Type-1.5 Superconductivity

Moshchalkov, Victor; Menghini, Mariela; Nishio, Toshiyuki; Chen, Qinghua; Silhanek, Alejandro; Dao, Vu Hung; Chibotaru, Liviu F.; Zhigadlo, N. D.; Karpiński, J.

doi:10.1103/physrevlett.102.117001

Cited by 268 publications

(349 citation statements)

References 28 publications

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“…It should be mentioned that this quest for new multiband superconductivity is a timely subject due to the possible emergence of nonmonotonic vortex-vortex interactions, a fingerprint of so-called type 1.5 superconductivity. [24][25][26] 174512-1 1098-0121/2013/88(17)/174512 (7) ©2013 American Physical Society…”

Section: Introductionmentioning

confidence: 99%

Temperature dependence of lower critical fieldHc1(T)shows nodeless superconductivity in FeSe

et al. 2013

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We investigate the temperature dependence of the lower critical field H c1 (T ) of a high-quality FeSe single crystal under static magnetic fields H parallel to the c axis. The temperature dependence of the first vortex penetration field has been experimentally obtained by two independent methods and the corresponding H c1 (T ) was deduced by taking into account demagnetization factors. A pronounced change in the H c1 (T) curvature is observed, which is attributed to anisotopic s-wave or multiband superconductivity. The London penetration depth λ ab (T ) calculated from the lower critical field does not follow an exponential behavior at low temperatures, as it would be expected for a fully gapped clean s-wave superconductor. Using either a two-band model with s-wave-like gaps of magnitudes 1 = 0.41 ± 0.1 meV and 2 = 3.33 ± 0.25 meV or a single anisotropic s-wave order parameter, the temperature dependence of the lower critical field H c1 (T ) can be well described. These observations clearly show that the superconducting energy gap in FeSe is nodeless.

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Section: Introductionmentioning

confidence: 99%

Temperature dependence of lower critical fieldHc1(T)shows nodeless superconductivity in FeSe

et al. 2013

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“…Solving the variational problem for θ = εf (z) sin(q y y) andφ = εg(z) cos(q y y) [16], we can find the threshold (q y , µ) when the nematic state (2) is linearly unstable with respect to periodic distortions along the y-direction. The incompressibility of the smec- tic layers (4) implies that the linear correction to the level set function φ + εφ should satisfy ∇φ = ∇n, leading to:…”

Section: (3±1)·10mentioning

confidence: 99%

“…The richness of thermotropic liquid crystal (LC) phases [1], their susceptibility to external fields and their unique optical properties make LCs ideally suited to study symmetry breaking phase transitions. These transitions often involve the formation of isolated topological defects or complex ordered spatial structures (topological defect patterns) [2], with analogues in magnetism (grain boundaries, domain walls) [3], superconductivity (Abrikosov lattice, stripes) [4] and cosmology (cosmic strings, monopoles) [5]. Contrary to cosmological or quantum systems, LC patterns can be studied at room temperature using polarization microscopy, whence the formation, organization and kinetics of the defect structures can be fully explored.…”

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confidence: 99%

Doubly periodic instability pattern in a smectic-Aliquid crystal

et al. 2013

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We report the observation of a doubly-periodic surface defect-pattern in the liquid crystal 8CB, formed during the nematic-smectic A phase transition. The pattern results from the antagonistic alignment of the 8CB molecules, which is homeotropic at the surface and planar in the bulk of the sample cell. Within the continuum Landau-deGennes theory of smectic liquid crystals, we find that the long period (≈10 µm) of the pattern is given by the balance between the surface anchoring and the elastic energy of curvature wall defects. The short period (≈1 µm) we attribute to a saddle-splay distortion, leading to a non-zero Gaussian curvature and causing the curvature walls to break up. [5]. Contrary to cosmological or quantum systems, LC patterns can be studied at room temperature using polarization microscopy, whence the formation, organization and kinetics of the defect structures can be fully explored. Patterns in the LC nematic phase, with long range orientational order but no positional order, are mostly well understood and readily explained within a continuum elastic theory of LC [1]. In contrast, patterns in smectic LC phases are more difficult to describe due to the additional one-dimensional positional order. Many, sometimes rather complex, smectic patterns have been observed, such as undulations of the smectic layers in an applied magnetic field (HelfrichHurault instability) [1,3] or other periodic structures, like stripes [6,7], squares [8], or hexagons [9]. Usually, those structures are explained by the formation of focal conic domains or curvature walls, characterized by one typical length scale [3,[10][11][12]. In this Letter we report the observation of a novel doubly-periodic defect pattern, which is formed during the nematic-smectic A (N-SmA) phase transition of a liquid crystal in an applied magnetic field. The field imposes an orientation of the LC molecules in the bulk that is orthogonal to the preferred orientation at the surface of the sample cell. Most strikingly, the pattern has two distinct periods: a long one (≈ 10 µm) along the field direction and a short one (≈ 1 µm) perpendicular to the field. Interestingly, a quite similar texture develops in LC colloidal shells on cooling towards the N-SmA phase transition [13]. We present a model describing the pattern using a geometric construction of a space-filling, energy minimizing, structure of equidistant (smectic) layers. Within this model we identify the driving mechanism as an elastic saddle-splay contribution [14][15][16] that breaks the symmetry in such a way that it naturally explains both distinct periodicities of the experiment and the orientation of the pattern with respect to the magnetic field direction.For our experiments we have used the liquid crystal 8CB (4-n-octyl-4'-cyanobiphenyl) which exhibits both a N and a SmA phase (SmAThe sample is contained in a cell consisting of two 0.4 mm thick borosilicate glass plates, spaced by a teflon ring with 4.5 mm inner diameter and 1.6 mm thickness (Fig. 1a). A 7 T static magnetic field B was a...

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“…They found that mesoscopic confinement stabilizes the chiral states and in this state the vortex cores in different band condensates do not coincide, as well as fractional flux vortex states with broken time-reversal symmetry [19]. Many phenomena of interest are related to the difference in the healing lengths of the band condensates, being a possible [13,20]. In this work, we calculate the vortex state in a superconducting simple MgB 2 ceramic film exposed to a homogeneous magnetic field.…”

Section: Introductionmentioning

confidence: 99%

“…Several studies in disks and square with structural defects and different boundary conditions were made to understand the vortex configurations and thermodynamics properties in mesoscopic samples. In these studies, it was found that the superconducting condensate is defined by the solutions of the time dependent linear Ginzburg-Landau (TDGL) equations [7][8][9][10][11][12][13][14]. Babaev et.…”

Section: Introductionmentioning

confidence: 99%

Superconducting state in two band MgB2 simple ceramic

Sjogreen-Blanco¹,

Joya²,

Barba-Ortega³

2014

AIP Conference Proceedings

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Abstract. Many phenomena of current physical interest are directly related to the difference in the healing lengths of the band condensates, such as the non-monotonic interaction between vortices, being a possible explanation for highly debated unusual vortex configurations observed in a simple ceramic MgB 2 . Effects due to the difference in the spatial profiles of different band condensates can be accounted for within the full microscopic numerical treatment with an enormous computational effort. These difficulties have stimulated a search for a general Ginzburg-Landau formalism with a coexistence of two band condensates with different healing lengths. In this work, we derive the free-energy functional for the extended formalism and the corresponding expression for the current density; also, using the time dependent Ginzburg-Landau theory, we calculate the vortex state in a superconducting simple ceramic exposed to a homogeneous magnetic field.

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Type-1.5 Superconductivity

Cited by 268 publications

References 28 publications

Temperature dependence of lower critical fieldHc1(T)shows nodeless superconductivity in FeSe

Temperature dependence of lower critical fieldHc1(T)shows nodeless superconductivity in FeSe

Doubly periodic instability pattern in a smectic-Aliquid crystal

Superconducting state in two band MgB2 simple ceramic

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