Abstract:

Charge and spin density waves (CDW and SDW) are two basic forms of order in solid, and have been one of the focus in condensed matter physics. In our study of various density wave systems, we found their microscopic mechanisms are often unconventional. In this talk I will give several examples about the rich and anomalous density waves in complex materials.
1. The Transition Metal Dichalcogenides (TMD) compound with 2H structure is the first system in which two dimensional Charge Density Wave (CDW) is discovered. However it had puzzles people for nearly 30 years that it can be explained neither by the Fermi surface nesting scenario, nor the saddle point scenario. We measured the electronic structure of 2H-NaxTaS2 and NbSe2 and proved that the CDW is not related to the Fermi Surface but to the ¡°Fermi Patch¡± region all over the Brillion zone. This new mechanism could explain the charge instability in many strongly coupled systems
2. Chinese scientists contribute a lot in the development of iron-arsenic based high temperature superconductor since its discovery in the year of 2008. Similar to the cuprate, there are coexistence of magnetic order and superconductivity in the iron-based systems; the mechanism of its itinerant magnetic ordering calls for further investigation. Normally itinerant magnetic ordering is induced by the Fermi surface nesting while we find in materials such as BaFe2As2 the Spin Density Wave is caused by the exchange splitting , moreover the coexistence of superconductivity and SDW is discovered in Sr0.8K0.2Fe2As2.
 
 
  Return