Poole-Frenkel effect and Variable-Range Hopping conduction in metal / YBCO resistive switching devices

Current-voltage (IV) characteristics and the temperature dependence of the contact resistance [$R(T)$] of Au / YBa$_2$Cu$_3$O$_{7-\delta}$ (optimally doped YBCO) interfaces have been studied at different resistance states. This states were produced by resistive switching after accumulating cyclic electrical pulses of increasing number and voltage amplitude. The IV characteristics and the $R(T)$ dependence of the different states are consistent with a Poole-Frenkel (P-F) emission mechanism with trapping-energy levels $E_t$ in the 0.06-0.11 eV range. $E_t$ remains constant up to a number-of-pulses-dependent critical voltage and increases linearly with further increasing the voltage amplitude of the pulses. The observation of a P-F mechanism reveals the existence of an oxygen-depleted layer of YBCO near the interface. A simple electrical transport scenario is discussed, where the degree of disorder, the trap energy level and the temperature range determine an electrical conduction dominated by non-linear effects, or by a P-F emission or by a Variable-Range Hopping regime.Comment: 16 pages, 5 figure

The decline of Spain (1500–1850): conjectural estimates

This article attempts to quantify the decline of Spain over the period 1500–1850. In contrast to earlier estimates that focus almost exclusively on Castilian agriculture, we look at trends in urbanisation and construct new measures of agricultural and aggregate output at both regional and national levels. A distinctive long-run behaviour is found across Spanish regions that rejects the identification between Castile and Spain. Per capita income grew in the sixteenth and early nineteenth centuries, while contraction and stagnation occurred in the seventeenth and eighteenth centuries. In the long run, output per head did not improve until the early nineteenth century. At the time of its imperial expansion Spain was a relatively affluent nation and, by 1590, was only behind the Low Countries and Italy in terms of per capita income. Spain's decline has its roots in the seventeenth century while its backwardness deepened in the first half of the nineteenth century.Publicad