Electrical properties ofNiS2−xSexsingle crystals: From Mott insulator to par

Abstract

Electrical resistivity () and Seebeck-coefficient measurements (␣) are reported for NiS 2Ϫx Se x single crystals in the range 0рxр0.71. There is a general trend toward increasing metallicity with increasing x. In the range 0.38рxр0.51 a pronounced rise of with temperature (T) is observed where the antiferromagnetic insulating ͑or antiferromagnetic metallic͒ phase changes over to the paramagnetic insulating phase. The analysis of ␣ vs T curves suggests that in the low-temperature insulating state both holes and electrons participate in charge transport. It is emphasized that the many changes in electrical characteristics occur without significant alterations in the pyrite crystal structure, and that physical properties are greatly altered solely by adjustment of the anion sublattice while the cation sublattice remains intact. The results concerning electrical transport for the samples with 0.38рxр0.55 are interpreted qualitatively on the basis of an onset of the Hubbard splitting into subbands at the transition to the insulating ͑semiconducting͒ state, which takes place in the temperature interval ͑50-100 K͒ upon heating the samples. The metallic state close to the metalsemiconductor boundary is viewed as being an antiferromagnetic semimetal, with an anisotropic Slater gap.

High-frequency thermoelectric response in correlated electronic systems

“…(27) and Eq. (28). The values of S * at open and closed circles are very close, indicating the consistency between the real and Matsubara frequency approach to calculate S * .…”

“…(27) and Eq. (28). The second method starts from computing ReL 11 (ω) and ReL 12 (ω) from spectral functions A k (ω) using Eq.…”

“…As temperature increases, the asymmetry between the two Hubbard bands near Fermi surface becomes less significant because more spectral weight from the higher Hubbard band takes part into the transport and the sign of S 0 is determined by the difference between the weight of lower and higher Hubbard. This crossover is thus considered to be responsible for the second sign change 9 and also has been observed experimentally 28 . Therefore, above T = 0.6D, the transport is completely dominated by incoherent excitations from both Hubbard bands.…”

X-ray photoemission study ofNiS2−xSexKrishnakumar1, Sarma2 2003Phys. Rev. B23580View full textAdd to dashboardCite

“…It is also found that for a narrow range of composition near x c , the system undergoes a transition from antiferromagnetic insulator to antiferromagnetic metal with decreasing temperature [7]. The low temperature antiferromagnetic metallic state vanishes around x = 1.0, leading to a paramagnetic metallic ground state of the system [7].…”

Density wave like transport anomalies in surface doped Na2IrO3

“…A prominent example of this is the correlated insulator NiS 2 . 18 Figure 3 (a) shows R s (T) data measured for the crystal etched for 20 minutes, while cooling and warming in various applied magnetic fields H. The sheet resistance increases on cooling below T = 305 K and reaches a maximum around 250 K. A step-like increase is observed in R s (T) at T 0 = 220 K after which there is a rapid decrease in sheet resistance suggesting metallic behaviour down to 20 K, below which a slight increase in sheet resistance is observed again. This upturn is stronger than observed for the 10 min sample and will be consistent with a stronger localization due to the increased disorder introduced due to etching for longer times.…”