arXiv subjects

Fanbao Meng

Publications and source records attributed to Fanbao Meng.

4 recordsLinked to original sources

arXiv2025

Nanoscale determination of the metal-insulator transition in intercalated bulk VSe$_{2}$

Two-dimensional (2D) materials provide unique opportunities to realize emergent phenomena by reducing dimensionality. Using scanning tunneling microscopy combined with first-principles calculations, we determine an intriguing case of a metal-insulator transition (MIT) in a bulk compound, (TBA)$_{0.3}$VSe$_2$. Atomic-scale imaging reveals that the initial $4a_0 \times 4a_0$ charge density wave (CDW) order in 1T-VSe$_2$ transforms to $\sqrt{7}a_0 \times \sqrt{3}a_0$ ordering upon intercalation, which is associated with an insulating gap with a magnitude of up to approximately 115 meV. Our calculations reveal that this energy gap is highly tunable through electron doping introduced by the intercalant. Moreover, the robustness of the $\sqrt{7}a_0 \times \sqrt{3}a_0$ CDW order against the Lifshitz transition points to the key role of electron-phonon interactions in stabilizing the CDW state. Our work clarifies a rare example of a CDW-driven MIT in quasi-2D materials and establishes cation intercalation as an effective pathway for tuning both the dimensionality and the carrier concentration without inducing strain or disorder.

cond-mat.mtrl-sci↗

arXiv2024

Superconducting stripes induced by ferromagnetic proximity in an oxide heterostructure

The intimate connection between magnetism and superconducting pairing routinely plays a central role in determining the occurrence of unconventional superconducting states. In high-transition-temperature (high-Tc) stripe-ordered cuprate superconductors and a magnetically ordered iron-based superconductor, the coupling between magnetism and superconductivity gives birth to novel phases of matter with modulation of the superconducting pairing in the real space. Further exploration of these phases can shed light on the mechanism of unconventional superconductivity. Here we report on the discovery of a peculiar spatially-varying superconducting state residing at the interface between (110)-oriented KTaO3 and ferromagnetic EuO. Electrical transport measurements reveal different Tc and upper critical fields (Hc2) with current applied along the two orthogonal in-plane directions. Such anisotropy persistently occurs in the low-carrier-density samples that are characterized by strong coupling between Ta 5d and Eu 4f electrons, whereas in the high-carrier-density samples the coupling is weakened and Tc and Hc2 becomes isotropic. Complemented by local imaging of diamagnetism and theoretical analysis, our observations imply an unprecedented emergence of superconducting stripes wherein the phase coherence is established ahead of the rest of the interface, arising from a band-filling-dependent ferromagnetic proximity. The realization of such exotic superconducting states provides impetus for the study of novel physics in heterostructures possessing both magnetism and superconductivity.

cond-mat.supr-con↗

arXiv2022

Tunable two-dimensional superconductivity and spin-orbit coupling at the EuO/KTaO3(110) interface

Unconventional quantum states, most notably the two-dimensional (2D) superconductivity, have been realized at the interfaces of oxide heterostructures where they can be effectively tuned by the gate voltage ($V_G$). Here we report that the interface between high-quality EuO (111) thin film and KTaO3 (KTO) (110) substrate shows superconductivity with onset transition temperature $T_c^{onset}$ = 1.35 K. The 2D nature of superconductivity is verified by the large anisotropy of the upper critical field and the characteristics of a Berezinskii-Kosterlitz-Thouless transition. By applying $V_G$, $T_c^{onset}$ can be tuned from ~ 1 to 1.7 K; such an enhancement can be possibly associated with a boosted spin-orbit energy $ε_{so}$ = $\hbar$ / $τ_{so}$, where $τ_{so}$ is the spin-orbit relaxation time. Further analysis of $τ_{so}$ based on the upper critical field ($H_{c2}$) and magnetoconductance reveals complex nature of spin-orbit coupling (SOC) at the EuO/KTO(110) interface with different mechanisms dominate the influence of SOC effects for the superconductivity and the magnetotransport in the normal state. Our results demonstrate that the SOC should be considered as an important factor determining the 2D superconductivity at oxide interfaces.

cond-mat.supr-con↗

arXiv2022

A new class of bilayer kagome lattice compounds with Dirac nodal lines and pressure-induced superconductivity

Kagome lattice composed of transition-metal ions provides a great opportunity to explore the intertwining between geometry, electronic orders and band topology. The discovery of multiple competing orders that connect intimately with the underlying topological band structure in nonmagnetic kagome metals $A$V$_3$Sb$_5$ ($A$ = K, Rb, Cs) further pushes this topic to the quantum frontier. Here we report the discovery and characterization of a new class of vanadium-based compounds with kagome bilayers, namely $A$V$_6$Sb$_6$ ($A$ = K, Rb, Cs) and V$_6$Sb$_4$, which, together with $A$V$_3$Sb$_5$, compose a series of kagome compounds with a generic chemical formula ($A_{m-1}$Sb$_{2m}$)(V$_3$Sb)$_n$ (m = 1, 2; n = 1, 2). Theoretical calculations combined with angle-resolved photoemission measurements reveal that these compounds feature Dirac nodal lines in close vicinity to the Fermi level. Pressure-induced superconductivity in $A$V$_6$Sb$_6$ further suggests promising emergent phenomena in these materials. The establishment of a new family of layered kagome materials paves the way for designer of fascinating kagome systems with diverse topological nontrivialities and collective ground states.

cond-mat.mtrl-sci↗