Superconductivity in Iron-Based Materials

Since the initial discovery of superconductivity in iron-pnictide compounds, iron-based materials have been the focus of intense research owing to their unconventional pairing mechanisms, multi-band electronic structure and high critical temperatures. These materials comprise several families, including iron-arsenides, iron-chalcogenides and iron-phosphides, each exhibiting a rich interplay between magnetism, structural distortions (nematic order) and electronic correlations. Parent compounds typically manifest antiferromagnetic or nematic ground states that can be suppressed by chemical substitution, pressure or interfacial engineering, giving rise to superconducting domes with transition temperatures reaching beyond 50 K. The multi-orbital nature of the iron d-electrons leads to a complex Fermi surface topology, with hole and electron pockets whose nesting properties and orbital character underpin spin-fluctuation-mediated pairing. Practical applications in loss-free power lines, superconducting magnets and quantum devices hinge on achieving higher transition temperatures, enhancing critical currents and controlling anisotropic vortex dynamics. Progress in thin films, heterostructures and high-pressure techniques continues to broaden the phenomenology and technological potential of iron-based superconductors.

Research from Nature Portfolio

Recent studies of FeSe-based superconductors have refined our understanding of the competitive and cooperative interactions that govern high-temperature superconductivity. High-pressure transport measurements have mapped a dome-shaped magnetic phase that suppresses nematic order and gives way to a superconducting region with Tc approaching 38 K, highlighting the close energy scales of magnetism and pairing. Angle-resolved photoemission work on (Li,Fe)OHFeSe crystals demonstrated that bulk and single-layer FeSe/SrTiO₃ share remarkably similar Fermi surface topologies and superconducting gap symmetries, suggesting an intrinsic electronic origin for enhanced Tc at interfaces. Systematic doping of FeSe layers revealed an anomalous phase diagram featuring a low-temperature nematic phase, a pronounced superconducting dome peaking near 46 K, a correlation-driven insulating state and a re-entrant metallic phase. Together, these findings underscore the crucial roles of orbital selectivity, electron correlations and lattice degrees of freedom in stabilising unconventional superconductivity.

Research from all publishers

Outside this portfolio, advances have been made in elucidating pairing strength near symmetry-breaking instabilities and in unifying magnetic and orbital interactions. High-field studies of nonmagnetic FeSe₁–ₓTeₓ compounds have revealed that nematic quantum critical fluctuations enhance the Pauli-limiting field and thus strengthen superconducting pairing, opening a route to higher transition temperatures via nonmagnetic criticality. Early work on LaFeAsO₁–ₓFₓ established the presence of an extended s-wave state with sign reversal between Fermi pockets, driven by antiferromagnetic spin fluctuations rather than conventional phonon mechanisms. A renormalisation-group analysis of multi-orbital models has shown that magnetic fluctuations not only drive s± superconductivity but also promote spontaneous orbital order; in systems with small Fermi pockets, nematicity precedes pairing, whereas in larger-pocket materials spin-density-wave order and superconductivity compete, explaining material-specific phase sequences.

Superconductivity in Iron-Based Materials publication trend

The graph below shows the total number of articles in superconductivity in iron-based materials across all publications each year (not limited to Nature Index journals).

Technical terms

Nematicity: An electronic state in which rotational symmetry is broken while translational symmetry remains, leading to anisotropic transport and lattice distortions.

Spin fluctuations: Time-dependent variations of electron spins that can mediate attractive interactions between electrons, supporting unconventional pairing.

Fermi surface nesting: The matching of sections of the Fermi surface by a reciprocal-space vector, enhancing susceptibility to collective electronic orders.

s± pairing: A superconducting order parameter that changes sign between different Fermi surface pockets, often stabilised by repulsive interband interactions.

Quantum critical point: A zero-temperature continuous phase transition marked by diverging fluctuations that influence finite-temperature properties and can boost superconducting correlations.

References

1. Enhanced Superconducting Pairing Strength near a Pure Nematic Quantum Critical Point. Physical Review X (2023).
2. Dome-shaped magnetic order competing with high-temperature superconductivity at high pressures in FeSe. Nature Communications (2016).
3. Unconventional Superconductivity with a Sign Reversal in the Order Parameter of LaFeAsO1-xFx. Physical Review Letters (2008).
4. Common electronic origin of superconductivity in (Li,Fe)OHFeSe bulk superconductor and single-layer FeSe/SrTiO3 films. Nature Communications (2016).
5. Magnetism, Superconductivity, and Spontaneous Orbital Order in Iron-Based Superconductors: Which Comes First and Why?. Physical Review X (2016).
6. Anomalous correlation effects and unique phase diagram of electron-doped FeSe revealed by photoemission spectroscopy. Nature Communications (2016).