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Stability of the topological quantum critical point between multi-Weyl semimetal and band insulator
Zhao-Kun Yang(杨兆昆), Jing-Rong Wang(王景荣), and Guo-Zhu Liu(刘国柱)
Chin. Phys. B, 2023, 32 (5): 056401
二重Weyl半金属和三重Weyl半金属是最近发现的物质拓扑态,在理论和实验上都得到了广泛的研究。如果在费米能级处打开普通带隙,则二重Weyl半金属和三重Weyl半金属可以转变为拓扑平庸的能带绝缘体。值得注意的是,在从二重Weyl半金属或三重Weyl半金属到能带绝缘体的相变中出现了拓扑量子临界点(TQCP)。这种TQCP很值得深入研究,因为它可能表现出惊人的特性。然而,尚不清楚这样的TQCP对弱扰动是否稳定。一个特别有趣的问题是检验TQCP对现实材料中总是存在的无序的稳定性。据我们所知,这个问题在以前的论文中从未被系统地讨论过。本文首次对这个问题进行了系统的理论研究。作者使用重整化群(RG)方法来处理在TQCP激发的无带隙费米子与各种类型的无序之间的相互作用,并得到了所有模型参数的耦合RG方程。研究结果证明二重Weyl半金属和带绝缘体之间的TQCP是不稳定的,并且可以很容易地通过任何类型的弱无序转变为可压缩的扩散金属。如果系统仅包含沿z轴的随机矢量势,则三重Weyl半金属和带绝缘体之间的TQCP流向稳定的强耦合不动点,但当存在其他类型的随机势时,TQCP变为可压缩的扩散金属。本文的研究有助于理解真实材料中多重外尔半金属到能带绝缘体拓扑相变点附近的新奇物理现象。
原文链接
Fig. 1. Dispersion of the low-energy fermions excited at double-TQCP(topological quantum critical point).
Enhanced phase sensitive amplification towards improving noise immunity
Hui Guo(郭辉), Zhi Li(李治), Hengxin Sun(孙恒信), Kui Liu(刘奎), and Jiangrui Gao(郜江瑞)
Chin. Phys. B, 2023, 32 (5): 054204
量子信息过程中,量子态无法避免信道噪声和损耗的影响。光学相敏放大器作为一种必不可少的工具,由于其在放大的过程中不引入额外噪声,保证了脆弱量子态在嘈杂环境中的量子特性,提高了量子态的环境容忍度,从而用于长距离量子通信,特别是可以用于量子测量协议中抵抗探测损耗的影响,从而推动实用化的量子测量技术。由于受技术噪声以及系统损耗的影响,目前相敏放大器的输出信噪比无法超越输入态的信噪比,无法满足实际应用需求。
本文报道了一种基于无噪声线性放大的增强型相敏放大器(MB-NLA enhanced PSA)。理论分析了三种通道损耗(传输损耗、探测损耗、放大器内部损耗)噪声下的量子态(压缩态和相干态)的输出特性。发现传统的相敏放大器只能克服探测损耗的影响,对于已经受损的信号没有信噪比的提高,而增强型相敏放大器对三种通道损耗均展现了明显的抵抗能力。并且,压缩态相比相干态具有更好的提升效果。基于理论分析,实验上完成了相干态的增强型相敏放大,实现了对通道噪声的有效抑制。对于传输损耗噪声和探测损耗噪声,分别实现了14.5%和43.8%的抗噪性能。本文的研究有望应用于基于压缩态的分布式量子传感网络中。
原文链接
Fig. 1. Example of a protocol for noise immunity against channel noise in sensing link. The probe state is received through the lossy channel and amplification is attempted via an MB-NLA enhanced PSA. Inset: schematic diagram of the PSA.
Visualizing interface states in In2Se3–WSe2 monolayer lateral heterostructures
Da Huo(霍达), Yusong Bai(白玉松), Xiaoyu Lin(林笑宇), Jinghao Deng(邓京昊), Zemin Pan(潘泽敏), Chao Zhu(朱超), Chuansheng Liu(刘传胜), and Chendong Zhang(张晨栋)
Chin. Phys. B, 2023, 32 (5): 056803
二维铁电材料的最新发现为基于范德瓦尔斯材料的二维铁电异质结构电子器件的发展以及在原子层厚度极限下的铁电器件应用提供了更多的可能性。本文报道了In2Se3-WSe2横向异质结构的原位制备及其界面电子结构的探测,并将其与已被广泛研究得的垂直铁电异质结构进行了比较。通过分子束外延技术,作者制备了单层WSe2(3个原子层)和单层In2Se3(5个原子层)组成的横向异质结构。发现反铁电β’-In2Se3或由铁电β*-In2Se3, 与WSe2组成的横向异质结构中均形成II型能带排列,其中得能带偏移可以通过铁电极化开关进行调制。更有趣的是, 两个横向异质结构中的界面态都表现为窄带隙量子线,并且β*-In2Se3-WSe2 异质结构中的界面态带隙小于 基于β'-In2Se3的异质结构中的带隙。二维铁电异质结构的制备和界面态的调制为铁电器件的开发提供了新的平台。
原文链接
Fig. 2. (a) Topography image of β'-In2Se3–WSe2 lateral HS. (b) Color-coded rendering of the real space imaging of the band profile plotted in terms of log(dI/dV). The dI/dV spectra were taken along the path shown by the red arrow in (a). The bandgap of the interface is marked by the white arrow. (c) A selective subset of log(dI/dV) spectra. The spectra taken on WSe2, interface, and β'-In2Se3 are represented by black, blue, and green, respectively. Set point: Vbias = 2 V, It = 100 pA.
Spin reorientation in easy-plane kagome ferromagnet Li9Cr3(P2O7)3(PO4)2
Yuanhao Dong(董元浩), Ying Fu(付盈), Yixuan Liu(刘以轩), Zhanyang Hao(郝占阳), Le Wang(王乐), Cai Liu(刘才), Ke Deng(邓可), and Jiawei Mei(梅佳伟)
Chin. Phys. B, 2023, 32 (5): 057506
本研究揭示了易面铁磁体在垂直磁场下自旋重排过程的新机制,该过程可以类比为磁振子的玻色-爱因斯坦凝聚现象。我们发现,磁振子的玻色-爱因斯坦凝聚相边界的决定因素是温度临界点Tc与磁场强度B之间的关系,具体表达式为Tc~|B-Bc |d/2,其中d是系统的空间维度。我们通过对笼目易面铁磁体Li9Cr3(P2O7)3(PO4)2的研究发现,在饱和临界场附近的相边界满足Tc~|B-Bc|的线性关系。因此,我们认为此项研究成功实现了一个二维磁振子玻色-爱因斯坦凝聚过程,其观测到的自旋重排相变对于理解磁场诱导的磁构型的量子相变具有重要意义。
原文链接
Fig. 1. (a) and (b): Crystal structure of Li9Cr3(P2O7)3(PO4)2 with Cr3+ forming the regular kagome lattice. (c) Field-induced T-B phase diagram for Li9Cr3(P2O7)3(PO4)2 with B//c. The phase boundary between the ordered phase and fully polarized phase is linear Tc~|B-Bc|, implying two-dimensional magnon Bose-Einstein condensation.
Prediction of LiCrTe2 monolayer as a half-metallic ferromagnet with a high Curie temperature
Li-Man Xiao(肖丽蔓), Huan-Cheng Yang(杨焕成), and Zhong-Yi Lu(卢仲毅)
Chin. Phys. B, 2023, 32 (5): 057505
自旋电子学是最有希望的下一代信息技术之一,自旋电子学器件充分利用电子的自旋自由度,有望降低功耗,提高器件的存储和处理能力。在传统的非磁材料中引入自旋极化对制备自旋电子学器件来说是非常重要的一个环节,其中最常见的方式是利用铁磁材料进行自旋注入。铁磁半金属材料的载流子自旋极化率可达100%,尤为适合作为自旋注入源材料。从实际应用角度出发,理想的铁磁半金属材料应具有较高的居里温度,足够大的自旋能隙以防止热激发导致的载流子自旋翻转以及较大的磁各向异性和大的磁化强度以提高自旋注入效率。此外,相比于块体材料,二维材料对多种调控手段更敏感且更容易集成到异质结器件中。
本文通过第一性原理电子结构计算提出了一种二维铁磁半金属材料——单层LiCrTe2。研究表明,单层LiCrTe2有着扭曲的四方结构,有良好的热力学、动力学和机械稳定性。其基态为铁磁,易磁化方向位于面内,每个Cr原子上的磁矩约为3.6 μB,基于经典海森堡模型的蒙特卡洛模拟估计单层LiCrTe2的居里温度高于600 K。双轴应变可以有效调节单层LiCrTe2的磁各向异性,当双轴压缩应变超过1%时,其易磁化方向从面内转变为面外。在-5%到5%的双轴应变下,其铁磁性、宽自旋能隙、大磁矩和高居里温度均可保持。单层LiCrTe2的发现为探索二维铁磁半金属材料提供了新的选择。
原文链接
Fig. 1. (a) Spin-resolved band structure of the LiCrTe2 monolayer with Ueff = 3 eV. (b) The evolution of the normalized S and auto-correlation along with temperature for Ueff = 3 eV (c) The magnetocrystalline anisotropy energy (MAE) under biaxial strains ranging from −5% to +5%. MAE < 0 and MAE > 0 represent the out-of-plane and in-plane magnetization, respectively.
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