Elliptical vortex and oblique vortex lattice in the FeSe superconductor based on the nematicity and mixed superconducting orders

Despite more than ten years of extensive research, the superconducting mechanism of iron-based superconductors (FeSCs) is still an open question. Generally, the hightemperature superconductivity is often observed with suppression of magnetic ordering, spin-density-wave, or even the structure transition by carrier doping. Furthermore, an electronic state ordering is also observed at temperatures close to or even above these transitions. Due to its proximity to the superconducting state and disappearance near the optimal superconductivity, it has been also suggested to interplay with superconductivity on a phenomenological level. Nevertheless, there is still no direct evidence to bridge the superconductivity to these transitions. Recently, another nematic order was observed in the superconducting state of heavily hole-doped compound AFe 2 As 2 (A = K, Rb, Cs), providing a possibility to explore the superconductivity gap symmetry nature. Here, by reviewing the recent experimental progresses on the nematic superconductivity in the FeSCs, we will introduce the progresses by various methods including the quasi-particle interference from scanning tunneling microscope, anisotropic gap magnitudes from angular resolved photoemission, the upper critical field and the superconducting transition temperatures from transport measurements. In addition, some recent reports and theoretical explanations for experimental results are followed.

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“…consistent with the elliptical vortex [35], where a mixed s-wave and d-wave superconducting order is coupled to the nematic order(Fig. 3(b)).…”

Section: Nematic Superconductivity In 11-systemsupporting

confidence: 75%

Progress of nematic superconductivity in iron-based superconductors

Wang

Zhou

et al. 2021

Advances in Physics: X

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“…8 further demonstrates that the observed anisotropy is of low symmetry. Very clearly, this low-symmetric angle dependence is neither compatible with the 4-fold symmetry which is reported for LiFeAs [3,8] nor with a thinkable 2-fold symmetry which would be expected for coupling to a nematic order parameter [63,64]. This is visualized by the dashed solid black curves representing the expected distribution of ξ GL (α) for generic 4-fold and 2-fold symmetries, respectively.…”

Section: Glmentioning

confidence: 65%

Absence of hexagonal to square structural transition in LiFeAs vortex matter

Hoffmann¹,

Schlegel²,

Salazar³

et al. 2022

Preprint

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We investigated magnetic vortices in two stoichiometric LiFeAs samples by means of scanning tunneling microscopy and spectroscopy. The vortices were revealed by measuring the local electronic density of states (LDOS) at zero bias conductance of samples in magnetic fields between 0.5 and 12 T. From single vortex spectroscopy we extract the Ginzburg-Landau coherence length of both samples as 4.4 ± 0.5 nm and 4.1 ± 0.5 nm, in accordance with previous findings. However, in contrast to previous reports, our study reveals that the reported hexagonal to square-like vortex lattice transition is absent up to 12 T both in field-cooling and zero-field-cooling processes. Remarkably, a highly ordered zero field cooled hexagonal vortex lattice is observed up to 8 T. We argue that several factors are likely to determine the structure of the vortex lattice in LiFeAs such as (i) details of the cooling procedure (ii) sample stoichiometry that alters the formation of nematic fluctuations, (iii) details of the order parameter and (iv) magnetoelastic coupling.

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“…11 the time evolution of a configuration starting with 4 superimposed n v = 1 vortices with both couplings to the nematic order parameter. Large n v configurations will be useful in the study of Abrikosov lattice formations [51,68]. Once appropriate boundary conditions are implemented [69] the extension to larger values of κ, typical in Fe-based superconductors, can be considered.…”

Section: Discussionmentioning

confidence: 99%

“…Vortices were also considered in Refs. [51,52] (for a case in which the nematic parameter is complex see [53]). Superconducting-nematic coupling of this kind was also considered in [37] in the study of strain detwined mixed states [54].…”

Section: Ginzburg-landau Model With Nematic Order Parameter and Tdgl ...mentioning

confidence: 99%

Vortices in a Ginzburg Landau Theory of Superconductors with Nematic Order

Severino,

Mininni,

Fradkin

et al. 2022

Preprint

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In this work we explore the interplay between superconductivity and nematicity in the framework of a Ginzburg Landau theory with a nematic order parameter coupled to the superconductor order parameter, often used in the description of superconductivity of Fe based materials. In particular, we focus on the study of the vortex-vortex interaction in order to determine the way nematicity affects its attractive or repulsive character. To do so, we use a dynamical method based on the solutions of the Time Dependent Ginzburg Landau equations in a bulk superconductor. An important contribution of our work is the implementation of a pseudo-spectral method to solve the dynamics, known to be highly efficient and of very high order in comparison to the usual finite differences/elements methods. The coupling between the superconductor and the (real) nematic order parameters is represented by two terms in the free energy: a biquadratic term and a coupling of the nematic order parameter to the covariant derivatives of the superconductor order parameter. Our results show that there is a competing effect: while the former independently of its competitive or cooperative character generates an attractive vortex-vortex interaction, the latter always generates a repulsive interaction.

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Elliptical vortex and oblique vortex lattice in the FeSe superconductor based on the nematicity and mixed superconducting orders

Cited by 14 publications

References 59 publications

Progress of nematic superconductivity in iron-based superconductors

Progress of nematic superconductivity in iron-based superconductors

Absence of hexagonal to square structural transition in LiFeAs vortex matter

Vortices in a Ginzburg Landau Theory of Superconductors with Nematic Order

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