159,953 research outputs found
Study of the Wealth Inequality in the Minority Game
To demonstrate the usefulness of physical approaches for the study of
realistic economic systems, we investigate the inequality of players' wealth in
one of the most extensively studied econophysical models, namely, the minority
game (MG). We gauge the wealth inequality of players in the MG by a well-known
measure in economics known as the modified Gini index. From our numerical
results, we conclude that the wealth inequality in the MG is very severe near
the point of maximum cooperation among players, where the diversity of the
strategy space is approximately equal to the number of strategies at play. In
other words, the optimal cooperation between players comes hand in hand with
severe wealth inequality. We also show that our numerical results in the
asymmetric phase of the MG can be reproduced semi-analytically using a replica
method.Comment: 9 pages in revtex 4 style with 3 figures; minor revision with a
change of title; to appear in PR
Steady-state phase error for a phase-locked loop subjected to periodic Doppler inputs
The performance of a carrier phase locked loop (PLL) driven by a periodic Doppler input is studied. By expanding the Doppler input into a Fourier series and applying the linearized PLL approximations, it is easy to show that, for periodic frequency disturbances, the resulting steady state phase error is also periodic. Compared to the method of expanding frequency excursion into a power series, the Fourier expansion method can be used to predict the maximum phase error excursion for a periodic Doppler input. For systems with a large Doppler rate fluctuation, such as an optical transponder aboard an Earth orbiting spacecraft, the method can be applied to test whether a lower order tracking loop can provide satisfactory tracking and thereby save the effect of a higher order loop design
Phase String Effect in the t-J Model: General Theory
We reexamine the problem of a hole moving in an antiferromagnetic spin
background and find that the injected hole will always pick up a sequence of
nontrivial phases from the spin degrees of freedom. Previously unnoticed, such
a string-like phase originates from the hidden Marshall signs which are
scrambled by the hopping of the hole. We can rigorously show that this phase
string is non-repairable at low energy and give a general proof that the
spectral weight Z must vanish at the ground-state energy due to the phase
string effect. Thus, the quasiparticle description fails here and the quantum
interference effect of the phase string dramatically affects the long-distance
behavior of the injected hole. We introduce a so-called phase-string
formulation of the t-J model for a general number of holes in which the phase
string effect can be explicitly tracked. As an example, by applying this new
mathematical formulation in one dimension, we reproduce the well-known
Luttinger-liquid behaviors of the asymptotic single-electron Green's function
and the spin-spin correlation function. We can also use the present phase
string theory to justify previously developed spin-charge separation theory in
two dimensions, which offers a systematic explanation for the transport and
magnetic anomalies in the high-T_c cuprates.Comment: Revtex, 36 pages, no figure, to appear in Phys. Rev. B
Exploring Quantum Phase Transitions with a Novel Sublattice Entanglement Scenario
We introduce a new measure called reduced entropy of sublattice to quantify
entanglement in spin, electron and boson systems. By analyzing this quantity,
we reveal an intriguing connection between quantum entanglement and quantum
phase transitions in various strongly correlated systems: the local extremes of
reduced entropy and its first derivative as functions of the coupling constant
coincide respectively with the first and second order transition points. Exact
numerical studies merely for small lattices reproduce several well-known
results, demonstrating that our scenario is quite promising for exploring
quantum phase transitions.Comment: 4 pages, 4 figure
Bulk Rotational Symmetry Breaking in Kondo Insulator SmB6
Kondo insulator samarium hexaboride (SmB6) has been intensely studied in
recent years as a potential candidate of a strongly correlated topological
insulator. One of the most exciting phenomena observed in SmB6 is the clear
quantum oscillations appearing in magnetic torque at a low temperature despite
the insulating behavior in resistance. These quantum oscillations show multiple
frequencies and varied effective masses. The origin of quantum oscillation is,
however, still under debate with evidence of both two-dimensional Fermi
surfaces and three-dimensional Fermi surfaces. Here, we carry out
angle-resolved torque magnetometry measurements in a magnetic field up to 45 T
and a temperature range down to 40 mK. With the magnetic field rotated in the
(010) plane, the quantum oscillation frequency of the strongest oscillation
branch shows a four-fold rotational symmetry. However, in the angular
dependence of the amplitude of the same branch, this four-fold symmetry is
broken and, instead, a twofold symmetry shows up, which is consistent with the
prediction of a two-dimensional Lifshitz-Kosevich model. No deviation of
Lifshitz-Kosevich behavior is observed down to 40 mK. Our results suggest the
existence of multiple light-mass surface states in SmB6, with their mobility
significantly depending on the surface disorder level.Comment: 15 pages, 9 figure
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