arXiv subjects

Andrzej Kozłowski

Publications and source records attributed to Andrzej Kozłowski.

5 recordsLinked to original sources

arXiv2026

Non-invasive super-resolution imaging through scattering media using highly nonlinear labels

While scattered light conveys most of the information we perceive, scattering may also distort that information before it reaches our detectors. The problem is acute in many applications, such as in high-resolution microscopy of biological tissue, where scattering degrades both resolution and signal-to-noise ratio. Here, for the first time, we demonstrate that combining two intrinsic properties of scattered light: speckle statistics and the memory effect, with highly non-linear optical response yields, rather surprisingly, super-resolution, low-background, non-invasive imaging of objects completely hidden behind a strongly scattering, opaque layers. Crucially, our technique of Nonlinear Imaging with Speckle Excitation (NISE) does not resort to wavefront shaping, adaptive optics, complicated optical setups, or iterative image reconstruction algorithms. Because the strategy relies solely on the properties of scattered light and high-order nonlinear response of the luminescent labels, it can be applied to any speckle-forming propagation, from biological tissue to multicore fibers, combined with any type of phenomenon that exhibits a sufficiently high order nonlinearity.

physics.optics↗

arXiv2026

Interactions between structural and magnetic domains through the Verwey transition in stoichiometric and doped magnetite

The magnetic response of magnetite as it cycles through the Verwey transition at $T_{\rm V}\approx 120$ K remains incompletely understood, despite numerous studies of both structural and magnetic domains. For example, although the alternating-current susceptibility increases upon heating through the Verwey temperature $T_{\rm V}$, the magnetization may either increase or decrease. Since many intertwined processes occur at $T_{\rm V}$, a multifaceted view of the magnetic changes may help clarify the nature of these processes and establish specific features of the transition as diagnostic tools. To this end, we report measurements of the magnetic response of magnetite upon heating through $T_{\rm V}$ under a wide range of applied-field conditions. We studied synthetic stoichiometric and doped (Zn, Ti, and Al) single crystals, as well as a natural polycrystalline sample, with the aim of explaining how and why the magnetization changes as a function of temperature through $T_{\rm V}$. The magnetic-field-induced reorientation of the monoclinic $c$ axis may broaden the transition, primarily in stoichiometric magnetite. These findings help clarify the mechanism of the transition.

cond-mat.str-el↗

arXiv2025

Correlation between magnetism and the Verwey transition in magnetite

Seeking to unravel the enigmatic Verwey transition and its interplay with magnetism, we have conducted comprehensive measurements on the temperature-dependent electrical resistivity and magnetic moment of stoichiometric and doped-magnetite single crystals at temperatures reaching 1000 K. These investigations have allowed us to identify the Curie temperature, $T_C$, and other characteristic temperatures of the electrical resistivity. Remarkably, we have identified correlations between these temperatures and the Verwey temperature, $T_V$, indicating that the electrical transport properties and the mechanism of the Verwey transition are closely related to the magnetic properties.

cond-mat.str-el↗

arXiv2021

Spaces of non-resultant systems of bounded multiplicity determined by a toric variety

The space of non-resultant systems of bounded multiplicity for a toric variety X is a generalization of the space of rational curves on it. In our earlier work we proved a homotopy stability theorem and determined explicitly the homotopy type of this space for the case X = CP^m. In this paper we consider the case of a general non-singular toric variety and prove a homotopy stability theorem generalising the one for CP^m.

math.AT↗

arXiv2021

Discovery of the soft electronic modes of the trimeron order in magnetite

The Verwey transition in magnetite (Fe$_3$O$_4$) is the first metal-insulator transition ever observed and involves a concomitant structural rearrangement and charge-orbital ordering. Due to the complex interplay of these intertwined degrees of freedom, a complete characterization of the low-temperature phase of magnetite and the mechanism driving the transition have long remained elusive. It was demonstrated in recent years that the fundamental building blocks of the charge-ordered structure are three-site small polarons called trimerons. However, electronic collective modes of this trimeron order have not been detected to date, and thus an understanding of the dynamics of the Verwey transition from an electronic point of view is still lacking. Here, we discover spectroscopic signatures of the low-energy electronic excitations of the trimeron network using terahertz light. By driving these modes coherently with an ultrashort laser pulse, we reveal their critical softening and hence demonstrate their direct involvement in the Verwey transition. These findings represent the first observation of soft modes in magnetite and shed new light on the cooperative mechanism at the origin of its exotic ground state.

cond-mat.str-el↗