arXiv subjects

Chi-Chang Kao

Publications and source records attributed to Chi-Chang Kao.

4 recordsLinked to original sources

arXiv2026

Observation of Subharmonic Charge-Density-Wave Correlations in La-Based Cuprates

Pair-density-wave (PDW) correlations have been proposed as an important ingredient in the complex phase diagram of high-$T_{\rm c}$ cuprates, yet bulk-sensitive experimental signatures remain scarce. Here we report resonant x-ray scattering measurements revealing a subharmonic charge-density-wave (CDW) scattering response in Sr-doped $1/8$-LBCO. The subharmonic response appears at approximately half the primary CDW ordering wave vector and emerges within a physically relevant temperature regime associated with the development of in-plane superconducting correlations. Comparable subharmonic behavior is also observed in a chemically distinct La-based cuprate, LSCO, within the same stripe-ordered, layer-decoupled regime. Together, these observations identify a bulk-sensitive scattering signature that is consistent with PDW correlations in La-based superconducting cuprates.

cond-mat.supr-con↗

arXiv2025

Introducing new resonant soft x-ray scattering capability in SSRL

Resonant soft X-ray scattering (RSXS) is a powerful technique for probing both spatial and electronic structures within solid-state systems. We present a newly developed RSXS capability at beamline 13-3 of the Stanford Synchrotron Radiation Lightsource (SSRL), designed to enhance materials science research. This advanced setup achieves a base sample temperature as low as 9.8 K combined with extensive angular motions (azimuthal ϕand flipping χ), enabling comprehensive exploration of reciprocal space. Two types of detectors, an Au/GaAsP Schottky photodiode and a CCD detector with over 95% quantum efficiency, are integrated to effectively capture scattered photons. Extensive testing has confirmed the enhanced functionality of this RSXS setup, including its temperature and angular performance. The versatility and effectiveness of the system have been demonstrated through studies of various materials, including superlattice heterostructures and high-temperature superconductors.

physics.ins-det↗

arXiv2010

High pressure evolution of Fe$_{2}$O$_{3}$ electronic structure revealed by X-ray absorption

We report the first high pressure measurement of the Fe K-edge in hematite (Fe$_2$O$_3$) by X-ray absorption spectroscopy in partial fluorescence yield geometry. The pressure-induced evolution of the electronic structure as Fe$_2$O$_3$ transforms from a high-spin insulator to a low-spin metal is reflected in the x-ray absorption pre-edge. The crystal field splitting energy was found to increase monotonically with pressure up to 48 GPa, above which a series of phase transitions occur. Atomic multiplet, cluster diagonalization, and density-functional calculations were performed to simulate the pre-edge absorption spectra, showing good qualitative agreement with the measurements. The mechanism for the pressure-induced phase transitions of Fe$_2$O$_3$ is discussed and it is shown that ligand hybridization significantly reduces the critical high-spin/low-spin pressure.

cond-mat.str-el↗

arXiv1999

Pressure induced high-spin to low-spin transition in FeS evidenced by x-ray emission spectroscopy

We report the observation of the pressure-induced high-spin to low-spin transition in FeS using new high-pressure synchrotron x-ray emission spectroscopy techniques. The transition is evidenced by the disappearance of the low-energy satellite in the Fe K$β$ emission spectrum of FeS. Moreover, the phase transition is reversible and closely related to the structural phase transition from a manganese phosphide-like phase to a monoclinic phase. The study opens new opportunities for investigating the electronic properties of materials under pressure.

cond-mat.mtrl-sci↗