Yasemin Demirhan

Interferometer measurements of terahertz waves from Bi2Sr2CaCu2O8+d mesas

We fabricated rectangular mesa structures of superconducting Bi2Sr2CaCu2O8+d (Bi2212) using e-beam lithography and Ar ion beam etching techniques for terahertz (THz) emission. c-axis resistance versus temperature (R?T), current?voltage (I?V) characteristics and bolometric THz power measurements were performed to characterize Bi2212 mesas. The emission frequency of mesas was determined using a Michelson interferometer setup which also demonstrates polarized emission. Interference patterns of THz radiation from Bi2212 mesas were detected by various detectors such as a liquid helium cooled silicon composite bolometer, a Golay cell and a pyroelectric detector. An emitted power as high as 0.06?mW was detected from Bi2212 mesas. For the first time, most of the pumped power was extracted as THz emission from a Bi2212 mesa. The radiation at 0.54?THz was detected using the Michelson interferometric setup.

Emission of the THz waves from large area mesas of superconducting Bi2Sr2CaCu2O8+δ by the injection of spin polarized current

The effect of electromagnetic wave irradiation on the phase dynamics of intrinsic Josephson junctions in high temperature superconductors is investigated. We predict three novel effects by variation of the radiation amplitude and frequency: changing of the longitudinal plasma wavelength at parametric resonance; double resonance of the Josephson oscillations with radiation and longitudinal plasma wave; charging of superconducting layers in the current interval corresponding to the Shapiro step. The ”bump” structure in IVC recently observed experimentally is demonstrated. We also observe ragged Shapiro steps at double resonance.

Fabrication of Bi2212 Single Crystal Bolometer for Detection of Terahertz Waves

Terahertz (THz) radiation is in powerful region of electromagnetic spectrum because of prosperous application areas yet deficiency still exists about sources and detectors in despite of improvements of the research field in this range. This gap can be filled by focusing on development of THz detectors. Therefore, bolometers were preferred through many detectors due to detection sensitivity above 1 THz. In this study, Bi2Sr2CaCu2O8+δ (Bi2212) single crystals were used to fabricate THz bolometric detector. Bi2212 single crystals were transferred on sapphire substrate by cleavage process and e-beam lithography and ion beam etching were used to fabricate the microchip clean room facilities. Custom-designed cryogenic cryostat was used for a-b axis electrical and THz response measurements with liquid nitrogen cooled system. After electrical measurements, Bi2212 microchips detected the signals using Stefan-Boltzmann Lamp and response time were calculated. This study have shown with our experimental results that Bi2212 single crystals are potential candidates for THz bolometric detectors.

An indium tin oxide metasurface filter for terahertz applications: Design, fabrication, and characterization

In this paper, using a cross-shaped complementary Indium Tin Oxide (ITO)-based metasurface design, the transmission of THz radiation is shown to be filtered within the 3 dB level from maximum in the frequency range of interest ( ∼333 GHz). Various metasurface structures primarily composed of cross-shaped openings with a 400 micron unit cell size are patterned on top of 1750 micron thick fused silica substrates. They are patterned using UV lithography methods after the films were grown using DC sputtering. The fabricated structures were characterized using Terahertz Time Domain Spectroscopy (THz-TDS) measurement technique. The measured transmission agrees well with the simulation of the structure for four different samples with different geometries. These results suggest that metasurface and/or metamaterial patterns based on ITO in visibly transparent media can be utilized for filtering of frequencies in the long wavelength spectrum. These types of filters can be very useful in the near future for THz communication and security applications.

Inhomogenity of Micron-Sized Triple Terahertz Emitters Fabricated from Intrinsic Josephson Junctions in Single Crystal Bi2Sr2CaCu2O8+δ

The as-grown Bi2Sr2CaCu2O8+δ (Bi2212) crystals were heat-treated at various temperatures either in Argon atmosphere or in vacuum. Bi2212 triple mesa structures were fabricated by electron beam lithography and Ar ion beam etching processes. A set of samples has identical size (50 × 300 μm2) are vertically mounted in vacuum on the cold finger of an optical LHe continuous-flow cryostat and resistance versus temperature and current-voltage measurements achieved. We investigated and compared characteristics of three mesas which are on same chip and next to each other. By this way, we searched the crystal inhomogenity in triple mesa structures and studied how critical current density varies with the doping conditions.

Area Dependence of Josephson Critical Current Density in Superconducting Bi2Sr2CaCu2O8+d for Terahertz Emission

Rapid increase in applications of the electromagnetic waves in the terahertz frequency range requires new techniques to obtain continues-wave terahertz radiation sources. It is shown that rectangular shaped mesa structure from Bi2Sr2CaCu2O8+d (Bi2212) is a good source for generation of terahertz radiation. In this study, we have fabricated triple mesa structures using e-beam lithography and argon ion beam etching techniques. Our aim is to find the critical current density dependence of mesa area to obtain maximum emission power for the terahertz radiation.

Fabrication of double mesa structures by E-beam lithography from high temperature superconducting Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) for powerful terahertz emission

We work on a frequency tunable solid state device to meet the needs of continuous, coherent, powerful terahertz emission sources that fill practically important terahertz gap. High temperature superconducting (HTS) coherently oscillating Josephson junctions in Bi2Sr2CaCu2O8+δ (Bi2212) crystal make this approach very promising. Since doping dependence of Bi2212 is an important parameter, Bi2212 crystals are annealed in vacuum or purified argon gas flow at 425 °C. For further processing we pattern both single and double rectangular mesa structures by using electron beam lithography on the cleaved surface of the crystal. Resistance-temperature (R-T), and current-voltage behavior (I-V) measurements achieved.