Chiral Tunneling of Topological States: Towards the Efficient Generation of Spin Current Using Spin-Momentum Locking

Habib, K. M. Masum; Sajjad, Redwan N.; Ghosh, Avik W.

doi:10.1103/physrevlett.114.176801

Phys. Rev. Lett.

2015

DOI: 10.1103/physrevlett.114.176801

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Chiral Tunneling of Topological States: Towards the Efficient Generation of Spin Current Using Spin-Momentum Locking

K. M. Masum Habib

Redwan N. Sajjad

Avik W. Ghosh

Abstract: We show that the interplay between chiral tunneling and spin-momentum locking of helical surface states leads to spin amplification and filtering in a 3D topological insulator (TI). Our calculations show that the chiral tunneling across a TI pn junction allows normally incident electrons to transmit, while the rest are reflected with their spins flipped due to spin-momentum locking. The net result is that the spin current is enhanced while the dissipative charge current is simultaneously suppressed, leading to… Show more

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Cited by 29 publications

(40 citation statements)

References 36 publications

(44 reference statements)

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“…This property provides the spin rectification effect and a few other spintronic applications. 19,20 Moreover, under a magnetic field an 1D electronic channel develops along the junction. 21 Due to layered structures of most of 3D TI crystals, the stack of n-and p-type TI crystals is feasible only in the vertical direction.…”

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confidence: 99%

Atomically Abrupt Topological p–n Junction

Kim

Jin

Kho³

et al. 2017

ACS Nano

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Topological insulators (TI's) are a new class of quantum matter with extraordinary surface electronic states, which bear great potential for spintronics and error-tolerant quantum computing. In order to put a TI into any practical use, these materials need to be fabricated into devices whose basic units are often p-n junctions. Unique electronic properties of a 'topological' p-n junction were proposed theoretically such as the junction electronic state and the spin rectification. However, the fabrication of a lateral topological p-n junction has been challenging because of materials, process, and fundamental reasons. Here, we demonstrate an innovative approach to realize a p-n junction of topological surface states (TSS's) of a three-dimensional (3D) topological insulator (TI) with an atomically abrupt interface. When a ultrathin Sb film is grown on a 3D TI of Bi 2 Se 3 with a typical n-type TSS, the surface develops a strongly p-type TSS through the substantial hybridization between the 2D Sb film and the Bi 2 Se 3 surface. Thus, the Bi 2 Se 3 surface covered partially with Sb films bifurcates into areas of n-and p-type TSS's as separated by atomic step edges with a lateral electronic junction of as short as 2 nm. This approach opens a different avenue toward various electronic and spintronic devices based on well defined topological p-n junctions with the scalability down to atomic dimensions.Keywords topological insulator, topological p-n junction, angle-resolved photoemission spectroscopy, scanning tunneling microscopy/spectroscopy, ultrathin Sb film Surface states of topological insulators, 1,2 called topological surface states (TSS's), are robustly protected by the bulk topological nature and form necessarily a Dirac band with their spins locked helically with momentum. 1-6 These unique properties find obvious merits in spintronic applications and can yield a Majorana Fermion in proximity with supercon-2 ductivity. 7,8 However, there has been a huge barrier in making devices based on TSS's. The challenge is closely related to the notorious issue of controlling impurities or dopants in a TI crystal. While quite a few works tried to control the chemical potential of a TSS by impurity doping, 4,9-14 the deterioration of the surface channel and the inclusion of bulk channels were inevitable in many cases. Especially, the tunability of the chemical potential was often not enough to make a good p-type TSS. Fabricating a well defined topological p-n junction is even more challenging, 15-18 which represents one of the most important technological issues in staging applications of TI's. Nevertheless, a topological p-n junction, defined as an electronic junction of a p-and a n-type TSS, features unique properties, which are not shared by conventional p-n junctions of semiconductors but promise attractive new applications. 7,8 At a topological p-n junction, the electron scattering and transport are largely governed by the spin polarization of TSS's involved. This property provides the spin rectification eff...

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mentioning

confidence: 99%

Atomically Abrupt Topological p–n Junction

Kim

Jin

Kho³

et al. 2017

ACS Nano

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“…Their helical spin-locked Dirac-cone surface states34 are ideal for ultralow dissipative electrical transport, which includes both spin and charge degrees of freedom, and a new design of a logical circuit applicable to various electronic devices can be considered567891011121314. One of the most important features for utilizing such intriguing spin-locked surface states is the topological p-n junction (TPNJ)789. Theoretically, the inverted helical spin structure in contact between p-type and n-type Dirac cones can bring about superior rectification of spin and charge current.…”

mentioning

confidence: 99%

In-plane topological p-n junction in the three-dimensional topological insulator Bi2−xSbxTe3−ySey

Tanabe

Satake

et al. 2016

Nat Commun

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A topological p-n junction (TPNJ) is an important concept to control spin and charge transport on a surface of three-dimensional topological insulators (3D-TIs). Here we report successful fabrication of such TPNJ on a surface of 3D-TI Bi2−xSbxTe3−ySey thin films and experimental observation of the electrical transport. By tuning the chemical potential of n-type topological Dirac surface of Bi2−xSbxTe3−ySey on its top half by using tetrafluoro-7,7,8,8-tetracyanoquinodimethane as an organic acceptor molecule, a half surface can be converted to p-type with leaving the other half side as the opposite n-type, and consequently TPNJ can be created. By sweeping the back-gate voltage in the field effect transistor structure, the TPNJ was controlled both on the bottom and the top surfaces. A dramatic change in electrical transport observed at the TPNJ on 3D-TI thin films promises novel spin and charge transport of 3D-TIs for future spintronics.

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“… 18 and references therein). With successful demonstrations of writing information into a conventional metallic magnet at room temperature using materials with SHE there is also intense theoretical interest and discussion 19 20 21 22 23 24 25 in understanding the physics and implications of this type of effect in TI with particular interest in their capability of spin current generation.…”

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confidence: 99%

Spin Circuit Model for 2D Channels with Spin-Orbit Coupling

Hong¹,

Sayed²,

Datta³

2016

Sci Rep

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In this paper we present a general theory for an arbitrary 2D channel with “spin momentum locking” due to spin-orbit coupling. It is based on a semiclassical model that classifies all the channel electronic states into four groups based on the sign of the z-component of the spin (up (U), down (D)) and the sign of the x-component of the velocity (+, −). This could be viewed as an extension of the standard spin diffusion model which uses two separate electrochemical potentials for U and D states. Our model uses four: U+, D+, U−, and D−. We use this formulation to develop an equivalent spin circuit that is also benchmarked against a full non-equilibrium Green’s function (NEGF) model. The circuit representation can be used to interpret experiments and estimate important quantities of interest like the charge to spin conversion ratio or the maximum spin current that can be extracted. The model should be applicable to topological insulator surface states with parallel channels as well as to other layered structures with interfacial spin-orbit coupling.

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Chiral Tunneling of Topological States: Towards the Efficient Generation of Spin Current Using Spin-Momentum Locking

Cited by 29 publications

References 36 publications

Atomically Abrupt Topological p–n Junction

Atomically Abrupt Topological p–n Junction

In-plane topological p-n junction in the three-dimensional topological insulator Bi2−xSbxTe3−ySey

Spin Circuit Model for 2D Channels with Spin-Orbit Coupling

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