14 research outputs found
Relevance of nonadiabatic effects in TiOCl
We analyze the effect of the phonon dynamics on a recently proposed model for
the uniform-incommensurate transition seen in TiOX compounds. The study is
based on a recently developed formalism for nonadiabatic spin-Peierls systems
based on bosonization and a mean field RPA approximation for the interchain
coupling. To reproduce the measured low temperature spin gap, a spin-phonon
coupling quite bigger than the one predicted from an adiabatic approach is
required. This high value is compatible with the renormalization of the phonons
in the high temperature phase seen in inelastic x-ray experiments. Our theory
accounts for the temperature of the incommensurate transition and the value of
the incommensurate wave vector at the transition point.Comment: 4 pages, 2 figure
Generation of chiral solitons in antiferromagnetic chains by a quantum quench
We analyze the time evolution of a magnetic excitation in a spin-1/2
antiferromagnetic Heisenberg chain after a quantum quench. By a proper
modulation of the magnetic exchange coupling, we prepare a static soliton of
total spin 1/2 as an initial spin state. Using bosonization and a numerical
time dependent density matrix renormalization group algorithm, we show that the
initial excitation evolves to a state composed of two counter-propagating
chiral states, which interfere to yield = 1/4 for each mode. We find that
these dynamically generated states remain considerably stable as time evolution
is carried out. We propose spin-Peierls materials and ultracold-atom systems as
suitable experimental scenarios in which to conduct and observe this mechanism.Comment: Published version. Title changed due to reinterpretation of results.
5 pages, 4 figure
Noncollinear exchange interaction in transition metal dichalcogenide edges
We study the Ruderman-Kittel-Kasuya-Yosida effective exchange interaction
between magnetic impurities embedded on the edges of transition-metal
dichalcogenide flakes, using a three-orbital tight-binding model. Electronic
states lying midgap of the bulk structure have strong one-dimensional (1D)
character, localized on the edges of the crystallite. This results in exchange
interactions with (or slower) decay with distance , similar to other
1D systems. Most interestingly, however, the strong spin-orbit interaction in
these materials results in sizable non-collinear Dzyaloshinskii-Moriya
interactions between impurities, comparable in size to the usual Ising and
in-plane components. Varying the relevant Fermi energy by doping or gating may
allow one to modulate the effective interactions, controlling the possible
helical ground state configurations of multiple impurities.Comment: 5 pages and 4 figure
Kondo effect in graphene with Rashba spin-orbit coupling
We study the Kondo screening of a magnetic impurity adsorbed in graphene in
the presence of Rashba spin-orbit interaction. The system is described by an
effective single-channel Anderson impurity model, which we analyze using the
numerical renormalization group. The nontrivial energy dependence of the host
density of states gives rise to interesting behaviors under variation of the
chemical potential or the spin-orbit coupling. Varying the Rashba coupling
produces strong changes in the Kondo temperature characterizing the many-body
screening of the impurity spin, and at half filling allows approach to a
quantum phase transition separating the strong-coupling Kondo phase from a
free-moment phase. Tuning the chemical potential close to sharp features of the
hybridization function results in striking features in the temperature
dependences of thermodynamic quantities and in the frequency dependence of the
impurity spectral function.Comment: 11 pages, 9 figures. Minor changes. Accepted in PR
Lateral Interfaces of Transition Metal Dichalcogenides: A Stable Tunable One-Dimensional Physics Platform
We study in-plane lateral heterostructures of commensurate transition-metal
dichalcogenides, such as MoS-WS and MoSe-WSe, and find
interfacial and edge states that are highly localized to these regions of the
heterostructure. These are one-dimensional (1D) in nature, lying within the
bandgap of the bulk structure and exhibiting complex orbital and spin
structure. We describe such heteroribbons with a three-orbital tight-binding
model that uses first principles and experimental parameters as input, allowing
us to model realistic systems. Analytical modeling for the 1D interfacial bands
results in long-range hoppings due to the hybridization along the interface,
with strong spin-orbit couplings. We further explore the
Ruderman-Kittel-Kasuya-Yosida indirect interaction between magnetic impurities
located at the interface. The unusual features of the interface states result
in effective long-range exchange non-collinear interactions between impurities.
These results suggest that transition-metal dichalcogenide interfaces could
serve as stable, tunable 1D platform with unique properties for possible use in
exploring Majorana fermions, plasma excitations and spintronics applications.Comment: 12 pages, 7 figure
Microscopic theory for the incommensurate transition in TiOCl
We propose a microscopic mechanism for the incommensurate phase in TiOX
compounds. The model includes the antiferromagnetic chains of Ti ions immersed
in the phonon bath of the bilayer structure. Making use of the Cross-Fisher
theory, we show that the geometrically frustrated character of the lattice is
responsible for the structural instability which leads the chains to an
incommensurate phase without an applied magnetic field. In the case of TiOCl,
we show that our model is consistent with the measured phonon frequencies at
and the value of the incommensuration vector at the transition
temperature. Moreover, we find that the dynamical structure factor shows a
progressive softening of an incommensurate phonon near the zone boundary as the
temperature decreases. This softening is accompanied by a broadening of the
peak which gets asymmetrical as well when going towards the transition
temperature. These features are in agreement with the experimental inelastic
X-ray measurements.Comment: 6 pages, 5 figures. Published versio
Hybridization and anisotropy in the exchange interaction in three-dimensional Dirac semimetals
We study the Ruderman-Kittel-Kasuya-Yosida interaction in three-dimensional Dirac semimetals. Using retarded Green's functions in real space, we obtain and analyze asymptotic expressions for the interaction, with magnetic impurities at different distances and relative angle with respect to high symmetry directions on the lattice. We show that the Fermi velocity anisotropy in these materials produces a strong renormalization of the magnitude of the interaction, as well as a correction to the frequency of oscillation in real space. Hybridization of the impurities to different conduction electron orbitals are shown to result in interesting anisotropic spin-spin interactions which can generate spiral spin structures in doped samples.Fil: Mastrogiuseppe, Diego Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina. Ohio University; Estados UnidosFil: Sandler, N.. Ohio University; Estados UnidosFil: Ulloa, S. E.. Ohio University; Estados Unido