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1.
Donald Marolf 《General Relativity and Gravitation》2009,41(4):903-917
This brief conference proceeding attempts to explain the implications of the anti-de Sitter/conformal field theory (AdS/CFT)
correspondence for black hole entropy in a language accessible to relativists and other non-string theorists. The main conclusion
is that the Bekenstein–Hawking entropy S
BH
is the density of states associated with certain superselections sectors, defined by what may be called the algebra of boundary
observables. Interestingly while there is a valid context in which this result can be restated as “S
BH
counts all states inside the black hole,” there may also be another in which it may be restated as “S
BH
does not count all states inside the black hole, but only those that are distinguishable from the outside.” The arguments
and conclusions represent the author’s translation of the community’s collective wisdom, combined with a few recent results. 相似文献
2.
U. P. Verma N. Devi S. Sharma P. Jensen 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,81(4):381-386
First-principles calculations based on the density functional theory are
performed to study the structural properties, spin-polarized electronic band
structures, density of states and magnetic properties of the zinc blende
In1−
x
Mn
x
Sb (x = 0.125, 0.25, 0.50, 0.75, 1.0).
The calculated lattice constants of In1−
x
Mn
x
Sb
obey the Vegard’s law with a marginal upward bowing. With the increase of Mn
concentration in In1−
x
Mn
x
Sb, a transition from
the semi-metallic to the half-metallic behavior happens such that the
majority-spin valence states crosses the Fermi level and the minority-spin
states have a gap at the Fermi level. A large exchange splitting
(∼ 4 eV) is observed between Mn 3d states of the majority-spins
and the minority-spins. The total magnetic moment of
In1−
x
Mn
x
Sb half-metallic ferromagnets per Mn
atom basis is 4μ
B. The total magnetic moment per Mn atom
indicate that Mn atoms act as acceptors in InSb and contribute to holes in
the lattice of InSb. Due to p-d hybridization, the free space charge of Mn
reduces that results a loss in its magnetic moment. The loss in the magnetic
moment of the Mn atoms is converted into a small local magnetic moments on
the In and Sb sites. 相似文献
3.
Yu. N. Ovchinnikov 《JETP Letters》1997,65(8):632-637
The magnetic induction in cylindrical superconductor samples in magnetic fields close to H
c2 is found. It is shown that vortex-type metastable states exist in a quite wide range of values of the Ginzburg-Landau parameter
κ<1 corresponding to type-I superconductors.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 600–605 (25 April 1997) 相似文献
4.
Mahendra K. Verma 《Pramana》2003,61(3):577-594
Energy cascade rates and Kolmogorov’s constant for non-helical steady magnetohydrodynamic turbulence have been calculated
by solving the flux equations to the first order in perturbation. For zero cross helicity and space dimensiond = 3, magnetic energy cascades from large length-scales to small length-scales (forward cascade). In addition, there are energy
fluxes from large-scale magnetic field to small-scale velocity field, large-scale velocity field to small-scale magnetic field,
and large-scale velocity field to large-scale magnetic field. Kolmogorov’s constant for magnetohydrodynamics is approximately
equal to that for fluid turbulence (≈ 1.6) for Alfvén ratio 05 ≤r
A ≤ ∞. For higher space-dimensions, the energy fluxes are qualitatively similar, and Kolmogorov’s constant varies asd
1/3. For the normalized cross helicity σc →1, the cascade rates are proportional to (1 − σc)/(1 + σc , and the Kolmogorov’s constants vary significantly with σcc. 相似文献
5.
S. F. Dubinin S. G. Teploukhov V. E. Arkhipov V. D. Parkhomenko é. A. Nefeld A. V. Korolev N. A. Ugryumova Ya. M. Mukovski 《Physics of the Solid State》2007,49(4):739-745
The structural and magnetic states of Pr1−x
Sr
x
MnO3 (x = 0.22, 0.24) manganite crystals were studied over a wide temperature range. Measurements of the magnetic susceptibility
and electrical resistivity demonstrated that these manganites belong to the class of ferromagnetic semiconductors. Thermal
neutron elastic scattering patterns revealed that, in the temperature range 4.2–350 K, the manganites have an orthorhombic
structure (space group Pnma) with a well-pronounced cooperative Jahn-Teller effect. Major emphasis was placed on the nuclear magnetic superstructure
with a wave vector q = (2π/2a, 0, 2π/2c). It was shown that this superstructure suggests 1/4-type charge ordering in the manganites under investigation.
Original Russian Text ? S.F. Dubinin, S.G. Teploukhov, V.E. Arkhipov, V.D. Parkhomenko, é.A. Neĭfel’d, A.V. Korolev, N.A.
Ugryumova, Ya.M. Mukovskiĭ, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 4, pp. 704–710. 相似文献
6.
L. P. Gor’kov 《JETP Letters》1998,68(9):738-744
For the vortex lattice in an anisotropic superconductor with well-separated cores (H
c1≪ B≪H
c2) it is shown that sizable de Haas-van Alphen oscillations are caused by the levels’ crossing of the energy threshold separating
localized and extended states of excitations moving in the average magnetic field B.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 9, 705–710 (10 November 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
7.
The magnetic behavior of a solid solution, Ca3 x Yx CO2 O6, based on the ‘exotic’ spin-chain compound, Ca3Co2O6, crystallizing in K4CdCl6-derived rhombohedral structure is investigated. Among the compositions investigated(x = 0.0, 0.3, 0.5, 0.75 and 1.0), single-phase formation persists up tox = 0.75, with the elongation of the c-axis. The present investigations reveal that the temperature at which the ‘so-called’
‘partially disordered antiferromagnetic structure’ sets in (which occurs at 24 K for the parent compound,x = 0.0) undergoes gradual reduction with the substitution of Y for Ca, attaining the value of about 2.2 K for the nominalx = 1.0. The trend observed in this characteristic temperature is opposite to that reported under external pressure, thereby
establishing that Y substitution exerts negative chemical pressure. Anomalous steps observed in the isothermal magnetization
at very low temperatures (around 2 K) forx = 0.0, which have been proposed to arise from ‘quantum tunneling effects’ are found to vanish by a small substitution (x = 0.3) of Y for Ca. Systematics in AC and DC magnetic susceptibility behavior with Y substitution for Ca have also been probed.
We believe that the present results involving the expansion of chain length without disrupting the magnetic chain may be useful
to the overall understanding of the novel magnetism of the parent compound. 相似文献
8.
A microscopic theory of interplay of superconductivity and antiferromagnetism in rare earth ternary systems is developed from
first principles for less than half filledf atomic shells. Self consistent equations for the superconducting order parameter Δ and magnetic order parameter Γ, are derived
using a Green’s function technique and equation of motion method. The theory is applied to explain the experimental results
in the antiferromagnetic superconductor SmRh4B4. The present model explains true coexistence of superconductivity and antiferromagnetism and the suppression of superconductivity
by antiferromagnetism. The behaviour of superconducting order parameter (Δ), magnetic order parameter (Γ), the specific heat,
the density of states, free energy and critical field (H
c) is also studied for the system SmRh4B4. 相似文献
9.
M. de Souza A.-A. Haghighirad U. Tutsch W. Assmus M. Lang 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,77(1):101-107
We report on synthesis, structural characterization, resistivity, magnetic and thermal expansion measurements on the as yet
unexplored δ’-phase of FeSe1
-x
, here synthesized under ambient- (AP) and high-pressure (HP) conditions. We show that in contrast to β-FeSe1
-x
, monophasic superconducting δ’-FeSe1
-x
can be obtained in off-stoichiometric samples with excess Fe atoms preferentially residing in the van der Waals gap between
the FeSe layers. The AP δ’-FeSe1
-x
sample studied here (T
c
@\simeq 8.5 K) possesses an unprecedented residual resistivity ratio RRR
@\simeq 16. Thermal expansion data reveal a small feature around ~90 K, which resembles the anomaly observed at the structural and
magnetic transitions for other Fe-based superconductors, suggesting that some kind of “magnetic state” is formed also in FeSe.
For HP samples (RRR
@\simeq 3), the disorder within the FeSe layers is enhanced through the introduction of vacancies, the saturated magnetic moment
of Fe is reduced and only spurious superconductivity is observed. 相似文献
10.
S. A. Nemov V. I. Proshin G. L. Tarantasov R. V. Parfen’ev D. V. Shamshur A. V. Chernyaev 《Physics of the Solid State》2009,51(3):491-494
The temperature dependences of the coefficient of the transverse Nernst-Ettingshausen effect in SnTe: In samples with different indium contents (1–16 at %) in the temperature range 100–300 K and the electrical resistivity at temperatures of 1.2–4.2 K and in magnetic fields of up to 10 kOe are investigated. The data obtained indicate the presence of resonant hole scattering into the band of quasi-local In impurity states in Sn1?x In x Te samples with In content x ≥ 0.05 and a superconducting transition with a critical temperature T c ~ 1.5–2.2 K. The SnTe: In samples with the degree of filling of impurity states by electrons, which is close to 1/2, and the Fermi level ?F pinned in the vicinity of the minimum energy dependence of the relaxation time τ(?) are characterized by inhomogeneities of a new type, i.e., inhomogeneities of the scattering parameter r = ?lnτ/?ln?| $ \varepsilon _F The temperature dependences of the coefficient of the transverse Nernst-Ettingshausen effect in SnTe: In samples with different
indium contents (1–16 at %) in the temperature range 100–300 K and the electrical resistivity at temperatures of 1.2–4.2 K
and in magnetic fields of up to 10 kOe are investigated. The data obtained indicate the presence of resonant hole scattering
into the band of quasi-local In impurity states in Sn1−x
In
x
Te samples with In content x ≥ 0.05 and a superconducting transition with a critical temperature T
c
∼ 1.5–2.2 K. The SnTe: In samples with the degree of filling of impurity states by electrons, which is close to 1/2, and
the Fermi level ɛF pinned in the vicinity of the minimum energy dependence of the relaxation time τ(ɛ) are characterized by inhomogeneities
of a new type, i.e., inhomogeneities of the scattering parameter r = ϖlnτ/∂lnɛ|, which are induced by fluctuations of the degree of filling of quasi-local states by electrons.
Original Russian Text ? S.A. Nemov, V.I. Proshin, G.L. Tarantasov, R.V. Parfen’ev, D.V. Shamshur, A.V. Chernyaev, 2009, published
in Fizika Tverdogo Tela, 2009, Vol. 51, No. 3, pp. 461–464. 相似文献
11.
D. N. Aristov 《JETP Letters》1999,70(6):410-414
The Landau quantization for the electron gas on the surface of a sphere is considered. It is shown that in the regime of strong
fields the lowest energy states are those with magnetic quantum numbers m of order of Φ /Φ0, the number of magnetic flux quanta piercing the sphere. For an electron gas of low density (semiconducting situation) it
leads to the formation of an electronic stripe on the equator of the sphere in high fields.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 6, 405–409 (25 September 1999)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
12.
R. B. Morgunov A. I. Dmitriev A. S. Chernen’kaya K. Yakushi K. Yamamoto Y. Tanimoto 《Journal of Experimental and Theoretical Physics》2010,111(5):857-864
Sharp changes in the integral intensity and linewidth of the ESR spectrum that accompany the localization of the charge carriers
have been revealed in α’-(BEDT-TTF)2IBr2 crystals. It has been found that the types of localization in two compounds under investigation are different: charge carriers
in β″-(BEDT-TTF)4NH4[Cr(C2O4)3] are localized on irregular defects of the crystal lattice, whereas charge carriers in α’-(BEDT-TTF)2IBr2 are localized at the regular positions of the unit cell. The exchange narrowing of the ESR line and a sharp decrease in the
dc and ac magnetic susceptibilities are observed in α’-(BEDT-TTF)2IBr2 at low temperatures T < 50 K. The dc and ac magnetic susceptibilities observed in α’-(BEDT-TTF)2IBr2 at high temperatures T > 50 K differ from each other, because the thermally activated hopping frequency of the charge carriers is higher than the
frequency of the measuring UHF field of an ESR spectrometer. 相似文献
13.
P Mukherjee 《Pramana》2001,57(1):5-9
Experimental studies of nuclear excitations have been an important subject from the earliest days when the institute was established.
The construction of 4 MeV proton cyclotron was mainly aimed to achieve this goal. Early experiments in nuclear spectroscopy
were done with radioactive nuclei with the help of beta and gamma ray spectrometers. Small NaI(Tl) detectors were used for
gamma-gamma coincidence, angular correlation and life time measurements. The excited states nuclear magnetic moments were
measured in perturbed gamma-gamma angular correlation experiments. A high transmission magnetic beta ray spectrometer was
used to measure internal conversion coefficients and beta-gamma coincidence studies. A large number of significant contributions
were made during 1950–59 using these facilities. Proton beam in the cyclotron was made available in the late 1950’s and together
with 14 MeV neutrons obtained from a C-W generator a large number of short-lived nuclei were investigated during 1960’s and
1970’s. The introduction of high resolution Ge gamma detectors and the improved electronics helped to extend the spectroscopic
work which include on-line (p
7
p′γ) and (p
7
nγ) reaction studies. Nuclear spectroscopic studies entered a new phase in the 1980’s with the availability of 40–80 MeV alpha
beam from the variable energy cyclotron at VECC, Calcutta. A number of experimental groups were formed in the institute to
study nuclear level schemes with (α
7
xnγ) reactions. Initially only two unsuppressed Ge detectors were used for coincidence studies. Later in 1989 five Ge detectors
with a large six segmented NaI(Tl) multiplicitysum detector system were successfully used to select various channels in (α
7
xnγ) reactions. From 1990 to date a variety of medium energy heavy ions were made available from the BARC-TIFR Pelletron and
the Nuclear Science Centre Pelletron. The state of the art gamma detector arrays in these centres enabled the Saha Institute
groups to undertake more sophisticated experiments. Front line nuclear spectroscopy works are now being done and new informations
are obtained for a large number of nuclei over a wide mass range. Currently Saha Institute is building a multi-element gamma
heavy ion neutron array detector (MEGHNAD), which will have six high efficiency clover Ge detector together with charged particle
ball and other accessories. The system is expected to be usable in 2002 and will be used in experiments using high energy
heavy ions from VECC. 相似文献
14.
Takasada Shibauchi Tsuyoshi Kawakami Yuhki Terao Minoru Suzuki Lia Krusin-Elbaum 《Pramana》2006,66(1):305-312
Vortex and pseudogap states in electron-doped Sm2−x
Ce
x
CuO4−δ (x ∼ 0.14) are investigated by the interlayer transport in magnetic fields up to 45 T. To extract intrinsic properties, we fabricated
small 30 nm-high mesa structures, sufficiently thin to be free of the recently reported partial decomposition problems. On
cooling, the c-axis resistivity ρc of the mesa structures reveals a semiconductive upturn above Tc, followed by a sharp superconducting transition at 20 K. When the magnetic fieldH is applied along the c-axis, ρc(T) shows a parallel shift without significant broadening, as also observed in the hole-doped underdoped cuprates. Above the
transition we observe negative magnetoresistance (MR), which can be attributed to the field suppression of the pseudogap,
whose magnitude is as small as 38 K. Our results in thex ∼ 0.14 samples closely correspond to the interlayer transport behavior in the ‘overdoped’ regime of hole-doped Bi2Sr2 CaCu2 O8+y. 相似文献
15.
A systematic semiquantitative account of all aspects of the strong and electromagnetic interactions of all the newly discovered
hadronic states (theψ’s, theχ’s, etc.) is presented within the framework of the paracharge scheme. Extensions of ideas familiar from the SU3 classification scheme to SU4 are shown to provide an understanding of the new states seen in the decays ofψ (3.1) andψ′ (3.7), including their masses and gross decay characteristics. The decays ofψ (3.1) andψ′ (3.7) themselves are studied in some detail. Since these are of electromagnetic origin in the scheme, their electromagnetic
mixing with the resonance at 4.15 GeV (theP-state of the scheme) is important. Once this is taken into account, the resulting picture is in excellent agreement with
available data. 相似文献
16.
The value of adjustable parameterC in the four-parameter potentialU(r) =D
e [(1 - exp[-b(r -r
e)])/(1 -C exp[-b(r -r
e)])]2 has been expressed in terms of molecular parameters and its significance has been brought out. The potential so constructed,
withC derived from the molecular parameters, has been applied to ten electronic states in addition to the states studied by Wei
Hua. Average mean deviation for these 25 states has been found to be 3.47 as compared to 6.93, 6.95 and 9.72 obtained from
Levine, Varshni and Morse potentials, respectively. Also Dunham’s method has been used to express rotation-vibration interaction
constant (αe) and anharmonicity constant (ωexe) in terms ofC and other molecular constants. These relations have been employed to determine these quantities for 37 electronic states.
For αe, the average mean deviation is 7.2% compared to 19.7% for Lippincott’s potential which is known to be the best to predict
these values. Average mean deviation for (ωexe) turns out to be 17.4% which is almost the same as found from Lippincott’s potential function. 相似文献
17.
H R Krishnamurthy 《Pramana》2005,64(6):1063-1074
Rare earth manganites doped with alkaline earths, namely Re1-xAxMnO3, exhibit colossal magnetoresistance, metal insulator transitions, competing magnetic, orbital and charge ordering, and many
other interesting but poorly understood phenomena. In this article I outline our recent theory based on the idea that in the
presence of strong Jahn-Teller, Coulomb and Hund’s couplings present in these materials, the low-energy electronic states
dynamically reorganize themselves into two sets: one set (ℓ) which are polaronic, i.e., localized and accompanied by large
local lattice distortion, and another (b) which are non-polaronic and band-like. The coexistence of the radically different
ℓ andb states, and the sensitive dependence of their relative energies and occupation upon dopingx, temperatureT, magnetic fieldH, etc., underlies the unique effects seen in manganites. I present results from strong correlation calculations using dynamical
mean-field theory and simulations on a new 2-fluid model which accord with a variety of observations. 相似文献
18.
O. Yu. Gorbenko R. V. Demin A. R. Kaul’ L. I. Koroleva R. Szymczak 《Physics of the Solid State》1998,40(2):263-267
A study is reported of the magnetic, electrical, and crystallographic properties of La1−x
SrxMnO3 (0.15⩽x⩽0.23) epitaxial films grown on single-crystal substrates of (001)ZrO2(Y2O3) having the fluorite structure and (001)LaAlO3 having the perovskite structure. It was found that films with close compositions for x=0.15 and 0.16, grown on different substrates, have different properties, namely, the film on a fluorite substrate is semiconducting
and has a coercive strength 30 times that of the film on a perovskite substrate; the temperature dependence of electrical
resistance of the latter film has a maximum around the Curie point T
C and follows metallic behavior for T<T
C. These differences are explained as due to different structures of the films. The x=0.23 film on the perovskite substrate has been found to exhibit a combination of giant magnetoresistance at room temperature
with a resistance of ≈300 Ω which is useful for applications. The maxima in resistance and absolute value of negative magnetoresistance
are accounted for by the existence of two-phase magnetic states in these films.
Fiz. Tverd. Tela (St. Petersburg) 40, 290–294 (February 1998) 相似文献
19.
V. A. Kul’bachinskii A. Yu. Kaminskii N. Miyajima M. Sasaki H. Negishi M. Inoue H. Kadomatsu 《JETP Letters》1999,70(11):767-771
The quantization of the Hall resistivity ρxy in the form of plateaus in the dependence of ρxy on the magnetic field B is observed in the semiconductors Bi2Te3 and Sb2Te3; the minima of the transverse magnetoresistivity ρxx correspond to the start of the plateaus. The quantization of ρxy is due to the presence of a current-carrier reservoir. An impurity band with a high density of states or a different band
with a much higher current-carrier effective mass serves as the reservoir.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 11, 754–758 (10 December 1999) 相似文献
20.
J. G. Du X. Y. Sun G. Jiang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,55(1):111-120
The equilibrium structures, electronic properties of bimetallic Ti1-4M
(M=V, Fe, Ni) clusters are investigated by using the density functional
method within generalized gradient approximation in conjunction with the
valence basis set. Considering the spin multiplicity effect, the geometries
with different spins are optimized to find the ground states. For the ground
states, the natural bonding orbital analysis (NBO) is performed and shows
that the 4s electrons always transfer to the 3d orbital in the bonding atoms
so that 4s and 3d orbitals hybridize with each other. The electron transfers
from Ti atoms to the ‘impurity’ atoms (V, Fe, and Ni) are also found. The
two kinds of electron transfer mechanisms are considered to be the
contributor for the stabilities of the studied clusters. The Wiberg bond order and
AIM (atoms in molecules) analyses indicate that the relative stabilities of
chemical bonds are: $\text{Ti-V/Ti-Fe} > \text{Ti-Ti} > \text{Ti-Ni}$\text{Ti-V/Ti-Fe} > \text{Ti-Ti} > \text{Ti-Ni}. The spin magnetic
moments are found to be mostly located at Ti atoms. Several clusters like
Ti2V, Ti3V, Ti3Ni and Ti4Ni present the high moments. 相似文献