Superconductivity
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Showing new listings for Thursday, 14 November 2024
- [1] arXiv:2411.08142 [pdf, html, other]
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Title: Evidence for Atomic-Scale Inhomogeneity in Superconducting Cuprate NMRComments: 17 pages, 12 figuresSubjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
In 1990, the Millis, Monien, and Pines (MMP) model and its improvement, the Zha, Barzykin, and Pines (ZBP) model in 1996, emerged as a realistic explanation of the cuprate NMR. These two models assume a single electronic component, translational symmetry, and that the electrons simultaneously have aspects of localized antiferromagnetic (AF) spins and delocalized Cu $d_{x^2-y^2}$ band states. NMR experiments were routinely fit to these models in the 1990s and early 2000s until they finally failed as NMR experiments developed further. It appears that cuprate theorists have given up on explaining the NMR and the NMR data is forgotten. Here, we assume a two-component model of electrons where the electrons reside in two regions, one metallic with delocalized band states, and the other antiferromagnetic with localized spins. This model breaks translational symmetry. We show that the normal state spin relaxation for the planar Cu, O, and Y atoms in $\mathrm{YBa_2Cu_3O_{7-\delta}}$ and their Knight shifts are explained by this two-component model. The temperature dependence of the Cu spin relaxation rate anisotropy in the superconducting state is also explained qualitatively.
- [2] arXiv:2411.08200 [pdf, other]
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Title: Atomic-scale mapping of superconductivity in the incoherent CDW mosaic phase of a transition metal dichalcogenideSandra Sajan, Haojie Guo, Tarushi Agarwal, Irián Sánchez-Ramírez, Chandan Patra, Maia G. Vergniory, Fernando de Juan, Ravi Prakash Singh, Miguel M. UgedaSubjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
The emergence of superconductivity in the octahedrally coordinated (1T) phase of TaS2 is preceded by the intriguing loss of long-range order in the charge density wave (CDW). Such decoherence, attainable by different methods, results in the formation of nm-sized coherent CDW domains bound by a two-dimensional network of domain walls (DW) - mosaic phase -, which has been proposed as the spatial origin of the superconductivity. Here, we report the atomic-scale characterization of the superconducting state of 1T-TaSSe, a model 1T compound exhibiting the CDW mosaic phase. We use high-resolution scanning tunneling spectroscopy and Andreev spectroscopy to probe the microscopic nature of the superconducting state in unambiguous connection with the electronic structure of the mosaic phase. Spatially resolved conductance maps at the Fermi level at the onset of superconductivity reveal that the density of states is mostly localized on the CDW domains compared to the domain walls, which suggests their dominant role in the formation of superconductivity. This scenario is confirmed within the superconducting dome at 340 mK, where superconductivity is fully developed, and the subtle spatial inhomogeneity of the superconducting gap remains unlinked to the domain wall network. Our results provide key new insights into the fundamental interplay between superconductivity and CDW in these relevant strongly correlated systems.
- [3] arXiv:2411.08391 [pdf, html, other]
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Title: A Simple Model of Superconductors: Insights from Free Fermion and Boson GasesComments: 8 pges, 2 pdf figuresSubjects: Superconductivity (cond-mat.supr-con); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
Superconductors at temperatures below the critical temperature $T_c$ can be modeled as a mixture of Fermi and Bose gases, where the Fermi gas consists of conduction electrons and the Bose gas comprises Cooper pairs. This simple model enables the computation of the temperature dependence of $2 r(T) / N$, where $N$ is the total number of conduction electrons and $r(T)$ is the number of Cooper pairs at temperature $T$. Analyzing $2 r(T) / N$ across various superconductors may provide significant insights into the mechanisms behind high-temperature superconductivity, especially regarding coherence in Cooper pairs.
- [4] arXiv:2411.08539 [pdf, html, other]
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Title: Evolution of Electronic Correlations in the Ruddlesden-Popper NickelatesZhe Liu, Jie Li, Mengwu Huo, Bingke Ji, Jiahao Hao, Yaomin Dai, Mengjun Ou, Qing Li, Hualei Sun, Bing Xu, Yi Lu, Meng Wang, Hai-Hu WenComments: 7 pages, 4 figures. Comments are welcome and appreciatedSubjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
We report on optical studies of the Ruddlesden-Popper nickelates La$_{n+1}$Ni$_{n}$O$_{3n+1}$ with $n = 2$ (La$_{3}$Ni$_{2}$O$_{7}$), $n = 3$ (La$_{4}$Ni$_{3}$O$_{10}$) and $n = \infty$ (LaNiO$_{3}$). As the number of the NiO$_{6}$ octahedra layers $n$ grows, the ratio of the kinetic energy determined from the experimental optical conductivity and that from band theory $K_{\text{exp}}/K_{\text{band}}$ increases, suggesting a reduction of electronic correlations. While the strong electronic correlations in the bilayer La$_{3}$Ni$_{2}$O$_{7}$ place it on the verge of the Mott insulating phase, the trilayer La$_{4}$Ni$_{3}$O$_{10}$ and infinite-layer LaNiO$_{3}$ exhibit moderate electronic correlations, falling into the regime of correlated metals. The evolution of the electronic correlations in La$_{n+1}$Ni$_{n}$O$_{3n+1}$ is likely to be dominated by the Ni-$d_{z^2}$ orbital. Our results provide important information for understanding the superconductivity in Ruddlesden-Popper nickelates.
- [5] arXiv:2411.08649 [pdf, html, other]
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Title: Maximum limit of connectivity in rectangular superconducting films with an oblique weak linkSubjects: Superconductivity (cond-mat.supr-con)
A method for measuring the electrical connectivity between parts of a rectangular superconductor was developed for weak links making an arbitrary angle with the long side of the sample. The method is based on magneto-optical observation of characteristic lines where the critical current makes discontinuous deviations in the flow direction to adapt to the non-uniform condition created by the presence of the weak link. Assuming the Bean critical state model in the full penetration regime for a sample submitted to a perpendicular magnetic field, the complete flow pattern of screening currents is reconstructed, from which the transparency of the weak link, i.e., the ratio between its critical current and that of the pristine sample, $\tau = \frac{J_i}{J_c}$, is then related to the angle $\theta$ formed by two characteristic discontinuity lines which, in turn, are intimately associated to the presence of the weak link. The streamline distribution is compared with magneto-optical observations of the flux penetration in Nb superconducting films, where a weak link was created using focused ion beam milling. The present work generalizes previous analyses in which the weak link was perpendicular to the long sides of the rectangular sample. Equations and measurements demonstrate that the relationship between the transparency and the angle $\theta$ is not affected by the tilting of the weak link. Noticeably, in order to attain optimum connectivity, the weak link critical current can be less than that of the pristine sample, namely, $\tau _{max}=\sin \Phi$, where $\Phi$ is the tilt angle of the weak link. This expression generalizes the previous result of $\tau _{max}=1$ for $\Phi=$ 90$^\circ$.
- [6] arXiv:2411.08677 [pdf, other]
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Title: Pressure-Induced Superconductivity in Pr4Ni3O10 Single CrystalsCuiying Pei, Mingxin Zhang, Di Peng, Shangxiong Huangfu, Shihao Zhu, Qi Wang, Juefei Wu, Zhenfang Xing, Lili Zhang, Yulin Chen, Jinkui Zhao, Wenge Yang, Hongli Suo, Hanjie Guo, Qiaoshi Zeng, Yanpeng QiComments: 15 pages,5 figuresSubjects: Superconductivity (cond-mat.supr-con); Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)
The recent discovery of superconductivity in pressurized Ruddlesden-Popper (RP) of nickelates has potential similarities with cuprate superconductors, which may provide unique perspectives on the mechanisms of high-temperature superconductivity. Up to now, most of high-pressure experiments concentrated on the lanthanum-related RP phase. Therefore, the discovery of new superconducting nickelate compounds is highly desired to explore the generality of pressure-induced superconductivity in RP nickelates. Here, we grow high-quality Pr4Ni3O10 single crystal with an optical floating zone furnace under high oxygen pressure and conduct high-pressure transport measurements with various pressure transmitting mediums. The density wave in Pr4Ni3O10 single crystal was suppressed by pressure, accompanying the arising of superconducting state beyond 10 GPa. The maximum and unsaturated Tc of 39 K is obtained within our research pressure. Although zero resistivity was not achieved in our experiments, the pressure and temperature-dependent diamagnetism along with the systematic evolution of resistivity with applied magnetic field, corroborate the superconductivity in Pr4Ni3O10 single crystals. Our findings provide a new platform for the investigation of the relationship among structural evolution, magnetism, correlation, and superconductivity in Ruddlesden-Popper nickelates.
New submissions (showing 6 of 6 entries)
- [7] arXiv:2411.08192 (cross-list from cond-mat.str-el) [pdf, html, other]
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Title: Accurate Electron-phonon Interactions from Advanced Density Functional TheoryYanyong Wang, Manuel Engel, Christopher Lane, Henrique Miranda, Lin Hou, Bernardo Barbiellini, Robert S. Markiewicz, Jian-Xin Zhu, Georg Kresse, Arun Bansil, Jianwei Sun, Ruiqi ZhangComments: 9 pages, 3 figures, 1 tableSubjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci); Superconductivity (cond-mat.supr-con)
Electron-phonon coupling (EPC) is key for understanding many properties of materials such as superconductivity and electric resistivity. Although first principles density-functional-theory (DFT) based EPC calculations are used widely, their efficacy is limited by the accuracy and efficiency of the underlying exchange-correlation functionals. These limitations become exacerbated in complex $d$- and $f$-electron materials, where beyond-DFT approaches and empirical corrections, such as the Hubbard $U$, are commonly invoked. Here, using the examples of CoO and NiO, we show how the efficient r2scan density functional correctly captures strong EPC effects in transition-metal oxides without requiring the introduction of empirical parameters. We also demonstrate the ability of r2scan to accurately model phonon-mediated superconducting properties of the main group compounds (e.g., MgB$_2$), with improved electronic bands and phonon dispersions over those of traditional density functionals. Our study provides a pathway for extending the scope of accurate first principles modeling of electron-phonon interactions to encompass complex $d$-electron materials.
Cross submissions (showing 1 of 1 entries)
- [8] arXiv:2401.15097 (replaced) [pdf, html, other]
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Title: The electronic and magnetic structures of bilayer La$_3$Ni$_2$O$_7$ at ambient pressureComments: 4 pages, 7 figures and supplemental materialSubjects: Superconductivity (cond-mat.supr-con); Strongly Correlated Electrons (cond-mat.str-el)
We carry out a systematic study of the electronic and magnetic structure of the ambient-pressure bilayer La$_3$Ni$_2$O$_7$. Employing the hybrid exchange-correlation functional, we show that the exchange-correlation pushes the bonding $d_{z^2}$ bands below the Fermi level to be fully occupied. The calculated Fermi surfaces and the correlation normalized band structure match well with the experimental findings at ambient pressure. Moreover, the electronic susceptibility calculated for this new band structure features nesting-induced peaks near the wave vector $Q=(\pi/2, \pi/2)$, suggesting a possible density wave instability in agreement with recent experiments. Through a mean field study and DFT+U calculation introducing a Hubbard U interaction within conventional density functional theory, we confirm the spin-charge intertwined double stripe order is the magnetic ground state. Our results provide a faithful description for the low-pressure La$_3$Ni$_2$O$_7$ electronic structure.
- [9] arXiv:2406.14612 (replaced) [pdf, html, other]
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Title: Superconducting Diode Effect in Multiphase SuperconductorsComments: 10 pages, 4 figures, published versionSubjects: Superconductivity (cond-mat.supr-con)
We identify a new mechanism for the intrinsic superconducting diode effect (SDE) in multiphase superconductors. Using a Ginzburg-Landau and a microscopic two-band model, we find phase transitions into a mixed phase with finite-momentum Cooper pairs and SDE with high (including maximal) diode efficiencies, despite the individual phases exhibiting no SDE and equal inversion parity. We thus show that parity mixing $-$ invoked in previous proposals $-$ is not a crucial ingredient for SDE. The new mechanism may be relevant in a multitude of known multiphase superconductors like UTe$_2$.
- [10] arXiv:2410.07835 (replaced) [pdf, html, other]
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Title: Numerical analysis of Josephson junction arrays for multi-order quantum voltage stepsSubjects: Superconductivity (cond-mat.supr-con)
The dynamics of overdamped Josephson junctions under varying microwave-driving conditions have been studied through numerical simulations using the resistively-shunted junction (RSJ) model. The aim is to determine the optimal junction characteristics and external microwave (rf) parameters that maximize the width of quantum voltage levels (Shapiro steps) from order n = 0 to n > 1. Both the rf and dc power requirements, along with the junction parameter spread and power attenuation, are analyzed as key factors that need to be optimized for improved performance of the quantum device. This work aims to advance the development of next-generation Programmable Josephson Voltage Standards with logic architectures that surpass the conventional binary and ternary codifications used in present quantum voltage arrays, while significantly reducing the overall number of junctions as well as the number of sub-arrays and bias lines.
- [11] arXiv:2410.05384 (replaced) [pdf, html, other]
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Title: Chiral superconductivity from parent Chern band and its non-Abelian generalizationComments: 5+3 pages, 4+1 figuresSubjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Superconductivity (cond-mat.supr-con)
We propose a minimal model starting from a parent Chern band with quartic dispersion that can describe the spin-valley polarized electrons in rhombohedral tetra-layer graphene. The interplay between repulsive and attractive interactions on top of that parent Chern band is studied. We conduct standard self-consistent mean-field calculations, and find a rich phase diagram that consists of metal, quantum anomalous Hall crystal, chiral topological superconductor, as well as trivial gapped Bose-Einstein condensate. In particular, there exists a topological phase transition from the chiral superconductor to the Bose-Einstein condensate at zero temperature. Motivated by the recent experimental and theoretical studies of composite Fermi liquid in rhombohedral stacked multi-layer graphene, we further generalize the physical electron model to its composite fermion counterpart based on a field theory analysis. The chiral superconductor phase of the composite fermion becomes the non-Abelian Moore-Read quantum Hall phase. We argue that a chiral (pseudo-)spin liquid phase can emerge in the vicinity of this Moore-Read quantum Hall phase. Our work suggests rhombohedral multi-layer graphene as a potential platform for rich correlated topological phases.