p$-polarized light within the mid-infrared spectral range, and we provide the full theory describing the origin of the perfect absorption as well as the methodology for achieving this effect with other materials. Furthermore, while this is reported for the uniaxial crystal hBN, this is equally applicable to biaxial crystals and more complicated crystal structures. Interferenceless absorption is of fundamental interest to the field of optics; moreover, such materials may provide additional layers of flexibility in the design of frequency selective surfaces, absorbing coatings, and sensing devices operating in the infrared.

We report an unusual transition behavior of charge stripes in ${\mathrm{La}}_{1.67}{\mathrm{Sr}}_{0.33}{\mathrm{NiO}}_4$ using x-ray scattering. The segregated holes in ${\mathrm{La}}_{1.67}{\mathrm{Sr}}_{0.33}{\mathrm{NiO}}_4$ are observed to form anisotropic stripes in the $a\times b$ plane of the crystal space below the transition temperature $T\simeq 238$ K, and at the same time, display an unusual inverse order-disorder transition along the $c$ axis. Using a phenomenological Landau theory, we show that this inverse transition is due to the interlayer coupling between the charge and spin orders. This discovery points to the importance of the interlayer correlations in the strongly correlated electrons system.

We study band alignment in wurtzite/zinc-blende polytype InAs heterostructured nanowires using temperature-dependent resonance Raman measurements. Nanowires having two different wurtzite fractions are investigated. Using visible excitation wavelengths in resonance Raman measurements, we probe the electronic band alignment of these semiconductor nanowires near a high-symmetry point of the Brillouin zone ($E_1$ gap). The strain in the crystal structure, as revealed from the shift of the phonon mode, explains the observed band alignment at the wurtzite/zinc-blende interface. Our experimental results are further supported by electronic-structure calculations for such periodic heterostructured interface.

We describe the proximity effect in a short disordered metallic junction between three superconducting leads. Andreev bound states in the multiterminal junction may cross the Fermi level. We reveal that for a quasicontinuous metallic density of states, crossings at the Fermi level manifest as a closing of the proximity-induced gap. We calculate the local density of states for a wide range of transport parameters using quantum circuit theory. The gap closes inside an area of the space spanned by the superconducting phase differences. We derive an approximate analytic expression for the boundary of the area and compare it to the full numerical solution. The size of the area increases with the transparency of the junction and is sensitive to asymmetry. The finite density of states at zero energy is unaffected by the electron-hole decoherence present in the junction, although decoherence is important at higher energies. Our predictions can be tested using tunneling transport spectroscopy. To encourage experiments, we calculate the current-voltage characteristic in a typical measurement setup. We show how the structure of the local density of states can be mapped out from the measurement.