, Junhyun Lee
, Eun-Gook Moon
Phys. Rev. B 103, 014435 (2021)
We show that lattice vibration may not be a decoherence source but an impetus of a novel coherent quantum many-body state. We demonstrate the possibility by studying the transverse-field Ising model on a chain with renormalization group and density-matrix renormalization group methods and theoretically discover a stable N=1 supersymmetric quantum criticality with central charge c=3/2. Thus, we propose an Ising spin chain with strong spin-lattice coupling as a candidate to observe supersymmetry. Generic precursor conditions of novel quantum criticality are obtained by generalizing the Larkin-Pikin criterion of thermal transitions. Our work provides the perspective that lattice vibration may be a knob for exotic quantum many-body states.
We study topological quantum phase transitions (TQPTs) between double-Weyl semimetals (DWSMs) and insulators, and argue that a novel class of quantum criticality appears at the TQPT characterized by emergent anisotropic non-Fermi-liquid behaviors, in which the interplay between the Coulomb interaction and electronic critical modes induces not only anisotropic renormalization of the Coulomb interaction but also strongly correlated electronic excitation in three spatial dimensions. Using the standard renormalization group methods, large Nf theory, and the ε=4−d method with a fermion flavor number Nf and spatial dimension d, we obtain the anomalous dimensions of electrons (ηf=0.366/Nf) in large Nf theory and the associated anisotropic scaling relations of various physical observables. Our results may be observed in candidate materials for DWSMs such as HgCr2Se4 or SrSi2 when the system undergoes a TQPT.
We study quantum phase transitions associated with splitting nodal Fermi points, motivated by topological phase transitions between Dirac and Weyl semimetals. A Dirac point in Dirac semimetals may be split into two Weyl points by breaking a lattice symmetry or time-reversal symmetry, and the Lifshitz transition is commonly used to describe the phase transitions. Here, we show that the Lifshitz description is fundamentally incorrect in quantum phase transitions with splitting nodal Fermi points. We argue that correlations between fermions, order parameter, and the long-range Coulomb interaction must be incorporated from the beginning. One of the most striking correlation effects we find is infinite anisotropy of physical quantities, which cannot appear in a Lifshitz transition. By using the standard renormalization group method, two types of infinitely anisotropic quantum criticalities are found in three spatial dimensions, varying with the number of the Dirac points N. Our renormalization group analysis is fully controlled by the fact that order parameter and fermion fluctuations are at the upper critical dimension, and thus our stable fixed points demonstrate the presence of weakly coupled quantum criticalities with infinite anisotropy.
and Eun-Gook Moon
Phys. Rev. B 97, 241101(R) (2018)
Chiral symmetry is one of the most fundamental symmetries in nature, which prohibits mass generation of fermions. Remarkable advances in topological matter reveal the chiral symmetry may be realized as lattice symmetries of topological state. A topological phase transition is intrinsically tied to breaking a chiral symmetry. The topological transition, however, is lack of the Lorentz symmetry in contrast to particle physics. In particular, the Coulomb interaction is instantaneous, and it is imperative to understand its effects on chiral symmetry breaking transitions. We show that a topological transition associated with chiral symmetry is stable under the presence of a Coulomb interaction and the electron velocity always becomes faster than the one of a chiral symmetry order parameter. Thus, the transition must not be relativistic, which implies that supersymmetry is intrinsically forbidden by the long-range Coulomb interaction. Asymptotically exact universal ratios of physical quantities such as the energy gap ratio are obtained, and connections with experiments and recent theoretical proposals are also discussed.
We show intriguing phenomena of interplay between symmetry and topology in three-dimensional topological phase transitions associated with line-nodal superconductors. More specifically, we discover an exotic universality class out of topological line-nodal superconductors. The order parameter of broken symmetries is strongly correlated with underlying line-nodal fermions, and this gives rise to a large anomalous dimension in sharp contrast to that of the Landau-Ginzburg theory. Remarkably, hyperscaling violation and emergent relativistic scaling appear in spite of the presence of nonrelativistic fermionic excitation. We also propose characteristic experimental signatures around the phase transitions, for example, a linear phase boundary in a temperature-tuning parameter phase diagram, and discuss the implication of recent experiments in pnictides and heavy-fermion systems.
"Explaining the Lepton Non-universality at the LHCb and CMS from an Unified Framework"
Sanjoy Biswas, Debtosh Chowdhury, SangEun Han
, and Seung J. Lee JHEP 02, 142 (2015)
- Department of Physics, University of Toronto, Toronto, Canada
November 2020 ~ Present
- School of Computational Sciences, KIAS, Seoul, Korea
August 2020 ~ October 2020
- Department of Physics, KAIST, Daejeon, Korea
March 2013 ~ August 2020
Candidate of Integrated Master's and Ph.D Program