3,160 research outputs found
Macroscopic Quantum Tunneling Effect of Z2 Topological Order
In this paper, macroscopic quantum tunneling (MQT) effect of Z2 topological
order in the Wen-Plaquette model is studied. This kind of MQT is characterized
by quantum tunneling processes of different virtual quasi-particles moving
around a torus. By a high-order degenerate perturbation approach, the effective
pseudo-spin models of the degenerate ground states are obtained. From these
models, we get the energy splitting of the ground states, of which the results
are consistent with those from exact diagonalization methodComment: 25 pages, 14 figures, 4 table
Spin-charge Separation in Nodal Antiferromagnetic Insulator
In this paper, by using two dimensional (2D) Hubbard models with pi-flux
phase and that on a hexagonal lattice as examples, we explore
spin-charge-separated solitons in nodal antiferromagnetic (AF) insulator - an
AF order with massive Dirac fermionic excitations (see detail in the paper). We
calculate fermion zero modes and induced quantum numbers on solitons (half
skyrmions) in the continuum limit, which are similar to that in the quasi
one-dimensional conductor polyacetylene (CH)x and that in topological band
insulator. In particular, we find some novel phenomena : thanks to an induced
staggered spin moment, a mobile half skyrmion becomes a fermionic particle;
when a hole or an electron is added, the half skyrmion turns into a bosonic
particle with charge degree of freedom only. Our results imply that nontrivial
induced quantum number on solitons may be a universal feature of spin-charge
separation in different systems
Anomalous Spin Dynamics of Hubbard Model on Honeycomb Lattices
In this paper, the honeycomb Hubbard model in optical lattices is
investigated using O(3) non-linear sigma model. A possible quantum non-magnetic
insulator in a narrow parameter region is found near the metal-insulator
transition. We study the corresponding dynamics of magnetic properties, and
find that the narrow region could be widened by hole doping.Comment: 9 pages, 12 figure
Influence of chemical and magnetic interface properties of Co-Fe-B / MgO / Co-Fe-B tunnel junctions on the annealing temperature dependence of the magnetoresistance
The knowledge of chemical and magnetic conditions at the Co40Fe40B20 / MgO
interface is important to interpret the strong annealing temperature dependence
of tunnel magnetoresistance of Co-Fe-B / MgO / Co-Fe-B magnetic tunnel
junctions, which increases with annealing temperature from 20% after annealing
at 200C up to a maximum value of 112% after annealing at 350C. While the well
defined nearest neighbor ordering indicating crystallinity of the MgO barrier
does not change by the annealing, a small amount of interfacial Fe-O at the
lower Co-Fe-B / MgO interface is found in the as grown samples, which is
completely reduced after annealing at 275C. This is accompanied by a
simultaneous increase of the Fe magnetic moment and the tunnel
magnetoresistance. However, the TMR of the MgO based junctions increases
further for higher annealing temperature which can not be caused by Fe-O
reduction. The occurrence of an x-ray absorption near-edge structure above the
Fe and Co L-edges after annealing at 350C indicates the recrystallization of
the Co-Fe-B electrode. This is prerequisite for coherent tunneling and has been
suggested to be responsible for the further increase of the TMR above 275C.
Simultaneously, the B concentration in the Co-Fe-B decreases with increasing
annealing temperature, at least some of the B diffuses towards or into the MgO
barrier and forms a B2O3 oxide
Translation-symmetry protected topological orders on lattice
In this paper we systematically study a simple class of translation-symmetry
protected topological orders in quantum spin systems using slave-particle
approach. The spin systems on square lattice are translation invariant, but may
break any other symmetries. We consider topologically ordered ground states
that do not spontaneously break any symmetry. Those states can be described by
Z2A or Z2B projective symmetry group. We find that the Z2A translation
symmetric topological orders can still be divided into 16 sub-classes
corresponding to 16 new translation-symmetry protected topological orders. We
introduced four topological indices at , , , to characterize those 16 new
topological orders. We calculated the topological degeneracies and crystal
momenta for those 16 topological phases on even-by-even, even-by-odd,
odd-by-even, and odd-by-odd lattices, which allows us to physically measure
such topological orders. We predict the appearance of gapless fermionic
excitations at the quantum phase transitions between those symmetry protected
topological orders. Our result can be generalized to any dimensions. We find
256 translation-symmetry protected Z2A topological orders for a system on 3D
lattice
Realization of Topological Quantum Computation with surface codes
In this paper, the degenerate ground states of Z2 topological order on a
plane with holes (the so-called surface codes) are used as the protected code
subspace to build a topological quantum computer by tuning their quantum
tunneling effect. Using a designer Hamiltonian - the Kitaev toric-code model as
an example, we study quantum tunneling effects of the surface codes and obtain
its effective theory. Finally, we show how to do topological quantum
computation including the initialization, the unitary transformation and the
measurement
Quench dynamics of topological quantum phase transition in Wen-plaquette model
We study the quench dynamics of the topological quantum phase transition in
the two-dimensional transverse Wen-plaquette model, which has a phase
transition from a Z2 topologically ordered to a spin-polarized state. By
mapping the Wen-plaquette model onto a one-dimensional quantum Ising model, we
calculate the expectation value of the plaquette operator Fi during a slowly
quenching process from a topologically ordered state. A logarithmic scaling law
of quench dynamics near the quantum phase transition is found, which is
analogous to the well-known static critical behavior of the specific heat in
the one-dimensional quantum Ising model.Comment: 8 pages, 5 figures,add new conten
Explaining the forgetting bias effect on value judgments: the influence of memory for a past test
People often feel that information that was forgotten is less important than remembered information. Prior work has shown that participants assign higher importance to remembered information while undervaluing forgotten information. The current study examined two possible accounts of this finding. In three experiments, participants studied lists of words in which each word was randomly assigned a point value denoting the value of remembering the word. Following the presentation of each list participants engaged in a free recall test. After the presentation of all lists participants were shown each of the words they had studied and asked to recall the point value that was initially paired with each word. Experiment 1 tested a fluency-based account by presenting items for value judgments in a low-fluency or high-fluency format. Experiment 2 examined whether value judgments reflect attributions based on the familiarity of an item when value judgments are made. Finally, in Experiment 3, we evaluated whether participants believe that forgotten words are less important by having them judge whether an item was initially recalled or forgotten prior to making a value judgment. Manipulating the fluency of an item presented for judgment had no influence on value ratings (Experiment 1) and familiarity exerted a limited influence on value judgments (Experiment 2). More importantly, participants’ value judgments appeared to reflect a theory that remembered information is more valuable than forgotten information (Experiment 3). Overall, the present work suggests that individuals may apply a theory about remembering and forgetting to retrospectively assess the value of information
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