arXiv subjects

Shane A. Cybart

Publications and source records attributed to Shane A. Cybart.

7 recordsLinked to original sources

arXiv2026

AC Response Across the Metal Insulator Transition of YBCO Josephson Junctions Fabricated with a Helium Ion Beam

Using focused helium ion beam (FHIB) irradiation, we fabricated in-plane, high-Tc YBCO Josephson junctions. By varying the dose of the irradiation, we tune the junction barriers from metallic (SNS) to insulating (SIS) and investigate how this transition affects microwave-driven dynamics. As the barrier transitions from metallic to insulating, the oscillatory response of the Shapiro steps to the RF power changes dramatically. On either side of the metal-insulator transition, the devices exhibit clean integer Shapiro steps without half-integer features, demonstrating that the current--phase relation is dominated by the first harmonic and that the excess current is minimal. The current-voltage response is well-described by the resistively, capacitively shunted junction model assuming a single-harmonic current--phase relation. This behavior indicates well-controlled junction properties suitable for a wide range of superconducting electronics, including detectors, mixers, and high-density integrated circuits.

cond-mat.supr-con↗

arXiv2023

Information dynamics of our brains in dynamically driven disordered superconducting loop networks

Complex systems of many interacting components exhibit patterns of recurrence and emergent behaviors in their time evolution that can be understood from a new perspective of physics of information dynamics, modeled after one such system, our brains. A generic brain-like network model is derived from a system of disordered superconducting loops with Josephson junction oscillators to demonstrate these behaviors. The loops can trap multiples of fluxons that represent quantized information units in many distinct memory configurations populating a state space. The state can be updated by exciting the junctions to allow the movement of fluxons through the network as the current through them surpasses their thresholds. Numerical simulations performed with a lumped circuit model of a 4-loop network show that information written through excitations is translated into stable states of trapped flux and their time evolution. Experimental implementation on the 4-loop network shows dynamically stable flux flow in each pathway characterized by the junction firing statistics. The network separates information from multiple excitations into state categories with large energy barriers observed in simulations that correspond to different flux (information) flow patterns observed across junctions in experiments. Strong evidence for associative and time-dependent (short-to-long-term) memories distributed across the network is observed, dependent on its intrinsic and geometrical properties as described by the model. Loop network topology abstraction using the model separates the flowing patterns of information from its physical constraints and describes systems of any scale and complexity. The accuracy of flow statistics are limited by the resolution of local external measuring clock(s) revealing the universal nature of information dynamics through the stated two principles.

cond-mat.dis-nn↗

arXiv2023

High-Temperature Superconductor Quantum Flux Parametron for Energy-Efficient Logic

As we rapidly advance through the information age, the power consumed by computers, data centers, and networks grows exponentially. This has inspired a race to develop alternative low-power computational technologies. A new adiabatic configuration of a decades-old superconducting digital logic device has darted into the lead called quantum flux parametrons (QFP). QFP operate with dissipation so low that they seemingly violate the laws of thermodynamics. In just a short span of time, they have gone from simple single NOT gates to complex processors containing thousands of gates. They are fabricated from elemental niobium superconductors cooled to just a few degrees above absolute zero. However, their efficiency is so great that for large high-performance computers with several gates, the energy savings are immense. For smaller computational platforms QFPs from high-temperature superconductors (high-Tc) are highly desirable. In this work, we take the first steps towards this goal with the demonstration of a high-T C QFP shift register. Our device is fabricated using focused helium ion beam lithography where the material is modified with an ion beam at the nanoscale to directly pattern these circuits into a high-T C thin film. We validate the correct logical operation at 25 K, over 6 times higher than niobium devices with an estimated bit energy of 0.1 attoJoule at 10 GHz.

physics.app-ph↗

arXiv2019

Nanoscale High Transition Temperature Superconducting Quantum Interference Device Transimpedance Amplifier

As the quantum generation of electronics takes the stage, a cast of important support electronics is needed to connect these novel devices to our classical worlds. In the case of superconducting electronics, this is a challenge because the Josephson junction devices they are based upon require tiny current pulses to create and manipulate the single flux quanta which guide their operation. Difficulty arises in transitioning these signals through large temperature gradients for connection to semiconductor components. In this work, we present nano superconducting quantum interference devices (SQUID) with critical dimensions as small as 10 nm from the high-transition-temperature superconductor YBa$_2$Cu$_3$O$_{7-δ}$ (YBCO). We integrate these nano-SQUIDs with nano-isolated inductively coupled control lines to create a low power superconducting output driver capable of transimpedance conversion over a very wide temperature range.

physics.app-ph↗

arXiv2019

Direct-Write Ion Beam Irradiated Josephson Junctions

We highlight the reproducibility and level of control over the electrical properties of YBa$_2$Cu$_3$O$_7$ Josephson junctions fabricated with irradiation from a focused helium ion beam. Specifically, we show the results of electrical transport properties for several junctions fabricated using a large range of irradiation doses. At the lower end of this range, junctions exhibit superconductor-normal metal-superconductor (SNS) Josephson junction properties. However, as dose increases there is a transition to electrical characteristics consistent with superconductor-insulator-superconductor (SIS) junctions. To investigate the uniformity of large numbers of helium ion Josephson junctions we fabricate arrays of both SNS and SIS Josephson junctions containing 20 connected in series. Electrical transport properties for these arrays reveal very uniform junctions with no appreciable spread in critical current or resistance.

cond-mat.supr-con↗

arXiv2016

Magnetic effects in sulfur-decorated graphene

The interaction between two different materials can present novel phenomena that are quite different from the physical properties observed when each material stands alone. Strong electronic correlations, such as magnetism and superconductivity, can be produced as the result of enhanced Coulomb interactions between electrons. Two-dimensional materials are powerful candidates to search for the novel phenomena because of the easiness of arranging them and modifying their properties accordingly. In this work, we report magnetic effects of graphene, a prototypical non-magnetic two-dimensional semi-metal, in the proximity with sulfur, a diamagnetic insulator. In contrast to the well-defined metallic behaviour of clean graphene, an energy gap develops at the Fermi energy for the graphene/sulfur compound with decreasing temperature. This is accompanied by a steep increase of the resistance, a sign change of the slope in the magneto-resistance between high and low fields, and magnetic hysteresis. A possible origin of the observed electronic and magnetic responses is discussed in terms of the onset of low-temperature magnetic ordering. These results provide intriguing insights on the search for novel quantum phases in graphene-based compounds.

cond-mat.mtrl-sci↗

arXiv2014

Nano Josephson Superconducting Tunnel Junctions in Y-Ba-Cu-O Direct- Patterned with a Focused Helium Ion Beam

Since the discovery of the unconventional copper-oxide high-transition-temperature superconductors (HTS), researchers have explored many methods to fabricate superconducting tunnel junctions from these materials for both superconducting electronics operating at the practical temperature of liquid nitrogen (77 K) and for fundamental measurements essential for testing and guiding theories of these remarkable superconductors. The difficulty is that the traditional estimate of the superconducting coherence length is very short and anisotropic in these materials, typically ~2 nm in the a-b plane and ~0.2 nm along the c-axis. The coherence volume encloses very few superconducting pairs, so even the presence of small scale inhomogeneities can locally disrupt superconductivity unlike in conventional superconductors. Therefore the electrical properties of Josephson junctions are sensitive to chemical variations and structural defects on atomic length scales, thus to make multiple uniform HTS junctions, control at the atomic level is required. In this letter, we demonstrate very high-quality all-HTS Josephson superconducting tunnel junctions (both Josephson and quasiparticle tunneling) created by using a 500 pm diameter focused beam of helium ions to direct-write tunnel barriers into YBa2Cu3O7(YBCO) thin films. With this method we demonstrate the ability to control the barrier properties continuously from conducting to insulating by varying the irradiation dose. This technique provides a reliable and reproducible pathway for the scaling up of quantum mechanical circuits operating at practical temperatures (~77 K) as well as an avenue to conduct superconducting tunneling studies in HTS for basic science.

cond-mat.supr-con↗