Fig1. Flow diagram of multipolar OPs prediction viaab initiocalculations.
Fig 2. (a) and (b),Meta-stableoctupolar states predicted in monolayerα-RuCl3. (c)-(d), Ground state Oc-IV inmonolayerα-RuI3 and its band structures. (e)Orthogonal magnetic moment My produced by the FM-O
octupole under a xz-plane rotating magnetic field.
Background
High-rank multipolar order parameters (OPs), induced by multiple orbital degrees of freedom themselves or their coupling to spin sector via strong spin-orbital coupling (SOC), have been found to be unexpectedly active in more and more correlated materials such as 4f, 4d and 5d systems.Different from conventional dipoles, much richer and exotic orders and low-energy excitations can be expected to arise from multipolar OPs due to their higher degrees of freedom.Recently, the important roles played by multipolar OPs are attracting extensive attention and are considered to be significant factors to interpret some exotic physical phenomena. However, such high-rank OPs pose a big challenge to experimental detections. Theoretically, it is also difficult to predict multipolar orders viaab initiocalculations in real materials.
What we discover?
In this work, based on linear response theory (LRT) under random phase approximation (RPA), we develop a numerical method starting from the density functional theory (DFT) calculations, to search for all possible multipolar OPs effectiveness (see flow diagram in Fig. 1). It has correctly reproduced the Zigzag magnetic ground state of monolayer α-RuCl3 as found in the neutron scattering experiments, which validates our method. More importantly, two pure meta-stable magnetic octupolar states, Oc-II with parallel arranged O(FM-O) and Oc-IV with anti-parallel arranged O(AFM-O), are predicted as shown in Fig. 2(a)-(b). These two octupolar states can be stabilized by doping I elements in α-RuCl3 or synthesizing α-RuI3 directly, where the AFM-O octupolar state becomes the ground state, as shown in Fig. 2(c)-(d). We propose that an orthogonal magnetization My∝H2cos2θ as shown in Fig. 2(e), can be detected as the fingerprint of the FM-O octupolar state.
Why is this important?
Multipolar physics in 4d/5d transition metal compounds are attracting more and more attentions recent years. This work provides an efficient method for prediction of multipolar Ops via ab initio calculations in real materials. The example presented in this work serves as a guidance for searching multipolar order parameters in other correlated materials. Furthermore, the external fields, such as magnetic field, can be applied into our scheme in future, which could expand the study ability of multipolar physics.
Who did the research?
Wen-Xuan Qiu1, Jin-Yu Zou1, Ai-Yun Luo1, Zhi-Hai Cui2, Zhi-Da Song2,3, Jin-Hua Gao1, Yi-Lin Wang4*, and Gang Xu1†
1 Wuhan National High Magnetic Field Center and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China.
2 Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
3 Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
4 Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China.
Funding:
This work is supported by the National Key Research and Development Program of China (2018YFA0307000) and the National Natural Science Foundation of China.
Link:https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.147202
