Spin and Valley Splittings in Multilayered Massless Dirac Fermion System

Quantum Hall effect in multilayered massless Dirac fermion systems with tilted cones

We report the first observation of Shubnikov-de Haas (SdH) oscillations and quantized Hall resistance in the multilayered massless Dirac fermion system $α$-(BEDT-TTF)$_2$I$_3$ with tilted cones. Holes were injected into the thin crystal fixed on a polyethylene naphthalate (PEN) substrate by contact electrification. The detection of SdH oscillations whose phase was modified by Berry's phase $π$ strongly suggested that the carrier doping was successful in this system. We succeeded in detecting the quantum Hall effect (QHE) with the steps which is the essence of two dimensional Dirac fermion syst…

Massless Fermions in multilayer graphitic systems with misoriented layers

We examine how the misorientation of a few stacked graphene layers affects the electronic structure of carbon nanosystems. We present {\it ab initio} calculations on bi- and trilayer systems to demonstrate that the massless Fermion behavior typical of single layered graphene is also found in incommensurate multilayered graphitic systems. We also investigate the consequences of this property on experimental fingerprints, such as Raman spectroscopy and scanning tunneling microscopy (STM). Our simulations reveal that STM images of turbostratic few layer graphite are sensitive to the layer arrange…

Temperature-driven single-valley Dirac fermions in HgTe quantum wells

We report on temperature-dependent magnetospectroscopy of two HgTe/CdHgTe quantum wells below and above the critical well thickness $d_c$. Our results, obtained in magnetic fields up to 16 T and temperature range from 2 K to 150 K, clearly indicate a change of the band-gap energy with temperature. The quantum well wider than $d_c$ evidences a temperature-driven transition from topological insulator to semiconductor phases. At the critical temperature of 90 K, the merging of inter- and intra-band transitions in weak magnetic fields clearly specifies the formation of gapless state, revealing the…

石墨烯中磁场可调的谷对比赝磁约束

Magnetic field-tunable valley-contrasting pseudomagnetic confinement in graphene

本研究利用应变石墨烯中的非均匀赝磁场实现无质量狄拉克费米子的量子约束，通过调节真实磁场打破两能谷有效磁场平衡，获得谷对比空间约束与可调谷极化受限态，为操控谷自由度提供新方法。

In-plane Chiral Tunneling and Out-of-plane Valley-polarized Quantum Tunneling in Twisted Graphene Trilayer

Here we show that twisted graphene trilayer made by misoriented stacking a graphene monolayer on top of a Bernal graphene bilayer can exhibit rich and tailored electronic properties. For the case that the graphene monolayer and bilayer are strongly coupled, both the massless Dirac fermions and massive chiral fermions coexist in the twisted trilayer, leading to unique in-plane chiral tunneling. For a weak coupling between the two graphene systems, the distinct chiralities and pseudospin textures of quasiparticles in monolayer and bilayer enable vertical valley-polarized quantum tunneling betwee…

Temperature-driven massless Kane fermions in HgCdTe crystals: verification of universal velocity and rest-mass description

It has recently been shown that the electronic states in bulk gapless HgCdTe offer another realization of pseudo-relativistic three-dimensional particles in a condensed matter system. These single valley relativistic states, referred to as massless Kane fermions, cannot be described by any other well-known relativistic massless particles. Furthermore, the HgCdTe band structure can be continuously tailored by modifying either the cadmium content or temperature. At the critical concentration or temperature, the bandgap, Eg, collapses as the system undergoes a semimetal-to-semiconductor topologic…