Effect of Cr doping on the electrical conductivity and Seebeck coefficient in the superconductors obtained from the Bi–Pb–Sr–Ca–Cu–Cr–O-type glassy precursors by annealing

2000 ◽  
Vol 15 (5) ◽  
pp. 1076-1082 ◽  
Author(s):  
H. K. Barik ◽  
S. K. Ghorai ◽  
S. Bhattacharya ◽  
D. Kilian ◽  
B. K. Chaudhuri
Keyword(s):  
Conduction Mechanism ◽  
Linear Part ◽  
Band Model ◽  
Phonon Drag ◽  
Temperature Dependent ◽  
Breaking Mechanism ◽  
Cr Concentration ◽  
Cr Doping ◽  
Two Band Model ◽  
Variable Range Hopping Conduction

Homogenous (Bi3Pb)Sr3Ca3 (Cu4−nCrn)Ox (n 4 0 to 0.20) type glassy precursors become high-Tc superconductors by annealing at 840 °C. The suppression of Tc with increase of Cr concentration supports the pair-breaking mechanism. The feeble semiconducting behavior shown by the doped samples above their respective Tc values followed Mott's variable range hopping conduction mechanism. Like Ti- and Fe-doped samples, studied earlier, the thermoelectric power (TEP) of the present Cr-containing sample showed small positive peak above Tc, which was considered to be associated with the phonon-drag effect. The linear part of the temperature-dependent TEP (above Tc) well fitted the two-band model.

Magnetic Field Dependence of the Thermoelectric Power of Iron

1972 ◽  
Vol 50 (22) ◽  
pp. 2836-2839 ◽  
Author(s):  
F. J. Blatt
Keyword(s):  
Magnetic Field ◽  
Thermoelectric Power ◽  
Magnetic Field Dependence ◽  
Cold Work ◽  
Transverse Magnetic ◽  
Band Model ◽  
Spin Orbit Coupling ◽  
Phonon Drag ◽  
Domain Alignment ◽  
Two Band Model

The thermoelectric power of iron exhibits a broad maximum of about 17 µV/K near 200 K. The relatively high temperature of this maxim and its dependence on alloying and cold work argue against phonon drag as the mechanism responsible for this peak. Recently, MacInnes and Schröder proposed that this peak derives from anisotropic (scew) scattering due to spin–orbit coupling, which may be simulated by a large effective transverse magnetic field. Their calculations, which reproduce experimental observations quite well, are based on an expression derived by Sondheimer that is valid for an ideal two-band model. According to this model and the suggestion of MacInnes and Schröder, the thermoèlectric power of iron should be strongly influenced by domain alignment. Measurements of the dependence of the thermoelectric power of iron in transverse and longitudinal magnetic fields reported here yield results contrary to the predictions of that model.

scholarly journals Temperature dependent magnetization of the two band model for diluted magnetic semiconductors

2014 ◽  
Vol 24 (2) ◽  
pp. 141
Author(s):  
Vu Kim Thai ◽  
Hoang Anh Tuan
Keyword(s):  
Diluted Magnetic Semiconductors ◽  
Magnetic Semiconductors ◽  
Magnetic Coupling ◽  
Band Model ◽  
Coupling Constant ◽  
Temperature Dependent ◽  
Impurity Bands ◽  
Diluted Magnetic ◽  
Two Band Model ◽  
Temperature Dependent Magnetization

The temperature dependent magnetization of a two band model for diluted magnetic semiconductors as a function of magnetic coupling constant, hopping parameters and carrier densities is calculated by using the coherent potential approximation.  It is shown that the degree of overlapping of the impurity bands  and carrier density are crucial parameters determining the magnetization behavior of the system.

scholarly journals Temperature-Dependent s± ↔ s++ Transitions in the Multiband Model for Fe-Based Superconductors with Impurities

Symmetry ◽  
2018 ◽  
Vol 10 (8) ◽  
pp. 323 ◽  
Author(s):  
V. Shestakov ◽  
M. Korshunov ◽  
O. Dolgov
Keyword(s):  
Narrow Range ◽  
Impurity Scattering ◽  
Band Model ◽  
Temperature Dependent ◽  
Clean Limit ◽  
Scattering Rate ◽  
Nonmagnetic Impurities ◽  
Multiband Model ◽  
Critical Temperature Tc ◽  
Two Band Model

We study the dependence of the superconducting gaps on both the disorder and the temperature within the two-band model for iron-based materials. In the clean limit, the system is in the s± state with sign-changing gaps. Scattering by nonmagnetic impurities leads to the change of the sign of the smaller gap, resulting in a transition from the s± to the s++ state with the sign-preserving gaps. We show here that the transition is temperature-dependent. Thus, there is a line of s±→s++ transition in the temperature–disorder phase diagram. There is a narrow range of impurity scattering rates, where the disorder-induced s±→s++ transition occurs at low temperatures, but then the low-temperature s++ state transforms back to the s± state at higher temperatures. With increasing impurity scattering rate, the temperature of such s++→s± transition shifts to the critical temperature Tc, and only the s++ state is left for higher amounts of disorder.

IONIZATION ENERGY AND IMPURITY BAND CONDUCTION OF SHALLOW DONORS IN n-GALLIUM ARSENIDE

1967 ◽  
Vol 45 (1) ◽  
pp. 119-126 ◽  
Author(s):  
J. Basinski ◽  
R. Olivier
Keyword(s):  
Ionization Energy ◽  
Impurity Band ◽  
Shallow Donor ◽  
Band Model ◽  
A Value ◽  
Transition Concentration ◽  
Temperature Electron ◽  
Two Band Model ◽  
Band Conduction ◽  
Made In

Hall effect and resistivity measurements have been made in the temperature range 4.2–360 °K on several samples of n-type GaAs grown under oxygen atmosphere and without any other intentional dopings. The principal shallow donor in this material is considered to be Si. All samples exhibited impurity-band conduction at low temperature. Electron concentrations in the conduction band were calculated, using a two-band model, and then fitted to the usual equation expressing charge neutrality. A value of 2.3 × 10−3 eV was obtained for the ionization energy of the donors, for donor concentration ranging from 5 × 1015 cm−3 to 2 × 1016 cm−3. The conduction in the impurity band was of the hopping type for these concentrations. A value of 3.5 × 1016 cm−3 was obtained for the critical transition concentration of the impurity-band conduction to the metallic type.

ENERGY BAND OVERLAPPING IN HIGH-Tc SUPERCONDUCTORS

1996 ◽  
Vol 10 (30) ◽  
pp. 1483-1490 ◽  
Author(s):  
M. MORENO ◽  
R. M. MÉNDEZ-MORENO ◽  
M. A. ORTIZ ◽  
S. OROZCO
Keyword(s):  
Weak Coupling ◽  
Cuprate Superconductors ◽  
Weak Coupling Limit ◽  
Band Model ◽  
Coupling Constant ◽  
High Tc Superconductors ◽  
Energy Bands ◽  
Effective Coupling ◽  
High Tc ◽  
Two Band Model

Multi-band superconductors are analyzed and the relevance of overlapping energy bands to the high-T c of these materials is studied. Within the BCS framework, a two band model with generalized Fermi surface topologies is developed. Values of the overlapped occupancy parameters for typical cuprate superconductors are obtained as a function of the ratio R and the effective coupling constant, λ, in the weak-coupling limit. The overlap scale is of the order or lower than the cutoff (Debye) energy. The typical behavior of the isotope effect is obtained. As these superconductors have transition temperatures above the phonon barrier, the results of this approach are important to the generic understanding of the high-T c superconducting mechanism.

Thermoelectric Power of the Liquid Sn—Te Alloy

1982 ◽  
Vol 37 (10) ◽  
pp. 1127-1131 ◽  
Author(s):  
D. H. Kurlat ◽  
M. Rosen
Keyword(s):  
Thermoelectric Power ◽  
Hard Sphere ◽  
Stoichiometric Composition ◽  
Band Model ◽  
Liquid Alloys ◽  
Sphere Approximation ◽  
The Difference ◽  
Predicted Values ◽  
Experimental Values ◽  
Two Band Model

The Seebeck coefficient (S) of Sni1-x- Tex liquid alloys was measured as a function of concentration and temperature. For 0 ≦ x <0.45 the behaviour is metallic; S values are small and negative, rising linearly with temperature. The predicted values of Ziman's theory when using the hard sphere approximation disagree with the experimental ones. The change in sign occurs for 0.45. For x = 0.5 (stoichiometric composition) the thermoelectric power decreases linearly with temperature. This fact is explained assuming a two-band model. For x ≧ 0.6 the liquid alloy becomes more semiconducting and presents a maximum in the isotherms of S for x = 0.65. For the excess tellurium concentration range we have calculated the difference EF - EV and γ/kB, assuming a S(1/T) law. The experimental values are compared with those of Dancy and Glazov.

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