373 research outputs found
Finite size effects and magnetic order in the spin-1/2 honeycomb lattice compound InCu{2/3}V{1/3}O{3}
High field electron spin resonance, nuclear magnetic resonance and
magnetization studies addressing the ground state of the quasi two-dimensional
spin-1/2 honeycomb lattice compound InCu{2/3}V{1/3}O{3} are reported.
Uncorrelated finite size structural domains occurring in the honeycomb planes
are expected to inhibit long range magnetic order. Surprisingly, ESR data
reveal the development of two collinear antiferromagnetic (AFM) sublattices
below ~ 20 K whereas NMR results show the presence of the staggered internal
field. Magnetization data evidence a spin reorientation transition at ~ 5.7 T.
Quantum Monte-Carlo calculations show that switching on the coupling between
the honeycomb spin planes in a finite size cluster yields a Neel-like AFM spin
structure with a substantial staggered magnetization at finite temperatures.
This may explain the occurrence of a robust AFM state in InCu{2/3}V{1/3}O{3}
despite an unfavorable effect of structural disorder.Comment: revised version, accepted as a Rapid Communication in Phys. Rev. B
(2010
Magnetic Properties of the low dimensional spin system (VO)PO: ESR and susceptibility
Experimental results on magnetic resonance (ESR) and magnetic susceptibility
are given for single crystalline (VO)PO. The crystal growth
procedure is briefly discussed. The susceptibility is interpreted numerically
using a model with alternating spin chains. We determine =51 K and
=0.2. Furthermore we find a spin gap of meV from our ESR
measurements. Using elastic constants no indication of a phase transition
forcing the dimerization is seen below 300 K.Comment: 7 pages, REVTEX, 7 figure
Acoustic Faraday effect in TbGaO
The transverse acoustic wave propagating along the [100] axis of the cubic
TbGaO (acoustic mode) is doubly degenerate. A magnetic
field applied in the direction of propagation lifts this degeneracy and leads
to the rotation of the polarization vector - the magneto-acoustic Faraday
rotation. Here, we report on the observation and analysis of the
magneto-acoustic Faraday-effect in TbGaO in static and pulsed
magnetic fields. We present also a theoretical model based on magnetoelastic
coupling of 4 electrons to both, acoustic and optical phonons and an
effective coupling between them. This model explains the observed linear
frequency dependence of the Faraday rotation angle
Lifetimes of ultralong-range Rydberg molecules in vibrational ground and excited state
Since their first experimental observation, ultralong-range Rydberg molecules
consisting of a highly excited Rydberg atom and a ground state atom have
attracted the interest in the field of ultracold chemistry. Especially the
intriguing properties like size, polarizability and type of binding they
inherit from the Rydberg atom are of interest. An open question in the field is
the reduced lifetime of the molecules compared to the corresponding atomic
Rydberg states. In this letter we present an experimental study on the
lifetimes of the ^3\Sigma (5s-35s) molecule in its vibrational ground state and
in an excited state. We show that the lifetimes depends on the density of
ground state atoms and that this can be described in the frame of a classical
scattering between the molecules and ground state atoms. We also find that the
excited molecular state has an even more reduced lifetime compared to the
ground state which can be attributed to an inward penetration of the bound
atomic pair due to imperfect quantum reflection that takes place in the special
shape of the molecular potential
GHz Rabi flopping to Rydberg states in hot atomic vapor cells
We report on the observation of Rabi oscillations to a Rydberg state on a
timescale below one nanosecond in thermal rubidium vapor. We use a
bandwidth-limited pulsed excitation and observe up to 6 full Rabi cycles within
a pulse duration of ~ 4 ns. We find good agreement between the experiment and
numerical simulations based on a surprisingly simple model. This result shows
that fully coherent dynamics with Rydberg states can be achieved even in
thermal atomic vapor thus suggesting small vapor cells as a platform for room
temperature quantum devices. Furthermore the result implies that previous
coherent dynamics in single atom Rydberg gates can be accelerated by three
orders of magnitude.Comment: 4 pages, 3 figure
Real space renormalization group approach to the 2d antiferromagnetic Heisenberg model
The low energy behaviour of the 2d antiferromagnetic Heisenberg model is
studied in the sector with total spins by means of a renormalization
group procedure, which generates a recursion formula for the interaction matrix
of 4 neighbouring " clusters" of size ,
from the corresponding quantities . Conservation
of total spin is implemented explicitly and plays an important role. It is
shown, how the ground state energies , approach each
other for increasing , i.e. system size. The most relevant couplings in the
interaction matrices are generated by the transitions
between the ground states
() on an -cluster of size , mediated
by the staggered spin operator Comment: 18 pages, 8 figures, RevTe
On the absence of ferromagnetism in typical 2D ferromagnets
We consider the Ising systems in dimensions with nearest-neighbor
ferromagnetic interactions and long-range repulsive (antiferromagnetic)
interactions which decay with a power, , of the distance. The physical
context of such models is discussed; primarily this is and where,
at long distances, genuine magnetic interactions between genuine magnetic
dipoles are of this form. We prove that when the power of decay lies above
and does not exceed , then for all temperatures, the spontaneous
magnetization is zero. In contrast, we also show that for powers exceeding
(with ) magnetic order can occur.Comment: 15 pages, CMP style fil
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