Variable-range hopping conductivity and structure of density of localized states in LaMnO₃₊δ under pressure

The temperature dependence of the resistivity, ρ, of ceramic LaMnO₃₊δ with δ = 0.065 and 0.154 (or simply # 065 and # 154), is investigated under hydrostatic pressure, p, between the temperatures T = 80 and 320 K in magnetic fields up to 10 T. The data for ρ(T) are analysed within a Shklovskii - Efros-like variable-range hopping conductivity model, governed by a soft Coulomb gap, Δ, and a riidid gap, γ, in the density of localized states. The validity of this approach to the resistivity of LaMnO₃₊δ under ambient pressure was established in recent investigations (Laiho et al 2005 J. Phys: Condens. Matter 17, 105). In the present work it is shown that upon increasing p up to 11 kbar (# 154) and 13 kbar (# 065) the magnetic Curie temperature, Tc, is increased by ~12-13%. Cores ondingly, Δ(p) is decreased by ~ 7-8% and γ(p) by ~ 8% in #154 and 12% in # 065. Similarly, the electron localization radius a(p) is increased by ~ 4% in # 154 and 8% in # 065, respectively. The influence of pressure on Tc, Δ, γ and a is iterpreted by increasing the electron bandwidth and decreasing the polaron potential well, which stimulates the delocalization of electrons when p is increasedyesBelgorod State Universit

Teleportation of the Relativistic Quantum Field

The process of teleportation of a completely unknown one-particle state of a free relativistic quantum field is considered. In contrast to the non-relativistic quantum mechanics, the teleportation of an unknown state of the quantum field cannot be in principle described in terms of a measurement in a tensor product of two Hilbert spaces to which the unknown state and the state of the EPR-pair belong. The reason is of the existence of a cyclic (vacuum) state common to both the unknown state and the EPR-pair. Due to the common vacuum vector and the microcausality principle (commutation relations for the field operators), the teleportation amplitude contains inevitably contributions which are irrelevant to the teleportation process. Hence in the relativistic theory the teleportation in the sense it is understood in the non-relativistic quantum mechanics proves to be impossible because of the impossibility of the realization of the appropriate measurement as a tensor product of the measurements related to the individual subsystems so that one can only speak of the amplitude of the propagation of the field as a whole.Comment: 11 page

Spin-glass like behaviour of (Zn₁₋xMnx)₃As₂

Magnetic properties of the diluted magnetic semiconductor (Zn₁₋xMnx)₃As₂ (ZMA) have been investigated for compositions 0 ≤ x ≤ 0.13 and temperatures 4 K ≤ T ≤ 300 K. Several phenomena typical to spin-glasses were observed: history dependence, maxima in the functions Xdc(T) and Xac and smearing out of the maximum of Xdc(T) in strong fields. For samples with x = 0.10 and 0.13 our data give magnetic freezing temperatures around 200 K which is unusually high for diluted magnetic semiconductorsyesBelgorod State Universit

Unconventional critical behavior of magnetic susceptibility as a consequence of phase separation and cluster formation in La₀.₇Ca₀.₃MnO₃ thin films

Nonuniversal critical behavior of the dc magnetic susceptibility is observed near the paramagnetic to ferromagnetic transition in La₀.₇Ca₀.₃MnO₃ film samplesyesBelgorod State Universit

Variable-range hopping conductivity in La₁₋xCaxMn₁₋yFeyO₃: evidence of a complex gap in density of states near the Fermi level

The resistivity, ρ, of ceramic La₁₋xCaxMn₁₋yFeyO₃ with x = 0.3 and y = 0.0–0.09 is found to obey, between a temperature Tv ≈ 310–330 K and the ferromagnetic-to-paramagnetic transition temperature, Tc = 259–119 K (decreasing with y), the Shklovskii–Efros-type variable-range hopping conductivity law, ρ(T) = ρ₀(T) exp[(T₀/T)¹/₂]. This behaviour is governed by generation of a soft Coulomb gap Δ ≈ 0.42 eV in the density of localized states and a rigid gap δ(T) ≈ δ(Tv)(T/Tv)1/2 with δ(Tv) ≈ 0.16, 0.13 and 0.12 eV at y = 0.03, 0.07 and 0.09, respectively. Deviations from the square root dependence of δ(T), decreasing when y is increased, are observed as T → TC. The prefactor of the resistivity follows the law ρ₀ (T) ~ Tm, where m changes from 9/2 at y = 0 to 5/2 in the investigated samples with y = 0.03, 0.07 and 0.09, which is connected to introduction of an additional fluctuating short-range potential by doping with FeyesBelgorod State Universit

Hopping conductivity of Ni-doped p-CdSb in strong magnetic fields

In this work detailed investigation of the hopping conductivity in p-CdSb:Ni in strong magnetic field is reported to complete the picture of hopping charge transfer in this materialyesBelgorod State Universit