arXiv subjects

Yantao Li

Publications and source records attributed to Yantao Li.

23 records · Page 2Linked to original sources

arXiv2021

Dirac Magic and Lifshitz Transitions in AA-Stacked Twisted Multilayer Graphene

We uncover a new type of magic-angle phenomena when an AA-stacked graphene bilayer is twisted relative to another graphene system with band touching. In the simplest case this constitutes a trilayer system formed by an AA-stacked bilayer twisted relative to a single layer of graphene. We find multiple anisotropic Dirac cones coexisting in such twisted multilayer structures at certain angles, which we call "Dirac magic." We trace the origin of Dirac magic angles to the geometric structure of the twisted AA-bilayer Dirac cones relative to the other band-touching spectrum in the moiré reciprocal lattice. The anisotropy of the Dirac cones and a concomitant cascade of saddle points induce a series of topological Lifshitz transitions that can be tuned by the twist angle and perpendicular electric field. We discuss the possibility of direct observation of Dirac magic as well as its consequences for the correlated states of electrons in this moiré system.

cond-mat.mes-hall↗

arXiv2020

Floquet-Engineered Topological Flat Bands in Irradiated Twisted Bilayer Graphene

We propose a tunable optical setup to engineer topologically nontrivial flat bands in twisted bilayer graphene under circularly polarized light. Using both analytical and numerical calculations, we demonstrate that nearly flat bands can be engineered at small twist angles near the magic angles of the static system. The flatness and the gaps between these bands can be tuned optically by varying laser frequency and amplitude. We study the effects of interlayer hopping variations on Floquet flat bands and find that lattice relaxation favors their formation. Furthermore, we find that, once formed, the flat bands carry nonzero Chern numbers. We show that at currently known values of parameters, such topological flat bands can be realized using circularly polarized UV laser light. Thus, our work opens the way to creating optically tunable, strongly correlated topological phases of electrons in moiré superlattices.

cond-mat.str-el↗

arXiv2014

Floquet poor man's Majorana fermions in double quantum dots

We consider a system consisting of two quantum dots connected by an s-wave superconductor in the presence of periodically varying electric or magnetic fields. The Floquet theory shows that there may be Floquet poor man's Majorana fermions (FPMMFs) in the high frequency region depending on the phase difference between the applied external fields to the two dots. Numerical results confirm this expectation and find in addition a lot of FPMMFs in the low frequency region. The FPMMFs survive for nonzero energy levels of the two dots and their interaction though the frequencies at which they emerge change and thus may be a promising candidate to be detected in experiments.

cond-mat.mes-hall↗

arXiv2014

Tunable Floquet Majorana Fermions in Driven Coupled Quantum Dots

We propose a system of coupled quantum dots in proximity to a superconductor and driven by separate ac potentials to realize and detect Floquet Majorana fermions. We show that the appearance of Floquet Majorana fermions can be finely controlled in the expanded parameter space of the drive frequency, amplitude, and phase difference across the two dots. While these Majorana fermions are not topologically protected, the highly tunable setup provides a realistic system for observing the exotic physics associated with Majorana fermions as well as their dynamical generation and manipulation.

cond-mat.mes-hall↗

arXiv2011

Functional renormalization group approach to the dynamics of first-order phase transitions

We apply the functional renormalization group theory to the dynamics of first-order phase transitions and show that a potential with all odd-order terms can describe spinodal decomposition phenomena. We derive a momentum-dependent dynamic flow equation which is decoupled from the static flow equation. We find the expected instability fixed points; and their associated exponents agree remarkably with the existent theoretical and numerical results. The complex renormalization group flows are found and their properties are shown. Both the exponents and the complex flows show that the spinodal decomposition possesses singularity with consequent scaling and universality.

cond-mat.stat-mech↗