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Minglei Sun

Publications and source records attributed to Minglei Sun.

3 recordsLinked to original sources

Emergent chiral symmetry breaking in moir\'e domain wall networks redirects topological boundary states in bilayer graphene

Lattice-mismatched bilayer graphene self-organizes into a moir\'e network of one-dimensional domain walls that conduct electrons with low dissipation, attractive for low-power electronics. We show these channels are not always straight: as the lattice relaxes to minimize strain, the network can spontaneously curve into chiral morphology. Atomistic simulations map a phase diagram in which the strain-flexibility balance selects one of three stable domain wall morphologies-straight, mono-chiral, or dual-chiral. Electronic structure calculations show that this morphology controls where low-energy electrons accumulate: straight channels concentrate states at the domain-wall-connecting nodes, while chiral channels shift that weight onto the domain walls themselves. This network geometric switch lets the same moir\'e material support either localized electronic hot spots or directional conducting channels-two strategies for guiding electrons in low-power graphene devices.

cond-mat.mes-hall

Protected valley states and generation of valley- and spin-polarized current in monolayer MA2Z4

The optical selection rules obeyed by two-dimensional materials with spin-valley coupling enable the selective excitation of carriers. We show that six members of the monolayer MA2Z4 (M = Mo and W; A = C, Si, and Ge; Z = N, P, and As) family are direct band-gap semiconductors with protected valley states and that circularly polarized infrared light can induce valley-selective inter-band transitions. Our optovalleytronic device demonstrates a close to 100% valley- and spin-polarized current under in-plane bias and circularly polarized infrared light, which can be exploited to encode, process, and store information.

cond-mat.mtrl-sci

Oxygenated (113) diamond surface for nitrogen-vacancy quantum sensors with preferential alignment and long coherence time from first principles

Shallow nitrogen-vacancy (NV) center in diamond is promising in quantum sensing applications however its sensitivity has been limited by surface terminators and defects. There is an immediate quest to find suitable diamond surfaces for NV sensors. In this work, the surface terminators of (113) diamond to host shallow NV centers are studied by means of first principles calculations. Results indicate that complete oxygen termination of (113) diamond creates positive electron affinity with neither strain on the surface nor in-gap levels. This is a very surprising result as the commonly employed oxygenated (001) diamond surface is often defective due to the disorder created by the strain of ether groups at the surface that seriously undermine the coherence properties of the shallow NV centers. The special atomic configurations on (113) diamond surface are favorable for oxygen bonding, in contrast to (001) and (111) diamond surfaces. These simulations imply that oxygenated diamond (113) surface can be produced by conventional diamond chemical vapor deposition growth. Combining this with the ~73% preferential alignment of as-grown NV centers in (113) oriented diamond, oxygenated (113) diamond is presently supposed to be the most prospective host for NV quantum sensors.

cond-mat.mes-hall