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The Institute for Theoretical Physics offers the following seminars:

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Ying Jiang (Int. Center for Quantum Materials, School of Physics, Peking) - Probing quantum nature of hydrogen bond with scanning probe microscopy and spectroscopy

It has been known that the complexity of hydrogen-bonding interaction largely arises from the quantum nature of light hydrogen nuclei (proton). The so-called nuclear quantum effects (NQEs) in terms of tunneling and zero-point motion play important roles in the structure, dynamics, and macroscopic properties of hydrogen-boned materials. Despite enormous theoretical efforts on pursuing proper treatment of the nuclear motion at a quantum-mechanical level, accurate and quantitative description of NQEs on the hydrogen-bonding interaction has proven experimentally challenging. In this talk, I will present our recent progresses on probing NQEs of interfacial water at single bond limit using a low-temperature scanning probe microscope (SPM). By gating the molecular frontier orbitals near the Fermi level via tip-water coupling, we are able to access the internal degrees of freedom of water molecules and locate the protons in real space [1,2]. These techniques allow us not only to directly visualize the many-body proton tunneling within the H-bonded network [3], but also to quantify the impact of nuclear quantum fluctuation on the strength of hydrogen bonds [4]. Our work opens up the possibility of directly assessing, in experiment, the impact of NQEs on hydrogen-bonding interaction, which is essential for elucidating the quantum nature of the hydrogen bonds.
ETH Science City HIT E 41.1 - Fri 10.07.2015 11:00

Maciej Koch-Janusz (Weizmann Institute of Science, Israel) - Affleck-Kennedy-Lieb-Tasaki State on a Honeycomb Lattice from t_2g Orbitals

The two-dimensional Affleck-Kennedy-Lieb-Tasaki (AKLT) model on a honeycomb lattice has been shown to be a universal resource for quantum computation. In this valence bond solid, however, the spin interactions involve higher powers of the Heisenberg coupling (S_i*S_j)^n, making these states seemingly unrealistic on bipartite lattices, where one expects a simple antiferromagnetic order. We show that those interactions can be generated by orbital physics in multi-orbital Mott insulators. We focus on t_2g electrons on the honeycomb lattice and propose a physical realization of the spin-3/2 AKLT state. We find a phase transition from the AKLT to the Néel state on increasing Hund’s rule coupling, which is confirmed by density matrix renormalization group simulations. An experimental signature of the AKLT state consists of protected, free S=1/2 spins on lattice vacancies, which may be detected in the spin susceptibility.
ETH Science City HIT E 41.1 - Thu 9.07.2015 11:00

 

 

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