Tadeusz. K. Kopec
Research Subjects
Tadeusz. K. Kopec has a total of 35 co-authors. Here are the top co-authors by number of shared publications:
- Tomasz A. Zaleski
Institute of Low Temperature and Structure Research
29 shared publications - Tomasz P. Polak
Adam Mickiewicz University of Poznan, Faculty of Physics, Umultowska 85, 61-614 Poznan, Poland
17 shared publications - Vardan Apinyan
Institute of Low Temperature and Structure Research Polish Academy of Sciences PO. Box 1410 50-950 Wroc law 2 Poland
12 shared publications G. Büttner
Theoretische Tieftemperaturphysik, Universität Duisburg, Lotharstrasse 1, 4100 Duisburg 1, Germany
10 shared publicationsV. Apinyan
8 shared publicationsK. D. Usadel
Theoretische Tieftemperaturphysik, Universität Duisburg–Essen, 47048 Duisburg, Germany
5 shared publications
Latest Publications
- 8 August 2025
- Published by American Physical Society (APS) in Physical Review B
- Vol. 112 (5)
Ground-state critical hopping amplitude scaling in two- and three-dimensional Bose-Hubbard models with large filling factors
- 8 August 2025
- Published by American Physical Society (APS) in Physical Review B
- Vol. 112 (5)
Ground-state critical hopping amplitude scaling in two- and three-dimensional Bose-Hubbard models with large filling factors
- 15 April 2025
- Published by American Physical Society (APS) in Physical Review B
- Vol. 111 (13)
Pair superfluidity in generalized Bose-Hubbard models
- 15 April 2025
- Published by American Physical Society (APS) in Physical Review B
- Vol. 111 (13)
Pair superfluidity in generalized Bose-Hubbard models
- 17 October 2024
- Published by American Physical Society (APS) in Physical Review B
- Vol. 110 (14)
Interaction-driven crossover from Mott insulator–superfluid criticality to Bose-Einstein condensation in a simple cubic lattice
- 17 October 2024
- Published by American Physical Society (APS) in Physical Review B
- Vol. 110 (14)
Interaction-driven crossover from Mott insulator–superfluid criticality to Bose-Einstein condensation in a simple cubic lattice
- Open Access
- 12 June 2024
- Published by AIP Publishing in Journal of Applied Physics
- Vol. 135 (22)
Excitonic correlations in the system of gated metallic wires with the applied Zeeman magnetic field
We have studied the electron–electron interactions in the system composed of two metallic one-dimensional point contact and zero-sized wires, in the applied electric field and exposed to the influence of the external Zeeman magnetic field. The interactions between the electrons within wires have been taken into account within the usual Hubbard model. We have considered different limits of particle-filling on the atomic lattice site positions. We show the existence of the excitonic pairing in this one-dimensional system in different limits of the electron–electron interactions, magnetic field, and temperature. We demonstrate that the usual Hubbard-U interaction leads to strong electron localization, which enhances the local antiferromagnetic order in the system.
- 12 June 2024
- Published by AIP Publishing in Journal of Applied Physics
- Vol. 135 (22)
Open AccessExcitonic correlations in the system of gated metallic wires with the applied Zeeman magnetic field
We have studied the electron–electron interactions in the system composed of two metallic one-dimensional point contact and zero-sized wires, in the applied electric field and exposed to the influence of the external Zeeman magnetic field. The interactions between the electrons within wires have been taken into account within the usual Hubbard model. We have considered different limits of particle-filling on the atomic lattice site positions. We show the existence of the excitonic pairing in this one-dimensional system in different limits of the electron–electron interactions, magnetic field, and temperature. We demonstrate that the usual Hubbard-U interaction leads to strong electron localization, which enhances the local antiferromagnetic order in the system.
- 21 August 2023
- Published by American Physical Society (APS) in Physical Review B
- Vol. 108 (7) , 075147
Canted antiferromagnetism and excitonic order in gated double-layer graphene
We study the effects of electron-electron interactions on the excitonic properties and charge-density modulations in AB-stacked double-layer (DL) graphene, placed in an external gate potential . The coexistence of canted antiferromagnetic order and an excitonic pairing gap has been studied with the help of the generalized Hubbard model. We calculate the chemical potential , the average charge-density difference between the layers , the antiferromagnetic gap function , and the excitonic order parameters in the zero-temperature limit. We found that the excitonic pairing order parameter has a larger energy scale than the canted antiferromagnetic gap function. Charge neutrality in the DL graphene system occurs only in the absence of an external gate potential . Moreover, we have shown that the values of the antiferromagnetic gap function and excitonic order parameter are always increasing at large values of the interlayer Coulomb interaction, while they are decreasing for large values of the applied gate potential .- 21 August 2023
- Published by American Physical Society (APS) in Physical Review B
- Vol. 108 (7) , 075147
Canted antiferromagnetism and excitonic order in gated double-layer graphene
We study the effects of electron-electron interactions on the excitonic properties and charge-density modulations in AB-stacked double-layer (DL) graphene, placed in an external gate potential . The coexistence of canted antiferromagnetic order and an excitonic pairing gap has been studied with the help of the generalized Hubbard model. We calculate the chemical potential , the average charge-density difference between the layers , the antiferromagnetic gap function , and the excitonic order parameters in the zero-temperature limit. We found that the excitonic pairing order parameter has a larger energy scale than the canted antiferromagnetic gap function. Charge neutrality in the DL graphene system occurs only in the absence of an external gate potential . Moreover, we have shown that the values of the antiferromagnetic gap function and excitonic order parameter are always increasing at large values of the interlayer Coulomb interaction, while they are decreasing for large values of the applied gate potential .- 10 May 2022
- Published by American Physical Society (APS) in Physical Review B
- Vol. 105 (17) , 174203
Emergence of a superglass phase in the random-hopping Bose-Hubbard model
We study an experimentally feasible system of strongly correlated bosons with random hoppings described by the infinite-range Bose-Hubbard model on a lattice with hopping integrals given by independent random variables of Gaussian distribution with nonzero mean. We solve this quantum model in the thermodynamic limit, employing the replica method and the Trotter-Suzuki formula. We find and describe a superglass phase that emerges at the interface between glass and superfluid phases. Both glassy and long-range orderings are present in the superglass and compete with each other, as revealed by the anticorrelation of their order parameters. We present phase diagrams in various cross sections of the multidimensional space of system parameters. In selected parameter subspaces, we compare the results to those of nondisordered, diagonally disordered, and once celebrated spin-glass systems.
- 10 May 2022
- Published by American Physical Society (APS) in Physical Review B
- Vol. 105 (17) , 174203
Emergence of a superglass phase in the random-hopping Bose-Hubbard model
We study an experimentally feasible system of strongly correlated bosons with random hoppings described by the infinite-range Bose-Hubbard model on a lattice with hopping integrals given by independent random variables of Gaussian distribution with nonzero mean. We solve this quantum model in the thermodynamic limit, employing the replica method and the Trotter-Suzuki formula. We find and describe a superglass phase that emerges at the interface between glass and superfluid phases. Both glassy and long-range orderings are present in the superglass and compete with each other, as revealed by the anticorrelation of their order parameters. We present phase diagrams in various cross sections of the multidimensional space of system parameters. In selected parameter subspaces, we compare the results to those of nondisordered, diagonally disordered, and once celebrated spin-glass systems.
- 2 May 2022
- Published by American Physical Society (APS) in Physical Review B
- Vol. 105 (18) , 184503
Excitonic condensation and metal-semiconductor transition in AA bilayer graphene in an external magnetic field
In this paper, the effects of the external transverse magnetic field (perpendicular to the surface of the layers) on electronic and excitonic properties are studied in AA-stacked bilayer graphene (BLG). The effects of the Coulomb interactions and excitonic pairing have been taken into account and analyzed in detail within the bilayer Hubbard model. Both half-filling and partial-filling regimes have been taken into account and the magnetic field dependence of a series of physical parameters was found. It is shown that the difference between the average electron concentrations in the layers vanishes at some critical value of magnetic field and the chemical potential is calculated numerically above and below that value. The role of the Coulomb interactions on the average carrier concentrations in the layers has been analyzed and the excitonic order parameters have been calculated for different spin orientations. We found a possibility for the particle population inversion between the layers when varying the external magnetic field. The calculated electronic band structure in AA-BLG shows the presence of a metal-semiconductor transition, governed by the strength of the applied magnetic field or the interlayer interaction potential. We show that for high magnetic fields, the band gap is approaches the typical values of the gaps in the usual semiconductors. It is demonstrated that, at some parameter regimes, AA-BLG behaves like a spin-valve device by permitting the electron transport with only one spin direction. All calculations have been performed at the zero-temperature limit.- 2 May 2022
- Published by American Physical Society (APS) in Physical Review B
- Vol. 105 (18) , 184503
Excitonic condensation and metal-semiconductor transition in AA bilayer graphene in an external magnetic field
In this paper, the effects of the external transverse magnetic field (perpendicular to the surface of the layers) on electronic and excitonic properties are studied in AA-stacked bilayer graphene (BLG). The effects of the Coulomb interactions and excitonic pairing have been taken into account and analyzed in detail within the bilayer Hubbard model. Both half-filling and partial-filling regimes have been taken into account and the magnetic field dependence of a series of physical parameters was found. It is shown that the difference between the average electron concentrations in the layers vanishes at some critical value of magnetic field and the chemical potential is calculated numerically above and below that value. The role of the Coulomb interactions on the average carrier concentrations in the layers has been analyzed and the excitonic order parameters have been calculated for different spin orientations. We found a possibility for the particle population inversion between the layers when varying the external magnetic field. The calculated electronic band structure in AA-BLG shows the presence of a metal-semiconductor transition, governed by the strength of the applied magnetic field or the interlayer interaction potential. We show that for high magnetic fields, the band gap is approaches the typical values of the gaps in the usual semiconductors. It is demonstrated that, at some parameter regimes, AA-BLG behaves like a spin-valve device by permitting the electron transport with only one spin direction. All calculations have been performed at the zero-temperature limit.- 16 August 2021
- Published by American Physical Society (APS) in Physical Review B
- Vol. 104 (7) , 075426
Antiferromagnetic ordering and excitonic pairing in AA-stacked bilayer graphene
In this paper, we describe the antiferromagnetic and excitonic correlations in the AA-stacked bilayer graphene. We consider the applied external electric field potential to the structure which leads to the electronic charge imbalance between the layers in the system. By using the generalized two-layer Hubbard Hamiltonian, we consider different particle-filling regimes in the layers. We calculate the important energy scales in the system and we establish the conditions for the appearance of the antiferromagnetic order in the system. We consider both large and small Coulomb interaction limits in the layers and the effect of the electric field potential on the calculated order parameters. We discuss the coexistence of antiferromagnetism and excitonic phases and we show that they can coexist only in the regime away from half-filling. In the case away from the half-filling, we show the existence of a critical value of the Coulomb interaction potential at which we establish the transition from the single-valued to the triple-valued excitonic states, governed by the strong electronic reconfiguration, in the system. The zero-temperature limit is considered in the problem.- 16 August 2021
- Published by American Physical Society (APS) in Physical Review B
- Vol. 104 (7) , 075426
Antiferromagnetic ordering and excitonic pairing in AA-stacked bilayer graphene
In this paper, we describe the antiferromagnetic and excitonic correlations in the AA-stacked bilayer graphene. We consider the applied external electric field potential to the structure which leads to the electronic charge imbalance between the layers in the system. By using the generalized two-layer Hubbard Hamiltonian, we consider different particle-filling regimes in the layers. We calculate the important energy scales in the system and we establish the conditions for the appearance of the antiferromagnetic order in the system. We consider both large and small Coulomb interaction limits in the layers and the effect of the electric field potential on the calculated order parameters. We discuss the coexistence of antiferromagnetism and excitonic phases and we show that they can coexist only in the regime away from half-filling. In the case away from the half-filling, we show the existence of a critical value of the Coulomb interaction potential at which we establish the transition from the single-valued to the triple-valued excitonic states, governed by the strong electronic reconfiguration, in the system. The zero-temperature limit is considered in the problem.- Open Access
- 1 October 2020
- Published by Elsevier in Physica E: Low-dimensional Systems and Nanostructures
- Vol. 124
High thermoelectric performance in excitonic bilayer graphene
- 1 October 2020
- Published by Elsevier in Physica E: Low-dimensional Systems and Nanostructures
- Vol. 124
Open AccessHigh thermoelectric performance in excitonic bilayer graphene
- Open Access
- 25 July 2020
- Published by Springer Nature in Journal of Low Temperature Physics
- Vol. 201 (3-4) , 340-372
Dimensional Crossover in the Bose–Einstein Condensation Confined to Anisotropic Three-Dimensional Lattices
The Bose–Einstein condensation (BEC) in three-dimensional (3D) anisotropic lattices is studied. We present theoretical results for the critical temperature for BEC, chemical potential, condensate fraction and relevant thermodynamic quantities like: internal energy, entropy, specific heat and compressibility as a function of anisotropy parameter being the ratio of the nearest-neighbor in-plane ( $$t_\parallel$$ ) and out-of-plane ( $$t_\perp$$ ) hopping amplitudes. In particular, considered scenarios include weakly coupled two-dimensional (2D) planes ( $$t_\perp /t_\parallel \ll 1$$ , relevant for layered structures) as well as a rod-like geometry of interacting one-dimensional (1D) chains ( $$t_\parallel /t_\perp \ll 1$$ ). The impact of the dimensional crossover as the system is tuned away from a set of disconnected 2D layers, or traverses from a set of separate 1D chains to a regime where a fully isotropic 3D structure emerges is elucidated. Both numerical and analytic approaches are employed, (the latter in a form of series expansions involving $$t_\parallel ,t_\perp$$ amplitudes) for internal energy, entropy, specific heat and isothermal compressibility. The theoretical outcome of the present study may be of interest to a number of scenarios in solid-state physics, where the relevant quasi-particles are bosonic-like, as well as might be applicable to the physics of cold bosons loaded in artificially engineered 3D optical lattices.- 25 July 2020
- Published by Springer Nature in Journal of Low Temperature Physics
- Vol. 201 (3-4) , 340-372
Open AccessDimensional Crossover in the Bose–Einstein Condensation Confined to Anisotropic Three-Dimensional Lattices
The Bose–Einstein condensation (BEC) in three-dimensional (3D) anisotropic lattices is studied. We present theoretical results for the critical temperature for BEC, chemical potential, condensate fraction and relevant thermodynamic quantities like: internal energy, entropy, specific heat and compressibility as a function of anisotropy parameter being the ratio of the nearest-neighbor in-plane ( $$t_\parallel$$ ) and out-of-plane ( $$t_\perp$$ ) hopping amplitudes. In particular, considered scenarios include weakly coupled two-dimensional (2D) planes ( $$t_\perp /t_\parallel \ll 1$$ , relevant for layered structures) as well as a rod-like geometry of interacting one-dimensional (1D) chains ( $$t_\parallel /t_\perp \ll 1$$ ). The impact of the dimensional crossover as the system is tuned away from a set of disconnected 2D layers, or traverses from a set of separate 1D chains to a regime where a fully isotropic 3D structure emerges is elucidated. Both numerical and analytic approaches are employed, (the latter in a form of series expansions involving $$t_\parallel ,t_\perp$$ amplitudes) for internal energy, entropy, specific heat and isothermal compressibility. The theoretical outcome of the present study may be of interest to a number of scenarios in solid-state physics, where the relevant quasi-particles are bosonic-like, as well as might be applicable to the physics of cold bosons loaded in artificially engineered 3D optical lattices.