Dome-shaped magnetic order competing with high-temperature superconductivity at high pressures in FeSe

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.

Electronic structure of FeS

“…Moreover, our samples exhibit quite high residual resistivity ratios (RRR) of about 40 [26], which is better than the typical RRR of FeCh (Ch = Te, Se, S) and close to the one as reported in Refs. [27][28][29]. Therefore, the x and y should be quite small.…”

Intrinsic pinning by naturally occurring correlated defects in FeSe1−xTexsuperconductors

“…In particular, the normal and superconducting states of Fe(Se 1-x Te x ) are strongly influenced by hydrostatic and chemical pressure [2,3]. Furthermore, due to the very rich thermodynamic phase diagram [4], slight differences in material synthesis yield a variation in composition and the appearance of defects that significantly change the electronic and magnetic properties.…”

Comparative Review on Thin Film Growth of Iron-Based Superconductors

“…Surprisingly, the magnetic order emerges around 1 GPa [224,225]. The magnetic transition temperature (T m ) increases up to 45 K with increasing pressure, and then T m disappears around 6 GPa [217]. Interestingly, in T c for FeSe under hydrostatic pressures, a characteristic three-step increase is observed [216]; the 2nd and 3rd increases in T c appear around 2 GPa and 6 GPa, respectively.…”

“…However, if it is revealed that the nematic QCP exists around x opt by evaluating the nematic fluctuations in FeSe 1−x Te x films as Ba122 [221,222] and FeSe 1−x S x [219], it can be concluded that the nematic fluctuation may enhance a superconducting transition temperature as suggested by some theoretical studies [223]. On the other hand, in the phase diagram of FeSe under hydrostatic pressures, T s also decreases with increasing applied pressure and disappears around 2 GPa [217]. Surprisingly, the magnetic order emerges around 1 GPa [224,225].…”

“…In bulk single crystals, the detailed phase diagram of FeSe under hydrostatic pressures [216][217][218] and FeSe 1−x S x [219,220] have been reported because the high-quality single crystals of FeSe 1−x S x and FeSe can be available. The S-substitution for Se introduces chemical pressure in FeSe, and T s gradually decreases with increasing S content x [219].…”