Yu Li

We demonstrate a model-free data analysis framework that leverages escort-weighted Shannon entropy and several divergence matrices to detect phase transitions in scattering and imaging datasets. By establishing a connection between physical entropy and informational entropy, this approach provides a sensitive method for identifying phase transitions without a physical model or order parameter. We further show that pairwise divergence matrices, in particular, Kullback-Leibler divergence, Jeffrey divergence, Jensen-Shannon divergence, and difference Kullback-Leibler divergence, provide more comprehensive measures of statistical changes than scalar entropy alone. Our approach successfully detects the onset of both long- and short-range order in neutron and x-ray scattering data, as well as a nontrivial phase transition in magnetic skyrmion lattices observed through Lorentz-transition electron microscopy. These results establish a framework for fast, automated, model-free detection of physical order in experimental data with broad applications in materials science and condensed matter physics.

Intertwined charge and spin correlations are ubiquitous in a wide range of transition metal oxides and are often perceived as intimately related to unconventional superconductivity. Theoretically envisioned as driven by strong electronic correlations, the intertwined order is usually found to be strongly coupled to the lattice as signaled by pronounced phonon softening. Recently, both charge and spin density waves (CDW and SDW) and superconductivity have been discovered in several Ruddlesden-Popper (RP) nickelates, in particular trilayer nickelates R E 4 Ni 3 O 10 ( R E = Pr , La). The nature of the intertwined order and the role of lattice-charge coupling are at the heart of the debate about these materials. Using inelastic x-ray scattering, we mapped the low-energy phonon dispersions in R E 4 Ni 3 O 10 and found no evidence of softening near the CDW wave vector over a wide temperature range, which contrasts with the pronounced anomalies frequently observed in cuprate superconductors. Calculations of the electronic susceptibility revealed a peak at the observed SDW ordering vector but not at the CDW wave vector. Our experimental and theoretical findings highlight the crucial role of the spin degree of freedom and establish a foundation for understanding the interplay between superconductivity and density-wave transitions in RP nickelate superconductors and beyond.

We have explored the magnetic relaxation of the spin glass phase in Bi₂Fe₃GaO₉, a geometrically frustrated magnet with a unique Cairo lattice made of pentagonal building blocks. Using dc magnetization measurements, we find the relaxation behavior in single crystals follows the Arrhenius law as a function of temperature but remains relatively constant under different magnetic fields. Through a carefully designed protocol, we observe significant rejuvenation and memory effects, reminiscent of classical dilute spin glasses rather than spin jamming systems. Our finding suggests that Bi₂Fe₃GaO₉ is probably located in the crossover between conventional spin glass and perfect spin jam and thus provides an excellent platform for investigating the evolution of underlying magnetic structure, paving the way for further neutron scattering research.

The coexistence of helical structural motifs with 21 screw axes and orthorhombic unit cell in CoTeMoO${}_{6}$ allows for subtle tunability under external uniaxial pressure, significantly affecting its magnetic and optical properties. The study here uncovers the presence of structural and magnetic domains, along with their intrinsic anisotropy. These findings highlight a complex interplay among structural, magnetic, and optical degrees of freedom, suggesting potential ferroic behavior.

The unusual anisotropy of the spin glass (SG) transition in the pseudobrookite system Fe₂TiO₅ has been interpreted as arising from an induced, van der Waals-like, interaction among magnetic clusters. Here we present susceptibility ( χ ) and specific heat data ( C ) for Fe₂TiO₅ diluted with non-magnetic Ga, (Fe_1−p Ga _p )₂TiO₅, for disorder parameter p = 0, 0.11, and 0.42, and elastic neutron scattering data for p = 0.20. A uniform suppression of T g is observed upon increasing p , along with a value of χ T g that increases as T g decreases, i.e. d χ ( T g ) / d T g < 0 We also observe C T ∝ T 2 in the low temperature limit. The observed behavior places (Fe_1−p Ga _p )₂TiO₅ in the category of a strongly geometrically frustrated SG.

The electronic and superconducting properties of Fe_1–δ Se single-crystal flakes grown hydrothermally are studied by the transport measurements under zero and high magnetic fields up to 38.5 T. The results contrast sharply with those previously reported for nematically ordered FeSe by chemical-vapor-transport (CVT) growth. No signature of the electronic nematicity, but an evident metal-to-nonmetal crossover with increasing temperature, is detected in the normal state of the present hydrothermal samples. Interestingly, a higher superconducting critical temperature T _c of 13.2 K is observed compared to a suppressed T _c of 9 K in the presence of the nematicity in the CVT FeSe. Moreover, the upper critical field in the zero-temperature limit is found to be isotropic with respect to the field direction and to reach a higher value of ∼42 T, which breaks the Pauli limit by a factor of 1.8.

Here we establish a combined electronic phase diagram of isoelectronic FeSe1-xSx (0.19 > x > 0.0) and FeSe1-yTey (0.04 < y < 1.0) single crystals. The FeSe1-yTey crystals with y = 0.04 - 0.30 are grown by a hydrothermal ion-deintercalation (HID) method. Based on combined experiments of the specific heat, electrical transport, and angle-resolved photoemission spectroscopy, no signature of the tetragonal-symmetry-broken transition to orthorhombic (nematic) phase is observed in the HID FeSe1-yTey samples, as compared with the FeSe1-xSx samples showing this transition at Ts. A ubiquitous dip-like temperature dependence of the Hall coefficient is observed around a characteristic temperature T* in the tetragonal regimes, which is well above the superconducting transition. More importantly, we find that the superconducting transition temperature Tc is positively correlated with the Hall-dip temperature T* across the FeSe1-xSx and FeSe1-yTey systems, suggesting that the tetragonal background is a fundamental host for the superconductivity.