Revisiting the Electron-Doped SmFeAsO:Enhanced Superconductivity up to 58.6 K by Th and F Codoping

In the iron-based high-To bulk superconductors, Tc above 50 K was only observed in the electron-doped 1111-type compounds. Here we revisit the electron-doped SmFeAsO polycrystals to make a further investigation for the highest Tc in these materials. To introduce more electron carriers and less crystal lattice distortions, we study the Th and F eodoping effects into the Sm-O layers with heavy electron doping. Dozens of Sm1-xThx FeAsO1-yFy samples are synthesized through the solid state reaction method, and these samples are carefully characterized by the structural, resistive, and magnetic measurements. We find that the codoping of Th and F clearly enhances the superconducting Tc more than the Th or F single-doped samples, with the highest record Tc up to 58.6K when x = 0.2 and y=0.225. Further element doping causes more impurities and lattice distortions in the samples with a weakened superconductivity.

Heat Transport of Electron-Doped Cobaltates

Within the t-J model, the heat transport of electron-doped cobaltates is studied based on the fermionspin theory. It is shown that the temperature-dependent thermal conductivity is characterized by the low-temperature peak located at a finite temperature. The thermal conductivity increases monotonously with increasing temperature at low-temperatures T 〈 0.1 J, and then decreases with increasing temperature for higher temperatures T 〉 0.1 J, in qualitative agreement with experimental result observed from NaxCoO2.

Growth and transport features of electron-doped superconductor Pr_(1-x)LaCe_xCuO_(4-δ) thin films

Tt-phase electron-doped superconductor Pr1-xLaCexCuO4-δ（PLCCO） thin films are successfully prepared on SrTiOs （100） substrates by using the dc magnetron sputtering method. It is found that the films each have a highly oriented structure along the c-axis. For optimally doped films with x ≈ 0.10, the superconducting transition temperature Tc is 25.5 K, which is similar to that of a single crystal. The quadratic temperature dependence of the resistivity is observed when T 〉 To, which can be attributed to the two-dimensional Fermi liquid behaviour. Besides, the optimal conditions for preparing the T1-phase PLCCO thin films are also discussed in detail.

Continuously Doping Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)into Electron-Doped Superconductor by CaH_(2)Annealing Method

As a typical hole-doped cuprate superconductor,Bi_(2)Sr_(2)CaCu_(2)O_(8+δ)(Bi2212)carrier doping is mostly determined by its oxygen content.Traditional doping methods can regulate its doping level within the range of hole doping.Here we report the first application of CaH_(2)annealing method in regulating the doping level of Bi2212.By continuously controlling the anneal time,a series of differently doped samples can be obtained.The combined experimental results of x-ray diffraction,scanning transmission electron microscopy,resistance and Hall measurements demonstrate that the CaH_(2)induced topochemical reaction can effectively change the oxygen content of Bi2212 within a very wide range,even switching from hole doping to electron doping.We also found evidence of a low-T_c superconducting phase in the electron doping side.

Research trends in electron-doped cuprate superconductors

In this review, we look back on some intriguing and puzzling issues in electron-doped cuprate superconductors, such as electron-hole asymmetry, two types of carriers, quantum critical points, order-parameter symmetry, etc. The necessity of study on this family is invoked in comparison with the hole-doped counterparts from several aspects. The related progress, especially in last few years, has been outlined point to point, as well as other hot topics like the discovery of ambipolar superconductors, the applications in superconducting electronics, and the emergency of superconductivity in parent compounds. In perspective, the utilization of blooming advanced techniques, electric double layer transistor and combinatorial film deposition, will bring some new insights into the mechanism such as electron-doped cuprate superconductors.

Anomalous in-plane magnetoresistance of electron-doped cuprate La_(2.x)Ce_xCuO_(4±δ)

We report systematic in-plane magnetoresistance measurements on the electron-doped cuprate La2-x,.CexCuO4±δ thin films as a function of Ce doping and oxygen content in the magnetic field up to 14 T. A crossover from negative to positive magnetoresistance occurs between the doping level x = 0.07 and 0.08. Above x = 0.08, the positive magnetoresistance effect appears, and is almost indiscernible at x = 0.15. By tuning the oxygen content, the as-grown samples show negative magnetoresistance effect, whereas the optimally annealed ones display positive magnetoresistance effect at the doping level x = 0.15. Intriguingly, a linear-field dependence of in-plane magnetoresistanee is observed at the underdoping level x = 0.06, the optimal doping level x = 0. i and slightly overdoping level x = 0.11. These anomalies of in-plane magnetoresistance may be related to the intrinsic inhomogeneity in the cuprates, which is discussed in the framework of network model.

Tunable strain effect on the charge/orbital ordering state in electron-doped La_(0.9)Hf_(0.1)MnO_3 films

The impact of the lattice strain on the charge/orbital ordering state was studied by using a heterostructure composed with elec- tron-doped La0.9Hf0.1MnO3 （LHMO） and ferro- and piezoelectric 0.67Pb（Mgl/3Nb2/3）O3-0.33PbTiO3. The ferroelectric poling induces a significant reduction in the biaxial tensile strain in the LHMO film, leading to a decrease in the film resistance over the whole temperature range and an increase in the insulator to metal transition temperature TIM. The resistance of LHMO film exhibits different responses to the external electric fields and lattice deformation, which is attributed to the coactions of con- verse piezoelectric effect and ferroelectric polarity effect. The modification of charge/orbital ordering phase by the electric fields and ferroelectric polarization suggests that the unstable states in the manganites are sensitive to strain effects.

A selective control of volatile and non-volatile superconductivity in an insulating copper oxide via ionic liquid gating

Manipulating the superconducting states of high transition temperature(high-Tc)cuprate superconductors in an efficient and reliable way is of great importance for their applications in next-generation electronics.Here,employing ionic liquid gating,a selective control of volatile and non-volatile superconductivity is achieved in pristine insulating Pr2CuO4±δ(PCO)films,based on two distinct mechanisms.Firstly,with positive electric fields,the film can be reversibly switched between superconducting and non-superconducting states,attributed to the carrier doping effect.Secondly,the film becomes more resistive by applying negative bias voltage up to-4V,but strikingly,a non-volatile superconductivity is achieved once the gate voltage is removed.Such phenomenon represents a distinctive route of manipulating superconductivity in PCO,resulting from the doping healing of oxygen vacancies in copper-oxygen planes as unravelled by high-resolution scanning transmission electron microscope and in situ X-ray diffraction experiments.The effective manipulation of volatile/non-volatile superconductivity in the same parent cuprate brings more functionalities to superconducting electronics,as well as supplies flexible samples for investigating the nature of quantum phase transitions in high-Tcsuperconductors.