14,594 research outputs found
Hidden spin current in doped Mott antiferromagnets
We investigate the nature of doped Mott insulators using exact
diagonalization and density matrix renormalization group methods. Persistent
spin currents are revealed in the ground state, which are concomitant with a
nonzero total momentum or angular momentum associated with the doped hole. The
latter determines a nontrivial ground state degeneracy. By further making
superpositions of the degenerate ground states with zero or unidirectional spin
currents, we show that different patterns of spatial charge and spin
modulations will emerge. Such anomaly persists for the odd numbers of holes,
but the spin current, ground state degeneracy, and charge/spin modulations
completely disappear for even numbers of holes, with the two-hole ground state
exhibiting a d-wave symmetry. An understanding of the spin current due to a
many-body Berry-like phase and its impact on the momentum distribution of the
doped holes will be discussed.Comment: 9 pages, 9 figures, update second version including more data and
discussion adde
Pairing versus phase coherence of doped holes in distinct quantum spin backgrounds
We examine the pairing structure of holes injected into two \emph{distinct}
spin backgrounds: a short-range antiferromagnetic phase versus a symmetry
protected topological phase. Based on density matrix renormalization group
(DMRG) simulation, we find that although there is a strong binding between two
holes in both phases, \emph{phase fluctuations} can significantly influence the
pair-pair correlation depending on the spin-spin correlation in the background.
Here the phase fluctuation is identified as an intrinsic string operator
nonlocally controlled by the spins. We show that while the pairing amplitude is
generally large, the coherent Cooper pairing can be substantially weakened by
the phase fluctuation in the symmetry-protected topological phase, in contrast
to the short-range antiferromagnetic phase. It provides an example of a non-BCS
mechanism for pairing, in which the paring phase coherence is determined by the
underlying spin state self-consistently, bearing an interesting resemblance to
the pseudogap physics in the cuprate.Comment: 9 pages, 6 figure
Binding of Vav to Grb2 through dimerization of Src homology 3 domains
The protooncogenic protein Vav has the structure of an intracellular signal transducer. It is exclusively expressed in cells of hematopoietic lineage and plays a crucial role in hematopoietic cell differentiation. Here we report that both in cell extracts and within intact mammalian cells Vav binds to Grb2 (Sem-5/ASH/Drk), an adaptor molecule which plays a key role in Ras activation. The interaction became evident from a yeast two-hybrid screen and its specificity was demonstrated by in vitro binding assays. It is mediated by an unusual protein-protein binding reaction: dimerization of specific intact Src homology 3 domains of each of the partners. Signaling during hematopoietic lineage differentiation may therefore involve the tissue-specific signal transducer Vav linking into the ubiquitous pathway involving Grb2 and ultimately Ras
Intrinsic translational symmetry breaking in a doped Mott insulator
A central issue of Mott physics, with symmetries being fully retained in the
spin background, concerns the charge excitation. In a two-leg spin ladder with
spin gap, an injected hole can exhibit either a Bloch wave or a density wave by
tuning the ladder anisotropy through a `quantum critical point' (QCP). The
nature of such a QCP has been a subject of recent studies by density matrix
renormalization group (DMRG). In this paper, we reexamine the ground state of
the one doped hole, and show that a two-component structure is present in the
density wave regime in contrast to the single component in the Bloch wave
regime. In the former, the density wave itself is still contributed by a
standing-wave-like component characterized by a quasiparticle spectral weight
in a finite-size system. But there is an additional charge incoherent
component emerging, which intrinsically breaks the translational symmetry
associated with the density wave. The partial momentum is carried away by
neutral spin excitations. Such an incoherent part does not manifest in the
single-particle spectral function, directly probed by the angle-resolved
photoemission spectroscopy (ARPES) measurement, however it is demonstrated in
the momentum distribution function. The Landau's one-to-one correspondence
hypothesis for a Fermi liquid breaks down here. The microscopic origin of this
density wave state as an intrinsic manifestation of the doped Mott physics will
be also discussed.Comment: 11 pages, 6 figures, an extended version of arXiv:1601.0065
Efficient single-photon-assisted entanglement concentration for partially entangled photon pairs
We present two realistic entanglement concentration protocols (ECPs) for pure
partially entangled photons. A partially entangled photon pair can be
concentrated to a maximally entangled pair with only an ancillary single photon
in a certain probability, while the conventional ones require two copies of
partially entangled pairs at least. Our first protocol is implemented with
linear optics and the second one is implemented with cross-Kerr nonlinearities.
Compared with other ECPs, they do not need to know the accurate coefficients of
the initial state. With linear optics, it is feasible with current experiment.
With cross-Kerr nonlinearities, it does not require the sophisticated
single-photon detectors and can be repeated to get a higher success
probability. Moreover, the second protocol can get the higher entanglement
transformation efficiency and it maybe the most economical one by far.
Meanwhile, both of protocols are more suitable for multi-photon system
concentration, because they need less operations and classical communications.
All these advantages make two protocols be useful in current long-distance
quantum communications
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