Seminarium Fizyki Ciała Stałego

Grey tin, also known as α-Sn, is a nominally zero-gap semiconductor stable below 13°C, in which various topological phases can be induced by external strain  [1, 2]. Inparticular, the application of biaxial compressive strain transforms α-Sn into atopological Dirac semimetal (DSM), which can be further converted into a Weylsemimetal (WSM) via an external magnetic field. One effective method of strain engineering is molecular beam epitaxy (MBE) on a lattice-matched substrates, which also stabilizes the α-Sn phase at room temperature and above.
During this seminar, we will present comprehensive experimental results on both DSMand WSM phases observed in epitaxial layers of grey tin grown by MBE on hybridCdTe/GaAs substrates. Biaxial compressive strain and high crystalline quality of thesamples were confirmed by X-ray diffraction, transmission electron microscopy, andatomic force microscopy. The DSM phase was verified by band structure calculations based on magneto-optical measurements and directly observed via angle-resolved photoemission spectroscopy.
The main focus of the talk will be on the rich set of observed magnetotransport phenomena, which highlight the topologically non-trivial nature of charge carriers ingrey tin. Shubnikov - de Haas oscillations exhibiting a π Berry phase, along with negative longitudinal magnetoresistance attributed to the chiral anomaly, both supportthe presence of the WSM phase  [3]. We will also present results on anisotropic magnetoresistance and the planar Hall effect, which reinforce the topological characterof the material.
Altogether, our findings establish grey tin as a model system for studying 3Dtopological semimetals, with potential applications in spintronics and topological electronics.
The research was partially supported by the “MagTop” project (FENG.02.01-IP.05-0028/23) carried out within the “International Research Agendas” programme of the Foundation for Polish Science co-financed by the European Union under the European Funds for Smart Economy 2021-2027 (FENG).

References
[1] Liang Fu and Charles Kane, Phys. Rev. B 76 (2007), 045302
[2] Huaquing Huang and Feng Liu, Phys. Rev. B 95 (2017), 201101(R)
[3] Jakub Polaczyński et al., Materials Today 75, 135 (2024)