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 Physics , 2011, DOI: 10.1103/PhysRevLett.107.266402 Abstract: Synchrotron X-ray diffraction experiment shows that the metal-insulator transition occurring in a ferromagnetic state of a hollandite K$_2$Cr$_8$O$_{16}$ is accompanied by a structural distortion from the tetragonal $I4/m$ to monoclinic $P112_{1}/a$ phase with a $\sqrt{2}\times\sqrt{2}\times 1$ supercell. Detailed electronic structure calculations demonstrate that the metal-insulator transition is caused by a Peierls instability in the quasi-one-dimensional column structure made of four coupled Cr-O chains running in the $c$-direction, leading to the formation of tetramers of Cr ions below the transition temperature. This furnishes a rare example of the Peierls transition of fully spin-polarized electron systems.
 V. Eyert Physics , 2001, DOI: 10.1209/epl/i2002-00452-6 Abstract: Results of first principles augmented spherical wave electronic structure calculations for niobium dioxide are presented. Both metallic rutile and insulating low-temperature NbO2, which crystallizes in a distorted rutile structure, are correctly described within density functional theory and the local density approximation. Metallic conductivity is carried to equal amounts by metal t_{2g} orbitals, which fall into the one-dimensional d_parallel band and the isotropically dispersing e_{g}^{pi} bands. Hybridization of both types of bands is almost negligible outside narrow rods along the line X--R. In the low-temperature phase splitting of the d_parallel band due to metal-metal dimerization as well as upshift of the e_{g}^{pi} bands due to increased p-d overlap remove the Fermi surface and open an optical band gap of about 0.1 eV. The metal-insulator transition arises as a Peierls instability of the d_parallel band in an embedding background of e_{g}^{pi} electrons. This basic mechanism should also apply to VO2, where, however, electronic correlations are expected to play a greater role due to stronger localization of the 3d electrons.
 Advances in Materials Physics and Chemistry (AMPC) , 2016, DOI: 10.4236/ampc.2016.64010 Abstract: The Peierls structural transition in quasi-one-dimensional organic crystals of TTF-TCNQ is investigated in the frame of a more complete physical model. The two most important electron-phonon interaction mechanisms are taken into account simultaneously. One is similar of that of deformation potential and the other is of polaron type. For simplicity, the 2D crystal model is considered. The renormalized phonon spectrum and the phonon polarization operator are calculated in the random phase approximation for different temperatures. The effects of interchain interaction on renormalized acoustic phonons and on the Peierls critical temperature are analyzed.
 Physics , 1998, Abstract: The electronic structure of VO$_2$ is studied in the frameworks of local density approximation (LDA) and LDA+$U$ to give a quantitative description of the metal-insulator (MI) transition in this system. It is found that, both structural distortion and the local Coulomb interaction, play important roles in the transition. An optical gap, comparable to the experimental value has been obtained in the monoclinic structure by using the LDA+$U$ method. Based on our results, we believe that both, the Peierls and the Mott-Hubbard mechanism, are essential for a description of the MI transition in this system.
 Physics , 2002, DOI: 10.1103/PhysRevB.66.085117 Abstract: The pressure dependence of phase transitions in the quasi one-dimensional vanadium oxide $\beta$-Na$_{1/3}$V$_2$O$_5$ has been studied by magnetic susceptibility and electrical resistivity measurements. The pressure dependence of the various transition temperatures is quite differently. The transition at T=240 K, previously reported and attributed to ordering on Na sites, and a second transition at $T \approx 222$ K, reported here for the first time and attributed to a further increase of order on Na sites, are almost independent of pressure. On the other hand, the metal-insulator (MI) transition at $T_{MI}=130$ K shifts to lower temperatures, while the magnetic transition at $T_N=24$ K shifts to higher temperatures with increasing pressure. We discuss the different pressure dependencies of $T_{MI}$ and $T_N$ in terms of increasing interchain coupling and the MI transition to be of Peierls type.
 Physics , 1999, Abstract: We follow the evolution of dressed coupled mini-bands as a function of an AC field intensity, non perturbatively, for a wide field frequency range. High and low frequency limits are characterized by two different dynamic localization regimes, clearly separated by a breakdown region in a quasi-energy map. Signatures of a insulator-metal like transition by means of a field induced suppression of a Peierls-like instability are identified.
 Physics , 2007, Abstract: A previously unknown effect-giant spatial redistribution of the electric field strength in a crystal under illumination of the structure - was discovered and investigated in real photoresistors on high-resistivity (semi-insulating) semiconductor CdTe crystals (in metal-thin insulator- semiconductor-thin insulator -metal structures). A new concept is proposed for photoelectric phenomena in high- resistivity semiconductor crystals. The concept is based on the idea that the redistribution of the field under such conditions that the carrier lifetime remains unchanged under illumination plays a determining role in these phenomena. The nature of the effect is described, the dependence of the characteristics of the structures on the parameters of the crystal and the insulator layers is explained by the manifestation of this effect, and ways to produce structures with prescribed photoelectric characteristics for new devices and scientific methods are examined.
 Physics , 2004, DOI: 10.1103/PhysRevB.68.235115 Abstract: We study how the Mott metal-insulator transition (MIT) is affected when we have to deal with electrons with different angular momentum quantum numbers. For that purpose we apply ab-initio quantum-chemical methods to lithium rings in order to investigate the analogue of a MIT. By changing the interatomic distance we analyse the character of the many-body wavefunction and discuss the importance of the $s-p$ orbital quasi-degeneracy within the metallic regime. The charge gap (ionization potential minus electron affinity) shows a minimum and the static electric dipole polarizability has a pronounced maximum at a lattice constant where the character of the wavefunction changes from significant $p$ to essentially $s$-type. In addition, we examine rings with bond alternation in order to answer the question under which conditions a Peierls distortion occurs.
 Physics , 2006, DOI: 10.1140/epjb/e2006-00282-x Abstract: The dielectric permittivity and resistivity have been measured simultaneously as a function of magnetic field in Pr1-xCaxMnO3 crystals with different doping. A huge increase of dielectric permittivity was detected near percolation threshold. The dielectric and conductive properties are found to be mutually correlated throughout insulator to metal transition evidencing the dielectric catastrophe phenomenon. Data are analyzed in a framework of Maxwell-Garnett theory and the Mott-Hubbard theory attributed to the role of strong Coulomb interactions.
 Physics , 2004, DOI: 10.1103/PhysRevB.69.153104 Abstract: We present measurements of the optical spectra on single crystals of spinel-type compound \cis. This material undergoes a sharp metal-insulator transition at 230 K. Upon entering the insulating state, the optical conductivity shows an abrupt spectral weight transfer and an optical excitation gap opens. In the metallic phase, Drude components in low frequencies and an interband transition peak at $\sim 2 eV$ are observed. In the insulating phase, a new peak emerges around $0.5 eV$. This peak is attributed to the transition of electrons from the occupied Ir$^{3+}$ $t_{2g}$ state to upper Ir$^{4+}$ $t_{2g}$ subband resulting from the dimerization of Ir$^{4+}$ ions in association with the simultaneous formations of Ir$^{3+}$ and Ir$^{4+}$ octamers as recently revealed by the x-ray diffraction experiment. Our experiments indicate that the band structure is reconstructed in the insulating phase due to the sudden structural transition.
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