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Physics Seminar

Electrolyte Gating of Complex Oxides

Speaker: Dr Chris Leighton (University of Minnesota, USA)
Date: Friday 23 August 2019
Time: 11:30
Venue: N/3.28

Recently, electrolyte gating techniques have proven highly effective in tuning very large carrier densities at surfaces. Electrolytes such as ionic liquids enable electric double layer transistors (EDLTs), where large capacitance generates electron/hole densities up to 10^15 cm^-2, i.e., significant fractions of an electron/hole per unit cell in most materials. This is sufficient to induce and control electronic phase transitions, generating great interest. Challenges remain, however, including understanding the true gating mechanisms (i.e., electrostatic vs. electrochemical [1]), developing operando characterization methods, and assessing the full power and universality of the approach. Here, I will review our work applying electrolyte gating using solid “ion gels” [1-6] to complex oxides (e.g., La1-xSrxCoO3-d, BaSnO3), mostly focused on control of magnetism. Our findings substantially clarify electrostatic vs. electrochemical response, culminating in a picture where electrostatic gating vs. oxygen vacancy formation can be understood and predicted based on bias polarity, and the enthalpy of formation and diffusivity of oxygen vacancies [1-4]. This understanding was achieved through development of operando probes, such as synchrotron X-ray diffraction [3,4] and neutron reflectometry [3,6]. Control of ferromagnetism in La1-xSrxCoO3-d is then demonstrated using both electrochemistry and electrostatics. In particular, working in electrostatic mode, and guided by theory [5], we have demonstrated reversible electrical modulation of Curie temperature over a record 150 K window, achieved via a novel gate-induced percolation approach [6].

[1] C. Leighton, Nat. Mater. 18, 13 (2019).
[2] J. Walter, H. Wang, B. Luo and C. Leighton, ACS Nano 10, 7799 (2016).
[3] J. Walter, G. Yu, B. Yu, A. Grutter, B. Kirby, J. Borchers, Z. Zhang, H. Zhou, T. Birol, M. Greven, and C. Leighton, Phys. Rev. Materials 1, 071403(R) (2017).
[4] H. Wang, J. Walter, K. Ganguly, B. Yu, G. Yu, H. Fu, M. Greven and C. Leighton, Phys. Rev. Materials 3, 075001 (2019).
[5] P.P. Orth, R.M. Fernandes, J. Walter, C. Leighton and B.I. Shklovskii, Phys. Rev. Lett. 118, 106801 (2017).
[6] J. Walter, T. Charlton, H. Ambaye, M. Fitzsimmons, P.Orth, R. Fernandes, B. Shklovskii and C. Leighton, Phys. Rev. Materials 2, 111406(R) (2018).