We develop a tractable theoretical model to investigate the thermoelectric （TE） transport properties of surface states in topological insulator thin films （TITFs） of Bi2Sea at room temperature. The hybridization b...We develop a tractable theoretical model to investigate the thermoelectric （TE） transport properties of surface states in topological insulator thin films （TITFs） of Bi2Sea at room temperature. The hybridization between top and bottom surface states in the TITF plays a significant role. With the increasing hybridization-induced surface gap, the electrical conductivity and electron thermal conductivity decrease while the Seebeck coefficient increases. This is due to the metal-semiconductor transition induced by the surface-state hybridization. Based on these TE transport coefficients, the TE figure-of-merit ZT is evaluated. It is shown that ZT can be greatly improved by the surface-state hybridization. Our theoretical results are pertinent to the exploration of the TE transport properties of surface states in TITFs and to the potential application of Bi2Sea-based TITFs as high-performance TE materials and devices.展开更多
From heavy fermion compounds and cuprates to iron pnictides and chalcogenides, a spin resonance at hΩ0 ∝ kBTc is a staple of nearly magnetic superconductors. Possible explanations include a two-particle bound state ...From heavy fermion compounds and cuprates to iron pnictides and chalcogenides, a spin resonance at hΩ0 ∝ kBTc is a staple of nearly magnetic superconductors. Possible explanations include a two-particle bound state or loss of magnon damping in the superconducting state. While both scenarios suggest a central role for magnetic fluctuations,distinguishing them is important to identify the right theoretical framework to understand these types of unconventional superconductors. Using an inelastic neutron scattering technique,we show that the spin resonance in the optimally doped Fe1.03 Se0.4 Te0.6 superconductor splits into three peaks in a high magnetic field,a signature of a two-particle S = 1 triplet bound state.展开更多
The iron-based nontoxic chalcogenide superconductor Fe(Te,Se)has great potential for high magnetic field applications while it lacks a reliable method to produce bulk superconductor so far.Here we report a one-step sy...The iron-based nontoxic chalcogenide superconductor Fe(Te,Se)has great potential for high magnetic field applications while it lacks a reliable method to produce bulk superconductor so far.Here we report a one-step synthesis method to grow high-quality Fe(Te,Se)single crystals free of interstitial iron atoms through minor Mn doping.Bulk superconductivity is revealed in the as-grown centimetersized crystals with the optimal doping level of 1% Fe atoms substituted by Mn,which is systematically demonstrated by sharp electrical resistivity and magnetic susceptibility transitions,and large specific heat jumps.Compared with the undoped sample,the optimally doped one shows a significantly enhanced upper critical field,and a large self-field critical current density J_(c) of 4.5×10^(5)A cm^(-2) at 2 K(calculated by the Bean model),which maintains large values under high fields.The absence of interstitial iron atoms is testified by the scanning tunneling microscopy,and the effect of Mn doping is discussed.Our results provide a practical method by minor Mn doping to directly synthesize high-performance Fe(Te,Se)bulks that allow for future high-field superconducting applications.展开更多
Iron-chalcogenide compounds with FeSe（Te, S） layers did not attract much attention until the discovery of high-Tc superconductivity （SC） in the iron-pnictide compounds at the begining of 2008. Compared with FeAs-b...Iron-chalcogenide compounds with FeSe（Te, S） layers did not attract much attention until the discovery of high-Tc superconductivity （SC） in the iron-pnictide compounds at the begining of 2008. Compared with FeAs-based superconductors, iron-chalcogenide superconductors have aroused enormous enthusiasm to study the relationship between SC and magnetisms with several distinct features, such as different antiferromagnetic ground states with relatively large moments in the parents, indicating possibly different superconducting mechanisms, the existence of the excess Fe atoms or Fe vacancies in the crystal lattice. Another reason is that the large single crystals are easily grown for the iron-chalcogenide compounds. This review will focus on our exploration for the iron-chalcogenide superconductors and discussion on several issues, including the crystal structure, magnetic properties, superconductivity, and phase separation. Some of them reach a consensus but some important questions still remain to be answered.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 11304316the Ministry of Science and Technology of China under Grant No 2011YQ130018the Department of Science and Technology of Yunnan Province,and the Chinese Academy of Sciences
文摘We develop a tractable theoretical model to investigate the thermoelectric （TE） transport properties of surface states in topological insulator thin films （TITFs） of Bi2Sea at room temperature. The hybridization between top and bottom surface states in the TITF plays a significant role. With the increasing hybridization-induced surface gap, the electrical conductivity and electron thermal conductivity decrease while the Seebeck coefficient increases. This is due to the metal-semiconductor transition induced by the surface-state hybridization. Based on these TE transport coefficients, the TE figure-of-merit ZT is evaluated. It is shown that ZT can be greatly improved by the surface-state hybridization. Our theoretical results are pertinent to the exploration of the TE transport properties of surface states in TITFs and to the potential application of Bi2Sea-based TITFs as high-performance TE materials and devices.
基金Supported by the National Basic Research Program of China under Grant Nos 2012CB921700 and 2011CBA00112the National Natural Science Foundation of China under Grant Nos 11034012 and 11190024+1 种基金the National Science Foundation under Grant No DMR-0645305,the US DOE under Grant No DE-FG02-07ER46358the US Department of Energy,Office of Science,Office of Basic Energy Sciences under Grant No DE-AC05-00OR22725
文摘From heavy fermion compounds and cuprates to iron pnictides and chalcogenides, a spin resonance at hΩ0 ∝ kBTc is a staple of nearly magnetic superconductors. Possible explanations include a two-particle bound state or loss of magnon damping in the superconducting state. While both scenarios suggest a central role for magnetic fluctuations,distinguishing them is important to identify the right theoretical framework to understand these types of unconventional superconductors. Using an inelastic neutron scattering technique,we show that the spin resonance in the optimally doped Fe1.03 Se0.4 Te0.6 superconductor splits into three peaks in a high magnetic field,a signature of a two-particle S = 1 triplet bound state.
基金supported by the National Key Research and Development Program of China(2018YFA0704200,2017YFA0302904,2019YFA0308500,and 2018YFA0305602)the National Natural Science Foundation of China(12074414,12074002,52072401,11804379,and 11774402)+1 种基金the Recruitment Program for Leading Talent Team of Anhui Province(2019-16)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB25000000)。
文摘The iron-based nontoxic chalcogenide superconductor Fe(Te,Se)has great potential for high magnetic field applications while it lacks a reliable method to produce bulk superconductor so far.Here we report a one-step synthesis method to grow high-quality Fe(Te,Se)single crystals free of interstitial iron atoms through minor Mn doping.Bulk superconductivity is revealed in the as-grown centimetersized crystals with the optimal doping level of 1% Fe atoms substituted by Mn,which is systematically demonstrated by sharp electrical resistivity and magnetic susceptibility transitions,and large specific heat jumps.Compared with the undoped sample,the optimally doped one shows a significantly enhanced upper critical field,and a large self-field critical current density J_(c) of 4.5×10^(5)A cm^(-2) at 2 K(calculated by the Bean model),which maintains large values under high fields.The absence of interstitial iron atoms is testified by the scanning tunneling microscopy,and the effect of Mn doping is discussed.Our results provide a practical method by minor Mn doping to directly synthesize high-performance Fe(Te,Se)bulks that allow for future high-field superconducting applications.
基金supported by the National Basic Research Program of China(Grant Nos.2011CBA00103,2012CB821404,and 2009CB929104)the National Natural Science Foundation of China(Grant Nos.10974175,10934005,and 11204059)+1 种基金the Natural Science Foundation of Zhejiang Province,China(Grant No.Q12A040038)the Fundamental Research Funds for the Central Universities of China
文摘Iron-chalcogenide compounds with FeSe（Te, S） layers did not attract much attention until the discovery of high-Tc superconductivity （SC） in the iron-pnictide compounds at the begining of 2008. Compared with FeAs-based superconductors, iron-chalcogenide superconductors have aroused enormous enthusiasm to study the relationship between SC and magnetisms with several distinct features, such as different antiferromagnetic ground states with relatively large moments in the parents, indicating possibly different superconducting mechanisms, the existence of the excess Fe atoms or Fe vacancies in the crystal lattice. Another reason is that the large single crystals are easily grown for the iron-chalcogenide compounds. This review will focus on our exploration for the iron-chalcogenide superconductors and discussion on several issues, including the crystal structure, magnetic properties, superconductivity, and phase separation. Some of them reach a consensus but some important questions still remain to be answered.
