arXiv subjects

Jiangping Hu

Publications and source records attributed to Jiangping Hu.

At least 73 records · Page 4Linked to original sources

arXiv2024

Paramagnetic contribution in superconductors with different-mass Cooper pairs

Cooper pairs formed by two electrons with different effective masses are common in multiband superconductors, pair density wave states, and other superconducting systems with multiple degrees of freedom. In this paper, we show that there are paramagnetic contributions to the superfluid stiffness in superconductors with different-mass Cooper pairs. This paramagnetic response is owing to the relative motion between two electrons with different mass. Additionally, we identify a particle-hole dichotomy effect related to this mass difference. We investigate the paramagnetic contributions based on the linear-response theory in two-band superconductors with interband pairings and in pair density wave states, respectively. Our results offer a different perspective of the electromagnetic superfluid stiffness in unconventional superconductors beyond the traditional BCS response.

cond-mat.supr-con↗

arXiv2024

Resolving the Electronic Ground State of La3Ni2O7-δ Films

The recent discovery of a superconductivity signature in La3Ni2O7-δ 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-δ 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-δ 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-δ under high pressure.

cond-mat.supr-con↗

arXiv2024

Charge 4$e$ superconductor: a wavefunction approach

We apply a wavefunction approach to study the charge 4$e$ superconductor. The wavefunction takes a similar structure to the BCS wavefunction for charge 2$e$ superconductors. The mean-field Hamiltonian and the Green's functions of charge 4$e$ are constructed. The physical properties including the density of states, gauge invariance, flux quantization, superfluid density and Josephson effects are systematically studied. All these results form a microscopic description of the charge 4$e$ SC and can be served as the hallmarks for experimental verifications.

cond-mat.supr-con↗

arXiv2024

Bulk high-temperature superconductivity in the high-pressure tetragonal phase of bilayer La2PrNi2O7

The Ruddlesden-Popper (R-P) bilayer nickelate, La3Ni2O7, was recently found to show signatures of high-temperature superconductivity (HTSC) at pressures above 14 GPa. Subsequent investigations achieved zero resistance in single- and poly-crystalline samples under hydrostatic pressure conditions. Yet, obvious diamagnetic signals, the other hallmark of superconductors, are still lacking owing to the filamentary nature with low superconducting volume fraction. The presence of a novel "1313" polymorph and competing R-P phases obscured proper identification of the phase for HTSC. Thus, achieving bulk HTSC and identifying the phase at play are the most prominent tasks at present. Here, we address these issues in the praseodymium (Pr)-doped La2PrNi2O7 polycrystalline samples. We find that the substitutions of Pr for La effectively inhibits the intergrowth of different R-P phases, resulting in nearly pure bilayer structure. For La2PrNi2O7, pressure-induced orthorhombic-to-tetragonal structural transition takes place at Pc ~ 11 GPa, above which HTSC emerges gradually upon further compression. The superconducting transition temperatures at 18-20 GPa reach Tconset = 82.5 K and Tczero = 60 K, which are the highest values among known nickelate superconductors. More importantly, bulk HTSC was testified by detecting clear diamagnetic signals below ~75 K corresponding to an estimated superconducting volume fraction ~ 57(5)% at 20 GPa. Our results not only resolve the existing controversies but also illuminate directions for exploring bulk HTSC in the bilayer nickelates.

cond-mat.supr-con↗

arXiv2024

Cooperation between electron-phonon coupling and electronic interaction in bilayer nickelates La$_3$Ni$_2$O$_7$

The recent observation of high-T$_c$ superconductivity in the bilayer nickelate La$_3$Ni$_2$O$_7$ under pressure has garnered significant interests. While researches have predominantly focused on the role of electron-electron interactions in the superconducting mechanism, the impact of electron-phonon coupling (EPC) has remained elusive. In this work, we perform first-principles calculations to study the phonon spectrum and electron-phonon coupling within La$_3$Ni$_2$O$_7$ under pressure and explore of the interplay between EPC and electronic interactions on the superconductivity by employing functional renormalization group approach. Our calculations reveal that EPC alone is insufficient to trigger superconductivity in La$_3$Ni$_2$O$_7$ under pressure. We identify unique out-of-plane and in-plane breathing phonon modes which selectively couple with the Ni $d_{z^2}$ and $d_{x^2-y^2}$ orbitals, showcasing an orbital-selective EPC. Within the bilayer two-orbital model, it is revealed that solely electronic interactions foster $s_{\pm}$-wave pairing characterized by notable frustration in the band space, leading to a low transition temperature. Remarkably, we find that this out-of-plane EPC can act in concert with electronic interactions to promote the onsite and interlayer pairing in the $d_{z^2}$ orbital, partially releasing the pairing frustration and thus elevating T$_c$. In contrast, the inclusion of in-plane EPC only marginally affects the superconductivity, distinct from the cuprates. Potential experimental implications in La$_3$Ni$_2$O$_7$ are also discussed.

cond-mat.supr-con↗

arXiv2024

van Hove Singularity-Driven Emergence of Multiple Flat Bands in Kagome Superconductors

The newly discovered Kagome superconductors AV$_3$Sb$_5$ (A=K, Rb and Cs) continue to bring surprises in generating unusual phenomena and physical properties, including anomalous Hall effect, unconventional charge density wave, electronic nematicity and time-reversal symmetry breaking. Here we report an unexpected emergence of multiple flat bands in the AV$_3$Sb$_5$ superconductors. By performing high-resolution angle-resolved photoemission (ARPES) measurements, we observed four branches of flat bands that span over the entire momentum space. The appearance of the flat bands is not anticipated from the band structure calculations and cannot be accounted for by the known mechanisms of flat band generation. It is intimately related to the evolution of van Hove singularities. It is for the first time to observe such emergence of multiple flat bands in solid materials. Our findings provide new insights in revealing the underlying mechanism that governs the unusual behaviors in the Kagome superconductors. They also provide a new pathway in producing flat bands and set a platform to study the flat bands related physics.

cond-mat.mtrl-sci↗

arXiv2024

Inversion-symmetric Electron Gases as New Platforms for Topological Planar Josephson Junctions

Intrinsic Rashba spin-orbital coupling (SOC) can exist in centrosymmetric materials with local inversion symmetry breaking. Here we show that such a SOC can induce topological superconductivity together with an in-plane Zeeman field in planar Josephson junctions formed by the centrosymmetric materials. A single Majorana mode can be created at each end of the junction. We demonstrate this result in a model based on iron-based superconductors. We derive the necessary Fermi surface condition for the topological planar junction and calculate the topological phase diagram with respect to the in-plane Zeeman field and the phase difference between the two superconductors. We provide experimental characteristics for the topological superconductivity, including the differential conductance and the Fano factor tomography which can be measured in the scanning tunneling spectroscopy. Our study reveals that the centrosymmetric systems with local-inversion-symmetry breaking can serve as new platforms for the topological planar Josephson junctions, and help to find more experimentally feasible materials for the topological superconductors.

cond-mat.supr-con↗

arXiv2024

Two Distinct Charge Orders in Infinite-layer PrNiO2+δ revealed by Resonant X-ray Diffraction

A broken translation symmetry has recently been revealed in infinite-layer nickelates, which has piqued considerable interest in its origin and relation to superconductivity, as well as in its comparison to charge order in cuprates. Here, by performing resonant x-ray scattering measurements in thin films of infinite-layer PrNiO2+δ, we find that the superlattice reflection at the Ni L3 absorption edge differs considerably from that at the Pr M5 resonance in their dependence on energy, temperature, and local symmetry, indicating they are two distinct charge orders despite the same in-plane wavevectors. These dissimilarities might be related to the excess oxygen dopants, considering that the resonant reflections were observed in an incompletely reduced PrNiO2+δ film. In addition, our azimuthal analysis suggests that the oxygen ligands should play a pivotal role in the charge modulation revealed at the Ni L3 resonance.

cond-mat.supr-con↗

arXiv2024

Tunable vortex bound states in multiband CsV3Sb5-derived kagome superconductors

Vortices and bound states offer an effective means of comprehending the electronic properties of superconductors. Recently, surface dependent vortex core states have been observed in the newly discovered kagome superconductors CsV3Sb5. Although the spatial distribution of the sharp zero energy conductance peak appears similar to Majorana bound states arising from the superconducting Dirac surface states, its origin remains elusive. In this study, we present observations of tunable vortex bound states (VBSs) in two chemically doped kagome superconductors Cs(V1-xTrx)3Sb5 (Tr=Ta or Ti), using low temperature scanning tunneling microscopy/spectroscopy. The CsV3Sb5-derived kagome superconductors exhibit full gap pairing superconductivity accompanied by the absence of long range charge orders, in contrast to pristine CsV3Sb5. Zero energy conductance maps demonstrate a field-driven continuous reorientation transition of the vortex lattice, suggesting multiband superconductivity. The Ta doped CsV3Sb5 displays the conventional cross shaped spatial evolution of Caroli de Gennes Matricon bound states, while the Ti doped CsV3Sb5 exhibits a sharp, non split zero bias conductance peak (ZBCP) that persists over a long distance across the vortex. The spatial evolution of the non split ZBCP is robust against surface effects and external magnetic field but is related to the doping concentrations. Our study reveals the tunable VBSs in multiband chemically doped CsV3Sb5 system and offers fresh insights into previously reported Y shaped ZBCP in a non quantum limit condition at the surface of kagome superconductor.

cond-mat.supr-con↗

arXiv2024

Electronic and magnetic excitations in La$_3$Ni$_2$O$_7$

The striking discovery of high-temperature superconductivity (HTSC) of 80 K in a bilayer nickelate La$_3$Ni$_2$O$_7$ under a moderately high pressure of about 14 GPa ignited a new wave of studying HTSC in nickelates. The properties of the parental phase at ambient pressure may contain key information on basic interactions therein and bosons that may mediate pairing giving birth to superconductivity. Moreover, the bilayer structure of La$_3$Ni$_2$O$_7$ may suggest a distinct minimal model in comparison to cuprate superconductors. Here using X-ray absorption spectroscopy and resonant inelastic X-ray scattering, we studied La$_3$Ni$_2$O$_7$ at ambient pressure, and found that Ni 3$d_{x^2-y^2}$, Ni 3$d_{z^2}$, and ligand oxygen 2$p$ orbitals dominate the low-energy physics with a small charge-transfer energy. Remarkably, well-defined optical-like magnetic excitations were found to soften into a quasi-static spin-density-wave ordering, evidencing the strong electronic correlations and rich magnetic properties. Based on a Heisenberg spin model, we found that the inter-layer effective magnetic superexchange interaction is much larger than the intra-layer ones, and proposed two viable magnetic structures. Our results set the foundation for further exploration of La$_3$Ni$_2$O$_7$ superconductor.

cond-mat.supr-con↗

arXiv2024

Enhancing Safety in Nonlinear Systems: Design and Stability Analysis of Adaptive Cruise Control

The safety of autonomous driving systems, particularly self-driving vehicles, remains of paramount concern. These systems exhibit affine nonlinear dynamics and face the challenge of executing predefined control tasks while adhering to state and input constraints to mitigate risks. However, achieving safety control within the framework of control input constraints, such as collision avoidance and maintaining system states within secure boundaries, presents challenges due to limited options. In this study, we introduce a novel approach to address safety concerns by transforming safety conditions into control constraints with a relative degree of 1. This transformation is facilitated through the design of control barrier functions, enabling the creation of a safety control system for affine nonlinear networks. Subsequently, we formulate a robust control strategy that incorporates safety protocols and conduct a comprehensive analysis of its stability and reliability. To illustrate the effectiveness of our approach, we apply it to a specific problem involving adaptive cruise control. Through simulations, we validate the efficiency of our model in ensuring safety without compromising control performance. Our approach signifies significant progress in the field, providing a practical solution to enhance safety for autonomous driving systems operating within the context of affine nonlinear dynamics.

eess.SY↗

arXiv2023

Probing topological phase transition with non-Hermitian perturbations

We demonstrate that non-Hermitian perturbations can probe topological phase transitions and unambiguously detect non-Abelian zero modes. We show that under carefully designed non-Hermitian perturbations, the Loschmidt echo(LE) decays into 1/N where N is the ground state degeneracy in the topological non-trivial phase, while it approaches 1 in the trivial phase. This distinction is robust against small parameter deviations in the non-Hermitian perturbations. We further study four well-known models that support Majorana or parafermionic zero modes. By calculating their dynamical responses to specific non-Hermitian perturbations, we prove that the steady-state LE can indeed differentiate between different phases. This method avoids the ambiguity introduced by trivial zero-energy states and thus provides an alternative and promising way to demonstrate the emergence of topologically non-trivial phases. The experimental realizations of non-Hermitian perturbations are discussed.

quant-ph↗

arXiv2023

Identifying Majorana Zero Modes in Vortex Lattices Using Fano Factor Tomography

In this work, we investigate the tunneling characteristics of Majorana zero modes (MZMs) in vortex lattices based on scanning tunneling microscopy measurement. We find that zero bias conductance does not reach the quantized value owing to the coupling between the MZMs. On the contrary, the Fano factor measured in the high voltage regime reflects the local particle-hole asymmetry of the bound states and is insensitive to the energy splitting between them. We propose using spatially resolved Fano factor tomography as a tool to identify the existence of MZMs. In both cases of isolated MZM or MZMs forming bands, there is a spatially resolved Fano factor plateau at one in the vicinity of a vortex core, regardless of the tunneling parameter details, which is in stark contrast to other trivial bound states. These results reveal new tunneling properties of MZMs in vortex lattices and provide measurement tools for topological quantum devices.

cond-mat.supr-con↗

arXiv2023

Observation of high-temperature superconductivity in the high-pressure tetragonal phase of La2PrNi2O7-δ

The recent discovery of high-temperature superconductivity in the Ruddlesden-Popper phase La3Ni2O7 under high pressure marks a significant breakthrough in the field of 3d transition-metal oxide superconductors. For an emerging novel class of high-Tc superconductors, it is crucial to find more analogous superconducting materials with a dedicated effort toward broadening the scope of nickelate superconductors. Here, we report on the observation of high-Tc superconductivity in the high-pressure tetragonal I4/mmm phase of La2PrNi2O7 above ~10 GPa, which is distinct from the reported orthorhombic Fmmm phase of La3Ni2O7 above 14 GPa. For La2PrNi2O7, the onset and the zero-resistance temperatures of superconductivity reach Tconset = 78.2 K and Tczero = 40 K at 15 GPa. This superconducting phase shares the samilar structural symmetry as many cuprate superconductors, providing a fresh platform to investigate underlying mechanisms of nickelate superconductors.

cond-mat.supr-con↗

arXiv2023

Classification of High-Ordered Topological Nodes towards Moiré Flat Bands in Twisted Bilayers

At magic twisted angles, Dirac cones in twisted bilayer graphene (TBG) can evolve into flat bands, serving as a critical playground for the study of strongly correlated physics. When chiral symmetry is introduced, rigorous mathematical proof confirms that the flat bands are locked at zero energy in the entire Moiré Brillouin zone (BZ). Yet, TBG is not the sole platform that exhibits this absolute band flatness. Central to this flatness phenomenon are topological nodes and their specific locations in the BZ. In this study, considering twisted bilayer systems that preserve chiral symmetry, we classify various ordered topological nodes in base layers and all possible node locations across different BZs. Specifically, we constrain the node locations to rotational centers, such as Γ and M points, to ensure the interlayer coupling retains equal strength in all directions. Using this classification as a foundation, we systematically identify the conditions under which Moiré flat bands emerge. Additionally, through the extension of holomorphic functions, we provide proof that flat bands are locked at zero energy, shedding light on the origin of the band flatness. Remarkably, beyond Dirac cones, numerous twisted bilayer nodal platforms can host flat bands with a degeneracy number of more than two, such as four-fold, six-fold, and eight-fold. This multiplicity of degeneracy in flat bands might unveil more complex and enriched correlation physics.

cond-mat.str-el↗

arXiv2023

Correlated BCS wavefunction approach to unconventional superconductors

We propose a modified BCS wavefunction as the ground state of a correlated superconductor with the correlation specified between $k$ and $-k$ electrons in the reciprocal space. Owing to this correlation, low-energy excitations are not conventional BCS Bogoliubov quasiparticles. They display at least four poles in the Green's function and their particle-hole weights in the tunneling and photon-emission spectrum become asymmetric. The superfluid density or superfluid stiffness also deviates from the BCS predictions with finite paramagnetic terms inside the total diamagnetic response. Moreover, a $d$-wave correlated pairing state becomes robust against weak disorders. Hence, this state can explain many mysterious features observed in unconventional superconductors like cuprates.

cond-mat.supr-con↗

arXiv2023

Effective model and pairing tendency in bilayer Ni-based superconductor La$_3$Ni$_2$O$_7$

Since the discovery of cuprate, the origin of high-T$_c$ superconductivity has been an outstanding puzzle. Recently, high-T$_c$ superconductivity was observed in a bilayer nickelate La$_3$Ni$_2$O$_7$ under pressure, whose structure hosts the apical oxygen between two layers, distinct from multi-layer cuprates. Motivated by this discovery, we investigate its electronic structure using first-principle calculations and superconducting instabilities from both weak-coupling and strong-coupling perspective. Based on the first-principle band structures, we construct a bilayer two-orbital model on a square lattice, consisting of $d_{x^2-y^2}$ and $d_{z^2}$ orbitals, which accurately captures the low-energy electronic properties. Within this model, we study pairing instability using both functional renormalization group approach and multi-orbital t-J model. An $s_{\pm}$-wave pairing with sign-reversal gaps on different Fermi surfaces is revealed, reminiscent of iron based superconductors. The Ni-$d_{z^2}$ orbital and its associated interlayer and intralayer exchange couplings are found to be crucial for the high-T$_c$ superconductivity. Our study provides valuable insights into unique nature of electronic structure and superconductivity in La$_3$Ni$_2$O$_7$ and contributes to the understanding of unconventional superconductors.

cond-mat.supr-con↗

arXiv2023

Pairing Symmetries of Unconventional High Temperature Superconductivity in a Zinc-Blende Structure

We classify the pairing symmetries of three-dimensional superconductivity in the zinc-blende structure which can support an electronic environment to host unconventional high temperature superconductivity, and calculate the pairing symmetry in the presence of strong electron-electron correlation by the slave boson mean-field approach. We find that the $d_{2z^2-x^2-y^2} \pm id_{x^2-y^2}$ pairing state, a three dimensional analogy of the $d\pm id$ pairing in a two dimensional square lattice, is ubiquitously favored near half filling upon hole doping in both single-orbital and three-orbital models. However, unlike the two dimensional counterpart, the Bogoliubov quasiparticle spectrum of the three dimensional state upholds the full $T_d$ point group symmetry and encompasses point nodes along certain high symmetric lines.

cond-mat.supr-con↗