Time-varying magnetic field induced electric field across a current-transporting type-II superconducting loop: beyond dynamic resistance effect

The emergence of a potential drop across a current-transporting type-II superconducting loop under a perpendicular oscillating magnetic field is revealed. We have derived analytical formulae to describe the effect under DC transport current in 1D, based on Bean’s critical state model. The analytical formulae are verified by a finite element model. To exploit this effect, we have developed a transformer-like ‘resistive switch’, and experimentally observed a switching effect. This work demonstrates a physically important general insight of the interaction between DC transport currents and time-varying magnetic fields in type-II superconducting loops, which extends beyond the well-known ‘dynamic resistance’ effect. It also provides a useful view on the interaction between a “transport-current” and a “screening-current” in the superconductor. The resulting demonstrated switch has the potential to be used in a variety of applications including superconducting rectifiers, fault current limiters, and superconducting magnetic energy storages.

Coexistence of ferromagnetism, antiferromagnetism, and superconductivity in magnetically anisotropic (Eu,La)FeAs2

Materials with exceptional magnetism and superconductivity usually conceive emergent physical phenomena. Here, we investigate the physical properties of the (Eu,La)FeAs2 system with double magnetic sublattices. The parent EuFeAs2 shows anisotropy-associated magnetic behaviors, such as Eu-related moment canting and exchange bias. Through La doping, the magnetic anisotropy is enhanced with ferromagnetism of Eu2+ realized in the overdoped region, and a special exchange bias of the superposed ferromagnetic/superconducting loop revealed in Eu0.8La0.2FeAs2. Meanwhile, the Fe-related antiferromagnetism shows unusual robustness against La doping. Theoretical calculation and 57Fe Mössbauer spectroscopy investigation reveal a doping-tunable dual itinerant/localized nature of the Fe-related antiferromagnetism. The coexistence of the Eu-related ferromagnetism, Fe-related robust antiferromagnetism, and superconductivity is further revealed in Eu0.8La0.2FeAs2, providing a platform for further exploration of potential applications and emergent physics. Finally, an electronic phase diagram is established for (Eu,La)FeAs2 with the whole superconducting dome adjacent to the Fe-related antiferromagnetic phase, which is of benefit for seeking underlying clues to high-temperature superconductivity.

A simple superconductor quantum interference device for testing gravity

A simple tabletop setup based on a superconductor quantum interference device is proposed to test the gravitational interaction. A D-shaped superconducting loop has the straight segment immersed inside a massive sphere while the half-circle segment is wrapped around the sphere. The superconducting condensate within the straight arm of the loop thus bathes inside a gravitational simple harmonic oscillator potential while the condensate in the half-circle arm bathes in the constant gravitational potential around the sphere. The resulting phase difference at the Josephson junctions on both sides of the straight arm induces a sinusoidal electric current that has a frequency determined by the precise gravitational potential due to the massive sphere.

Theoretical Studies on the Creation of Artificial Magnetic Monopoles

In this study, we discuss the theoretical studies on the creation of artificial magnetic monopole, and new electromagnetic equations. Employing Lorentz transformation, radial electrostatic fields, and a stationary wave derived from a superconducting loop, we demonstrate the existence of a magnetic monopole whereby the divergence of the magnetic field is not zero. We develop a device wherein a condenser provides electrostatic fields along the radial direction to the superconducting loop and discuss the nodes of the resulting stationary wave along the superconducting loop. We employ the Lorentz transformation with respect to the vector and electrostatic potentials. Then, because the nodes have no three-dimensional vector potential and have zero magnetic field rotation, the conserved energy is converted into new form that is associated with the magnetic field potential to yield the Lorentz transformation. As a result, we derived the relationship between the electric and the magnetic fields. This dependent relationship involves the exchange of the distribution characteristics of the static electric and static magnetic fields, and new electromagnetic equations of both electric and magnetic fields are obtained. We also analyzed the magnetic field from the magnetic monopole whose result assists the theory.

nanoSQUID operation using kinetic rather than magnetic induction

We report on a method of nanoSQUID modulation which uses kinetic inductance rather than magnetic inductance to manip-ulate the internal fluxoid state. We produced modulation using injected current rather than an applied magnetic field. Using this injected current, we were able to observe the triangle-wave shaped modulation of the device critical current which was periodic according to the London fluxoid quantization condition. The measurement results also confirmed that the fluxoid state inside a superconducting loop can be manipulated using primarily kinetic inductance. By using primarily kinetic inductance rather than magnetic inductance, the size of the coupling inductor was reduced by a factor of 10. As a result, this approach may provide a means to reduce the size of SQUID-based superconducting electronics. Additionally, this method provides a convenient way to perform kinetic inductance characterizations of superconducting thin films.