Anomalous hysteresis as an evidence for a magnetic field-induced chiral superconducting state in LiFeAs

Abstract

Magnetometry measurements in high quality LiFeAs single-crystals reveal a change in the sign of the magnetic hysteresis in the vicinity of the upper critical field $H_{c2}$, from a clear diamagnetic response dominated by the pinning of vortices, to a considerably smaller net hysteretic response of opposite sign, which \emph{disappears} at $H_{c2}$. If the diamagnetic response at high fields results from pinned vortices and associated screening super-currents, this sign change must result from currents circulating in the opposite sense, which give rise to a small field-dependent magnetic moment \emph{below} $H_{c2}$. This behavior seems to be extremely sensitive to the sample quality or stoichiometry, as we have observed it only in a few fresh crystals, which also display the de Haas van Alphen-effect. We provide arguments against the surface superconductivity, the flux compression, and the random $\pi$ junction scenarios, which have been previously put forward to explain a paramagnetic Meissner effect, below the lower critical field $H_{c1}$. The observed anomalous hysteresis at high fields will be compatible with the existence of chiral gap wave-functions, which possess a field dependent magnetic moment. Within a Landau-Ginzburg framework, we demonstrate how a $(d_{x^2-y^2}+i{d}_{xy})$ or a $(p_x+i{p}_y)$ chiral superconducting component can be stabilized in the mixed state of $s_{\pm }$ superconductor, due to the combined effects of the magnetic field and the presence of competing pairing channels. The realization of a particular chiral pairing depends on the microscopic details of the strengths of the competing pairing channels.

12 pages, 10 figures

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Cited by in corpus (10)

• Spin fluctuations in iron pnictides and chalcogenides: From antiferromagnetism to superconductivity
• Bulk evidence for a time reversal symmetry broken superconducting state in URu2Si2
• Unusual temperature evolution of superconductivity in LiFeAs
• Anomalous superconducting state in LiFeAs implied by the ${}^{75}$As Knight shift measurement
• Small and nearly isotropic hole-like Fermi surfaces in LiFeAs detected through de Haas van Alphen-effect
• High field paramagnetic Meissner effect in Mo${}_{100-x}$Re${}_x$ alloy superconductors
• Two-dimensional superconductivity in a bulk single-crystal
• Defect states in LiFeAs as seen by low temperature scanning tunneling microscopy and spectroscopy
• Absence of hexagonal to square structural transition in LiFeAs vortex matter
• Paramagnetic excited vortex states in superconductors