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Item Phase-resolved electrical detection of coherently coupled magnonic devices(AIP, 2021-05) Li, Yi; Zhao, Chenbo; Amin, Vivek P.; Zhang, Zhizhi; Vogel, Michael; Xiong, Yuzan; Sklenar, Joseph; Divan, Ralu; Pearson, John; Stiles, Mark D.; Zhang, Wei; Hoffmann, Axel; Novosad, Valentyn; Physics, School of ScienceWe demonstrate the electrical detection of magnon–magnon hybrid dynamics in yttrium iron garnet/Permalloy (YIG/Py) thin film bilayer devices. Direct microwave current injection through the conductive Py layer excites the hybrid dynamics consisting of the uniform mode of Py and the first standing spin wave (n = 1) mode of YIG, which are coupled via interfacial exchange. Both the two hybrid modes, with Py- or YIG-dominated excitations, can be detected via the spin rectification signals from the conductive Py layer, providing phase resolution of the coupled dynamics. The phase characterization is also applied to a nonlocally excited Py device, revealing the additional phase shift due to the perpendicular Oersted field. Our results provide a device platform for exploring hybrid magnonic dynamics and probing their phases, which are crucial for implementing coherent information processing with magnon excitations.Item Preliminary efforts to evaluate an initiative introducing computation across the undergraduate physics curriculum(2021) Gavrin, Andrew; Vemuri, Gautam; Maric, Danka; Physics, School of ScienceWe report our preliminary efforts to evaluate a departmental project: the inclusion of computational methods across our undergraduate curriculum. Our overarching goal is for students to consider computational approaches as a "normal" way to solve physics problems, on par with analytical approaches. In this paper, we focus on our efforts to evaluate the development of our students' attitudes and self-efficacy with respect to key computational methods. We describe our efforts to develop and deploy a survey instrument students complete each semester. This allows us to study, e.g., the points in the curriculum at which students gain confidence with particular methods, or adopt more expert-like attitudes regarding computation in general. We investigated the reliability of our instrument using a split-half process and found the Spearman-Brown coefficients for unequal length were r = 0.818, r = 0.895, and r = 0.917 for the three constructs in our survey. We also provide preliminary data from the early use of the survey and outline next steps for the project.Item Nonvolatile Voltage Controlled Molecular Spin-State Switching for Memory Applications(MDPI, 2021-03) Ekanayaka, Thilini K.; Hao, Guanhua; Mosey, Aaron; Dale, Ashley S.; Jiang, Xuanyuan; Yost, Andrew J.; Sapkota, Keshab R.; Wang, George T.; Zhang, Jian; N’Diaye, Alpha T.; Marshall, Andrew; Cheng, Ruihua; Naeemi, Azad; Xu, Xiaoshan; Dowben, Peter A.; Physics, School of ScienceNonvolatile, molecular multiferroic devices have now been demonstrated, but it is worth giving some consideration to the issue of whether such devices could be a competitive alternative for solid-state nonvolatile memory. For the Fe (II) spin crossover complex [Fe{H2B(pz)2}2(bipy)], where pz = tris(pyrazol-1-yl)-borohydride and bipy = 2,2′-bipyridine, voltage-controlled isothermal changes in the electronic structure and spin state have been demonstrated and are accompanied by changes in conductance. Higher conductance is seen with [Fe{H2B(pz)2}2(bipy)] in the high spin state, while lower conductance occurs for the low spin state. Plausibly, there is the potential here for low-cost molecular solid-state memory because the essential molecular thin films are easily fabricated. However, successful device fabrication does not mean a device that has a practical value. Here, we discuss the progress and challenges yet facing the fabrication of molecular multiferroic devices, which could be considered competitive to silicon.Item Magnetic Field Perturbations to a Soft X-ray-Activated Fe (II) Molecular Spin State Transition(MDPI, 2021-10) Hao, Guanhua; N’Diaye, Alpha T.; Ekanayaka, Thilini K.; Dale, Ashley S.; Jiang, Xuanyuan; Mishra, Esha; Mellinger, Corbyn; Yazdani, Saeed; Freeland, John W.; Zhang, Jian; Cheng, Ruihua; Xu, Xiaoshan; Dowben, Peter A.; Physics, School of ScienceThe X-ray-induced spin crossover transition of an Fe (II) molecular thin film in the presence and absence of a magnetic field has been investigated. The thermal activation energy barrier in the soft X-ray activation of the spin crossover transition for [Fe{H2B(pz)2}2(bipy)] molecular thin films is reduced in the presence of an applied magnetic field, as measured through X-ray absorption spectroscopy at various temperatures. The influence of a 1.8 T magnetic field is sufficient to cause deviations from the expected exponential spin state transition behavior which is measured in the field free case. We find that orbital moment diminishes with increasing temperature, relative to the spin moment in the vicinity of room temperature.Item Detectable Signature of Quantum Friction on a Sliding Particle in Vacuum(Wiley, 2021-05) Lombardo, Fernando C.; Decca, Ricardo S.; Viotti, Ludmila; Villar, Paula I.; Physics, School of ScienceSpatially separated bodies in a relative motion through vacuum experience a tiny friction force known as quantum friction (QF). This force has so far eluded experimental detection due to its small magnitude and short range. Quantitative details revealing traces of the QF in the degradation of the quantum coherence of a particle are presented. Environmentally induced decoherence for a particle sliding over a dielectric sheet can be decomposed into contributions of different signatures: one solely induced by the electromagnetic vacuum in the presence of the dielectric and another induced by motion. As the geometric phase (GP) has been proved to be a fruitful venue of investigation to infer features of the quantum systems, herein it is proposed to use the accumulated GP acquired by a particle as a QF sensor. Furthermore, an innovative experiment designed to track traces of QF by measuring the velocity dependence of corrections to the GP and coherence is proposed. The experimentally viable scheme presented can spark renewed optimism for the detection of non-contact friction, with the hope that this non-equilibrium phenomenon can be readily measured soon.Item Monitoring Dark-State Dynamics of a Single Nitrogen-Vacancy Center in Nanodiamond by Auto-Correlation Spectroscopy: Photonionization and Recharging(MDPI, 2021-04-10) Zhang, Mengdi; Li, Bai-Yan; Liu, Jing; Physics, School of ScienceIn this letter, the photon-induced charge conversion dynamics of a single Nitrogen-Vacancy (NV) center in nanodiamond between two charge states, negative (NV−) and neutral (NV0), is studied by the auto-correlation function. It is observed that the ionization of NV− converts to NV0, which is regarded as the dark state of the NV−, leading to fluorescence intermittency in single NV centers. A new method, based on the auto-correlation calculation of the time-course fluorescence intensity from NV centers, was developed to quantify the transition kinetics and yielded the calculation of transition rates from NV− to NV0 (ionization) and from NV0 to NV− (recharging). Based on our experimental investigation, we found that the NV−-NV0 transition is wavelength-dependent, and more frequent transitions were observed when short-wavelength illumination was used. From the analysis of the auto-correlation curve, it is found that the transition time of NV− to NV0 (ionization) is around 0.1 μs, but the transition time of NV0 to NV− (recharging) is around 20 ms. Power-dependent measurements reveal that the ionization rate increases linearly with the laser power, while the recharging rate has a quadratic increase with the laser power. This difference suggests that the ionization in the NV center is a one-photon process, while the recharging of NV0 to NV− is a two-photon process. This work, which offers theoretical and experimental explanations of the emission property of a single NV center, is expected to help the utilization of the NV center for quantum information science, quantum communication, and quantum bioimaging.Item Annihilation and Control of Chiral Domain Walls with Magnetic Fields(ACS, 2021-02-10) Karna, Sunil K.; Marshall, Madalynn; Xie, Weiwei; DeBeer-Schmitt, Lisa; Young, David P.; Vekhter, Ilya; Shelton, William A.; Kovács, Andras; Charilaou, Michalis; DiTusa, John F.; Physics, School of ScienceThe control of domain walls is central to nearly all magnetic technologies, particularly for information storage and spintronics. Creative attempts to increase storage density need to overcome volatility due to thermal fluctuations of nanoscopic domains and heating limitations. Topological defects, such as solitons, skyrmions, and merons, may be much less susceptible to fluctuations, owing to topological constraints, while also being controllable with low current densities. Here, we present the first evidence for soliton/soliton and soliton/antisoliton domain walls in the hexagonal chiral magnet Mn1/3NbS2 that respond asymmetrically to magnetic fields and exhibit pair-annihilation. This is important because it suggests the possibility of controlling the occurrence of soliton pairs and the use of small fields or small currents to control nanoscopic magnetic domains. Specifically, our data suggest that either soliton/soliton or soliton/antisoliton pairs can be stabilized by tuning the balance between intrinsic exchange interactions and long-range magnetostatics in restricted geometries.Item Molecular-Scale Nanodiamond with High-Density Color Centers Fabricated from Graphite by Laser Shocking(Elsevier, 2020-05) Motlag, Maithilee; Liu, Xingtao; Nurmalasari, Ni Putu Dewi; Jin, Shengyu; Nian, Qiong; Park, Charles; Jin, Linrui; Huang, Libai; Liu, Jing; Cheng, Gary J.; Physics, School of ScienceNanodiamonds (NDs) with nitrogen vacancy (NV) color centers have the potential for quantum information science and bioimaging due to their stable and non-classical photon emission at room temperature. Large-scale fabrication of molecular-size nanodiamonds with sufficient color centers may economically promote their application in versatile multidisciplinary fields. Here, the manufacture of molecular-size NV center-enriched nanodiamonds from graphite powder is reported. We use an ultrafast laser shocking technique to generate intense plasma, which transforms graphite to nanodiamonds under the confinement layer. Molecular dynamics simulations suggest that the high pressure of 35 GPa and the high temperature of 3,000K result in the metaphase transition of graphite to nanodiamonds within 100 ps. A high concentration of NV centers is observed at the optimal laser energy of 3.82 GW/cm2, at which point molecular-size (∼5 nm) nanodiamonds can individually host as many as 100 NV centers. Consecutive melamine annealing following ultrafast laser shocking enriches the number of NV centers >10-fold and enhances the spontaneous decay rate of the NV center by up to 5 times. Our work may enhance the feasibility of nanodiamonds for applications, including quantum information, electromagnetic sensing, bioimaging, and drug delivery.Item Observation of two PT transitions in an electric circuit with balanced gain and loss(Springer, 2020-08) Wang, Tishuo; Fang, Jianxiong; Xie, Zhongyi; Dong, Nenghao; Joglekar, Yogesh N.; Wang, Zixin; Li, Jiaming; Luo, Le; Physics, School of ScienceWe investigate 𝓟𝓣-symmetry breaking transitions in a dimer comprising two LC oscillators, one with loss and the second with gain. The electric energy of this four-mode model oscillates between the two LC circuits, and between capacitive and inductive energy within each LC circuit. Its dynamics are described by a non-Hermitian, 𝓟𝓣-symmetric Hamiltonian with three different phases separated by two exceptional points. We systematically measure the eigenfrequencies of energy dynamics across the three regions as a function of gain-loss strength. In addition to observe the well-studied 𝓟𝓣 transition for oscillations across the two LC circuits, at higher gain-loss strength, transition within each LC circuit is also observed. With their extraordinary tuning ability, 𝓟𝓣-symmetric electronics are ideally suited for classical simulations of non-Hermitian systems.Item Exceptional points in a time-delayed anti-parity-time symmetric system(Optica, 2021) Wilkey, Andrew; Joglekar, Yogesh N.; Vemuri, Gautam; Physics, School of ScienceWe report on the experimental realization of an anti-PT symmetric system in a pair of time-delay coupled semiconductor lasers, and via numerical and analytical modeling investigate the properties of exceptional points in it.