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We study the superconducting vortex states induced by the interplay of long-range Pearl repulsion and short-range intervortex attraction using Langevin dynamics simulations. We show that at low temperatures the vortices form an ordered Abrikosov lattice both in low and high fields. The vortices show distinctive modulated structures at intermediate fields depending on the effective intervortex attraction: ordered vortex chain and kagome-like vortex structures for weak attraction; bubble, stripe and antibubble lattices for strong attraction. Moreover, in the regime of the chain state, the vortices display structural transitions from chain to labyrinthine (or disordered chain) and/or to disordered states depending on the strength of the disorder.

We study the superconducting vortex states induced by the interplay of long-range Pearl repulsion and short-range intervortex attraction using Langevin dynamics simulations. We show that at low temperatures the vortices form an ordered Abrikosov lattice both in low and high fields. The vortices show distinctive modulated structures at intermediate fields depending on the effective intervortex attraction: ordered vortex chain and kagome-like vortex structures for weak attraction; bubble, stripe and antibubble lattices for strong attraction. Moreover, in the regime of the chain state, the vortices display structural transitions from chain to labyrinthine (or disordered chain) and/or to disordered states depending on the strength of the disorder.

We study the superconducting vortex states induced by the interplay of long-range Pearl repulsion and short-range intervortex attraction using Langevin dynamics simulations. We show that at low temperatures the vortices form an ordered Abrikosov lattice both in low and high fields. The vortices show distinctive modulated structures at intermediate fields depending on the effective intervortex attraction: ordered vortex chain and kagome-like vortex structures for weak attraction; bubble, stripe and antibubble lattices for strong attraction. Moreover, in the regime of the chain state, the vortices display structural transitions from chain to labyrinthine (or disordered chain) and/or to disordered states depending on the strength of the disorder.

We study the superconducting vortex states induced by the interplay of long-range Pearl repulsion and short-range intervortex attraction using Langevin dynamics simulations. We show that at low temperatures the vortices form an ordered Abrikosov lattice both in low and high fields. The vortices show distinctive modulated structures at intermediate fields depending on the effective intervortex attraction: ordered vortex chain and kagome-like vortex structures for weak attraction; bubble, stripe and antibubble lattices for strong attraction. Moreover, in the regime of the chain state, the vortices display structural transitions from chain to labyrinthine (or disordered chain) and/or to disordered states depending on the strength of the disorder.

Based on a model appropriate for “marginally type-II” superconducting system, we study the dynamics of vortices with competing interactions by Langevin dynamics simulation. In addition to pinned states and plastic flow, we find that the moving vortex system forms ordered bubble configurations and stripe structures, depending on pinning strength and driving force. The vortex system exhibits a marked hysteresis in its velocity-force characteristic, which results from a dynamical stripe reordering due to intervortex attraction.

Based on a model appropriate for “marginally type-II” superconducting system, we study the dynamics of vortices with competing interactions by Langevin dynamics simulation. In addition to pinned states and plastic flow, we find that the moving vortex system forms ordered bubble configurations and stripe structures, depending on pinning strength and driving force. The vortex system exhibits a marked hysteresis in its velocity-force characteristic, which results from a dynamical stripe reordering due to intervortex attraction.

We study numerically the dynamics relating to negative vortex motion in inhomogeneous pinning systems. We show that this dynamical phenomenon results from the internal field effect produced by the growing local barriers with decreasing temperature. We find that the negative motion is characterized by a peak of negative voltage or resistance in resistance–temperature transport measurements. We also demonstrate that the time window to observe the negative motion is determined by the magnitude of driving force in addition to the temperature scanning rate.

We study numerically the dynamics relating to negative vortex motion in inhomogeneous pinning systems. We show that this dynamical phenomenon results from the internal field effect produced by the growing local barriers with decreasing temperature. We find that the negative motion is characterized by a peak of negative voltage or resistance in resistance–temperature transport measurements. We also demonstrate that the time window to observe the negative motion is determined by the magnitude of driving force in addition to the temperature scanning rate.

We study numerically the dynamics relating to negative vortex motion in inhomogeneous pinning systems. We show that this dynamical phenomenon results from the internal field effect produced by the growing local barriers with decreasing temperature. We find that the negative motion is characterized by a peak of negative voltage or resistance in resistance–temperature transport measurements. We also demonstrate that the time window to observe the negative motion is determined by the magnitude of driving force in addition to the temperature scanning rate.

We study numerically the dynamics relating to negative vortex motion in inhomogeneous pinning systems. We show that this dynamical phenomenon results from the internal field effect produced by the growing local barriers with decreasing temperature. We find that the negative motion is characterized by a peak of negative voltage or resistance in resistance–temperature transport measurements. We also demonstrate that the time window to observe the negative motion is determined by the magnitude of driving force in addition to the temperature scanning rate.

We study numerically the dynamics relating to negative vortex motion in inhomogeneous pinning systems. We show that this dynamical phenomenon results from the internal field effect produced by the growing local barriers with decreasing temperature. We find that the negative motion is characterized by a peak of negative voltage or resistance in resistance–temperature transport measurements. We also demonstrate that the time window to observe the negative motion is determined by the magnitude of driving force in addition to the temperature scanning rate.

We perform 2D Langevin simulations studying the peak effect (PE) of the critical current taking into account the temperature dependence of the competing forces. We observe and report that the PE results from the competition of vortex-vortex interactions and vortex-pin interactions which have different temperature dependencies. The simulations reveal that the PE can take place only for certain pinning strengths, densities of pinning centres, and driving forces, which is in good agreement with experiments. No apparent vortex order-disorder transition is observed across the PE regime. In addition, the PE is a dynamical phenomenon, and thermal fluctuations can speed up the process for the formation of the PE.

We perform 2D Langevin simulations studying the peak effect (PE) of the critical current taking into account the temperature dependence of the competing forces. We observe and report that the PE results from the competition of vortex-vortex interactions and vortex-pin interactions which have different temperature dependencies. The simulations reveal that the PE can take place only for certain pinning strengths, densities of pinning centres, and driving forces, which is in good agreement with experiments. No apparent vortex order-disorder transition is observed across the PE regime. In addition, the PE is a dynamical phenomenon, and thermal fluctuations can speed up the process for the formation of the PE.

We perform 2D Langevin simulations studying the peak effect (PE) of the critical current taking into account the temperature dependence of the competing forces. We observe and report that the PE results from the competition of vortex-vortex interactions and vortex-pin interactions which have different temperature dependencies. The simulations reveal that the PE can take place only for certain pinning strengths, densities of pinning centres, and driving forces, which is in good agreement with experiments. No apparent vortex order-disorder transition is observed across the PE regime. In addition, the PE is a dynamical phenomenon, and thermal fluctuations can speed up the process for the formation of the PE.

We perform 2D Langevin simulations studying the peak effect (PE) of the critical current taking into account the temperature dependence of the competing forces. We observe and report that the PE results from the competition of vortex-vortex interactions and vortex-pin interactions which have different temperature dependencies. The simulations reveal that the PE can take place only for certain pinning strengths, densities of pinning centres, and driving forces, which is in good agreement with experiments. No apparent vortex order-disorder transition is observed across the PE regime. In addition, the PE is a dynamical phenomenon, and thermal fluctuations can speed up the process for the formation of the PE.

We perform 2D Langevin simulations studying the peak effect (PE) of the critical current taking into account the temperature dependence of the competing forces. We observe and report that the PE results from the competition of vortex-vortex interactions and vortex-pin interactions which have different temperature dependencies. The simulations reveal that the PE can take place only for certain pinning strengths, densities of pinning centres, and driving forces, which is in good agreement with experiments. No apparent vortex order-disorder transition is observed across the PE regime. In addition, the PE is a dynamical phenomenon, and thermal fluctuations can speed up the process for the formation of the PE.

We investigate the transport of vortices in superconductors with inhomogeneous pinning under a driving force. The inhomogeneity of pinning is simplified as strong-weak pinning regions. It is demonstrated that the interactions between the vortices captured by strong pinning potentials and the vortices in the weak pinning region cause absolute negative motion (ANM) of vortices: The vortices which are climbing toward the high barriers induced by the strong pinning with the help of driving force move toward the opposite direction of the force and back to their equilibrium positions in the weak pinning region as the force decreases or is withdrawn. Our simulations reveal that the hysteresis of ANM is determined by the competition between the speed of the negative motion which depends on the pinning inhomogeneity in superconductors and the speed of the driving force. Under the conditions of either larger force scanning rate or higher pinning inhomogeneity, a marked ANM and a larger hysteretic speed-force loop could be observed. This indicates that the time window to observe the ANM should be chosen properly. Moreover, the V-I characteristics of Ag-sheathed Bi-2223 tapes are measured, and experimental observations are qualitatively in agreement with the simulation.

We investigate the transport of vortices in superconductors with inhomogeneous pinning under a driving force. The inhomogeneity of pinning is simplified as strong-weak pinning regions. It is demonstrated that the interactions between the vortices captured by strong pinning potentials and the vortices in the weak pinning region cause absolute negative motion (ANM) of vortices: The vortices which are climbing toward the high barriers induced by the strong pinning with the help of driving force move toward the opposite direction of the force and back to their equilibrium positions in the weak pinning region as the force decreases or is withdrawn. Our simulations reveal that the hysteresis of ANM is determined by the competition between the speed of the negative motion which depends on the pinning inhomogeneity in superconductors and the speed of the driving force. Under the conditions of either larger force scanning rate or higher pinning inhomogeneity, a marked ANM and a larger hysteretic speed-force loop could be observed. This indicates that the time window to observe the ANM should be chosen properly. Moreover, the V-I characteristics of Ag-sheathed Bi-2223 tapes are measured, and experimental observations are qualitatively in agreement with the simulation.

We investigate the transport of vortices in superconductors with inhomogeneous pinning under a driving force. The inhomogeneity of pinning is simplified as strong-weak pinning regions. It is demonstrated that the interactions between the vortices captured by strong pinning potentials and the vortices in the weak pinning region cause absolute negative motion (ANM) of vortices: The vortices which are climbing toward the high barriers induced by the strong pinning with the help of driving force move toward the opposite direction of the force and back to their equilibrium positions in the weak pinning region as the force decreases or is withdrawn. Our simulations reveal that the hysteresis of ANM is determined by the competition between the speed of the negative motion which depends on the pinning inhomogeneity in superconductors and the speed of the driving force. Under the conditions of either larger force scanning rate or higher pinning inhomogeneity, a marked ANM and a larger hysteretic speed-force loop could be observed. This indicates that the time window to observe the ANM should be chosen properly. Moreover, the V-I characteristics of Ag-sheathed Bi-2223 tapes are measured, and experimental observations are qualitatively in agreement with the simulation.

We study numerically the effect of vortex pinning on the hysteresis voltage-temperature (V-T) loop of vortex matter. It is found that different types of the V-T loops result from different densities of vortex pinning center. An anticlockwise V-T loop is observed for the vortex system with dense pinning centers, whereas a clockwise V-T loop is brought about for vortices with dilute pinning centers. It is shown that the size of the V-T loop becomes smaller for lower experimental speed, higher magnetic field, or weak pinning strength. Our numerical observation is in good agreement with experiments.

We study numerically the effect of vortex pinning on the hysteresis voltage-temperature (V-T) loop of vortex matter. It is found that different types of the V-T loops result from different densities of vortex pinning center. An anticlockwise V-T loop is observed for the vortex system with dense pinning centers, whereas a clockwise V-T loop is brought about for vortices with dilute pinning centers. It is shown that the size of the V-T loop becomes smaller for lower experimental speed, higher magnetic field, or weak pinning strength. Our numerical observation is in good agreement with experiments.

We study numerically the effect of vortex pinning on the hysteresis voltage-temperature (V-T) loop of vortex matter. It is found that different types of the V-T loops result from different densities of vortex pinning center. An anticlockwise V-T loop is observed for the vortex system with dense pinning centers, whereas a clockwise V-T loop is brought about for vortices with dilute pinning centers. It is shown that the size of the V-T loop becomes smaller for lower experimental speed, higher magnetic field, or weak pinning strength. Our numerical observation is in good agreement with experiments.

We study numerically the effect of vortex pinning on the hysteresis voltage-temperature (V-T) loop of vortex matter. It is found that different types of the V-T loops result from different densities of vortex pinning center. An anticlockwise V-T loop is observed for the vortex system with dense pinning centers, whereas a clockwise V-T loop is brought about for vortices with dilute pinning centers. It is shown that the size of the V-T loop becomes smaller for lower experimental speed, higher magnetic field, or weak pinning strength. Our numerical observation is in good agreement with experiments.

Cylindrical single grains of GdBa 2Cu3Oy sGd-123d with a diameter of 25 mm were successfully fabricated by melt-texture growth sMTGd process in air to study the influence of different starting powders on flux pinning. Measurements of the magnetic critical current density sJcd showed that it was possible to fabricate large Gd-123 single grain with a high Jc at high temperatures and fields by means of properly controlling the starting powders of Gd 2O3, BaCO3 , and CuO before the process.

Cylindrical single grains of GdBa 2Cu3Oy sGd-123d with a diameter of 25 mm were successfully fabricated by melt-texture growth sMTGd process in air to study the influence of different starting powders on flux pinning. Measurements of the magnetic critical current density sJcd showed that it was possible to fabricate large Gd-123 single grain with a high Jc at high temperatures and fields by means of properly controlling the starting powders of Gd 2O3, BaCO3 , and CuO before the process.

Cylindrical single grains of GdBa 2Cu3Oy sGd-123d with a diameter of 25 mm were successfully fabricated by melt-texture growth sMTGd process in air to study the influence of different starting powders on flux pinning. Measurements of the magnetic critical current density sJcd showed that it was possible to fabricate large Gd-123 single grain with a high Jc at high temperatures and fields by means of properly controlling the starting powders of Gd 2O3, BaCO3 , and CuO before the process.

The influence of surface barrier on the third harmonics ac susceptibility (chi3) is studied numerically. The surface barrier is described by a critical current density in surfaces which are higher than the inside one. The model can act as the critical state one, the flux creep one, or the flux flow one when temperature (or field) changes. The numerical results based on the model are more close to the popular experimental data probing the harmonics as a function of temperature (or field). Besides, the surface barrier will lead to new peaks in the real and imaginary parts of the third harmonics, which are the finger signature of the surface barrier. Comparison of the peaks with those of the real part of elemental harmonic shows that they are located at the same temperature where dips in chi[prime] caused by the surface barrier occur, which is in well agreement with experiments.

The influence of surface barrier on the third harmonics ac susceptibility (chi3) is studied numerically. The surface barrier is described by a critical current density in surfaces which are higher than the inside one. The model can act as the critical state one, the flux creep one, or the flux flow one when temperature (or field) changes. The numerical results based on the model are more close to the popular experimental data probing the harmonics as a function of temperature (or field). Besides, the surface barrier will lead to new peaks in the real and imaginary parts of the third harmonics, which are the finger signature of the surface barrier. Comparison of the peaks with those of the real part of elemental harmonic shows that they are located at the same temperature where dips in chi[prime] caused by the surface barrier occur, which is in well agreement with experiments.

The influence of surface barrier on the third harmonics ac susceptibility (chi3) is studied numerically. The surface barrier is described by a critical current density in surfaces which are higher than the inside one. The model can act as the critical state one, the flux creep one, or the flux flow one when temperature (or field) changes. The numerical results based on the model are more close to the popular experimental data probing the harmonics as a function of temperature (or field). Besides, the surface barrier will lead to new peaks in the real and imaginary parts of the third harmonics, which are the finger signature of the surface barrier. Comparison of the peaks with those of the real part of elemental harmonic shows that they are located at the same temperature where dips in chi[prime] caused by the surface barrier occur, which is in well agreement with experiments.

Cylindrical single grains of GdBa 2Cu3Oy sGd-123d with a diameter of 25 mm were successfully fabricated by melt-texture growth sMTGd process in air to study the influence of different starting powders on flux pinning. Measurements of the magnetic critical current density sJcd showed that it was possible to fabricate large Gd-123 single grain with a high Jc at high temperatures and fields by means of properly controlling the starting powders of Gd 2O3, BaCO3 , and CuO before the process.

The influence of surface barrier on the third harmonics ac susceptibility (chi3) is studied numerically. The surface barrier is described by a critical current density in surfaces which are higher than the inside one. The model can act as the critical state one, the flux creep one, or the flux flow one when temperature (or field) changes. The numerical results based on the model are more close to the popular experimental data probing the harmonics as a function of temperature (or field). Besides, the surface barrier will lead to new peaks in the real and imaginary parts of the third harmonics, which are the finger signature of the surface barrier. Comparison of the peaks with those of the real part of elemental harmonic shows that they are located at the same temperature where dips in chi[prime] caused by the surface barrier occur, which is in well agreement with experiments.

According to the observational limits on the radius and mass, the fastest rotating pulsar (PSR 1937+21) is probably a strange star, or at least some neutron star equations of state should be ruled out, if we suggest that a dipole magnetic field is relevant to its radio emission. We presume that the millisecond pulsar is a strange star with {\em much} low mass, small radius, and weak magnetic moment., Comment: 9 pages, 2 figures, 1 table, to be published in Chinese Physics Letters (2001), http://vega.bac.pku.edu.cn/~rxxu

According to the observational limits on the radius and mass, the fastest rotating pulsar (PSR 1937+21) is probably a strange star, or at least some neutron star equations of state should be ruled out, if we suggest that a dipole magnetic field is relevant to its radio emission. We presume that the millisecond pulsar is a strange star with {\em much} low mass, small radius, and weak magnetic moment., Comment: 9 pages, 2 figures, 1 table, to be published in Chinese Physics Letters (2001), http://vega.bac.pku.edu.cn/~rxxu