Vortex lattice structure dependent on pairing symmetry in Rashba superconductors

Hiasa, Norihito; Saiki, Taro; Ikeda, Ryusuke

doi:10.1103/physrevb.80.014501

Cited by 23 publications

(58 citation statements)

References 31 publications

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“…Therefore, by combining the prospect of manipulating both the time reversal and space inversion symmetries, these superlattices offer a new avenue for detailed study of exotic superconducting phases, e.g. a helical superconducting phase [23], and novel vortex physics [24].…”

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confidence: 99%

Anomalous Upper Critical Field inCeCoIn5/YbCoIn5Superlattices with a Rashba-Type Heavy Fermion Interface

et al. 2012

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We report a highly unusual angular variation of the upper critical field (Hc2) in epitaxial superlattices CeCoIn5(n)/YbCoIn5(5), formed by alternating layers of n and a 5 unit-cell thick heavy-fermion superconductor CeCoIn5 with a strong Pauli effect and normal metal YbCoIn5, respectively. For the n = 3 superlattice, Hc2(θ) changes smoothly as a function of the field angle θ. However, close to the superconducting transition temperature, Hc2(θ) exhibits a cusp near the parallel field (θ = 0 • ). This cusp behavior disappears for n = 4 and 5 superlattices. This sudden disappearance suggests the relative dominance of the orbital depairing effect in the n = 3 superlattice, which may be due to the suppression of the Pauli effect in a system with local inversion symmetry breaking. Taking into account the temperature dependence of Hc2(θ) as well, our results suggest that some exotic superconducting states, including a helical superconducting state, might be realized at high magnetic fields.PACS numbers: 74.25. Op, 81.15.Hi In the absence of time reversal symmetry or space inversion symmetry, the Fermi surface (FS) can often be split into portions with different spin structures. To stabilize superconductivity under such conditions where spin degeneracy is lifted, unconventional pairing of quasiparticles is needed, leading to exotic superconducting states very different from the conventional BCS pairing state of (k ↑, -k ↓). Considering the situation of the broken time reversal symmetry alone, Fulde and Ferrell [1], and Larkin and Ovchinnikov [2] proposed the pairing state of (k ↑, -k+q ↓) on a Zeeman-split FS. This so-called FFLO pairing state leads to the modulation of the superconducting order parameter in real space with the modulation wavelength of the order of 1/|q|. On the other hand, in the lack of space inversion symmetry, a Rashba-type spin-orbit coupling splits the FS into branches with spins of opposite rotation sense [3]. When the magnetic field is applied to such a system, a pairing state with a finite center-of-mass momentum can also be realized, resulting in a helical superconducting state analogous to the FFLO phase.However, such exotic superconducting states have been poorly explored because of the lack of suitable materials. Recent advancement in heavy fermion thin film fabrication technology [4,5] has enabled the preparation of superlattices formed by alternate stacking of c-axis oriented CeCoIn 5 and YbCoIn 5 with atomic layer thicknesses. The large Fermi velocity mismatch across the interface between CeCoIn 5 and YbCoIn 5 significantly reduces the transmission probability of quasiparticles, thereby ensuring quasi-two-dimensional superconductivity confined within CeCoIn 5 layers [6,7]. This provides a unique opportunity to explore the physics discussed above. This is because bulk CeCoIn 5 with strong Pauli effect has been reported to host the FFLO phase at low temperatures and high magnetic field [8][9][10][11]. In the superlattice, the electronic structure becomes two-dimensional, which is expec...

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Anomalous Upper Critical Field inCeCoIn5/YbCoIn5Superlattices with a Rashba-Type Heavy Fermion Interface

et al. 2012

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“…One of the main results in the present work is the presence of a critical end point of a first-order structural transition of the vortex lattice in the low-temperature and intermediate-field regime which cannot be well described by the previous GL approach [17]. We argue that the presence of this critical end point is related to the helical phase modulation in the vortex-free limit mentioned above and to the field-induced compression of the vortex lattice structure due to the PPB.…”

Section: Introductionmentioning

confidence: 80%

“…[17], the validity of this identification has been tested in the simplest s-wave pairing case by comparing with the exact result obtained by determining the Q value minimizing the free energy at each magnetic field, and the simplified treatment based on the identification Q = 2δN Q 0 has been shown not to affect the phase diagram even quantitatively (see Fig. 3 and its related discussions in Ref.…”

Section: Model and Theoretical Approachmentioning

confidence: 99%

“…It has been found in the previous GL approach [16,17] that the structural symmetry of the vortex lattice in Rashba superconductors in the in-plane field configuration dramatically changes as the field increases through first-order transitions or continuous crossovers. This is a consequence of the enhanced role of the higher LLs induced by the PPB.…”

Section: Introductionmentioning

confidence: 99%

“…However, the LL expansion of the order parameter has been applied to the quasiclassical (EilenbergerLarkin-Ovchinnnikov) approach to examine the diamagnetic properties [15] by incorporating an approximation analogous to the so-called Pesch approximation [18]. We have chosen to use this LL expansion method in the quasiclassical approach [15] to address the low-temperature vortex lattice states which cannot be examined in the GL approach [17].…”

Section: Introductionmentioning

confidence: 99%

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Quasiclassical analysis of vortex lattice states in Rashba noncentrosymmetric superconductors

Dan

Ikeda

2015

Phys. Rev. B

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Vortex lattice states occurring in noncentrosymmetric superconductors with a spin-orbit coupling of Rashba type under a magnetic field parallel to the symmetry plane are examined by assuming the s-wave pairing case and in an approach combining the quasiclassical theory with the Landau level expansion of the superconducting order parameter. The resulting field-temperature phase diagrams include not only a discontinuous transition but a continuous crossover between different vortex lattice structures, and, further, a critical end point of a structural transition line is found at an intermediate field and a low temperature in the present approach. It is pointed out that the strange field dependence of the vortex lattice structure is a consequence of that of its anisotropy stemming from the Rashba spin-orbit coupling, and that the critical end point is related to the helical phase modulation peculiar to these materials in the ideal Pauli-limited case. Furthermore, calculation results on the local density of states detectable in STM experiments are also presented.

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Magnetoelectric Effects, Helical Phases, and FFLO Phases

Agterberg

2012

Non-Centrosymmetric Superconductors

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This chapter emphasizes new magnetic properties that arise when inversion symmetry is broken in a superconductor. There are two aspects that will be covered in detail. The first topic encompasses physics related to superconducting magnetoelectric effects that arise from broken inversion symmetry. Broken inversion symmetry allow for Lifshitz invariants in the free energy which can be viewed as a coupling between the magnetic induction and the supercurrent. There are similarities between these invariants and the better known Dzyaloshinskii-Moyira interaction in magnetic systems. These Lifshitz invariants give rise to anomalous magnetic properties as well as new phases in the presence of magnetic fields. Here, we will describe the consequences of these Lifshitz invariants, provide estimates for the relative magnitudes of the novel effects, and discuss the important role that crystal symmetry plays in understanding this physics. Finally, we provide a discussion of the fate of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phases in broken inversion superconductors. In particular, we show how broken inversion symmetry can have a profound effect on the stability, existence, and properties of FFLO phases.

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Vortex lattice structure dependent on pairing symmetry in Rashba superconductors

Cited by 23 publications

References 31 publications

Anomalous Upper Critical Field inCeCoIn5/YbCoIn5Superlattices with a Rashba-Type Heavy Fermion Interface

Anomalous Upper Critical Field inCeCoIn5/YbCoIn5Superlattices with a Rashba-Type Heavy Fermion Interface

Quasiclassical analysis of vortex lattice states in Rashba noncentrosymmetric superconductors

Magnetoelectric Effects, Helical Phases, and FFLO Phases

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