arXiv subjects

Anubhab Chakraborty

Publications and source records attributed to Anubhab Chakraborty.

4 recordsLinked to original sources

arXiv2025

Tailoring Charge-Transfer at Metal-Organic Interfaces Using Designer Shockley Surface States

Metal-organic interfaces determine critical processes in organic electronic devices. The frontier molecular orbitals (highest occupied and lowest unoccupied molecular orbital, HOMO and LUMO) are crucial in determining charge-injection and -collection processes into and from the organic semiconductor films. Here we show that we are able to tune the interfacial electronic structure of a strongly interacting interfacial system formed by adsorption of the electron acceptor 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HATCN, C18N12) on Ag thin films on Cu(111). The thickness-dependent Shockley surface state emerging on this layered metallic system couples to the LUMO, which allows precise control over the energetic position and filling of the charge-transfer interface state relative to the Fermi level (EF). Our ability to tune the interfacial electronic structure while maintaining the structure of the molecular film represents an important step towards designing organic semiconductor interfaces.

cond-mat.mtrl-sci↗

arXiv2025

Dial It Down: The Effect of Strongly Interacting Adsorbates on the BiAg2 Rashba Surface State

Organic semiconductors interfaced with spin-orbit coupled materials offer a rich playground for fundamental studies of controlling spin dynamics in spintronic devices. The adsorbate-surface interactions at such interfaces play a key role in determining the valence electronic and spin structure and consequently, the device physics as well. Here we present the adsorption and electronic structure of the strong organic electron acceptor 2,7-dinitropyrene-4,5,9,10-tetrone (NO2-PyT, C16H4N2O8) on the Rashba spin-orbit coupled surface alloy BiAg2/Ag(111). We show that the strong adsorbate-surface alloy interaction leads to weakening of the electronic coupling between the surface alloy atoms and quench the spin-orbit coupled surface state in BiAg2/Ag(111). Our findings demonstrate an important challenge associated with using molecular adsorbates to tailor the spin polarization in BiAg2/Ag(111), and our work provides guidelines to consider while designing interfacial systems to engineer the spin polarization in Rashba surface alloys.

cond-mat.mtrl-sci↗

arXiv2023

Frontier Orbital Degeneracy: A new Concept for Tailoring the Magnetic State in Organic Semiconductor Adsorbates

Kondo resonances in molecular adsorbates are an important building block for applications in the field of molecular spintronics. Here, we introduce the novel concept of using frontier orbital degeneracy for tailoring the magnetic state, which is demonstrated for the case of the organic semiconductor 1,4,5,8,9,11-Hexaazatriphenylenehexacarbonitrile (HATCN, C18N12) on Ag(111). Low-temperature scanning tunneling microscopy/spectroscopy (LT-STM/STS) measurements reveal the existence of two types of adsorbed HATCN molecules with distinctly different appearances and magnetic states, as evident from the presence or absence of an Abrikosov-Suhl-Kondo resonance. Our DFT results show that HATCN on Ag(111) supports two almost isoenergetic states, both with one excess electron transferred from the Ag surface, but with magnetic moments of either 0 or 0.65 uB. Therefore, even though all molecules undergo charge transfer of one electron from the Ag substrate, they exist in two different molecular magnetic states that resemble a free doublet or an entangled spin state. We explain how the origin of this behavior lies in the twofold degeneracy of the lowest unoccupied molecular orbitals of gas phase HATCN, lifted upon adsorption and charge-transfer from Ag(111). Our combined STM and DFT study introduces a new pathway to tailoring the magnetic state of molecular adsorbates on surfaces, with significant potential for spintronics and quantum information science.

cond-mat.mtrl-sci↗

arXiv2020

Ultrafast Carrier Dynamics in Two-Dimensional Electron Gas-Like K-doped MoS2

Electronic interactions associated with atomic adsorbates on transition metal dichalcogenides such as MoS2 can induce massive electronic reconstruction that results in the formation of a new type of heavily doped transition metal dichalcogenide that exhibits characteristics of a two-dimensional electron gas. The impact of quantum confinement and reduced dimensionality on the carrier dynamics in such two-dimensional systems is at present not known, but is of paramount importance if they are to find application in optoelectronic devices. Here we show by a combination of angle-resolved photoemission and advanced x-ray spectroscopies that many-body interactions in reduced dimension drastically shorten carrier lifetimes to below 0.5 fs, and reveal how potassium intercalation in MoS2 forces orbital rehybridization to create a two-dimensional electron gas.

cond-mat.mtrl-sci↗