4 Corners Southwestern Ontario Condensed Matter Symposium 2017

Conference Date: 
Thursday, May 25, 2017 (All day)
Scientific Areas: 
Condensed Matter

 

This tenth annual one-day symposium aims to provide an opportunity for condensed matter researchers in Southwest Ontario to gather and discuss informally their most recent research.  The general format of the meeting consists of 2 guest speakers and 5-7 contributed talks.  The names of the contributing speakers and title of their talks will be announced later.  Registration begins at 9:30 am.  The meeting is expected to start around 9:45 am and end between 5-5:30 pm.  A lunch will be provided by the Black Hole Bistro.

There will be two keynote speaker for the sympsoium; Professor Andrew Mackenzie from the Max Planck Institute for Chemical Physics of Solids, Dresden and Professor Anders Sandvik from Boston University.  Professor Mackenzie's talk is entitled "Delafossite layered metals: intriguing physics in the high purity limit" and Professor Sandvik's talk is "Nearly fractionalized excitations in 2D quantum antiferromagnets".

Past speakers for this event were as follows:

To register for this event, please click here.

Andrew MackenzieMax Planck Institute for Chemical Physics of Solids, Dresden

Delafossite layered metals: intriguing physics in the high purity limit

In this talk I will introduce a relatively little-studied but intriguing family of metals, the delafossite series of layered oxides ABO2 in which the A site is occupied by Pd or Pt, and the B site by a transition metal. For reasons that are not perfectly understood, these materials have amazingly high electrical conductivity, with mean free paths of hundreds of angstroms (longer than even elemental copper or silver) at room temperature, growing to tens of microns at low temperatures.  The electronic structure that yields these properties is in one way very simple, with a single half filled conduction band, but in another sense very rich, because the nearly free electrons originate mainly from the (Pt,Pd) layers in the crystal structure, while the adjacent transition metal oxide layers host Mott insulating states to which the conduction electrons also have some coupling.  My group is interested in the delafossites for a number of reasons.  Firstly, they are possible hosts for electronic transport at the crossover between ballistic and hydrodynamic regimes, which we investigate by fabricating size-restricted microstructures using focused ion beam techniques.  As layered materials that can be cleaved at low temperatures, they are also well suited to study by angle resolved photoemission spectroscopy, and host a variety of interesting surface states in addition to a simple single-band bulk electronic structure.  I will discuss our findings on non-magnetic PdCoO2, PtCoO2 and PdRhO2 and magnetic PdCrO2.

Anders Sandvik, Boston University

Nearly fractionalized excitations in 2D quantum antiferromagnets

The 2D S = 1/2 square-lattice Heisenberg model is a keystone of theoretical studies of quantum magnetism. It also has very good realizations in several classes of layered insulators with localized electronic spins. While spin-wave theory provides a good understanding of the antiferromagnetic ground state and low-lying excitations of the Heisenberg model, an anomaly in the excitations at higher energy around wave-number q = (\pi, 0) has been diffi_cult to explain. At first sight, the anomaly is just a suppression of the excitation energy by a few percent, but it also represents a more dramatic shift of spectral weight in the dynamic spin structure factor from the single- magnon (spin wave) pole to a continuum. Recent neutron scattering experiments on the quasi-2D material Cu(DCOO)2_.4D2O (the best realization so far of the 2D Heisenberg model) were even interpreted as a complete lack of magnon pole at the anomaly; instead it was suggested that the excitations there are fractional (spinons) [1]. I will discuss recent quantum Monte Carlo and stochastic analytic continuation results pointing to the existence of fragile q~(\pi,0) magnon excitations in the Heisenberg model [2], which can be fractionalized by interactions competing with the nearest-neighbor exchange coupling. This phenomenon can be understood phenomenologically within a simple theory of magnon-spinon mixing.

 
[1]  B. Dalla Piazza et al., Nature Physics 11, 62 (2015).
[2]  H. Shao, Y. Q. Qin, S. Capponi, S. Chesi, Z. Y. Meng, and A. W. Sandvik (in progress).
 

Scientific Organizer:

  • Michel Gingras, University of Waterloo