Scanning SQUID susceptometry of a paramagnetic superconductor

Kirtley, J. R.; Kalisky, Beena; Bert, Julie A.; Bell, C. H.; Kim, Minu; Hikita, Y.; Hwang, Harold Y.; Ngai, J. H.; Segal, Y.; Walker, Frederick J.; Ahn, Charles; Moler, Kathryn A.

doi:10.1103/physrevb.85.224518

Cited by 53 publications

(46 citation statements)

References 30 publications

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“…In Fig. 2D, the solid line is a fit to the SQUID susceptibility expression for a thin diamagnetic film, ϕðzÞ=ϕ s = ð−a=ΛÞð1 − 2 z= ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 + 4 z 2 p Þ, ϕðzÞ ≡ ΦðzÞ=IΦ 0 , where ΦðzÞ is the flux through the pickup loop, I is the current through the field coil, and z = z=a, using the Pearl length, Λ, as a fitting parameter (43). Taking a = 8.4 μm, the sensor self-inductance ϕ s = 800 1/A, and estimating a minimum height of the SQUID pickup loop above the sample surface z 0 = 2.5 μm, we obtain the Pearl length of ∼110 μm.…”

Section: Methodsmentioning

confidence: 99%

Ultrathin two-dimensional superconductivity with strong spin–orbit coupling

Nam

Chen

Liu

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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We report on a study of epitaxially grown ultrathin Pb films that are only a few atoms thick and have parallel critical magnetic fields much higher than the expected limit set by the interaction of electron spins with a magnetic field, that is, the Clogston-Chandrasekhar limit. The epitaxial thin films are classified as dirty-limit superconductors because their mean-free paths, which are limited by surface scattering, are smaller than their superconducting coherence lengths. The uniformity of superconductivity in these thin films is established by comparing scanning tunneling spectroscopy, scanning superconducting quantum interference device (SQUID) magnetometry, double-coil mutual inductance, and magneto-transport, data that provide average superfluid rigidity on length scales covering the range from microscopic to macroscopic. We argue that the survival of superconductivity at Zeeman energies much larger than the superconducting gap can be understood only as the consequence of strong spin-orbit coupling that, together with substrate-induced inversionsymmetry breaking, produces spin splitting in the normal-state energy bands that is much larger than the superconductor's energy gap.superconductivity is a topic of growing interest in contemporary condensed matter physics. Early experimental work in this field used granular thin films to study phase transitions to insulating normal states driven by weakened superfluid rigidity in the ultrathin film regime. Recent experimental progress (1-12) in epitaxial growth of uniform 2D superconductors whose properties are largely intrinsic has opened up new possibilities for the design of superconducting systems with specific desirable physical properties. Indeed, these almost ideal 2D systems have yielded (6, 12, 13) surprisingly robust superconductivity in films that are only one or two atomic layers thick, and very recently the observation of an astonishingly high T c in singlelayer FeSe on SrTiO 3 (14-17). In addition, because 2D superconductors must be placed on a substrate, they necessarily have broken inversion symmetry and Rashba-type spin-orbit interactions that break the spin degeneracy of quasiparticle levels in the normal state, and enable the possibility of achieving topological (18-21) superconducting states.Here, we investigate the superconducting properties of strong spin-orbit coupling 2D superconductors using epitaxially grown, ultrathin Pb films on Si. By establishing that the superfluid rigidity vanishes at essentially the same T c when measured on different length scales, from atomic to macroscopic (greater than millimeter), we demonstrate the uniformity of the superconductivity in our films and obtain highly reliable quantitative superfluid density (SFD) values. We then perform magneto-transport measurements in parallel fields, which clearly establish that the Clogston-Chandrasekhar (CC) limit does not apply to our films. Superconductivity at Zeeman fields well in excess of the superconducting energy gap can be understood only as a consequence of strong...

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Section: Methodsmentioning

confidence: 99%

Ultrathin two-dimensional superconductivity with strong spin–orbit coupling

Nam

Chen

Liu

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…Scanning SQUID experiments yield a very low value of the superfluid density in this system [57,58]. Although no comparison has been made with bulk doped STO, a tempting explanation for these low values is that only d xz /d yz heavy electrons (that appear at the underdoped end-point of the dome) pair thus naturally explaining that the superfluid density is low, most of the interfacial carriers being xy in character and not participating to the superfluid density.…”

Section: Bulk and Interface Superconductivitymentioning

confidence: 99%

Interface superconductivity

Gariglio

Gabay

Mannhart

et al. 2015

Physica C: Superconductivity and its Applications

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Low dimensional superconducting systems have been the subject of numerous studies for many years. In this article, we focus our attention on interfacial superconductivity, a field that has been boosted by the discovery of superconductivity at the interface between the two band insulators LaAlO 3 and SrTiO 3 .We explore the properties of this amazing system that allows the electric field control and on/off switching of superconductivity. We discuss the similarities and differences between bulk doped SrTiO 3 and the interface system and the possible role of the interfacially induced Rashba type spin-orbit. We also, more briefly, discuss interface superconductivity in cuprates, in electrical double layer transistor field effect experiments, and the recent observation of a high T c in a monolayer of FeSe deposited on SrTiO 3 .

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“…Hartree shifts in the 3d shell affect the band structure [15], and Rashba coupling at the interface may mix singlet and triplet pairing channels [5,16]. The superfluid density in the 2DEL is much lower than the normal-state Hall density, [11,17] suggesting that 2D fluctuations influence the superconducting properties [8,18]. Some experiments have reported evidence of magnetic order coexisting with, or phase segregated from, the superconducting phase [19][20][21][22].…”

Section: Introductionmentioning

confidence: 99%

Modulation of the superconducting critical temperature due to quantum confinement at the LaAlO3/SrTiO3 interface

et al. 2017

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Superconductivity develops in bulk doped SrTiO 3 and at the LaAlO 3 /SrTiO 3 interface with a dome-shaped density dependence of the critical temperature T c , despite different dimensionalities and geometries. We propose that the T c dome of LaAlO 3 /SrTiO 3 is a shape resonance due to quantum confinement of superconducting bulk SrTiO 3 . We substantiate this interpretation by comparing the exact solutions of a three-dimensional and quasi-two-dimensional two-band BCS gap equation. This comparison highlights the role of heavy bands for T c in both geometries. For bulk SrTiO 3 , we extract the density dependence of the pairing interaction from the fit to experimental data. We apply quantum confinement in a square potential well of finite depth and calculate T c in the confined configuration. We compare the calculated T c to transport experiments and provide an explanation as to why the optimal T c 's are so close to each other in two-dimensional interfaces and the three-dimensional bulk material.

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Scanning SQUID susceptometry of a paramagnetic superconductor

Cited by 53 publications

References 30 publications

Ultrathin two-dimensional superconductivity with strong spin–orbit coupling

Ultrathin two-dimensional superconductivity with strong spin–orbit coupling

Interface superconductivity

Modulation of the superconducting critical temperature due to quantum confinement at the LaAlO3/SrTiO3 interface

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