Carnegie Mellon University

"Seeing'' The Covalent Bond: Simulating Atomic Force Microscopy Images

Speaker(s): 
Jim Chelikowsky
Dates: 
Monday, February 19, 2018 - 10:30am to 11:30am

Advances in atomic force microscopy (AFM) have made it possible to achieve unprecedented images of covalent bonds, in some cases even to resolve the bond order in polycyclic aromatics.   However, fundamental questions remain about interpreting the images and modeling the AFM tip.  For example, the bright spots in non-contact AFM images can have a close correspondence to the atomic structure of a given specimen, but there can be contrast changes with tip height that cannot be interpreted directly by atomic positions.  While the nature of the tip can be crucial in...

Fractional Statistics from Topological Magnetism

Speaker(s): 
Kenneth Burch
Dates: 
Wednesday, March 28, 2018 - 4:30pm

There is considerable excitement about in realizing non-Abelian Anyons, particles whose phase upon exchange depends on the path taken. Their observation signals the emergence of new topological phases and offers a route to quantum computation. I will outline the reasons to expect such particles in a particular quantum spin-liquid, where there is long-range entanglement but no magnetic order. I will then describe a particularly promising van-der-Walls material for realizing such particles, RuCl3. Via Raman spectroscopy, we have uncovered the Fermi statistics emerging from the Majorana...

Molecular Phenotypes of Structurally Homologous ETS Transcriptions Factors

Speaker(s): 
Gregory Poon
Dates: 
Thursday, September 28, 2017 - 4:30pm

 ETS transcription factors comprise an evolutionarily related family of genetic regulators that are ubiquitous in animals and control a myriad of physiologically critical processes. ETS proteins are united by a highly conserved DNA-binding domain, with overlapping target DNA preferences on the one hand, but are functionally diverse and non-redundant on the other. This so-called ìspecificity conundrumî besets not only our understanding of ETS homologs but also the structure-activity relationships of eukaryotic transcription factors in general. Translationally, it hampers efforts to develop...

The Hall Effects Edwin Hall Never Imagined

Speaker(s): 
Xiaofeng Jin
Dates: 
Thursday, September 14, 2017 - 4:30pm

The anomalous Hall Effect (AHE) is one of the oldest and most prominent transport phenomena in magnetic materials. However, the microscopic mechanism of the AHE has remained unresolved for more than a century because its rich phenomenology defies standard classification, prompting conflicting claims of the dominant processes. We differentiate these processes through temperature--‐dependent measurements on epitaxial Fe, Ni, Co, and NixCu1--‐x  Films of varying thickness [1],  [2]. The results allow an unambiguous identification of both intrinsic and extrinsic mechanisms of the anomalous...