The discovered in 2008 Fe-based superconductors (SC) are a paramagnetic semimetal at ambient temperature and in some cases they become superconductor upon doping. In spite of so many years since its discovery it is st...The discovered in 2008 Fe-based superconductors (SC) are a paramagnetic semimetal at ambient temperature and in some cases they become superconductor upon doping. In spite of so many years since its discovery it is still not known the mechanism that leads to superconductivity. The electronic structure study is used for determining key features of the SC mechanism in these materials. The calculations were performed using the modern suite of programs MOLPRO 2021. We performed quantum calculations of a cluster embedded in a background charge distribution that represents the infinite crystal. The Natural Population Analysis was used for determining the charge and spin distribution in the studied materials. As follows from our results, the possible mechanism for superconductivity corresponds to the RVB theory proposed by Anderson for high T<sub>c</sub> superconductivity in cuprates.展开更多
It is a great discovery in physics of the twentieth century that the elementary particles in nature are dictated by gauge forces,characterized by a nonintegrable phase factor that an elementary particle of charge q ac...It is a great discovery in physics of the twentieth century that the elementary particles in nature are dictated by gauge forces,characterized by a nonintegrable phase factor that an elementary particle of charge q acquires from A to B points:P exp(iq/hc∫A^(B)A_(μ)dxμ),where Aμis the gauge potential and P stands for path ordering.In a many-body system of strongly correlated electrons,if the so-called Mott gap is opened up by interaction,the corresponding Hilbert space will be fundamentally changed.A novel nonintegrable phase factor known as phase-string will appear and replace the conventional Fermi statistics to dictate the low-lying physics.Protected by the Mott gap,which is clearly identified in the high-Tc cuprate with a magnitude>1.5 e V,such a singular phase factor can enforce a fractionalization of the electrons,leading to a dual world of exotic elementary particles with a topological gauge structure.A non-Fermi-liquid“parent”state will emerge,in which the gapless Landau quasiparticle is only partially robust around the so-called Fermi arc regions,while the main dynamics are dominated by two types of gapped spinons.Antiferromagnetism,superconductivity,and a Fermi liquid with full Fermi surface can be regarded as the low-temperature instabilities of this new parent state.Both numerics and experiments provide direct evidence for such an emergent physics of the Mottness,which lies in the core of a high-Tc superconducting mechanism.展开更多
In this study, we thoroughly examined the impact of heat treatments and hole count (p) on the properties of LnSrBaCu<sub>3</sub>O<sub>6+z</sub> (Ln = Eu, Sm, Nd) compounds. We focused on prepar...In this study, we thoroughly examined the impact of heat treatments and hole count (p) on the properties of LnSrBaCu<sub>3</sub>O<sub>6+z</sub> (Ln = Eu, Sm, Nd) compounds. We focused on preparation, X-ray diffraction with Rietveld refinement, AC susceptibility, DC resistivity measurements, and heat treatment effects. Two heat treatment types were applied: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. As the rare earth Ln’s ionic radius increased, certain parameters notably changed. Specifically, c parameter, surface area S, and volume V increased, while critical temperature Tc and holes (p) in the CuO<sub>2</sub> plane decreased. The evolution of these parameters with rare earth Ln’s ionic radius in [AO] heat treatment is linear. Regardless of the treatment, the structure is orthorhombic for Ln = Eu, tetragonal for Ln = Nd, orthorhombic for Ln = Sm [AO], and pseudo-tetragonal for Sm [O]. The highest critical temperature is reached with Ln = Eu (Tc [AO] = 87.1 K). Notably, for each sample, Tc [AO] surpasses Tc [O]. Observed data stems from factors including rare earth ionic size, improved cationic and oxygen chain order, holes count p in Cu(2)O<sub>2</sub> planes, and in-phase purity of [AO] samples. Our research strives to clearly demonstrate that the density of holes (p) within the copper plane stands as a determinant impacting the structural, electrical, and superconducting properties of these samples. Meanwhile, the other aforementioned parameters contribute to shaping this density (p).展开更多
The magnetocaloric effect （MCE） in many rare earth （RE） based intermetallic compounds has been extensively in- vestigated during the last two decades, not only due to their potential applications for magnetic refr...The magnetocaloric effect （MCE） in many rare earth （RE） based intermetallic compounds has been extensively in- vestigated during the last two decades, not only due to their potential applications for magnetic refrigeration but also for better understanding of the fundamental problems of the materials. This paper reviews our recent progress on studying the magnetic properties and MCE in some binary or ternary intermetallic compounds of RE with low boiling point metal（s） （Zn, Mg, and Cd）. Some of them exhibit promising MCE properties, which make them attractive for low temperature magnetic refrigeration. Characteristics of the magnetic transition, origin of large MCE, as well as the potential application of these compounds are thoroughly discussed. Additionally, a brief review of the magnetic and magnetocaloric properties in the quaternary rare earth nickel boroncarbides RENi2B2C superconductors is also presented.展开更多
文摘The discovered in 2008 Fe-based superconductors (SC) are a paramagnetic semimetal at ambient temperature and in some cases they become superconductor upon doping. In spite of so many years since its discovery it is still not known the mechanism that leads to superconductivity. The electronic structure study is used for determining key features of the SC mechanism in these materials. The calculations were performed using the modern suite of programs MOLPRO 2021. We performed quantum calculations of a cluster embedded in a background charge distribution that represents the infinite crystal. The Natural Population Analysis was used for determining the charge and spin distribution in the studied materials. As follows from our results, the possible mechanism for superconductivity corresponds to the RVB theory proposed by Anderson for high T<sub>c</sub> superconductivity in cuprates.
基金by the National Key R&D Program of China(Grant No.2017YFA0302902)。
文摘It is a great discovery in physics of the twentieth century that the elementary particles in nature are dictated by gauge forces,characterized by a nonintegrable phase factor that an elementary particle of charge q acquires from A to B points:P exp(iq/hc∫A^(B)A_(μ)dxμ),where Aμis the gauge potential and P stands for path ordering.In a many-body system of strongly correlated electrons,if the so-called Mott gap is opened up by interaction,the corresponding Hilbert space will be fundamentally changed.A novel nonintegrable phase factor known as phase-string will appear and replace the conventional Fermi statistics to dictate the low-lying physics.Protected by the Mott gap,which is clearly identified in the high-Tc cuprate with a magnitude>1.5 e V,such a singular phase factor can enforce a fractionalization of the electrons,leading to a dual world of exotic elementary particles with a topological gauge structure.A non-Fermi-liquid“parent”state will emerge,in which the gapless Landau quasiparticle is only partially robust around the so-called Fermi arc regions,while the main dynamics are dominated by two types of gapped spinons.Antiferromagnetism,superconductivity,and a Fermi liquid with full Fermi surface can be regarded as the low-temperature instabilities of this new parent state.Both numerics and experiments provide direct evidence for such an emergent physics of the Mottness,which lies in the core of a high-Tc superconducting mechanism.
文摘In this study, we thoroughly examined the impact of heat treatments and hole count (p) on the properties of LnSrBaCu<sub>3</sub>O<sub>6+z</sub> (Ln = Eu, Sm, Nd) compounds. We focused on preparation, X-ray diffraction with Rietveld refinement, AC susceptibility, DC resistivity measurements, and heat treatment effects. Two heat treatment types were applied: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. As the rare earth Ln’s ionic radius increased, certain parameters notably changed. Specifically, c parameter, surface area S, and volume V increased, while critical temperature Tc and holes (p) in the CuO<sub>2</sub> plane decreased. The evolution of these parameters with rare earth Ln’s ionic radius in [AO] heat treatment is linear. Regardless of the treatment, the structure is orthorhombic for Ln = Eu, tetragonal for Ln = Nd, orthorhombic for Ln = Sm [AO], and pseudo-tetragonal for Sm [O]. The highest critical temperature is reached with Ln = Eu (Tc [AO] = 87.1 K). Notably, for each sample, Tc [AO] surpasses Tc [O]. Observed data stems from factors including rare earth ionic size, improved cationic and oxygen chain order, holes count p in Cu(2)O<sub>2</sub> planes, and in-phase purity of [AO] samples. Our research strives to clearly demonstrate that the density of holes (p) within the copper plane stands as a determinant impacting the structural, electrical, and superconducting properties of these samples. Meanwhile, the other aforementioned parameters contribute to shaping this density (p).
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11374081 and 11004044)the Fundamental Research Funds for the Central Universities+4 种基金China(Grant Nos.N150905001L1509006and N140901001)the Japan Society for the Promotion of Science Postdoctoral Fellowships for Foreign Researchers(Grant No.P10060)the Alexander von Humboldt(Av H)Foundation(Research stipend to L.Li)
文摘The magnetocaloric effect （MCE） in many rare earth （RE） based intermetallic compounds has been extensively in- vestigated during the last two decades, not only due to their potential applications for magnetic refrigeration but also for better understanding of the fundamental problems of the materials. This paper reviews our recent progress on studying the magnetic properties and MCE in some binary or ternary intermetallic compounds of RE with low boiling point metal（s） （Zn, Mg, and Cd）. Some of them exhibit promising MCE properties, which make them attractive for low temperature magnetic refrigeration. Characteristics of the magnetic transition, origin of large MCE, as well as the potential application of these compounds are thoroughly discussed. Additionally, a brief review of the magnetic and magnetocaloric properties in the quaternary rare earth nickel boroncarbides RENi2B2C superconductors is also presented.
