Vortex-flow electromagnetic emission in stacked intrinsic Josephson junctions

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Vortex-?ow electromagnetic emission in stacked intrinsic Josephson junctions

Myung-Ho Bae and Hu-Jong Lee

Department of Physics,Pohang University of Science and Technology,Pohang 790-784,Republic of Korea

(Dated:February 6,2008)

We con?rmed the existence of the collective transverse plasma modes excited by the motion of the Josephson vortex lattice in stacked intrinsic Josephson junctions of Bi 2Sr 2CaCu 2O 8+x by observ-ing the multiple subbranches in the Josephson-vortex-?ow current-voltage characteristics.We also observed the symptom of the microwave emission from the resonance between the Josephson vor-tex lattice and the collective transverse plasma modes,which provides the possibility of developing Josephson-vortex-?ow electromagnetic oscillators.

PACS numbers:74.72.Hs,74.50.+r,74.78.Fk,85.25.Cp

The generation of THz-range electromagnetic waves using the Josephson-vortex dynamics in naturally stacked Bi 2Sr 2CaCu 2O 8+x (Bi-2212)intrinsic Joseph-son junctions (IJJs)has been attempted extensively be-cause of the coherent (thus,high-power),continuous,and frequency-tunable characters of the generated waves [1].The characters of this technique are distinctive from those by other attempts [2]based on quantum cascade,relativistic electron bunches,and optical parametric con-trol.This electromagnetic emission from the Joseph-son vortex system is induced by the resonance between moving Josephson vortices and the collective transverse plasma (CTP)modes in the stacked IJJs [3].

A stack of Bi-2212containing N IJJs exhibits N eigen CTP modes,which can be excited by the moving Joseph-son vortex lattice (JVL)that forms in a high magnetic ?eld [4].If the frequency of the temporal oscillation of the phase di?erence across a junction due to moving JVL matches with that of a transverse plasma mode,a reso-nant plasma oscillation is excited with microwave emis-sion at the boundary of stacked IJJs.The JVL also trans-forms its lattice con?guration along the c -axis direction in accordance with the c -axis standing-wave mode of the strongly ampli?ed plasma oscillations.The resonance of JVL to the CTP modes appears as the multiple collective Josephson vortex-?ow branches in the tunneling current-voltage (I-V )curves of stacked junctions [5].

We report the observation of the CTP modes induced by the JVL motion and the excitation of corresponding electromagnetic waves in a stack of IJJs in Bi-2212.The existence of the CTP modes was con?rmed by observing the multiple branches in the Josephson vortex-?ow re-gion.In addition,for a proper bias,the emission of the electromagnetic waves by the collective vortex resonance motion in a stack of IJJs (the oscillator stack)was ex-amined using another stack of IJJs (the detector stack),which was placed within a fraction of μm from the os-cillator stack.The microwave emission from the oscilla-tor stack and the resulting irradiation onto the detector stack was evidenced by the suppression of the tunnel-ing critical current revealed in the quasiparticle branches and the increase of Josephson vortex-?ow voltages in the detector stack.Our numerical calculation for the e?ect of microwave irradiation on the detector stack was also

FIG.1:The H -?eld dependence of the Josephson-vortex-?ow branches and the quasiparticle branches of SP1in (a)H =3.5T and (b)5.5T.Inset of (a):the sample con?guration.Inset of (b):multiple quasiparticle branches of SP1in zero ?eld.

consistent with our observed results.

Bi-2212single crystals,prepared by the conventional solid-state-reaction method,were slightly overdoped.We fabricated,using the double-side cleaving technique [6],two samples of IJJs,each sandwiched between two Au electrodes at its top and bottom without the basal part [the inset of Fig.1(a)].Adopting the geometry with the basal part eliminated enabled us to measure the Joseph-son vortex dynamics in coupled IJJs without the interfer-ence of the vortex motion in the basal stack.The detailed fabrication procedure is described in Ref.[7].In the in-set of Fig.1(a)the left and right stacks are the oscillator and detector stacks,respectively.The lateral size of each oscillator of two samples was 16×1.5μm 2[SP1]and 15

2

×1.4μm 2[SP2],respectively.The magnetic ?eld was aligned in parallel with the junction planes within 0.01degree to avoid the pinning of Josephson vortices by the formation of pancake vortices in CuO 2bilayers.

Figs.1(a)and (b)show the magnetic ?eld dependence of I-V curves of SP1at 4.2K in 3.5and 5.5T,respec-tively.The contact resistance caused by the two-terminal con?guration adopted was subtracted numerically.The current-bias point corresponding to the dotted vertical arrow in each ?gure originates from the zero-?eld Joseph-son critical current.Thus,the voltage-bias region below the critical point corresponds to the pair-tunneling state,although it is resistive due to the Josephson vortex ?ow in high ?elds.The set of multiple branches in the volt-age (McCumber)bias region above the critical point are the quasiparticle branches,while those below the critical

point are the collective Josephson vortex-?ow branches [5].Estimated from the number of zero-?eld quasiparti-cle branches as in the inset of Fig.1(b)for SP1,stacks in SP1and SP2contained 45and 22IJJs,respectively.The numbers of the Josephson-vortex-?ow branches below the critical bias points for SP1and SP2are ～42and ～18(not shown),respectively,which are similar to the numbers of the IJJs in the respective samples.In ad-dition,the multiple Josephson-vortex-?ow branches be-come clearer and wider for a higher transverse magnetic ?eld,which is in contrast to the shrinking quasiparticle branches with increasing ?elds [see Fig.1(a)and (b)].The collective transverse plasma oscillation excited by the moving JVL is expected to emit electromagnetic waves at the junction edge [8].Detection of this mi-crowave emission,in turn,would be more positive con?r-mation that the observed multiple branches resulted from the moving JVL in resonance with the CTPs.A sepa-rate stack for the microwave detection was positioned a fraction of μm apart from the oscillator stack.In the direction facing the applied ?eld,the detector was 0.7μm wide,which was longer than the Josephson penetra-tion depth of 0.3μm and thus was in a long-junction limit.The oscillator and the detector stacks,connected by the bottom Au common-ground electrode,acted as a microwave coupler [see the inset of Fig.1(a)].The fre-quency of emitted microwaves may reach a THz range so that a conventional Nb-based Josephson detector cannot be used,because its gap size is smaller than the energy of the emitted waves.

The response of IJJs in the detector stack to the emit-ted microwaves from the oscillator stack may be revealed as the appearance of the Shapiro steps,the suppression of the c -axis tunneling critical current,I c ,revealed in the quasiparticle branches,or the increase of the volt-age of the low-bias region due to the resistive motion of microwave-induced vortices [9,10].The inset of Fig.2shows the bias conditions,V osc ,displayed by dots in the Josephson vortex-?ow branches of the oscillator stack of SP1in 3T.The black I-V curves in the main panels are the quasiparticle branches of the detector stack with-out any bias in the oscillator stack.For the biases of

FIG.2:(Color online)Response of the quasiparticle branches of the detector stack of SP1to biasing the oscillator stack.The curves are shifted for clarity.Inset:the bias condition of the oscillator stack as denoted by dots and the corresponding local temperature of the detector stack,with the base tem-perature at 4.2K,for varying bias in the oscillator stack.

V osc =10.4and 75mV (corresponding to 110and 800GHz [11],respectively)in the oscillator,I c in the quasiparticle branches of the detector stack is suppressed signi?cantly.Our previous studies [7,10]con?rmed that the irradia-tion of microwaves on the IJJs suppresses the I c revealed in the quasiparticle branches.

The temperature increase of the detector stack by the self-heating in the oscillator for a ?nite dc bias may cause the similar suppression of the I c [12].We directly moni-tored the actual temperature variation in the detector for any ?nite bias in the oscillator.Details of the thermom-etry are explained in Ref.[13],which con?rms that both stacks in our measurement con?guration should be at an identical temperature.The inset of Fig.2shows that the actual temperature increase in this measurement turned out to be less than 4.5K,so that the observed suppression of the I c around 4.2K should not have been caused by the bias-induced self-heating.One may also attribute the behavior to the leakage of the bias current from the os-cillator to the detector through the bottom Au common-ground electrode,rather than the microwave emission.However,any shift of the I-V curves due to a dc o?set current in the detector was not observed for any biases used.We thus attribute the suppression of the I c in the quasiparticle branches to the response of the stacked IJJs in the detector to the mircowave irradiation.

Fig.3shows the change in the Josephson vortex-?ow branch in the detector of the specimen SP2with vary-ing the bias voltage V osc of its oscillator.For V osc =4.5mV (corresponding to 100GHz)little variation of the I-V curves from the zero-bias condition is visible.The bias of 4.5mV corresponds to the near-triangular JVL in the oscillator stack,which represents the out-of-phase Josephson vortex distribution between adjacent junctions and thus corresponds to the weakest emission power,as illustrated in Figure 3.For V osc =18.1mV (corresponding to 400GHz),however,a distinct increase of the Joseph-

FIG.3:(Color online)The change in the Josephson vortex-?ow branch in the detector of SP2for the bias voltage of its oscillator V osc=0,4.5,and18.1mV.Upper inset:bias condition(denoted by dots)of the oscillator stack.Lower inset:numerically calculated I-V curves for the ac(ω=1.2)?eld component of h ac=0and0.075in a dc magnetic?eld of h=1.8.

son vortex-?ow voltage from the zero-bias condition is seen.We interpret it as arising from the?ow of ad-ditional Josephson vortices generated by the magnetic-?eld component of emitted higher-intensity microwaves from the oscillator with JVL close to the highly coherent square-lattice con?guration.

We numerically calculated vortex-?ow feature,in the detector stack induced,by the magnetic-?eld component of any irradiated microwaves[14].For simplicity,we con-sider a detector consisting of a single Josephson junction. The perturbed sine-Gordon equation for the dynamics of the phase di?erence across a Josephson junction,φ,is

?2φ

?t2?sinφ=α

?φ

Lett.78,4010(2001).

[7]M.-H.Bae,H.-J.Lee,J.Kim,and K.-T.Kim,Appl.

Phys.Lett.83,2187(2003).

[8]G.Hecht?scher,R.Kleiner,https://www.wendangku.net/doc/3612653694.html,tinov,and P.M¨u ller,

Phys.Rev.Lett.79,1365(1997).

[9]Y.-J.Doh,J.Kim,K.-T.Kim,and H.-J.Lee,Phys.Rev.

B.61,R3834(2000);H.B.Wang,P.H.Wu,and T.

Yamashita,Phys.Rev.Lett.87,107002(2001);Yu.I.

Latyshev,M.B.Gaifullin,T.Yamashita,M.Machida, and Y.Matsuda,Phys.Rev.Lett.87,247007(2001). [10]Y.-J.Doh,J.Kim,H.-S.Chang,S.Chang,H.-J.Lee,

K.-T.Kim,W.Lee,and J.-H.Choy,Phys.Rev.B.63,

144523(2001).

[11]The frequency is estimated based on the frequency-

voltage(per junction)conversion relation,f=2eV osc/Nh (=483.6GHz/mV×V osc/N).

[12]Private communications with E.Kume.

[13]M.-H.Bae,J.-H.Choi,and H.-J.Lee,Appl.Phys.Lett.

86,232502(2005).

[14]E.Goldobin(2003),URL https://www.wendangku.net/doc/3612653694.html,/Sil-

iconValley/Heights/7318/StkJJ.htm.

[15]F.L.Barkov,M.V.Fistul,and https://www.wendangku.net/doc/3612653694.html,tinov,Phys.

Rev.B.70,134515(2004).

ELECTROMAGNETIC COMPATIBILITY

ECE 407ELECTROMAGNETIC COMPATIBILITY Spring 2006 MWF 12:40-1:30 118 FAE Instructor: Ed Rothwell Office: C133 Engineering Research Phone: 355-5231 E-mail: rothwell@https://www.wendangku.net/doc/3612653694.html, Office Hours: MWF 11:30-12:20, 2234 EB (EM lab) Web site: https://www.wendangku.net/doc/3612653694.html,/~rothwell Text: Introduction to Electromagnetic Compatibility, Clayton R. Paul, John Wiley & Sons, New York, 2nd edition, 2006. Course notes: Posted to https://www.wendangku.net/doc/3612653694.html,/em/research/goali/notes/ Course web site: MSU ANGEL system (https://www.wendangku.net/doc/3612653694.html,) Principal reference: Noise Reduction Techniques in Electronic Systems, Henry W. Ott, John Wiley & Sons, 1988. Grading: Homework 15% Exam 1 20% Exam 2 20% Project 1 5% Project 2 15% Lab 25% Suggested References ------------- 1. Handbook of Electromagnetic Compatibility, Reinaldo Perez, ed., Academic Press, 1995. 2.Principles and Techniques of Electromagnetic Compatibility, Christos Christopoulos, CRC Press, 1995. 3.EMC: Electromagnetic Theory to Practical Design, P.A. Chatterton and M.A. Houlden, John Wiley & Sons, 1992. 4.Electromagnetic Compatibility: Principles and Applications, David A. Weston, Marcel Dekker, Inc., 1991. 5.Grounding and Shielding Techniques in Instrumentation, Ralph Morrison, John Wiley & Sons, 1967. 6.EMI Suppression Handbook, William D. Kimmel and Daryl D. Gerke, Seven Mountains Scientific, Inc., 1998. 7.Principles of Electromagnetic Compatibility, Bernhard Keiser, Artech House, 1987.

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samual jackson barnett elements of electromagnetic theory (1903)英文版电力电磁电气工程教程教材电子版

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