Tunnel diode oscillator for 0.001 ppm measurements at low temperatures

Degrift, Craig T. Van

doi:10.1063/1.1134272

Cited by 218 publications

(109 citation statements)

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“…To detect changes in the low-energy quasiparticle excitations, we measure the magnetic penetration depth l at low temperatures, a fundamental property of superconductors whose T-dependence is directly related to the excited quasiparticles. Tunnel diode oscillators (TDOs) 19,20 in 3 He and dilution refrigerators operating at 13 MHz are used to measure the temperature dependence of l down to 0.4 K and 80 mK, respectively 21,22 . The frequency shift of the TDO is also used to determine the bulk superconducting transition of each crystal.…”

Section: Resultsmentioning

confidence: 99%

Disorder-induced topological change of the superconducting gap structure in iron pnictides

et al. 2014

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In superconductors with unconventional pairing mechanisms, the energy gap in the excitation spectrum often has nodes, which allow quasiparticle excitations at low energies. In many cases, such as in d-wave cuprate superconductors, the position and topology of nodes are imposed by the symmetry, and thus the presence of gapless excitations is protected against disorder. Here we report on the observation of distinct changes in the gap structure of ironpnictide superconductors with increasing impurity scattering. By the successive introduction of nonmagnetic point defects into BaFe 2 (As 1 À x P x ) 2 crystals via electron irradiation, we find from the low-temperature penetration depth measurements that the nodal state changes to a nodeless state with fully gapped excitations. Moreover, under further irradiation the gapped state evolves into another gapless state, providing bulk evidence of unconventional sign-changing s-wave superconductivity. This demonstrates that the topology of the superconducting gap can be controlled by disorder, which is a strikingly unique feature of iron pnictides.

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Section: Resultsmentioning

confidence: 99%

Disorder-induced topological change of the superconducting gap structure in iron pnictides

et al. 2014

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“…An external dc magnetic field (0 − 7 kOe) was applied parallel to the ac field (∼ 5 mOe). The oscillator frequency shift ∆f = f (T ) − f (T min ) is proportional to the ac susceptibility and, therefore, to the change in penetration depth, ∆λ = λ(B, T ) − λ(B, T min ) via ∆f = −G∆λ, where G is a calibration constant [13,14]. For an ac magnetic field along the c-axis, only ab-plane rf screening currents are excited.…”

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confidence: 99%

“…We compare data in [12] and N b (T c ∼ 9.3 K). The penetration depth was measured with an 11 M Hz tunnel-diode driven LC resonator [13,14] mounted in a 3 He refrigerator. An external dc magnetic field (0 − 7 kOe) was applied parallel to the ac field (∼ 5 mOe).…”

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confidence: 99%

Campbell penetration depth of a superconductor in the critical state

et al. 2003

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The magnetic penetration depth λ(T, H, j) was measured in the presence of a slowly relaxing supercurrent, j. In single crystal Bi2Sr2CaCu2O8 below approximately 25 K, λ(T, H, j) is strongly hysteretic. We propose that the irreversibility arises from a shift of the vortex position within its pinning well as j changes. The Campbell length depends upon the ratio j/jc where jc is the critical current defined through the Labusch parameter. Similar effects were observed in other cuprates and in an organic superconductor.

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“…By utilizing a tunnel-diode-oscillator (TDO) based technique [17], precise measurements of London penetration depth ∆λ(T ) were carried out in a 3 He cryostat down to 0.45 K, and in a dilution refrigerator with a base temperature of about 0.06 K. Due to the flat needle like shape of the crystals, samples were cut into typical sizes of (250 − 450) × (250 − 450) × (50 − 150) µm 3 with the plane being parallel to the chain direction. The sample was mounted on a sapphire rod so as to be inserted into the coil without any contact.…”

Section: Methodsmentioning

confidence: 99%

Evidence for nodal superconductivity in a layered compound Ta₄Pd₃Te₁₆

Pang

Smidman

Jiao

et al. 2018

J. Phys.: Condens. Matter

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We report an investigation of the London penetration depth ∆λ(T ) on single crystals of the layered superconductor Ta4Pd3Te16, where the crystal structure has quasi-one-dimensional characteristics. A linear temperature dependence of ∆λ(T ) is observed for T ≪ Tc, in contrast to the exponential decay of fully gapped superconductors. This indicates the existence of line nodes in the superconducting energy gap. A detailed analysis shows that the normalized superfluid density ρs(T ), which is converted from ∆λ(T ), can be well described by a multigap scenario, with nodes in one of the superconducting gaps, providing clear evidence for nodal superconductivity in Ta4Pd3Te16. * msmidman@zju.edu.cn † hqyuan@zju.edu.cn I. INTRODUCTIONRecently the layered Pd-based ternary chalcogenides have attracted much research interest. New compounds with similar crystal structures were discovered, which opened up new opportunities to investigate the relationship between superconductivity and reduced crystal dimensionality [1][2][3]. Unusual superconducting properties were revealed in Ta 2 Pd x S 5 (x 1.0) and Nb 2 Pd 0.81 S 5 , where extremely large upper critical fields of µ 0 H c2 (0) = 31 T and µ 0 H c2 (0) = 37 T were observed respectively, both of which are almost twice the size of the Pauli limiting field (H P ) [4,5]. These are reminiscent of the quasi-one-dimensional (Q1D) organic compounds (TMTSF) 2 X (TMTSF = tetramethyltetraselenafulvalene, X = PF 6 , ClO 4 ), which are believed to be unconventional superconductors [6,7]. Moreover, subsequent specific heat measurements in Nb 2 Pd(S 1−x Se x ) and Ta 2 PdSe 5 show a slight deviation from the typical behavior of single band s-wave superconductors, which likely indicates multi-band superconductivity in these systems [8,9].A new layered Pd-based ternary compound Ta 4 Pd 3 Te 16 was found to exhibit superconductivity at T c ≈4.6 K [10]. It possesses a layered crystal structure as well as quasi-one-dimensional (Q1D) characteristics, with chains running along the b axis. Band structure calculations for Ta 4 Pd 3 Te 16 reveal that its Fermi surface consists of four branches, including two one-dimensional nested sheets, a two-dimensional cylindrical sheet and a three-dimensional one, which drives this compound to be an anisotropic but three-dimensional metal [11]. This is also consistent with the results of upper critical field measurements where a moderate anisotropy of µ 0 H c2 was observed and the coherence lengths along all three axes are much larger than the interchain distance [12]. High field measurements uncover a quasi-linear magnetoresistance without any sign of saturation up to about 50 T, as well as a violation of Kohler's rule, indicating the existence of charge density wave (CDW) fluctuations in this compound [13], which has also been suggested from scanning tunneling spectroscopy (STS) experiments [14]. Meanwhile, there have also been various studies to characterize the superconducting order parameter, which could give the crucial information about the pairing mecha...

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Tunnel diode oscillator for 0.001 ppm measurements at low temperatures

Cited by 218 publications

References 10 publications

Disorder-induced topological change of the superconducting gap structure in iron pnictides

Disorder-induced topological change of the superconducting gap structure in iron pnictides

Campbell penetration depth of a superconductor in the critical state

Evidence for nodal superconductivity in a layered compound Ta₄Pd₃Te₁₆

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Tunnel diode oscillator for 0.001 ppm measurements at low temperatures

Cited by 218 publications

References 10 publications

Disorder-induced topological change of the superconducting gap structure in iron pnictides

Disorder-induced topological change of the superconducting gap structure in iron pnictides

Campbell penetration depth of a superconductor in the critical state

Evidence for nodal superconductivity in a layered compound Ta4Pd3Te16

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Product

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Evidence for nodal superconductivity in a layered compound Ta₄Pd₃Te₁₆