Range Of Hole Concentration Research Articles

Fe-substitution Effects on the Cu-spin Correlation in La2-xSrxCu1-yFeyO4 Studied by Muon Spin Relaxation

Abstract We have investigated the low-frequency Cu-spin dynamics of partially Fe-substituted La 2−x SrxCu 1−y FeyO4 with x = 0.06 – 0.235 and y = 0.01 from zero-field muon-spin-relaxation measurements. We find that the magnetic transition temperature, T mid N , is enhanced through the 1% Fe substitution in a wide range of hole concentration per Cu, N p, where superconductivity appears in La 2−x Sr x CuO 4 . The T mid N exhibits a local maximum at p ∼ 0.115 and exists even in the overdoped regime of p > 0.15. To the surprise, T mid N in the overdoped regime of 0.15 p ≤ 0.225 is larger than in the underdoped regime of 0.05 ≤ p ≤ 0.09. These results suggest that the substitution of Fe as a magnetic impurity is effective for the stabilization of the so-called stripe order in high- T c cuprates in the underdoped regime and that the nature of the magnetic order induced through the Fe substitution in the overdoped regime might be different from that in the underdoped regime.

Stability of the positively charged manganese centre in GaAs heterostructures examined theoretically by the effective mass approximation calculation near the Γ critical point

This paper describes an n—i—p—i—n model heterostructure with a manganese (Mn)-doped p-type base region to check the stability of a positively charged manganese A+Mn centre with two holes weakly bound by a negatively charged 3d5(Mn) core of a local spin S = 5/2 in the framework of the effective mass approximation near the Γ critical point (k ∼ 0). By including the carrier screening effect, the ground state energy and the binding energy of the second hole in the positively charged centre A+Mn are calculated within a hole concentration range from 1 × 1016 cm−3 to 1 × 1017 cm−3, which is achievable by biasing the structure under photo-excitation. For comparison, the ground-state energy of a single hole in the neutral A0Mn centre is calculated in the same concentration range. It turns out that the binding energy of the second hole in the A+Mn centre varies from 9.27 meV to 4.57 meV. We propose that the presence of the A+Mn centre can be examined by measuring the photoluminescence from recombination of electrons in the conduction band with the bound holes in the A+Mn centre since a high frequency dielectric constant of ∊∞ = 10.66 can be safely adopted in this case. The novel feature of the ability to tune the impurity level of the A+Mn centre makes it attractive for optically and electrically manipulating local magnetic spins in semiconductors.

Development of Cu-spin correlation in Bi1.74Pb0.38Sr1.88Cu1−yZnyO6+δhigh-temperature superconductors observed by muon spin relaxation

A systematic muon-spin-relaxation study in Bi-2201 high-Tc cuprates has revealed for the first time that the Cu-spin correlation (CSC) is developed at low temperatures below 2 K in a wide range of hole concentration where superconductivity appears. The CSC tends to become weak gradually with increasing hole-concentration. Moreover, CSC has been enhanced through the 3% substitution of Zn for Cu. These results are quite similar to those observed in La-214 high-Tc cuprates. Accordingly, it has been suggested that the intimate relation between the so-called spin-charge stripe correlations and superconductivity is a universal feature in hole-doped high-Tc cuprates. Furthermore, apparent development of CSC, which is suppressed through the Zn substitution oppositely, has been observed in non-superconducting heavily overdoped samples, being argued in the context of a recently proposed ferromagnetic state in heavily overdoped cuprates.

Neutron-Scattering Study of Fe-Substitution Effect on the Static Spin Correlation in La2-xSrxNiO4

We have performed elastic neutron scattering measurements on the Fe-doped La 2- x Sr x NiO 4 (LSNO) with 0.12 ≤ x ≤0.50 to study the magnetic impurity effects on the static spin correlations. In the pristine LSNO system, it is well known that both spin and charge stripe orders are stabilized at low temperatures in the wide hole concentration range from 0.12 to 0.70. The incommensurability (e) increases upon Sr-doping and tends to saturate with e max ∼0.47 (r.l.u.) for x > 0.5. We found that 4% Fe-substitution for Ni ion reduces e at the fixed Sr concentration for the all measured samples with 0.12 ≤ x ≤0.5. The e in the Fe-substituted samples with x = 0.25, 0.33, 0.37, and 0.50 was 0.02–0.04 (r.l.u.) smaller than that in the pristine samples. Furthermore, we observed commensurate peak in the Fe-doped x = 0.12 sample. No well-defined incommensurate magnetic peaks were detected, unlike to the result for the pristine x = 0.12 sample. The effect of Fe-substitution on the magnetic ordering temperature ( T spin...

Hole trapping by Ni, Kondo effect, and electronic phase diagram in nonsuperconducting Ni-substitutedLa2−xSrxCu1−yNiyO4

In order to investigate the electronic state in the normal state of high-Tc cuprates in a wide range of temperature and hole-concentration, specific-heat, electrical-resistivity, magnetization and muon-spin-relaxation (muSR) measurements have been performed in non-superconducting Ni-substituted La2-xSrxCu1-yNiyO4 where the superconductivity is suppressed through the partial substitution of Ni for Cu without disturbing the Cu-spin correlation in the CuO2 plane so much. In the underdoped regime, it has been found that there exist both weakly localized holes around Ni and itinerant holes at high temperatures. With decreasing temperature, all holes tend to be localized, followed by the occurrence of variable-range hopping conduction at low temperatures. Finally, in the ground state, it has been found that each Ni2+ ion traps a hole strongly and that a magnetically ordered state appears. In the overdoped regime, on the other hand, it has been found that a Kondo-like state is formed around each Ni2+ spin at low temperatures. In conclusion, the ground state of non-superconducting La2-xSrxCu1-yNiyO4 changes upon hole doping from a magnetically ordered state with the strong hole-trapping by Ni2+ to a metallic state with Kondo-like behavior due to Ni2+ spins, and the quantum phase transition is crossover-like due to the phase separation into short-range magnetically ordered and metallic regions.

Hole-trapping and Kondo effect in Ni-substituted La2−xSrxCu1−yNiyO4 with x = 0.08–0.30

We have measured the specific heat in a wide range of hole-concentration in partially Ni-substituted La2−xSrxCu1−yNiyO4, in order to investigate Ni-substitution effects on the electronic state. For 10% Ni-substituted samples of y=0.10, it has been found that the electronic specific heat divided by temperature, Cel/T, decreases with decreasing temperature at low temperatures for x⩽0.20, which is concluded to be due to a decrease in the effective hole-concentration caused by strong hole-trapping by Ni2+ ions. For x>0.20, on the other hand, an increase in Cel/T with decreasing temperature has been observed, which is due to the Kondo effect. In fact, both a logarithmic temperature-dependence of the electrical resistivity and a negative magnetoresistance have been observed for x>0.20. It has been concluded that the ground state of non-superconducting La2−xSrxCu1−yNiyO4 changes upon hole doping from a magnetically ordered state to a metallic state and that the quantum phase transition is crossover-like due to the phase separation in the overdoped regime.

Theory of the spin-EPR shift of Mn2+ in p-Sn1−xMnxTe

We calculate the spin-electron paramagnetic resonance (EPR) shift (Ps) of Mn2+ ion in p-type Sn1−xMnxTe using a theory for the quantity derived earlier. The theory includes the effect of the spin–orbit interaction from first principles. The spin–orbit interaction gives rise to the effective g-factor, apart from modifying the expression for the shift through the usual changes in the energy eigenvalues and the eigenfunctions. We derive a theory, as appropriate for the p-type SnTe and Sn1−xMnxTe, where is the momentum operator in the presence of the spin–orbit interaction. We consider a six-band model for SnTe, which includes, apart from the band-edge levels, two additional levels both above and below the band gap. The band-edge states are treated exactly and the effect of the far bands is included through second-order perturbation. The calculated EPR shift shows considerable anisotropy due mainly to the spin–orbit interactions. We have explicitly shown the relative contributions of the single-band, two-band and far-band terms to the shift. Our results for moderate carrier concentrations agree fairly well with the experiment. In addition, we have calculated the Fermi energy, the density of states and the effective masses and g-factors for a wide range of hole concentrations for p-type SnTe.

Ni-substitution effects on Cu-spin correlation in relating to hole trapping and stripe pinning

In order to investigate Ni-impurity effects on the Cu-spin dynamics in a wide range of hole concentration, we have performed zero-field muon-spin-relaxation measurements in La 2-x Sr x Cu 1-y Ni y O 4 (LSCNO) with x = 0.08-0.30 and y = 0-0.10. It has been found that the hole-trapping effect of Ni clearly appears in heavily Ni-substituted LSCNO with y≥0.05, while the stripe-pinning effect of Ni is marked in lightly Ni-substituted LSCNO around x = 1 /8 .

Study on the origin of large thermopower in hole doped LaRhO3 based on ab-initio downfolding

We study the origin of the large thermopower and its peculiar hole concentration in the Ni-doped LaRhO3. We calculate the band structure and construct the maximally localized Wannier functions, from which a tightbinding Hamiltonian is obtained. The Seebeck coefficient is calculated within the Boltzmann's equation approach using this effective Hamiltonian. We find that the Seebeck coefficient remains nearly constant within a large hole concentration range, which is consistent with the experimental observation. The origin of this peculiar doping concentration is discussed.

First-principles study on the origin of large thermopower in hole-dopedLaRhO3 and CuRhO2

Based on first-principles calculations, we study the origin of the large thermopower in Ni-dopedLaRhO3 andMg-doped CuRhO2. We calculate the band structure and construct the maximally localized Wannier functionsfrom which a tight binding Hamiltonian is obtained. The Seebeck coefficient is calculatedwithin the Boltzmann’s equation approach using this effective Hamiltonian. ForLaRhO3, we find that the Seebeck coefficient remains nearly constant within a large holeconcentration range, which is consistent with the experimental observation. ForCuRhO2, the overall temperature dependence of the calculated Seebeck coefficient is in excellentagreement with the experiment. The origin of the large thermopower is discussed.

Change of the Dynamics of Internal Fields in the Normal State of La2-xSrxCuO4 Observed by Muon-Spin-Relaxation

Zero-field and longitudinal-field muon-spin-relaxation measurements have been carried out in order to investigate the electronic and magnetic states in La 2- x Sr x CuO 4 over a wide range of hole concentration from x =0.024 to 0.15. It has been found that the dynamic depolarization rate of muon spins in zero field starts to increase monotonically with decreasing temperature at a high temperature around 100 K. This effect is enhanced around the hole concentration of 1/8 per Cu but easily suppressed by the application of a small external field of a couple of ten gauss. The present study suggests that the dynamics of fluctuating internal fields at the muon site in the normal state of La 2- x Sr x CuO 4 changes at a high temperature around 100 K and is correlated with the mobility of holes. Possible relationships with spin-hole stripes and the spin-gap state in the normal state are discussed.

Effects of Zn substitution in La2−xSrxCu1−yZnyO4: interplay among superconductivity, pseudogap, and stripe order

The effect of Zn substitution on the superconducting transition temperature,Tc, was investigatedfor the La2−xSrxCu1−yZnyO4 (Zn-LSCO) compounds over a wide range of hole concentrations,p (), and Zn content (y) in the CuO2 plane. A Zn-induced rate of suppression ofTc,dTc(p)/dy, was found tobe strongly p-dependent and showed a systematic variation with hole concentration, except in the vicinity ofp∼0.12, i.e. nearthe so-called 1/8th anomaly where the charge/spin stripe correlations are at their strongest inLa2−xSrxCuO4.Near p∼0.12, the static striped charge ordering is widely believed to dominate theT–p phasediagram. dTc(p)/dy decreased strongly around this hole concentration i.e. Zn became less effective in degradingTc near p∼0.12. This observation is indicative of an intricate and competing interplay among thesuperconducting, pseudogap, and stripe correlations in Zn substituted LSCO.

Impurity effect on spin correlations in lightly doped [formula omitted

A review is given of the impurity effect on the static spin correlations in lightly doped La 2 - x Sr x CuO 4 studied by the neutron scattering technique. Zn doping reduces the incommensurability just slightly. On the other hand, Ni doping quickly reduces the incommensurability and restores Néel ordering, indicating a strong effect on hole localization. This suggests that Ni is doped as Ni 3 + or that doped Ni 2 + and hole form a strongly bound state with the Zhang–Rice character. It was found that this behavior is universal in a wide range of hole concentration in La 2 - x Sr x CuO 4 ( 0.01 ⩽ x ⩽ 0.07 ).

Critical fluctuations and phase diagram of La 2− xSr xCuO 4 thin films

We present a systematic study of the critical fluctuations of the superconducting to the normal-state transition of La 2− x Sr x CuO 4 (LSCO) thin films with a wide range of hole concentrations ( x = 0.07–0.20), which are probed by the frequency-dependent complex conductivity measurements and their dynamic scaling analyses. Our results clearly indicate that the critical dynamics of LSCO is essentially two-dimensional, except for the 3D- XY critical dynamics observed only near the optimally doped region. We argue possible origin of the anomalous dimensional crossovers with hole doping, including an implication of a hidden quantum critical point near the optimally doped region.

Raman Studies of Carbon-Doped GaAs Layers Grown by a Metallic-Arsenic-Based Metalorganic Chemical Vapor Deposition System

High-quality p type GaAs epilayers were grown by metalorganic chemical vapor deposition using trimethylgallium and metallic arsenic as gallium and arsenic sources, respectively. The range of hole concentration analyzed goes from 1017 to 1019 cm−3, as measured by the Hall−van der Pauw method. For controlling the hole concentration, a mixture of hydrogen and nitrogen was used as the carrier gas. Raman scattering spectra show transversal optical mode at 270 cm−1 for low-doped samples and a longitudinal optical (LO) mode at 292 cm−1 produced by phonon-hole-plasmon coupling for high-doped samples. The relative intensity of the LO mode for the doped samples correlates very well with the hole concentration. As the carrier concentration increases, the LO phonon-plasmon-coupled mode increases. The corresponding decrease of the intensity of the LO mode is interpreted as the decrease in the depletion layer as the carrier concentration increases.

Magnitude and crystalline anisotropy of hole magnetization in(Ga,Mn)As

Theory of hole magnetization ${M}_{c}$ in zinc-blende diluted ferromagnetic semiconductors is developed relaxing the spherical approximation of earlier approaches. The theory is employed to determine ${M}_{c}$ for $(\mathrm{Ga},\mathrm{Mn})\mathrm{As}$ over a wide range of hole concentrations and a number of crystallographic orientations of Mn magnetization. It is found that anisotropy of ${M}_{c}$ is practically negligible but the obtained magnitude of ${M}_{c}$ is significantly greater than that determined in the spherical approximation. Its sign and value compares favorably with the results of available magnetization measurements and ferromagnetic resonance studies.

Electronic structure of layered manganite La 1.1 Sr 1.9 Mn 2 O 7 studied by angle-resolved photoemission spectroscopy at low temperatures

To clarify an electronic structure of an layered manganite, we have performed angle-resolved photoemission spectroscopy on La 2−2 x Sr 1+2 x Mn 2 O 7 ( x = 0.45 ), in which a phase transition occurs from an antiferromagnetic insulating phase to a canted antiferromagnetic metallic phase at 95 K. A spectral weight at the Fermi level is suppressed at 10 K, which is in contrast with the findings that a finite spectral weight exists for x = 0.40 [N. Mannella, W. Yang, X.J. Zhou, H. Zheng, J.F. Mitchell, J. Zaanen, T.P. Devereaux, N. Nagaosa, Z. Hussain, Z.-X. Shen, Nature (London) 438 (2005) 474; Z. Sun, Y.-D. Chuang, A.V. Fedorov, J.F. Douglas, D. Reznik, F. Weber, N. Aliouane, D.N. Argyriou, H. Zheng, J.F. Mitchell, T. Kimura, Y. Tokura, A. Revcolevschi, D.S. Dessau, Phys. Rev. Lett. 97 (2006) 056401; Y.-D. Chuang, et al., Science 292 (2001) 1509]. On the other hand, the mapping of the spectral weight in the vicinity of the Fermi level possesses a rather straight part in the Brillouin zone. This is a common feature of an electronic structure in a wide hole concentration range of the La 2−2 x Sr 1+2 x Mn 2 O 7 system, which is independent of a magnetic structure.

Intrinsically coupled stripes within the CuO2 planes of the high-Tc materials

Analysis of the electronic state of the CuO2 planes of high-Tc materials has been performed with special regard to the influence of the coulomb interactions separated after moments. Using this analysis to derive the basic structure of the electronic states within the CuO2 planes of the high-Tc materials, different symmetry breaking effects were revealed. First of all, a commensurate charge and bonding fluctuation state (CBF) with the period (2a,2b) is established which exists collinearly with the antiferromagnetic spin state. It is concluded that the CBF state and the antiferromagnetic spin state are results of the same electronic renormalizations. Furthermore, the existence of localized topological hole states under hole doping is established. As a natural consequence of this, the local symmetry is broken. It is proven that a quadrupolar polarization induced attractive hole–hole interaction can exist between such topological hole states. This interaction creates an ordered topological hole structure which leads to a global symmetry breaking. This highly ordered topological hole structure, which will be referred as bonded holes (b-holes), can be characterized as parallel one-dimensional electronic states (stripes) along particular ⋯Cu–O–Cu⋯ bonding directions which are intrinsically coupled to each other. The highly ordered topological b-hole state exists undisturbed for hole concentrations nh in the range of 0.125 holes/copper⩽nh⩽0.25 holes/copper. The total correlation energy per b-hole |ECtot| was deduced to be ⩾160meV. In addition to b-holes, holes which are not intrinsically bonded exist in the concentration range of nh>0.125 holes/copper. These non-bonded holes are termed as free holes (f-holes). The inevitable consequence is an electronic two fluid behaviour (b-holes, f-holes) within the hole concentration range of 0.125 holes/copper<nh⩽0.25 holes/copper. The characteristics of the electronic state deduced here, enable a more complex understanding of various experimental results, and gives in particular insight into the foundations of the 1/8 problem and the creation of checkerboard structures.

Anomalous pseudogap and superconducting-state properties of heavily disorderedY1−xCaxBa2(Cu1−yZny)3O7−δ

The role of substantial in-plane disorder (Zn) on the transport and AC susceptibility of Y1-xCaxBa2(Cu1-yZny)3O7-delta was investigated over a wide range of planar hole concentration, p. Resistivity, r(T), for a number of overdoped to underdoped samples with y equals/greater than 0.055 showed clear downturns at a characteristic temperature similar to that found at T* in Zn-free underdoped samples because of the presence of the pseudogap. Contrary to the widely observed behavior for underdoped cuprates at lower Zn contents (where the pseudogap energy increases almost linearly with decreasing p in the same way as for the Zn-free compounds), this apparent pseudogap temperature at high Zn content showed very little or no p-dependence. It also increases systematically with increasing Zn concentration in the CuO2 planes. This anomalous behavior appears quite abruptly, e.g., samples with y less than/equals 0.05 exhibit the usual T*(p) behavior. AC susceptibility of these heavily disordered samples showed the superfluid density to be extremely low. Magneto-transport, r(T,H), measurements are provisionally interpreted in terms of high-strength pinning centers for vortices in these samples. We also discuss various possible scenarios that might lead to a Zn induced pseudogap in the cuprates.

Metal–insulator transition in manganese‐doped InSb crystals

AbstractTransport properties of manganese‐doped InSb crystals with hole concentration close to the critical concentration Ncr of the metal–insulator transition (MIT) in p‐InSb(Mn) was found to be different from MIT in semiconductors doped with non‐magnetic impurities such as p‐Ge(Ga), p‐Si(P) and p‐InSb(Ge). On the insulator side of the transition (NMn ≤ Ncr = 2 × 1017 cm–3) in the range of hole concentration p = 1–2 × 1017 cm–3 an activation type of conductivity with energy gap Δ = 7 × 10–6–10–3 eV was observed. Thus, the usually observed variable range hopping conductivity in crystal semiconductors doped with non‐magnetic impurities at low and super‐low temperatures was not revealed in p‐InSb(Mn) at p ≤ Ncr. An external magnetic field decreased Δ and caused a giant decrease of specific resistivity (ρ0/ρB ∼ 104 at T ≤ 0.3 K and B ≥ 3 T). On cooling to temperatures below T = 1.5 K the Hall constant changed sign at B &lt; 3 T. The change of Hall constant sign with decrease of temperature means that conductivity of p‐InSb(Mn) and crystals compensated with Te – p‐InSb(Mn, Te) – at low temperatures was caused by electrons. The proposed model associated an activation energy Δ at p ∼ Ncr with the energy gap between sub‐bands formed in the impurity band. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)