Probing topological quantum matter with scanning tunnelling microscopy

Abstract

The search for topological phases of matter is evolving towards strongly interacting systems, including magnets and superconductors, where exotic effects emerge from the quantum-level interplay between geometry, correlation and topology. Over the past decade or so, scanning tunnelling microscopy has become a powerful tool to probe and discover emergent topological matter, because of its unprecedented spatial resolution, high-precision electronic detection and magnetic tunability. Scanning tunnelling microscopy can be used to probe various topological phenomena, as well as complement results from other techniques. We discuss some of these proofof-principle methodologies applied to probe topology, with particular attention to studies performed under a tunable vector magnetic field, which is a relatively new direction of recent focus. We then project the future possibilities for atomic-resolution tunnelling methods in providing new insights into topological matter. Key points• Explorations of quasi-particle interference and Landau quantization behaviours in materials can be used to elucidate the nature of chiral or helical fermions and their interplay with symmetrybreaking order, such as magnetism, charge order or superconductivity. • Bulk-boundary connectivity and its relationship with atomically resolved lattice and magnetic structure probed via topographic measurements are central to understanding emergent topology, such as in kagome lattices. • Tunable vector magnetic field capability allows for exploring field-induced novel states in topological matter, including emergent magnetism, superconductivity and strongly correlated phases. • In the presence of magnetic field control, spectro-microscopy plays an important role in identifying the nature of localized zero modes or in-gap states, such as the Majorana mode. • Scanning tunnelling microscopy-based study on topological materials can be further extended for visualizing Wannier-Bloch duality and can be employed in sub-nanoscale engineering in developing quantum information science platforms.

Intrinsic nature of chiral charge order in the kagome superconductor RbV3Sb5

“…For instance, insulating kagome magnets have been investigated for decades in the hopes of realizing quantum spin liquids [2]. Recently, focused STM research on correlated kagome magnets has revealed many topological and many-body phenomena [3], including Chern gapped phases [4,5], tunable electronic nematicity [4], orbital magnetism [6][7][8], and many-body interplay [9,10]. These observations are all closely related to the emergent physics arising from the fundamental kagome band structure, which includes Dirac cones, flat bands, and Van Hove singularities.…”

Robust topological state against magnetic impurities observed in the superconductor PbTaSe2

“…1(g) inset]. This distinct feature has been identified as a fingerprint for the topological surface states in this material as well as others, including topological insulators [4,[18][19][20][21][22][23][24]. It arises from the warping of a closed Fermi surface with helical spin texture [25], where the quasiparticle scattering is allowed only along the arc directions.…”

“…The interplay between magnetism, topology, and superconductivity is at the quantum frontier with many open questions [1][2][3][4], where inducing magnetism in a superconductor with a topological band structure is a promising research direction [5]. PbTaSe 2 is a noncentrosymmetric superconductor [6][7][8][9][10][11][12] with the space group of P 6m2 (No.187) and superconducting transition temperature of 3.8 K [Fig.…”

“…1(e)]. The standing waves propagate anisotropically instead of simple ringlike signals, indicative of nontrivial scattering processes [4]. We further performed dI/dV mapping on a large Pb surface with native Pb vacancies, as shown in Figs.…”

Wave Packet Dynamical Simulation of Quasiparticle Interferences in 2D Materials

“…Experimentally, the real-space modulation of the LDOS is accessible by fast Fourier transformation (FFT) of the topography or tunneling conductance maps, measured by scanning tunneling microscopy [11]. The great advantage of the STM is that it allows us to understand the basic mechanism of quasiparticle scattering at the atomic scale.…”