Quantum Materials

Magnetic and superconducting materials play a significant role in the functional devices used for memory, imaging etc. Typically transition metal oxides are model systems to realize a wide spectrum of magnetic and superconducting phases. Strong electron correlation has been the driving force in realizing these phases; for example, 3d complex oxides such as cuprates and manganites have been heavily investigated for high T_c-superconductivity and magnetism respectively. Spin-orbit coupling is an energy scale, which is often ignored, unless large Z elements are present in the material. Particularly, in a new class of materials called topological insulators, which show unusual electronic and optical properties, spin-orbit coupling plays an important role in determining their electronic structure. Such a limit can be achieved in 5d transition metal oxides, where a competition between strong correlation and spin-orbit coupling has been expected to throw several surprises in terms of unusual electronic phase diagrams. There are several theoretical predictions on various topological and other interesting phases in these systems. Extending the possibilities, heterostructures based on 3d and 5d transition metal based oxides are also candidates to realize these ground states. Due to the complicated nature of such phase diagrams, it is often possible that several interesting phases are not easily accessible by conventional tuning parameters such as chemical doping, pressure etc. We will use alternative parameters such as electric field effect, strain in thin film structures to explore and study new phases. Moreover, this research effort will also include the exploring quantum mechanical phenomena such as quantum Hall effect etc. in complex oxide based heterostructures.

Relevant Publications:

• Y. Liu, S. Niu, T. Orvis, H. Zhang, H. Wang, J. Ravichandran, “Epitaxial Growth and Electrical Properties of VO₂ on LSAT (111) substrate”, Journal of Vacuum Science & Technology A, 36, 061506 (2018).

• G. Singh-Bhalla, P. B. Rossen, G. K. Palsson, S. J. Suresha, D. Yi, A. Dasgupta, D. Doennig, V. G. Ruiz, A. K. Yadav, M. Trassin, J. T. Heron, C. S. Fadley, R. Pentcheva, J. Ravichandran, R. Ramesh, “Anomalous Termination Switching and Polarity Compensation in LaAlO₃/SrTiO₃ heterostructures”,  Physical Review Materials, 2, 112001(R) (2018). [Editor’s Suggestion, Rapid Communication]

• J. Ravichandran, C. R. Serrao, D. K. Efetov, D. Yi, Y. S. Oh, S-W. Cheong, R. Ramesh and P. Kim, “Ambipolar Transport and Magneto-resistance Crossover in a Mott Insulator, Sr₂IrO₄”, Journal of Physics: Condensed Matter 28, 505304 (2016) [IOPSelect – Articles from the last 12 months that have been chosen by our editors for their novelty, significance and potential impact on future research].

• G. Singh-Bhalla, C. Bell, J. Ravichandran, W. Siemons, Y. Hikita, S. Salahuddin, A. F. Hebard, H. Y. Hwang and R. Ramesh, “Built-in and induced polarization across LaAlO₃/SrTiO₃ heterojunctions”, Nature Physics, 7, 80 (2011).