Takehiro Hatakeda

New Intercalation Superconductor Lix(C6H16N2)yFe2−zSe2 with a Very Large Interlayer-Spacing and Tc = 38 K

A new iron-based superconductor, Lix(C6H16N2)yFe2−zSe2, with Tc = 38 K has successfully been synthesized via the intercalation of lithium and hexamethylenediamine into FeSe. The superconducting transition has been confirmed not only by magnetic susceptibility measurements but also by electrical resistivity ones. The interlayer spacing, namely, the distance between neighboring Fe layers, d, is 16.225(5) A, which is the largest among those of FeSe-based intercalation compounds. It has been found that the dependence of Tc on d in FeSe-based intercalation superconductors appears domic.

New Superconducting Phase of Lix(C6H16N2)yFe2−zSe2 with Tc = 41 K Obtained through the Post-Annealing

Post-annealing effects on the crystal structure and superconductivity of the lithium- and hexamethylenediamine (HMDA)-intercalated superconductor Lix(C6H16N2)yFe2−zSe2 have been investigated. Through the post-annealing, a two-step reduction of the interlayer spacing between neighboring Fe layers, d, has been observed. It has been found that a new phase of Lix(C6H16N2)yFe2−zSe2 with d = 10.30(2) A and Tc = 41 K different from the as-intercalated phase is stabilized owing to the possible stable inclination of HMDA intercalated between FeSe layers. This result supports the domic relation between Tc and d in the FeSe-based intercalation superconductors. The reason why Tc increases with a decrease in d through the post-annealing is discussed.

Resistive superconducting transition and effects of atmospheric exposure in the intercalation superconductor Ax(C2H8N2)yFe2- zSe2 (A = Li, Na)

We have succeeded in observing zero-resistivity in newly discovered intercalation superconductors Ax(C2H8N2)yFe2-zSe2 (A = Li, Na) with Tc = 45 K, using the sintered pellet samples. The electrical resistivity, \r{ho}, in the normal state is metallic and Tconset defined in the

New Alkali-Metal- and 2-Phenethylamine-Intercalated Superconductors Ax(C8H11N)yFe1−zSe (A = Li, Na) with the Largest Interlayer Spacings and Tc ∼ 40 K

\rho

Enhanced superconducting transition temperature in hyper-interlayer-expanded FeSe despite the suppressed electronic nematic order and spin fluctuations

measurements, is as high as ~ 57 K. We have also investigated effects of the atmospheric exposure in Lix(C2H8N2)yFe2-zSe2. It has been found that both the crystal structure and superconductivity are maintained at least up to several days, indicating this material is comparatively resistant to the atmospheric exposure.

Superconductivity and Intercalation State in the Lithium-Hexamethylenediamine-Intercalated Superconductor Lix(C6H16N2)yFe2−zSe2: Dependence on the Intercalation Temperature and Lithium Content

New FeSe-based intercalation superconductors,

New Li-Ethylenediamine-Intercalated Superconductor Li

A_x

_x

(C

(C

_8

_2

H