Quantifying spin for future spintronics: Spin-momentum locking induced anisotropic magnetoresistance in monolayer WTe2

A RMIT-led, worldwide collaboration printed this week has noticed massive in-plane anisotropic magnetoresistance (AMR) in a quantum spin Corridor insulator and the spin quantization axis of the sting states might be well-defined.

A quantum spin Corridor insulator (QSHIs) is a two-dimensional state of matter with an insulating bulk and non-dissipative helical edge states that show spin-momentum locking, that are promising choices for growing future low-energy nano-electronic and spintronic units.

The FLEET collaboration of researchers at RMIT, UNSW and South China Regular College (China) affirm for the primary time the existence of enormous in-plane AMR in monolayer WTe2 which is a novel QSHI with increased important temperatures.

By permitting electrical conduction with out wasted dissipation of vitality, such supplies might kind the premise of a brand new future technology of ultra-low vitality electronics.


The rise of topological insulators has provided important hope for researchers looking for non-dissipative transport, and thus an answer to the already noticed plateauing of Moore’s regulation.


In contrast to previously-reported quantum-well programs, which might solely exhibit quantized edge transport at low temperatures, the latest statement of quantized edge transport at 100 Okay in a predicted massive band-gap QSHI, monolayer WTe2 , has shed extra gentle on the functions of QSHI.

“Though we had gained a lot expertise in stacking van der Waals (vdW) heterostructures, fabricating monolayer vdW units was nonetheless difficult for us,” the examine’s first creator Dr Cheng Tan says.

“As a result of monolayer WTe2 nanoflakes are troublesome to acquire, we firstly centered on a extra mature materials, graphene, to develop the easiest way for fabricating monolayer WTe2 vdW units” says Cheng, who’s a FLEET Analysis Fellow at RMIT College in Melbourne.

Because the monolayer WTe2 nanoflakes are additionally very delicate to the air, protecting ‘fits of amours’ manufactured from inert hBN nanoflakes ought to be utilized to encapsulate them. Extra, the meeting was carried out in an oxygen- and water-free glove field earlier than sequence of assessments exterior. After some effort, the crew then efficiently fabricated the monolayer WTe2 units with gate electrodes and noticed typical transport behaviours of gated monolayer WTe2.

“For supplies for use in future spintronic units, we want a technique to find out spin traits, particularly the course of spin,” says Dr Guolin Zheng (additionally at RMIT).


“Nonetheless, in monolayer WTe2, spin-momentum locking (an important property of QSHI) and whether or not spin quantization axis in its helical edge states might be decided had but to be experimentally demonstrated.”

Anisotropic magnetoresistance (AMR) is an efficient transport measurement technique to disclose the connection between the electrons’ spin and momentum when the present is spin-polarized.

Contemplating that the sting states of a QSHI solely permit the transport of spin-polarized electrons, the crew then used AMR measurements to discover the potential spin-momentum locking within the edge states of monolayer WTe2.

“Fortuitously, we discovered the correct technique to cope with the monolayer WTe2 nanoflakes,” says co-author Dr Feixiang Xiang (UNSW). “So then we carried out angular-dependent transport measurements to discover the potential spin options within the edge states.”


Nonetheless, the topological edge states should not the one attainable trigger for spin-momentum locking and in-plane AMR results in a QSHI. Rashba splitting might additionally generate related results, which can make the experimental outcomes unclear.

“Fortuitously, topological edge states and Rashba splitting induce very totally different gate-dependent in-plane AMR behaviours, as a result of the band construction beneath these two conditions are nonetheless very totally different.” says co-author Prof Alex Hamilton (additionally at UNSW).

“Many of the samples present that minimal of in-plane AMR occurs when the magnetic subject is almost perpendicular to the sting present course.” says Cheng.

Additional theoretical calculations by collaborators at South China Regular College additional confirmed that electrons’ spins within the edge states of monolayer WTe2 ought to be all the time perpendicular to their propagation instructions, so-called ‘spin-momentum locking’.

“The amplitudes of the in-plane AMR noticed in monolayer WTe2 could be very massive, as much as 22%” says co-author A/Prof Lan Wang (additionally at RMIT).

“Whereas the earlier amplitudes of in-plane AMR in different 3D topological insulators are solely round 1%. By AMR measurements, we will additionally exactly decide the spin quantization axis of the spin polarized electrons within the edge states.”

“Once more, this work demonstrates the promising potential of QSHI for designing and growing novel spintronic units and show AMR as a useful gizmo for the design and improvement of QSHI-based spintronic units, that are one of many promising routes for FLEET to comprehend low-energy units in future.”