Z. D. Wang

Competition between ferromagnetic metallic and paramagnetic insulating phases in manganites

La0.67Ca0.33Mn1−xCuxO3 (x=0 and 0.15) epitaxial thin films were grown on the (100) LaAlO3 substrates, and the temperature dependence of their resistivity was measured in magnetic fields up to 12 T by a four-probe technique. We found that the competition between the ferromagnetic metallic (FM) and paramagnetic insulating (PI) phases plays an important role in the observed colossal magnetoresistance (CMR) effect. Based on a scenario that the doped manganites approximately consist of phase-separated FM and PI regions, a simple phenomenological model was proposed to describe the CMR effect. Using this model, we calculated the resistivity as functions of temperature and magnetic field. The model not only qualitatively accounts for some main features related to the CMR effect, but also quantitatively agrees with the experimental observations.

A generic two-band model for unconventional superconductivity and spin-density-wave order in electron- and hole-doped iron-based superconductors

Based on experimental data on the newly synthesized iron-based superconductors and the relevant band structure calculations, we propose a minimal two-band BCS-type Hamiltonian with the interband Hubbard interaction included. We illustrate that this two-band model is able to capture the essential features of unconventional superconductivity and spin-density-wave (SDW) ordering in this family of materials. It is found that bound electron-hole pairs can be condensed to reveal the SDW ordering for zero and very small doping, while the superconducting ordering emerges at small finite doping, whose pairing symmetry is qualitatively analyzed to be of nodal d-wave. The derived analytical formulas not only give out a nearly symmetric phase diagram for electron and hole doping, but also are likely able to account for existing main experimental results. Moreover, we also derive two important relations for a general two-band model and elaborate how to apply them to determine the band width ratio and the effective interband coupling strength from experimental data.

A Low‐Operating‐Power and Flexible Active‐Matrix Organic‐Transistor Temperature‐Sensor Array

An organic flexible temperature-sensor array exhibits great potential in health monitoring and other biomedical applications. The actively addressed 16 × 16 temperature sensor array reaches 100% yield rate and provides 2D temperature information of the objects placed in contact, even if the object has an irregular shape. The current device allows defect predictions of electronic devices, remote sensing of harsh environments, and e-skin applications.

High performance organic transistor active-matrix driver developed on paper substrate

The fabrication of electronic circuits on unconventional substrates largely broadens their application areas. For example, green electronics achieved through utilization of biodegradable or recyclable substrates, can mitigate the solid waste problems that arise at the end of their lifespan. Here, we combine screen-printing, high precision laser drilling and thermal evaporation, to fabricate organic field effect transistor (OFET) active-matrix (AM) arrays onto standard printer paper. The devices show a mobility and on/off ratio as high as 0.56 cm2V−1s−1 and 109 respectively. Small electrode overlap gives rise to a cut-off frequency of 39 kHz, which supports that our AM array is suitable for novel practical applications. We demonstrate an 8 × 8 AM light emitting diode (LED) driver with programmable scanning and information display functions. The AM array structure has excellent potential for scaling up.

Jahn-Teller effect and stability of the charge-ordered state in La1-xCaxMnO3 (0.5 ≤ x ≤ 0.9) manganites

The longitudinal ultrasonic sound velocity and attenuation, the resistivity, and lattice parameters were studied as a function of temperature from 30 K to 300 K in La 1 − x Ca x MnO3 (0.5 ≤ x ≤ 0.9). For all the samples, a dramatic stiffening of the sound velocity below the charge ordering transition temperature TCO was directly driven by distinct changes of the lattice parameters due to the formation of long-range ordering of Jahn-Teller–distorted MnO 6 octahedra. The relative change of the sound velocity (ΔV/V) below TCO depends on the Ca concentration x and reaches the maximum at x = 0.75, implying that the effective strength of the electron-lattice interaction with the Jahn-Teller distortion is the strongest at x = 0.75 and hence the charge-ordered state is mostly stabilized near x = 0.75 and insensitive to the application of a magnetic field, which is supported by the charge transport properties under high magnetic fields up to 14 T.

Simple unconventional geometric scenario of one-way quantum computation with superconducting qubits inside a cavity

We propose a simple unconventional geometric scenario to achieve a kind of nontrivial multiqubit operation with superconducting charge qubits placed in a microwave cavity. The proposed quantum operations are insensitive not only to the thermal state of the cavity mode but also to certain random operation errors, and thus may lead to high-fidelity quantum-information processing. By executing the designated quantum operations, a class of highly entangled cluster states may be generated efficiently in the present scalable solid-state system, enabling one to achieve one-way quantum computation.

Ag nanoparticle dispersed PbTiO3 percolative composite thin film with high permittivity

Ag nanoparticle dispersed PbTiO3 percolative composite thin films were prepared in situ by sol-gel method using Pb(NO3)2, Ti(C4H9O)4, and AgNO3 as raw materials and lactic acid along with citric acid as complexing agent. The size of the Ag nanoparticles measured by ultraviolet-visible spectra is about 3nm. The percolation effect occurs in composite thin films. The composite exhibits relatively high dielectric constant which is about five times higher than that of PbTiO3 thin film and comparatively low dielectric loss comparable to pure PbTiO3 system. It is highly attractive in application of high quality dielectric devices and miniaturization.

General monogamy relation for the entanglement of formation in multiqubit systems.

We prove exactly that the squared entanglement of formation, which quantifies the bipartite entanglement, obeys a general monogamy inequality in an arbitrary multiqubit mixed state. Based on this kind of exotic monogamy relation, we are able to construct two sets of useful entanglement indicators: the first one can detect all genuine multiqubit entangled states even in the case of the two-qubit concurrence and n-tangles being zero, while the second one can be calculated via quantum discord and applied to multipartite entanglement dynamics. Moreover, we give a computable and nontrivial lower bound for multiqubit entanglement of formation.

Exploring multipartite quantum correlations with the square of quantum discord

We explore the quantum correlation distribution in multipartite quantum states based on the square of quantum discord (SQD). For tripartite quantum systems, we derive the necessary and sufficient condition for the SQD to satisfy the monogamy relation. Particularly, we prove that the SQD is monogamous for three-qubit pure states, based on which a genuine tripartite quantum correlation measure is introduced. In addition, we also address the quantum correlation distributions in four-qubit pure states. As an example, we investigate multipartite quantum correlations in the dynamical evolution of multipartite cavity-reservoir systems.

High Sensitivity, Wearable, Piezoresistive Pressure Sensors Based on Irregular Microhump Structures and Its Applications in Body Motion Sensing.

UNLABELLED A pressure sensor based on irregular microhump patterns has been proposed and developed. The devices show high sensitivity and broad operating pressure regime while comparing with regular micropattern devices. Finite element analysis (FEA) is utilized to confirm the sensing mechanism and predict the performance of the pressure sensor based on the microhump structures. Silicon carbide sandpaper is employed as the mold to develop polydimethylsiloxane (PDMS) microhump patterns with various sizes. The active layer of the piezoresistive pressure sensor is developed by spin coating PEDOT PSS on top of the patterned PDMS. The devices show an averaged sensitivity as high as 851 kPa(-1) , broad operating pressure range (20 kPa), low operating power (100 nW), and fast response speed (6.7 kHz). Owing to their flexible properties, the devices are applied to human body motion sensing and radial artery pulse. These flexible high sensitivity devices show great potential in the next generation of smart sensors for robotics, real-time health monitoring, and biomedical applications.