2Charge density wave (CDW) transitions are a frequent occurrence in transition metal chalcogenides due to their low structural dimensionality. Layered MX 2 compounds and chain-based MX 3 compounds, where M is a group 4 or 5 metal and X = S, Se, or Te, are the best known examples [1][2][3][4][5][6][7]. These transitions arise to allow electronic systems to minimize their energy by removing electronic states at the Fermi level. This is achieved by introducing a new structural periodicity at the Fermi wave vector, inducing a band gap. Superconductivity and the CDW state are two very different cooperative electronic phenomena, and yet both occur due to Fermi surface instabilities and electron-phonon coupling. A number of CDW-bearing materials are also superconducting [8][9][10][11][12][13], and the idea that superconductivity and CDW states are competing electronic states at low temperatures is one of the fundamental concepts of condensed matter physics. Surprisingly, no system has yet been reported in which the emergence of a superconducting state after a charge density wave state has been suppressed via doping has been studied in detail: a transition that implies a deep connection between the two states, i.e., that the same electrons are participating in both transitions. TiSe 2 was one of the first CDW-bearing compounds known, and is also one of the most frequently studied as the nature of its CDW transition has been controversial for decades. The CDW transition, at approximately 200 K, is to a state with a commensurate (2a,2a,2c) wavevector without an intermediate incommensurate phase [3,16,17]. The commensurate CDW wavevector and electronic structure calculations indicate that, unlike the case in most materials, the CDW in TiSe 2 is not driven by Fermi surface nesting. The normal state is presently believed to be either a semimetal or a semiconductor with a small indirect gap [3, 16, 18 -22] (Fig. 1a, inset). This results in a systematic expansion of the unit cell with Cu content in Cu x TiSe 2 , as evidenced by the lattice parameters shown in Fig. 1a. The expansion of the cell parameters is maintained up to x = 0.11. For higher Cu contents, both a and c remain unchanged from their value at x = 0.11. It can therefore be concluded that the solubility limit for Cu in TiSe 2 is x = 0.11 ± 0.01.Of particular interest is the evolution of the charge density wave with Cu doping.Electron and X-ray diffraction studies of pure TiSe 2 at low temperatures show the presence of reflections corresponding to the basic trigonal structure and also the 2a, 2c superstructure reflections associated with the CDW state [3,19]. increases with Cu content. This suggests that the Cu doping introduces carriers into the conduction band in TiSe 2 , increasing the electronic density of states and therefore the Pauli paramagnetism. This is further confirmed by specific heat measurements, described below. A drop in the susceptibility of pure TiSe 2 is seen as the temperature is lowered below the CDW transition at 200 K, consistent with th...

A topological insulator protected by time-reversal symmetry is realized via spinorbit interaction driven band inversion. The topological phase in the Bi 1−x Sb x system is due to an odd number of band inversions. A related spin-orbit system, the Pb 1−x Sn x Te, has long been known to contain an even number of inversions based on band theory. Here we experimentally investigate the possibility of a mirror symmetry protected topological crystalline insulator phase in the Pb 1−x Sn x Te class of materials which has been theoretically predicted to exist in its end compound SnTe. Our experimental results show that at a finite-Pb composition above the topological inversion phase transition, the surface exhibits even number of spin-polarized Dirac cone states revealing mirror-protected topological order distinct from that observed in Bi 1−x Sb x . Our observation of the spin-polarized Dirac surface states in the inverted Pb 1−x Sn x Te and their absence in the non-inverted compounds related via a topological phase transition provide the experimental groundwork for opening the research on novel topological order in quantum devices.

Nanoparticles composed of magnetic cores with continuous Au shell layers simultaneously possess both magnetic and plasmonic properties. Faceted and tetracubic nanocrystals consisting of wüstite with magnetite-rich corners and edges retain magnetic properties when coated with an Au shell layer, with the composite nanostructures showing ferrimagnetic behavior. The plasmonic properties are profoundly influenced by the high dielectric constant of the mixed-iron-oxide nanocrystalline core. A comprehensive theoretical analysis that examines the geometric plasmon tunability over a range of core permittivities enables us to identify the dielectric properties of the mixed-oxide magnetic core directly from the plasmonic behavior of the core-shell nanoparticle.

The synthesis, structure, and basic magnetic properties of Na 2 Co 2 TeO 6 and Na 3 Co 2 SbO 6 are reported. The crystal structures were determined by neutron powder diffraction. Na 2 Co 2 TeO 6 has a two-layer hexagonal structure (space group P6 3 22) while Na 3 Co 2 SbO 6 has a single-layer monoclinic structure (space group C2/m). The Co, Te, and Sb ions are in octahedral coordination, and the edge sharing octahedra form planes interleaved by sodium ions. Both compounds have full ordering of the Co 2+ and Te 6+ /Sb 5+ ions in the ab plane such that the Co 2+ ions form a honeycomb array. The stacking of the honeycomb arrays differ in the two compounds. Both Na 2 Co 2 TeO 6 and Na 3 Co 2 SbO 6 display magnetic ordering at low temperatures, with what appears to be a spin-flop transition found in Na 3 Co 2 SbO 6 .

Integrating multiple functionalities into individual nanoscale complexes is of tremendous importance in biomedicine, expanding the capabilities of nanoscale structures to perform multiple parallel tasks. Here, the ability to enhance two different imaging technologies simultaneously—fluorescence optical imaging and magnetic resonance imaging—with antibody targeting and photothermal therapeutic actuation is combined all within the same nanoshell‐based complex. The nanocomplexes are constructed by coating a gold nanoshell with a silica epilayer doped with Fe3O4 and the fluorophore ICG, which results in a high T2 relaxivity (390 mM−1 s−1) and 45× fluorescence enhancement of ICG. Bioconjugate nanocomplexes target HER2+ cells and induce photothermal cell death upon near‐IR illumination.