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The switching behaviour of dihydroazulene/vinylheptafulvene molecule with different anchoring groups sandwiched between two zigzag-edged graphene nanoribbons (ZGNRs) electrodes is investigated by applying nonequilibrium Green's function formalism combined with first-principles density functional theory. The calculated results show that the anchoring groups play a significant role in determining the electronic transport properties and switching behaviour of the molecular junctions. A higher current switching ratio without any oscillation can be obtained for the molecular junctions with carbon atom anchoring group, which suggests that this system has a broader application in future logic and memory devices.

We carry out an extensive study, within the infinite matrix product state algorithm, one-dimensional spin-1 Blume–Capel model on the spin-chain and subject to a changeable external magnetic field. The phase transition points are obtained by investigating the behavior of physical observable and as well as exacting the critical exponent from the scaling relationship. The final results are achieved for the physical observable-quantum entanglement entropy, local order parameter and its scaling: the scaling relationship between quantum entanglement entropy and truncation dimension, the scaling of Schmidt decomposition coefficient λ m a x and truncation dimension, the critical exponent of local order parameter near the phase transition point is extracted with the scaling behavior for the model with exchange coupling γ = 0 . 6 . These techniques are an easy way to exact the critical exponent for quantum phase transitions.

Quantum phase transitions are driven by quantum fluctuations due to the uncertainty principle in many-body physics. In quantum phase transitions, the ground-state changes dramatically. The quantum entanglement, specific heat, magnetization and other physical quantities diverge according to certain functions, and show specific scaling behaviors. In addition, there is a topological quantum phase transition beyond the conventional Landau-Ginzburg-Wilson paradigm, which is relevant to emergent phenomena in strongly correlated electron systems, with topological nonlocal order parameters as a salient feature. Thus, topological order is a new paradigm in the study of topological quantum phase transitions.To investigate competition mechanism of the different quantum spin interactions, in this paper, the one-dimensional spin-1 bond-alternating Heisenberg model with Dzyaloshinskii-Moriya (DM) interaction is considered. The DM interaction drives the quantum fluctuations resulting in a phase transition. By using the one-dimensional infinite matrix product state algorithm in tensor network representation, the quantum entanglement entropy and order parameters are calculated from the ground-state function. The numerical result shows that with the change of bond alternating strength, there is a quantum phase transition from the topological ordered Haldane phase to the local ordered dimer phase. Based on the von Neumann entropy and order parameter, the phase diagram of this model is obtained. There is a critical line that separates the Haldane and the dimer phase. The DM interaction inhibits the dimerization of the quantum spin system and finally breaks the fully dimerization. Due to the fact that the structurally symmetry of system is broken, the local dimer order exists in the whole parameter range when the bond-alternative strength parameter changes. The first derivative of the local dimer order behaves as a peak corresponding to the critical point. Furthermore, from the numerical scaling of the first derivative of dimer order and the non-local string order near the phase transition point, the characteristic critical exponents α and β are obtained, respectively. It shows that the characteristic critical exponent α decreases, and β increases gradually with the interaction strength of DM increasing. The resulting state i.e. the anti-symmetric anisotropic DM interaction produced by spin-orbit coupling, affects the critical properties of the system in the phase transition. This reveals that the competition mechanism of the quantum spin interaction, also provides some guidance for the future study of the critical behavior in topological quantum phase transition with the DM interaction.

We investigated the quantum phase transition occurred in one-dimensional quantum Heisenberg XYZ model with Dzyaloshinskii–Moriya interaction via the infinite matrix product state representation with the infinite time evolving block decimation method. Entanglement entropy and local order parameter in and near the transition point are given. Scaling relation plays crucial roles on identifying a quantum system with a physically different phase. The scaling relation of the entanglement entropy, local order parameter and finite correlation length with the truncation dimension are also obtained. All the interesting results give a theoretical justification for the high accuracy of infinite time evolved block decimation algorithm which works in the thermodynamical limit.

Based on the tensor network representations, we have developed an efficient scheme to calculate the global geometric entanglement as a multipartite entanglement measure for the three-leg spin tubes. From the geometric entanglement, the phase diagram of a spin-3 / 2 isosceles triangle spin tube has been investigated varying the base interaction α. Two Berezinsky-Kosterlitz-Thouless phase transitions are estimated to be α c1 ≃ 0.68 and α c2 ≃ 3.85, respectively. Then, even though the spin tube is in gapless spin liquid phases for α < α c1 and α > α c2, the geometrical structure difference between the groundstate wavefunctions for the two regions is found to reflect the global geometric entanglement that contains bipartite and multipartite contributions. Further, the phase transition points from the von Neumann entropies and fidelity are consistent with that from the geometric entanglement. As a result, the global geometric entanglement can be used to explore a geometrical nature of quantum phases as well as an indicator for quantum phase transitions in many-body lattice systems.

A novel solid catalyst for coupling reaction has been successfully prepared by immobilizing palladium in the nanocages of the ethylenediamine-functionalized mesoporous material SBA-16. The structure and composition of the solid catalyst were characterized by N2 adsorption–desorption, XRD, TEM, FT-IR and TGA. These results revealed that Pd(II) was successfully embedded inside the nanocages of SBA-16. This catalyst afforded high activity (over 91% conversion) for the Suzuki coupling of various aryl bromides and phenyiboronic acids in ethanol solvent at 60 °C even at the loading of 0.5 mol% Pd. Moreover, the SBA-16-2 N-Pd(II) catalyst could be separated easily from reaction mixture and reused for ten times without obvious loss of catalytic activity, showing the superiority over the homogeneous catalysts in industrial applications.

A palladium-based catalyst supported on thiol-modified superparamagnetic nanoparticles was successfully prepared by co-precipitation method. These magnetic nanomaterials were characterized by elemental analysis (EA), inductively coupled plasma (ICP), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fourier transform-infrared (FT-IR), thermogravimetric analysis (TGA) and vibrating sample magnetometry (VSM). The conversions of various aromatic nitro and unsaturated compounds can receive a really high yield with the existence of magnetic nanomaterials. The turn-over frequency (TOF) can be 66.46 h−1 in ethanol under a H2 atmosphere at room temperature. In this paper, the conversions of aromatic nitro bearing a variety of substituents were 93.56–100%, moreover, the catalyst afforded over 90% yield in the reducing unsaturated compounds. Another advantage is that the magnetite nanoparticles modified by thiol group can be separated just through the external magnetic force and can be reused atleast ten times without any significant loss in activity.

Quantum correlation and interference effects are investigated in mesoscopic interferometers connected to a normal metal and a superconductor. For quasiparticle excitation energies smaller than superconducting gap, a Fano-Andreev antiresonance for zero excitation energy is shown to be split into two zero-transmissions located at energies lower and higher than the Fano-Andreev antiresonance energy. For an excitation energy bigger than the gap, the higher energy antiresonance disappears for electron-like quasiparticle transport. In the presence of a superconductor interface potential Z, we find that the transport and the circulating currents normalized by their amplitudes for a clean interface have the same I(Z)-Z curve. We discuss a transition among the three types of normalized currents, which shows a characteristic transition diagram in association with the excitation energy. Also, as a demonstration of the existence of Andreev holes, we show that only the Andreev hole current can circulate along the interferometer loop.

Dimerized phase and quantum entanglement are investigated in the one-dimensional spin-1 bilinear biquadratic model. Employing the infinite matrix product state representation, groundstate wavefunctions are numerically obtained by using the infinite time evolving block decimation method in the infinite lattice system. From a bipartite entanglement measure of the groundstates, i.e., von Neumann entropy, the phase transition points can be clearly extracted. Moreover, the even-bond and odd-bond von Neumann entropies show two different values in the spontaneous dimerized phase. It implies that the quantum entanglement can distinguish the two degenerate groundstates. Then, we define a dimer entropy in the spontaneous dimerized phase. Comparing to the dimer order parameter, the dimer entropy can play a role of a local order parameter to characterize the spontaneous dimerized phase.

Coherent quantum tunneling effects on quantum interference are investigated in electron transport through a mesoscopic interferometer. An evanescent wave tunneling through a potential barrier in one arm can interfere with a propagating wave passing through the other arm of the interferometer. It is shown that, even for the same arm lengths, such a quantum interference can induce a circulating current, where Fano antiresonances do not occur in electron transmission. It is found that there exists a critical value of asymmetric arm lengths that gives rise to a Fano antiresonance in electron transmission for quantum interference between evanescent and propagating waves. We discuss the effects of Fano antiresonances originating from asymmetric arm lengths on circulating currents.

By applying first-principles method based on density functional theory combined with nonequilibrium Green’s function, we investigate the effect of torsion angle on the electronic transport properties in dipyrimidinyl–diphenyl co-oligomer molecular device with tailoring graphene nanoribbon electrodes. The results show that the torsion angle plays an important role on the electronic transport properties of the molecular device. When the torsion angle rotates from 0[Formula: see text] to 90[Formula: see text], the molecular devices exhibit very different current–voltage characteristics which can realize the on and off states of the molecular switch.

Ground-state entanglement entropies were investigated for the one-dimension quantum two- and three-spin interaction models, the four-state Potts model, and the XXZ model with uniaxial single-ion-type anisotropy, which were obtained on an infinite-size lattice in one spatial dimension. Thus we show that the entanglement, a key concept of quantum information science, is quantified by the ground-state entanglement entropy. The relationships between ground-state entanglement entropy and quantum phase transition was analyzed. These results were obtained using the infinite matrix product state algorithm which works in the thermodynamical limit.

The characterization of the quantum phase transition in a lowdimensional system has attracted a considerable amount of attention in quantum manybody systems. As one of the fundamental models in quantum magnetism, spin-1 models have richer phase diagrams and show more complex physical phenomena. In the spin-1 antiferromagnetic XXZ model, the Haldane phase and the Nel phase are the gapped topologic phases which cannot be characterized by the local order parameters. To characterize the nature in such phases, one has to calculate the non-local long range order parameters. Normally, the non-local order parameter in the topological phase is obtained from the extrapolation of finite-sized system in numerical study. However, it is difficult to extract the critical exponents with such an extrapolated non-local order parameter due to the numerical accuracy. In a recently developed tensor network representation, i.e., the infinite matrix product state (iMPS) algorithm, it was shown that the non-local order can be directly calculated from a very large lattice distance in an infinite-sized system rather than an extrapolated order parameter in a finite-sized system. Therefore, it is worthwhile using this convenient technique to study the non-local orders in the topological phases and characterize the quantum criticalities in the topological quantum phase transitions. In this paper, by utilizing the infinite matrix product state algorithm based on the tensor network representation and infinite time evolving block decimation method, the quantum entanglement, fidelity, and critical exponents of the topological phase transition are investigated in the one-dimensional infinite spin-1 bond-alternating XXZ Heisenberg model. It is found that there is always a local dimerization order existing in the whole parameter range when the bond-alternative strength parameter changes from 0 to 1. Also, due to the effect of the bond-alternating, there appears a quantum phase transition from the long-rang ordering topological Nel phase to the local ordering dimerization phase. The von Neumann entropy, fidelity per lattice site, and order parameters all give the same phase transition point at c = 0.638. To identify the type of quantum phase transition, the central charge c 0.5 is extracted from the ground state von Neumann entropy and the finite correlation length, which indicates that the phase transition belongs to the two-dimensional Ising universality class. Furthermore, it is found that the Nel order and the susceptibility of Nel order have power-law relations to |-c|. From the numerical fitting of the Nel order and its susceptibility, we obtain the characteristic critical exponents ' = 0.236 and ' = 0.838. It indicates that such critical exponents from our method characterize the nature of the quantum phase transition. Our critical exponents from the iMPS method can provide guidance for studying the properties of the phase transition in quantum spin systems.

We have developed an efficient tensor network algorithm for spin ladders, which generates ground-state wave functions for infinite-size quantum spin ladders. The algorithm is able to efficiently compute the ground-state fidelity per lattice site, a universal phase transition marker, thus offering a powerful tool to unveil quantum many-body physics underlying spin ladders. To illustrate our scheme, we consider the two-leg and three-leg Heisenberg spin ladders with staggering dimerization, the two-leg Heisenberg spin ladder with cyclic four-spin exchange, and the ferromagnetic frustrated two-leg ladder. The ground-state phase diagrams thus yielded are reliable, compared with the previous studies based on the the exact diagonalization and the density matrix renormalization group. Our results indicate that the ground-state fidelity per lattice site successfully captures quantum criticalities in spin ladders.

An IQ mismatch calibration and compensation technique based on the digital baseband for wideband wireless communication transmitters is proposed. The digital baseband transmits the signal used for IQ mismatch calibration. The signal passes through the RF transmitter path, the calibration loop (which is composed of a square power detector and a band-pass filter in the RF transceiver) and the variable gain amplifier of the receiver. The digital baseband samples the signal for IQ mismatch estimation and compensates for it. Compared with the self-calibration technique in the RF chip, the proposed technique saves area and power consumption for the wireless local area network solution. This technique has been successfully used for the 802.11n system and satisfies the requirement of the standard by achieving over 50 dB image suppression.

A 4×4 64-QAM multiple-input multiple-output (MIMO) detector is presented for the application of an IEEE 802.11n wireless local area network. The detectoris the implementation of a novel adaptive tree search(ATS) algorithm, and multiple ATS cores need to be instantiated to achieve the wideband requirement in the 802.11n standard. Both the ATS algorithm and the architectural considerations are explained. The latency of the detector is 0.75 μs, and the detector has a gate count of 848 k with a total of 19 parallel ATS cores. Each ATS core runs at 67 MHz. Measurement results show that compared with the floating-point ATS algorithm, the fixed-point implementation achieves a loss of 0.9 dB at a BER of 10−3.