In a series of papers, we have proposed a non-perturbative field-theoretic approach to deal with strong electron-phonon and strong Coulomb interactions. The key ingredient of such an approach is to determine the full fermion-boson vertex corrections by solving a number of self-consistent Ward-Takahashi identities. Palle (see Phys. Rev. B 110, 026501 (2024), arXiv:2404.02918) argued that our Ward-Takahashi identities failed to include some important additional terms and thus are incorrect. We agree that our Ward-Takahashi identities have ignored some potentially important contributions and here give some remarks on the role played by the additional terms.
{"title":"Reply to \"Comment on `Towards exact solutions of superconducting $T_c$ induced by electron-phonon interaction' \"","authors":"Guo-Zhu Liu, Zhao-Kun Yang, Xiao-Yin Pan, Jing-Rong Wang, Xin Li, Hao-Fu Zhu, Jie Huang","doi":"arxiv-2408.03857","DOIUrl":"https://doi.org/arxiv-2408.03857","url":null,"abstract":"In a series of papers, we have proposed a non-perturbative field-theoretic\u0000approach to deal with strong electron-phonon and strong Coulomb interactions.\u0000The key ingredient of such an approach is to determine the full fermion-boson\u0000vertex corrections by solving a number of self-consistent Ward-Takahashi\u0000identities. Palle (see Phys. Rev. B 110, 026501 (2024), arXiv:2404.02918)\u0000argued that our Ward-Takahashi identities failed to include some important\u0000additional terms and thus are incorrect. We agree that our Ward-Takahashi\u0000identities have ignored some potentially important contributions and here give\u0000some remarks on the role played by the additional terms.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141968661","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}
There is rich experimental evidence that granular superconductors and superconducting films often exhibit a higher transition temperature, $T_{c}$, than that in bulk samples of the same material. This paper suggests that this enhancement hinges on random matrix phonons mediating Cooper pairing more efficiently than bulk phonons. We develop the Eliashberg theory of superconductivity in chaotic grains, calculate the random phonon spectrum and solve the Eliashberg equations numerically. Self-averaging of the effective electron-phonon coupling constant is noted, which allows us to fit the numerical data with analytical results based on a generalization of the Berry conjecture. The key insight is that the phonon density of states, and hence $T_{c}$, shows an enhancement proportional to the ratio of the perimeter and area of the grain - the Weyl law. We benchmark our results for aluminum films, and find an enhancement of $T_{c}$ of about $10%$ for a randomly-generated shape. A larger enhancement of $T_{c}$ is readily possible by optimizing grain geometries. We conclude by noticing that mesoscopic shape fluctuations in realistic granular structures should give rise to a further enhancement of global $T_{c}$ due to the formation of a percolating Josephson network.
{"title":"Enhanced Cooper Pairing via Random Matrix Phonons in Superconducting Grains","authors":"Andrey Grankin, Mohammad Hafezi, Victor Galitski","doi":"arxiv-2408.03927","DOIUrl":"https://doi.org/arxiv-2408.03927","url":null,"abstract":"There is rich experimental evidence that granular superconductors and\u0000superconducting films often exhibit a higher transition temperature, $T_{c}$,\u0000than that in bulk samples of the same material. This paper suggests that this\u0000enhancement hinges on random matrix phonons mediating Cooper pairing more\u0000efficiently than bulk phonons. We develop the Eliashberg theory of\u0000superconductivity in chaotic grains, calculate the random phonon spectrum and\u0000solve the Eliashberg equations numerically. Self-averaging of the effective\u0000electron-phonon coupling constant is noted, which allows us to fit the\u0000numerical data with analytical results based on a generalization of the Berry\u0000conjecture. The key insight is that the phonon density of states, and hence\u0000$T_{c}$, shows an enhancement proportional to the ratio of the perimeter and\u0000area of the grain - the Weyl law. We benchmark our results for aluminum films,\u0000and find an enhancement of $T_{c}$ of about $10%$ for a randomly-generated\u0000shape. A larger enhancement of $T_{c}$ is readily possible by optimizing grain\u0000geometries. We conclude by noticing that mesoscopic shape fluctuations in\u0000realistic granular structures should give rise to a further enhancement of\u0000global $T_{c}$ due to the formation of a percolating Josephson network.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"85 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141931810","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}
The doping evolution behaviors of the normal state magnetic excitations (MEs) of the nickelate La3Ni2O7 are theoretically studied in this paper. For a filling of n = 3.0 which corresponds roughly to the material which realizes the superconductivity of about 80 K under moderately high pressures above 14 GPa, the MEs exhibit a square-like pattern centered at (0,0) which originates from the intrapocket particle-hole scatterings. Furthermore, it was found that the MEs show very strong modulations on the interlayer momentum qz. With the increasing of qz, the patterns of the MEs change dramatically. In the large qz regime, they turn to be ruled by the interpocket excitation modes with significantly larger intensity which may play a vital role in the superconducting pairing. This hidden feature of the MEs was not revealed by previous studies. The established features of the MEs are found to be very robust against doping. They persist in the wide hole- or electron-doping regime around n = 3.0. However, in the heavily electron-doped regime, a Lifshitz transition will occur. Consequently, the behaviors of the MEs change qualitatively across this transition. With the absence of the hole pocket, we predict that a strong tendency toward the spin-density-wave (SDW) order will develop due to the perfect nesting between the electron and the hole pockets at n = 4.0. Thus, we have investigated the normal state behaviors of the MEs and their doping evolutions which may shed light on the mechanism of superconductivity in pressurized La3Ni2O7.
本文从理论上研究了镍酸盐 La3Ni2O7 正常态磁激发（MEs）的掺杂演化行为。对于 n = 3.0（大致相当于在 14 GPa 以上的中等高压下实现约 80 K 超导性的材料）的填充，MEs 表现出以（0,0）为中心的方形图案，该图案源于套内粒子-空穴散射。此外，研究还发现，MEs 对层间动量 qz 的调制作用非常强烈。随着 qz 的增大，ME 的模式发生了显著变化。在qz较大的情况下，它们转而由强度显著增大的层间激发模式所支配，这可能在超导配对中起着至关重要的作用。以往的研究并未揭示 MEs 的这一隐藏特征。研究发现，ME 的既有特征对掺杂具有很强的稳定性。它们在 n = 3.0 左右的宽空穴或电子掺杂区持续存在。然而，在电子掺杂较多的情况下，会发生利夫希茨转变。因此，在这一转变过程中，ME 的行为会发生质的变化。在没有空穴袋的情况下，我们预测在 n = 4.0 时，由于电子袋和空穴袋之间的完美嵌套，将出现强烈的自旋密度波（SDW）秩序倾向。因此，我们研究了ME的正常态行为及其掺杂演变，这可能会揭示加压La3Ni2O7中的超导机制。
{"title":"Doping evolution of the normal state magnetic excitations in pressurized La3Ni2O7","authors":"Hai-Yang Zhang, Yu-Jie Bai, Fan-Jie Kong, Xiu-Qiang Wu, Yu-Heng Xing, Ning Xu","doi":"arxiv-2408.03763","DOIUrl":"https://doi.org/arxiv-2408.03763","url":null,"abstract":"The doping evolution behaviors of the normal state magnetic excitations (MEs)\u0000of the nickelate La3Ni2O7 are theoretically studied in this paper. For a\u0000filling of n = 3.0 which corresponds roughly to the material which realizes the\u0000superconductivity of about 80 K under moderately high pressures above 14 GPa,\u0000the MEs exhibit a square-like pattern centered at (0,0) which originates from\u0000the intrapocket particle-hole scatterings. Furthermore, it was found that the\u0000MEs show very strong modulations on the interlayer momentum qz. With the\u0000increasing of qz, the patterns of the MEs change dramatically. In the large qz\u0000regime, they turn to be ruled by the interpocket excitation modes with\u0000significantly larger intensity which may play a vital role in the\u0000superconducting pairing. This hidden feature of the MEs was not revealed by\u0000previous studies. The established features of the MEs are found to be very\u0000robust against doping. They persist in the wide hole- or electron-doping regime\u0000around n = 3.0. However, in the heavily electron-doped regime, a Lifshitz\u0000transition will occur. Consequently, the behaviors of the MEs change\u0000qualitatively across this transition. With the absence of the hole pocket, we\u0000predict that a strong tendency toward the spin-density-wave (SDW) order will\u0000develop due to the perfect nesting between the electron and the hole pockets at\u0000n = 4.0. Thus, we have investigated the normal state behaviors of the MEs and\u0000their doping evolutions which may shed light on the mechanism of\u0000superconductivity in pressurized La3Ni2O7.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"32 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141931747","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}
Superconductivity in the recently discovered altermagnetic materials hosts large prospects for both fundamental physics and technological applications. In this work we show that a characteristic spin-sublattice locking in altermagnets puts severe constraints on possible superconducting pairing. In particular, we uncover that the most common form of superconductivity, uniform $s$-wave spin-singlet pairing is not possible to achieve in altermagnets. Considering an effective model for a $d_{x^2-y^2}$-wave altermagnet on a square lattice, we instead find that the most likely forms of spin-singlet pairing have $d_{x^2-y^2}$- or extended $s$-wave symmetry. We also find that the simplest form of equal-spin-triplet $p$-wave pairing is not allowed, but it can only exist as a mixed-spin-triplet $p$-wave state. We verify these constraints on pairing within an interaction-induced model of altermagnetism, where we also establish their validity for finite-momentum pairing. Additionally we discuss the possible pairing symmetries for odd-frequency superconducting pairing. Due to the generality of our results, they are applicable to both intrinsic superconductivity and proximity-induced superconductivity in altermagnet-superconductor hybrid junctions.
{"title":"Constraints on superconducting pairing in altermagnets","authors":"Debmalya Chakraborty, Annica M. Black-Schaffer","doi":"arxiv-2408.03999","DOIUrl":"https://doi.org/arxiv-2408.03999","url":null,"abstract":"Superconductivity in the recently discovered altermagnetic materials hosts\u0000large prospects for both fundamental physics and technological applications. In\u0000this work we show that a characteristic spin-sublattice locking in altermagnets\u0000puts severe constraints on possible superconducting pairing. In particular, we\u0000uncover that the most common form of superconductivity, uniform $s$-wave\u0000spin-singlet pairing is not possible to achieve in altermagnets. Considering an\u0000effective model for a $d_{x^2-y^2}$-wave altermagnet on a square lattice, we\u0000instead find that the most likely forms of spin-singlet pairing have\u0000$d_{x^2-y^2}$- or extended $s$-wave symmetry. We also find that the simplest\u0000form of equal-spin-triplet $p$-wave pairing is not allowed, but it can only\u0000exist as a mixed-spin-triplet $p$-wave state. We verify these constraints on\u0000pairing within an interaction-induced model of altermagnetism, where we also\u0000establish their validity for finite-momentum pairing. Additionally we discuss\u0000the possible pairing symmetries for odd-frequency superconducting pairing. Due\u0000to the generality of our results, they are applicable to both intrinsic\u0000superconductivity and proximity-induced superconductivity in\u0000altermagnet-superconductor hybrid junctions.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"19 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141931800","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}
H. J. Elmers, O. Tkach, Y. Lytvynenko, P. Yogi, M. Schmitt, D. Biswas, J. Liu, S. V. Chernov, M. Hoesch, D. Kutnyakhov, N. Wind, L. Wenthaus, M. Scholz, K. Rossnagel, A. Gloskovskii, C. Schlueter, A. Winkelmann, A. -A. Haghighirad, T. -L. Lee, M. Sing, R. Claessen, M. Le Tacon, J. Demsar, G. Schonhense, O. Fedchenko
Using x-ray photoelectron diffraction (XPD) and angle-resolved photoemission spectroscopy, we study photoemission intensity changes related to changes in the geometric and electronic structure in the kagome metal CsV$_3$Sb$_5$ upon transition to an unconventional charge density wave (CDW) state. The XPD patterns reveal the presence of a chiral atomic structure in the CDW phase. Furthermore, using circularly polarized x-rays, we have found a pronounced non-trivial circular dichroism in the angular distribution of the valence band photoemission in the CDW phase, indicating a chirality of the electronic structure. This observation is consistent with the proposed orbital loop current order. In view of a negligible spontaneous Kerr signal in recent magneto-optical studies, the results suggest an antiferromagnetic coupling of the orbital magnetic moments along the $c$-axis. While the inherent structural chirality may also induce circular dichroism, the observed asymmetry values seem to be too large in the case of the weak structural distortions caused by the CDW.
我们利用 X 射线光电子衍射（XPD）和角度分辨光发射光谱法，研究了神户金属 CsV$_3$Sb$_5$ 在过渡到非常规电荷密度波（CDW）态时与几何和电子结构变化有关的光发射强度变化。此外，利用圆偏振 X 射线，我们发现 CDW 相中价带光辐射的角度分布存在明显的非三重圆二色性，这表明电子结构具有手性。这一观察结果与所提出的轨道环流顺序是一致的。鉴于最近的磁光研究中自发的克尔信号可以忽略不计，研究结果表明轨道磁矩沿 c$ 轴存在反铁磁耦合。虽然固有的结构奇异性也可能诱发圆二色性，但在由 CDW 引起的微弱结构畸变的情况下，观察到的不对称值似乎过大。
{"title":"Chirality in the Kagome Metal CsV$_3$Sb$_5$","authors":"H. J. Elmers, O. Tkach, Y. Lytvynenko, P. Yogi, M. Schmitt, D. Biswas, J. Liu, S. V. Chernov, M. Hoesch, D. Kutnyakhov, N. Wind, L. Wenthaus, M. Scholz, K. Rossnagel, A. Gloskovskii, C. Schlueter, A. Winkelmann, A. -A. Haghighirad, T. -L. Lee, M. Sing, R. Claessen, M. Le Tacon, J. Demsar, G. Schonhense, O. Fedchenko","doi":"arxiv-2408.03750","DOIUrl":"https://doi.org/arxiv-2408.03750","url":null,"abstract":"Using x-ray photoelectron diffraction (XPD) and angle-resolved photoemission\u0000spectroscopy, we study photoemission intensity changes related to changes in\u0000the geometric and electronic structure in the kagome metal CsV$_3$Sb$_5$ upon\u0000transition to an unconventional charge density wave (CDW) state. The XPD\u0000patterns reveal the presence of a chiral atomic structure in the CDW phase.\u0000Furthermore, using circularly polarized x-rays, we have found a pronounced\u0000non-trivial circular dichroism in the angular distribution of the valence band\u0000photoemission in the CDW phase, indicating a chirality of the electronic\u0000structure. This observation is consistent with the proposed orbital loop\u0000current order. In view of a negligible spontaneous Kerr signal in recent\u0000magneto-optical studies, the results suggest an antiferromagnetic coupling of\u0000the orbital magnetic moments along the $c$-axis. While the inherent structural\u0000chirality may also induce circular dichroism, the observed asymmetry values\u0000seem to be too large in the case of the weak structural distortions caused by\u0000the CDW.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"8 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141969758","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}
Hanbin Deng, Guowei Liu, Z. Guguchia, Tianyu Yang, Jinjin Liu, Zhiwei Wang, Yaofeng Xie, Sen Shao, Haiyang Ma, William Liège, Frédéric Bourdarot, Xiao-Yu Yan, Hailang Qin, C. Mielke III, R. Khasanov, H. Luetkens, Xianxin Wu, Guoqing Chang, Jianpeng Liu, Morten Holm Christensen, Andreas Kreisel, Brian Møller Andersen, Wen Huang, Yue Zhao, Philippe Bourges, Yugui Yao, Pengcheng Dai, Jia-Xin Yin
Superconductivity and magnetism are antagonistic quantum matter, while their intertwining has long been considered in frustrated-lattice systems1-3. In this work, we utilize scanning tunneling microscopy and muon spin resonance to discover time-reversal symmetry-breaking superconductivity in kagome metal Cs(V,Ta)3Sb5, where the Cooper pairing exhibits magnetism and is modulated by it. In the magnetic channel, we observe spontaneous internal magnetism in a full-gap superconducting state. Under perturbations of inverse magnetic fields, we detect a time-reversal asymmetrical interference of Bogoliubov quasi-particles at a circular vector. At this vector, the pairing gap spontaneously modulates, which is distinct from pair density waves occurring at a point vector and consistent with the theoretical proposal of unusual interference effect under time-reversal symmetry-breaking. The correlation between internal magnetism, Bogoliubov quasi-particles, and pairing modulation provides a chain of experimental clues for time-reversal symmetry-breaking kagome superconductivity.
{"title":"Evidence chain for time-reversal symmetry-breaking kagome superconductivity","authors":"Hanbin Deng, Guowei Liu, Z. Guguchia, Tianyu Yang, Jinjin Liu, Zhiwei Wang, Yaofeng Xie, Sen Shao, Haiyang Ma, William Liège, Frédéric Bourdarot, Xiao-Yu Yan, Hailang Qin, C. Mielke III, R. Khasanov, H. Luetkens, Xianxin Wu, Guoqing Chang, Jianpeng Liu, Morten Holm Christensen, Andreas Kreisel, Brian Møller Andersen, Wen Huang, Yue Zhao, Philippe Bourges, Yugui Yao, Pengcheng Dai, Jia-Xin Yin","doi":"arxiv-2408.02898","DOIUrl":"https://doi.org/arxiv-2408.02898","url":null,"abstract":"Superconductivity and magnetism are antagonistic quantum matter, while their\u0000intertwining has long been considered in frustrated-lattice systems1-3. In this\u0000work, we utilize scanning tunneling microscopy and muon spin resonance to\u0000discover time-reversal symmetry-breaking superconductivity in kagome metal\u0000Cs(V,Ta)3Sb5, where the Cooper pairing exhibits magnetism and is modulated by\u0000it. In the magnetic channel, we observe spontaneous internal magnetism in a\u0000full-gap superconducting state. Under perturbations of inverse magnetic fields,\u0000we detect a time-reversal asymmetrical interference of Bogoliubov\u0000quasi-particles at a circular vector. At this vector, the pairing gap\u0000spontaneously modulates, which is distinct from pair density waves occurring at\u0000a point vector and consistent with the theoretical proposal of unusual\u0000interference effect under time-reversal symmetry-breaking. The correlation\u0000between internal magnetism, Bogoliubov quasi-particles, and pairing modulation\u0000provides a chain of experimental clues for time-reversal symmetry-breaking\u0000kagome superconductivity.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"30 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141931812","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}
Hanbin Deng, Hailang Qin, Guowei Liu, Tianyu Yang, Ruiqing Fu, Zhongyi Zhang, Xianxin Wu, Zhiwei Wang, Youguo Shi, Jinjin Liu, Hongxiong Liu, Xiao-Yu Yan, Wei Song, Xitong Xu, Yuanyuan Zhao, Mingsheng Yi, Gang Xu, Hendrik Hohmann, Sofie Castro Holbæk, Matteo Dürrnage, Sen Zhou, Guoqing Chang, Yugui Yao, Qianghua Wang, Zurab Guguchia, Titus Neupert, Ronny Thomale, Mark H. Fischer, Jia-Xin Yin
Superconductivity involving finite momentum pairing can lead to spatial gap and pair density modulations, as well as Bogoliubov Fermi states within the superconducting gap. However, the experimental realization of their intertwined relations has been challenging. Here, we detect chiral kagome superconductivity modulations with residual Fermi arcs in KV3Sb5 and CsV3Sb5 by normal and Josephson scanning tunneling microscopy down to 30mK with resolved electronic energy difference at microelectronvolt level. We observe a U-shaped superconducting gap with flat residual in-gap states. This gap exhibits chiral 2 by 2 spatial modulations with magnetic field tunable chirality, which align with the chiral 2 by 2 pair density modulations observed through Josephson tunneling. These findings demonstrate a chiral pair density wave (PDW) that breaks time-reversal symmetry. Quasiparticle interference imaging of the in-gap zero-energy states reveals segmented arcs, with high-temperature data linking them to parts of the reconstructed V d-orbital states within the charge order. The detected residual Fermi arcs can be explained by the partial suppression of these d-orbital states through an interorbital 2 by 2 PDW and thus serve as candidate Bogoliubov Fermi states. Additionally, we differentiate the observed PDW order from impurity-induced gap modulations. Our observations not only uncover a chiral PDW order with orbital-selectivity, but also illuminate the fundamental space-momentum correspondence inherent in finite momentum paired superconductivity.
涉及有限动量配对的超导现象可导致空间间隙和配对密度调制，以及超导间隙内的波哥留布夫费米态。然而，要在实验中实现它们之间的相互关联一直是个挑战。在这里，我们通过普通和约瑟夫森扫描隧道显微镜在 KV3Sb5 和 CsV3Sb5 中检测到了手性卡戈米超导电性调制与残余费米弧，波长低至 30mK，在微电子伏级解析了电子能差。我们观察到一个具有平坦残余隙内态的 U 型超导隙。该间隙表现出手性2乘2空间调制，具有磁场可调的手性，这与通过约瑟夫通道观测到的手性2乘2磁对密度调制相吻合。这些发现证明了打破时间反向对称性的手性对密度波（PDW）。对空隙内零能态的准粒子干涉成像揭示了分段弧，高温数据将它们与电荷阶内重建的 V d 轨道态的一部分联系起来。此外，我们还将观测到的 PDW 秩与杂质引起的间隙调制区分开来。我们的观测结果不仅揭示了具有轨道选择性的手性 PDW 秩，而且还阐明了有限动量派超导中固有的基本空间-动量对应关系。
{"title":"Chiral kagome superconductivity modulations with residual Fermi arcs in KV3Sb5 and CsV3Sb5","authors":"Hanbin Deng, Hailang Qin, Guowei Liu, Tianyu Yang, Ruiqing Fu, Zhongyi Zhang, Xianxin Wu, Zhiwei Wang, Youguo Shi, Jinjin Liu, Hongxiong Liu, Xiao-Yu Yan, Wei Song, Xitong Xu, Yuanyuan Zhao, Mingsheng Yi, Gang Xu, Hendrik Hohmann, Sofie Castro Holbæk, Matteo Dürrnage, Sen Zhou, Guoqing Chang, Yugui Yao, Qianghua Wang, Zurab Guguchia, Titus Neupert, Ronny Thomale, Mark H. Fischer, Jia-Xin Yin","doi":"arxiv-2408.02896","DOIUrl":"https://doi.org/arxiv-2408.02896","url":null,"abstract":"Superconductivity involving finite momentum pairing can lead to spatial gap\u0000and pair density modulations, as well as Bogoliubov Fermi states within the\u0000superconducting gap. However, the experimental realization of their intertwined\u0000relations has been challenging. Here, we detect chiral kagome superconductivity\u0000modulations with residual Fermi arcs in KV3Sb5 and CsV3Sb5 by normal and\u0000Josephson scanning tunneling microscopy down to 30mK with resolved electronic\u0000energy difference at microelectronvolt level. We observe a U-shaped\u0000superconducting gap with flat residual in-gap states. This gap exhibits chiral\u00002 by 2 spatial modulations with magnetic field tunable chirality, which align\u0000with the chiral 2 by 2 pair density modulations observed through Josephson\u0000tunneling. These findings demonstrate a chiral pair density wave (PDW) that\u0000breaks time-reversal symmetry. Quasiparticle interference imaging of the in-gap\u0000zero-energy states reveals segmented arcs, with high-temperature data linking\u0000them to parts of the reconstructed V d-orbital states within the charge order.\u0000The detected residual Fermi arcs can be explained by the partial suppression of\u0000these d-orbital states through an interorbital 2 by 2 PDW and thus serve as\u0000candidate Bogoliubov Fermi states. Additionally, we differentiate the observed\u0000PDW order from impurity-induced gap modulations. Our observations not only\u0000uncover a chiral PDW order with orbital-selectivity, but also illuminate the\u0000fundamental space-momentum correspondence inherent in finite momentum paired\u0000superconductivity.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"33 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141931749","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 his seminal work published in Acta Physica Sinica in 1965, Yu Lu pointed out that the superconducting gap exhibits weak modulations near the pair-breaking magnetic impurity in a superconductor. In the past ten years, a series of high-resolution scanning tunneling microscopy works reported weak superconducting gap modulations in certain superconductors and explained these phenomena as pair density waves. In line with Yu's discovery, Lee DH et al. pointed out that in many cases, the interference effect of pair-breaking scattering can also lead to superconducting gap modulations in space. We will discuss the distinction and unification of these two kinds of mechanisms, as well as their relevance to recent experimental observations.
1965 年，Yu Lu 在他发表于《中国物理学报》的开创性著作中指出，超导体中的对断裂磁性杂质附近的超导间隙表现出微弱的调制。近十年来，一系列高分辨率扫描隧道显微镜研究报告了某些超导体中的微弱超导间隙调制，并将这些现象解释为磁对密度波。与 Yu 的发现相一致，Lee DH 等人指出，在许多情况下，对破散射的干涉效应也会导致空间超导间隙调制。我们将讨论这两种机制的区别和统一，以及它们与最新实验观测的相关性。
{"title":"Superconducting gap modulations: are they from pair density waves or pair-breaking scattering?","authors":"Jia-Xin Yin, Qianghua Wang","doi":"arxiv-2408.02890","DOIUrl":"https://doi.org/arxiv-2408.02890","url":null,"abstract":"In his seminal work published in Acta Physica Sinica in 1965, Yu Lu pointed\u0000out that the superconducting gap exhibits weak modulations near the\u0000pair-breaking magnetic impurity in a superconductor. In the past ten years, a\u0000series of high-resolution scanning tunneling microscopy works reported weak\u0000superconducting gap modulations in certain superconductors and explained these\u0000phenomena as pair density waves. In line with Yu's discovery, Lee DH et al.\u0000pointed out that in many cases, the interference effect of pair-breaking\u0000scattering can also lead to superconducting gap modulations in space. We will\u0000discuss the distinction and unification of these two kinds of mechanisms, as\u0000well as their relevance to recent experimental observations.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"47 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141931754","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}
We recently showed that strong enhancement of superconductivity can occur in systems with a resonant anti-shielding effect wherein the nonlocal dielectric function of the environment vanishes. This effect is universal, since it relies on the fact that Cooper pairs, regardless of the pairing mechanism, are simply charges that can be affected by external charges / fields induced in an engineered dielectric environment. In our earlier work, we proposed a composite system containing a superconductor and a topological insulator that satisfies the stringent conditions for the anti-shielding. Here, we propose a superlattice system containing a metal-organic framework medium that also satisfies these conditions, but with the effect even stronger and more controllable. Our estimates show that ambient temperature and pressure operation could be achievable in this configuration with e.g. MgB2, or even with cuprate superconductors.
{"title":"Strong enhancement of superconductivity via engineered dielectric environment","authors":"Krzysztof Kempa, Michael J. Naughton","doi":"arxiv-2408.03288","DOIUrl":"https://doi.org/arxiv-2408.03288","url":null,"abstract":"We recently showed that strong enhancement of superconductivity can occur in\u0000systems with a resonant anti-shielding effect wherein the nonlocal dielectric\u0000function of the environment vanishes. This effect is universal, since it relies\u0000on the fact that Cooper pairs, regardless of the pairing mechanism, are simply\u0000charges that can be affected by external charges / fields induced in an\u0000engineered dielectric environment. In our earlier work, we proposed a composite\u0000system containing a superconductor and a topological insulator that satisfies\u0000the stringent conditions for the anti-shielding. Here, we propose a\u0000superlattice system containing a metal-organic framework medium that also\u0000satisfies these conditions, but with the effect even stronger and more\u0000controllable. Our estimates show that ambient temperature and pressure\u0000operation could be achievable in this configuration with e.g. MgB2, or even\u0000with cuprate superconductors.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141969759","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}
Zhongjin Zhang, Anatoly Kuklov, Nikolay Prokof'ev, Boris Svistunov
In systems with linear electron-phonon interaction (EPI), bound states of polarons, or bipolarons, form by gaining energy from the lattice deformation. The quadratic EPI case is fundamentally different: bipolarons form because electrons lose less energy when the total charge density is "compacted". As the coupling constant is increased, the bipolarons first appear as extended (but finite radius) soliton-type states. They subsequently decrease in radius until their size reaches the inter-atomic scale. We present the first numerically exact solution of the bipolaron problem from quadratic EPI in the presence of both on-site Hubbard and long-range Coulomb repulsion, and compute estimates of the largest superconducting transition temperature within the bipolaron mechanism. We find that $T_c/Omega$ ratios, where $Omega$ is the optical phonon frequency, can be several times larger than what one may expect from the linear EPI provided the phonon frequency is increased by orders of magnitude on occupied sites. Electron-electron repulsion can be tolerated at the expense of stronger EPI and the most detrimental effect comes from the Coulomb potential because it easily eliminates extended soliton states.
{"title":"Superconductivity of bipolarons from quadratic electron-phonon interaction","authors":"Zhongjin Zhang, Anatoly Kuklov, Nikolay Prokof'ev, Boris Svistunov","doi":"arxiv-2408.03266","DOIUrl":"https://doi.org/arxiv-2408.03266","url":null,"abstract":"In systems with linear electron-phonon interaction (EPI), bound states of\u0000polarons, or bipolarons, form by gaining energy from the lattice deformation.\u0000The quadratic EPI case is fundamentally different: bipolarons form because\u0000electrons lose less energy when the total charge density is \"compacted\". As the\u0000coupling constant is increased, the bipolarons first appear as extended (but\u0000finite radius) soliton-type states. They subsequently decrease in radius until\u0000their size reaches the inter-atomic scale. We present the first numerically\u0000exact solution of the bipolaron problem from quadratic EPI in the presence of\u0000both on-site Hubbard and long-range Coulomb repulsion, and compute estimates of\u0000the largest superconducting transition temperature within the bipolaron\u0000mechanism. We find that $T_c/Omega$ ratios, where $Omega$ is the optical\u0000phonon frequency, can be several times larger than what one may expect from the\u0000linear EPI provided the phonon frequency is increased by orders of magnitude on\u0000occupied sites. Electron-electron repulsion can be tolerated at the expense of\u0000stronger EPI and the most detrimental effect comes from the Coulomb potential\u0000because it easily eliminates extended soliton states.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"46 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141931750","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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