Investigating thermodynamic properties of correlated electronic phases in graphene by chemical potential measurements

Monday, September 13, 2021

10:00 - 11:00 am

Strong electronic interactions in narrow electronic bands give rise to emergent phases such as fractional quantum Hall (FQH) states, charge density waves, and magnetism. Quantitative understanding of these phases requires probing thermodynamics quantities, which cannot be directly accessed through convential transport measurements that are only sensitive to electron scattering. My talk will focus on using chemical potential measurements to study thermodynamic quantities in several electron-correlated states hosted in graphene heterostructures. Applied to partially filled Landau levels in monolayer graphene, this approach enables us to precisely measure the ground state energy of the FQH liquids and electron solid states. I will discuss the comparison between our experimental results and theoretical calculations which reveals microscopic pictures of these phases. Recently, intrinsic narrow bands have been discovered in twisted bilayer graphene with specific rotating angle. A combined spin and valley (isospin) degeneracy is spontaneously broken by strong electronic interactions in the narrow band. I will also discuss the measurements of chemical potential to investigate isospin magnetism in the system. By determining magnetization and entropy, our measurements indicate an isospin ferromagnetic state that "melts" into an unpolarized Fermi liquid with decreasing temperatures. Our findings imply that isospin fluctuations at finite temperatures might be an important mechanism in understanding certain temperature dependent resistivity phenomena and superconductivity in such systems.

virtual (zoom)
Fangyuan Yang
UC Santa Barbara