Caltech Logo

Materials Science Research Lecture

Wednesday, April 12, 2023
4:00pm to 5:00pm
Add to Cal
Noyes 147 (J. Holmes Sturdivant Lecture Hall)
Response of Weyl fermions - topological protection, fragility and cooperation
Haim Beidenkopf, PhD, Weizmann Institute of Science,


Topological electronic materials host exotic boundary modes, that cannot be realized as standalone states, but only at the boundaries of a topologically classified bulk. Topological semimetals, whose bulk electrons exhibit chiral Dirac-like dispersion, host Fermi-arc states on their boundaries. These surface bands disperse along open momentum contours terminating at the surface projections of the bulk Dirac nodes with opposite chirality. Such reduction of the surface degrees of freedom by their segregation to opposite surfaces of the sample is common to all topological states of matter and provides topological protection from their surface elimination. I will discuss three topological semimetallic systems that show distinct, though consistent, level of robustness. In the inversion symmetry broken Weyl semimetal TaAs the Fermi arc surface states hardly adhere to the underlying lattice potential. In contrast, in the time reversible symmetry broken Weyl semimetal Co3Sn2S2 the dispersion of the topological Fermi-arc bands, and even their inter-Weyl node connectivity, are found to vary with the surface potential. Our recent study of the ferromagnetic nodal line semimetal Fe3GeTe2 reveals that Weyl fermions may in fact cooperate with disorder and interactions to induce an anomalous Hall state of potentially superior protection akin to the role of disorder in stabilizing the integer quantum Hall effect. Our studies across material systems thus show a diverse response of topological semimetals to perturbations that may accordingly offer diverse ability to control and manipulate them.

More about the Speaker:

Haim Beidenkopf did his PhD at the Weizmann Institute of Science as an Adams Fellow awarded by the Israeli National Academy of Sciences and Humanities. He then did his postdoc in Ali Yazdani's group as a Dicke fellow where he studied topological insulators using scanning tunnelling microscopy. He joined the Weizmann Institute of Science as a researcher at the condensed matter physics department in 2012. His lab studies topological and correlated states of matter using combined scanning tunnelling microscopy with MBE material growth. He was elected member of the young Israel academy since 2018 and during the last year he chaired it. During 2022-2023 he is on sabbatical at UCSB's quantum foundry.

For more information, please contact Jennifer Blankenship by email at [email protected].