arXiv subjects

N. Kida

Publications and source records attributed to N. Kida.

22 records · Page 2Linked to original sources

arXiv2004

Ferroelectric properties controlled by magnetic fields in DyMn2O5

Cross-correlation between magnetic and dielectric properties has been attracting renewed interest because of the fundamental as well as technological importance of controlling the electric (magnetic) polarization by an external magnetic (electric) field. Here, we report the novel phenomenon that an external magnetic field induces and/or modifies ferroelectric states in a magnetic material, DyMn2O5. Measurements of temperature dependence of hysteretic polarization curves, pyroelectric current, specific heat, optical second harmonic generation, and x-ray superlattice peaks have revealed successive phase transitions between 43 K and 4 K, accompanying three ferroelectric phases. The zero-field lowest-temperature phase (<8 K) induced by the Dy-moment ordering is a reentrant paraelectric state, but is turned to a ferroelectric state with increasing the magnetic field. The phenomenon is closely related to the metamagnetic transitions of the Dy f-moment, indicating that all the ferroelectric phases of this material are strongly tied to the antiferromagnetic Mn spin structure affected by the f-d exchange interaction. The electric phase diagram for DyMn2O5 is presented in the plane of temperature and magnetic field.

cond-mat.str-el↗

arXiv2001

Partial and macroscopic phase coherences in underdoped Bi${}_{2}$Sr${}_{2}$CaCu${}_{2}$O${}_{8+δ}$ thin film

A combined study with use of time-domain pump-probe spectroscopy and time-domain terahertz transmission spectroscopy have been carried out on an underdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ thin film. It was observed that the low energy multi-excitation states were decomposed into superconducting gap and pseudogap. The pseudogap locally opens below $T^*{\simeq}210$ K simultaneously with the appearance of the high-frequency partial pairs around 1.3 THz. With decreasing temperature, the number of the local domains with the partial phase coherence increased and saturated near 100 K, and the macroscopic superconductivity appeared below 76 K through the superconductivity fluctuation state below 100 K. These experimental results indicate that the pseudogap makes an important role for realization of the superconductivity as a precursor to switch from the partial to the macroscopic phase coherence.

cond-mat.mtrl-sci↗

arXiv2001

Terahertz radiation from magnetoresistive Pr$_{\text{0.7}}$Ca$_{\text{0.3}}$MnO$_{\text3}$ thin films

Terahertz (THz) radiation with its spectrum extending up to 1 THz has been observed by an illumination of femtosecond optical pulses to optical switching devices fabricated on magnetoresistive manganite thin films; Pr$_{0.7}$Ca$_{0.3}$MnO$_3$. The THz radiation strongly depends on temperature $T$ and its $T$ trend reverses sign across charge-orbital and spin ordering $T$'s.

cond-mat.str-el↗

arXiv2000

Low-energy charge dynamics in La$_{\text{0.7}}$Ca$_{\text{0.3}}$MnO$_{\text3}$: THz time-domain spectroscopic studies

Direct experimental estimations of the low-energy ($1.5\sim10$ meV) complex dielectric constants spectrum and its temperature variation have been investigated for La$_{0.7}$Ca$_{0.3}$MnO$_3$ thin films using terahertz time-domain spectroscopy. At low temperatures, a clear Drude-term emerges. With increasing temperature, the scattering rate increases, while the plasma frequency decreases, derived both from a simple Drude model. Finally, a Drude-term submerges well below the insulator-metal transition temperature. On the basis of the present results, low-energy charge dynamics are discussed.

cond-mat.mtrl-sci↗