Nematicity, magnetism and superconductivity in FeSe

Böhmer, Anna E.; Kreisel, Andreas

doi:10.1088/1361-648x/aa9caa

Cited by 202 publications

(175 citation statements)

References 255 publications

Supporting

Mentioning

171

Contrasting

Unclassified

Order By: Relevance

“…The phase diagram of FeSe is quite distinct from that of all other known FeSCs because its orthorhombic distortion is not accompanied by magnetic order [8]. The existence of the phase with decoupled lattice and spin degrees of freedom in FeSe has been interpreted as implying the importance of orbital ordering, particularly, in the context of nematicity.…”

Section: Resultsmentioning

confidence: 99%

Lattice dynamics in FeSe via inelastic x-ray scattering and first-principles calculations

et al. 2020

View full text Add to dashboard Cite

We report an inelastic x-ray scattering investigation of phonons in FeSe superconductor. Comparing the experimental phonon dispersion with density functional theory (DFT) calculations in the non-magnetic state, we found a significant disagreement between them. Improved overall agreement was obtained by allowing for spin-polarization in the DFT calculations, despite the absence of magnetic order in the experiment. This calculation gives a realistic approximation, at DFT level, of the disordered paramagnetic state of FeSe, in which strong spin fluctuations are present.

show abstract

Section: Resultsmentioning

confidence: 99%

Lattice dynamics in FeSe via inelastic x-ray scattering and first-principles calculations

et al. 2020

View full text Add to dashboard Cite

show abstract

“…It is not clear whether such a behavior is compatible with the FFLO state in a superconductor whose anisotropy is much smaller than Josephson coupled 2D organic compounds. For a deeper understanding of the FFLO pairing state, further superconductors revealing this state are strongly required.The layered iron-chalcogenide superconductor FeSe (T c ≈ 9 K) has aroused enormous enthusiasm to study the exotic superconductivity with various distinct features [17][18][19]. FeSe is a compensated semimetal, which exhibits a structural transition from tetragonal to orthorhombic crystal symmetry at T s ≈ 90 K [20].…”

mentioning

confidence: 99%

Evidence for an Fulde-Ferrell-Larkin-Ovchinnikov State with Segmented Vortices in the BCS-BEC-Crossover Superconductor FeSe

et al. 2020

View full text Add to dashboard Cite

We present resistivity and thermal-conductivity measurements of superconducting FeSe in intense magnetic fields up to 35 T applied parallel to the ab plane. At low temperatures, the upper critical field µ0H ab c2 shows an anomalous upturn, while thermal conductivity exhibits a discontinuous jump at µ0H * ≈ 24 T well below µ0H ab c2 , indicating a first-order phase transition in the superconducting state. This demonstrates the emergence of a distinct field-induced superconducting phase. Moreover, the broad resistive transition at high temperatures abruptly becomes sharp upon entering the highfield phase, indicating a dramatic change of the magnetic-flux properties. We attribute the high-field phase to the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state, where the formation of planar nodes gives rise to a segmentation of the flux-line lattice. We point out that strongly orbital-dependent pairing as well as spin-orbit interactions, the multiband nature, and the extremely small Fermi energy are important for the formation of the FFLO state in FeSe.Exotic superconductivity with a nontrivial Cooperpairing state has been a longstanding issue of interest in condensed-matter physics. Among possible exotic states, a spatially nonuniform superconducting state in the presence of strong magnetic fields caused by the paramagnetism of conduction electrons has been the subject of great interest after the pioneering work by Fulde and Ferrell as well as Larkin and Ovchinnikov (FFLO) [1,2]. In the FFLO state, pair breaking due to the Pauli paramagnetic effect is reduced by forming a new pairing state (k↑, −k + q↓) with |q| ∼ gµ B H/ υ F (υ F is the Fermi velocity, g the g-factor, and µ B the Bohr magneton) between Zeeman split parts of the Fermi surface, instead of (k↑, −k↓) pairing in BCS superconductors [Figs. 1(a) and 1(b)]. The fascinating aspect of the FFLO state is that the superconducting order parameter, in its simplest form, is modulated as ∆ ∝ sin q · r, and periodic planar nodes appear perpendicular to the magnetic field near the upper critical field H c2 , leading to a segmentation of the vortices into pieces of length Λ = π/|q| [ Fig. 1(c)].Despite tremendous efforts in the search for the FFLO states in the past half century, indications of its experimental realization have been reported in only a few candidate materials, including quasi-two-dimensional (2D) organic superconductors and the heavy-fermion superconductor CeCoIn 5 [3-5]. In both systems, a thermodynamic phase transition occurs below H c2 and a high-field superconducting phase emerges at low temperatures [6][7][8][9]. In the former, each superconducting layer is very weakly coupled via the Josephson effect. The FFLO state is observed in a magnetic field H applied parallel to the layers, where the magnetic flux is concentrated in the regions between the layers forming coreless Josephson vortices. Therefore, the segmentation of the vortices by FFLO nodes, which is one of the most fascinating properties of the FFLO state, is not expected. The presence of the FFLO...

show abstract

“…At the moment, there is no clear-cut experimental confirmation for either mechanism (for recent experimental reviews, see Refs. [19,20]). …”

mentioning

confidence: 99%

Dynamical susceptibility of a near-critical nonconserved order parameter and quadrupole Raman response in Fe-based superconductors

Klein¹,

Lederer

Chowdhury

et al. 2018

Phys. Rev. B

View full text Add to dashboard Cite

We analyze the dynamical response of a two-dimensional system of itinerant fermions coupled to a scalar boson φ, which undergoes a continuous transition towards nematic order with a d-wave form factor. We consider two cases: (a) when φ is a soft collective mode of fermions near a Pomeranchuk instability, and (b) when it is an independent critical degree of freedom, such as a composite spin order parameter. In both cases, the order parameter is not a conserved quantity and the d-wave fermionic polarization (q, ) remains finite even at q = 0. The polarization (0, ) has similar behavior in the two cases, but the relations between (0, ) and the bosonic susceptibility χ (0, ) are different, leading to different forms of χ (0, ), as measured by Raman scattering. We compare our results with polarization-resolved Raman data for the Fe-based superconductors FeSe 1−x S x , NaFe 1−x Co x As, and BaFe 2 As 2 .

show abstract

Nematicity, magnetism and superconductivity in FeSe

Cited by 202 publications

References 255 publications

Lattice dynamics in FeSe via inelastic x-ray scattering and first-principles calculations

Lattice dynamics in FeSe via inelastic x-ray scattering and first-principles calculations

Evidence for an Fulde-Ferrell-Larkin-Ovchinnikov State with Segmented Vortices in the BCS-BEC-Crossover Superconductor FeSe

Dynamical susceptibility of a near-critical nonconserved order parameter and quadrupole Raman response in Fe-based superconductors

Contact Info

Product

Resources

About