Yafei Ren

Topological phases in two-dimensional materials: a review

Topological phases with insulating bulk and gapless surface or edge modes have attracted intensive attention because of their fundamental physics implications and potential applications in dissipationless electronics and spintronics. In this review, we mainly focus on recent progress in the engineering of topologically nontrivial phases (such as [Formula: see text] topological insulators, quantum anomalous Hall effects, quantum valley Hall effects etc) in two-dimensional systems, including quantum wells, atomic crystal layers of elements from group III to group VII, and the transition metal compounds.

Current Partition at Topological Channel Intersections

An intersection between one-dimensional chiral channels functions as a topological current splitter. We find that the splitting of a chiral zero-line mode obeys very simple yet highly counterintuitive partition laws that relate current paths to the geometry of the intersection. Our results have far reaching implications for electron beam splitter and interferometer device proposals based on chiral transport, and for understanding transport in systems in which multiple topological domains lead to a statistical network of chiral channels.

Single-Valley Engineering in Graphene Superlattices

The two inequivalent valleys in graphene preclude the protection against inter-valley scattering offered by an odd-number of Dirac cones characteristic of Z2 topological insulator phases. Here we propose a way to engineer a chiral single-valley metallic phase with quadratic crossover in a honeycomb lattice through tailored \sqrt{3}N *\sqrt{3}N or 3N *3N superlattices. The possibility of tuning valley-polarization via pseudo-Zeeman field and the emergence of Dresselhaus-type valley-orbit coupling are proposed in adatom decorated graphene superlattices. Such valley manipulation mechanisms and metallic phase can also find applications in honeycomb photonic crystals.

Gate-tunable current partition in graphene-based topological zero lines

We demonstrate new mechanisms for gate tunable current partition at topological zero-line intersections in a graphene-based current splitter. Based on numerical calculations of the non-equilibrium Greens functions and Landauer-Buttiker formula, we show that the presence of a perpendicular magnetic field on the order of a few Teslas allows for carrier sign dependent current routing. In the zero-field limit the control on current routing and partition can be achieved within a range of

Quantum anomalous Hall effect in atomic crystal layers from in-plane magnetization

10\%

Tunable current partition at zero-line intersection of quantum anomalous Hall topologies

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Spin-pairing correlations and spin polarization of Majorana bound states in two-dimensional topological-insulator systems

90\%

In-plane magnetization-induced quantum anomalous Hall effect in atomic crystals of group-V elements

of the total incoming current by tuning the carrier density at tilted intersections, or by modifying the relative magnitude of the bulk band gaps via gate voltage. We discuss the implications of our findings in the design of topological zero-line networks where finite orbital magnetic moments are expected when the current partition is asymmetric.

Transmission spectra and valley processing of graphene and carbon nanotube superlattices with inter-valley coupling

We theoretically report that, with \textit{in-plane} magnetization, the quantum anomalous Hall effect (QAHE) can be realized in two-dimensional atomic crystal layers with preserved inversion symmetry but broken out-of-plane mirror reflection symmetry. We take the honeycomb lattice as an example, where we find that the low-buckled structure, which makes the system satisfy the symmetric criteria, is crucial to induce QAHE. The topologically nontrivial bulk gap carrying a Chern number of

Three-dimensional quantum Hall effect and metal-insulator transition in ZrTe5.

\mathcal{C}=\pm1