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Abstract
The coexistence and competition between superconductivity and electronic orders, such as spin or charge density waves, have been a central issue in high transition-temperature (Tc) superconductors. Unlike other iron-based superconductors, FeSe exhibits nematic ordering without magnetism whose relationship with its superconductivity remains unclear. Moreover, a pressure-induced fourfold increase of Tc has been reported, which poses a profound mystery. Here we report high-pressure magnetotransport measurements in FeSe up to ∼15 GPa, which uncover the dome shape of magnetic phase superseding the nematic order. Above ∼6 GPa the sudden enhancement of superconductivity (Tc≤38.3 K) accompanies a suppression of magnetic order, demonstrating their competing nature with very similar energy scales. Above the magnetic dome, we find anomalous transport properties suggesting a possible pseudogap formation, whereas linear-in-temperature resistivity is observed in the normal states of the high-Tc phase above 6 GPa. The obtained phase diagram highlights unique features of FeSe among iron-based superconductors, but bears some resemblance to that of high-Tc cuprates.
Highlights
The coexistence and competition between superconductivity and electronic orders, such as spin or charge density waves, have been a central issue in high transition-temperature (Tc) superconductors
More recent studies under better hydrostatic pressure conditions revealed a complex temperature–pressure (T–P) phase diagram featured by a suppression of Ts around 2 GPa, a sudden development of static magnetic order above B1 GPa, and an enhancement of Tc in a three-plateau process[24], that is, TcB10(2) K for 0–2 GPa, TcB20(5) K for 3–5 GPa, and TcB35(5) K for 6–8 GPa
When the obtained Tm(P) and Tc(P) data are plotted in Fig. 1, we uncover a previously unknown dome-shaped magnetic order with two ends situated near the boundaries separating the threeplateau Tc(P)
Summary
The coexistence and competition between superconductivity and electronic orders, such as spin or charge density waves, have been a central issue in high transition-temperature (Tc) superconductors. The first jump of Tc from B10 to B20 K seems to coincide with the suppression of the nonmagnetic nematic state and the development of the long-range magnetic order at Tm evidenced by mSR measurements[22] The observation that both Tc and Tm increase with pressure in the pressure range 1–2.5 GPa has been taken as evidence for the cooperative promotion of superconductivity by the static magnetic order[22]. Our results provide compelling evidence linking intimately the sudden enhancement of Tc to 38 K to the suppression of long-rang magnetic order This highlights a competing nature between magnetic order and high-Tc superconductivity in the phase diagram of FeSe, which is a key material among the iron-based superconductors
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