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Facile integration of giant exchange bias in Fe5GeTe2/oxide heterostructures by atomic layer deposition

Physical Review Materials 2023年第1期7卷 014008-014008页

作者： Jierui Liang Shanchuan Liang Ti Xie Andrew F. May Thomas Ersevim Qinqin Wang Hyobin Ahn Changgu Lee Xixiang Zhang Jian-Ping Wang Michael A. McGuire Min Ouyang Cheng Gong Department of Electrical and Computer Engineering and Quantum Technology Center University of Maryland College Park Maryland 20742 USA Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831 USA Department of Physics University of Maryland College Park Maryland 20742 USA SKKU Advanced Institute of Nanotechnology Sungkyunkwan University Suwon Gyeonggido 16419 Republic of Korea Department of Mechanical Engineering Sungkyunkwan University Suwon Gyeonggido 16419 Republic of Korea King Abdullah University of Science and Technology (KAUST) Physical Sciences and Engineering Division (PSE) Thuwal Saudi Arabia Department of Electrical and Computer Engineering University of Minnesota Minneapolis Minnesota 55455 USA

Exchange bias arises from the interfacial exchange coupling in ferromagnet-antiferromagnet bilayers and manifests as a horizontal shift of the magnetic hysteresis loop, constituting a critical component underpinning a broad range of magnetoresistive logic and memory devices. The facile implementation of exchange bias in van der Waals (vdW) magnets would be a key step towards practical devices for emerging vdW spintronics. Here, we report an easy approach to establishing strong exchange bias in the vdW magnet Fe5GeTe2 by a single-step process—atomic layer deposition (ALD) of oxides on Fe5GeTe2. We successfully created exchange bias of 300–1500 Oe in Fe5GeTe2/Al2O3, Fe5GeTe2/ZnO, and Fe5GeTe2/V2O5 heterostructures, at 130 K. Control experiments showed that increasing the oxidant pulse duration in each ALD cycle or utilizing the stronger oxidant O3 can enhance the exchange bias strength, revealing the key role of the ALD oxidants. Our systematic work elucidates the essential role of ALD-enabled oxidization of Fe5GeTe2 in the formation of exchange bias, and establishes ALD of oxides as a facile, controllable, and generally effective approach to creating giant exchange bias in vdW magnets, representing an integral advance towards practical vdW spintronic devices.

关键词： Exchange bias Magnetism Ferromagnets Van der Waals systems

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Stable Symmetry-Protected Topological Phases in Systems with Heralded Noise

arXiv

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arXiv 2024年

作者： Chirame, Sanket Burnell, Fiona J. Gopalakrishnan, Sarang Prem, Abhinav School of Physics and Astronomy University of Minnesota MinneapolisMN55455 United States Department of Electrical and Computer Engineering Princeton University PrincetonNJ08544 United States School of Natural Sciences Institute for Advanced Study PrincetonNJ08540 United States

We present a family of local quantum channels whose steady-states exhibit stable mixed-state symmetry-protected topological (SPT) order. Motivated by recent experimental progress on "erasure conversion" techniques that allow one to identify (herald) decoherence processes, we consider open systems with biased erasure noise, which leads to strongly symmetric heralded errors. We utilize this heralding to construct a local correction protocol that effectively confines errors into short-ranged pairs in the steady-state. Using a combination of numerical simulations and mean-field analysis, we show that our protocol stabilizes SPT order against a sufficiently low rate of decoherence. As the rate of heralded noise increases, SPT order is eventually lost through a directed percolation transition. We further find that while introducing unheralded errors destroys SPT order in the limit of long length- and time-scales, the correction protocol is sufficient for ensuring that local SPT order persists, with a correlation length that diverges as ξ ∼ (1−fe)−1/2, where fe is the fraction of errors that are heralded. © 2024, CC BY.

关键词： Quantum channel

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Stabilizing Non-Abelian Topological Order against Heralded Noise via Local Lindbladian Dynamics

arXiv

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arXiv 2024年

作者： Chirame, Sanket Prem, Abhinav Gopalakrishnan, Sarang Burnell, Fiona J. School of Physics and Astronomy University of Minnesota MinneapolisMN55455 United States School of Natural Sciences Institute for Advanced Study PrincetonNJ08540 United States Department of Electrical and Computer Engineering Princeton University PrincetonNJ08544 United States

An important open question for the current generation of highly controllable quantum devices is understanding which phases can be realized as stable steady-states under local quantum dynamics. In this work, we show how robust steady-state phases with both Abelian and non-Abelian mixed-state topological order can be stabilized against generic "heralded" noise using active dynamics that incorporate measurement and feedback, modeled as a fully local Lindblad master equation. These topologically ordered steady states are two-way connected to pure topologically ordered ground states using local quantum channels, and preserve quantum information for a time that is exponentially large in the system size. Specifically, we present explicit constructions of families of local Lindbladians for both Abelian (Z2) and non-Abelian (D4) topological order whose steady-states host mixed-state topological order when the noise is below a threshold strength. As the noise strength is increased, these models exhibit first-order transitions to intermediate mixed state phases where they encode robust classical memories, followed by (first-order) transitions to a trivial steady state at high noise rates. When the noise is imperfectly heralded, steady-state order disappears but our active dynamics significantly enhances the lifetime of the encoded logical information. To carry out the numerical simulations for the non-Abelian D4 case, we introduce a generalized stabilizer tableau formalism that permits efficient simulation of the non-Abelian Lindbladian dynamics. © 2024, CC BY.

关键词： Topology

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Giant magnetoresistance, Fermi-surface topology, Shoenberg effect, and vanishing quantum oscillations in the type-II Dirac semimetal candidates MoSi2 and WSi2

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Physical Review B 2022年第7期105卷 075141-075141页

作者： Orest Pavlosiuk Przemysław Wojciech Swatek Jian-Ping Wang Piotr Wiśniewski Dariusz Kaczorowski Institute of Low Temperature and Structure Research Polish Academy of Sciences Okólna 2 50-422 Wrocław Poland Electrical and Computer Engineering Department University of Minnesota Minneapolis Minnesota 55455 USA Institute of Molecular Physics Polish Academy of Sciences Smoluchowskiego 17 60-179 Poznań Poland

We performed comprehensive theoretical and experimental studies of the electronic structure and the Fermi surface topology of two novel quantum materials, MoSi2 and WSi2. The theoretical predictions of the electronic structure in the vicinity of the Fermi level was verified experimentally by thorough analysis of the observed quantum oscillations in both electrical resistivity and magnetostriction. We established that the Fermi surface sheets in MoSi2 and WSi2 consist of 3D dumbbell-shaped holelike pockets and rosette-shaped electronlike pockets, with nearly equal volumes. Based on this finding, both materials were characterized as almost perfectly compensated semimetals. In conjunction, the magnetoresistance attains giant values of 104 and 105% for WSi2 and MoSi2, respectively. In turn, the anisotropic magnetoresistance achieves −95% and −98% at T=2 K and in B=14 T for WSi2 and MoSi2, respectively. Furthermore, for both compounds we observed the Shoenberg effect in their Shubnikov-de Haas oscillations that persisted at as high temperature as T=25 K in MoSi2 and T=12 K in WSi2. In addition, we found for MoSi2 a rarely observed spin-zero phenomenon. Remarkably, the electronic structure calculations revealed type-II Dirac cones located near 480 and 710 meV above the Fermi level in MoSi2 and WSi2, respectively.

关键词： Electronic structure Fermi surface Magnetoresistance Shubnikov-de Haas effect Topological phases of matter

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Methodological framework for materials discovery using machine learning

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Physical Review Materials 2022年第4期6卷 043802-043802页

作者： Eng Hock Lee Wei Jiang Hussain Alsalman Tony Low Vladimir Cherkassky Department of Electrical and Computer Engineering University of Minnesota 200 Union St SE Minneapolis Minnesota 55455 USA School of Physics Beijing Institute of Technology Beijing 100081 China King Abdulaziz City for Science and Technology (KACST) Riyadh 6086-11442 Kingdom of Saudi Arabia

Traditionally, materials discovery has been guided by basic physical rules, and such rules embody the basic understanding of the physical characteristics of interest of the material. However, the discovery of physical rules remains a challenging task due to the inherent difficulty in recognizing patterns in the high-dimensional and highly nonuniform distributed materials space. The standard data analytics approach using machine learning (ML) may fall short in producing meaningful results due to fundamental differences between the underlying assumptions and goals of ML vs materials discovery. ML is mainly focused on estimating complex black-box predictive models (that are nonlinear and multivariate), whereas in materials discovery, the goal is to come up with interpretable data-driven physical rules. Here, we attempt to tackle this problem by proposing a robust data analytics framework that allows us to derive basic physical rules from data. We introduce the concept of global and local modeling, utilizing both supervised and unsupervised learning, for highly nonuniformly distributed materials data. To enhance the model interpretation, we also introduce a model-independent interpretation technique to assist human experts in extracting useful physical rules. The proposed framework for extracting data-derived physical rules at the global and local level is illustrated using two case studies: (1) classification of van der Waals (vdW) and non-vdW (nvdW) materials and (2) classification of wide bandgap and non-wide bandgap vdW materials.

关键词： Machine learning 2-dimensional systems Superlattices Van der Waals systems Density functional theory

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High-fidelity Database-free Deep Learning Reconstruction for Real-time Cine Cardiac MRI

High-fidelity Database-free Deep Learning Reconstruction for...

引用

Annual International Conference of the IEEE engineering in Medicine and Biology Society (EMBC)

作者： Ömer Burak Demirel Chi Zhang Burhaneddin Yaman Merve Gulle Chetan Shenoy Tim Leiner Peter Kellman Mehmet Akçakaya Department of Electrical and Computer Engineering University of Minnesota Minneapolis MN USA Center for Magnetic Resonance Research University of Minnesota Minneapolis MN USA Department of Medicine (Cardiology) University of Minnesota Minneapolis MN USA Department of Radiology Mayo Clinic Rochester MN USA National Heart-Lung and Blood Institute Bethesda MD USA

Real-time cine cardiac MRI provides an ECG-free free-breathing alternative to clinical gold-standard ECG-gated breath-hold segmented cine MRI for evaluation of heart function. Real-time cine MRI data acquisition during free breathing snapshot imaging enables imaging of patient cohorts that cannot be imaged with segmented or breath-hold acquisitions, but requires rapid imaging to achieve sufficient spatial-temporal resolutions. However, at high acceleration rates, conventional reconstruction techniques suffer from residual aliasing and temporal blurring, including advanced methods such as compressed sensing with radial trajectories. Recently, deep learning (DL) reconstruction has emerged as a powerful tool in MRI. However, its utility for free-breathing real-time cine MRI has been limited, as database-learning of spatio-temporal correlations with varying breathing and cardiac motion patterns across subjects has been challenging. Zero-shot self-supervised physics-guided deep learning (PG-DL) reconstruction has been proposed to overcome such challenges of database training by enabling subject-specific training. In this work, we adapt zero-shot PG-DL for real-time cine MRI with a spatio-temporal regularization. We compare our method to TGRAPPA, locally low-rank (LLR) regularized reconstruction and database-trained PG-DL reconstruction, both for retrospectively and prospectively accelerated datasets. Results on highly accelerated real-time Cartesian cine MRI show that the proposed method outperforms other reconstruction methods, both visibly in terms of noise and aliasing, and quantitatively.

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Giant piezoelectricity in group IV monochalcogenides with ferroelectric AA layer stacking

arXiv

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arXiv 2024年

作者： Lee, Seungjun Kim, Hyeong-Ryul Jiang, Wei Kwon, Young-Kyun Low, Tony Department of Electrical and Computer Engineering University of Minnesota MinneapolisMN55455 United States Department of Physics Research Institute for Basic Sciences Kyung Hee University Seoul02447 Korea Republic of Department of Information Display Kyung Hee University Seoul02447 Korea Republic of

The piezoelectricity of group IV monochalcogenides (MXs, with M = Ge, Sn and X = S, Se) has attracted much attention due to their substantially higher piezoelectric coefficients compared to other 2D materials. However, with increasing layer number, their piezoelectricity rapidly disappears due to the antiferroelectric stacking order, severely limiting their practical applications. Using first-principles calculations, we investigated the piezoelectricity of MXs with the ferroelectric AA stacking configuration, which has recently been stabilized in experiments. We found that AA-stacked MXs have a ferroelectric ground state with the smallest lattice constant among other stacking configurations, resulting in a giant piezoelectric coefficient, which is the first demonstration of a strategy where the piezoelectric coefficients can increase with the number of layers. This can be attributed to a strong negative correlation between the lattice constant along the armchair direction and the piezoelectric coefficient, and spontaneous compressive strain stabilized in ferroelectric AA stacking configuration. © 2024, CC BY.

关键词： Piezoelectricity

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Transport Study of Charge-Carrier Scattering in Monolayer WSe2

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Physical Review Letters 2024年第5期132卷 056303-056303页

作者： Andrew Y. Joe Kateryna Pistunova Kristen Kaasbjerg Ke Wang Bumho Kim Daniel A. Rhodes Takashi Taniguchi Kenji Watanabe James Hone Tony Low Luis A. Jauregui Philip Kim Department of Physics Harvard University Cambridge Massachusetts 02138 USA Department of Physics and Astronomy University of California Riverside California 92521 USA Nordea Markets Nordea Bank Abp DK-2300 København S Denmark Department of Mechanical Engineering Columbia University New York New York 10027 USA National Institute for Materials Science Tsukuba Japan Department of Electrical and Computer Engineering University of Minnesota Minneapolis Minnesota 55455 USA Department of Physics and Astronomy The University of California Irvine California 92697 USA

Employing flux-grown single crystal WSe2, we report charge-carrier scattering behaviors measured in h-BN encapsulated monolayer field effect transistors. We observe a nonmonotonic change of transport mobility as a function of hole density in the degenerately doped sample, which can be explained by energy dependent scattering amplitude of strong defects calculated using the T-matrix approximation. Utilizing long mean-free path (>500 nm), we also demonstrate the high quality of our electronic devices by showing quantized conductance steps from an electrostatically defined quantum point contact, showing the potential for creating ultrahigh quality quantum optoelectronic devices based on atomically thin semiconductors.

关键词： electrical conductivity electrical properties Electronic structure Hall effect Quantum transport Valley degrees of freedom Transition metal dichalcogenides

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Metallicity and Anomalous Hall Effect in Epitaxially-Strained, Atomically-thin RuO2 Films

arXiv

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arXiv 2025年

作者： Jeong, Seung Gyo Lee, Seungjun Lin, Bonnie Yang, Zhifei Choi, In Hyeok Oh, Jin Yo ung Song, Sehwan Lee, Seung wook Nair, Sreejith Choudhary, Rashmi Parikh, Juhi Park, Sungkyun Choi, Woo Seok Lee, Jong Seok LeBeau, James M. Low, Tony Jalan, Bharat Department of Chemical Engineering and Materials Science University of Minnesota−Twin Cities MinneapolisMN55455 United States Department of Electrical and Computer Engineering University of Minnesota MinneapolisMN55455 United States Department of Materials Science and Engineering Massachusetts Institute of Technology CambridgeMA02139 United States Gwangju61005 Korea Republic of Department of Physics Sungkyunkwan University Suwon16419 Korea Republic of Department of Physics Pusan National University Busan46241 Korea Republic of

The anomalous Hall effect (AHE), a hallmark of time-reversal symmetry breaking, has been reported in rutile RuO2, a debated metallic altermagnetic candidate. Previously, AHE in RuO2 was observed only in strain-relaxed thick films under extremely high magnetic fields (~50 T). Yet, in ultrathin strained films with distinctive anisotropic electronic structures, there are no reports, likely due to disorder and defects suppressing metallicity thus hindering its detection. Here, we demonstrate that ultrathin, fully-strained 2 nm TiO2/t nm RuO2/TiO2 (110) heterostructures, grown by hybrid molecular beam epitaxy, retain metallicity and exhibit a sizeable AHE at a significantly lower magnetic field (2 (110) thin films. These findings establish ultrathin RuO2 as a platform for strain-engineered magnetism and underscore the transformative potential of epitaxial design in advancing spintronic technologies. © 2025, CC BY.

关键词： Molecular beam epitaxy

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从四方到立方:高性能太阳能电池的钙钛矿相结构演变

引用

Science Bulletin 2023年第2期68卷 141-145,M0003页

作者：魏旗梁昊 Yuki Haruta Makhsud Saidaminov 米启兮 Michael Saliba 崔光磊宁志军 School of Physical Science and Technology ShanghaiTech UniversityShanghai 201210China High Performance Computing Department National Supercomputing Center in ShenzhenShenzhen 200441China Department of Chemistry and Department of Electrical&Computer Engineering and Centre for Advanced Materials and Related Technologies(CAMTEC) University of VictoriaVictoria V8P 5C2Canada Institute for Photovoltaics University of StuttgartStuttgart 70569Germany Qingdao Industrial Energy Storage Research Institute Qingdao Institute of Bioenergy and Bioprocess TechnologyChinese Academy of SciencesQingdao 266101China

Crystal structure, which is generally determined by the composition, ionic radius and valence state of constituent elements, plays a significant role in the material’s fundamental properties such as optical, electronic, and mechanical characters. The manipulation of the crystal structure through compositional engineering, and understanding the relationship between crystal structure and properties are essential for the development of materials.

关键词：太阳能电池结构演变钙钛矿相

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