Cedomir Petrovic

Addresses a need to gain scientific insights from one-dimensional (1D) scientific spectra in model-independent ways. A powerful approach for this is to take differences between pairs of spectra and look for meaningful changes that might indicate underlying chemical, structural, or other modifications. The challenge is that the difference curve may contain uninteresting differences such as experimental inconsistencies and benign physical changes such as the effects of thermal expansion. allows researchers to apply simple transformations, or “morphs,” to one of the datasets to remove the unwanted differences, revealing, when they are present, nontrivial differences. is an open-source Python package available on the Python Package Index and conda-forge. Here, we describe its functionality and apply it to solve a range of experimental challenges on diffraction and pair distribution function data from x-rays and neutrons, though we note that it may be applied to any 1D function in principle.

The interactions among lattice, charge, and spin degrees of freedom fundamentally shape material properties. In FeSe, symmetry-breaking perturbations serve as highly sensitive probes of these couplings. Previous work has shown that defects and isoelectronic substitution can substantially alter these interactions, giving rise to additional phonon modes. In this study, uniaxial strain is employed as a tunable symmetry-breaking control parameter to probe the intrinsic lattice response in the absence of disorder. The temperature evolution of phonon excitations was examined with a temperature resolution of 3 K in the vicinity of the nemato-structural transition temperature T s , under strain applied along the 〈 110 〉 and 〈 100 〉 crystallographic directions. A subtle asymmetry of the A 1 g p h mode appears in the unstrained crystal within a narrow temperature window around T s , originating from the emergence of an additional mode in the fully symmetric channel. With applied strain, this feature becomes more distinctly resolved. The anomaly is attributed to modifications of the coupling between lattice and electronic degrees of freedom driven by the ordering fluctuations right above the nematic transition. These fluctuations may enhance the susceptibility of the electron-lattice system and enable two-phonon Raman scattering involving the acoustic mode near the X and R points. The presence of this two-phonon scattering depends on both the strength and the direction of the applied strain, indicating a high sensitivity of FeSe to local symmetry breaking.

Superconductivity is intrinsically linked to the crystal structure of materials, and structural heterogeneity under high pressure often yields broadened or mixed superconducting transitions. Here instead we report multiple superconducting phases in compressed ${\mathrm{PbSnSe}}_{2}$: two well-separated superconducting transitions that coexist over a broad pressure range and are associated with two crystallographically distinct phases as established by in situ high-pressure x-ray diffraction. Electrical transport and DC magnetization measurements, reproduced across independent samples, consistently resolve both transitions and their evolution under compression. First-principles calculations show that the two structures possess distinct electron-phonon coupling, dominated in both cases by Se-related phonon modes, providing a direct link between the structural symmetry and the superconducting pairing strength. These results illuminate the microscopic connection between phase transitions and superconductivity in layered chalcogenides, and provide a clean platform for exploring the intricacy of the underlying physics.

The Remeika series superconductor, ( Ca x Sr 1 − x ) 3 Rh 4 Sn 13 , shows a rare nonmagnetic quantum critical point (QCP) associated with the continuous charge-density wave (CDW) and structural transition under the “dome” of superconductivity achieved by tuning composition and applying pressure. Here, we use a nonmagnetic pointlike disorder induced by 2.5 MeV electron irradiation to suppress the CDW and drive the system to and even beyond the QCP. This conclusion is based on a clear evolution of temperature-dependent resistivity, ρ ( T ) , from the Fermi liquid to the non-Fermi liquid regime with increasing amount of disorder. Starting on the CDW side, below the suggested QCP concentration of x c = 0.9 , added disorder resulted in a progressively larger linear term and a reduced quadratic term in ρ ( T ) . Nearly perfect T − linear dependence is observed at the dose at which long-range CDW order is suppressed to T = 0 , consistent with the expectations. We refine the QCP location in this system and place it in the interval between x = 0.75 and 0.85. Our results strongly support the concept that the disorder can tune the system to the quantum critical regime and even beyond. It follows from the argument by Imry and Ma that any ordered phase is unstable toward quenched disorder. Introduced in a controlled way, this disorder becomes a nonthermal tuning parameter likely applicable to a variety of different systems.

Intermetallic superconductors feature mechanical properties such as ductility and strength suitable for wire fabrication. Here, we show that Mo8Ga41 crystals host superconducting critical temperature similar to NbTi, the most widely used practical superconductor, combined with a critical current density at magnetic fields at 0.5 T as high as 104 A/cm2. Together with very low Hc2 anisotropy, this suggests that an enhancement of critical current densities in Mo8Ga41 could be expected through more effective flux pinning caused by irradiation or doping. Our work points to possibilities for new high-performance superconducting cables.

CeTe3 is a 2-dimensional (2D) Van der Waals (VdW) material with incommensurate charge density waves (CDW), extremely high transition temperature (TCDW), and a large momentum-dependent CDW gap that leaves a significant portion of the Fermi surface intact. It is also considered to be a weak Kondo system, a property unexpected for a material with incommensurate CDW, where each atomic site is slightly different. Here, we study the properties of the CDW state in several RTe3 (R is rare earth) materials and examine the hybridization of itinerant states with the localized Ce 4f multiplet in CeTe3 by using angle resolved photoemission spectroscopy. We find that the renormalization of the itinerant states originating from the hybridization with the deeper localized 4f states at −260 meV is k−dependent and extends to the Fermi level. As these localized states are far from the Fermi level, the observed hybridization affects the effective masses only marginally and does not lead to heavy fermions. However, since the same renormalizing mechanism normally leads to the heavy fermion physics when the localized 4f states are near the Fermi level, our observation of its strong k−dependence suggests that this could be the reason for discrepancy between the heavy masses in specific heat and light ones in Shubnikov de Haas oscillations, often observed in heavy fermions.

Although the pyrite space group is a high-pressure polymorph of FeTe₂, here we report Fe_0.6Pd_0.4Te₂ with the pyrite space group Pa-3 prepared using Pd substitution on the Fe atomic site with ambient pressure crystal growth methods. Fe_0.6(1)Pd_0.4(1)Te₂ single crystals show metal behavior above 15 K abided by the Bloch-Grüneisen relation and display resistivity upturn below 15 K due to disorder-related scattering of correlated electronic states.