arXiv subjects

Ioannis Ioannidis

Publications and source records attributed to Ioannis Ioannidis.

6 recordsLinked to original sources

arXiv2026

Supercurrent detection and manipulation of topological phase transitions in Shiba-Majorana hybrid systems

The non-Abelian statistics of Majorana zero modes has inspired numerous proposals for their detection and manipulation in topological superconductors. Implementations based on magnetic adatoms deposited on superconductors draw particular attention due to their capabilities for precise atomic manipulation and the control over disorder. Here, we propose a scheme for detecting changes in the ground state parity of a topologically non-trivial adatom system by passing supercurrent through their low-energy modes. We unravel characteristic discontinuities in the critical current driven by zero-energy level crossings. We apply these findings to a setup where the Majorana coupling is mediated by a single control magnetic adatom hosting a Yu-Shiba-Rusinov state, and test the robustness of our results against finite temperatures and different tunneling regimes. Our findings introduce a non-invasive approach for reading out and controlling the ground state parity of Majorana states in Shiba-Majorana hybrid systems.

cond-mat.supr-con↗

arXiv2026

Time-reversal symmetric topological superconductivity in Machida-Shibata lattices

Recent experiments engineered special spin-degenerate Andreev bound states in atomic cages of adatoms on superconductors, the Machida-Shibata states, a promising building block for quantum matter. Here, we investigate the formation of time-reversal symmetric bands by hybridizing multiple such states and analyzing their electronic topological properties assuming small on-site electron repulsion. The low-energy theory shows that competing emerging singlet and triplet superconducting pairings drive the formation of topologically non-trivial phases in symmetry class DIII. We, therefore, predict Kramers pairs of Majorana zero modes appear at the ends of Machida-Shibata chains, while two-dimensional lattices host helical Majorana edge modes. Additionally, we discover extended regions in the Brillouin zone with vanishing superconducting pairings, which are lifted by the repulsive electron interactions. Our findings offer new perspectives for manipulating topological superconductivity and pairings in non-magnetic adatom systems.

cond-mat.supr-con↗

arXiv2026

In-plane ferromagnetism-driven topological nodal-point superconductivity with tilted Weyl cones

The potential application of topological superconductivity in quantum transport and quantum information has fueled an intense investigation of hybrid materials with emergent electronic properties, including magnet-superconductor heterostructures. Here, we report evidence of a topological nodal-point superconducting phase in a one-atom-thick in-plane ferromagnet in direct proximity to a conventional $s$-wave superconductor. Low-temperature scanning tunneling spectroscopy data reveal the presence of a double-peak low-energy feature in the local density of states of the hybrid system, which is rationalized via model calculations to be an emergent topological nodal-point superconducting phase with tilted Weyl cones. Our results further establish the combination of in-plane ferromagnetism and conventional superconductivity as a route to design two-dimensional topological quantum phases.

cond-mat.supr-con↗

arXiv2024

Non-local detection of coherent Yu-Shiba-Rusinov quantum projections

Probing spatially confined quantum states from afar - a long-sought goal to minimize external interference - has been proposed to be achievable in condensed matter systems via coherent projection. The latter can be tailored by sculpturing the eigenstates of the electron sea that surrounds the quantum state using atom-by-atom built cages, so-called quantum corrals. However, assuring the coherent nature of the projection, and manipulating its quantum composition, has remained an elusive goal. Here, we experimentally realize the coherent projection of a magnetic impurity-induced, Yu-Shiba-Rusinov quantum state using the eigenmodes of corrals on the surface of a superconductor, which enables us to manipulate the particle-hole composition of the projected state by tuning corral eigenmodes through the Fermi energy. Our results demonstrate a controlled non-local method for the detection of magnet superconductor hybrid quantum states.

cond-mat.supr-con↗

arXiv2024

Controlling Majorana hybridization in magnetic chain-superconductor systems

We propose controlling the hybridization between Majorana zero modes at the ends of magnetic adatom chains on superconductors by an additional magnetic adatom deposited close by. By tuning the additional adatom's magnetization, position, and coupling to the superconductor, we can couple and decouple the Majorana modes as well as control the ground state parity. The scheme is independent of microscopic details in ferromagnetic and helical magnetic chains on superconductors with and without spin-orbit coupling, which we show by studying their full microscopic models and their common low-energy description. Our results show that scanning tunneling microscopy and electron spin resonance techniques are promising tools for controlling the Majorana hybridization in magnetic adatoms-superconductor setups, providing a basis for Majorana parity measurements, fusion, and braiding techniques.

cond-mat.mes-hall↗

arXiv2022

Proximity superconductivity in atom-by-atom crafted quantum dots

Gapless materials in electronic contact with superconductors acquire proximity-induced superconductivity in a region near the interface. Numerous proposals build on this addition of electron pairing to originally non-superconducting systems like ferromagnets and predict intriguing quantum phases of matter, including topological-, odd-frequency-, or nodal-point superconductivity. However, atomic-scale experimental investigations of the microscopic mechanisms leading to proximity-induced Cooper pairing in surface or interface states are missing. Here, we investigate the most miniature example of the proximity effect on only a single quantum level of a surface state confined in a quantum corral on a superconducting substrate, built atom-by-atom by a scanning tunneling microscope. Whenever an eigenmode of the corral is pitched close to the Fermi energy by adjusting the corral's size, a pair of particle-hole symmetric states enters the superconductor's gap. We identify the in-gap states as scattering resonances theoretically predicted 50 years ago by Machida and Shibata, which had so far eluded detection. We further show that the observed anticrossings of the in-gap states indicate proximity-induced pairing in the quantum corral's eigenmodes. Our results have direct consequences on the interpretation of in-gap states in unconventional or topological superconductors, corroborate concepts to induce superconductivity into a single quantum level and further pave the way towards superconducting artificial lattices.

cond-mat.supr-con↗