Shun Tan

Superconductivity with Topological Surface State in SrxBi2Se3

By intercalation of alkaline earth metal Sr in Bi2Se3, superconductivity with large shielding volume fraction (∼91.5% at 0.5 K) has been achieved in Sr0.065Bi2Se3. Analysis of the Shubnikov-de Hass oscillations confirms the half-shift expected from a Dirac spectrum, giving transport evidence of the existence of surface states. Importantly, SrxBi2Se3 superconductor is stable under air, making SrxBi2Se3 an ideal material base for investigating topological superconductivity.

Exchange bias-like phenomenon in SrRuO3

Exchange bias-like phenomenon is observed in the SrRuO3 polycrystalline. After the sample is cooled down to 4K in a magnetic field, the magnetic hysteresis loop shifts in the opposite direction to the applied biasing field. The shift decreases as the sweeping range of the measuring field increases. This phenomenon may arise from the spin glass property of SrRuO3. Since SrRuO3 is widely used in spintronics devices, the observation of exchange bias-like shift in SrRuO3 itself suggests that the application of SrRuO3 should be more carefully considered.

Perfect charge compensation in WTe2 for the extraordinary magnetoresistance: From bulk to monolayer

The electronic structure of WTe2 bulk and layers are investigated by using the first principles calculations. The perfect electron-hole (n-p) charge compensation and high carrier mobilities are found in WTe2 bulk, which may result in the large and non-saturating magnetoresistance (MR) observed very recently in the experiment [Ali et al., Nature 514, 205 (2014)]. The monolayer and bilayer of WTe2 preserve the semimetallic property, with the equal hole and electron carrier concentrations. Moreover, the very high carrier mobilities are also found in WTe2 monolayer, indicating that the WTe2 monolayer would have the same extraordinary MR effect as the bulk, which could have promising applications in nanostructured magnetic devices.

Effect of Ru doping in La 0.5 Sr 0.5 Mn O 3 and La 0.45 Sr 0.55 Mn O 3

We investigated the structural, magnetic, and transport properties of polycrystalline doping systems La0.5Sr0.5Mn1−xRuxO3 0 x 0.15 with ferromagnetic matrix and La0.45Sr0.55Mn1−yRuyO3 0 y 0.5 with antiferromagnetic matrix. X-ray photoelectron spectroscopy shows that Ru ions exist mainly in the form of Ru4+ while there also exist a small quantity of Ru5+. For the low doping samples 0.05 x y 0.15 0.2 , the ferromagnetism is enhanced and Curie temperature TC rises with increasing Ru doping level, but TC is much higher than the temperature TIM corresponding to insulating-metallic transition. For the high doping samples 0.3 y 0.5 , oppositely the ferromagnetism is suppressed and the insulating property is enhanced with further increasing Ru doping level. These results show that there is an exchange interaction between Mn3+ and Ru4+ Ru5+ . The electron spin resonance spectra clearly and directly inspect that the interaction between Mn3+ and Ru4+ Ru5+ is ferromagnetic. Furthermore, the electron spin resonance spectra also show that a Ru-Ru antiferromagnetic interaction takes place in the high doping region y=0.4,0.5 . We explained the disagreement between TC and TIM.

Abnormal temperature dependence of low-field magnetization of FeCr2−xAlxS4

In this letter, the abnormal temperature dependence of low-field magnetization of FeCr2−xAlxS4 (0⩽x⩽0.7) is reported. In addition to a large irreversibility between zero-field-cooling (ZFC) and field-cooling (FC) magnetization for all samples, a cusp is also observed in both FC and ZFC curves for x⩽0.2. The cusp and the irreversibility are suppressed under an applied field of 0.5 T. The study of magnetic hysteresis loop reveals that this abnormal low-field magnetic behavior is closely related to coercitivity of the system. Accordingly, the abnormal magnetic behavior is explained qualitatively by taking account of large magnetic anisotropy and domain wall pinning of nonmagnetic ions.

Structural and elemental analysis on the nanocrystalline SnO2 in the surface of ancient chinese black mirrors

Abstract There were two sorts of black mirrors in ancient China: Heiqigu and common black mirrors (CBM). Their surface layers of about 100 μm thickness were studied by XRD, HREM, and Roman spectrometry. It was proved that the layers were mainly composed of nanometer-sized particles of Sn1 − x(CuFePbSi)xO2 (about 5 nm) with cassiterite structure. These results are of interest for further investigation into the corrosion- resisting property and formation mechanism of the nanometer structure.

Superconducting Fiber with Transition Temperature up to 7.43 K in Nb2PdxS5−δ (0.6 < x <1)

Wiring systems powered by highly efficient superconductors have long been a dream of scientists, but researchers have faced practical challenges such as finding flexible materials. Here we report superconductivity in Nb2PdxS5-δ fibers with transition temperature up to 7.43 K, which have typical diameters of 0.3-3 μm. Superconductivity occurs in a wide range of Pd (0.6 < x <1) and S (0 < δ <0.61) contents, suggesting that the superconductivity in this system is very robust. Long fibers with suitable size provide a new route to high-power transmission cables and electronic devices.

Superconductivity in BiO1?xFxBiS2 and possible parent phase of Bi4O4S3 superconductor

We report the discovery of superconductivity in BiOFxBiS2, an isostructural compound of the REOFxBiS2 (RE: La, Nd, Pr, Ce, and Yb) superconductors. The parent compound, Bi2OS2, is nonsuperconductive. Superconductivity is observed in a wide range of F-doping content (0.06 x 0.27). The optimal F-doping concentration is about 0.24 in BiOFxBiS2, where the highest transition temperature of 3.5 K is achieved. We suppose that the superconductivity in BiOFxBiS2, as well as that in Bi3O2S3 and Bi4O4S3, is induced by partial substitution or insertion in the Bi2OS2 parent phase.

Size Dependence of Phonon Raman Spectra in Mn2O3 Nanocrystals

Nanometer manganic oxide (Mn2O3) has been prepared by the chemical liquid homogeneous precipitation (CLHP) method. The size dependence of phonon Raman spectra in Mn2O3 nanocrystals has been investigated. Transmission electron micrographs and X-ray powder diffraction patterns show that the average particle sizes are in the range of 9 to 50 nm. From the Raman spectra patterns of the nanometer Mn2O3 particle, we determined the broadening of the Raman peak in the lower frequency region. This phenomenon was explained by a spatial correlation model. We also found that the intensities of the main Raman peak decrease with the decrease in the grain size of Mn2O3 nanocrystals.

Anisotropy and extremely high coercivity in weak ferromagnetic LuFeO3

The temperature dependence of the structural anisotropy of weak ferromagnetic LuFeO3 is investigated through the XRD spectra at different temperatures. The structural anisotropy decreases with heating, which is in agreement with the magnetization-temperature measurement. The magnetic hysteresis loops reveal exceptionally high coercivity and saturation field. Its high energy of magnetocrystalline anisotropy may be responsible for the peculiar phenomenon. Thus, LuFeO3 is a super hard magnetic material. The magnetized LuFeO3 can steadily provide weak permanent magnetic field, which can be considered as a kind of useful application.