The two-dimensional organic conductor $\alpha \text{−}{\left(\text{BEDT-TTF}\right)}_2{\mathrm{I}}_3$ undergoes a metal-insulator transition at $T_{\mathrm{CO}}=135\mathrm{K}$ due to electronic charge ordering. We have conducted time-resolved investigations of its electronic properties in order to explore the field- and temperature-dependent dynamics. At a certain threshold field, the system switches from a low-conducting to a high-conducting state, accompanied by a negative differential resistance. Our time-dependent infrared investigations indicate that close to $T_{\mathrm{CO}}$, the strong electric field pushes the crystal into a metallic state with optical properties similar to the one for $T>T_{\mathrm{CO}}$. Well into the insulating state, however, at $T=80\mathrm{K}$, the spectral response evidences a completely different electronically induced high-conducting state. Applying a two-state model of hot electrons explains the observations by excitation of charge carriers with a high mobility. They resemble the Dirac-like charge carriers with a linear dispersion of the electronic bands found in $\alpha \text{−}{\left(\text{BEDT-TTF}\right)}_2{\mathrm{I}}_3$ at high pressure. Extensive numerical simulations quantitatively reproduce our experimental findings in all details.

We discuss a self-consistent scheme for treating the optical response of large, hybrid networks of semiconducting quantum dots (SQDs) and plasmonic metallic nanoparticles (MNPs). Our method is efficient and scalable and becomes exact in the limiting case of weakly interacting SQDs. The self-consistent equations obtained for the steady state are analogous to the von Neumann equations of motion for the density matrix of a SQD placed in an effective electric field computed within the discrete dipole approximation. Illustrative applications of the theory to square and honeycomb SQD, MNP, and hybrid SDQ-MNP lattices as well as SQD-MNP dimers are presented. Our results demonstrate that hybrid SQD-MNP lattices can provide flexible platforms for light manipulation with tunable resonant characteristics.

In a recent paper [Phys. Rev. B 89, 125418 (2014)], the authors argue that it is possible to map the electronic properties of twisted bilayer graphene to those of bilayer graphene in an in-plane magnetic field. However, their description of the low-energy dynamics of twisted bilayer graphene is restricted to the extended zone scheme and therefore neglects the effects of the superperiodic structure. If the energy spectrum is studied in the supercell Brillouin zone, we find that the comparison with an in-plane magnetic field fails because (i) the energy spectra of the two situations exhibit different symmetries and (ii) the low-energy spectra are very different.

In the Comment, the authors argue that due to the different symmetry properties, the comparison between the twisting and in-plane magnetic field in bilayer graphene fails. However, we do not think it addresses the main result of our work. Here from the perspective of tunable chirality and quantum transmission signature, we review the feature shared by twisting and in-plane magnetic field in bilayer graphene and show that the Comment does not contradict our main results.

The developments in nanophotonics demand more efficient and delicate control of light. It has recently been proposed to achieve this goal by combining plasmonics and magneto-optics in so-called magnetoplasmonic nanostructures. However, significant challenges still remain because of the difficulty in the design of spectrally tunable systems exhibiting novel plasmonic and magneto-optical responses simultaneously. Here we report a magnetoplasmonic structure which consists of a two-dimensional nickel nanodisk array on top of a cobalt film substrate. We demonstrate that a tunable Fano resonance can be generated in this system with properly designed geometric parameters. Furthermore, the magneto-optical Kerr responses in this system can be manipulated due to the concerted actions of free electrons in the resonance. Our results reveal the possibility of fabricating large-area magnetoplasmonic structures by a simple, mass-producible method, and tuning the plasmonic and magneto-optical responses simultaneously.

We consider superconducting properties of a two-dimensional Dirac material such as graphene under strain that produces a flat-band spectrum in the normal state. We show that in the superconducting state, such a model results in a highly increased critical temperature compared to the case without the strain, inhomogeneous order parameter with two-peak shaped local density of states and yet a large and almost uniform and isotropic supercurrent. This model could be realized in strained graphene or ultracold atom systems and could be responsible for unusually strong superconductivity observed in some graphite interfaces and certain IV-VI semiconductor heterostructures.

The properties of Josephson tunneling between a single-band $s$-wave superconductor and a two-band $s_{\pm }$ superconductor are studied, in relation to recent experiments involving iron-based superconductors. We study both a single junction and a loop consisting of two junctions. In both cases, the relative phase between the order parameters of the two superconductors is tuned and the energy of the system is calculated. In a single junction, we find four types of behaviors characterized by the location of minima in the energy/phase relations. These phases include a newly found double minimum junction, which appears only when the order parameters are treated self-consistently. We analyze the loop geometry setup in light of our results for a single junction, where the phase difference in the junctions is controlled by a threaded flux. We find four types of energy/flux relations. These include states for which the energy is minimized when the threaded flux is an integer or half-integer number of flux quanta, a time reversal broken state and a metastable state.

The recent discovery of the topologically protected surface states in the $\beta$ phase of ${\mathrm{PdBi}}_2$ has reignited the research interest in this class of superconductors. Here, we show results of our muon spin relaxation and rotation ($\mu \mathrm{SR}$) measurements carried out to investigate the superconducting and magnetic properties and the topological effect in the superconducting ground state of $\beta -{\mathrm{PdBi}}_2$. Zero-field $\mu \mathrm{SR}$ data reveal that no sizable spontaneous magnetization arises with the onset of superconductivity implying that the time reversal symmetry is preserved in the superconducting state of $\beta -{\mathrm{PdBi}}_2$. Further, a strong diamagnetic shift of the applied field has been observed in the transverse-field (TF) $\mu \mathrm{SR}$ experiments, indicating that any triplet-pairing channel, if present, does not dominate the superconducting condensate. Using TF-$\mu \mathrm{SR}$, we estimate that the magnetic penetration depth $\lambda =263\left(10\right)$ nm at zero temperature. The nature of $\lambda \left(T\right)$ provides evidence for the existence of a nodeless single $s$-wave type isotropic energy gap of 0.78(1) meV at zero temperature. Our results further suggest that the topologically protected surface states have no effect on the bulk of the superconductor.

We have studied a disordered $N_{\mathrm{c}}\times N_{\mathrm{c}}$ plaquette Hubbard model on a two-dimensional square lattice at half-filling using a coherent potential approximation (CPA) in combination with a single-site dynamical mean field theory (DMFT) approach with a paramagnetic bath. Such a model conveniently interpolates between the ionic Hubbard model at $N_{\mathrm{c}}=\sqrt{2}$ and the Anderson model at $N_{\mathrm{c}}=\infty$ and enables the analysis of the various limiting properties. We confirmed that within the CPA approach a band insulator behavior appears for noninteracting strongly disordered systems with a small plaquette size $N_{\mathrm{c}}=4$, while the paramagnetic Anderson insulator with nearly gapless density of states is present for large plaquette sizes $N_{\mathrm{c}}=48$. When the interaction $U$ is turned on in the strongly fluctuating random potential regions, the electrons on the low energy states push each other into high energy states in DMFT in a paramagnetic bath and correlated metallic states with a quasiparticle peak and Hubbard bands emerge, though a larger critical interaction $U$ is needed to obtain this state from the paramagnetic Anderson insulator ($N_{\mathrm{c}}=48$) than from the band insulator ($N_{\mathrm{c}}=4$). Finally, we observe a Mott insulator behavior in the strong interaction $U$ regions for both $N_{\mathrm{c}}=4$ and $N_{\mathrm{c}}=48$ independent of the disorder strength. We discuss the application of this model to real materials.

Very recently we showed that quantum centroid molecular dynamics (CMD) simulations of the velocity autocorrelation function provide, through the Gaussian approximation (GA), an appropriate representation of the single-molecule dynamic structure factor of liquid ${\mathrm{H}}_2$, as witnessed by a straightforward absolute-scale agreement between calculated and experimental values of the total neutron cross section (TCS) at thermal and epithermal incident energies. Also, a proper quantum evaluation of the self-dynamics was found to guarantee, via the simple Sköld model, a suitable account of the distinct (intermolecular) contributions that influence the neutron TCS of para-${\mathrm{H}}_2$ for low-energy neutrons (below 10 meV). The very different role of coherent nuclear scattering in ${\mathrm{D}}_2$ makes the neutron response from this liquid much more extensively determined by the collective dynamics, even above the cold neutron range. Here we show that the Sköld approximation maintains its effectiveness in producing the correct cross section values also in the deuterium case. This confirms that the true key point for reliable computational estimates of the neutron TCS of the hydrogen liquids is, together with a good knowledge of the static structure factor, the modeling of the self part, which must take into due account quantum delocalization effects on the translational single-molecule dynamics. We demonstrate that both CMD and ring polymer molecular dynamics (RPMD) simulations provide similar results for the velocity autocorrelation function of liquid ${\mathrm{D}}_2$ and, consequently, for the neutron double differential cross section and its integrals. This second investigation completes and reinforces the validity of the proposed quantum method for the prediction of the scattering law of these cryogenic liquids, so important for cold neutron production and related condensed matter research.

Two magnetic phase transitions have been noted for ${\mathrm{SrCoO}}_{3-y}$ for near-stoichiometric oxygen concentrations (small $y$). Using muon-spin rotation and neutron scattering experiments, we have established that the two transitions represent separate, spatially distinct magnetic phases that coexist in a two-phase equilibrium mixture. The two phases most likely represent areas of the sample with different effective valence charge densities. Further, the phases exist over regions with a length scale intermediate between nanoscale charge inhomogeneity and systems such as manganites or superoxygenated cuprates with large length scale phase separations.

Spin glasses have competing interactions that lead to a rough energy landscape which is highly susceptible to small perturbations. These chaotic effects strongly affect numerical simulations and, as such, gaining a deeper understanding of chaos in spin glasses is of much importance. The use of thermal boundary conditions is an effective approach to study chaotic phenomena. Here we generalize population annealing Monte Carlo, combined with thermal boundary conditions, to study bond chaos due to small perturbations in the spin-spin couplings of the three-dimensional Edwards-Anderson Ising spin glass. We show that bond and temperature-induced chaos share the same scaling exponents and that bond chaos is stronger than temperature chaos.

Junction systems of odd-frequency (OF) superconductors are investigated based on a mean-field Hamiltonian formalism. One-dimensional two-channel Kondo lattice (TCKL) is taken as a concrete example of OF superconductors. Properties of normal and Andreev reflections are examined in a normal metal/superconductor junction. Unlike conventional superconductors, normal reflection is always present due to the normal self energy that necessarily appears in the present OF pairing state. The conductance reflects the difference between repulsive and attractive potentials located at the interface, which is in contrast with the preexisting superconducting junctions. Josephson junction is also constructed by connecting TCKL with the other types of superconductors. The results can be understood from symmetry of the induced Cooper pairs at the edge in the presence of spin/orbital symmetry breaking. It has also been demonstrated that the symmetry argument for Cooper pairs is useful in explaining Meissner response in bulk.

By making use of conformal mapping, we construct various time-evolution operators in (1+1)-dimensional conformal field theories (CFTs), which take the form $\int dxf\left(x\right)\mathcal{H}\left(x\right)$, where $\mathcal{H}\left(x\right)$ is the Hamiltonian density of the CFT and $f\left(x\right)$ is an envelope function. Examples of such deformed evolution operators include the entanglement Hamiltonian and the so-called sine-square deformation of the CFT. Within our construction, the spectrum and the (finite-size) scaling of the level spacing of the deformed evolution operator are known exactly. Based on our construction, we also propose a regularized version of the sine-square deformation, which, in contrast to the original sine-square deformation, has the spectrum of the CFT defined on a spatial circle of finite circumference $L$, and for which the level spacing scales as $1/L^2$, once the circumference of the circle and the regularization parameter are suitably adjusted.

We extend the formulation of density functional perturbation theory to treat nonlocal density functionals, accounting for van der Waals interactions, in a rigorous and efficient way. We provide a general formalism, suitable for any functional in this family, and give specific equations for the most widely used ones. We then study the lattice dynamics of graphite, comparing several nonlocal functionals and the local density approximation, showing that our recent revision of the VV10 functional [R. Sabatini et al., Phys. Rev. B 87, 041108(R) (2013)] gives the best comparison with experiments.

The stannide family of materials $A_3{T}_4{\mathrm{Sn}}_{13}$ ($A=\mathrm{La},\mathrm{Sr},\mathrm{Ca}$; $T=\mathrm{Ir},\mathrm{Rh}$) is interesting due to the interplay between a tunable lattice instability and phonon-mediated superconductivity with $T_c\sim 5–7\mathrm{K}$. In ${\mathrm{Sr}}_3{\mathrm{Ir}}_4{\mathrm{Sn}}_{13}$, a structural transition temperature $T^{☆}\sim 147\mathrm{K}$ associated with this instability has been reported, which is believed to result from a superlattice distortion of the high-temperature phase on cooling. Here we report an experimental study of the electronic structure of a member of this material family, ${\mathrm{Sr}}_3{\mathrm{Ir}}_4{\mathrm{Sn}}_{13}$, through measurements of quantum oscillations and comparison with density functional theory calculations. Our measurements reveal good agreement with theory using the lattice parameters consistent with a body-centered-cubic lattice of symmetry $I\overline{4}3d$ of the low-temperature phase. The study of the fermiology of ${\mathrm{Sr}}_3{\mathrm{Ir}}_4{\mathrm{Sn}}_{13}$ that we present here should help inform models of multiband superconductivity in the superconducting stannides.

We present a relativistic formulation of the quantum Hall effect on Haldane sphere. An explicit form of the pseudopotential is derived for the relativistic quantum Hall effect with/without mass term. We clarify particular features of the relativistic quantum Hall states with the use of the exact diagonalization study of the pseudopotential Hamiltonian. Physical effects of the mass term to the relativistic quantum Hall states are investigated in detail. The mass term acts as an interpolating parameter between the relativistic and nonrelativistic quantum Hall effects. It is pointed out that the mass term unevenly affects the many-body physics of the positive and negative Landau levels as a manifestation of the “parity anomaly.” In particular, we explicitly demonstrate the instability of the Laughlin state of the positive first relativistic Landau level with the reduction of the charge gap.