Superconductivity in a misfit layered compound (SnSe)_1.16(NbSe₂)

Abstract

The large size single crystals of (SnSe)(NbSe) misfit layered compound were grown and superconductivity with T of 3.4 K was first discovered in this system. Powder x-ray diffraction and high resolution transmission electron microscopy clearly display the misfit feature between SnSe and NbSe subsystems. The Sommerfeld coefficient γ inferred from specific-heat measurements is 16.73 mJ mol K, slightly larger than the usual misfit compounds. The normalized specific heat jump [Formula: see text] is about 0.98, and the electron-phonon coupling constant [Formula: see text] is estimated to be 0.80. The estimated value of the in-plane upper critical magnetic field, [Formula: see text](0), is about 7.82 T, exceeding the Pauli paramagnetic limit slightly. Both the specific-heat and H data suggest that (SnSe)(NbSe) is a multi-band superconductor.

Multi-band Superconductivity in a misfit layered compound (SnSe)1.16(NbSe2)2

“…We calculated the lattice parameters of (SnSe) 1.16 (NbSe 2 ) 2 from the SAED patterns and summarized in table 1. The values of a and b are close to those of (SnSe) 1.16 (NbSe 2 ) for both subsystems [14], but the space group of two subsystems are both changed. We can obtained the incommensurate factor as 1+y=2a 2 /a 1 ≈1.…”

“…Moreover, it is found that about 4% Se are substituted by Br, which is unavoidably caused by the bromine transport agent. Such a halogen contamination also occurs in other MLCs such as (SnSe) 1.16 (NbSe 2 ) and (PbSe) 1.12 (TaSe 2 ) which were grown by the same CVT method [14,15]. Figure 1(b) shows the XRD pattern of a (SnSe) 1.16 (NbSe 2 ) 2 single crystal at room temperature, and the inset is a photograph of the typical as-grown single crystal.…”

“…Moreover, the electron-phonon coupling constant λ e-ph is estimated to be 0.96 from the McMillan equation where μ * is the Coulomb pseudopotential, and an empirical value of 0.15 is used. Comparing with (SnSe) 1.16 (NbSe 2 ) (λ e-ph =0.80) [14], the λ e-ph of (SnSe) 1.16 (NbSe 2 ) 2 is enhanced. This value indicates that (SnSe) 1.16 (NbSe 2 ) 2 is close to strong coupling regime.…”

“…In the MLCs family, many superconductors have been discovered [1, 2, 3-6, 7-12, 13-15]. Their T c values are in the range of about 0.4-5.3 K. The upper critical field (H c2 ) of most MLC superconductors are usually small in both in-plane and out-of-plane directions, [8,2,13,[15][16][17][18], and only a few MLC superconductors exhibit unusually large H c2 [14,19].…”

“…Although the NbSe 2 based-MLC (SnSe) 1.16 (NbSe 2 ) has already been reported [23] before and its superconductivity has been investigated recently [14], there is no report on (SnSe) 1.16 (NbSe 2 ) 2 with n=2 up to now. Here, we report the successful synthesis of (SnSe) 1.16 (NbSe 2 ) 2 single crystals and the discovery of superconductivity with an onset transition temperature of 5.3K.…”