Lateral imaging of the superconducting vortex lattice using Doppler-modulated scanning tunneling microscopy

Fridman, I.; Kloc, Christian; Petrović, C.; Wei, J. Y. T.

doi:10.1063/1.3659412

Cited by 18 publications

(21 citation statements)

References 23 publications

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“…Note also that this is very different from the observations made in refs 19,20 (at a single bias voltage and azimuthal angle and as a function of the value of the magnetic field) which show just stripes and no vortices. In our data, from the vortex density we obtain θ = 87.5°in 16 .…”

Section: Resultscontrasting

confidence: 53%

“…When the magnetic field was close to being parallel to the hexagonal planes, they observed elongated vortex cores, instead of the sixfold cores seen in perpendicular fields, and a peculiar pattern of stripes. More recently, this pattern of stripes was addressed in STM measurements with the field exactly in-plane focusing on the influence of the structure of the vortex lattice and of screening currents 19,20 . Until now, there is no systematic study of the vortex core shape with the in-plane direction of the magnetic field and the relation of the observed stripe pattern with vortex core states remains unclear.…”

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confidence: 99%

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Tilted vortex cores and superconducting gap anisotropy in 2H-NbSe2

et al. 2018

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The superconductor 2H-NbSe 2 features vortices with a sixfold star shape when the magnetic field is applied perpendicular to the plane of the hexagonal crystal structure. This is due to the anisotropy in the quasi-two-dimensional Fermi surface tubes oriented along the c axis. But the properties of another, three-dimensional, pocket are unknown, in spite that it has a dominant contribution in many experiments. Here we measure vortices in tilted magnetic fields using a scanning tunneling microscope. We find patterns of stripes due to in-plane vortices and show how these change with the in-plane direction of the magnetic field. The shape of outgoing vortices is successfully compared with detailed calculations of vortex cores. Our data show that vortices exit at an angle with the surface and that the sixfold gap anisotropy is present over the whole Fermi surface.

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Section: Resultscontrasting

confidence: 53%

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confidence: 99%

Tilted vortex cores and superconducting gap anisotropy in 2H-NbSe2

et al. 2018

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“…[187,188], with a STM mounted in such a way that the magnetic field lies parallel to the surface. No sign of Andreev bound states was reported.…”

Section: Basic Vortex Imaging Techniquesmentioning

confidence: 99%

Imaging superconducting vortex cores and lattices with a scanning tunneling microscope

Suderow¹,

Guillamón²,

Rodrigo³

et al. 2014

Supercond. Sci. Technol.

101

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Abstract. The observation of vortices in superconductors was a major breakthrough in developing the conceptual background for superconducting applications. Each vortex carries a flux quantum, and the magnetic field radially decreases from the center. Techniques used to make magnetic field maps, such as magnetic decoration, give vortex lattice images in a variety of systems. However, strong type II superconductors allow penetration of the magnetic field over large distances, of order of the magnetic penetration depth λ. Superconductivity survives up to magnetic fields where, for imaging purposes, there is no magnetic contrast at all. Static and dynamic properties of vortices are largely unknown at such high magnetic fields. Reciprocal space studies using neutron scattering have been employed to obtain insight into the collective behavior. But the microscopic details of vortex arrangements and their motion remain difficult to obtain. Direct real space visualization can be made using scanning tunneling microscopy and spectroscopy (STM/S). Instead of using magnetic contrast, the electronic density of states describes spatial variations of the quasiparticle and pair wavefunction properties. These are of order of the superconducting coherence length ξ, which is much smaller than λ. In principle, individual vortices can be imaged using STM up to the upper critical field where vortex cores, of size ξ, overlap. In this review, we describe recent advances in vortex imaging made with scanning tunneling microscopy and spectroscopy. We introduce the technique and discuss vortex images which reveal the influence of the Fermi surface distribution of the superconducting gap on the internal structure of vortices, the collective behavior of the lattice in different materials and conditions, and the observation of vortex lattice melting. We consider challenging lines of work, which include imaging vortices in nanostructures, multiband and heavy fermion superconductors, single layers and van-der-Waals crystals, studying current driven dynamics and the liquid vortex phases.

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“…Alternatively, scanning tunneling microscopy (STM) measurements can also be employed to probe the MBSs at the ends of the effective wires. In our scheme, at least one MBS is always localized below an outer MTJ of the array and can therefore be accessed by a lateral STM technique [63].…”

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confidence: 99%

Wireless Majorana Bound States: From Magnetic Tunability to Braiding

et al. 2016

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We propose a versatile platform to investigate the existence of Majorana bound states (MBSs) and their nonAbelian statistics through braiding. This implementation combines a two-dimensional electron gas formed in a semiconductor quantum well grown on the surface of an s-wave superconductor, with a nearby array of magnetic tunnel junctions (MTJs). The underlying magnetic textures produced by MTJs provide highly-controllable topological phase transitions to confine and transport MBSs in two dimensions, overcoming the requirement for a network of wires. Obtained scaling relations confirm that various semiconductor quantum well materials are suitable for this proposal. PACS numbers: 74.78.Na,74.25.Ha,74.45.+c In condensed-matter systems Majorana bound states (MBSs) are emergent quasiparticles with exotic non-Abelian statistics and particle-antiparticle symmetry [1][2][3][4][5][6][7]. Elucidating their properties is further motivated by the prospect to use them for fault-tolerant quantum computing [8][9][10]. Typical material systems envisioned for experimental implementations of MBSs include superconducting regions [11] such as those relying on the native p-wave pairing in a vortex core [12], Sr 2 RuO 4 [13,14], and Bechgaard salts [15]. They can also occur with common proximity-induced s-wave pairing when combined with a nontrivial spin structure, which can be provided by spin-orbit coupling (SOC) and magnetic textures [16][17][18][19][20][21][22][23][24] to yield an effective p-wave pairing.Impressive advances in fabricating complex superconducting systems for an unambiguous detection of MBSs remain actively debated [23,[25][26][27][28][29][30]. Observed MBS signatures, such as a zero-bias tunneling conductance peak, may have other origins [31][32][33][34][35] and should be supplemented by additional measurements [36][37][38][39][40]. However, those signatures do not directly probe non-Abelian statistics [2][3][4]8]. While realizing the non-Abelian braiding statistics under exchange would provide both an ultimate proof for the MBS existence and the key element for topological quantum computing, even theoretical schemes imply a significant complexity to implement such braiding [10]. Exchanging vortices on the surface of the p-wave superconductor to close the braiding loop would require an experimental tour de force. Frequently examined one-dimensional (1D) superconductor/semiconductor wire systems avoid the need for challenging vortex manipulation, but that geometry alone is insufficient. Braiding statistics are ill-defined in 1D and complex wire networks must be used instead of single wires, posing additional obstacles [10,41].To address these challenges, in Fig. 1 we propose a versatile platform to realize MBSs and enable their braiding in 2D superconductor/semiconductor systems without the need for wire networks. This proposal seemingly contradicts prior knowledge. In semiconductor wires with SOC-based effective p-wave pairing, the energetically isolated MBSs do not survive the transition to 2D, but rather ev...

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Lateral imaging of the superconducting vortex lattice using Doppler-modulated scanning tunneling microscopy

Cited by 18 publications

References 23 publications

Tilted vortex cores and superconducting gap anisotropy in 2H-NbSe2

Tilted vortex cores and superconducting gap anisotropy in 2H-NbSe2

Imaging superconducting vortex cores and lattices with a scanning tunneling microscope

Wireless Majorana Bound States: From Magnetic Tunability to Braiding

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