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Light-Induced Phonon-Mediated Magnetization in Monolayer MoS$_{2}$
Shengjie Zhang, Yufei Pei, Shiqi Hu, Na Wu, Da-Qiang Chen, Chao Lian, and Sheng Meng
Chin. Phys. Lett.    2023, 40 (7): 077502 .   DOI: 10.1088/0256-307X/40/7/077502
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Light-induced ultrafast spin dynamics in materials is of great importance for developments of spintronics and magnetic storage technology. Recent progresses include ultrafast demagnetization, magnetic switching, and magnetic phase transitions, while the ultrafast generation of magnetism is hardly achieved. Here, a strong light-induced magnetization (up to $0.86\mu_{\scriptscriptstyle{\rm B}}$ per formula unit) is identified in non-magnetic monolayer molybdenum disulfide (MoS$_{2}$). With the state-of-the-art time-dependent density functional theory simulations, we demonstrate that the out-of-plane magnetization can be induced by circularly polarized laser, where chiral phonons play a vital role. The phonons strongly modulate spin-orbital interactions and promote electronic transitions between the two conduction band states, achieving an effective magnetic field $\sim$ $380$ T. Our study provides important insights into the ultrafast magnetization and spin-phonon coupling dynamics, facilitating effective light-controlled valleytronics and magnetism.
Magnetic-Field-Induced Sign Changes of Thermal Expansion in DyCrO$_{4}$
Jin-Cheng He, Zhao Pan, Dan Su, Xu-Dong Shen, Jie Zhang, Da-Biao Lu, Hao-Ting Zhao, Jun-Zhuang Cong, En-Ke Liu, You-Wen Long, and Young Sun
Chin. Phys. Lett.    2023, 40 (6): 066501 .   DOI: 10.1088/0256-307X/40/6/066501
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The anharmonicity of lattice vibration is mainly responsible for the coefficient of thermal expansion (CTE) of materials. External stimuli, such as magnetic and electric fields, thus cannot effectively change the CTE, much less the sign variation from positive to negative or vice versa. In this study, we report significant magnetic field effects on the CTE of zircon- and scheelite-type DyCrO$_{4}$ prepared at ambient and high pressures, respectively. At zero field, the zircon-type DyCrO$_{4}$ exhibits a negative CTE below the ferromagnetic-order temperature of 23 K. With increasing field up to $\ge $1.0 T, however, the sign of the CTE changes from negative to positive. In the scheelite phase, magnetic field can change the initially positive CTE to be negative with a field up to 2.0 T, and then a reentrant positive CTE is induced by enhanced fields $\ge $3.5 T. Both zircon and scheelite phases exhibit considerable magnetostrictive effects with the absolute values as high as $\sim$ $800$ ppm at 2 K and 10 T. The strong spin–lattice coupling is discussed to understand the unprecedented sign changes of the CTE caused by applying magnetic fields. The current DyCrO$_{4}$ provides the first example of field-induced sign change of thermal expansion, opening up a way to readily control the thermal expansion beyond the conventional chemical substitution.
Digital Simulation of Projective Non-Abelian Anyons with 68 Superconducting Qubits
Shibo Xu, Zheng-Zhi Sun, Ke Wang, Liang Xiang, Zehang Bao, Zitian Zhu, Fanhao Shen, Zixuan Song, Pengfei Zhang, Wenhui Ren, Xu Zhang, Hang Dong, Jinfeng Deng, Jiachen Chen, Yaozu Wu, Ziqi Tan, Yu Gao, Feitong Jin, Xuhao Zhu, Chuanyu Zhang, Ning Wang, Yiren Zou, Jiarun Zhong, Aosai Zhang, Weikang Li, Wenjie Jiang, Li-Wei Yu, Yunyan Yao, Zhen Wang, Hekang Li, Qiujiang Guo, Chao Song, H. Wang, and Dong-Ling Deng
Chin. Phys. Lett.    2023, 40 (6): 060301 .   DOI: 10.1088/0256-307X/40/6/060301
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Non-Abelian anyons are exotic quasiparticle excitations hosted by certain topological phases of matter. They break the fermion-boson dichotomy and obey non-Abelian braiding statistics: their interchanges yield unitary operations, rather than merely a phase factor, in a space spanned by topologically degenerate wavefunctions. They are the building blocks of topological quantum computing. However, experimental observation of non-Abelian anyons and their characterizing braiding statistics is notoriously challenging and has remained elusive hitherto, in spite of various theoretical proposals. Here, we report an experimental quantum digital simulation of projective non-Abelian anyons and their braiding statistics with up to 68 programmable superconducting qubits arranged on a two-dimensional lattice. By implementing the ground states of the toric-code model with twists through quantum circuits, we demonstrate that twists exchange electric and magnetic charges and behave as a particular type of non-Abelian anyons, i.e., the Ising anyons. In particular, we show experimentally that these twists follow the fusion rules and non-Abelian braiding statistics of the Ising type, and can be explored to encode topological logical qubits. Furthermore, we demonstrate how to implement both single- and two-qubit logic gates through applying a sequence of elementary Pauli gates on the underlying physical qubits. Our results demonstrate a versatile quantum digital approach for simulating non-Abelian anyons, offering a new lens into the study of such peculiar quasiparticles.
Superconductivity Observed in Tantalum Polyhydride at High Pressure
X. He, C. L. Zhang, Z. W. Li, S. J. Zhang, B. S. Min, J. Zhang, K. Lu, J. F. Zhao, L. C. Shi, Y. Peng, X. C. Wang, S. M. Feng, J. Song, L. H. Wang, V. B. Prakapenka, S. Chariton, H. Z. Liu, and C. Q. Jin
Chin. Phys. Lett.    2023, 40 (5): 057404 .   DOI: 10.1088/0256-307X/40/5/057404
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We report experimental discovery of tantalum polyhydride superconductor. It was synthesized under high-pressure and high-temperature conditions using diamond anvil cell combined with in situ high-pressure laser heating techniques. The superconductivity was investigated via resistance measurements at pressures. The highest superconducting transition temperature $T_{\rm c}$ was found to be $\sim$ $30$ K at 197 GPa in the sample that was synthesized at the same pressure with $\sim$ $2000$ K heating. The transitions are shifted to low temperature upon applying magnetic fields that support the superconductivity nature. The upper critical field at zero temperature $\mu_{0}H_{\rm c2}$(0) of the superconducting phase is estimated to be $\sim$ $20$ T that corresponds to Ginzburg–Landau coherent length $\sim$ $40$ Å. Our results suggest that the superconductivity may arise from $I\bar{4}3d$ phase of TaH$_{3}$. It is, for the first time to our best knowledge, experimental realization of superconducting hydrides for the VB group of transition metals.
Augmenting Density Matrix Renormalization Group with Disentanglers
Xiangjian Qian and Mingpu Qin
Chin. Phys. Lett.    2023, 40 (5): 057102 .   DOI: 10.1088/0256-307X/40/5/057102
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Density matrix renormalization group (DMRG) and its extensions in the form of matrix product states are arguably the choice for the study of one-dimensional quantum systems in the last three decades. However, due to the limited entanglement encoded in the wave-function ansatz, to maintain the accuracy of DMRG with the increase of the system size in the study of two-dimensional systems, exponentially increased resources are required, which limits the applicability of DMRG to only narrow systems. We introduce a new ansatz in which DMRG is augmented with disentanglers to encode area-law-like entanglement entropy (entanglement entropy supported in the new ansatz scales as $l$ for an $l \times l$ system). In the new method, the $O(D^3)$ low computational cost of DMRG is kept (with an overhead of $O(d^4)$ and $d$ the dimension of the physical degrees of freedom). We perform benchmark calculations with this approach on the two-dimensional transverse Ising and Heisenberg models. This new ansatz extends the power of DMRG in the study of two-dimensional quantum systems.
Lu–H–N Phase Diagram from First-Principles Calculations
Fankai Xie, Tenglong Lu, Ze Yu, Yaxian Wang, Zongguo Wang, Sheng Meng, and Miao Liu
Chin. Phys. Lett.    2023, 40 (5): 057401 .   DOI: 10.1088/0256-307X/40/5/057401
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Employing a comprehensive structure search and high-throughput first-principles calculation method on 1561 compounds, the present study reveals the phase diagram of Lu–H–N. In detail, the formation energy landscape of Lu–H–N is derived and utilized to assess the thermodynamic stability of each compound that is created via element substitution. The result indicates that there is no stable ternary structure in the Lu–H–N chemical system, however, metastable ternary structures, such as Lu$_{20}$H$_{2}$N$_{17}$ $(C2/m)$ and Lu$_{2}$H$_{2}$N ($P\bar{3}m1$), are observed to have small $E_{\rm hull}$ ($ < 100$ meV/atom). It is also found that the energy convex hull of the Lu–H–N system shifts its shape when applying hydrostatic pressure up to 10 GPa, and the external pressure stabilizes a couple of binary phases such as LuN$_{9}$ and Lu$_{10}$H$_{21}$. Additionally, interstitial voids in LuH$_{2}$ are observed, which may explain the formation of Lu$_{10}$H$_{21}$ and LuH$_{3-\delta}$N$_{\epsilon}$. To provide a basis for comparison, x-ray diffraction patterns and electronic structures of some compounds are also presented.
Giant Tunneling Magnetoresistance in Spin-Filter Magnetic Tunnel Junctions Based on van der Waals A-Type Antiferromagnet CrSBr
Guibin Lan, Hongjun Xu, Yu Zhang, Chen Cheng, Bin He, Jiahui Li, Congli He, Caihua Wan, Jiafeng Feng, Hongxiang Wei, Jia Zhang, Xiufeng Han, and Guoqiang Yu
Chin. Phys. Lett.    2023, 40 (5): 058501 .   DOI: 10.1088/0256-307X/40/5/058501
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Two-dimensional van der Waals magnetic materials have demonstrated great potential for new-generation high-performance and versatile spintronic devices. Among them, magnetic tunnel junctions (MTJs) based on A-type antiferromagnets, such as CrI$_{3}$, possess record-high tunneling magnetoresistance (TMR) because of the spin filter effect of each insulating unit ferromagnetic layer. However, the relatively low working temperature and the instability of the chromium halides hinder applications of this system. Using a different technical scheme, we fabricated the MTJs based on an air-stable A-type antiferromagnet, CrSBr, and observed a giant TMR of up to 47000% at 5 K. Meanwhile, because of a relatively high Néel temperature of CrSBr, a sizable TMR of about 50% was observed at 130 K, which makes a big step towards spintronic devices at room temperature. Our results reveal the potential of realizing magnetic information storage in CrSBr-based spin-filter MTJs.
Electron-Exciton Coupling in 1T-TiSe$_{2}$ Bilayer
Li Zhu, Wei-Min Zhao, Zhen-Yu Jia, Huiping Li, Xuedong Xie, Qi-Yuan Li, Qi-Wei Wang, Li-Guo Dou, Ju-Gang Hu, Yi Zhang, Wenguang Zhu, Shun-Li Yu, Jian-Xin Li, and Shao-Chun Li
Chin. Phys. Lett.    2023, 40 (5): 057101 .   DOI: 10.1088/0256-307X/40/5/057101
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Excitons in solid state are bosons generated by electron-hole pairs as the Coulomb screening is sufficiently reduced. The exciton condensation can result in exotic physics such as super-fluidity and insulating state. In charge density wave (CDW) state, 1T-TiSe$_{2}$ is one of the candidates that may host the exciton condensation. However, to envision its excitonic effect is still challenging, particularly at the two-dimensional limit, which is applicable to future devices. Here, we realize the epitaxial 1T-TiSe$_{2}$ bilayer, the two-dimensional limit for its $2 \times 2\times 2$ CDW order, to explore the exciton-associated effect. By means of high-resolution scanning tunneling spectroscopy and quasiparticle interference, we discover an unexpected state residing below the conduction band and right within the CDW gap region. As corroborated by our theoretical analysis, this mysterious phenomenon is in good agreement with the electron-exciton coupling. Our study provides a material platform to explore exciton-based electronics and opto-electronics.
Empirical Determination of the Pion Mass Distribution
Y.-Z. Xu, K. Raya, Z.-F. Cui, C. D. Roberts, and J. Rodríguez-Quintero
Chin. Phys. Lett.    2023, 40 (4): 041201 .   DOI: 10.1088/0256-307X/40/4/041201
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Existing pion+nucleus Drell-Yan and electron+pion scattering data are used to develop ensembles of model-independent representations of the pion generalized parton distribution (GPD). Therewith, one arrives at a data-driven prediction for the pion mass distribution form factor, $\theta_2^\pi $. Compared with the pion elastic electromagnetic form factor, $\theta_2^\pi$ is harder: the ratio of the radii derived from these two form factors is $r_\pi^{\theta_2}/r_\pi = 0.79(3)$. Our data-driven predictions for the pion GPD, related form factors and distributions should serve as valuable constraints on theories of pion structure.
A 700 W$\cdot$h$\cdot$kg$^{-1}$ Rechargeable Pouch Type Lithium Battery
Quan Li, Yang Yang, Xiqian Yu, and Hong Li
Chin. Phys. Lett.    2023, 40 (4): 048201 .   DOI: 10.1088/0256-307X/40/4/048201
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High-energy-density rechargeable lithium batteries are being pursued by researchers because of their revolutionary potential nature. Current advanced practical lithium-ion batteries have an energy density of around 300 W$\cdot$h$\cdot$kg$^{-1}$. Continuing to increase the energy density of batteries to a higher level could lead to a major explosion development in some fields, such as electric aviation. Here, we have manufactured practical pouch-type rechargeable lithium batteries with both a gravimetric energy density of 711.3 W$\cdot$h$\cdot$kg$^{-1}$ and a volumetric energy density of 1653.65 W$\cdot$h$\cdot$L$^{-1}$. This is achieved through the use of high-performance battery materials including high-capacity lithium-rich manganese-based cathode and thin lithium metal anode with high specific energy, combined with extremely advanced process technologies such as high-loading electrode preparation and lean electrolyte injection. In this battery material system, the structural stability of cathode material in a widened charge/discharge voltage range and the deposition/dissolution behavior of interfacial modified thin lithium electrode are studied.
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