arXiv subjects

Yu Mizukoshi

Publications and source records attributed to Yu Mizukoshi.

5 recordsLinked to original sources

arXiv2026

Spectroscopic signatures of mode-selective electron-phonon coupling in transient reflectivity change on charge-density-wave TiSe$_2$

We report on time- and spectrally resolved pump-probe spectroscopy measurement on the charge-density wave (CDW) state of TiSe$_2$ at helium temperatures. The non-oscillatory component of the spectrally resolved signals exhibit a sign reversal near 1.5 eV, which was interpreted as a redshift of the optical transition energy originated from the interband transition between the Se $p$-based valence band to the Ti $d$-derived conduction band. Furthermore, the oscillatory components exhibit distinct spectral dependences between the optical phonons and the CDW-derived modes, suggesting the mode-selective coupling.

cond-mat.mtrl-sci↗

arXiv2026

Phonon scattering mechanisms in WTe$_2$ observed by ultrafast coherent phonon spectroscopy

Revealing the mechanisms of phonon scattering is crucial for understanding material properties such as transport characteristics and optical responses. It can be discussed by measuring the temperature dependence of the phonon energy and lifetime. To gain insight into these mechanisms in Weyl semimetal T$_d$-WTe$_2$, we investigated coherent phonons using time-resolved pump-probe spectroscopy in a wide temperature range from 4.6 to 300 K. The temperature dependence of the frequency and decay rate of the two high-frequency optical modes was described by the conventional anharmonic phonon-phonon scattering model. In contrast, the low-frequency mode at 2.4 THz exhibited anomalous behavior, which can be interpreted as the contribution of phonon-electron scattering.

cond-mat.mtrl-sci↗

arXiv2025

Role of interlayer shear phonons on lattice symmetry switching in the transition metal dichalcogenide WTe$_{2}$

Coherent phonon control using ultrashort pulse trains is the key to realizing structural phase transitions in solids by non-thermal pathways. By combining double-pulse excitation and time-resolved second harmonic generation techniques under high-density electronic excitation in a 2D layered material, WTe$_{2}$, we demonstrate that the lattice symmetry switching from the Weyl semimetallic T$_{d}$ to the semimetallic 1T$^{\prime}$ phases is independent of the amplitude of the coherent interlayer shear phonons after the arrival of the second pump pulse. This finding provides new insights into the mechanisms for symmetry switching that electronic excitation-driven shear sliding plays a dominant role.

cond-mat.mtrl-sci↗

arXiv2024

Spin dependent bandgap renormalization and state filling effect in Bi$_2$Se$_3$ observed by ultrafast Kerr rotation

We investigate the ultrafast spin dynamics of the prototypical topological insulator $\mathrm{Bi_{2}Se_{3}}$ using time-resolved Kerr-rotation (polarization-change) measurements across near-infrared wavelengths. The Kerr-rotation angle $Δθ_{K}$ of $\mathrm{Bi_{2}Se_{3}}$ was found to significantly depend on photon energy around a resonance transition ($\sim 1.0\ \mathrm{eV}$) of bulk states, as well as the ellipticity of the pump light, in the presence of spin excitation. The observed photon-energy dependence of $Δθ_{K}$ can be well simulated by assuming spin-dependent refractive-index changes in the presence of band-gap renormalization and state-filling effect upon photoexcitation. Our study delivers comprehensive insights into the opto-spintronic properties of bulk $\mathrm{Bi_{2}Se_{3}}$ and the fundamental physical processes underlying polarization changes. These findings are expected to be crucial in developing ultrafast magneto-optical memory devices, which can perform read-and-write operations in the Terahertz regime.

cond-mat.mtrl-sci↗

arXiv2023

Ultrafast melting of charge-density wave fluctuations at room temperature in ${1T-TiSe_2}$ monitored under non-equilibrium conditions

We investigate the ultrafast lattice dynamics in ${1T-TiSe_2}$ using femtosecond reflection pump-probe and pump-pump-probe techniques at room temperature. The time-domain signals and Fourier-transformed spectra show the $A_{1g}$ phonon mode at 5.9 THz. Moreover, we observe an additional mode at $\approx$ 3 THz, corresponding to the charge-density wave (CDW) amplitude mode, which is generally visible below T$_c \approx 200\ $K. We argue that the emergence of the CDW amplitude mode at room temperature can be a consequence of fluctuations of order parameters, based on the additional experiment using the pump-pump-probe technique, which exhibited suppression of the AM signal within the ultrafast time scale of $\sim$ 0.5 ps.

cond-mat.mtrl-sci↗