1,298 research outputs found
New approach to extract important degrees of freedom in quantum dynamics using singular value decomposition: Application to linear optical spectrum in two-dimensional Mott insulators
We propose a new approach to extract the important degrees of freedom in
quantum dynamics induced by an external stimulus. We calculate the coefficient
matrix numerically, where the element of the matrix is the coefficient of
the lth basis state at the ith discretized time in the solution of the
time-dependent Schr\"odinger equation induced by the external stimulus. By
performing a randomized singular value decomposition of the coefficient matrix,
a practically exact solution is obtained using a linear combination of the
important modes, where the number of modes is much smaller than the dimensions
of the Hilbert space in many cases. We apply this method to analysis of the
light absorption spectrum in two-dimensional (2D) Mott insulators using an
effective model of the 2D Hubbard model in the strong interaction case. From
the dynamics induced by an ultrashort weak light pulse, we find that the
practically exact light absorption spectrum can be reproduced by as few as 1000
energy eigenstates in the -dimension Hilbert space of a
26-site cluster. These one-photon active energy eigenstates are classified into
free holon and doublon (H-D) and localized H-D states. In the free H-D states,
the main effect of the spin degrees of freedom on the transfer of a holon (H)
and a doublon (D) is the phase shift, and the H and the D move freely. In the
localized H-D states, an H and a D are localized with relative distances of
or . The antiferromagnetic (AF) spin orders in the
localized H-D states are much stronger than those in the free H-D states, and
the charge localization is of magnetic origin. There are sharp peaks caused by
excitations to the localized H-D states below the broad band caused by
excitations to the free H-D states in the light absorption spectrum
New records of lichens from the Russian Far East. I. Fuscidea submollis and other arctic-alpine species
Summary. Fuscidea submollis Mas. Inoue is reported for the first time from the Russian Far East. Distinctive features of the taxon are discussed, and a comparison with known saxicolous Fuscidea V. Wirth & Vězda species with amyloid medulla is made. Three arctic-alpine species: Sporastatia testudinea (Ach.) A. Massal., Buellia concinna Th. Fr., Amygdalaria panaeola (Ach.) Hertel et Brodo, and Aspilidea myrinii (Fr.) Hafellner are recorded for the first time in the South Far East from the Sikhote Alin Range (Primorye Territory). Calvitimela aglaea (Sommerf.) Hafellner is reported for the first time from Sikhote Alin Range and Primorye Territory. © 2019 Altai State University. All rights reserved.Japan Society for the Promotion of Science, JSPS: 19-54-50010Russian Foundation for Basic Research, RFBRThe reported study was funded by RFBR and JSPS according to the research project № 19-54-50010
Rate- and State-Dependent Friction Law and Statistical Properties of Earthquakes
In order to clarify how the statistical properties of earthquakes depend on
the constitutive law characterizing the stick-slip dynamics, we make an
extensive numerical simulation of the one-dimensional spring-block model with
the rate- and state-dependent friction law. Both the magnitude distribution and
the recurrence-time distribution are studied with varying the constitutive
parameters characterizing the model. While a continuous spectrum of seismic
events from smaller to larger magnitudes is obtained, earthquakes described by
this model turn out to possess pronounced ``characteristic'' features.Comment: Minor revisions are made in the text and in the figures. Accepted for
publication in Europhys. Letter
Pressure-induced phase transition of Bi2Te3 into the bcc structure
The pressure-induced phase transition of bismuth telluride, Bi2Te3, has been
studied by synchrotron x-ray diffraction measurements at room temperature using
a diamond-anvil cell (DAC) with loading pressures up to 29.8 GPa. We found a
high-pressure body-centered cubic (bcc) phase in Bi2Te3 at 25.2 GPa, which is
denoted as phase IV, and this phase apperars above 14.5 GPa. Upon releasing the
pressure from 29.8 GPa, the diffraction pattern changes with pressure
hysteresis. The original rhombohedral phase is recovered at 2.43 GPa. The bcc
structure can explain the phase IV peaks. We assumed that the structural model
of phase IV is analogous to a substitutional binary alloy; the Bi and Te atoms
are distributed in the bcc-lattice sites with space group Im-3m. The results of
Rietveld analysis based on this model agree well with both the experimental
data and calculated results. Therefore, the structure of phase IV in Bi2Te3 can
be explained by a solid solution with a bcc lattice in the Bi-Te (60 atomic%
tellurium) binary system.Comment: 12 pages, 5 figure
p-wave superconductivity in iron-based superconductors
The possibility of p-wave pairing in superconductors has been proposed more than five decades ago, but has not yet been convincingly demonstrated. One difficulty is that some p-wave states are thermodynamically indistinguishable from s-wave, while others are very similar to d-wave states. Here we studied the self-field critical current of NdFeAs(O,F) thin films in order to extract absolute values of the London penetration depth, the superconducting energy gap, and the relative jump in specific heat at the superconducting transition temperature, and find that all the deduced physical parameters strongly indicate that NdFeAs(O,F) is a bulk p-wave superconductor. Further investigation revealed that single atomic layer FeSe also shows p-wave pairing. In an attempt to generalize these findings, we re-examined the whole inventory of superfluid density measurements in iron-based superconductors and show quite generally that single-band weak-coupling p-wave superconductivity is exhibited in iron-based superconductors. © 2019, The Author(s).Japan Science and Technology Corporation, JST: JPMJCR18J4Government Council on Grants, Russian FederationJapan Society for the Promotion of Science, JSPS: 16H04646АААА-А18-118020190104-3The authors thank Prof. Jeffery L. Tallon (Victoria University of Wellington, New Zealand) and Prof. Christian Bernhard (University of Fribourg, Switzerland) for helpful discussions, and also for reading and commenting on the manuscript. EFT is grateful for financial support provided by the state assignment of Minobrnauki of Russia (theme “Pressure” No. АААА-А18-118020190104-3) and by Act 211 of the Government of the Russian Federation, contract No. 02.A03.21.0006. KI and HI acknowledge support by the Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for Scientific Research (B) Grant Number 16H04646, as well as JST CREST Grant Number JPMJCR18J4. The Article Processing Charge for this publication was provided by Ural Federal University, Russia
Superconducting and structural properties of the type-I superconductor PdTe<sub>2</sub> under high pressure
The transition metal dichalcogenide PdTe has attractive features based on
its classification as a type-II Dirac semimetal and the occurrence of type-I
superconductivity, providing a platform for discussion of a topological
superconductor. Our recent work revealed that type-I superconductivity persists
up to pressures of GPa and the superconducting transition temperature
reaches a maximum at around 1 GPa, which is inconsistent with the
theoretical prediction. To understand its non-monotonic variation and
investigate superconductivity at higher pressures, we performed structural
analysis by x-ray diffraction at room temperature below 8 GPa and electrical
resistivity measurements at low temperatures from 1 to 8 GPa. With regard to
the superconductivity beyond 1 GPa, the monotonic decrease in is
reproduced without any noticeable anomalies; changes from 1.8 K at
1 GPa to 0.82 K at 5.5 GPa with K/GPa. The crystal
structure with spacegroup \={3}1 is stable in the pressure range we
examined. On the other hand, the normalized pressure-strain analysis (finite
strain analysis) indicates that the compressibility changes around 1 GPa,
suggesting that a Lifshitz transition occurs. We here discuss the effect of
pressure on the superconducting and structural properties based on the
comparison of these experimental results
Dissociation dynamics of ethylene molecules on a Ni cluster using ab initio molecular dynamics simulations
is investigated by ab initio molecular-dynamics simulations. The activation free energy to
dehydrogenate an ethylene molecule on the Ni cluster and the corresponding reaction rate is
estimated. A remarkable finding is that the adsorption energy of ethylene molecules on the Ni
cluster is considerably larger than the activation free energy, which explains why the actual
reaction rate is faster than the value estimated based on only the activation free energy. It is
also found from the dynamic simulations that hydrogen molecules and an ethane molecule
are formed from the dissociated hydrogen atoms, whereas some exist as single atoms on the
surface or in the interior of the Ni cluster. On the other hand, the dissociation of the C-C bonds
of ethylene molecules is not observed. On the basis of these simulation results, the nature of
the initial stage of carbon nanotube growth is discussed.
Keywords: nickel cluster, ethylene molecule, dissociation, ab initio molecular dynamics
simulation, activation energy, adsoption energ
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