Superconducting diode effect reverses direction in magnetic field

Physicists at the University of Regensburg (UR) have made a groundbreaking discovery regarding the supercurrent diode effect. Led by the research groups of Professor Dr. Christoph Strunk, Dr. Nicola Paradiso, and Professor Dr. Jaroslav Fabian, the teams have experimentally demonstrated a significant sign change in this effect. Their findings have been published in a recent issue of Nature Nanotechnology. Remarkably, the experimental data obtained align precisely with the theoretical predictions put forth by Dr. Andreas Costa, also a physicist at the University of Regensburg.

In conventional transistors, including those found in computer CPUs, heat generation is a prevalent issue due to the resistive nature of most conductors. However, “Josephson junction field effect transistors” offer a solution by operating without generating heat. These transistors rely on Josephson junctions, which are weak connections between two superconductors capable of carrying a zero-resistance current known as a supercurrent.

Since their discovery by Nobel laureate Brian Josephson, Josephson junctions have found applications in diverse fields such as medicine, metrology, and astrophysics. More recently, they have become integral components of quantum computers, particularly in the implementation of transmons, the most popular qubits used in superconducting quantum processors.

Given this context, the recent discovery of the first superconducting diode based on a Josephson junction by Nicola Paradiso and Christoph Strunk’s group at the University of Regensburg has garnered significant attention. This diode was created in a synthetic crystal grown by Michael J. Manfra and his team at Purdue University.

The significance of this discovery lies in the potential of superconducting diodes to serve as fundamental building blocks for novel superconducting circuits. Such circuits could eventually replace resistive circuits, leading to advanced technological applications.

Ordinary semiconducting diodes are characterized by their asymmetry, resulting in varying resistance depending on the polarity of the applied voltage. This asymmetry enables the diode’s essential property of current rectification.

In contrast, a superconducting diode exhibits no resistance, necessitating a different working principle. Paradiso and his colleagues discovered that a superconducting diode demonstrates distinct inductance for the two possible polarities of direct current (DC). Furthermore, the observed critical current, which denotes the threshold at which the device switches to a resistive state, is higher for the polarity with lower inductance. This establishes the existence of a preferred current direction.

The determining factor behind this preferred direction was previously considered an inherent material characteristic. However, the researchers at the University of Regensburg have recently made an exciting breakthrough. They have observed that at higher magnetic fields, the preferred direction can reverse. While this effect was predicted by theorists about a decade ago, it had not been experimentally confirmed until now. In their paper published in Nature Nanotechnology, the Strunk group presents compelling experimental evidence of a remarkable sign change in the supercurrent diode effect. Importantly, the experimental results align quantitatively with the theory developed by Dr. Andreas Costa, also affiliated with the University of Regensburg.

Undoubtedly, this discovery will have a profound impact on the scientific community. The superconducting diode effect has emerged as a captivating area of research in quantum electronics, holding tremendous promise for both technological applications and fundamental scientific investigations.

Source: Universit├Ąt Regensburg

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