[Seminar] Prof. Sumiran Pujari "«Anticommuting» Z2 quantum spin liquids"

Speaker

Professor Sumiran Pujari / Indian Institute of Technology Bombay

Title

«Anticommuting» Z2 quantum spin liquids

Abstract

We will discuss lattice S=1/2 quantum Hamiltonians with bond-dependent Ising couplings that have extensively many local Z2 conserved charges. These charges have a mutually non-commuting Pauli-like "«anticommuting»" algebra that leads to the nomenclature of these quantum spin liquids. This mutual algebra is like the algebra of quantum spin-1/2 degrees of freedom however arising in the structure of local conserved charges whose support is not restricted to single lattice sites. As provable consequences, these models have finite residual entropy density in the ground state with a simple but non-trivial degeneracy counting and concomitant quantum spin liquidity, as elaborated in Ref.~[1]. The spin liquidity relies also on a geometrically site-interlinked character of the local conserved Z2 charges composed of spin-1/2 operators or Paulis. This site-interlinked character of the charges is rather natural in presence of the «anticommuting» structure. This is in contrast to for example the bond-interlinked character of the local conserved Z2 charges on the hexagonal plaquettes of the Kitaev honeycomb spin-1/2 model which gives way to a mutually commuting algebra for them. Here, we further discuss the connections and differences of this kind of quantum spin liquidity in relation to the many-body topological order found in some gapped quantum spin liquids whose canonical example is the Kitaev toric code. The toric code belongs to the more general class of Levin-Wen or string net constructions with mutually commuting algebras for the conserved charges. We will make several exact statements on the kinds of many-body order that can be present within the class of «anticommuting» Z2 quantum spin liquids co-existing with the extensive residual ground state entropy. We will also point out "hidden" conserved charges with mutually commuting algebras that are local as well. They capture non-trivial quantum resonances in elementary plaquette motifs with an even number of bonds of the underlying lattice that support these «anticommuting» Z2 quantum spin liquid Hamiltonians.

Profile of Speaker

1983-2001: Rourkela, Odisha, India (schooling, matriculation and higher secondary certificate)
2001-2005: IIT Bombay, Mumbai (undergraduate studies in Engineering Physics)
2005-2011: Ithaca, NY, USA (Ph.D. under the guidance of late Prof. Christopher L. Henley)
2011-2014: Toulouse, France (postdoc as part of an Indo-French collaboration between Dr. Fabien Alet, Toulouse, France and Prof. Kedar Damle, TIFR, Mumbai)
2014-2016: Lexington, KY, USA (postdoc as part of Prof. Ribhu Kaul group)
2016-2017: Mumbai, India (postdoc as part of Prof. Kedar Damle group)
2017-now: Mumbai, India (permanent at IIT Bombay)

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