@misc{Novotný2027,
title = {Superconducting nanohybrids out of equilibrium},
author = {Ireneusz Weymann},
year = {2027},
date = {2027-12-01},
abstract = {We will study the out-of-equilibrium properties of superconducting nanoscopic hybrid devices consisting of active elements, e.g., a set of semiconducting nanowires, connected to superconducting leads. Such devices, apart from their applications in quantum information processing and sensor technology, provide an ideal setup to study quantum phenomena in controlled conditions. Using complementary methods previously developed and/or mastered by both collaborating teams, including numerical renormalization group, diagrammatic perturbation techniques and quantum Monte Carlo, we will evaluate linear response properties such as thermopower or microwave response, which have been only recently measured. Moreover, some of these methods will be further generalized to strong out-of-equilibrium situations to provide results on AC Josephson systems driven by finite voltage or quenched systems undergoing a sudden change of parameters. We plan to build up a toolbox of theoretical methods for a reliable description of nonequilibrium nanohybrids to address both existing as well as future experiments.

Project is realized in partnership with Prof. Dr hab. Tadeusz Domański from the Marie Curie Skłodowska University in Lublin and with Dr hab. Tomáš Novotný from the Charles University in Prague.},
howpublished = {2023},
note = {Weave-UNISONO bilateral Polish-Czech project (co-operation with Tomáš Novotný and Tadeusz Domański), budget: 321 000€ + 307 457€ [Cz + Pl]},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}

@misc{Weymann2027,
title = {Critical phenomena and transport in correlated hybrid nanostructures},
author = {Ireneusz Weymann},
url = {http://zfmezo.home.amu.edu.pl/opus23.php},
year = {2027},
date = {2027-01-16},
abstract = {Transport properties of correlated hybrid nanostructures, involving molecules and atoms as well as their artificial counterparts, coupled to external contacts are the subject of extensive theoretical and experimental studies not only due to various fundamental aspects and new physical phenomena, but also because of possible applications in nanoelectronics and quantum technologies for storing and processing information. However, to further progress the development of quantum technologies or to propose any working device, it is of crucial importance to fully understand the system’s behavior under different conditions, involving both equilibrium and out-of-equilibrium situations as well as the stationary and transient regimes. In this regard, a special attention has been recently paid to the timedependent phenomena and dynamical quantum critical behavior triggered upon a controllable change of the system’s parameters, which may lead to dynamical phase transitions – a counterpart of conventional phase transitions but taking place in time. Up to now, such phase transitions have been mainly studied in the case of global parameter changes, and only very recently it has been demonstrated that the concept of dynamical phase transitions can be extended to mesoscopic hybrid systems involving nanoscale objects. In such systems, local perturbations can be performed in a fully controllable fashion, allowing for more flexible exploration of dynamical phenomena in artificial heterostructures.

The considerations performed in this project will be based upon very accurate numerical methods, such as time-dependent numerical renormalization group method, which allow for obtaining high-quality quantitative results with all the correlations and interactions taken into account in an essentially exact manner. The planned investigations and calculations will thus provide very reliable results for the time-dependent and transport phenomena that will be of relevance to both theoretical and experimental works. Moreover, our theoretical predictions shall foster further investigations of physical properties of hybrid nanoscale systems and devices. Finally, because the research in the highly specialized areas, as described in this proposal, is very important not only for fundamental science but also for high-tech industry and innovation, the execution of the project will contribute to the development of new competitive and environmental-friendly technologies.},
howpublished = {2023},
note = {NCN OPUS, No. 2022/45/B/ST3/02826, budget: 1 482 300 PLN},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}

@misc{Weymann2022,
title = {Majorana fermions in transport through correlated nanoscale systems},
author = {Ireneusz Weymann},
url = {https://projekty.ncn.gov.pl/index.php?projekt_id=408273},
year = {2023},
date = {2023-09-20},
abstract = {Nearly half a century has passed since P. W. Anderson published in Science his seminal paper \textit{More is Different}. In this paper Anderson discusses the hierarchical structure of science and puts forward the conjecture that the knowledge of behavior of a few particles cannot be extrapolated to predict the behavior of more complex systems. This straightforwardly leads to the conclusion that with increasing the system’s complexity, some completely new properties may emerge. In fact, over recent decades we have witnessed several astonishing discoveries, with topologically protected states of matter (Nobel awarded to Thouless, Haldane and Kosterlitz in 2016) being a very important example. Such states are very robust against local perturbations, since they are protected by symmetry, and can extend over entire sample. This makes them very promising for quantum spintronics and quantum computation and, in fact, puts their investigations in the forefront of nowadays physics. Besides, topological materials also constitute an excellent playground for more fundamental research. In particular, it turns out that the long-searched Majorana fermions, i.e. particles that are their own antiparticles, predicted by Ettore Majorana already in 1937, can emerge at the ends of topological superconducting wires as zero-energy quasiparticles.

\textbf{The Majorana quasiparticles and their interactions with strongly correlated low-dimensional systems are the central object of interest of this research project. }

The emergence of Majorana quasiparticles at the ends of topological superconducting nanowires can be confirmed by performing transport spectroscopy experiments, where their presence gives rise to a zero-bias peak in the differential conductance of the device. Moreover, Majorana quasiparticles can also affect the transport behavior of side-attached zero-dimensional systems, such as quantum dots, where the leakage of Majorana modes results in fractional value of the conductance. In fact, such hybrid, coupled zero and one-dimensional systems provide an exceptional opportunity to test fundamental interactions between topologically-protected states of matter and various electronic correlations, such as the ones leading to the Kondo effect. The Kondo effect emerges when a magnetic impurity interacts with continuum of states and its signature is an additional resonance in the local density of states of the impurity. The studies of the interplay between the Kondo and Majorana physics have been so far mainly restricted to relatively simple models. Nevertheless, since to understand the behavior of real systems minimal descriptions are not necessarily sufficient, it is important to address the question of what are the transport properties of considered hybrid systems, where more exotic Kondo phenomena can emerge. The investigations will be performed by using the state-of-the-art numerical and analytical methods, which will be appropriately adapted to determine the transport behavior of considered hybrid systems. These methods include, among others, the density-matrix numerical renormalization group method – the approach known for its accuracy in determining the transport properties of nanostructures, or the Keldysh nonequilibrium Green’s function formalism. },
howpublished = {2019},
note = {NCN Opus 15, No. 2018/29/B/ST3/00937, budget: 1 146 920,00 PLN},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}

@misc{Weymann2021,
title = {Nonequilibrium phenomena and dynamics in nanoscale systems},
author = {Ireneusz Weymann},
url = {https://projekty.ncn.gov.pl/index.php?projekt_id=390993},
year = {2023},
date = {2023-05-31},
abstract = {The rapid progress in miniaturization of electronic devices inevitably brings the current technology closer to a certain natural limit, when the manipulation of individual molecules, atoms or spins will constitute the basis for processing and storing information. Regardless of how distant this perspective seems to be, comprehensive understanding of physics at the nanoscale will certainly be of vital importance. The theoretical studies of transport properties of nanoscale systems, such as molecules, quantum dots or nanowires, due to strong electron correlations, are very demanding and the methods used are very often based on a series of approximations. Consequently, there are relatively few results that can be considered as benchmarks, and which can be directly compared to experiments. The aim of this project is to provide very accurate results and new predictions for problems that have not been studied yet. One of such open problems is undoubtedly the accurate quantitative calculation of transport characteristics in non-equilibrium conditions and the determination of dynamics with exact treatment of correlations. Therefore, the main goal of this project is to develop and adapt advanced numerical methods based on renormalization group techniques to study transport properties of correlated nanoscale systems, with particular emphasis on non-equilibrium and dynamical phenomena. },
howpublished = {2018},
note = {NCN Opus 14, No. 2017/27/B/ST3/00621, budget: 1 506 300,00 PLN},
keywords = {},
pubstate = {published},
tppubtype = {misc}
}