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Proton transfer through hydrogen bonds plays a fundamental role in many physical, chemical and biological processes. Proton dynamics is susceptible to quantum tunnelling, which typically involves many hydrogen bonds simultaneously, leading to correlated many-body tunnelling. In contrast to the well-studied incoherent single-particle tunnelling, our understanding of many-body tunnelling is still in its infancy. Here we report the real-space observation of concerted proton tunnelling in a cyclic water tetramer using a cryogenic scanning tunnelling microscope. This is achieved by monitoring the reversible interconversion of the hydrogen-bonding chirality of the water tetramer with a chlorine-terminated scanning tunnelling microscope tip. We found that the presence of the Cl anion at the tip apex may either enhance or suppress the concerted tunnelling process, depending on the details of the coupling symmetry between the Cl ion and the protons. Our work opens up the possibility of controlling the quantum states of protons with atomic-scale precision. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The total reciprocal space magnetic flux threading through a closed Fermi surface is a topological invariant for a three-dimensional metal. For a Weyl metal, the invariant is nonzero for each of its Fermi surfaces. We show that such an invariant can be related to the magneto-valley-transport effect, in which an external magnetic field can induce a valley current. We further show that a strain field can drive an electric current, and that the effect is dictated by a second-class Chern invariant. These connections open the pathway to observe the hidden topological invariants in metallic systems. [ABSTRACT FROM AUTHOR]

We propose a general variational principle for mapping the interacting systems in continuous space to lattice models. Based on the principle, we derive a set of self-consistent nonlinear equations for the Wannier functions (or, equivalently for the Bloch functions). These equations show that the Wannier functions can be strongly influenced by the interaction and be significantly different from their non-interacting counterparts. The approach is demonstrated with interacting bosons in an optical lattice, and illustrated quantitatively by a simple model of interacting bosons in a double well potential. It is shown that the so-determined lattice model parameters can be significantly different from their non-interacting values. [ABSTRACT FROM AUTHOR]

We review experimental advances in the study of the electron transport in three-dimensional topological insulators with emphasis on experiments that attempted to identify the surface transport. Recent results on transport properties of topological insulator thin films will be discussed in the context of weak antilocalization and electron-electron interactions. Current status of gate-voltage control of the chemical potential in topological insulators will also be described. [ABSTRACT FROM AUTHOR]

A cDNA library was constructed from the heading leaf in the early phase of the heading stage of Chinese cabbage (Brassica rapa L. ssp. pekinensis). By sequencing the randomly selected clones, 1363 sequences longer than 200 bp were found, with better trace data. After removing the poly(A) and contamination sequences, 1162 ESTs longer than 150 bp were obtained, of which 1102 shared significant similarity with known sequences in protein and nucleotide databases of the National Center for Biotechnology Information (NCBI) as revealed by searches using the BLASTX and BLASTN engines. Functional assignment of the ESTs was based on the method used in the Arabidopsis thaliana genome-sequencing project. About 77% of the putative protein sequences with known biological functions best matched with those of A. thaliana deposited in the non-redundant database of NCBI. These data suggest that Chinese cabbage is closely related to A. thaliana. This result is different from that reported in other Brassica species. At nucleotide level, however, 51% of the ESTs were homologous to those deposited for A. thaliana when all ESTs were searched against the est-others database. In addition, 60 ESTs had no homology with any of the plant gene sequences deposited in GenBank. These ESTs are very important for understanding the unique developmental process of Chinesecabbage and elaborating its genetic mapping. Among the genes with assigned functions, the most abundant representatives were those involved in protein synthesis and energy metabolism. With the 1162 ESTs, 895 non-redundant contigs were generated after being aligned using the Seqman II module of DNAStar software at the threshold of more than 80% homology over a minimum of 40 base pairs. Of these, 723 were singletons containing only one EST sequence, indicating that many kinds of such genes are expressed in the heading leaf of Chinese cabbage. An expression profile of Chinese cabbage heading leaf with the 1162 ESTs was therefore acquired in this work. This could be very useful for uncovering the mechanism of the heading process, which is the most obvious characteristic of Chinese cabbage and perhaps other related species, such as Brassica oleracea. This work could accelerate the finding and characterization of genes specifically expressed in the heading stage of Chinese cabbage. [ABSTRACT FROM PUBLISHER]

We construct a density functional theory for two-dimensional electron (hole) gases subjected to both strong magnetic fields and external potentials. In particular, we are focused on regimes near even-denominator filling factors, in which the systems form composite fermion liquids. Our theory provides a systematic and rigorous approach to determine the properties of ground states in a fractional quantum Hall regime that is modified by artificial structures. We also propose a practical way to construct an approximated functional. [ABSTRACT FROM AUTHOR]