arXiv subjects

Nianpeng Lu

Publications and source records attributed to Nianpeng Lu.

6 recordsLinked to original sources

arXiv2025

Ultrahigh room-temperature hole conductivity in a perovskite cuprate with vanishing electron-correlation

Electron-correlated two-dimensional (2D) cuprates have been extensively studied since the discovery of high-Tc superconductivity, in contrast, the three-dimensional (3D) counterpart perovskite cuprates remain largely unexplored due to their chemical instability and synthesis challenges. Herein, we develop an efficient two-step approach that combines symmetry-selective growth and topotactic oxidization to synthesize high-quality perovskite LaCuO3 films, and furthermore reveal its exotic electronic states. The compressively strained LaCuO3 films exhibit an unexpected ultrahigh p-type conductivity of ~1.5*10^5 S/cm with a hole mobility of ~30 cm2 V-1 s-1 at room-temperature. X-ray absorption spectra and first-principles calculations unveil a ligand-hole state of p-d hybridization with degenerate eg orbitals and light effective mass, indicating nearly-vanishing electron-correlation. These features contrast sharply with 2D cuprates and offer physical insights into the design of high-performance electronic devices.

cond-mat.str-el↗

arXiv2021

Manipulate the Electronic State of Mott Iridate Superlattice through Protonation Induced Electron-Filling

Spin-orbit-coupled Mott iridates show great similarity with parent compounds of superconducting cuprates, attracting extensive research interests especially for their electron-doped states. However, previous experiments are largely limited within a small doping range due to the absence of effective dopants, and therefore the electron-doped phase diagram remains elusive. Here we utilize an ionic-liquid-gating induced protonation method to achieve electron-doping into a 5d Mott-insulator built with SrIrO3/SrTiO3 superlattice, and achieve a systematic mapping of its electron-doped phase diagram with the evolution of the iridium valence state from 4+ to 3+, equivalent to doping of one electron per iridium ion. Along increasing doping level, the parent Mott-insulator is first turned into a localized metallic state with gradually suppressed magnetic ordering, and then further evolved into a nonmagnetic band insulating state. This work forms an important step forward for the study of electron-doped Mott iridate systems, and the strategy of manipulating the band filling in an artificially designed superlattice structure can be readily extended into other systems with more exotic states to explore.

cond-mat.str-el↗

arXiv2020

Robust ferromagnetism in highly strained SrCoO3 thin films

Epitaxial strain provides important pathways to control the magnetic and electronic states in transition metal oxides. However, the large strain is usually accompanied by a strong reduction of the oxygen vacancy formation energy, which hinders the direct manipulation of their intrinsic properties. Here using a post-deposition ozone annealing method, we obtained a series of oxygen stoichiometric SrCoO3 thin films with the tensile strain up to 3.0%. We observed a robust ferromagnetic ground state in all strained thin films, while interestingly the tensile strain triggers a distinct metal to insulator transition along with the increase of the tensile strain. The persistent ferromagnetic state across the electrical transition therefore suggests that the magnetic state is directly correlated with the localized electrons, rather than the itinerant ones, which then calls for further investigation of the intrinsic mechanism of this magnetic compound beyond the double-exchange mechanism.

cond-mat.str-el↗

arXiv2018

A protonated brownmillerite electrolyte for superior low-temperature proton conductivity

Design novel solid oxide electrolyte with enhanced ionic conductivity forms one of the Holy Grails in the field of materials science due to its great potential for wide range of energy applications. Conventional solid oxide electrolyte typically requires elevated temperature to activate the ionic transportation, while it has been increasing research interests to reduce the operating temperature due to the associated scientific and technological importance. Here, we report a conceptually new solid oxide electrolyte, HSrCoO2.5, which shows an exceptional enhanced proton conductivity at low temperature region (from room temperature to 140 oC). Combining both the experimental results and corresponding first-principles calculations, we attribute these intriguing properties to the extremely-high proton concentration as well as the well-ordered oxygen vacancy channels inherited from the novel crystalline structure of HSrCoO2.5. This result provides a new strategy to design novel solid oxide electrolyte with excellent proton conductivity for wide ranges of energy-related applications.

cond-mat.mtrl-sci↗

arXiv2018

Electric-field Control of Magnetism with Emergent Topological Hall Effect in SrRuO3 through Proton Evolution

Ionic substitution forms an essential pathway to manipulate the carrier density and crystalline symmetry of materials via ion-lattice-electron coupling, leading to a rich spectrum of electronic states in strongly correlated systems. Using the ferromagnetic metal SrRuO3 as a model system, we demonstrate an efficient and reversible control of both carrier density and crystalline symmetry through the ionic liquid gating induced protonation. The insertion of protons electron-dopes SrRuO3, leading to an exotic ferromagnetic to paramagnetic phase transition along with the increase of proton concentration. Intriguingly, we observe an emergent topological Hall effect at the boundary of the phase transition as the consequence of the newly-established Dzyaloshinskii-Moriya interaction owing to the breaking of inversion symmetry in protonated SrRuO3 with the proton compositional film-depth gradient. We envision that electric-field controlled protonation opens a novel strategy to design material functionalities.

cond-mat.str-el↗

arXiv2018

Anomalous Hall Effect and Spin Fluctuations in Ionic Liquid Gated SrCoO$_3$ Thin Films

The recent realization of epitaxial SrCoO$_3$ thin films has triggered a renewed interest in their electronic, magnetic, and ionic properties. Here we uncover several unusual magneto-transport properties of this compound, suggesting that it hosts persistent spin fluctuation down to low temperatures. We achieve the metallic SrCoO$_3$ with record-low resistivity from insulating SrCoO$_{2.5}$ by the ionic liquid gating. We find a linear relationship between the anomalous Hall resistivity and the longitudinal resistivity, which cannot be accounted for by the conventional mechanisms. We theoretically propose that the impurity induced chiral spin fluctuation gives rise to such a dependence. The existence of spin fluctuation manifests itself as negatively enhanced magneto-resistance of SrCoO$_3$ when the temperature approaches zero. Our study brings further insight into the unique spin state of SrCoO$_3$ and unveils a novel skew scattering mechanism for the anomalous Hall effect.

cond-mat.mes-hall↗