2D Ferroelectric Rashba Lead Chalcogenides

Monolayers and heterostructures of 2D electronic materials with spin-orbit effects offer promise for observing many novel physical effects. For instance, topological insulators or Rashba semiconductors coupled with a superconductor may host Majorana fermions, which are the building blocks for quantum computers. In this research, we found ferroelectric Rashba buckled lead chalcogenides monolayers. Because of the inversion symmetry breaking (out-of-plane buckling) and the heavy lead element with strong spin-obit interaction, this class of materials is ferroelectric and possesses giant Rashba splitting and belongs to a new class of matters, the ferroelectric Rashba semiconductors (FERSC). FERSC is particularly attractive for spintronic applications as the Rashba spin-texture can be switched in a non-volatile way by external electric fields or mechanical strains.

“Ingridients” for FERSC

The spin-orbit splitting of the bands occurs in crystals without inversion symmetry, where it is known as Dresselhaus effect, and in 2D structures or surfaces, as Rashba effect. However, suitable atomically thin 2D materials with large Rashba coefficient are hard to find. To have Rashba splitting there are two key properties that should present: strong SOI and broken inversion symmetry. In graphene and non-polar two-dimensional materials, such as transition metal dichalcogenides, breaking inversion symmetry is often achieved by application of out-of-plane electric field or through interfacial effects. However, the respective spin splitting graphene is rather small rendering the spin polarization unusable at room temperature. Spin-splitting in WSe$_2$ monolayer is a Zeeman-type splitting because the out-of plane mirror symmetry suppresses the Rashba term. Before going into the details of my research, let’s start with overview of Rashba effects in two-dimensional electron gas (2DEG).

To be continued

References: [1] P. Z. Hanakata, A. S. Rodin, Alexandra Carvalho, Harold S. Park, David K. Campbell, and A. H. Castro Neto, Phys. Rev. B Rapid, 96, 161401(R) (2017).
[2] A. S. Rodin, P. Z. Hanakata, Alexandra Carvalho, Harold S. Park, David K. Campbell, and A. H. Castro Neto, Phys. Rev B, 96, 115450 (2017).