15 research outputs found
Understanding the entanglement entropy and spectra of 2D quantum systems through arrays of coupled 1D chains
We describe an algorithm for studying the entanglement entropy and spectrum
of 2D systems, as a coupled array of one dimensional chains in their
continuum limit. Using the algorithm to study the quantum Ising model in 2D,
(both in its disordered phase and near criticality) we confirm the existence of
an area law for the entanglement entropy and show that near criticality there
is an additive piece scaling as with .
\textcolor{black}{Studying the entanglement spectrum, we show that entanglement
gap scaling can be used to detect the critical point of the 2D model. When
short range (area law) entanglement dominates we find (numerically and
perturbatively) that this spectrum reflects the energy spectrum of a single
quantum Ising chain.Comment: 8 pages (4 + supplementary material). 10 figure
Magnetic Response in the Underdoped Cuprates
We examine the dynamical magnetic response of the underdoped cuprates by
employing a phenomenological theory of a doped resonant valence bond state
where the Fermi surface is truncated into four pockets. This theory predicts a
resonant spin response which with increasing energy (0 to 100meV) appears as an
hourglass. The very low energy spin response is found at (pi,pi +- delta) and
(pi +- delta,pi) and is determined by scattering from the pockets' frontside to
the tips of opposite pockets where a van Hove singularity resides. At energies
beyond 100 meV, strong scattering is seen from (pi,0) to (pi,pi). This theory
thus provides a semi-quantitative description of the spin response seen in both
INS and RIXS experiments at all relevant energy scales
Quantum quenches in two spatial dimensions using chain array matrix product states
We describe a method for simulating the real time evolution of extended quantum systems in two dimensions (2D). The method combines the benefits of integrability and matrix product states in one dimension to avoid several issues that hinder other applications of tensor based methods in 2D. In particular, it can be extended to infinitely long cylinders. As an example application we present results for quantum quenches in the 2D quantum [(2+1)-dimensional] Ising model. In quenches that cross a phase boundary we find that the return probability shows nonanalyticities in time
Itinerant effects and enhanced magnetic interactions in Bi-based multilayer cuprates
The cuprate high temperature superconductors exhibit a pronounced trend in which the superconducting transition temperature Tc increases with the number of CuO2 planes n in the crystal structure. We compare the magnetic excitation spectrum of Bi2+xSr2−xCuO6+δ (Bi-2201) and Bi2Sr2Ca2Cu3O10+δ (Bi-2223), with n = 1 and 3, respectively, using Cu L3-edge resonant inelastic x-ray scattering. Near the antinodal zone boundary we find the paramagnon energy in Bi-2223 is substantially higher than that in Bi-2201, indicating that multilayer cuprates host stronger effective magnetic exchange interactions, providing a possible explanation for the Tc vs n scaling. In contrast, the nodal direction exhibits very strongly damped, almost nondispersive excitations. We argue that this implies that the magnetism in the doped cuprates is partially itinerant in nature
Entanglement in gapless resonating valence bond states
We study resonating-valence-bond (RVB) states on the square lattice of spins
and of dimers, as well as SU(N)-invariant states that interpolate between the
two. These states are ground states of gapless models, although the
SU(2)-invariant spin RVB state is also believed to be a gapped liquid in its
spinful sector. We show that the gapless behavior in spin and dimer RVB states
is qualitatively similar by studying the R\'enyi entropy for splitting a torus
into two cylinders, We compute this exactly for dimers, showing it behaves
similarly to the familiar one-dimensional log term, although not identically.
We extend the exact computation to an effective theory believed to interpolate
among these states. By numerical calculations for the SU(2) RVB state and its
SU(N)-invariant generalizations, we provide further support for this belief. We
also show how the entanglement entropy behaves qualitatively differently for
different values of the R\'enyi index , with large values of proving a
more sensitive probe here, by virtue of exhibiting a striking even/odd effect.Comment: 44 pages, 14 figures, published versio
Finite Temperature Dynamical Structure Factor of Alternating Heisenberg Chains
We develop a low-temperature expansion for the finite temperature dynamical
structure factor of the spin half Heisenberg chain with alternating nearest
neighbour exchange in the limit of strong alternation of the exchange
constants. We determine both the broadening of the low lying triplet lines and
the contribution of the thermally activated intraband scattering.Comment: 11 pages, 4 eps-figure
Laser-induced transient magnons in Sr<sub>3</sub>Ir<sub>2</sub>O<sub>7</sub> throughout the Brillouin zone
Although ultrafast manipulation of magnetism holds great promise for new physical phenomena and applications, targeting specific states is held back by our limited understanding of how magnetic correlations evolve on ultrafast timescales. Using ultrafast resonant inelastic X-ray scattering we demonstrate that femtosecond laser pulses can excite transient magnons at large wavevectors in gapped antiferromagnets and that they persist for several picoseconds, which is opposite to what is observed in nearly gapless magnets. Our work suggests that materials with isotropic magnetic interactions are preferred to achieve rapid manipulation of magnetism
High-Energy Magnetic Excitations in the Cuprate Superconductor Bi2Sr2CaCu2O8+delta: Towards a Unified Description of Its Electronic and Magnetic Degrees of Freedom
We investigate the high-energy magnetic excitation spectrum of the high-
cuprate superconductor BiSrCaCuO (Bi-2212) using Cu
edge resonant inelastic x-ray scattering (RIXS). Broad, dispersive
magnetic excitations are observed, with a zone boundary energy of 300 meV
and a weak dependence on doping. These excitations are strikingly similar to
the bosons proposed to explain the high-energy `kink' observed in
photoemission. A calculation of the spin-response based on the ARPES-derived
electronic structure and YRZ-quasi-particles reproduces the key features of the
observed magnetic dispersions with no adjustable parameters. These results show
that it is possible to reconcile the magnetic and electronic properties of the
cuprates within a unified framework.Comment: To appear in Phys. Rev. Lett. 5 pages, 3 figures, 4 page
supplementary inf