Probing the electronic nematic phase of FeSe with in-plane uniaxial stress
Clifford Hicks
Max Planck Institute for Chemical Physics of Solids
August 9th, 2018, 14:00, Science Hall 614
FeSe is an unconventional superconductor with a critical temperature of 9 K. It is also famous for having an electronic nematic transition at about 90 K. A nematic transition is a transition in which the point-group symmetry of a system is reduced, for example, from tetragonal to orthorhombic, but without any reduction in translation symmetry. In contrast to other iron-based superconductors, this transition occurs in FeSe without any nearby magnetic order. It is associated with a spontaneous increase in coherence of quasiparticles derived from xz (or yz) orbitals, and decrease in coherence of yz (or xz) quasiparticles. Although FeSe is mechanically extremely delicate, by affixing single crystals to substrates we have been able to apply, using piezoelectric actuators, tunable in-plane compressions of up to ~0.5%. In this seminar I will show that this anisotropic strain couples strongly to the nematic order. The most intriguing result is a strong contrast between the response to strain at low and high temperatures. At low temperatures, either the xz or yz contributes to conduction and the other does not, while at high temperature both orbitals contribute, and this change is most visible in the change of resistivity with strain (i.e. the elastoresistivity).