共查询到20条相似文献,搜索用时 31 毫秒
1.
V. Vescoli F. Zwick W. Henderson L. Degiorgi M. Grioni G. Gruner L.K. Montgomery 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(3):503-511
Combined optical and photoemission experiments on the quasi-one dimensional Bechgaard salts reveal the non-Fermi liquid character
of these prototype quasi-one dimensional interacting electron systems. We show that various aspects of the exotic normal state
properties along the chains are consistent with the predictions of the Tomonaga-Luttinger liquid theory. We also discuss the
effect of interchain coupling on the insulator-metal transition, associated with the electron confinement-deconfinement crossover.
Received 17 May 1999 and Received in final form 13 July 1999 相似文献
2.
F. Pfuner J. G. Analytis J.-H. Chu I. R. Fisher L. Degiorgi 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(4):513-517
We report on a thorough optical investigation of BaFe2As2 over a broad spectral range and as a function of temperature, focusing our attention on its spin-density-wave (SDW) phase
transition at TSDW = 135 K. While BaFe2As2 remains metallic at all temperatures, we observe a depletion in the far infrared energy interval of the optical conductivity
below TSDW, ascribed to the formation of a pseudogap-like feature in the excitation spectrum. This is accompanied by the narrowing of
the Drude term consistent with the dc transport results and suggestive of suppression of scattering channels in the SDW state.
About 20% of the spectral weight in the far infrared energy interval is affected by the SDW phase transition. 相似文献
3.
B. Ruzicka L. Degiorgi U. Ammerahl G. Dhalenne A. Revcolevschi 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):301-305
The optical reflectivity as a function of temperature of the title compound for x
=0, 5 and 12 has been measured over a broad spectral range from 4 meV up to 12 eV. Our findings suggest a very anisotropic dynamics
of the charge excitation spectrum when measuring along or perpendicular to the ladders. Moreover, a metal-insulator transition
develops at low temperatures, leading to a suppression of Drude spectral weight in the far and mid-infrared spectral range.
We identify this behaviour as a consequence of the localization effects for small Ca substitution, and of the possible formation
of a charge density wave condensate for large Ca substitution.
Received: 18 June 1998 /
Accepted: 17 July 1998 相似文献
4.
B. Ruzicka A. Brglez B. Malic L. Degiorgi D. Mihailovic 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):205-208
We present the results of a dc transport and optical investigation of WO3 and NaxWO3 with x
=0.01. Upon Na-doping we find a (Drude) metallic component in the optical conductivity, while the transport data display a crossover
from an activated to a variable range hopping regime around 210 K. We suggest the possible formation of polarons (and bipolarons)
and speculate that superconductivity could be induced, provided the dc percolation threshold is achieved.
Received 28 March 2000 相似文献
5.
L. Liu J.T. Liu 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(3):381-388
For photons propagating in a periodic dielectric lattice, the dispersion curve forms photonic bands separated by forbidden
gaps. When the dielectric lattice deviates only slightly from being homogenous, the photonic band structure resembles the
linear dispersion relation for photons folded into the first Brillouin zone, i.e., the so-called empty lattice bands. Using group theoretical technique, we calculate the splitting of the accidental degeneracies
in the empty lattice bands at symmetry points for a simple cubic dielectric lattice.
Received 23 June 1998 相似文献
6.
A. Nayak G.L. Bhalla G.C. Trigunayat 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):319-323
Highly purified single crystals of cadmium iodide obtained through repeated zone refining have been subjected to laser beam
exposure (Argon ion laser), both for various time durations and to various beam intensities, and then subjected to band gap
determination by UV spectroscopy. The band gap has been found to decrease gradually with increase in the laser beam intensity,
whereas its variation with increase in time of exposure shows an unusual behaviour such that it initially falls sharply followed
by a gradual rise back to its original value. The results have been analysed and interpreted in terms of indirect band gap
character of the material and an unusual variation in phonon frequency. The interpretation is well supported by X-ray diffraction
and scanning electron microscopy (SEM) studies.
Received: 26 May 1997 / Revised: 6 August 1997 / Accepted: 15 September 1997 相似文献
7.
S.V. Dordevic D.N. Basov R.C. Dynes B. Ruzicka V. Vescoli L. Degiorgi H. Berger R. Gaál L. Forró E. Bucher 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):15-23
We present a comprehensive analysis of the optical constants of the two-dimensional dichalcogenide materials 2
H
-
TaSe
2
and 2
H
-
NbSe
2
, in an attempt to address the physics of two-dimensional correlated systems. The title compounds were studied over several
decades in frequency, from the far-infrared to the ultraviolet. Measurements with linearly polarized light have allowed us
to obtain both the in-plane and out-of-plane components of the conductivity tensor. Although the electromagnetic response
of dichalcogenides is strongly anisotropic, both the in-plane and out-of-plane components of the conductivity tensor share
many common features, including the presence of a well-defined metallic component, as well as a “mid-infrared band”. We discuss
the implications of these results in the context of the spectroscopic results of other classes of low-dimensional conductors
such as the high-temperature superconducting cuprates. In particular, the analysis of the redistribution of the spectral weight
as a function of temperature, as well as the behavior of the quasiparticles relaxation rate, points to significant distinctions
between the charge dynamics of dichalcogenides and other classes of low dimensional conductors.
Received 28 October 2002 / Received in final form 10 March 2003 Published online 23 May 2003
RID="a"
ID="a"e-mail: degiorgi@solid.phys.ethz.ch 相似文献
8.
Studies on CdS nanoparticles dispersed in silica matrix prepared by sol-gel technique 总被引:2,自引:0,他引:2
B. Bhattacharjee S.K. Bera D. Ganguli S. Chaudhuri A.K. Pal 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(1):3-9
SiO2/CdS-nanoparticle composite films (SiO2:CdS=85:15, 80:20, 75:25 and 70:30) were prepared by the sol-gel route. The films were characterized by studying microstructural
(XRD and TEM) and optical (transmittance and photoluminescence) properties. Band gaps of these films annealed at different
temperatures (373-473 K) for different times (10-120 min) indicated that the signature of nanocrystallinity is retained throughout
the range of our experimental conditions. A thermal diffusion process controlled growth in the crystallite size with increasing
annealing time and temperature. The average radii of the nanoparticles varied as the cube root of the annealing time but showed
exponential dependence on the inverse of annealing temperature. Photoluminescence (PL) studies of the composite films indicated
excitonic transitions. Theoretical analysis of the line shapes of the PL peaks recorded at 300 K and 80 K could be accounted
for by the combined effects of size distribution and phonon broadening. It was observed that the deformation potential (E
d) effectively controlled the line shapes of the PL measurements.
Received 24 May 2002 Published online 27 January 2003
RID="a"
ID="a"e-mail: msakp@mahendra.iacs.res.in 相似文献
9.
F. Pfuner L. Degiorgi K. Y. Shin I. R. Fisher 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(1):11-16
We investigate the rare-earth polychalcogenide R2Te5 (R=Nd, Sm and Gd) charge-density-wave (CDW) compounds by optical reflectivity measurements. We obtain the optical conductivity
through Kramers-Kronig transformation of the reflectivity spectra. From the real part of the optical conductivity we then
extract the excitation energy of the CDW gap and estimate the fraction of the Fermi surface which is gapped by the formation
of the CDW condensate. In analogy to previous findings on the related RTen (n=2 and 3) families, we establish the progressive closing of the CDW gap and the moderate enhancement of the metallic component
upon chemically compressing the lattice. 相似文献
10.
F. Bassani V. Lucarini 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(4):567-573
We use the Kubo response function formalism to derive the asymptotic behaviour of the harmonic generation susceptibilities
to all orders n. The results show a stringent correspondence with the ones previously obtained from the classical anharmonic oscillator model.
They are characterized by a dependence and a coefficient proportional to the trace of the (n+1)th derivative of the potential energy on the equilibrium density matrix. Using the above results we derive new Kramers-Kr?nig
relations and sum rules for all orders of harmonics susceptibilities.
Received 17 April 2000 相似文献
11.
From selective to wide-band light reflection: a simple thermal diffusion in a glassy cholesteric liquid crystal 总被引:1,自引:0,他引:1
M. Mitov A. Boudet P. Sopéna 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):327-330
Due to their helicoidal structure, cholesteric liquid crystals exhibit remarkable optical properties. Selective light reflection
occurs when the pitch (repeat distance) is of the order of the wavelength of incident light propagating along the helix axis.
The wavelength bandwidth, due to the optical anisotropy, is typically limited to 50 nm which is insufficient for some applications
(full-colors displays, for example). By introducing a pitch gradient in the helix during a novel two-step process in a cholesteric
glass, we show that reflection may occur over a wavelength bandwidth greater than 300 nm. First, the reflection bandwidth
is adjusted by thermal annealing. Then, the optical properties are permanently stored by quenching the viscous material to
a glass at room temperature. The two steps, pitch gradient establishment and film hardening, are independently controlled.
The present process exhibits some reversibility and properties intrinsic to the glassy state are gained: laser-writing high
resolution full-color images on solid films for image recording or high-density optical data-storage are indeed conceivable.
Received 17 December 1998 相似文献
12.
L. Degiorgi F.B.B. Anders G. Grüner 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):167-170
We show that the optical response of metals with strong electron-electron correlation consists of two excitations, a renormalized
Drude response at zero energy and a mid-infrared peak occurring at frequencies around 2000 cm-1. The latter originates from a dynamical, correlation-induced gap, as evinced from a many body theoretical approach based
on the periodic Anderson model. At very low temperatures, it can be viewed as optical gap between two renormalized quasi-particle
bands. The gap size is proportional to the geometric mean of the characteristic lattice Kondo temperature of the material
and its bandwidth.
Received 28 August 2000 and Received in final form 31 October 2000 相似文献
13.
O.K. Moune Y. Rabinovitch D. Tétard M. Pham-Thi E. Lallier M.D. Faucher 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(3):275-291
This paper presents an investigation of Pr3+ doped in the D2 site of Y3Al5O12 (YAG), for the first time on a translucent ceramic sample free of spurious phases, impurity or pair sites. The optical study
is carried out by optical absorption, excitation, and emission by selective excitation into 1D2 and 3P0, at different temperatures between 20 K and 60 K, in the 4 300-23 000 cm-1 range. A detailed account of the line assignments is given. 67 over 91 levels of the 4f2 configuration are determined. Several crystal field calculations within the ground configuration 4f2 and the larger matrix 4f2+4f6p are carried out. The energy level fit is slightly improved by configuration interaction. The 3P2 and 1I6 levels are strongly mixed together by the large 6th order crystal field parameters. In sintered samples with different Pr3+ concentrations, satellite lines with intensities increasing quadratically with the concentration are observed. A few weak
lines forbidden in D2 site symmetry are observed.
Received 9 November 2001 and Received in final form 8 February 2002 相似文献
14.
15.
W. Henderson V. Vescoli P. Tran L. Degiorgi G. Grüner 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):365-368
Optical experiments are reported for the metallic state of the linear chain compound (TMTSF)2ClO4. For the electric field polarized both along the highly (a) and intermediately (b
) conducting directions, a zero energy (ZE) mode and a finite energy mode (FE) are observed. The large anisotropy in the spectral
weight of the FE mode is consistent with the band structure, however the spectral weight of the ZE mode is surprisingly isotropic.
In the least conducting (c
*) direction, the low frequency optical conductivity along with the dc conductivity indicate the presence of a (small) Drude
component only at temperatures below 10 K. These observations provide evidence for a correlation induced semimetallic state,
with a 3D to 2D crossover with increasing temperature.
Received 20 May 1999 相似文献
16.
C. Z. Bi J. Y. Ma J. Yan X. Fang D. Z. Yao B. R. Zhao X. G. Qiu 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(2):167-171
Near-normal incident infrared reflectivity spectra of a
(001) YVO4 single crystal have been measured at different
temperatures in the frequency region between 100 and 6000 cm-1.
The reflectivity spectra are analyzed with the factorized form of
the dielectric function, and the dielectric properties and optical
conductivity of the YVO4 crystal are obtained. From the TO/LO
splitting, effective charges at different temperatures are
calculated to study the ionicity of YVO4. The internal modes
of the VO43- ion and the external modes of the Y(VO4) lattice
are compared with SiO44- in zircon and with other rare-earth vanadates. 相似文献
17.
A. Takahashi H. Shiba 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):413-417
The optical absorption in ferromagnetic metal La1-xSrxMnO3 is anomalous; it has a wide-range absorption up to about 1 eV even at zero temperature. Since 3d electrons in La1-xSrxMnO3 partially fill doubly degenerate eg orbitals, the orbital degrees of freedom are crucial to understand this metallic system. We argue that the interband transition
within eg orbitals is important in the optical absorption. The optical spectrum is modified also by the inter-orbital Coulomb interaction.
We have examined perturbatively the effect of the Coulomb interaction on the spectrum. Available experiments are discussed
by comparing with the present results.
Received: 13 February 1998 / Accepted: 17 March 1998 相似文献
18.
19.
R. Schuster M. Knupfer D. R.T. Zahn H. Berger 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):25-28
We have investigated the polarization and momentum
dependence of singlet excitons in pentacene molecular crystals
using inelastic electron scattering. Our results demonstrate that
both the direction as well as the absolute value of the momentum
are decisive for the spectral intensity of these excitons.
Possible implications of this observation for a microscopic
understanding of excitons in organic molecular crystals are
discussed. 相似文献
20.
T.M. Nieuwenhuizen C.N.A. van Duin 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):191-209
In realistic spinglasses, such as , and , magnetic atoms are located at random positions. Their couplings are determined by their relative positions. For such systems
a field theory is formulated. In certain limits it reduces to the Hopfield model, the Sherrington-Kirkpatrick model, and the
Viana-Bray model. The model has a percolation transition, while for RKKY couplings the “concentration scaling” occurs. Within the Gaussian approximation the Ginzburg-Landau expansion is considered in the clusterglass phase, that is
to say, for not too small concentrations. Near special points, the prefactor of the cubic term, or the one of the replica-symmetry-breaking
quartic term, may go through zero. Around such points new spin glass phases are found.
Received: 27 April 1998 / Received in final form: 27 July 1998 / Accepted: 13 August 1998 相似文献