arXiv subjects

Dechao Geng

Publications and source records attributed to Dechao Geng.

4 recordsLinked to original sources

arXiv2026

Magnetic-Free Quantum Interference and Universal Josephson Diode Effect Driven by a Supercurrent Gauge Field

The Josephson effect, a hallmark of superconducting phase coherence, drives modern quantum technologies. However, Josephson-based quantum interference has hitherto been tethered to magnetic fields, despite phase coherence being a quintessential, intrinsic trait of superconductivity. Moreover, the Josephson diode effect (JDE) is typically viewed as an anomalous phenomenon indicative of broken symmetries in exotic phases of matter. Here, in planar Josephson junctions made with $\mathrm{Bi}_2\mathrm{O}_2\mathrm{Se}$ and bilayer graphene, we demonstrate that the JDE is a missing universal property of the Josephson effect. Simultaneously, we present an all-electric technology that replaces magnetic flux for controlling and measuring supercurrent interference. Central to our approach is a supercurrent gauge field (SGF), generated and amplified through high-kinetic-inductance superconductors and novel device architectures. By establishing the physical equivalence between the SGF and a magnetic field, we eliminate the reliance on external fields in quantum interference and reveal a universal, field-free JDE mechanism with broad implications for detecting broken-symmetry states. Finally, we show that the SGF offers capabilities beyond those of a conventional magnetic field by experimentally demonstrating a magnetic-free, phase-sensitive technique to construct and characterize finite-momentum superconductivity, opening new frontiers for exploring novel phases of matter and superconducting quantum architectures.

cond-mat.supr-con↗

arXiv2026

Observation of field-odd and field-free superconducting diode effects in $\mathrm{Mo}_2\mathrm{C}$ nanoflakes

The superconducting diode effect (SDE) enables nonreciprocal supercurrent flow, holding immense potential for ultra-low-power quantum electronics. Intrinsic SDE typically requires materials with inherent symmetry breakings. Here, we report the discovery of SDE in chemical vapor deposition-grown molybdenum carbide ($\mathrm{Mo}_2\mathrm{C}$) nanoflakes, a material traditionally considered centrosymmetric. Strikingly, this system uniquely hosts both field-odd and field-free SDEs. Transport measurements reveal a field-odd SDE with tunable efficiency exceeding 40% at 4 K under a perpendicular in-plane magnetic field. In a separate sample, a robust field-free SDE persists under zero-field and field-coolings. Out-of-plane field sweeps confirm the intrinsic nature of these phenomena. We propose that domain-boundary supercurrents or charge density wave-like orders drive this unexpected combination of symmetry breakings. Our findings establish air-stable $\mathrm{Mo}_2\mathrm{C}$ as an ideal platform for nonreciprocal superconducting electronics operating at liquid-helium temperatures, expanding the search for SDE into nominally centrosymmetric superconductors.

cond-mat.supr-con↗

arXiv2018

Pattern Evolution Characterizes the Mechanism and Efficiency of CVD Graphene Growth

Growing large-area single-crystal monolayers is the holy grail of graphene synthesis. In this work, the efficiency of graphene growth and the quality of their continuous films are explored through the time evolution of individual domains and their surface coverage on the substrate. Our phase-field modeling results and experimental characterization clearly demonstrate the critical roles of the deposition flux, edge-reaction kinetics and the surface diffusion of active carbon sources in modulating the pattern evolution and rate of growth. The contrast in edge-kinetics-limited and surface-diffusion-limited regimes is remarkable, which can be characterized by the evolution of domain patterns and considered as an indicator of the growth regime. Common features exist in these two regimes, showing that the growth rate scales with time as t2 in the early stage of growth and is regime-independent, which is explained by the coarsen profiles of carbon concentration for both the compact and dendritic domains. The rate decays rapidly in the final stage of growth due to the competition between neighboring domains on the limited carbon sources diffusing on the substrate, which is highly regime-sensitive and extremely low in the surface-diffusion-limited regime with narrow gaps between the domains to be filled. Based on these findings, synthesis strategies to improve the growth efficiency and film quality are discussed.

cond-mat.mtrl-sci↗

arXiv2013

Hierarchy of Graphene Wrinkles Induced by Thermal Strain Engineering

Graphene is only one atom thick and becomes the ultimate thin film to explore membrane physics and mechanics. Here we study hierarchy of graphene wrinkles induced by thermal strain engineering and demonstrate that the wrinkling hierarchy can be accounted for by the wrinklon theory. We derive an equation λ = (ky)0.5 explaining evolution of wrinkling wavelength λ with the distance to the edge y observed in our experiment by considering both bending energy and stretching energy of the graphene flakes. The prefactor k in the equation is determined to be about 55 nm, which is independent of the size of the graphene flakes. Our experimental result indicates that the classical membrane behavior of graphene persists down to about 100 nm of the wrinkling wavelength.

cond-mat.mes-hall↗