Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session P23: Superconductivity: Josephson Effects I |
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Sponsoring Units: DCMP Chair: George Crabtree, Argonne National Laboratory Room: D165 |
Wednesday, March 23, 2011 8:00AM - 8:12AM |
P23.00001: Tunable terahertz emission from Bi2Sr2CaCu2O8 mesa devices Timothy Benseman, Ulrich Welp, Wai-Kwong Kwok, Alexei Koshelev, Cihan Kurter, Lutfi Ozyuzer, Kazuo Kadowaki, Takashi Yamamoto The so-called ``terahertz gap,'' covering frequencies from approximately 0.3 to 1.5 THz, is of particular interest for a number of scientific and security applications, although no bright sources of coherent radiation presently exist in this range. However, stacks of high-temperature superconducting intrinsic Josephson junctions are a promising candidate. [1] Here we discuss recent progress in improving the performance of these devices. In particular, we demonstrate that via control of bias voltage and operating temperature, the emission from an 80-$\mu $m wide Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ mesa can be tuned continuously over a frequency range in excess of 10{\%} in the vicinity of 0.5 THz. We find that as the emission frequency increases from 0.420 to 0.492 THz, the linewidth increases from $<$2.25 GHz (limited by instrument resolution) to $\sim $9 GHz. \\[4pt] [1] L. Ozyuzer et al., Science 318 (2007) 1291-1293. [Preview Abstract] |
Wednesday, March 23, 2011 8:12AM - 8:24AM |
P23.00002: The relationship between oscillation modes and single crystalline Bi2212 mesa structures T. Kashiwagi, K. Deguchi, M. Tsujimoto, N. Orita, T. Koike, R. Nakayama, K. Delfanazari, H. Minami, T. Yamamoto, K. Kadowaki Continuous electromagnetic (EM) radiation in terahertz region has been observed from a rectangular mesa structure of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$(Bi2212) single crystals.\footnote{L. Ozyuzer \textit{et al.}, Science \textbf{318} (2007) 1291.} It has been established that the radiation frequency is determined by both ac Josephson effect and geometrical cavity resonance condition.\footnote{K. Kadowaki \textit{et al.}, J. Phys. Soc. Jpn. \textbf{79} (2010) 023703} The observed radiation frequencies in the many rectangular mesas studied were inversely proportional to the width of the mesa and the fundamental modes equal to twice the mesa width. Recently, several mesas show different radiation characteristics which suggest the existence of the higher excitation modes such as one wave length excitation mode. The observed frequencies from above mesas are almost explained by the geometrical cavity model. In order to clarify the detail of the excitation modes, we also measured the radiation pattern of EM waves. [Preview Abstract] |
Wednesday, March 23, 2011 8:24AM - 8:36AM |
P23.00003: Coherent THz-wave emission from voltage- and number-controlled intrinsic Josephson junctions in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ Manabu Tsujimoto, Ryo Nakayama, Naoki Orita, Takashi Koike, Kota Deguchi, Kaveh Delfanazari, Takashi Yamamoto, Takanari Kashiwagi, Hidetoshi Minami, Masashi Tachiki, Kazuo Kadowaki Intense and coherent terahertz electromagnetic wave (THz-wave) emission from the intrinsic Josephson junctions (IJJs) in single crystalline high-$T_{c}$ superconductor Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta }$ (Bi-2212) was reported in 2007 [L. Ozyuzer \textit{et al}., Science \textbf{318}, (2007) 1291.]. In the present work, we demonstrate the relationship between the bias condition and the resonance state by controlling both the applied voltage, $V$, and the number of resistive junctions, $N$. We directly observed that if $N$ junctions are in resistive state, the resonance frequency, $f_{J}$, varies in accordance with the ac-Josephson relation; $f_{J}$ = (2$\vert e\vert $/$h)V$/$N$, although frequency $f_{J}$ has previously been thought to be uniquely determined by the geometrical condition due to the cavity resonance effect [M. Tsujimoto \textit{et al}., Phys. Rev. Lett. \textbf{105}, (2010) 037005.]. We also found that the emission intensity varies as a function of both $f_{J}$ and $N$. [Preview Abstract] |
Wednesday, March 23, 2011 8:36AM - 8:48AM |
P23.00004: Angular distribution and Josephson plasma modes of THz radiation emitted from Bi2212 mesas with various shapes Kazuo Kadowaki, Takanari Kashiwagi, Manabu Tsujimoto, Takashi Yamamoto, Hidehiro Asai, Hidetoshi Minami So far, we have measured angular dependence of the intensity of the THz emission from mesas of high-$T_c$ superconductor $\mathrm{Bi_2Sr_2CaCu_2O_{8+\delta}}$ with various shapes such as rectangulars, squares, cylinders, triangulars, etc. and various dimensions larger or smaller than the penetration depth $\lambda_c$. The results have been analized by a model developed by Klemm and Kadowaki{\footnote{Richard A. Klemm and K. Kadowaki, J. Phys. Condens. Matter {\bf{22}} (2010) 375701.}}, which assumes coherent generation of the standing of wave cavity modes in a mesa due to the ac-Josephson effect. The higher harmonic modes are observed in some cases as expected in the model. However, it is often observed that the emission frequency does not obey the simple cavity mode, indicating that the cavity resonance may not be a stringent condition for the emission of the THz radiation. The implication is argued in terms of the emission dynamics from the Bi2212 mesa structure. [Preview Abstract] |
Wednesday, March 23, 2011 8:48AM - 9:00AM |
P23.00005: Superconductivity induced by current injection into non-superconducting Bi$_2$Sr$_2$CaCu$_2$O$_8$ Y. Simsek, Y. Koval, X.Y. Jin, S. Probst, P. M\"uller The carrier-doping induced transition from the antiferromagnetic state to the superconducting phase is still one of the most fascinating properties of high-Tc materials. Usually hole doping is achieved by non-stoichiometry. However, we already have shown that we can change the carrier concentration of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ single crystals by current injection along the c-axis. This effect is persistent up to annealing temperatures of approximately 270 K. Now, the interesting question is if ``chemical'' doping by oxygen excess is necessary at all. For this purpose we performed current-injection experiments on fully oxygen depleted Bi$_2$Sr$_2$CaCu$_2$O$_8$ which was not superconducting above 4.2 K. In order to eliminate the contact resistance of the highly resistive depleted material, we realized a ``true'' 4-point geometry by fabricating double cross-bar crystal stacks. C-axis resistivity, critical current, and critical temperature were measured by c-axis transport. We have observed that by carrier injection the conductivity can be increased until superconductivity above 4.2 K is reached. Continuing the doping by current injection, optimum-doped and even overdoped states were obtained. Using current injection at higher bias, we were able to reduce the hole concentration again. [Preview Abstract] |
Wednesday, March 23, 2011 9:00AM - 9:12AM |
P23.00006: Magnetic-field-driven phase transitions in Josephson arrays Joshua Paramanandam, Matthew Bell, Aleksandr Verevkin, Lev Ioffe, Michael Gershenson We have studied the phase transitions induced by the magnetic field $B$ in arrays of small Josephson junctions. The number of nearest-neighbor junctions connected to a single superconducting island varied between 4 and 11 for different arrays. When frustrated by the magnetic field, the arrays demonstrated several quantum phase transitions at different critical values of the resistance between $R $=3-10~k, which is in line with earlier observations. In particular, with increasing $B$ we observed transitions between three states$: $ a) the superconducting state with zero $R$, b) the ``metallic'' state with a weak $R$ dependence on T in the range 40mK$<$T$<$200mK, and c) the ``insulating'' state with an activation dependent $R(T)$. The activation energy, extracted from the current-voltage characteristics and the Arrhenius fitting of $R(T)$ in the ``insulating'' regime, has been studied in detail as a function of the temperature and the magnetic field. The data indicate the possible development of a strongly inhomogeneous state when approaching the superconducting-to-insulating transition. [Preview Abstract] |
Wednesday, March 23, 2011 9:12AM - 9:24AM |
P23.00007: Series-parallel two dimensional arrays of YBa$_{2}$Cu$_{3}$O$_{7-\delta }$ thin film ion damage Josephson junctions Jasper Drisko, Shane Cybart, Steven Anton, Stephen Wu, James Parker, Robert Dynes We have fabricated a number of series-parallel two dimensional arrays of YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ thin film ion damage Josephson junctions. The arrays contain 1,000 to 15,000 Superconducting QUantum Interference Devices (SQUIDs) in different dimensional configurations and different SQUID area distributions. We have measured the electrical transport characteristics of each array and compare it to computer simulations based on the resistively shunted junction model to investigate the effect of mutual inductance between the SQUIDS within the array. We find there is good agreement between our simulation model and our experimental device when the parallel dimension of the device is less than 15 SQUIDs. [Preview Abstract] |
Wednesday, March 23, 2011 9:24AM - 9:36AM |
P23.00008: Properties of linear arrays of Josephson junctions capacitively coupled to a diffusive metal Alejandro Lobos, Thierry Giamarchi Josephson junctions arrays (JJAs) are strongly-correlated quantum systems showing a rich and complex behavior at low-temperatures.\footnote{R. Fazio and H. van der Zant, Physics Reports \textbf{355}, 235 (2001)} Besides their potential uses in applications, JJAs allow to investigate (under controlled conditions) many aspects of low-dimensional superconductivity which remain to be understood. In this work we study the phase diagram and the low-energy properties of a one-dimensional (1D) JJA capacitively coupled to a diffusive two-dimensional electron gas (2DEG) placed at a distance $d$, which provides dissipation.\footnote{A. M. Lobos and T. Giamarchi, Phys. Rev. B \textbf{82}, 104517 (2010)} We derive an effective field-theoretical model for the 1D JJA coupled to the 2DEG, and predict a superconductor-insulator transition (SIT) at $T=0$, in agreement with former theoretical predictions. We discuss implications for transport experiments and for the observed SIT in 1DJJAs. Both in the superconducting and insulating phases, the coupling to the 2DEG produces deviations with respect to the resistivity as a function of $T$ predicted for an isolated array. [Preview Abstract] |
Wednesday, March 23, 2011 9:36AM - 9:48AM |
P23.00009: Measurement of Aharonov-Casher effect in a Josephson junction chain Ioan Mihai Pop, Florent Lecocq, Bernard Pannetier, Olivier Buisson, Wiebke Guichard We have recently measured the effect of superconducting phase-slips on the ground state of a Josephson junction chain\footnote{I. M. Pop et al. Nature Physics 6, 589\textendash{}592 (2010)} and a rhombi chain.\footnote{I. M. Pop et al. PRB, 78, 104504 (2008)} Here we report clear evidence of Aharonov-Casher effect in a chain of Josephson junctions. This phenomenon is the dual of the well known Aharonov-Bohm interference. Using a capacitively coupled gate to the islands of the chain, we induce oscillations of the supercurrent by tuning the polarization charges on the islands. We observe complex interference patterns for different quantum phase slip amplitudes, that we understand quantitatively as Aharonov-Casher vortex interferences. [Preview Abstract] |
Wednesday, March 23, 2011 9:48AM - 10:00AM |
P23.00010: Josephson Junction as a Magnetic Switch Liufei Cai, Eugene Chudnovsky We study electromagnetic interaction of a nanomagnet with a weak superconducting link. Equations that govern coupled dynamics of the two systems are derived and investigated numerically. We show that despite very weak magnetic field generated by the weak link, a time-dependent bias voltage applied to the link can initiate a non-linear dynamics of the nanomagnet that leads to the reversal of its magnetic moment. We also consider quantum problem in which a nanomagnet interacting with a weak link is treated as a two-state spin system due to quantum tunneling between spin-up and spin-down states. L. Cai and E. M. Chudnovsky, Phys. Rev B \textbf{82}, 104429 (2010). [Preview Abstract] |
Wednesday, March 23, 2011 10:00AM - 10:12AM |
P23.00011: Switching Experiments on a Current-Biased MgB$_2$ Josephson Junction Roberto Ramos, Jerome Mlack, Joseph Lambert, Steven Carabello As the current through a Josephson junction is increased, the voltage across the junction switches from zero to a finite voltage. This is analogous to the escape of a phase particle originally oscillating with a plasma frequency $\omega$ in a washboard potential well, to the running state. We report results of our switching experiments on current-biased MgB$_2 $/I/Pb thin film junctions through a broad range of sub-Kelvin temperatures. Our results exhibit features in the escape rate $\Gamma$ suggestive of substructure within the pi gap of MgB$_2 $, which is consistent with our recent work demonstrating sub- structure within the pi and sigma superconducting energy gaps of MgB$_2$. Upon irradiation of microwaves with frequencies resonant with the plasma frequency, we observe enhancement of escape rates, which is a clear demonstration of microwave resonant activation in these devices. By manipulating frequency and power, we demonstrate good control over the escape of the phase particle. [Preview Abstract] |
Wednesday, March 23, 2011 10:12AM - 10:24AM |
P23.00012: ABSTRACT WITHDRAWN |
Wednesday, March 23, 2011 10:24AM - 10:36AM |
P23.00013: Cavity mode waves during terahertz radiation from rectangular Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ mesas Richard Klemm, Erica LaBerge, Dustin Morley, Takanari Kashiwagi, Manabu Tsujimoto, Kazuo Kadowaki We re-examined the angular dependence of the radiation from the intrinsic Josephson junctions in rectangular mesas of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$, in order to determine if the cavity mode part of the radiation arises from waves across the width $w$ or along the length $\ell$ of the mesas, associated with ``hot spots'' [Wang {\it et al.}, Phys. Rev. Lett. {\bf 105}, 057002 (2010)]. Fits to the data of Kadowaki {\it et al.} [J. Phys. Soc. Jpn. {\bf 79}, 02373 (2010)] using both a uniform $ac$ Josephson current source and a non-uniform cavity mode (or magnetic surface current) source suggest that both scenarios are equally probable. However, when $n\ell/2w$ is integral, where $n$ is the index of the rectangular TM$^z(n,0)$ mode, standing cavity wave modes along the length of the mesa do not radiate in the $xz$ plane perpendicular to the length of the mesa, suggesting experiments on such mesas could help to resolve the question. [Preview Abstract] |
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