Electric control of spin in monolayer WSe₂field effect transistors

Abstract

We report a first principles theoretical investigation of quantum transport in monolayer WSe2 field effect transistor (FET). Due to a strong spin-orbit interaction (SOI) and the atomic structure of the two-dimensional (2D) lattice, monolayer WSe2 has an interesting electronic structure that exhibits Zeeman-like up-down spin texture near the K and K ′ points of the Brillouin zone. In a FET, the gate electric field induces an extra, externally tunable SOI that re-orients the spins into a Rashba-like texture thereby realizing electric control of the spin. Quantum transport is modulated by the spin texture, namely by if the spin orientation of the carrier after the gated channel region, matches or miss-matches that of the FET drain electrode. The carrier current in the FET is labelled both the spin index and the valley index, realizing spintronics and valleytronics in the same device.PACS numbers: 75.70.Tj, 73.25.+i, Electronic materials in reduced dimension have attracted great attention for decades. The newest member of such material is the two dimensional (2D) transitionmetal dichalcogenides (TMDC). Since the exfoliation of monolayer TMDC (ML-TMDC) three years ago[1, 2], very interesting electronic and optical properties of these materials have been already discovered both experimentally and theoretically [3][4][5][6][7][8]. TMDC is in the form of MX 2 where M denotes heavy elements such as Mo, W, and X denotes S, Se, etc.. The most important properties of several ML-TMDC, for instance WSe 2 and MoS 2 , are the direct band gap in the visible frequency range [1,2] and the strong spin-orbit interaction (SOI). ML-TMDC materials have honeycomb lattice shown in Fig. 1(a) and in the momentum space there are two inequivalent valleys at K and K ′ of the first Brillouin zone (BZ, Fig. 1(a)). Due to the well-separation of K from K ′ , it was proposed [4][5][6][7] that the valley index τ = K, K ′ may be used as quantum numbers for valleytronics. At the same time, the strong SOI are fundamentally important for spintronics. Being able to realize both valleytronics and spintronics in a single material is a very exciting new opportunity and ML-TMDC may well be the emerging electronic material for new generations of nanoelectronics. It is the purpose of this work to theoretically investigate fundamental properties of quantum transport in ML-TMDC material WSe 2 in the form of a field effect transistor (FET).In particular, by atomistic first principles analysis we found that the spins in WSe 2 can be well controlled by an external electric field -here by a gate voltage of the FET, and such a control has direct consequences to quantum transport properties of the device. Achieving efficient electric control of spin is a long-sought goal of spintronics [9][10][11][12], for WSe 2 it is due to not only the strong SOI but also to its 2D lattice structure. Conceptually, SOI is proportional toŝ · (∇V (r) × k), where s is the spin and k the momentum of the carrier while E = −∇V (r) the electric field seen by the carrier. One may view ...

Electrical contacts to two-dimensional semiconductors

“…Combining broken inversion symmetry and strong spin-orbit coupling in monolayer TMDCs leads to an interesting spinsplit valence band, which enables the electrical manipulation of spins [106][107][108] and makes semiconducting TMDCs an interesting material family for spintronics. Calculations have also predicted giant magnetoresistance in Fe/MoS 2 /Fe sandwich structures 109 .…”

Electronic transport properties of transition metal dichalcogenide field-effect devices: surface and interface effects

“…The diversity of materials that exist in van der Waals layer structure offers an unlimited catalogue of 2D materials with a range of intriguing properties as discussed in recent reviews. Most notably, exploration of group 6 TMDs such as MoS 2 and WSe 2 , which are stable semiconducting compounds with a band gap in the visible to near infrared (NIR) frequencies, revealed their remarkable features such as excellent electrostatic coupling, 12 layer-dependent tunable bandgaps, 13 direct-to-indirect bandgap crossover, 13 gate tunable superconductivity, 14 photo-switching, 15 and valley-selective optical excitation 16,17 to name a few. 11 The past few years have seen rapid development of 2D materials research focusing on the family of transition metal dichalcogenides (TMDs).…”

Electronic Transport Inhibiting of Carbon Nanotubes by 5f Elements

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