Emergent phenomena in correlated complex oxides
报告人: 陈航晖 (上海纽约大学)
报告时间: 2021年1月11日 13:30
Complex oxides exhibit a wide range of exotic phenomena including metal-insulator transition, colossal magnetoresistance and high-temperature superconductivity due to strong correlation effects arising from the d-orbital of transition metal ions. In this talk, we discuss two particular examples. The first example is (SrRuO3)1/(SrTiO3)N superlattices in which the Ru magnetic anisotropy changes from two-fold along <001> axis (𝑵<𝟑) to eightfold along <111> axis (𝑵≥𝟑) . Our first-principles calculations show that increasing the thickness of SrTiO3 layers enhances the correlation effects on Ru, which induces a metal-insulator transition and a new orbital ordering. It is precisely this new orbital ordering that changes the underlying spin-orbit interaction and reorients the Ru magnetic easy axis. The second example is infinite-layer nickelates RNiO2 (R is rare-earth elements) in which unconventional superconductivity has recently been discovered upon hole doping. We combine density-functional-theory and dynamical-mean-field-theory calculations to show  that there is a strong hybridization between correlated Ni-d orbitals and itinerant electrons in the rare-earth spacer layer. This makes the electronic structure of RNiO2 distinct from that of superconducting infinite-layer cuprates CaCuO2. As a consequence of hybridization, our calculations find that itinerant electrons screen the local moment on Ni site and increase the critical UNi that is needed to stabilize antiferromagnetic ordering. The results imply that the superconductivity observed in RNiO2 does not emerge from a doped Mott insulator as in cuprates.
 Z. Cui, A. J. Grutter, H. Zhou, H. Cao, Y. Dong, D. A. Gilbert, Y. Liu, J. Ma, Z. Hu, J. Guo, E. Arenholz, H. Chen, X. Zhai, Y. Lu, Science Advances 6 eaay0114 (2020).
 Y. Gu, S. Zhu, X. Wang, J. Hu and H. Chen, Communications Physics 3 84 (2020).
Biography: Dr. Hanghui Chen is an Assistant Professor of Physics of NYU Shanghai and a Global Network Assistant Professor of New York University. Prior to joining NYU Shanghai, he was a post-doctoral fellow at Columbia University working with Professor Andrew Millis. He holds a Ph.D from Yale University and a B.S. from Peking University. Dr. Chen’s research interests lie in first-principles modelling and design of complex meta-materials, in particular transition metal oxides and their heterostructures.