Zero-energy Andreev bound states in iron-based superconductor Fe(Te,Se)

Hou, Zhe; Klinovaja, Jelena

doi:10.48550/arxiv.2109.08200

Cited by 2 publications

(4 citation statements)

References 86 publications

(100 reference statements)

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“…The predicted spectrum of CdGM states in trivial superconductors lacks a zero energy level. These features establish the difference between CdGM and MZMs spectra and underlie the interpretation of experimental observations of zero-bias peaks inside vortices [5,[22][23][24][25][26][27][28][29][30]. From Eq.…”

Section: Introductionsupporting

confidence: 55%

Near zero energy Caroli–de Gennes–Matricon vortex states in the presence of impurities

et al. 2023

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Caroli-de Gennes-Matricon (CdGM) states are localized states with a discrete energy spectrum bound to the core of vortices in superconductors. In topological superconductors, CdGM states are predicted to coexist with zero energy, chargeless states widely known as Majorana zero modes (MZMs). Due to their energy difference, current experiments rely on scanning tunneling spectroscopy methods to distinguish between them. This work shows that electrostatic inhomogeneities can push trivial CdGM states arbitrarily close to zero energy in nontopological systems where no MZM is present. Furthermore, the BCS charge of CdGM states is suppressed under the same mechanism. Through exploration of the impurity parameter space, we establish that these two phenomena generally happen in consonance. Our results show that energy and charge shifts in CdGM may be enough to imitate the spectroscopic signatures of MZMs even in cases where the estimated CdGM level spacing (in the absence of impurities) is much larger than the typical experimental level broadening.

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Section: Introductionsupporting

confidence: 55%

Near zero energy Caroli–de Gennes–Matricon vortex states in the presence of impurities

et al. 2023

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“…[23] These inhomogeneities result in inconsistent MBS observations within magnetic field induced vortex cores and raise questions as to the existence of MBS for the system. [19,32] For our Fe(Te,Se)/Bi 2 Te 3 system, we do not observe topological surface states on the surfaces of our 20 ML Fe(Te,Se) films with y ≤ 0.35. However, we do find superconductivity down to the ML limit.…”

Section: Discussionmentioning

confidence: 68%

“…[25] A larger As reported previously, only a small fraction of the magnetically induced superconducting vortices in bulk Fe(Te,Se) showed an isolated, pure MBS and this was related to the inhomogeneities from the heavy Se doping. [19,23,32] To investigate if the reduction of the Se doping in the Fe(Te,Se)/Bi 2 Te 3 films reduces electronic inhomogeneities, we used STM to measure the surface homogeneity of the 20 ML Fe(Te,Se) grown on Bi 2 Te 3 for y = 0.1 and y = 0.25 with the results shown in Figure 3. In Figure 3a,b, the fourfold atomic surface structure of the Fe(Te,Se) is observed for both y = 0.1 and y = 0.25, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…[19] Inhomogeneities in the chemical potential arising from heavy Se doping can create mixed phases and even induce zero energy Andreev bound states that can appear as MBS and raise questions as to the origins of the observed MBS signatures in tunneling experiments. [23,32] Despite these challenges, one principal advantage for pursuing the bulk Fe(Te,Se) system over other proximity-induced topological superconducting systems involving TIs and superconductors as NbSe 2 is the higher superconducting T c . [33,34] The energy spacing between MBS and trivial in-gap Caroli-de Gennes-Matricon states scales with the superconducting gap (Δ) and E F as Δ 2 /E F and higher T c materials with larger Δ will make MBS easier to interrogate.…”

Section: Introductionmentioning

confidence: 99%

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Monolayer Superconductivity and Tunable Topological Electronic Structure at the Fe(Te,Se)/Bi₂Te₃ Interface

Moore

Jeon

et al. 2023

Advanced Materials

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quasiparticles as Majorana-bound states (MBS) that demonstrate non-Abelian statistics which can be used for topological quantum computation applications. [1,2] There are several possible avenues for creating topological superconductivity which hosts MBS. [3] For example, these MBS can be realized on the boundary of a superconductor with an intrinsic oddparity, for example, spin-triplet or p-wave, pairing state. [3,4] However, only a few candidate p-wave superconductors exist, such as Cu x Bi 2 Se 3 and UTe 2 , which tend to have a low superconducting transition temperature (T c ) and are sensitive to disorder. [5][6][7][8][9][10][11] Another example is nanowire heterojunctions between semiconducting and superconducting materials with large spin-orbit coupling which can host MBS at the ends of the wires when placed in a magnetic field. [12,13] Unfortunately, the existence of MBS in these systems is also sensitive to uniformity arising from materials and device fabrication processes. [14] Finally, there are several avenues to create MBS via topological superconductivity from proximity-induced effects. [3] Prominent examples include superconducting materials with topological surface states and the interface between a s-wave superconductor and a topological insulator (TI), where the superconducting proximity effect induces an effective p-wave pairing in the TIS . [3,15] Among this class of candidate topological superconductors, the Fe(Te,Se) system has attracted considerable attention. [16][17][18][19][20][21][22][23][24] Both FeTe and FeSe, as well as the alloyed Fe(Te,Se) system, have an electronic band structure that is related to the ironpnictide family of high-T c superconductors. [18,[25][26][27] In general, the Fermi surfaces are dominated by bands derived from the Fe d-orbitals that result in hole pockets at the Brillouin zone center (Γ) and electron pockets at the zone boundary (M). First principles calculations for the two parent compounds reveal FeTe to have a larger Fermi surface and larger density of states at the Fermi level compared to FeSe. [25] These differences are due to subtle changes in the band shapes and relative energies arising from height differences between Se/Te and the Fe plane. As the two materials are alloyed, the Fe(Te,Se) system reveals spin-helical Dirac surface states due to the topological band inversion between the p z and d xy /d yz bands as the p z bandThe interface between 2D topological Dirac states and an s-wave superconductor is expected to support Majorana-bound states (MBS) that can be used for quantum computing applications. Realizing these novel states of matter and their applications requires control over superconductivity and spin-orbit coupling to achieve spin-momentum-locked topological interface states (TIS) which are simultaneously superconducting. While signatures of MBS have been observed in the magnetic vortex cores of bulk FeTe 0.55 Se 0.45 , inhomogeneity and disorder from doping make these signatures unclear and inconsistent between vortices. Here superconduc...

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Zero-energy Andreev bound states in iron-based superconductor Fe(Te,Se)

Cited by 2 publications

References 86 publications

Near zero energy Caroli–de Gennes–Matricon vortex states in the presence of impurities

Near zero energy Caroli–de Gennes–Matricon vortex states in the presence of impurities

Monolayer Superconductivity and Tunable Topological Electronic Structure at the Fe(Te,Se)/Bi₂Te₃ Interface

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Zero-energy Andreev bound states in iron-based superconductor Fe(Te,Se)

Cited by 2 publications

References 86 publications

Near zero energy Caroli–de Gennes–Matricon vortex states in the presence of impurities

Near zero energy Caroli–de Gennes–Matricon vortex states in the presence of impurities

Monolayer Superconductivity and Tunable Topological Electronic Structure at the Fe(Te,Se)/Bi2Te3 Interface

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Monolayer Superconductivity and Tunable Topological Electronic Structure at the Fe(Te,Se)/Bi₂Te₃ Interface