Evidence for nodal superconductivity in a layered compound Ta₄Pd₃Te₁₆

Abstract

We report an investigation of the London penetration depth ∆λ(T ) on single crystals of the layered superconductor Ta4Pd3Te16, where the crystal structure has quasi-one-dimensional characteristics. A linear temperature dependence of ∆λ(T ) is observed for T ≪ Tc, in contrast to the exponential decay of fully gapped superconductors. This indicates the existence of line nodes in the superconducting energy gap. A detailed analysis shows that the normalized superfluid density ρs(T ), which is converted from ∆λ(T ), can be well described by a multigap scenario, with nodes in one of the superconducting gaps, providing clear evidence for nodal superconductivity in Ta4Pd3Te16. * msmidman@zju.edu.cn † hqyuan@zju.edu.cn I. INTRODUCTIONRecently the layered Pd-based ternary chalcogenides have attracted much research interest. New compounds with similar crystal structures were discovered, which opened up new opportunities to investigate the relationship between superconductivity and reduced crystal dimensionality [1][2][3]. Unusual superconducting properties were revealed in Ta 2 Pd x S 5 (x 1.0) and Nb 2 Pd 0.81 S 5 , where extremely large upper critical fields of µ 0 H c2 (0) = 31 T and µ 0 H c2 (0) = 37 T were observed respectively, both of which are almost twice the size of the Pauli limiting field (H P ) [4,5]. These are reminiscent of the quasi-one-dimensional (Q1D) organic compounds (TMTSF) 2 X (TMTSF = tetramethyltetraselenafulvalene, X = PF 6 , ClO 4 ), which are believed to be unconventional superconductors [6,7]. Moreover, subsequent specific heat measurements in Nb 2 Pd(S 1−x Se x ) and Ta 2 PdSe 5 show a slight deviation from the typical behavior of single band s-wave superconductors, which likely indicates multi-band superconductivity in these systems [8,9].A new layered Pd-based ternary compound Ta 4 Pd 3 Te 16 was found to exhibit superconductivity at T c ≈4.6 K [10]. It possesses a layered crystal structure as well as quasi-one-dimensional (Q1D) characteristics, with chains running along the b axis. Band structure calculations for Ta 4 Pd 3 Te 16 reveal that its Fermi surface consists of four branches, including two one-dimensional nested sheets, a two-dimensional cylindrical sheet and a three-dimensional one, which drives this compound to be an anisotropic but three-dimensional metal [11]. This is also consistent with the results of upper critical field measurements where a moderate anisotropy of µ 0 H c2 was observed and the coherence lengths along all three axes are much larger than the interchain distance [12]. High field measurements uncover a quasi-linear magnetoresistance without any sign of saturation up to about 50 T, as well as a violation of Kohler's rule, indicating the existence of charge density wave (CDW) fluctuations in this compound [13], which has also been suggested from scanning tunneling spectroscopy (STS) experiments [14]. Meanwhile, there have also been various studies to characterize the superconducting order parameter, which could give the crucial information about the pairing mecha...

Normal-state properties of the quasi-one-dimensional superconductor Ta4Pd3Te16

“…Li 0.9 Mo 6 O 17 [4] and (TMTSF) 2 PF 6 [16], categorizes it as an anisotropic but threedimensional superconductor in nature. Detailed analyses of the specific heat capacity, thermal conductivity, London penetration depth and scanning tunneling spectroscopy (STS) give the consistent evidences of Ta 4 Pd 3 Te 16 as a multiband superconductor possibly with a nodal superconducting gap structure [12,14,17,18], whereas the other similar STS study as well as NMR/NQR data characterizes it as an s-wave nodeless superconductor [19,20]. As a layered superconductor with Q1D chains, Ta 4 Pd 3 Te 16 has been experimentally argued to be proximal to CDW ordering [11,14].…”