Junren Shi
Chinese Academy of Sciences
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Publication
Featured researches published by Junren Shi.
Nature Communications | 2012
Ting Cao; Gang Wang; Wenpeng Han; Huiqi Ye; Chuanrui Zhu; Junren Shi; Qian Niu; Ping-Heng Tan; Enge Wang; Baoli Liu; Ji Feng
A two-dimensional honeycomb lattice harbors a pair of inequivalent valleys in the k-space electronic structure, in the vicinities of the vertices of a hexagonal Brillouin zone, K±. It is particularly appealing to exploit this emergent degree of freedom of charge carriers, in what is termed “valleytronics”, if charge carrier imbalance between the valleys can be achieved. The physics of valley polarization will make possible electronic devices such as valley filter and valley valve, and optoelectronic Hall devices, all very promising for next-generation electronic and optoelectronic applications. The key challenge lies with achieving valley imbalance, of which a convincing demonstration in a two-dimensional honeycomb structure remains evasive, while there are only a handful of examples for other materials. We show here, using first principles calculations, that monolayer MoS2, a novel two-dimensional semiconductor with a 1.8 eV direct band gap, is an ideal material for valleytronics by valley-selective circular dichroism, with ensuing valley polarization and valley Hall effect.
Physical Review Letters | 2011
Hai-Zhou Lu; Junren Shi; Shun-Qing Shen
A magnetoconductivity formula is presented for the surface states of a magnetically doped topological insulator. It reveals a competing effect of weak localization and weak antilocalization in quantum transport when an energy gap is opened at the Dirac point by magnetic doping. It is found that, while random magnetic scattering always drives the system from the symplectic to the unitary class, the gap could induce a crossover from weak antilocalization to weak localization, tunable by the Fermi energy or the gap. This crossover presents a unique feature characterizing the surface states of a topological insulator with the gap opened at the Dirac point in the quantum diffusion regime.
Physical Review Letters | 2005
Di Xiao; Junren Shi; Qian Niu
Liouvilles theorem on the conservation of phase-space volume is violated by Berry phase in the semiclassical dynamics of Bloch electrons. This leads to a modification of the phase-space density of states, whose significance is discussed in a number of examples: field modification of the Fermi-sea volume, connection to the anomalous Hall effect, and a general formula for orbital magnetization. The effective quantum mechanics of Bloch electrons is also sketched, where the modified density of states plays an essential role.
Physical Review B | 2011
Jun Chen; X. Y. He; Kehui Wu; Z. Q. Ji; Li Lu; Junren Shi; J. H. Smet; Yongqing Li
We demonstrate that the weak antilocalization effect can serve as a convenient method for detecting decoupled surface transport in topological insulator thin films. In the regime where a bulk Fermi surface coexists with the surface states, the low-field magnetoconductivity is well described by the Hikami-Larkin-Nagaoka equation for single-component transport of noninteracting electrons. When the electron density is lowered, the magnetotransport behavior deviates from the single-component description and strong evidence is found for independent conducting channels at or near the bottom and top surfaces. The magnetic-field-dependent part of corrections to conductivity due to Zeeman energy is shown to be negligible for the fields relevant to the weak antilocalization despite considerable electron-electron interaction effects on the temperature dependence of the conductivity.
Physical Review Letters | 2006
Junren Shi; Ping Zhang; Di Xiao; Qian Niu
The conventional definition of spin current is incomplete and unphysical in describing spin transport in systems with spin-orbit coupling. A proper and measurable spin current is established in this study, which fits well into the standard framework of near-equilibrium transport theory and has the desirable property to vanish in insulators with localized orbitals. Experimental implications of our theory are discussed.
Nature Materials | 2014
Jing Guo; Xiangzhi Meng; Ji Chen; Jinbo Peng; Jiming Sheng; Xin-Zheng Li; Limei Xu; Junren Shi; Enge Wang; Ying Jiang
Water/solid interfaces are vital to our daily lives and are also a central theme across an incredibly wide range of scientific disciplines. Resolving the internal structure, that is, the O-H directionality, of water molecules adsorbed on solid surfaces has been one of the key issues of water science yet it remains challenging. Using a low-temperature scanning tunnelling microscope, we report submolecular-resolution imaging of individual water monomers and tetramers on NaCl(001) films supported by a Au(111) substrate at 5 K. The frontier molecular orbitals of adsorbed water were directly visualized, which allowed discrimination of the orientation of the monomers and the hydrogen-bond directionality of the tetramers in real space. Comparison with ab initio density functional theory calculations reveals that the ability to access the orbital structures of water stems from the electronic decoupling effect provided by the NaCl films and the precisely tunable tip-water coupling.
Physical Review B | 2009
Tianyi Cai; Sheng Ju; Jaekwang Lee; Na Sai; Alexander A. Demkov; Qian Niu; Zhen-Ya Li; Junren Shi; E. G. Wang
Ferromagnet/ferroelectric/normal-metal superlattices are proposed to realize the large room-temperature magnetoelectric effect. Spin-dependent electron screening is the fundamental mechanism at the microscopic level. We also predict an electric control of magnetization in this structure. The naturally broken inversion symmetry in our tricomponent structure introduces a magnetoelectric coupling energy of PM(2). Such a magnetoelectric coupling effect is general in ferromagnet/ferroelectric heterostructures, independent of particular chemical or physical bonding, and will play an important role in the field of multiferroics.
Proceedings of the National Academy of Sciences of the United States of America | 2013
Xiao Li; Ting Cao; Qian Niu; Junren Shi; Ji Feng
Conventional electronics are based invariably on the intrinsic degrees of freedom of an electron, namely its charge and spin. The exploration of novel electronic degrees of freedom has important implications in both basic quantum physics and advanced information technology. Valley, as a new electronic degree of freedom, has received considerable attention in recent years. In this paper, we develop the theory of spin and valley physics of an antiferromagnetic honeycomb lattice. We show that by coupling the valley degree of freedom to antiferromagnetic order, there is an emergent electronic degree of freedom characterized by the product of spin and valley indices, which leads to spin–valley-dependent optical selection rule and Berry curvature–induced topological quantum transport. These properties will enable optical polarization in the spin–valley space, and electrical detection/manipulation through the induced spin, valley, and charge fluxes. The domain walls of an antiferromagnetic honeycomb lattice harbors valley-protected edge states that support spin-dependent transport. Finally, we use first-principles calculations to show that the proposed optoelectronic properties may be realized in antiferromagnetic manganese chalcogenophosphates (MnPX3, X = S, Se) in monolayer form.
Physical Review Letters | 2005
X. Zhou; Junren Shi; T. Yoshida; Tanja Cuk; Wanli Yang; V. Brouet; J. Nakamura; Norman Mannella; Seiki Komiya; Yoichi Ando; Fang Zhou; W. X. Ti; J. W. Xiong; Z.X. Zhao; T. Sasagawa; T. Kakeshita; H. Eisaki; S. Uchida; A. Fujimori; Zhenyu Zhang; E. W. Plummer; R. B. Laughlin; Z. Hussain; Zhi-Xun Shen
High resolution angle-resolved photoemission spectroscopy data along the (0, 0)-(pi,pi) nodal direction with significantly improved statistics reveal fine structure in the electron self-energy of the underdoped (La2-xSrx)CuO4 samples in the normal state. Fine structure at energies of (40-46) meV and (58-63) meV, and possible fine structure at energies of ( 23 - 29) meV and ( 75 - 85) meV, have been identified. These observations indicate that, in (La2-xSrx) CuO4, more than one bosonic modes are involved in the coupling with electrons.
Physical Review Letters | 2012
Hua Jiang; Zhenhua Qiao; Haiwen Liu; Junren Shi; Qian Niu
We study the possibility of realizing topological phases in graphene with randomly distributed adsorbates. When graphene is subjected to periodically distributed adatoms, the enhanced spin-orbit couplings can result in various topological phases. However, at certain adatom coverages, the intervalley scattering renders the system a trivial insulator. By employing a finite-size scaling approach and Landauer-Büttiker formula, we show that the randomization of adatom distribution greatly weakens the intervalley scattering, but plays a negligible role in spin-orbit couplings. Consequently, such a randomization turns graphene from a trivial insulator into a topological state.