掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Applied  

A quantum point contact (QPC) - a constriction in a semiconducting two-dimensional electron system with a quantized conductance - is a building block of novel spintronic and topological electronic circuits. QPCs can also be used as readout electronics, charge sensors, or switches in quantum nanocircuits. A short and impurity-free constriction with superconducting contacts is a Cooper-pair QPC analogue known as a superconducting quantum point contact (SQPC). The technological development of such quantum devices has been prolonged due to the challenges of maintaining their geometrical requirement and near-unity superconductor-semiconductor interface transparency. Here, we develop advanced nanofabrication, material and device engineering techniques and report on an innovative realization of nanoscale hybrid SQPC arrays with split gate technology in semiconducting 2D electron systems. We exploit the special gate tunability of the quantum wells, and demonstrate the first experimental observation of conductance quantization in hybrid InGaAs-Nb SQPCs. We observe reproducible quantized conductance at zero magnetic fields in multiple quantum nanodevices fabricated in a single chip and systematically investigate the quantum transport of SQPCs at low and high magnetic fields for their potential applications in quantum metrology, for extremely accurate voltage standards, and fault-tolerant quantum technologies.

DOI： 10.1103/PhysRevApplied.21.014051

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Scopus

その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevApplied.21.014051/fulltext

掲載種別：研究論文（学術雑誌）   出版者・発行元：Advanced Electronic Materials  

Stable, reproducible, scalable, addressable, and controllable hybrid superconductor–semiconductor (S–Sm) junctions and switches are key circuit elements and building blocks of gate-based quantum processors. The electrostatic field effect produced by the split gate voltages facilitates the realization of nano-switches that can control the conductance or current in the hybrid S–Sm circuits based on 2D semiconducting electron systems. Here, a novel realization of large-scale scalable, and gate voltage controllable hybrid field effect quantum chips is experimentally demonstrated. Each chip contains arrays of split gate field effect hybrid junctions, that work as conductance switches, and are made from In0.75Ga0.25As quantum wells integrated with Nb superconducting electronic circuits. Each hybrid junction in the chip can be controlled and addressed through its corresponding source–drain and two global split gate contact pads that allow switching between their (super)conducting and insulating states. A total of 18 quantum chips are fabricated with 144 field effect hybrid Nb- In0.75Ga0.25As 2DEG-Nb quantum wires and the electrical response, switching voltage (on/off) statistics, quantum yield, and reproducibility of several devices at cryogenic temperatures are investigated. The proposed integrated quantum device architecture allows control of individual junctions in a large array on a chip useful for emerging cryogenic quantum technologies.

DOI： 10.1002/aelm.202300453

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s42005-023-01384-w

その他リンク： https://www.nature.com/articles/s42005-023-01384-w

担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Materials Chemistry C  

A low-dimensional magnetic system promotes strong interactions between quantum spins and leads to fascinating quantum phenomena. To realize quantum devices based on the spin-liquid ground state, a two-dimensional magnetic system with strong spin-frustration is highly desired. A honeycomb-layered tellurate with a 3d transition metal within its slabs is a potential system that can host Kitaev quantum spin-liquid although conclusive evidence for the spin-liquid phase has not been reported to date. This might be partially due to the presence of an interslab exchange coupling between magnetic honeycomb slabs which stabilizes antiferromagnetic ordering and potentially suppresses Kitaev interactions. Here, we report the magnetic and spin frustration properties of Ag-based honeycomb layered tellurates with magnetic honeycomb slabs separated by Ag bilayers which are expected to screen the interslab exchange coupling. From magnetization measurements, we observe antiferromagnetic ordering and signatures of enhanced spin-frustration for the tellurates containing Ag-bilayers relative to other honeycomb layered tellurates without bilayers. The results might be promising for the realization of the Kitaev quantum spin liquid.

DOI： 10.1039/d3tc01915b

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Review Applied  

A ferromagnetic-antiferromagnetic (FM-AFM) thin-film heterostructure is proposed to be a potential system that can induce perpendicular magnetic anisotropy (PMA) in a ferromagnet, although there are few material combinations available and the underlying mechanism is not sufficiently understood. Here, we demonstrate that the AFM phase of an Fe-Rh ordered alloy induces PMA in an adjacent Fe layer in an Fe/Fe-Rh heterostructure, which manifests itself as an additional mode of ferromagnetic resonance. The induced interfacial PMA disappears following a magnetic phase transition of Fe-Rh from the AFM to the FM state, suggesting that the AFM order is crucial for the stabilization of PMA. The absence of the additional resonance mode in an Fe/Rh/Fe-Rh control sample suggests that the PMA originates from a magnetic exchange coupling at the Fe/Fe-Rh interface. The results are promising for the development of high-density spintronic devices, in which PMA is controllable through the phase transition of Fe-Rh.

DOI： 10.1103/PhysRevApplied.19.064077

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Scopus

その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevApplied.19.064077/fulltext

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

In recent years, antiferromagnetic materials have been attracting increasing interest for their stability in high magnetic fields and ultrafast magnetization dynamics. Since the energy scale of an interlayer exchange coupling (IEC) in a synthetic antiferromagnet (SAF) consisting of ferromagnetic/nonmagnetic/ferromagnetic multilayers is relatively smaller than that of an exchange coupling in antiferromagnetic materials, magnetic ordering of a SAF can be potentially controlled by an electric field, which is promising for energy-saving spintronic memory devices. However, an electric field-induced magnetoelastic response of SAFs on ferroelectric materials has not been sufficiently understood due to the presence of IEC that complicates magnetization dynamics. In this study, we prepare Co/Ru/Co SAFs with various amplitude of IEC on ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 substrates and systematically investigate their electric field-induced magnetoelastic response. We demonstrate that the magnetoelastic response disappears at the boundary where a switching between the antiferromagnetic and ferromagnetic IEC coupling occurs. The result provides insight into the coupling of the magnetoelastic effect and IEC and is useful in designing spintronic memory devices based on SAFs.

DOI： 10.1063/5.0151832

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

In La1−xSrxMnO3 (LSMO)/BaTiO3 (BTO) heterostructures with a multiferroic interface, an artificial modulation of the magnetic structure is observed. The saturation magnetization of La1−xSrxMnO3 changes discontinuously due to in-plane distortions caused by a structural phase transition of a BaTiO3 substrate. Polarity reversal of the external electric field also causes a reversible switching in the magnetization. The magnitude of both magnetic modulations, due to the magnetoelastic and electric field effects, is concomitantly enhanced at a critical composition x c ∼ 0.55 , locating at a border of the magnetic phase transition. The polarity-dependent change in magnetization is possibly attributed to a change in the concentration of oxygen ions at the LSMO/BTO interface, indicating that the exchange interaction is reciprocally driven from being ferromagnetic to antiferromagnetic by the electric field polarity.

DOI： 10.1063/5.0150917

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掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：2023 IEEE International Magnetic Conference - Short Papers, INTERMAG Short Papers 2023 - Proceedings  

Various attempts to realize electric field controlled energy-saving spintronic devices have been made in recent years. Artificial multiferroic heterostructures have attracted much attention because of its ability to control magnetization by an electric field due to the inverse magnetoelectric effect. In this study, as a new artificial multiferroic heterostructure, we investigate the electric field effects on the magnetic properties of a synthetic antiferromagnet composed of Co/Ru/Co deposited on ferroelectric (011) oriented Pb(Mg1/3Nb2/3)O3-PbTiO3. Spin-flop transition, which is characteristic of interlayer coupled synthetic antiferromagnets, is observed. The magnetic field direction at which the spin-flop behavior occurs is rotated by 90° upon the application of an electric field. The results are promising to be used in next-generation spintronic devices.

DOI： 10.1109/intermagshortpapers58606.2023.10228509

Scopus

出版者・発行元：2023 IEEE International Magnetic Conference - Short Papers, INTERMAG Short Papers 2023 - Proceedings  

Piezoelectric LiNbO3 has been widely utilized to generate and detect spin waves in surface acoustic wave devices. Here we demonstrate an epitaxial Co-based Heusler alloy on a LiNbO3 128° Y-cut (LN-128Y) substrate by molecular beam epitaxy. Although there is no matching between the lattice length and symmetry, the insertion of a bcc metal buffer layer enables to grow L21 - ordered epitaxial Co2FeSi films on the LN-128Y substrate. The epitaxial Co2FeSi/LN- 128Y multiferroic heterostructures show a high saturation magnetization of ~1235 eμcc and a low damping constant of ~6 × 10-3. This study will open a way for an efficient electric-field control of the spin waves in surface acoustic wave devices.

DOI： 10.1109/INTERMAGShortPapers58606.2023.10228793

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACS Applied Electronic Materials  

A two-dimensional interfacial electronic phase often emerges at the interface between different oxide layers, which may display remarkably distinct properties from its bulk phases. The mechanism of evolution of such an additional phase at the interface and its properties, however, are not fully understood yet. Herein, we detect an additional structural and magnetic phase and so-called quasi two-dimensional electronic states of La0.7Sr0.3MnO3(LSMO) that interface with SrTiO3(STO), while LSMO interfaced with a [Pb(Mg1/3Nb2/3)O3]0.7-[PbTiO3]0.3(PMN-PT) substrate shows a single phase. We find that the additional phase exhibits a lower Curie temperature, a larger effective saturation magnetization, and a larger Gilbert damping coefficient than its bulk counterpart. We discuss that the lattice mismatch-induced strain plays an important role in the formation of the additional state. These results will give an insight into designing full-oxide electronics, including 2D spintronics.

DOI： 10.1021/acsaelm.2c00967

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Communications  

Materials with strongly correlated electrons often exhibit interesting physical properties. An example of these materials is the layered oxide perovskite Sr2RuO4, which has been intensively investigated due to its unusual properties. Whilst the debate on the symmetry of the superconducting state in Sr2RuO4 is still ongoing, a deeper understanding of the Sr2RuO4 normal state appears crucial as this is the background in which electron pairing occurs. Here, by using low-energy muon spin spectroscopy we discover the existence of surface magnetism in Sr2RuO4 in its normal state. We detect static weak dipolar fields yet manifesting at an onset temperature higher than 50 K. We ascribe this unconventional magnetism to orbital loop currents forming at the reconstructed Sr2RuO4 surface. Our observations set a reference for the discovery of the same magnetic phase in other materials and unveil an electronic ordering mechanism that can influence electron pairing with broken time reversal symmetry.

DOI： 10.1038/s41467-021-26020-5

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PubMed

その他リンク： https://www.nature.com/articles/s41467-021-26020-5

掲載種別：研究論文（学術雑誌）   出版者・発行元：American Chemical Society (ACS)  

DOI： 10.1021/acs.nanolett.1c01607

担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

DOI： 10.7566/jpsj.90.024702

掲載種別：研究論文（学術雑誌）   出版者・発行元：American Physical Society (APS)  

DOI： 10.1103/physrevmaterials.5.014413

その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevMaterials.5.014413/fulltext

開催年月日： 2023年3月

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開催年月日： 2022年11月

会議種別：口頭発表（招待・特別）  

開催年月日： 2022年11月

会議種別：口頭発表（招待・特別）  

開催年月日： 2021年10月

開催年月日： 2021年9月