Soiree

STM experiments

Markus Ternes - Max Planck Institute for Solid State Research

Ivan Rungger - NPL

Thursday 5th September
Time: 4pm
Venue: The Council Room, King's College London
Contact: Cedric Weber
Tel: +44 020 7848 7165

Correlations and entanglement in atomic scale spin structures detected with scanning probe methods

Markus Ternes

Scanning probe microscopes have been very successful tools for studying individual atoms and molecules as well as complex structures. Systems which bear magnetic spin moments can be build with them on surfaces and stabilized in junctions. When such spins interact with each other or with the supporting electron baths, entanglement and correlated many-particle states can emerge, making them ideal prototypical quantum systems.

My presentation will discuss how transition metal atoms, metal hydrates as well as metallorganic molecules in conjunction with model Hamiltonians [1, 2] can be used as model systems to explore this fascinating quantum world. Specially crafted tips, in which the apex is functionalized can be used to detail the manipulation of the spin moment [3] or the transition mechanism between different quantum phases. Furthermore, controlling the couplings enables the quantification of spin-spin correlations [4], the detection “dark” moments [5] as well as the emergence of entanglement [6].

 

1. M. Ternes, New J. Phys. 17, 063016 (2015)

2. M. Ternes, Prog. Surf. Sci. 92, 83 (2017)

3. P. Jacobson, et al., Nature Communications 6, 8536 (2015)

4. M. Muenks, et al., Nature Communications 8, 14119 (2017)

5. B. Verlhac, et al., arXiv:1901.04862v1 [cond-mat.mes-hall] (2019)

6. D.-J. Choi, et al., Nano Lett. 17, 6203 (2017)

 

First principles simulations of strongly correlated molecules probed by scanning tunneling microscopy

Ivan Rungger

Molecules deposited on surfaces exhibit a number of complex phenomena due to the interaction of the electrons on the molecule with those in the substrate. To gain a detailed understanding of the physics, measurements at the single molecule level are required. The scanning tunneling microscope (STM) is an ideal tool for this purpose, and the latest 4-probe STMs allow to measure multiple parts of the surface at the same time.

Here we present the first principles methods that we have developed to simulate STM measurements. We combine density functional theory (DFT) with the non-equilibrium Green’s function technique to calculate the measured conductance of molecules on surfaces [1]. This allows us to determine the local contact geometry for complex interfaces, such as the one between molecules and graphite [2]. We further extend this method by including an Anderson impurity model to treat the strong electron correlations in the linear response [3], and finally include the renormalized super-perturbation theory to obtain a low-order expansion of the conductance on finite temperature, voltage and magnetic field [4].

 

1. A. Rocha et al., PRB 73, 085414 (2006); I. Rungger et al., PRB 78, 035407 (2008)

2. A. Rudnev et al., Science Adv. 3, e1602297 (2017)

3. A. Droghetti and I. Rungger, PRB 95, 085131 (2017)

4. W. Appelt et al., Nanoscale 10, 17738 (2018)

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