By using density functional theory(DFT)-based first-principles calculations, the structural stability and electronic properties for two kinds of silicene domain boundaries, forming along armchair edge and zigzag edge, have been investigated. The results indicate that a linkage of tetragonal and octagonal rings(4|8) appears along the armchair edge, while a linkage of paired pentagonal and octagonal rings(5|5|8) appears along the zigzag edge. Different from graphene, the buckling properties of silicene lead to two mirror symmetrical edges of silicene line-defect. The formation energies indicate that the 5|5|8 domain boundary is more stable than the 4|8 domain boundary. Similar to graphene, the calculated electronic properties show that the 5|5|8 domain boundaries exhibit metallic properties and the 4|8 domain boundaries are half-metal.Both domain boundaries create the perfect one-dimensional(1D) metallic wires. Due to the metallic properties, these two kinds of nanowires can be used to build the silicene-based devices.
Transmission spectroscopy of two Nb double superconducting split-ring samples with different thicknesses on MgO substrates was measured by a continuous Tera-Hertz spectrometer.The transmission curves of two different samples with the thicknesses of 50 and 150 nm at 7.5 K show dips at 480,545 GHz,respectively,which origin from the different capacities and inductances of the samples.For the sample of 50 nm,the dip shifts to lower frequency,also decreases in depth and increases in width with temperature or field increasing below T c of Nb film,while the sample of 150 nm does not show such a phenomenon.This thickness-dependent transmission behavior is due to the kinetic inductance and conductivity change of superfluid electrons in Nb film and may suggest a practical tunable THz filter based on the thinner samples.
Full gap closing is a prerequisite for hosting Majorana zero modes in Josephson junctions on the surface of topological insulators.Previously,we have observed direct experimental evidence of gap closing in Josephson junctions constructed on Bi_2Te_3 surface.In this paper we report further investigations on the position dependence of gap closing as a function of magnetic flux in single Josephson junctions constructed on Bi_2Te_3 surface.
Frequency-domain terahertz transmission spectra of Mn3 and Mn12 single molecule magnets (SMMs) have been measured at different temperatures, and hence the anisotropic parameters D2 and D4 of the spin Hamiltonian H D2 S z2 D4 S z4have been calculated. For Mn12 SMM, D2= 10.9 GHz and D4= 2.59×10 2 GHz, while for Mn3 SMM, D2= 22.0 GHz and D4 can be considered negligible. This suggests Mn3 SMM can be considered as a simpler and more suitable candidate for magnetic quantum tunneling research.
LIU RuiYuanZUO JunWeiLI YanRongZHOU YuRongWANG YunPing
We perform both dc and ac magnetic measurements on the single crystal of Mn3O(Et-sao)3(ClO4)(MeOH)3singlemolecule magnet(SMM) when the sample is preserved in air for different durations. We find that, during the oxidation process, the sample develops into another SMM with a smaller anisotropy energy barrier and a stronger antiferromagnetic intermolecular exchange interaction. The antiferromagnetic transition temperature observed at 6.65 K in the new SMM is record-high for the antiferromagnetic phase transition in all the known SMMs. Compared to the original SMM, the only apparent change for the new SMM is that each molecule has lost three methyl groups as revealed by four-circle x-ray diffraction(XRD), which is thought to be the origin of the stronger antiferromagnetic intermolecular exchange interaction.
The Institute of Physics, Chinese Academy of Sciences, is in charge of the construction of the Synergetic Extreme Condition User Facility(SECUF) in Huairou, Beijing. The SECUF is a comprehensive facility focused on providing extreme physical conditions for scientific research, including an ultralow temperature, ultrahigh pressure, ultrahigh magnetic field, and ultrafast laser. The ultralow temperature will be realized by the sub-millikelvin(sub-mK) station, whose main component is an adiabatic nuclear demagnetization refrigerator(ANDR). The refrigerator is designed to have a base temperature below 1 mK and a magnetic field up to 16 T for experiments, as well as a characteristic parameter of B/T≥10~4 T/K.In this review, we introduce adiabatic nuclear demagnetization refrigeration, thermometry from 10 mK to sub-mK, the properties and parameters of the ANDR of the SECUF, and related prospective research topics.
The low-temperature specific heat of Ni4 single-molecule magnets (SMMs) is measured in a PPMS He-3 system. The tem- perature-dependent specific heat of Ni4 SMMs shows an antiferromagnetic phase transition at 0.91 K. The experimental results are in good consistency with Monte Carlo simulation of 3D-Ising model, indicating two independent diamond-like antiferro-magnetic structures with an exchange energy J = 0.020 K in Ni4 system.
ZUO JunWei LIU HaiQing LI YanRong SU ShaoKui WANG YunPing
Adsorption behavior of Fe atoms on a metal-free naphthalocyanine(H2Nc) monolayer on Ag(111) surface at room temperature has been investigated using scanning tunneling microscopy combined with density functional theory(DFT)based calculations. We found that the Fe atoms were adsorbed on the centers of H2 Nc molecules and formed Fe–H2Nc complexes at low coverage. DFT calculations show that Fe sited in the center of the molecule is the most stable configuration, in good agreement with the experimental observations. After an Fe–H2Nc complex monolayer was formed, the extra Fe atoms self-assembled to Fe clusters of uniform size and adsorbed dispersively at the interstitial positions of Fe–H2Nc complex monolayer. Therefore, the H2 Nc monolayer grown on Ag(111) could be a good template to grow dispersed magnetic metal atoms and clusters at room temperature for further investigation of their magnetism-related properties.
