9,959 research outputs found
Realizing Majorana Zero Modes by Proximity Effect between Topological Insulators and d-wave High-Temperature Superconductors
We theoretically study superconducting proximity effect between a topological
insulator (TI) and a high-temperature d-wave superconductor (dSC). When the
TI-dSC heterostructure violates 90 degree-rotation and certain reflection
symmetries, we show that a sizable s-wave pairing, coexisting with a d-wave
one, emerges in the proximity-induced superconductivity in the TI's top surface
states. Weak disorder further suppresses d-wave pairing but not s-wave one in
the TI's surface states. More importantly, the pairing gap in surface states is
found to be nodeless and nearly-isotropic when the Fermi pocket of surface
states is relatively small. Our theoretical results qualitatively explain
recent experimental evidences of a nearly-isotropic pairing gap on surface
states of Bi_2Se_3 induced by proximity with high-T_c cuprate
Bi_2Ca_2Cu_2O_{8+\delta}. We also demonstrate convincing evidences of Majorana
zero modes in a magnetic hc/2e vortex core, which may be detectable in future
experiments.Comment: 4.5 pages, 4 figure
Majorana-time-reversal symmetries: a fundamental principle for sign-problem-free quantum Monte Carlo simulations
A fundamental open issue in physics is whether and how the fermion sign
problem in quantum Monte Carlo (QMC) simulations can be solved generically.
Here, we show that Majorana-time-reversal (MTR) symmetries can provide a
unifying principle to solve the fermion sign problem in interacting fermionic
models. By systematically classifying Majorana-bilinear operators according to
the anti-commuting MTR symmetries they respect, we rigorously proved that there
are two and only two fundamental symmetry classes which are sign-problem-free
and which we call the "Majorana class" and "Kramers class", respectively. Novel
sign-problem-free models in the Majorana class include interacting topological
superconductors and interacting models of charge-4e superconductors. We believe
that our MTR unifying principle could shed new light on sign-problem-free QMC
simulation on strongly correlated systems and interacting topological matters.Comment: Accepted by Phys. Rev. Lett. Added more references and moved part of
the paper into the Supplemental Materia
Fermion-sign-free Majarana-quantum-Monte-Carlo studies of quantum critical phenomena of Dirac fermions in two dimensions
Quantum critical phenomena may be qualitatively different when massless Dirac
fermions are present at criticality. Using our recently-discovered
fermion-sign-free Majorana quantum Monte Carlo (MQMC) method introduced by us
in Ref. [1], we investigate the quantum critical phenomena of {\it spinless}
Dirac fermions at their charge-density-wave (CDW) phase transitions on the
honeycomb lattice having sites with largest . By finite-size
scaling, we accurately obtain critical exponents of this so-called Gross-Neveu
chiral-Ising universality class of {\it two} (two-component) Dirac fermions in
2+1D: , , and , which are
qualitatively different from the mean-field results but are reasonably close to
the ones obtained from renormalization group calculations.Comment: 5.3 pages, Published as part of "Focus on Topological Physics: From
Condensed Matter to Cold Atoms and Optics" in New Journal of Physic
Solving fermion sign problem in quantum Monte Carlo by Majorana representation
In this paper, we discover a new quantum Monte Carlo (QMC) method to solve
the fermion sign problem in interacting fermion models by employing Majorana
representation of complex fermions. We call it "Majorana QMC" (MQMC).
Especially, MQMC is fermion sign free in simulating a class of spinless fermion
models on bipartite lattices at half filling and with arbitrary range of
(unfrustrated) interactions. To the best of our knowledge, MQMC is the first
auxiliary field QMC method to solve fermion sign problem in spinless (more
generally, odd number of species) fermion models. MQMC simulations can be
performed efficiently both at finite and zero temperatures. We believe that
MQMC could pave a new avenue to solve fermion sign problem in more generic
fermionic models.Comment: Selected as an Editors' Suggestion in PRB Rapid Communication,
published version with updated referenc
Statistical properties and decoherence of two-mode photon-subtracted squeezed vacuum
We investigate the statistical properties of the photon-subtractions from the
two-mode squeezed vacuum state and its decoherence in a thermal environment. It
is found that the state can be considered as a squeezed two-variable Hermite
polynomial excitation vacuum and the normalization of this state is the Jacobi
polynomial of the squeezing parameter. The compact expression for Wigner
function (WF) is also derived analytically by using the Weyl ordered operators'
invariance under similar transformations. Especially, the nonclassicality is
discussed in terms of the negativity of WF. The effect of decoherence on this
state is then discussed by deriving the analytical time evolution results of
WF. It is shown that the WF is always positive for any squeezing parameter and
photon-subtraction number if the decay time exceeds an upper bound (}$\kappa
t>{1/2}\ln \frac{2\bar{n}+2}{2\bar{n}+1}).Comment: 17 pages, 11 figure
Study on the radiative decays of
In this work, we investigate the characteristics of the spin-singlet state
of the bottomonia family via the radiative decays of . The theoretical estimation of the decay widths is carried out
in terms of the light-front quark model (LFQM). Recently CLEO and BaBar
collaborations have measured and the
mass of . In terms of the data we fix the concerned input parameters
in our calculations of . A special attention is
paid on the transition of . The BELLE data
showed that the width of is two orders
larger than that of , thus some
theoretical explanations have been proposed. Among them, it is suggested the
inelastic final state interaction (IFSI) may be a natural one. If so, a similar mechanism also
applies to , the precise
measurement would serve as a good test whether possess exotic
components. Our calculation in the LFQM indicates that the rate of the direct
process is not anomalous compared to
, thus if the IFSI does apply, the
rate of should be larger than the others by
orders.Comment: 7 pages, 4 figures; Rectification made and a footnote adde
The heavy-to-light transitions in the light-cone QCD sum rules
We have analyzed the and semileptonic form factors
and processes in the light-cone QCD sum
rules. In order to enhance the predictivity and reliability of numerical
results the chiral-current correlator is employed and the twist-3 light-cone
wavefunction can be effectively eliminated from the sum rules.Comment: Talk given at Internatinal Comference on Flavor Physics (ICFP 2001),
Zhang-Jia-Jie city, Hunan, China, 31 May - 6 Jun, 200
Deconfined quantum criticality and emergent SO(5) symmetry in fermionic systems
Deconfined quantum criticality with emergent SO(5) symmetry in correlated
systems remains elusive. Here, by performing numerically-exact state-of-the-art
quantum Monte Carlo (QMC) simulations, we show convincing evidences of
deconfined quantum critical points (DQCP) between antiferromagnetic and
valence-bond-solid phases in the extended Hubbard model of fermions on the
honeycomb lattice with large system sizes. We further demonstrate evidences of
the SO(5) symmetry at the DQCP. It is important to note that the critical
exponents obtained by finite-size scaling at the DQCP here are consistent with
the rigourous conformal bounds. Consequently, we established a promising arena
of DQCP with emergent SO(5) symmetry in interacting systems of fermions. Its
possible experimental relevances in correlated systems of Dirac fermions will
be discussed briefly.Comment: 5.6 pages + Supplemental Materials, 4 figure
New 3-mode squeezing operator and squeezed vacuum state in 3-wave mixing
In a 3-wave mixing process occurring in some nonlinear optical medium when
}{\small mode interacts with both }{\small
mode and }{\small mode, we theoretically study the squeezing
effect generated by the operator }{\small . The new 3-mode squeezed vacuum state in Fock space
is derived, and the uncertainty relation for it is demonstrated, It turns out
that }{\small may exhibit enhanced squeezing. By virtue of the technique
of integration within an ordered product (IWOP) of operators, we also derive
}{\small 's normally ordered expansion. The Wigner function of new
3-mode squeezed vacuum state is calculated by using the Weyl ordering
invariance under similar transformations.Comment: 10 pages, 2 figures, submitted to EP
Atomic coherent state in Schwinger bosonic realization for optical Raman coherent effect
For optical Raman coherent effect we introduce the atomic coherent state (or
the angular momentum coherent state with various angular momemtum values) in
Schwinger bosonic realization, they are the eigenvectors of the Hamiltonian
describing the Raman effect. Similar to the fact that the photon coherent state
describes laser light, the atomic coherent state is related to Raman process.Comment: 6 page
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