Monthly Spring 290S/290K Quantum Materials Seminar speakers Zhi-Qiang Gao and Tomo Soejima (both UC Berkeley) on Wednesday, February 15 at 2:00 pm PST in Physics South 402

Time/Venue Wednesday, February 15 at 2:00 pm PST in Physics South 402
Host Bob Birgeneau
Speaker 1 Zhi-Qiang Gao (Dung-Hai Lee Group)
Title Is the Coherence Peak Modulation in Eu-1144 Iron Pnictide Superconductor Due to Pair Density Wave?
Abstract Coherence peak modulation has been detected in recent STM experiments performed in high critical temperature superconductor iron pnictide Eu-1144. Such a particle-hole symmetric modulation is observed to appear simultaneously with a ferromagnetic order. It is argued to be a pair density wave, and absence of other density wave orders further implies it not to be a secondary order of other density waves. In this talk I will introduce an impurity scattering scenario proposed to explain the experiments. I will show that in this nodeless superconductor, magnetic impurity scattering can induce the particle-hole symmetric coherence peak modulation in the presence of a ferromagnetic order or a Zeeman field, which is consistent with the experimental observations. Therefore, according to our theory, the coherence peak modulation in Eu-1144 is originated from impurity scattering, instead of a pair density wave.
Speaker 2 Tomo Soejima (Zaletel Group)
Title Can we see ground states of twisted bilayer graphene?
Abstract The Magic angle twisted bilayer graphene has been shown to exhibit a variety of strong-correlated behavior, most notably superconductivity and correlated insulating phenomenon.
There have been a plethora of theoretical proposals about the nature of such correlated insulating states, but there has not been any definitive experimental confirmation.
In this talk, I will showcase how atomically-resolved Scanning Tunneling Microscopy (STM) can be used to detect symmetry breaking in twisted bilayer graphene.
This can be used to differentiate between popular ground state candidates by directly probing their symmetry breaking. I will in particular on Kramers Intervalley Coherent (K-IVC) insulator and Incommensurate Kekule Spiral (IKS) state, which show drastically different symmetry properties