Penetration depth in conventional layered superconductors: A proximity-effect model

Zhao, Songqing; Yang, Qs

doi:10.1103/physrevb.59.14630

Cited by 6 publications

(3 citation statements)

References 27 publications

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“…In Table IV, H c and ρ n,fit decrease as the Al thickness increases. This result is consistent with previous reports [51][52][53][54] . Note that λ 0 of Al-5L is longer than that of Al-0L, although the proximity effect is expected to reduce λ 0 (Refs.…”

Section: The Proximity Effectsupporting

confidence: 94%

Engineering nonlinear response of superconducting niobium microstrip resonators via aluminum cladding

Kwon

Tang

Mohebbi³

et al. 2019

Journal of Applied Physics

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In this work, we find that Al cladding on Nb microstrip resonators is an efficient way to suppress nonlinear responses induced by local Joule heating, resulting in improved microwave power handling capability. This improvement is likely due to the proximity effect between the Al and the Nb layers. The proximity effect is found to be controllable by tuning the thickness of the Al layer. We show that improving the film quality is also helpful as it enhances the microwave critical current density, but it cannot eliminate the local heating.

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Section: The Proximity Effectsupporting

confidence: 94%

Engineering nonlinear response of superconducting niobium microstrip resonators via aluminum cladding

Kwon

Tang

Mohebbi³

et al. 2019

Journal of Applied Physics

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“…In previous work, we found that the total magnetic susceptibility of superconducting Al layers fabricated on Bi2Se3 was much lower than that of similar Al layers fabricated on bare oxidized silicon [23], indicating that the inverse proximity effect of the bulk states in the Bi2Se3 suppressed superconductivity. The bulk of 3D-HgTe could potentially be conducting due to dislocations or doping; in the presence of high bulk conduction of the normal layer, the inverse proximity effect is expected to manifest as suppressed superfluid density of the bilayer [23,[47][48][49]. However, in the absence of bulk conduction, the total superfluid density of a Nb/3D-HgTe bilayer is expected to be close to that of the Nb layer alone.…”

mentioning

confidence: 99%

Nonsinusoidal Current-Phase Relationship in Josephson Junctions from the 3D Topological Insulator HgTe

et al. 2015

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We use Superconducting QUantum Interference Device (SQUID) microscopy to characterize the current-phase relation (CPR) of Josephson Junctions from 3-dimentional topological insulator HgTe (3D-HgTe). We find clear skewness in the CPRs of HgTe junctions ranging in length from 200 nm to 600 nm. The skewness indicates that the Josephson current is predominantly carried by Andreev bound states with high transmittance, and the fact that the skewness persists in junctions that are longer than the mean free path suggests that the effect may be related to the helical nature of the Andreev bound states in the surface of HgTe.Topological insulators (TI) have a special band structure with important consequences for proximity-induced superconductivity. In 3-dimentional topological insulators (3D-TI), the inversion of the conduction and valence bands leads to conducting 2D surface states with energies that are linearly proportional to their momenta [1][2][3][4][5]. Spinmomentum locking protects the charge carriers at the surface against elastic backscattering [6,7]. These special properties are reflected in the superconducting proximity effect in an S/3D-TI bilayer or an S/TI/S junction, which may host Majorana fermions in a quasi-1D channel or vortex core [8][9][10]. Most previous works characterized current-voltage characteristics to determine the critical current's dependence on temperature, gate voltage, or magnetic field [11][12][13][14][15][16][17][18][19][20][21][22], while a few studies characterized the CPR [23,24].Here, we use a scanning SQUID microscope to perform contactless measurements of the diamagnetic response of Nb/HgTe bilayers and of the CPR of Nb/HgTe/Nb junctions. In contrast to previous CPR results [23,24], we find no evidence for bulk states, 2 and we observe that the CPRs of many junctions of different sizes consistently exhibit forward skewness.The CPR in an S/TI/S junction is a key diagnostic [8,[25][26][27][28][29][30][31][32]. Weak disorder in the TI far from the superconducting contacts theoretically does not affect the induced superconducting state [33,34]; therefore, Andreev bound states should form in hightransmittance surface channels [8,26,27,29,31]. A CPR with forward skewness -that is, a deviation from a perfect sinusoidal form -is a signature of such high-transmittance Andreev bound states [35][36][37].To our knowledge, there have not been direct observations of forward skewed CPRs in topological insulators [23,24], although the skewness has been indirectly inferred [24] from the Fraunhofer interference pattern. Previous CPR experiments in topological insulators [23,24] were complicated in part by bulk states, self-inductance effects, and bias voltage, factors that are eliminated in this work.Moreover, a skewed CPR can also result from ballistic transport [35]. Measurements in metallic break junctions showed that the CPR approaches the predictions for quantum point contacts in the ballistic limit [38]. In metallic atomic point contacts, the CPR was significantly skewed only in contacts wi...

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“…The variable θ(x, E) is complex and ranges in magnitude from 0 to π/2. The Usadel equations [31]- [33] are…”

Section: Theory Of a Proximity Bilayermentioning

confidence: 99%

Electromagnetic Properties of Aluminum-Based Bilayers for Kinetic Inductance Detectors

Zhang

Barry

Cecil

et al. 2023

IEEE Trans. Appl. Supercond.

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The complex conductivity of a superconducting thin film is related to the quasiparticle density, which depends on the physical temperature and can also be modified by external pair breaking with photons and phonons. This relationship forms the underlying operating principle of Kinetic Inductance Detectors (KIDs), where the detection threshold is governed by the superconducting energy gap. We investigate the electromagnetic properties of thin-film aluminum that is proximitized with either a normal metal layer of copper or a superconducting layer with a lower TC , such as iridium, in order to extend the operating range of KIDs. Using the Usadel equations along with the Nam expressions for complex conductivity, we calculate the density of states and the complex conductivity of the resulting bilayers to understand the dependence of the pair breaking threshold, surface impedance, and intrinsic quality factor of superconducting bilayers on the relative film thicknesses. The calculations and analyses provide theoretical insights in designing aluminum-based bilayer kinetic inductance detectors for detection of microwave photons and athermal phonons at the frequencies well below the pair breaking threshold of a pure aluminum film.

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Penetration depth in conventional layered superconductors: A proximity-effect model

Cited by 6 publications

References 27 publications

Engineering nonlinear response of superconducting niobium microstrip resonators via aluminum cladding

Engineering nonlinear response of superconducting niobium microstrip resonators via aluminum cladding

Nonsinusoidal Current-Phase Relationship in Josephson Junctions from the 3D Topological Insulator HgTe

Electromagnetic Properties of Aluminum-Based Bilayers for Kinetic Inductance Detectors

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