共查询到20条相似文献,搜索用时 15 毫秒
1.
We analyze measurements of the magnetization, differential susceptibility and specific heat of quasi-onedimensional insulator Cu(C4H4N2)(NO3)2 (CuPzN) subjected to magnetic fields. We show that the thermodynamic properties are defined by quantum spin liquid formed with spinons, with the magnetic field tuning the insulator CuPzN towards quantum critical point related to fermion condensation quantum phase transition (FCQPT) at which the spinon effective mass diverges kinematically. We show that the FCQPT concept permits to reveal and explain the scaling behavior of thermodynamic characteristics. For the first time, we construct the schematic T–H (temperature-magnetic field) phase diagram of CuPzN that contains Landau–Fermi-liquid, crossover and non-Fermi liquid parts, thus resembling that of heavy-fermion compounds. 相似文献
2.
G.S. Uhrig F. Schönfeld M. Laukamp E. Dagotto 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(1):67-77
A quantum mechanical picture is presented to describe the behavior of confined spinons in a variety of S
=1/2 chains. The confinement is due to dimerization and frustration and it manifests itself as a nonlinear potential , centered at chain ends () or produced by modulation kinks (b
> 1). The calculation extends to weak or zero frustration some previous ideas valid for spinons in strongly frustrated spin chains.
The local magnetization patterns of the confined spinons are calculated. A (minimum) enhancement of the local moments of about
11/3 over a single S
=1/2 is found. Estimates for excitation energies and binding lengths are obtained.
Received: 8 May 1998 / Revised and Accepted: 12 August 1998 相似文献
3.
4.
B. Schmidt V. Yushankhai L. Siurakshina P. Thalmeier 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):43-47
A pronounced Curie-like upturn of the magnetic susceptibility χ(
T
) of the quasi one-dimensional spin chain compound Ba2V3O9 has been found recently [#!kaul:02!#]. Frequently this is taken as a signature for a staggered field mechanism due to the
presence of g-factor anisotropy and Dzyaloshinskii-Moriya interaction. We calculate this contribution within a realistic structure of vanadium
3
d- and oxygen 2
p-orbitals and conclude that this mechanism is far too small to explain experimental results. We propose that the Curie term
is rather due to a segmentation of spin chains caused by broken magnetic bonds which leads to uncompensated S
= ? spins of segments with odd numbers of spins. Using the finite-temperature Lanczos method we calculate their effective moment
and show that ∼ 1% of broken magnetic bonds is sufficient to reproduce the anomalous low-T behavior of χ(
T
) in Ba2V3O9.
Received 19 December 2002 / Received in final form 29 January 2003 Published online 14 March 2003 相似文献
5.
A.S.T. Pires 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):65-71
We calculate the excitation gap, the soliton energy, and the soliton density at finite temperature, of the spin-1/2 one dimensional
antiferromagnet coupled to phonons, using a self-consistent harmonic approximation, and the thermal-Green function technique.
The spin degrees of freedom are represented by the phase Hamiltonian with the help of the boson representation of the spinless
fermions. We estimate the critical field Hc above which begins the incommensurate phase. We also present a theoretical calculation for the specific heat in this phase.
We use CuGeO3 as an example of a compound where our theory could be applied.
Received 22 October 2002 / Received in final form 21 January 2003 Published online 14 March 2003 相似文献
6.
B. Pedrini S. Wessel J. L. Gavilano H. R. Ott S. M. Kazakov J. Karpinski 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(3):219-228
We report results of susceptibility χ and 7Li NMR measurements on LiVSi2O6. The temperature dependence of the magnetic susceptibility χ(T) exhibits a broad maximum, typical for low-dimensional magnetic
systems. Quantitatively it is in agreement with the expectation for an S=1 spin chain, represented by the structural arrangement
of V ions.
The NMR results indicate antiferromagnetic ordering below TN=24 K. The intra- and interchain coupling J and Jp for LiVSi2O6, and also for its sister compounds LiVGe2O6, NaVSi2O6 and NaVGe2O6, are obtained via a modified random phase approximation which takes into account results of quantum Monte Carlo calculations.
While Jp is almost constant across the series, J varies by a factor of 5, decreasing with increasing lattice constant along the chain
direction. The comparison between experimental and theoretical susceptibility data suggests the presence of an easy-axis magnetic
anisotropy, which explains the formation of an energy gap in the magnetic excitation spectrum below TN, indicated by the variation of the NMR spin-lattice relaxation rate at T≪TN. 相似文献
7.
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
8.
Subir Sachdev 《Journal of Physics and Chemistry of Solids》2002,63(12):2269-2276
We argue that aspects of the anomalous, low temperature, spin and charge dynamics of the high temperature superconductors can be understood by studying the corresponding physics of undoped Mott insulators. Such insulators display a quantum transition from a magnetically ordered Néel state to a confining paramagnet with a spin gap; the latter state has bond-centered charge order, a low energy S=1 spin exciton, confinement of S=1/2 spinons, and a free S=1/2 moment near non-magnetic impurities. We discuss how these characteristics, and the quantum phase transitions, evolve upon doping the insulator into a d-wave superconductor. This theoretical framework was used to make a number of predictions for STM measurements and for the phase diagram of the doped Mott insulator in an applied magnetic field. 相似文献
9.
X. W. Zhang J. B. Xia 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(3):263-268
The electronic structure, spin splitting energies, and g factors of
paramagnetic In1-xMnxAs nanowires under magnetic and electric
fields are investigated theoretically including the sp-d exchange
interaction between the carriers and the magnetic ion. We find that the
effective g factor changes dramatically with the magnetic field. The spin
splitting due to the sp-d exchange interaction counteracts the
Zeeman spin splitting. The effective g factor can be tuned to zero by the
external magnetic field. There is also spin splitting under an electric
field due to the Rashba spin-orbit coupling which is a relativistic effect.
The spin-degenerated bands split at nonzero kz (kz is the wave
vector in the wire direction), and the spin-splitting bands cross at
kz = 0, whose kz-positive part and negative part are symmetrical. A
proper magnetic field makes the kz-positive part and negative part of
the bands asymmetrical, and the bands cross at nonzero kz. In the
absence of magnetic field, the electron Rashba coefficient increases almost
linearly with the electric field, while the hole Rashba coefficient
increases at first and then decreases as the electric field increases. The
hole Rashba coefficient can be tuned to zero by the electric field. 相似文献
10.
A. S. Fedorov A. F. Sadreev 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,69(3):363-368
By use both of the plane wave DFT and the empirical
exp-6 Lennard-Jones potential methods we calculate the inner
potential in narrow single-wall carbon nanotubes (SWCNT) (6, 0),
(7, 0) and (3, 3) which affects the hydrogen molecules. The inner
potential forms a goffered potential surface and can be
approximated as V(z,r,φ)≈V0sin (2πz/a)+V(r). We
show that in these SWCNTs transport of molecules is given mainly
by thermoactivated hoppings between minima of the periodic
potential along the tube axis. The rate hoppings is substantially
depends on temperature because of thermal fluctuations of tube
wall. 相似文献
11.
We study the magnetization of gapped spin 1/2 XXZ Heisenberg Ising chains and calculate the scattering length among massive spinons. We obtain the magnetization close to the critical external magnetic field. The leading correction term determined by the scattering length among massive spinons is given. Our results are in agreement with exact results and with experimental results. We show that the deviation from the massive free hard core boson picture can be accounted very well by the leading correction term due to the spinon-spinon interaction. We show that the deviation increases along with the increasing of the Ising term. 相似文献
12.
M. S. B. Darby T. C. May-Smith R. W. Eason 《Applied Physics A: Materials Science & Processing》2008,93(2):477-481
We have demonstrated pulsed laser deposition of Nd-doped gadolinium gallium garnet on Y3Al5O12 by the simultaneous ablation of two separate targets of Nd:Gd3Ga5O12 (GGG) and Ga2O3. Such an approach is of interest as a method of achieving stoichiometry control over films whilst the growth parameters are
kept constant and optimal for high quality crystal growth. We show here how the stoichiometry and resultant lattice parameter
of a film can be controlled by changing the relative deposition rates from the two targets. Films have been grown with enough
extra Ga to compensate for the deficiency that commonly occurs when depositing only from a GGG target. We have also grown
crystalline GGG films with an enriched Ga concentration, and this unconventional approach to film stoichiometry control may
have potential applications in the fabrication of films with advanced compositionally graded structures. 相似文献
13.
Ali H. Reshak S. Auluck I. V. Kityk Y. Al-Douri R. Khenata A. Bouhemadou 《Applied Physics A: Materials Science & Processing》2009,94(2):315-320
We report theoretical calculations of the band structure and density of states for orthorhombic LiGaS2 (LGS) and LiGaSe2 (LGSe). These calculations are based on the full potential linear augmented plane wave (FP-LAPW) method within a framework
of density functional theory. Our calculations show that these crystals have similar band structures. The valence band maximum
(VBM) and the conduction band minimum (CBM) are located at Γ, resulting in a direct energy band gap. The VBM is dominated by S/Se-p and Li-p states, while the CBM is dominated by Ga-s,
S/Se-p and small contributions of Li-p and Ga-p. From the partial density of states we find that Li-p hybridizes with Li-s
below the Fermi energy (E
F), while Li-s/p hybridizes with Ga-p below and above E
F. Also, we note that S/Se-p hybridizes with Ga-s below and above E
F. 相似文献
14.
M. Aoki K. Miwa T. Noritake N. Ohba M. Matsumoto H.-W. Li Y. Nakamori S. Towata S. Orimo 《Applied Physics A: Materials Science & Processing》2008,92(3):601-605
We have investigated the structural and dehydriding properties of Ca(BH4)2. It was found that Ca(BH4)2 undergoes a structural phase transformation from an orthorhombic low-temperature (LT) modification into a tetragonal high-temperature
(HT) modification between 433 K and 523 K. The amount of hydrogen desorbed from Ca(BH4)2 during the pressure–composition (p–c) isotherm measurement was 5.9 mass%. This hydrogen desorption is caused by the partial dehydrogenation of Ca(BH4)2 accompanied by the formation of CaH2 and orthorhombic intermediate phases. 相似文献
15.
We study the magnetization of gapped spin 1/2 XXZ Heisenberg Ising chains and calculate the scattering length among massive spinons. We obtain the magnetization close to the critical external magnetic field. The leading correction term determined by the scattering length among massive spinons is given. Our results are in agreement with exact results and with experimental results. We show that the deviation from the massive free hard core boson picture can be accounted very well by the leading correction term due to the spinon-spinon interaction. We show that the deviation increases along with the increasing of the Ising term. 相似文献
16.
A. Bhattacharyya S. Chatterjee S. Giri S. Majumdar 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(3):347-351
The magnetotransport and magnetic properties of the binary intermetallic compound Ho2In have been investigated. Clear signature of long range ferromagnetic order in the resistivity and the magnetization data
at TC = 85 K is observed. A further spin reorientation type transition is also apparent in our measured data at around Tt = 32 K. The sample exhibits negative magnetoresistance (peak value of –14% at 5 T) over a wide temperature range that extends
well above TC. Substantially large magneto-caloric effect is also observed in the sample (maximum value of –8.5 J kg-1K-1 for 0 → 5 T), which peaks around the TC of the sample. The observed magnetoresistance and magnetocaloric effect are related to the suppression of spin disorder by
an external magnetic field. Ho2In can be an interesting addition to the list of rare-earth based magnetic refrigerant materials showing magneto-caloric effect
across a second order phase transition. 相似文献
17.
Magnetic excitations in the antiferromagnetic Bi2CuO4 (T N =42K) are investigated on the basis of anisotropic exchange interaction between spins of Cu2+ ions. We calculate the dispersion curves and evaluate the intensity of the inelastic neutron scattering by spin wave excitations. Spin contraction at OK and the effect of spin wave interaction are studied. 相似文献
18.
A. Avella F. Mancini 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(1):27-33
The magnetic properties of the La2CuO4 are analyzed by means of the paramagnetic solution of the Hubbard model within the composite operator method. The experimental
findings of the inelastic neutron magnetic scattering [R. Coldea et al., Phys. Rev. Lett. 86, 5377 (2001)] for the spin spectrum, the spin-wave intensity and the behavior of the dispersion at the zone boundary are
well described by our results although the difference in phase. The Hubbard model emerges has a minimal model capable to describe
the anomalous magnetic behavior of such a strongly correlated material.
Received 29 July 2002 / Received in final form 2 January 2003 Published online 14 March 2003 相似文献
19.
L. S. Ewe I. Hamadneh H. Salama N. A. Hamid S. A. Halim R. Abd-Shukor 《Applied Physics A: Materials Science & Processing》2009,95(2):457-463
The magnetotransport and magnetoresistive (MR) properties of manganese-based La0.67Ca0.33MnO3 perovskite with different grain sizes are reported. The electrical resistivity was measured as a function of temperature
in magnetic fields of 0.5 and 1 T. The insulator–metal transition temperature, T
IM, shifted to a higher temperature with the application of the magnetic field. In zero field, T
IM is almost constant (∼271 K) for all samples except for the sample with the largest grain size, where T
IM=265 K. The temperature dependence of resistivity was fitted with several equations in the metallic (ferromagnetic) region
and the insulating (paramagnetic) region. The density of states at the Fermi level, N(E
F), and the activation energy of electron hopping were estimated by fitting the resistivity versus temperature curves. The
ρ–T
2 curves are nearly linear in the metallic regime, but the ρ–T
2.5 curves exhibit a deviation from linearity. The variable range hopping model and small polaron hopping model fit the data
well in the high-temperature region, indicating the existence of the Jahn–Teller distortion that localizes the charge carriers.
MR was found to increase with an increase in the magnetic field, an effect which is attributed to the intergrain spin tunneling
effect. 相似文献
20.
R. M. Eremina T. P. Gavrilova A. Günther Z. Wang R. Lortz M. Johnsson H. Berger H. A. Krug von Nidda J. Deisenhofer A. Loidl 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,84(3):391-395
We report on magnetization and specific heat measurements on single-crystalline
CuTe2O5. The experimental data are directly compared to
theoretical results for two different spin structures, namely an alternating spin-chain
and a two-dimensional (2D) coupled dimer model, obtained by Das et al. [Phys. Rev. B
77, 224437 (2008)]. While the analysis of the specific heat does not allow
to distinguish between the two models, the magnetization data is in good agreement with
the 2D coupled dimer model. 相似文献