Browsing by Author "Dai, MC"

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Exact solution of the Ginzburg-Landau equation for the upper critical field of a d(x2-y2) superconductor
(1999-04-01)
Dai, MC
;
Yang, TJ
;
Ting, CS
;
電子物理學系
;
Department of Electrophysics
A d(x2-y2) superconductor is modeled as the superconducting layers in the a-b plane, whose coupling in the c direction is approximated by the effective mass, within the Ginzburg-Landau theory. In this work, this model is applied to the system where the, coherence length along the c direction is greater than the layer spacing. Based on our model, we calculate the upper critical field in a magnetic field lying in a-e plane and tilted by an angle from the c axis. According to our results, the curvature of H-c2(T) is upward, and the slope - dH(c2)(T)/dT depends on the angle between the c axis and the external field. The most interesting feature is that the ratio of the c-direction parameter related to the effective mass to the n-b plane parameter connected with the effective mass can influence H-c2. As the rafio is decreased, H-c2. becomes increased. We also find that there is no admixture of s-wave component in the critical regime and believe that the upward curvature of the H-c2(T) is the characteristic property of a d-wave superconductor. [S0163-1829(99)01914-1].
Magnetic properties for anisotropic d(x(2)-y(2))-wave superconductivity
(1998-09-01)
Dai, MC
;
Yang, TJ
;
電子物理學系
;
Department of Electrophysics
The single vortex structure is derived in the presence of applied magnetic field. According to our results, the winding number of the s-wave does not change regardless of the vector potential. The generic London equation for a d(x2-y2)-wave superconductor with mass anisotropy is expressed. By neglecting higher order terms, this work analyzes the magnetic-field distribution with and without a vortex. The interaction force between two parallel vortices is derived as well. Our results further reveal the presence of a torque between vortices irrespective of s- or d-wave order parameter, which is expected to vanish for isotropic cases. (C) 1998 Elsevier Science B.V. All rights reserved.
Non-d-wave superconducting induced by current in d-wave superconductors with mass anisotropy
(1998-04-01)
Dai, MC
;
Yang, TJ
;
電子物理學系
;
Department of Electrophysics
Underlain by the Ginzburg-Landau theory of a d-wave superconductor with mass anisotropy lambda = m(x)/m(y), we derived the non-zero subsidiary order parameter induced by an external current. The amplitude of induced s-component depends on the amplitude and direction of the current. The extreme values appear in some specific conditions. Unlike the isotropic case, we find that the current density is not parallel to the wave vector except for lambda = 1.
The anomalous Hall effect for a mixed s- and d-wave symmetry superconductor
(1999)
Dai, MC
;
Yang, TJ
;
電子物理學系
;
Department of Electrophysics
By taking account of the complex relaxation times for s- and d-wave order parameters in the time-dependent Ginzburg-Landau equations, our results indicate that the imaginary parts of the relaxation times can change the sign of the Hall angle for mixed s- and d-wave superconductors. The effect of the concentration of the nonmagnetic impurities on the Hall angle is investigated, and it is found that the concentration of the nonmagnetic impurities can affect the parameters in the Ginzburg-Landau free energy and the relaxation times. The results of the anomalous Hall effect arising from the nonmagnetic impurities are discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.
The anomalous Hall effect viewed from the time-dependent Ginzburg-Landau equations for d-wave superconductors
(2000-07-01)
Yang, TJ
;
Dai, MC
;
電子物理學系
;
Department of Electrophysics
From time-dependent Ginzburg-Landau theory of d-wave superconductors, the rate of increase of the total free energy plus the rate of dissipation are demonstrated to be equal to the inflow of energy current. The equation of motion of a single vortex for h much less than H-c2 in the presence of an applied current is derived. The imaginary parts of the relaxation time for s- and d-wave order parameters play a key role in the sign change of Hall effect. The concentration of non-magnetic impurities affecting the sign change of Hall effect is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.
Time-dependent Ginzburg-Landau equation for d(x2-y2)-wave superconductors: Hall effect in the low field regime
(1999-11-01)
Yang, TJ
;
Dai, MC
;
電子物理學系
;
Department of Electrophysics
The Hall effect is studied by using a phenomenological time-dependent Ginzburg-Landau equation with mixing of s-and d-wave components in d(x)2-(y)2-wave superconductors within a low field regime. An equation of motion for a single vortex is derived and the Hall angle is obtained under an external driving current along the crystal axis. We find that not only the imaginary parts of s- and d-wave relaxation time but also the mixed gradient terms may change the sign of the Hall effect.