arXiv subjects

S. A. Chen

Publications and source records attributed to S. A. Chen.

2 recordsLinked to original sources

arXiv2026

Long-lived dynamics of the charge density wave in TiSe2 observed by time-resolved neutron diffraction

We use time-resolved elastic neutron scattering combined with laser heating to probe the temporal evolution of periodic lattice distortions (PLD) due to the formation of a charge density wave (CDW) state in 1T-TiSe$_{2}$ under extreme non-equilibrium conditions. Below the transition temperature, the PLD is manifested as a 2x2x2 superlattice superimposed on the average Bragg structure. Following rapid energy deposition with the laser, kinetic bottlenecks lead to a separation of timescales between the superlattice and the underlying lattice response. The superlattice melts on a characteristic timescale of approximately 3 s, whereas the average lattice responds more slowly to heating. Upon removal of the heat source, the Bragg lattice recovers within approximately 11 s, while the superlattice re-establishes on nearly twice that timescale. These results reveal an asymmetric evolution of short- and long-range order under extreme non-equilibrium conditions, in which local PLD correlations are destroyed prior to, and recover more slowly than, the average lattice structure.

cond-mat.mtrl-sci↗

arXiv2015

Evidence for two distinct superconducting phases in EuBiS$_2$F under pressure

We present a pressure study of the electrical resistivity, AC magnetic susceptibility and powder x-ray diffraction (XRD) of the newly discovered BiS$_2$-based superconductor EuBiS$_2$F. At ambient pressure, EuBiS$_2$F shows an anomaly in the resistivity at around $T_0\approx 280$ K and a superconducting transition at $T_c\approx 0.3$ K. Upon applying hydrostatic pressure, there is little change in $T_0$ but the amplitude of the resistive anomaly is suppressed, whereas there is a dramatic enhancement of $T_c$ from 0.3 K to about 8.6 K at a critical pressure of $p_c$ $\approx{1.4}$ GPa. XRD measurements confirm that this enhancement of $T_c$ coincides with a structural phase transition from a tetragonal phase ($P4/nmm$) to a monoclinic phase ($P2_1$/m), which is similar to that observed in isostructural LaO$_{0.5}$F$_{0.5}$BiS$_2$. Our results suggest the presence of two different superconducting phases with distinct crystal structures in EuBiS$_2$F, which may be a general property of this family of BiS$_2$-based superconductors.

cond-mat.supr-con↗