摘要 :
By combining experimental measurements of the quasiparticle and dynamical magnetic properties of optimally electron-doped Pr_(0.88)LaCe_(0.12)CuO_4 with theoretical calculations, we demonstrate that the conventional fermiology app...
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By combining experimental measurements of the quasiparticle and dynamical magnetic properties of optimally electron-doped Pr_(0.88)LaCe_(0.12)CuO_4 with theoretical calculations, we demonstrate that the conventional fermiology approach cannot possibly account for the magnetic fluctuations in these materials. In particular, we perform tunneling experiments on the very same sample for which a dynamical magnetic resonance has been reported recently and use photoemission data by others on a similar sample to characterize the fermionic quasiparticle excitations in great detail. We subsequently use this information to calculate the magnetic response within the conventional fermiology framework as applied in a large body of work for the hole-doped superconductors to find a profound disagreement between the theoretical expectations and the measurements: this approach predicts a steplike feature rather than a sharp resonance peak, it underestimates the intensity of the resonance by an order of magnitude, it suggests an unreasonable temperature dependence of the resonance, and most severely, it predicts that most of the spectral weight resides in incommensurate wings which are a key feature of the hole-doped cuprates but have never been observed in the electron-doped counterparts. Our findings strongly suggest that the magnetic fluctuations reflect the quantum-mechanical competition between antiferromagnetic and superconducting orders.
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We use bulk magnetic susceptibility, electronic specific heat, and neutron scattering to study structural and magnetic phase transitions in Fe_(1+y)Se_xTe_(1-x)Fe_(1.068)Te exhibits a first-order phase transition near 67 K with a ...
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We use bulk magnetic susceptibility, electronic specific heat, and neutron scattering to study structural and magnetic phase transitions in Fe_(1+y)Se_xTe_(1-x)Fe_(1.068)Te exhibits a first-order phase transition near 67 K with a tetragonal-to-monoclinic structural transition and simultaneously develops a collinear antiferromagnetic (AF) order responsible for the entropy change across the transition. Systematic studies of the FeSe_(1-x)Te_x. system reveal that the AF structure and lattice distortion in these materials are different from those of FeAs-based pnictides. These results call into question the conclusions of present density-functional calculations, where FeSe_(1-x)Te_x and Fe As-based pnictides are expected to have similar Fermi surfaces and therefore the same spin-density wave AF order.
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We use neutron scattering to study the Pr~(3+) crystalline electric field (CEF) excitations in the filled skutteru-dite PrOs_4As_(12). By comparing the observed levels and their strengths under neutron excitation with the theoreti...
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We use neutron scattering to study the Pr~(3+) crystalline electric field (CEF) excitations in the filled skutteru-dite PrOs_4As_(12). By comparing the observed levels and their strengths under neutron excitation with the theoretical spectruniand neutron
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Recently, high-transition-temperature (high-T_c) superconductivity was discovered in the iron pnictide RFeAsO_(1-x)F_x (R, rare-earth metal) family of materials. We use neutron scattering to study the structural and magnetic phase...
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Recently, high-transition-temperature (high-T_c) superconductivity was discovered in the iron pnictide RFeAsO_(1-x)F_x (R, rare-earth metal) family of materials. We use neutron scattering to study the structural and magnetic phase transitions in CeFeAsO_(1-x)F_x as the system is tuned from a semimetal to a high-T_c superconductor through fluorine (F) doping, x. In the undoped state, CeFeAsO develops a structural lattice distortion followed by a collinear antiferromagnetic order with decreasing temperature. With increasing fluorine doping, the structural phase transition decreases gradually and vanishes within the superconductivity dome near x = 0.10, whereas the antiferromagnetic order is suppressed before the appearance of superconductivity for x > 0.06, resulting in an electronic phase diagram remarkably similar to that of the high-T_c copper oxides. Comparison of the structural evolution of CeFeAsO_(1-x)F_x with other Fe-based superconductors suggests that the structural perfection of the Fe-As tetrahedron is important for the high-T_c superconductivity in these Fe pnictides.
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We use neutron scattering to study the structural distortion and antiferromagnetic (AFM) order in LaFeAsO_(1-x)F_x as the system is doped with fluorine (F) to induce superconductivity. In the undoped state, LaFeAsO exhibits a stru...
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We use neutron scattering to study the structural distortion and antiferromagnetic (AFM) order in LaFeAsO_(1-x)F_x as the system is doped with fluorine (F) to induce superconductivity. In the undoped state, LaFeAsO exhibits a structural distortion, changing the symmetry from tetragonal (space group PAInmm) to orthorhombic (space group Cmma) at 155 K, and then followed by an AFM order at 137 K. Doping the system with F gradually decreases the structural distortion temperature, but suppresses the long range AFM order before the emergence of superconductivity. Therefore, while superconductivity in these Fe oxypnictides can survive in either the tetragonal or the orthorhombic crystal structure, it competes directly with static AFM order.
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Zero-field (ZF) muon-spin-relaxation (μSR) measurements have revealed static commensurate magnetic order of Fe moments in NdFeAsO below T_N～ 135 K, with the ordered moment size nearly equal to that in LaFeAsO, and confirmed simi...
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Zero-field (ZF) muon-spin-relaxation (μSR) measurements have revealed static commensurate magnetic order of Fe moments in NdFeAsO below T_N～ 135 K, with the ordered moment size nearly equal to that in LaFeAsO, and confirmed similar behavior in BaFe_2As_2, In single crystals of superconducting Ba_(0.55)K_(0.45)Fe_2As_2, μSR spectra indicate static magnetism with incommensurate or short-ranged spin structure in ～70% of volume below T_N～80 K, coexisting with the remaining volume which exhibits a superfluid response below T_c～30 K.
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We report the study of temperature- and magnetic-field dependent in-plane tunneling conductance on the electron-doped Nd_(1. 85)Ce_(0.15)CuO_(4-y). and Pr_(1-x)LaCe_xCuO(4-y) single crystals. The previously reported normal state g...
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We report the study of temperature- and magnetic-field dependent in-plane tunneling conductance on the electron-doped Nd_(1. 85)Ce_(0.15)CuO_(4-y). and Pr_(1-x)LaCe_xCuO(4-y) single crystals. The previously reported normal state gap (NSG) Δ_(ps) and superconducting gap Δ_(sc) were observed simultaneously in superconducting state. Combined with an investigation on the evolution of low-energy spectral weight with temperature, our data present evidence for electron-doped cuprates that Δ_(ps)and Δ_(sc) are most possibly two different energy scales with very different field dependencies, and that superconductivity is condensed from the residual quasiparticle density of states (DOS) of the NSG state.
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Polarized and unpolarized neutron-diffraction measurements have been carried out to investigate the iron magnetic order in undoped NdFeAsO. Antiferromagnetic order is observed below 141(6) K, which is in close proximity to the str...
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Polarized and unpolarized neutron-diffraction measurements have been carried out to investigate the iron magnetic order in undoped NdFeAsO. Antiferromagnetic order is observed below 141(6) K, which is in close proximity to the structural distortion observed in this material. The magnetic structure consists of chains of parallel spins that are arranged antiparallel between chains, which is the same in-plane spin arrangement as observed in all the other iron oxypnictide materials. Nearest-neighbor spins along the c axis are antiparallel like LaFeAsO. The ordered moment is 0.25(7) μ_B, which is the smallest moment found so far in these systems.
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We use thermodynamic and neutron-scattering measurements to study the effect of oxygen annealing on the superconductivity and magnetism in Pr_(0.88)LaCe_(0.12)CuO(4-δ). Although the transition temperature T_c measured by suscepti...
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We use thermodynamic and neutron-scattering measurements to study the effect of oxygen annealing on the superconductivity and magnetism in Pr_(0.88)LaCe_(0.12)CuO(4-δ). Although the transition temperature T_c measured by susceptibility and superconducting coherence length increases smoothly with gradual oxygen removal from the annealing process, bulk superconductivity, marked by a specific-heat anomaly at T_c and the presence of a neutron magnetic resonance, only appears abruptly when T_c is close to the largest value. These results suggest that the effect of oxygen annealing must first be determined in order to establish a Ce doping dependence of antiferromagnetism and superconductivity phase diagram for electron-doped copper oxides.
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The quantum spin fluctuations of the S = 1/2 Cu ions are important in determining the physical properties of high-transition-temperature (high T_c) copper oxide superconductors, but their possible role in the electron pairing of s...
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The quantum spin fluctuations of the S = 1/2 Cu ions are important in determining the physical properties of high-transition-temperature (high T_c) copper oxide superconductors, but their possible role in the electron pairing of superconductivity remains an open question. The principal feature of the spin fluctuations in optimally doped high-T_c superconductors is a well defined magnetic resonance whose energy (E_R) tracks T_c (as the composition is varied) and whose intensity develops like an order parameter in the superconducting state. We show that the suppression of superconductivity and its associated condensation energy by a magnetic field in the electron-doped high-T_c superconductor Pr_(0.88)LaCe_(0.12)CuO_(4-δ) (T_c = 24 K), is accompanied by the complete suppression of the resonance and the concomitant emergence of static antiferromag-netic order. Our results demonstrate that the resonance is intimately related to the superconducting condensation energy, and thus suggest that it plays a role in the electron pairing and superconductivity.
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