Professor Fazel Tafti 

Boston College

Friday, Jan 20, 2023

11:00 a.m.

214 Mudd and Zoom

Title: Chemical tuning of anisotropic exchange interactions in Kitaev materials  

Abstract:

Honeycomb iridate materials, such as α-Li2IrO3 and Na2IrO3, have been intensely studied in the past two decades due to a potential realization of the Kitaev spin liquid phase. They provide the basic ingredients of the Kitaev model, i.e. a honeycomb lattice, spin ½ ions, and bond-directional Ising-like interactions due to strong spin-orbit coupling. However, non-Kitaev interactions such as the Heisenberg and off-diagonal exchange are also present in real materials. These competing interactions create a complex phase diagram with non-collinear magnetic orders. In this talk, I will explain how topochemical synthesis methods can be used to tune the competing interactions and access different regimes in the phase diagram of Kitaev magnets. In a typical topochemical reaction, alkali ions are replaced by monovalent transition metal ions. As a result, the bond angles across the super-exchange paths change, providing a mechanism for tuning the relative strength of different exchange interactions and a potential route toward a quantum spin liquid phase. We will present several materials synthesized by topochemical reactions including Cu2IrO3 that exhibits a competition between static and dynamic magnetism, Ag3LiIr2O6 that exhibits thermodynamic evidence of proximity to the Kitaev spin liquid phase, and Ag3LiRh2O6 that falls is a dramatically different regime in the phase diagram, far from the spin liquid phase.

Biography:

Fazel Tafti completed his PhD at the University of Toronto with Prof. Steven Julian. His thesis was focused on developing transport experiments under ultrahigh pressures in diamond anvil cells. His first postdoc position at the University of Sherbrook with Prof. Louis Taillefer was focused on the thermal conductivity and thermoelectric measurements in iron-based superconductors under intense magnetic fields. He then changed fields from physics to chemistry and completed a second postdoc at Princeton University with Prof. Bob Cava. His research was focused on the chemical synthesis of topological and magnetic materials.  He has been an assistant professor at Boston College in the physics department since 2016. His lab is interdisciplinary between physics, chemistry, and materials science. 

Zoom:
https://columbiauniversity.zoom.us/j/97826865089?pwd=VG9Jc2JycnZXWnFPMG42cS91YzlLZz09

Meeting ID: 978 2686 5089
Passcode: 339868