Topological superconductivity in an ultrathin, magnetically-doped topological insulator proximity coupled to a conventional superconductor

Kim, Young-Seok; Philip, Timothy M.; Park, Moon Jip; Gilbert, Matthew J.

doi:10.1103/physrevb.94.235434

Cited by 5 publications

(6 citation statements)

References 58 publications

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“…Using the self-consistent calculation of the superconductivity described in Eqs. (13)(14)(15)(16)(17)(18)(19), we now present the numerical calculations of the ground state energy with finite momentum pairing. Fig.…”

Section: Inverse Proximity Effectmentioning

confidence: 99%

“…This spin-orbit coupled band has been explored for potential applications to spintronics [5][6][7][8] and topological quantum computation [9][10][11][12][13] . Among these various applications, the superconducting surface state has gathered a lot of interest due to the possible emergence of the Majorana fermions when proximity coupled to BCS superconductor [9][10][11][12][13][14] . The underlying idea of this proximity coupled system is that resulting system mimics a p + ip superconductor 9 .…”

Section: Introductionmentioning

confidence: 99%

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Fulde-Ferrell states in inverse proximity-coupled magnetically doped topological heterostructures

et al. 2017

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We study the superconducting properties of the thin film BCS superconductor proximity coupled to a magnetically doped topological insulator(TI). Using the mean field theory, we show that Fulde-Ferrell(FF) pairing can be induced in the conventional superconductor by having inverse proximity effect(IPE). This occurs when the IPE of the TI to the superconductor is large enough that the normal band of the superconductor possesses a proximity induced spin-orbit coupling and magnetization. We find that the energetics of the different pairings are dependent on the coupling strength between the TI and the BCS superconductor and the thickness of the superconductor film. As the thickness of the superconductor film is increased, we find a crossover from the FF pairing to the BCS pairing phase. This is a consequence of the increased number of the superconducting bands, which favor the BCS pairing, implying that the FF phase can only be observed in the thin-film limit. In addition, we also propose transport experiments that show distinct signatures of the FF phase.arXiv:1702.07383v1 [cond-mat.supr-con]

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Section: Inverse Proximity Effectmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Fulde-Ferrell states in inverse proximity-coupled magnetically doped topological heterostructures

et al. 2017

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“…7,8 Numerous papers have studied the interesting phenomena that have been discovered in topological insulators with proximity-induced superconductivity. [9][10][11][12][13][14][15][16][17][18][19][20][21][22] To our knowledge, however, much less attention has been paid to the inverse superconducting, or topological, 23 proximity effect, i.e. the effect that the topological insulator has on the superconductor order parameter.…”

Section: Introductionmentioning

confidence: 99%

Inverse proximity effect in s -wave and d -wave superconductors coupled to topological insulators

et al. 2019

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We study the inverse proximity effect in a bilayer consisting of a thin s-or d-wave superconductor (S) and a topological insulator (TI). Integrating out the topological fermions of the TI, we find that spin-orbit coupling is induced in the S, which leads to spin-triplet p-wave (f -wave) correlations in the anomalous Green's function for an s-wave (d-wave) superconductor. Solving the self-consistency equation for the superconducting order parameter, we find that the inverse proximity effect can be strong for parameters for which the Fermi momenta of the S and TI coincide. The suppression of the gap is approximately proportional to e −1/λ , where λ is the dimensionless superconducting coupling constant. This is consistent with the fact that a higher λ gives a more robust superconducting state. For an s-wave S, the interval of TI chemical potentials for which the suppression of the gap is strong is centered at µTI = ± 2mv 2 F µ, and increases quadratically with the hopping parameter t. Since the S chemical potential µ typically is high for conventional superconductors, the inverse proximity effect is negligible except for t above a critical value. For sufficiently low t, however, the inverse proximity effect is negligible, in agreement with what has thus far been assumed in most works studying the proximity effect in S-TI structures. In superconductors with low Fermi energies, such as high-Tc cuprates with d-wave symmetry, we again find a suppression of the order parameter. However, since µ is much smaller in this case, a strong inverse proximity effect can occur at µTI = 0 for much lower values of t. Moreover, the onset of a strong inverse proximity effect is preceded by an increase in the order parameter, allowing the gap to be tuned by several orders of magnitude by small variations in µTI. arXiv:1808.03650v3 [cond-mat.supr-con]

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“…In contrast, the inter-orbital triplet pairing, ∆ 0 , pairs electrons solely within each of the Zeeman split Fermi surfaces. Thus, the effect of Zeeman coupling is to break the TRS within the model and imbalance the two pairing potentials in the favor of ∆ 0 which couples the electrons solely within each Zeeman split Fermi surface [33].…”

Section: Introductionmentioning

confidence: 99%

Effect of Zeeman coupling on the Majorana vortex modes in iron-based topological superconductors

et al. 2020

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In the superconducting regime of FeTe (1−x) Sex, there exist two types of vortices which are distinct by the presence or absence of zero energy states in their core. To understand their origin, we examine the interplay of Zeeman coupling and superconducting pairings in three-dimensional metals with band inversion. Weak Zeeman fields are found to suppress the intra-orbital spin-singlet pairing, known to localize the states at the ends of the vortices on the surface. On the other hand, an orbital-triplet pairing is shown to be stable against Zeeman interactions, but leads to delocalized zero-energy Majorana modes which extend through the vortex. In contrast, the finite-energy vortex modes remain localized at the vortex ends even when the pairing is of orbital-triplet form. Phenomenologically, this manifests as an observed disappearance of zero-bias peaks within the cores of topological vortices upon increase of the applied magnetic field. The presence of magnetic impurities in FeTe (1−x) Sex, which are attracted to the vortices, would lead to such Zeeman-induced delocalization of Majorana modes in a fraction of vortices that capture a large enough number of magnetic impurities. Our results provide an explanation to the dichotomy between topological and non-topological vortices recently observed in FeTe (1−x) Sex.Introduction: To date, one of the major impediments in the search for Majorana fermions (MFs) is that a requisite topological superconductivity, either intrinsic [1,2] or induced in a host material via a proximity coupling to a standard s-wave superconductor [3-6]. Of the available materials that possess topology, superconductivity and magnetism, iron-based superconductors are of recent interest [7][8][9][10][11][12][13][14][15]. In particular, the iron-based superconductor FeTe 0.55 Se 0.45 (FTS) has recently been shown to have strong spin-orbit interactions and band inversion that result in a helical, topologically-protected, Dirac cone on the surface [16][17][18][19]. The phenomenology of vortices, proliferated in the presence of magnetic fields, is also noteworthy in FTS [20][21][22][23]. The low charge density in the superconducting phase of this system is experimentally advantageous as it results in large Caroli-de Gennes-Matricon (CDM) vortex mode gaps [24] which facilitates the spectral detection of zero-energy vortex modes via scanning tunneling microscopy (STM). Intriguingly, vortices in FTS show two distinct types of behavior: topological, carrying zero energy states consistent with the presence of MF, and trivial vortices that lack the zero energy state but carry finite energy CDMs.

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Topological superconductivity in an ultrathin, magnetically-doped topological insulator proximity coupled to a conventional superconductor

Cited by 5 publications

References 58 publications

Fulde-Ferrell states in inverse proximity-coupled magnetically doped topological heterostructures

Fulde-Ferrell states in inverse proximity-coupled magnetically doped topological heterostructures

Inverse proximity effect in s -wave and d -wave superconductors coupled to topological insulators

Effect of Zeeman coupling on the Majorana vortex modes in iron-based topological superconductors

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