Heavy Fermions

Scientists are interested in studying heavy fermion behaviour because it could lead to the design of new materials for high temperature super-conductors.

Cornell University Scientists imaging the electronic properties of a material composed of uranium, ruthenium and silicon, have found that the effects of heavy fermions begin to appear as the material is cooled below 55K, and, an even more unusual electronic phase transition occurs below 17.5K.

This phase transition was studied using spectroscopic imaging scanning tunneling microscopy (SI-STM) which measures the wavelength of electrons on the surface of the material in relation to their energy. From the wavelength and energy measurements scientists calculated the effective electron mass and found that these electrons were either very heavy, or, that they were acting like very heavy electrons because they were being slowed down. This suggests that these electrons are interacting with the uranium atoms, that is, acting as particles rather than acting as a wave.

Reference:
A. R. Schmidt, M. H. Hamidian, P. Wahl, F. Meier, A. V. Balatsky, J. D. Garrett, T. J. Williams, G. M. Luke & J. C. Davis. Imaging the Fano lattice to 'hidden order' transition in URu₂Si₂. Nature, 2010; DOI: 10.1038/nature09073

Study Questions

1/ What is a fermion?

2/ What is a super-conductor?

3/ What could high temperature superconductors be used for?

4/ What is the atomic symbol for:

• uranium
• ruthenium
• silicon

5/ To which group of the Periodic Table do each of the following elements belong?

• uranium
• ruthenium
• silicon

6/ Convert the following temperatures in Kelvin to ^oC.

• 55K
• 17.5K

7/ What is the relationship between mass, energy and wavelength that would allow Scientists to calculate the effective mass of an electron?

8/ Why would electrons appear to be heavier if they are slowed down?