Abstract:  

Metamaterials are engineered to have properties not found in nature, such as a negative optical index of refraction, one-way light or vibration waves, or exotic elastic behavior.  Made-to-order structures at length scales as short as a micron can now be fabricated with advanced materials processing like 3D printing. Topology is a unifying mathematical concept related to properties that do not change under continuous changes in parameters.  Topological materials, like topological insulators, have bulk excitation spectra characterized by topological invariants, associated with the opening of bandgaps, that determine physical properties like the Hall conductivity or the nature of edge excitations.  This talk will discuss mechanical metamaterials with topologically protected zero-energy edge states in an idealized limit.  These states exist at every wavenumber on a surface so that any surface shape distortion costs no energy. Changing the topological class of the material causes one or more zero modes per wavenumber to move from one side of a sample to the opposite creating rigid and supersoft edges.

 

[1] K. Sun, A. Souslov, X. M. Mao, and T.C. Lubensky, PNAS 109, 12369-12374 (2012).

[2] C.L. Kane and T.C. Lubensky, Nature Physics 10, 39-45 (2014)

[3] T. C. Lubensky, C. L. Kane, X. Mao, A. Souslov, K. Sun, Rep. Prog. Phys. 78, 073901 (2015).

[4]  D. Z. Rocklin, B. G. G. Chen, M. Falk, V. Vitelli, and T. C. Lubensky, "Mechanical Weyl Modes in Topological Maxwell Lattices," Phys. Rev. Lett. 116, 135503 (2016).

[5] O. Stenull, C. L. Kane, and T. C. Lubensky, "Topological Phonons and Weyl Lines in Three Dimensions," Phys. Rev. Lett. 117 (6), 068001 (2016).

[6]  J. E. S. Socolar, T. C. Lubensky, and C. L. Kane, "Mechanical graphene," New Journal of Physics 19, 025003 (2017).

 

Please note: The Colloquium Ehrenfestii takes place on Wednesday evenings starting at 19:30 hours in the main auditorium of the Oort building. Before the Colloquium, there is a common dinner in the canteen located on the ground floor of the  Oort building. The dinner starts at 18:00 hours sharp and is free of charge, under the condition that one attends the colloquium and that one has made a reservation before noon on the Tuesday preceding the colloquium. The registration form is only accessible from within the University (to block spammers); if you would like to register for the dinner from outside the University, please send an email to fran@lorentz.leidenuniv.nl. The revolving doors to the Oort building  are accessible until 9 pm after that they are locked and one should instead use the sliding doors directly adjacent to the Huygens building: these can be opened with an electronic key (seek help from locals).