Etching-dependent reproducible memory switching in vertical SiO2 structures

Vertical structures of SiO$_{2}$ sandwiched between a top tungsten electrode and conducting non-metal substrate were fabricated by dry and wet etching methods. Both structures exhibit similar voltage-controlled memory behaviors, in which short voltage pulses (1 $\mu$s) can switch the devices between high- and low-impedance states. Through the comparison of current-voltage characteristics in structures made by different methods, filamentary conduction at the etched oxide edges is most consistent with the results, providing insights into similar behaviors in metal/SiO/metal systems. High ON/OFF ratios of over 10$^{4}$ were demonstrated.Comment: 6 pages, 3 figures + 2 suppl. figure

Approximation for discrete Fourier transform and application in study of three-dimensional interacting electron gas

The discrete Fourier transform is approximated by summing over part of the terms with corresponding weights. The approximation reduces significantly the requirement for computer memory storage and enhances the numerical computation efficiency with several orders without loosing accuracy. As an example, we apply the algorithm to study the three-dimensional interacting electron gas under the renormalized-ring-diagram approximation where the Green's function needs to be self-consistently solved. We present the results for the chemical potential, compressibility, free energy, entropy, and specific heat of the system. The ground-state energy obtained by the present calculation is compared with the existing results of Monte Carlo simulation and random-phase approximation.Comment: 11 pages, 13 figure

Time-reversal-symmetry-broken quantum spin Hall effect

Quantum spin Hall (QSH) state of matter is usually considered to be protected by time-reversal (TR) symmetry. We investigate the fate of the QSH effect in the presence of the Rashba spin-orbit coupling and an exchange field, which break both inversion and TR symmetries. It is found that the QSH state characterized by nonzero spin Chern numbers $C_{\pm}=\pm 1$ persists when the TR symmetry is broken. A topological phase transition from the TR symmetry-broken QSH phase to a quantum anomalous Hall phase occurs at a critical exchange field, where the bulk band gap just closes. It is also shown that the transition from the TR symmetry-broken QSH phase to an ordinary insulator state can not happen without closing the band gap.Comment: 5 pages, 5 figure

Spin entanglement induced by spin-orbit interactions in coupled quantum dots

We theoretically explore the possibility of creating spin quantum entanglement in a system of two electrons confined respectively in two vertically coupled quantum dots in the presence of Rashba type spin-orbit coupling. We find that the system can be described by a generalized Jaynes - Cummings model of two modes bosons interacting with two spins. The lower excitation states of this model are calculated to reveal the underlying physics of the far infrared absorption spectra. The analytic perturbation approach shows that an effective transverse coupling of spins can be obtained by eliminating the orbital degrees of freedom in the large detuning limit. Here, the orbital degrees of freedom of the two electrons, which are described by two modes of bosons, serve as a quantized data bus to exchange the quantum information between two electrons. Then a nontrivial two-qubit logic gate is realized and spin entanglement between the two electrons is created by virtue of spin-orbit coupling.Comment: 7 pages, 5 figure

Dual-mode mechanical resonance of individual ZnO nanobelts

©2003 American Institute of Physics. The electronic version of this article is the complete one and can be found online at: http://link.aip.org/link/?APPLAB/82/4806/1DOI:10.1063/1.1587878The mechanical resonance of a single ZnO nanobelt, induced by an alternative electric field, was studied by in situ transmission electron microscopy. Due to the rectangular cross section of the nanobelt, two fundamental resonance modes have been observed corresponding to two orthogonal transverse vibration directions, showing the versatile applications of nanobelts as nanocantilevers and nanoresonators. The bending modulus of the ZnO nanobelts was measured to be ~52 GPa and the damping time constant of the resonance in a vacuum of 5×10–8 Torr was ~1.2 ms and quality factor Q = 500

The properties of kaonic nuclei in relativistic mean-field theory

The static properties of some possible light and moderate kaonic nuclei, from C to Ti, are studied in the relativistic mean-field theory. The 1s and 1p state binding energies of $K^-$ are in the range of $73\sim 96$ MeV and $22\sim 63$ MeV, respectively. The binding energies of 1p states increase monotonically with the nucleon number A. The upper limit of the widths are about $42\pm 14$ MeV for the 1s states, and about $71\pm 10$ MeV for the 1p states. The lower limit of the widths are about $12\pm 4$ MeV for the 1s states, and $21\pm 3$ MeV for the 1p states. If $V_{0}\leq 30$ MeV, the discrete $K^-$ bound states should be identified in experiment. The shrinkage effect is found in the possible kaonic nuclei. The interior nuclear density increases obviously, the densest center density is about $2.1\rho_{0}$.Comment: 9 pages, 2 tables and 1 figure, widths are considered, changes a lo

Enhanced heat transport by turbulent two-phase Rayleigh-B\'enard convection

We report measurements of turbulent heat-transport in samples of ethane (C$_2$H$_6$) heated from below while the applied temperature difference $\Delta T$ straddled the liquid-vapor co-existance curve $T_\phi(P)$. When the sample top temperature $T_t$ decreased below $T_\phi$, droplet condensation occurred and the latent heat of vaporization $H$ provided an additional heat-transport mechanism.The effective conductivity $\lambda_{eff}$ increased linearly with decreasing $T_t$, and reached a maximum value $\lambda_{eff}^*$ that was an order of magnitude larger than the single-phase $\lambda_{eff}$. As $P$ approached the critical pressure, $\lambda_{eff}^*$ increased dramatically even though $H$ vanished. We attribute this phenomenon to an enhanced droplet-nucleation rate as the critical point is approached.Comment: 4 gages, 6 figure