Observation of the second harmonic in superconducting current-phase relation of Nb/Au/(001)YBa ₂ Cu ₃ O _x heterojunctions

Abstract

Abstract. -The superconducting current-phase relation (CPR) of Nb/Au/(001)YBa2Cu3Ox heterojunctions prepared on epitaxial c-axis oriented YBa2Cu3Ox thin films has been measured in a single-junction interferometer. For the first time, the second harmonic of the CPR of such junctions has been observed. The appearance of the second harmonic and the relative sign of the first and second harmonics of the CPR can be explained assuming, that the macroscopic pairing symmetry of our YBa2Cu3Ox thin films is of the d + s type.Introduction. It is now well established that the dominant component of the superconducting order parameter in the cuprates has d-wave symmetry (see [1] and references therein). Moreover, it has become clear that in orthorhombic materials such as YBa 2 Cu 3 O x (YBCO), a finite component with s-wave symmetry is admixed to the dominant d-wave order parameter. The early in-plane phase sensitive experiments imply that the d-wave component remains coherent through the whole sample [1], while an elegant c-axis tunneling experiment shows directly that the s-wave order parameter component does change sign across the twin boundary [2].The above picture of the YBCO pairing state is challenged by the experimental observation of a finite c-axis Josephson current between heavily twinned YBCO and a Pb counterelectrode [3]. Namely, the contribution of the s-wave part of the YBCO order parameter to

Josephson Effect In The Cuprates: Microscopic Implications

“…In addition, our picture implies that the Josephson product for junctions between the cuprates and low-T c superconductors is renormalized by the factor α, in semiquantitative agreement with experiment [21]. It also may be relevant for the experiment [22], where a large second harmonic has been found in a c-axis Josephson junction between YBCO and Nb.…”

Examples of superconducting technology application: Sensing and interfacing

“…The demonstrated progress for implementation of multilayer processes for Josephson junction fabrication [13,14] is not enough for the fabrication of scalable superconducting electronic circuits. Nevertheless single-layer structures exploiting socalled grain-boundary junctions can be used for sensitive low-frequency magnetometry [15,16].…”

Josephson systems based on ballistic point contacts between single-band and multi-band superconductors

“…where 1 I и 2 I are currents flowing through the contacts, e Φ is the external magnetic field, 1 L and 2 L are the inductance of each branch of the dc SQUID. These inductances can be…”

“…From a technical point of view, it is based on the study of the characteristics of a one-contact interferometer (a Josephson junction in a superconducting ring) or a dc SQUID (a SQUID ring with two Josephson junctions). In this geometry, one of the superconductors forming the junction has an isotropic swave symmetry of the order parameter, while the second one is an unusual superconductor with the symmetry of the order parameter to be revealed [1,2]. It is important to note that the Josephson interferometry has already proved itself as a useful technique that greatly helped in the identification of d-wave pairing mechanism of Cooper pairs in cuprate high-T c superconductors (see, e.g., review Ref.…”