Double reentrant superconductor-insulator transition in thin TiN films

Hadacek, N.; Sanquer, M.; Villégier, J.C.

doi:10.1103/physrevb.69.024505

Cited by 67 publications

(79 citation statements)

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“…Extensive experimental research of critically disordered superconducting films revealed a wealth of unusual and striking phenomena, including nonmonotonic temperature and magnetic field dependence of the resistance [2,4,5,6], activated behavior of resistivity in the insulating state [1,5,6,7,8], nonmonotonic magnetic field dependence of the activation temperature, and the voltage threshold behavior [8,9,10]. These features find a theoretical explanation based on the concept of disorder-induced spatial inhomogeneity in the superconducting order parameter [10,11,12,13,14].…”

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Disorder-Induced Inhomogeneities of the Superconducting State Close to the Superconductor-Insulator Transition

et al. 2008

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Scanning tunneling spectroscopy at very low temperature on homogeneously disordered superconducting Titanium Nitride thin films reveals strong spatial inhomogeneities of the superconducting gap ∆ in the density of states. Upon increasing disorder, we observe suppression of the superconducting critical temperature Tc towards zero, enhancement of spatial fluctuations in ∆, and growth of the ∆/Tc ratio. These findings suggest that local superconductivity survives across the disorder-driven superconductor-insulator transition.PACS numbers: 74.50.+r, 74.78.Db, A pioneering idea that in the critical region of the superconductor-insulator transition (SIT) the disorderinduced inhomogeneous spatial structure of isolated superconducting droplets develops [1,2], grew into a new paradigm [3]. Extensive experimental research of critically disordered superconducting films revealed a wealth of unusual and striking phenomena, including nonmonotonic temperature and magnetic field dependence of the resistance [2,4,5,6], activated behavior of resistivity in the insulating state [1,5,6,7,8], nonmonotonic magnetic field dependence of the activation temperature, and the voltage threshold behavior [8,9,10]. These features find a theoretical explanation based on the concept of disorder-induced spatial inhomogeneity in the superconducting order parameter [10,11,12,13,14]. Numerical simulations confirmed that indeed in the high-disorder regime, the homogeneously disordered superconducting film breaks up into superconducting islands separated by an insulating sea [15,16]. At the same time the direct observation of superconducting islands near the SIT justifying the fundamental but yet hypothetical concept of the disorder-induced granularity on the firm experimental foundation was still lacking.In this Letter, we report on the combined low temperature Scanning Tunneling Spectroscopy (STS) and transport measurements performed on thin Titanium Nitride films on approach to the SIT. The local tunneling density of states (LDOS) measured at 50 mK reveals disorderinduced spatial fluctuations of the superconducting gap, ∆, with both, standard deviation σ to the average gap and the gap to the critical temperature ratios, σ/∆ and ∆/T c , respectively, increasing towards the transition.Our samples were thin TiN films synthesized by atomic layer chemical vapor deposition onto a Si/SiO 2 substrate. TiN1 was a 3.6 nm thick film deposited at 400• C while TiN2 and TiN3 were 5.0 nm thick films deposited at 350 • C. TiN3 was then slightly plasma etched in order to reduce its thickness. Electron transmission images revealed that the films comprise of the densely-packed crystallites with a typical size of 4 to 6 nm. The samples were patterned into the Hall bridges using conventional UV lithography and plasma etching. It is worth noticing that identically fabricated TiN films undergo the disorder-and magnetic field-driven SIT [4,8]. Transport measurements and STS were carried out during the same run in a STM attached to a dilution refrigerator. The STM Pt/Ir t...

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Disorder-Induced Inhomogeneities of the Superconducting State Close to the Superconductor-Insulator Transition

et al. 2008

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“…We find that nanopatterning enhances the role of the two-dimensional Coulomb interaction in the system transforming the originally insulating film into a more pronounced insulator. We observe magnetoresistance oscillations reflecting collective behaviour of the multiconnected nanopatterned superconducting film in the wide range of temperatures and uncover the physical mechanism of these oscillations as phase slips in superconducting weak link network.That a thin film of the same material can be a superconductor but can very well turn an insulator, is one of the most remarkable aspects of disordered superconductors [1][2][3][4][5][6][7]. The engine driving the transition between the superconducting and insulating states is disorder the effect of which is two-fold.…”

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“…That a thin film of the same material can be a superconductor but can very well turn an insulator, is one of the most remarkable aspects of disordered superconductors [1][2][3][4][5][6][7]. The engine driving the transition between the superconducting and insulating states is disorder the effect of which is two-fold.…”

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Nanopattern-stimulated superconductor-insulator transition in thin TiN films

Baturina

Vinokur²,

Mironov³

et al. 2011

EPL

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We present the results of the comparative study of the influence of disorder on transport properties in continuous and nanoperforated TiN films. We show that nanopatterning turns a thin TiN film into an array of superconducting weak links and stimulates both, the disorder-and magnetic field-driven superconductor-to-insulator transitions, pushing them to lower degree of disorder. We find that nanopatterning enhances the role of the two-dimensional Coulomb interaction in the system transforming the originally insulating film into a more pronounced insulator. We observe magnetoresistance oscillations reflecting collective behaviour of the multiconnected nanopatterned superconducting film in the wide range of temperatures and uncover the physical mechanism of these oscillations as phase slips in superconducting weak link network.That a thin film of the same material can be a superconductor but can very well turn an insulator, is one of the most remarkable aspects of disordered superconductors [1][2][3][4][5][6][7]. The engine driving the transition between the superconducting and insulating states is disorder the effect of which is two-fold. On the one hand, disorder limits the electron diffusion enhancing thus the Coulomb electron-electron interaction which competes with the Cooper pairing [8,9]. The latter in an interplay with the disorder-induced inhomogeneities localizes Cooper pairs to form an insulating state, Cooper-pair insulator. A restricted geometry is critical to effects of disorder -for the insulating state to be observed the superconducting material is to be thinned down till its thickness d becomes comparable to or smaller than the superconducting coherence length ξ. One of the major experimental challenges in these studies remains the optimization of material parameters taking it to the closest proximity of the direct superconductor-insulator transition and identifying the systems that exhibit such a transition at available temperatures. In this Letter we meet this challenge via creating a metamaterial with the desirable properties, the multiconnected thin superconducting film. We show that nanopatterning a thin TiN film into a regular sievelike configuration turns it into an array of weak links and, therefore, stimulates the direct superconductor-toinsulator transition. Depending on the original degree of disorder it either suppresses the critical temperature T c , or drives the initially superconducting film into an insulating state, or else, transforms the originally insulating film into an even more pronounced insulator.As a starting material we have chosen a 5 nm thin TiN film which was identical by its parameters to those that experienced the superconductor-insulator transition after soft plasma etching [10][11][12][13] and which were fully characterized by the high resolution electron beam, infrared [14], and low-temperature scanning tunnelling spectroscopy [15]. The smooth, continuous, and uniform TiN film was formed on the Si/SiO 2 substrate by atomic layer deposition. The film had the super...

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“…[5][6][7][8] In TiN, a SIT has been evidenced few years ago in $5 nm thick films by magnetic field and thickness changes. 9,10 Several studies also report the presence of an inhomogeneous superconducting phase close to the SIT. [11][12][13][14][15] One expects to recover a classical BCS superconducting phase when going to lower disorder/thicker films.…”

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Homogeneous superconducting phase in TiN film: A complex impedance study

Diener

Schellevis

Baselmans

2012

Applied Physics Letters

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The low frequency complex impedance of a high resistivity 92 μ Ω cm and 100 nm thick TiN superconducting film has been measured via the transmission of several high sensitivity GHz microresonators, down to TC/50. The temperature dependence of the kinetic inductance follows closely BCS local electrodynamics, with one well defined superconducting gap. This evidences the recovery of a homogeneous superconducting phase in TiN far from the disorder and composition driven transitions. Additionally, we observe a linearity between resonator quality factor and frequency temperature changes, which can be described by a two fluid model.

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Double reentrant superconductor-insulator transition in thin TiN films

Cited by 67 publications

References 22 publications

Disorder-Induced Inhomogeneities of the Superconducting State Close to the Superconductor-Insulator Transition

Disorder-Induced Inhomogeneities of the Superconducting State Close to the Superconductor-Insulator Transition

Nanopattern-stimulated superconductor-insulator transition in thin TiN films

Homogeneous superconducting phase in TiN film: A complex impedance study

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