arXiv subjects

Cezariusz Jastrzębski

Publications and source records attributed to Cezariusz Jastrzębski.

7 recordsLinked to original sources

arXiv2026

Tuning Superconductivity by Isovalent Antimony Substitution in PrFeAs(O,F)

We investigate the effects of isovalent Sb substitution at the As site in fluorine-doped PrFeAs1-xSbxO0.7F0.3 (x = 0 to 1.0) through structural, Raman spectroscopy, density functional theory (DFT), transport, magnetotransport, and magnetic measurements. The superconducting transition temperature decreases gradually from ~48 K for the parent compound to ~44 K up to x = 0.3, followed by a rapid suppression at higher Sb concentrations due to increasing disorder and secondary phase formation. Raman spectroscopy and DFT reveal lattice expansion and pronounced softening of pnictogen related vibrational modes upon Sb substitution. Magnetotransport measurements up to 9 T show enhanced upper critical fields and increased vortex activation energy for moderate Sb doping, indicating stronger vortex pinning. However, the critical current density remains low because of poor intergranular connectivity. The results demonstrate a crossover from an electronically tuned superconducting state to a disorder-dominated regime in isovalently substituted iron pnictides.

cond-mat.supr-con↗

arXiv2026

Effect of Mn Substitution on Superconductivity in PrFeAs(O,F): Role of Magnetic Impurities

We investigate Mn substitution at the Fe site in PrFe1-xMnxAsO0.7F0.3 (0 to 0.1) using structural, Raman, density functional theory (DFT), transport, and magnetic measurements. X-ray diffraction and Raman analyses confirm preferential Mn incorporation into the FeAs planes, accompanied by lattice expansion and suppression of Fe-related vibrational modes. Electrical transport reveals a systematic decrease of the superconducting transition temperature from 48 K (x = 0) to complete suppression at x = 0.1, together with low-temperature resistivity upturns evolving toward insulating-like behavior. Magnetization and magnetotransport measurements show degradation of superconducting coherence, critical current density, upper critical field, and vortex activation energy with increasing Mn content. The results demonstrate that Mn acts as an efficient magnetic impurity, strongly perturbing the electronic and magnetic environment of the FeAs layers. Comparative analysis indicates relatively enhanced robustness of superconductivity in the Pr-based system, highlighting the role of rare-earth-dependent electronic correlations in impurity effects.

cond-mat.supr-con↗

arXiv2026

Complete electronic phase diagram and enhanced superconductivity in fluorine-doped PrFeAsO1-xFx

Establishing a complete electronic phase diagram for REFeAsO (RE = rare earth, RE1111) ironbased superconductors has remained experimentally challenging. Here, we report a systematic investigation of PrFeAsO1-xFx over the full nominal fluorine-doping range 0 to 1 and construct the first comprehensive electronic phase diagram for this system. The evolution from the nonsuperconducting parent compound to the fluorine-rich limit reveals a broad dome shaped superconducting region. Structural refinement demonstrates a systematic lattice contraction with increasing fluorine content (x), corroborated by Raman spectroscopy through softening of the Pr(A1g) phonon mode and hardening of the Fe(B1g) mode, confirming effective fluorine incorporation at the oxygen sites. The maximum superconducting transition temperature (Tc) reaches up to 52.3 K, approximately 5 K higher than previous reports for Pr1111. Magnetotransport measurements yield large upper critical fields Hc2(0) exceeding 100 T, while analysis of resistive transition broadening reveals thermally activated flux flow with a crossover from single-vortex to collective pinning regimes. Specific-heat measurements exhibit a reduced jump deltaC/γTc < 1.43, reflecting strong superconducting fluctuations and multiband pairing. These results establish clear structure property correlations and provide a unified description of superconductivity across the entire doping range of the Pr1111 system.

cond-mat.supr-con↗

arXiv2025

Praseodymium doping effect on the superconducting properties of FeSe$_{0.5}$Te$_{0.5}$ bulks under ambient and high-pressure growth conditions

A series of Pr-doped FeSe$_{0.5}$Te$_{0.5}$ (Fe$_{1-x}$Pr$_x$Se$_{0.5}$Te$_{0.5}$; $x = 0$ to 0.3) bulks are prepared by conventional synthesis process at ambient pressure (CSP), and high gas pressure and high temperature synthesis (HP-HTS) methods. These bulks are well characterized by structural and microstructural analysis, Raman spectroscopy, transport, and magnetic measurements. The HP-HTS process of the parent bulks has enhanced the onset transition temperature ($T_c^{\rm onset}$) by 1.5 K and the critical current density ($J_c$) by two orders of magnitude compared to the CSP method. Pr-doped FeSe$_{0.5}$Te$_{0.5}$ up to 10% doping content prepared, either CSP or HP-HTS, slightly increases the unit cell volume, and high-pressure growth produces an almost pure superconducting phase, which confirms the successful Pr-doping at Fe sites. Raman spectroscopy measurements and DFT calculations suggest the substitution of Pr-atoms in the interlayer spacing of Fe(Se,Te) lattice. High-pressure growth of Fe$_{1-x}$Pr$_x$Se$_{0.5}$Te$_{0.5}$ also makes the sample less dense compared to the parent sample grown by HP-HTS. Transport and magnetic measurements depict that Tconset is almost unaffected by Pr-doping, whereas $J_c$ of Pr-doped FeSe$_{0.5}$Te$_{0.5}$ is enhanced by one order of magnitude relative to the parent sample developed by CSP but lower than that of the parent sample grown by HP-HTS. Hence, Pr-doping at Fe sites preserves $T_c^{\rm onset}$ and improves $J_c$ of FeSe$_{0.5}$Te$_{0.5}$ regardless of the doping contents and growth conditions. These results are promising for the practical application of iron-based superconductors to improve $J_c$ properties without affecting $T_c^{\rm onset}$ through CSP process and congruent with discoveries from other superconductors, like cuprates and MgB$_2$.

cond-mat.supr-con↗

arXiv2024

High-pressure growth effects on the superconducting properties of Sm-based oxypnictide superconductors

High-pressure synthesis can be an effective method for improving the sample quality of materials as well as their superconducting properties. In this paper, the synthesis process of F- doped SmFeAsO has been optimized by preparing a series of bulk SmFeAsO0.8F0.2 (Sm1111) using the high gas pressure and high-temperature synthesis (HP-HTS) method, considering various growth parameters like growth pressures (0-1 GPa) and heating time (0.5-2 h). Structural, microstructural, Raman spectroscopic, transport, and magnetic measurements are employed to comprehensively analyze these bulks and derive the conclusive findings. The parent SmFeAsO0.8F0.2 prepared by the conventional synthesis process at ambient pressure (CSP) has a transition temperature (Tc) of around 53-54 K, and the critical current density (Jc) of 103 A/cm2 at 5 K with a small amount of the impurity phases (SmOF and SmAs), consistent with previous reports. Interestingly, all bulks synthesized by HP-HTS have almost the same Tc and Jc as the parent sample. The optimal growth conditions are obtained as 900C, 1 hour, and 0.5 GPa with the sealed Ta-tube, which slightly improved the sample quality and the superconducting properties compared to other bulks grown by HP-HTS. Our study confirms that the existence of the impurity phases in the 1111 family is very robust and cannot be reduced by HP-HTS, leading to only a small variation in the observed superconducting properties of Sm1111 whether prepared by CSP or HP-HTS. This is the first comprehensive investigation of the high-pressure development of Sm1111, which shows distinct behaviour from other families of iron-based superconductors.

cond-mat.supr-con↗

arXiv2024

Optimization of the plasmonic properties of titanium nitride films sputtered at room temperature through microstructure and thickness control

A current approach to depositing highly plasmonic titanium nitride films using the magnetron sputtering technique assumes that the process is performed at temperatures high enough to ensure the atoms have sufficient diffusivities to form dense and highly crystalline films. In this work, we demonstrate that the plasmonic properties of TiN films can be efficiently tuned even without intentional substrate heating by influencing the details of the deposition process and entailed films' stoichiometry and microstructure. We also discuss the dependence of the deposition time/films' thickness on the optical properties, which is another degree of freedom in controlling the optical response of the refractory metal nitride films. The proposed strategy allows for robust and cost-effective production of large-scale substrates with good plasmonic properties in a CMOS technology-compatible process that can be further processed, e.g., structurized. All reported films are characterized by the maximal values of the plasmonic Figure of Merit (FoM = -e1/e2) ranging from 0.8 to 2.6, and the sample with the best plasmonic properties is characterized by FoM at 700 nm and 1550 nm that is equal 2.1 in both cases. These are outstanding results, considering the films' polycrystallinity and deposition at room temperature onto a non-matched substrate.

physics.optics↗

arXiv2014

Temperature-dependent nonlinear phonon shifts in a supported MoS2 monolayer

We report Raman spectra measurements on a MoS2 monolayer supported on SiO2 as a function of temperature. Unlike in previous studies, the positions of the two main Raman modes, E2g1 and A1g exhibited nonlinear temperature dependence. Temperature dependence of phonon shifts and widths is explained by optical phonon decay process into two acoustic phonons. On the basis of Raman measurements, local temperature change under laser heating power at different global temperatures is derived. Obtained results contribute to our understanding of the thermal properties of two-dimensional atomic crystals and can help to solve the problem of heat dissipation, which is crucial for use in the next generation of nanoelectronic devices.

cond-mat.mes-hall↗