Terahertz radiation from magnetoresistive Pr0.7_{\text{0.7}}Ca0.3_{\text{0.3}}MnO3_{\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.Comment: Revtex4, 4 pages including 3 figure

Terahertz radiation by ultrafast spontaneous polarization modulation in multiferroic BiFeO3_3 thin films

Terahertz (THz) radiation has been observed from multiferroic BiFeO$_3$ thin films via ultrafast modulation of spontaneous polarization upon carrier excitation with illumination of femtosecond laser pulses. The radiated THz pulses from BiFeO$_3$ thin films were clarified to directly reflect the spontaneous polarization state, giving rise to a memory effect in a unique style and enabling THz radiation even at zero-bias electric field. On the basis of our findings, we demonstrate potential approaches to ferroelectric nonvolatile random access memory with nondestructive readability and ferroelectric domain imaging microscopy using THz radiation as a sensitive probe.Comment: 4 pages, 4 figures, submitted to Physical Review Letter

Isolation and Characterization of a Novel Facultative Anaerobic Filamentous Fungus from Japanese Rice Field Soil

A novel filamentous fungus strain designated RB-1 was isolated into pure culture from Japanese rice field soil through an anaerobic role tube technique. The strain is a mitosporic fungus that grows in both aerobic and strict anaerobic conditions using various mono-, di-, tri-, and polysaccharides with acetate and ethanol productions. The amount of acetate produced was higher than that of ethanol in both aerobic and anaerobic cultures. The characteristic verrucose or punctuate conidia of RB-1 closely resembled those of some strains of the genus Thermomyces, a thermophilic or mesophilic anamorphic ascomycete. However, based on phylogenetic analysis with the small subunit (SSU) and large subunit (LSU) rDNA sequences, RB-1 was characterized as a member of the class Lecanoromycetes of the phylum Ascomycota. Currently, RB-1 is designated as an anamorphic ascomycete and is phylogenetically considered an incertae sedis within the class Lecanoromycetes

Fotonsko-mikrovalna konverzija u poluvodičima kontrolom vala nosioca u optičkom području

The ultrafast carrier dynamics in the optically excited semiconductors is studied by observing the THz radiation. We developed the pump and probe THz beam generation system with variable sample temperature control, and employed it to examine the ultrafast carrier scattering processes. The results proved that the THz beam generation, especially pump and probe method, is a powerful tool to study the ultrafast phenomena. We propose the new model to explain the ultrafast carrier dynamics just after photon arrivals in low-temperature-grown GaAs, which includes the intervalley scattering process.Proučavana je dinamika ultrabrzog nosioca u optički pobuđenim poluvodičima promatranjem generiranja zraka u THz području. Razvijen je sustav za generiranje THz zrake pumpe i probe s temperaturnom kontrolom varijabilnim uzorkom. Sustav je korišten za ispitivanje procesa raspršenja ultrabrzog nosioca. Rezultati ukazuju na činjenicu da je generiranje THz zraka, a posebno metoda pumpe i probe, snažan alat za proučavanje ultrabrzih pojava. Predložen je novi model za objašnjenje dinamike ultrabrzog nosioca, upravo nakon upada fotona GaAs dobiven pomoću niskotemperaturnog procesa. Model sadrži proces raspršenja među energetskim pojasevima

Partial and macroscopic phase coherences in underdoped Bi2{}_{2}Sr2{}_{2}CaCu2{}_{2}O8+δ{}_{8+{\delta}} 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$_{8+{\delta}}$ 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.Comment: Revtex4, 4 pages, 4 figure

Sub-diffraction thin-film sensing with planar terahertz metamaterials

Planar metamaterials have been recently proposed for thin dielectric film sensing in the terahertz frequency range. Although the thickness of the dielectric film can be very small compared with the wavelength, the required area of sensed material is still determined by the diffraction-limited spot size of the terahertz beam excitation. In this article, terahertz near-field sensing is utilized to reduce the spot size. By positioning the metamaterial sensing platform close to the sub-diffraction terahertz source, the number of excited resonators, and hence minimal film area, are significantly reduced. As an additional advantage, a reduction in the number of excited resonators decreases the inter-cell coupling strength, and consequently the resonance Q factor is remarkably increased. The experimental results show that the resonance Q factor is improved by 113%. Moreover, for a film with a thickness of \lambda/375 the minimal area can be as small as 0.2\lambda by 0.2\lambda. The success of this work provides a platform for future metamaterial-based sensors for biomolecular detection.Comment: 8 pages, 6 figure