共查询到20条相似文献,搜索用时 0 毫秒
1.
2.
R. K. Kremer E. Sigmund V. Hizhnyakov F. Hentsch A. Simon K. A. Müller M. Mehring 《Zeitschrift für Physik B Condensed Matter》1992,86(3):319-324
We report on the formation of conducting phases in slightly doped La2CuO4 samples by the existence of a percolative phase separation. Phase separation can be quenched by rapid cooling and can be restored by the application of a 3 T magnetic field. Magnetically polarizable quasiparticles are shown to be formed by hole doping which fuse to form percolative conducting and below 37 K superconducting phases. 相似文献
3.
We report 17O nuclear-magnetic-resonance (NMR) results in the stripe ordered La(1.8-x)Eu0.2Sr(x)CuO4 system. Below a temperature T(q) approximately 80 K, the local electric field gradient and the absolute intensity of the NMR signal of the planar O site exhibit a dramatic decrease. We interpret these results as microscopic evidence for a spatially inhomogeneous charge distribution, where the NMR signal from O sites in the domain walls of the spin density modulation are wiped out due to large hyperfine fields, and the remaining signal arises from the intervening Mott insulating regions. 相似文献
4.
We study the effects of spin-orbit coupling in the d-density wave (DDW) phase. In the low-temperature orthorhombic phase of La(2-x)Ba(x)CuO4, we find that spin-orbit coupling induces ferromagnetic moments in the DDW phase, which are polarized along the [110] direction with a considerable magnitude. This effect does not exist in the superconducting phase. On the other hand, if the d-density wave order does not exist at zero field, a magnetic field along the [110] direction always induces such a staggered orbital current. We discuss experimental constraints on the DDW states in light of our theoretical predictions. 相似文献
5.
Hawthorn DG Hill RW Proust C Ronning F Sutherland M Boaknin E Lupien C Tanatar MA Paglione J Wakimoto S Zhang H Taillefer L Kimura T Nohara M Takagi H Hussey NE 《Physical review letters》2003,90(19):197004
The transport of heat and charge in cuprates was measured in single crystals of La(2-x)Sr(x)CuO(4+delta) (LSCO) across the doping phase diagram at low temperatures. In underdoped LSCO, the thermal conductivity is found to decrease with increasing magnetic field in the T-->0 limit, in striking contrast to the increase observed in all superconductors, including cuprates at higher doping. In heavily underdoped LSCO, where superconductivity can be entirely suppressed with an applied magnetic field, we show that a novel thermal metal-to-insulator transition takes place upon going from the superconducting state to the field-induced normal state. 相似文献
6.
Three valency models for orthorhombic La2-x
Sr
x
CuO4 were investigated for increasing Sr concentrationsx (0x0.21): 1. Cu2+Cu3+, 2. apex O2–O– and 3. in-plane O2–O–. All calculations were done by using structural parameters valid for the temperature range from 10 to 22 K. We thereby calculated the electrostatic interaction energy which, next to ionization potentials and electron affinities, comprises a major of the binding energyE
B
of crystals. Second-order effects were accounted for by calculating the strength of ionic dipole moments induced by crystal electric fields at relevant lattice sites. Their largest strengths are comparable to the dipole moment of the water molecule. Three out of five dipoles in La2-x
Sr
x
CuO4 vanish during the transition from the orthorhombic to the tetragonal phase. The binding energy differences between the different models suggest that the system is in a state of model 1. However, the differences are very small, being in the order of 0.3 to 0.76 eV atx=0.13. 相似文献
7.
Y. Takahashi 《Zeitschrift für Physik B Condensed Matter》1987,68(4):411-416
The frequency dependence of the reflectivity spectra of doped La2–x
Sr
x
CuO4 in a high frequency region is analyzed based on a picture of correlated hole hopping within a lower Hubbard subband. It is shown that experimental trends are fairly well accounted for by this model, suggesting that the normal state of this compound is quite different from the metallic state. 相似文献
8.
Suter A Morenzoni E Prokscha T Wojek BM Luetkens H Nieuwenhuys G Gozar A Logvenov G Božović I 《Physical review letters》2011,106(23):237003
We show, by means of low-energy muon-spin rotation measurements, that few-unit-cells thick La(2)CuO(4) layers synthesized digitally by molecular beam epitaxy are antiferromagnetically ordered. Below a thickness of about 5 CuO(2) layers the long-range ordered state breaks down, and a magnetic state appears with enhanced quantum fluctuations and a reduced spin stiffness. This magnetic state can exist in close proximity (few ?) to high-temperature superconducting layers, without transmitting supercurrents. 相似文献
9.
G.M. Luke K. Kojima M. Larkin J. Merrin B. Nachumi Y.J. Uemura Y. Nakamura S. Uchida M. Crawford 《Hyperfine Interactions》1997,105(1-4):113-117
We present μSR experiments on La2-x Bax CuO4 and La1.6-x Nd0.4 Srx CuO4 for x=0.125. Both of these materials order magnetically with TN\approx30\ K, while a superconducting sample of La1.4 Nd0.4 Sr0.2 CuO4 showed no evidence for static copper moments. Our results support the conclusion that the so‐called “1/8” anomaly in La2-x Bax CuO4 is a result of static (pinned) charge segregation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
We present measurements of the magnetic penetration depth, lambda(-2)(T), in Pr(2-x)Ce(x)CuO(4-y) and La(2-x)Ce(x)CuO(4-y) films at three Ce doping levels, x, near optimal. Optimal and overdoped films are qualitatively and quantitatively different from underdoped films. For example, lambda(-2)(0) decreases rapidly with underdoping but is roughly constant above optimal doping. Also, lambda(-2)(T) at low T is exponential at optimal and overdoping but is quadratic at underdoping. In light of other studies that suggest both d- and s-wave pairing symmetry in nominal optimally doped samples, our results are evidence for a transition from d- to s-wave pairing near optimal doping. 相似文献
11.
The significance of heterovalent, substitutional disorder for the distribution of charge carriers in La2?x Sr x CuO4 has been investigated. Disorder is shown to cause strong variations of binding energies of the ions ranging to some eV for Sr contentsx=0.1. Balancing the energy for a hole transport, Cu3++O2?→Cu2++O?, and taking binding energy variations into account, the process is realized to become possible without consuming energy for a subset Θ for allx Cu3+ in one formula unit of La2?x Sr x CuO4. The functions Θ(x) are presented for hole transports to apex and in-plane oxygens, respectively. The delocalization of charge carriers is interpreted to be caused by valency disorder on metal lattice sites. 相似文献
12.
The significance of heterovalent, substitutional disorder for the distribution of charge carriers in La2−x
Sr
x
CuO4 has been investigated. Disorder is shown to cause strong variations of binding energies of the ions ranging to some eV for
Sr contentsx=0.1. Balancing the energy for a hole transport, Cu3++O2−→Cu2++O−, and taking binding energy variations into account, the process is realized to become possible without consuming energy for
a subset Θ for allx Cu3+ in one formula unit of La2−x
Sr
x
CuO4. The functions Θ(x) are presented for hole transports to apex and in-plane oxygens, respectively. The delocalization of charge carriers is interpreted
to be caused by valency disorder on metal lattice sites. 相似文献
13.
Steeneken PG Tjeng LH Sawatzky GA Tanaka A Tjernberg O Ghiringhelli G Brookes NB Nugroho AA Menovsky AA 《Physical review letters》2003,90(24):247005
We report on an x-ray absorption and resonant photoemission study on single crystals of the high-T(c) cuprates La2-xSrxCuO4 and Nd(2-x)Ce(x)CuO(4-delta). Using an intrinsic energy reference, we find that the chemical potential of La2-xSrxCuO4 lies near the top of the La2CuO4 valence band whereas in Nd(2-x)Ce(x)CuO(4-delta) it is situated near the bottom of the Nd2CuO4 conduction band. The data clearly establish that the introduction of Ce in Nd2CuO4 results in electrons being doped into the CuO2 planes. We infer that the states closest to the chemical potential have a Cu 3d(10) singlet origin in Nd(2-x)Ce(x)CuO(4-delta) and a 3d(9)L singlet origin in La2-xSrxCuO4. 相似文献
14.
We presented the recent Hall effect data for a number of carriers in La(2-x)Sr(x)CuO4 as the sum of two components: the temperature independent term n0(x), which is due to external doping, and the thermally activated contribution. Their balance determines the crossover temperature T*(x) from the marginal Fermi liquid to pseudogap regime. The activation energy Delta(x) for thermally excited carriers equals the energy between the Fermi surface "arc" and the band bottom, as seen in angle-resolved photoemission spectroscopy experiments. Other implications for the (T, x)-phase diagram of cuprates are also discussed. 相似文献
15.
We have performed a series of elastic neutron scattering measurements on 1/8-hole doped La(1.875)-Ba(0.125-x)Sr(x)CuO(4) single crystals with x = 0.05, 0.06, 0.075, and 0.085. Both charge-density-wave (CDW) and spin-density-wave orders are found to develop simultaneously below the structural transition temperature between the low-temperature orthorhombic (LTO) and low-temperature tetragonal (LTT) or low-temperature less-orthorhombic (LTLO) phases. In the ground state the CDW order is observed only in the LTT/LTLO phase and drastically degrades towards the LTO boundary. The x dependence of T(c) strongly suggests a direct effect of the CDW order on the suppression of superconductivity. 相似文献
16.
Dual nature of the electronic structure of (La(2--x--y)Nd(y)Sr(x))CuO(4) and La(1.85)Sr(0.15)CuO(4).
X J Zhou T Yoshida S A Kellar P V Bogdanov E D Lu A Lanzara M Nakamura T Noda T Kakeshita H Eisaki S Uchida A Fujimori Z Hussain Z X Shen 《Physical review letters》2001,86(24):5578-5581
High resolution angle-resolved photoemission measurements have been carried out on (La(1.4--x)-Nd(0.6)Sr(x))CuO(4), a model system with static one-dimensional (1D) charge ordering (stripe), and (La(1.85)-Sr(0.15))CuO(4), a high temperature superconductor (T(c) = 40 K) with possible dynamic stripes. In addition to the straight segments near ( pi,0) and ( 0,pi) antinodal regions, we have identified the existence of spectral weight along the [1,1] nodal direction in the electronic structure of both systems. This observation of nodal state, together with the straight segments near antinodal regions, reveals the dual nature of the electronic structure of stripes due to the competition of order and disorder. 相似文献
17.
Ono S Ando Y Murayama T Balakirev FF Betts JB Boebinger GS 《Physical review letters》2000,85(3):638-641
We measure the normal-state in-plane resistivity of Bi(2)Sr(2-x)La(x)CuO(6+delta) single crystals at low temperatures by suppressing superconductivity with 60 T pulsed magnetic fields. With decreasing hole doping, we observe a crossover from a metallic to an insulating behavior in the low-temperature normal state. This crossover is estimated to occur near 1/8 doping, well inside the underdoped regime, and not at optimum doping as reported for other cuprates. The insulating regime is marked by a logarithmic temperature dependence of the resistivity over two decades of temperature, suggesting that a peculiar charge localization is common to the cuprates. 相似文献
18.
P. Steiner J. Albers V. Kinsinger I. Sander B. Siegwart S. Hüfner C. Politis 《Zeitschrift für Physik B Condensed Matter》1987,66(3):275-278
Photoemission spectra of the La2–x
Sr
x
CuO4 system which recently has been demonstrated of being capable to produce high temperature (T
c
>35 K) superconducting compounds are reported. The photoemission spectra of the basic system (La2CuO4) and of samples which contain up to 20% Sr are not significantly different. The density of states at the Fermi energy is small (smaller than that of metallic Cu) and the samples show a possible small shift of the Cu 2p lines towards the trivalent position with increasing tendency to superconductivity. From the Sr 3d spectra a considerable amount of oxygen defects coordinated to the Sr ions is estimated. 相似文献
19.
Based on a simple argument, it is shown that a small concentration of holes in a single band Hubbard Hamiltonian on a quadratic lattice with moderateU/t ratio is enough to destroy the long range antiferromagnetic order in the ground state. The particular emphasis is made on the role of large amplitude zero-point quantum spin fluctuations inherent in low-dimensional spin system with the small magnitude of spinS=1/2. The relevance to the highT
c
superconductivity materials La2–x
Sr
x
CuO4 is discussed. 相似文献
20.
Summary
139La NQR spin-spin and spin-lattice relaxation measurements in La2−x
Sr
x
CuO4−y
are presented, forx ranging from zero to 0.3 and for variable oxygen content, in the temperature range (1.6÷450) K. The data are analysed in
terms of the different possible relaxation mechanisms. The dominant relaxation mechanism over most of thex andT range is associated with the Cu++−Cu++ magnetic correlations and spin dynamics. To explain the data we introduce a heuristic model whereby the degree of magnetic
correlations, that would result from the strength of the Cu−Cu exchange coupling, is reduced by mobile charge defects (solitons
or holons) causing a liquidlike thermal bath of magnetic excitations described by a concentration-dependent and thermally
activated correlation time τd. The activation energy for τd is inversely proportional to the concentration of mobile defects. It is shown that theT
1 data yield thex andT dependence of the correlation length, with quantitative estimate in agreement with neutron scattering results. Some implications
of the model on other quantities, like magnetic susceptibility,x dependence of the Neel temperature and electric conductivity, are briefly discussed.
Riassunto Sono presentate misure di rilassamento NQR spin-spin e spin-reticolo per139La in La2−x Sr x CuO4−y , perx compreso tra 0 e 0.3 e a contenuto variabile di ossigeno, nell'intervallo di temperaturaT tra 1.6 e 450 K. I risultati delle misure vengono dapprima analizzati alla luce dei possibili meccanismi di rilassamento e si mostra come in un ampio intervallo di valori dix e diT il meccanismo dominante è costituito dalla dinamica e dalle correlazioni degli spin di Cu++. Allo scopo di spiegare i risultati ottenuti, viene introdotto un modello euristico in cui il grado di correlazione magnetica che conseguirebbe dall'interazione di superscambio Cu−Cu viene ridotto da difetti mobili (solitoni o holoni) che insediano un bagno termico di eccitazioni magnetiche simile a un liquido, descritto da un tempo di correlazione τd che dipende dalla concentrazione di tali difetti ed è termicamente attivato. L'energia di attivazione per τd risulta inversamente proporzionale alla concentrazione di difetti mobili. Oltre a giustificare compiutamente le risultanze sperimentali, tale modello consente di ricavare quantitativamente la dipendenza dax e daT della lunghezza di correlazione, che risulta in accordo con quella nota aT=77K dallo scattering di neutroni. Sono anche brevemente discusse le implicazioni del modello su altre grandezze come la suscettività magnetica, la dipendenza della temperatura di Neel dax e la conducibilità elettrica.
Резюме Приводятся результаты измерений139La NQR спин-спиновой и спинрешеточной релаксации в La2−x Sr x CuO4−y дляx в области от 0 доx=0.3 и для различного содержания кислорода, в области температур (1.6÷450)K. Полученные данные анализируются в терминах различных механизмов релаксации. Доминиркющий механизм релаксации для большенства значенийx и в рассматриваемой области температур связан с магнитными корреляциями Cu++−Cu++ и спиновой динамикой. Для объяснения полученных данных мы вводим эвристическую модель, с помощью которой степень магнитных корреляций, которые зависят от силы Cu−Cu обменной связи, сводится к подвижным заряженным дефектам (солитовы или голоны), обусловленным термостатом магнитных возбужений, описываемых зависящим от концентрации и термически активированным временем корреляции τd. Энергия активации для τd обратно пропорциональна концентрации подвижных дефектов. Показывается, что данные дляT 1 определяют зависимость корреляции отx и отT, причем количественная оценка согласуется с данными по рассеянию нейтронов. Вкратце обсуждаются возможные применения предложенной модели к другим величинам: магнитной восприимчивости, зависимости температуры Нееля (точки Кюри) отx и электропроводности.相似文献