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Yang C, Chen Z, Yu C, Cao J, Ke G, Zhu W, Liang W, Huang J, Cai W, Saha C, Sabuj MA, Rai N, Li X, Yang J, Li Y, Huang F, Guo X. Regulation of quantum spin conversions in a single molecular radical. NATURE NANOTECHNOLOGY 2024; 19:978-985. [PMID: 38448520 DOI: 10.1038/s41565-024-01632-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2023] [Accepted: 02/13/2024] [Indexed: 03/08/2024]
Abstract
Free radicals, generally formed through the cleavage of covalent electron-pair bonds, play an important role in diverse fields ranging from synthetic chemistry to spintronics and nonlinear optics. However, the characterization and regulation of the radical state at a single-molecule level face formidable challenges. Here we present the detection and sophisticated tuning of the open-shell character of individual diradicals with a donor-acceptor structure via a sensitive single-molecule electrical approach. The radical is sandwiched between nanogapped graphene electrodes via covalent amide bonds to construct stable graphene-molecule-graphene single-molecule junctions. We measure the electrical conductance as a function of temperature and track the evolution of the closed-shell and open-shell electronic structures in real time, the open-shell triplet state being stabilized with increasing temperature. Furthermore, we tune the spin states by external stimuli, such as electrical and magnetic fields, and extract thermodynamic and kinetic parameters of the transition between closed-shell and open-shell states. Our findings provide insights into the evolution of single-molecule radicals under external stimuli, which may proof instrumental for the development of functional quantum spin-based molecular devices.
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Affiliation(s)
- Caiyao Yang
- Beijing National Laboratory for Molecular Sciences, National Biomedical Imaging Centre, College of Chemistry and Molecular Engineering, Peking University, Beijing, P. R. China
- School of Materials Science and Engineering, Peking University, Beijing, P. R. China
| | - Zhongxin Chen
- Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, P. R. China
| | - Cuiju Yu
- Department of Chemical Physics, University of Science and Technology of China, Hefei, P. R. China
| | - Jiawen Cao
- Beijing National Laboratory for Molecular Sciences, National Biomedical Imaging Centre, College of Chemistry and Molecular Engineering, Peking University, Beijing, P. R. China
| | - Guojun Ke
- Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, P. R. China
| | - Weiya Zhu
- Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, P. R. China
| | - Weixuan Liang
- Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, P. R. China
| | - Jiaxing Huang
- Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, P. R. China
| | - Wanqing Cai
- Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, P. R. China
| | - Chinmoy Saha
- Dave C. Swalm School of Chemical Engineering and Centre for Advanced Vehicular Systems, Mississippi State University, Mississippi State, MS, USA
| | - Md Abdus Sabuj
- Dave C. Swalm School of Chemical Engineering and Centre for Advanced Vehicular Systems, Mississippi State University, Mississippi State, MS, USA
| | - Neeraj Rai
- Dave C. Swalm School of Chemical Engineering and Centre for Advanced Vehicular Systems, Mississippi State University, Mississippi State, MS, USA
| | - Xingxing Li
- Department of Chemical Physics, University of Science and Technology of China, Hefei, P. R. China.
| | - Jinlong Yang
- Department of Chemical Physics, University of Science and Technology of China, Hefei, P. R. China
| | - Yuan Li
- Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, P. R. China.
| | - Fei Huang
- Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, P. R. China.
| | - Xuefeng Guo
- Beijing National Laboratory for Molecular Sciences, National Biomedical Imaging Centre, College of Chemistry and Molecular Engineering, Peking University, Beijing, P. R. China.
- Centre of Single-Molecule Sciences, Institute of Modern Optics, Frontiers Science Centre for New Organic Matter, Tianjin Key Laboratory of Micro-scale Optical Information Science and Technology, College of Electronic Information and Optical Engineering, Nankai University, Tianjin, P. R. China.
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Huguet A, Wrześniewski K, Weymann I. Spin effects on transport and zero-bias anomaly in a hybrid Majorana wire-quantum dot system. Sci Rep 2023; 13:17279. [PMID: 37828058 PMCID: PMC10570336 DOI: 10.1038/s41598-023-44254-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Accepted: 10/05/2023] [Indexed: 10/14/2023] Open
Abstract
We examine the impact of spin effects on the nonequilibrium transport properties of a nanowire hosting Majorana zero-energy modes at its ends, coupled to a quantum dot junction with ferromagnetic leads. Using the real-time diagrammatic technique, we determine the current, differential conductance and current cross-correlations in the nonlinear response regime. We also explore transport in different magnetic configurations of the system, which can be quantified by the tunnel magnetoresistance. We show that the presence of Majorana quasiparticles gives rise to unique features in all spin-resolved transport characteristics, in particular, to zero-bias anomaly, negative differential conductance, negative tunnel magnetoresistance, and it is also reflected in the current cross-correlations. Moreover, we study the dependence of the zero-bias anomaly on various system parameters and demonstrate its dependence on the magnetic configuration of the system as well as on the degree of spin polarization in the leads. A highly nontrivial behavior is also found for the tunnel magnetoresistance, which exhibits regions of enhanced or negative values-new features resulting from the coupling to Majorana wire.
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Affiliation(s)
- Alexandre Huguet
- Institute of Spintronics and Quantum Information, Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614, Poznań, Poland.
- Université de Rennes 1, Campus de Beaulieu, F-35000, Rennes, France.
| | - Kacper Wrześniewski
- Institute of Spintronics and Quantum Information, Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614, Poznań, Poland.
| | - Ireneusz Weymann
- Institute of Spintronics and Quantum Information, Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614, Poznań, Poland
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Child T, Sheekey O, Lüscher S, Fallahi S, Gardner GC, Manfra M, Mitchell A, Sela E, Kleeorin Y, Meir Y, Folk J. Entropy Measurement of a Strongly Coupled Quantum Dot. PHYSICAL REVIEW LETTERS 2022; 129:227702. [PMID: 36493429 DOI: 10.1103/physrevlett.129.227702] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2022] [Accepted: 10/28/2022] [Indexed: 06/17/2023]
Abstract
The spin 1/2 entropy of electrons trapped in a quantum dot has previously been measured with great accuracy, but the protocol used for that measurement is valid only within a restrictive set of conditions. Here, we demonstrate a novel entropy measurement protocol that is universal for arbitrary mesoscopic circuits and apply this new approach to measure the entropy of a quantum dot hybridized with a reservoir. The experimental results match closely to numerical renormalization group (NRG) calculations for small and intermediate coupling. For the largest couplings investigated in this Letter, NRG calculations predict a suppression of spin entropy at the charge transition due to the formation of a Kondo singlet, but that suppression is not observed in the experiment.
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Affiliation(s)
- Timothy Child
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia, V6T1Z4, Canada
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, V6T1Z1, Canada
| | - Owen Sheekey
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia, V6T1Z4, Canada
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, V6T1Z1, Canada
| | - Silvia Lüscher
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia, V6T1Z4, Canada
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, V6T1Z1, Canada
| | - Saeed Fallahi
- Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA
- Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
| | - Geoffrey C Gardner
- Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
- School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, USA
| | - Michael Manfra
- Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA
- Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
- School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, USA
- Elmore Family School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA
| | - Andrew Mitchell
- School of Physics, University College Dublin, Belfield, Dublin 4, Ireland
- Centre for Quantum Engineering, Science, and Technology, University College Dublin, Dublin 4, Ireland
| | - Eran Sela
- Raymond and Beverly Sackler School of Physics and Astronomy, Tel-Aviv University, IL-69978 Tel Aviv, Israel
| | - Yaakov Kleeorin
- Center for the Physics of Evolving Systems, University of Chicago, Chicago, Illinois 60637, USA
| | - Yigal Meir
- Department of Physics, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel
- The Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel
| | - Joshua Folk
- Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia, V6T1Z4, Canada
- Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, V6T1Z1, Canada
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A Robust Protocol for Entropy Measurement in Mesoscopic Circuits. ENTROPY 2022; 24:e24030417. [PMID: 35327927 PMCID: PMC8948648 DOI: 10.3390/e24030417] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/24/2022] [Revised: 03/11/2022] [Accepted: 03/13/2022] [Indexed: 02/01/2023]
Abstract
Previous measurements utilizing Maxwell relations to measure change in entropy, S, demonstrated remarkable accuracy in measuring the spin-1/2 entropy of electrons in a weakly coupled quantum dot. However, these previous measurements relied upon prior knowledge of the charge transition lineshape. This had the benefit of making the quantitative determination of entropy independent of scale factors in the measurement itself but at the cost of limiting the applicability of the approach to simple systems. To measure the entropy of more exotic mesoscopic systems, a more flexible analysis technique may be employed; however, doing so requires a precise calibration of the measurement. Here, we give details on the necessary improvements made to the original experimental approach and highlight some of the common challenges (along with strategies to overcome them) that other groups may face when attempting this type of measurement.
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Pyurbeeva E, Hsu C, Vogel D, Wegeberg C, Mayor M, van der Zant H, Mol JA, Gehring P. Controlling the Entropy of a Single-Molecule Junction. NANO LETTERS 2021; 21:9715-9719. [PMID: 34766782 DOI: 10.1021/acs.nanolett.1c03591] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Single molecules are nanoscale thermodynamic systems with few degrees of freedom. Thus, the knowledge of their entropy can reveal the presence of microscopic electron transfer dynamics that are difficult to observe otherwise. Here, we apply thermocurrent spectroscopy to directly measure the entropy of a single free radical molecule in a magnetic field. Our results allow us to uncover the presence of a singlet to triplet transition in one of the redox states of the molecule, not detected by conventional charge transport measurements. This highlights the power of thermoelectric measurements which can be used to determine the difference in configurational entropy between the redox states of a nanoscale system involved in conductance without any prior assumptions about its structure or microscopic dynamics.
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Affiliation(s)
- Eugenia Pyurbeeva
- School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom
| | - Chunwei Hsu
- Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, Delft 2628 CJ, The Netherlands
| | - David Vogel
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland
| | - Christina Wegeberg
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland
| | - Marcel Mayor
- Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056 Basel, Switzerland
- Institute for Nanotechnology (INT), Karlsruhe Institute of Technology (KIT), P.O. Box 3640, 76021 Karlsruhe, Germany
- Lehn Institute of Functional Materials (LIFM), School of Chemistry, Sun Yat-Sen University (SYSU), 510275 Guangzhou, China
| | - Herre van der Zant
- Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, Delft 2628 CJ, The Netherlands
| | - Jan A Mol
- School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom
| | - Pascal Gehring
- IMCN/NAPS, Université Catholique de Louvain (UCLouvain), 1348 Louvain-la-Neuve, Belgium
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