Topological surface states (TSSs) in a topological insulator are expected to be able to produce a spin-orbit torque that can switch a neighboring ferromagnet. This effect may be absent if the ferromagnet is conductive because it can completely suppress the TSSs, but it should be present if the ferromagnet is insulating. This study reports TSS-induced switching in a bilayer consisting of a topological insulator Bi 2 Se 3 and an insulating ferromagnet BaFe 12 O 19 . A charge current in Bi 2 Se 3 can switch the magnetization in BaFe 12 O 19 up and down. When the magnetization is switched by a field, a current in Bi 2 Se 3 can reduce the switching field by ~4000 Oe. The switching efficiency at 3 K is 300 times higher than at room temperature; it is ~30 times higher than in Pt/BaFe 12 O 19 . These strong effects originate from the presence of more pronounced TSSs at low temperatures due to enhanced surface conductivity and reduced bulk conductivity.
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Thermoelectric transport contribution from topological surface states vs 2D-electron gas in 10 nm Bi 2 Se 3
Topological surface states (TSSs) coexist with a rapidly formed two-dimensional electron gas (2DEG) at the surface of Bi 2 Se 3 . While this complex band structure has been widely studied for its interactions between the two states in terms of electrical conductivity and carrier density, the resulting thermopower has not been investigated as thoroughly. Here, we report measurements of the temperature dependent Seebeck coefficient ( S) and electrical conductivity ( σ) on an undoped 10 nm thin Bi 2 Se 3 film over the temperature range of 100–300 K to find an overall metal-like behavior. The measured S is consistent with the theory when assuming that both the TSS and the 2DEG contribute to thermoelectric transport. Our analysis further shows that the coefficient corresponds to a Fermi level situated well above the conduction band minima of the 2DEG, resulting in comparable contributions from the TSS and the 2DEG. The thermoelectric power factor ( S 2 σ) at 300 K increases by 10%–30% over the bulk. This work provides insights into understanding and enhancing thermoelectric phenomena in topological insulators.
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- Award ID(s):
- 2016136
- NSF-PAR ID:
- 10425499
- Date Published:
- Journal Name:
- Journal of Applied Physics
- Volume:
- 132
- Issue:
- 16
- ISSN:
- 0021-8979
- Page Range / eLocation ID:
- 164301
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1063/5.0100991
