Atomic Molecular Junctions

Inelastic Noise Spectroscopy

During my doctoral research, I developed the ‘Inelastic shot noise spectroscopy’ to probe electron-phonon coupling in atomic chains. Federica Haupt at Universität Konstanz and Remi Avriller and A. Levy Yeyati at Universidad Autónoma de Madrid has implemented ab-initio DFT computation and non-equilibrium Keldysh formalism to probe the electron-vibron coupling in quantum conductor via inelastic shot noise [1]. Our experimental measurement on gold atomic chain at cryogenic temperature perfectly replicated the mathematical model developed by Madrid [2] and Konstanz group [3]. The inelastic signature in noise is highly transmission dependence. At perfect transmission, the inelastic signature is seen as higher noise than elastic noise however negative shot noise seen at lower transmission. This decrease in noise is very unusual, attributed to coherent two-electron process mediated by vibron and Pauli exclusion principle [4]. Further on, my work was replicated by Oren Tal at Weizmann and Elke Scheer at Konstanz.

References:

  1. A study of electron scattering through noise spectroscopy PhD thesis : Faculteit der Wiskunde en Natuurwetenschappen (2012)
  2. R. Avriller and A. Levy Yeyati, Phys. Rev. B 80, 041309 (2009).
  3. F. Haupt, T. Novotný, and W. Belzig, Phys. Rev. Lett. 103, 136601 (2009)
  4. M. Kumar, R. Avriller, A. Levy Yeyati and Jan van Ruitenbeek, Phys. Rev. Lett. 108, 146602 (2012)

Itinerant magnetism in atomic chain

One of the underlying intriguing topic in atomic spintronics is itinerant magnetism in a atomic chain. The bulk Platinum is paramagnetic in nature. However Alexander Smogunov and Erio Tosatti’s density functional calculation has predicted Pt nanowire will overcomes Stoner criterion and shows enhanced ferromagnetism [1]. Pt readily forms a long atomic chain at lower temperature, a ferromagnetic system. The atomic Pt chain coupled to paramagnetic bulk leads provides an excellent platform to study spin transport via elastic noise spectroscopy. On contrary to the theoretical prediction, our noise studies have shown the electronic transport in Pt atomic chain is weakly affected by spontaneous magnetic state formed in the chain [2]. This observation was confirmed theoretically via ab-intio calculation [3]. Later, Elke Scheer group experimentally shown the formation of local magnetic moment in Pt atomic contacts via magneto-conductance measurement though it requires field as high as +/-8T [4]. The magneto-conductance measurement shows complex role of bulk leads in spin transport. In our earlier experiment in ferromagnetic molecular contact (Ni-D2-Ni) role of bulk lead, spin polarization is seen in shot noise but signature was very weak [5]. On other hand in Kondo-like ferromagnetic molecular contact, dominant signature of spin polarization was seen in shot noise [6].

References:

  1. A. Smogunov, A. Dal Corso, A. Delin, R. Weht and E. Tosatti, Nature Nanotechnology 3, 22 (2008)
  2. M. Kumar, O. Tal, R. H. M. Smit, A. Smogunov, E. Tosatti, and Jan M. Ruitenbeek Phys. Rev. B 88, 245431 (2013)
  3. Xiao, L. & Wang, L. J. Phys. Chem. A 108, 8605–8614 (2004)
  4. F. Strigl, C. Espy, M. Bückle, E. Scheer and T. Pietsch, Nature Communications 6, 6172 (2015)
  5. M. Kumar, K. K. V. Sethu, and Jan van Ruitenbeek, Phys. Rev. B 91, 245404 (2015).
  6. R. Vardimon M. Klionsky and O. Tal . Nano Letters 15, 3894 (2015)