Dresden 2020 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 20: 2D semiconductors and van der Waals heterostructures II (joint session HL/DS)
HL 20.7: Talk
Monday, March 16, 2020, 17:15–17:30, POT 81
Band filling and cross quantum capacitance in ion gated semiconducting transition metal dichalcogenide monolayers — •Haijing Zhang1,2, Christophe Berthod2, Helmuth Berger3, Thierry Giamarchi2, and Alberto Morpurgo2 — 1Max-Planck-Institute for Chemical Physics of Solids, Dresden, Germany — 2University of Geneva, Geneva, Switzerland — 3École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
Ionic liquid gated field-effect transistors based on semiconducting transition metal dichalcogenides are used to study a rich variety of extremely interesting phenomena, while important aspects of how charge carriers are accumulated in these systems remain elusive. Here we present a thorough analysis of charge accumulation in MoSe_2 and WSe_2 monolayers. We identify the conditions when the chemical potential enters different valleys in the monolayer band structure and find that an independent electron picture describes the occupation of states well. Unexpectedly, however, the same analysis of the experiments shows that the total device capacitance cannot be simply described in terms of the series connection of a geometrical capacitance and of a quantum capacitance given by C_Q=e^2/(dμ/dn), as commonly assumed. This unexpected behavior occurs because a cross quantum capacitance contribution is present, which originates physically from mutual screening of the electric field generated by charges on one plate from charges sitting on the other plate. Our findings reveal an important contribution to the capacitance of physical systems that had been virtually neglected until now.