@article {han_lattice_2021,
title = {Lattice vibration as a knob on exotic quantum criticality},
journal = {Phys. Rev. B},
volume = {103},
number = {1},
year = {2021},
note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article},
month = {jan},
abstract = {Control of quantum coherence in a many-body system is one of the key issues in modern condensed matter, and conventional wisdom is that lattice vibration is an innate source of decoherence. Much research has been conducted to eliminate lattice effects. Challenging this wisdom, 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.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.103.014435},
author = {Han, SangEun and Lee, Junhyun and Moon, Eun-Gook}
}
@article {yoo_nonequilibrium_2020,
title = {Nonequilibrium steady state phases of the interacting {Aubry}-{Andre}-{Harper} model},
journal = {Phys. Rev. B},
volume = {102},
number = {19},
year = {2020},
note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article},
month = {nov},
abstract = {Here, we study the phase diagram of the Aubry-Andre-Harper model in the presence of strong interactions as the strength of the quasiperiodic potential is varied. Previous work has established the existence of a many-body localized phase at a large potential strength; here, we find a rich phase diagram in the delocalized regime characterized by spin transport and unusual correlations. We calculate the nonequilibrium steady states of a boundary-driven strongly interacting Aubry-Andre-Harper model by employing the time-evolving block decimation algorithm on matrix product density operators. From these steady states, we extract spin transport as a function of system size and quasiperiodic potential strength. These data show spin transport going from superdiffusive to subdiffusive well before the localization transition; comparing to previous results, we also find that the transport transition is distinct from a transition observed in the speed of operator growth in the model. We also investigate the correlation structure of the steady state and find an unusual oscillation pattern for intermediate values of the potential strength. The unusual spin transport and quantum correlation structure suggest multiple dynamical phases between the much-studied thermal and many-body localized phases.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.102.195142},
author = {Yoo, Yongchan and Lee, Junhyun and Swingle, Brian}
}
@article {saha_strongly_2020,
title = {Strongly interacting spin-orbit coupled {Bose}-{Einstein} condensates in one dimension},
journal = {Phys. Rev. Res.},
volume = {2},
number = {1},
year = {2020},
note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article},
month = {mar},
abstract = {We theoretically study dilute superfluidity of spin-1 bosons with antiferromagnetic interactions and synthetic spin-orbit coupling (SOC) in a one-dimensional lattice. Employing a combination of density matrix renormalization group and quantum field theoretical techniques we demonstrate the appearance of a robust superfluid spin-liquid phase in which the spin sector of this spinor Bose-Einstein condensate remains quantum disordered even after introducing quadratic Zeeman and helical magnetic fields. Despite remaining disordered, the presence of these symmetry-breaking fields lifts the perfect spin-charge separation and thus the nematic correlators obey power-law behavior. We demonstrate that, at strong coupling, the SOC induces a charge density wave state that is not accessible in the presence of linear and quadratic Zeeman fields alone. In addition, the SOC induces oscillations in the spin and nematic expectation values as well as the bosonic Green{\textquoteright}s function. These nontrivial effects of an SOC are suppressed under the application of a large quadratic Zeeman field. We discuss how our results could be observed in experiments on ultracold gases of Na-23 in an optical lattice.},
doi = {10.1103/PhysRevResearch.2.013252},
author = {Saha, Siddhartha and Konig, E. J. and Lee, Junhyun and Pixley, J. H.}
}
@article {ISI:000468026100013,
title = {Emergent gauge field and the Lifshitz transition of spin-orbit coupled bosons in one dimension},
journal = {Sci Rep},
volume = {9},
year = {2019},
month = {MAY 16},
pages = {7471},
publisher = {NATURE PUBLISHING GROUP},
type = {Article},
abstract = {In the presence of strong spin-independent interactions and spin-orbit coupling, we show that the spinor Bose liquid confined to one spatial dimension undergoes an interaction-or density-tuned quantum phase transition similar to one theoretically proposed for itinerant magnetic solid-state systems. The order parameter describes broken Z2 inversion symmetry, with the ordered phase accompanied by non-vanishing momentum which is generated by fluctuations of an emergent dynamical gauge field at the phase transition. This quantum phase transition has dynamical critical exponent z similar or equal to 2, typical of a Lifshitz transition, but is described by a nontrivial interacting fixed point. From direct numerical simulation of the microscopic model, we extract previously unknown critical exponents for this fixed point. Our model describes a realistic situation of 1D ultracold atoms with Raman-induced spin-orbit coupling, establishing this system as a platform for studying exotic critical behavior of the Hertz-Millis type.},
issn = {2045-2322},
doi = {10.1038/s41598-019-43929-6},
author = {Cole, William S. and Lee, Junhyun and Mahmud, Khan W. and Alavirad, Yahya and Spielman, I. B. and Sau, Jay D.}
}
@article { ISI:000452326000001,
title = {Chiral anomaly without Landau levels: From the quantum to the classical regime},
journal = {PHYSICAL REVIEW B},
volume = {98},
number = {24},
year = {2018},
month = {DEC 6},
pages = {245109},
abstract = {We study the chiral anomaly in disordered Weyl semimetals, where the broken translational symmetry prevents the direct application of Nielsen and Ninomiya{\textquoteright}s mechanism and disorder is strong enough that quantum effects are important. In the weak disorder regime, there exist rare regions of the random potential where the disorder strength is locally strong, which gives rise to quasilocalized resonances and their effect on the chiral anomaly is unknown. We numerically show that these resonant states do not affect the chiral anomaly only in the case of a single Weyl node. At energies away from the Weyl point, or with strong disorder where one is deep in the diffusive regime, the chiral Landau level itself is not well defined and the semiclassical treatment is not justified. In this limit, we analytically use the supersymmetry method and find that the Chern-Simons term in the effective action which is not present in nontopological systems gives rise to a nonzero average level velocity which implies chiral charge pumping. We numerically establish that the nonzero average level velocity serves as an indicator of the chiral anomaly in the diffusive limit.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.98.245109},
author = {Lee, Junhyun and Pixley, J. H. and Sau, Jay D.}
}
@article { ISI:000452324400004,
title = {Chiral supercurrent through a quantum Hall weak link},
journal = {PHYSICAL REVIEW B},
volume = {98},
number = {21},
year = {2018},
month = {DEC 6},
pages = {214504},
abstract = {We use an effective model to calculate properties of the supercurrent carried by chiral edge states of a quantum Hall weak link. This {\textquoteleft}{\textquoteleft}chiral{{\textquoteright}{\textquoteright}} supercurrent is qualitatively distinct from the usual Josephson supercurrent in that it cannot be mediated by a single edge alone, i.e., both right- and left-going edges are needed. Moreover, the chiral supercurrent was previously shown to obey an unusual current-phase relation with period 2 phi(0) = h/e, which is twice the period of conventional Josephson junctions. We show that the {\textquoteleft}{\textquoteleft}chiral{{\textquoteright}{\textquoteright}} nature of this supercurrent is sharply defined, and is robust to interactions to infinite order in perturbation theory. We compare our results with recent experimental findings {[}Amet et al., Science 352 966 (2016)] and find that quantitative agreement in the magnitude of the supercurrent can be attained by making reasonable but critical assumptions about the superconductor quantum Hall interface.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.98.214504},
author = {Alavirad, Yahya and Lee, Junhyun and Lin, Ze-Xun and Sau, Jay D.}
}