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1.
M. Bokor T. Marek K. Tompa P. Gütlich A. Vértes 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(4):567-571
19
F and
11
B spin-lattice relaxation times were measured in [
Zn
(
ptz
)
6
] (
BF
4
)
2
and in the spin-crossover compound [
Fe
(
ptz
)
6
] (
BF
4
)
2
. For both compounds BF
4
-
anion reorientation is active above 50 K. For [
Zn
(
ptz
)
6
] (
BF
4
)
2
, the anion-reorientation dynamics is different in the temperature regions of 50-90 K, 90-120 K, and above 150 K; between
120 and 150 K it changes rapidly reflecting a structural change. In [
Fe
(
ptz
)
6
] (
BF
4
)
2
the mechanism for the paramagnetic relaxation involving the
19
F nuclei is found to be of the diffusion-limited type according to the theory of Lowe and Tse. The present results prove that
the spin-crossover takes place in a dynamic surrounding and not in a static crystal lattice.
Received 09 February 1999 and Received in final form 14 June 1999 相似文献
2.
P. Cacciani F. Brandi I. Velchev C. Lyngå C.-G. Wahlström W. Ubachs 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(1):47-56
Rotationally resolved spectral lines in the C
-
X
(1, 0) band of carbon monoxide are investigated under high resolution using a coherent vacuum ultraviolet laser source, continuously
tunable near 107 nm. Transition frequencies are determined by calibrating against a reference standard of iodine lines, recorded
with saturation spectroscopy in the visible range, yielding an absolute accuracy of 0.003 cm-1 in the vacuum ultraviolet. Improved molecular constants for the excited state are derived and no effects of perturbation
are found at the present level of accuracy. Line broadening measurements result in information on the excited state lifetime
of the C
1
Σ
+
,
v
= 1 state for five natural isotopomers of carbon monoxide: τ(
12
C
17
O
) = 280 ps, τ(
12
C
18
O
) = 210 ps, τ(
13
C
16
O
) = 295 ps, τ(
13
C
17
O
) = 160 ps, and τ(
13
C
18
O
) = 150 ps. Within the accuracy of the present measurements no effects of J-dependent lifetimes were observed, for neither of the isotopomers. In addition direct time domain measurements of the lifetime
of the C
1
Σ
+
,
v
= 0 and v
= 1 states of the main isotopomer are performed in a pump-probe experiment using a picosecond VUV-laser, yielding τ(
12
C
16
O
) = 1780 ps for v
= 0 and τ(
12
C
16
O
) = 625 ps for v
= 1. For C
1
Σ
+
,
v
= 0 in 12C16O and 13C16O the same lifetime is found; this lifetime matches experimental values of the oscillator strength and hence supports previous
results showing pure radiative decay in this state; the error margins however do not exclude some low level of predissociation.
The measurements indicate that the C
1
Σ
+
,
v
= 0 state of the 13C18O isotopomer is predissociated with an estimated yield of 17% (i.e. above the level of predissociation for 12C16O.) From the combined data predissociation yields upon excitation of the C
1
Σ
+
,
v
= 1 state are derived, lying in the range 0.84-0.91 for the five less abundant isotopomers; for the main 12C16O isotopomer a strongly deviating predissociation yield of 0.65 is deduced.
Received 21 December 2000 and Received in final form 26 March 2001 相似文献
3.
D. Ashkenasi S. Kröger H.-D. Kronfeldt 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(2):197-205
The isotope shift (IS) and hyperfine structure (hfs) of nine levels (31720 to 38921 cm-1) assigned to the configuration 4
f
12
6
s
7
s in neutral erbium have been determined experimentally using Doppler-reduced saturation absorption spectroscopy in a gas discharge.
We performed a fine structure analysis in the SL-coupling scheme of the single configuration 4
f
12
6
s
7
s, confirming and extending the classification of even parity Er I levels. We discriminated the different hfs contributions
of the 4f12 core and the (6
s
+7
s) outer electrons of the shell in a non-relativistic JJ-coupling approach and in the relativistic effective tensor operator formalism in SL-coupling. The relativistic one-electron parameters of the hfs for 167Er were fitted to the experimental data by a least squares fit procedure: [0pt] a
01
4f
=-147(3) MHz, [0pt] a
10
6s
+
a
10
7s
=-1840(30) MHz, [0pt] b
02
4f
=6560(80) MHz. The level dependencies of the isotope shift were evaluated based on crossed second order (CSO) effects. We obtained
the following results for the CSO parameters for the isotope pairs 170-168Er: d
6s7s
=-740(30) MHz, z
4f
= 0(5) MHz, (
g
3,6s
(
f
, 6
s
)+
g
3, 7s
(
f
, 7
s
))= -24(15) MHz and for 170-166Er: d
6s7s
=-1500(50) MHz, z
4f
=0(10) MHz, (
g
3,6s
(
f
,6
s
)+
g
3,7s
(
f
+7
s
))=-50(29) MHz. The resulting parameters for the hfs are compared with those known for other configurations of the Er atom and ion.
Received 16 May 1999 and Received in final form 31 January 2000 相似文献
4.
D. Rubio Temprano J. Mesot S. Janssen K. Conder A. Furrer A. Sokolov V. Trounov S.M. Kazakov J. Karpinski K.A. Müller 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):5-8
The copper isotope effect (63Cu vs.
65Cu) on the relaxation rate of crystal-field excitations in the slightly underdoped high-temperature superconductor HoBa2Cu4O8 has been investigated by inelastic neutron scattering. For the 63Cu compound there is clear evidence for the opening of an electronic gap in the normal state at T
*
≈ 160 K far above T
c
= 79.0 K. Upon substitution of 63Cu by 65Cu, T
c
decreases marginally to 78.6 K, whereas T
*
is increased to about 185 K. This large copper isotope shift Δ
T
*
(
Cu
) =
T
*
(
65
Cu
) -
T
*
(
63
Cu
) ≈ 25 K - together with the corresponding oxygen isotope shift Δ
T
*
(
O
) =
T
*
(
18
O
) -
T
*
(
16
O
) ≈ 50 K found in an earlier investigation - suggests that phonons or lattice fluctuations involving both the copper and the oxygen
ions are important for the pairing mechanism in high-T
c
materials.
Received 13 October 2000 相似文献
5.
K. Hagdorn D. Hohlwein J. Ihringer K. Knorr W. Prandl H. Ritter H. Schmid Th. Zeiske 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(2):243-254
Ho0.1Ca0.9MnO3 is a canted antiferromagnet with the magnetic space group Pn
'
ma
'. The magnetic structure is a superposition C
x
F
y
A
z of the three types of order allowed in Pn
'
ma
'. In the Ca-rich corner of the system Ho
1-x
Ca
x
MnO
3
the title compound has a strong magnetoelastic distortion , the highest metallic conductivity and a ferromagnetic component F
y close to the maximum in the series. Among the areas ab, bc, ca calculated from the lattice constants only ca shows a strong magnetoelastic effect below T
N
= 106
K. The x-, y-, z-spin components depend differently on the temperature. This gives rise to spin rotation which is particularly strong close
to T
N. MnO
6
octahedra have short bond lengths with a temperature independent average . They are practically regular at room temperature and show a Jahn-Teller distortion of 3.5% in the magnetically ordered state.
Above T
N we find small polaron conductivity. The presence of the Jahn-Teller distortion due to the only small abundance (10%) of Mn
3+
in the t
2g
3
e
g configuration is attributed to delocalised e
g electrons. In the magnetically ordered state the averaged magnetic moment of Mn is reduced appreciably from the paramagnetic
value due to spin disorder.
Received 21 January 1999 相似文献
6.
S. Cohen M. Aymar A. Bolovinos M. Kompitsas E. Luc-Koenig H. Mereu P. Tsekeris 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(2):165-180
The even parity 5
pnpJ
= 0, 1 and 2 doubly excited autoionizing states of strontium were investigated both experimentally and theoretically. Sr atoms
in an atomic beam were excited through the two-step Isolated Core Excitation (ICE) scheme 5s2
1
S
0
-λ
1
→ 5
sn'p
1
P
1
(
n'
= 12-16)-λ
2
→ [5
p
3/2
np
]
J
. The final ICE transition probes the [5
p
3/2
np
]
J
resonances. However, the [5
p
1/2
np
]
J
series below the 5
p
1/2
threshold were excited also due to their mixing with the [5
p
3/2
np
]
J
perturbers. An extended energy region was covered below and above the 5
p
1/2
ionization limit by saturating the central ICE lobe and recording as many as possible “red” and “blue” secondary lobes. J identification was achieved by using mutually parallel and perpendicular linear polarizations of the laser beams. The ICE
spectra were compared to those obtained by employing a two-step excitation scheme using the bound 4
d
5
p
1
P
1
valence state as an intermediate one. Final identification for very complex structures was achieved after comparison with
theoretical energy level positions and excitation profiles produced by the R-matrix method combined with the multichannel quantum defect theory (MQDT) method. The agreement between theoretical and observed
structures is quite satisfactory.
Received 31 May 2000 相似文献
7.
8.
V.G. Yarzhemsky F.P. Larkins 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,5(2):179-184
The theory of the shapes of Auger decay lines of satellite two-hole-one particle states accompanying photoionization based
on the Green's function method is developed. The lineshapes of Auger decay of satellite states [2
s
2
p
](
1,3
P
)3
s
(
2
P
), [2
s
2
p
](
1
P
)4
s
(
2
P
) and [3
s
3
p
](
3
P
)4
s
(
2
P
) in valence p-photoelectron spectra of Ne and Ar atoms are calculated (hole states are indicated by square brackets throughout). It is
shown that in some cases the Auger lineshapes reproduce the shape of the photoelectron satellite line, but in other cases
Auger line may be narrower then the photoelectron line and may have opposite direction of asymmetry. The theoretical results
are in agreement with experimental low-energy Auger spectra.
Received: 25 May 1998 / Accepted: 2 October 1998 相似文献
9.
H.-D. Zhou R.-K. Zheng G. Li S.-J. Feng F. Liu X.-J. Fan X.-G. Li 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):467-471
The transport properties of the La1-xCaxMnO3 ( 0.5 ?
x
< 1) system in magnetic fields up to 14 T were studied. We found that the relationship between the charge ordering temperature
T
CO
and Mn4+ content n
Mn4 +
obeys the formula T
CO
/
T
max
= 1 -
a
(
n
Mn4 +
-
n
0
)
2
, here n0 and a are constants and T
max
is the maximum of T
CO
. For x
= 0.65, T
CO
arrives at the maximum value of 249.5 K in zero magnetic field, while the charge ordered (CO) state is most stable around
x
= 0.75. For x
= 0.5 when H
< 6 T the resistivity displays Mott's variable-range hopping (VRH) behavior, when 6 <
H
< 12 T it is suggested that two kinds of conduction mechanism, i.e., VRH and magnetic polarons, coexist in the material, and when H
> 12 T the resistivity shows metallic-like behavior and the transport mechanism is attributed to coexistence of magnetic polarons
and free carriers. For x
= 0.95, the conduction mechanism accords with the coexistence of VRH and magnetic polarons.
Received 4 January 2002 and Received in final form 28 January 2002 相似文献
10.
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
11.
C. Langhammer F. Steglich M. Lang T. Sasaki 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):413-416
We report low-temperature measurements 0.07
K
?
T
? 2 K of the specific heat, C, of the perovskite superconductor Sr2RuO4. Based on a detailed analysis of our data with respect to both sample quality (as measured by T
c
= 0.43
K
- 1.17 K) and magnetic-field dependence, it is shown that the electronic contribution to the specific heat, which contains the desired
information on the gap structure, is superimposed by at least two additional contributions: a Schottky-type hump at T
≈ 0.1 - 0.2 K and a low-temperature upturn in C
/
T at T
< 0.1 K. We discuss possible origins of these additional contributions and their implications for the interpretation of low-temperature
C
(
T
) data.
Received 23 August 2001 相似文献
12.
P. Pellegrini O. Dulieu F. Masnou-Seeuws 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(1):77-86
This paper proposes a general method to investigate Feshbach resonances in atomic collisions similar to Cs(6
s
) + Cs(6
p
) in the thermal or cold regime. In order to compute the predissociation widths of the C
1
Π
u
(6
s
+ 5
d
) bound vibrational levels of Cs2, coupled both with the (2)
3
Σ
+
u
(6
s
+ 6
p
) continuum and with the (2)
3
Π
u
(6
s
+ 5
d
) vibrational series, a Fourier grid method is implemented, with an optical potential. A convenient way of optimizing the latter
is proposed. A large number of resonances are found and calculations of their cross-sections for stabilization into ground
state molecules show that the rate may be important. This confirms the interpretation of Lintz and Bouchiat [Phys. Rev. Lett.
80, 2570 (1998)] who observed dimer formation in cell experiments. Possible generalization to the cold regime relies on the
possibility to tune the position of a resonance to coincide with the maximum of the collisional energy distribution.
Received 14 February 2002 Published online 28 June 2002 相似文献
13.
M. Vogel K. Hansen A. Herlert L. Schweikhard 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(2):163-166
The dimer dissociation energies of gold cluster ions Au
+
n
, n
= 9, 11, 13, 15 have been determined with an extension of a recently developed model-independent method. Monomer-dimer decay
pathway branching ratios provide the energy dependent process which is needed in this method. The measured values are D
2
(
Au
+
9
) = 3.66(8)(9) eV, D
2
(
Au
+
11
) = 4.27(11)(8) eV, D
2
(
Au
+
13
) = 4.50(9)(7) eV and D
2
(
Au
+
15
) = 4.29(10)(6) eV.
Received 13 May 2002 / Received in final form 22 July 2002 Published online 24 September 2002
RID="a"
ID="a"e-mail: manuel.vogel@uni-mainz.de 相似文献
14.
A. Fioretti C. Amiot C.M. Dion O. Dulieu M. Mazzoni G. Smirne C. Gabbanini 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(2):189-198
We report the detailed analysis of translationally cold rubidium molecule formation through photoassociation. Cold molecules
are formed after spontaneous decay of photoexcited molecules from a laser cooled atomic sample, and are detected by selective
mass spectroscopy after two-photon ionization into Rb
2
+
ions. A spectroscopic study of the 0
g
-
(5
S
+ 5
P
3/2
) pure long-range state of 87Rb2 is performed by detecting the ion yield as a function of the photoassociation laser frequency; the spectral data are theoretically
analyzed within the semiclassical RKR approach. Molecular ionization is resonantly enhanced through either the 2
3
Π
g
or the 2
3
Σ
+
g
intermediate molecular states. Some vibrational levels of the latter electronic state are observed and assigned here for
the first time. Finally, cold molecules formation rates are calculated and compared to the experimentally measured ones, and
the vibrational distribution of the formed molecules in the a
3
Σ
+
u
ground triplet state is discussed.
Received 18 January 2001 and Received in final form 10 April 2001 相似文献
15.
J.B. Fouet P. Sindzingre C. Lhuillier 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(2):241-254
We have investigated the quantum J
1
-
J
2
-
J
3
model on the honeycomb lattice with exact diagonalizations and linear spin-wave calculations for selected values of J
2
/
J
1
, J
3
/
J
1
and antiferromagnetic (J
1
> 0) or ferromagnetic (J
1
< 0) nearest neighbor interactions. We found a variety of quantum effects: “order by disorder" selection of a Néel ordered ground-state,
good candidates for non-classical ground-states with dimer long range order or spin-liquid like. The purely antiferromagnetic
Heisenberg model is confirmed to be Néel ordered. Comparing these results with those observed on the square and triangular
lattices, we enumerate some conjectures on the nature of the quantum phases in the isotropic models.
Received 17 November 2000 and Received in final form 21 January 2001 相似文献
16.
R.S. Gonnelli A. Calzolari D. Daghero L. Natale G.A. Ummarino V.A. Stepanov M. Ferretti 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(4):411-414
We present new Au/La2-xSrxCuO4 (LSCO) point-contact conductance measures as a function of voltage and temperature in samples with 0.08 ?
x
? 0.2. Andreev reflection features disappear at about the bulk T
c
, giving no evidence of gap for T
>
T
c
. The fit of the normalized conductance at any T
<
T
c
supports a (s
+
d)-wave symmetry of the gap, whose dominant low-T
s component follows the T
c
(
x
) curve in contrast with recent angle-resolved photoemission spectroscopy and quasiparticle tunneling data. These results prove
the separation between pseudogap and phase-coherence superconducting gap in LSCO at x
0.2.
Received 14 June 2001 相似文献
17.
18.
M. Jourdan N. Blümer H. Adrian 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(1):25-30
Superconducting SrTiO
3 - δ
was obtained by annealing single crystalline SrTiO3 samples in ultra high vacuum. An analysis of the V
(
I
) characteristics revealed very small critical currents I
c
which can be traced back to an unavoidable doping inhomogeneity. R
(
T
) curves were measured for a range of magnetic fields B at I
≪
I
c
, thereby probing only the sample regions with the highest doping level. The resulting curves B
c2
(
T
) show upward curvature, both at small and strong doping. These results are discussed in the context of bipolaronic and conventional
superconductivity with Fermi surface anisotropy. We conclude that the special superconducting properties of SrTiO
3 - δ
can be related to its Fermi surface and compare this finding with properties of the recently discovered superconductor MgB2.
Received 4 December 2002 / Received in final form 10 March 2003 Published online 23 May 2003
RID="a"
ID="a"e-mail: jourdan@uni-mainz.de 相似文献
19.
V. Skumryev F. Ott J. M. D. Coey A. Anane J. -P. Renard L. Pinsard-Gaudart A. Revcolevschi 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):401-406
The magnetic properties of (
La
1-x
Sr
x
)
MnO
3
crystals have been studied. The ac susceptibility has been measured at frequencies ranging from 10 Hz to 1 000 Hz. The x
= 0.25 crystal shows a typical ferromagnetic behaviour with a dimensionless SI susceptibility of 6 below T
c
= 350
K limited by the demagnetizing field. Both x
= 0 and x
= 0.06 crystals show very sharp peaks in and at the Néel points, 139 K and 135 K respectively. This is quite unlike the usual behaviour of an antiferromagnet. Magnetization
measurements on an untwinned single crystal of LaMnO
3
show a weak moment of at 4.2 K which is directed along the c axis. The origin of this canted antiferromagnetic structure is discussed in terms of anisotropy and of Dzyaloshinskii-Moriya
interaction. It is concluded that anistropy is insufficient to explain the canted antiferromagnetism.
Received 8 January 1999 相似文献
20.
The synthesis and characterization of the new ligands L
1
, L
2
and L
4
are described with the series of four europium complexes of formula [EuL
n
(TTA)3] in which TTA refers to 2-thenoyltrifluoroacetonate and L
n
to tridentate ligands with nitrogen containing heterocyclic structure, such as a 2,6-bis(3-methyl-pyrazolyl)-4-(p-toluyl-ethynyl)-triazine for L
1
, or terpyridines functionalized at the 4′ position by a phenyl-vinylene for L
2
, a p-dimethylamino-phenylene for L
3
, or a p-aminophenyl-ethynylene for L
4
. The spectroscopic properties of the ligands and of the complexes are studied by means of UV–Vis absorption spectroscopy,
as well as steady-state and time-resolved luminescence spectroscopy. All complexes display europium centred luminescence upon
ligand excitation. Careful examination of the excitation spectra revealed differences in the ligand based sensitization efficiencies.
For complexes of L
1
and L
2
, excitation of europium is mainly achieved through the TTA moieties and the photo-physical studies on [EuL
1
(TTA)3] evidenced a weaker coordination of the bispyrazolyltriazine tridentate ligand, resulting from a partial decomplexation upon
dilution. Complexes of L
3
and L
4
display intense excitation through the tridentate units, which extend down to 460 nm in the visible region. In the case of
L
3
, selective excitation reveals the presence of a ligand-centred emission band at 520 nm which is likely ascribed to a L
3
centred charge transfer state. 相似文献