Recently, the in-situ quantum transport group at the Beijing Academy of Quantum Information Sciences (BAQIS), along with their collaborators, discovered a three-dimensional hidden phase in the kagome metal CsV₃Sb₅. On June 12, 2024, the resulted paper was published in Nature Communications, entitled "Three-dimensional hidden phase probed by in-plane magnetotransport in kagome metal CsV₃Sb₅".

The recently discovered kagome topological metal AV₃Sb₅ (A=Cs, Rb, K) has proven to be a valuable material platform for studying topological states and electron correlations. It features a wealth of states of matter and interesting electronic behaviors, including topological surface states, superconductivity with pair density wave, electronic nematicity, charge density wave, chiral transport, anomalous Hall effect and time-reversal symmetry breaking, among others. Such intricate and diverse range of states has sparked great interest, and numerous experiments are quickly focused on the search for potentially impactful quantum states within this system, such as unconventional superconductivity, Majorana zero mode, and orbital current order. Taking CsV₃Sb₅(CVS) as an example, the two most visible phase transitions are the CDW transition at around 90 K and the superconductivity transition at around 2.5 K. Interestingly, an increasing number of experiments have suggested the presence of additional phase transitions between these two temperatures, with one potential transition at approximately 35 K. Muon spin-rotation (μSR) experiments that showed a sudden increase in the relaxation rate below ~35 K; STM, nuclear magnetic resonance (NMR), and elastoresistance measurement (EM) have pointed to the formation of electronic nematic order below ~35 K; A second-harmonic generation (SHG) experiment found prominent chirality along the out-of-plane direction emerges below ~35 K. With the limited number of experimental findings, much remains unknown about this hidden phase, including the exact mechanism that breaks time reversal symmetry, the spatial symmetry of the order, and its magnetotransport characteristics.

Research group has long been dedicated to studying the physics of low-dimensional quantum material devices and has completed a series of important research works in the fields of high-mobility materials, topological materials, and magnetic materials with collaborators. These achievements include the discovery of dimension-dependent effects and exotic magnetoresistance effects in topological materials [Physical Review B 103, 155408 (2021); Physical Review B 104, 125439 (2021); 2D Materials, 10, 015010(2023); Science Bulletin 68, 1488(2023)], the realization of electrically controlled magnon valve in two-dimensional antiferromagnets, and the discovery of magnon transport anisotropy (Nature Communications 12,6279 (2021); Nature Communications, 14, 2526(2023)). Notably, in 2023, the research group observed dimension-dependent unsaturated linear magnetoresistance in thin CVS devices. Through analysis of the electron scattering rate and Fermi surface structure of this system, it was determined that the unsaturated linear magnetoresistance originates from two-dimensional charge density wave fluctuations, representing a combined effect of electron correlation and dimensionality.

Recently, researchers observed a pronounced anisotropic in-plane magnetoresistance (MR) in CVS thin films as a function of magnetic field direction, which exhibits significant temperature and magnetic field dependencies (see Figure 1). By extracting the rotational symmetric components of in-plane MR, distinct physical mechanisms were identified for the two-fold symmetry component (C2) and the six-fold symmetry component (C6). The C2 component emerges concurrently with the charge density wave and shares the same symmetry as the electronic nematic order, indicating a correlation among them. Below approximately 35 K, the C6 component appears and is tunable by the magnetic field, consistent with the picture of orbital current order. Additionally, below this temperature, the in-plane MR decreases linearly with increasing magnetic field, regardless of whether the magnetic field is perpendicular or parallel to the current direction (i.e., linear in-plane negative MR). These experimental data suggest the existence of a magnetic field-tunable three-dimensional orbital current order below 35 K (see Figure 2). This study not only provides a comprehensive description of the hidden phase physics in CVS but also serves as an example for studying the interactions between exotic quantum states of matter and detecting hidden orders.

Figure 1

Figure 2

The first co-authors of this work are Assistant Researcher Xinjian Wei at BAQIS and Dr. Congkuan Tian at Peking University. The corresponding author is Joint Researcher Jian-Hao Chen at Peking University/BAQIS. Other authors include Senior Engineers Yuanjun Song, Ya Feng, and Miaoling Huang from the BAQIS's Synergetic Testing Platform, Academician X. C. Xie from Peking University, Professors Yugui Yao and Zhiwei Wang from Beijing Institute of Technology, Professor Qihua Xiong from Tsinghua University, and Researcher Yi Liu from Beijing Normal University. This project has been supported by the National Key R&D Program of China, the Innovation Program for Quantum Science and Technology, the National Natural Science Foundation of China, Beijing Municipal Natural Science Foundation.

Link to the article：https://doi.org/10.1038/s41467-024-49248-3