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Finding ways to achieve higher values of the transition temperature, [T.sub.c], in superconductors remains a great challenge. The super-conducting phase is often one of several competing types of electronic order, including antiferromagnetism and charge density waves (1-5). An emerging trend documented in heavy-fermion (1) and organic (2) conductors is that the maximum [T.sub.c] for superconductivity occurs under external conditions that cause the critical temperature for a competing order to go to zero. Recently, such competition has been found in multilayer copper oxide high-temperature superconductors (HTSCs (3-5)) that possess two crystallographically inequivalent Cu[O.sub.2] planes in the unit cell. However, whether the competing electronic state can be suppressed to enhance [T.sub.c] in HTSCs remains an open question. Here we show that pressure-driven phase competition leads to an unusual two-step enhancement of [T.sub.c] in optimally doped trilayer [Bi.sub.2][Sr.sub.2][Ca.sub.2][Cu.sub.3][O.sub.10+δ] (Bi2223). We find that [T.sub.c] first increases with pressure and then decreases after passing through a maximum. Unexpectedly, [T.sub.c] increases again when the pressure is further raised above a critical value of around 24 GPa, surpassing the first maximum. The presence of this critical pressure is a manifestation of the crossover from the competing order to superconductivity in the inner of the three Cu[O.sub.2] planes. We suggest that the increase at higher pressures occurs as a result of competition between pairing and phase ordering in different Cu[O.sub.2] planes., We used Bi2223 single crystals in the present investigation. The structure of Bi2223 consists of two insulating Bi-O and Sr-O blocking layers intercalating in the c-axis direction with two structurally [...]

Iron in crustal and mantle minerals adopts several possible oxidation states: this has implications for biogeochemical processes (1), oxygenation of the atmosphere (2) and the oxidation state of the mantle [...]

Author(s): Jung-Fu Lin (corresponding author) [1, 4]; Viktor V. Struzhkin [1]; Steven D. Jacobsen [1]; Michael Y. Hu [2]; Paul Chow [2]; Jennifer Kung [3]; Haozhe Liu [2]; Ho-kwang Mao [...]

Finding ways to achieve higher values of the transition temperature, Tc, in superconductors remains a great challenge. The superconducting phase is often one of several competing types of electronic order, including antiferromagnetism and charge density waves. An emerging trend documented in heavy-fermion and organic conductors is that the maximum Tc for superconductivity occurs under external conditions that cause the critical temperature for a competing order to go to zero. Recently, such competition has been found in multilayer copper oxide high-temperature superconductors (HTSCs) that possess two crystallographically inequivalent CuO2 planes in the unit cell. However, whether the competing electronic state can be suppressed to enhance Tc in HTSCs remains an open question. Here we show that pressure-driven phase competition leads to an unusual two-step enhancement of Tc in optimally doped trilayer Bi2Sr2Ca2Cu3O10+δ (Bi2223). We find that Tc first increases with pressure and then decreases after passing through a maximum. Unexpectedly, Tc increases again when the pressure is further raised above a critical value of around 24 GPa, surpassing the first maximum. The presence of this critical pressure is a manifestation of the crossover from the competing order to superconductivity in the inner of the three CuO2 planes. We suggest that the increase at higher pressures occurs as a result of competition between pairing and phase ordering in different CuO2 planes. [ABSTRACT FROM AUTHOR]

Iron is the most abundant transition-metal element in the mantle and therefore plays an important role in the geochemistry and geodynamics of the Earth's interior. Pressure-induced electronic spin transitions of iron occur in magnesiowüstite, silicate perovskite and post-perovskite. Here we have studied the spin states of iron in magnesiowüstite and the isolated effects of the electronic transitions on the elasticity of magnesiowüstite with in situ X-ray emission spectroscopy and X-ray diffraction to pressures of the lowermost mantle. An observed high-spin to low-spin transition of iron in magnesiowüstite results in an abnormal compressional behaviour between the high-spin and the low-spin states. The high-pressure, low-spin state exhibits a much higher bulk modulus and bulk sound velocity than the low-pressure, high-spin state; the bulk modulus jumps by ∼35 per cent and bulk sound velocity increases by ∼15 per cent across the transition in (Mg0.83,Fe0.17)O. Although no significant density change is observed across the electronic transition, the jump in the sound velocities and the bulk modulus across the transition provides an additional explanation for the seismic wave heterogeneity in the lowermost mantle. The transition also affects current interpretations of the geophysical and geochemical models using extrapolated or calculated thermal equation-of-state data without considering the effects of the electronic transition. [ABSTRACT FROM AUTHOR]