We use a combination of three computational methods to investigate the notoriously difficult frustrated three-dimensional pyrochlore $S=\frac{1}{2}$ quantum antiferromagnet, at finite temperature $T$: canonical typicality for cluster $2\ifmmode\times\else\texttimes\fi{}2\ifmmode\times\else\texttimes\fi{}2$ unit cells (i.e., 32 sites), finite-$T$ matrix product state method on larger with 48 sites, and numerical linked expansion (NLCE) using clusters up 25 lattice including nontrivial...

We address the ground-state properties of long-standing and much-studied three-dimensional quantum spin liquid candidate, $S=\frac{1}{2}$ pyrochlore Heisenberg antiferromagnet. By using SU(2) density-matrix renormalization group (DMRG), we are able to access cluster sizes up 128 spins. Our most striking finding is a robust spontaneous inversion symmetry breaking, reflected in an energy density difference between two sublattices tetrahedra, familiar as starting point earlier perturbative...

In crystalline solids, the interactions of charge and spin can result in a variety emergent quantum ground states, especially partially filled, topological flat bands such as Landau levels or “magic angle” graphene layers. Much less explored is rhombohedral graphite (RG), perhaps simplest structurally most perfect condensed matter system to host band protected by symmetry. By scanning tunneling microscopy, we map density 8, 10, 14, 17 layers identify domain structure emerging from...

We calculate the phase, temperature and junction length dependence of supercurrent for ballistic graphene Josephson-junctions. For low temperatures we find non-sinusoidal on superconductor phase difference both short long junctions. The skewness, which characterizes deviation current-phase relation from a simple sinusoidal one, shows linear critical current small currents. discuss similarities differences with respect to classical theory Josephson junctions, where weak link is formed by...

We investigate the low-lying excitation spectrum and ground-state properties of narrow graphene nanoribbons with zigzag edge configurations. Nanoribbons comparable widths have been synthesized very recently [P. Ruffieux et al., Nature (London) 531, 489 (2016)], their descriptions require more sophisticated methods since in this regime conventional methods, like mean-field or density-functional theory local-density approximation, fail to capture enhanced quantum fluctuations. Using unbiased...

We consider sudden quenches across quantum phase transitions in the $S=1$ $XXZ$ model starting from Haldane phase. demonstrate that dynamical may occur during these are identified by nonanalyticities rate function for return probability. In addition, we show temporal behavior of string order parameter is intimately related to subsequent transitions. furthermore find can be accompanied enhanced two-site entanglement.

We investigate the ground-state properties of nearest-neighbor $S=1$ pyrochlore Heisenberg antiferromagnet using two complementary numerical methods, density-matrix renormalization group (DMRG) and pseudofermion functional (PFFRG). Within DMRG, we are able to reliably study clusters with up 48 spins by keeping 20 000 SU(2) states. The investigated 32-site 48-site both show indications a robust ${C}_{3}$ rotation symmetry breaking spin correlations cluster additionally features inversion...

We investigate the local electronic structure of a Sinai-like, quadrilateral graphene quantum billiard with zigzag and armchair edges using scanning tunneling microscopy (STM) at room temperature. It is revealed that besides $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R{30}^{\ensuremath{\circ}}$ superstructure, which caused by intervalley scattering, its overtones also appear in STM measurements, are attributed to Umklapp processes. point out these results can be well understood...

We investigate the ground state of a $p\text{-wave}$ Kondo-Heisenberg model introduced by Alexandrov and Coleman with an Ising-type anisotropy in Kondo interaction correlated conduction electrons. Our aim is to understand how they affect stability Haldane obtained SU(2)-symmetric case without Hubbard interaction. By applying density-matrix renormalization group algorithm calculating entanglement entropy we show that anisotropic phase transition occurs N\'eel emerges above critical value...

We investigate an extended version of the periodic Anderson model (the so-called Anderson-Hubbard model) with aim to understand role interaction between conduction electrons in formation heavy-fermion and mixed-valence states. Two methods are used: (i) variational calculation Gutzwiller wave function optimizing numerically ground-state energy (ii) exact diagonalization Hamiltonian for short chains. The $f$-level occupancy renormalization factor quasiparticles calculated as a $f$ orbital wide...

We investigate the behavior of periodic Anderson model in presence $d$--$f$ Coulomb interaction (${U}_{df}$) using mean-field theory, variational calculation, and exact diagonalization finite chains. The approach based on Gutzwiller trial wave function gives a critical value ${U}_{df}$ two quantum points (QCPs), where valence susceptibility diverges. derive exponent for how position QCP depends other parameters Hamiltonian. For larger values ${U}_{df}$, Kondo regime is bounded by first-order...

We study the ground-state properties of an extended periodic Anderson model to understand role Hund's coupling between localized and itinerant electrons using density-matrix renormalization group algorithm. By calculating von Neumann entropies we show that two phase transitions occur new phases appear as hybridization is increased in symmetric half-filled case due competition Kondo effect coupling. In intermediate phase, which bounded by critical points, found a dimerized ground state, while...

We investigate the effect of Coulomb interaction, ${U}_{cf}$, between conduction and $f$ electrons in periodic Anderson model using density matrix renormalization group algorithm. calculate excitation spectrum half-filled symmetric with an emphasis on spin charge excitations. In one-dimensional version model, it is found that gap smaller than below a certain value ${U}_{cf}$ reversed inequality valid for stronger ${U}_{cf}$. This behavior also verified by correlation functions. perform...

We studied the energy levels of graphene-based Andreev billiards consisting a superconductor region on top monolayer graphene sheet. For case retroreflection we show that billiard can be mapped to normal-metal-superconducting with same geometry. also derived semiclassical quantization rule in billiards. The exact and semiclassically obtained spectrum agree very well both for specular reflection.

We study the nonequilibrium dynamics of a one-dimensional topological Kondo insulator, modelled by $p$-wave Anderson lattice model, following quantum quench on-site interaction strength. Our goal is to examine how influences properties system, and therefore our main focus time evolution string order parameter, entanglement spectrum, topologically protected edge states. point out that postquench local observables can be well captured thermal ensemble up certain results demonstrate after are...

Molybdenum disulfide nanoribbons with zigzag edges show ferromagnetic and metallic properties based on previous \emph{ab-initio} calculations. The investigation of the role disorder magnetic is, however, still lacking due to computational costs these methods. In this work we fill gap by studying electronic several nanometer long MoS$_2$ using tight-binding Hubbard Hamiltonians. Our results reveal that proper parameters for edge atoms are crucial obtain quantitatively states nanoribbons. With...

We investigate the ground-state properties of triangular graphene nanoflakes with zigzag edge configurations. The description zero-dimensional nanostructures requires accurate many-body techniques since widely used density-functional theory local density approximation or Hartree-Fock methods cannot handle strong quantum fluctuations. Applying unbiased density-matrix renormalization group algorithm we calculate magnetization and entanglement patterns high accuracy for different interaction...

We investigate an extended version of the periodic Anderson model where interaction is switched on between doubly occupied d-and f -sites.We perform variational calculations using Gutzwiller trial wave function.We calculate -level occupancy as a function energy with different strengths.It shown that region valence transition sharpened due to new interaction.

We add a Heisenberg interaction term $\ensuremath{\propto}\ensuremath{\lambda}$ in the one-dimensional $\text{SU}(2)\ensuremath{\bigotimes}\mathit{\text{XY}}$ spin-orbital model introduced by Kumar. At $\ensuremath{\lambda}=0$ spin and orbital degrees of freedom can be separated unitary transformation leading to an exact solution model. show that finite $\ensuremath{\lambda}>0$ leads spontaneous dimerization system which thermodynamic limit becomes smooth phase transition at...

We study the $S=\frac{1}{2}$ pyrochlore Heisenberg antiferromagnet in a magnetic field. Using large-scale density-matrix renormalization group calculations for clusters with up to 128 spins, we find indications of finite triplet gap, causing threshold field nonzero magnetization curve. obtain robust saturation consistent magnon crystal, although corresponding $5/6$ plateau is very slim and possibly unstable. Most remarkably, there pronounced apparently $1/2$ where ground state breaks...

Graphene nanoribbons (GNRs) have been proposed as potential building blocks for field effect transistor (FET) devices due to their quantum confinement bandgap. Here, we propose a novel GNR device concept, enabling the control of both charge and spin signals, integrated within simplest three-terminal configuration. In conventional FET device, gate electrode is employed tune Fermi level system in out static By contrast, switching mechanism here, applied voltage can dynamically open close an...

We study the phase diagram of antiferromagnetic $J_1$-$J_2$ Heisenberg model on pyrochlore lattice with $S=1$ spins at zero and finite temperatures. use a combination complementary state-of-the-art quantum many-body approaches such as density matrix renormalization group (DMRG), density-matrix purification pseudo-Majorana functional (PMFRG). present an efficient approach to preserve applicability PMFRG for spin-1 systems temperatures despite inevitable presence unphysical spin states. The...

We investigate an extended version of the periodic Anderson model where interaction is switched on between doubly occupied d- and f-sites. perform variational calculations using Gutzwiller trial wave function. calculate f-level occupancy as a function energy with different strengths. It shown that region valence transition sharpened due to new interaction.