Soma Yoshida, Yukio Tanaka, Alexander A. Golubov, Shu-Ichiro Suzuki
We present a method for detecting the chirality $chi$ of a ($d_{zx}+i chi d_{yz}$)-wave superconductor through the analysis of the local density of states (LDOS) at the vortex core. Employing the quasiclassical Eilenberger theory, we examine the LDOS in a semi-infinite superconductor with a quantum vortex penetrating the surface perpendicularly. We show that $mathrm{sgn}[chi]$ changes completely the LDOS at the core-surface intersection. Remarkably, the difference between LDOS for the $chi = 1$ and $chi = -1$ states becomes more prominent when the surface is dirtier, meaning that one does not need to pay close attention to the surface quality of the sample. The difference between these two states arises from the symmetry of the subdominant Cooper pairs induced at the core-surface intersection: whether the subdominant $s$-wave Cooper pairs are present or not. Due to the unique nature of this phenomenon in the ($d_{zx}+i chi d_{yz}$)-wave superconductor, one can potentially demonstrate the realization of the ($d_{zx}+i chi d_{yz}$)-wave superconductivity and determine its chirality by, for instance, through scanning tunnel spectroscopy experiments.
我们提出了一种通过分析涡旋核心的局域态密度（LDOS）来探测（$d_{zx}+i chid_{yz}$）波超导体的手性$chi$的方法。利用准经典艾伦伯格理论，我们研究了量子涡旋垂直穿透表面的半无限超导体中的LDOS。我们发现，$mmathrm{sgn}[chi]$ 完全改变了核心-表面交汇处的 LDOS。值得注意的是，当表面更脏时，$chi = 1$ 和$chi = -1$ 状态的 LDOS 差异会变得更明显，这意味着我们不需要密切关注样品的表面质量。这两种状态之间的差异来自于在核心-表面交汇处诱导的次主导库珀对的对称性：即次主导 $s$ 波库珀对是否存在。由于这种现象在（$d_{zx}+i chi d_{yz}$）波超导体中的独特性质，人们可以通过扫描隧道光谱实验等方法证明（$d_{zx}+i chi d_{yz}$）波超导的实现并确定其手性。
{"title":"Chirality Detection through Vortex Bound States in ($d+id'$)-Wave Superconductor","authors":"Soma Yoshida, Yukio Tanaka, Alexander A. Golubov, Shu-Ichiro Suzuki","doi":"arxiv-2409.07711","DOIUrl":"https://doi.org/arxiv-2409.07711","url":null,"abstract":"We present a method for detecting the chirality $chi$ of a ($d_{zx}+i chi\u0000d_{yz}$)-wave superconductor through the analysis of the local density of\u0000states (LDOS) at the vortex core. Employing the quasiclassical Eilenberger\u0000theory, we examine the LDOS in a semi-infinite superconductor with a quantum\u0000vortex penetrating the surface perpendicularly. We show that\u0000$mathrm{sgn}[chi]$ changes completely the LDOS at the core-surface\u0000intersection. Remarkably, the difference between LDOS for the $chi = 1$ and\u0000$chi = -1$ states becomes more prominent when the surface is dirtier, meaning\u0000that one does not need to pay close attention to the surface quality of the\u0000sample. The difference between these two states arises from the symmetry of the\u0000subdominant Cooper pairs induced at the core-surface intersection: whether the\u0000subdominant $s$-wave Cooper pairs are present or not. Due to the unique nature\u0000of this phenomenon in the ($d_{zx}+i chi d_{yz}$)-wave superconductor, one can\u0000potentially demonstrate the realization of the ($d_{zx}+i chi d_{yz}$)-wave\u0000superconductivity and determine its chirality by, for instance, through\u0000scanning tunnel spectroscopy experiments.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"28 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209980","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}
Debashish Mondal, Amartya Pal, Arijit Saha, Tanay Nag
We theoretically investigate the transport and shot noise properties of a one-dimensional semiconducting nanowire with Rashba spin-orbit coupling~(SOC) placed in closed proximity to a bulk $s$-wave superconductor and an altermagnet with $d$-wave symmetry. Such heterostructure with vanishing net magnetization manifests itself as an alternative route to anchor Majorana zero modes~(MZMs) characterized by appropriate topological index~(winding number $W$). Interestingly, this system also hosts accidental zero modes~(AZMs) emerged with vanishing topological index indicating their non-topological nature. Furthermore, by incorporating three terminal setup, we explore the transport and shot noise signatures of these zero modes. At zero temperature, we obtain zero bias peak (ZBP) in differential conductance to be quantized with value $|W|times 2 e^{2}/h$ for MZMs. On the other hand, AZMs exhibit non-quantized value at zero bias. Moreover, zero temperature shot noise manifests negative~(positive) value for MZMs~(AZMs) within the bulk gap. At finite temperature, shot noise exhibits negative value~(negative to positive transition) concerning MZMs~(AZMs). Thus, the obtained signatures clearly distinguish between the MZMs and non-topological AZMs. We extend our analysis by switching on the next to nearest neighbour hopping amplitude and SOC. Our conclusion remains unaffected for this case as well. Hence, our work paves the way to differentiate between emergent MZMs and AZMs in a semiconductor/ superconductor/ altermagnet heterostructure.
{"title":"Distinguishing between topological Majorana and trivial zero modes via transport and shot noise study in an altermagnet heterostructure","authors":"Debashish Mondal, Amartya Pal, Arijit Saha, Tanay Nag","doi":"arxiv-2409.08009","DOIUrl":"https://doi.org/arxiv-2409.08009","url":null,"abstract":"We theoretically investigate the transport and shot noise properties of a\u0000one-dimensional semiconducting nanowire with Rashba spin-orbit coupling~(SOC)\u0000placed in closed proximity to a bulk $s$-wave superconductor and an altermagnet\u0000with $d$-wave symmetry. Such heterostructure with vanishing net magnetization\u0000manifests itself as an alternative route to anchor Majorana zero modes~(MZMs)\u0000characterized by appropriate topological index~(winding number $W$).\u0000Interestingly, this system also hosts accidental zero modes~(AZMs) emerged with\u0000vanishing topological index indicating their non-topological nature.\u0000Furthermore, by incorporating three terminal setup, we explore the transport\u0000and shot noise signatures of these zero modes. At zero temperature, we obtain\u0000zero bias peak (ZBP) in differential conductance to be quantized with value\u0000$|W|times 2 e^{2}/h$ for MZMs. On the other hand, AZMs exhibit non-quantized\u0000value at zero bias. Moreover, zero temperature shot noise manifests\u0000negative~(positive) value for MZMs~(AZMs) within the bulk gap. At finite\u0000temperature, shot noise exhibits negative value~(negative to positive\u0000transition) concerning MZMs~(AZMs). Thus, the obtained signatures clearly\u0000distinguish between the MZMs and non-topological AZMs. We extend our analysis\u0000by switching on the next to nearest neighbour hopping amplitude and SOC. Our\u0000conclusion remains unaffected for this case as well. Hence, our work paves the\u0000way to differentiate between emergent MZMs and AZMs in a semiconductor/\u0000superconductor/ altermagnet heterostructure.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"18 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209984","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 derived a simple reduced form from the exact solution of the mixed magnetic and quadrupolar nuclear spin-lattice relaxation function at the central transition line of a quadrupole-split NMR spectrum for nuclear spin $I$ = 3/2. From the application of the reduced form to the $^{63}$Cu nuclear spin-lattice relaxation curves in the high-$T_mathrm{c}$ superconductors of $^{63}$Cu-enriched triple-layer HgBa$_2$Ca$_2$Cu$_3$O$_{delta}$, we estimated the nuclear electric quadrupole spin-lattice relaxation rate $^{63}W_Q$ and the upper limit.
{"title":"Quest for nuclear quadrupole relaxation in HgCa$_{2}$Ba$_{2}$Cu$_{3}$O$_δ$","authors":"Yutaka Itoh, Akihiro Ogawa, Seiji Adachi","doi":"arxiv-2409.08408","DOIUrl":"https://doi.org/arxiv-2409.08408","url":null,"abstract":"We derived a simple reduced form from the exact solution of the mixed\u0000magnetic and quadrupolar nuclear spin-lattice relaxation function at the\u0000central transition line of a quadrupole-split NMR spectrum for nuclear spin $I$\u0000= 3/2. From the application of the reduced form to the $^{63}$Cu nuclear\u0000spin-lattice relaxation curves in the high-$T_mathrm{c}$ superconductors of\u0000$^{63}$Cu-enriched triple-layer HgBa$_2$Ca$_2$Cu$_3$O$_{delta}$, we estimated\u0000the nuclear electric quadrupole spin-lattice relaxation rate $^{63}W_Q$ and the\u0000upper limit.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"39 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142253564","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}
Jiao-Jiao Song, Qi-Yi Wu, Chen Zhang, Steve M. Gilbertson, Peter S. Riseborough, Jan Rusz, John J. Joyce, Kevin S. Graham, Clifford G. Olson, Paul H. Tobash, Eric D. Bauer, Bo Chen, Hao Liu, Yu-Xia Duan, Peter M. Oppeneer, George Rodriguez, Tomasz Durakiewicz, Jian-Qiao Meng
This study investigates the 5$f$-electron-conduction electron hybridization process in the heavy fermion superconductor UPd$_2$Al$_3$ using a combination of angle-resolved photoemission spectroscopy (ARPES) and time-resolved photoemission spectroscopy (tr-PES). ARPES measurements reveal the formation of a hybridization gap at a temperature of approximately 75 K, which becomes more pronounced as the temperature decreases. Notably, the persistence of a flat U 5$f$ band at temperatures well above the hybridization onset challenges conventional understanding. Our findings demonstrate a non-monotonic temperature dependence of the quasiparticle relaxation time, with an anomalous decrease at 20 K, suggesting complex electronic and magnetic interactions. These findings provide detailed insights into the 5$f$-electron hybridization process in UPd$_2$Al$_3$, with significant implications for the understanding of heavy fermion superconductivity and the role of 5$f$-electron hybridization in uranium-based materials.
本研究采用角度分辨光发射光谱（ARPES）和时间分辨光发射光谱（tr-PES）相结合的方法，研究了重费米子超导体 UPd$_2$Al$_3$ 中的 5$f$ 电子-传导电子杂化过程。ARPES 测量显示在大约 75 K 的温度下形成了杂化间隙，随着温度的降低，杂化间隙变得更加明显。值得注意的是，在远高于杂化起始温度的条件下，U5$f$平坦带的持续存在挑战了传统的理解。我们的发现证明了类粒子弛豫时间的非单调温度依赖性，在 20 K 时出现异常减少，这表明存在复杂的电子和磁相互作用。这些发现提供了对 UPd$_2$Al$_3$ 中 5$f$ 电子杂化过程的详细见解，对理解重费米子超导性和 5$f$ 电子杂化在铀基材料中的作用具有重要意义。
{"title":"Unveiling the 5$f$ electron hybridization process in UPd$_2$Al$_3$ via ARPES and Time-resolved PES","authors":"Jiao-Jiao Song, Qi-Yi Wu, Chen Zhang, Steve M. Gilbertson, Peter S. Riseborough, Jan Rusz, John J. Joyce, Kevin S. Graham, Clifford G. Olson, Paul H. Tobash, Eric D. Bauer, Bo Chen, Hao Liu, Yu-Xia Duan, Peter M. Oppeneer, George Rodriguez, Tomasz Durakiewicz, Jian-Qiao Meng","doi":"arxiv-2409.07816","DOIUrl":"https://doi.org/arxiv-2409.07816","url":null,"abstract":"This study investigates the 5$f$-electron-conduction electron hybridization\u0000process in the heavy fermion superconductor UPd$_2$Al$_3$ using a combination\u0000of angle-resolved photoemission spectroscopy (ARPES) and time-resolved\u0000photoemission spectroscopy (tr-PES). ARPES measurements reveal the formation of\u0000a hybridization gap at a temperature of approximately 75 K, which becomes more\u0000pronounced as the temperature decreases. Notably, the persistence of a flat U\u00005$f$ band at temperatures well above the hybridization onset challenges\u0000conventional understanding. Our findings demonstrate a non-monotonic\u0000temperature dependence of the quasiparticle relaxation time, with an anomalous\u0000decrease at 20 K, suggesting complex electronic and magnetic interactions.\u0000These findings provide detailed insights into the 5$f$-electron hybridization\u0000process in UPd$_2$Al$_3$, with significant implications for the understanding\u0000of heavy fermion superconductivity and the role of 5$f$-electron hybridization\u0000in uranium-based materials.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"10 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209989","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}
Jun Li, Wenqi Fang, Shangjian Jin, Tengdong Zhang, Yanling Wu, Xiaodan Xu, Yong Liu, Dao-Xin Yao
Energy band theory is a foundational framework in condensed matter physics. In this work, we employ a deep learning method, BNAS, to find a direct correlation between electronic band structure and superconducting transition temperature. Our findings suggest that electronic band structures can act as primary indicators of superconductivity. To avoid overfitting, we utilize a relatively simple deep learning neural network model, which, despite its simplicity, demonstrates predictive capabilities for superconducting properties. By leveraging the attention mechanism within deep learning, we are able to identify specific regions of the electronic band structure most correlated with superconductivity. This novel approach provides new insights into the mechanisms driving superconductivity from an alternative perspective. Moreover, we predict several potential superconductors that may serve as candidates for future experimental synthesis.
{"title":"A deep learning approach to search for superconductors from electronic bands","authors":"Jun Li, Wenqi Fang, Shangjian Jin, Tengdong Zhang, Yanling Wu, Xiaodan Xu, Yong Liu, Dao-Xin Yao","doi":"arxiv-2409.07721","DOIUrl":"https://doi.org/arxiv-2409.07721","url":null,"abstract":"Energy band theory is a foundational framework in condensed matter physics.\u0000In this work, we employ a deep learning method, BNAS, to find a direct\u0000correlation between electronic band structure and superconducting transition\u0000temperature. Our findings suggest that electronic band structures can act as\u0000primary indicators of superconductivity. To avoid overfitting, we utilize a\u0000relatively simple deep learning neural network model, which, despite its\u0000simplicity, demonstrates predictive capabilities for superconducting\u0000properties. By leveraging the attention mechanism within deep learning, we are\u0000able to identify specific regions of the electronic band structure most\u0000correlated with superconductivity. This novel approach provides new insights\u0000into the mechanisms driving superconductivity from an alternative perspective.\u0000Moreover, we predict several potential superconductors that may serve as\u0000candidates for future experimental synthesis.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"58 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209979","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}
Yusuke Iguchi, Huiyuan Man, S. M. Thomas, Filip Ronning, Jun Ishizuka, Manfred Sigrist, Priscila F. S. Rosa, Kathryn A. Moler
Chiral superconductors are theorized to exhibit spontaneous edge currents. Here, we found magnetic fields at the edges of UTe$_2$, a candidate odd-parity chiral superconductor, that seem to agree with predictions for a chiral order parameter. However, we did not detect the chiral domains that would be expected, and recent polar Kerr and muon spin relaxation data in nominally clean samples argue against chiral superconductivity. Our results show that hidden sources of magnetism must be carefully ruled out when using spontaneous edge currents to identify chiral superconductivity.
{"title":"Magnetic edge fields in UTe$_2$ near zero background fields","authors":"Yusuke Iguchi, Huiyuan Man, S. M. Thomas, Filip Ronning, Jun Ishizuka, Manfred Sigrist, Priscila F. S. Rosa, Kathryn A. Moler","doi":"arxiv-2409.07668","DOIUrl":"https://doi.org/arxiv-2409.07668","url":null,"abstract":"Chiral superconductors are theorized to exhibit spontaneous edge currents.\u0000Here, we found magnetic fields at the edges of UTe$_2$, a candidate odd-parity\u0000chiral superconductor, that seem to agree with predictions for a chiral order\u0000parameter. However, we did not detect the chiral domains that would be\u0000expected, and recent polar Kerr and muon spin relaxation data in nominally\u0000clean samples argue against chiral superconductivity. Our results show that\u0000hidden sources of magnetism must be carefully ruled out when using spontaneous\u0000edge currents to identify chiral superconductivity.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"25 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209981","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}
Planar Josephson junctions are theoretically predicted to harbor zero-energy Majorana bound states (MBS) in a tunable two-dimensional geometry, at the two ends of the middle metallic channel. Here we show that three distinct topological superconducting regimes, governing the localization of the near-zero-energy MBS, appear in these planar Josephson junctions. The topologically-protected MBS appear near the narrow edges of the junction -- not only in the middle metallic channel but also in the superconducting leads which have widths similar to the values used in recent experiments. We incorporate random fluctuation in the chemical potential to investigate the influence of non-magnetic disorder on the localization of the MBS in different topological regimes and find that the MBS are quite robust against disorder because of the two-dimensional geometry. Interestingly, moderate amount of disorder reduces the splitting between the MBS pairs, possibly by minimizing the wave function overlap of the MBS. We also discuss the changes in the topological superconducting phases when the superconducting lead width is varied. Our results reveal a rich structure of the localization of topologically protected multiple MBS in experimentally-accessible planar Josephson junctions, and call for their experimental confirmation.
{"title":"Multiple Majorana bound states and their resilience against disorder in planar Josephson junctions","authors":"Pankaj Sharma, Narayan Mohanta","doi":"arxiv-2409.07532","DOIUrl":"https://doi.org/arxiv-2409.07532","url":null,"abstract":"Planar Josephson junctions are theoretically predicted to harbor zero-energy\u0000Majorana bound states (MBS) in a tunable two-dimensional geometry, at the two\u0000ends of the middle metallic channel. Here we show that three distinct\u0000topological superconducting regimes, governing the localization of the\u0000near-zero-energy MBS, appear in these planar Josephson junctions. The\u0000topologically-protected MBS appear near the narrow edges of the junction -- not\u0000only in the middle metallic channel but also in the superconducting leads which\u0000have widths similar to the values used in recent experiments. We incorporate\u0000random fluctuation in the chemical potential to investigate the influence of\u0000non-magnetic disorder on the localization of the MBS in different topological\u0000regimes and find that the MBS are quite robust against disorder because of the\u0000two-dimensional geometry. Interestingly, moderate amount of disorder reduces\u0000the splitting between the MBS pairs, possibly by minimizing the wave function\u0000overlap of the MBS. We also discuss the changes in the topological\u0000superconducting phases when the superconducting lead width is varied. Our\u0000results reveal a rich structure of the localization of topologically protected\u0000multiple MBS in experimentally-accessible planar Josephson junctions, and call\u0000for their experimental confirmation.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"26 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209983","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 discovery of superconductivity under high pressure with $T_c$ exceeding 80 K in a bilayer nickelate La$_3$Ni$_2$O$_7$ has led to a strong desire to realize similar high $T_c$ phenomena at ambient pressure. As one possible path toward realizing superconductivity at ambient pressure, we here propose to consider Sr$_3$Ni$_2$O$_5$Cl$_2$ as a possible candidate. In this study, we theoretically investigate the electronic structure of Sr$_3$Ni$_2$O$_5$Cl$_2$ and its structural stability. Our phonon calculation shows that this compound with the $I4/mmm$ tetragonal structure is dynamically stable even at ambient pressure. The characteristic crystal field in this compound lowers the Ni-$d_{3z^2-r^2}$ orbital energy, by which the Ni-$d_{3z^2-r^2}$ orbital becomes rather closer to the half-filling in Sr$_3$Ni$_2$O$_5$Cl$_2$ than La$_3$Ni$_2$O$_7$. As a result, we find that superconductivity is enhanced even though a relatively strong orbital hybridization between the $t_{2g}$ and $e_g$ orbitals is somewhat detrimental for superconductivity. We also check the formation enthalpy, which shows that the high-pressure synthesis can be a good way to actually produce Sr$_3$Ni$_2$O$_5$Cl$_2$. We find that Sr$_3$Ni$_2$O$_5$Cl$_2$ is a promising new candidate of bilayer-nickelate superconductors, which can possess even higher $T_c$ than pressurized La$_3$Ni$_2$O$_7$, at ambient pressure.
{"title":"Theoretical study on the crystal structure of a bilayer nickel-oxychloride Sr$_3$Ni$_2$O$_5$Cl$_2$ and analysis on the occurrence of possible unconventional superconductivity","authors":"Masayuki Ochi, Hirofumi Sakakibara, Hidetomo Usui, Kazuhiko Kuroki","doi":"arxiv-2409.06935","DOIUrl":"https://doi.org/arxiv-2409.06935","url":null,"abstract":"The discovery of superconductivity under high pressure with $T_c$ exceeding\u000080 K in a bilayer nickelate La$_3$Ni$_2$O$_7$ has led to a strong desire to\u0000realize similar high $T_c$ phenomena at ambient pressure. As one possible path\u0000toward realizing superconductivity at ambient pressure, we here propose to\u0000consider Sr$_3$Ni$_2$O$_5$Cl$_2$ as a possible candidate. In this study, we\u0000theoretically investigate the electronic structure of Sr$_3$Ni$_2$O$_5$Cl$_2$\u0000and its structural stability. Our phonon calculation shows that this compound\u0000with the $I4/mmm$ tetragonal structure is dynamically stable even at ambient\u0000pressure. The characteristic crystal field in this compound lowers the\u0000Ni-$d_{3z^2-r^2}$ orbital energy, by which the Ni-$d_{3z^2-r^2}$ orbital\u0000becomes rather closer to the half-filling in Sr$_3$Ni$_2$O$_5$Cl$_2$ than\u0000La$_3$Ni$_2$O$_7$. As a result, we find that superconductivity is enhanced even\u0000though a relatively strong orbital hybridization between the $t_{2g}$ and $e_g$\u0000orbitals is somewhat detrimental for superconductivity. We also check the\u0000formation enthalpy, which shows that the high-pressure synthesis can be a good\u0000way to actually produce Sr$_3$Ni$_2$O$_5$Cl$_2$. We find that\u0000Sr$_3$Ni$_2$O$_5$Cl$_2$ is a promising new candidate of bilayer-nickelate\u0000superconductors, which can possess even higher $T_c$ than pressurized\u0000La$_3$Ni$_2$O$_7$, at ambient pressure.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"43 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209986","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 theoretically study topological superconductivity in elongated planar Josephson junctions. Josephson junctions host a topological phase accompanied by the presence of zero-energy Majorana-bound states in a certain region of the superconducting phase difference with a span determined by the strength of an external magnetic field. We demonstrate that the topological superconducting phase range can be greatly increased by elongation of the junction, which causes an amplification of the Zeeman-induced phase shift of Andreev bound states. We show that the appearance of trivial in-gap states that occurs in elongated junctions can prohibit the creation of Majorana modes, but it can be mitigated by further proximitization of the junction with additional superconducting contacts. The topological transition in this system can be probed by measurements of the critical current and we show that the elongation of the junction leads to a linear decrease of the transition critical magnetic field beneficial for experimental studies.
{"title":"Enhancement of topological regime in elongated Josephson junctions","authors":"D. Kuiri, P. Wójcik, M. P. Nowak","doi":"arxiv-2409.07418","DOIUrl":"https://doi.org/arxiv-2409.07418","url":null,"abstract":"We theoretically study topological superconductivity in elongated planar\u0000Josephson junctions. Josephson junctions host a topological phase accompanied\u0000by the presence of zero-energy Majorana-bound states in a certain region of the\u0000superconducting phase difference with a span determined by the strength of an\u0000external magnetic field. We demonstrate that the topological superconducting\u0000phase range can be greatly increased by elongation of the junction, which\u0000causes an amplification of the Zeeman-induced phase shift of Andreev bound\u0000states. We show that the appearance of trivial in-gap states that occurs in\u0000elongated junctions can prohibit the creation of Majorana modes, but it can be\u0000mitigated by further proximitization of the junction with additional\u0000superconducting contacts. The topological transition in this system can be\u0000probed by measurements of the critical current and we show that the elongation\u0000of the junction leads to a linear decrease of the transition critical magnetic\u0000field beneficial for experimental studies.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"23 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209985","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}
Hidden singularities in correlated electron systems, which are caused by pair fluctuations of electron-electron or electron-hole bubbles obeying Bose-Einstein statistics, are unveiled theoretically. The correlation function of each pair fluctuation is shown to have a bound in the zero Matsubara frequency branch, similarly as the chemical potential of ideal Bose gases. Once the bound is reached, the self-energy starts to acquire a component proportional to Green's function itself, i.e., the structure called one-particle reducible, to keep the correlation function within the bound. The singularities are closely related with, but distinct from, phase transitions with broken symmetries. Passing down through them necessarily accompanies a change in the single-particle density of states around the excitation threshold, such as the pseudo-gap behavior found here for the negative-$U$ Hubbard model above the superconducting transition temperature.
{"title":"Hidden Bose-Einstein Singularities in Correlated Electron Systems","authors":"Takafumi Kita","doi":"arxiv-2409.07660","DOIUrl":"https://doi.org/arxiv-2409.07660","url":null,"abstract":"Hidden singularities in correlated electron systems, which are caused by pair\u0000fluctuations of electron-electron or electron-hole bubbles obeying\u0000Bose-Einstein statistics, are unveiled theoretically. The correlation function\u0000of each pair fluctuation is shown to have a bound in the zero Matsubara\u0000frequency branch, similarly as the chemical potential of ideal Bose gases. Once\u0000the bound is reached, the self-energy starts to acquire a component\u0000proportional to Green's function itself, i.e., the structure called\u0000one-particle reducible, to keep the correlation function within the bound. The\u0000singularities are closely related with, but distinct from, phase transitions\u0000with broken symmetries. Passing down through them necessarily accompanies a\u0000change in the single-particle density of states around the excitation\u0000threshold, such as the pseudo-gap behavior found here for the negative-$U$\u0000Hubbard model above the superconducting transition temperature.","PeriodicalId":501069,"journal":{"name":"arXiv - PHYS - Superconductivity","volume":"64 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209982","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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