Within the charge-spin separation fermion-spin theory, we show that themechanism of superconductivity in the electron doped cobaltate Na_x CoO_2 · gH_2O is ascribed toits kinetic energy. The dressed fermions inte...Within the charge-spin separation fermion-spin theory, we show that themechanism of superconductivity in the electron doped cobaltate Na_x CoO_2 · gH_2O is ascribed toits kinetic energy. The dressed fermions interact occurring directly through the kinetic energy byexchanging magnetic excitations. This interaction leads to a net attractive force between dressedfermions, then the electron Cooper pairs originating from the dressed fermion pairing state are dueto the charge-spin recombination, and their condensation reveals the superconducting ground state.The superconducting transition temperature is identical to the dressed fermion pair transitiontemperature, and is suppressed to a lower temperature due to the strong magnetic frustration. Theoptimal superconducting transition temperature occurs in the electron doping concentration δ ≈0.29, and then decreases for both underdoped and overdoped regimes, in qualitative agreement withthe experimental results.展开更多
Monodispersed manganese ferrite （MnFe2O4） nanocrystals could be successfully synthesized in large quantities via a facile synthetic technique based on the pyrolysis of organometallic compound precursor, in which oct...Monodispersed manganese ferrite （MnFe2O4） nanocrystals could be successfully synthesized in large quantities via a facile synthetic technique based on the pyrolysis of organometallic compound precursor, in which octadecene was used as solvent, and oleic acid and oleylamine were used as capping ligands. MnFe204 nanocrystals were obtained with size in a tunable range of 4- 15 nm and their morphologies could be tuned from spherical to triangle-shaped by varying the surfactants. The phase structure, morphology, and size of the products were characterized in detail by X-ray diffraction （XRD） and transmission electron microscopy （TEM）. Magnetic properties of MnFe2O4 nanocrystals with different morphologies were measured using a superconducting quantum interference device （SQUID）. Both monodisperse MnFe204 nanocrystals with spherical and triangle-shapes are superparamagnetic at room temperature while ferromagnetic at 2 K. The pyrolysis method may provide an effective route to synthesize other spinel ferrites or metal oxides nanocrystals.展开更多
Topological materials, hosting topological nontrivial electronic band, have attracted widespread attentions. As an application of topology in physics, the discovery and study of topological materials not only enrich t...Topological materials, hosting topological nontrivial electronic band, have attracted widespread attentions. As an application of topology in physics, the discovery and study of topological materials not only enrich the existing theoretical framework of physics, but also provide fertile ground for investigations on low energy excitations, such as Weyl fermions and Majorana fermions, which have not been observed yet as fundamental particles. These quasiparticles with exotic physical properties make topological materials the cutting edge of scientific research and a new favorite of high tech. As a typical example, Majorana fermions, predicted to exist in the edge state of topological superconductors, are proposed to implement topological error-tolerant quantum computers. Thus, the detection of topological superconductivity has become a frontier in condensed matter physics and materials science. Here, we review a way to detect topological superconductivity triggered by the hard point contact: tip-induced superconductivity(TISC) and tip-enhanced superconductivity(TESC). The TISC refers to the superconductivity induced by a non-superconducting tip at the point contact on non-superconducting materials. We take the elaboration of the chief experimental achievement of TISC in topological Dirac semimetal Cd_3As_2 and Weyl semimetal Ta As as key components of this article for detecting topological superconductivity. Moreover, we also briefly introduce the main results of another exotic effect, TESC, in superconducting Au_2Pb and Sr_2RuO_4 single crystals, which are respectively proposed as the candidates of helical topological superconductor and chiral topological superconductor. Related results and the potential mechanism are conducive to improving the comprehension of how to induce and enhance the topological superconductivity.展开更多
Three electrodeposited Fe-Ni,Fe-Co,and Fe-Ni-Co cores of thin film transformer are prepared on silicon(100) substrates,which are sputtered a 90 nm thick film of Cu acting as the seed layer.The core films consisting of...Three electrodeposited Fe-Ni,Fe-Co,and Fe-Ni-Co cores of thin film transformer are prepared on silicon(100) substrates,which are sputtered a 90 nm thick film of Cu acting as the seed layer.The core films consisting of Fe-Ni 20:80,Fe-Co 60:40 and Fe-Ni-Co 10:60:30,respectively,are deposited using direct current electrodeposition.The surface texture,electrical and magnetic properties are surveyed by scanning electron microscopy(SEM),superconducting quantum interference device(SQUID),etc.The wave transmission ability and efficiency of thin film transformer with these cores,inputting the sine wave,are compared.All the analyses indicate that FeNi alloy films display the optimal magnetic properties and excellent transformer performance.展开更多
We prepared the DNA-cetyltrimethyl ammonium complex, as well as the same complex intercalated with stable organic free radicals, and studied their magnetic properties by electron magnetic resonance (EMR) spectroscopy ...We prepared the DNA-cetyltrimethyl ammonium complex, as well as the same complex intercalated with stable organic free radicals, and studied their magnetic properties by electron magnetic resonance (EMR) spectroscopy and by measuring the magnetization on a superconducting quantum interference device (SQUID). The UV-vis and CD spectra of DNA-quaternary alkyl ammonium complex (DNA--Q+) in organic solvent clearly demonstrated that it retained the double helical B-form conformation. The interhelical spacing of double strand DNA (dsDNA) increased when the counter ions (Na+) of phosphate groups of the natural DNA were replaced with the long alkyl quaternary ammonium groups. The inter-helical distance of DNA-cetyltrimethyl ammonium (CTMA) was 39.1 as confirmed by X-ray diffractometry. In general, the magnetization of the DNA-CTMA complex solid was found to be significantly lower than that of natural DNA. Moreover, intercalation of the complex with stable organic free radicals did not improve magnetization, which again was in marked contrast to natural DNA. EMR spectroscopic behavior of the complex in the solid state also was quite different from that of natural DNA: The unique broad EMR signal of natural DNA in the low field region with g-value greater than 10 disappeared in the DNA-CTMA complex.展开更多
文摘Within the charge-spin separation fermion-spin theory, we show that themechanism of superconductivity in the electron doped cobaltate Na_x CoO_2 · gH_2O is ascribed toits kinetic energy. The dressed fermions interact occurring directly through the kinetic energy byexchanging magnetic excitations. This interaction leads to a net attractive force between dressedfermions, then the electron Cooper pairs originating from the dressed fermion pairing state are dueto the charge-spin recombination, and their condensation reveals the superconducting ground state.The superconducting transition temperature is identical to the dressed fermion pair transitiontemperature, and is suppressed to a lower temperature due to the strong magnetic frustration. Theoptimal superconducting transition temperature occurs in the electron doping concentration δ ≈0.29, and then decreases for both underdoped and overdoped regimes, in qualitative agreement withthe experimental results.
基金Project(2010QZZD008) supported by the Prospect Key Projects of Fundamental Research Funds for the Central UniversitiesProject(2007FJ3008) supported by the Hunan Provincial Key Science and Technology Program of China
文摘Monodispersed manganese ferrite （MnFe2O4） nanocrystals could be successfully synthesized in large quantities via a facile synthetic technique based on the pyrolysis of organometallic compound precursor, in which octadecene was used as solvent, and oleic acid and oleylamine were used as capping ligands. MnFe204 nanocrystals were obtained with size in a tunable range of 4- 15 nm and their morphologies could be tuned from spherical to triangle-shaped by varying the surfactants. The phase structure, morphology, and size of the products were characterized in detail by X-ray diffraction （XRD） and transmission electron microscopy （TEM）. Magnetic properties of MnFe2O4 nanocrystals with different morphologies were measured using a superconducting quantum interference device （SQUID）. Both monodisperse MnFe204 nanocrystals with spherical and triangle-shapes are superparamagnetic at room temperature while ferromagnetic at 2 K. The pyrolysis method may provide an effective route to synthesize other spinel ferrites or metal oxides nanocrystals.
基金financially supported by the National Program on Key Basic Research Project(2018YFA0305604 and 2017YFA0303302)National Natural Science Foundation of China(11774008,381/0401210001)+2 种基金the Key Research Program of the Chinese Academy of Sciences(XDPB08-2)the Open Research Fund Program of the State Key Laboratory of Low-Dimensional Quantum Physics,Tsinghua University(KF201703)China Postdoctoral Science Foundation(130/0401130005)
文摘Topological materials, hosting topological nontrivial electronic band, have attracted widespread attentions. As an application of topology in physics, the discovery and study of topological materials not only enrich the existing theoretical framework of physics, but also provide fertile ground for investigations on low energy excitations, such as Weyl fermions and Majorana fermions, which have not been observed yet as fundamental particles. These quasiparticles with exotic physical properties make topological materials the cutting edge of scientific research and a new favorite of high tech. As a typical example, Majorana fermions, predicted to exist in the edge state of topological superconductors, are proposed to implement topological error-tolerant quantum computers. Thus, the detection of topological superconductivity has become a frontier in condensed matter physics and materials science. Here, we review a way to detect topological superconductivity triggered by the hard point contact: tip-induced superconductivity(TISC) and tip-enhanced superconductivity(TESC). The TISC refers to the superconductivity induced by a non-superconducting tip at the point contact on non-superconducting materials. We take the elaboration of the chief experimental achievement of TISC in topological Dirac semimetal Cd_3As_2 and Weyl semimetal Ta As as key components of this article for detecting topological superconductivity. Moreover, we also briefly introduce the main results of another exotic effect, TESC, in superconducting Au_2Pb and Sr_2RuO_4 single crystals, which are respectively proposed as the candidates of helical topological superconductor and chiral topological superconductor. Related results and the potential mechanism are conducive to improving the comprehension of how to induce and enhance the topological superconductivity.
基金supported by the National Natural Science Foundation of China (Grant No. 60874101)
文摘Three electrodeposited Fe-Ni,Fe-Co,and Fe-Ni-Co cores of thin film transformer are prepared on silicon(100) substrates,which are sputtered a 90 nm thick film of Cu acting as the seed layer.The core films consisting of Fe-Ni 20:80,Fe-Co 60:40 and Fe-Ni-Co 10:60:30,respectively,are deposited using direct current electrodeposition.The surface texture,electrical and magnetic properties are surveyed by scanning electron microscopy(SEM),superconducting quantum interference device(SQUID),etc.The wave transmission ability and efficiency of thin film transformer with these cores,inputting the sine wave,are compared.All the analyses indicate that FeNi alloy films display the optimal magnetic properties and excellent transformer performance.
基金Young-Wan Kwon would like to express his gratitude to the Korean National Foundation for the support (2010-0013225)
文摘We prepared the DNA-cetyltrimethyl ammonium complex, as well as the same complex intercalated with stable organic free radicals, and studied their magnetic properties by electron magnetic resonance (EMR) spectroscopy and by measuring the magnetization on a superconducting quantum interference device (SQUID). The UV-vis and CD spectra of DNA-quaternary alkyl ammonium complex (DNA--Q+) in organic solvent clearly demonstrated that it retained the double helical B-form conformation. The interhelical spacing of double strand DNA (dsDNA) increased when the counter ions (Na+) of phosphate groups of the natural DNA were replaced with the long alkyl quaternary ammonium groups. The inter-helical distance of DNA-cetyltrimethyl ammonium (CTMA) was 39.1 as confirmed by X-ray diffractometry. In general, the magnetization of the DNA-CTMA complex solid was found to be significantly lower than that of natural DNA. Moreover, intercalation of the complex with stable organic free radicals did not improve magnetization, which again was in marked contrast to natural DNA. EMR spectroscopic behavior of the complex in the solid state also was quite different from that of natural DNA: The unique broad EMR signal of natural DNA in the low field region with g-value greater than 10 disappeared in the DNA-CTMA complex.
