Bulletin of the American Physical Society
2024 APS March Meeting
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session A59: Rational Design of Hybrid Organic-Inorganic Interfaces IFocus
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Sponsoring Units: DCOMP Chair: Oliver Monti, University of Arizona Room: 206AB |
Monday, March 4, 2024 8:00AM - 8:36AM |
A59.00001: The significant role of interfaces in potential low energy nonvolatile voltage controlled multiferroic spintronic transistors Invited Speaker: Peter A Dowben Here the influence of heteromolecular interfaces will be compared with interfaces with a magnetoelectric oxide and in each case the local magnetic moment plays a significant role. These interface effects matters because the control of interface interactions is essential to two very different approaches to a competitive multiferroic voltage controlled nonvolatile spintronic transistor with a delay time less than CMOS and an energy cost much less than CMOS. Molecular spintronic transistors have now been shown to be possible without ferromagnetism. The spin crossover (SCO) phenomenon, specifically the spin state in 3d transition metal compounds, can be exploited to create voltage-controlled isothermal changes in the electronic structure and conductance, through the manipulation of an organic ferroelectric interface. This nonvolatile isothermal voltage-controlled spin state switching, at room temperature, is evident in both spectroscopy and transport studies of thin film bilayer devices [1,2]. The role of the interface is not only crucial, but the influence of the interface extends far beyond just those spin crossover molecules in intimate contact with the organic ferroelectric. Interfaces also play a role in the spintronic transistor based on antiferromagnetic magnetoelectric oxides and possible 2D semiconductor channels. Through detailed studies of the electronic band structure, the pertinent interfaces, more is understood about the influence of the voltage-controlled boundary polarization of the magneto-electric oxide Cr2O3(001) on a 2D semiconductor channel or metal with large Stoner susceptibility. The existing working voltage controlled nonvolatile oxide magneto-electric spintronic transistors, the influence of the boundary spin polarization does not extend very far from the interface except in special cases (Pd on Cr2O3(001)), which will be discussed. Like the molecular spin crossover heterostructures, no applied external magnetic field is required [3]. |
Monday, March 4, 2024 8:36AM - 8:48AM |
A59.00002: Ultrafast Generation of Spin Polarization in an Organic / 2D Heterostructure Oliver L Monti, Sara Zachritz, Benito Arnoldi, Sebastian Hedwig, Martin Aeschlimann, Benjamin Stadtmueller The ability to generate spin polarization and spin current on femtosecond time-scales is of vital importance for spintronics, quantum information science and novel spin-based low-energy electronics modalities. Current approaches relying on superdiffusive spin-transport in ferromagnetic structures are however limiting due to the need for external magnetic fields. Here we show instead by time-, spin- and angle-resolved photoemission that the combination of C60 and WSe2, two diamagnetic materials, create a 2D heterostructure that upon ultrafast excitation generates transient spin polarization without the need for an external magnetic field or ferromagnets. Optical excitation drives electron-transfer from C60 to WSe2 in a few hundred fs, and the charge-separation is accompanied by the build-up of a layer-dependent electric field across the heterointerface. This electric field induces a time- and layer-dependent Stark shift of the energy levels and valence bands at the interface, which due to spin-valley-layer locking in WSe2 results in a transient spin polarization. This constitutes a new path for ultrafast spin manipulation without the need for external magnetic fields and may pave the way to ultrafast generation of spin currents. |
Monday, March 4, 2024 8:48AM - 9:00AM |
A59.00003: A computational investigation of spin filtering behavior in all-organic radicals Kevin Batzinger, Manuel Smeu All-organic radicals have been identified as a class of molecules which can have either excellent spin filter efficiency or exceptional conductance, with the ability to switch between the two regimes by applying bias voltage. However, this remarkable behavior was only identified for phenalenyl (PLY)-based radicals with thiol (-SH) anchoring groups. Changing anchoring groups, to methyl-sulfur (-SMe) or dihydrobenzothiophene (-BT), may affect the previously identified properties. We calculate bias-dependent charge transport across a variety of heteroatom substituted PLY radicals as well as the closed-shell molecule, naphthalene with -SH, -SMe and -BT anchoring groups using the non-equilibrium Green’s function technique in conjunction with density functional theory (NEGF-DFT). Our simulations highlight the importance that anchoring groups play in the role of charge transport across molecular devices, and touch on the interplay of design principles, electronic conductance, and spin filtering. |
Monday, March 4, 2024 9:00AM - 9:12AM |
A59.00004: Screened-Exchange Range-Separated Hybrid Functionals for Surfaces and Interfaces Jiawei Zhan, Marco Govoni, Giulia Galli Electronic structure calculations based on density functional theory have successfully predicted numerous ground-state properties of a variety of molecules and materials. However, exchange and correlation functionals currently used in the literature, including semi-local and hybrid functionals, are often inaccurate to describe the electronic properties of heterogeneous solids, especially systems composed of building blocks with large dielectric mismatch. Here, we present a dielectric-dependent range separated hybrid functional, screened-exchange range-separated hybrid (SE-RSH) [1], for the investigation of heterogeneous materials. We define a spatially dependent fraction of exact exchange inspired by the static Coulomb-hole and screened-exchange (COHSEX) approximation used in many-body perturbation theory, and we show that the proposed functional accurately predicts the electronic structure of several nonmetallic interfaces, three- and two-dimensional, pristine, and defective solids and nanoparticles. |
Monday, March 4, 2024 9:12AM - 9:48AM |
A59.00005: Ab-initio studies of molecular magnets for quantum information science applications Invited Speaker: Kyungwha Park Magnetic molecules have been proposed to be versatile for potential magnetic storage, molecular spintronics, quantum sensing, quantum register, and quantum computing applications, by modifying the local chemical environments. Compared to solid-state systems where many practical advances have been made for these applications, magnetic molecular systems are currently being explored to identify ideal molecular candidates and corresponding robust chemical environments for such applications. One popular approach is to design molecular systems whose properties are analogous to the representative solid-state systems for the applications. A few examples are Cr-based molecules in which electron spin qubits were optically addressed and controlled, and rare-earth-based magnetic molecules in which entanglement of nuclear spin qubits was achieved via electric or optical means. In all these systems, electron or nuclear spin qubit states are provided by 3d or 4f electrons which are strongly correlated and/or can form multiconfigurational states. Therefore, an understanding of their properties in the ground and excited states requires ab-initio methods beyond density-functional theory. In this talk, we present our calculated ground- and excited-state electronic and magnetic properties of several molecular systems which passed proof of concept tests for quantum computing applications, such as Cr-based molecules, rare-earth-based molecules, and magnetic adatoms on an insulating substrate, by using ab-initio multireference methods including spin-orbit coupling and relativistic hyperfine coupling. Our results will be useful for designing magnetic molecular systems for quantum information science applications. |
Monday, March 4, 2024 9:48AM - 10:00AM |
A59.00006: To be a metal, or not to be? Distinguishing semiconductors from metals in high-throughput Kohn-Sham DFT Flaviano J dos Santos, Nicola Marzari In non-interacting theories (e.g., Kohn-Sham DFT), the bandgap is the energy that separates valence bands from conduction bands in semiconductors and insulators. In most first-principles calculations, one computes the electronic band structure with a finite sampling in reciprocal space; thus, a finite (if small) gap always exists at zero temperature between the highest occupied state and the lowest unoccupied one. The problem is made more severe when a coarse k-point grid is used and/or when the gap is very small (a few tenths of an eV). We investigate current numerical methods to determine the bandgap and their sensitivity to k-point sampling and smearing. Furthermore, we explore alternative descriptors that separate metals from nonmetals, such as the electronic entropy. |
Monday, March 4, 2024 10:00AM - 10:12AM |
A59.00007: Dark excitons and dark polaritons in hybrid perovskites. Eric R Bittner Dark optical processes are often elusive and difficult to quantify. In my talk, I will discuss how exciton/exciton scattering within the manifold of dark (i.e., non-optical) states leads to tell-tale signatures in the non-linear optical response of low-dimensional semiconductors and polariton forming microcavity systems. Our theoretical approach is based on a non-equilibrium/non-stationary stochastic model derived from a composite-boson treatment of electron/hole excitations, allowing us to compute their non-linear coherent optical responses. We shall also discuss how correlated noise can affect the decoherence and fidelity of a quantum state. While the talk will focus on 2D lead-halide perovskite semiconductors, I will make contact with recent experiments of the Silva group in which these materials are embedded in a polaritonic microcavity. |
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