Anomalous quantization trajectory and parity anomaly in Co cluster decorated BiSbTeSe2 nanodevices

Abstract

Dirac Fermions with different helicities exist on the top and bottom surfaces of topological insulators, offering a rare opportunity to break the degeneracy protected by the no-go theorem. Through the application of Co clusters, quantum Hall plateaus were modulated for the topological insulator BiSbTeSe2, allowing an optimized surface transport. Here, using renormalization group flow diagrams, we show the extraction of two sets of converging points in the conductivity tensor space, revealing that the top surface exhibits an anomalous quantization trajectory, while the bottom surface retains the 1/2 quantization. Co clusters are believed to induce a sizeable Zeeman gap ( > 4.8 meV) through antiferromagnetic exchange coupling, which delays the Landau level hybridization on the top surface for a moderate magnetic field. A quasi-half-integer plateau also appears at −7.2 Tesla. This allows us to study the interesting physics of parity anomaly, and paves the way for further studies simulating exotic particles in condensed matter physics.

Enhancement in surface mobility and quantum transport of Bi2−xSbxTe3−ySey topological insulator by controlling the crystal growth conditions

“…The difficulty in isolating bulk contributions from surface state transport limits the implementation of TIs in electronic devices 12 . More recent studies focus on the ternary and quaternary tetradymite Bi-based TI, namely Bi2Te2Se (BTS) [13][14][15][16][17] and Bi2-xSbxTe3-ySey [18][19][20][21][22][23][24][25] , which show a large bulk resistivity, ambipolar surface transport and clear quantum oscillations. Particularly, the stoichiometric BiSbTeSe2 (BSTS) is a very promising TI candidate as it manifests high quality integer quantum Hall effect originating from its surface states [23][24][25] .…”

“…Various growth techniques have been reported to prepare BSTS single crystals. Among those, melting [17][18][19][20][21][22]24,25 and vertical Bridgman 13,14,23 methods are the most widely used synthetic methods.…”

“…Obviously, melting growth can cause polycrystalline ingot as there is no fixed single nucleation site. However, numerous literature has claimed that they achieved single crystal growth using the melting method [17][18][19][20][21][22]24,25 . On the other hand, the vertical Bridgman method applies a vertical motion to translate the materials along a temperature gradient from hot to cold zones at a very slow rate, as shown in Fig.…”

Topological Insulator-Based van der Waals Heterostructures for Effective Control of Massless and Massive Dirac Fermions

“…Quaternary Bi-based TI compounds of the form Bi2-xSbxTe3-ySey exhibit a large bulk band gap and more intrinsic bulk conduction which allow probing of the surface states 3 . Integer quantum Hall effect (QHE) in magnetotransport of 3D TIs provides a strong signature of the topological surface states (TSS) 4,5,6,7,8,9 and has been observed at a strong external magnetic field in BiSbTeSe2 (BSTS) crystals 5,6,8,9 . The quantization of Hall conductivity in units of (n+½) e 2 /h, where n is the (integer) Landau level index of the TSS, is due to two unique characteristics of TSS, namely spin nondegeneracy and π Berry's phase 5,6,10 .…”

Layered Topological Insulators and Semimetals for Magnetoresistance Type Sensors

“…Anomalous in‐plane AMR was observed in Bi 2 Se 3 TI films grown by MBE (Figure b), which is likely induced by the anisotropy of spin scattering probability of topological SSs. The Bi 2‐ x Sb x Te 3‐ y Se y (BSTS) TI is preferable with an insulating bulk to develop a high AMR ratio . Sulaev et al.…”