1,124 research outputs found
Emergent SU(3) symmetry in random spin-1 chains
We show that generic SU(2)-invariant random spin-1 chains have phases with an
emergent SU(3) symmetry. We map out the full zero-temperature phase diagram and
identify two different phases: (i) a conventional random singlet phase (RSP) of
strongly bound spin pairs (SU(3) "mesons") and (ii) an unconventional RSP of
bound SU(3) "baryons", which are formed, in the great majority, by spin trios
located at random positions. The emergent SU(3) symmetry dictates that
susceptibilities and correlation functions of both dipolar and quadrupolar spin
operators have the same asymptotic behavior.Comment: 5 pages plus 3-page Supplemental Material, 5 figures; published
versio
Emergent SU(N) symmetry in disordered SO(N) spin chains
Strongly disordered spin chains invariant under the SO(N) group are shown to
display random-singlet phases with emergent SU(N) symmetry without fine tuning.
The phases with emergent SU(N) symmetry are of two kinds: one has a ground
state formed of randomly distributed singlets of strongly bound pairs of SO(N)
spins (a `mesonic' phase), while the other has a ground state composed of
singlets made out of strongly bound integer multiples of N SO(N) spins (a
`baryonic' phase). The established mechanism is general and we put forward the
cases of and as prime candidates for experimental
realizations in material compounds and cold-atoms systems. We display universal
temperature scaling and critical exponents for susceptibilities distinguishing
these phases and characterizing the enlarging of the microscopic symmetries at
low energies.Comment: 5 pages, 2 figures, Contribution to the Topical Issue "Recent
Advances in the Theory of Disordered Systems", edited by Ferenc Igl\'oi and
Heiko Riege
Highly-symmetric random one-dimensional spin models
The interplay of disorder and interactions is a challenging topic of
condensed matter physics, where correlations are crucial and exotic phases
develop. In one spatial dimension, a particularly successful method to analyze
such problems is the strong-disorder renormalization group (SDRG). This method,
which is asymptotically exact in the limit of large disorder, has been
successfully employed in the study of several phases of random magnetic chains.
Here we develop an SDRG scheme capable to provide in-depth information on a
large class of strongly disordered one-dimensional magnetic chains with a
global invariance under a generic continuous group. Our methodology can be
applied to any Lie-algebra valued spin Hamiltonian, in any representation. As
examples, we focus on the physically relevant cases of SO(N) and Sp(N)
magnetism, showing the existence of different randomness-dominated phases.
These phases display emergent SU(N) symmetry at low energies and fall in two
distinct classes, with meson-like or baryon-like characteristics. Our
methodology is here explained in detail and helps to shed light on a general
mechanism for symmetry emergence in disordered systems.Comment: 26 pages, 12 figure
Multi-Fluid Simulation of the Magnetic Field Evolution in Neutron Stars
Using a numerical simulation, we study the effects of ambipolar diffusion and
ohmic diffusion on the magnetic field evolution in the interior of an isolated
neutron star. We are interested in the behavior of the magnetic field on a long
time scale, over which all Alfven and sound waves have been damped. We model
the stellar interior as an electrically neutral plasma composed of neutrons,
protons and electrons, which can interact with each other through collisions
and electromagnetic forces. Weak interactions convert neutrons and charged
particles into each other, erasing chemical imbalances. As a first step, we
assume that the magnetic field points in one fixed Cartesian direction but can
vary along an orthogonal direction. We start with a uniform-density background
threaded by a homogeneous magnetic field and study the evolution of a magnetic
perturbation as well as the density fluctuations it induces in the particles.
We show that the system evolves through different quasi-equilibrium states and
estimate the characteristic time scales on which these quasi-equilibria occur.Comment: It will be published in AIP Proceedings of the Conference '40 Years
of Pulsars: Milisecond Pulsars, Magnetars and More' held at University of
McGill, Montreal, Canada, August 2007. Contributed Talk at Conference '40
Years of Pulsars: Milisecond Pulsars, Magnetars and More
Valence-bond theory of highly disordered quantum antiferromagnets
We present a large-N variational approach to describe the magnetism of
insulating doped semiconductors based on a disorder-generalization of the
resonating-valence-bond theory for quantum antiferromagnets. This method
captures all the qualitative and even quantitative predictions of the
strong-disorder renormalization group approach over the entire experimentally
relevant temperature range. Finally, by mapping the problem on a hard-sphere
fluid, we could provide an essentially exact analytic solution without any
adjustable parameters.Comment: 5 pages, 3 eps figure
Measurement of low frequency mechanical vibrations based on an inverted magnetic pendulum
In this paper is presented the mathematical model, design and construction of a prototype of a vibration frequency meter in an adjustable range of 2 Hz to 30 Hz; The experimental results and their analysis are also presented, making a comparative evaluation with the theoretical model. The device is based on the principle of resonance applied in an inverted magnetic pendulum whose natural frequency can be modified by variations of physical parameters. The oscillation of the pendulum is recorded detecting variations in the magnetic field using hall effect sensors; the data recorded with a microprocessor is analyzed and the results are simultaneously plotted in a computer interface. The data obtained were processed to be plotted in the frequency domain, facilitating its analysis. It was proved that the prototype can be used as a frequency meter and that the adjustable character of the device works according to the mathematical model. Finally, The effect of the friction force was studied, it was concluded that the friction force affects the measurement after a considerable period of time of oscillation, but not in the first moments
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