“Itinerant density wave instability at continuous thermal and quantum phase transitions”, Yejun Feng (Okinawa Institute of Science and Technology )

Date: 
Wednesday, March 22, 2017 - 4:00pm
Series: 
Condensed Matter Journal Club Seminars

Instability at the Fermi surface underlies many types of correlated electron states such as charge and spin density waves, magnetic and excitonic insulators, and superconductivity.  While the pairing of electronic states is relatively well understood in superconductors, this topic remains a major contentious issue in density wave systems, especially in light of numerical calculations in recent decade. Here I will address this topic of Fermi surface instability through an experimental perspective [1], using x-ray diffraction to provide microscopic insights, and using high pressure as a tuning technique to tilt the relative coupling strength between lattice and itinerant carriers. Our analysis reveals that the Fermi surface instability dominates at the incipience of a continuous phase transition, and in the case of spin density wave, results a purely sinusoidal wave which is decoupled from the charge background. Within the ordered state, the itinerant instability is always disguised by the finite order parameter strength and lattice coupling. Our work also highlights the importance to establish model systems for continuous quantum phase transition, which is an interest of decades-long search and helped in here by our microscopic x-ray diffraction probe.

 

[1] Y. Feng et al., Nature Physics, 11, 865 (2015). 

Location: 
PAB 4-330