Speaker: 陈航晖 (上海纽约大学)

Time: January 11, 2021 13:30

Place: 理科楼C302

报告摘要：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) [1]. 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 [2] 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 U_Ni 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.

参考文献：

[1] 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).

[2] Y. Gu, S. Zhu, X. Wang, J. Hu and H. Chen, Communications Physics 3 84 (2020).

报告人简介：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.