We investigate proximity effects in a correlated heterostructure of a two-dimensional Mott insulator (MI) and a topological insulator (TI) by employing inhomogeneous dynamical mean-field theory. We show that the edge state of the TI induces strongly renormalized midgap states inside the MI region, which still have a remnant of the helical energy spectrum. The penetration of low-energy electrons, which is controlled by the interface tunneling $V$, largely enhances the electron mass inside the MI and also splits a single Dirac cone at edge sites into the spatially separated two Dirac cones in the strong $V$ region.

We propose novel interaction-based routes to half-metal states for interacting electrons on two-dimensional lattices. Magnetic field applied parallel to the lattice is used to tune one of the spin densities to a particular value commensurate with the lattice in which the system spontaneously “locks in” via the Van Hove enhanced density wave state. Electrons of opposite spin polarization retain their metallic character and provide for the half-metal state which, in addition, supports the magnetization plateau in a finite interval of external magnetic field. A similar half-metal state is realized in the finite-U Hubbard model on a triangular lattice at $1/3$ of the maximum magnetization.

We propose a method for dynamically controlling the properties of a metamaterial that mimics electromagnetically induced transparency (EIT) by introducing varactor diodes to manipulate the structural symmetry of the metamaterial. Dynamic modulation of the EIT property enables the storage and retrieval of electromagnetic waves. We confirmed that the electromagnetic waves were stored and released, while maintaining the phase distribution in the propagating direction.

Resonant x-ray diffraction experiments were performed for the metallic iridium oxide IrO${}_2$. We observed anisotropic tensor of susceptibility (ATS) scattering, the spectrum of which shows a sharp contrast between the $L_3$ and $L_2$ edges. At the $L_3$ edge, resonance excitations were clearly observed from the core 2$p$ orbitals to both the 5$d$ $t_{2g}$ and $e_g$ orbitals. In contrast, the resonance mode associated with 5$d$ $t_{2g}$ orbitals was indiscernible at the $L_2$ edge. This contrasting behavior indicates that Ir 5$d$ $t_{2g}$ orbitals are fairly close to the $J_{\mathrm{eff}}=1/2$ state due to the strong spin-orbit coupling in 5$d$ transition-metal ions, as in the Mott insulator Sr${}_2$IrO${}_4$. Our results clearly demonstrate that ATS scattering is a useful probe for investigating complex orbital states in a metallic material, where novel phenomena such as the spin Hall effect are expected.

We obtain an exact matrix-product-state (MPS) representation of a large series of fractional quantum Hall (FQH) states in various geometries of genus 0. The states in question include all paired $k=2$ Jack polynomials, such as the Moore-Read and Gaffnian states, as well as the Read-Rezayi $k=3$ state. We also outline the procedures through which the MPSs of other model FQH states can be obtained, provided their wave function can be written as a correlator in a $1+1$ conformal field theory (CFT). The auxiliary Hilbert space of the MPS, which gives the counting of the entanglement spectrum, is then simply the Hilbert space of the underlying CFT. This formalism enlightens the link between entanglement spectrum and edge modes. Properties of model wave functions such as the thin-torus root partitions and squeezing are recast in the MPS form, and numerical benchmarks for the accuracy of the new MPS prescription in various geometries are provided.

Three-dimensional anisotropy of the Landé $g$ factor and its electrical modulation are studied for single uncapped InAs self-assembled quantum dots (QDs). The $g$ factor is evaluated from measurement of inelastic cotunneling via Zeeman substates in the QD for various magnetic field directions. We find that the value and anisotropy of the $g$ factor depends on the type of orbital state which arises from the three-dimensional confinement anisotropy of the QD potential. Furthermore, the $g$ factor and its anisotropy are electrically tuned by a side gate which modulates the confining potential.

We show that the lack of inversion symmetry in monolayer MoS${}_2$ allows strong optical second harmonic generation. The second harmonic of an 810-nm pulse is generated in a mechanically exfoliated monolayer, with a nonlinear susceptibility on the order of 10${}^{-7}$ m/V. The susceptibility reduces by a factor of seven in trilayers, and by about two orders of magnitude in even layers. A proof-of-principle second harmonic microscopy measurement is performed on samples grown by chemical vapor deposition, which illustrates potential applications of this effect in the fast and noninvasive detection of crystalline orientation, thickness uniformity, layer stacking, and single-crystal domain size of atomically thin films of MoS${}_2$ and similar materials.

In the recent paper, we explained why the maximum bulk resistivity of topological insulators (TIs) such as Bi${}_2$Se${}_3$ is so small [B. Skinner, T. Chen, and B. I. Shklovskii, Phys. Rev. Lett. 109, 176801 (2012)]. Using the model of completely compensated semiconductor we showed that when the Fermi level is pinned in the middle of the gap the activation energy of resistivity is $\Delta =0.3(E_g/2)$, where $E_g$ is the semiconductor gap. In this paper, we consider a strongly compensated $n$-type semiconductor. We find the position of the Fermi level $\mu$ calculated from the bottom of the conduction band $E_c$ and the activation energy of resistivity $\Delta$ as a function of compensation $K$, and show that $\Delta =0.3(E_c-\mu )$ holds at any $0<1-K\ll 1$. In the same range of relatively high temperatures, the Peltier energy (heat) $\Pi$ is even smaller: $\Pi \simeq \Delta /2=0.15(E_c-\mu )$. We also show that at low temperatures, the activated conductivity crosses over to variable range hopping (VRH) and find the characteristic temperature of VRH, $T_{\mathrm{ES}}$, as a function of $K$.

We present a theory for the metal-insulator transition (MIT) in the quantum spin liquid candidate material Na${}_4$Ir${}_3$O${}_8$. We consider an extended Hubbard model on the hyperkagome lattice, which incorporates atomic spin-orbit coupling (SOC) and multiorbital interactions of iridium 5$d$ electrons. This model is analyzed using the slave-rotor mean-field theory, and thermodynamic properties across the MIT are studied. The ground state in the insulating side is a U(1) quantum spin liquid with spinon Fermi surfaces that consist of multiple particle-like and hole-like pockets. It is shown that the Wilson ratio in the quantum spin liquid phase is highly enhanced compared to the metallic state. This originates from the fact that the magnetic susceptibility in the quantum spin liquid phase acquires multiple enhancements due to the strong SOC, reduced bandwidth, and on-site spin-orbital exchange, while the heat capacity does not change much across the MIT. This explains the large Wilson ratio of the insulating phase observed in the previous experiment on Na${}_4$Ir${}_3$O${}_8$. Possible connections to other existing and future experiments, in particular on the metallic phase, are discussed.

We study the nonequilibrium energy transport across a topological insulator superconductor junction by deriving an interfacial heat current formula through the scattering wave approach. Several anomalous thermal properties are uncovered, such as thermal energy's Klein tunneling, asymmetric Kapitza resistance, and negative differential thermal resistance. We expect these findings will have potential applications for energy control in various hybridized mesoscopic systems.

Recently observed photoluminescence (PL) in ZnO, positioned at 3.324 eV and known to be related to Ge impurities, is investigated here by uniaxial stress and Zeeman spectroscopy measurements. The 3.324-eV PL line shifts but does not split under uniaxial stress both parallel and perpendicular to the $c$ axis, indicating trigonal defect symmetry. This reinforces the findings of prior work that the defect center is related to a substitutional Ge impurity in ZnO. Applied magnetic fields result in linear splittings of the line into two components for fields parallel and perpendicular to the $c$ axis. This result, combined with the temperature dependence of the Zeeman spectra, enables the line to be assigned to neutral donor bound-exciton recombination, most likely at a partially compensated Ge${}_{\mathrm{Zn}}$ double-donor impurity.

We present a resonance Raman study of the disorder-induced $D$ mode in a sample highly enriched with semiconducting (9,7) single-walled carbon nanotubes in the excitation energy range of $1.49–2.05\mathrm{eV}$. The intensity of the $D$ mode shows a resonance behavior near the optical transition of the (9,7) tube. The well-known dispersion of the $D$-mode frequency, on the other hand, is not observed at the resonance, but only above a certain excitation energy. We explain our results by numerical simulations of the $D$-mode spectra.

Energy spectra and the magnetic moments of semiconductor core-shell nanocylinders, subjected to a magnetic field, are theoretically studied for different numbers of electrons in the shell and different height-to-radius ratios of the cylinder. The electron-electron interaction is taken into account within the Hartree-Fock approximation. We focus on the perspectives to experimentally detect the Aharonov-Bohm oscillations in the magnetic moment of multielectron core-shell nanowires. Among the different factors that influence the shape and magnitude of these oscillations, the destructive effect due to the interaction of electrons with randomly distributed charged impurities appears most important. Nevertheless, Aharonov-Bohm oscillations of a sufficiently high magnitude survive when averaged over an assembly of nanowires with different impurity distributions.

We study theoretically nonequilibrium Landau-Zener-Stueckelberg (LZS) dynamics in a driven double quantum dot (DQD) including dephasing and, importantly, energy relaxation due to environmental fluctuations. We derive effective nonequilibrium Bloch equations. These allow us to identify clear signatures for LZS oscillations observed but not recognized as such and to identify the full environmental fluctuation spectra acting on a DQD in experiments [Petersson, Petta, Lu, and Gossard, Phys. Rev. Lett. 105, 246804 (2010)]. We find that the dominant dephasing and relaxation channels vary while driving. In detail, super-Ohmic fluctuations, typically due to phonons, are the main relaxation channel for a detuned DQD while dephasing is due to slow noise. In contrast, at zero detuning Ohmic fluctuations dominate dephasing and relaxation.

Manganese deposited on the N-polar face of wurtzite gallium nitride [GaN (000$\overline{1}$)] results in two unique surface reconstructions, depending on the deposition temperature. At lower temperature (less than 105${}^{\circ }$C), it is found that a metastable $3\times 3$ structure forms. Mild annealing of this Mn $3\times 3$ structure leads to an irreversible phase transition to a different, much more stable $\sqrt{3}\times \sqrt{3}-R{30}^{\circ }$ structure which can withstand high-temperature annealing. Scanning tunneling microscopy (STM) and reflection high-energy electron diffraction data are compared with results from first-principles theoretical calculations. Theory finds a lowest-energy model for the $3\times 3$ structure consisting of Mn trimers bonded to the Ga adlayer atoms but not with N atoms. The lowest-energy model for the more stable $\sqrt{3}\times \sqrt{3}-R{30}^{\circ }$ structure involves Mn atoms substituting for Ga within the Ga adlayer and thus bonding with N atoms. Tersoff-Hamman simulations of the resulting lowest-energy structural models are found to be in very good agreement with the experimental STM images.

We study graphene nanoribbons and carbon nanotubes containing ordered defect lines built of octagonal rings. We show that octagonal defect lines are a robust source of state localization at the Fermi energy, in some cases leading to spontaneous magnetization. We also prove that the localization at chains of octagons is a consequence of the zigzag nature of the graphene edges forming the defect lines.

The magnetic excitation spectrum of AgCrS${}_2$, a layered multiferroic compound with a collinear four-sublattice antiferromagnetic order, has been investigated by means of time-of-flight inelastic neutron scattering between 5 and 300 K. Coupling mean-field and spin-wave calculations, the experimental spectrum is well reproduced introducing, in the model Hamiltonian, a ferromagnetic exchange interaction between nearest neighbors and a non-negligible antiferromagnetic in-plane next-nearest-neighbor interaction. This study shows that the sign of the magnetic interaction between chromium ions depends on the Cr-Cr distance with a threshold value above which it becomes ferromagnetic and emphasizes the role of the magnetoelastic coupling in the understanding of the physical properties of AgCrS${}_2$.

SmN is ferromagnetic below 27 K, and its net magnetic moment of 0.03 Bohr magnetons per formula unit is one of the smallest magnetizations found in any ferromagnetic material. The near-zero moment is a result of the nearly equal and opposing spin and orbital moments in the ${}^6$H${}_{5/2}$ ground state of the Sm${}^{3+}$ ion, which leads finally to a nearly complete cancellation for an ion in the SmN ferromagnetic state. Here we explore the spin alignment in this compound with x-ray magnetic circular dichroism at the Sm L${}_{2,3}$ edges. The spectral shapes are in qualitative agreement with computed spectra based on an LSDA+$U$ (local spin density approximation with Hubbard-$U$ corrections) band structure, though there remain differences in detail which we associate with the anomalous branching ratio in rare-earth L edges. The sign of the spectra determines that in a magnetic field the Sm 4$f$ spin moment aligns antiparallel to the field; the very small residual moment in ferromagnetic SmN aligns with the 4$f$ orbital moment and antiparallel to the spin moment. Further measurements on very thin (1.5 nm) SmN layers embedded in GdN show the opposite alignment due to a strong Gd-Sm exchange, suggesting that the SmN moment might be further reduced by about 0.5$\%$ Gd substitution.