We performed point-contact spectroscopy tunneling measurements on single crystal BaPb1−xBixO3 for x = 0, 0.19, 0.25, and 0.28 at temperatures ranging from T = 2 − 40 K and find a suppression in the density of states at low bias-voltages, which has not previously been reported. The classic square root dependence observed in the density of states fits within the theoretical framework of disordered metals, and we find that the correlation gap disappears around a critical concentration xc = 0.30. We also report a linear dependence of the zero-temperature conductivity, σ0, with concentration, where σ0 = 0 at xc = 0.30. We conclude that a disorder driven metalinsulator transition occurs in this material before the onset of the charge disproportionated charge density wave insulator. We explore the possibility of a scaling theory being applicable for this material. In addition, we estimate the disorder-free critical temperature using theory developed by Belitz [1] and Fukuyama et. al.[2] and compare these results to Ba1−xKxBiO3.

We report the effects of growth conditions on the superconducting properties of FeSe films epitaxially grown on LaAlO 3 substrates by pulsed laser deposition (PLD). Customary materials characterization techniques [X-ray diffraction (XRD), in-situ X-ray photoelectron spectroscopy (XPS), in-situ ultra-violet photoelectron spectroscopy (UPS), and scanning electron microscopy (SEM)] revealed the films had a c-axis oriented tetragonal structure with lattice constants dependent on the growth temperature (varied from 100 to 600°C). The standard four-point probe method was used to measure the resistivity and superconducting transitions. Films grown at 400-550°C showed a clear superconducting onset but no zero resistance down to

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We performed point-contact spectroscopy tunneling measurements on CuxTiSe2 bulk with x = 0.02 and 0.06 at temperatures ranging from T = 4 − 40 K and observe a suppression in the density of states around zero-bias that we attribute to enhanced Coulomb interactions due to disorder. We find that the correlation gap associated with this suppression is related to the zero-temperature resistivity. We use our results to estimate the disorder-free transition temperature and find that the clean limit Tc0 is close to the experimentally observed Tc.