The theory of thermodynamic and magnetic properties of multi-band superconductors

2010

J Supercond Nov Magn

A brief review of works on the microscopic theory of determining the upper critical field in twoband isotropic and anisotropic superconductors is given. The research is based on a set of the Ginzburg-Landau equations for the order parameters in a magnetic field that are studied in terms of the classical approach to a superconducting system in a magnetic field. Two inequivalent energy bands with different topology of Fermi surface cavities overlapping on the Fermi surface are discussed. The cases of the direction of the external magnetic field // the (ab) plane and // the crystallographic c axis are studied. The equations for determining H c2 (ab) and H c2 (c) for a pure superconductor and a superconductor doped with electrons and holes are derived. The analytical solutions to these equations in the vicinity of the superconducting transition temperature (T c -T<

Section: Introductionmentioning

confidence: 99%

The Upper Critical Field H c2 in Advanced Superconductors with Anisotropic Energy Spectrum

2010

J Supercond Nov Magn

“…Equation (16) contains complex integral dependences f mn (11)- (14); it is possible to solve this equation in the entire temperature interval 0 < T < T c only by numerical methods. However, it is possible to find its analytical solutions for two limit cases: a) in the vicinity of the critical temperature ρ n << 1, when T c -T<< T c and b) in the range of low temperatures ρ n >> 1 аt T<< T c .…”

Section: Calculation Of the Temperature Dependence Of The Upper Critimentioning

confidence: 99%

“…Many books and a lot of articles concerning this problem were published. Let us mention some publications related to the history of multiband superconductivity: books [3][4][5][6] reviews [7][8][9], and articles [10][11][12]. These works contain the names of scientists from various countries who have contributed to the development of the theory of two-band superconductivity.…”

Section: Introductionmentioning

confidence: 99%

Analytical solutions of the microscopic two-band theory for the temperature dependence of the upper critical fields of pure MgB2 compared with experimental data

Low Temperature Physics

Surdu

Ursu

et al. 2011

Main theoretical results of the microscopic two-band theory for the temperature dependence of the upper critical fields H c2 (ab) and H c2 (c) in pure two-band systems like MgB 2 are presented. The analytical solutions for the upper critical fields near the superconducting transition temperature and near the zero temperature were transformed to be directly compared with experimental data. The experimental H c2 (ab) and H c2 (c) temperature dependences of textured MgB 2 films near the superconducting transition temperature were measured and compared with the respective theoretical formulas. The results of this theoretical approach were also compared with earlier published experimental data of other authors. The chosen method allows obtaining an accurate match between the theoretical expressions and experimental results.PACS: 74.20.-z Theories and models of superconducting state.

“…From the general standpoint, this situation in superconductivity is not new and is known in the literature [5]- [7]. The history of the development of the theory of multiband superconductors is expounded, for example, in [8], [9].…”

Section: Introductionmentioning

confidence: 99%

Incommensurable state of a spin density wave and superconductivity in quasi-two-dimensional systems with an anisotropic energy spectrum

2011

Theor Math Phys

We investigate phase transitions in quasi-two-dimensional systems with an anisotropic energy spectrum and a deviation from the half-filling of the energy band (μ = 0). We demonstrate the possibility of the transition of an insulator into a half-metallic state when the nesting condition is violated because the parameter μ = 0 and of taking the umklapp processes into account. We obtain the basic equations for the parameters of the superconducting (Δ) and magnetic (M ) orders and determine the conditions for the emergence of superconductivity on the background of a spin-density-wave state and also for the coexistence of superconductivity and magnetism. We show that the transition of a magnetic system into a superconducting state as the parameter μ increases can be a first-order phase transition at low temperatures. We also obtain an expression for the heat capacity jump CS − CN at T = Tc, which depends on M and μ and differs essentially from the case of the Bardeen-Cooper-Schrieffer theory. We also consider the transformations related to the density of electron states of the relevant anisotropic system, which can undergo essential changes under pressure or doping.