In-plane Tunneling Spectrum into a [110]-Oriented High-TcT_c Superconductor in the Pseudogap Regime

Both the differential tunneling conductance and the surface local density of states (LDOS) of a [110]-oriented high-temperature superconductor in the pseudogap (PG) regime are studied theoretically. As a competing candidate for the mechanism of PG state, the charge-density wave (CDW), spin-density wave (SDW), $d$-density wave (DDW), and d-wave superconducting (DSC) orderings show distinct features in the tunneling conductance. For the CDW, SDW, and DSC orderings, the tunneling conductance approaches the surface LDOS as the barrier potential is increased. For the DDW ordering, we show for the first time that there exist midgap states at the [110] surface, manifesting themselves as a sharp zero-energy peak in the LDOS, as in the case of DSC ordering. However, due to the particle-hole pair nature of the DDW state, these states do not carry current, and consequently the one-to-one correspondence between the tunneling conductance and the surface LDOS is absent.Comment: 5 pages, 4 figures embedded in the tex

Spin state dependence of electrical conductivity of spin crossover materials

We studied the spin state dependence of the electrical conductivity of the spin crossover compound [Fe(Htrz)2(trz)](BF4) (Htrz = 1H-1,2,4-triazole) by means of dc electrical measurements. The low spin state is characterized by higher conductance and lower thermal activation energy of the conductivity, when compared to the high spin state

Theory of the STM detection of Wigner molecules in spin incoherent CNTs

The linear conductance of a carbon nanotube quantum dot in the Wigner molecule regime, coupled to two scanning tunnel microscope tips is inspected. Considering the high temperature regime, the nanotube quantum dot is described by means of the spin-incoherent Luttinger liquid picture. The linear conductance exhibits spatial oscillations induced by the presence of the correlated, molecular electron state. A power-law scaling of the electron density and of the conductance as a function of the interaction parameter are found. They confirm local transport as a sensitive tool to investigate the Wigner molecule. The double-tip setup allows to explore different transport regimes with different shapes of the spatial modulation, all bringing information about the Wigner molecule

Polaronic state and nanometer-scale phase separation in colossal magnetoresistive manganites

High resolution topographic images obtained by scanning tunneling microscope in the insulating state of Pr0.68Pb0.32MnO3 single crystals showed regular stripe-like or zigzag patterns on a width scale of 0.4 - 0.5 nm confirming a high temperature polaronic state. Spectroscopic studies revealed inhomogeneous maps of zero-bias conductance with small patches of metallic clusters on length scale of 2 - 3 nm only within a narrow temperature range close to the metal-insulator transition. The results give a direct observation of polarons in the insulating state, phase separation of nanometer-scale metallic clusters in the paramagnetic metallic state, and a homogeneous ferromagnetic state