Ferroelectric-like SrTiO3 surface dipoles probed by graphene

Area of Science:

• Materials Science
• Condensed Matter Physics
• Surface Science

Background:

• Graphene's electrical transport properties are sensitive to its surrounding environment.
• Strontium titanate (STO) possesses a high dielectric constant, theoretically beneficial for reducing charged impurity scattering in graphene.
• Previous studies suggested surface dipole moments on STO, potentially influencing graphene's electronic behavior.

Purpose of the Study:

• To investigate the effect of transferring graphene onto strontium titanate (STO) using a novel technique.
• To understand the controversial scattering mechanisms affecting graphene mobility on STO.
• To explore the role of STO's surface properties on graphene's electrical transport.

Main Methods:

• Fabrication of graphene devices transferred onto STO from SiO2 using a new technique.
• Electrical transport measurements, including resistivity and mobility, near the Dirac point.
• Analysis of hysteresis in resistivity to probe surface dipole interactions.

Main Results:

• A moderate enhancement in graphene mobility was observed near the Dirac point on STO.
• Strong and asymmetric resistivity hysteresis was detected in graphene on STO.
• The observed hysteresis is consistent with ferroelectric-like dipole moments originating from oxygen displacements on the STO surface.

Conclusions:

• The surface dipole moments on STO significantly influence graphene's electrical transport properties.
• These dipoles lead to hysteresis and reduce STO's effectiveness in screening Coulomb impurities.
• The findings clarify the complex scattering mechanisms impacting graphene mobility on STO, highlighting the role of surface ferroelectricity.