Time: 10:30 AM (Taipei time)
Venue: Online Zoom [Registration] is required
Speaker: Hitesh J. Changlani (Florida State University)
Title: Search for quantum spin liquid phases with accurate material-specific effective model Hamiltonians.
Abstract: Quantum spin liquids (QSL) are enigmatic phases of matter characterized by the absence of symmetry breaking and the presence of fractionalized quasiparticles. While theories for QSLs are now in abundance, tracking them down in real materials has turned out to be remarkably tricky. I will present our recent work on candidate QSLs in three-dimensional frustrated pyrochlore systems [1,2,3], which benefited from determination of accurate material-specific effective model Hamiltonians. These Hamiltonians required a careful comparison with neutron scattering, magnetization and specific heat experiments and employed quantum and classical many-body techniques that were instrumental in explaining their findings. I will discuss the example of one such investigation in the context of Ce2Zr2O7 whose magnetic properties emerge from interacting cerium ions, and whose ground state "dipole-octupole" doublet (with J = 5/2,m_J = ±3/2) arises from strong spin-orbit coupling and crystal field effects. Our numerically determined effective Hamiltonian suggests the realization of a U(1) π-flux QSL phase [3] and allows us to make predictions for responses in an applied magnetic field that highlight the important role played by octupoles in the disappearance of spectral weight.  Motivated by the questions that arise in the first part of the talk,  the second part will take a broader viewpoint and will attempt to bridge the gap between the world of materials and models. In particular, I will pose the problem of effective model Hamiltonian determination precisely using the language of many-body wavefunctions, a desirable feature for strongly correlated systems. I offer a solution in the form of the "density matrix downfolding" technique [4,5], a form of Hilbert space operator renormalization.

Zoom Link: https://us02web.zoom.us/j/89793143331?pwd=Q2lJRFBwSXdWbDBmbW14NTF1N1FIdz09