High-temperature superconductivity in iron-based materials

Abstract

The surprising discovery of superconductivity in layered iron-based materials, with transition temperatures climbing as high as 55 K, has lead to thousands of publications on this subject over the past two years. While there is general consensus on the unconventional nature of the Cooper pairing state of these systems, several central questions remain - including the role of magnetism, the nature of chemical and structural tuning, and the resultant pairing symmetry - and the search for universal properties and principles continues. Here we review the progress of research on iron-based superconducting materials, highlighting the major experimental benchmarks that have been so far reached and the important questions that remain to be conclusively answered

Phase Diagram of (Li1–xFex)OHFeSe: A Bridge between Iron Selenide and Arsenide Superconductors

“…We find that the physical properties of the non-SC samples of (Li 1-x Fe x )OHFeSe are very similar to those of FeAsbased superconductors. [1][2][3][4]29 An emergent AFM SDW transition is observed at ~127 K in the absence of the well-known √5×√5 Fe vacancy ordered state associated with the AFM order in A y Fe 2-x Se 2 . In the optimal SC sample of (Li 1-x Fe x )OHFeSe with T c = 40 K, one dominant superstructure with a unique modulation wave vector q=1/2 (1,1,0) is observed by means of selected-area electron diffraction and high-resolution TEM.…”

“…The SDW transition temperatures are much lower than that of the AFM transition of A y Fe 2-x Se 2 (its Neel temperature T N ~ 500 K). 5,13,[19][20][21]24,25 By contrast, such a SDW transition at 100-150 K has been commonly seen in the FeAs-based parent compounds of REFeAsO (RE = rare earth element), [1][2][3][4] whose structural skeleton containing FeAs layers is of the same P4/nmm symmetry as the present (Li 1-x Fe x )OHFeSe samples. The similar SDW transition indicates that its magnetic coupling strength is comparable to the FeAs-based counterparts, in consistent with the fact that their T c 's are similar.…”

Relationship between Superconductivity and Antiferromagnetism in LaFe(As1−xPx)O Revealed by 31P-NMR

“…[1][2][3][4] The relationship between superconductivity and AFM fluctuations in recent-discovered iron-based superconductors has also been discussed. [5][6][7][8][9][10][11][12][13][14][15][16] Up to now, it has been reported that superconductivity appears around the AFM quantum critical point in the Ba122 system, indicative of the strong relationship between superconductivity and low-energy AFM fluctuations. 10,[12][13][14][15][16] On the other hand, superconductivity is linked not to the low-energy AFM fluctuations probed by NMR spectroscopy but to the local stripe spin correlation with Q stripe = (π, 0) (unfolded Brillouin zone) in LaFeAs(O 1−x F x ).…”

Synthesis, Structural, and Transport Properties of Cr-Doped BaTi2As2O

“…From the viewpoint of theoretical and experimental evidences, [3][4][5] these superconductivities often emerge in the proximity of the ordering of spin/charge density wave instabilities, in contrast to that of conventional BCS superconductivity 6 .…”