Researchers Roberto Capecelatro, Marco Marciani, Gabriele Campagnano, Roberta Citro, and Procolo Lucignano from the University of Salerno in Italy have published new findings in the journal Physical Review Letters that could have significant implications for the energy sector, particularly in the development of superconducting technologies.
The team investigated the electronic transport properties of a specific type of Josephson junction, a device that plays a crucial role in superconducting electronics. This junction consists of a quantum dot sandwiched between two superconductors and coupled to a ferromagnetic metal reservoir, all in the presence of an external magnetic field. The researchers described the device using an effective non-Hermitian Hamiltonian, a mathematical tool that helps understand the system’s behavior.
In their study, the researchers found that the complex eigenvalues of the Hamiltonian encode both the energy (real part) and the broadening (imaginary part) of the Andreev quasi-bound states. When they extended the Andreev current formula to this non-Hermitian case, they discovered a novel contribution to the current that is proportional to the phase derivative of the levels broadening. This term becomes particularly relevant in the presence of exceptional points (EPs) in the spectrum, but its experimental detection is not straightforward.
The researchers identified optimal Andreev spectrum configurations where this novel current contribution can be clearly highlighted. They also outlined an experimental protocol for its detection. Notably, they pointed out that the phase dependence in the levels imaginary part originates from the breaking of a time-reversal-like symmetry. This means that spectral configurations in the broken phase of the symmetry and without EPs can be obtained, where this novel contribution can be easily resolved.
The proposed protocol would allow researchers to probe for the first time a fingerprint of non-Hermiticity in open junctions that is not strictly related to the presence of EPs. This could lead to a better understanding of non-Hermitian systems and their potential applications in the energy sector, such as in the development of more efficient and robust superconducting devices.
In practical terms, this research could contribute to the advancement of superconducting technologies, which are already used in various energy applications, including magnetic resonance imaging (MRI) machines, particle accelerators, and fusion reactors. A deeper understanding of these systems could lead to more efficient and reliable energy technologies.
This article is based on research available at arXiv.