Multiband effects and possible Dirac fermions inFe1+yTe0.6Se0.4

Abstract

We investigated the transport properties of Fe1+yTe0.6Se0.4 single crystals with different amounts of excess Fe prepared by O2 annealing. The O2 annealing remarkably improves transport properties. In particular, a strongly nonlinear Hall resistivity was observed only in the fully-annealed crystal, and the magnetoresistance (MR) is drastically enhanced after annealing, reaching a value larger than 17% at 16 K and 14 T. The obvious change of transport properties after the annealing indicates that the band structure of Fe1+yTe0.6Se0.4 is affected by the excess Fe. The nonlinear Hall resistivity and violation of (modified) Kohler's scaling of the large MR prove the multiband effects in the Fe1+yTe0.6Se0.4 single crystal. The MR for the fully-annealed crystal develops linearly against magnetic field from intermediate field (e. g. 2 T at 16 K) to the measurement limit of 14 T. This phenomenon is interpreted by the existence of Dirac cone state, in which all the Dirac fermions occupy only the lowest Landau level in the quantum limit.

Unabridged phase diagram for single-phased FeSexTe1-x thin films

“…Figure 4(d) demonstrates that the R H of all three films is almost temperature independent from 80 K to room temperature. This phenomenon is similar to that in both films819 and single crystal20. In the low temperature regime below 80 K, R H for all three films shows an obvious divergence with temperature.…”

Transition-metal substitutions in iron chalcogenides

“…At y = 0 the R H is positive; it rises as T is lowered down from 300 K to about 55 K, and has a downturn at lower T . Such a behavior, reported before [19,21], results from the interplay between different T dependencies of charge carrier densities and their mobilities in the multiband system. The T dependencies of ρ/ρ 300 for doped crystals acquire low-temperature upturns, which increase progressively with increasing y.…”

“…Few attempts of the transitionmetal doping of single crystals of FeTe 1−x Se x have been reported, and for a limited impurity contents [12][13][14][15]. The studies are complicated by two types of magnetic correlations existing throughout the phase diagram [16,17] and by crystal inhomogeneities, such as Fe excess [16,[18][19][20][21] or Fe vacancies [22][23][24]. In this Rapid Communication we report on a comprehensive study of the transport properties of FeTe 0.65 Se 0.35 single crystals, doped over a wide doping range by transition-metal elements, Co and Ni [25].…”

Influence of interstitial Fe to the phase diagram of Fe1+yTe1−xSex single crystals

“…In the parent compound Fe 1+ y Te, the long-range ( π, 0) order can be tuned from commensurate to incommensurate by changing the amount of interstitial Fe19. Furthermore, the magnetic moment from interstitial Fe will act as a pair breaker and also localize the charge carriers3031. Thus, the existence of interstitial Fe, which is easily formed in the standard growth technique employing slow cooling and their amount varies among different groups32, makes the phase diagram of Fe 1+ y Te 1− x Se x still unclear until now.…”