Publications

Order by: publication date number of citations

• Probing Chern number by opacity and topological phase transition by a nonlocal Chern marker

  Paolo Molignini, Bastien Lapierre, Ramasubramanian Chitra, Wei Chen

  SciPost Phys. Core 6, 059 (2023) · published 29 August 2023 | Toggle abstract · pdf

  In 2D semiconductors and insulators, the Chern number of the valence band Bloch state is an important quantity that has been linked to various material properties, such as the topological order. We elaborate that the opacity of 2D materials to circularly polarized light over a wide range of frequencies, measured in units of the fine structure constant, can be used to extract a spectral function that frequency-integrates to the Chern number, offering a simple optical experiment to measure it. This method is subsequently generalized to finite temperature and locally on every lattice site by a linear response theory, which helps to extract the Chern marker that maps the Chern number to lattice sites. The long range response in our theory corresponds to a Chern correlator that acts like the internal fluctuation of the Chern marker, and is found to be enhanced in the topologically nontrivial phase. Finally, from the Fourier transform of the valence band Berry curvature, a nonlocal Chern marker is further introduced, whose decay length diverges at topological phase transitions and therefore serves as a faithful indicator of the transitions, and moreover can be interpreted as a Wannier state correlation function. The concepts discussed in this work explore multi-faceted aspects of topology and should help address the impact of system inhomogeneities.

  12 citations

• An effective field theory of magneto-elasticity

  Shashin Pavaskar, Riccardo Penco, Ira Z. Rothstein

  SciPost Phys. 12, 155 (2022) · published 11 May 2022 | Toggle abstract · pdf

  We utilize the coset construction to derive the effective field theory of magnon-phonon interactions in (anti)-ferromagnetic and ferrimagnetic insulating materials. The action is used to calculate the equations of motion which generalize the Landau-Lifshitz and stress equations to allow for magneto-acoustic couplings to all orders in the fields at lowest order in the derivative expansion. We also include the symmetry breaking effects due to Zeeman, and Dzyaloshinsky-Moriya interactions. This effective theory is a toolbox for the study of magneto-elastic phenomena from first principles. As an example we use this theory to calculate the leading order contribution to the magnon decay width due to its the decay into phonons.

  12 citations

• Laughable borders: Making the case for the humorous in migration studies

  Anja K. Franck

  Mig. Pol. 1, 004 (2022) · published 14 June 2022 | Toggle abstract · pdf

  Humor is widely recognized as a fundamental aspect of the human experience, that has also played a vital role in the way marginalized groups comment on and mock power. Yet, in migration research the methodological and analytical value of humor has been largely overlooked. Rather, migration studies has commonly centered its analysis around suffering and tragedy and, in the process, depicted migrant trajectories as endeavors largely devoid of laughter, humor, irony and play. This article suggests that such humorless representations of the migration process – and indeed of the migrant subject itself – has broader implications for the types of knowledge that we (re)produce around migrants’ experiences, subjectivities and struggles. In fact, it argues that migration studies’ failure to recognize migrants as humorous individuals risks feeding into processes of exceptionalization and de-humanization through setting “the migrant” up as an obscure figure that lacks “essentially human” qualities. In order to make the case for the humorous in migration research, the article illustrates how refugees arriving to the Greek island of Lesvos in the early summer of 2015 laughed at their own predicament as well as the technologies put in place to control their freedom of movement and how their laughter, humor and comic displays did important political work in refusing subjugation, in speaking truth to power and in capturing the absurdity of the violence that they faced.

  12 citations

• From "weak" to "strong" hole confinement in a Mott insulator

  Krzysztof Bieniasz, Piotr Wrzosek, Andrzej M. Oles, Krzysztof Wohlfeld

  SciPost Phys. 7, 066 (2019) · published 27 November 2019 | Toggle abstract · pdf

  We study the problem of a single hole in an Ising antiferromagnet and, using the magnon expansion and analytical methods, determine the expansion coefficients of its wave function in the magnon basis. In the 1D case, the hole is "weakly" confined in a potential well and the magnon coefficients decay exponentially in the absence of a string potential. This behavior is in sharp contrast to the 2D square plane where the hole is "strongly" confined by a string potential and the magnon coefficients decay superexponentially. The latter is identified here to be a fingerprint of the strings in doped antiferromagnets that can be recognized in the numerical or cold atom simulations of the 2D doped Hubbard model. Finally, we attribute the differences between the 1D and 2D cases to the magnon-magnon interactions being crucially important in a 1D spin system.

  12 citations

• 3d N=4 Bootstrap and Mirror Symmetry

  Chi-Ming Chang, Martin Fluder, Ying-Hsuan Lin, Shu-Heng Shao, Yifan Wang

  SciPost Phys. 10, 097 (2021) · published 30 April 2021 | Toggle abstract · pdf

  We investigate the non-BPS realm of 3d ${\cal N} = 4$ superconformal field theory by uniting the non-perturbative methods of the conformal bootstrap and supersymmetric localization, and utilizing special features of 3d ${\cal N} = 4$ theories such as mirror symmetry and a protected sector described by topological quantum mechanics (TQM). Supersymmetric localization allows for the exact determination of the conformal and flavor central charges, and the latter can be fed into the mini-bootstrap of the TQM to solve for a subset of the OPE data. We examine the implications of the $\mathbb{Z}_2$ mirror action for the SCFT single- and mixed-branch crossing equations for the moment map operators, and apply numerical bootstrap to obtain universal constraints on OPE data for given flavor symmetry groups. A key ingredient in applying the bootstrap analysis is the determination of the mixed-branch superconformal blocks. Among other results, we show that the simplest known self-mirror theory with $SU(2) \times SU(2)$ flavor symmetry saturates our bootstrap bounds, which allows us to extract the non-BPS data and examine the self-mirror $\mathbb{Z}_2$ symmetry thereof.

  12 citations

• AdS black holes with a bouncing interior

  Sean A. Hartnoll, Navonil Neogi

  SciPost Phys. 14, 074 (2023) · published 18 April 2023 | Toggle abstract · pdf

  We construct planar black hole solutions of AdS gravity minimally coupled to a scalar field with an even, super-exponential potential. We show that the evolution of the black hole interior exhibits an infinite sequence of Kasner epochs, as the scalar field rolls back and forth in its potential. We obtain an analytic expression for the 'bounces' between each Kasner epoch and also give an explicit formula for the times and strengths of the bounces at late interior times, thereby fully characterizing the interior evolution. In this way we show that the interior geometry approaches the Schwarzschild singularity at late times, even as the scalar field is driven higher up its potential with each bounce.

  12 citations

• Stroboscopic aliasing in long-range interacting quantum systems

  Shane P. Kelly, Eddy Timmermans, Jamir Marino, S.-W. Tsai

  SciPost Phys. Core 4, 021 (2021) · published 10 September 2021 | Toggle abstract · pdf

  We unveil a mechanism for generating oscillations with arbitrary multiplets of the period of a given external drive, in long-range interacting quantum many-particle spin systems. These oscillations break discrete time translation symmetry as in time crystals, but they are understood via two intertwined stroboscopic effects similar to the aliasing resulting from video taping a single fast rotating helicopter blade. The first effect is similar to a single blade appearing as multiple blades due to a frame rate that is in resonance with the frequency of the helicopter blades' rotation; the second is akin to the optical appearance of the helicopter blades moving in reverse direction. Analogously to other dynamically stabilized states in interacting quantum many-body systems, this stroboscopic aliasing is robust to detuning and excursions from a chosen set of driving parameters, and it offers a novel route for engineering dynamical $n$-tuplets in long-range quantum simulators, with potential applications to spin squeezing generation and entangled state preparation.

  11 citations

• Nonlinear response in diffusive systems

  Luca V. Delacrétaz, Ruchira Mishra

  SciPost Phys. 16, 047 (2024) · published 12 February 2024 | Toggle abstract · pdf

  Nonintegrable systems thermalize, leading to the emergence of fluctuating hydrodynamics. Typically, this hydrodynamics is diffusive. We use the effective field theory (EFT) of diffusion to compute higher-point functions of conserved densities. We uncover a simple scaling behavior of correlators at late times, and, focusing on three and four-point functions, derive the asymptotically exact universal scaling functions that characterize nonlinear response in diffusive systems. This allows for precision tests of thermalization beyond linear response in quantum and classical many-body systems. We confirm our predictions in a classical lattice gas.

  11 citations

• Chiral $p$-wave superconductivity in twisted bilayer graphene from dynamical mean field theory

  B. Pahlevanzadeh, P. Sahebsara, David Sénéchal

  SciPost Phys. 11, 017 (2021) · published 21 July 2021 | Toggle abstract · pdf

  We apply cluster dynamical mean field theory with an exact-diagonalization impurity solver to a Hubbard model for magic-angle twisted bilayer graphene, built on the tight-binding model proposed by Kang and Vafek (2018), which applies to the magic angle $1.30^\circ$. We find that triplet superconductivity with $p+ip$ symmetry is stabilized by CDMFT, as well as a subdominant singlet $d+id$ state. A minimum of the order parameter exists close to quarter-filling and three-quarter filling, as observed in experiments.

  11 citations

• Light dark matter annihilation and scattering in LHC detectors

  Martin Bauer, Patrick Foldenauer, Peter Reimitz, Tilman Plehn

  SciPost Phys. 10, 030 (2021) · published 5 February 2021 | Toggle abstract · pdf

  We systematically study models with light scalar and pseudoscalar dark matter candidates and their potential signals at the LHC. First, we derive cosmological bounds on models with the Standard Model Higgs mediator and with a new weak-scale mediator. Next, we study two processes inspired by the indirect and direct detection process topologies, now happening inside the LHC detectors. We find that LHC can observe very light dark matter over a huge mass range if it is produced in mediator decays and then scatters with the detector material to generate jets in the nuclear recoil.

  11 citations