Voltage response of non-uniform arrays of bi-superconductive quantum interference devices (original) (raw)

Low-field magnetic response of multi-junction superconducting quantum interference devices

The European Physical Journal B, 2008

The magnetic states of multi-junction superconducting quantum interference device containing 2N identical conventional Josephson junctions are studied by means of a perturbation analysis of the non-linear first-order ordinary differential equations governing the dynamics of the Josephson junctions in these devices. In the zero-voltage state, persistent currents are calculated in terms of the externally applied magnetic flux Φex. The resulting d.c. susceptibility curves show that paramagnetic and diamagnetic states are present, depending on the value of Φex. The stability of these states is qualitatively studied by means of the effective potential notion for the system.

Macroscopic quantum behavior of superconducting quantum interference devices

Fortschritte der Physik, 2003

Superconducting quantum interference devices (SQUIDs) are made by a superconducting loop interrupted by one or more Josephson junctions. They are described in terms of a macroscopic variable, the magnetic flux, which shows quantum effects such as tunnelling through a potential barrier. Besides making up the source of a quantum state, SQUIDs also provide the instruments necessary for its probing: as a fact, SQUID based magnetometers have a sensitivity approaching the quantum limit. In this paper I will review the working principle of these devices and illustrate the system of SQUIDs realized in my group to test the quantum behavior at a macroscopic level. *

Nb nano superconducting quantum interference devices with high spin sensitivity for operation in magnetic fields up to 0.5 T

Applied Physics Letters, 2013

We investigate electric transport and noise properties of microstrip-type submicron direct current superconducting quantum interference devices (dc SQUIDs) based on Nb thin films and overdamped Josephson junctions with a HfTi barrier. The SQUIDs were designed for optimal spin sensitivity S 1/2 µ upon operation in intermediate magnetic fields B (tens of mT), applied perpendicular to the substrate plane. Our so far best SQUID can be continuously operated in fields up to B ≈ ±50 mT with rms flux noise S 1/2 Φ,w ≤ 250 nΦ0/Hz 1/2 in the white noise regime and spin sensitivity S 1/2 µ ≤ 29 µB/Hz 1/2 . Furthermore, we demonstrate operation in B = 0.5 T with high sensitivity in flux S 1/2 Φ,w ≈ 680 nΦ0/Hz 1/2 and in electron spin S 1/2 µ ≈ 79 µB/Hz 1/2 . We discuss strategies to further improve the nanoSQUID performance.

Enhanced quantum interference effects in normal and superconducting arrays

Superlattices and Microstructures, 1992

We have generalized the Aharanov-Bohm effect from a single loop to a twodimensional rectangular network containing MxN loops. each of equal area. For a given geometry, as the total number of loops increases, the periodic principal maxima m the t'lux-dependent conductance exhihit a spacing ol h/e per loop while becoming increasingly narrow and pronounced, and we observe M-2 subsidiary maxima between consecutive principal maxima. We predict a similar enhancement and narrowing of the principal maxima in the flux-dependent crttical current of a multi-junction SQUID array, although in this case the llux periodicity is N2e.

Superconducting quantum interference device instruments and applications

Review of Scientific Instruments, 2006

Superconducting quantum interference devices ͑SQUIDs͒ have been a key factor in the development and commercialization of ultrasensitive electric and magnetic measurement systems. In many cases, SQUID instrumentation offers the ability to make measurements where no other methodology is possible. We review the main aspects of designing, fabricating, and operating a number of SQUID measurement systems. While this article is not intended to be an exhaustive review on the principles of SQUID sensors and the underlying concepts behind the Josephson effect, a qualitative description of the operating principles of SQUID sensors and the properties of materials used to fabricate SQUID sensors is presented. The difference between low and high temperature SQUIDs and their suitability for specific applications is discussed. Although SQUID electronics have the capability to operate well above 1 MHz, most applications tend to be at lower frequencies. Specific examples of input circuits and detection coil configuration for different applications and environments, along with expected performance, are described. In particular, anticipated signal strength, magnetic field environment ͑applied field and external noise͒, and cryogenic requirements are discussed. Finally, a variety of applications with specific examples in the areas of electromagnetic, material property, nondestructive test and evaluation, and geophysical and biomedical measurements are reviewed.

Performance of asymmetric superconducting quantum interference devices

Physica C: Superconductivity, 2002

Low T c superconducting quantum interference devices with asymmetric shunt resistances (SQUIDARs) have been numerically and experimentally investigated. Numerical simulations show that the flux to voltage transfer coefficient V U and magnetic flux noise S U are strongly dependent on both the asymmetry parameter q and damping parameter c ¼ R=R d , where R and R d are the SQUID normal resistance and damping resistance, respectively. For small c values, SQUIDARs show larger V U and smaller S U than symmetric devices. Asymmetric SQUIDs can then improve the performance of standard sensors in most of the magnetometric applications. By increasing c, V U several times larger than that of symmetric SQUIDs can be achieved. Therefore, it is possible to couple SQUIDAR magnetometers to an external preamplifier without the need of an external circuit, simplifying the read-out electronics. Experimental values of the magnetic field sensitivity of 6-7 fT/Hz 1=2 have been so far obtained. These results, already suitable for biomagnetic applications, can be further improved by properly optimizing the device parameters. Ó