Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
Browse
2 results
Search Results
Article Citation - WoS: 150Citation - Scopus: 146Direct Observation of Tetrahertz Electromagnetic Waves Emitted From Intrinsic Josephson Junctions in Single Crystalline Bi2sr2cacu2o8+?(Elsevier Ltd., 2008) Kadowaki, K.; Yamaguchi, H.; Kawamata, K.; Yamamoto, T.; Minami, H.; Kakeya, I.; Welp, U.; Özyüzer, Lütfi; Koshelev, A. E.; Kurter, Cihan; Gray, Kenneth E.; Kwok, W. K.We have observed intense, coherent, continuous and monochromatic electromagnetic (EM) emission at terahertz frequencies generated from a single crystalline mesa structure of the high-Tc superconductor Bi2Sr2CaCu2O8+δ intrinsic Josephson junction system. The mesa is fabricated by the Argon-ion-milling and photolithography techniques on the cleaved surface of Bi2Sr2CaCu2O8+δ single crystal. The frequency, ν, of the EM radiation observed from the sample obeys simple relations: ν = c/nλ = c/2nw and ν = 2eV/hN, where c is the light velocity in vacuum, n the refractive index of a superconductor, λ the wave length of the EM emission in vacuum, w the shorter width of the mesa, V the voltage applied to the mesa, N the number of layers of intrinsic Josephson junctions, e and h are the elementary charge and the Planck constant, respectively. These two relations strongly imply that the mechanism of the emission is, firstly, due to the geometrical resonance of EM waves to the mesa like a cavity resonance occuring in the mesa structure, and forming standing waves as cavity resonance modes, and secondly, due to the ac-Josephson effect, which works coherently in all intrinsic Josephson junctions. The peculiar temperature dependence of the power intensity emitted form samples shows a broad maximum in a temperature region between 20 and 40 K, suggesting that the nonequilibrium effect plays an essential role for the emission of EM waves in this system. The estimated total power is significantly improved in comparison with the previous report [L. Ozyuzer et al., Science 318 (2007) 1291, K. Kadowaki, et al., Physica C 437-438 (2006) 111, I.E. Batov, et al., Appl. Phys. Lett. 88 (2006) 262504], and reached as high as 5 μW from single mesa with w = 60 μm at 648 GHz, which enables us to use it for some of applications. So far, we succeeded in fabricating the mesa emitting EM waves up to 960 GHz in the fundamental mode in the w = 40 μm mesa, whereas the higher harmonics up to the 4-th order were observed, resulting in a frequency exceeding 2.5 THz. In sharp contrast to the previous reports [K. Kadowaki, et al., Physica C 437-438 (2006) 111, M.-H. Bae, et al., Phys. Rev. Lett. 98, (2007) 027002], all the present measurements were done in zero magnetic field. Lastly, a plausible theoretical model for the mechanism of emission is discussed.Conference Object Citation - WoS: 4Citation - Scopus: 4Probing the Phase Diagram of Bi2sr2cacu 2o8+? With Tunneling Spectroscopy(Institute of Electrical and Electronics Engineers Inc., 2003) Özyüzer, Lütfi; Zasadzinski, John F.; Gray, Kenneth E.; Hinks, David G.; Miyakawa, NobuakiTunneling measurements are performed on Ca-rich single crystals of Bi 2Sr2CaCu2O8+δ (Bi2212), with various oxygen doping levels, using a novel point contact method. At 4.2 K, SIN and SIS tunnel junctions are obtained with well-defined quasiparticle peaks, robust dip and hump features and in some cases Josephson currents. The doping dependence of tunneling conductances of Ca-rich Bi2212 are analyzed and compared to stoichiometric Bi2212. A similar profile of energy gap vs. doping concentration is found although the Ca-rich samples have a slighly smaller optimum Tc and therefore smaller gap values for any doping level. The evolution of tunneling conductance peak height to background ratios with hole concentration are compared. For a given doping level, the Ca-rich spectra showed more broadened features compared to the stoichiometric counterparts, most likely due to increased disorder from the excess Ca. Comparison of the dip and hump features has provided some potential insights into their origins.