@article{PhysRevB.107.094402,
title = {Electronic processes occurring during ultrafast demagnetization of cobalt triggered by x-ray photons tuned to the Co $L_3$ resonance},
author = {Flavio Capotondi and Alexander Lichtenstein and Serguei Molodtsov and Leonard Mueller and Andre Philippi-Kobs and Przemysław Piekarz and Konrad J. Kapcia and Victor Tkachenko and Beata Ziaja},
url = {https://link.aps.org/doi/10.1103/PhysRevB.107.094402},
doi = {10.1103/PhysRevB.107.094402},
year = {2023},
date = {2023-03-01},
journal = {Phys. Rev. B},
volume = {107},
pages = {094402},
publisher = {American Physical Society},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Baranski2023,
title = {Quench dynamics of Fano-like resonances in the presence of the on-dot superconducting pairing},
author = {Jan Bara{ń}ski and Magaldena Bara{ń}ska and Tomasz Zienkiewicz and Konrad J. Kapcia},
url = {https://doi.org/10.1038/s41598-023-34376-5},
doi = {10.1038/s41598-023-34376-5},
issn = {2045-2322},
year = {2023},
date = {2023-01-01},
journal = {Scientific Reports},
volume = {13},
number = {1},
pages = {7639},
abstract = {We explore the electron dynamics of a system composed of double quantum dot embedded between metallic and superconducting leads in a “T-shape” geometry. In nanoscopic systems, where electron transfer between electrodes can be realized via different paths, interference effects play an important role. For double quantum dot system in the chosen geometry, interference of electrons transferred between electrodes via the interfacial quantum dot and electrons scattered on the side dot gives rise to Fano-like interference. If such a system is additionally coupled to a superconducting electrode, together with the well-understood Fano resonance an additional resonance appears on the opposite side of the Fermi level. In the recent work (Barański et al. in Sci Rep 10:2881, 2020), we showed that this resonance occurs solely as a result of the local pairing of non-scattered electrons with scattered ones. In this work, considering the quench dynamics, we explore how much time is required for formation of each of these resonances. In particular, (i) we analyze the charge oscillations between subsystems; (ii) we estimate the time required for each resonance to achieve stable equilibrium upon an abrupt change of interdot connection; (iii) we discuss a typical energy and time scales for experiments on similar architectures.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{SKORKA2023105888,
title = {Chiral phonons in binary compounds ABi (A = K, Rb, Cs) with P21/c structure},
author = {Jakub Skórka and Konrad J. Kapcia and Paweł T. Jochym and Andrzej Ptok},
url = {https://www.sciencedirect.com/science/article/pii/S2352492823005792},
doi = {https://doi.org/10.1016/j.mtcomm.2023.105888},
issn = {2352-4928},
year = {2023},
date = {2023-01-01},
journal = {Materials Today Communications},
volume = {35},
pages = {105888},
abstract = {Binary compounds ABi (A = K, Rb, Cs) crystallize in P21/c structure containing both clockwise and anticlockwise chiral chains of Bi atoms. Electronic band structure exhibits the insulating nature of these systems, with the band gap about 0.25eV. The presented study of dynamical properties confirm a stability of the system with P21/c symmetry. The crystal structure contains the quasi-one-dimensional Bi chains, exhibiting four-fold-like rotational “local” symmetry. Nevertheless, the system formally possesses two-fold rotational symmetry. Independently of the absence of the three-fold (or higher) rotational symmetry axes for the whole crystal, the chiral modes propagate along the Bi atom chains in these systems. We discuss basic properties of these modes in monoatomic chiral chains. We show that the two-fold rotational symmetry axis affects the main properties of the chiral phonons, which are not realized at the high-symmetry points, but along some paths between them in the reciprocal space. In addition, in the doped system, the chiral phonons possess non-zero total angular momentum.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Jan_Baranski2023-id,
title = {Dynamics of Fano-Like Resonances in Double-Quantum-Dot Systems},
author = {Jan Barański and Konrad J. Kapcia},
url = {http://appol.ifpan.edu.pl/index.php/appa/article/view/143_143},
year = {2023},
date = {2023-01-01},
journal = {Acta Physica Polonica A},
volume = {143},
number = {2},
pages = {143},
abstract = {Quantum interference effects appearing in mesoscopic
heterostructures have been extensively studied in static
conditions over the last decades. It is interesting to examine
the dynamics of these phenomena and get insight into the process
of the formation of interference patterns. In this work, we
analyze the time required for the formation of Fano-like
resonances in a double quantum dot system. We examined the time
evolution of conductance upon establishing an abrupt connection
between quantum dots. Asymmetric Fano lines are characterized by
the close coexistence of resonant enhancement and resonant
suppression. Therefore, we pay particular attention to voltages,
which in the static case, correspond to both these features. Our
research shows that the analyzed resonances are characterized by
two time scales: (i) the first one related to charge oscillations
between subsystems and mostly governed by the interdot coupling
constant and the relative position of energy levels of quantum
dots, and (ii) the second one associated to the electron
scattering on a continuum of states and responsible for the
relaxation. We also show that the time required for achieving a
static solution is different for voltages corresponding to local
minima and local maxima.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Kapcia2022,
title = {Modeling of ultrafast X-ray induced magnetization dynamics in magnetic multilayer systems},
author = {Konrad J. Kapcia and V. Tkachenko and F. Capotondi and A. Lichtenstein and S. Molodtsov and L. Müller and A. Philippi-Kobs and P. Piekarz and B. Ziaja},
url = {https://www.nature.com/articles/s41524-022-00895-4},
doi = {10.1038/s41524-022-00895-4},
year = {2022},
date = {2022-10-01},
journal = {npj Computational Materials},
volume = {8},
pages = {212},
abstract = {In this work, we report on modeling results obtained with our recently developed simulation tool enabling nanoscopic description of electronic processes in X-ray irradiated ferromagnetic materials. With this tool, we have studied the response of Co/Pt multilayer system irradiated by an ultrafast extreme ultraviolet pulse at the M-edge of Co (photon energy ~60 eV). It was previously investigated experimentally at the FERMI free-electron-laser facility, using the magnetic small-angle X-ray scattering technique. Our simulations show that the magnetic scattering signal from cobalt decreases on femtosecond timescales due to electronic excitation, relaxation, and transport processes both in the cobalt and in the platinum layers, following the trend observed in the experimental data. The confirmation of the predominant role of electronic processes for X-ray induced demagnetization in the regime below the structural damage threshold is a step toward quantitative control and manipulation of X-ray induced magnetic processes on femtosecond timescales.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Rybak2022,
title = {Stress-Tuned Optical Transitions in Layered 1T-MX2 (M=Hf, Zr, Sn; X=S, Se) Crystals },
author = {Miłosz Rybak and Tomasz Woźniak and Magdalena Birowska and Filip Dybała and Alfredo Segura and Konrad J. Kapcia and Paweł Scharoch and Robert Kudrawiec},
url = {https://www.mdpi.com/2079-4991/12/19/3433},
doi = {10.3390/nano12193433},
year = {2022},
date = {2022-09-30},
journal = {Nanomaterials},
volume = {12},
number = {19},
pages = {3433},
abstract = {Optical measurements under externally applied stresses allow us to study the materials’ electronic structure by comparing the pressure evolution of optical peaks obtained from experiments and theoretical calculations. We examine the stress-induced changes in electronic structure for the thermodynamically stable 1T polytype of selected MX2 compounds (M=Hf, Zr, Sn; X=S, Se), using the density functional theory. We demonstrate that considered 1T-MX2 materials are semiconducting with indirect character of the band gap, irrespective to the employed pressure as predicted using modified Becke–Johnson potential. We determine energies of direct interband transitions between bands extrema and in band-nesting regions close to Fermi level. Generally, the studied transitions are optically active, exhibiting in-plane polarization of light. Finally, we quantify their energy trends under external hydrostatic, uniaxial, and biaxial stresses by determining the linear pressure coefficients. Generally, negative pressure coefficients are obtained implying the narrowing of the band gap. The semiconducting-to-metal transition are predicted under hydrostatic pressure. We discuss these trends in terms of orbital composition of involved electronic bands. In addition, we demonstrate that the measured pressure coefficients of HfS2 and HfSe2 absorption edges are in perfect agreement with our predictions. Comprehensive and easy-to-interpret tables containing the optical features are provided to form the basis for assignation of optical peaks in future measurements.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Cichy2022,
title = {Connection between the semiconductor-superconductor transition and the spin-polarized superconducting phase in the honeycomb lattice},
author = {Agnieszka Cichy and Konrad J. Kapcia and Andrzej Ptok},
url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.105.214510},
doi = {10.1103/PhysRevB.105.214510},
year = {2022},
date = {2022-06-14},
journal = {Phys. Rev. B},
volume = {105},
pages = {214510},
abstract = {The band structure of noninteracting fermions in the honeycomb lattice exhibits the Dirac cones at the corners of the Brillouin zone. As a consequence, fermions in this lattice manifest a semiconducting behavior below some critical value of the on-site attraction Uc. However, above Uc, the superconducting phase can occur. We discuss an interplay between the semiconductor-superconductor transition and the possibility of realization of the spin-polarized superconductivity (the so-called Sarma phase). We show that the critical interaction can be tuned by the next-nearest-neighbor (NNN) hopping in the absence of the magnetic field. Moreover, a critical value of the NNN hopping exists, defining a range of parameters for which the semiconducting phase can emerge. In the weak-coupling limit case, this quantum phase transition occurs for the absolute value of the NNN hopping equal to one third of the hopping between the nearest neighbors. Similarly, in the presence of the magnetic field, the Sarma phase can appear but only in a range of parameters for which initially the semiconducting state is observed. Both of these aspects are attributed to the Lifshitz transition, which is induced by the NNN hopping as well as the external magnetic field.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}

@article{Inoue2022,
title = {Delayed Onset and Directionality of X-Ray-Induced Atomic Displacements Observed on Subatomic Length Scales},
author = {Ichiro Inoue and Victor Tkachenko and Konrad J. Kapcia and Vladimir Lipp and Beata Ziaja and Yuichi Inubushi and Toru Hara and Makina Yabashi and Eiji Nishibori},
url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.223203},
doi = {10.1103/PhysRevLett.128.223203},
year = {2022},
date = {2022-06-01},
journal = {Phys. Rev. Lett.},
volume = {128},
pages = {223203},
abstract = {Transient structural changes of Al2O3 on subatomic length scales following irradiation with an intense x-ray laser pulse (photon energy: 8.70 keV; pulse duration: 6 fs; fluence: 8×102  J/cm2) have been investigated by using an x-ray pump x-ray probe technique. The measurement reveals that aluminum and oxygen atoms remain in their original positions by ∼20  fs after the intensity maximum of the pump pulse, followed by directional atomic displacements at the fixed unit cell parameters. By comparing the experimental results and theoretical simulations, we interpret that electron excitation and relaxation triggered by the pump pulse modify the potential energy surface and drives the directional atomic displacements. Our results indicate that high-resolution x-ray structural analysis with the accuracy of 0.01 Å is feasible even with intense x-ray pulses by making the pulse duration shorter than the timescale needed to complete electron excitation and relaxation processes, which usually take up to a few tens of femtoseconds.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}