@article{Siuda2025c,
title = {Competition between Nagaoka ferromagnetism and superconducting pairing in hybrid quantum dots},
author = {Emil Siuda and Ireneusz Weymann},
url = {https://www.nature.com/articles/s41598-025-10867-5},
doi = {/10.1038/s41598-025-10867-5},
year = {2025},
date = {2025-07-14},
journal = {Sci. Rep.},
volume = {15},
pages = {25349},
abstract = {We examine the interplay between the Nagaoka ferromagnetism and superconducting pairing correlations in a two-by-two quantum dot array proximitized by an s-wave superconductor. Focusing on the subgap regime, we determine the phase diagram of the system, demonstrating that Nagaoka ferromagnetism becomes greatly affected by the presence of superconductor and, depending on the strength of direct and crossed Andreev reflections, can be fully suppressed. This happens at some critical value of the induced on-dot pairing potential, for which we provide the corresponding analytical formulas in the limit of large Coulomb correlations. Moreover, we also shed light on the competition between Nagaoka ferromagnetism and superconductivity visible in the transport characteristics. Using the real-time diagrammatic technique, we determine the nonequilibrium current and differential conductance assuming that the quantum dot plaquette is weakly coupled to external lead that can be used to probe the system’s properties. We not only uncover the impact of Nagaoka ferromagnetism on the Andreev current and differential conductance, but also demonstrate a spin quintuplet blockade of the Andreev transport.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Siuda2025b,
title = {Spin caloritronics of a quantum dot coupled to a magnetic insulator and normal metal},
author = {Emil Siuda and Piotr Trocha},
url = {https://www.nature.com/articles/s41598-025-04413-6},
doi = {10.1038/s41598-025-04413-6},
year = {2025},
date = {2025-07-02},
journal = {Sci. Rep.},
volume = {15},
pages = {23208},
abstract = {We investigate the generation of spin current through temperature gradients in a quantum dot-based hybrid system. In particular, we study a quantum dot coupled to a magnetic insulator and a (non)magnetic metallic electrode. Generally, each electrode is maintained at a different temperature, resulting in a finite spin current. In this system, spin current of the magnonic type is converted into electric spin current, and vice versa, depending on the direction of the temperature gradient. We examine the influence of the magnonic energy-dependent density of states and many-body magnon interactions on thermally induced spin current. Additionally, the system can work as a spin Seebeck engine, converting heat into spin current. We establish the conditions under which the system operates as a heat engine and present results on its performance. Furthermore, we propose a device based on the system that acts as an efficient thermal spin-diode–allowing spin current to pass in one direction of the temperature bias while completely suppressing it in the opposite direction.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Siuda2025,
title = {Thermal Gradient Powering Spin Current in Quantum Dot-Magnetic Insulators Hybrid},
author = {Emil Siuda and Piotr Trocha },
url = {https://link.springer.com/article/10.1007/s10948-025-06921-y},
doi = {10.1007/s10948-025-06921-y},
year = {2025},
date = {2025-02-07},
journal = {Journal of Superconductivity and Novel Magnetism},
volume = {38},
number = {81},
abstract = {The growing energy consumption of the computational sector worldwide necessitates the search for sustainable methods of powering and performing calculations. The fast-emerging field of spin caloritronics offers a promising solution by combining the advantages of performing computations on spins instead of charges and driving these computations through temperature differences rather than voltage. Among the various approaches, spin waves and their quanta of excitations, known as magnons, are considered promising carriers of spin-encoded information. In this article, we examine the magnon current generated in a system composed of a magnetic insulator/quantum dot/magnetic insulator, driven by a small temperature difference applied between the two insulators. By expanding the magnon current in terms of the applied temperature bias, we analyze the contributions of successive terms up to the third order of the temperature difference. Each term exhibits a similar structure, consisting of a driving-like and a damping-like component. The driving-like term is dependent on the coupling strength between the quantum dot and the electrodes. We explicitly show that the second-order term of the magnon current vanishes when the couplings of the quantum dot to the magnetic insulators are equal. Overall, the first two terms are sufficient to capture the behavior of the magnon current across the full range of temperature differences. For extreme values of the temperature gradient, the approximate results align with the exact ones only when there is significant asymmetry in the coupling strengths. Finally, we demonstrate that the system can function as a spin diode, capable of rectifying the magnon current when the temperature bias is reversed.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Siuda2024,
title = {Thermal generation of spin current in a quantum dot coupled to magnetic insulators},
author = {Emil Siuda and Piotr Trocha},
url = {https://www.sciencedirect.com/science/article/pii/S0304885323011459},
doi = {/10.1016/j.jmmm.2023.171495},
year = {2024},
date = {2024-01-01},
journal = {Journal of Magnetism and Magnetic Materials},
volume = {589},
pages = {171495},
abstract = {In this work, we study thermally-generated spin current in the system consisting of a quantum dot connected to two magnetic insulators. The external leads are kept at different temperatures which leads to an imbalance of magnon populations in two magnetic insulators resulting in the flow of the magnon (spin) current. We take into account many-body magnon interactions and incorporate energy-dependent density of states of the magnetic insulators. Both features can strongly affect magnon distribution in the magnetic insulators and the coupling strengths between the leads and the dot, and thus, the thermally generated spin current. All the calculations are carried out in the weak coupling regime. We show, that results obtained with a density of states being a function of energy differ significantly from the ones obtained with a density of states taken as a constant. In turn, magnon interactions in the leads proved to be important at high temperatures and large values of energy of transported spin waves.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Trocha2022c,
title = {Spin-thermoelectric effects in a quantum dot hybrid system with magnetic insulator},
author = {Piotr Trocha and Emil Siuda},
url = {https://www.nature.com/articles/s41598-022-09105-z},
doi = {10.1038/s41598-022-09105-z},
year = {2022},
date = {2022-03-30},
journal = {Scientific Reports},
volume = {12},
number = {5348},
abstract = {We investigate spin thermoelectric properties of a hybrid system consisting of a single-level quantum dot attached to magnetic insulator and metal electrodes. Magnetic insulator is assumed to be of ferromagnetic type and is a source of magnons, whereas metallic lead is reservoir of electrons. The temperature gradient set between the magnetic insulator and metallic electrodes induces the spin current flowing through the system. The generated spin current of magnonic (electric) type is converted to electric (magnonic) spin current by means of quantum dot. Expanding spin and heat currents flowing through the system, up to linear order, we introduce basic spin thermoelectric coefficients including spin conductance, spin Seebeck and spin Peltier coefficients and heat conductance. We analyse the spin thermoelectric properties of the system in two cases: in the large ondot Coulomb repulsion limit and when these interactions are finite.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Trocha2022b,
title = {Spin-polarized transport in quadruple quantum dots attached to ferromagnetic leads},
author = {Piotr Trocha and Emil Siuda and Ireneusz Weymann},
url = {https://www.sciencedirect.com/science/article/pii/S0304885321010453},
doi = {10.1016/j.jmmm.2021.168835},
year = {2022},
date = {2022-03-15},
journal = {Journal of Magnetism and Magnetic Materials},
volume = {546},
number = {168835},
abstract = {Motivated by the experimental evidence of the Nagaoka ferromagnetism in quantum dot systems by Dehollain et al. (2020), we search for possible confirmation of such kind of ferromagnetism by analyzing the spin-resolved transport properties of a quadruple quantum dot system focusing on the linear response regime. In particular, we consider four quantum dots arranged in a two-by-two square lattice, coupled to external ferromagnetic source and drain electrodes. Turning on and off the specific conditions for the Nagaoka ferromagnetism to occur by changing the value of the intra-dot Coulomb interactions, we determine the transport coefficients, including the linear conductance, tunnel magnetoresistance and current spin polarization. We show that a sign change of the current spin polarization may be an indication of a ferromagnetic order of Nagaoka type which develops in the system.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}