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B. Gross,
S. Guenon,
J. Yuan,
M. Y. Li,
J. Li,
A. Iishi,
R. G. Mints,
T. Hatano,
P. H. Wu,
D. Koelle, H. B. Wang,
R. Kleiner
[show abstract]
[hide abstract]
ABSTRACT: We have studied experimentally and numerically temperature profiles and the
formation of hot spots in intrinsic Josephson junction stacks in Bi2Sr2CaCu2O8
(BSCCO). The superconducting stacks are biased in a state where all junctions
are resistive. The formation of hot spots in this system is shown to arise
mainly from the strongly negative temperature coefficient of the c-axis
resistivity of BSCCO at low temperatures. This leads to situations where the
maximum temperature in the hot spot can be below or above the superconducting
transition temperature Tc. The numerical simulations are in good agreement with
the experimental observations.
06/2012;
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M. Y. Li,
J. Yuan,
N. Kinev,
J. Li,
B. Gross,
S. Guenon,
A. Ishii,
K. Hirata,
T. Hatano,
D. Koelle,
R. Kleiner,
V. P. Koshelets, H. B. Wang,
P. H. Wu
[show abstract]
[hide abstract]
ABSTRACT: We report on measurements of the linewidth {\Delta}f of THz radiation emitted
from intrinsic Josephson junction stacks, using a Nb/AlN/NbN integrated
receiver for detection. Previous resolution limited measurements indicated that
{\Delta}f may be below 1 GHz - much smaller than expected from a purely
cavity-induced synchronization. While at low bias we found {\Delta}f to be not
smaller than ? 500 MHz, at high bias, where a hotspot coexists with regions
which are still superconducting, {\Delta}f turned out to be as narrow as 23
MHz. We attribute this to the hotspot acting as a synchronizing element.
{\Delta}f decreases with increasing bath temperature, a behavior reminiscent of
motional narrowing in NMR or ESR, but hard to explain in standard
electrodynamic models of Josephson junctions.
06/2012;
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B Gross,
S Guénon,
J Yuan,
Z G Jiang,
Y Y Zhong,
M Grünzweig,
A Ishii,
R G Mints,
P H Wu,
T Hatano,
D Koelle, H B Wang,
R Kleiner
[show abstract]
[hide abstract]
ABSTRACT: We have studied experimentally and numerically temperature profiles and the formation of hot spots in intrinsic Josephson junction stacks in Bi2Sr2CaCu2O8 (BSCCO). The superconducting stacks are biased in a state where all junctions are resistive. The formation of hot spots in this system is shown to arise mainly from the strongly negative temperature coefficient of the c-axis resistivity of BSCCO at low temperatures. This leads to situations where the maximum temperature in the hot spot can be below or above the superconducting transition temperature Tc. The numerical simulations are in good agreement with the experimental observations.
Phys. Rev. B. 01/2012; 86:094524.
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J Yuan,
M Y Li,
B Gross,
A Iishi,
K Yamaura,
T Hatano,
K Hirata,
E Takayama-Muromachi,
P H Wu,
D Koelle,
R Kleiner, H B Wang
[show abstract]
[hide abstract]
ABSTRACT: Terahertz emission has been detected from intrinsic Josephson junction (IJJ) stacks made of Bi$_2$Sr$_2$CaCu$_2$O$_8+delta$ (BSCCO). The mostly employed structure is a mesa on a pedestal of a single crystal with a gold top electrode. In this work, an IJJ stack with superconducting electrodes was prepared with a double-sided fabrication process, and signignificant terahertz emission was detected. The integrated power is $sim 10,mu$W, not weakened by the superconducting upper electrode. This suggests that off-chip terahertz emission from IJJs can be obtained not only from mesa structures, and most importantly, the emission power can be potentially enhanced in integrated multi-stack radiation sources.
Supercond. Sci. Technol. 01/2012; 25:075015.
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H B Wang,
S Guénon,
B Gross,
J Yuan,
Z G Jiang,
Y Y Zhong,
M Grünzweig,
A Iishi,
P H Wu,
T Hatano,
D Koelle,
R Kleiner
[show abstract]
[hide abstract]
ABSTRACT: We report on THz emission measurements and low temperature scanning laser imaging of Bi2Sr2CaCu2O8 intrinsic Josephson junction stacks. Coherent emission is observed at large dc input power, where a hot spot and a standing wave, formed in the "cold" part of the stack, coexist. By changing bias current and bath temperature, the emission frequency can be varied by more than 40%; the variation matches the Josephson-frequency variation with voltage. The linewidth of radiation is much smaller than expected from a purely cavity-induced synchronization. Thus, an additional mechanism seems to play a role. Some scenarios, related to the presence of the hot spot, are discussed.
Physical Review Letters 07/2010; 105(5):057002. · 7.37 Impact Factor
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S Guénon,
M. Grünzweig,
B. Gross,
J Yuan,
Z G Jiang,
Y. Y. Zhong,
A. Iishi,
P H Wu,
T Hatano,
D. Koelle, H. B. Wang,
R. Kleiner
[show abstract]
[hide abstract]
ABSTRACT: At high enough input power in stacks of Bi_2Sr_2CaCu_2O8 intrinsic Josephson junctions a hot spot (a region heated to above the superconducting transition temperature) coexists with regions still in the superconducting state. In the ``cold'' regions cavity resonances can occur, synchronizing the ac Josephson currents and giving rise to strong coherent THz emission. We investigate the interplay of hot spots and standing electromagnetic waves by low temperature scanning laser microscopy and THz emission measurements, using stacks of various geometries. For a rectangular and a arrow-shaped structure we show that the standing wave can be turned on and off in various regions of the stack structure, depending on the hot spot position. We also report on standing wave and hot spot formation in a disk shaped mesa structure.
05/2010;
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H. B. Wang,
S. Guenon,
B. Gross,
J Yuan,
Z G Jiang,
Y. Y. Zhong,
M. Gruenzweig,
A. Iishi,
P H Wu,
T Hatano,
D. Koelle,
R. Kleiner
[show abstract]
[hide abstract]
ABSTRACT: We report on THz emission measurements and low temperature scanning laser imaging of Bi_2Sr_2CaCu_2O_8 intrinsic Josephson junction stacks. Coherent emission is observed at large dc input power, where a hot spot and a standing wave, formed in the "cold" part of the stack, coexist. By varying the hot spot size the cavity resonance frequency and the emitted radiation can be tuned. The linewidth of radiation is much smaller than expected from the quality factor of the cavity mode excited. Thus, an additional mechanism of synchronization seems to play a role, possibly arising from nonequilibrium processes at the hot spot edge. Comment: 4.1 pages, 5 figures
05/2010;
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S.~Guénon,
M.~Grünzweig,
B.~Gross,
J.~Yuan,
Z.~G.~Jiang,
Y.~Y.~Zhong,
A.~Iishi,
P.~H.~Wu,
T.~Hatano,
D.~Koelle, H.~B.~Wang,
R.~Kleiner
[show abstract]
[hide abstract]
ABSTRACT: At high enough input power in stacks of Bi$_2$Sr$_2$CaCu$_2$O$_8$ intrinsic Josephson junctions a hot spot (a region heated to above the superconducting transition temperature) coexists with regions still in the superconducting state. In the "cold" regions cavity resonances can occur, synchronizing the ac Josephson currents and giving rise to strong and stable terahertz (THz) emission. We investigate the interplay of hot spots and standing electromagnetic waves by low temperature scanning laser microscopy and THz emission measurements, using stacks of various geometries. Standing electromagnetic wave patterns and THz emission are observed for a disk-shaped sample. The growth of a hot spot with increasing input power is monitored by small detector junctions surrounding a large rectangular mesa. For two rectangular mesas equipped with two current injectors and one arrow-shaped structure we show that the standing wave can be turned on and off in various regions of the stack structure, depending on the hot-spot position. The results support the picture of the hot spot acting as a reflective termination of the cavity, formed by the cold part of the mesa.
Phys. Rev. B. 01/2010; 82:214506.
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H. B. Wang,
B. Y. Zhu,
C. Gürlich,
M. Ruoff,
S. Kim,
T. Hatano,
B. R. Zhao,
Z. X. Zhao,
E. Goldobin,
D. Koelle,
R. Kleiner
[show abstract]
[hide abstract]
ABSTRACT: We demonstrate the operation of a deterministic fluxon ratchet made of a stack of 30 intrinsic Bi2Sr2CaCu2O8 Josephson junctions. The ratchet has the shape of a gear with 20 asymmetric teeth (periods). It produces a rectified voltage of about 100 μV at a 12 GHz drive frequency. The effect of coupling between intrinsic junctions, i.e., the mode of fluxon motion for ratchet operation, has been studied within the framework of the two-dimensional coupled sine-Gordon equations. Further, we used low-temperature scanning laser microscopy to demonstrate that voltage rectification indeed is due to directed fluxon motion, in agreement with numerical simulations.
Phys. Rev. B. 12/2009; 80(22).
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H. B. Wang,
B. Y. Zhu,
C. Gürlich,
M. Ruoff,
S. Kim,
T. Hatano,
B. R. Zhao,
Z. X. Zhao,
E. Goldobin,
D. Koelle,
R. Kleiner
[show abstract]
[hide abstract]
ABSTRACT: We demonstrate the operation of a deterministic fluxon ratchet made of a
stack of 30 intrinsic
Bi2Sr2CaCu2O8 Josephson
junctions. The ratchet has the shape of a gear with 20 asymmetric teeth
(periods). It produces a rectified voltage of about 100μV at a 12
GHz drive frequency. The effect of coupling between intrinsic junctions,
i.e., the mode of fluxon motion for ratchet operation, has been studied
within the framework of the two-dimensional coupled sine-Gordon
equations. Further, we used low-temperature scanning laser microscopy to
demonstrate that voltage rectification indeed is due to directed fluxon
motion, in agreement with numerical simulations.
Physical review. B, Condensed matter 11/2009; 80(22):224507.
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[show abstract]
[hide abstract]
ABSTRACT: Recently, it has been shown that large stacks of intrinsic Josephson junctions in Bi2Sr2CaCu2O8 emit synchronous THz radiation, the synchronization presumably triggered by a cavity resonance. To investigate this effect we use low temperature scanning laser microscopy to image electric field distributions. We verify the appearance of cavity modes at low bias and in the high input-power regime we find that standing-wave patterns are created through interactions with a hot spot, possibly pointing to a new mode of generating synchronized radiation in intrinsic Josephson junction stacks.
Physical Review Letters 02/2009; 102(1):017006. · 7.37 Impact Factor
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H B Wang,
B Y Zhu,
C Gürlich,
M Ruoff,
S Kim,
T Hatano,
B R Zhao,
Z X Zhao,
E Goldobin,
D Koelle,
R Kleiner
[show abstract]
[hide abstract]
ABSTRACT: We demonstrate the operation of a deterministic fluxon ratchet made of a stack of 30 intrinsic Bi$_2$Sr$_2$CaCu$_2$O$_8$ Josephson junctions. The ratchet has the shape of a gear with 20 asymmetric teeth (periods). It produces a rectified voltage of about $100 unitsmu V$ at a $12 unitsGHz$ drive frequency, extrapolating to more than 2 mV for a emphsingle tooth device. We analyze the device in the framework of the coupled 2D sine-Gordon equations and argue that intrinsic junction ratchets can rectify an input ac current with a frequency up to about $200unitsGHz$.
Phys. Rev. B. 01/2009; 80:224507.
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[show abstract]
[hide abstract]
ABSTRACT: We report an experimental observation of the macroscopic quantum tunnelling (MQT) in a d-wave high-temperature superconductor (HTSC) Bi2Sr2CaCu2O8+δ intrinsic Josephson junction (IJJs). It is well known that the current-biased Josephson tunnel junction provides an ideal stage for studying a variety of macroscopic quantum phenomena such as MQT. They have been studied and observed in low-temperature superconductor (LTSC) Josephson junctions since the early 1980s and have been established well by now. On the other hand, in the case of HTSC the d-wave pairing symmetry allows for dissipative quasiparticle excitations within the superconducting energy gap, which is expected to severely interfere with an observation of MQT. Contrary to this naive conception, our experimental results have explained that the effects of the nodal quasiparticles are not strong enough to obscure the observation of the MQT. Furthermore, we found that the MQT in IJJs was observed at approximately 1 K, which was ten times higher than that of LTSC Josephson junctions. This higher classical-to-quantum crossover temperature is due to their high plasma frequency. We also discuss the resonant activation of IJJs in the presence of microwave radiation.
Superconductor Science and Technology 01/2007; 20(2):S105. · 2.66 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Intrinsic Josephson junctions (IJJs) with lateral sizes down to submicron have been fabricated in high temperature cuprate superconductor Bi2Sr2CaCu2O8+δ single crystals. With in-plane magnetic fields applied perpendicular to the short edges, equally spaced current steps with intervals up to millivolts have been observed in current-voltage characteristics, indicating that terahertz oscillation has been excited in the junctions. The one-by-one switching to the same resonance frequency will make possible to employ a submicron sized IJJs stack as a building block for solid state terahertz continuous wave sources.
Applied Physics Letters 12/2006; 89(25):252506-252506-3. · 3.84 Impact Factor
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M Nagao,
S. Urayama,
S. M. Kim, H. B. Wang,
K. S. Yun,
Y Takano,
T Hatano,
I. Iguchi,
T Yamashita,
M. Tachiki,
H Maeda,
M Sato
[show abstract]
[hide abstract]
ABSTRACT: We measured the Josephson vortex flow resistance as a function of magnetic field applied parallel to the ab-planes using annealed Y1Ba2Cu3Ox intrinsic Josephson junctions having high anisotropy (around 40) by oxygen content reduction. Periodic oscillations were observed in magnetic fields above 45-58 kOe, corresponding to dense-dilute boundary for Josephson vortex lattice. The observed period of oscillations, agrees well with the increase of one fluxon per two junctions ($H_{p}$\textit{=$\Phi $}$_{0}$\textit{/2Ls}), may correspond to formation of a triangular lattice of Josephson vortices as has been reported by Ooi et al. for highly anisotropic (larger than 200) Bi-2212 intrinsic Josephson junctions. Comment: 5 pages, 4 figures
06/2006;
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[show abstract]
[hide abstract]
ABSTRACT: To investigate in-phase structures (rectangular lattice) of Josephson vortex lattice (JVL) in intrinsic Josephson junctions (IJJs) of Bi2Sr2CaCu2O8+d, we fabricated IJJs with various lateral sizes down to a size of non-linear core of Josephson vortex using focused-ion-beam etching and measured flux flow resistance (RFF) with in-plane magnetic fields (H). We have found that above a size-independent critical field, the critical current shows Fraunhofer pattern in narrow-length IJJs (0.29-2.77 mm), and then the RFF~H oscillates with H0 period. Most strikingly, such oscillations become pulse-like in sub-micron IJJs, indicating that between the pulses, the rectangular JVLs become major structures.
03/2006;
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[show abstract]
[hide abstract]
ABSTRACT: With annular intrinsic Josephson junctions structured from a slice of Bi2Sr2CaCu2O8+δ single crystal 200 nm thick, we have devised a way to inject fluxons into the junctions only by sweeping the bias current. The stacks have shown typical properties concerning Josephson fluxon conservation. These annular junctions are sensitive to microwave irradiation, and quite sharp Shapiro steps have been observed at ∼ 20 GHz which is much lower than the plasma frequency of the junctions, indicating many applications can be possible with practically accessible microwave sources.
Applied Physics Letters 02/2006; 88(6):063503-063503-3. · 3.84 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We investigate both experimentally and theoretically transport properties of the Josephson vortices (JV) with a finite bias current along the c axis of the intrinsic Josephson junctions in layered high-Tc superconductor of Bi2Sr2CaCu2O8+δ. Employing the perturbed sine-Gordon equation and integrating a novel characterization factor of the difference between current distributions on neighboring layers ΔJ, we are successful in explaining new phenomena such as (1) oscillation with period Hp corresponding to adding one JV per layer, (2) its peak splitting, and (3) reverse of the peaks and valleys with increase of current in JV flow resistance as a function of magnetic field observed in our experiments. Additionally, our simulation shows concrete evidence for the sample size dependent phase transition between Hp∕2-period and Hp-period oscillations. The novel phenomena are expected to be useful for designing practical devices in experiments.
Phys. Rev. B. 11/2005; 72(17).
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[show abstract]
[hide abstract]
ABSTRACT: While Josephson-junction-like structures intrinsic to the layered cuprate high temperature superconductors offer an attractive stage for exploiting possible applications to new quantum technologies, the low energy quasiparticle excitations characteristically present in these d-wave superconductors may easily destroy the coherence required. Here we demonstrate for the first time the feasibility of macroscopic quantum tunneling in the intrinsic Josephson junctions of a high temperature superconductor Bi(2)Sr(2)CaCu(2)O(8 + delta), and find it to be characterized by a high classic-to-quantum crossover temperature and a relatively weak quasiparticle dissipation.
Physical Review Letters 10/2005; 95(10):107005. · 7.37 Impact Factor
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M. Nagao,
K.S. Yun, H.B. Wang,
K. Inomata,
S. Kim,
Y. Takano,
T. Hatano,
T. Yamashita,
M. Tachiki,
H. Maeda,
M. Sato
[show abstract]
[hide abstract]
ABSTRACT: Single-crystal whiskers of Y<sub>1</sub>Ba<sub>2</sub>Cu<sub>3</sub>O<sub>x</sub> with a length of about 4 mm were grown from an Sb-doped precursor. The optimum nominal composition of precursors in this Sb-doping method is Y<sub>2</sub>Ba<sub>2.75</sub>Cu<sub>3</sub>Sb<sub>0.5</sub>O<sub>x</sub>. Sb is not detected in the whiskers by energy-dispersive x-ray spectroscopy (EDS). The standard 4-probe transport measurements for the as-grown whiskers show a critical temperature T<sub>C</sub> of about 90 K and a c-axis critical current density J<sub>C</sub> of 9.51×10<sup>4</sup> A/cm<sup>2</sup> at 89 K.
IEEE Transactions on Appiled Superconductivity 07/2005; · 1.04 Impact Factor
