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Entanglement and excited-state quantum phase transition in an extended Dicke model
Gui-Lei Zhu, Xin-You Lü, Shang-Wu Bin, Cai You, Ying Wu
Front. Phys. . 2019, 14 (5 ): 52602-.
https://doi.org/10.1007/s11467-019-0921-4
We investigate the properties of entanglement and excited-state quantum phase transition (ESQPT) in a hybrid atom-optomechanical system in which an optomechanical quadratic interaction is introduced into a normal Dicke model. Interestingly, by preparing the ancillary mode in a coherent state, both the quantum entanglement and ESQPT can be realized in a relative weak-coupling condition. Moreover, the entanglement is immune to the A 2 term, and a reversed trend of the entropy is obtained when the A 2 term is included. Density of states (DoS) and Peres lattice are used to investigate ESQPTs. Compared to a normal Dicke model, the DoS enlarges exp(2r α ) times if the ancillary mode is prepared in a coherent state. This work is an extension of the ground-state quantum phase transition, which may inspire further exploration of the quantum criticality in many-body systems.
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Controllable electromagnetically induced grating in a cascade-type atomic system
Jin-Peng Yuan, Chao-Hua Wu, Yi-Hong Li, Li-Rong Wang, Yun Zhang, Lian-Tuan Xiao, Suo-Tang Jia
Front. Phys. . 2019, 14 (5 ): 52603-.
https://doi.org/10.1007/s11467-019-0924-1
A controllable electromagnetically induced grating (EIG) is experimentally realized in a coherent rubidium ensemble with 5S 1/2 –5P 3/2 –5D 5/2 cascade configuration. In our work, a whole picture describing the relation between the first-order diffraction efficiency and the power of the coupling field is experimentally presented for the first time, which agrees well with the theoretical prediction. More important, by fine tuning the experimental parameters, the first-order diffraction efficiency of as high as 25% can be achieved and a clear three-order diffraction pattern is also observed. Such a controllable periodic structure can provide a powerful tool for studying the control of light dynamics, pave the way for realizing new optical device.
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Recent advances in controlling the crystallization of two-dimensional perovskites for optoelectronic device
Shi-Qiang Luo, Ji-Fei Wang, Bin Yang, Yong-Bo Yuan
Front. Phys. . 2019, 14 (5 ): 53401-.
https://doi.org/10.1007/s11467-019-0901-8
Though three-dimensional (3D) organic–inorganic halide perovskites (OIHP) is very promising for low cost and distributed PV generation, the stability issue of 3D OIHP is still a problem for its commercialization. Two-dimensional (2D) perovskites, protected by periodic organic ligands, is promising due to its excellent optoelectronic property and superior stability. However, 2D perovskite is anisotropic in its crystal structure and optoelectronic properties, and the resulted film is often a mixture of different phase. So, methods to manipulate 2D perovskite crystal orientation and its phase separation are vital. In this review, the major advances on the composition engineering, crystal orientation, phase separation, and interfacial capping are summarized. Besides, efforts on understanding the formation process of 2D perovskite crystal are also discussed, which is important for making full use of 2D perovskite in functional optoelectronic devices.
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Possible phase transition of anisotropic frustrated Heisenberg model at finite temperature
Ai-Yuan Hu, Lin Wen, Guo-Pin Qin, Zhi-Min Wu, Peng Yu, Yu-Ting Cui
Front. Phys. . 2019, 14 (5 ): 53601-.
https://doi.org/10.1007/s11467-019-0895-2
The frustrated spin-1/2 J 1 a –J 1 b –J 2 antiferromagnet with anisotropy on the two-dimensional square lattice was investigated, where the parameters J 1 a and J 1 b represent the nearest neighbor exchanges and along the x and y directions, respectively. J 2 represents the next-nearest neighbor exchange. The anisotropy includes the spatial and exchange anisotropies. Using the double-time Green’s function method, the effects of the interplay of exchanges and anisotropy on the possible phase transition of the Néel state and stripe state were discussed. Our results indicated that, in the case of anisotropic parameter 0≤η <1, the Néel and stripe states can exist and have the same critical temperature as long as J 2 = J 1 b /2. Under such parameters, a first-order phase transformation between the Néel and stripe states can occur below the critical point. For J 2 ≠J 1 b /2, our results indicate that the Néel and stripe states can also exist, while their critical temperatures differ. When J 2 >J 1 b /2, a first-order phase transformation between the two states may also occur. However, for J 2 <J 1 b /2, the Néel state is always more stable than the stripe state.
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Skyrmion Hall effect with spatially modulated Dzyaloshinskii–Moriya interaction
Liping Zhou, Ren Qin, Ya-Qing Zheng, Yong Wang
Front. Phys. . 2019, 14 (5 ): 53602-.
https://doi.org/10.1007/s11467-019-0897-0
The skyrmion Hall effect is theoretically studied in the chiral ferromagnetic film with spatially modulated Dzyaloshinskii–Moriya interaction. Three cases including linear, sinusoidal, and periodic rectangular modulations have been considered, where the increase, decrease, and the periodic modification of the size and velocity of the skyrmion have been observed in the microscopic simulations. These phenomena are well explained by the Thiele equation, where an effective force on the skyrmion is induced by the inhomogeneous Dzyaloshinskii–Moriya interaction. The results here suggest that the skyrmion Hall effect can be manipulated by artificially tuning the Dzyaloshinskii–Moriya interaction in chiral ferromagnetic film with material engineering methods, which will be useful to design skyrmion-based spintronics devices.
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β-PtO2 : Phononic, thermodynamic, and elastic properties derived from first-principles calculations
Quan Chen (陈泉), Wei Li (李伟), Yong Yang (杨勇)
Front. Phys. . 2019, 14 (5 ): 53604-.
https://doi.org/10.1007/s11467-019-0900-9
β-PtO2 is a useful transition metal dioxide, but its fundamental thermodynamic and elastic properties remain unexplored. Using first-principles calculations, we systematically studied the structure, phonon, thermodynamic and elastic properties of β-PtO2 . The lattice dynamics and structural stability of β-PtO2 under pressure were studied using the phonon spectra and vibrational density of states. The vibrational frequencies of the optical modes of β-PtO2 increase with elevating pressure; this result is comparable with the available experimental data. Then, the heat capacities and their pressure responses were determined based on the phonon calculations. The pressure dependence of the Debye temperature was studied, and the results were compared in two distinct aspects. The elastic moduli of β-PtO2 were estimated through the Voigt–Reuss–Hill approximation. The bulk modulus of β-PtO2 increases linearly with pressure, but the shear modulus is nearly independent of pressure. Our study revealed that the elastic stiffness coefficients C 44 , C 55 and C 66 play a primary role in the slow variation of the shear modulus.
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Comment to “Dynamics of supercooled confined water measured by deep inelastic neutron scattering”
Y. Finkelstein, R. Moreh
Front. Phys. . 2019, 14 (5 ): 53605-.
https://doi.org/10.1007/s11467-019-0926-z
We comment on the findings of “Dynamics of supercooled confined water measured by deep inelastic neutron scattering”, by V. De Michele, G. Romanelli, and A. Cupane [Front. Phys . 13, 138205 (2018)]. We show that the current sensitivity of the deep inelastic neutron scattering (DINS) method, cannot detect with confidence small differences in the proton kinetic energy, Ke(H), involved in a liquid-liquid transition in supercooled water confined in nanoporous silica. We also critisize the calculation of Ke(H) carried out in Front. Phys. 13, 138205 (2018).
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Reply to “Comment to ‘Dynamics of supercooled confined water measured by deep inelastic neutron scattering’ by Y. Finkelstein and R. Moreh”
V. De Michele, G. Romanelli, A. Cupane
Front. Phys. . 2019, 14 (5 ): 53606-.
https://doi.org/10.1007/s11467-019-0927-y
We reply to the comment [Front. Phys . 14(5), 53605 (2019)] by Y. Finkelstein and R. Moreh on our article Front. Phys . 13(1), 138205 (2018). We agree with some of their criticisms about our calculation of the temperature effect on the kinetic energy of hydrogen atoms of supercooled confined water; we also agree with their statement that, in view of the current sensitivity of the technique, possible effects of the liquid–liquid water transition are hardly detected with deep inelastic neutron scattering (DINS). However, we disagree with their use of the translational mass ratio of a single water molecule and, in general, with their underestimation of collective effects.
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12 articles