More information:

Loading Events

« All Events

  • This event has passed.

Quantum Many-Body Days – S. Sachdev & M. Metlitski

September 28, 2021 @ 10:00 am - 12:00 pm

The conference on Recent Progress in Many-Body Theories (RPMBT) will take place here at UNC in September 2022.
As a bridge program, this year we are hosting a series of virtual talks in September 2021: the Quantum Many-Body Days.
The format of these talks will be 45 minutes for presentation and 15 minutes for questions and discussion. Please see below links for more information.

Local organizing committee
J. Drut (Chair), G. Basar, A. Nicholson, S. Chandrasekharan, L. Mitas, and T. Papenbrock

September 28th, 2021: Universal behavior and strongly coupled theories
“Fermi surfaces large and small: unifying theories of the Kondo lattice and Hubbard models”
S. Sachdev – 10am

Fermi surfaces which obey the Luttinger theorem are often referred to as “large”. However, it is possible to have “small” Fermi surfaces with electron-like quasiparticles, in certain metallic states (sometimes called FL*) which evade the Luttinger theorem using emergent gauge fields. It is relatively easy to construct FL* states in Kondo lattice models, but much harder in a single band Hubbard model. I will describe a new approach which yields a variational wavefunction for FL* in the Hubbard model, and also a theory for the transition between small and large Fermi surfaces. The key idea is to avoid fractionalizing the electron, and to instead fractionalize a paramagnon into a pair of ancilla qubits. I will note applications to the phase diagram of the cuprates.

“Boundary criticality of the O(N) model in d = 3 critically revisited”
M. Metlitski – 11am
Session chair: Basar

It is known that the classical O(N) model in dimension d > 3 at its bulk critical point admits three boundary universality classes: the ordinary, the extra-ordinary and the special. The extraordinary fixed point corresponds to the bulk transition occurring in the presence of an ordered boundary, while the special fixed point corresponds to a boundary phase transition between the ordinary and the extra-ordinary classes. While the ordinary fixed point survives in d = 3, it is less clear what happens to the extra-ordinary and special fixed points when d = 3 and N is greater or equal to 2. I’ll show that formally treating N as a continuous parameter, there exists a critical value Nc > 2 separating two distinct regimes. For N < Nc the extra-ordinary fixed point survives in d = 3, albeit in a modified form: the long-range boundary order is lost, instead, the order parameter correlation function decays as a power of log r. For N > Nc there is no fixed point with order parameter correlations decaying slower than power law. I’ll discuss how these findings compare to recent Monte-Carlo studies of classical and quantum spin models with SO(3) symmetry. Based on arXiv:2009.05119.


September 28, 2021
10:00 am - 12:00 pm