Nanomechanics of van der Waals and Complex Oxide Membranes
November 5th, 2021 MARTIN LEE TU Delft

Van der Waals materials and complex oxides independently span a myriad of ground states. Therefore, combining the two classes of materials together can open new doors to unexpected emergent physics and/or novel device concepts. However, studies so far have only used one type of a material as a substrate for the other. In my presentation I will show you that free-standing ferroelectric complex oxide, barium titanate BaTiO3 (BTO) flakes sandwiched between graphene electrodes can be used as an ultra-thin piezoelectric actuator - a technology our society depends on for telecommunication applications. Due to the thinness of the BTO, we expect our device to be operating well within the 6G bandwidth. Moreover, the heterostructure displays ferroelectric hystereses in the mechanical observables such as the resonance frequency, Q factor, magnitude and phase, demonstrating a mechanical read out of ferroelectric memory. Although this work is among the first demonstrations of van der waals heterostructure of 2D materials and free-standing complex oxide, we anticipate many more works to stem out in this direction.

In the second part - if time allows - I will briefly talk about how the specific heat can be extracted from nanomechanical vibrations of suspended 2D materials. Traditional methods of extracting the specific heat from materials are inadequate for van der Waals flakes, which are typically a few nanometers in thickness and a few microns in diameter. Since many van der waals materials have layer dependence in the transition temperature, a new methodology needs to be invented to extract the specific heat in flake level devices. In this part of the talk, I will show you that the temperature dependence of the resonance frequency can be used to extract the specific heat of 2D flakes. For example, we show that the antiferromagnetic transition in FePS3 and charge density wave transition in TaS2 can be detected while extracting the specific heat.

Seminar, November 5, 2021, 11:00. Seminar Room

Hosted by Prof Dmitri Efetov