arXiv subjects

Xin-Cheng Xie

Publications and source records attributed to Xin-Cheng Xie.

9 recordsLinked to original sources

arXiv2025

Fermi lune and transdimensional orbital magnetism in rhombohedral multilayer graphene

The symmetry and geometry of the Fermi surface play an essential role in governing the transport properties of a metallic system. A Fermi surface with reduced symmetry is intimately tied to unusual transport properties such as anomalous Hall effect and nonlinear Hall effect. Here, combining theoretical calculations and transport measurements, we report the discovery of a new class of bulk Fermi surface structure with unprecedented low symmetry, the ``Fermi lune", with peculiar crescent shaped Fermi energy contours, in rhombohedral multilayer graphene. This emergent Fermi-lune structure driven by electron-electron interactions spontaneously breaks time-reversal, mirror, and rotational symmetries, leading to two distinctive phenomena: giant intrinsic non-reciprocity in longitudinal transport and a new type of magnetism termed ``transdimensional orbital magnetism". Coupling the Fermi lune to a superlattice potential further produces a novel Chern insulator exhibiting quantized anomalous Hall effect controlled by in-plane magnetic field. Our work unveils a new symmetry breaking state of matter in the transdimensional regime, which opens an avenue for exploring correlated and topological quantum phenomena in symmetry breaking phases.

cond-mat.mes-hall↗

arXiv2024

Observation of electrical high-harmonic generation

High-harmonic generation (HHG), an extreme nonlinear effect, introduces an unprecedented paradigm to detect emergent quantum phases and electron dynamics inconceivable in the framework of linear and low-order nonlinear processes. As an important manifestation, the optical HHG (o-HHG) enables extraordinary opportunities to underpin attosecond physics. In addition to nonlinear optics, emerging nonlinear electric transport has been demonstrated recently and opens new paradigms to probe quantum phase transition, symmetry breaking, band geometrical and topological properties. Thus far, only electrical second-/third-harmonic generation in perturbative regime has been elucidated, while the electrical HHG (e-HHG) that can advance to extreme non-perturbative physics remains elusive. Here we report the observation of e-HHG up to 300th-order. Remarkably, the e-HHG shows a clear non-perturbative character and exhibits periodic oscillations with the reciprocal of driving current. Further, theoretical simulations corroborate the experiments, suggesting the contribution of singular distribution of Berry curvature near band edges. Our results demonstrate e-HHG in extreme nonlinear regime and may shed light on a plethora of exotic physics and applications, such as extreme non-equilibrium quantum phenomena, ultra-fast and coherent electrical signal generations and detections.

cond-mat.mes-hall↗

arXiv2021

Giant oscillatory Gilbert damping in superconductor/ferromagnet/superconductor junctions

Interfaces between materials with differently ordered phases present unique opportunities for exotic physical properties, especially the interplay between ferromagnetism and superconductivity in the ferromagnet/superconductor heterostructures. The investigation of zero- and pi-junctions has been of particular interest for both fundamental physical science and emerging technologies. Here, we report the experimental observation of giant oscillatory Gilbert damping in the superconducting Nb/NiFe/Nb junctions with respect to the NiFe thickness. This observation suggests an unconventional spin pumping and relaxation via zero-energy Andreev bound states that exist only in the Nb/NiFe/Nb pi-junctions, but not in the Nb/NiFe/Nb zero-junctions. Our findings could be important for further exploring the exotic physical properties of ferromagnet/superconductor heterostructures, and potential applications of ferromagnet pi-junctions in quantum computing, such as half-quantum flux qubits.

cond-mat.supr-con↗

arXiv2021

Half-integer Shapiro Steps in Strong Ferromagnetic Josephson Junctions

We report the experimental observation of half-integer Shapiro steps in the strong ferromagnetic Josephson junction (Nb-NiFe-Nb) by investigating the current-phase relation under radiofrequency microwave excitation. The half-integer Shapiro steps are robust in a wide temperature range from T = 4 to 7 K. The half-integer Shapiro steps could be attributed to co-existence of 0- and pi-states in the strong ferromagnetic NiFe Josephson junctions with the spatial variation of the2 NiFe thickness. This scenario is also supported by the high-resolution transmission electron microscopy characterization of the Nb/NiFe/Nb junction.

cond-mat.supr-con↗

arXiv2019

Interface ferromagnetism and anomalous Hall effect of CdO/ferromagnetic insulator heterostructures

The experimental observation of quantum anomalous Hall effect (QAHE) in magnetic topological insulators has stimulated enormous interest in condensed-matter physics and materials science. For the purpose of realizing high-temperature QAHE, several material candidates have been proposed, among which the interface states in the CdO/ferromagnetic insulator heterostructures are particularly interesting and favorable for technological applications. Here, we report the experimental observation of the interfacial ferromagnetism and anomalous Hall effect in the Fe3O4/CdO/Fe3O4 heterostructures grown via oxide molecular-beam epitaxy. Systematical variation of the CdO thickness reveals the interface ferromagnetism as the major cause for the observed planar magnetoresistance and anomalous Hall effect. Our results might pave the way to engineer oxide interface states for the exploration of QAHE towards exotic quantum-physical phenomena and potential applications.

cond-mat.mtrl-sci↗

arXiv2017

Magnetic tunneling induced Weyl node annihilation in TaP

Weyl nodes are topological objects in three-dimensional metals. Their topological property can be revealed by studying the high-field transport properties of a Weyl semimetal. While the energy of the lowest Landau band (LLB) of a conventional Fermi pocket always increases with magnetic field due to the zero point energy, the LLB of Weyl cones remains at zero energy unless a strong magnetic field couples the Weyl fermions of opposite chirality. In the Weyl semimetal TaP, we achieve such a magnetic coupling between the electron-like Fermi pockets arising from the W1 Weyl fermions. As a result, their LLBs move above chemical potential, leading to a sharp sign reversal in the Hall resistivity at a specific magnetic field corresponding to the W1 Weyl node separation. By contrast, despite having almost identical carrier density, the annihilation is unobserved for the hole-like pockets because the W2 Weyl nodes are much further separated. These key findings, corroborated by other systematic analyses, reveal the nontrivial topology of Weyl fermions in high-field measurements.

cond-mat.str-el↗

arXiv2014

The Coexistence and Decoupling of Bulk and Edge States in Disordered Two-dimensional Topological Insulators

We investigate the scattering and localization properties of edge and bulk states in a disordered two-dimensional topological insulator when they coexist at the same fermi energy. Due to edge-bulk backscattering (which is not prohibited \emph{a priori} by topology or symmetry), Anderson disorder makes the edge and bulk states localized indistinguishably. Two methods are proposed to effectively decouple them and to restore robust transport. The first kind of decouple is from long range disorder, since edge and bulk states are well separated in $k$ space. The second one is from an edge gating, owing to the edge nature of edge states in real space. The latter can be used to electrically tune a system between an Anderson insulator and a topologically robust conductor, i.e., a realization of a topological transistor.

cond-mat.mes-hall↗

arXiv2010

Topological insulator Bi2Se3 thin films grown on double-layer graphene by molecular beam epitaxy

Atomically flat thin films of topological insulator Bi2Se3 have been grown on double-layer graphene formed on 6H-SiC(0001) substrate by molecular beam epitaxy. By a combined study of reflection high energy electron diffraction and scanning tunneling microscopy, we identified the Se-rich condition and temperature criterion for layer-by-layer growth of epitaxial Bi2Se3 films. The as-grown films without doping exhibit a low defect density of 1.0\pm 0.2x1011/cm2, and become a bulk insulator at a thickness of 10 quintuple layers, as revealed by in situ angle resolved photoemission spectroscopy measurement.

cond-mat.mes-hall↗

arXiv2009

Growth dynamics and thickness-dependent electronic structure of topological insulator Bi2Te3 thin films on Si

We use real-time reflection high energy electron diffraction intensity oscillation to establish the Te-rich growth dynamics of topological insulator thin films of Bi2Te3 on Si(111) substrate by molecular beam epitaxy. In situ angle resolved photoemission spectroscopy (ARPES), scanning tunneling microscopy and ex situ transport measurements reveal that the as-grown Bi2Te3 films without any doping are an intrinsic topological insulator with its Fermi level intersecting only the metallic surface states. Experimentally, we find that the single-Dirac-cone surface state develops at a thickness of two quintuple layers (2 QL). Theoretically, we show that the interaction between the surface states from both sides of the film, which is determined by the penetration depth of the topological surface state wavefunctions, sets this lower thickness limit.

cond-mat.mes-hall↗