A new type of low temperature conductivity in InSb doped with Mn

Abstract

We investigated unusual low temperature transport properties of InSb single crystals doped with manganese to concentrations in the range of 1017<NMn<2*1017cm-3 which includes the critical concentration for metal-insulator transition Ncr= 2*1017cm-3. It was found that in the temperature range T=10÷1.5K the resisitivity had an unusual behavior described by an exponential quadratic function ρ ∼ exp(Δ1/kT)2 where Δ1 varied from Δ1=0.3meV to Δ1=0. Coexistence of electrons and holes at temperatures around the metal-insulator transition in p-InSb(Mn) crystals gives the ground to explain the unusual temperature - resistivity dependence in the framework of excitonic insulator phase model (L. V. Keldysh and Yu. V. Kopaev, Sov. Phys. Solid State 6, 2219 (1965))

Analysis of the experimental data for impurity‐band conduction in Mn‐doped InSb

“…5, the Arrhenius plot of σT 3/2 shows a linear dependence below 5 K while that of σ shows saturation behaviour above 1.5 K showing a quadratic dependence. The activation energy Δ 3 = k B T 3 has been deduced to be 0.45 meV in the present study while Obukhov [7] deduced Δ 3 = 0.38 meV with neglecting the temperature dependence of the preexponential factor. Also for the other samples reported in Refs.…”

“…Finally, we comment on the temperature dependence of the conductivity. Obukhov [5][6][7] found that the conductivity of Mn-doped samples with Mn concentrations in the range of 1-3 × 10 17 cm −3 can be described by an unusual exponential quadratic temperature dependence as σ = σ 01 exp(−Δ 1 /k B T) 2 in the temperature range of 1.5-10 K while it can be described by a usual exponential dependence as σ = σ 3 exp(−Δ 3 /k B T) below 1.5 K. Obukhov [5][6][7] attributed this unusual dependence of σ to the formation of an excitonic insulator phase and related Δ 1 to the excitonic binding energy. On the other hand, we will show in the following that the unusual temperature dependence observed in the temperature range of 1.5-10 K can be well explained within the ordinary theory on NNH.…”

“…Therefore, for the conductivity data on the samples reported in Refs. [6,7], σT 3/2 was plotted against the reciprocal temperature.…”

“…For Mn-doped InSb, Obukhov [5][6][7] found that the resistivity due to impurityband conduction exhibits an unusual temperature dependence described by an exponential quadratic function ρ ~ exp(Δ 1 /k B T) 2 in the temperature range of 10-1.5 K. In addition, Obukhov and his coworkers [8][9][10] as well as Partin et al [11] found an anomalous sign reversal of the Hall coefficient in the temperature range of impurity-band conduction in Mn-doped InSb. Obukhov [5][6][7] associated these phenomena with the excitonic insulator phase and attributed the negative sign of the Hall coefficient at low temperatures to electron conduction. Partin et al [11] also attributed the negative sign to electron conduction and speculated that electrons are caused by residual donors as unintentional background impurities.…”

“…In the present study, we perform the analyses of the resistivity and the Hall-effect measurement data on the Mndoped InSb samples reported by Obukhov and his coworkers [5][6][7]10] and by Partin et al [11] along the lines of Holstein [12] and Emin [13] rather than the excitonic insulator phase model proposed by Obukhov [5][6][7]. It is shown that the anomalous sign reversal of the Hall coefficient in Mn-doped InSb can be well reproduced by including the negative Hall factor for hopping conduction in an acceptor impurity band.…”