Jianpeng Liu

Hai-Yang Ma, Mengli Hu, Nantao Li, Jianpeng Liu, W. Yao, J. Jia, Junwei Liu

We propose a new type of spin-valley locking (SVL), named C-paired SVL, in antiferromagnetic systems, which directly connects the spin/valley space with the real space, and hence enables both static and dynamical controls of spin and valley to realize a multifunctional antiferromagnetic material. The new emergent quantum degree of freedom in the C-paired SVL is comprised of spin-polarized valleys related by a crystal symmetry instead of the time-reversal symmetry. Thus, both spin and valley can be accessed by simply breaking the corresponding crystal symmetry. Typically, one can use a strain field to induce a large net valley polarization/magnetization and use a charge current to generate a large noncollinear spin current. We predict the realization of the C-paired SVL in monolayer V2Se2O, which indeed exhibits giant piezomagnetism and can generate a large transverse spin current. Our findings provide unprecedented opportunities to integrate various controls of spin and valley with nonvolatile information storage in a single material, which is highly desirable for versatile fundamental research and device applications. Quantum degrees of freedom, such as spin or valleys, lie at the basis of many intriguing phenomena. In this theory work, the authors present a new type of spin-valley locking enabled by a crystalline symmetry, which allows for the generation of valley polarizations and net magnetization via strain, and non-collinear spin currents via charge currents.

Shan Jiang, Xuejun Liu, Jianpeng Liu, D. Ye, Yong-Qing Duan, Kan Li, Z. Yin, Yongan Huang

Over the last decade, extensive efforts have been made on utilizing advanced materials and structures to improve the properties and functionalities of flexible electronics. While the conventional ways are approaching their natural limits, a revolutionary strategy, namely metamaterials, is emerging toward engineering structural materials to break the existing fetters. Metamaterials exhibit supernatural physical behaviors, in aspects of mechanical, optical, thermal, acoustic, and electronic properties that are inaccessible in natural materials, such as tunable stiffness or Poisson's ratio, manipulating electromagnetic or elastic waves, and topological and programmable morphability. These salient merits motivate metamaterials as a brand‐new research direction and have inspired extensive innovative applications in flexible electronics. Here, such a groundbreaking interdisciplinary field is first coined as “flexible metamaterial electronics,” focusing on enhancing and innovating functionalities of flexible electronics via the design of metamaterials. Herein, the latest progress and trends in this infant field are reviewed while highlighting their potential value. First, a brief overview starts with introducing the combination of metamaterials and flexible electronics. Then, the developed applications are discussed, such as self‐adaptive deformability, ultrahigh sensitivity, and multidisciplinary functionality, followed by the discussion of potential prospects. Finally, the challenges and opportunities facing flexible metamaterial electronics to advance this cutting‐edge field are summarized.

Yimeng Guo, Jiang-Xu Li, Xue-Peng Zhan, Chun-Wen Wang, Min Li, Biao Zhang, Zirui Wang, Yue-Yang Liu, Kai-Ning Yang, Hai Wang, Wanying Li, Pingfan Gu, Zhaoping Luo, Ying-Jia Liu, Pei-Tao Liu, Bo Chen, Kenji Watanabe, T. Taniguchi, Xing-Qiu Chen, Cheng-Bing Qin, Jiezhi Chen, Dongming Sun, Jing Zhang, Runsheng Wang, Jianpeng Liu, Yu Ye, Xiuyan Li, Yanglong Hou, Wu Zhou, Han-Yi Wang, Z. Han

Vertical three-dimensional integration of two-dimensional (2D) semiconductors holds great promise, as it offers the possibility to scale up logic layers in the z axis1–3. Indeed, vertical complementary field-effect transistors (CFETs) built with such mixed-dimensional heterostructures4,5, as well as hetero-2D layers with different carrier types6–8, have been demonstrated recently. However, so far, the lack of a controllable doping scheme (especially p-doped WSe2 (refs. 9–17) and MoS2 (refs. 11,18–28)) in 2D semiconductors, preferably in a stable and non-destructive manner, has greatly impeded the bottom-up scaling of complementary logic circuitries. Here we show that, by bringing transition metal dichalcogenides, such as MoS2, atop a van der Waals (vdW) antiferromagnetic insulator chromium oxychloride (CrOCl), the carrier polarity in MoS2 can be readily reconfigured from n- to p-type via strong vdW interfacial coupling. The consequential band alignment yields transistors with room-temperature hole mobilities up to approximately 425 cm2 V−1 s−1, on/off ratios reaching 106 and air-stable performance for over one year. Based on this approach, vertically constructed complementary logic, including inverters with 6 vdW layers, NANDs with 14 vdW layers and SRAMs with 14 vdW layers, are further demonstrated. Our findings of polarity-engineered p- and n-type 2D semiconductor channels with and without vdW intercalation are robust and universal to various materials and thus may throw light on future three-dimensional vertically integrated circuits based on 2D logic gates. We develop a method for high-density vertical stacking of active-device multi-layers, implementing memory and logic functions, using unique VIP-FETs where a van der Waals intercalation layer modulates the p- or n-type nature of the FETs.

Jian Xie, Zi-Hao Huo, Xin Lu, Zuo Feng, Zai-Zhe Zhang, Wen-Xuan Wang, Qiu Yang, Kenji Watanabe, T. Taniguchi, Kai-Hui Liu, Zhi-Da Song, X.-C. Xie, Jianpeng Liu, Xiaobo Lu

Fractional Chern insulators (FCIs) showing a transport effect with fractionally quantized Hall plateaus emerging under zero magnetic field, provide a radically new opportunity to engineer topological quantum electronics. By construction of topological flat band with moire engineering, intrinsic FCIs have been observed in twisted MoTe2 system and rhombohedral pentalayer graphene/hBN moire superlattices with anomalous Hall resistivity quantization number C<= 2/3 including the gapless composite Fermi-liquid state with C = 1/2. Here, we experimentally demonstrate a new system of rhombohedral hexalayer graphene (RHG)/hBN moire superlattices, which exhibit both integer and fractional quantum anomalous Hall effects with rich tunability including electric displacement field, perpendicular magnetic field and in-plane magnetic field. By tuning the electrical and magnetic fields at 0<v<1, we have observed a quantum phase transition showing a sign reversal of the Hall resistivity at finite magnetic fields. Surprisingly, the FCI state at v = 2/3 survives in the phase transitions, exhibiting a robust quantized Hall resistivity across both phases. Finally we have further demonstrated the indispensable role moire potential plays in the formation of the flat Chern band from a theoretical perspective. Our work has established RHG/hBN moire superlattices as a promising platform for exploring quasi-particles with fractional charge and non-Abelian anyons at zero magnetic field.

Yijie Liu, Jichi Zhang, Yuan Ji, Jiawei Cao, Sen Xu, Peng Luo, Jianpeng Liu, Lina Ma, Guo-lin Gao, Yadong Wu, Zai-Xing Jiang