valleytronics

As I walk through the valley of bulk molybdenum disulfide, I take a look at my spin, and see it has become polarised

This week’s pick comes from Nature Nanotechnology and regards a material that I am very unfamiliar with.  “Valley-dependent spin polarization in bulk MoS2 with broken inversion symmetry” by Suzuki et al experimentally detects momentum dependent spin polarisation in the transition metal dichalcogenide (TMDC) MoS2 in accordance with theoretical predictions.  TMDC based 2D atomic crystals are a promising and interesting class of materials for reasons such as their good performance as a field effect transistor, their ability to show electric field induced superconductivity, as well as their strong photoluminescence which is handy for this paper’s investigation.  A monolayer of MoS2 is a semiconductor with a finite band gap and Berry curvature, while it also has a strong spin-orbit interaction and a non centrosymmetric structure which allows it to display the coupled spin-valley physics required for valleytronics (that is electronics where the valley degree of freedom acts as a carrier of information).

 

This paper focuses on layered MoS2 that adapts a 3R structure which has bulk inversion asymmetry.  For this phase the authors experimentally observe out of plane spin polarisation at certain positions in the valence band using a combination of spin and angle resolved photo emission spectroscopy (SARPES), which has previously been shown to be capable of detecting momentum dependent spin polarisations in non centrosymmetric materials, and photoluminescence.  The reasonable agreement between the experimentally detected spin polarisations with theoretical calculations indicates the potential of MoS2 as a valleytronic material.

http://www.nature.com/nnano/journal/v9/n8/full/nnano.2014.148.html

Image: Severin Sadjina, Some rights reserved

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