127 research outputs found
Quantum order by disorder in a semiclassical spin ice
We study the S>1 nearest-neighbor Heisenberg model with a ferromagnetic
interaction J and a large non-collinear easy-axis anisotropy D on a
pyrochlore lattice. For a finite D>>|J|, the low-energy physics is described by
a Ising model with second- and third-neighbor exchange interactions.
The extensive degeneracy of the ground state manifold in the infinite
anisotropic limit is lifted by the transverse quantum fluctuations, and a q=0
ordered state is selected via the quantum order by disorder machanism, through
a first-order phase transition at low temperature.Comment: 4 pages, 5 figure
Frequency Evolution of Neutron Peaks Below Tc: Commensurate and Incommensurate Structure in LaSrCuO and YBaCuO
We study the evolution of the neutron cross-section with variable frequency
and fixed below in two different cuprate families. Our
calculations, which predominantly probe the role of d-wave pairing, lead to
generic features, independent of Fermi surface shapes. Among our findings,
reasonably consistent with experiment, are (i) for near the gap
energy , both optimal {LaSrCuO} and slightly underdoped YBCO exhibit
(comparably) incommensurate peaks (ii) peak sharpening below is seen in
{LaSrCuO}, (iii) quite generically, a frequency evolution from incommensurate
to commensurate and then back to incommensurate structure is found with
increasing . Due to their narrow regime of stability,
commensurate peaks in {LaSrCuO} should be extremely difficult to observe.Comment: RevTex 5pages, 4figures; Manuscript rewritten, figures revised, and
direct comparisons with experiments adde
Steady States of Infinite-Size Dissipative Quantum Chains via Imaginary Time Evolution
Directly in the thermodynamic limit, we show how to combine imaginary and
real time evolution of tensor networks to efficiently and accurately find the
nonequilibrium steady states (NESS) of one-dimensional dissipative quantum
lattices governed by the Lindblad master equation. The imaginary time evolution
first bypasses any highly correlated portions of the real-time evolution
trajectory by directly converging to the weakly correlated subspace of the
NESS, after which real time evolution completes the convergence to the NESS
with high accuracy. We demonstrate the power of the method with the dissipative
transverse field quantum Ising chain. We show that a crossover of an order
parameter shown to be smooth in previous finite-size studies remains smooth in
the thermodynamic limit.Comment: 5+3 pages, 5 figures, 2 table
Spin-1/2 J1-J2 Heisenberg antiferromagnet on a square lattice: a plaquette renormalized tensor network study
We apply the plaquette renormalization scheme of tensor network states [Phys.
Rev. E, 83, 056703 (2011)] to study the spin-1/2 frustrated Heisenberg J1-J2
model on a L*L square lattice with L = 8, 16 and 32. By treating tensor
elements as variational parameters, we obtain the ground states for different
J2/J1 values, and investigate the staggered magnetic order parameters, the
nearest-neighbor spin-spin correlations and the plaquette order parameters. In
addition to the well-known N\'eel-order and collinear-order at low and high
J2/J1, we observe a plaquette order at intermediate J2/J1. A continuous
transition between the N\'eel order and the plaquette order near J2 = 0.40J1 is
observed. The collinear order emerges at J2 = 0.62J1 through a first-order
phase transition.Comment: 6 pages, 5 figures total; added one figure; Revised argument in
section 3, results unchanged; added note and reference wherei
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