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Recently, photothermal therapy (PTT) in the second near-infrared (NIR-II) biowindow has emerged as a promising treatment modality; however, its therapeutic outcomes are still limited by heterogeneous heat distribution and insufficient control of metastatic lesions. Tremendous efforts have been made to overcome the PTT's shortcomings by combining PTT with immunotherapy, but unfortunately current strategies still suffer from low response rates, primary/acquired resistance or severe immune-related adverse events. Herein, a novel photothermal agent and gene co-delivery nanoparticle (CSP), with CuS inside the SiO2 pore channels and PDMAEMA polycation on the outside of SiO2 surface, is explored for tumor localized NIR-II PTT and in situ immunotherapy through local generation of IL-12 cytokine. The resulting CSP integrated with the plasmid encoding IL-12 gene (CSP@IL-12) exhibited good gene transfection efficiency, outstanding NIR-II PTT effect and excellent therapeutic outcomes both in vitro and in vivo. Meanwhile, such an in situ joint therapy modality could significantly induce systemic immune responses including promoting DC maturation, CD8+ T cell proliferation and infiltration to efficiently eliminate possible metastatic lesions through abscopal effects. Hence, this creative combinational strategy of NIR-II PTT and IL-12 cytokine therapy might provide a more efficient, controllable and safer alternative strategy for future photo-immunotherapy.

The development of nanotheranostic agents integrating diagnosis and therapy has gained tremendous attention in the past few decades, but many of them are inherently hydrophobic and need complicated phase-transfer and tedious surface modifications. This work proposed a facile method of transferring hydrophobic Fe3O4@Cu2-xS nanoparticles from oil to water by using red blood cell membrane to create theranostic nanobeads for T2-weighted MRI and second near-infrared photothermal ablation. The obtained nanoplatform, namely SCS@RBCM, showed a core-shell structure with the inner core densely packed with Fe3O4@Cu2-xS nanoclusters and the surface coated with a layer of RBCM. SCS@RBCM displayed a stable nanostructure, high NIR II light absorption and photothermal conversion ability, T2-weighted MR imaging and magnetic field targeting ability. Meanwhile, the RBCM cloaking endowed SCS with reduced elimination by macrophages. With the navigation of an external magnetic field (MF), the tumor accumulation of SCS@RBCM was dramatically increased, thus achieving good performance of MR imaging and antitumor efficacy through the PTT effect under NIR II irradiation. Therefore, our strategy presents a new and desirable paradigm in the phase-transfer of hydrophobic nanotheranostics for optimizing their biomedical performance.

Swift electrons can undergo inelastic interactions not only with electrons but also with near-fields, which may result in an energy loss or gain. Developments in photon-induced near-field electron microscopy (PINEM) enable direct imaging of the plasmon near-field distribution with nanometer resolution. Here, we report an analysis of the surface plasmonic near-field structure based on PINEM observations of silver nanowires. Single-photon order-selected electron images revealed the wavelike and banded structure of electric equipotential regions for a confined near-field integral associated with typical absorption of photon quanta (nℏω). Multimodal plasmon oscillations and second-harmonic generation were simultaneously observed, and the polarization dependence of plasmon wavelength and symmetry properties were analyzed. Based on advanced imaging techniques, our work has implications for future studies of the localized-field structures at interfaces and visualization of novel phenomena in nanostructures, nanosensors, and plasmonic devices.

Fabricating multifunctional theranostic nanoparticles is highly pursued but still challenging for effective cancer treatment. Herein is reported a new theranostic nanoagent as both an MRI and targeted chemo/photothermal therapeutic agent. Prussian blue nanoparticles (PB) were first decorated with polydopamine (PDA), then conjugated with polyethylene glycol (PEG) and folic acid (FA), and finally loaded with doxorubicin (DOX) (denoted as PB@PDA@PEG-FA-DOX). The nanoagent was estimated to have an average size of 40 nm with a DOX-loading capacity of 36%, photothermal conversion efficiency of 45.7% and a transverse relaxation rate of 0.366 mM−1 s−1. In vitro release investigations showed a dual-responsive release by a mild acid and near-infrared (NIR) laser irradiation. PB@PDA@PEG-FA illustrated negligible cytotoxicity against the HL-7702 cell line and 38.2% cell viability under NIR against the HeLa cell line. PB@PDA@PEG-FA-DOX exhibited 45.2% cell viability. In contrast, the cell viability of PB@PDA@PEG-FA-DOX was dramatically decreased to 18.4% under NIR. Exclusive of folic acid, PB@PDA@PEG-DOX demonstrated 40.5% cell viability. These results demonstrated the potential of the nanoagent for integrated photothermal therapy (PTT) and chemotherapy, also embracing the FA targeting effect. In vivo MRI confirmed the effective nanoparticle accumulation, while infrared thermal images revealed the dramatically increased temperature under NIR at a tumor site. In vivo combination treatment-induced tumors were nearly completely destroyed without significant body weight loss after 14 days. H&E and Ki67 staining indicated remarkable necrosis and weak cell proliferation in the tumor area. Histologic examination revealed a lower toxicity in the vital organs. Therefore, this combination of chemo/photothermal therapy could provide an efficient route for cancer treatment.

Understanding the photoinduced ultrafast structural transitions and electronic dynamics in single-walled carbon nanotubes (SWCNTs) is important for the development of SWCNT-based optoelectronic devices. In this study, we conducted femtosecond-resolved electron diffraction and electron energy-loss spectroscopy (EELS) measurements on SWCNTs using ultrafast transmission electron microscopy. The experimental results demonstrated that dominant time constants of the dynamic processes were ∼1.4 ps for electron-driven lattice expansion, ∼17.4 ps for thermal phonon-driven lattice expansion associated with electron–phonon coupling. The time-resolved EELS measurements clearly revealed a notable red shift of plasmon peaks by ∼100 meV upon femtosecond laser excitation. Different features of charge carrier excitation and relaxation were carefully discussed in correlation with the lattice dynamics and photoinduced absorption signals of SWCNTs. Our results provide a comprehensive understanding of the ultrafast dynamics in SWCNTs and powerful techniques to characterize the dynamics of low-dimensional structures.

Structural dynamics and changes in electronic structures driven by photoexcited carriers are critical issues in both semiconducting and optoelectronic nanodevices. Herein, a phase diagram for the transient states and relevant dynamic processes in multiwalled boron nitride nanotubes (BNNTs) has been extensively studied for a full reversible cycle after a fs-laser excitation in ultrafast TEMs, and the significant structural features and evolution of electronic natures have been investigated using pulsed electron diffraction and femtosecond-resolved electron energy-loss spectroscopy (EELS). It is revealed that nonthermal anisotropic alterations of the lattice apparently precede the phonon-driven thermal transients along the radial and axial directions. Ab initio calculations support these findings and show that electrons excited from the π to π* orbitals in the BN nanotubes weaken the intralayer bonds while strengthening the interlayer bonds along the radial direction. Importantly, time-resolved EELS measurements show contraction of the energy bandgap after fs-laser excitation associated with nonthermal structural transients. This fact verifies that laser-induced bandgap renormalization in semiconductors can essentially be correlated with both the rapid processes of excited carriers and nonthermal lattice evolution.

A simple approach for constructing theranostic nanobeads is developed by using doxorubicin as a phase transfer agent to solubilize small iron oxide nanoclusters. The nanobeads can be specifically internalized into cancer cells with the guidance of an external magnetic field, resulting in good MRI and chemotherapy.

A new design scheme for ultrafast transmission electron microscopy (UTEM) has been developed based on a Schottky-type field emission gun (FEG) at the Institute of Physics, Chinese Academy of Sciences (IOP CAS). In this UTEM setup, electron pulse emission is achieved by integrating a laser port between the electron gun and the column and the resulting microscope can operate in either continuous or pulsed mode. In pulsed mode, the optimized electron beam properties are an energy width of ~0.65 eV, micrometer-scale coherence lengths and sub-picosecond pulse durations. The potential applications of this UTEM, which include electron diffraction, high-resolution imaging, electron energy loss spectroscopy, and photon-induced near-field electron microscopy, are demonstrated using ultrafast electron pulses. Furthermore, we use a nanosecond laser (~10 ns) to show that the laser-driven FEG can support high-quality TEM imaging and electron holography when using a stroboscopic configuration. Our results also indicate that FEG-based ultrafast electron sources may enable high-performance analytical UTEM.

Summary Immunotherapy has achieved notable success in tumor treatment, but it is restricted to a small number of patients due to multiple immunosuppressive pathways in the tumor microenvironment. Here, we present a step-by-step protocol to prepare functional cellular nanovesicles from HEK293-FT cells displaying PD1 and TRAIL. TRAIL specifically induces immunogenic cancer cell death to initiate an immune response, and ectogenic PD1 blocks the PD1/PDL1 checkpoint signal to reactivate anergic tumor-specific CD8+ T cells. For complete details on the use and execution of this protocol, please refer to Wu et al. (2020)., Graphical Abstract, Highlights • Established stable HEK293 FT cells expressing PD1 and TRAIL • Prepare functional cellular nanovesicles (FCNVs) from stable HEK293 FT cells • FCNVs can boost antitumor response by the cooperative roles of PD1 and TRAIL, Immunotherapy has achieved notable success in tumor treatment, but it is restricted to a small number of patients due to multiple immunosuppressive pathways in the tumor microenvironment. Here, we present a step-by-step protocol to prepare functional cellular nanovesicles from HEK293-FT cells displaying PD1 and TRAIL. TRAIL specifically induces immunogenic cancer cell death to initiate an immune response, and ectogenic PD1 blocks the PD1/PDL1 checkpoint signal to reactivate anergic tumor-specific CD8+ T cells.

In this work, structural investigation and physical measurements of layered transition-metal dichalcogenides (TMDs) 1 T -MX2materials revealed a series of remarkable phenomena in correlation with structural transitions. Our results show that notable structural transformations, such as charge density wave (CDW) transitions, atomic ordering, and micro-twinning could be introduced via chemical substitution in 1 T -MX2. It was demonstrated that substitution of S by Se in 1 T -TaS2- x Se x resulted in clear changes in the incommensurability of the CDW state; substitution of Se by Te could destruct the CDW state and yield atomic ordering with visible trimerization of the metallic ions. Furthermore, these structural changes yielded a monoclinic stacking along the c -axis direction. Additionally, on substitution of the metal atoms in 1 -MX2, e.g. , 1 -NbTe2, structural distortion in the a – b plane could clearly be observed, and high-density twinning lamella often appeared in the crystals because of enhanced intralayer structural deformation. These phase transitions and their relevant structural features could primarily be corelated with alteration of the superconductivity and other physical properties. FullText for HTML: https://doi.org/10.1209/0295-5075/130/47001

Theranostic nanoprobes integrated with dual-modal imaging and therapeutic functions, such as photodynamic therapy (PDT), have exhibited significant potency in cancer treatments due to their high imaging accuracy and non-invasive advantages for cancer elimination. However, biocompatibility and highly efficient accumulation of these nanoprobes in tumor are still unsatisfactory for clinical application. In this study, a photosensitizer -loaded magnetic nanobead with surface further coated with a layer of cancer cell membrane (SSAP-Ce6@CCM) was designed to improve the biocompatibility and cellular uptake and ultimately achieve enhanced MR/NIR fluorescence imaging and PDT efficacy. Compared with similar nanobeads without CCM coating, SSAP-Ce6@CCM showed significantly enhanced cellular uptake, as evidenced by Prussian blue staining, confocal laser scanning microscopy (CLSM) and flow cytometric analysis. Consequently, SSAP-Ce6@CCM displayed a more distinct MR/NIR imaging ability and more obvious photo-cytotoxicity towards cancer cells under 670 nm laser irradiation. Furthermore, the enhanced PDT effect benefited from the surface coating of cancer cell membrane was demonstrated in SMMC-7721 tumor-bearing mice through tumor growth observation and tumor tissue pathological examination. Therefore, this CCM-disguised nanobead that integrated the abilities of MR/NIR fluorescence dual-modal imaging and photodynamic therapy might be a promising theranostic platform for tumor treatment.

The structural features and the electron energy loss spectrum of black phosphorus (BP) have been experimentally analyzed and they are discussed based on a theoretical calculation. The low-energy loss spectra of typical samples reveal that the emerging high-mobility two-dimensional material BP often exhibits both bulk and surface plasmon modes. The surface modes of BP are strongly thickness dependent. Electrodynamic analysis indicates that the Fuchs–Kliewer-like surface plasmon modes consist of two branches with different charge symmetry: the upper side and lower side have the same charge polarity as the lower branch and the opposite charge polarity to the upper branch. This study provides fundamental insight into the characteristic nature of BP plasmonics.

Tumor microenvironment activated nanodevices have remarkable superiority to enhance therapeutic efficacy and minimize side effects, but their practical applications are dramatically reduced by the low abundance and heterogeneous distribution of specific stimuli at the tumor site. Herein, programmable vesicular nanodevices based on the triblock copolymer containing poly(ethylene glycol) (PEG) and poly(caprolactone) (PCL) with peroxalate esters (PO) as hydrogen peroxide-responsive linkage (PEG-PO-PCL-PO-PEG), are developed for co-delivery of hypoxia-activated prodrug (AQ4N) and glucose oxidase (GOD). The obtained nanodevices (PAG) can be activated by the high level of H2 O2 in tumor microenvironment to improve the permeability of membranes for glucose entrance. Afterward, the oxidation of glucose catalyzed by GOD produces amplified H2 O2 amounts which in turn induce complete destruction of PAG for fast release of AQ4N and GOD. Ultimately, the PAG can exert programmable therapeutic effects from the following aspects: 1) starvation therapy by cutting off the energy supply from glucose through GOD catalysis; 2) oxidative cytotoxicity after H2 O2 amplification; 3) chemotherapy of AQ4N activated by the intensified tumor hypoxia microenvironment after oxygen consumption. The stimuli amplification, controlled drug release, synergistic therapy, and corresponding mechanisms of PAG are demonstrated. Therefore, the presented work could provide significant new insights for cancer treatment.

In situ heating transmission electron microscopy observations clearly reveal remarkable interlayer expansion and inner-layer inward contraction in multi-walled boron nitride nanotubes (BNNTs) as the specimen temperature increases. We interpreted the observed inward contraction as being due to the presence of the strong constraints of the outer layers on radial expansion in the tubular structure upon in situ heating. The increase in specimen temperature upon heating can create pressure and stress toward the tubular center, which drive the lattice motion and yield inner diameter contraction for the multi-walled BNNTs. Using a simple model involving a wave-like pattern of layer-wise distortion, we discuss these peculiar structural alterations and the anisotropic thermal expansion properties of the tubular structures. Moreover, our in situ atomic images also reveal Russian-doll-type BN nanotubes, which show anisotropic thermal expansion behaviors.

The resistance of polycrystalline divalent-ion-doped LaMnO 3 has been shown to be highly sensitive to low magnetic fields. To enable direct study of the properties of isolated grain boundaries, we developed a new method to form artificial boundaries in manganite thin films. Metal slits about 70 nm in width were printed by 30 KV focused Ga ion beam nanolithography on a 4 μ m La 2 / 3 Sr 1 / 3 MnO 3 bridge, and the materials in these slits were then irradiated by accelerated H 2 + ions. Using this method, magnetoresistance (MR) > 8 % and > 16 % were, respectively, obtained at 150 and at 10 K in a magnetic field of 1 T. This technique is very promising in terms of its simplicity and flexibility of fabrication and has the potential for high-density integration.

Pb0.35Sr0.65TiO3 (PST) thin films have been fabricated on LaAlO3 (LAO) and MgO substrates using the pulsed laser deposition technique. The microstructure characteristics of the films were examined by means of X-ray diffraction, atomic force microscopy, scanning electron microscopy and Raman spectroscopy, and the results indicate that the films are epitaxially grown and show good crystallinity. The dielectric constant dependence on DC bias voltage and temperature were measured in a planar capacitor configuration for these films. Compared to the PST thin film grown on LAO, the film grown on MgO showed a higher temperature of the capacitance maximum and a higher dielectric constant at zero bias. We explain the results by taking into account the lattice-mismatch strain between the substrate and the film. In contrast to the in-plane compressive strain induced by the LAO substrate, the in-plane tensile strain induced by the MgO substrate enlarges the unit cell of PST and enhances the magnitude of dipole moments, which increases the dielectric constant. These results indicate that a reasonable in-plane tensile strain could improve the dielectric properties of PST thin films. (c) 2006 Elsevier B.V All rights reserved.

Epitaxial bilayered thin films of BaxSr1−xTiO3 (BSTO, x = 0.1 and 0.5)/YBa2Cu3O7−δ (YBCO), with different YBCO film thicknesses, have been grown in situ by pulsed-laser deposition on 1.2° vicinal LaAlO3 substrates. The critical thickness for the transformation of the growth mode in YBCO between two-dimensional (2D) step flow and three-dimensional island is experimentally confirmed to be around 180 nm. As the YBCO-film thickness increases from 145 to 250 nm, the tremendous degradation of the film quality, due to the growth-mode change in YBCO, leads to drastic deterioration in the dielectric properties of BSTO thin films, with severe decrease in the figure of merit factor from 148 to 10 in Ba0.1Sr0.9TiO3/YBCO (at 77 K and 100 kHz) and from 56 to 6 in Ba0.5Sr0.5TiO3/YBCO (at 300 K and 100 kHz). As a result, the dielectric properties of BSTO thin films could be significantly enhanced by strictly tailoring the growth mode in YBCO as a 2D step flow for this kind of BSTO/YBCO bilayers.

We have fabricated and tested a high- T c dc-SQUID magnetometer patterned on a YBCO thin film deposited on a SrTiO 3 bicrystal substrate. The measurement of noise spectrum at 77 K showed that the magnetometer has a white noise of 333 fT/Hz 1/2 without superconducting shield, corresponding to a flux sensitivity of 14.5 μΦ 0 /Hz 1/2 . We constructed a test system for eddy current non-destructive evaluation of conducting aluminum plates by using the magnetometer. Flaws over 10 mm below the surface can be clearly identified. By mapping the magnetic field distribution, we can locate the flaw position. The signals caused by flaw were expanded due to the use of double-D type driving coil with a wider central slit. The experimental results confirmed that this test system could operate in a magnetic unshielded environment.

We have proposed a novel type of high-T-c superconducting quantum interference device (SQUID) planar gradiometer that could measure the mixed partial derivative of magnetic fields partial derivative(2) B-z/partial derivativexpartial derivativey. The device consists of two parts, one is the signal pickup antenna formed by four square pickup loops, and another one is a SQUID directly coupled to the common line which separates the antenna loops. The four pickup loops were arranged to a two-dimensional array. The loops in the diagonal direction are connected in series. The total current in the common line in this configuration is directly proportional to the mixed partial derivative of the magnetic field. We have made a device of such design on a STO bicrystal substrate and tested the device in gradient field. (C) 2004 Elsevier B.V. All rights reserved.

High quality superconducting YBa2Cu3O7-delta (YBCO) thin films have been successfully deposited on silicon-on-insulator (SOI) substrates buffered by an yttria-stabilized zirconia (YSZ) layer using the in situ pulsed laser deposition (PLD) method. X-ray diffraction (XRD) theta-2theta-scan and phi-scan, and reflection high energy electron diffraction (RHEED), indicate that both the YSZ and YBCO thin films are of high crystallinity and good lattice orientation. Atomic force microscopy (AFM) shows that the root mean square roughness R-q of YSZ thin films is less than 0.9 nm in an area of I mum x I mum, and that of YBCO thin films is about 3 nm in an area of 2 /tm x 2 mum. The zero-resistance temperature T-C0 of the YBCO/YSZ/SOI multilayers is up to 88 K, measured by a four-probe method. However, scanning electron microscopy (SEM) demonstrates many clear cracks in YBCO thin films due to the lattice constant and thermal expansion coefficient mismatch between SOI and YBCO. The crack width changes with the thickness of YBCO thin films.

Double-sided Tl2Ba2CaCu2O8 (Tl-2212) thin films have been prepared on lanthanum aluminate (LaAlO3) substrates by a two-step method in which Tl-free amorphous Ba2CaCu2Ox., precursor films were first deposited on the substrates by pulsed laser deposition (PLD) and the subsequent thalliation, crystallization and oriented growth of the superconducting Tl-2212 films were obtained in a long-duration annealing process in argon atmosphere at temperature around 730-750degreesC. The films were characterized by means of x-ray diffraction (XRD), electron simulated x-ray microanalysis in the energy dispersive mode (EDX), scanning electron microscopy (SEM) and transport measurements. The results show that the as-prepared films are predominately single phase, except for the presence of some submicron particles on the film surface. The films show epitaxial growth with c-axis perpendicular to the substrate surface, as confirmed by XRD. The full width at half maximum (FWHM) of the (0012) peak determined from the rocking curves is 0.92degrees and 1.21degrees for the two sides of a double-sided Tl-2212 film, respectively. The zero-resistance transition temperature (T-C0) is 108.8 K for one side and 106.7 K for the other side of the film. The critical current density (J(C)) is in excess of 106 A cm(-2) for both sides of the films.

Electrical and magnetic transitions in Pr1−x Srx MnO3 and Pr1−x Srx Mn0.95Fe0.05O3 ceramic samples with x = 1/4, 3/8, and 1/ 2h ave been investigated. It is proved that 5% Fe doping in the system suppresses electrical conduction and ferromagnetism severely, but favours antiferromagnetism. The existence of spin clusters at temperatures above the ferromagnetic transition TC is demonstrated in the Fe-dopedx = 1/ 2s ample, which is caused by the Fe-doping-induced magnetic inhomogeneity. The transport behaviour above TC in this sample is governed by variable-range hopping of the magnetic polarons. For the Fe-doped x = 1/ 4s ampl e, the insulator-to-metal (I–M) transition drops behind TC by nearly 80 K; accordingly, two magnetoresistance peaks appear. One is around TC ,a nd the other lies just at the I–M transition temperature. The possible underlying mechanism is discussed qualitatively. (Some figures in this article are in colour only in the electronic version)

We have carried out structure, magnetic and specific heat measurements on aluminum doped magnetism diboride samples Mg 1− x Al x B 2 in order to investigate possible superconductivity at the x =0.5 concentration. A diamagnetic signal was observed in magnetization measurements accompanied by a decrease in resistivity. However, the diamagnetic signal was extremely small as compared to what expected from full diamagnetism. Also, the transition both in magnetization and resistance was very broad. We propose that the diamagnetism is due to a very small amount of superconducting phase such as MgB 2 and the resistive transition is due to the percolation behavior. Furthermore, we performed specific heat measurements, which are considered as a tool to investigate the bulk nature of superconducting transition, on the x =0.5 sample to verify the existence of superconductivity. We observed no evident superconducting transition in the entire temperature region from 2 to 300 K. The undistinguishable data between 0 and 5 T magnetic fields also indicated the absence of bulk superconductivity in the x =0.5 sample.

An epitaxial La0.67Sr0.33MnO3 thin film covered with a monolayer of colloidal spheres was ion-milled so that structural discontinuities were involved. Nonlinear V-I characteristics have been observed, revealing that the zero-field resistance of the sample decreases with increasing measuring current I. In a magnetic field, however, the resistance varies non-monotonically with I. An inflexion appears around I = 50 nA. Accordingly, the magnetoresistance also correlates with I. A maximum value as high as − 700% (ΔR/RH) is recorded at liquid nitrogen in 1.5 T when I = 1 nA. The drastic current dependence of the magnetoresistance is believed to come from the ion-milling–induced structural and magnetic disorders and to be related to the inelastic scattering of the spin-polarized electrons at the disorders. The possible underlying mechanisms are discussed in detail.

The effects of Eu substituting for Ba on structural and superconducting properties were investigated for a series of superconductors Eu 1+ x Ba 2− x Cu 3 O 7− δ ( x =0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, and 0.2). With Eu content increasing, the random substitution of excessive Eu for Ba ion forms a Eu–Ba non-stoichiometric distribution on Ba site, which deviates from the ideal 123 phase stoichiometry. The analysis of crystallographic structure shows that the solid solubility x of Eu on Ba site is over 0.2. Eu 1+ x Ba 2− x Cu 3 O 7− δ take on an orthorhombic–tetragonal (O–T) phase transition from x =0.06, and end in x =0.18. Corresponding to the O–T phase transition, superconducting critical temperature T c rapidly decreases with Eu content increasing, which is attributed to the decline of carrier density and the proximity effects of non-superconducting clusters. The positron annihilation measurements show anomalous changes for lifetime spectra and Doppler-broadened radiation spectra when the O–T phase transition occurs. By the model of excessive oxygen defects in Cu–O chain regions, we discuss effects of Eu–Ba non-stoichiometric distribution on structural and superconducting properties.

The existence of the irreversibility line is one of the most intrigue features of high temperature superconductors. The irreversibility line is resulted from the short coherence length, large anisotropy and high working temperature of high-T. oxides. For low temperature superconductors, however, there has been experimental evidence of the existence of the irreversibility line even though it is previously thought that the irreversibility line is too close to the upper critical field line to be observed. In this work, systematic measurements of dc magnetization, ac susceptibility and magnetoresistivity as a function of applied field and temperature have been performed on Nb alloy samples in order to investigate the irreversibility line in low temperature superconductors. The results show that there exits an observable region below the mean-field critical field, H-c2, where the magnetization is reversible during a cycle of increasing and decreasing field. Furthermore, results obtained on other low temperature superconductors such as the Chevrel phase superconductor PbMo6S8, Ba0.25Pb0.75BiO3, the newly discovered intermetallic compound MgB2 and overdoped cuprate Tl2Ba2CuO6+delta (T-c similar to 20 K) are also discussed. (C) 2002 Elsevier Science B.V. All rights reserved.

In this research, c-axis oriented epitaxial anatase TiO 2 thin films were grown on SrTiO 3 (100) substrates using a ceramic Ti 0.95 Co 0.05 O 2 target by Pulsed Laser Deposition (PLD). The film growth processes were monitored by reflective high energy electronic diffraction (RHEED). Microstructure, conductivity, and magnetism of these doped films are found strongly affected by the oxygen pressure and substrate temperature Ts. Grown at a Ts around 750 ° C in an oxygen pressure of 0.2 mbar, the dopants are found existing as oxide inclusions. The doped film thus behaves as an insulator and shows diamagnetism in a magnetic field parallel to the film surface. However, in the doped film grown at a reduced temperature of 630 ° C in a vacuum, no impurity phase can be identified. The film shows a saturated magnetic moment of 0.16μ B / Co and a fairly good conductivity at room temperature. It is then concluded that nonequilibrium growth at lower temperatures in vacuum is essential for a high solubility of Co in the TiO 2 lattice and thus the ferromagnetism.

We have investigated the structural and superconducting properties of a series of Al doped MgB2 samples. The results show that the superconductivity of MgB2 is destroyed when Al is alloyed into MgB2 as reported previously. A structural instability was observed from the data of X-ray diffraction. Further study by TEM shows that the Al substitution leads to an ordering occupation on Mg sites. This corresponds to a superstructure with a repeat period of 2c along the c-axis. The superstructure was identified to be a form of MgAlB4 structure which intergrows with MgB2. Measurements on the low doping level samples showed that the upper critical field B-c2, irreversible field B-irr and the critical current density J(c) of these samples were reduced as the All content was increased. Analysis of the upper critical field data suggests that the density of states near the Fermi surface N(E-F) is reduced by Al doping. This is consistent with the decrease in the superconducting transition temperature T-c. The field dependence of pinning force is also discussed for these samples. (C) 2002 Elsevier Science B.V. All rights reserved.

( Y 0.74 Ca 0.26 ) Ba 2 Cu 3 O 7 − δ (YCBCO) and ( Y 0.84 La 0.16 ) ( Ba 1.74 La 0.26 ) Cu 3 O 7 − δ (YLBLCO) thin films were epitaxially grown on (1 0 0) SrTiO3 substrates by laser ablation. Both of them show onset temperatures of superconductivity above 83 K. By using the same deposition condition, YCBCO/YLBLCO multilayers were deposited. These films are highly c-axis oriented. Several modulation wavelengthes of the sublayers were selected for preparing the multilayers. The resistivities of these single YCBCO and YLBLCO thin films, and YCBCO/YLBLCO multilayers were studied and compared. The resistive characteristics suggest that the charge redistribution may only happen around the interfaces within a quite limited range (possibly, around one unit-cell along the c-axis), and have no evidence of increasing the superconcuting transition temperature.

The irreversibility line of superconductors is most usually established from magnetization curves. However, many low-${T}_{c}$ materials show extremely reversible magnetization curves, while still having a finite critical current. Confirmation of a reversibility line requires other measurements. We have made measurements of dc magnetization, ac susceptibility, and magnetoresistivity as a function of applied field and temperature on Nb alloy samples in order to investigate the irreversibility line in low-${T}_{c}$ superconductors. The results show that there exists an observable field region below the mean-field critical field ${B}_{c2},$ where the magnetization is reversible during a cycle of increasing and decreasing field, which is in agreement with a previous report by Suenaga et al. In addition to dc magnetization, ac susceptibility and magnetoresistivity measurements were also carried out on the same sample as alternative techniques to probe the irreversibility line to determine the best way of distinguishing a genuine thermally activated reversibility from a finite, but low, critical current density. The results showed that the collapse of the dc magnetic hysteresis, the onset of the diamagnetic ac susceptibility (or the peak of the ac loss) and the zero resistance occur at nearly the same field, namely, the irreversibility field ${B}_{\mathrm{irr}}.$ These experimental observations indicate that the irreversibility line is not unique to high-${T}_{c}$ oxides but also exists in conventional superconducting metallic alloys although much closer to ${B}_{c2}.$ However, it is difficult to reconcile these results with measurements on other low-${T}_{c}$ materials which show zero resistance up to the surface critical field ${B}_{c3}.$

The dc magnetization of a superconducting ${\mathrm{BaPb}}_{0.75}{\mathrm{Bi}}_{0.25}{\mathrm{O}}_{3}$ sample has been measured as a function of magnetic field and temperature. The results showed that an irreversibility line lies considerably below the superconducting normal phase transition boundary ${B}_{c2}(T),$ similar to that commonly observed in high-temperature superconductors, even though ${\mathrm{BaPb}}_{0.75}{\mathrm{Bi}}_{0.25}{\mathrm{O}}_{3}$ displays a very long coherence length. We attributed the observed large magnetically reversible region to a very small thermodynamic field, which leads to low condensation energies. The reversible magnetization data obtained in the region above the irreversibility line enable us to determine a full set of superconducting parameters for the material.

We propose a simple, systematic, and efficient method to enlarge the gap of a photonic crystal. In this method, we add a small fraction of a third component into the existing photonic crystal. The dielectric property of the third component as well as its insertion position in a unit cell are chosen according to the held-energy distribution of two Bloch states at the band edges. The method is very general. It can be applied to ally microstructure and is independent of the dimensionality of the original photonic crystal. Thus, it: opens up a way to engineer photonic band gaps. Here, we demonstrate the validity of this method explicitly in two dimensions for both s and p waves. We show that, for certain microstructures, absolute gaps can be significantly enlarged. The method is also demonstrated in microwave experiments.

Chevrel phase superconductors with upper critical field values of up to 50 T, are candidate materials for the next generation of high field magnets. We have investigated the effect of doping lead-molybdenum-sulphide with the magnetic ion gadolinium to improve the critical parameters and the flux pinning in this material. Samples were prepared at 1500/spl deg/C to ensure the gadolinium was uniformly distributed throughout the material and then sintered using a hot isostatic press operating at a pressure of 2000 atmospheres. Calorimetric measurements have been completed In magnetic fields up to 15 T as a function of temperature. The temperature dependence of the upper critical field of these isotropic Chevrel phase materials are presented. Upper critical field values of more than 60 T have been determined for both doped and undoped samples. The calorimetric data reported here show that material with low levels of gadolinium doping offers the possibility of strong flux pinning and high critical current densities in high magnetic fields. In highly doped materials, the low critical current density and irreversibility fields found are probably due to a reduction in the fundamental properties and not poor grain boundaries.

A series of samples of Chevrel phase superconductor with nominal composition Pb/sub 1-x/Gd/sub x/Mo/sub 6/S/sub 8/ (0/spl les//spl times//spl les/0.04) have been made using a hot isostatic pressing (HIP) process. DC magnetic measurements have been carried out on the samples. A small increase followed by a decrease of J/sub c/ is observed by increasing the Gd content. The irreversibility field B/sub irr/ also exhibits a similar change. However, despite the change in J/sub c/ and the irreversibility line it was found that the pinning force curves for all samples follow the Kramer scaling relation F/sub p/=J/sub c/,/spl times/B/spl prop/b/sup 1/2/(1-b)/sup 2/ over a wide temperature range. This striking feature indicates that J/sub c/ is limited by one dominant flux pinning mechanism in these samples. A grain boundary pinning mechanism has been proposed previously to account for the scaling relation. In order to test this suggestion further, measurements have been carried out on powdered samples which consist of few grain boundaries. Magneto-resistivity and ac susceptibility measurements have been performed on the samples to investigate the change of B/sub c2/ and other parameters in the Gd doped samples.

Magnetic measurements have been carried out on the hot-isostatically-pressed Chevrel-phase superconductor ${\mathrm{PbMo}}_{6}$${\mathrm{S}}_{8}$ at temperatures from 4.2 K to ${\mathit{T}}_{\mathit{c}}$ and for magnetic fields up to 12 T. The results show that for the ${\mathrm{PbMo}}_{6}$${\mathrm{S}}_{8}$ compound there is a wide magnetically reversible region, between the irreversibility field ${\mathit{B}}_{\mathrm{}\mathrm{irr}}$ and the upper critical field ${\mathit{B}}_{\mathit{c}2}$, on the isothermal magnetic hysteresis curves. The ${\mathit{B}}_{\mathrm{irr}}$(T) line, i.e., the irreversibility line, was found to obey a power-law expression: ${\mathit{B}}_{\mathrm{irr}}$=${\mathit{B}}^{\mathrm{*}}$(1-T/${\mathit{T}}_{\mathit{c}}$${)}^{\mathrm{\ensuremath{\alpha}}}$ with \ensuremath{\alpha}\ensuremath{\approxeq}1.5. Magnetic relaxation measurements revealed that the flux-creep effect in the material studied is substantial and is greater than those observed in conventional metallic alloys, but smaller than in high-temperature superconductors. The existence of the irreversibility line and pronounced flux-creep effect in ${\mathrm{PbMo}}_{6}$${\mathrm{S}}_{8}$ is attributed to the short coherence length of the material. From the reversible magnetization data, the values of the penetration depth, the coherence length, and the critical fields are obtained together with the Ginzburg-Landau parameter \ensuremath{\kappa}. At 4.2 K, the critical current density ${\mathit{J}}_{\mathit{c}}$ is ${10}^{9}$ A ${\mathrm{m}}^{\mathrm{\ensuremath{-}}2}$ at zero field, and decreases to 2\ifmmode\times\else\texttimes\fi{}${10}^{8}$ A ${\mathrm{m}}^{\mathrm{\ensuremath{-}}2}$ at 10 T. Pinning force curves measured at different temperatures obey a Kramer-scaling law of the form: ${\mathit{F}}_{\mathit{p}}$(=${\mathit{J}}_{\mathit{c}}$\ifmmode\times\else\texttimes\fi{}B)\ensuremath{\propto}${\mathit{b}}^{1/2}$(1-b${)}^{2}$, which indicates that the ${\mathit{J}}_{\mathit{c}}$ is limited by one predominant flux-pinning mechanism.

A series of variable temperature AC magnetization measurements have been completed from 4.2 K up to T/sub c/ in magnetic fields up to 10 T on bulk PbMo/sub 6/S/sub 8/ (PMS). The properties of hot isostatically pressed (HIP'ed) PMS fabricated at a pressure of 2/spl times/10/sup 8/ N.m/sup -2/ (2000 bar) are compared with those of PMS fabricated at ambient pressure. After HIP'ing the PMS, the critical current density increased by more than a factor of 20 and T/sub c/ increased by 0.5 K. Using Bean's critical state model, the magnetic measurements suggest that the HIP'ed sample has a critical current density of greater than 3/spl times/10/sup 8/ A.m/sup -2/ at 6 K, and 5 T. >

We present a tunneling study of the superconducting gap and pseudogap from near optimally doped submicron Bi${}_{2}$Sr${}_{2\ensuremath{-}x}$La${}_{x}$CuO${}_{6+\ensuremath{\delta}}$ intrinsic Josephson junctions whose self-heating is significantly suppressed. We find that as temperature decreases a pseudogap develops around ${T}^{\ensuremath{\star}}$ $=$ 165 K while the superconducting gap starts to open at ${T}_{c0}$ $=$ 40 K, which is well above the superconducting transition temperature ${T}_{c}$ of 30 K. We discuss the temperature-dependent properties of the superconducting phase and pseudogap phase. Our results demonstrate a clear two-gap feature of the system with precursor pairing up to ${T}_{c0}$.

Epitaxial heterostructures of CoFe(2)O(4)/LaTiO(3)/LaAlO(3) have been successfully prepared by using the pulsed laser deposition technique. The magnetoresistance (MR) of the samples is negative and linear with field at H≥2 T, exhibiting no dependence on field directions. Nevertheless, when H2 T, the MR is negative in a field parallel to the sample plane, but positive in that along the film normal. This novel observed anisotropic MR is explained in terms of the magnetic anisotropy in the ferrimagnetic layer, as well as the magnetoelastic coupling between the two. In fields of different directions, the top CoFe(2)O(4) layer contracts or expands in the sample plane due to the significant magnetostriction effect, changing its resistance accordingly and exerting compressive or tensile strains on the bottom LaTiO(3) layer. Apparently the orbital status and the one-electron bandwidth in the LaTiO(3) layer are altered, which leads to a change in resistance.

We present an adiabatic geometric quantum computation strategy based on the non-degenerate energy eigenstates in (but not limited to) superconducting phase qubit systems. The fidelity of the designed quantum gate was evaluated in the presence of simulated thermal fluctuations in a superconducting phase qubits circuit and was found to be quite robust against random errors. In addition, it was elucidated that the Berry phase in the designed adiabatic evolution may be detected directly via the quantum state tomography developed for superconducting qubits. We also analyze the effects of control parameter fluctuations on the experimental detection of the Berry phase.

The structural and transport properties of LaTiO3+beta/2 epitaxial thin films, grown at different oxygen pressures ranging from 6.6 x 10(-4) to 5 Pa, have been investigated. X-ray diffraction peaks of the films shift to lower angles with increasing oxygen pressure, indicative of a variation of the corresponding lattice spacing. All the films show T 2 dependence of resistivity over a large temperature range of similar to 200 K, suggesting a band-filling-induced metallic Fermi-liquid behaviour. Upturns in resistivity have been revealed at low temperatures, which could be ascribed to the Anderson-localization effect caused by the cation vacancies. Furthermore, for the thin films grown at high oxygen pressures of 0.5 and 5 Pa, the dependence of resistivity on temperature shows a maximum at high temperatures. The maximum seems to support the argument that transition between t-orbital ordering and disordering plays an important role in dominating transport properties at high temperatures. Carrier density deduced from Hall coefficient increases with the decrease of oxygen content, and shows strong temperature dependence. From the experimental data, it can be asserted that in the LaTiO3+beta/2 thin films, besides the band filling effect, localization or disorder caused by La and Ti vacancy effects controls the unique transport properties.

A La(2/3)Ca(1/3)MnO(3) Hall bar with its long dimension roughly along the hard axis [110] was fabricated on a single-crystal-like tensilely strained film on SrTiO(3)(001). The anisotropic magnetoresistance (AMR) and planar Hall effect (PHE) have been studied at various external magnetic fields and temperatures. A phenomenological model in the high field limit is developed, and the galvanomagnetic tensor based on a tetragonal symmetry 4/mmm (D(4h)), applicable to epitaxial films on a substrate, has been obtained by expanding the tensor to the sixth order. The derived in-plane transverse resistance R(xy) shows a sin2φ(M) angular dependence, while the longitudinal R(xx) is constituted by not only a two-fold cos2φ(M) term, but also a four-fold cos4φ(M) term due to the square symmetry of the lattice. The model is in good agreement with the experimental results in high fields, while deviations are observed near the {100} easy axis with the decreasing field. Close inspection of the fitting parameters reveals the evolution of these term weights with temperature and magnetic field, which is distinct from conventional ferromagnetic metals and cannot be explained by the phenomenological model. An alternative mechanism for AMR, stemming from the magnetization-induced local orbit deformation through spin-orbit interaction, as previously proposed by O'Donnell et al, may be prevalent in manganites and other systems of complicated crystal structure.

The resistivity of superconducting Pb-doped Bi–Sr–Ca–Cu–O single crystal, with 2212 structure, has been measured using Montgomery technique. The resistivity, like in other high T c oxide superconductors, shows very strong anisotropic characteristic, with a typical metallic behavior but remains a residual resistivity at T = 0 K in the direction parallel to the a − b plane and a "semiconducting-like" temperature dependence in the c direction. The anisotropy (ρc/ρab) is about 104. But the value of resistivity in a − b plane is larger than that of Bi 2 Sr 2 CaCu 2 O y crystal. This may imply that the Bi–O plane plays an important role in superconductivity in this kind of structure.

We use interfacial transport and transmission electron microscopy to study the YBa2Cu3O7-delta(YBCO)/La0.67Ca0.33MnO3(LCMO) junction that form a d(x)2(-y)2-wave superconductor and a ferromagnet (FM) heterostructure. Zero bias conductance peaks (ZBCPs) caused by Andreev reflection at zero bias were observed in the interfacial differential conductance spectra for the sample with an orderly mixed c- and a-axis [with (001) and (100)/(110)] orientation of YBCO in the interface. When the YBCO film is oriented with the c-axis normal to the interface, a zero bias conductance dip (ZBCD) is observed. These results evidence the existence of surface Andreev bound states (midgap states) in the {110} surface of YBCO, which can lead ZBCP to appear in all directions except the {100} surface of YBCO where ZBCD occurs. Furthermore, the absence of any obvious influence of spin-polarization of LCMO on ZBCP in zero magnetic field implies that the LCMO is not half-metallic in the interface of YBCO/LCMO, while strong magnetic field dependence of ZBCP shows that the applied magnetic field enhances the spin polarization of LCMO and suppresses ZBCPs in YBCO.

The superconducting and structural properties of a series of Mg1-xAlxB2 samples have been investigated. X-ray diffraction results confirmed the existence of a structural transition associated with a significant change in interboron layer distance as reported previously by Slusky Moreover, transmission-electron-microscopy observations revealed the existence of a superstructure with doubled lattice constant along the c-axis direction. We propose that this superstructure is probably related to the structural transition. The modifications of the superconducting transition temperature T-c, the normal-state resistivity, and the upper critical field B-c2(0) by Al doping are discussed in terms of Al-substitution-induced changes in the electronic structure at the Fermi energy.

We propose a feasible experimental scheme to demonstrate the geometric phase in flux qubits by means of a detuning coherent microwave pulse technique. Through measuring the probability of the persistent current state in the flux qubits, one can detect the Berry phase that is acquired with the system’s Hamiltonian adiabatical circular evolution in the parameter space. Furthermore, we show that one could choose an appropriate amplitude of pulses in an experiment to obtain high readout resolution when the detuning frequency of the pulses is fixed, and controlled phase shift gates can be implemented based on the geometric phases by inductance coupling of two flux qubits.

Pr0.4Ca0.6Ba2Cu3O7−δ thin films have been grown on SrTiO3 (STO) substrates by pulsed laser deposition. The dependence of growth orientation and superconducting properties on substrate temperature were studied. As characterized by X-ray diffraction (XRD), good quality c-axis and a-axis orientated films could be grown on STO by changing the substrate temperature. However, the highest TC0 (∼16.8 K) was observed in samples with mixed orientations. Almost all samples exhibited a semiconducting-like temperature dependence of resistivity, which could be attributed to the scattering due to the localized electronic states. Furthermore, films grown on LAO, MgO and YSZ substrates were also studied.