Session: 08-01: Micro/Nanoscale Heat Conduction

Paper Number: 122048

122048 - Phonons in Ultrathin Membranes and Topological Waveguides 

Abstract: 

Phonons in Ultrathin Membranes and Topological Waveguides

 

 Clivia M. Sotomayor-Torres^1,2,*

¹Catalan Institute of Nanoscience and Nanotechnology (ICN2), Campus UAB, 08193 Bellaterra, Spain,

² Institució Catalana de Recerca i Estudis Avançats, 08010 Barcelona, Spain

*present address : International Iberian Nanotechnology Laboratpory, Av. Mestre José Veiga s/n
4715-330 Braga – Portugal
 

clivia.sotomayor@inl.int

 

Our recent endeavours to achieve topological protection in phononic waveguides will be reported. Our experimental work is anchored in scalable Si-based laboratory-scale devices operating a room temperature.  In the solid state, the valley electrons have non-trivial Berry curvatures which results in anomalous quantum Hall states in graphene [1]. The same analogy can be applied to mechanical waves to obtain protected transport of phonons at kHz [2], MHz [3] and GHz [4] frequencies. Such two-dimensional chiral states are topologically protected as long as there is no inter-valley scattering generated by geometrical defects. In figure 1(a) top, the unit cell of the Valley-Hall Phononic crystal with periodic distance a is shown. It is composed of two rounded and inverted triangles connected by three equally spaced bars. The crystal is designed for fabrication in silicon-on-insulator (SOI) wafers of 220 nm thickness and with a periodic distance a of the crystal of 381 nm. We calculated the dispersion relation along the entire first Brillouin zone for the two phononic bands that shows Dirac points in each vertex of the reciprocal space. The frequency of this Dirac point is approximately 13.5 GHz.  

A phononic gap at the Dirac point can be opened by perturbing the mass distribution of the original arrangement. In this case, modifying the size of the triangles composing the unit cell, so that one of them becomes larger and the other becomes smaller results in the opening of a gap spanning from 13 to 14 GHz. Once the degeneracy in the Dirac points is lifted, it is possible to create topological waveguides by breaking the crystal symmetry. Flipping the unit cell to form two different crystals and joining them, a topological interface can be created as highlighted by the dashed line in Figure 2(a).

We obtained the simulated phononic dispersion relation for the selected geometry. The considered material is the [110] crystalline silicon used in SOI wafers. We find an isolated mode inside the gap going from 13 GHz for k_x = 0, to 13.7 GHz for k_x = π/a with out-of-plane displacement fully localized at the topological interface. Samples have been recently fabricated in SOI wafers and Brillouin light scattering experiments [5] are in progress.

Work with Omar Florez, Sara Purjamal, And Jouni Ahopelto.

References

¹ F. D. M. Haldane, and S. Raghu, Phys. rev. Lett. 100, 013904 (2008).

² C. He et al, Nat. Phys. 12, 1124-1129 (2016).

³ J. Lu et al, Nat. Phys. 13, 369-374 (2017).

⁴ Q. Zhang et al, Nat. Electron. 5, 157-163 (2022).

⁵ O. Florez et al, Nat. Nanotechnol. 17, 947-951 (2022)

Presenting Author: Clivia M. Sotomayor Torres International Iberian Nanotechnology Laboratory

Presenting Author Biography: Prof. Dr. Clivia. M Sotomayor Torres was born in Arica, Chile, and obtained her PhD in Physics in 1984 from the University of Manchester, UK. She held tenured academic appointments at Saint Andrews and Glasgow universities in the UK, a C4 professorship at Wuppertal University in Germany, was a research professor at the National university of Ireland University College Cork (Tyndall National Institute). From 2007 to 2023 she was an ICREA research professor and group leader of the Phononic and Photonic Nanostructures group at the Catalan Institute of Nanoscience and Nanotechnology in Spain. Clivia received awards from the Royal Society of Edinburgh, the Nuffield Foundation and an Amelia Earhart Fellowship from ZONTA International (USA). She carries out research in the science and engineering of phononic nanostructures, nanophotonics and thermal transport. She was a guest professor at the P. Sabatier Univ. Toulouse, at the Royal Institute of Technology (KTH) in Sweden and the Mittlesten-Schied Guest Professor at the University of Wuppertal in Germany. She has supervised over 20 PhD theses and more than 60 postdoctoral researchers. She has published extensively and has been cited over 12 000 times. Clivia has been and is an active participant in European level research since 1989 and coordinated several projects. She has held several commissions of trust including membership of the Danish National Research Council board, vice-chair of the Scientific Board of the Silicon Austria Laboratory and co-Chair and Chair of the Advisory Group of the EU Future and Emerging Technologies. In 2020 she was elected to the Academia Europaea and since 2021 she is a holder of an ERC Advanced Grant carrying out research on phonons for information and communication Technologies. Since September 2023 she is the Director General of the International Iberian Nanotechnology Laboratory (INL) in Braga, Portugal.

Authors:

Clivia M. Sotomayor Torres International Iberian Nanotechnology Laboratory