Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session M1: Invited Session: Tunable, Intense, Coherent THz Emission From a High Temperature Superconductor |
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Sponsoring Units: DCMP Chair: Ulrich Welp, Argonne National Laboratory Room: Ballroom I |
Wednesday, March 20, 2013 8:00AM - 8:36AM |
M1.00001: Hot Spot and THz Wave Generation in Bi$_2$Sr$_2$CaCu$_2$O$_8$ Intrinsic Josephson Junction Stacks Invited Speaker: Reinhold Kleiner Stacks of intrinsic Josephson junctions made of the high temperature superconductor Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ have been shown to emit coherent radiation at THz frequencies [1]. Emission is observed both in a low bias regime and a high bias regime. While at low bias the temperature of the stack is close to the bath temperature, at high bias a hot spot and a standing wave, formed in the ``cold'' part of the stack, coexist [2-5]. THz radiation is very stable in this regime, exhibiting a linewidth which is much smaller than expected from a purely cavity-induced synchronization mechanism [6]. We investigate the interaction of hot spots and THz waves using a combination of transport measurement, direct electromagnetic wave detection and low temperature scanning laser microscopy (LTSLM). In this talk recent developments will be presented, with a focus on the mechanism of hot spot formation.\\[4pt] In collaboration with B. Gross, S. Gu\'{e}non, M. Y. Li, J. Yuan, N. Kinev, J. Li, A. Ishii, K. Hirata, T. Hatano, R. G. Mints, D. Koelle, V. P. Koshelets, H. B. Wang and P. H. Wu.\\[4pt] [1] L. Ozyuzer, et al., Science \textbf{318}, 1291 (2007).\\[0pt] [2] H.~B. Wang, et al., Phys. Rev. Lett. \textbf{102}, 017006 (2009).\\[0pt] [3] H. B. Wang, et al., Phys. Rev. Lett. \textbf{105}, 057002 (2010).\\[0pt] [4] S. Guenon, et al, Phys. Rev B \textbf{82}, 214506 (2010).\\[0pt] [5] B. Gross, et al., Phys. Rev. B \textbf{86}, 094524 (2012).\\[0pt] [6] M. Y. Li, et al., Phys. Rev. B \textbf{86}, 060505 (R) (2012). [Preview Abstract] |
Wednesday, March 20, 2013 8:36AM - 9:12AM |
M1.00002: Towards practical applications of powerful and widely-tunable THz sources made of layered superconductors Invited Speaker: Huabing Wang Terahertz (THz) emission from intrinsic Josephson junction stacks made of high temperature superconductor Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ have been obtained both in a low bias and a high bias regime [1, 2]. While at low bias the temperature distribution in the stack is almost homogeneous, at high bias an over-heated part (hot spot area) and a cold part of the sample coexist [2, 3]. Previous resolution-limited measurements indicated that the linewidth $\Delta f$ of THz emission may be below 1 GHz, showing no difference between two regimes. In this talk, we report on measurements of the linewidth of THz radiation using a Nb/AlN/NbN integrated receiver for detection [4]. While at low bias we found $\Delta f$ to be not smaller than $\sim$500 MHz, at high bias $\Delta f$ turned out to be as narrow as a few MHz. We attribute this to the hot spot acting as a synchronizing element. Also thanks to the variable size of the hot spot and the temperature rise due to the self-heating, the emission frequency can be tuned over a wide range of up to 500 GHz. Last but not least, the emission power was measured to be above 25 $\mu$W. All these properties imply that THz sources made of layered cuprate superconductors can be employed for practical applications.\\[4pt] [1] L. Ozyuzer, et al., Science 318, 1291 (2007).\\[0pt] [2] H. B. Wang, et al., Phys. Rev. Lett. 105, 057002 (2010).\\[0pt] [3] S. Gu\'enon, et al., Phys. Rev. B 82, 214506 (2010).\\[0pt] [4] M. Y. Li, et al., Phys. Rev. B.86, 060505(R) (2012). [Preview Abstract] |
Wednesday, March 20, 2013 9:12AM - 9:48AM |
M1.00003: THz Radiation from Mesas of Intrinsic Josephson Junction of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ under Extreme Thermal Inhomogeneity Invited Speaker: Kazuo Kadowaki After the discovery of intense, coherent and continuous electromagnetic waves at terahertz frequencies (THz waves) in 2007,\footnote{L. Ozyuzer et al.,Science 318 (2007) 1291, Kadowaki et al., Physica C468 (2008) 634.} a number of experimental and theoretical works have been carried out to understand the THz radiation phenomena from mesa structure of layered high temperature superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (hereafter abbreviated as Bi2212). At present after five year intensive studies, the basic mechanism of the THz wave emission can be understood by two principles: one is the ac-Josephson effect working in-between individual intrinsic Josephson junctions in the mesa of Bi2212 and the other is the cavity resonance effect associated with both the geometrical shape and the electromagnetic properties of the mesa structures of Bi2212. However, the precise conditions to obtain strong THz radiation are not yet established well at the stage of mesa fabrication.\footnote{M. Tsujimoto et al., PRL 108 (2012) 107006.} Moreover, it appears that our recent results of measurement of the inhomogeneous temperature distribution due to the hot-spot formation producing gigantic Joule heat in the mesa may give us much more complicated situations to understand physics of the THz radiation.\footnote{H. minami et al., submitted to PRL.} In this talk based on the experimental results we will provide a unified picture of the THz radiation phenomena in spite of highly nonequilibrium thermal condition, which hopefully will give us a hint to improve the performance and the efficiency of the emission power exceeding 1 mW from a single mesa structure. This will be also useful for various applications. [Preview Abstract] |
Wednesday, March 20, 2013 9:48AM - 10:24AM |
M1.00004: Modelling the coherent THz radiation from Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ mesas of various geometries Invited Speaker: Richard Klemm Mesa structures of the high-temperature superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ have been prepared in a variety of ways. Groove mesas have so far been made in rectangular, square, circular, triangular, and pentagonal shapes. There are distinct differences in the properties of the radiation that depend strongly on the type and shape of the mesas. Two types of experiments have provided information regarding the mechanism of the coherent radiation: Angular distribution studies and frequency spectrum measurements. In analyzing the angular distribution measurements, we used the Love equivalence principles to model the radiation as arising from two effective sources: the uniform $ac$ Josephson current source, and the radiation from the excitation of an EM cavity mode, and modelled the substrate by a simple image model. We generally found the fractions of the output from these two sources to be comparable in magnitude, implying that the quality factor $Q$ of the EM cavity is very low, allowing for a high degree of output frequency tunability. The largest tunability observed to date from the outer current-voltage characteristic branch was found for an acute isosceles triangular mesa shape. In several geometries, radiation was observed at frequencies far from EM cavity mode frequencies. [Preview Abstract] |
Wednesday, March 20, 2013 10:24AM - 11:00AM |
M1.00005: Intrinsic line shape of electromagnetic radiation from a stack of intrinsic Josephson junctions synchronized by an internal cavity resonance Invited Speaker: Alexei Koshelev Stacks of intrinsic Josephson-junctions are realized in mesas fabricated out of layered superconducting single crystals, such as Bi$_2$Sr$_2$CaCu$_2$O$_8$ (BSCCO). Synchronization of phase oscillations in different junctions can be facilitated by the coupling to the internal cavity mode leading to powerful and coherent electromagnetic radiation in the terahertz frequency range. An important characteristic of this radiation is the shape of the emission line. A finite line width appears due to different noise sources leading to phase diffusion. We investigated the intrinsic line shape caused by the thermal noise for a mesa fabricated on the top of a BSCCO single crystal. In the ideal case of fully synchronized stack the finite line width is coming from two main contributions, the quasiparticle-current noise inside the mesa and the fluctuating radiation in the base crystal. We compute both contributions and conclude that for realistic mesa's parameters the second mechanism typically dominates. The role of the cavity quality factor in the emission line spectrum is clarified. Analytical results were verified by numerical simulations. In real mesa structures part of the stack may not be synchronized and chaotic dynamics of unsynchronized junctions may determine the real line width. [Preview Abstract] |
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