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We present resistivity and thermal-conductivity measurements of superconducting FeSe in intense magnetic fields up to 35 T applied parallel to the ab plane. At low temperatures, the upper critical field μ0Hc2ab shows an anomalous upturn, while thermal conductivity exhibits a discontinuous jump at μ0H∗≈24  T well below μ0Hc2ab, indicating a first-order phase transition in the superconducting state. This demonstrates the emergence of a distinct field-induced superconducting phase. Moreover, the broad resistive transition at high temperatures abruptly becomes sharp upon entering the high-field phase, indicating a dramatic change of the magnetic-flux properties. We attribute the high-field phase to the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state, where the formation of planar nodes gives rise to a segmentation of the flux-line lattice. We point out that strongly orbital-dependent pairing as well as spin-orbit interactions, the multiband nature, and the extremely small Fermi energy are important for the formation of the FFLO state in FeSe. [ABSTRACT FROM AUTHOR]

The electrical resistivity ρ and Hall coefficient RH of the tetragonal single-layer cuprate La1.6-xNd0.4SrxCuO4 were measured in magnetic fields up to H=37.5 T, large enough to access the normal state at T→0, for closely spaced dopings p across the pseudogap critical point at p☆=0.23. Below p☆, both coefficients exhibit an upturn at low temperature, which gets more pronounced with decreasing p. Taken together, these upturns show that the normal-state carrier density n at T=0 drops upon entering the pseudogap phase. Quantitatively, it goes from n=1+p at p=0.24 to n=p at p=0.20. By contrast, the mobility does not change appreciably, as revealed by the magnetoresistance. Our data are in excellent agreement with recent high-field data on YBa2Cu3Oy and La2-xSrxCuO4. The quantitative consistency across three different cuprates shows that a drop in carrier density from 1+p to p is a universal signature of the pseudogap transition at T=0. We discuss the implication of these findings for the nature of the pseudogap phase. [ABSTRACT FROM AUTHOR]

In underdoped cuprates, an incommensurate charge density wave (CDW) order is known to coexist with superconductivity. A dip in T_{c} at the hole doping level where the CDW is strongest (n_{p}≃0.12) suggests that CDW order may suppress superconductivity. We investigate the interplay of charge order with superconductivity in underdoped YBa_{2}Cu_{3}O_{7-δ} by measuring the temperature dependence of the Hall coefficient R_{H}(T) at high magnetic field and at high hydrostatic pressure. We find that, although pressure increases T_{c} by up to 10 K at 2.6 GPa, it has very little effect on R_{H}(T). This suggests that pressure, at these levels, only weakly affects the CDW and that the increase in T_{c} with pressure cannot be attributed to a suppression of the CDW. We argue, therefore, that the dip in T_{c} at n_{p}≃0.12 at ambient pressure is probably not caused by the CDW formation.