Dependence of penetration depth, microwave surface resistance and energy gap of MgB<sub>2</sub> thin films on their normal-state resistivity

Jin, B. B.; Dahm, Thomas; Iniotakis, Christian; Gubin, A. I.; Choi, Eun Mi; Kim, Hyun Jung; Lee, Sung Ik; Kang, Won Nam; Wang, S. F.; Zhou, Yueliang; Pogrebnyakov, A. V.; Redwing, Joan M.; Xi, X. X.; Klein, N.

doi:10.1088/0953-2048/18/1/l01

Cited by 34 publications

(21 citation statements)

References 26 publications

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“…By fitting the curve, the conductance contributions from the and bands are calculated to be about 89% and 11%, respectively. is consistent with the estimation obtained from other method [11]. Fig.…”

Section: B I-v and Di/dv-v Characteristicssupporting

confidence: 92%

Study of the Josephson Current of ${\rm MgB}_{2}/{\rm Insulator/Pb}$ Tunnel Junctions

Chen

2009

IEEE Trans. Appl. Supercond.

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We have fabricated MgB 2 Insulator Pb Josephson tunnel junctions on MgB 2 films deposited by hybrid physical-chemical vapor deposition using native oxide as the tunnel barrier. For the critical current of the junction onMgB 2 (0001) film, its temperature dependence follows the Ambegaokar-Baratoff relation and its magnetic field dependence exhibits a Fraunhofer pattern. From analysing the magnetic field dependence of the critical current of the junction on -axis tilted MgB 2 film, we find small contribution of the Josephson current from the -plane tunneling, which may suggest a phase difference between the order parameters of MgB 2 and bands.

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Section: B I-v and Di/dv-v Characteristicssupporting

confidence: 92%

Study of the Josephson Current of ${\rm MgB}_{2}/{\rm Insulator/Pb}$ Tunnel Junctions

Chen

2009

IEEE Trans. Appl. Supercond.

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“…From the period of the oscillation the London penetration depth of the MgB 2 film in c-axis is estimated to be 35 nm, consistent with theoretical prediction 25 and prior experimental measurements. 26 In contrast with the ideal Fraunhofer pattern, the minima of I c ͑B͒ do not reach zero and the oscillation amplitude does not decay monotonically at high field, indicating a nonuniform current distribution over the junction area. This may partially be due to that the Josephson penetration depth of this junction ͑20 m͒ is comparable to the length of the junction ͑20 m͒ ͑Ref.…”

Section: 18mentioning

confidence: 85%

High-Jc MgB2 Josephson junctions with operating temperature up to 40 K

Chen

Zhuang

et al. 2010

Applied Physics Letters

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Sandwich-type MgB 2 / MgO/ MgB 2 Josephson junctions with Au or MgB 2 interconnection were fabricated using hybrid physical-chemical vapor deposited MgB 2 thin films and RF-magnetron-sputtered MgO barrier. The junctions show properties similar to those in high-J c Nb junctions with J c up to 275 kA/ cm 2 at 4 K, which remains nonzero up to 40 K. Critical current modulations by applied magnetic field and constant voltage steps under microwave radiation were observed. Combined with the larger energy gaps in MgB 2 than in Nb, the junctions presented here allow simple MgB 2 digital circuits to work over 20 K or with a clock speed above 1 THz. © 2010 American Institute of Physics. ͓doi:10.1063/1.3298366͔Superconducting integrated circuits using Josephson junctions have higher speed and lower power consumption than semiconductor circuits.1-3 However, the only mature technology uses Nb ͑critical temperature T c = 9.25 K͒, which requires a low operating temperature of about 4 K. Superconducting circuits using the 40 K superconductor MgB 2 can operate above 20 K ͑Ref. 4͒ cooled by more efficient, more compact, and less costly cryocoolers than those used at 4 K. 5Such a breakthrough requires fabrication technologies for MgB 2 Josephson junctions with high critical current density J c and multilayers consisting of superconducting, insulating and resistive films. There have been reports of Josephson junctions with one MgB 2 and one low-T c superconductor electrodes, 6-8 which cannot operate above the lower T c . All-MgB 2 weak-link junctions 9-13 are not ideal for integrated circuits. All-MgB 2 sandwich-type Josephson junctions have been reported, 14-16 some with near-ideal Fraunhofer patterns, however, the J c values are very low and drop quickly to zero at 20-25 K. In this letter, we report MgB 2 / MgO/ MgB 2 sandwich-type Josephson junctions with high J c up to 275 kA/ cm 2 at 4 K, which remains nonzero up to 40 K. The ultimate speed limit of Josephson junction-based rapid single flux quantum ͑RSFQ͒ circuits is proportional to the product I c R n , where I c is the critical current and R n the resistance of the junction in the normal state.1 To eliminate hysteresis in I − V characteristics, tunnel junctions in RSFQ circuits are usually critically damped by an external shunt resistor, and the maximum circuit speed is approximately proportional to J c 1/2 . 17 The highest operating speed for Nb circuit, 770 GHz, has been demonstrated by an RSFQ toggle flip-flop ͑TFF͒ frequency divider with J c greater than 60 kA/ cm 2 . 18 The energy gap in MgB 2 ͑ϳ2.2 meV for the smaller of the two gaps 19 ͒ is larger than that of Nb ͑ϳ1.5 meV͒, implying a limiting clock speed for MgB 2 digital circuits of above 1 THz. 2,18The structure of the MgB 2 / MgO/ MgB 2 sandwich-type Josephson junctions were illustrated in Fig. 1͑a͒. A 100 nmthick MgB 2 film was first grown on a SiC͑0001͒ substrate by hybrid physical-chemical vapor deposition ͑HPCVD͒ 20 at 710°C under conditions similar to those described in Ref. 8. The root-mean-square roughness...

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“…For this reason the nonlinear coefficient in MgB 2 becomes smaller than the one for YBCO at about 27 K. However, due to the presence of the small gap the nonlinear response in MgB 2 is The foregoing analysis has been made in the clean limit without any impurity scattering. However, in most current MgB 2 films, the scattering rate as judged from the residual resistivity is larger than the two gaps [9]. For this reason, in the following we also want to discuss the dirty limit.…”

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confidence: 99%

Nonlinear microwave response of MgB2

Dahm

Scalapino

2004

Applied Physics Letters

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We calculate the intrinsic nonlinear microwave response of the two gap superconductor MgB2 in the clean and dirty limits. Due to the small value of the π band gap, the nonlinear response at low temperatures is larger than for a single gap Bardeen-Cooper-Schrieffer (BCS) s-wave superconductor with a transition temperature of 40 K. Comparing this result with the intrinsic nonlinear d-wave response of YBa2Cu3O7 (YBCO) we find a comparable response at temperatures around 20 K. Due to its two gap nature, impurity scattering in MgB2 can be used to reduce the nonlinear response if the scattering rate in the π band is made larger than the one in the σ band.

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Dependence of penetration depth, microwave surface resistance and energy gap of MgB₂ thin films on their normal-state resistivity

Cited by 34 publications

References 26 publications

Study of the Josephson Current of ${\rm MgB}_{2}/{\rm Insulator/Pb}$ Tunnel Junctions

Study of the Josephson Current of ${\rm MgB}_{2}/{\rm Insulator/Pb}$ Tunnel Junctions

High-Jc MgB2 Josephson junctions with operating temperature up to 40 K

Nonlinear microwave response of MgB2

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Dependence of penetration depth, microwave surface resistance and energy gap of MgB2 thin films on their normal-state resistivity

Cited by 34 publications

References 26 publications

Study of the Josephson Current of ${\rm MgB}_{2}/{\rm Insulator/Pb}$ Tunnel Junctions

Study of the Josephson Current of ${\rm MgB}_{2}/{\rm Insulator/Pb}$ Tunnel Junctions

High-Jc MgB2 Josephson junctions with operating temperature up to 40 K

Nonlinear microwave response of MgB2

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Dependence of penetration depth, microwave surface resistance and energy gap of MgB₂ thin films on their normal-state resistivity