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Quantum criticality and emergent Lorentz symmetry in non-Hermitian Dirac materials

日程 : 2024年11月27日(水) 1:00 am - 2:00 am 場所 : 物性研究所本館6階 第6セミナー室 (A616) および Zoom(ハイブリッド開催) 講師 : Prof. Bitan Roy 所属 : Lehigh University, PA, USA 世話人 : 押川正毅 (ex. 63275)
e-mail: oshikawa@issp.u-tokyo.ac.jp
講演言語 : 英語

From the Standard model for elementary particles to various quantum crystals, such as graphene, the dynamics of underlying fermionic degrees of freedom is governed by the Dirac Hamiltonian that manifestly preserves the Lorentz symmetry. In this talk, first I will propose a general construction of the Lorentz invariant Dirac operator in non-Hermitian (NH) systems, featuring two velocity parameters vH and vNH, associated with the Hermitian and anti-Hermitian components of such operators, respectively. I will show that in such noninteracting systems, all the observables, such as the energy spectrum, density of states, and frequency dependent optical conductivity and shear viscosity are governed by an effective Fermi velocity vF = (vH2– vNH2)1/2. Next, I will consider interactions between NH Dirac quasiparticles and bosonic degrees of freedom, such as (a) the scalar order-parameter fluctuations mediated by short-range Hubbard-like repulsions, yielding Yukawa interactions and (b) relativistic helical photons, giving rise to NH quantum electrodynamics. In both scenarios, although the system primarily loses the Lorentz symmetry at the lattice or ultraviolet scale, it gains a NH Lorentz symmetry through various quantum corrections in the deep infrared regime in terms of a unique terminal velocity for all the participating degrees of freedom, generically tagged as the speed of light. If time permits, I will show such a generic outcome for spin-3/2 NH birefringent Dirac fermions toward the end of the talk.

References:
V. Juricic and B. Roy, Communications Physics 7, 169 (2024)
Sk A. Murshed and B. Roy, Journal of High Energy Physics 2024, 143 (2024)
Sk A. Murshed and B. Roy, arXiv:2407.18250

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(公開日: 2024年11月19日)