1 Creati on of Chiral Interface Channels for Quantized Transport in Magnetic Topological Insulator Multilayer Heterostructures

2025-04-28 0 0 806.2KB 20 页 10玖币

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Creation of Chiral Interface Channels for Quantized Transport in Magnetic

Topological Insulator Multilayer Heterostructures

Yi-Fan Zhao1,5, Ruoxi Zhang1,5, Jiaqi Cai2, Deyi Zhuo1, Ling-Jie Zhou1, Zi-Jie Yan1, Moses H.

W. Chan1, Xiaodong Xu2,3, and Cui-Zu Chang1,4

1 Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA

2 Department of Physics, University of Washington, Seattle, WA 98195, USA

3 Department of Material Science and Engineering, University of Washington, Seattle, WA 98195,

USA

4 Materials Research Institute, The Pennsylvania State University, University Park, PA 16802,

USA

5 These authors contributed equally: Yi-Fan Zhao and Ruoxi Zhang

Corresponding authors: cxc955@psu.edu (C.-Z. C.)

Abstract: One-dimensional (1D) topologically protected states are usually formed at the

interface between two-dimensional (2D) materials with different topological invariants1,2.

Therefore, 1D chiral interface channels (CICs) can be created at the boundary of two

quantum anomalous Hall (QAH) insulators with different Chern numbers3-5. Such a QAH

junction can function as a chiral edge current distributer at zero magnetic field, but its

realization remains challenging. Here, by employing an in-situ mechanical mask, we use

molecular beam epitaxy (MBE) to synthesize QAH insulator junctions, in which two QAH

insulators with different Chern numbers are connected along a 1D junction. For the junction

between C = 1 and C = -1 QAH insulators, we observe quantized transport and demonstrate

the appearance of the two parallel propagating CICs along the magnetic domain wall at zero

magnetic field. Moreover, since the Chern number of the QAH insulators in magnetic

topological insulator (TI)/TI multilayers can be tuned by altering magnetic TI/TI bilayer

periods6,7, the junction between two QAH insulators with arbitrary Chern numbers can be

achieved by growing different periods of magnetic TI/TI on the two sides of the sample. For

the junction between C = 1 and C = 2 QAH insulators, our quantized transport shows that a

single CIC appears at the interface. Our work lays down the foundation for the development

of QAH insulator-based electronic and spintronic devices, topological chiral networks, and

topological quantum computations.

Main text: Topological materials are unique solid-state systems that exhibit topologically

protected boundary states (i.e., edge/surface states). As a consequence of the intrinsic protection

that prevents impurity scattering and allows for manipulations and measurements, these

topological edge/surface states have been predicted to be useful for the next generation of

quantum-based electronic and spintronic devices as well as topological quantum computations1,2.

Over the past ~15 years, topological band theory has played a key role in the discovery of new

topological materials1,2,8,9. The interplay between the bulk topology and protected edge/surface

states in topological materials is usually referred to as the bulk-boundary correspondence. In other

words, the formation of the topological edge/surface states is guaranteed by the topological

character of the bulk bands. In addition to the edge/surface states in naturally occurring topological

materials, topologically protected interface states can also be engineered at the interfaces between

two materials with different topological invariants.

The quantum anomalous Hall (QAH) insulator is a prime example of two-dimensional (2D)

topological states and possesses dissipation-free chiral edge states (CESs) on its boundaries 3,9-14.

In QAH insulators, the Hall resistance is quantized at h/e2 and the longitudinal resistance vanishes

under zero magnetic field. The QAH effect was first realized in magnetically doped topological

insulators (TI), specifically, Cr-doped and/or V-doped (Bi, Sb)2Te3 thin films 3,12,13,15-19. More

recently, the QAH effect was also observed in thin flakes of intrinsic magnetic TI MnBi2Te4 (Ref.20)

and moiré materials formed from graphene21 or transition metal dichalcogenides 22. According to

topological band theory, chiral interface channels (CICs) also appear at the interfaces between

two QAH insulators with different Chern numbers C. The CIC number is determined by the

difference in C between these two adjacent QAH insulator domains. The CIC propagating

direction (i.e., chirality) is dictated by the relative orientation of the spontaneous magnetization in

the two QAH insulators 1,2,23. Therefore, the creation and manipulation of CESs and/or CICs can

facilitate the development of topological chiral networks24,25, which have the potential for

applications in energy-efficient QAH-based electronic and spintronic devices. Moreover, it has

been proposed that chiral Majorana physics in QAH/superconductor heterostructures can be probed

by placing a grounded superconductor island on the domain boundary between C = +1 and C =-1

QAH insulators in a Mach-Zehnder interferometer configuration26,27. Magnetic force microscope

(MFM)28 and the Meissner effect of a bulk superconductor cylinder29 have been employed to create

a magnetic domain wall (DW) in QAH insulators, which is unfeasible for device fabrication.

Therefore, the synthesis of a designer magnetic DW in a QAH insulator (i.e., a junction between

C = +1 to C = -1 QAH insulators) and the junction between two QAH insulators with arbitrary C

are highly desirable with exceptional promise for potential topological circuit applications.

In this work, we synthesize QAH insulator junctions in magnetic TI/TI multilayer

heterostructures by employing an in-situ mechanical mask in our MBE chamber. Our electrical

transport measurements show quantized transport in these QAH insulator junctions, which

indicates the appearance of the CICs near the magnetic DW. For the junction between C = +1 to

C = -1 QAH insulators, we find two parallel propagating CICs at the magnetic DW. For the

junction between C = 1 to C = 2 QAH insulators, one CES tunnels through the QAH DW entirely,

while the second CIC propagates along the QAH DW. The number of CICs is determined by the

difference in C between the two QAH insulators. We show these QAH insulator junctions with

robust CICs are feasible for device fabrication and thus provide a platform for the development of

QAH-based electronic and spintronic devices and topological quantum computations.

All QAH junction samples are grown on heat-treated ~0.5 mm thick SrTiO3(111) substrates in

a commercial MBE chamber (Omicron Lab10) (Method; Supplementary Figs. 1 and 2). The Bi/Sb

ratio in each layer is optimized to tune the chemical potential of the sample near the charge neutral

point 6,7,12,13,30. The electrical transport measurements are carried out in a Physical Property

Measurements System (Quantum Design DynaCool, 2 K, 9 T) and a dilution refrigerator (Leiden

Cryogenics, 10 mK, 9 T) with the magnetic field applied perpendicular to the sample plane. The

mechanically scratched Hall bars are used for electrical transport measurements. More details

about the MBE growth and electrical transport measurements can be found in Methods.

We first focus on the junction between C = +1 to C = -1 QAH insulators (Fig. 1a). To create

this junction, we grow 2 quintuple layers (QL) (Bi,Sb)1.74Cr0.26Te3/2 QL (Bi,Sb)2Te3/2 QL

(Bi,Sb)1.74Cr0.26Te3 sandwich heterostructure. Next, by placing an in-situ mechanical mask as close

as possible to the sample surface, we deposit 2 QL (Bi, Sb)1.78V0.22Te3 on one side of the sample.

Since the coercive field (0Hc) of V-doped (Bi, Sb)2Te3 films is much larger than that of Cr-doped

(Bi, Sb)2Te3 films 13,31, the 0Hc of the Cr-doped (Bi, Sb)2Te3 sandwich layer is enhanced as a result

of the existence of the interlayer exchange coupling32-34. We note that the middle 2 QL undoped

(Bi, Sb)2Te3 layer is chosen here to couple the magnetizations of the two Cr-doped (Bi, Sb)2Te3

layers. As a consequence, the areas with (i.e., Domain II) and without (i.e., Domain I) 2 QL (Bi,

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摘要：

1CreationofChiralInterfaceChannelsforQuantizedTransportinMagneticTopologicalInsulatorMultilayerHeterostructuresYi-FanZhao1,5,RuoxiZhang1,5,JiaqiCai2,DeyiZhuo1,Ling-JieZhou1,Zi-JieYan1,MosesH.W.Chan1,XiaodongXu2,3,andCui-ZuChang1,41DepartmentofPhysics,ThePennsylvaniaStateUniversity,UniversityPark,PA1...

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1 Creati on of Chiral Interface Channels for Quantized Transport in Magnetic Topological Insulator Multilayer Heterostructures

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