Condensed-Matter Physics & Materials Science Seminar

"Quantum Transport in Oxide Channels with Organic Gates"

Presented by Masashi Kawasaki, WPI Advanced Institute for Materials Research, Tohoku University, Japan

Monday, April 13, 2009, 1:00 pm — Small Seminar Room, Bldg. 510

WPI Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai 980-8577, Japan
Institute for Materials Research (IMR), Tohoku University, Sendai 980-8577, Japan
CREST Japan Science and Technology Agency, Tokyo, 102-007, Japan

We present quantum Hall effect (QHE) in ZnO and superconductivity in SrTiO3, both of which could be modulated by an electric field effect using organic gate structures.
ZnO is a promising material for ultraviolet light emitting diodes [2]. Through fine-tuning of film growth processes, we found that two dimensional electron gas (2DEG) with a sheet charge density of 1011-1013 cm-2 emerges at the interfaces of ZnO and (MgZn)O due to the discontinuity in spontaneous polarizations of these piezoelectric materials [2]. With spin-coating of poly (3,4-ethylenedioxythiophene) poly (styrenesulfonate) (PEDOT:PSS) on ZnO, nearly ideal Schottky junctions could be formed [3]. From capacitance-voltage (C-V) relations, we could profile the carrier concentration along depth that clearly indicated the presence of 2DEG as designed. Metal-semiconductor field effect transistors (MES-FET) with a Hall-bar geometry clearly showed that the quantum transport such as Shubnikov-de Haas (SdH) oscillation and QHE were modulated by the tuning of the sheet charge density in the channel of the MES-FET.
Another example is inducing superconductivity in a pristine SrTiO3 crystal with accumulating electrons at the surface by an electric double layer (EDL) gating with polymer electrolyte. Polyethylene-oxide electrolyte with KClO4 as a supporting salt was applied on an atomically flat SrTiO3 surface [4]. The key was to make very good Ohmic contacts by using self-assembled ion bombardment metallization for contact pads. By applying 2.5-3.5V at the Pt electrode in the electrolyte, electrons with a sheet charge density of 1013-1014cm-2 could be induced. The system underwent to superconducting state with a TC of about 0.4K [5]. Surprisingly, TC was almost u

Hosted by: Praveen Chaudhari

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