938 research outputs found
Competing effects of interactions and spin-orbit coupling in a quantum wire
We study the interplay of electron-electron interactions and Rashba
spin-orbit coupling in one-dimensional ballistic wires. Using the
renormalization group approach we construct the phase diagram in terms of
Rashba coupling, Tomonaga-Luttinger stiffness and backward scattering strength.
We identify the parameter regimes with a dynamically generated spin gap and
show where the Luttinger liquid prevails. We also discuss the consequences for
the operation of the Datta-Das transistor.Comment: 4 pages, 2 figure
Complex-mass scheme and perturbative unitarity
We derive cutting rules for loop integrals containing propagators with
complex masses. Using a field-theoretical model of a heavy vector boson
interacting with a light fermion, we demonstrate that the complex-mass scheme
respects unitarity order by order in a perturbative expansion provided that the
renormalized coupling constant remains real.Comment: Accepted for publication in International Journal of Modern Physics
In the beginning was game semantics
This article presents an overview of computability logic -- the
game-semantically constructed logic of interactive computational tasks and
resources. There is only one non-overview, technical section in it, devoted to
a proof of the soundness of affine logic with respect to the semantics of
computability logic. A comprehensive online source on the subject can be found
at http://www.cis.upenn.edu/~giorgi/cl.htmlComment: To appear in: "Games: Unifying Logic, Language and Philosophy". O.
Majer, A.-V. Pietarinen and T. Tulenheimo, eds. Springer Verlag, Berli
Magnetization plateau in the S=1/2 spin ladder with alternating rung exchange
We have studied the ground state phase diagram of a spin ladder with
alternating rung exchange in
a magnetic filed, in the limit where the rung coupling is dominant. In this
limit the model is mapped onto an Heisenberg chain in a uniform and
staggered longitudinal magnetic fields, where the amplitude of the staggered
field is . We have shown that the magnetization curve of the
system exhibits a plateau at magnetization equal to the half of the saturation
value. The width of a plateau scales as , where in the
case of ladder with isotropic antiferromagnetic legs and in the case
of ladder with isotropic ferromagnetic legs. We have calculated four critical
fields ( and ) corresponding to transitions between
different magnetic phases of the system. We have shown that these transitions
belong to the universality class of the commensurate-incommensurate transition.Comment: 6 pages, 2 figure
Magnetic properties of the spin Heisenberg chain with hexamer modulation of exchange
We consider the spin-1/2 Heisenberg chain with alternating spin exchange %on
even and odd sites in the presence of additional modulation of exchange on odd
bonds with period three. We study the ground state magnetic phase diagram of
this hexamer spin chain in the limit of very strong antiferromagnetic (AF)
exchange on odd bonds using the numerical Lanczos method and bosonization
approach. In the limit of strong magnetic field commensurate with the
dominating AF exchange, the model is mapped onto an effective Heisenberg
chain in the presence of uniform and spatially modulated fields, which is
studied using the standard continuum-limit bosonization approach. In absence of
additional hexamer modulation, the model undergoes a quantum phase transition
from a gapped string order into the only one gapless L\"uttinger liquid (LL)
phase by increasing the magnetic field. In the presence of hexamer modulation,
two new gapped phases are identified in the ground state at magnetization equal
to 1/3 and 2/3 of the saturation value. These phases reveal themselves also in
magnetization curve as plateaus at corresponding values of magnetization. As
the result, the magnetic phase diagram of the hexamer chain shows seven
different quantum phases, four gapped and three gapless and the system is
characterized by six critical fields which mark quantum phase transitions
between the ordered gapped and the LL gapless phases.Comment: 21 pages, 5 figures, Journal of Physics: Condensed Matter, 24,
116002, (2012
Magnetic phase diagram of the dimerized spin ladder
The ground-state magnetic phase diagram of a spin two-leg ladder with
alternating rung exchange is
studied using the analytical and numerical approaches. In the limit where the
rung exchange is dominant, we have mapped the model onto the effective quantum
sine-Gordon model with topological term and identified two quantum phase
transitions at magnetization equal to the half of saturation value from a
gapped to the gapless regime. These quantum transitions belong to the
universality class of the commensurate-incommensurate phase transition. We have
also shown that the magnetization curve of the system exhibits a plateau at
magnetization equal to the half of the saturation value. We also present a
detailed numerical analysis of the low energy excitation spectrum and the
ground state magnetic phase diagram of the ladder with rung-exchange
alternation using Lanczos method of numerical diagonalizations for ladders with
number of sites up to N=28. We have calculated numerically the magnetic field
dependence of the low-energy excitation spectrum, magnetization and the on-rung
spin-spin correlation function. We have also calculated the width of the
magnetization plateau and show that it scales as , where critical
exponent varies from in the case of a ladder with isotropic
antiferromagnetic legs to in the case of ladder with
ferromagnetic legs. Obtained numerical results are in an complete agreement
with estimations made within the continuum-limit approach.Comment: 8 pages, 6 figures. arXiv admin note: text overlap with
arXiv:cond-mat/0603153, arXiv:1110.446
General properties of phase diagrams of heavy-fermion metals
We study the temperature-magnetic field T-B phase diagrams of heavy fermion
(HF) metals, and show that at sufficiently high temperatures outside the
ordered phase the crossover temperature T*(B), regarded as the energy scale,
follows a linear B-dependence, crossing the origin of the T-B phase diagram.
This behavior of T*(B) constitutes the general property, and is formed by the
presence of fermion condensation quantum phase transition hidden within the
ordered phase. Our result is in good agreement with the experimental T-B phase
diagram of the HF metals YbRh2Si2, Yb(Rh{0.93}Co{0.07})2Si2, and
Yb(Rh{0.94}Ir{0.06})2Si2. To support our observations, we analyze the
isothermal magnetization M, and demonstrate that dM/dT exhibits a universal
temperature behavior over magnetic field scaling. The obtained results are in
good agreement with the corresponding data collected on YbRh2Si2 as a function
of magnetic field at different temperatures under hydrostatic pressure.Comment: 6 pages, 6 figures. arXiv admin note: substantial text overlap with
arXiv:1311.062
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