We report the synthesis and characterization of a Si-based ternary semiconductor Mg_(3)Si_(2)Te_(6),which exhibits a quasitwo-dimensional structure,where the trigonal Mg_(3)Si_(2)Te_(6)layers are separated by Mg ions....We report the synthesis and characterization of a Si-based ternary semiconductor Mg_(3)Si_(2)Te_(6),which exhibits a quasitwo-dimensional structure,where the trigonal Mg_(3)Si_(2)Te_(6)layers are separated by Mg ions.Ultraviolet-visible absorption spectroscopy and density functional theory calculations were performed to investigate the electronic structure.The experimentally determined direct band gap is 1.39 eV,consistent with the value of the density function theory calculations.Our results reveal that Mg_(3)Si_(2)Te_(6)is a direct gap semiconductor,which is a potential candidate for near-infrared optoelectronic devices.展开更多
Superconductivity has been realized in films of La_(1-x)Sr_(x)NiO_(2). Here we report synthesis and characterization of polycrystalline samples of La_(1-x)Sr_(x)NiO_(3) and La_(1-x) Sr_(x)NiO_(2)(0 ≤ x ≤ 0.2). Magne...Superconductivity has been realized in films of La_(1-x)Sr_(x)NiO_(2). Here we report synthesis and characterization of polycrystalline samples of La_(1-x)Sr_(x)NiO_(3) and La_(1-x) Sr_(x)NiO_(2)(0 ≤ x ≤ 0.2). Magnetization and resistivity measurements reveal that La_(1-x)Sr_(x)NiO_(3) are paramagnetic metal and La_(1-x)Sr_(x)NiO_(2) exhibit an insulating behavior. Superconductivity is not detected in bulk samples of La_(1-x)Sr_(x)NiO_(2). The absence of superconductivity in bulk La_(1-x)Sr_(x)NiO_(2) may be due to the generation of hydroxide during reduction, a small amount of nickel impurity, or incomplete reduction of apical oxygen.The effect of interface in films of La_(1-x)Sr_(x)NiO_(2) may also play a role for superconductivity.展开更多
Charge and spin orders are intimately related to superconductivity in copper oxide superconductors.Elucidation of the competing orders in various nickel oxide compounds is crucial,given the fact that superconductivity...Charge and spin orders are intimately related to superconductivity in copper oxide superconductors.Elucidation of the competing orders in various nickel oxide compounds is crucial,given the fact that superconductivity has been discovered in Nd_(0.8)Sr_(0.2)NiO_(2)films.Herein,we report structural,electronic transport,magnetic,and thermodynamic characterizations of single crystals of La_(3)Ni_(2)O_(7)and La_(3)Ni_(2)O_(6).La_(3)Ni_(2)O_(7)is metallic with mixed Ni^(2+)and Ni^(3+)valent states.Resistivity measurements yield two transition-like kinks at~110 and 153 K.The kink at 153 K is further revealed from magnetization and specific heat measurements,indicative of the formation of charge and spin density waves.La_(3)Ni_(2)O_(6)single crystals obtained from the topochemical reduction of La_(3)Ni_(2)O_(7)are insulating and show an anomaly at~176 K on magnetic susceptibility.The transition-like behaviors of La_(3)Ni_(2)O_(7)and La_(3)Ni_(2)O_(6)are analogous to those observed in La_(4)Ni_(3)O_(10) and La_(4)Ni_(3)O_(8),suggesting that charge and spin density waves are a common feature in the ternary La-Ni-O system with mixed-valent states of nickel.展开更多
We report a comprehensive high-pressure study,up to 21.1 GPa,on the antiferromagnetic topological insulator EuSn_(2)As_(2) achieved through synchrotron X-ray diffraction,Raman scattering,electrical resistance,magnetic...We report a comprehensive high-pressure study,up to 21.1 GPa,on the antiferromagnetic topological insulator EuSn_(2)As_(2) achieved through synchrotron X-ray diffraction,Raman scattering,electrical resistance,magnetic resistance,and Hall transport measurements in combination with first-principles calculations.The Néel temperatures determined from resistance are increased from(24±1)to(77±8)K under pressure,which is a result of enhanced magnetic exchange couplings between Eu^(2+) ions yielded by our first-principles calculations.The negative magnetoresistance of EuSn_(2)As_(2) persists to higher temperatures accordingly.However,the enhancement of the observed Néel temperatures deviates from the calculations above 10.0 GPa.In addition,the magnitude of the magnetoresistance,Hall coefficients,and charge carrier densities show abrupt changes between 6.9 and 10.0 GPa.The abrupt changes likely originate from a pressure-induced valence change of Eu ions from a divalent state to a divalent and trivalent mixed state or are related to the structural transition revealed by Raman scattering measurements.Our results provide insight into magnetism variation in EuSn_(2)As_(2) and similar antiferromagnetic topological insulators under pressure.展开更多
基金the National Natural Science Foundation of China(Grant Nos.12174454,11904414,11904416,and 12104427)the Guangdong Basic and Applied Basic Research Foundation,China(Grant No.2021B1515120015)+1 种基金the Guangzhou Basic and Applied Basic Research Foundation(Grant No.202201011123)the National Key Research and Development Program of China(Grant No.2019YFA0705702).
文摘We report the synthesis and characterization of a Si-based ternary semiconductor Mg_(3)Si_(2)Te_(6),which exhibits a quasitwo-dimensional structure,where the trigonal Mg_(3)Si_(2)Te_(6)layers are separated by Mg ions.Ultraviolet-visible absorption spectroscopy and density functional theory calculations were performed to investigate the electronic structure.The experimentally determined direct band gap is 1.39 eV,consistent with the value of the density function theory calculations.Our results reveal that Mg_(3)Si_(2)Te_(6)is a direct gap semiconductor,which is a potential candidate for near-infrared optoelectronic devices.
基金supported by the National Natural Science Foundation of China (Grant Nos. 12174454, 11904414, 11904416, and U2130101)the Guangdong Basic and Applied Basic Research Foundation (Grant No. 2021B1515120015)+1 种基金the Guangzhou Basic and Applied Basic Research Foundation (Grant No. 202201011123)the National Key Research and Development Program of China (Grant No. 2019YFA0705702)。
文摘Superconductivity has been realized in films of La_(1-x)Sr_(x)NiO_(2). Here we report synthesis and characterization of polycrystalline samples of La_(1-x)Sr_(x)NiO_(3) and La_(1-x) Sr_(x)NiO_(2)(0 ≤ x ≤ 0.2). Magnetization and resistivity measurements reveal that La_(1-x)Sr_(x)NiO_(3) are paramagnetic metal and La_(1-x)Sr_(x)NiO_(2) exhibit an insulating behavior. Superconductivity is not detected in bulk samples of La_(1-x)Sr_(x)NiO_(2). The absence of superconductivity in bulk La_(1-x)Sr_(x)NiO_(2) may be due to the generation of hydroxide during reduction, a small amount of nickel impurity, or incomplete reduction of apical oxygen.The effect of interface in films of La_(1-x)Sr_(x)NiO_(2) may also play a role for superconductivity.
基金supported by the National Natural Science Foundation of China(Grant Nos.12174454,11904414,11904416,and U2130101)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2021B1515120015)+1 种基金the Guangzhou Basic and Applied Basic Research Foundation(Grant No.202201011123)the National Key Research and Development Program of China(Grant Nos.2019YFA0705702,2020YFA0406003,2021YFA1400401,and 2021YFA0718900)。
文摘Charge and spin orders are intimately related to superconductivity in copper oxide superconductors.Elucidation of the competing orders in various nickel oxide compounds is crucial,given the fact that superconductivity has been discovered in Nd_(0.8)Sr_(0.2)NiO_(2)films.Herein,we report structural,electronic transport,magnetic,and thermodynamic characterizations of single crystals of La_(3)Ni_(2)O_(7)and La_(3)Ni_(2)O_(6).La_(3)Ni_(2)O_(7)is metallic with mixed Ni^(2+)and Ni^(3+)valent states.Resistivity measurements yield two transition-like kinks at~110 and 153 K.The kink at 153 K is further revealed from magnetization and specific heat measurements,indicative of the formation of charge and spin density waves.La_(3)Ni_(2)O_(6)single crystals obtained from the topochemical reduction of La_(3)Ni_(2)O_(7)are insulating and show an anomaly at~176 K on magnetic susceptibility.The transition-like behaviors of La_(3)Ni_(2)O_(7)and La_(3)Ni_(2)O_(6)are analogous to those observed in La_(4)Ni_(3)O_(10) and La_(4)Ni_(3)O_(8),suggesting that charge and spin density waves are a common feature in the ternary La-Ni-O system with mixed-valent states of nickel.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.11904414,11904416,11574404,11974432,and 12174454)National Key Research and Development Program of China(Grant Nos.2019YFA0705702,2018YFA0306001,and 2017YFA0206203)+3 种基金Guangdong Basic and Applied Basic Research Fund(Grant No.2019A1515011337)Fundamental Research Funds for the Central Universities(Grant No.18lgpy73)Key-Area Research and Development Program of Guangdong Province(Grant No.2019B030330001)Science and Technology Projects in Guangzhou(Grant No.202102080361).
文摘We report a comprehensive high-pressure study,up to 21.1 GPa,on the antiferromagnetic topological insulator EuSn_(2)As_(2) achieved through synchrotron X-ray diffraction,Raman scattering,electrical resistance,magnetic resistance,and Hall transport measurements in combination with first-principles calculations.The Néel temperatures determined from resistance are increased from(24±1)to(77±8)K under pressure,which is a result of enhanced magnetic exchange couplings between Eu^(2+) ions yielded by our first-principles calculations.The negative magnetoresistance of EuSn_(2)As_(2) persists to higher temperatures accordingly.However,the enhancement of the observed Néel temperatures deviates from the calculations above 10.0 GPa.In addition,the magnitude of the magnetoresistance,Hall coefficients,and charge carrier densities show abrupt changes between 6.9 and 10.0 GPa.The abrupt changes likely originate from a pressure-induced valence change of Eu ions from a divalent state to a divalent and trivalent mixed state or are related to the structural transition revealed by Raman scattering measurements.Our results provide insight into magnetism variation in EuSn_(2)As_(2) and similar antiferromagnetic topological insulators under pressure.