α-RuCl_{3} is a leading candidate material for the observation of physics related to the Kitaev quantum spin liquid (QSL). By combined susceptibility, specific-heat, and nuclear-magnetic-resonance measurements, we demonstrate that α-RuCl_{3} undergoes a quantum phase transition to a QSL in a magnetic field of 7.5 T applied in the ab plane. We show further that this high-field QSL phase has gapless spin excitations over a field range up to 16 T. This highly unconventional result, unknown in either Heisenberg or Kitaev magnets, offers insight essential to establishing the physics of α-RuCl_{3}.
Motivated by the recent discovery of noncentrosymmetric superconductors, such as CePt 3 Si, CeRhSi 3 , and CeIrSi 3 , we investigate theoretically the impurity resonance states with coexisting s-wave and p-wave pairing symmetries. Due to the nodal structure of the gap function, we find single nonmagnetic impurity-induced resonances appearing in the local density of state. In particular, we analyze the evolution of the local density of states for coexisting isotropic s-wave and p-wave superconducting states, and compare with that of anisotropic s-wave and p-wave symmetries of the superconducting gap. Our results show that the scanning tunneling microscopy can shed light on the particular structure of the superconducting gap in noncentrosymmetric superconductors.
In recent years, organic−inorganic hybrid halide perovskites have attracted wide attention due to their excellent photoelectric properties. MAPbI 3 and FAPbI 3 have particularly shown great application prospects. However, due to the low thermal and chemical stability of these monoamino organic cation 3D perovskites, the durability of the devices in which they are used is affected. In this paper, an inorganic skeleton was introduced to functional diamino organic cations (PDA and DAB) to obtain more stable diamino 3D perovskites (PDAPbI 4 and DABPbI 4 ). For comparison with the 3D perovskites, two monoamino perovskites with the same molecular chain length ((PT) 2 PbI 4 and (MBA) 2 PbI 4 ) were also designed. The geometrical structures, thermodynamic stability, electronic properties, transport properties, and optical absorption properties of the four perovskites were calculated by the first-principles method. The results demonstrate that diamino organic cations can, to a certain extent, provide favorable channels for carrier migration, especially for carrier migration between Pb−I inorganic layers, and increase the coupling effect between Pb−I inorganic layers. In addition, the excellent optical absorption properties of diamino organic cation 3D perovskites in the solar irradiation range can contribute to the design and synthesis of more effective and stable organic−inorganic perovskite optoelectronic devices in the future.
Summary In China, a considerable proportion of reinforced concrete (RC) industrial chimneys in operation was designed and constructed in accordance with less rigorous outdated seismic criteria during the end of 19th and early 20th century. However, few research works have been reported till date on a realistic overall assessment of the seismic performance of these existing aging RC chimney structures. Therefore, in this study, fragilities of existing RC chimney were studied. For this purpose, an existing 240 m tall RC chimney was selected and structurally modeled with a lumped mass beam (stick) model by means of the OpenSees analysis program. In order to capture the uncertainties in ground motion realizations, a series of 21 ground motions are selected from the Next Generation Attenuation database as the input motions. To develop the analytical fragility curves, nonlinear incremental dynamic analysis of the studied RC chimney was then carried out using the selected input motions, which were normalized to different excitation levels. The section curvature ductility ratio was considered as the damage index. Based on material strain and sectional analysis, four limit states (LSs) were defined for five damage state. The seismic responses of the all sections were utilized to evaluate the likelihood of exceeding the LSs. Then the peak ground acceleration (PGA)‐based seismic fragility curves of the structure were constructed assuming a lognormal distribution. Finally, under the light of these fragility curves, the damage risks in existing RC chimney were discussed. The analytical results indicated that for design level earthquake of PGA = 0.1 g (g is the gravitational acceleration) and the maximum considered earthquake of PGA = 0.22 g, the probabilities of exceeding the light damage state were around 1.5% and 44%, respectively, while the exceedance probabilities corresponding to moderate, extensive and complete damage states were approximately zero in both cases. On the other hand, fragility analysis revealed that the RC chimney structure had considerable ductility capacity and was capable to withstand a strong earthquake with some structural damages. Copyright © 2014 John Wiley & Sons, Ltd.
The charge transport of electron doped Mott insulators on a triangular lattice is investigated within the t-J model. The conductivity spectrum shows a low-energy peak and an unusual midinfrared band, while the resistivity is characterized by a crossover from the high temperature metallic-like to low temperature insulating-like behavior, in qualitative agreement with experiments. Our results also show that the mechanism that causes this unusual charge transport is closely related to a competition between the kinetic energy and magnetic energy in the system. PACS: 74.25.Fy, 74.25.Gz, The recent discovery of superconductivity in doped cobaltates, Na x CoO 2 · yH 2 O with the superconducting transition temperature T c ∼ 5K, has generated great interests due to the role of strong electron correlations 1 . This compound has a lamellar structure consisting of the two-dimensional (2D) CoO 2 layers separated by a thick insulating layer of Na + ions and H 2 O molecules, where the one-half spin Co 4+ ions are arranged on a triangular lattice. This structure is similar to cuprates superconductors in the sense that they also have a layered structure of the square lattice of the CuO 2 plane separated by insulating layers 2 . It has been well established that Cu 2+ ions exhibit an antiferromagnetic (AF) long-range order (AFLRO) in the parent compounds of cuprate superconductors, where superconductivity occurs when the AFLRO state is suppressed by hole or electron doping 2,3 . However, Na x CoO 2 ·yH 2 O is viewed as an electron doped Mott insulator, where superconductivity appears with electron doping 1 . A fundamental similarity between cuprate and cobaltate superconductors has been seen in the decreases in the superconducting transition temperature for both underdoped and overdoped materials 4 . The optimal doping for superconductivity occurs at 0.3 electrons per Co above the ground-state Na 0 CoO 2 · 1.3H 2 O, which is a half-filled two-electron t 2g derived band, while for cuprates, the optimal doping occurs at 0.15 holes (electrons) added to the half-filled band of the parent compound 4 . On the other hand, doped Mott insulators on a triangular lattice, where the geometric spin frustration exists, are also of interests in their own right, with many unanswered fascinating questions. Historically the undoped Mott insulator on a triangular lattice was firstly proposed to be a model for microscopic realization of the spin liquid due to the existence of the strong spin frustration 5 . It has been argued that this spin liquid state may play a crucial role in the mechanism for superconductivity in doped cuprates 6 . Thus the unexpected finding of superconductivity in doped cobaltates has raised the hope that it may help solve the unusual physics in doped cuprates.Some experimental studies have revealed a non-Fermi liquid behavior in doped cobaltates 1,7,8 . Among the striking features in the normal-state, a hallmark is the charge transport, where the resistivity shows a temperature linear variation in a wide range of temperature...
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