We study the entanglement between the internal (coin) and the external (position) degrees of freedom in the dynamic and the static deterministic aperiodic quantum walks (QWs). For the dynamic (static) aperiodic QWs, the coin depends on the time (position) and takes two coins C(α) and C(β) arranged in the two classes of generalized Fibonacci (GF) and the Thue-Morse (TM) sequences. We found that for the dynamic QWs, the entanglement of three kinds of the aperiodic QWs are close to the maximal value, which are all much larger than that of the homogeneous QWs. Further, the first class of GF (1st GF) QWs can achieve the maximum entangled state, which is similar to that of the dynamic disordered QWs. And the entanglement of 1st GF QWs is greater than that of the TM QWs, being followed closely by the entanglement of the second class of GF (2nd GF) QWs. For the static QWs, the entanglement of three kinds of the aperiodic QWs are also close to the maximal value and 1st GF QWs can achieve the maximum entangled state. The entanglement of the TM QWs is between 1st GF QWs and 2nd GF QWs. However, the entanglement of the static disordered QWs is less than that of three kinds of the aperiodic QWs. This is different from those of the dynamic QWs. From these results, we can conclude that the dynamic and static 1st GF QWs can also be considered as maximal entanglement generators.
Inspired by the recent experimental progress in noisy kicked rotor systems, we investigate the effect of temporal disorder or quasi-periodicity in one-dimensional kicked lattices with pulsed on-site potential. We found that, unlike the spatial disorder or quasi-periodicity which usually leads to localization, the effect of the temporal one is more complex and depends on the spatial configuration. If the kicked on-site potential is periodic in real space, then the wave packet will stay diffusive in the presence of temporal disorder or quasi-periodicity. On the other hand, if the kicked on-site potential is spatially quasi-periodic, then the temporal disorder or quasi-periodicity may lead to a shift of the transition point of the dynamical localization and destroy the dynamical localization in a certain parameter range. The results we obtained can be readily tested by experiments and may help us better understand the dynamical localization.
We design an asymmetric transmission system (ATS) with two flat acoustic metasurfaces (AMs) to yield bidirectional asymmetric acoustic focusing (BAAF). The acoustic waves could be focused on both sides of the ATS with different focal lengths and intensities. To achieve high intensity energy concentration, the accelerating acoustic beams are selected to realize the BAAF. The working bandwidth of the BAAF based on our ATS could reach~0.4 kHz. It is found that by adjusting the distance between two flat AMs, the focal length and intensity of the bidirectional focusing could easily be modulated. Because the distance between two flat AMs is large enough, the BAAF even could be converted into a unidirectional acoustic focusing. The proposed BAAF may find applications in non-destructive evaluation, biomedical imaging and medical diagnosis.
The spin-polarized band structures of an ultrathin Pb/MoTe2/Pb heterostructure are calculated via first-principles density functional theory. The electron-phonon interaction and the superconducting properties of the ultrathin Pb/MoTe2/Pb heterostructure are studied by using the fully anisotropic Migdal-Eliashberg theory powered by Wannier-Fourier interpolation. Due to the complex Fermi surface in this low-dimensional system, the electron-phonon interaction and the superconducting gap display significant anisotropy. The temperature dependence of the superconducting gap can be fitted by solving numerically the Bardeen-Cooper-Schrieffer (BCS) gap equation with an adjustable parameter α, suggesting that phonon-mediated mechanism as its superconducting origin. Large Rashba spin-splitting and superconductivity coexist in this heterostructure, suggesting that this hybrid low-dimensional system will have some specific applications.
Synthetic dimensions in time (Sambe space) can be utilized in a periodic time-dependent system. By subjecting the system into a time-periodic potential and measuring the physical quantities at distinct time in one period, one is able to simulate the models in higher dimension. To verify this approach, we show that the Bloch oscillation of wave packets along the magnetic field in a three-dimensional (3D) Weyl metal can be simulated on a two-dimensional (2D) insulator. Different from the chiral anomaly, this Bloch oscillation is anisotropic when the initial wave packet is not on the 0-th Landau level.
We numerically investigate the valley-polarized current in symmetric and asymmetric zigzag graphene nanoribbons (ZGNRs) by the adiabatic pump, and the effect of spatial symmetry is considered by introducing different pumping regions. It is found that pumping potentials with the symmetry Vp(x,y)=Vp(-x,y) can generate the largest valley-polarized current. The valley-polarized currents I13L with the pumping potential symmetry Vp(x,y)=Vp(x,-y) and I14L with Vp(x,y)=Vp(-x,-y) of symmetric ZGNRs are much smaller than those of asymmetric ZGNRs. We also find I13L and I14L of symmetric ZGNRs decrease and increase with the increasing pumping amplitude, respectively. Moreover, the dephasing effect from the electron-phonon coupling within the Buttiker dephasing scheme is introduced. The valley-polarized current of the symmetric ZGNRs with Vp(x,y)=Vp(x,-y) increases with the increase of the dephasing strength while that with Vp(x,y)=Vp(-x,-y) decreases as the dephasing strength increases.
For several types of the applied electric field configuration on the normal-zigzag black phosphorus nanoribbon (nZZ-BPNR) we investigate the band structure and the linear optical absorption spectrum, especially for the edge states and the corresponding low-energy absorption peaks. The obtained results show that the applied electric field can not only open another band gap at k=0.5 point, but also can change completely the spacial probabilities of edge states in the two edge bands. The strength of electric field can tune the two band gaps at the Γ point and 0.5 point. Further, one remarkable feature is that the forbidden transition E12 and E21 are allowed. The lowest-excited-energy linear absorption peak E11 originates from the transition between two edge bands at the Γ point. Finally, in comparison with the lowest-excited-energy peaks among various configurations, the second type of electric field configuration can move this peak blue-shift larger than other configurations.
We theoretically investigate the influence of off-resonant circularly polarized light field and perpendicular electric field on the quantum transport in a monolayer silicene-based normal/superconducting/normal junction. Owing to the tunable band structure of silicene, a pure crossed Andreev reflection process can be realized under the optical and electrical coaction. Moreover, a switch effect among the exclusive crossed Andreev reflection, the exclusive elastic cotunneling and the exclusive Andreev reflection, where the former two are the nonlocal transports and the third one is the local transport, can be obtained in our system by the modulation of the electric and light fields. In addition, the influence of the relevant parameters on the nonlocal and local transports is calculated and analyzed as well.
In this work, we experimentally investigated the thermal stability of the interlayer exchange coupling field (Hex) and strength (-Jiec) in synthetic antiferromagnetic (SAF) structure of[Pt(0.6)/Co(0.6)]2/Ru(tRu)/[Co(0.6)/Pt(0.6)]4 multilayers with perpendicular anisotropy. Depending on the thickness of the spacing ruthenium (Ru) layer, the observed interlayer exchange coupling can be either ferromagnetic or antiferromagnetic. The Hex were studied by measuring the magnetization hysteresis loops in the temperature range from 100 K to 700 K as well as the theoretical calculation of the -Jiec. It is found that the interlayer coupling in the multilayers is very sensitive to the thickness of Ru and temperature. The Hex exhibits either a linear or a non-linear dependence on the temperature for different thickness of Ru. Furthermore, our SAF multilayers show a high thermal stability even up to 600 K (Hex=3.19 kOe, -Jiec=1.97 erg/cm2 for tRu=0.6 nm, the unit 1 Oe=79.5775 A·m-1), which was higher than the previous studies.
Most of the reported observations are about the dynamic properties of individual domain-walls in magnetic nanowires, but the properties of multiple stripe-domains have rarely been investigated. Here, we demonstrate a simple but efficient scenario for multiple domains injection in magnetic nanowires. The domain-chains (DCs), a cluster of multiple domains, can be dynamically generated with tunable static properties. It is found that the number of domains in a single DC can be dynamically adjusted by varying the frequency of microwave field (MF) and the period of spin-polarized current (SPC) intensity. The static properties of the DCs, i.e., its length, spacing, and period between neighboring DCs, can be dynamically controlled by regulating the frequency of MF and the intensity of SPC. We have also discussed the possibility of using domain-chains as information carries, which provides a meaningful approach for flexible multi-bit information storage applications.
Super-resolution optical fluctuation imaging is dependent on the blinking frequency of fluorophores. Consequently, improvement of the photoluminescence (PL) blink frequency is important. This is achieved for 3C-SiC nanocrystals (NCs) by simply increasing the excitation power. Using an excitation of 488 nm with powers of 5 μW to 50 μW, individual 3C-SiC NC always exhibits PL blinking with a short on-state sojourn time (<0.1 s). A fast Fourier transform method is exploited to determine the PL switching frequency. It is found that the frequency of the bright state increases from 2 Hz to 20 Hz as the excitation power increases from 5 μW to 50 μW, which is explained by the Auger photonionization model.
