Observability of superconductivity in Sr-doped 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>Bi</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mrow><mml:mi>Se</mml:mi></mml:mrow><mml:mn>3</mml:mn></mml:msub></mml:math>
 at the surface using scanning tunneling microscope

Bagchi, Mahasweta; Brede, Jens; Ando, Yoichi

doi:10.1103/physrevmaterials.6.034201

Cited by 5 publications

(4 citation statements)

References 48 publications

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“…In the present case, the Majorana surface states are expected to comprise dispersive 2D gapless modes, and time-reversal symmetry dictates that they have a helical spin-momentum locking [1]. The experimental difficulty in observing such Majorana surface states in this family of materials comes from the quasi-2D nature of the Fermi surface [1] and the destruction of superconductivity at a major portion of the surface [16,27,40]. The former implies that the Majorana surface states do not appear on the top surface, and the latter implies that the area where the superconductivity reaches the surface is surrounded by nonsuperconducting areas, causing the possible Majorana states (which may appear at the boundary) to merge with the surrounding metallic states, such that little spectral feature can be observed via STM.…”

Section: Discussionmentioning

confidence: 99%

“…Tip forming is done until a clean signature of the surface state is observed in spectroscopy. Prior to STM measurements, the crystals were cleaved under UHV conditions as described in [27].…”

Section: Discussionmentioning

confidence: 99%

“…where f (E ) is the Fermi-Dirac distribution function at the effective temperature T eff . The effective temperature of our STM experiments at the fridge temperature of 0.35 K was independently determined by a measurement of pure Nb [27] to be 0.7 K, so we fixed T eff = 0.7 K and used , 0 , and 1 as fitting parameters. In Fig.…”

Section: B Superconducting Gap Spectramentioning

confidence: 99%

“…S11 within the SM [21]), even though the value of 0 and 1 varies significantly. This large variation appears to reflect the fact the the superconductivity in CPSBS (and in all other Bi 2 Se 3 -based superconductors) is weakened or disappear at a larger part of the surface, whose origin is a topic of on-going research: For example, in a recent paper [27] it was proposed that a strong electric field due to intrinsic surface band bending may break Cooper pairs near the surface. In the case of CPSBS, the strength of surface band bending would vary depending on the density of Cu dopants found on the surface.…”

Section: B Superconducting Gap Spectramentioning

confidence: 99%

See 3 more Smart Citations

Rotation of gap nodes in the topological superconductor Cux(PbSe)5(Bi2Se3)6

Bagchi,

Brede,

Ramires

et al. 2024

Phys. Rev. B

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Among the family of odd-parity topological superconductors derived from Bi 2 Se 3 , Cu x (PbSe) 5 (Bi 2 Se 3 ) 6 (CPSBS) has been elucidated to have gap nodes. Although the nodal gap structure has been established by specific-heat and thermal-conductivity measurements, there has been no direct observation of the superconducting gap of CPSBS using scanning tunneling spectroscopy (STS). Here we report the first STS experiments on CPSBS down to 0.35 K, which found that the vortices generated by out-of-plane magnetic fields have an elliptical shape, reflecting the anisotropic gap structure. The orientation of the gap minima is found to be aligned with the bulk direction when the surface lattice image shows twofold symmetry, but, surprisingly, it is rotated by 30 • when twofold symmetry is absent. In addition, the superconducting gap spectra in zero magnetic field suggest that the gap nodes are most likely lifted. We argue that only an emergent symmetry at the surface, allowing for a linear superposition of gap functions with different symmetries in the bulk, can lead to the rotation of the gap nodes. The absence of inversion symmetry at the surface additionally lifts the nodes. This result establishes the subtle but crucial role of crystalline symmetry in topological superconductivity.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: B Superconducting Gap Spectramentioning

confidence: 99%

Section: B Superconducting Gap Spectramentioning

confidence: 99%

See 2 more Smart Citations

Rotation of gap nodes in the topological superconductor Cux(PbSe)5(Bi2Se3)6

Bagchi,

Brede,

Ramires

et al. 2024

Phys. Rev. B

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Modulated Kondo screening along magnetic mirror twin boundaries in monolayer MoS2

van Efferen,

Fischer,

Costi

et al. 2023

Nat. Phys.

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When a single electron is confined to an impurity state in a metal, a many-body resonance emerges at the Fermi energy if the electron bath screens the impurity’s magnetic moment. This is the Kondo effect, originally introduced to explain the abnormal resistivity behaviour in bulk magnetic alloys, and it has been realized in many quantum systems over the past decades, ranging from heavy-fermion lattices down to adsorbed single atoms. Here we describe a Kondo system that allows us to experimentally resolve the spectral function consisting of impurity levels and a Kondo resonance in a large Kondo temperature range, as well as their spatial modulation. Our approach is based on a discrete half-filled quantum confined state within a MoS2 grain boundary, which—in conjunction with numerical renormalization group calculations—enables us to test the predictive power of the Anderson model that is the basis of the microscopic understanding of Kondo physics.

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Magnetisation control of the nematicity direction and nodal points in a superconducting doped topological insulator

Khokhlov,

Akzyanov,

Kapranov

2024

J. Phys.: Condens. Matter

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We study the effects of magnetisation on the properties of the doped topological insulator of the $\text{Bi}_2\text{Se}_3$ family with nematic superconductivity. We found that the direction of the in-plane magnetisation fixes the direction of the nematicity in the system. The chiral state is more favourable than the nematic state for large values of out-of-plane magnetisation. Overall, the critical temperature of the nematic superconductivity is robust against magnetisation. We explore in detail the spectrum of the system with the pinned direction of the nematic order parameter $\Delta_{y}$. Without magnetisation, there is a full gap in the spectrum because of finite hexagonal warping. At an out-of-plane $m_z$ or orthogonal in-plane $m_x$ magnetisation that is strong enough, the spectrum is closed at the nodal points that are split by the magnetisation. Flat Majorana surface states connect such split bulk nodal points. Parallel magnetisation $m_y$ lifts the nodal points and opens a full gap in the spectrum. We discuss relevant experiments and propose experimental verifications of our theory.

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Observability of superconductivity in Sr-doped Bi2Se3 at the surface using scanning tunneling microscope

Cited by 5 publications

References 48 publications

Rotation of gap nodes in the topological superconductor Cux(PbSe)5(Bi2Se3)6

Rotation of gap nodes in the topological superconductor Cux(PbSe)5(Bi2Se3)6

Modulated Kondo screening along magnetic mirror twin boundaries in monolayer MoS2

Magnetisation control of the nematicity direction and nodal points in a superconducting doped topological insulator

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