Research Topics

Brief Description

3. Phase transitions in superconducting networks

We are interested in investigating from a theoretical point of view the possible phase diagrams Superconductor-Normal-Insulator and the properties of the phase trasitions in arrays of ultrasmall Josephson junctions (JJA). Experimentally, the size of each junction is of the order of micrometers. Because of this, charging effects are important since the charging energy Ec at each junction becomes comparable, or even larger than the the corresponding Josephson junction interaction energy EJ.

The competition of these two energies gives rise to two regimes:

• Classical regime in wich EJ > Ec and the quantum regime in which EJ < Ec. In the former phase transitions are driven by thermal fluctuations while in the latter phase transitions are driven by quantum fluctuations.
• The quantum fluctuations are related to the vacuum fluctuations in the number of charges in the superconducting state. One may consider two dimensional or cuasi-two-dimensional networks of JJA’s considering self-capacitance as well as mutual-capacitance effects. One can also study the effect of an external perpendicular magnetic field that introduces frustration effects in the phases of the superconducting order parameter. These sytems are studied by means of extensive Path integral Monte Carlo simulations.

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