The superconducting properties of high purity niobium

Stromberg, T. F.

doi:10.31274/rtd-180813-2251

Cited by 2 publications

(3 citation statements)

References 12 publications

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“…1 where this length scale was determined from the direct EM imaging, providing further evidence of the importance of the film morphology in determining the magnetic response. Overall, our films show a much larger magnetic hysteresis compared to the bulk samples and single crystals [36,43]. However, a very large demagnetizing factor and thin-film geometry play a significant role in diminishing the interval and the magnitude of the reversible magnetic moment, which is proportional to a very small film volume, whereas irreversible Bean currents flow in the entire sample [44][45][46][47][48].…”

Section: Resultsmentioning

confidence: 82%

Quasiparticle spectroscopy, transport, and magnetic properties of Nb films used in superconducting transmon qubits

Joshi¹,

Ghimire²,

Tanatar³

et al. 2022

Preprint

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Niobium thin films on silicon substrate used in the fabrication of superconducting qubits have been characterized using scanning and transmission electron microscopy, electrical transport, magnetization, quasiparticle spectroscopy, and real-space real-time magneto-optical imaging. We study niobium films to provide an example of a comprehensive analytical set that may benefit superconducting circuits such as those used in quantum computers. The films show outstanding superconducting transition temperature of Tc = 9.35 K and a fairly clean superconducting gap, along with superfluid density enhanced at intermediate temperatures. These observations are consistent with the recent theory of anisotropic strong-coupling superconductivity in Nb. However, the response to the magnetic field is complicated, exhibiting significantly irreversible behavior and insufficient heat conductance leading to thermo-magnetic instabilities. These may present an issue for further improvement of transmon quantum coherence. Possible mitigation strategies are discussed.

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Section: Resultsmentioning

confidence: 82%

Quasiparticle spectroscopy, transport, and magnetic properties of Nb films used in superconducting transmon qubits

Joshi¹,

Ghimire²,

Tanatar³

et al. 2022

Preprint

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show abstract

“…2(c)], without breaking the reservoir's own superconductivity. Our choice, Niobium, as the large gap superconductor has a higher critical field (B 0 ∼ 0.82 T) compared to Tantalum (B 0 ∼ 0.08 T) [11][12][13]. Therefore Niobium can sustain the supercurrent that produce the magnetizing B field without breaking its own superconductivity.…”

Section: (B)mentioning

confidence: 97%

“…Niobium is also type II, and therefore it can enter a mixed state with normal vortices. It is still acceptable as the lower critical field above which Niobium enters a mixed state has been measured around 0.19 T [12,13], which is still higher than the critical field of Tantalum. We also assume that the Kapitza coupling [14][15][16] across the tunnel junctions can be avoided by carefully choosing the disordered tunnel barriers such that it causes phonon mismatch, and prevents phonon mediated heat transport.…”

Section: (B)mentioning

confidence: 98%

Superconducting Quantum Refrigerator: Breaking and Rejoining Cooper Pairs with Magnetic Field Cycles

2019

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We propose a solid state refrigeration technique based on repeated adiabatic magnetization/demagnetization cycles of a superconductor which acts as the working substance. The gradual cooling down of a substrate (normal metal) in contact with the working substance is demonstrated for different initial temperatures of the substrate. Excess heat is given to a hot large-gap superconductor. The on-chip refrigerator works in a cyclic manner because of an effective thermal switching mechanism: Heat transport between N/N versus N/S junctions is asymmetric because of the appearance of the energy gap. This switch permits selective cooling of the metal. We find that this refrigeration technique can cool down a 0.3cm 3 block of Cu by almost two orders of magnitude starting from 200mK, and down to about 1mK starting from the base temperature of a dilution fridge (10mK). The corresponding cooling power at 200mK and 10mK for a 1cm×1cm interface are 25 nW and 0.06 nW respectively, which scales with the area of the interface. arXiv:1902.00063v2 [cond-mat.supr-con]

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The superconducting properties of high purity niobium

Cited by 2 publications

References 12 publications

Quasiparticle spectroscopy, transport, and magnetic properties of Nb films used in superconducting transmon qubits

Quasiparticle spectroscopy, transport, and magnetic properties of Nb films used in superconducting transmon qubits

Superconducting Quantum Refrigerator: Breaking and Rejoining Cooper Pairs with Magnetic Field Cycles

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