Contrasting effects of magnetic ions on the superconductivity in Tl_0.4K_0.4Fe_2−y−xM_xSe₂(M= Mn and Ni)

Abstract

The transport and magnetic properties together with the superconductivity of Tl 0.4 K 0.4 Fe 2−y−x M x Se 2 (M = Mn and Ni) single crystals are studied. On the transport side, both Mn doping and Ni doping lead to a decrease of charge carrier density. However, contrasting effects on superconductivity are found, i.e. substitution of Fe by Ni results in a drastic depression of the onset superconducting transition temperature (T onset c ), while the T onset c value remains nearly unchanged in Mn-doped samples. A remarkable ferromagnetic interaction is found in Ni-doped samples but is absent in Mn-doped samples. The present results suggest that the magnetic pair-breaking effect alone cannot explain the different behavior of depression of superconductivity in Mn-doped and Ni-doped samples. The occurrence of ferromagnetic interaction is responsible for the rapid decrease of T onset c in Ni-doped samples.

Magnetic order, spin dynamics and transport properties of the pyrochlore iridate Y2Ir2O7

“…However, the FM component coexists with AFM order. Thus, the depression of resonance intensity is possibly due to the enhancement of AFM magnetic fluctuation, as observed in ironbased superconductors [24,25]. The evolution of H res and relative intensity [I(T)/I(300 K)] of the low-field peak confirms that the detected ESR signal originates from the Y 2 Ir 2 O 7 sample, but not from some unreacted Ir impurity.…”

Exchange bias in structure-phase separated K0.8Fe2−xNixSe2 (x=0.015) single crystal: Interface evidence

“…However, we also found a curvature at T$ 27.5 K for x¼0.015 sample, which is very close to the superconducting transition temperature T c in K 0.8 Fe 2 Se 2 system. Since the Ni doping could suppress the T c fast in 122 iron-selenides compounds [21], T c ¼24.5 K for x¼ 0.005 in our case, the observed kink at T$ 27.5 K in R-T curve for x¼0.015 sample might not be related to the superconducting transition when reminding of the higher doping level, which is consist with the temperature dependence of magnetization measurements.…”

“…the contribution of phase 2 as seen in XRD, which shows the phase 2 might be some weak ferromagnetism. As increasing the Ni doping in K 0.8 Fe 2 Se 2 , the superconductivity (SC) transition temperature (T c ) was quenched down to 24.5 K at x¼0.005 [inset of (b)], and we could not see any trace of SC transition at x¼0.015 and x¼0.025 except the kinks, which indicates the SC might be thoroughly destructed at high doping level as could compare to the single phase Co doped K 0.8 Fe 2 Se 2 system [20] and Ni doped Tl 0.4 K 0.4 Fe 2 Se 2 system [21]. Moreover, the absence of superconducting transition for the Ni doped samples was also checked by the temperature dependent resistivity measurements, which shows the semiconducting behavior as the temperature decrease for x¼0.015 sample, as shown in Fig.…”

Intermediate gapless phase and topological phase transition of the Kitaev model in a uniform magnetic field

“…However, the study of Kitaev model in the magnetic field beyond perturbation theory is very limited until recently. Motivated by recent experimental search of KSL in real materials [3][4][5][6][7], which were often conducted in a uniform magnetic field to suppress the magnetic order in real materials at low temperature, several theoretical groups studied the Kitaev model in uniform magnetic field, [111] direction or tilted, employing the exact diagonalization (ED) and density matrix renormalization group (DMRG) method [8][9][10]. All these works reveal intriguing behaviors of anti-ferromagnetic (AFM) Kitaev model in a uniform magnetic field beyond perturbation regime, e.g., the gapless AFM Kitaev model exhibits a phase transition from gapped phase in weak magnetic field to a mysterious gapless phase in an intermediate magnetic field before the system reaches the trivial polarized state at higher magnetic field.…”