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  • 1
    Electronic Resource
    Electronic Resource
    Anisotropic random resistor networks: A model for piezoresistive response of thick-film resistors (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 92 (2002), S. 1981-1986 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Considerable evidence suggests that thick-film resistors are close to a metal–insulator transition and that tunneling processes between metallic grains are the main source of resistance. We consider as a minimal model for description of transport properties in thick-film resistors a percolative resistor network, with conducting elements governed by tunneling. For both oriented and randomly oriented networks, we show that the piezoresistive response to an applied strain is model dependent when the system is far away from the percolation thresold, while in the critical region it acquires universal properties. In particular close to the metal–insulator transition, the piezoresistive anisotropy shows a power law behavior. Within this region, there exists a simple and universal relation between the conductance and the piezoresistive anisotropy, which could be experimentally tested by common cantilever bar measurements of thick-film resistors. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1495067
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  • 2
    Electronic Resource
    Electronic Resource
    Gauge factor of thick-film resistors: Outcomes of the variable-range-hopping model (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 4164-4169 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Despite a large amount of data and numerous theoretical proposals, the microscopic mechanism of transport in thick-film resistors remains unclear. However, recent low-temperature measurements point toward a possible variable-range-hopping mechanism of transport. Here, we examine how such a mechanism affects the gauge factor of thick-film resistors. We find that at sufficiently low temperatures T, for which the resistivity follows the Mott's law R(T)∼exp(T0/T)1/4, the gauge factor (GF) is proportional to (T0/T)1/4. Moreover, the inclusion of Coulomb gap effects leads to GF∼(T0′/T)1/2 at lower temperatures. In addition, we study a simple model which generalizes the variable-range-hopping mechanism by taking into account the finite mean intergrain spacing. Our results suggest a possible experimental verification of the validity of the variable-range hopping in thick-film resistors. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1290738
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  • 3
    Electronic Resource
    Electronic Resource
    Gauge factor enhancement driven by heterogeneity in thick-film resistors (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 322-327 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a simple picture of the gauge factor (GF) enhancement in highly heterogeneous materials such as thick-film resistors. We show that when the conducting phase is stiffer than the insulating one, the local strains within the latter are enhanced with respect to the averaged macroscopic strain. Within a simple model of electron tunneling processes, we show that the enhanced local strain leads to values of GF higher than those expected for a homogeneous system. Moreover, we provide formulas relating the enhancement of GF to the elastic and microstructural characteristics of thick-film resistors. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1376672
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  • 4
    Electronic Resource
    Electronic Resource
    The effect of the chemical composition of a ferrallitic soil on neutron probe calibration
    Amsterdam : Elsevier
    Soil Technology 7 (1994), S. 233-247 
    Details
    ISSN: 0933-3630
    Keywords: Boron ; Ferrallitic soil ; Neutron probe calibration ; Tourmaline
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0933-3630(94)90024-8
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  • 5
    Electronic Resource
    Electronic Resource
    -wave nonadiabatic superconductivity (2000)
    Springer
    The European physical journal 17 (2000), S. 235-243 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 63.20.Kr Phonon-electron and phonon-phonon interactions - 71.38.+i Polarons and electron-phonon interactions - 74.20.Mn Nonconventional mechanisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The inclusion of nonadiabatic corrections to the electron-phonon interaction leads to a strong momentum dependence in the generalized Eliashberg equations beyond Migdal's limit. For a s-wave symmetry of the order parameter, this induced momentum dependence leads to an enhancement of when small momentum transfer is dominant. Here we study how the d-wave symmetry affects the above behavior. We find that the nonadiabatic corrections depend only weakly on the symmetry of the order parameter provided that only small momentum scatterings are allowed for the electron-phonon interaction. In this situation, We show that also for a d-wave symmetry of the order parameter, the nonadiabatic corrections enhance . We also discuss the possible interplay and crossover between s- and d-wave depending on the material's parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510070137
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  • 6
    Electronic Resource
    Electronic Resource
    Spin susceptibility in small Fermi energy systems: effects of nonmagnetic impurities (2002)
    Springer
    The European physical journal 30 (2002), S. 511-517 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 74.25.-q General properties; correlations between physical properties in normal and superconducting states – 71.28.+d Narrow-band systems; intermediate-valence solids – 74.62.Dh Effects of crystal defects, doping and substitution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: In small Fermi energy metals, disorder can deeply modify superconducting state properties leading to a strong suppression of the critical temperature Tc. In this paper, we show that also normal state properties can be seriously influenced by disorder when the Fermi energy E F is sufficiently small. We calculate the normal state spin susceptibility χ for a narrow band electron-phonon coupled metal as a function of the non-magnetic impurity scattering rate . We find that as soon as is comparable to E F, χ is strongly reduced with respect to its value in the clean limit. The effects of the electron-phonon interaction including the nonadiabatic corrections are discussed. Our results strongly suggest that the recent finding on irradiated MgB2 samples can be naturally explained in terms of small E F values associated with the σ-bands of the boron plane, sustaining therefore the hypothesis that MgB2 is a nonadiabatic metal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2002-00408-2
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  • 7
    Electronic Resource
    Electronic Resource
    Nonadiabatic superconductivity: Electron phonon interaction beyond Migdal's Theorem (1995)
    Springer
    Journal of low temperature physics 99 (1995), S. 535-543 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A common characteristic of all the high Tc materials, oxides and Fullerene compounds, is that the Fermi energy is much smaller than in usual metals and it is of the order of the Debye phonon frequencies. This requires a generalization of the usual BCS-Eliashberg scheme to include non adiabatic effects beyond Migdal's Theorem. We have developed the first steps of this generalization and here we discuss the main results, the possible lines of development and the main open problems. The key point is that the first order non adiabatic effects (vertex corrections and similar processes) depend crucially on the momentum (q) of the exchanged phonons. If small q scattering is predominant, one obtains a strong enhancement of Tc and various other effecs also for the normal state that should lead to precise experimental predictions. The predominance of small q scattering can be naturally obtained from electronic correlations but it could arise also from different properties like peaks in the density of states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00752336
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  • 8
    Electronic Resource
    Electronic Resource
    Superconductivity of Rb 3 C 60 : breakdown of the Migdal-Eliashberg theory (2001)
    Springer
    The European physical journal 21 (2001), S. 383-391 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 74.70.Wz Fullerenes and related materials – 74.20.-z Theories and models of superconducting state – 63.20.Kr Phonon-electron and phonon-phonon interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: In this paper, through an exhaustive analysis within the Migdal-Eliashberg theory, we show the incompatibility of experimental data of Rb3C60 with the basic assumptions of the standard theory of superconductivity. For different models of the electron-phonon spectral function α 2 F (Ω) we solve numerically the Eliashberg equations to find which values of the electron-phonon coupling λ, of the logarithmic phonon frequency and of the Coulomb pseudopotential μ * reproduce the experimental data of Rb3C60. We find that the solutions are essentially independent of the particular shape of α 2 F (Ω) and that, to explain the experimental data of Rb3C60, one has to resort to extremely large couplings: λ = 3.0±0.8. This results differs from the usual partial analyses reported up to now and we claim that this value exceeds the maximum allowed λ compatible with the crystal lattice stability. Moreover, we show quantitatively that the obtained values of λ and strongly violate Migdal's theorem and consequently are incompatible with the Migdal-Eliashberg theory. One has therefore to consider the generalization of the theory of superconductivity in the nonadiabatic regime to account for the experimental properties of fullerides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00011123
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  • 9
    Electronic Resource
    Electronic Resource
    The physical origin of the electron-phonon vertex correction (1999)
    Springer
    The European physical journal 10 (1999), S. 247-255 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 63.20.Kr Phonon-electron and phonon-phonon interactions - 71.38.+i Polarons and electron-phonon interactions - 74.20.Mn Nonconventional mechanisms (spin fluctuations, polarons and bipolarons, resonating valence bond model, anyon mechanism, marginal Fermi liquid, Luttinger liquid, etc.)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: In the theory of nonadiabatic superconductivity several features are governed by the electron-phonon vertex correction which has a complex structure both in momentum and frequency. We derive a physical interpretation of such nonadiabatic effects that permits to link them to specific material properties. We show how the nonadiabatic vertex correction can be decomposed into two terms with different physical origins. In particular, the first term describes the lattice polarization induced by the electrons and it is essentially a single-electron process whereas the second term is governed by the particle-hole excitations due to the exchange part of the phonon-mediated electron-electron interaction. We show that by weakening the influence of the exchange interaction the vertex takes mostly positive values giving rise to an enhanced effective coupling in the scattering with phonons. This weakening of the exchange interaction can be obtained by lowering the density of the electrons, or by considering only long-ranged (small q) electron-phonon couplings.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510050852
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  • 10
    Electronic Resource
    Electronic Resource
    Die ≪Thermozahl≫ des Terpentinöls (1915)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 54 (1915), S. 382-383 
    Details
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01378901
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