Direct evidence for the occurrence of superconductivity in the magnetic compound YFe4Al8

Abstract

For the first time we present the direct evidence for superconductivity in the ternary magnetic compound YFe 4 Al 8 with the ThMn 12 type structure found via point-contact (PC) experiments on contacts between silver needle and single-crystal YFe 4 Al 8 , revealing the distinct Andreev-reflection current. The spectra measured prove the existence of normal-superconducting interface and exhibit the triangular-like shape in a vicinity of zero-bias voltage, inferring the unconventional type of superconductivity. The derived dependences of the order parameter versus temperature ∆(T) and magnetic field ∆(H) are presented. ∆(T) follows BCS theory, whereas ∆(H) do not satisfy any theoretical predictions. In some cases there exists noticeable superconductivity enhancement by a weak magnetic field. The data obtained imply the very inhomogeneous distribution of superconductivity over the sample volume in spite of its single crystal structure. We assume that the reason is associated with inherent magnetic inhomogeneities of this material. The highest values for the critical temperature T c , upper critical magnetic field H c2 , and ratio 2∆(0)/kT c are 7.4 K, 5 T, and 7.2, respectively. [3]. In this work we give, for the first time, the direct evidence for the existence of superconductivity in the rare-earth ternary magnetic compound YFe 4 Al 8 in an Andreevreflection experiment.The family of ternary magnetic compounds ReM 4 Al 8 (Re is a rare earth, M is a transition metal) with the ThMn 12 type structure is known for about two decade and their physical properties have been investigated extensively [4][5][6]. However, weak signs of superconductivity in some of the compounds belonging to this family were discovered only recently in the radio-frequency impedance and heat capacity experiments [7,8]. This is very surprising, because the compounds of this type have a

Evidence for superconductivity and a pseudogap in the new magnetic compound PrAg6In6

“…In this case the Fermi surface is not gapped entirely and this explains the unusual shape of our dV/dI V ( ) characteristics. The triangular-shaped PC Andreev-reflection spectra were recently observed by us in YFe Al 4 8 [6]. Earlier, similar behavior of the PC spectra was reported in [14] for the heavy-fermion UPt 3 .…”

“…Then, if the superconducting features in our spectra were caused by the Andreev reflection from In clusters, the shape of spectra would agree with that typical for N-S contacts based on conventional superconductors [10]. Because such spectra were never observed, this is reliable proof that superconductivity in PrAg 6 In 6 is not due to a free In component. Moreover, the In clusters should result in wide variations of gap-feature voltages in different contacts [11], and that was not observed as well.…”

“…Figs. 3 and 4) gives evidence for intrinsic structural or/and magnetic inhomogeneities in the given materials, as was earlier seen in contacts with YFe Al 4 8 single crystals [6]. In this case, a lot of uncompensated magnetic moments of irregular ordering should appear, which may result in an exotic symmetry of the Cooper pairing and the unconventional behavior of PC spectra in the field.…”

“…4). In these spectra, after practically full suppression of the low-magnetic-field Andreev-reflection structure typical for PrAg 6 In 6 (at 0.08 T for the contact in Fig. 4), there arises another pseudogap-like structure.…”

“…Recently [6], we have proved an existence of a superconducting phase in YFe Al 4 8 by the point-contact (PC) Andreev-reflecton technique. The character of the measured PC spectra (differential resistance vs voltage, dV/dI V ( )) implied an unconventional type of superconductivity in this compound.…”