Effects of doping on the electronic properties of niobium triselenide

The results of magnetization, Electron Spin Resonance(ESR), and electrical resistivity measurements on both undoped and doped samples of the Charge Density Wave (CDW) material NbSe3 are reported. The magnetic studies show that both magnetic(V) and nonmagnetic(Ta) impurities may be introduced into NbSe3; a sensitive electron microscopy technique for measuring the impurity concentration is described. Magnetic impurities form delocalized states near the Fermi level, and the process by which they lose most of their magnetic moment may be qualitatively described by the Anderson modeL A broad Conduction Electron Spin Resonance(CESR) is observed in undoped, Ta doped, and V doped samples; we explain the temperature dependence of the resonance intensity, g-shift, and linewidth result from modification of the non-CDW band structure by CDW gap formation. Below the CDW transition temperatures, the resistivity is dominated by two types of carriers on the non-CDW band. Magnetoresistivity measurements indicate that electron-electron scattering of pockets of electrons dominates in un doped and lightly doped samples, while a metal-insulator transition affecting the electrons on flat sections of the same band qualitatively changes the temperature dependence of the resistivity in the more heavily doped samples. Below 1.6 K, we observe inhomogeneous superconductivity in doped NbSe3, with transition temperatures Tc depending strongly on the impurity leveL We propose that the superconductivity involves electrons on the non-CDW band and that the impurity dependence of Tc can be explained by considering the effect of impurities on the pairing interaction. We analyze the electric field dependence of the resistivity and show that the CDW depinning process may be considered an example of a dynamic critical phenomenon.U of I OnlyThesi