Transport phenomena in normal metals and superconductors

Transport phenomena in normal metals, superconductors and systems with strongly correlated electrons

Transport phenomena in normal metals and superconductors

● Novel features of scattering of the conduction electrons in normal metals are discovered under the conditions of size effect and strong magnetic field, depending on impurity concentration and weak deformation. Phonon drag effect has been studied in metal sandwiches [1].

● In a normal metal, negative differential conductivity is found [2].

● The effect of excess resistance of a normal metal contacting to a superconductor is discovered experimentally [3].

● Thermopower, fluctuation conductivity, and magnetic susceptibility have been studied in high-temperature bismuth cuprate crystals [4].

● Bernoulli effect has been observed in superconducting indium [5].

● It has been discovered that the conductance of a pure normal metal near a single NS boundary measured across the probes placed entirely in a normalregion behaves non-monotonically while temperature is changed. The effect is connected with the relation between the distance from the probes tothe boundary and coherence length for time-reversal excitations of Andreev type [6].

● Quantum magnetoresistive h/2e-oscillations in the conductivity of the domain structure in the intermediate state have been revealed and studied on various superconductors (Pb, Sn, In) with macroscopic elastic mean free path of electrons. Phase-sensitive magnetoresistive oscillations have been detected at temperatures T < 4 K in hybrid quasi-ballistic doubly connected SNS structures with single-crystal normal spacers of macroscopic sizes in all dimensions and elastic mean free path of electrons on the same scale (~ 100 mcm) which fact indicates that phase-breaking length in a pure metal may be macroscopic [7-12].

1. Chiang Yu.N. and Shevchenko O.G. Observation of phonon drag in a metal transmitted across a nonconducting medium // Physica 108B, 883 (1981).
2. Tszyan (Chiang) Yu.N. and Logvinov I.I. Detection of an electric field temperature domain in a metal specimen // Sov. J. Low Temp. Phys., 8, 388 (1982).
3. Tszyan (Chiang) Yu.N. and Shevchenko O.G. Measurement of resistance of the normal metal - superconductor (N–S) boundary // Sov. J. Low Temp., Phys. 14, 299 (1988).
4. Xiang (Chiang) Yu.N., Shevchenko O.G., Panfilov A.S. Thermopower and fluctuation effects in bismuth cuprate high-T_c crystals // Sov. J. Low Temp. Phys. 18, 916 (1992).
5. Chiang Yu.N. and Shevchenko O.G. Direct measurements of the Bernoulli effect in superconductors // Low Temp. Phys. 22, 513 (1996).
6. Chiang Yu.N. and Shevchenko O.G. Contribution of Andreev reflection to the increase in the resistance of the normal metal in a bimetallic N-S structure // JETP 86, 582 (1998).
7. Tsyan (Chiang) Yu.N. Resistance quantum oscillations in the intermediate state of singly connected Pb and Sn samples // JETP Lett. 71, 334 (2000).
8. Chiang Yu.N. and Shevchenko O.G. Mesoscopic quantum oscillations of the resistance in the intermediate state of type I superconductors // Low Temp. Phys. 27, 1000 (2001); Chiang Yu. and Shevchenko O. Mesoscopic normal-metal conductivity in the macroscopic NS system // In: High-T_c Superconductors and Related Materials, eds. S.-L. Drechsler and T. Mishonov. Kluwer Academic Publ., p. 447 (2001).
9. Chiang Yu.N. and Shevchenko O.G. Observation of subgap resistive oscillations in doubly-connected SNS systems with the suppressed proximity effect // JETP Lett. 76, 670 (2002).
10. Chiang Yu.N. and Shevchenko O.G. Phase-sensitive quantum effects in the Andreev conductance of an SNS system of metals with a macroscopic phase-breaking length // Low Temp. Phys. 29, 996 (2003).

11. Chiang Yu.N., Shevchenko O.G., Kolenov R.N. Direct measurements of spin-dependent and coherent effects in conductance of a ferromagnet/ superconductor system (cond-mat/0510352).
12. Chiang Yu.N. and Shevchenko O.G. Phase-sensitive Andreev conductance of an SNS system with the suppressed proximity effect // IJMP B19, 131 (2005).

Transport and electrical properties of the systems with strongly correlated electrons

● For the first time magnetotransport properties of rare-earth multilayer structures Er/Sc are studied. The conductivity increase is revealed at temperature-induced re-building of their magnetic ordering from antiferromagnetic to ferromagnetic, connected with spin-dependent mechanism of the conduction electrons scattering [1].

· Influence of the spin state on the thermopower of compounds ReACoO_y (Re = Ho, Er; A = Ca, Sr) is studied:
• Correlation between relative content of ions Co⁴⁺/Co and the magnitude of Seebeck factor, S, is found associated with the disproportionality of Co³⁺ and Co⁴⁺ ions [2-4].

• It is shown that the change in a spin state of ions Co3+ and emergence of mobile carriers of electric charges while introducing in the compound LaCoO3 alkaline-earth elements Sr and Ca and replacing La for Ho or Er essentially improves thermoelectric properties of the compound [2-4].

• Differential spectrophotometric method for definition of total quantity of ions Co3+ and Co4+ in ceramics is offered [2-4].

· Temperature and magnetic field dependences of electrical resistance from ceramic samples HoSrCoO and ErSrCoO are investigated at temperatures from 5 K to room temperature and in magnetic fields up to 7 kOe applied perpendicular to the current flow direction:

• It is observed that at low currents, the dependence of sample resistance on the magnitude of transport current is nonlinear, and the resistance magnitude manifests high sensitivity to low magnetic field [5, 6].

• Magnetoresistance of the samples HoSrCoO changes a sign in a narrow interval of temperatures and in comparable fields, varying from -50 % to +120 % [5].

• An abnormal increase of conductivity and a high magnetoresistance were revealed in a narrow region of Er and Sr concentration that was narrower and more shifted towards a metal phase than in La manganites [6].

• The behaviors of conductivity and magnetoresistance, including the nonlinear effects, are explained from the united point of view: by magnetostructure phase transitions, induced by corresponding dopant concentration, temperature or magnetic field, and the existence of spin-dependent contribution to the mechanism of electron correlation, connected with a double exchange of delocalization electrons between cobalt ions of different valence [5, 6].

1. Chiang Yu.N., Shevchenko O.G., Kolenov R.N. Magnetotransport properties of Er/Sc artificial multilayer structures // Low Temp. Phys. 31, 852 (2005).
2. Khirnyi V.Ph., Kozlovskii A.A., Chiang Yu.N., Shevchenko O.G., Puzikov V.M., Semenov A.V., Gaiduk O.V. Influence of the spin state of Co ions on thermopower of compounds Hox(Erx) Sr1-x(Ca1-x)CoO3-d // Novi Tekhnologii, 19, 11 (2008).
3. Khirnyi V.Ph., Chiang Yu.N., Shevchenko O.G., Kozlovskii A.A., Puzikov V.M., Semenov A.V. Influence of the spin state of Co ions on conductance of compounds Ho1-x Sr_xCoO_3-d // Novi Tekhnologii, 20, 4 (2008).
4. Khirnyi V.Ph., Kozlovskii A.A., Chiang Yu.N., Shevchenko O.G., Puzikov V.M., Semenov A.V. Influence of the spin state on conductivity of Co compounds of type RACoO3-d (R = Ho; A = Sr) // Proc. Third Int. Scientific-Engineering Conf. "Materials for Electronics and Current Information Technologies", Kremenchuk, Ukraine, p. 22 (2008).
5. Chiang Yu.N., Khirnyi V.Ph., Shevchenko O.G., Kozlovskii A.A., Semenov A.V., Puzikov V.M., and Deineka T.G. Transport properties of cobaltites containing holmium // Low Temp. Phys., 34, 947 (2008).
6. Chiang Yu.N., Dzyuba M.O., Khirnyi V.Ph., Shevchenko O.G., Kozlovskii A.A. Electrical properties of Er-cobaltites // Low Temp. Phys., 35, 876 (2009).