Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session S39: Molecular MagnetsFocus Live
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Sponsoring Units: GMAG DMP Chair: Selvan Demir, Michigan State University |
Thursday, March 18, 2021 11:30AM - 11:42AM Live |
S39.00001: Spin Echo and Coherence Time of Cr7Mn Nanomagnet Guanchu Chen, Gajadhar Joshi, James Logan, Daniel Sava, Grigore Timco, Richard Winpenny, Jonathan R Friedman Molecular nano-magnets (MNMs) are one of the promising systems for use as qubits for reduced decoherence thanks to the versatile tunability of the spin environment and unmatched scalability. Cr7Mn is in a family of heterometallic rings where avoided level crossing presents at zero magnetic field. This makes the magnet insensitive to the fluctuation of the field hence increases the coherence. We measured T2 and observed it to peak around zero field. We also saw Electron Spin Echo Envelope Modulation (ESEEM) outside of clock transition resulting from the coupling between spin and nucleus. This could provide an additional mechanism that preserves the information away from clock transition. Combined with the CPMG pulse sequence, ESEEM oscillations can be demodulated and have long coherence time. Dimers of coupled Cr7Mn molecules with different transition frequencies could be addressed individually with radio-frequency radiation, and the coupling between the two qubits could lead to new properties and applications. |
Thursday, March 18, 2021 11:42AM - 11:54AM Live |
S39.00002: Magneto-elastic coupling in multiferroic metal-organic framework [(CH3)2NH2]Co(HCOO)3 Komalavalli Thirunavukkuarasu, Rachael Richardson, Zhengguang Lu, Nicholas Combs, Nan Huang, Ganesh Pokharel, Dmitry Smirnov, David George Mandrus The family of MOFs comprised of methylammonum (A= (CH3)2NH2) and metal (B=Co, Cu, Fe, Mn, Ni) cations with a formate (X=HCOO3) anion has attracted a lot attention recently due to their intriguing multiferroic properties. In the infrared studies under applied magnetic fields, it was concluded that Co complex adopts a different mechanism for facilitating saturation of magnetic states by involving formate stretching distortions unlike other complexes in the family that use the formate bending mode [Inorg. Chem. 57, 11569 (2018).]. Concurrently, we performed Raman spectroscopy on [(CH3)2NH2]Co(HCOO)3 at magnetic fields up to 31T to probe the magneto-elastic coupling. We find that a weak Raman active vibrational mode at about 798 cm-1 corresponding to symmetric bending of the formate ion does exhibit magnetic-field-induced frequency shifts. The results of our investigations and its implications will be discussed in detail in the presentation. |
Thursday, March 18, 2021 11:54AM - 12:30PM Live |
S39.00003: Molecular Approaches to Magnetic Relaxation in Noisy, Magnetic Environments Invited Speaker: Joseph Zadrozny Magnetic relaxation is a fundamental property of molecule-based spins that is important for many different applications, spanning spin-based information processing to biomedical imaging. We know that, generally, slow magnetic relaxation rates are necessary for these applications, and such slowing of rates typically occurs when the local magnetic environment (the "spin bath") is quiet. However, biomedical imaging applications require function in environments full of magnetic nuclei. Similarly, applications for spins in devices are likely to experience stray magnetic fields. Thus, strategies to slow down magnetic relaxation times in noisy confines is a clear next frontier in this area. Understanding the environmental sensitivity of magnetic molecules is paramount to said strategies. In this talk, I will discuss our lab's recent results in studying the environmental sensitivity of electron and nuclear spin dynamics in magnetic molecules. |
Thursday, March 18, 2021 12:30PM - 12:42PM Live |
S39.00004: Information and decoherence in muon-fluorine coupled systems Stephen Blundell, John M Wilkinson Quantum systems remain coherent due to their unitary time evolution. However, when a subsystem interacts with the rest of the system (the environment) then interactions can result in a degrading of the quantum information in the subsystem. This situation is realised when a spin-polarised positive muon is implanted in a fluoride crystal. We have developed a method [1] to model this problem and account for our experimental data in a variety of fluorides without resorting to phenomenological stretched exponential functions that have been used in most previous treatments. These new ideas shed light on the muon site problem and provide some new insights into the process of decoherence in spin systems. [1] J. M. Wilkinson and S. J. Blundell, Phys. Rev. Lett. 125, 087201 (2020). |
Thursday, March 18, 2021 12:42PM - 12:54PM Live |
S39.00005: Topologically protected ground state degeneracies in an interacting two-spin system György Frank, Andras Palyi, Zoltán Scherübl, Szabolcs Csonka, Gergely Zaránd We theoretically study geometrical and topological aspects of a simple, yet experimentally relevant quantum magnet: two localized interacting electrons subject to spin-orbit coupling [1]. In our topological considerations the parameter space is the external magnetic field, and we search for the degeneracies of the ground state. These degeneracies carry a topological charge, which is the Chern number obtained as the integral of the ground-state Berry curvature for a surface containing them. The Hamiltonian is simple enough to find degeneracies analytically, however complex enough to have a rich geometrical classification [2]. We identify ten different possible geometrical patterns formed by these degeneracies and study their stability under small perturbations of the Hamiltonian. We expect that near-term experiments will be able to measure the Berry curvature and the Chern number associated to these degeneracy patterns [3]. |
Thursday, March 18, 2021 12:54PM - 1:06PM Live |
S39.00006: Coherence Time Enhancement in the [VO(TPP)] Molecular Nanomagnet Brendan C. Sheehan, Fabio Santanni, Guanchu Chen, Gajadhar Joshi, Lorenzo Sorace, Roberta Sessoli, Jonathan R Friedman The metal-organic [VO(TPP)] molecular nanomagnet has shown promise as a quantum memory qubit due to its impressive coherence time T2.1 Here, we investigate its behavior in the microwave regime with continuous wave (cw) and pulsed electron-spin resonance (ESR) techniques, using a homebuilt ESR spectrometer. We report progress on mapping ESR transitions in cw across varying frequency and field, with the ultimate goal of identifying an atomic-clock transition2 in the sub-GHz regime. Eight ESR transitions can clearly be seen due to hyperfine coupling in this S = 1/2, I = 7/2 system. Pulsed ESR experiments show long T2 times at several frequencies in excess of 8 μs through usage of the CPMG pulse sequence, suggesting improvement over previous work. Diluted samples of 2% [VO(TPP)] allow for a reduction in dipolar interactions and therefore a further enhancement of the coherence time. Finally, we discuss progress towards measuring T2 at the clock transitions, where decoherence from dipole and hyperfine interactions is expected to be minimized. |
Thursday, March 18, 2021 1:06PM - 1:18PM Live |
S39.00007: A Fast, Clock-Transition-Protected CNOT Gate with Molecular Nanomagnet Dimers Alexander Gardner, Charles Collett
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Thursday, March 18, 2021 1:18PM - 1:30PM Live |
S39.00008: Jahn-Teller Solid, Liquid and Gas spin Spin-crossover System Mn(taa) Jie-Xiang Yu, Dian-Teng Chen, Jie Gu, Jia Chen, Jun Jiang, Long Zhang, Yue Yu, Xiaoguang Zhang, Vivien Zapf, Hai-Ping Cheng Magnetoelectric coupling is of fundamental interest to understanding spin-charge-lattice interactions, |
Thursday, March 18, 2021 1:30PM - 2:06PM Not Participating |
S39.00009: Molecular approaches to next-generation magnetic materials at the nanoscale Invited Speaker: George Christou Molecular chemistry can bring many powerful advantages to the study of nanoscale |
Thursday, March 18, 2021 2:06PM - 2:18PM Not Participating |
S39.00010: Accessing the effect of support on the electronic structure of Fe[qsal(2,4-diterbutyl)]2 Spin crossover molecule: A First-Principles Study Tao Jiang, Duy Le, Talat S. Rahman Selection of supporting substrate for spin crossover (SCO) molecules is important for electronic application. Applying density functional theory calculations to the SCO molecule Fe[qsal(2,4-diterbutyl)]2 adsorbed on Au(111), graphene, and hexagonal boron nitride (h-BN), we showed a contrast in the influence of the substrate on electronic structure and magnetic properties of the molecule. We find that while the nature of the adsorption of the molecule on the three substrates is similar, mainly via van der Waals interaction, the charge transfer from the highest occupied molecular orbital of the molecule to the substrates is not the same. It donates about 0.82 electron to the Au surface and as much as 0.56 electron to graphene, but hardly any to h-BN. As a result, electronic structure of SCO is affected by the Au surface and graphene with an introduction of an partially occupied state at near the Fermi level. The contrasting effects of the substrates are traced to differences in the orbital alignment between the molecular orbital of the SCO and the substrates. Extension of calculations to overlayers of the SCO molecules on the substrates points to interesting differences in the underlying physics. |
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