共查询到12条相似文献,搜索用时 15 毫秒
1.
U. Beierlein C. Hess C. Schlenker J. Dumas R. Buder D. Groult E. Steep D. Vignolles G. Bonfait 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(2):215-226
Resistivity, thermoelectric power and magnetotransport measurements have been performed on single crystals of the quasi two-dimensional
monophosphate tungsten bronzes (PO2)4(WO3)2m for m
=5 with alternate structure, between 0.4 K and 500 K, in magnetic fields of up to 36 T. These compounds show one charge density
instability (CDW) at 160 K and a possible second one at 30 K. Large positive magnetoresistance in the CDW state is observed. The anisotropic Shubnikov-de Haas and de Haas-van Alphen
oscillations detected at low temperatures are attributed to the existence of small electron and hole pockets left by the CDW
gap openings. Angular dependent magnetoresistance oscillations (AMRO) have been found at temperatures below 30 K. The results are discussed in terms of a weakly corrugated cylindrical Fermi surface. They are shown to be consistent
with a change of the Fermi surface below 30 K.
Received 23 November 1999 and Received in final form 23 March 2000 相似文献
2.
H. Guyot J. Dumas M. V. Kartsovnik J. Marcus C. Schlenker I. Sheikin D. Vignolles 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(1):25-30
The purple molybdenum bronze KMo6O17 is a quasi-two-dimensional
compound which shows a Peierls transition towards a commensurate metallic
charge density wave (CDW) state. High magnetic field measurements have
revealed several transitions at low temperature and have provided an unusual
phase diagram “temperature-magnetic field”. Angular studies of the
interlayer magnetoresistance are now reported. The results suggest that the
orbital coupling of the magnetic field to the CDW is the most likely
mechanism for the field induced transitions. The angular dependence of the
magnetoresistance is discussed on the basis of a warped quasi-cylindrical
Fermi surface and provides information on the geometry of the Fermi surface
in the low temperature density wave state. 相似文献
3.
G. Montambaux 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(3):377-383
The stability of a Charge Density Wave (CDW) in a one-dimensional ring pierced by a Aharonov-Bohm flux is studied in a mean-field
picture. It is found that the stability depends on the parity of the number N of electrons. When the size of the ring becomes as small as the coherence length , the CDW gap increases for even N and decreases for odd N. Then when N is even, the CDW gap decreases with flux but it increases when N is odd. The variation of the BCS ratio with size and flux is also calculated. We derive the harmonics expansion of the persistent
current in a presence of a finite gap.
Received: 16 September 1997 / Received in final form: 12 November 1997 / Accepted: 13 November 1997 相似文献
4.
P. Foury-Leylekian J.P. Pouget M. Greenblatt E. Wang 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(2):157-167
We present a structural investigation of the family of quasi-one-dimensional (quasi-1D) conductors, which exhibit intriguing charge transport properties where, for x small, the conductivity exhibits a crossover from a semiconducting to a metallic like regime when the temperature decreases.
In these materials the double zig-zag chains, together with the diphosphate groups, delimit channels which are partially filled with the ions. It is found, from an X-ray diffuse scattering investigation, that at room temperature the ions are locally ordered on a lattice of well-defined sites in the channel direction and not ordered between neighboring
channels. These ions form 1D incommensurate concentration waves whose periodicity depends on the stoichiometry. In upon cooling, the intrachannel order increases significantly, and an interchannel order between the 1D concentration waves develops. But, probably because of kinetic effects, no tridimensional (3D) long range order of the ions is achieved at low temperature. The 3D low-temperature local order has been determined and it is found that the phase
shift between the concentration waves minimizes their Coulomb repulsions. This local order is increasingly reduced as the Cs concentration
diminishes. We interpret the intriguing features of the electrical conductivity in relationship with the thermal evolution
of the Cs ordering effects. We suggest that in , for x small, a localization-delocalization transition of the Anderson type occurs due to the thermal variation of the Cs disorder.
When x increases, the enhancement of the disorder leads to a localization of the electronic wave function in the whole temperature
range measured. Finally, and probably because of the disorder, no charge density wave instability is revealed by our X-ray
diffuse scattering investigation.
Received: 10 October 1997 / Received in final form: 11 December 1997 /
Accepted: 16 December 1997 相似文献
5.
S. Haffner M. Dressel D. Groult C. Schlenker 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(2):167-175
The potassium doped monophosphate tungsten bronzes KxP4W8O32 are two-dimensional metals which show a metal-to-metal transition at a critical temperature which depends on the doping level.
The metal-to-metal transition is accompanied by the formation of a commensurate charge density wave with wave vector (π/b,0) which is independent of the doping level. Undoped P4W8O32, on the other hand, has two metal-to-metal transitions which are connected to the formation of incommensurate charge density
waves. We measured the infrared reflectivity of the series KxP4W8O32 (x
= 0 - 1.57) in the spectral range from 100 to 10 000 cm-1 for room temperature and well below the critical temperature. Polarization-dependent infrared spectra find a two-dimensional
behavior in the normal and the charge density wave state and show signatures of hybridization between one- and two-dimensional
conduction bands. In undoped P4W8O32 the essentials of the charge density wave state can be understood from the nesting vectors of the calculated Fermi surface
and two gaps are observed in the infrared spectra. The gap sizes are a factor of about 2.5 bigger than the predictions from
mean-field theory in the weak-coupling limit which suggests medium- or strong electron-phonon coupling. For potassium doped
KxP4W8O32 one gap is observed in the charge density wave state. The energetics of the charge density formation may be dominated by
the energy required for the lattice modulation.
Received 27 April 2001 and Received in final form 21 September 2001 相似文献
6.
A. A. Sinchenko Yu. I. Latyshev A. P. Orlov A. A. Ivanov P. Monceau 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(2):199-204
We have measured the Hall effect and the transverse
magnetoresistance in NbSe3 single crystals. In the liquid helium
temperature range we observed an absolute negative magnetoresistance
(NMR) — the value of the resistance under magnetic field being much
lower than that at zero field — in NbSe3 single crystals with a
thickness less than 5 μm with the magnetic field oriented in the
(b, c) plane. We show that this NMR effect is observed in the
magnetic field range in which the Hall constant changes its sign.
The results are qualitatively explained by the change of the surface
scattering contribution to the magnetoconductance in the magnetic
field range near the Hall voltage zero crossing. 相似文献
7.
Y. Liu J. Dong D.Y. Xing 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):185-188
Minimizing total free energy by numerical calculations, we obtain the magnetic phase diagram of perovskite Mn oxides, such
as with , Ca, Sr, etc. in the whole doping region from x
=0 to x
=1 at temperature T
=0. It is discovered that a spiral state is stable in a low concentration of X ions while a canted state is stable in a high
concentration of X ions, and a ferromagnetic phase can exist in the intermediate concentrations when the antiferromagnetic
interaction is weak. The energy difference between spiral and canted states is found to be small when the Hund coupling is
large. Magnetic field induced spiral/canted phase transition is considered as a possible mechanism of the colossal magnetoresistance
(CMR) in the Mn oxides.
Received: 11 July 1996 / Revised: 7 December 1996 / Accepted: 24 July 1997 相似文献
8.
A. Kobelkov F. Gleisberg W. Wonneberger 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(1):21-27
Starting from the static Fukuyama-Lee-Rice equation for a three-dimensional incommensurate charge density wave (CDW) in quasi
one-dimensional conductors a solvable model for local phase pinning by impurities is defined and studied. We find that average
CDW energy and average pinning force show critical behaviour with respect to the pinning parameter h. Specifically the pinning force exhibits a threshold at h=1 with exponent . Our model exemplifies a general concept of local impurity pinning in which the force exerted by the impurity on the periodic
CDW structure becomes multivalued and metastable states appear beyond a threshold. It is found that local impurity pinning
becomes less effective at low temperatures and may eventually cease completely. These results are independent of spatial dimensionality
as expected for local impurity pinning. Comparison with Larkin's model is also made.
Received 8 July 1998 相似文献
9.
P. Roussel P. Foury-Leylekian B. Domengès D. Groult P. Labbé J.-P. Pouget 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(4):497-508
A new variety of P
4
W
10
O
38
, m
= 5 member of the monophosphate tungsten-bronze family with pentagonal tunnels (MPTB
p), , has been isolated and studied by X-ray diffraction measurements. The structure has been solved by direct methods from single
crystal X-ray data. The monoclinic unit cell corresponds to a regular stacking of WO
3
-type slabs which are all five-WO
6
-octahedra thick and connected through PO
4
tetrahedra. This structure is comparable to that previously described for the MPTB
p'series with m
= 4 (P
4
W
8
O
32
) and m
= 6 (P
4
W
12
O
44
). An X-ray diffuse scattering investigation has revealed that this member is subjected to charge density wave instabilities
(CDW) located on chains running along the directions. Two CDW transitions have been observed at and , bearing some resemblance with those exhibited by the m
= 4 member. The corresponding modulation wave vectors can be accounted for by a hidden nesting mechanism which connects the crossing
points of differently oriented quasi-planar Fermi surfaces, as found for the low m (4 and 6) members of the MPTB's.
Received 12 March 1999 and received in final form 20 May 1999 相似文献
10.
M. Pinterić T. Vuletić M. Lončarić S. Tomić J.U. von Schütz 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(3):487-493
We report a detailed characterization of an unique 3-fold commensurate insulating state in single crystals of the organic
– inorganic d hybrid Cu(DMe-DCNQI)2 systems with deuterated and partially deuterated DCNQI ring, by means of low-frequency dielectric spectroscopy. A broad relaxation
mode of strength centred at kHz is observed in the hysteresis temperature region in which the insulating phase coexists with metallic islands. At lower
temperatures, outside the nucleation range, the relaxation narrows, approaching a Debye-like form for an overdamped response
of a system with a single degree of freedom. Both, the relaxation strength and the mean relaxation time () are much larger than that expected for single-particle excitations. These features suggest the origin of the dielectric
relaxation as an intrinsic property of the N = 3 charge density wave state.
Received 1 December 1999 and Received in final form 5 April 2000 相似文献
11.
D. Vignolles A. Audouard R. B. Lyubovskii M. Nardone E. Canadell E. I. Zhilyaeva R. N. Lyubovskaya 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(4):489-495
Pressure dependence of the Shubnikov-de Haas (SdH)
oscillations spectra of the quasi-two dimensional organic metal
(ET)8[ Hg4Cl12(C6H5Br)2] have been studied up
to 1.1 GPa in pulsed magnetic fields of up to 54 T. According to
band structure calculations, its Fermi surface can be regarded as
a network of compensated orbits. The SdH spectra exhibit many
Fourier components typical of such a network, most of them being
forbidden in the framework of the semiclassical model. Their
amplitude remains large in all the pressure range studied which
likely rules out chemical potential oscillation as a dominant
contribution to their origin, in agreement with recent
calculations relevant to compensated Fermi liquids. In addition to
a strong decrease of the magnetic breakdown field and effective
masses, the latter being likely due to a reduction of the strength
of electron correlations, a sizeable increase of the scattering
rate is observed as the applied pressure increases. This latter
point, which is at variance with data of most charge transfer
salts is discussed in connection with pressure-induced features of
the temperature dependence of the zero-field interlayer
resistance. 相似文献
12.
C. Proust A. Audouard V. Laukhin L. Brossard M. Honold M.-S. Nam E. Haanappel J. Singleton N. Kushch 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(1):31-37
We report on the inter-layer oscillatory conductance of the two-dimensional organic superconductor (BEDO-TTF)2ReO4H2O measured in static and pulsed magnetic fields of up to 15 and 52 T, respectively. In agreement with previous in-plane studies,
two Shubnikov-de Haas oscillation series linked to the two electron and the hole orbits are observed. The influence of the
magnitude and orientation of the magnetic field with respect to the conducting plane is studied in the framework of the conventional
two- and three-dimensional Lifshits-Kosevich (LK) model. Deviations of the data from this model are observed in low fields
strongly tilted with respect to the normal to the conducting plane. In this latter case, the observed behaviour is consistent
with an unexplained lowering of the cyclotron effective mass. At high magnetic field, the oscillatory data could have been
compatible with the occurrence of a magnetic breakdown orbit built from the hole and electron orbits. However, the increase
of the cyclotron effective mass, linked to the electron orbits, as the magnetic field increases above ∼12 T is consistent with a field-induced phase transition. In the lower field range, where the conventional LK model holds,
the analysis of the angle dependence of the oscillations amplitude suggests significant renormalisation of the effective Landé
factor.
Received 22 August 2000 and Received in final form 20 December 2000 相似文献