PARADIM Highlight #75

Topological insulators have great potential in novel electronic devices but are handicapped due to the difficulties in making macroscopic specimens insulating. Topological Kondo Insulators (TKI) have been proposed as a solution as the direct coupling between localized and delocalized electrons necessary for the Kondo effect forces insulating behavior in the bulk. Due to crystal availability constraints, most work on TKIs has focused on the material SmB₆.

To understand and elucidate the universal behaviors of surface states of a TKI, researchers at NHMFL teamed up with PARADIM to produce crystals of YbB₁₂, another TKI. With this first successful growth in the US, crystals of YbB₁₂ from PARADIM are enabling a new generation of studies of surface states in TKIs.

Planar tunneling spectroscopy at NHMFL shows the existence of surface Dirac fermions, with many similarities, and some key differences, to that found in SmB₆. The work advances the understanding of the surface chemistry and electronic structure of topological Kondo insulators, and the production of improved single crystals of this novel electronic material lay the groundwork for future explorations.

What has been achieved:

Topological insulators have great potential in novel electronic devices but are handicapped due to the difficulties in making macroscopic specimens insulating. Topological Kondo Insulators (TKI) have been proposed as a solution as the direct coupling between localized and delocalized electrons necessary for the Kondo effect forces insulating behavior in the bulk. Due to crystal availability constraints, most work on TKIs has focused on the material SmB₆. To understand and elucidate the universal behaviors of surface states of a TKI, researchers at NHMFL teamed up with PARADIM to produce crystals of YbB₁₂, another TKI. Previously only grown in Japan in limited scales, crystals of YbB₁₂ from PARADIM are enabling a new generation of studies of surface states in TKIs [1]. Planar tunneling spectroscopy at NHMFL shows the existence of surface Dirac fermions, with many similarities, and some key differences, to that found in SmB6. The work advances the understanding of the surface chemistry and electronic structure of topological Kondo insulators, and the production of improved single crystals of this novel electronic material lay the groundwork for future explorations.

Importance of the Achievement:

Topological Kondo Insulators offer a unique route to topological surface states with great potentials both for devices as well as to probe the fundamental physics of topology. The NHMFL team came to PARADIM to gain access to what is only the second known topological Kondo insulator, YbB₁₂. Working with PARADIM trainee Lucas Pressley and PARADIM REU Julia Trowbridge, laser floating zone was successfully used to produce untwinned single crystals of YbB₁₂, a very high, incongruently melting, boride, marking the first time this material was produced outside of Japan, and the first time with the laser FZ technique. It has enabled not just a direct comparisons with the other TKI (SmB₆) but also new measurements under high magnetic fields to explore the origins of quantum oscillations in an insulator.

Full reference:

A. Gupta, A. Weiser, L. Pressley, Y. Luo, C. Lygouras, J. Trowbridge, W.A. Phelan, C.L. Broholm, T.M. McQueen, and W.K. Park, “Topological surface states in the Kondo insulator YbB12 revealed via planar tunneling spectroscopy,“ Phys. Rev. B 107, 165132 (2023); DOI: 10.1103/PhysRevB.107.165132

Acknowledgments:

The work at NHMFL and FSU was supported by Grants No. NSF/DMR-2003405, No. NSF/DMR-1644779, and the State of Florida. The work at JHU was funded by Grant No. DOE/BES EFRC DE-SC0019331, JHU Catalyst Fund, and Grant No. NSF/DMR(PARADIM)-2039380.

Additional Information:

Access to data associated with materials growth is provided through the PARADIM Data Collective at DOI: https://doi.org/10.34863/r874-fw50.