The effect of substrate and surface plasmons on symmetry breaking at the substrate interface of the topological insulator Bi2Te3

Abstract

A pressing challenge in engineering devices with topological insulators (TIs) is that electron transport is dominated by the bulk conductance, and so dissipationless surface states account for only a small fraction of the conductance. Enhancing the surface-to-volume ratio is a common method to enhance the relative contribution of such states. In thin films with reduced thickness, the confinement results in symmetry-breaking and is critical for the experimental observation of topologically protected surface states. We employ micro-Raman and tip-enhanced Raman spectroscopy to examine three different mechanisms of symmetry breaking in Bi 2 Te 3 TI thin films: surface plasmon generation, charge transfer, and application of a periodic strain potential. These mechanisms are facilitated by semiconducting and insulating substrates that modify the electronic and mechanical conditions at the sample surface and alter the long-range interactions between Bi 2 Te 3 and the substrate. We confirm the symmetry breaking in Bi 2 Te 3 via the emergence of the Raman-forbidden mode. Our results suggest that topological surface states can exist at the Bi 2 Te 3 /substrate interface, which is in a good agreement with previous theoretical results predicting the tunability of the vertical location of helical surface states in TI/substrate heterostructures.

Investigations of proximity-induced superconductivity in the topological insulator Bi2Te3 by microRaman spectroscopy

“…The work function of Bi 2 Te 3 is W TI = 5.3 eV 18 and of YBCO is W YBCO = 6.1 eV 49 . Thus, once the materials are in contact, electron transfer is possible between the Bi 2 Te 3 and YBCO.…”

“…Thus, once the materials are in contact, electron transfer is possible between the Bi 2 Te 3 and YBCO. The infra-red (IR) active mode A 1u 2 (which is Raman-inactive in bulk Bi 2 Te 3 ) can be seen because of symmetry breaking due to charge transfer between a substrate and the TI 18 . As the pseudogap develops into a superconducting gap at temperatures T < 100 K, the intensity of the A 1u 2 mode decreases (see the violet line in Supplementary Fig.…”

“…Information about processes occurring at the interface can be also obtained from Raman scattering experiments for TI layers thinner than the penetration depth of the laser beam 18 .…”

Effect of an external/internal magnetic field on the photocurrent in Py-topological insulator heterojunction Ni80Fe20/TI (Bi2Te3/Bi2Se3/Bi2Te2Se)/p-Si devices

“…Simultaneously to investigate massless Dirac fermions, it is important to disrupt the time-reversal symmetry (TRS) of the topological surfaces via the perpendicular ferromagnetic ordering. 8 Consequently, the existence of robust spin-orbit coupling (SOC) and an exchange gap within the magnetic topological system not only gives rise to a diverse range of physics phenomena that break the time-reversal symmetry but also presents prospects for the development of advanced spintronics devices. 9,10 These devices would enable the efficient manipulation of spin states through the interplay between the topological and magnetic characteristics of the material.…”

Effect of Substrates and Thermal Treatments on Metalorganic Chemical Vapor Deposition-Grown Sb2Te3Thin Films

“…34,38,42 An efficient growth of topological insulators on crystalline silicon substrates, such as Si(111) or Si(100), would be attractive for their compatibility with the complementary metal-oxide semiconductor (CMOS) technology. 43,44 However, in view of the integration of TI-based components into electronic devices, it is pivotal to study their growth behavior on oxides (SiO 2 and Al 2 O 3 ), 45,46 as they are relevant, for instance, to develop thermoelectric materials, to investigate the topological states at the interface with the substrate, 47 or to allow back-gating. 48 The crystallinity and the morphological quality are relevant evaluation criteria.…”