Kento Nakamura

Thermoreflectance microscopy measurements of the Joule heating characteristics of high- Tc superconducting terahertz emitters

Joule heating is the central issue in order to develop high-power and high-performance terahertz (THz) emission from mesa devices employing the intrinsic Josephson junctions in a layered high transition-temperature Tc superconductor. Here, we describe a convenient local thermal measurement technique using charge-coupled-device-based thermoreflectance microscopy, with the highest spatial resolution to date. This technique clearly proves that the relative temperature changes of the mesa devices between different bias points on the current-voltage characteristics can be measured very sensitively. In addition, the heating characteristics on the surface of the mesa devices can be detected more directly without any special treatment of the mesa surface such as previous coatings with SiC micro-powders. The results shown here clearly indicate that the contact resistance strongly affects the formation of an inhomogeneous temperature distribution on the mesa structures. Since the temperature and sample dependencies...

Improved excitation mode selectivity of high- T c superconducting terahertz emitters

Using our recent design of thermally managed sandwich device structures, we studied the radiation frequency characteristics of three such devices of the same rectangular dimensions made from the same single crystal of the high-Tc superconductor Bi2Sr2CaCu2O8+δ, and all three devices exhibit similar characteristics. Their observed radiation intensities appear to be enhanced at many transverse magnetic TMn,m cavity mode frequencies, possibly including some higher TM0,m modes with waves solely along the rectangular length, none of which have previously been reported. In addition, the temperature dependences of the radiation frequencies correspond strongly to the temperature dependences of the maximum bias voltages applied to the devices. The excitations of many cavity modes higher in frequency than that of the usually observed TM1,0 mode and the high reproducibility of the radiation frequency characteristics both appear to originate from the reduction in the Joule self-heating of the thermally managed sandwich structures. The information provided here should aid in the design of future devices to obtain the desired emission frequency ranges.Using our recent design of thermally managed sandwich device structures, we studied the radiation frequency characteristics of three such devices of the same rectangular dimensions made from the same single crystal of the high-Tc superconductor Bi2Sr2CaCu2O8+δ, and all three devices exhibit similar characteristics. Their observed radiation intensities appear to be enhanced at many transverse magnetic TMn,m cavity mode frequencies, possibly including some higher TM0,m modes with waves solely along the rectangular length, none of which have previously been reported. In addition, the temperature dependences of the radiation frequencies correspond strongly to the temperature dependences of the maximum bias voltages applied to the devices. The excitations of many cavity modes higher in frequency than that of the usually observed TM1,0 mode and the high reproducibility of the radiation frequency characteristics both appear to originate from the reduction in the Joule self-heating of the thermally managed sandwi...

Coherent and Continuous Terahertz Emitters from High-Tc Superconductor Mesa structures

View Online Nano-Micro Conf., 2017, 1, 01013 | 1 Published by Nature Research Society http://nrs.org Coherent and Continuous Terahertz Emitters from High-Tc Superconductor Mesa structures K. Kadowaki,* T. Yuasa, T. Tanaka, Y. Komori, R. Ota, G. Kuwano, Y. Tanabe, K. Nakamura, M. Tsujimoto, H. Minami, T. Kashiwagi, Richard A. Klemm* Graduate School of Pure & Applied Science, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 205-8573, Japan Division of Materials Science, Faculty of Pure & Applied Sciences, University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8573, Japan Department of Physics, University of Central Florida, Orlando, Florida 32816-2385, USA Corresponding Author. Email: K. Kadowaki, kadowaki@ims.tsukuba.ac.jp; Richard A. Klemm, Richard.Klemm@ucf.edu Received: 04 June 2017, Accepted: 18 June 2017, Published Online: 07 October 2017 Citation Information: K. Kadowaki, T. Yuasa, T. Tanaka, Y. Komori, R. Ota, G. Kuwano, Y. Tanabe, K. Nakamura, M. Tsujimoto, H. Minami, T. Kashiwagi, Richard A. Klemm, Nano-Micro Conference, 2017, 1, 01013 doi: 10.11605/cp.nmc2017.01013