Invited Review Article: Multi-tip scanning tunneling microscopy: Experimental techniques and data analysis

Voigtländer, Bert; Cherepanov, Vasily; Korte, Stefan; Leis, Arthur; Cuma, David; Just, Sven; Lüpke, Felix

doi:10.1063/1.5042346

Cited by 47 publications

(51 citation statements)

References 87 publications

(104 reference statements)

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“…Conceptual sketch of the electrical measurement setup and the resulting potential along the line of the linearly arranged STM tips. While a NM voltage probe senses the local spin-averaged potential indicated by the black line (that is logarithmically-shaped in case of a two-dimensional infinite plane 31 ), a magnetised FM tip acquires the spin-chemical potential V s . As the spin voltage scales with the current density according to Eq.…”

Section: Figurementioning

confidence: 99%

“…To magnetise the nickel tip in-situ, we use an electromagnet inside the STM chamber. With only one of the two voltage probes being sensitive to the spin orientation of charge carriers, the measured voltage difference between the two comprises an ohmic component V Ω and a spin-dependent component V s , as for purely two-dimensional charge transport 31 . The corresponding distances are depicted in Fig.…”

Section: Figurementioning

confidence: 99%

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Room temperature in-situ measurement of the spin voltage of a BiSbTe3 thin film

Leis

Schleenvoigt

Jalil

et al. 2020

Sci Rep

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One of the hallmarks of topological insulators (TIs), the intrinsic spin polarisation in the topologically protected surface states, is investigated at room temperature in-situ by means of four-probe scanning tunnelling microscopy (STM) for a BiSbTe 3 thin film. To achieve the required precision of tip positions for measuring a spin signal, a precise positioning method employing STM scans of the local topography with each individual tip is demonstrated. From the transport measurements, the spin polarisation in the topological surface states (TSS) is estimated as p ~ 0.3 -0.6, which is close to the theoretical limit.

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Section: Figurementioning

confidence: 99%

Section: Figurementioning

confidence: 99%

Room temperature in-situ measurement of the spin voltage of a BiSbTe3 thin film

Leis

Schleenvoigt

Jalil

et al. 2020

Sci Rep

Self Cite

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“…Analogous to the role of local temperature in thermal transport at the nanoscale, the knowledge of local electrochemical potential is not only important as a source of information about electrical properties of a nanosystem, but also is of fundamental importance to understand and explore charge transport at the nanoscale [452][453][454]. In practice, a local electrochemical potential of electrons can be measured by a scanning tunneling potentiometry with the spatial resolution down to several nanometers [455][456][457][458].…”

Section: Local Electrochemical Potential Of Two-dimensional Networkmentioning

confidence: 99%

Local temperatures out of equilibrium

2019

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The temperature of a physical system is operationally defined in physics as "that quantity which is measured by a thermometer" weakly coupled to, and at equilibrium with the system. This definition is unique only at global equilibrium in view of the zeroth law of thermodynamics: when the system and the thermometer have reached equilibrium, the "thermometer degrees of freedom" can be traced out and the temperature read by the thermometer can be uniquely assigned to the system. Unfortunately, such a procedure cannot be straightforwardly extended to a system out of equilibrium, where local excitations may be spatially inhomogeneous and the zeroth law of thermodynamics does not hold. With the advent of several experimental techniques that attempt to extract a single parameter characterizing the degree of local excitations of a (mesoscopic or nanoscale) system out of equilibrium, this issue is making a strong comeback to the forefront of research. In this paper, we will review the difficulties to define a unique temperature out of equilibrium, the majority of definitions that have been proposed so far, and discuss both their advantages and limitations. We will then examine a variety of experimental techniques developed for measuring the non-equilibrium local temperatures under various conditions. Finally we will discuss the physical implications of the notion of local temperature, and present the practical applications of such a concept in a variety of nanosystems out of equilibrium. Figure 4: (a) The product of the density of states η(E) times the global distribution function ϕ|ρ|ϕ forms a strongly pronounced peak at the expectation value of the global system energyĒ. (b) The logarithm of the local distribution function a|ρ|a (solid line) and the logarithm of a canonical distribution (dashed line) with the same local temperature for a harmonic chain. (a) and (b) are reprinted with permission from [74].

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“…Four-tip STM measurements in UHV ( Fig. 8(a)) [138], however, revealed that the resistance as a function of distance between the tips is not described by a 3D transport model only, but required a sizable contribution from a parallel 2D transport channel ( Fig. 8(b)−(c)).…”

Section: Edge States Of Weak Topological Insulatorsmentioning

confidence: 99%

“…With four-tip STM, two tips can be used to inject the current, while a third tip is scanned in between to probe the nullifying voltage [138,142]. Consequently, the current induced potential is mapped.…”

Section: Edge States Of Weak Topological Insulatorsmentioning

confidence: 99%

Strong and Weak 3D Topological Insulators Probed by Surface Science Methods

Morgenstern

Pauly

Kellner

et al. 2020

Physica Status Solidi (b)

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We review the contributions of surface science methods to discover and improve 3D topological insulator materials, while illustrating with examples from our own work. In particular, we demonstrate that spin-polarized angularresolved photoelectron spectroscopy is instrumental to evidence the spin-helical surface Dirac cone, to tune its Dirac point energy towards the Fermi level, and to discover novel types of topological insulators such as dual ones or switchable ones in phase change materials. Moreover, we introduce procedures to spatially map potential fluctuations by scanning tunneling spectroscopy and to identify topological edge states in weak topological insulators. I. INTRODUCTIONTopology became a classification scheme for solid state electronic properties in the 1980s while describing the robustness of the quantum Hall effect [1,2]. This achievement has been honored most notably by the Noble prize 2016 for physics [3,4]. The well-deserved appreciation was largely triggered by the experimental discovery of 2D topological insulators (2DTIs) in 2007 [5]. This discovery initiated a major effort in experimental and theoretical solid state physics leading to a multitude of other types of topologies in crystalline solids, mostly appearing without magnetic fields [6][7][8]. The overwhelming success has also led to activities in other fields of physics enabling, e.g., the guiding of light or sound along arbitrarily shaped edges [9][10][11][12]. The attractive robustness of the topological properties, tied to the integer character of the topological indices, implied a multitude of proposals also for electronic applications [13][14][15]. This currently culminates in the actively pursued dream to realize topological quantum computation via parafermions [16][17][18][19]. The central advantage of this approach is the robustness of corresponding quantum operations against local perturbations as long as the quasiparticles remain in their topologically protected subspace.From the point of view of materials science, the intriguing observation that a lot of wellknown materials are three-dimensional strong topological insulators added a crucial view on electronic band structure properties [6][7][8]. It turned out that a large amount of bulk insulators necessarily provide spin helical conductive surface states [20,21] via the symmetry of their bulk band structure described by a topological index [22,23]. The presence of such 2 surface states is totally independent on details of the confining surfaces and, moreover, these surface states are protected against backscattering by their spin helicity [6,24]. Hence, such materials can be thought of as a third conductivity class besides conductors and insulators, being insulating in the interior of the system but conducting on its surfaces. Favorably, a simple classification scheme exists in case of inversion symmetry of the crystal [24]. It simply multiplies the parities (point inversion symmetries) of occupied single-electron states at the time-reversal invariant momenta (TRIMs) of ...

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Invited Review Article: Multi-tip scanning tunneling microscopy: Experimental techniques and data analysis

Cited by 47 publications

References 87 publications

Room temperature in-situ measurement of the spin voltage of a BiSbTe3 thin film

Room temperature in-situ measurement of the spin voltage of a BiSbTe3 thin film

Local temperatures out of equilibrium

Strong and Weak 3D Topological Insulators Probed by Surface Science Methods

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