More Like this

1. Twisted-bilayer FeSe and the Fe-based superlattices

   https://doi.org/10.21468/SciPostPhys.15.3.081  

   Eugenio, Paul Myles ; Vafek, Oskar ( January 2023 , SciPost Physics)

   We derive BM-like continuum models for the bands of superlattice heterostructures formed out of Fe-chalcogenide monolayers: (I) a single monolayer experiencing an external periodic potential, and (II) twisted bilayers with long-range moire tunneling. A symmetry derivation for the inter-layer moire tunnelling is provided for both the\Gamma$\Gamma$andM$M$high-symmetry points. In this paper, we focus on moire bands formed from hole-band maxima centered on\Gamma$\Gamma$, and show the possibility of moire bands withC=0$C=0$or±1$\pm 1$topological quantum numbers without breaking time-reversal symmetry. In theC=0$C=0$region for\theta→0$\theta \to 0$(and similarly in the limit of large superlattice period for I), the system becomes a square lattice of 2D harmonic oscillators. We fit our model to FeSe and argue that it is a viable platform for the simulation of the square Hubbard model with tunable interaction strength.

    

   more » « less
2. Melting of charge order in the low-temperature state of an electronic ferroelectric-like system

   https://doi.org/10.1038/s41535-020-0217-5  

   Hassan, Nora M. ; Thirunavukkuarasu, Komalavalli ; Lu, Zhengguang ; Smirnov, Dmitry ; Zhilyaeva, Elena I. ; Torunova, Svetlana ; Lyubovskaya, Rimma N. ; Drichko, Natalia ( March 2020 , npj Quantum Materials)

   Strong electronic interactions can drive a system into a state with a symmetry breaking. Lattice frustration or competing interactions tend to prevent symmetry breaking, leading to quantum disordered phases. In spin systems frustration can produce a spin liquid state. Frustration of a charge degree of freedom also can result in various exotic states, however, experimental data on these effects is scarce. In this work we demonstrate how in a Mott insulator on a weakly anisotropic triangular lattice a charge ordered state melts on cooling down to low temperatures. Raman scattering spectroscopy finds that$$\kappa$$$\kappa$-(BEDT-TTF)$${}_{2}$$${}_2$Hg(SCN)$${}_{2}$$${}_2$Cl enters an insulating “dipole solid” state at$$T=30\,{\mathrm{K}}$$$T=30K$, but below$$T=15\,{\mathrm{K}}$$$T=15K$the order melts, while preserving the insulating energy gap. Based on these observations, we suggest a phase diagram relevant to other quantum paraelectric materials.

    

   more » « less
3. Field Theory of Interacting Boundary Gravitons

   https://doi.org/10.21468/SciPostPhys.13.2.038  

   Ebert, Stephen ; Hijano, Eliot ; Kraus, Per ; Monten, Ruben ; Myers, Richard M. ( January 2022 , SciPost Physics)

   Pure three-dimensional gravity is a renormalizable theory with twofree parameters labelled byG$G$and\Lambda$\Lambda$.As a consequence, correlation functions of the boundary stress tensor inAdS_3${}_3$are uniquely fixed in terms of one dimensionless parameter, which is thecentral charge of the Virasoro algebra. The same argument implies thatAdS_3${}_3$gravity at a finite radial cutoff is a renormalizable theory, but nowwith one additional parameter corresponding to the cutoff location. Thistheory is conjecturally dual to aT\overline{T}$T\overline{T}$-deformedCFT, assuming that such theories actually exist. To elucidate this, westudy the quantum theory of boundary gravitons living on a cutoff planarboundary and the associated correlation functions of the boundary stresstensor. We compute stress tensor correlation functions to two-loop order(G$G$being the loop counting parameter), extending existing tree levelresults. This is made feasible by the fact that the boundary gravitonaction simplifies greatly upon making a judicious field redefinition,turning into the Nambu-Goto action. After imposing Lorentz invariance,the correlators at this order are found to be unambiguous up to a singleundetermined renormalization parameter.

    

   more » « less
4. QLBT: a linear Boltzmann transport model for heavy quarks in a quark-gluon plasma of quasi-particles

   https://doi.org/10.1140/epjc/s10052-022-10308-x  

   Liu, Feng-Lei ; Xing, Wen-Jing ; Wu, Xiang-Yu ; Qin, Guang-You ; Cao, Shanshan ; Wang, Xin-Nian ( April 2022 , The European Physical Journal C)

   We develop a new heavy quark transport model, QLBT, to simulate the dynamical propagation of heavy quarks inside the quark-gluon plasma (QGP) created in relativistic heavy-ion collisions. Our QLBT model is based on the linear Boltzmann transport (LBT) model with the ideal QGP replaced by a collection of quasi-particles to account for the non-perturbative interactions among quarks and gluons of the hot QGP. The thermal masses of quasi-particles are fitted to the equation of state from lattice QCD simulations using the Bayesian statistical analysis method. Combining QLBT with our advanced hybrid fragmentation-coalescence hadronization approach, we calculate the nuclear modification factor$$R_\mathrm {AA}$$$R_{\mathrm{AA}}$and the elliptic flow$$v_2$$$v_2$ofDmesons at the Relativistic Heavy-Ion Collider and the Large Hadron Collider. By comparing our QLBT calculation to the experimental data on theDmeson$$R_\mathrm {AA}$$$R_{\mathrm{AA}}$and$$v_2$$$v_2$, we extract the heavy quark transport parameter$$\hat{q}$$$\hat{q}$and diffusion coefficient$$D_\mathrm {s}$$$D_s$in the temperature range of$$1-4~T_\mathrm {c}$$$1-4T_c$, and compare them with the lattice QCD results and other phenomenological studies.

    

   more » « less
5. Spin-resolved topology and partial axion angles in three-dimensional insulators

   https://doi.org/10.1038/s41467-024-44762-w  

   Lin, Kuan-Sen ; Palumbo, Giandomenico ; Guo, Zhaopeng ; Hwang, Yoonseok ; Blackburn, Jeremy ; Shoemaker, Daniel P. ; Mahmood, Fahad ; Wang, Zhijun ; Fiete, Gregory A. ; Wieder, Benjamin J. ; et al ( January 2024 , Nature Communications)

   Symmetry-protected topological crystalline insulators (TCIs) have primarily been characterized by their gapless boundary states. However, in time-reversal- ($${{{{{{{\mathcal{T}}}}}}}}$$$T$-) invariant (helical) 3D TCIs—termed higher-order TCIs (HOTIs)—the boundary signatures can manifest as a sample-dependent network of 1D hinge states. We here introduce nested spin-resolved Wilson loops and layer constructions as tools to characterize the intrinsic bulk topological properties of spinful 3D insulators. We discover that helical HOTIs realize one of three spin-resolved phases with distinct responses that are quantitatively robust to large deformations of the bulk spin-orbital texture: 3D quantum spin Hall insulators (QSHIs), “spin-Weyl” semimetals, and$${{{{{{{\mathcal{T}}}}}}}}$$$T$-doubled axion insulator (T-DAXI) states with nontrivial partial axion angles indicative of a 3D spin-magnetoelectric bulk response and half-quantized 2D TI surface states originating from a partial parity anomaly. Using ab-initio calculations, we demonstrate thatβ-MoTe₂realizes a spin-Weyl state and thatα-BiBr hosts both 3D QSHI and T-DAXI regimes.

    

   more » « less