@article {ISI:000461964300002,
title = {Braiding and gapped boundaries in fracton topological phases},
journal = {Phys. Rev. B},
volume = {99},
number = {12},
year = {2019},
month = {MAR 19},
pages = {125132},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We study gapped boundaries of Abelian type-I fracton systems in three spatial dimensions. Using the X-cube model as our motivating example, we give a conjecture, with partial proof, of the conditions for a boundary to be gapped. In order to state our conjecture, we use a precise definition of fracton braiding and show that bulk braiding of fractons has several features that make it insufficient to classify gapped boundaries. Most notable among these is that bulk braiding is sensitive to geometry and is {\textquoteleft}{\textquoteleft}nonreciprocal{{\textquoteright}{\textquoteright}}; that is, braiding an excitation a around b need not yield the same phase as braiding b around a. Instead, we define fractonic {\textquoteleft}{\textquoteleft}boundary braiding,{{\textquoteright}{\textquoteright}} which resolves these difficulties in the presence of a boundary. We then conjecture that a boundary of an Abelian fracton system is gapped if and only if a {\textquoteleft}{\textquoteleft}boundary Lagrangian subgroup{{\textquoteright}{\textquoteright}} of excitations is condensed at the boundary; this is a generalization of the condition for a gapped boundary in two spatial dimensions, but it relies on boundary braiding instead of bulk braiding. We also discuss the distinctness of gapped boundaries and transitions between different topological orders on gapped boundaries.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.99.125132},
author = {Bulmash, Daniel and Iadecola, Thomas}
}
@article { ISI:000493516700001,
title = {Gauging fractons: Immobile non-Abelian quasiparticles, fractals, and position-dependent degeneracies},
journal = {Phys. Rev. B},
volume = {100},
number = {15},
year = {2019},
month = {OCT 29},
pages = {155146},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {The study of gapped quantum many-body systems in three spatial dimensions has uncovered the existence of quantum states hosting quasiparticles that are confined, not by energetics but by the structure of local operators, to move along lower dimensional submanifolds. These so-called {\textquoteleft}{\textquoteleft}fracton{{\textquoteright}{\textquoteright}} phases are beyond the usual topological quantum field theory description, and thus require new theoretical frameworks to describe them. Here we consider coupling fracton models to topological quantum field theories in (3 + 1) dimensions by starting with two copies of a known fracton model and gauging the Z(2) symmetry that exchanges the two copies. This yields a class of exactly solvable lattice models that we study in detail for the case of the X-cube model and Haah{\textquoteright}s cubic code. The resulting phases host finite-energy non-Abelian immobile quasiparticles with robust degeneracies that depend on their relative positions. The phases also host non-Abelian string excitations with robust degeneracies that depend on the string geometry. Applying the construction to Haah{\textquoteright}s cubic code in particular provides an exactly solvable model with finite energy yet immobile non-Abelian quasiparticles that can only be created at the corners of operators with fractal support.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.100.155146},
author = {Bulmash, Daniel and Barkeshli, Maissam}
}
@article {ISI:000457732400002,
title = {Wiedemann-Franz law and Fermi liquids},
journal = {Phys. Rev. B},
volume = {99},
number = {8},
year = {2019},
month = {FEB 4},
pages = {085104},
publisher = {AMER PHYSICAL SOC},
type = {Article},
abstract = {We consider in depth the applicability of the Wiedemann-Franz (WF) law, namely that the electronic thermal conductivity (K) is proportional to the product of the absolute temperature (T) and the electrical conductivity (a) in a metal with the constant of proportionality, the so-called Lorenz number L-0, being a materials-independent universal constant in all systems obeying the Fermi liquid (FL) paradigm. It has been often stated that the validity (invalidity) of the WF law is the hallmark of an FL {[}non-Fermi liquid (NFL)]. We consider, both in two (2D) and three (3D) dimensions, a system of conduction electrons at a finite temperature T coupled to a bath of acoustic phonons and quenched impurities, ignoring effects of electron-electron interactions. We find that the WF law is violated arbitrarily strongly with the effective Lorenz number vanishing at low temperatures as long as phonon scattering is stronger than impurity scattering. This happens both in 2D and in 3D for T < T-BG, where T-BG is the Bloch-Griineisen temperature of the system. In the absence of phonon scattering (or equivalently, when impurity scattering is much stronger than the phonon scattering), however, the WF law is restored at low temperatures even if the impurity scattering is mostly small angle forward scattering. Thus, strictly at T = 0 the WF law is always valid in a FL in the presence of infinitesimal impurity scattering. For strong phonon scattering, the WF law is restored for T > T-BG (or the Debye temperature T-D, whichever is lower) as in usual metals. At very high temperatures, thermal smearing of the Fermi surface causes the effective Lorenz number to go below L-0, manifesting a quantitative deviation from the WF law. Our paper establishes definitively that the uncritical association of an NFL behavior with the failure of the WF law is incorrect.},
issn = {2469-9950},
doi = {10.1103/PhysRevB.99.085104},
author = {Lavasani, Ali and Bulmash, Daniel and S. Das Sarma}
}
@article { ISI:000434628400002,
title = {Higgs mechanism in higher-rank symmetric U(1) gauge theories},
journal = {PHYSICAL REVIEW B},
volume = {97},
number = {23},
year = {2018},
month = {JUN 8},
pages = {235112},
issn = {2469-9950},
doi = {10.1103/PhysRevB.97.235112},
author = {Bulmash, Daniel and Barkeshli, Maissam}
}