Heavy fermions

Heavy fermions:  
In heavy fermion physics there is the widely discussed “small to large Fermi surface transition”. This is strikingly analogous to the carrier density transition in the cuprates discussed above. Because of such similarity we had a discussion session on the heavy fermion phases and phase transitions. Several candidate materials where the quantum paramagnet with small Fermi surface (analogous to the state in cuprates with x carrier concentration but no symmetry breaking) are discussed. Another focal point in heavy fermion physics is SmB₆. It is proposed by a participant of our workshop that this system is a “Kondo topological insulator”. There are several experimental evidence supporting this proposal. However the experimental result of another participant raised some doubts. The most striking observation is a state which conduct heat as a metal does but it does not conduct electricity. Moreover such state seems to have some kind of Fermi surface giving rise to the oscillation of magnetization as a function of magnetic field. These results arose the interests of many participants. We also learned of recent experiments that demonstrate the existence of a large number of phases in the vicinity of the coexistence between antiferromagnetism and superconductivity. One of the conclusions is that superconductivity seems to prefer C_2 instead of C_4 symmetry.