The Kondo resonance line shape in scanning tunnelling spectroscopy: instrumental aspects

Gruber, Manuel; Berndt, Richard

doi:10.1088/1361-648x/aadfa3

Cited by 39 publications

(30 citation statements)

References 77 publications

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“…3f) and that the contrast between the two extremities almost vanishes at +1.0 V. From additional STM measurements and simulations, we determined that the height asymmetry is discernible up to V ≈ 0.5 V. The zero-bias features are broadened by the modulation voltage used (amplitude V m = 5.7 mV for the top curve, 7 mV for the others). 54 The green curve is vertically shifted by +0.3 nS for clarity. Figures 4a-b show that the Fe atoms next to the tpy ligands exhibit different apparent heights and widths.…”

Section: Resultsmentioning

confidence: 99%

Fragmentation and Distortion of Terpyridine-Based Spin-Crossover Complexes on Au(111)

et al. 2019

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Spin-crossover complexes are attractive for their spinswitching functionality. However, only few compounds have been found to remain intact in direct contact to metal surfaces. For the design of new spin-crossover complexes, it is important to understand the mechanisms leading to fragmentation. Here, we investigate, using low-temperature scanning tunneling microscopy along with density functional theory calculations, two Fe(terpyridine) 2 complexes deposited on Au(111) by electrospray ionization with in-line mass selection. Only fragments of the first compound are observed on the surface, while the second compound is strongly flattened. Based on a detailed analysis of the adsorbates on the surface, possible mechanisms for the fragmentation and molecular distortion are proposed.

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Section: Resultsmentioning

confidence: 99%

Fragmentation and Distortion of Terpyridine-Based Spin-Crossover Complexes on Au(111)

et al. 2019

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“…[59]). In addition, it is rather challenging to unambiguously prove that a resonance close to zero bias is due to a Kondo effect [95].…”

Section: Identification Of the Spin States With Stmmentioning

confidence: 99%

“…The spin state identification with STM so far relies on comparison with quantities determined from DFT calculations, or on the presence/absence of a Kondo resonance, which is difficult to unambiguously prove [95]. More direct observations, such as spin excitation spectroscopy, would be desirable.…”

Section: Identification Of the Spin States With Stmmentioning

confidence: 99%

Spin-Crossover Complexes in Direct Contact with Surfaces

Gruber

Berndt

2020

Magnetochemistry

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The transfer of the inherent bistability of spin crossover compounds to surfaces has attracted considerable interest in recent years. The deposition of the complexes on surfaces allows investigating them individually and to further understand the microscopic mechanisms at play. Moreover, it offers the prospect of engineering switchable functional surfaces. We review recent progress in the field with a particular focus on the challenges and limits associated with the dominant experimental techniques used, namely near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and scanning tunneling microscopy (STM). One of the main difficulties in NEXAFS-based experiments is to ascertain that the complexes are in direct contact with the surfaces. We show that molecular coverage determination based on the amplitude of the edge-jump of interest is challenging because the latter quantity depends on the substrate. Furthermore, NEXAFS averages the signals of a large number of molecules, which may be in different states. In particular, we highlight that the signal of fragmented molecules is difficult to distinguish from that of intact and functional ones. In contrast, STM allows investigating individual complexes, but the identification of the spin states is at best done indirectly. As quite some of the limits of the techniques are becoming apparent as the field is gaining maturity, their detailed descriptions will be useful for future investigations and for taking a fresh look at earlier reports.

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“…Appendix D: Comparison between S and linear-response thermocurrent I th /∆T = GSWhile the linear-response thermopower S (T ) and thermocurrent I th /∆T = GS [see discussion following Eq (13). in Sec.…”

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Magnetic field dependence of the thermopower of Kondo-correlated quantum dots: Comparison with experiment

Costi

2019

Phys. Rev. B

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Signatures of the Kondo effect in the electrical conductance of strongly correlated quantum dots are well understood both experimentally and theoretically, while those in the thermopower have been the subject of recent interest, both theoretically and experimentally. Here, we extend theoretical work [T. A. Costi, Phys. Rev. B 100, 161106(R) (2019)] on the field-dependent thermopower of such systems to the mixed valence and empty orbital regimes, and carry out calculations in order to address a recent experiment on the field dependent thermoelectric response of Kondo-correlated quantum dots [A. Svilans et al., Phys. Rev. Lett. 121, 206801 (2018)]. In addition to the sign changes in the thermopower at temperatures T 1 (B) and T 2 (B) (present also for B = 0) in the Kondo regime, an additional sign change was found [T. A. Costi, Phys. Rev. B 100, 161106(R) (2019)] at a temperature T 0 (B) < T 1 (B) < T 2 (B) for fields exceeding a gate-voltage dependent value B 0 , where B 0 is comparable to, but larger, than the field B c at which the Kondo resonance splits. We describe the evolution of the Kondo-induced sign changes in the thermopower at temperatures T 0 (B), T 1 (B) and T 2 (B) with magnetic field and gate voltage from the Kondo regime to the mixed valence and empty orbital regimes and show that these temperatures merge to the single temperature T 0 (B) upon entry into the mixed valence regime. By carrying out detailed numerical renormalization group calculations for the above quantities, using appropriate experimental parameters, we address a recent experiment which measures the field-dependent thermoelectric response of InAs quantum dots exhibiting the Kondo effect [A. Svilans et al., Phys. Rev. Lett. 121, 206801 (2018)]. This allows us to understand the overall trends in the measured field-and temperature-dependent thermoelectric response as a function of gate voltage. In addition, we determine which signatures of the Kondo effect (sign changes at T 0 (B), T 1 (B) and T 2 (B)) have been observed in this experiment, and find that while the Kondoinduced signature at T 1 (B) is indeed measured in the data, the signature at T 0 (B) can only be observed by carrying out further measurements at a lower temperature. In addition, the less interesting (high-temperature) signature at T 2 (B) Γ, where Γ is the electron tunneling rate onto the dot, is found to lie above the highest temperature in the experiment, and was therefore not accessed. Our calculations provide a useful framework for interpreting future experiments on direct measurements of the thermopower of Kondo-correlated quantum dots in the presence of finite magnetic fields, e.g., by extending zero-field measurements of the thermopower [B. Dutta et al., Nano Lett. 19, 506 (2019)] to finite magnetic fields. arXiv:1910.08785v1 [cond-mat.str-el]

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The Kondo resonance line shape in scanning tunnelling spectroscopy: instrumental aspects

Cited by 39 publications

References 77 publications

Fragmentation and Distortion of Terpyridine-Based Spin-Crossover Complexes on Au(111)

Fragmentation and Distortion of Terpyridine-Based Spin-Crossover Complexes on Au(111)

Spin-Crossover Complexes in Direct Contact with Surfaces

Magnetic field dependence of the thermopower of Kondo-correlated quantum dots: Comparison with experiment

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