arXiv subjects

Nian Lin

Publications and source records attributed to Nian Lin.

7 recordsLinked to original sources

arXiv2026

In vacuo synthesis of single-layer Ni3(HITP)2 on HOPG surface using metallo-organic precursor

Single-layer conjugated metal-organic frameworks (SL c-MOFs) are predicated theoretically to host rich quantum phases. To date, however, the experimental synthesis has largely resulted in SL c-MOFs on metal substrates, whose intrinsic properties are strongly screened due to substrate hybridization. To overcome this obstacle, here we develop a method to grow clean SL c-MOF Ni3(HITP)2 on a chemically inert substrate of highly oriented pyrolytic graphite (HOPG). By means of an ultra-high vacuum based multi-step protocol using nickel acetylacetonate [Ni(acac)2] precursor, we obtain continuous single-layer Ni3(HITP)2. Scanning tunneling microscopy reveals a well-defined hexagonal framework with a uniform azimuthal orientation rotated by approximately 30 degrees with respect to the underlying graphite lattice. Furthermore, we control the growth of bilayer Ni3(HITP)2 which features an unusual AA stacking configuration. This work establishes metallo-organic chemistry as an efficient route for integrating 2D c-MOFs onto inert substrates, which opens a new avenue for exploring the exotic quantum properties of SL c-MOFs.

cond-mat.mtrl-sci↗

arXiv2024

Artificially built Kondo chains with organic radicals on metallic surfaces: new model system of heavy fermion quantum criticality

Heavy fermion quantum criticality is an extremely rich domain of research which represents a framework to understand strange metals as a consequence of a Kondo breakdown transition. Here we provide an experimental realization of such systems in terms of organic radicals on a metallic surface. The ground state of organic radicals is a Kramer's doublet that can be modeled by a spin 1/2 degree of freedom. Using on-surface synthesis and scanning tunneling microscopy (STM) tip manipulation, one can controllably engineer and characterize chains of organic radicals on a Au(111) surface. The spatial-resolved differential conductance reveals site-dependent low-energy excitations, which support the picture of emergent many-body Kondo physics. Using quantum Monte Carlo simulations, we show that a Kondo lattice model of spin chains on a metallic surface reproduces accurately the experimental results. This allows us to interpret the experimental results in terms of a heavy fermion metal, below the coherence temperature. We foresee that the tunability of these systems will pave the way to realize quantum simulators of heavy fermion criticality.

cond-mat.mes-hall↗

arXiv2021

Proximity Effect of Epitaxial Iron Phthalocyanine Molecules on High-Quality Graphene Devices

Depositing magnetic insulators on graphene has been a promising route to introduce magnetism via exchange proximity interaction in graphene for future spintronics applications. Molecule-based magnets may offer unique opportunities because of their synthesis versatility. Here, we investigated the magnetic proximity effect of epitaxial iron phthalocyanine (FePc) molecules on high-quality monolayer and bilayer graphene devices on hexagonal boron nitride substrate by probing the local and non-local transport. Although the FePc molecules introduce large hole doping effects combined with mobility degradation, the magnetic proximity gives rise to a canted antiferromagnetic state under a magnetic field in the monolayer graphene. On bilayer graphene and FePc heterostructure devices, the non-local transport reveals a pronounced Zeeman spin-Hall effect. Further analysis of the scattering mechanism in the bilayer shows a dominated long-range scattering. Our findings in graphene/organic magnetic insulator heterostructure provide a new insight for the use of molecule-based magnets in two-dimensional spintronic devices.

cond-mat.mes-hall↗

arXiv2021

Lattice reconstruction induced multiple ultra-flat bands in twisted bilayer WSe2

Moir\'e superlattices in van der Waals heterostructures provide a tunable platform to study emergent properties that are absent in the natural crystal form. Twisted bilayer transition metal dichalcogenides (TB-TMDs) can host moir\'e flat bands over a wide range of twist angles. For twist angle close to 60{\deg}, it was predicted that TB-TMDs undergo a lattice reconstruction which causes the formation of ultra-flat bands. Here, by using scanning tunneling microscopy and spectroscopy, we show the emergence of multiple ultra-flat bands in twisted bilayer WSe2 when the twist angle is larger than 57{\deg}. The bandwidth, manifested as narrow tunneling conductance peaks, is estimated less than 10meV, which is only a fraction of the estimated on-site Coulomb repulsion energy. The number of these ultra-flat bands and spatial distribution of the wavefunctions match the theoretical predictions incredibly well, strongly evidencing that the observed ultra-flat bands are induced by lattice reconstruction. Our work provides a foundation for further study of the exotic correlated phases in TB-TMDs.

cond-mat.mes-hall↗

arXiv2020

Investigation of Edge States in Artificial Graphene Nano-Flakes

Graphene nano-flakes (GNFs) are predicted to host spin-polarized metallic edge states, which are envisioned for exploration of spintronics at the nanometer scale. To date, experimental realization of GNFs is only in its infancy because of the limitation of precise cutting or synthesizing methods at the nanometer scale. Here, we use low temperature scanning tunneling microscope (STM) to manipulate coronene molecules on a Cu(111) surface to build artificial triangular and hexagonal GNFs with either zigzag or armchair type of edges. We observe that the metallic edge states only exist in the GNFs with zigzag edge and localize at the most outside one type of the sublattice. The experimental results agree well with the tight-binding calculations. To our knowledge, our work renders the first systematic experimental confirmation of the predicated electronic properties of the GNFs.

cond-mat.mes-hall↗

arXiv2020

Giant nonlinear Hall effect in twisted WSe$_2$

The recently discovered nonlinear Hall effect (NHE) in a few non-interacting systems provides a novel mechanism to generate second harmonic electrical Hall signals under time-reversal-symmetric conditions. Here, we introduce a new approach to engineering NHE by using twisted moir\'e structures. We find that the twisted WSe$_2$ bilayer exhibits a NHE when tuning the Fermi level to the moir\'e flat bands. Near half-filling of the first moir\'e band, the nonlinear Hall signal shows a sharp peak with the generation efficiency at least two orders of magnitude larger than those in previous experiments. We propose that the giant NHE and diverging generation efficiency originate from a mass-diverging type continuous Mott transition, which is evidenced by resistivity measurements. This work demonstrates not only how interaction effects can couple to Berry curvature dipoles to produce novel quantum phenomena, but also what NHE measurements can provide for developing a new tool to study the quantum criticality.

cond-mat.mes-hall↗

arXiv2015

A New Platform for Engineering Topological Superconductors: Superlattices on Rashba Superconductors

The search for topological superconductors which support Majorana fermion excitations has been an important topic in condensed matter physics. In this work, we propose a new experimental scheme for engineering topological superconductors. In this scheme, by manipulating the superlattice structure of organic molecules placed on top of a superconductor with Rashba spin-orbit coupling, topological superconducting phases can be achieved without fine-tuning the chemical potential. Moreover, superconductors with different Chern numbers can be obtained by changing the superlattice structure of the organic molecules.

cond-mat.supr-con↗