11,202 research outputs found
The A-Cycle Problem In XY model with Ring Frustration
Traditionally, the transverse spin-1/2 XY model is mapped to a fermionic
"c-cycle" problem, where the prior periodic boundary condition is applied to
the fermionic chain and the additional boundary term has been neglected.
However, the "a-cycle" problem (the original problem without any approximation)
has not been treated seriously up to now. In this paper, we consider the XY
model with ring frustration and diagonalize it without any approximation with
the help of parity constraint. Then two peculiar gapless phases have been
found.Comment: 6 pages, 1 figures, to appear in Modern Physics Letters
Potential thermoelectric materials (M=Sn and Pb) in perovskite structures from the first-principles calculations
The thermoelectric properties of halide perovskites (M=Sn
and Pb) are investigated from a combination of first-principles calculations
and semiclassical Boltzmann transport theory by considering both the electron
and phonon transport. The electronic part is performed using a modified Becke
and Johnson (mBJ) exchange potential, including spin-orbit coupling (SOC),
while the phonon part is computed using generalized gradient approximation
(GGA). It is found that SOC has remarkable detrimental effect on n-type power
factor, while has a negligible influence in p-type doping, which can be
explained by considering SOC effect on conduction and valence bands. Calculated
results show exceptionally low lattice thermal conductivities in
and , and the corresponding
room-temperature lattice thermal conductivity is 0.54 and 0.25 . At 1000 K, the maximal figure of
merit is up to 0.63 and 0.64 for and
with scattering time = s, and the peak is 0.49 and 0.41
with = s. These results make us believe that
(M=Sn and Pb) in perovskite structures may be potential thermoelectric
materials.Comment: 6 pages, 6 figure
Pressure enhanced thermoelectric properties in Mg2Sn
Pressure dependence of electronic structures and thermoelectric properties of
are investigated by using a modified Becke and Johnson (mBJ)
exchange potential, including spin-orbit coupling (SOC). The corresponding
value of spin-orbit splitting at point is 0.47 eV, which is in good
agreement with the experimental value 0.48 eV. With the pressure increasing,
the energy band gap first increases, and then decreases. In certain doping
range, the power factor for n-type has the same trend with energy band gap,
when the pressure increases. Calculated results show that the pressure can lead
to significantly enhanced power factor in n-type doping below the critical
pressure, and the corresponding lattice thermal conductivity near the critical
pressure shows the relatively small value. These results make us believe that
thermoelectric properties of can be improved in n-type doping
by pressure.Comment: 4 pages, 6 figure
Spin-orbital coupling effect on power factor in semiconducting transition-metal dichalcogenide monolayers
The electronic structures and thermoelectric properties of semiconducting
transition-metal dichalcogenide monolayers (M=Zr, Hf, Mo, W and
Pt; X=S, Se and Te) are investigated by combining first-principles and
Boltzmann transport theory, including spin-orbital coupling (SOC). It is found
that the gap decrease increases from S to Te in each cation group, when the SOC
is opened. The spin-orbital splitting has the same trend with gap reducing.
Calculated results show that SOC has noteworthy detrimental effect on p-type
power factor, while has a negligible influence in n-type doping except W cation
group, which can be understood by considering the effects of SOC on the valence
and conduction bands. For (X=S, Se and Te), the SOC leads to
observably enhanced power factor in n-type doping, which can be explained by
SOC-induced band degeneracy, namely bands converge. Among all cation groups, Pt
cation group shows the highest Seebeck coefficient, which leads to best power
factor, if we assume scattering time is fixed. Calculated results show that
(M=Zr, Hf, Mo, W and Pt) have best p-type power factor for all
cation groups, and that (M=Zr and Hf), and
(M=Mo and Pt) have more wonderful n-type power factor in
respective cation group. Therefore, these results may be useful for further
theoretical prediction or experimental search of excellent thermoelectric
materials from semiconducting transition-metal dichalcogenide monolayers.Comment: 8 pages, 8 figure
Entanglement in the scattering process by local impurity
We study entanglement in the scattering processes by fixed impurity and Kondo
impurity. The fixed impurity plays a role as spin state filter that is employed
to concentrate entanglement between the scattering particle and the
unscattering particle. One Kondo impurity can entangle two noninteracting
scattering particles while one scattering particle can entangle two separate
noninteracting Kondo impurities.Comment: 8 page
Projective symmetry group classification of parafermion spin liquids on a honeycomb lattice
To study exotic excitations described by parafermions in the possible spin
liquid states of SU() spin systems, we introduce a parafermion parton
approach. The SU() spin operators can be represented by clock and shift
matrices, which are shown to be the polynomials of parafermion operators in the
parafermion representation. We find that SU() spins can be decomposed into
parafermion matrices of degree one. In this decomposition, the spin has a
gauge symmetry. As an application, we study
the one-dimensional three-state clock model and generalized Kitaev model by a
mean-field theory, both of them have been proved to be related to parafermion
excitations. We find that with the symmetries of translations, -fold
rotation and combination of parity and time reversal, there are types and
solutions for two-dimensional parafermion spin liquids on the
honeycomb lattice. On the contrast, there are types and solutions if
both parity and time-reversal symmetries are present. Our results provide a
novel route for the systematic search of new types of spin liquids with exotic
anyon excitations.Comment: 13 pages, 1 figure
Spectral properties of the square-lattice antiferromagnetic J1-J2 Heisenberg model: confinement and deconfinement of spinons
Based on the mapping between spin operators and hard-core bosons, we
extend the cluster perturbation theory to spin systems and study the whole
excitation spectrum of the antiferromagnetic - Heisenberg model
on the square lattice. In the N\'eel phase for , in
addition to the dominant magnon excitation, there is an obvious continuum close
to in the Brillouin zone indicating the deconfined spin-1/2 spinon
excitations. In the stripe phase for , we find similar
high-energy two-spinon continuums at and ,
respectively. The intermediate phase is characterized by a spectrum with
completely deconfined broad continuum, which is attributed to a quantum
spin liquid with the aid of a variational-Monte-Carlo analysis.Comment: 7 pages, 6 figure
The A-Cycle Problem for Transverse Ising Ring
Traditionally, the transverse Ising model is mapped to the fermionic c-cycle
problem, which neglects the boundary effect due to thermodynamic limit. If
persisting on a perfect periodic boundary condition, we can get a so-called
a-cycle problem that has not been treated seriously so far (Lieb et al., 1961
\textit{Ann. of Phys.} \textbf{16} 407). In this work, we show a little
surprising but exact result in this respect. We find the odevity of the number
of lattice sites, , in the a-cycle problem plays an unexpected role even in
the thermodynamic limit, , due to the boundary constraint.
We pay a special attention to the system with ,
which is in contrast to the one with , because
the former suffers a ring frustration. As a new effect, we find the ring
frustration induces a low-energy gapless spectrum above the ground state. By
proving a theorem for a new type of Toeplitz determinant, we demonstrate that
the ground state in the gapless region exhibits a peculiar longitudinal
spin-spin correlation. The entangled nature of the ground state is also
disclosed by the evaluation of its entanglement entropy. At low temperatures,
new behavior of specific heat is predicted. We also propose an experimental
protocol for observing the new phenomenon due to the ring frustration.Comment: 24 pages, 9 figure
SU() spin-wave theory: Application to spin-orbital Mott insulators
We present the application of the SU() () spin-wave theory to
spin-orbital Mott insulators whose ground states exhibit magnetic orders. When
taking both the spin and orbital degrees of freedom into account rather than
projecting onto the Kramers doublet, the lowest spin-orbital locking energy
levels, due to the inevitable spin-orbital multipole exchange interactions, the
SU() spin-wave theory should take the place of the SU() one. To implement
the application, we introduce an efficient general local mean field approach
which involves all the local fluctuations into the SU() linear spin-wave
theory. Our approach is tested firstly by calculating the multipolar spin-wave
spectra of the SU() antiferromagnetic model. Then we apply it to
spin-orbital Mott insulators. It is revealed that the Hund's coupling would
influence the effectiveness of the isospin- representation when the spin
orbital coupling is not large enough. Besides, we also calculate the spin-wave
spectra based on the first principle calculations for two concrete materials,
-RuCl and SrIrO. The SU() spin-wave theory appropriately
depicts the low-energy magnons and the spin-orbital excitations qualitatively.Comment: 9 pages, 5 figure
Rigorous proof for the non-local correlation functions in the antiferromagnetic seamed transverse Ising ring
An unusual correlation function is conjectured by M. Campostrini et al.
(Phys. Rev. E 91, 042123 (2015)) for the ground state of a transverse Ising
chain with geometrical frustration in one of the translationally invariant
cases. Later, we demonstrated the correlation function and showed its non-local
nature in the thermodynamic limit based on the rigorous evaluation of a
Toeplitz determinant (J. Stat. Mech. 113102 (2016)). In this paper, we prove
rigorously that all the states that forming the lowest gapless spectrum
(including the ground state) in the kink phase exhibit the same asymptotic
correlation function. So, in a point of view of cannonical ensemble, the
thermal correlation function is inert to temperature within the energy range of
the lowest gapless spectrum.Comment: 8 pages, 0 figure
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