Modulation of persistent current in graphene quantum rings

We investigate the effect of long-range impurity potentials on the persistent current of graphene quantum rings in the presence of an uniform perpendicular magnetic field. The impurity potentials are modeled as finite regions of the ring with a definite length. We show that, due to the relativistic and massless character of the charge carriers in graphene, the effect of such non-uniform potentials on the energy spectrum and on the persistent current of the rings can be reliably modeled by assuming a non-perturbed ring and including an additional phase due to the interaction of the charge carriers with the potential. In addition, the results show the presence of localized states in the impurity regions. Moreover, we show that for the case of a potential created by a p-n-p junction, the persistent current can be modulated by controlling the voltage at the junction.

Drag Voltages in a Superconductor/Insulator/Ferromagnet Trilayer

The interaction between two spatially separated systems is of strong interest in order to study a wide class of unconventional effects at cryogenic temperatures. Here we report on drag transverse voltage effects in multilayered systems containing superconducting and ferromagnetic materials. The sample under test is a conventional superconductor/insulator/ferromagnet (S/I/F) trilayer in a cross configuration. S/F as well as S/N (here N stands for normal metal) bilayers in the same geometry are also analyzed for comparison. Current–voltage (I–V) characteristics measured at T = 4.2 K in the presence of a perpendicular magnetic field show strong peculiarities related to the interaction between the layers. The results are interpreted in terms of interaction effects between the layers.

Solving Dirac oscillator in commutative and noncommutative planes by supersymmetry structures

Based on the supersymmetry structures, we propose to solve the model of a charged Dirac oscillator interacting with a uniform perpendicular magnetic field on both commutative and noncommutative planes in a unified way by employing unitary transformations. The unitary operators are constructed out of the generators of the supersymmetry structures of the model.

Dynamic Resistance Measurement of a Four-Tape YBCO Stack in a Perpendicular Magnetic Field

Dynamic resistance occurs when HTS (high-temperature superconductor) coated conductors carry dc current under ac magnetic field. This dissipative effect can play a critical role in many HTS applications. Here, we report on dynamic resistance measurements of a four-tape YBCO stack comprising 4-mm-wide coated conductors, which experience an applied ac perpendicular magnetic field with an amplitude of up to 100 mT. Each tape within the stack carries the same dc current. The magnetic field amplitude, the frequency of the magnetic field, and the dc current magnitude are varied to investigate the influence of these parameters on the dynamic resistance. We find that the threshold field of the stack is significantly larger than that of a single tape when dc current is small, which we attribute to coherent shielding effects from circulating currents present in each wire in the stack. © 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

Dynamic Resistance Measurement of a Four-Tape YBCO Stack in a Perpendicular Magnetic Field

Dynamic resistance occurs when HTS (high-temperature superconductor) coated conductors carry dc current under ac magnetic field. This dissipative effect can play a critical role in many HTS applications. Here, we report on dynamic resistance measurements of a four-tape YBCO stack comprising 4-mm-wide coated conductors, which experience an applied ac perpendicular magnetic field with an amplitude of up to 100 mT. Each tape within the stack carries the same dc current. The magnetic field amplitude, the frequency of the magnetic field, and the dc current magnitude are varied to investigate the influence of these parameters on the dynamic resistance. We find that the threshold field of the stack is significantly larger than that of a single tape when dc current is small, which we attribute to coherent shielding effects from circulating currents present in each wire in the stack. © 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.