ISSN 0253-2778

CN 34-1054/N

2018 Vol. 48, No. 12

Display Method:
Room-temperature ferroelectricity and ferroelectric device application in 2D materials
LI Yue, WAN Siyuan, ZENG Hualing
2018, 48(12): 955-967. doi: 10.3969/j.issn.0253-2778.2018.12.001
Room-temperature ultrathin ferroelectrics are crucial to building high density non-volatile memory. In the past decades, conventional ferroelectric thin films, for example complex ferroelectric perovskite oxide, has attracted enormous attention. However, limited by the possible critical size effect or the ferroelectricity vanishing below a critical film thickness, developing modern nanoelectronic devices based on conventional ferroelectric thin film poses a great challenge. Two-dimensional (2D) van der Waals (vdW) material, which has a naturally stable layered structure, saturated surface chemistry, and weak inter-layer interaction, offers an excellent platform for realizing ferroelectricity at atomic scale in the 2D limit. The layered 2D ferroelectrics provide the opportunity and possibility for further miniaturization of nanoelectronics as well as developing novel flexible electronics. In this paper, the research background of conventional ferroelectrics was reviewed, recent research progresses of 2D ferroelectricity and related device applications in vdW materials were highlighted, and a brief outlook on future application of 2D ferroelectrics was presented.
Experimental investigation of high-fidelity quantum logic gates on solid-state spin systems
TUSUN Maimaitiyiming, GENG Jianpei, RONG Xing
2018, 48(12): 968-976. doi: 10.3969/j.issn.0253-2778.2018.12.002
Quantum computation is capable of solving several intractable problems in classical computation, such as large number factorization with utilizing the principles of quantum mechanics. The quantum system is always affected by decoherence while realizing quantum information processing and controlling, and decoherence is caused by interaction between the quantum system and the external environment. Therefore, it is of great significance to implement a high-fidelity quantum logic gate, which can suppress decoherence in quantum computation. In this paper, the requirements for realizing quantum computing for physical system was introduced, and then, based on the NV center in diamond system, several experimental works about the experimental implementation of the
Research progress of strongly correlated physics in heavy hole doped iron-based superconductors
ZHAO Dan, LI Jian, LI Shunjiao, WU Tao
2018, 48(12): 977-995. doi: 10.3969/j.issn.0253-2778.2018.12.003
Strong correlated physics has been a frontier field in the research of high-temperature superconductors and is considered to be closely related to the microscopic mechanism of high-temperature superconductivity. The discovery of iron-based superconductors in 2008 brought a brand new material platform to the research of high-temperature superconductors. And the research team from the University of Science and Technology of China has made significant contributions to the discovery of iron-based superconductors. With further in-depth study of iron-based superconductors, it has been found that iron-based superconductors are different from copper-based high-temperature superconductors with weaker electronic correlation effects. The picture based on strongly correlated physics for high-temperature superconductivity is greatly challenged. Theoretically, iron-based superconductors are still considered to have the features of the strong correlated physics, but their manifestations are featured by orbital selectivity due to multiple orbitals and the Hund’s coupling. The exploration of strong correlated physics in iron-based superconductors has become a frontier issue in current research of high-temperature superconductors. In this paper, our nuclear magnetic resonance (NMR) studies on the heavily hole-doped iron-based superconductors AFe2As2 (A=K, Rb, Cs) were reviewed. Our results indicate that the electronic correlation effect is very strong in the heavily hole-doped region and many features are consistent with the orbital selective Mott physics. First, the localization and itinerancy of electrons can coexist, and an electronic coherent state similar to the heavy fermion system emerges at the low temperature; secondly, based on site-selective NMR detection, orbital-selective local spin susceptibility measurements were achieved, further confirming the orbital-selective electron correlation effects in iron-based superconductors; finally, for the first time, a new electronic nematic state was observed in heavily hole-doped CsFe2As2 systems. These findings reveal similar strong correlation features between iron-based superconductors and copper-based superconductors and heavy fermion superconductors, which will help to establish a unified high-temperature superconducting mechanism.
Research onself-organization of wireless network based on reinforcement learning
WANG Chao, WANG Zhiyang, SHEN Cong
2018, 48(12): 996-1011. doi: 10.3969/j.issn.0253-2778.2018.12.004
Traditional wireless communication technologies are gradually unable to meet the increasingly complex requirements of the 5G system. The technologies related to self-organizing network (SON) provide scalable solutions for network intelligent management. The implementation of reinforcement learning (RL) algorithms in SON illustrates its capability on network recognition and optimization. In this paper, three modules in SON and their applications were introduced, which were self-configuration, self-optimization and self-healing. Then, related RL algorithms from different criteria were evaluated, such as scalability, complexity, robustness and convergence. Finally, this research was summarized by analyzing the challenges associated with the application of RL in future wireless networks and identifying the directions for future research.
Spatial distributions and vertical structures of multilevel warm cloud systems over global oceans
QI Lin, LIU Qi, WEI Junbo, DING Yuhao, DENG Shumei
2018, 48(12): 1012-1021. doi: 10.3969/j.issn.0253-2778.2018.12.005
The collocated data from quasi-synchronous Aqua/MODIS and CloudSat/CPR measurements during 2008 were used to investigate the spatial distributions and vertical structures of multilevel warm cloud systems over global oceans. By modifying the traditionally warm cloud determination scheme that is based singly on cloud top temperature criterion, it is found that most oceanic warm-cloud units are of three dominant structures, including single-layer warm cloud, double-layer semi-warm cloud and double-layer warm cloud. The statistical results show that on the global scale, single-layer warm cloud (SWC), double-layer semi-warm cloud (DSC) and double-layer warm cloud (DWC) account for 77.14%, 19.15% and 3.71%, respectively. In the global distribution, the difference between the three configurations of warm clouds is obvious, especially at the geolocation with frequent occurrences. In terms of structural parameters such as cloud top height, cloud base height and cloud thickness, the statistical characteristics of the lower warm cloud in DSC are very close to that of SWC, showing the similarity of the two kinds of warm clouds on the geometric structure. This indicates that the upper cold cloud in DSC does not cause changes in the lower warm cloud, and the upper and the lower clouds may have originated from independent cloud-formation processes. The structure of the upper warm cloud in the DWC configuration is obviously different from that in the SWC, while the lower one is close to that of SWC, but with smaller cloud top height and cloud thickness. In addition, the thinner the lower warm cloud, the stronger the upper warm cloud can develop upward. These results suggest that there is probably a relevance between the upper and lower warm clouds in DWC, and these two cloud layers are closely correlated during their evolution.
Analysis of the characteristics of narrow bipolar event in a thunderstorm process in Jianghuai region
CHEN Yanling, LIU Feifan, ZHU Baoyou, PENG Changzhi, MA Ming
2018, 48(12): 1022-1032. doi: 10.3969/j.issn.0253-2778.2018.12.006
The relationship between narrow bipolar events (NBEs) and thunderstorm parameters and the isolation and radiation intensity of NBEs in different regions of a thunderstorm on August 5th, 2014 in Jianghuai region was investigated based on the satellite-based NCEP/CPC Global IR data, TRMM PR/TIM data, and the ground-based radar and lightning detection data. The results show that NBEs mainly occurred in the convective areas of the thunderstorm with the cloud top temperature being less than 210 K and the polarization correction temperature(PCT-85) less than 100 K. By analyzing the correlation between NBEs and the maximum height of 30 dBZ radar echo and lightning frequency, the results also show that NBEs mainly occurred during the high frequency period of lightning, and that the correlation between NBEs and lightning frequency is stronger than that between NBEs and the maximum height of 30 dBZ radar echo. The investigation of NBE isolation and the pulse peak intensity of VLF/LF band indicates that most isolated NBEs occurred in the early stage of the thunderstorm, and that the NBE radiation intensity below 20 dBZ was the strongest and most isolated.