In this Comment, it is argued that Stishov et al. [Phys. Rev. B 86, 064433 (2012)] incorrectly estimated concentrations of (supposed) paramagnetic centers with ${\mu }_{\mathrm{eff}}\approx 4.8{\mu }_{\mathrm{B}}$ in the investigated CoSi crystals. Correct estimation gives concentrations of such centers from 25 to 50 times smaller than reported ($\sim 0.04\%–0.16\%$ instead of $\sim 2\%–4\%$). Also, the reported data on temperature dependences of resistivity $\rho \left(T\right)$ of four CoSi crystals, prepared in different laboratories, are so close to each other at $T\approx 250–300\mathrm{K}$ that it is extremely unlikely to be reproducible for any reasonable accuracy of resistivity measurements. These and some other problems in the paper are related to the key points of the authors argumentation. As a result, their main conclusions become unjustified.

In the Comment, it is argued that concentrations of paramagnetic centers in our CoSi crystals were estimated incorrectly [Phys. Rev. B 86, 064433 (2012)]. Doubts also are raised about the temperature dependence of the resistivity of four CoSi crystals prepared in different laboratories. These criticisms, even if they were valid, do not invalidate our main conclusions [Phys. Rev. B 86, 064433 (2012)].

The electric field gradient (EFG) at the highly dilute nuclear probe ${}^{111}$Cd in the heavy fermion systems Ce$M$In${}_5$, $M=$ Co, Rh, and Ir and YCoIn${}_5$ has been investigated by perturbed angular correlation (PAC) measurements of the nuclear electric quadrupole interaction (QI) of ${}^{111}$Cd on In sites. Pure and Sn-doped single crystals prepared by In-flux synthesis and polycrystalline samples prepared by arc melting have been studied. The samples were doped with the PAC probe ${}^{111}$Cd by diffusion of the mother isotope ${}^{111}$In. In all samples, several fractions of ${}^{111}$Cd probe nuclei subject to different QI's have been observed, among them a large fraction of ${}^{111}$Cd in unreacted In metal. Detailed calculations of the EFG at In nuclei and at Cd probes on In sites of pure and Sn-doped Ce$M$In${}_5$ were preformed, using the full-potential augmented plane wave+local orbital (APW+lo) formalism and taking into account different variables such as the electronic structure of the hyperfine probes, probe induced structural distortions, and impurity doping. The excellent agreement between the predicted EFG's and the experimental results allows us to assign two of the observed EFG components to the lattice sites 1$c$ and 4$i$ of the Ce$M$In${}_5$ compounds and to explain the pronounced difference of the EFG at In and Cd probes on the same lattice position. Structural distortions induced by the Cd probe and Sn-doping were found to have little effect on the EFG at the Cd probes. We also show that the local spin density approximation (LSDA) and LDA+$U$ calculations predict very similar equilibrium structures and EFG's at the In/Cd sites. The extension of the experiments and the calculations from Ce$M$In${}_5$ to YCoIn${}_5$ and LaCoIn${}_5$ have established that the influence of the 4$f$ electrons on the EFG's at impurity sites is negligibly small.

The anomalous temperature-independent behavior of the Seebeck coefficient and the lattice thermal conductivity of B${}_{13}$C${}_2$ are explained through polaron and phonon evolutions found using ab initio molecular dynamics (AIMD). Analyses of lattice dynamics show that the unique icosahedron structures dominate the optical phonon modes and CBC intericosahedral bonds dominate the local acoustic vibration. We identify that the temperature-induced Jahn-Teller distortion and electron-phonon coupling in icosahedron structures create small polarons (i.e., charge trapping and phonon softening). We also verify that large-displacement chain atoms scatter heat-conducting phonons. Using equilibrium and nonequilibrium AIMD methods (including entropy and energy analyses), we predict the Seebeck coefficient and its components as well as the lattice thermal conductivity, and we find good agreement with experiments. Softened and localized phonons make a significant vibrational contribution to the Seebeck coefficient and allow for an amorphous-like lattice thermal conductivity.

Recent works have given indication that the defect-induced magnetism in diluted magnetic semiconductors (DMSs), transition metal oxides (TMOs), and related materials is facilitated and enhanced by codoping and the synergistic action among the codopants. In the present work we demonstrate that the proposed defect-induced ferromagnetic coupling (FMC) exhibits the following features: bipartition, synergy, and locality, and is based on the formation and interaction among spin-polarized neighborhoods analogous to spin-polarized radicals centered at the codopant sites. The FMC is mediated by the molecular orbitals (MOs) of these radicals and is greatly facilitated if the codopant-centered radicals could form bipartite configurations within the host lattices. Within this picture, the origin of magnetism in DMSs and TMOs appears to be the synergy and the interplay between correlated spin-polarization processes that take place in a successive way within neighborhoods centered at the codopants and include their first nearest neighbors (1nns). The proposed model can be used as a practical guide for choosing the appropriate pair of codopants for a specific semiconductor environment that can lead to the fabrication of DMSs and TMOs with enhanced magnetic properties.

van der Waals (vdW) interactions within density functional theory are shown to strongly reduce the distance between manganese phthalocyanine (MnPc) and a Cu(001) surface to that found by x-ray standing wave experiments. Thus, the physisorbed ground state that is predicted within the generalized-gradient approximation formalism is replaced by a chemisorbed ground state once vdW interactions are taken into account. These findings indicate how to systematically obtain the correct theoretical adsorption distance for complex molecules and thus accurately predict the properties of the ensuing molecule/metal interface. The reduction of the experimental work function upon molecular adsorption is satisfactorily accounted for and explained in terms of Friedel-like oscillations of the charge density at the vicinity of the MnPc molecule that change the sign of the charge transfer electric dipole. This shows how vdW interactions can strongly impact charge injection in organic electronic devices.

We consider the electronic structure of a slightly twisted graphene bilayer and show the coexistence of van Hove singularities (VHSs) and superlattice Dirac points in a continuum approximation. The graphene-on-graphene moiré pattern gives rise to a periodic electronic potential, which leads to the emergence of the superlattice Dirac points due to the chiral nature of the charge carriers. Because of the distinguishing real and reciprocal structures, the sublattice exchange even and sublattice exchange odd structures of the twisted graphene bilayer result in two different structures of the superlattice Dirac points. We calculate the effect of a strain on the low-energy electronic structure of the twisted graphene bilayer and demonstrate that the strain affects the position of the VHSs dramatically.

Scanning tunneling microscopy studies show that coarsening of arrays of rectangular single-layer Ag islands on Ag(110) at 220 K and below occurs by one-dimensional (1D) decay of narrower islands, which maintain roughly constant width in the $\langle 001\rangle$ direction. Adatoms mainly detach from the island ends with $\langle 001\rangle$ step edges. 1D decay derives from the absence of corner rounding diffusion from $\langle 001\rangle$ to $\langle \overline{1}10\rangle$ edges and from inhibited nucleation of new layers on $\langle \overline{1}10\rangle$ edges. In contrast, rounding from $\langle \overline{1}10\rangle$ to $\langle 001\rangle$ edges is active. The island decay rate exhibits an unexpectedly low effective Arrhenius energy due to a combination of strong anisotropy in terrace diffusion and a decrease with temperature of typical island end-to-end separations. Behavior is described by atomistic modeling, which accurately captures both the thermodynamics and the edge diffusion kinetics of the system, in contrast to previous treatments. Kinetic Monte Carlo (KMC) simulations assess model behavior and clarify the driving force for coarsening, as well as various detailed features of the 1D decay process. Refined “atom-tracking” KMC simulations for island configurations matching the experiment recover the experimentally observed island decay times and further elucidate spatial aspects of the transfer of adatoms between islands.

Scanning tunneling microscopy (STM) studies of the fullerene C${}_{60}$ molecule adsorbed on the silicon carbide SiC(0001)-$3\times 3$ surface, combined with density functional theory (DFT) calculations, show that chemisorption of individual C${}_{60}$ molecules occurs through the formation of one bond to one silicon adatom only in contrast to multiple bond formation on other semiconducting surfaces. We observe three stable adsorption sites with respect to the Si adatoms of the surface unit cell. Comprehensive DFT calculations give different adsorption energies for the three most abundant sites showing that van der Waals forces between the C${}_{60}$ molecule and the neighboring surface atoms need to be considered. The C${}_{60}$ molecules are observed to form small clusters even at low coverage indicating the presence of a mobile molecular precursor state and nonnegligible intermolecular interactions.

Spatially inhomogeneous strains in graphene can simulate the effects of valley-dependent magnetic fields. As demonstrated in recent experiments [N. Levy et al., Science 329, 544 (2010) and K. K. Gomes et al., Nature (London) 483, 306 (2012)], the realizable magnetic fields are large enough to give rise to well-defined flat pseudo-Landau levels, potentially having counterpropagating edge modes. In this work, we address the conditions under which such edge modes are visible. We find that, whereas armchair edges do not support counterpropagating edge modes, zigzag edges do so, through a selective-hybridization mechanism. We then discuss effects of interactions on the stability of counterpropagating edge modes and find that, for the experimentally relevant case of Coulomb interactions, interactions typically decrease the stability of the edge modes. Finally, we generalize our analysis to address the case of spontaneous valley polarization, which is expected to occur in charge-neutral strained graphene [P. Ghaemi et al., Phys. Rev. Lett. 108, 266801 (2012) and D. A. Abanin and D. A. Pesin, Phys. Rev. Lett. 109, 066802 (2012)] .

Hybrid density functionals show great promise for chemically accurate first-principles calculations, but their high computational cost limits their application in nontrivial studies, such as exploration of reaction pathways of adsorbents on periodic surfaces. One factor responsible for their increased cost is the dense Brillouin-zone sampling necessary to accurately resolve an integrable singularity in the exact exchange energy. We analyze this singularity within an intuitive formalism based on Wannier-function localization and analytically prove Wigner-Seitz truncation to be the ideal method for regularizing the Coulomb potential in the exchange kernel. We show that this method is limited only by Brillouin-zone discretization errors in the Kohn-Sham orbitals, and hence converges the exchange energy exponentially with the number of $k$ points used to sample the Brillouin zone for all but zero-temperature metallic systems. To facilitate the implementation of this method, we develop a general construction for the plane-wave Coulomb kernel truncated on the Wigner-Seitz cell in one, two, or three lattice directions. We compare several regularization methods for the exchange kernel in a variety of real systems including low-symmetry crystals and low-dimensional materials. We find that our Wigner-Seitz truncation systematically yields the best $k$-point convergence for the exchange energy of all these systems and delivers an accuracy to hybrid functionals comparable to semilocal and screened-exchange functionals at identical $k$-point sets.

We use a combination of numerical density matrix renormalization group calculations and several analytical approaches to comprehensively study a simplified model for a spatially anisotropic spin-$\frac{1}{2}$ triangular lattice Heisenberg antiferromagnet: the three-leg triangular spin tube (TST). The model is described by three Heisenberg chains, with exchange constant $J$, coupled antiferromagnetically with exchange constant $J^{\prime }$ along the diagonals of the ladder system, with periodic boundary conditions in the shorter direction. Here, we determine the full phase diagram of this model as a function of both spatial anisotropy (between the isotropic and decoupled chain limits) and magnetic field. We find a rich phase diagram, which is remarkably dominated by quantum states: the phase corresponding to the classical ground state appears only in an exceedingly small region. Among the dominant phases generated by quantum effects are commensurate and incommensurate coplanar quasiordered states, which appear in the vicinity of the isotropic region for most fields, and in the high-field region for most anisotropies. The coplanar states, while not classical ground states, can at least be understood semiclassically. Even more strikingly, the largest region of phase space is occupied by a spin density wave phase, which has incommensurate collinear correlations along the field. This phase has no semiclassical analog, and may be ascribed to enhanced one-dimensional fluctuations due to frustration. Cutting across the phase diagram is a magnetization plateau, with a gap to all excitations and “up-up-down” spin order, with a quantized magnetization equal to $\frac{1}{3}$ of the saturation value. In the TST, this plateau extends almost but not quite to the decoupled chains limit. Most of the above features are expected to carry over to the two-dimensional system, which we also discuss. At low field, a dimerized phase appears, which is particular to the one-dimensional nature of the TST, and which can be understood from quantum Berry phase arguments.

The electronic states in a corner-overgrown bent GaAs/AlGaAs quantum well heterostructure are studied with numerical Hartree simulations. Transmission electron microscope pictures of the junction sharpness are shown to justify the sharp-corner potential assumed for these calculations. In a tilted magnetic field, both facets of the bent quantum well are brought to a quantum Hall (QH) state, and the corner hosts an unconventional hybrid system of coupled counter-propagating quantum Hall edges and an additional 1D accumulation wire. We show how, in contrast to coplanar barrier-junctions of QH systems, the coupling between the three subsystems increases as a function of the applied magnetic field, and discuss the implications of the numerical results for the interpretation of experimental data on bent quantum Hall systems reported elsewhere.

Temperature-dependent London penetration depth $\lambda \left(T\right)$ was measured in optimally doped $x=0.35$, as-grown [$T_c\approx 25$ K, $\text{RRR}=\rho \left(300\text{K}\right)/\rho \left(T_c\right)=4.5$], and annealed ($T_c\approx 35$ K, $\text{RRR}=6.4$) single crystals of SrFe${}_2$(As${}_{1-x}$P${}_x$)${}_2$ iron-based superconductor. Annealing increases the residual resistivity ratio (RRR) and decreases the absolute value of the London penetration depth from $\lambda \left(0\right)=300\pm 10$ nm in the as-grown sample to $\lambda \left(0\right)=275\pm 10$ nm. At low temperatures, $\lambda \left(T\right)\sim T$ indicating a superconducting gap with line nodes. Analysis of the full-temperature range superfluid density is consistent with the line nodes, but differs from the simple single-gap $d$ wave. The observed behavior is very similar to that of BaFe${}_2$(As${}_{1-x}$P${}_x$)${}_2$, showing that isovalently substituted pnictides are inherently different from the charge-doped materials.

We present and analyze unique phenomena of enhanced transmission through systems of subwavelength dielectric cylinders embedded in an epsilon near zero host. Our analysis shows that these phenomena are due to Mie-resonance modes arisen in the dielectric cylinders. Subwavelength waveguides and lenses are proposed based on coupling of these modes between neighboring cylinders. Finally, the proposed phenomena and their possible applications are numerically demonstrated in the THz regime in a realistic polaritonic material of LiF rods in KCl.

We use high-resolution synchrotron x-ray diffraction to uncover a second, low-temperature, charge density wave (CDW) in TbTe${}_3$. Its $T_c$${}_2=41.0\pm 0.4$ K is the lowest discovered so far in the rare earth telluride series. The CDW wave vectors of the high temperature and low temperature states differ significantly and evolve in opposite directions with temperature, indicating that the two nested Fermi surfaces are separated and the CDWs coexist independently. Both the in-plane and out-of-plane correlation lengths are robust, implying that the density waves on different Te layers are well coupled through the TbTe layers. Finally, we rule out any low-temperature CDW in GdTe${}_3$ for temperatures above 8 K, an energy scale sufficiently low to make pressure tuning of incipient CDW order a realistic possibility.

We design a spintronic quantum eraser to quantitatively probe the two-electron entanglement. It is shown that the concurrence of two spin-entangled electrons is directly given by the Aharonov-Bohm oscillation amplitude of the Fano factor, a measurable current-current correlation, making it rather promising to experimentally quantify the two-electron entanglement. The singlet and triplet entangled states are distinguished by the opposite signs in the Fano factor. Since the main building blocks in the designed setup, an electronic Mach-Zehnder interferometer and a spin filter, have already been implemented, our proposal is particularly pertinent to experiments.

Magnetoluminescence studies in electron bilayers reveal the hallmarks of the even denominator and other quantum Hall states in the intensities and energies of the interband optical recombination lines. In the presence of a small tunneling gap between the layers the magneto-optical emission from the lowest antisymmetric subband, not populated in a single-electron picture, displays maxima at filling factors 1 and 2/3. These findings uncover a loss of pseudospin polarization, where the pseudospin describes the layer index degree of freedom that is linked to an anomalous population of the antisymmetric level due to excitonic correlations. The results demonstrate a new realm to probe the impact of interlayer Coulomb interaction in quantum Hall bilayers.

We study the fine structure of the phonon $G$ peak in the inelastic light scattering spectra of strained graphene in the presence of a quantizing magnetic field. We show that under the conditions of magnetophonon resonance (MPR), the spectral line shape in Raman spectra of the $\Gamma$-point longitudinal optic–transverse optical phonon undergoes multiple splitting and acquires a strong dependence on the polarization of the incoming and detected light. Interference of strain and MPR leads to the modification of the anticrossing branches, introducing the variation of the light polarization preferences depending on the proximity to the resonance, and their better resolution between neighboring anticrossings.