The correlations between stripe order, superconductivity, and crystal structure in La2−x Bax CuO4 single crystals have been studied by means of x-ray and neutron diffraction as well as static magnetization measurements. The derived phase diagram shows that charge stripe order (CO) coexists with bulk superconductivity in a broad range of doping around x = 1/8, although the CO order parameter falls off quickly for x = 1/8. Except for x = 0.155, the onset of CO always coincides with the transition between the orthorhombic and the tetragonal low temperature structures. The CO transition evolves from a sharp drop at low x to a more gradual transition at higher x, eventually falling below the structural phase boundary for optimum doping. With respect to the interlayer CO correlations, we find no qualitative change of the stripe stacking order as a function of doping, and in-plane and out-of-plane correlations disappear simultaneously at the transition. Similarly to the CO, the spin stripe order (SO) is also most pronounced at x = 1/8. Truly static SO sets in below the CO and coincides with the first appearance of in-plane superconducting correlations at temperatures significantly above the bulk transition to superconductivity (SC). Indications that bulk SC causes a reduction of the spin or charge stripe order could not be identified. We argue that CO is the dominant order that is compatible with SC pairing but competes with SC phase coherence. Comparing our results with data from the literature, we find good agreement if all results are plotted as a function of x ′ instead of the nominal x, where x ′ represents an estimate of the actual Ba content, extracted from the doping dependence of the structural transition between the orthorhombic phase and the tetragonal high-temperature phase.

Neutron scattering is used to probe antiferromagnetic spin fluctuations in the d-wave heavy fermion superconductor CeCoIn5 (T_(c)=2.3 K). Superconductivity develops from a state with slow (variant Planck's over 2piGamma=0.3+/-0.15 meV) commensurate [Q_(0)=(1/2,1/2,1/2)] antiferromagnetic spin fluctuations and nearly isotropic spin correlations. The characteristic wave vector in CeCoIn5 is the same as CeIn3 but differs from the incommensurate wave vector measured in antiferromagnetically ordered CeRhIn5. A sharp spin resonance (variant Planck's over 2piGamma<0.07 meV) at variant Planck's over 2piomega=0.60+/-0.03 meV develops in the superconducting state removing spectral weight from low-energy transfers. The presence of a resonance peak is indicative of strong coupling between f-electron magnetism and superconductivity and consistent with a d-wave gap order parameter satisfying Delta(q+Q0)=-Delta(q).

Herein, we report the synthesis of multiscale nanostructured p-type (Bi,Sb)(2)Te(3) bulk materials by melt-spinning single elements of Bi, Sb, and Te followed by a spark plasma sintering process. The samples that were most optimized with the resulting composition (Bi(0.48)Sb(1.52)Te(3)) and specific nanostructures showed an increase of approximately 50% or more in the figure of merit, ZT, over that of the commercial bulk material between 280 and 475 K, making it suitable for commercial applications related to both power generation and refrigeration. The results of high-resolution electron microscopy and small angle and inelastic neutron scattering along with corresponding thermoelectric property measurements corroborate that the 10-20 nm nanocrystalline domains with coherent boundaries are the key constituent that accounts for the resulting exceptionally low lattice thermal conductivity and significant improvement of ZT.

In conventional superconductors, the interaction that pairs the electrons to form the superconducting state is mediated by lattice vibrations (phonons) 1 . In hightransition temperature (high-T c ) copper oxides, it is generally believed that magnetic excitations play a fundamental role in the superconducting mechanism because superconductivity occurs when mobile 'electrons' or 'holes' are doped into the antiferromagnetic parent compounds 2 . Indeed, a sharp magnetic excitation termed "resonance" has been observed by neutron scattering in a number of hole-doped materials 3-11 . The resonance is intimately related to superconductivity 12 , and its interaction with charged quasi-particles observed by photoemission 13,14 , optical conductivity 15 , and tunneling 16 suggests that it plays a similar role as phonons in conventional superconductors. However, the relevance of the resonance to high-T c superconductivity has been in doubt because so far it has been found only in holedoped materials 17 . Here we report the discovery of the resonance in electron-doped superconducting Pr 0.88 LaCe 0.12 CuO 4-δ (T c = 24 K). We find that the resonance energy (E r ) is proportional to T c via E r = 5.8k B T c (k B is the Boltzmann's constant) for all high-T c superconductors irrespective of electron-or hole-doping (Fig. 1e). Our results demonstrate that the resonance is a fundamental property of the superconducting copper oxides and therefore must play an essential role in the mechanism of superconductivity.Although the interaction of electrons with phonons or magnetic excitations can cause electron pairing and superconductivity, we focus on magnetic excitations because the resonance is intimated related to superconductivity and also present in several classes of hole-doped high-T c materials. The resonance is a sharp magnetic excitation centered at the wavevector Q = (1/2, 1/2) in the two-dimensional reciprocal space of the CuO 2 planes, which corresponds to the antiferromagnetic (AF) Bragg position of the undoped compounds (Fig. 1a). It was first discovered in the hole-doped bilayer (each lattice unit cell has two CuO 2 planes) high-T c superconductor YBa 2 Cu 3 O 6+x (YBCO) 3 . Its intensity grows below T c and its energy ( ω) scales approximately with k B T c (Fig. 1e) We first probe the low-energy magnetic excitations of PLCCO using the SPINS cold neutron triple-axis spectrometer. The magnetic excitations are commensurate and The energy scans at Q = (1/2, 1/2, 0) confirm that the magnetic scattering between 0.5 meV and 4.5 meV is virtually temperature independent between 2 K and 30 K ( 2), the integrated intensity above background around (1/2, 1/2, 0) at ω = 8 and 10 meV shows a significant enhancement on cooling from 30 K to 2 K, but hardly changes on warming from 30 K to 80 K (Fig. 4d). The Q-width of the peak at ω = 10 meV is temperature independent and resolution-limited, giving a minimum ξ 45 ± 5 Å ( Fig. 3c). Similar scans using better collimations on BT-9 ( Figure 4a shows the energy dependence of the scattering...

We present new x-ray and neutron-scattering measurements of stripe order in La 1.875 Ba 0.125 CuO 4 , along with low-field susceptibility, thermal conductivity, and specific-heat data. We compare these with previously reported results for resistivity and thermopower. Temperature-dependent features indicating transitions ͑or cross-overs͒ are correlated among the various experimental quantities. Taking into account recent spectroscopic studies, we argue that the most likely interpretation of the complete collection of results is that an unusual form of two-dimensional superconducting correlations appears together with the onset of spin-stripe order. Recent theoretical proposals for a sinusoidally modulated superconducting state compatible with stripe order provide an intriguing explanation of our results and motivate further experimental tests. We also discuss evidence for one-dimensional pairing correlations that appear together with the charge order. With regard to the overall phenomenology, we consider the degree to which similar behavior may have been observed in other cuprates and describe possible connections to various puzzling phenomena in cuprate superconductors.

Superconductivity in the high-transition-temperature (high-T(c)) copper oxides competes with other possible ground states. The physical explanation for superconductivity can be constrained by determining the nature of the closest competing ground state, and establishing if that state is universal among the high-T(c) materials. Antiferromagnetism has been theoretically predicted to be the competing ground state. A competing ground state is revealed when superconductivity is destroyed by the application of a magnetic field, and antiferromagnetism has been observed in hole-doped materials under the influence of modest fields. None of the previous experiments have revealed the quantum phase transition from the superconducting state to the antiferromagnetic state, because they failed to reach the upper critical field B(c2). Here we report the results of transport and neutron-scattering experiments on electron-doped Nd1.85Ce0.15CuO4 (refs 13, 14), where B(c2) can be reached. The applied field reveals a static, commensurate, anomalously conducting long-range ordered antiferromagnetic state, in which the induced moment scales approximately linearly with the field strength until it saturates at B(c2). This and previous experiments on the hole-doped materials therefore establishes antiferromagnetic order as a competing ground state in the high-T(c) copper oxide materials, irrespective of electron or hole doping.

The spin-wave excitations of the geometrically frustrated triangular lattice antiferromagnet CuFeO2 have been measured using high resolution inelastic neutron scattering. Antiferromagnetic interactions up to third nearest neighbors in the ab plane (J1, J2, J3, with J{2}/J{1} approximately 0.44 and J{3}/J{1} approximately 0.57), as well as out-of-plane coupling (J{z}, with J{z}/J{1} approximately 0.29) are required to describe the spin-wave dispersion relations, indicating a three-dimensional character of the magnetic interactions. Two energy dips in the spin-wave dispersion occur at the incommensurate wave vectors associated with multiferroic phase and can be interpreted as dynamic precursors to the magnetoelectric behavior in this system.

High-transition-temperature superconductivity arises in copper oxides when holes or electrons are doped into the CuO 2 planes of their insulating parent compounds.While hole-doping quickly induces metallic behavior and superconductivity in many cuprates, electron-doping alone is insufficient in materials such as R 2 CuO 4 (R is Nd, Pr, La, Ce, etc.), where it is necessary to anneal an as-grown sample in a low-oxygen environment to remove a tiny amount of oxygen in order to induce superconductivity. Here we show that the microscopic process of oxygen reduction repairs Cu deficiencies in the as-grown materials and creates oxygen vacancies in the stoichiometric CuO 2 planes, effectively reducing disorder and providing itinerant carriers for superconductivity. The resolution of this long-standing materials issue suggests that the fundamental mechanism for superconductivity is the same for electron-and hole-doped copper oxides.The parent compounds of the high-transition-temperature (high-T c ) copper-oxide superconductors are antiferromagnetic (AF) Mott insulators composed of twodimensional CuO 2 planes separated by charge reservoir layers [1][2][3] . When holes are doped into these planes, the static long-range AF order is quickly destroyed and the lamellar copper-oxide materials become metallic and superconducting over a wide hole-doping range. In the case of electron-doped materials such as the T'-structured R 2 CuO 4 (R is Nd, Pr, La, Ce, etc.), electron-doping alone is insufficient, and annealing the as-grown sample in a low oxygen environment to remove a tiny amount of oxygen is necessary to induce superconductivity 2,3 . Previous work [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] suggests that oxygen reduction may influence mobile carrier concentrations 7 , decrease disorder/impurity scattering 8,10,11,23 , or suppress the long-range AF order 16,17,22 . However, the microscopic process of oxygen reduction, its effect on the large electron-hole phase diagram asymmetry and mechanism of superconductivity 2,3 are still unknown. Here we use x-ray and neutron scattering data, combined with chemical and thermo-gravimetric analysis measurements in the electron-doped Pr 0.88 LaCe 0.12 CuO 4 to show that the microscopic process of oxygen reduction is to repair Cu deficiencies in the as-grown materials 12,13 and to create oxygen vacancies in the stoichiometric CuO 2 (refs. 16,17,22), effectively repairing disorder in the CuO 2 planes and providing itinerant carriers for superconductivity.The role of the reduction process in the superconductivity of electron-doped high-T c copper oxides has been a long-standing unsolved problem. For the hole-doped cuprates, low doping levels (e.g. 5%) entirely suppress AF order and superconductivity appears over a wide range of hole concentrations (from 6% to 30%). In the case of T' structured electron-doped superconductors, doping alone by substituting the trivalent ions R 3+ in R 2 CuO 4 with tetravalent Ce 4+ is insufficient to induce superconductivity a...