Tunneling Spectroscopy and Vortex Imaging in Boron-Doped Diamond

Sacépé, Benjamin; Chapelier, Claude; Marcenat, C.; Kačmarčı́k, J.; Klein, Thierry; Bernard, M.; Bustarret, Étienne

doi:10.1103/physrevlett.96.097006

Cited by 77 publications

(53 citation statements)

References 21 publications

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“…This is in steep contrast with previous studies on polycrystalline samples [11][12][13][14]. To our knowledge, such homogeneous hard gap was observed only in the case of a single crystal [15].…”

Section: O Onufriienko Et Alcontrasting

confidence: 99%

Superconducting Density of States in B-Doped Diamond

et al. 2017

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In the presented work, we investigated the superconducting boron doped diamond polycrystalline film prepared by chemical vapor deposition by means of scanning tunneling microscopy/spectroscopy. Differential conductance spectra measured at various temperatures were used to obtain the values of superconducting critical temperature and energy gap. Comparing various theoretical models fitted to the differential conductance spectra measured at 0.5 K suggests weak pair breaking. However, this cannot account for the high 2∆ k B T C ratio, which therefore indicates strong coupling.

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Section: O Onufriienko Et Alcontrasting

confidence: 99%

Superconducting Density of States in B-Doped Diamond

et al. 2017

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“…We indeed observe smearing out of these coherence peaks. However, we can well describe this effect with BCS formulas with the effective temperature T ef f which is higher than the expected 250 mK set-up resolution [25]. Note at this point that BCS expressions do not describe the observed upturn in the LDOS above the gap (see Fig.…”

Section: Shown Inmentioning

confidence: 69%

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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“…Indeed, whereas 2H-NbSe 2 is strongly influenced by CDW, vortex core features in other systems, as e.g. high T c cuprate and related superconductors, boron doped diamond, or YNi 2 B 2 C have a rather rich and intriguing behavior [43,44,45], with, however, no clear bias symmetric peak appearing at the Fermi level LDOS at the center of the cores.…”

Section: Figmentioning

confidence: 99%

Superconducting Density of States and Vortex Cores of 2H-NbS2

et al. 2008

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Scanning tunneling microscopy and spectroscopy (STM/S) measurements in the superconducting dichalcogenide 2H-NbS2 show a peculiar superconducting density of states with two well defined features at 0.97 meV and 0.53 meV, located respectively above and below the value for the superconducting gap expected from single band s-wave BCS model (∆=1.76kBTc=0.9 meV). Both features have a continuous temperature evolution and disappear at Tc = 5.7 K. Moreover, we observe the hexagonal vortex lattice with radially symmetric vortices and a well developed localized state at the vortex cores. The sixfold star shape characteristic of the vortex lattice of the compound 2H-NbSe2 is, together with the charge density wave order (CDW), absent in 2H-NbS2.PACS numbers: 71.45. Lr, 74.25.Jb,74.50.+r,74.70.Ad The study of the coexistence of superconductivity with competing physical phenomena such as magnetic or charge order has historically produced great interest on the scientific community. Anisotropies or modulations of the superconducting properties (in real and/or reciprocal space) often appear as a consequence of competing orders within the same system [1,2]. In the compound 2H-NbSe 2 , superconductivity appears within a CDW state (T CDW =33K and T c =7.2 K) [3]. Low lying excitations measured deep in the superconducting state long time ago by specific heat [4,5] have been explained by recent experiments and theoretical calculations with a multiband superconductivity and a peculiar anisotropy of the superconducting gap [6,7]. Recent angular resolved photoemission spectroscopy measurements demonstrate that the superconducting gap has, close to T c (at 5.7 K), largest values at k-space positions connected with CDW wavevectors [8,9]. Hess et al. [10,11,12] found that the local superconducting density of states (LDOS) at the center of the vortex core shows a high peak close to the Fermi level highlighting the lowest quasiparticle state bound within the vortex core well [13]. Around the vortex core, the LDOS is far from respecting in-plane symmetry and intriguing vortex lattice images with patterns showing strong in-plane LDOS modulations are obtained [10,11,12]. 2H-NbSe 2 belongs to the transition-metal dichalcogenides (2H-MX 2 with M = Ta, Nb and X = Se, S), a family of systems which is unique to study the interplay between CDW order and superconductivity. The 2H-MX 2 compounds share a double layered structure made of two hexagonal X sheets with an intercalated M sheet (X-M-X), connected through very weak van der Waals bonds [14]. This produces highly anisotropic, quasi two dimensional electronic properties. The features of the Fermi Surface (FS) expected to be common in all systems of the series are two concentric cylindrical FS sheets centered on both Γ and K points, derived from the transition-metal d bands [15,16,17,18]. When going over the series from 2H-TaSe 2 and 2H-TaS 2 to 2H-NbSe 2 and 2H-NbS 2 , the ratio of the intralayer lattice constant with the interlayer distance a/c increases, as well as T c , whereas T CDW decreas...

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Tunneling Spectroscopy and Vortex Imaging in Boron-Doped Diamond

Cited by 77 publications

References 21 publications

Superconducting Density of States in B-Doped Diamond

Superconducting Density of States in B-Doped Diamond

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

Superconducting Density of States and Vortex Cores of 2H-NbS2

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