We theoretically investigate Josephson junctions comprising superconductors and ferromagnets on the surface of three-dimensional topological insulators. We use Bogoliubov-deGennes formalism and show the in-plane magnetization creates a difference between the upward and downward population of Andreev modes and produces a planar Hall supercurrent. Due to the strong spin-orbit interaction of Dirac fermions, bending on the supercurrent imposes a spin transfer torque on the junction. We develop a theory and demonstrate the relation between planar Hall supercurrent and spin transfer torque. The parallel component of in-plane magnetization creates an anomalous supercurrent that can flow even in zero superconducting phase difference and make $deltaphi$-junction. We show in some range,$pi/2d leq m_y leq pi/d$, there is a $pi$ shift in the Josephson supercurrent. This research advances our understanding of quantum transport in 3DTIs and highlights their potential in emerging quantum technologies.
{"title":"Planar Hall supercurrent and δφ-shift in the topological Josephson junction","authors":"Morteza Salehi","doi":"arxiv-2409.04848","DOIUrl":"https://doi.org/arxiv-2409.04848","url":null,"abstract":"We theoretically investigate Josephson junctions comprising superconductors\u0000and ferromagnets on the surface of three-dimensional topological insulators. We\u0000use Bogoliubov-deGennes formalism and show the in-plane magnetization creates a\u0000difference between the upward and downward population of Andreev modes and\u0000produces a planar Hall supercurrent. Due to the strong spin-orbit interaction\u0000of Dirac fermions, bending on the supercurrent imposes a spin transfer torque\u0000on the junction. We develop a theory and demonstrate the relation between\u0000planar Hall supercurrent and spin transfer torque. The parallel component of\u0000in-plane magnetization creates an anomalous supercurrent that can flow even in\u0000zero superconducting phase difference and make $deltaphi$-junction. We show\u0000in some range,$pi/2d leq m_y leq pi/d$, there is a $pi$ shift in the\u0000Josephson supercurrent. This research advances our understanding of quantum\u0000transport in 3DTIs and highlights their potential in emerging quantum\u0000technologies.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210178","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this work, we propose a mechanism of inducing stable nodal superconductivity for multiple-flat-band systems. This mechanism is based on the degenerate flat band nature, so that not only intra-eigen-band pairing, but also inter-eigen-band pairing has a significant influence on the superconductivity properties. Based on the Bogoliubov de Gennes formalism of the heavy fermion model for the twisted bilayer graphene as an example, we show that although the nodal nematic d-wave pairing has higher energy around the nodal points compared to the chiral d-wave pairing in the momentum space, the inter-eigen-band pairing can lower the energy in other momenta away from the nodes, so that the nematic d-wave pairing is energetically favored for its overall condensation energy. This type of mechanism is particular to multiple-flat-band systems with no Fermi surfaces.
在这项工作中，我们提出了一种诱导多平带系统稳定结点超导的机制。该机制基于退化平带性质，因此不仅特征带内配对，特征带间配对也对超导特性有重要影响。我们以扭曲双层石墨烯的重费米子模型的波哥留波夫-德-吉恩形式主义为例，说明虽然在动量空间中，节点向列 d 波配对在节点附近的能量比手性 d 波配对高，但特征带间配对可以降低远离节点的其他时刻的能量，从而使向列 d 波配对在能量上更有利于其整体凝聚能。这种机制特别适用于没有费米面的多平带系统。
{"title":"Nodal Nematic Superconductivity in Multiple-Flat-Band Land","authors":"Chao-Xing Liu, B. Andrei Bernevig","doi":"arxiv-2409.04917","DOIUrl":"https://doi.org/arxiv-2409.04917","url":null,"abstract":"In this work, we propose a mechanism of inducing stable nodal\u0000superconductivity for multiple-flat-band systems. This mechanism is based on\u0000the degenerate flat band nature, so that not only intra-eigen-band pairing, but\u0000also inter-eigen-band pairing has a significant influence on the\u0000superconductivity properties. Based on the Bogoliubov de Gennes formalism of\u0000the heavy fermion model for the twisted bilayer graphene as an example, we show\u0000that although the nodal nematic d-wave pairing has higher energy around the\u0000nodal points compared to the chiral d-wave pairing in the momentum space, the\u0000inter-eigen-band pairing can lower the energy in other momenta away from the\u0000nodes, so that the nematic d-wave pairing is energetically favored for its\u0000overall condensation energy. This type of mechanism is particular to\u0000multiple-flat-band systems with no Fermi surfaces.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210177","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Two-dimensional (2D) magnets have attracted significant attentions in recent years due to their importance in the research on both fundamental physics and spintronic applications. Here, we report the discovery of a new ternary compound FePd2Te2. It features a layered quasi-2D crystal structure with one-dimensional Fe zigzag chains extending along the b-axis in the cleavage plane. Single crystals of FePd2Te2 with centimeter-size could be grown. Density functional theory calculations, mechanical exfoliation and atomic force microscopy on these crystals reveal that they are 2D materialsthat can be thinned down to 5 nm. Magnetic characterization shows that FePd2Te2 is an easy-plane ferromagnet with Tc 183 K and strong in-plane uniaxial magnetic anisotropy. Magnetoresistance and anomalous Hall effect demonstrate that ferromagnetism could maintain in FePd2Te2 flakes with large coercivity. A crystal twinning effect is observed by scanning tunneling microscopy which makes the Fe chains right-angle bent in the cleavage plane and creates an intriguing spin texture. Our results show that FePd2Te2 is a correlated anisotropic 2D magnets that may attract multidisciplinary research interests.
由于二维（2D）磁体在基础物理和自旋电子应用研究中的重要性，近年来二维（2D）磁体备受关注。在此，我们报告了一种新的三元化合物 FePd2Te2 的发现。它具有层状的准二维晶体结构，一维的 Fe 人字链沿着裂平面的 b 轴延伸。可以生长出厘米大小的 FePd2Te2 单晶体。对这些晶体进行的密度函数理论计算、机械剥离和原子力显微镜分析表明，它们是二维材料，可细化至 5 纳米。磁性表征表明，FePd2Te2 是一种宙平面铁磁体，Tc 为 183 K，具有很强的面内单轴磁性各向异性。磁阻和反常霍尔效应表明，FePd2Te2 片状铁磁体能保持较大的矫顽力。扫描隧道显微镜观察到了晶体孪生效应，这使得铁链在裂解面上呈直角弯曲，并产生了一种引人入胜的自旋纹理。我们的研究结果表明，FePd2Te2 是一种相关各向异性的二维磁体，可能会吸引多学科的研究兴趣。
{"title":"FePd2Te2: An Anisotropic Two-Dimensional Ferromagnet with One-Dimensional Fe Chains","authors":"Bingxian Shi, Yanyan Geng, Hengning Wang, Jianhui Yang, Chenglin Shang, Manyu Wang, Shuo Mi, Jiale Huang, Feihao Pan, Xuejuan Gui, Jinchen Wang, Juanjuan Liu, Daye Xu, Hongxia Zhang, Jianfei Qin, Hongliang Wang, Lijie Hao, Mingliang Tian, Zhihai Cheng, Guolin Zheng, Peng Cheng","doi":"arxiv-2409.04800","DOIUrl":"https://doi.org/arxiv-2409.04800","url":null,"abstract":"Two-dimensional (2D) magnets have attracted significant attentions in recent\u0000years due to their importance in the research on both fundamental physics and\u0000spintronic applications. Here, we report the discovery of a new ternary\u0000compound FePd2Te2. It features a layered quasi-2D crystal structure with\u0000one-dimensional Fe zigzag chains extending along the b-axis in the cleavage\u0000plane. Single crystals of FePd2Te2 with centimeter-size could be grown. Density\u0000functional theory calculations, mechanical exfoliation and atomic force\u0000microscopy on these crystals reveal that they are 2D materialsthat can be\u0000thinned down to 5 nm. Magnetic characterization shows that FePd2Te2 is an\u0000easy-plane ferromagnet with Tc 183 K and strong in-plane uniaxial magnetic\u0000anisotropy. Magnetoresistance and anomalous Hall effect demonstrate that\u0000ferromagnetism could maintain in FePd2Te2 flakes with large coercivity. A\u0000crystal twinning effect is observed by scanning tunneling microscopy which\u0000makes the Fe chains right-angle bent in the cleavage plane and creates an\u0000intriguing spin texture. Our results show that FePd2Te2 is a correlated\u0000anisotropic 2D magnets that may attract multidisciplinary research interests.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210183","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xiaolin Ren, Ronny Sutarto, Xianxin Wu, Jianfeng Zhang, Hai Huang, Tao Xiang, Jiangping Hu, Riccardo Comin, X. J. Zhou, Zhihai Zhu
The recent discovery of a superconductivity signature in La3Ni2O7-{delta} under a pressure of 14 GPa, with a superconducting transition temperature of around 80 K, has attracted considerable attention. An important aspect of investigating electronic structures is discerning the extent to which the electronic ground state of La3Ni2O7-{delta} resembles the parent state of the cuprate superconductor, a charge transfer insulator with long-range antiferromagnetism. Through X-ray absorption spectroscopy, we have uncovered the crucial influence of oxygen ligands on the electronic ground states of the Ni ions, displaying a charge transfer nature akin to cuprate but with distinct orbital configurations. Both in-plane and out-of-plane Zhang-Rice singlets associated with Ni d_(x^2-y^2 ) and d_(z^2) orbitals are identified, together with a strong interlayer coupling through inner apical oxygen. Additionally, in La3Ni2O7-{delta} films, we have detected a superlattice reflection (1/4, 1/4, L) at the Ni L absorption edge using resonant X-ray scattering measurements. Further examination of the resonance profile indicates that the reflection originates from the Ni d orbitals. By evaluating the reflection's azimuthal angle dependence, we have confirmed the presence of collinear antiferromagnetic spin ordering and charge-like anisotropy ordered with the same periodicity. Notably, our findings reveal a microscopic relationship between these two components in the temperature dependence of the scattering intensity of the reflection. This investigation enriches our understanding of high-temperature superconductivity in La3Ni2O7-{delta} under high pressure.
最近在 14 GPa 压力下的 La3Ni2O7-{delta} 中发现了超导特征，其超导转变温度约为 80 K，这引起了人们的极大关注。研究电子结构的一个重要方面是辨别 La3Ni2O7-{delta} 的电子基态在多大程度上与杯状超导体的母态相似，后者是一种具有长程反铁磁性的电荷转移绝缘体。通过 X 射线吸收光谱，我们发现了氧配位体对镍离子电子基态的关键影响，其电荷转移性质与铜氧化物相似，但具有不同的矢量构型。我们发现了与镍的 d_(x^2-y^2 ) 和 d_(z^2) 轨道相关的面内和面外 Zhang-Rice 单电子，以及通过内顶端氧的强层间耦合。此外，在 La3Ni2O7-{delta} 薄膜中，我们利用共振 X 射线散射测量在 Ni L 吸收边缘检测到了超晶格反射（1/4，1/4，L）。通过评估反射的方位角依赖性，我们证实了共线反铁磁有序和电荷类各向异性以相同的周期有序存在。这项研究丰富了我们对La3Ni2O7-{delta}在高压下的高温超导性的理解。
{"title":"Resolving the Electronic Ground State of La3Ni2O7-δ Films","authors":"Xiaolin Ren, Ronny Sutarto, Xianxin Wu, Jianfeng Zhang, Hai Huang, Tao Xiang, Jiangping Hu, Riccardo Comin, X. J. Zhou, Zhihai Zhu","doi":"arxiv-2409.04121","DOIUrl":"https://doi.org/arxiv-2409.04121","url":null,"abstract":"The recent discovery of a superconductivity signature in La3Ni2O7-{delta}\u0000under a pressure of 14 GPa, with a superconducting transition temperature of\u0000around 80 K, has attracted considerable attention. An important aspect of\u0000investigating electronic structures is discerning the extent to which the\u0000electronic ground state of La3Ni2O7-{delta} resembles the parent state of the\u0000cuprate superconductor, a charge transfer insulator with long-range\u0000antiferromagnetism. Through X-ray absorption spectroscopy, we have uncovered\u0000the crucial influence of oxygen ligands on the electronic ground states of the\u0000Ni ions, displaying a charge transfer nature akin to cuprate but with distinct\u0000orbital configurations. Both in-plane and out-of-plane Zhang-Rice singlets\u0000associated with Ni d_(x^2-y^2 ) and d_(z^2) orbitals are identified, together\u0000with a strong interlayer coupling through inner apical oxygen. Additionally, in\u0000La3Ni2O7-{delta} films, we have detected a superlattice reflection (1/4, 1/4,\u0000L) at the Ni L absorption edge using resonant X-ray scattering measurements.\u0000Further examination of the resonance profile indicates that the reflection\u0000originates from the Ni d orbitals. By evaluating the reflection's azimuthal\u0000angle dependence, we have confirmed the presence of collinear antiferromagnetic\u0000spin ordering and charge-like anisotropy ordered with the same periodicity.\u0000Notably, our findings reveal a microscopic relationship between these two\u0000components in the temperature dependence of the scattering intensity of the\u0000reflection. This investigation enriches our understanding of high-temperature\u0000superconductivity in La3Ni2O7-{delta} under high pressure.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210186","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yanyu Jia, Tiancheng Song, Zhaoyi Joy Zheng, Guangming Cheng, Ayelet J Uzan, Guo Yu, Yue Tang, Connor J. Pollak, Fang Yuan, Michael Onyszczak, Kenji Watanabe, Takashi Taniguchi, Shiming Lei, Nan Yao, Leslie M Schoop, N. P. Ong, Sanfeng Wu
Introducing superconductivity in topological materials can lead to innovative electronic phases and device functionalities. Here, we present a new strategy for quantum engineering of superconducting junctions in moire materials through direct, on-chip, and fully encapsulated 2D crystal growth. We achieve robust and designable superconductivity in Pd-metalized twisted bilayer molybdenum ditelluride (MoTe2) and observe anomalous superconducting effects in high-quality junctions across ~ 20 moire cells. Surprisingly, the junction develops enhanced, instead of weakened, superconducting behaviors, exhibiting fluctuations to a higher critical magnetic field compared to its adjacent Pd7MoTe2 superconductor. Additionally, the critical current further exhibits a striking V-shaped minimum at zero magnetic field. These features are unexpected in conventional Josephson junctions and indeed absent in junctions of natural bilayer MoTe2 created using the same approach. We discuss implications of these observations, including the possible formation of mixed even- and odd-parity superconductivity at the moire junctions. Our results also demonstrate a pathway to engineer and investigate superconductivity in fractional Chern insulators.
在拓扑材料中引入超导性可以带来创新的电子相位和器件功能。在这里，我们提出了一种新策略，通过直接、片上和完全封装的二维晶体生长，在摩尔材料中实现超导结的量子工程。我们在钯金属化扭曲双层钼碲化物（MoTe2）中实现了稳健的可设计超导性，并在约 20 个摩尔单元的高质量结中观察到了异常超导效应。令人惊讶的是，与相邻的钯7碲化钼2超导体相比，该结点的超导行为非但没有减弱，反而增强了，表现出较高临界磁场的波动。此外，临界电流在零磁场时进一步表现出惊人的 V 形最小值。这些特征在传统的约瑟夫森结中是意想不到的，而且在使用相同方法制造的天然双层 MoTe2 结中也不存在。我们讨论了这些观察结果的意义，包括在摩尔结上可能形成的偶数和奇数混合超导。我们的研究结果还展示了在分数切尔宁缓冲器中设计和研究超导性的途径。
{"title":"Anomalous Superconductivity in Twisted MoTe2 Nanojunctions","authors":"Yanyu Jia, Tiancheng Song, Zhaoyi Joy Zheng, Guangming Cheng, Ayelet J Uzan, Guo Yu, Yue Tang, Connor J. Pollak, Fang Yuan, Michael Onyszczak, Kenji Watanabe, Takashi Taniguchi, Shiming Lei, Nan Yao, Leslie M Schoop, N. P. Ong, Sanfeng Wu","doi":"arxiv-2409.04594","DOIUrl":"https://doi.org/arxiv-2409.04594","url":null,"abstract":"Introducing superconductivity in topological materials can lead to innovative\u0000electronic phases and device functionalities. Here, we present a new strategy\u0000for quantum engineering of superconducting junctions in moire materials through\u0000direct, on-chip, and fully encapsulated 2D crystal growth. We achieve robust\u0000and designable superconductivity in Pd-metalized twisted bilayer molybdenum\u0000ditelluride (MoTe2) and observe anomalous superconducting effects in\u0000high-quality junctions across ~ 20 moire cells. Surprisingly, the junction\u0000develops enhanced, instead of weakened, superconducting behaviors, exhibiting\u0000fluctuations to a higher critical magnetic field compared to its adjacent\u0000Pd7MoTe2 superconductor. Additionally, the critical current further exhibits a\u0000striking V-shaped minimum at zero magnetic field. These features are unexpected\u0000in conventional Josephson junctions and indeed absent in junctions of natural\u0000bilayer MoTe2 created using the same approach. We discuss implications of these\u0000observations, including the possible formation of mixed even- and odd-parity\u0000superconductivity at the moire junctions. Our results also demonstrate a\u0000pathway to engineer and investigate superconductivity in fractional Chern\u0000insulators.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210179","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Based on the energy level structure of neutral oxygen atom O and its anions, through in-depth analysis of the bonding process and formation mechanism of anion O$^{x-}$ ($1
{"title":"O-bridged electron pairing: the microscopic mechanism for high-temperature superconductivity in cuprates and nickelates","authors":"Jun-jie Shi, Yao-hui Zhu","doi":"arxiv-2409.04036","DOIUrl":"https://doi.org/arxiv-2409.04036","url":null,"abstract":"Based on the energy level structure of neutral oxygen atom O and its anions,\u0000through in-depth analysis of the bonding process and formation mechanism of\u0000anion O$^{x-}$ ($1<xleq{2}$) in oxide superconductors dominated by ionic\u0000bonds, we propose an emerging and important novel idea of electron pairing with\u0000oxygen atoms as a bridge, different from the previously proposed electronic\u0000pairing schemes. This microscopic electronic pairing image is very intuitive\u0000and vivid, which can naturally explain the d-wave symmetry of Cooper pairs,\u0000large superconducting energy gaps, and small electron-pair sizes in copper\u0000oxide high-temperature superconductors. It is the electron-electron pairing\u0000mechanism mediated by oxygen atoms that directly determines the unconventional\u0000high-temperature superconductivity of cuprates and nickelates.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210191","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this account, we will give an overview of our research progress on novel quantum properties in topological quantum materials with kagome lattice. Here, there are mainly two categories of kagome materials: magnetic kagome materials and nonmagnetic ones. On one hand, magnetic kagome materials mainly focus on the 3d transition-metal-based kagome systems, including Fe$_3$Sn$_2$, Co$_3$Sn$_2$S$_2$, YMn6Sn6, FeSn, and CoSn. The interplay between magnetism and topological bands manifests vital influence on the electronic response. For example, the existence of massive Dirac or Weyl fermions near the Fermi level signicantly enhances the magnitude of Berry curvature in momentum space, leading to a large intrinsic anomalous Hall effect. In addition, the peculiar frustrated structure of kagome materials enables them to host a topologically protected skyrmion lattice or noncoplaner spin texture, yielding a topological Hall effect that arises from the realspace Berry phase. On the other hand, nonmagnetic kagome materials in the absence of longrange magnetic order include CsV3Sb5 with the coexistence of superconductivity, charge density wave state, and band topology and van der Waals semiconductor Pd$_3$P$_2$S$_8$. For these two kagome materials, the tunability of electric response in terms of high pressure or carrier doping helps to reveal the interplay between electronic correlation effects and band topology and discover the novel emergent quantum phenomena in kagome materials.
{"title":"Topological Quantum Materials with Kagome Lattice","authors":"Qi Wang, Hechang Lei, Yanpeng Qi, Claudia Felser","doi":"arxiv-2409.04211","DOIUrl":"https://doi.org/arxiv-2409.04211","url":null,"abstract":"In this account, we will give an overview of our research progress on novel\u0000quantum properties in topological quantum materials with kagome lattice. Here,\u0000there are mainly two categories of kagome materials: magnetic kagome materials\u0000and nonmagnetic ones. On one hand, magnetic kagome materials mainly focus on\u0000the 3d transition-metal-based kagome systems, including Fe$_3$Sn$_2$,\u0000Co$_3$Sn$_2$S$_2$, YMn6Sn6, FeSn, and CoSn. The interplay between magnetism and\u0000topological bands manifests vital influence on the electronic response. For\u0000example, the existence of massive Dirac or Weyl fermions near the Fermi level\u0000signicantly enhances the magnitude of Berry curvature in momentum space,\u0000leading to a large intrinsic anomalous Hall effect. In addition, the peculiar\u0000frustrated structure of kagome materials enables them to host a topologically\u0000protected skyrmion lattice or noncoplaner spin texture, yielding a topological\u0000Hall effect that arises from the realspace Berry phase. On the other hand,\u0000nonmagnetic kagome materials in the absence of longrange magnetic order include\u0000CsV3Sb5 with the coexistence of superconductivity, charge density wave state,\u0000and band topology and van der Waals semiconductor Pd$_3$P$_2$S$_8$. For these\u0000two kagome materials, the tunability of electric response in terms of high\u0000pressure or carrier doping helps to reveal the interplay between electronic\u0000correlation effects and band topology and discover the novel emergent quantum\u0000phenomena in kagome materials.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210184","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Nonreciprocal superconductivity, also called as superconducting diode effect that spontaneously breaks time-reversal symmetry, is characterized by asymmetric critical currents under opposite applied current directions. This distinct state unveils a rich ore of intriguing physical properties, particularly in the realm of nanoscience application of superconductors. Towards the experimental realization of superconducting diode effect, the construction of two-dimensional heterostructures of magnets and $s$-wave superconductors is considered to be a promising pathway. In this study, we present our findings of superconducting diode effect manifested in the magnetic Mott insulator $alpha$-RuCl$_3$. This phenomenon is induced by the proximity effect within a van der Waals heterostructure, consisting of thin $alpha$-RuCl$_3$/NbSe$_2$ flakes. Through transport property measurements, we have confirmed a weak superconducting gap of 0.2 meV, which is significantly lower than the intrinsic gap of NbSe$_2$(1.2 meV). Upon the application of a weak magnetic field below 70 mT, we observed an asymmetry in the critical currents under positive and negative applied currents. This observation demonstrates a typical superconducting diode effect in the superconducting $alpha$-RuCl$_3$. The superconducting diode effect and nonreciprocal resistance are observed exclusively when the magnetic field is aligned out-of-plane. This suggests that an Ising-type spin-orbit coupling in the superconducting $alpha$-RuCl$_3$ may be responsible for the mechanism. Our findings furnish a platform for the exploration of superconducting diode effect via the artificial construction of heterostructures.
{"title":"Observation of superconducting diode effect in antiferromagnetic Mott insulator $α$-RuCl$_3$","authors":"Jiadian He, Yifan Ding, Xiaohui Zeng, Yiwen Zhang, Yanjiang Wang, Peng Dong, Xiang Zhou, Yueshen Wu, Kecheng Cao, Kejing Ran, Jinghui Wang, Yulin Chen, Kenji Watanabe, Takashi Taniguchi, Shun-Li Yu, Jian-Xin Li, Jinsheng Wen, Jun Li","doi":"arxiv-2409.04093","DOIUrl":"https://doi.org/arxiv-2409.04093","url":null,"abstract":"Nonreciprocal superconductivity, also called as superconducting diode effect\u0000that spontaneously breaks time-reversal symmetry, is characterized by\u0000asymmetric critical currents under opposite applied current directions. This\u0000distinct state unveils a rich ore of intriguing physical properties,\u0000particularly in the realm of nanoscience application of superconductors.\u0000Towards the experimental realization of superconducting diode effect, the\u0000construction of two-dimensional heterostructures of magnets and $s$-wave\u0000superconductors is considered to be a promising pathway. In this study, we\u0000present our findings of superconducting diode effect manifested in the magnetic\u0000Mott insulator $alpha$-RuCl$_3$. This phenomenon is induced by the proximity\u0000effect within a van der Waals heterostructure, consisting of thin\u0000$alpha$-RuCl$_3$/NbSe$_2$ flakes. Through transport property measurements, we\u0000have confirmed a weak superconducting gap of 0.2 meV, which is significantly\u0000lower than the intrinsic gap of NbSe$_2$(1.2 meV). Upon the application of a\u0000weak magnetic field below 70 mT, we observed an asymmetry in the critical\u0000currents under positive and negative applied currents. This observation\u0000demonstrates a typical superconducting diode effect in the superconducting\u0000$alpha$-RuCl$_3$. The superconducting diode effect and nonreciprocal\u0000resistance are observed exclusively when the magnetic field is aligned\u0000out-of-plane. This suggests that an Ising-type spin-orbit coupling in the\u0000superconducting $alpha$-RuCl$_3$ may be responsible for the mechanism. Our\u0000findings furnish a platform for the exploration of superconducting diode effect\u0000via the artificial construction of heterostructures.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210188","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. S. Ianovskaia, G. A. Bobkov, A. M. Bobkov, I. V. Bobkova
The magnetic proximity effect in superconductor/ferromagnet (S/F) heterostructures leads to a suppression of the superconducting order parameter and appearance of spin splitting of the local electronic density of states (LDOS). In classical thin-film heterostructures with a large number of atomic layers it has been well studied. However, with the discovery of 2D materials that open up unprecedented opportunities for the design of new functional materials, an intensive study of proximity effects in van der Waals (vdW) S/F heterostructures has begun. In particular, it was shown that in monolayer S/monolayer F heterostructures the physical mechanism of the proximity effect is determined by the hybridization of their electronic states, what makes its observable manifestations completely different from the classical results and allows for effective control over the proximity effect using gate voltage. Here we demonstrate that the hybridization mechanism of the proximity effect clearly manifests itself in the evolution of the magnetic proximity effect in vdW S/F heterostructures with varying number of the superconducting layers. In particular, the number of superconducting layers determines the number of minima in the dependence of the order parameter on the ferromagnetic exchange field and gating. The spin splitting of the LDOS is very unusual and in general cannot be described by an effective Zeeman field. Physical reasons of such a behavior and possible experimental manifestations are discussed in details.
超导体/铁磁体（S/F）异质结构中的磁接近效应会导致超导有序参数的抑制和局部电子态密度（LDOS）自旋分裂的出现。在具有大量原子层的经典薄膜异质结构中，这种现象已经得到了很好的研究。然而，随着二维材料的发现为新型功能材料的设计带来了前所未有的机遇，人们开始深入研究范德华（vdW）S/F 异质结构中的邻近效应。研究特别表明，在单层 S/ 单层 F 异质结构中，邻近效应的物理机制是由其电子态的杂化决定的，这使得其可观察到的表现形式与经典结果完全不同，并允许使用栅极电压对邻近效应进行有效控制。在这里，我们证明了邻近效应的杂化机制在不同超导层数的 vdW S/Fheterostructures 中磁性邻近效应的演化过程中得到了清晰的体现。特别是，超导层的数量决定了有序参数对铁磁交换场和门控的依赖性的最小值数量。LDOS 的自旋分裂非常不寻常，一般无法用有效的泽曼场来描述。本文详细讨论了这种行为的物理原因和可能的实验表现。
{"title":"Magnetic proximity effect in superconductor/ferromagnet van der Waals heterostructures: dependence on the number of superconducting monolayers","authors":"A. S. Ianovskaia, G. A. Bobkov, A. M. Bobkov, I. V. Bobkova","doi":"arxiv-2409.04227","DOIUrl":"https://doi.org/arxiv-2409.04227","url":null,"abstract":"The magnetic proximity effect in superconductor/ferromagnet (S/F)\u0000heterostructures leads to a suppression of the superconducting order parameter\u0000and appearance of spin splitting of the local electronic density of states\u0000(LDOS). In classical thin-film heterostructures with a large number of atomic\u0000layers it has been well studied. However, with the discovery of 2D materials\u0000that open up unprecedented opportunities for the design of new functional\u0000materials, an intensive study of proximity effects in van der Waals (vdW) S/F\u0000heterostructures has begun. In particular, it was shown that in monolayer\u0000S/monolayer F heterostructures the physical mechanism of the proximity effect\u0000is determined by the hybridization of their electronic states, what makes its\u0000observable manifestations completely different from the classical results and\u0000allows for effective control over the proximity effect using gate voltage. Here\u0000we demonstrate that the hybridization mechanism of the proximity effect clearly\u0000manifests itself in the evolution of the magnetic proximity effect in vdW S/F\u0000heterostructures with varying number of the superconducting layers. In\u0000particular, the number of superconducting layers determines the number of\u0000minima in the dependence of the order parameter on the ferromagnetic exchange\u0000field and gating. The spin splitting of the LDOS is very unusual and in general\u0000cannot be described by an effective Zeeman field. Physical reasons of such a\u0000behavior and possible experimental manifestations are discussed in details.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210189","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
For the two-mode electron pairing, we propose a local stacking force pairing mechanism driven by strong local fluctuations, with two straight pairing orbits where the tying Cooper pairing $C_{-kdownarrow}C_{kuparrow}e^{ikcdot r}$ replaces the itinerant pairing. Based on coherent interaction and action-counteraction principles, the strong local variational theory is constructed, with the energy extremum and gap equations forming self-consistent pairs, involving the local variational parameter $lambda$, energy gap $Delta$, and the energy cut-off $hbar omega_0$. As $hbar omega_0(j)$ approaches its cut-off, $lambda$ and $Delta$ converge to fixed values. The theory predicts that the coupling strength $Vg(0)$ reduces to $tilde{V}g(0)=e^{-left(1-alpha_{1}right)^{2} k^{2} / 4 lambda^{2}} Vg(0)$, and the Cooper pair reduces similarly. For weak coupling, $alpha_1=1$, and when $Vg(0)=0.1$, $Delta_{mathrm{A cdot C}}=108 Delta_{text{BCS}}$, but $Delta_{mathrm{A cdot C}}$ decreases to $28 Delta_{text{BCS}}$ at $Vg(0)=0.2$. For strong coupling, $alpha_1=0$, if $Vg(0)=1.4$, $tilde{V} g(0)$ reduces to 0.2, and the smaller Cooper pair $widetilde{C_{k uparrow} C_{-k downarrow}}$ reduces to $0.14 C_{k uparrow} C_{-k downarrow}$. Additionally, $Delta_{mathrm{A cdot C}} = 0.5676~text{eV} gg hbar omega_{text{D}}$, and the local stacking force is $widetilde{V}_{text{st}}=0.264 ~text{eV}$. With $k^2/lambda^2 =$ const, the local strength increases, causing the stacking force to grow significantly. Thus, $hbar omega_0$ and $Delta$ yield a unique solution.
{"title":"Strong local variational approach for superconductivity theory, and the principles of coherent interaction and action-counteraction","authors":"ChaoFan Yu, Xuyang Chen, ZhiHua Luo","doi":"arxiv-2409.04317","DOIUrl":"https://doi.org/arxiv-2409.04317","url":null,"abstract":"For the two-mode electron pairing, we propose a local stacking force pairing\u0000mechanism driven by strong local fluctuations, with two straight pairing orbits\u0000where the tying Cooper pairing $C_{-kdownarrow}C_{kuparrow}e^{ikcdot r}$\u0000replaces the itinerant pairing. Based on coherent interaction and\u0000action-counteraction principles, the strong local variational theory is\u0000constructed, with the energy extremum and gap equations forming self-consistent\u0000pairs, involving the local variational parameter $lambda$, energy gap\u0000$Delta$, and the energy cut-off $hbar omega_0$. As $hbar omega_0(j)$\u0000approaches its cut-off, $lambda$ and $Delta$ converge to fixed values. The\u0000theory predicts that the coupling strength $Vg(0)$ reduces to\u0000$tilde{V}g(0)=e^{-left(1-alpha_{1}right)^{2} k^{2} / 4 lambda^{2}} Vg(0)$,\u0000and the Cooper pair reduces similarly. For weak coupling, $alpha_1=1$, and\u0000when $Vg(0)=0.1$, $Delta_{mathrm{A cdot C}}=108 Delta_{text{BCS}}$, but\u0000$Delta_{mathrm{A cdot C}}$ decreases to $28 Delta_{text{BCS}}$ at\u0000$Vg(0)=0.2$. For strong coupling, $alpha_1=0$, if $Vg(0)=1.4$, $tilde{V}\u0000g(0)$ reduces to 0.2, and the smaller Cooper pair $widetilde{C_{k uparrow}\u0000C_{-k downarrow}}$ reduces to $0.14 C_{k uparrow} C_{-k downarrow}$.\u0000Additionally, $Delta_{mathrm{A cdot C}} = 0.5676~text{eV} gg hbar\u0000omega_{text{D}}$, and the local stacking force is\u0000$widetilde{V}_{text{st}}=0.264 ~text{eV}$. With $k^2/lambda^2 =$ const, the\u0000local strength increases, causing the stacking force to grow significantly.\u0000Thus, $hbar omega_0$ and $Delta$ yield a unique solution.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210233","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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