Contact: Prof. Alain Junod

Team fall 2003

3D plot of the singular part of the magnetic entropy of UAs. Each line along the T (or B) direction is a specific heat (or magnetocaloric) run. The phase diagram is shown below

Specific Heat of Novel Materials in High Magnetic Fields and at High Pressures
Our laboratory specialises in thermodynamic studies of superconductors and new materials. Specific heat as a function of temperature (1-300 K), magnetic field (0-16 T), and pressure (0 to over 10 GPa) is a basic characterisation that has gained renewed interest as it allows unconventional properties of superconductors to be assessed in the bulk.

Most novel materials are only available as microscopic single crystals or thin films. This has challenged traditional experimental techniques. In addition to adiabatic and relaxation calorimetry, alternating heating, heat-flux, and magneto-calorimetry have been implemented in Geneva. Thin film and high pressure experiments are at various stages of development [1]. Several classes of materials have been studied in our laboratory: A15, Chevrel phases, cuprates [2], UAs [3], MgB2 [4], etc. Specific heat is well suited for studying transitions versus temperature, magnetic field and pressure, and to characterise their anisotropy and their critical behaviour. Recently, it has given bulk information on the melting of the vortex lattice, on the d-wave symmetry of Cooper pairs in high temperature superconductors, and confirmed the two-gap structure of MgB2. More generally, as a volume-sensitive probe, it complements research based on surface-sensitive spectroscopies.

References:
[1] F. Bouquet et al., Solid State Commun. 113, 367 (2000).
[2] B. Revaz et al. Phys. Rev B 58, 11153 (1998(; Y. Wang et al., Phys. Rev B 63, 094508 (2001).
[3] T. Plackowski et al., Phys. Rev. B 67, 184406 (2003).
[4] F. Bouquet et al., Physica C 385, 192 (2003).