The pseudogap in high-temperature superconductors: an experimental survey

We present an experimental review of the nature of the pseudogap in the cuprate superconductors. Evidence from various experimental techniques points to a common phenomenology. The pseudogap is seen in all high temperature superconductors and there is general agreement on the temperature and doping range where it exists. It is also becoming clear that the superconducting gap emerges from the normal state pseudogap. The d-wave nature of the order parameter holds for both the superconducting gap and the pseudogap. Although an extensive body of evidence is reviewed, a consensus on the origin of the pseudogap is as lacking as it is for the mechanism underlying high temperature superconductivity.Comment: review article, 54 pages, 50 figure

ESR on spin-polarized atomic hydrogen at temperatures below 0.5 K

Spin-polarized atomic hydrogen (H↓) gas at low temperatures (<0.5 K) has been studied using Electron Spin Resonance (ESR) techniques which allow direct measurements of the densities of H atoms in each of the two lower hyperfine states (a and b). It has been demonstrated that ESR can be made to yield accurate and detailed information about the decay of H↓ densities in time. Crucial to the analysis of the data is the ability to confine the sample of H↓, gas inside the liquid ⁴He coated microwave cavity where the magnetic field and temperature are well known. Measurements of K[sub aa] and K[sub ab], the two surface recombination rate constants, and their ratio γ=K[sub aa]/K[sub ab] have been made and from these results the binding energy of H on liquid ⁴He has been extracted. Also reported are the results of the first detailed study of the one-body surface relaxation rate which we find is due to microscopic magnetic impurities in the cell walls. Theoretical calculations of the two-body dipole-dipole relaxation rate of H↓ in the gas and on the surface are also presented.Science, Faculty ofPhysics and Astronomy, Department ofGraduat

Microwave absorption by ortho pairs in solid hydrogen

The microwave absorption spectra of ortho pairs in low ortho concentration samples of solid hydrogen is studied theoretically and experimentally. A theory is developed for several line broadening mechanisms and a comparison made with experiment. Phonon induced lifetime effects are calculated to be less than 2 MHz in the temperature range T=1.2-4.2 K but have not yet been observed experimentally. Inhomogeneous broadening due to isolated ortho molecules and to isotopic mass defect impurities is observed and found to be consistent with theory. Several new lines in the out-of-plane pair configuration are reported which confirm the assignments made previously, whereas two new lines in the next nearest neighbor configuration support a reassignment of these transitions. Also, three excited state transitions which fix the position of the 10 P level are reported and compared with the theoretical predictions of Harris et al. (1977) and Luryi and Van Kranendonk (1979).Science, Faculty ofPhysics and Astronomy, Department ofGraduat

Influence of linker molecules on charge transport through self-assembled single-nanoparticle devices

We investigate electrical characteristics of single-electron electrode/nanoisland/electrode devices formed by alkanedithiol assisted self-assembly. Contrary to predictions of the orthodox model for double tunnel junction devices, we find a significant (∼fivefold) discrepancy in single-electron charging energies determined by Coulomb blockade (CB) voltage thresholds in current-voltage measurements versus those determined by an Arrhenius analysis of conductance in the CB region. The energies do, however, scale with particle sizes, consistent with single-electron charging phenomena. We propose that the discrepancy is caused by a multibarrier junction potential that leads to a voltage divider effect. Temperature and voltage dependent conductance measurements performed outside the blockade region are consistent with this picture. We simulated our data using a suitably modified orthodox model. © 2005 The American Physical Society