Software Utilities

dfree & d-imp

Features and Description

The free-energy difference between the superconducting and normal state can be used to calculate the thermodynamic critical field of a superconductor. It is the field at which the free-energy of the normal state equals that of the superconducting state.

From the gap as a function of temperature and external magnetic field, one can calculate the supercooling and superheating limits of the superconductor. Increasing and decreasing the external field does not result in the same thermodynamic critical fields, which is a hysteresis-effect. Superconductivity may break down at a higher field if the field is zero and turned up, than the onset of superconductivity is, when turning the field down from a higher value.

The difference between s- and d- wave superconductors lies in the order parameter (energy gap). The gap of an s-wave superconductor is the same for all wave-vectors k, while that of a d-wave superconductor has nodes and is thus a function of k. This results in similar, but different superconducting properties, including a slightly higher upper critical field for d-wave superconductors.

In a superconductor, two electrons with opposite spin pair up to build a so-called Cooper-pair. When an external field is switched on, there are two mechanisms that break up the Cooper-pair: paramagnetic and orbital pair-breaking.

Assuming that the external field lies in the superconducting plane, only paramagnetic pair-breaking takes effect in a 2d superconductor. Increasing the film thickness causes an increase in the orbital pair-breaking effect and reduces the upper critical field, which means that the field, at which superconductivity breaks down, gets smaller. The same happens when increasing the tilt-angle of the external field from parallel to perpendicular.

Impurities have the opposite effect. As the mean electron-path is lessened because of scattering on impurity-sites, orbital pair-breaking is lessened and the upper critical field increases. d-imp considers the effect of impurity scattering.

Download

Installation

• Unpack the tarball:

  tar -zxvf free_energy*.tar.gz

• Compile the program:

  make dfree && make d-imp

• To run the program use:

  dfree dfree.cfg temperaturefile outputname

  or

  d-imp d-imp.cfg temperaturefile outputname

• Read the README.dfree and README.d-impfor details on how to use this programs.

Documentation and Results

Feedback & Links

• hc2 on freshmeat: http://freshmeat.net/projects/hc2/
• Please send all bugreports and feedback to: