Noise properties of nanoscale YBa2Cu3O7−δJosephson

Abstract

We present electric noise measurements of nanoscale biepitaxial YBa 2 Cu 3 O 7−δ (YBCO) Josephson junctions fabricated by two different lithographic methods. The first (conventional) technique defines the junctions directly by ion milling etching through an amorphous carbon mask. The second (soft patterning) method makes use of the phase competition between the superconducting YBCO (Y123) and the insulating Y 2 BaCuO 5 (Y211) phase at the grain boundary interface on MgO (110) substrates. The voltage noise properties of the two methods are compared in this study. For all junctions (having a thickness of 100 nm and widths of 250-500 nm), we see a significant amount of individual charge traps. We have extracted an approximate value for the effective area of the charge traps from the noise data. From the noise measurements, we infer that the soft-patterned junctions with a grain-boundary (GB) interface manifesting a large c-axis tunneling component have a uniform barrier and a superconductor-insulator-superconductor (SIS) -like behavior. The noise properties of soft-patterned junctions having a GB interface dominated by transport parallel to the ab planes are in accordance with a resonant tunneling barrier model. The conventionally patterned junctions, instead, have suppressed superconducting transport channels with an area much less than the nominal junction area. These findings are important for the implementation of nanosized Josephson junctions in quantum circuits.

Spectroscopy of a Cooper-pair box coupled to a two-level system via charge and critical current

“…Our extracted tunneling matrix element values are also significantly smaller than those reported by Z. Kim, et al, 10 Discrete critical current fluctuators have been reported in current biased Josephson junctions, identified via either a random telegraph signal in the voltage time trace or a signature Lorentzian bump in the noise spectrum. 23,24,40,41 One way we can compare our TLS's to others is to calculate the effective defect area A eff given by A eff = (∆E J /E J ) A j . For our device find A eff ≈ 18, 000 nm 2 where A j = 350 × 150 nm 2 is the junction area.…”

Toward ultra high magnetic field sensitivity YBa2Cu3O7−δ nanowire based superconducting quantum interference devices

“…Critical current fluctuations, in ordinary tunnel-like Josephson junctions (JJs), are usually associated to bistable charge trapping states in the junction barrier. 26,27 In our nanowires instead, the critical current noise might be caused by fluctuations of the electronic nematic order. 28,29 However, the detailed understanding of the physical mechanisms responsible for such behavior in our nanowires is not known yet and would require further systematic studies, which goes well beyond the scope of the present work.…”

Microwave Response of SuperconductingYBa2Cu3O7−δNanowire Bridges Sustaining the Critical Depairing Current: Evidence of Josephson-li

“…The patterning of HTS films on the nano scale is an extremely challenging task. The most viable technology is the pattern transfer through a hard mask using Ar ion etching [22,23]. However, the detrimental effect of the Ar ion etching on the exposed surfaces of YBCO causes damaged layers having reduced superconducting or even insulating properties [24].…”

“…We drastically improved the nano-patterning of YBCO obtaining nano bridges without any deterioration of the superconducting properties, as we will show below. This has been achieved by using electron beam lithography in combination with a 100 nm thick carbon mask and a very gentle ion milling to define the nanobridges [22,25]. Here we used an ion acceleration voltage close to the threshold value of V 300 V, below which YBCO is not etched.…”