ES22-Ganesh

Author: Ganesh, Panchapakesan - Center for Nanophase Materials Sciences, Oak Ridge National Laboratory

Title: Harnessing Electron Correlations and Anharmonicity for Energy Efficient Computing

Abstract: Metal oxide-based Resistive Random-Access Memory (RRAM) exhibits multiple resistance states, arising from the activation/deactivation of a conductive filament (CF) formed by oxygen vacancies inside a switching layer – due an underlying metal-insulator transition (MIT). You can make scalable memory/logic units using the crossbar architecture. So, you have a highly dense  information-storage system, that you want to be reliable, and fast switching and utilizing low- power. This can enable emulating ‘brain like’ neuromorphic computing. Similarly, ferroelectric  materials – such as Hafnia – are promising candidates for synaptic weight elements in neural network hardware because of their nonvolatile multilevel memory effects. But conventional RRAM materials require high forming potentials (not viable in crossbars), show high variability (device-to-device or cycle-to-cycle). Similarly, less reliability and voltage-time dilemma are suspected to plague ferroelectric synapses. To address these challenges, we are working to answer these open questions such as: what material characteristics we need when choosing a memristor material? What factors triggers a state-change (e.g. MIT, magnetic-transition, or ferroelectric-switching) in these materials? What determines the dynamics of the switching mechanism?br />
Using a combination of high-throughput phase-field and machine-learning methods [1] we discovered that harnessing electron-electron correlations in binary oxides can be advantageous for improved performance of RRAM devices. Using a combination of various correlated electronic structure methods, such as Quantum Monte Carlo (QMC) and Dynamical Mean Field Theory (DMFT), we further uncovered the underlying factors that control the MIT in correlated binary oxides – such as VO2 – when defects such as oxygen vacancies are present [2,3]. We subsequently demonstrated how many of the correlated perovskite metals that undergo MIT are negative charge-transfer metals, with the magnitude of ligand-hole being the key to controlling MIT. As such, the underlying mechanism of MIT is similar in such charge-transfer metals, irrespective of whether the MIT is induced by changes in stoichiometry or chemistry or pressure [4]. This work provides a fundamental understanding to resistive switching in RRAM’s. For ferroelectric-based synapses, we explored the recently discovered 2D layered-thiophosphate family of materials [5]. We discovered [6] presence of strong anharmonic coupling in these materials between the polar-mode and a strain-tunable Raman active symmetric-mode, even down to single-layer thickness, which could alleviate the voltage-time dilemma in conventional ferroelectrics. We further show our recent findings of scale-free ferroelectricity in this 2D layered ferroelectric family of materials [7].


[1] High-throughput phase-field simulations and machine learning of resistive switching in resistive random-access memory”, npj Computational Materials volume 6, Article number: 198 (2020), Kena Zhang, Jianjun Wang, Yuhui Huang, Long-Qing Chen, P. Ganesh* & Ye Cao.
[2] Doping a bad metal: Origin of suppression of the metal-insulator transition in nonstoichiometric VO2”, Phys. Rev. B 101, 155129, (2020), P. Ganesh*, Frank Lechermann, Ilkka Kylänpää, Jaron T. Krogel, Paul R. C. Kent, and Olle Heinonen
[3] Metal–insulator transition tuned by oxygen vacancy migration across -TiO2/VO2 interface”, Scientific Reports, 10, 1854 (2020), Qiyang Lu, Changhee Sohn, Guoxiang Hu, XiangGao, Matthew F. Chisholm, Ilkka Kylänpää, JaronT. Krogel, Paul R. C. Kent, Olle Heinonen, P.Ganesh and Ho Nyung Lee 

4] Origin of Metal-Insulator Transitions in Correlated Perovskite Metals”, Phys. Rev. Research 4, L022005 (2022), M. Chandler Bennett, Guoxiang Hu, Guangming Wang, Olle Heinonen, Paul R. C. Kent, Jaron T. Krogel, P. Ganesh*.
[5] Tunable quadruple-well ferroelectric van der Waals crystals”, Nature Materials, 19, 43 (2020), John A. Brehm, Sabine M. Neumayer, Lei Tao, Andrew O’Hara, Marius Chyasnavichus, Michael A. Susner, Michael A. McGuire, Sergei V. Kalinin, Stephen Jesse, P. Ganesh, Sokrates T. Pantelides, Petro Maksymovych and Nina Balke
[6] Origin and stabilization of ferrielectricity in CuInP2Se6”, PHYSICAL REVIEW RESEARCH 4, 013094 (2022), Nikhil Sivadas, Peter Doak, P. Ganesh*
[7] Scale Free Ferroelectric Polarization and Responses in 2D Ferroelectrics”, Nikhil Sivadas, Bobby G. Sumpter and P. Ganesh*, (under review)