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The work function of palladium is known to be sensitive to hydrogen by the formation of a surface dipole layer or Pd hydride. One approach to detect such a change in the work function can be based on the formation of a Schottky barrier between the palladium metal and a semiconductor. Here, we study the hydrogen sensitivity of Schottky barrier field-effect transistors made for the first time from diameter- and chirality-sorted semiconducting single-walled carbon nanotubes (s-SWNTs) in contact with Pd electrodes. We observe an unrivaled 100-fold change in the on-state conductance at 100 ppm H2compared to air for devices with s-SWNT and diameters between 1 and 1.6 nm. Hydrogen sensing is not observed for devices of Pd-contacted few-layer graphene (FLG), as expected due to the absence of a significant Schottky barrier. Unexpectedly, we observe also a vanishing sensitivity for small-diameter SWNTs. We explain this observation by changes in the nanotube work function caused by spillover and chemisorption of atomic hydrogen onto small-diameter nanotubes. We also observe that long-term sensing stability is only achieved if the gate voltage is inverted periodically. Under constant gate bias, the sensitivity reduces with time, which we relate to gate screening by accumulated charges in the substrate.

The weak itinerant ferromagnetic order of single-crystalline UIr has been characterised by specific heat, thermal expansion and neutron diffraction measurements for temperatures from 5 to 250 K and applied magnetic fields up to 14 T. At the Curie temperature $T_{\text{C}}=45$ K, pronounced anomalies are observed in the specific heat and in the thermal expansion. The coefficients of linear thermal expansion along the [$10\bar{1}$], [101], and [010] axes of the monoclinic crystal structure all exhibit negative steps. This implies that the uniaxial pressure dependencies of the Curie temperature, determined by the Ehrenfest relation, are all negative. The calculated hydrostatic pressure dependence of the Curie temperature is found to amount to $\mathrm{d}T_{\text{C}}/\mathrm{d}p=-1.6$ K/kbar. The effective Grüneisen parameter is determined in order to analyse the volume dependence of the characteristic energy scales. An enhanced volume dependence of the ferromagnetic spin fluctuations is observed at low temperatures.

Abstract: The temperatureT and magnetic fieldB dependence of the superconducting order parameter Δ and DOS broadening parameter Γ in Zn were evaluated from the measured differential resistancedV/dI vs. voltageV of Zn−Ag point contacts (PC) using the modified BTK theory. The Δ(T) of all PC follows BCS theory while Δ(B) shows both a first-order transition atB c PC c bulk for some PC and continuous decrease of Δ(B) to zero atB c PC ≫B c bulk . The Γ is almost independent ofB in the first case in contrast to the increase with aB in the second case. Moreover, in zero field Γ increases with PC resistance.