@article { WOS:000680428500001,
title = {Anomalies and unusual stability of multicomponent Luttinger liquids in Z(n) x Z(n) spin chains},
journal = {Phys. Rev. B},
volume = {104},
number = {4},
year = {2021},
month = {JUL 30},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We study translationally invariant spin chains where each unit cell contains an n-state projective representation of a Z(n) x Z(n) internal symmetry, generalizing the spin-1/2 XYZ chain. Such spin chains possess a generalized Lieb-Schultz-Mattis (LSM) constraint, and we demonstrate that certain (n - 1)-component Luttinger liquids possess the correct anomalies to satisfy these LSM constraints. For n = 3, using both numerical and analytical approaches, we find that such spin chains with nearest-neighbor interactions appear to be gapless for a wide range of microscopic parameters and described by a two-component conformally invariant Luttinger liquid. This implies the emergence of n - 1 conserved U(1) charges from only discrete microscopic symmetries. Remarkably, the system remains gapless for an unusually large parameter regime despite the apparent existence of symmetryallowed relevant operators in the field theory. This suggests that either these spin chains have hidden conserved quantities not previously identified, or the parameters of the field theory are simply unusual due to frustration effects of the lattice Hamiltonian. We argue that similar features are expected to occur in (1) Z(n) x Z(n) symmetric chains for n odd and (2) S-n x Z(n) symmetric chains for all n > 2. Finally, we suggest the possibility of a lower bound growing with n on the minimum central charge of field theories that possess such LSM anomalies.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.104.045151},
author = {Alavirad, Yahya and Barkeshli, Maissam}
}
@article {lavasani_measurement-induced_2021,
title = {Measurement-induced topological entanglement transitions in symmetric random quantum circuits},
journal = {Nat. Phys.},
volume = {17},
number = {3},
year = {2021},
note = {Place: HEIDELBERGER PLATZ 3, BERLIN, 14197, GERMANY Publisher: NATURE RESEARCH Type: Article},
month = {mar},
pages = {342+},
abstract = {Random quantum circuits, in which an array of qubits is subjected to a series of randomly chosen unitary operations, have provided key insights into the dynamics of many-body quantum entanglement. Recent work has shown that interleaving the unitary operations with single-qubit measurements can drive a transition between high- and low-entanglement phases. Here we study a class of symmetric random quantum circuits with two competing types of measurement in addition to unitary dynamics. We find a rich phase diagram involving robust symmetry-protected topological, trivial and volume law entangled phases, where the transitions are hidden to expectation values of any operator and are only apparent by averaging the entanglement entropy over quantum trajectories. In the absence of unitary dynamics, we find a purely measurement-induced critical point, which maps exactly to two copies of a classical two-dimensional percolation problem. Numerical simulations indicate that this transition is a tricritical point that splits into two critical lines in the presence of arbitrarily sparse unitary dynamics with an intervening volume law entangled phase. Our results show that measurements alone are sufficient to induce criticality and logarithmic entanglement scaling, and arbitrarily sparse unitary dynamics can be sufficient to stabilize volume law entangled phases in the presence of rapid, yet competing, measurements.},
issn = {1745-2473},
doi = {10.1038/s41567-020-01112-z},
author = {Lavasani, Ali and Alavirad, Yahya and Barkeshli, Maissam}
}
@article {21626,
title = {Topological Order and Criticality in (2+1)D Monitored Random Quantum Circuits},
journal = {Phys. Rev. Lett.},
volume = {127},
year = {2021},
month = {Dec},
pages = {235701},
doi = {10.1103/PhysRevLett.127.235701},
url = {https://link.aps.org/doi/10.1103/PhysRevLett.127.235701},
author = {Lavasani, Ali and Alavirad, Yahya and Barkeshli, Maissam}
}
@article {alavirad_ferromagnetism_2020,
title = {Ferromagnetism and its stability from the one-magnon spectrum in twisted bilayer graphene},
journal = {Phys. Rev. B},
volume = {102},
number = {23},
year = {2020},
note = {Place: ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA Publisher: AMER PHYSICAL SOC Type: Article},
month = {dec},
abstract = {We study ferromagnetism and its stability in twisted bilayer graphene. We work with a Hubbard-like interaction that corresponds to the screened Coulomb interaction in a well-defined limit where the Thomas-Fermi screening length l(TF) is much larger than monolayer graphene{\textquoteright}s lattice spacing l(g) {\textless}{\textless} l(TF) and much smaller than the moire superlattice{\textquoteright}s spacing l(TF) {\textless}{\textless} l(moire). We show that in the perfectly flat band {\textquotedblleft}chiral{\textquotedblright} limit and at filling fractions +/- 3/4, the saturated ferromagnetic (spin- and valley-polarized) states are ideal ground-state candidates in the large band-gap limit. By assuming a large enough substrate (hBN) induced sublattice potential, the same argument can be applied to filling fractions +/- 1/4. We estimate the regime of stability of the ferromagnetic phase around the chiral limit by studying the exactly calculated spectrum of one-magnon excitations. The instability of the ferromagnetic state is signaled by a negative magnon excitation energy. This approach allows us to deform the results of the idealized chiral model (by increasing the bandwidth and/or modified interactions) toward more realistic systems. Furthermore, we use the low-energy part of the exact one-magnon spectrum to calculate the spin-stiffness of the Goldstone modes throughout the ferromagnetic phase. The calculated value of spin-stiffness can determine the excitation energy of charged skyrmions.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.102.235123},
author = {Alavirad, Yahya and Sau, Jay}
}
@article {ISI:000480388400001,
title = {Almost linear Haldane pseudopotentials and emergent conformal block wave functions in a Landau level},
journal = {Phys. Rev. B},
volume = {100},
number = {7},
year = {2019},
month = {AUG 12},
pages = {075122},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We consider a two-dimensional model of particles interacting in a Landau level. We work in a finite disk geometry and take the particles to interact with a linearly decreasing two-body Haldane pseudopotential. We show that the ground-state subspace of this model is spanned by the wave functions that can be written as polynomial conformal blocks (of an arbitrary conformal field theory) consistent with the filling fraction (scaling dimension). To remove degeneracies, we then add a quadratic perturbation to the Hamiltonian and show that (1) conformal blocks constructed using the Moore-Read construction (e.g., Laughlin, Pfaffian, and Read-Rezayi states) remain exact eigenstates of this model in the thermodynamic limit, and (2) by tuning an externally imposed single-body -L-z(2) potential we can enforce Moore-Read conformal blocks to become exact ground states of this model in the thermodynamic limit. We cannot rule out the possibility of residual degeneracies in this limit. This model has no filling dependence and is comprised only from two-body long-range interactions and external single-body potentials. Our results provide insight into how conformal block wave functions can emerge in a Landau level.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.100.075122},
author = {Alavirad, Yahya}
}
@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:000462882400010,
title = {Scrambling in the Dicke model},
journal = {Phys. Rev. A},
volume = {99},
number = {4},
year = {2019},
month = {APR 1},
pages = {043602},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {The scrambling rate lambda(L) associated with the exponential growth of out-of-time-ordered correlators can be used to characterize quantum chaos. Here we use a particular Majorana fermion representation of spin-1/2 systems to study quantum chaos in the Dicke model. We take the system to be in thermal equilibrium and compute lambda(L) throughout the phase diagram to leading order in 1/N. We find that the chaotic behavior is strongest close to the critical point. At high temperatures lambda(L) is nonzero over an extended region that includes both the normal and superradiant phases. At low temperatures lambda(L) is nonzero in (a) close vicinity of the critical point and (b) a region within the superradiant phase. In the process we also derive an effective theory for the superradiant phase at finite temperatures Our formalism does not rely on the assumption of total spin conservation.},
issn = {2469-9926},
doi = {10.1103/PhysRevA.99.043602},
author = {Alavirad, Yahya and Lavasani, Ali}
}
@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.}
}
@article {ISI:000402483300015,
title = {Global Phase Diagram of a Three-Dimensional Dirty Topological Superconductor},
journal = {PHYSICAL REVIEW LETTERS},
volume = {118},
number = {22},
year = {2017},
month = {JUN 1},
pages = {227002},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We investigate the phase diagram of a three-dimensional, time-reversal symmetric topological superconductor in the presence of charge impurities and random s-wave pairing. Combining complimentary field theoretic and numerical methods, we show that the quantum phase transition between two topologically distinct paired states (or thermal insulators), described by thermal Dirac semimetal, remains unaffected in the presence of sufficiently weak generic randomness. At stronger disorder, however, these two phases are separated by an intervening thermal metallic phase of diffusive Majorana fermions. We show that across the insulator-insulator and metal-insulator transitions, normalized thermal conductance displays single parameter scaling, allowing us to numerically extract the critical exponents across them. The pertinence of our study in strong spin-orbit coupled, three-dimensional doped narrow gap semiconductors, such as CuxBi2Se3, is discussed.}, \%\%Address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA},
issn = {0031-9007},
doi = {10.1103/PhysRevLett.118.227002},
author = {Roy, Bitan and Alavirad, Yahya and Sau, Jay D.}
}
@article { ISI:000415687200020,
title = {Z(3) Parafermionic Zero Modes without Andreev Backscattering from the 2/3 Fractional Quantum Hall State},
journal = {PHYSICAL REVIEW LETTERS},
volume = {119},
number = {21},
year = {2017},
month = {NOV 20},
issn = {0031-9007},
doi = {10.1103/PhysRevLett.119.217701},
author = {Alavirad, Yahya and Clarke, David and Nag, Amit and Sau, Jay D.}
}
@article {ISI:000384068400002,
title = {Role of boundary conditions, topology, and disorder in the chiral magnetic effect in Weyl semimetals},
journal = {PHYSICAL REVIEW B},
volume = {94},
number = {11},
year = {2016},
month = {SEP 27},
pages = {115160},
issn = {2469-9950},
doi = {10.1103/PhysRevB.94.115160},
author = {Alavirad, Yahya and Sau, Jay D.}
}