I. N. Askerzade

On the Ginzburg-Landau analysis of the upper critical field Hc2 in MgB2

We study the temperature dependence of the upper critical field Hc2(T) for superconducting magnesium diboride, MgB2 in the vicinity of Tc using a two-band Ginzburg-Landau (G-L) theory. The temperature dependence of Hc2(T) near Tc exhibits a positive curvature. In addition, the calculated temperature dependence and its higher-order derivatives are also shown to be in good agreement with the experimental data. In analogy with the multi-band character of the Eliashberg microscopic theory, the positive curvature of Hc2(T) is described reasonably by solving the two-band G-L theory.

Two-band Ginzburg-Landau theory for the lower critical field Hc1 in MgB2

The temperature dependence of the lower critical field Hc1(T) for the superconducting magnesium diboride, MgB2, is studied in the vicinity of Tc using a two-band Ginzburg–Landau (G–L) theory. The theoretically calculated Hc1(T) near Tc exhibits a negative curvature. The results are shown to be in good agreement with the experimental data. In addition, two-band G–L theory calculations give a temperature dependence of the Ginzburg–Landau parameter κ (T) = λ (T)/ξ (T), which varies little with the temperature in a manner similar to the microscopic single-band BSC theory.

Josephson-Effect Samplers: A Review

Studies on Josephson samplers are reviewed. The dynamic properties of Josephson junctions used as sensitive comparators in the samplers are analyzed. A theory in terms of which the time resolution and sensitivity of Josephson comparators can be estimated is put forward, and analytical formulas for the limiting characteristics of the samplers are derived. The performance of Josephson samplers based on high-temperature superconductors is discussed. It is shown that samplers with a subpicosecond resolution and nanoampere sensitivity are a feasibility.

Effects of the superconductivity transition on the response of YBCO edge transition bolometers

Dependence of the phase and magnitude of the response of Y–Ba–Cu–O edge transition bolometers on the superconducting transition is studied. The responses of both large and small area devices were investigated and several anomalies are observed. The response of small area LaAlO3 devices considerably differed from that expected based on the dR/dT curve. This discrepancy is observed to be strongly dependent on the superconducting transition. Both the phase and magnitude/(dR/dT) of the response of the devices showed abrupt changes for below the Tc-onset when measured versus temperature, while the phase variation also showed strong dependence on the modulation frequency. We present the analysis and propose mechanisms responsible for the modulation frequency dependence of the response characteristics versus temperature, within the superconductivity transition region of the devices.

Thermodynamic Magnetic Field and Specific Heat Jump of a Bulk Superconductor MgB2 Using Two-Band Ginzburg–Landau Theory

Temperature dependence of the thermodynamic magnetic field for the superconducting magnesium diboride, MgB 2 , is studied in the vicinity of T c using a two-band Ginzburg–Landau (G–L) theory. The results are shown to be in good agreement with calculations from experimental data. In addition, the two-band G–L theory gives a smaller specific heat jump, than a single-band G–L theory.

London penetration depth λ(T) in two-band Ginzburg–Landau theory: application to MgB2

Abstract Two-band Ginzburg–Landau (G–L) theory equations were solved analytically to determine the temperature dependence of the London penetration depth λ(T). Its temperature dependence is non-linear near Tc. The strength of the non-linearity is mainly dependent on the interaction coupling between the order parameters of two separate bands. In addition, the inter-gradient interaction as well as the ratio of effective masses of two separate bands was also found to be important in determining its temperature dependence. The solutions were applied to MgB2, which was characterized as a two-band superconductor. The results of the calculations are in good agreement with the experimental data for bulk MgB2.

Transfer Characteristic of a Goto Pair in Small-Size Josephson Junctions

The response of a Goto pair, based on small-size Josephson junctions, to voltage jumps has been studied within the framework of a resistive model. An analytical formula for the time of establishment of the transfer characteristic is obtained and the corresponding estimates are calculated.

Numerical Study of Josephson Junction Qubits With an Unharmonic Current–Phase Relation

This paper numerically analyzes the influence of second harmonics on the characteristics of Josephson junction quantum bits (qubits). It is shown that the splitting of energy states of phase qubits is sensitive to energy scale and unharmonicity parameters. On the other hand, for charge qubits, the expectation value of the Cooper-pair number is not affected by the inclusion of unharmonicity parameters, whereas the expectation value of the superconducting current is strongly influenced by energy scale and unharmonicity parameters. The numerical results seem to present the importance of second harmonics in the realization of superconducting qubits.

Alternative numerical modeling of a superconducting charge qubit as an eigenvalue problem

Purpose – The purpose of this paper is to employ an alternative numerical approach to analyze the characteristics of superconducting charge qubit based on a single Cooper pair box (SCB), also to study the influence of the bias current.Design/methodology/approach – The paper starts with the circuit model of a charge qubit system based on Josephson junction using Hamiltonian formalism. Corresponding Schrodinger eigenvalue problem with periodic boundary condition is converted to the Mathieu type eigenvalue problem. By applying finite difference technique, energy spectrum of charge qubit is obtained and the solutions in the lowest band are obtained in the form of Bloch waves whose superposition provides a wave packet to investigate the effect of bias current to the Coulomb blockade.Findings – The paper identifies a periodic tridiagonal Hermitian matrix form of the eigenvalue problem that is believed to be a special eigenvalue problem. The paper emphasizes that Schrodinger formalism is very useful to model sup...

Effect of the anharmonic phase dependence of the supercurrent on I-V hysteresis in a Josephson junction

The effect of the anharmonic phase dependence of the supercurrent on I-V hysteresis in a Josephson junction is studied in terms of a modified resistive model.