We identify states favored by Coulomb interactions projected onto the Wannier basis of four narrow bands "magic angle" twisted bilayer graphene. At filling two electrons/holes per moire unit cell, such favor an insulating SU(4) ferromagnet. The kinetic terms select ground state in which valleys with opposite spins are equally mixed, vanishing magnetic moment particle. also find extended excited states, gap to decreases field. An stripe ferromagnetic phase is at one electron/hole cell.

We use the DMRG to study correlated electron states favored by Coulomb interaction projected onto narrow bands of twisted bilayer graphene within a spinless one-valley model. The Hilbert space is constructed from pair hybrid Wannier with opposite Chern numbers. Depending on parameters in BM model, this basis determines ground state at one particle per unit cell be either QAH or no Hall effect which nearly product state. Based form, we then apply variational method their competition, thus...

We develop a two stage renormalization group which connects the continuum Hamiltonian for twisted bilayer graphene at length scales shorter than moire superlattice period to active narrow bands only is valid distances much longer period. In first stage, Coulomb interaction renormalizes Fermi velocity and interlayer tunnelings in such way as suppress ratio of same sublattice opposite sublatice tunneling, hence approaching so-called chiral limit. second tunneling treated non-perturbatively....

Quantum Monte Carlo simulations of so-called ``magic angle'' twisted bilayer graphene reveal three novel insulating phases that may help elucidate the origin unusual electronic behaviors in this material.

Abstract Magic-angle twisted bilayer graphene has recently become a thriving material platform realizing correlated electron phenomena taking place within its topological flat bands. Several numerical and analytical methods have been applied to understand the phases therein, revealing some similarity with quantum Hall physics. In this work, we provide Mott-Hubbard perspective for TBG system. Employing large-scale density matrix renormalization group on lattice model containing projected...

We report an implementation of the momentum space quantum Monte Carlo (QMC) method on interaction model for twisted bilayer graphene (TBG) at integer fillings. The long-range Coulomb repulsion is treated exactly with flat bands, spin and valley degrees freedom electrons taking into account. prove absence minus sign problem QMC simulation fillings when either two or are considered. By realistic parameters twist angle interlayer tunnelings simulation, we benchmark data exact band gap obtained...

Using the method developed in companion paper [O. Vafek and J. Kang, Continuum effective Hamiltonian for graphene bilayers an arbitrary smooth lattice deformation from microscopic theories, Phys. Rev. B 107, 075123 (2023)], we construct continuum theories two different tight-binding models of twisted bilayer at a twist angle $1.{05}^{\ensuremath{\circ}}$, one Slater-Koster based other ab initio Wannier based. The energy spectra obtained theory---either rigid or including relaxation---are...

We provide a systematic real space derivation of the continuum Hamiltonian for graphene bilayer starting from microscopic lattice theory, allowing an arbitrary inhomogeneous smooth deformation, including twist. Two different models are analyzed: first, Slater-Koster like model and second, ab-initio derived model. envision that our effective can be used in conjunction with experimentally determined atomic deformation twisted specific device to predict compare electronic spectra scanning...

Abstract Magnonics or magnon spintronics is an emerging field focusing on generating, detecting, and manipulating magnons. As charge‐neutral quasi‐particles, magnons are promising information carriers because of their low energy dissipation long coherence length. In the past decade, topological phases in magnonics have attracted intensive attention due to fundamental importance condensed‐matter physics potential applications spintronic devices. this review, we mainly focus recent progress...

We study the correlated insulating phases of twisted bilayer graphene (TBG) in absence lattice strain at integer filling $\nu=\pm3$. Using self-consistent Hartree-Fock method on a particle-hole symmetric model and allowing translation symmetry breaking terms, we obtain phase diagram with respect to ratio $AA$ interlayer hopping $(w_0)$ $AB$ $(w_1)$. When is close chiral limit ($w_0/w_1 \lesssim 0.5$), quantum anomalous Hall state Chern number $\nu_c = \pm 1$ can be observed consistent...

We propose an SU(4) spin-valley-fermion model to investigate the superconducting instabilities of twisted bilayer graphene (TBG). In this approach, bosonic fluctuations associated with emergent symmetry, corresponding combined rotations in valley and spin spaces, couple low-energy fermions that comprise flat bands. These are peaked at zero wave-vector, reflecting "ferromagnetic-like" ground state recently found strong-coupling solutions microscopic models for TBG. Focusing on electronic...

Multiband superconductivity, involving resonant pair scattering between different bands, has emerged as a possible explanation of some the main characteristics recently discovered iron pnictides. A key feature such interband pairing mechanism is that it can generate or enhance superconductivity irrespective whether attractive repulsive. The latter case typically leads to superconducting gap switching its sign among sections Fermi surface. In pnictides, natural scenario changes hole and...

The origin of the high-temperature superconducting state observed in FeSe thin films, whose phase diagram displays no sign magnetic order, remains a hotly debated topic. Here we investigate whether fluctuations arising due to proximity nematic phase, which is this material, can promote superconductivity. We find that alone highly degenerate pairing state, both s-wave and d-wave symmetries are equally favored, T_{c} consequently suppressed. However, presence sizable spin-orbit coupling or...

In most magnetically-ordered iron pnictides, the magnetic moments lie in FeAs planes, parallel to modulation direction of spin stripes. However, recent experiments hole-doped pnictides have observed a reorientation from in-plane out-of-plane. Interestingly, this is accompanied by change ground state stripe antiferromagnet tetragonal nonuniform configuration. Motivated these observations, here we investigate origin anisotropy using an itinerant microscopic electronic model that respects all...

Bulk FeSe is a special iron-based material in which superconductivity emerges inside well-developed nematic phase. We present microscopic model for this superconducting state, takes into account the mixing between $s-$wave and $d-$wave pairing channels changes orbital spectral weight promoted by sign-changing order parameter. show that nematicity gives rise to $\cos2\theta$ variation of gap on hole pocket agrees with ARPES STM data experimentally-extracted Fermi surface parameters. further...

We present a microscopic calculation of the phase diagram Ising superconductor ${\mathrm{NbSe}}_{2}$ in presence both in-plane magnetic field and Rashba spin-orbit coupling (SOC). Repulsive interactions lead to two distinct instabilities, singlet triplet interaction channels. While we recover previously predicted nodal topological superconducting state absence SOC at large with six pairs nodes along $\mathrm{\ensuremath{\Gamma}}\text{\ensuremath{-}}M$ lines, finite breaks symmetry that...

We review analytical and numerical studies of correlated insulating states in twisted bilayer graphene, focusing on real-space lattice models constructions their unbiased quantum many-body solutions. show that by constructing localized Wannier for the narrow bands, projected Coulomb interactions can be approximated cluster charges with assisted nearest neighbor hopping terms. With interaction part only, Hamiltonian is SU (4) symmetric considering both spin valley degrees freedom. In strong...

Using polarized and unpolarized neutron scattering we show that interstitial Fe in superconducting Fe_{1+y}Te_{1-x}Se_x induces a magnetic Friedel-like oscillation diffracts at Q_(in-plane)=(1/2,0) involves >50 neighboring sites. The >2 mu_B moment is surrounded by compensating ferromagnetic four spin clusters may seed double stripe ordering Fe_{1+y}Te. A semi-metallic 5-band model with (1/2,1/2) Fermi surface nesting fold symmetric super-exchange between two in-plane nearest neighbors...

Most iron-based superconductors undergo a transition to magnetically ordered state characterized by staggered stripes of parallel spins. With ordering vectors $(\pi,0)$ or $(0,\pi)$, this magnetic breaks the high-temperature tetragonal symmetry system, which is manifested splitting lattice Bragg peaks. Remarkably, recent experiments in hole-doped iron arsenides reported an that displays peaks at and $(0,\pi)$ but remains tetragonal. Despite being inconsistent with stripe configuration,...

Abstract The superconducting gap structure in iron-based high-temperature superconductors (Fe-HTSs) is non-universal. In contrast to other unconventional superconductors, the Fe-HTSs both d -wave and extended s pairing symmetries are close energy. Probing proximity between these very different states identifying experimental parameters that can tune them of central interest. Here we report high-pressure muon spin rotation experiments on temperature-dependent magnetic penetration depth...

We revisit the localized Wannier state description of twisted bilayer graphene, focusing on chiral limit. provide a simple method for constructing such 2D exponentially -- yet valley polarized states, centered sites honeycomb lattice, paying particular attention to maintaining all unobstructed symmetries. This includes unitary particle-hole symmetry, and combination $C_2\mathcal{T}$ symmetry. The symmetry alone remains topologically obstructed is not represented in site-to-site fashion. also...

We theoretically study the topological properties of magnons and relevant magnon thermal Hall effect in trimerized Lieb lattice ferromagnets presence next-nearest-neighbor Dzyaloshinskii-Moriya interactions. By calculating band structures their Chern numbers with linear spin-wave theory, we show that system can undergo a phase transition between magnonic insulator trivial phase. The main results are presented form diagrams, where or conductivity shown as function two trimerization...

In the limit of perfect nesting, physics iron pnictides is governed by density wave formation at zone-edge vector $\mathbf{M}$. At high energies, various spin- (SDW), charge-, and orbital/pocket- (PDW) waves, their linear combinations, all appear equally likely, unified within unitary order parameter $\mathrm{U}(4)\ifmmode\times\else\texttimes\fi{}\mathrm{U}(4)$ symmetry. Nesting imperfections low-energy interactions reduce this symmetry to that real materials. Nevertheless, generic ground...