Interplay Between Conducting and Magnetic Systems in the Antiferromagnetic Organic Superconductor κ-(BETS)2FeBr4

Abstract

The mutual influence of the conduction electron system provided by organic donor layers and magnetic system localized in insulating layers of the molecular charge transfer salt κ-(BETS)2FeBr4 has been studied. It is demonstrated that besides the high-field re-entrant superconducting state, the interaction between the two systems plays important role for the low-field superconductivity. The coupling of normal-state charge carriers to the magnetic system is reflected in magnetic quantum oscillations and can be evaluated based on the angle-dependent beating behaviour of the oscillations. On the other hand, the conduction electrons have their impact on the magnetic system, which is revealed through the pressure-induced changes of the magnetic phase diagram of the material.

Interplay between the d - and π -electron systems in magnetic torque of the layered organic conductor κ -(BETS) 2MnVyaselev1, Biberacher2, Kushch3 et al. 2017Phys. Rev. B8180View full textAdd to dashboardCite

“…For example, a considerable π-d coupling in λ-(BETS) 2 FeCl 4 leads to a metal-insulator transition in the π-electron system triggered by an antiferromagnetic (AF) ordering of localized Fe 3+ spins [7] and to a spectacular phenomenon of superconductivity induced by a strong magnetic field [8,9]. In the κ-(BETS) 2 FeX 4 salts the π-d coupling is weaker; however it can be readily traced in a reconstruction of the Fermi surface caused in the AF state [10][11][12], high-field re-entrant superconductivity [13,14], and protection of the low-field superconductivity by the AF ordering [13,15].In the present compound the π-d interactions seem to be even weaker. While the metalinsulator transition at T MI ≈ 21 K [1] might, at first glance, appear similar to that in λ-(BETS) 2 FeCl 4 , it is most likely driven by purely the Mott-insulating instability of the π-electron system and not by an AF instability of the localized d-electron spins.…”

Experimental evidence for Zeeman spin–orbit coupling in layered antiferromagnetic conductors

“…Given the experimental error bars, we cannot exclude a nonzero g ? t 0:2, yet even such a small finite value would be in stark contrast with the textbook g = 2.0, found from the SdH oscillations in the high-field, PM state 46 . Below we argue that, in fact, g ?…”

“…The oscillation amplitude exhibits spin zeros as a function of the field strength and orientation, which is fairly well described by a field-dependent spin-reduction factor R s (θ, B), with the g-factor g = 2.0 ± 0.2 in the presence of an exchange field B J ≈ −13 T, imposed by PM Fe 3+ ions on the conduction electrons 46,57 . In the Supplementary Note VI, we provide further details of the SdH oscillation studies on κ-BETS.…”

“…For example, in the simplest case of a spherical Fermi surface, R s possesses no angular dependence whatsoever, hence no spin zeros. By contrast, in quasi-2D metals with their vanishingly weak interlayer dispersion such as in layered organic and cuprate conductors, spin zeros are [42][43][44][45][46][47] a robust consequence of the monotonic increase of the cyclotron mass, m / 1= cos θ, with tilting the field by an angle θ away from the normal to the conducting layers.…”

Fermi surface properties of the bifunctional organic metal κ−(BETS)2Mn[N(CN)2]Zverev1, Biberacher2, Oberbauer3 et al. 2019Phys. Rev. B8020View full textAdd to dashboardCite

“…The π -d exchange * mark.kartsovnik@wmi.badw.de coupling is known to be at the core of the metal-insulator transition of another hybrid organic salt λ-(BETS) 2 FeCl 4 [9,10]. Moreover, in some BETS salts with Fe-containing tetrahedral anions the π -d coupling is clearly manifest already in the metallic state, playing, for example, a crucial role in stabilizing superconductivity in a magnetic field [1,[11][12][13][14][15]. In the present material this coupling seems to be considerably weaker.…”