Influence of inelastic relaxation time on intrinsic spin Hall effects in a disordered two-dimensional electron gas

The influence of inelastic relaxation time on the intrinsic spin Hall effects in a disordered two-dimensional electron gas with Rashba interaction is studied, which clarifies the controversy of impurity effects in the system. We reveal that, due to the existence of inelastic scattering, the spin Hall conductivity does not vanish when the impurity concentration diminishes to zero no matter it is non-magnetically or magnetically disordered. The spin accumulation is evaluated by using the obtained spin Hall conductivity, and an alternate route is suggested to verify the intrinsic spin Hall effect by measuring the spin accumulation at different ratios.Comment: Revtex 6 pages, 1 figure, extended with more detail

Towards practical high-speed high dimensional quantum key distribution using partial mutual unbiased basis of photon's orbital angular momentum

Quantum Key Distribution (QKD) guarantees the security of communication with quantum physics. Most of widely adopted QKD protocols currently encode the key information with binary signal format---qubit, such as the polarization states. Therefore the transmitted information efficiency of the quantum key is intrinsically upper bounded by 1 bit per photon. High dimensional quantum system is a potential candidate for increasing the capacity of single photon. However, due to the difficulty in manipulating and measuring high dimensional quantum systems, the experimental high dimensional QKD is still at its infancy. Here we propose a sort of practical high-speed high dimensional QKD using partial mutual unbiased basis (PMUB) of photon's orbital angular momentum (OAM). Different from the previous OAM encoding, the high dimensional Hilbert space we used is expanded by the OAM states with same mode order, which can be extended to considerably high dimensions and implemented under current state of the art. Because all the OAM states are in the same mode order, the coherence will be well kept after long-distance propagation, and the detection can be achieved by using passive linear optical elements with very high speed. We show that our protocol has high key generation rate and analyze the anti-noise ability under atmospheric turbulence. Furthermore, the security of our protocol based on PMUB is rigorously proved. Our protocol paves a brand new way for the application of photon's OAM in high dimensional QKD field, which can be a breakthrough for high efficiency quantum communications.Comment: Comments are welcom

Momentum distribution functions in ensembles: the inequivalence of microcannonical and canonical ensembles in a finite ultracold system

It is demonstrated that in many thermodynamic textbooks the equivalence of the different ensembles is achieved in the thermodynamic limit. In this present work we remark the inequivalence of microcannonical and canonical ensembles in a finite ultracold system at low energies. We calculate the microcanonical momentum distribution function (MDF) in a system of identical fermions (bosons). We find that, the microcanonical MDF deviates from the canonical one, which is the Fermi-Dirac (Bose-Einstein) function, in a finite system at low energies where the single-particle density of states and its inverse are finite.Comment: 6 pages, 3 figure

Identifying the closeness of eigenstates in quantum many-body systems

We propose a new quantity called modulus fidelity to measure the closeness of two quantum pure states. Especially, we use it to investigate the closeness of eigenstates of quantum many-body systems. When the system is integrable, the modulus fidelity of neighbor eigenstates displays a large fluctuation. But the modulus fidelity is close to a constant when system becomes non-integrable with fluctuation reduced drastically. Average modulus fidelity of neighbor eigenstates increases with the increase of parameters that destroy the integrability, which also indicates the integrable-chaos transition. In non-integrable case, it is found two eigenstates are closer to each other if their level spacing is small. We also show that the closeness of eigenstates in non-integrable domain is the underlying mechanism of \emph{eigenstate thermalization hypothesis} (ETH) which explains the thermalization in nonintegrable system we studied.Comment: 7 pages, 4 figure

Nonvanishing spin Hall currents in the presence of magnetic impurities

The intrinsic spin Hall conductivity in a two dimensional electron gas with Rashba spin-orbit coupling is evaluated by taking account of anisotropic coupling between magnetic impurities and itinerant electrons. In our calculation Kubo's linear response formalism is employed and the vertex correction is considered. In the semiclassical limit $\mu \gg 1/\tau$, a non-vanishing spin Hall conductivity $\sigma^{}_{sH}$ is found to depend on the momentum relaxation time $\tau$, spin-orbit splitting $\Delta$ and the anisotropic coefficient of interaction between itinerant electrons and magnetic impurities. The clean limit of $\sigma^{}_{sH}$ is in the region of $e/8\pi \sim e/6\pi$, depending on the anisotropic coefficient.Comment: Revtex, 6 pages, 4 figures, version to appear in PR

Synchronous phase clustering in a network of neurons with spatially decaying excitatory coupling

Synchronization is studied in a spatially-distributed network of weekly-coupled, excitatory neurons of Hodgkin-Huxley type. All neurons are coupled to each other synaptically with a fixed time delay and a coupling strength inversely proportional to the distance between two neurons. We found that a robust, noise-resistant phase clustering state occurred regardless of the initial phase distribution. This has not been shown in previous studies where similar clustering states were found only when the coupling was inhibitory. The spatial distribution of neurons in each synchronous cluster is determined by the spatial distribution of the coupling strength. Phase-interaction properties of the model neurons in the network are used to explain why can such a clustering state be robust

Correlations of spin-polarized and entangled electrons with Berry phase

The correlation and fluctuation of both entangled electrons and spin-polarized pairs affected by two rotating magnetic fields in a setup proposed by J. Carlos Egues etc. (Phys. Rev. Lett. {\bf 89}(2002) 176401) are studied theoretically by using scattering approach. Differing from polarized pair, the entangled electron pairs are shown to behave like a composite particle with the total spins and its $z$ components. The singlet and triplet states exhibit different bunching and antibunching features, which can be easily adjusted by the magnetic fields. The correlations and variances can show up distinguish output signals for the four incident states. Our results are expected to be tested by using coincident technique.Comment: 11 pages, 12 figures, 3 table

Three-body force effect on nucleon momentum distributions in asymmetric nuclear matter within the framework of the extended BHF approach

We have investigated the three-body force (TBF) effect on the neutron and proton momentum distributions in asymmetric nuclear matter within the framework of the extended Brueckner-Hartree-Fock approach by adopting the $AV18$ two-body interaction plus a microscopic TBF. In asymmetric nuclear matter, it is shown that the neutron and proton momentum distributions become different from their common distribution in symmetric nuclear matter. The predicted depletion of the proton hole states increases while the neutron one decreases as a function of isospin-asymmetry. The TBF effect on the neutron and proton momentum distributions turns out to be negligibly weak at low densities around and below the normal nuclear density. The TBF effect is found to become sizable only at high densities well above the saturation density, and inclusion of the TBF leads to an overall enhancement of the depletion of the neutron and proton Fermi seas.Comment: 9 pages, 4 figure

Numerically Fitting The Electron Fermi Energy and The Electron Fraction in A Neutron Star

Based on the basic definition of Fermi energy of degenerate and relativistic electrons, we obtain a special solution to electron Fermi energy, $E_{\rm F}(e)$, and express $E_{\rm F}(e)$ as a function of electron fraction, $Y_{e}$, and matter density, $\rho$. Several useful analytical formulae for $Y_{e}$ and $\rho$ within classical models and the work of Dutra et al. 2014 (Type-2) in relativistic mean field theory are obtained using numerically fitting. When describing the mean-field Lagrangian, density, we adopt the TMA parameter set, which is remarkably consistent with with the updated astrophysical observations of neutron stars. Due to the importance of the density dependence of the symmetry energy, $S$, in nuclear astrophysics, a brief discussion on the symmetry parameters $S_v$ and $L$ (the slope of $S$) is presented. Combining these fit formulae with boundary conditions for different density regions, we can evaluate the value of $E_{\rm F}(e)$ in any given matter density, and obtain a schematic diagram of $E_{\rm F}(e)$ as a continuous function of $\rho$. Compared with previous study on the electron Fermi energy in other models, our methods of calculating $E_{\rm F}(e)$ are more simple and convenient, and can be universally suitable for the relativistic electron regions in the circumstances of common neutron stars. We have deduced a general expression of $E_{\rm F}(e)$ and $n_{e}$, which could be used to indirectly test whether one EoS of a NS is correct in our future studies on neutron star matter properties. Since URCA reactions are expected in the center of a massive star due to high-value electron Fermi energy and electron fraction, this study could be useful in the future studies on the NS thermal evolution.Comment: 30 pages, 14 figure

Robust Room-Temperature Quantum Spin Hall Effect in Methyl-functionalized InBi honeycomb film

Two-dimensional (2D) group-III-V honeycomb films have attracted significant interest for their potential application in fields of quantum computing and nanoeletronics. Searching for 2D III-V films with high structural stability and large-gap are crucial for the realizations of dissipationless transport edge states using quantum spin Hall (QSH) effect. Based on first-principles calculations, we predict that the methyl-functionalized InBi monolayer (InBiCH3) has no dynamic instability, and host a QSH state with a band gap as large as 0.29 eV, exhibiting an interesting electronic behavior viable for room-temperature applications. The topological characteristic is confirmed by s-pxy bands inversion, topological invariant Z2 number, and the time-reversal symmetry protected helical edge states. Noticeably, the QSH states are tunable and robust against the mechanical strain, electric field and different levels of methyl coverages. We also find that InBiCH3 supported on h-BN substrate maintains a nontrivial QSH state, which harbors the edge states lying within the band gap of substrate. These findings demonstrate that the methyl-functionalized III-V films may be a good QSH platform for device design and fabrication in spintronics.Comment: 24 pages, 6 figure