CDW based memory devices

1T-TaS₂ is an example of a layered transition metal dichalcogenide, which exhibits a variety of thermodynamic equilibrium states, ranging from metallic at high temperature, incommensurate and nearly commensurate charge density wave (CDW) states at intermediate temperatures and an insulating commensurate CDW Mott state below 180 Kelvin. In addition, superconductivity [1] and spin liquid states [2] are found when pressure is applied or if the material is cooled to low temperatures, respectively. Finally, a variety of long-lived metastable photo- and electrically-induced states are found, which are stable at low temperatures [3-6].

In this project, we investigate the photo- and electrically-induced topologically protected hidden (H) state, which has a few orders of magnitude lower resistivity than the thermodynamically stable CDW state and is stable at low temperatures [3]. The transition time to the photoinduced state is below half a picosecond, making the material an ideal candidate for ultrafast low energy non-volatile memory device [7]. We work in collaboration with the Jozef Stefan Institute (JSI) in Ljubljana, where the material is synthesized and characterized using optical methods and scanning tunneling microscopy. We are using the state-of-the-art cleanroom facilities at PSI to prepare the samples for measurements with x-rays from PSI’s accelerator-based photon sources to shine light on the nonequilibrium states in 1T-TaS₂ using reciprocal space analysis.

[1] B. Sipos, H. Berger, L. Forro, E. Tutis, A. F. Kusmartseva, Nature Materials 2008, 7, 960.

[2] M. Klanjsek, A. Zorko, R. Zitko, J. Mravlje, Z. Jagličić, P. K. Biswas, P. Prelovsek, D. Mihailović, D. Arčon, Nat Phys 2017, 13, 1130.

[3] L. Stojchevska, I. Vaskivskyi, T. Mertelj, P. Kusar, D. Svetin, S. Brazovskii, D. Mihailovic, Science 2014, 344, 177.

[4] I. Vaskivskyi, J. Gospodaric, S. Brazovskii, D. Svetin, P. Sutar, E. Goreshnik, I. A. Mihailovic, T. Mertelj, D. Mihailovic, Science Advances 2015, 1, e1500168.

[5] I. Vaskivskyi, I. A. Mihailovic, S. Brazovskii, J. Gospodaric, T. Mertelj, D. Svetin, P. Sutar, D. Mihailovic, Nat Comms 2016, 7, 11442.

[6] Y. A. Gerasimenko, I. Vaskivskyi, M. Litskevich, J. Ravnik, J. Vodeb, M. Diego, V. Kabanov, D. Mihailovic, Nat. Mat. 2019, 317, 505. 

[7] J. Ravnik, I. Vaskivskyi, T. Mertelj, D. Mihailović, Phys Rev B 2018, 97, e1400173.