Hall Coefficient Data Research Articles

Self-doped Mott insulator for parent compounds of nickelate superconductors

We propose the parent compound of the newly discovered superconducting nickelate Nd$_{1-x}$Sr$_{x}$NiO$_{2}$ as a self-doped Mott insulator, in which the low-density Nd-$5d$ conduction electrons couple to localized Ni-3$% d_{x^{2}-y^{2}}$ electrons to form Kondo spin singlets at low temperatures. This proposal is motivated with our analyses of the reported resistivity and Hall coefficient data in the normal state, showing logarithmic temperature dependence at low temperatures. In the strong Kondo coupling limit, we derive a generalized $t$-$J$ model with both Kondo singlets and nickel holons moving through the lattice of otherwise nickel spin-1/2 background. The antiferromagnetic long-range order is therefore suppressed as observed in experiments. With Sr-doping, the number of holons on the nickel sites increases, giving rise to the superconductivity and a strange metal phase analogous to those in superconducting copper oxides.

Influence of Induced Electrical Polarization on the Magnetoresistance and Magnetoimpedance in the Spin‐Disordered TmxMn1−xS Solid Solution

The transport properties of the TmxMn1–xS (x ≤ 0.15) solid solutions in the temperature range of 200–600 K have been investigated. The temperatures of lattice polaron pinning accompanied by the lattice strain, condensation of the infrared modes, and thermionic emission have been determined. The change of the carrier sign with temperature has been found from the Hall coefficient data and dragging of electrons by phonons, from the thermopower data. The dependence of the magnetoresistance on the concentration, current, and voltage has been established from the I–V characteristics measured without field and in an applied magnetic field of H = 8 kOe in the temperature range of 300–500 K. The functional temperature dependence of the carrier relaxation time has been determined using the impedance data. The concentration region with the magnetoimpedance sign varying with frequency and temperature has been found. The increase in the relaxation time of the induced electric polarization with increasing concentration of thulium ions has been observed. The experimental data have been interpreted in the framework of the Debye and Maxwell–Wagner models, as well as the theoretical model for the Rashba spin–orbit interaction.

Hall effect measurements of high-quality Mn3CuN thin films and the electronic structure

The physical properties of $\mathrm{M}{\mathrm{n}}_{3}\mathrm{CuN}$ were studied using thin films. We found that an annealing process was very effective to improve the film quality, the key of which was the use of Ti that prevented the formation of oxide impurities. Using these high-quality thin films, we found strong strain dependence for the ferromagnetic transition temperature (${T}_{C}$) and a sign change of the Hall coefficient at ${T}_{C}$. The analysis of Hall coefficient data revealed a sizable decrease of hole concentration and a large increase of electron mobility below ${T}_{C}$, which is discussed in relation to the electronic structure of this material.

Physical properties of the type-I clathrate phase Ba8−xEuxAuySi46−y

The effect of the substitution of rare–earth atoms for guest atoms on the low-temperature transport and magnetic properties is investigated for single-crystalline type–I clathrates with the nominal composition Ba8−xEuxAuySi46−y (x = 1.0, 1.68 and y = 4.77, 5.32). The Seebeck coefficient and Hall coefficient data show that a transition from n- to p-type conduction takes place with increasing Au content. The n-type sample presents a large maximum in the thermal conductivity due to the freezing of three phonon Umklapp scattering processes at low temperatures, whereas the maximum of thermal conductivity in the p-type sample is strongly reduced due to dominant phonon-electron scattering process. Both samples are metal–like and ferromagnetic, with Curie temperatures TC of 3.1 K and 10.0 K for x = 1.0 and 1.68, respectively. The magnetization measurement confirmed the Eu2+ state in both samples and the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction model explains the FM-type of order in which the nearest-neighbor (NNN) and the next-nearest-neighbor (NN) interactions play a major role at x = 1.0 and 1.68, respectively.

Normal-state magnetotransport properties of β-FeSe superconductors

We present β-FeSe magnetotransport data, and describe them theoretically. Using a simplified microscopic model with two correlated effective orbitals, we determined the normal state electrical conductivity and Hall coefficient, using Kubo formalism. With model parameters relevant for Fe-chalcogenides, we describe the observed effect of the structural transition on the ab-plane electrical resistivity, as well as on the magnetoresistance. Temperature-dependent Hall coefficient data were measured at 16 tesla, and their theoretical description improves upon inclusion of moderate electron correlations. We confirm the effect of the structural transition on the electronic structure, finding deformation-induced band splittings comparable to those reported in angle-resolved photoemission.

Electronic transport properties of MFe2As2 (M = Ca, Eu, Sr) at ambient and high pressures up to 20 GPa

We experimentally investigated the electronic transport properties of four iron pnictide crystals, namely, EuFe2As2, SrFe2As2, and CaFe2As2 parent compounds, and superconducting CaFe1.94Co0.06As2 at ambient and high pressures up to 20 GPa. At ambient pressure we examined the electrical resistivity, Hall and magnetoresistance effects of the samples in a temperature range from 1.5 to 380 K in high magnetic fields up to 13.6 T. In this work we carried out the first simultaneous investigations of the in-plane and out-of-plane Hall coefficients, and found new peculiarities of the low-temperature magnetic and structural transitions that occur in these materials. In addition, the Hall coefficient data suggested that the parent compounds are semimetals with a multi-band conductivity that includes hole-type and electron-type bands. We measured the pressure dependence of the thermoelectric power (the Seebeck effect) of these samples up to 20 GPa, i.e. across the known phase transition from the tetragonal to the collapsed tetragonal lattice. The high-pressure behavior of the thermopower of EuFe2As2 and CaFe2As2 showing the p-n sign inversions was consistent with the semimetal model described above. By means of thermopower, we found in single-crystalline CaFe2As2 direct evidence of the band structure crossover related to the formation of As–As bonds along the c-axis on the tetragonal → collapsed tetragonal phase transition near 2 GPa. We showed that this feature is distinctly observable only in high-quality samples, and already for re-pressurization cycles this crossover was strongly smeared because of the moderate deterioration of the sample. We also demonstrated by means of thermopower that the band structure crossover that should accompany the tetragonal → collapsed tetragonal phase transition in EuFe2As2 near 8 GPa is hardly visible even in high-quality single crystals. This behavior may be related to a gradual valence change of the Eu ions under pressure that leads to an injection of free electrons and the steady shift of the conduction to n-type.

Electrical properties of n-type GaSb substrates and p-type GaSb buffer layers for InAs/InGaSb superlattice infrared detectors

Lightly doped n-type GaSb substrates with p-type GaSb buffer layers are the preferred templates for growth of InAs/InGaSb superlattices used in infrared detector applications because of relatively high infrared transmission and a close lattice match to the superlattices. We report here temperature dependent resistivity and Hall effect measurements of bare substrates and substrate-p-type buffer layer structures grown by molecular beam epitaxy. Multicarrier analysis of the resistivity and Hall coefficient data demonstrate that high temperature transport in the substrates is due to conduction in both the high mobility zone center Γ band and the low mobility off-center L band. High overall mobility values indicate the absence of close compensation and that improved infrared and transport properties were achieved by a reduction in intrinsic acceptor concentration. Standard transport measurements of the undoped buffer layers show p-type conduction up to 300 K indicating electrical isolation of the buffer layer from the lightly n-type GaSb substrate. However, the highest temperature data indicate the early stages of the expected p to n type conversion which leads to apparent anomalously high carrier concentrations and lower than expected mobilities. Data at 77 K indicate very high quality buffer layers.

Influence of Defects on the Charge Density Wave of ([SnSe](1+δ))1(VSe2)1 Ferecrystals.

A series of ferecrystalline compounds ([SnSe]1+δ)1(VSe2)1 with varying Sn/V ratios were synthesized using the modulated elemental reactant technique. Temperature-dependent specific heat data reveal a phase transition at 102 K, where the heat capacity changes abruptly. An abrupt increase in electrical resistivity occurs at the same temperature, correlated with an abrupt increase in the Hall coefficient. Combined with the magnitude and nature of the specific heat discontinuity, this suggests that the transition is similar to the charge density wave transitions in transition metal dichalcogenides. An ordered intergrowth was formed over a surprisingly wide compositional range of Sn/V ratios of 0.89 ≤ 1 + δ ≤ 1.37. X-ray diffraction and transmission electron microscopy reveal the formation of various volume defects in the compounds in response to the nonstoichiometry. The electrical resistivity and Hall coefficient data of samples with different Sn/V ratios show systematic variation in the carrier concentration with the Sn/V ratio. There is no significant change in the onset temperature of the charge density wave transition, only a variation in the carrier densities before and after the transition. Given the sensitivity of the charge density wave transitions of transition metal dichalcogenides to variations in composition, it is very surprising that the charge density wave transition observed at 102 K for ([SnSe]1.15)1(VSe2)1 is barely influenced by the nonstoichiometry and structural defects. This might be a consequence of the two-dimensional nature of the structurally independent VSe2 layers.

Thermoelectric properties of CeAl3 prepared by hot-press method

We present data on the heavy fermion compound CeAl3 as a potential p-type thermoelectric material at cryogenic temperatures. Samples of CeAl3 were synthesized by arc-melting, ball milling and hot pressing the nano-powder at different temperatures. Thermal conductivity (κ), Seebeck coefficient (S), electrical resistivity (ρ) and Hall coefficient (RH) of the samples were measured at temperatures ranging from 5 to 330K. The thermoelectric properties of this compound are highly dependent on the hot-pressing (HP) temperature. The thermal conductivity increases with increase in HP temperature which is compensated by increased power factor (S2ρ−1). As a result the samples with higher HP temperatures exhibit higher ZT values. The highest ZT value of 0.016 at 55K was observed for the sample hot-pressed at 800°C. The Hall coefficient data reflects an increase in carrier concentration and a decrease in carrier mobility with decreasing hot pressing temperature.

Thermoelectric properties of Zn doped Cu2SnSe3

Zn doped ternary compounds Cu2ZnxSn1−xSe3 (x = 0, 0.025, 0.05, 0.075) were prepared by solid state synthesis. The undoped compound showed a monoclinic crystal structure as a major phase, while the doped compounds showed a cubic crystal structure confirmed by powder XRD (X-Ray Diffraction). The surface morphology and elemental composition analysis for all the samples were studied by SEM (Scanning Electron Microscopy) and EPMA (Electron Probe Micro Analyzer), respectively. SEM micrographs of the hot pressed samples showed the presence of continuous and homogeneous grains confirming sufficient densification. Elemental composition of all the samples revealed an off-stoichiometry, which was determined by EPMA. Transport properties were measured between 324 K and 773 K. The electrical resistivity decreased up to the samples with Zn content x = 0.05 in Cu2ZnxSn1−xSe3, and slightly increased in the sample Cu2Zn0.075Sn0.925Se3. This behavior is consistent with the changes in the carrier concentration confirmed by room temperature Hall coefficient data. Temperature dependent electrical resistivity of all samples showed heavily doped semiconductor behavior. All the samples exhibit positive Seebeck coefficient (S) and Hall coefficient indicating that the majority of the carriers are holes. A linear increase in Seebeck coefficient with increase in temperature indicates the degenerate semiconductor behavior. The total thermal conductivity of the doped samples increased with a higher amount of doping, due to the increase in the carrier contribution. The total and lattice thermal conductivity of all samples showed 1/T dependence, which points toward the dominance of phonon scattering at high temperatures. The maximum 1/TZT = 0.48 at 773 K was obtained for the sample Cu2SnSe3 due to a low thermal conductivity compared to the doped samples.

Hall effect in a magnetogranulated structure of a semiconductor-ferromagnetic system at high pressures

The Hall coefficient of magnetogranulated p-Cd1 − xMnxGeAs2 (x = 0.18 and 0.3) semiconductor-ferromagnetic structures has been measured at high hydrostatic pressures of up to p = 7 GPa. Semiconductor-metal transitions have been identified and investigated using resistivity and Hall coefficient versus pressure data. Normal and anomalous contributions to the Hall coefficient have been evaluated from magnetic-field dependences of the Hall resistance in magnetic fields H ≤ 0.5 T at temperatures in the range T = 77–400 K. The pressure of the ferromagnetic-paramagnetic phase transition in the materials has been determined from anomalous Hall resistance hysteresis loops.

Thermoelectric properties of Indium doped Cu2GeSe3

Cu2Ge1−xInxSe3 (x = 0, 0.05, 0.1, 0.15) compounds were prepared by a solid state synthesis. The powder X-ray diffraction pattern of the undoped sample revealed an orthorhombic phase. The increase in doping content led to the appearance of additional peaks related to cubic and tetragonal phases along with the orthorhombic phase. This may be due to the substitutional disorder created by Indium doping. Scanning Electron Microscopy micrographs showed a continuous large grain growth with low porosity, which confirms the compaction of the samples after hot pressing. Elemental composition was measured by Electron Probe Micro Analyzer and confirmed that all the samples are in the stoichiometric ratio. The electrical resistivity (ρ) systematically decreased with an increase in doping content, but increased with the temperature indicating a heavily doped semiconductor behavior. A positive Seebeck coefficient (S) of all samples in the entire temperature range reveal holes as predominant charge carriers. Positive Hall coefficient data for the compounds Cu2InxGe1−xSe3 (x = 0, 0.1) at room temperature (RT) confirm the sign of Seebeck coefficient. The trend of ρ as a function of doping content for the samples Cu2InxGe1−xSe3 with x = 0 and 0.1 agrees with the measured charge carrier density calculated from Hall data. The total thermal conductivity increased with rising doping content, attributed to an increase in carrier thermal conductivity. The thermal conductivity revealed 1/T dependence, which indicates the dominance of Umklapp phonon scattering at elevated temperatures. The maximum thermoelectric figure of merit (ZT) = 0.23 at 723 K was obtained for Cu2In0.1Ge0.9Se3.

Enhanced upper critical fields in a new quasi-one-dimensional superconductor Nb2PdxSe5

We report the discovery of superconductivity with Tc = 5.5 K in Nb2PdxSe5, in which one-dimensional (1D) Nb–Se chains existing along the b-direction hybridize each other to form the conducting b–c* plane. The magnetic susceptibility and specific heat data in both single crystal and polycrystal show evidence of bulk superconductivity. The resistivity, Hall coefficient and magneto-resistance data all indicate the presence of an energy scale T* = ∼ 50 K, which becomes systematically lowered under hydrostatic pressure and competes with the stabilization of superconductivity. Combined with the band calculation results showing the Fermi surfaces with 1D character, we postulate that the energy scale T* is related to the formation of a density wave or a stabilization of low-dimensional electronic structure. The zero-temperature upper critical field, Hc2(0), of the single crystal is found to be 10.5, 35 and 22 T in the a′, b and c* directions, respectively. While the linearly increasing Hc2(T) for H//c* indicates the multi-band effect, Hc2(0) for H//b and c* are found to be much bigger than the Bardeen–Cooper–Schrieffer (BCS) Pauli limiting field, 1.84 Tc ∼ 9 T. The suppressed Pauli paramagnetic effect points to the possibility of enhanced spin–orbit scattering related to the low-dimensional electronic structure or the presence of heavy elements such as Pd.

Multiband conduction in the type-I clathrate Ba8Ge43□3

Hall effect and magnetoresistance measurements were carried out on a single-phase polycrystalline sample of the type-I clathrate Ba${}_{8}$Ge${}_{43}$\ensuremath{\square}${}_{3}$ in the 2--350 K temperature range. These experiments were complemented by electronic band structure and Fermi surface calculations performed by an all-electron, full potential first-principles method. These calculations have revealed the presence of three pieces of the Fermi surface originating from both holelike and electronlike bands crossing the Fermi level suggesting that both types of carriers play a role in the electrical conduction of this material. These results were experimentally confirmed via a strongly temperature-dependent and dominant holelike signal in the Hall coefficient and a breakdown of Kohler's rule in the magnetoresistance data. We analyze the Hall coefficient and magnetoresistance data within the framework of a two-band model with temperature-dependent carrier concentrations and mobilities and discuss its limits in capturing the essential features governing the magnetotransport. Combined with the temperature dependences of the thermopower and the electrical resistivity, all these results suggest that Ba${}_{8}$Ge${}_{43}$\ensuremath{\square}${}_{3}$ can be classified as a nearly compensated semimetal.

Growth and characterization of Tl 3InSe 4 single crystals

Tl 3InSe 4 single crystal has been successfully prepared by the Bridgman crystal growth technique. The crystal that is reported for the first time is found to be of tetragonal structure with lattice parameters of a=0.8035 and c=0.6883 nm. The electrical resistivity and Hall effect measurements on the crystal revealed a conductivity type conversion from p- to n-type at a critical temperature of 283 K. The electron to hole mobility ratio is found to be 1.10. The analysis of the temperature-dependent electrical resistivity, Hall coefficient and carrier concentration data reveals the extrinsic type of conduction with donor impurity levels that behave as acceptor levels when are empty. The data analysis allowed the calculation of the hole and the electron effective masses as 0.654 m 0 and 0.119 m 0, respectively. In addition, the temperature-dependent Hall mobility in the n -region is found to be limited by the electron–phonon short-range interactions scattering with an electron–phonon coupling constant of 0.21.

Thermoelectric power and Hall coefficient measurements onBa(Fe1−xTx)2As2(T=Coand Cu)

Temperature dependent thermoelectric power (TEP) data on Ba(Fe1-xTMx)2As2 (TM = Co and Cu), complemented by the Hall coefficient data on the samples from the same batches, have been measured. For Co-doping we clearly see a change in the temperature dependent TEP and Hall coefficient data when the sample is doped to sufficient $e$ (the number of extra electrons associated with the TM doping) so as to stabilize low temperature superconductivity. Remarkably, a similar change is found in the Cu-doped samples at comparable e-value, even though these compounds do not superconduct. These changes possibly point to a significant modification of the Fermi surface / band structure of Ba(Fe1-xTM_x)2As2 at small electron doping, that in the case of Co-doping is just before, and probably allows for, the onset of superconductivity. These data further suggest that suppression of the structural / magnetic phase transition and the establishment of a proper e-value are each necessary but, individually, not sufficient conditions for superconductivity.

Absence of superconductivity in hole-dopedBaFe2−xCrxAs2single crystals

We investigate the physical properties and electronic structure upon Cr doping in the iron arsenide layers of ${\text{BaFe}}_{2}{\text{As}}_{2}$. This form of hole doping leads to suppression of the magnetic/structural phase transition in ${\text{BaFe}}_{2\ensuremath{-}x}{\text{Cr}}_{x}{\text{As}}_{2}$ for $x>0$, but does not lead to superconductivity. For $x\ensuremath{\le}0.75$ values, temperature dependence of the resistivity, specific heat, magnetic susceptibility, Hall coefficient, and single-crystal x-ray diffraction data are presented. The resulting phase diagram is suggestive that superconductivity does not derive simply from the suppression of the structural/magnetic transitions. The materials show signatures of approaching a ferromagnetic state for $x$ as little as 0.36 by an enhanced Wilson ratio. Such results reflect renormalization due to spin fluctuations and they are supported by density-functional supercell calculations for slightly higher doping level of $x=1$. Calculations show a strong interplay between magnetic ordering and chemical ordering of Fe and Cr, with a ferromagnetic ground state.

Improvement in the Thermoelectric Figure of Merit by La/Ag Cosubstitution in PbTe

The thermoelectric properties of La-doped and Ag/La codoped PbTe were investigated in the temperature range of 300 to ∼720 K. All samples crystallize in the NaCl-type structure without noticeable secondary phase and exhibit narrow bandgaps of 0.26−0.30 eV, typical of PbTe. La doping (≤5 at %) in PbTe significantly enhances the room temperature electrical conductivity to >5000 S/cm, indicating that La is an efficient electron donor. Hall coefficient data confirm the significant increase in electron carrier concentration from ∼2 × 1018 cm−3 at 300 K for PbTe to ∼5.3 × 1019 cm−3 for Pb0.99La0.01Te, and ∼1.7 × 1020 cm−3 for Pb0.95La0.05Te. Ag doping in Pb0.99La0.01Te has an opposite effect on the electron carrier concentration (∼2.0 × 1019 cm−3 at 300 K for Ag0.05Pb0.99La0.01Te and ∼1.5 × 1019 cm−3 for Ag0.1Pb0.99La0.01Te), consistent with the role of Ag as electron acceptor. The temperature dependence of mobility is discussed in detail using the physics of electron scattering and possible scattering mechanis...

Electrical characterization of InAs thin films

AbstractIt is known that parallel conduction as a result of surface and /or interface charge accumulation significantly shields the bulk electrical properties of InAs thin films when characterized using Hall measurements. This parallel conduction in InAs can be modeled by using the two‐layer model of Nedoluha and Koch [Zeitschrift für Physik 132, 608 (1952)]; where an InAs epilayer is treated as consisting of two conductors connected in parallel viz. a bulk and a surface layer. Here, this two‐layer model is used to simulate Hall coefficient and conductivity data of InAs thin films ranging from strongly n‐doped (n = 1018 cm–3) to strongly p‐doped (p ∼ 1019 cm–3) material. Conventional Hall approximations, i.e. those that assume uniform conduction from a single band, are then used to predict the apparent carrier concentration and mobility that will be determined from conventional Hall measurements, with the aim of illustrating the error of such a simplified analysis of InAs Hall data. Results show that, in addition to ignoring parallel conduction, the approximations of conventional Hall data analysis have a further inadequacy for p‐type InAs, in that the high electron to hole mobility ratio in InAs is not taken into account. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Anomalous Hall effect in IV–VI semimagnetic semiconductors

The purpose of our work was to study the anomalous Hall effect in narrow gap ferromagnetic semiconductors. We investigated transport and magnetic properties of IV–VI compounds: Sn 1− x Mn x Te, Sn 1− x− y Mn x Er y Te and Sn 1− x− y Mn x Eu y Te in high magnetic fields using the very same samples. The simultaneous analysis of the total Hall coefficient and magnetization measurements data enabled us to determine the anomalous Hall coefficient R S value and its temperature behavior.