Successive superconducting transitions and Anderson localization effect inTa2S2C

Abstract

A complex carbide Ta2S2C consists of van der Waals (vdw)-bonded layers with a stacking sequence · · · C-Ta-S-vdw-S-Ta-C-· · · along the c axis. The magnetic properties of this compound have been studied from DC and AC magnetic susceptibility. Ta2S2C undergoes successive superconducting transitions of a hierachical nature at T cl = 3.61 ± 0.01 K [H (l) c1 (0) = 28 ± 2 Oe and H (l) c2 (0) = 7.7 ± 0.2 kOe] and Tcu = 9.0 ± 0.2 K [H (u) c2 (0) = 6.0 ± 0.3 kOe]. The intermediate phase between Tcu and T cl , where δχ(= χF C − χZF C ) ≈ 0, is an intra-grain superconductive state occurring in the Ta-C layers in Ta2S2C. The low temperature phase below T cl , where δχ clearly appears, is an inter-grain superconductive state. The magnetic susceptibility at H well above H (l)c2 (0) is described by a sum of a diamagnetic susceptibility and a Curie-like behavior. The latter is due to the localized magnetic moments of conduction electrons associated with the Anderson localization effect, occurring in the 1T-TaS2 type structure in Ta2S2C.

Successive superconducting transitions inTa2S2Cstudied by electrical resistivity and nonlinear ac magnetic susceptibility

“…III D and is compared with that of T cu (H) and T cl (H). 1 In Sec. IV A we will show that ρ at H = 50 kOe is proportional to ln T at low temperatures.…”

“…In our previous paper, 1 we have shown that the difference δχ (= χ F C − χ ZF C ) shows a kink at T cl = 3.60 K. However, it does not reduce to zero at T = T cl , but exhibit a broad tail above T cl . In Fig.…”

“…A van der Waals (vdw) gap is between adjacent S layers. 1,2 The structure of Ta 2 S 2 C can be viewed as a structural sum of TaC and TaS 2 layers. The structural part corresponding to the TaS 2 layer is identical to the atom disposition of either 1T-TaS 2 in the case of 3R-Ta 2 S 2 C or a hypothetical 2H b -TaS 2 (MoS 2 -type) in the case of 1T-Ta 2 S 2 C (see the schematic diagram of the structure of Ta 2 S 2 C elsewhere 2,3 ).…”

“…In our previous paper 1 we have undertaken an extensive study on the DC and AC magnetic susceptibility of 3R-Ta 2 S 2 C. We have shown that this compound undergoes successive superconducting phase transitions at T cl (= 3.60 ± 0.02 K) and T cu (= 9.0 ± 0.2 K). Between T cu and T cl the two-dimensional (2D) superconducting phase mainly occurs in each TaC layer.…”

“…1 We note that the susceptibility at low T for 1T-TaS 2 layer shows a Curie-like behavior due to the localized magnetic moments of conduction electrons related to the Anderson localization effect. Figure 9 shows the H-T phase diagram.…”