Transport properties and the large anisotropic magnetoresistance of Cu_xNbS₂single crystals

Abstract

The transport properties of Cu(x)NbS(2) (x = 0.09, 0.44 and 0.55) single crystals were systematically studied. The in-plane and out-of-plane resistivities decrease with increasing Cu content, and a transition with hysteresis shows up for the crystals with x = 0.44 and 0.55. The thermopower and Hall coefficient of Cu(x)NbS(2) show opposite signs, indicating that there are two kinds of carriers in this system. The angular dependences of the in-plane magnetoresistance (MR(ab) = (ρ(ab)(H)-ρ(ab)(0))/ρ(ab)(0) × 100%) at different temperatures were also studied. The single crystals with x = 0.44 and 0.55 show a strong anisotropic MR(ab). For the x = 0.55 sample, MR(ab) reaches 80% with a magnetic field of 14 T applied along the c-axis, while MR(ab) is less than 5% for the magnetic field applied within the ab-plane. These results can be well understood in the light of the anisotropic Fermi surface in the multiband system.

Spontaneous self-intercalation of copper atoms into transition metal dichalcogenides

“…S17), suggesting that a saturation of Cu intercalation state would be reached at this point. The homogeneous Cu 1.2 NbS 2 has a much higher intercalation state than the previous ones synthesized at high temperatures (16)(17)(18)(19)(20)(21). Our experimental saturation of Cu intercalation state is very close to that from the DFT calculations (table S1).…”

“…To reveal the origin of low intercalation concentration at high temperatures, ab initio molecular dynamic (AIMD) simulation was first used to investigate the stability of different Cu coverages on the surface of 2H-NbS 2 at 900°C, a typical temperature used for the synthesis of Cu x NbS 2 by the solid-state or CVT reaction route (fig. S2) (18,20,29). It revealed that some of Cu atoms were peeled off the surface of 2H-NbS 2 at this high temperature, until the atomic ratio drops to 0.6:1.0 (Cu:Nb).…”

“…A large number of transition metal atoms could intercalate into group IV and V layered TMDs to form well-defined intercalation compounds, M′ x MX 2 (M′ is the intercalation metal different from the one in the host material, x intercalation state) (14,15). Most of them were synthesized by the solid-state reaction or chemical iodine-vapor transport (CVT) methods, both at the elevated temperatures (650° to 1100°C) (16)(17)(18)(19)(20)(21). This high-temperature solid or vapor phase reaction forms homogeneous intercalation compounds; however, some defects are introduced into TMDs hosts, and meanwhile, the process is energy and time intensive.…”