共查询到20条相似文献,搜索用时 15 毫秒
1.
Nb/Al-AlOx/Nb tunnel junctions are often used in the studies of macroscopic quantum phenomena and superconducting qubit applications of the Josephson devices. In this work, we describe a convenient and reliable process using electron beam lithography for the fabrication of high-quality, submicron-sized Nb/Al-AlOx/Nb Josephson junctions. The technique follows the well-known selective Nb etching process and produces high-quality junctions with Vm=100 mV at 2.3 K for the typical critical current density of 2.2 kA/cm^2, which can be adjusted by controlling the oxygen pressure and oxidation time during the formation of the tunnelling barrier. We present the results of the temperature dependence of the sub-gap current and in-plane magnetic-field dependence of the critical current, and compare them with the theoretical predictions. 相似文献
2.
Nb/Al-AlOx/Nb tunnel junctions with controllable critical current density Jc are fabricated using the standard selective Nb etching process.Tunnel barriers are formed in different oxygen exposure conditions (oxygen pressure P and oxidation time t),giving rise to Jc ranging from 100 A/cm2 to above 2000 A/cm2.Jc shows a familiar linear dependence on P × t in logarithmic scales.We calculate the energy levels of the phaseand flux-type qubits using the achievable junction parameters and show that the fabricated Nb/Al-AlOx/Nb tunnel junctions can be used conveniently for quantum computation applications in the future. 相似文献
3.
D. Cassel G. Pickartz M. Siegel E. Goldobin H. H. Kohlstedt A. Brinkman A. A. Golubov M. Yu. Kupriyanov H. Rogalla 《Physica C: Superconductivity and its Applications》2001,350(3-4):276-290
The transparency of the tunnel barriers in double-barrier junctions influences the critical current density and the form of the current–voltage characteristics (IVC). Moreover, the barrier asymmetry is an important parameter, which has to be controlled in the technological process. We have performed a systematic study of the influence of the barrier transparency on critical current, IC, and normal resistance, RN, by preparing SIS and SINIS junctions under identical technological conditions and comparing their transport properties. We have fabricated Nb/Al2O3/Nb and Nb/Al2O3/Al/Al2O3/Nb devices with different current densities using a conventional fabrication process, varying pressure and oxidation time. The thickness of the Al middle electrode in all Nb/Al2O3/Al/Al2O3/Nb junctions was 6 nm. Patterning of the multilayers was done using conventional photolithography and the selective niobium etching process. The current density of SIS junctions was changed in the range from 0.5 to 10 kA/cm2. At the same conditions the current density of SINIS devices revealed 1–100 A/cm2 with non-hysteretic IVC and characteristic voltages, ICRN, of up to 200 μV. By comparing the experimental and theoretical temperature dependence of the ICRN product we estimated the barrier transparency and its asymmetry. The comparison shows a good agreement of experimental data with the theoretical model of tunneling through double-barrier structures in the dirty limit and provides the effective barrier transparency parameter γeff≈300. A theoretical framework is developed to study the influence of the barrier asymmetry on the current–phase relationship and it is proposed to determine the asymmetry parameter by measuring the critical current suppression as function of applied microwave power. The theoretical approach to determine the non-stationary properties of double-barrier junctions in the adiabatic regime is formulated and the results of calculations of the I–V characteristics are given in relevant limits. The existence and the magnitude of a current deficit are predicted as function of the barrier asymmetry. 相似文献
4.
I. Puica V. Popescu P. Mazzetti A. Stepanescu Gh. Ciobanu 《Physica C: Superconductivity and its Applications》1997,290(3-4):303-310
The 1/f voltage noise in bulk polycrystalline high-temperature superconductors (HTSC) under bias current and magnetic field has its origin in the noise current-dependence of the grain boundary junctions (GBJs), due in turn to the correlated effects of junction critical current and normal resistance fluctuations. The analogy between the results obtained by varying the bias current through the specimen and those performed with temperature as variable is evidenced. The noise maxima obtained in both sets of measurements turn out to be caused by the junction critical current fluctuations, which dominate when the currents flowing through the GBJs are close to the Josephson critical current. The anti-phase correlation between the normal resistance and the critical current fluctuations is responsible for the monotonical decrease of the noise at constant bias current, with the temperature exceeding the value corresponding to the noise maximum. In contrast, varying the bias current at fixed temperature, the voltage noise exhibits a local minimum followed by an increasing tendency after passing through the maximum. 相似文献
5.
A. Di Chiara G. Peluso G. Pepe U. Scotti di Uccio F. C. Matacotta R. Mele E. Olzi 《Il Nuovo Cimento D》1988,10(7):863-867
Summary Preparation procedure and sample characterization of 112 BiSCCO pellets exhibiting high-T
c superconductivity are discussed. TypicalI–V and dV/dI curves of Nb/BiSCCO point conctact junctions at various temperatures are presented. 相似文献
6.
《Physica C: Superconductivity and its Applications》2001,350(3-4):187-192
Double-barrier highly asymmetric Nb–Al oxide–Al–Nb oxide–Nb structures with reproducible characteristics were fabricated. The heterocontacts with the middle Al layer thickness ranging from 4 to 6 nm exhibited a well-defined d.c. Josephson supercurrent Ic at 4.2 K and characteristic voltages Vc=IcRN (RN is the normal resistance, Vc defines the response time of the junction) from 0.3 to 0.4 mV. Two prominent features in the quasiparticle current–voltage curves have been observed: a so-called ‘knee' in the energy-gap region and an additional (to the linear voltage dependence) current at higher biases. They are discussed within a simple Landauer–Büttiker scattering approach to the phase-coherent quasiparticle transport in a quasiballistic S–I1–N–I2–S heterostructure with an extremely great difference between the barrier transparencies. 相似文献
7.
8.
Summary The recent improvements in the fabrication technology have succeeded in obtaining high-quality Josephson tunnel junctions.
TheI–V characteristics of these junctions exhibit now lesser and lesser differences from the theoretical predictions. The various
figures of merit, so far introduced to qualify the junctions, appear now focused on too limited aspects and a direct comparison
with the detailed prediction of the theory is in order. For this awaken interest in the detailed predictions of the BCS theory,
we have revisited the relevant formulae for the quasi-particle tunnelling current. A detailed discussion of the analytical
transformation necessary for a simple numerical evaluation of this current is reported. SeveralI–V curves are obtained using the parameter values corresponding to the case of Nb-based junctions, which is the actual running
technology. Peculiar interesting aspects are outlined. 相似文献
9.
Toshiyuki Usagawa Jianguo Wen Tadashi Utagawa Satoshi Koyama Youichi Enomoto 《Physica C: Superconductivity and its Applications》2000,340(4):269-275
We report on I–V characteristics for in situ formed Nb/Au/(1 1 0)YBa2Cu3O7−δ (YBCO) Josephson junction, where the homoepitaxial (1 1 0)YBCO film shows ultra-smooth surface morphology. The field dependence of critical supercurrent Ic shows anisotropic large junction behavior with normal Fraunhofer patterns expected from BCS model of dx2−y2 wave superconductors. This strongly suggests that the Nb/Au/(1 1 0)YBCO junctions cannot be regarded as atomic scaled corner junctions, in contrast with (0 0 1)/(1 1 0)YBCO grain boundary junctions to show “π-junction” with a pronounced dip near zero fields in field modulation of Ic. 相似文献
10.
11.
C. Hoffmann F. Lefloch M. Sanquer 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(4):629-633
We studied electronic relaxation in long diffusive superconductor/normal metal/superconductor (S/N/S) junctions by means of
current noise and transport measurements down to very low temperature (100mK). Samples with normal metal lengths of 4, 10
and 60μm have been investigated. In all samples the shot noise increases very rapidly with the voltage. This is interpreted
in terms of enhanced heating of the electron gas confined between the two S/N interfaces. Experimental results are analyzed
quantitatively taking into account electron-phonon interaction and heat transfer through the S/N interfaces. Transport measurements
reveal that in all samples the two S/N interfaces are connected incoherently, as shown by the reentrance of the resistance
at low temperature. The complementarity of noise and transport measurements allows us to show that the energy dependence of
the reentrance at low voltage is essentially due to the increasing effective temperature of the quasiparticles in the normal
metal.
Received 5 February 2002 / Received in final form 6 September 2002 Published online 31 October 2002
RID="a"
ID="a"e-mail: hoffmann@drfmc.ceng.cea.fr 相似文献
12.
在超导中通过外加塞曼磁场,研究正常金属/超导/正常金属双隧道结中的量子相干输运。同时考虑从一个正常金属电极注入一电子,从另一个正常金属电极注入一空穴,推导出系统的微分电导的一般公式。研究表明,电导谱随偏压展示振荡行为,随着温度和磁场的增大,其振荡振幅被降低,且塞曼能可导致电导峰的塞曼劈裂。在隧道极限下,超导体中会形成一系列束缚态。 相似文献
13.
14.
Zeeman effects on Josephson current in d-wave superconductor/d-wave superconductor junctions 下载免费PDF全文
This paper solves a self-consistent equation for the d-wave
superconducting gap and the effective exchange field in the
mean-field approximation, and studies the Zeeman effects on the
d-wave superconducting gap and thermodynamic potential. The Josephson
currents in the d-wave superconductor(S)/insulating layer(I)/d-wave S
junctions are calculated as a function of the temperature, exchange
field, and insulating barrier strength under a Zeeman magnetic field
on the two d-wave Ss. It is found that the Josephson critical
currents in d-wave S/d-wave S junction to a great extent depend on
the relative orientation of the effective exchange field of the two S
electrodes, and the crystal orientation of the d-wave S. The exchange
field under certain conditions can enhance the Josephson critical
current in a d-wave S/I/d-wave S junction. 相似文献
15.
A large positive magnetoresistance (MR) has been found in micro-sized Fex–C1−x composites. At a magnetic field of 5 T, the Fe0.2–C0.8 composite has the largest MR, 53.8% and 190% at room temperature and at 5 K, respectively. The magnetic field dependence of the MR can be described approximately as MR∝Bn, and the value of exponent n is determined by the Fe weight concentration and temperature, ranging from 1/4 to 6/4. It appears that Fex–C1−x has a linear field dependence of the positive MR at different temperatures. The possible mechanism for the positive MR is discussed. 相似文献
16.
E.S. Otabe M. Kiuchi S. Kawai Y. Morita J. Ge B. Ni Z. Gao L. Wang Y. Qi X. Zhang Y. Ma 《Physica C: Superconductivity and its Applications》2009,469(21):1940-1944
The critical current densities of polycrystalline bulk SmFeAsO1−xFx prepared by the powder-in-tube (PIT) method and by a conventional solid-state reaction were investigated using the remnant magnetic moment method and Campbell’s method. Two types of shielding current, corresponding to global and local critical current densities Jc were observed using both measurement methods. The global and local Jc were on the order of 107 A/m2 and 1010 A/m2 at 5 K, respectively. The local Jc decreased slightly with increasing magnetic field. The global Jc was independent of the preparation method, while the local Jc was larger for samples prepared by PIT than for those prepared by solid-state reaction. 相似文献
17.
S. Piano J. W.A. Robinson G. Burnell M. G. Blamire 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(2):123-126
The physics of the π phase shift in ferromagnetic
Josephson junctions may enable a range of applications for
spin-electronic devices and quantum computing. We investigate
transitions from “0” to “π” states in Nb/Fe/Nb Josephson
junctions by varying the Fe barrier thickness from 0.5 nm to 5.5 nm. From magnetic measurements we estimate for Fe a magnetic
dead
layer of about 1.1 nm. By fitting the characteristic voltage
oscillations with existing theoretical models we extrapolate an
exchange energy of 256 meV, a Fermi velocity of 1.98 ×105
m/s and an electron mean free path of 6.2 nm, in agreement with
other reported values. From the temperature dependence of the
ICRN product we show that its decay rate exhibits a nonmonotonic
oscillatory behavior with the Fe barrier thickness. 相似文献
18.
P. Michalowski M. Schmidt F. Schmidl V. Grosse D. Kuhwald C. Katzer U. Hübner P. Seidel 《固体物理学:研究快报》2011,5(8):268-270
We prepared and investigated grain boundary Josephson junctions based on SrTiO3 bicrystal substrates. During the deposition of YBa2Cu3O7–δ (YBCO) gold nanocrystals forming from an intermediate gold layer can modify the crystalline structure and thus the properties of the YBCO grain boundaries. The variation of the film thickness of the Au seed layer changes the growth conditions of the YBCO film and the Au nanocrystals. The values of the characteristic ICRN product do not change whereas the values of the critical current IC decrease.
19.
考虑到铁磁半导体和d波超导体中空穴的有效质量和费米速度错配,运用推广了的B londer-Tinkham-K lapw ijk(BTK)理论模型,研究了铁磁半导体/d波超导隧道结的电导谱。研究表明:(1)铁磁半导体和d波超导体中空穴的有效质量和费米速度错配对系统的微分电导影响显著;(2)铁磁半导体的磁交换能对Andreev反射有抑制作用。 相似文献
20.
由Bogoliubov-de Gennes方程得到铁磁超导共存态(FS)的自洽方程,利用推广的Furusaki-Tsukada的电流公式计算了铁磁超导态/绝缘层/自旋三重态p波超导体(FS/I/p)结的直流Josephson电流随结的温度、相位差以及FS中磁交换能、结界面的势垒散射强度的变化关系.研究表明:FS中磁交换能、结界面的势垒散射均抑制FS/I/p结的直流Josephson电流.当自旋三重态超导体具有px波配对势时,自旋三重态超导体结的直流Josephson电流随结两侧相位差的振荡周期是π.
关键词:
铁磁超导态
自旋三重态超导体
p波超导体
直流Josephson电流 相似文献