1,503 research outputs found
Magnetic phase diagram of a quasi-one-dimensional quantum spin system
We propose an analytical ansatz, using which the ordering temperature of a
quasi-one-dimensional (quasi-1D) antiferromagnetic (AF) system (weakly coupled
quantum spin-1/2 chains) in the presence of the external magnetic field is
calculated. The field dependence of the critical exponents for correlation
functions of 1D subsystems plays a very important role. It determines the
region of possible re-entrant phase transition, governed by the field. It is
shown how the quantum critical point between two phases of the 1D subsystem,
caused by spin-frustrating next-nearest neighbor (NNN) and multi-spin ring-like
exchanges, affects the field dependence of the ordering temperature. Our
results qualitatively agree with the features, observed in experiments on
quasi-1D AF systems
Quantum phase transitions in a new exactly solvable quantum spin biaxial model with multiple spin interactions
The new integrable quantum spin model is proposed. The model has a biaxial
magnetic anisotropy of alternating coupling between spins together with
multiple spin interactions. Our model gives the possibility to exactly find
thermodynamic characteristics of the considered spin chain. The ground state of
the model can reveal spontaneous values of the total magnetic and
antiferromagnetic moments, caused by multiple spin couplings. Also, in the
ground state, depending on the strength of multiple spin couplings, our model
manifests several quantum critical points, some of which are governed by the
external magnetic field
Possibility of direct observation of edge Majorana modes in quantum chains
Several scenarios for realization of edge Majorana modes in quantum chain
systems: spin chains, chains of Josephson junctions, and chains of coupled
cavities in quantum optics, are considered. For all these systems excitations
can be presented as superpositions of a spinless fermion and a hole,
characteristic for Majorana fermion. We discuss the features of our exact
solution with respect to possible experiments, in which edge Majorana fermions
can be directly observed when studying magnetic, superconducting, and optical
characteristics of such systems.Comment: 8 pages (including supplemental information), 7 figure
Spin Dynamics in Chains with Next-Nearest-Neighbor Exchange Interactions
Low-energy magnetic excitations in the spin-1/2 chain compound
(CHN)CuCl [known as (6MAP)CuCl] are probed by means of
tunable-frequency electron spin resonance. Two modes with asymmetric (with
respect to the line) frequency-field dependences are resolved,
illuminating the striking incompatibility with a simple uniform
Heisenberg chain model. The unusual ESR spectrum is explained in terms of the
recently developed theory for spin-1/2 chains, suggesting the important role of
next-nearest-neighbor interactions in this compound. Our conclusion is
supported by model calculations for the magnetic susceptibility of
(6MAP)CuCl, revealing a good qualitative agreement with experiment
New physics in frustrated magnets: Spin ices, monopoles, etc
During recent years the interest to frustrated magnets has grown
considerably. Such systems reveal very peculiar properties which distinguish
them from standard paramagnets, magnetically ordered regular systems (like
ferro-, ferri-, and antiferromagnets), or spin glasses. In particular great
amount of attention has been devoted to the so-called spin ices, in which
magnetic frustration together with the large value of the single-ion magnetic
anisotropy of a special kind, yield peculiar behavior. One of the most exciting
features of spin ices is related to low-energy emergent excitations, which,
from many viewpoints can be considered as analogies of Dirac's monopoles. In
this article we review the main achievements of theory and experiment in this
field of physics.Comment: review article, 70 pages, 27 figures, accepted for publication in
"Low Temperature Physics" ("Fizika Nizkikh Temperatur"
Magnetic ordering of weakly coupled frustrated quantum spin chains
The ordering temperature of a quasi-one-dimensional system, consisting of
weakly interacting quantum spin-1/2 chains with antiferromagnetic
spin-frustrating couplings (or zig-zag ladder) is calculated. The results show
that a quantum critical point between two phases of the one-dimensional
subsystem plays a crucial role. If the one-dimensional subsystem is in the
antiferromagnetic-like phase in the ground state, similar to the phase of a
spin chain without frustration, weak couplings yield magnetic ordering of the
Neel type. For intra-chain spin-frustrating interactions larger than the
critical one (at which the quantum phase transition takes place), the
quasi-one-dimensional spin system manifests a spiral magnetic incommensurate
ordering. The obtained results of our quantum theory are compared with the
quasi-classical approximations. The calculated features of magnetic ordering
are expected to be generic for weakly coupled quantum spin chains with gapless
excitations and spin-frustrating nearest and next-nearest neighbor
interactions.Comment: 6 pages, 2 figure
Spin-orbit and impurity scattering in an integrable electron model: Exact results for dynamic correlations
We introduce an integrable model of spin-polarized interacting electrons
subject to a spin-conserving spin-orbit interaction. Using Bethe Ansatz and
conformal field theory we calculate the exact large-time single-electron and
density correlations and find that while the spin-orbit interaction enhances
the single-electron Green's function, the density correlations get suppressed.
Adding a localized impurity and coupling it to the electrons so that
integrability is preserved, the dynamic correlations are found to change
significantly after a quantum quench with the impurity interaction switched on
suddenly. When the electrons are confined to a periodic structure, the
correlations are indifferent to the location of the impurity and only carry an
imprint of its intrinsic properties. We conjecture that this unusual feature
originates from the integrability of the model.Comment: 8 pages, 1 figur
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