Hall Effect Of Single Crystals Research Articles

The Hall Effect in Single Crystals of Topological Semimetals WTe<sub>2</sub> and MoTe<sub>2</sub>

The Hall effect in single crystals of topological semimetals WTe2 and MoTe2 is studied in the temperature range from 2 to 100 K and in magnetic fields up to 9 T. It is established that the Hall resistivity of WTe2 shows a nonlinearly dependence on the magnetic field at temperatures below 100 K. At the same time, the Hall resistivity of MoTe2 depends linearly with the magnetic field at temperatures range from 2 to 25 K and a nonlinear contribution appears at 50 K. Along with the known mechanism of compensation/decompensation of electron and hole charge carriers, the nonlinear dependence of the Hall resistivity of WTe2 and MoTe2 single crystals on the magnetic field is associated with the scattering of charge carriers on the surface.

The Hall Effect in Single Crystals of Topological Semimetals WTe2 and MoTe2

The Hall Effect in Single Crystals of Topological Semimetals WTe2 and MoTe2

Sizable Suppression of Thermal Hall Effect upon Isotopic Substitution in SrTiO_{3}.

We report measurements of the thermal Hall effect in single crystals of both pristine and isotopically substituted strontium titanate. We discovered a 2 orders of magnitude difference in the thermal Hall conductivity between SrTi^{16}O_{3} and ^{18}O-enriched SrTi^{18}O_{3} samples. In most temperature ranges, the magnitude of thermal Hall conductivity (κ_{xy}) in SrTi^{18}O_{3} is proportional to the magnitude of the longitudinal thermal conductivity (κ_{xx}), which suggests a phonon-mediated thermal Hall effect. However, they deviate in the temperature of their maxima, and the thermal Hall angle ratio (|κ_{xy}/κ_{xx}|) shows anomalously decreasing behavior below the ferroelectric Curie temperature T_{c}∼25 K. This observation suggests a new underlying mechanism, as the conventional scenario cannot explain such differences within the slight change in phonon spectrum. Notably, the difference in magnitude of thermal Hall conductivity and rapidly decreasing thermal Hall angle ratio in SrTi^{18}O_{3} is correlated with the strength of quantum critical fluctuations in this displacive ferroelectric. This relation points to a link between the quantum critical physics of strontium titanate and its thermal Hall effect, a possible clue to explain this example of an exotic phenomenon in nonmagnetic insulating systems.

Hall effect and conductivity in zinc oxide (ZnO) doped by thermal diffusion of indium and copper

AbstractMeasurements of the conductivity and the Hall effect of single crystals were performed on zinc oxide (ZnO) samples after a thermal diffusion of indium (In) and copper (Cu) with different time periods. Single crystals of ZnO were growth by hydrothermal method and annealed previously to diffusion process. Diffusion was carried out in ZnO at 1000 ΩC in N2 atmosphere for 3, 6, and 15 h. Hall effect measurements were carried out using the Van der Pauw configuration with a current of 1 mA and a magnetic field of 0.37 T at room temperature. Results showed an increase in donor concentration from 4.6x1014 cm–3 to 1.15×1017 cm–3 when In is diffused and up to 9.9×1015 cm–3 when Cu is introduced in ZnO. Mobility decreased from 134.9 (undoped ZnO) to 44.7 cm2/V s, in In‐doped, and 101.9 cm2/V s, in Cu‐doped. Resistivity decreased with time from 1.29x102 Ω cm to 1.26 Ω cm and 6.25 Ω cm, in the same order as described. Based on measurements, introduction of indium is faster than copper and the higher concentration of donors is result of substitution of Zn by an ion with a different valence. This is a relative simple method to control the conductivity and donor concentration in single crystals of ZnO. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Roles of multiband effects and electron-hole asymmetry in the superconductivity and normal-state properties ofBa(Fe1−xCox)2As2

We report a systematic investigation, together with a theoretical analysis, of the resistivity and Hall effect in single crystals of Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$, over a wide doping range. We find a surprisingly great disparity between the relaxation rates of the holes and the electrons, in excess of an order of magnitude in the low-doping, low-temperature regime. The ratio of the electron to hole mobilities diminishes with temperature and doping (away from the magnetically ordered state) and becomes more conventional. We also find a straightforward explanation of the large asymmetry (compared to cuprates) of the superconducting dome: in the underdoped regime the decisive factor is the competition between AF and superconductivity (SC), while in the overdoped regime the main role is played by degradation of the nesting that weakens the pairing interaction. Our results indicate that spin-fluctuations due to interband electron-hole scattering play a crucial role not only in the superconducting pairing, but also in the normal transport.

The Hall effect in Ni-doped p-CdSb in a strong magnetic field

The Hall effect in single crystals of the group II–V semiconductor p-CdSb doped with 2 at% of Ni is investigated between T = 1.5 and 300 K in pulsed magnetic fields up to B = 25 T. The Hall resistivity, ρH, exhibits a nonlinear dependence on B, which is strongly pronounced below ∼10 K but is still observed even up to 300 K. The analysis of ρH(B) gives evidence for the presence of a positive normal and a negative anomalous contribution, ρN = R0B and ρA, respectively. The temperature dependence of the (normal) Hall coefficient R0 is determined by the activation of holes into the valence band with a small contribution of the itinerant holes from the acceptor band at lowest T. The dependence of ρA on T is quite different within two temperature intervals, being weak between ∼50 and 300 K and very strong below ∼50 K, the latter resembling that of the resistivity, ρ. Analysis of ρA below ∼77 K demonstrates that it scales approximately as ρn with n = 1.6 ± 0.1 within four decades of ρA and more than two decades of ρ. The anomalous Hall effect in p-CdSb:Ni is attributable to the presence of magnetic Ni-rich nanoclusters, whose properties have previously been investigated by the analysis of the magnetization data.

Explanation of the temperature variation of Hall coefficient of doped bismuth

The Hall effect in single crystals of bismuth doped with tin and lead has been measured in the temperature range 80 to 300 K. An attempt has been made here to explain the observed variations of Hall coefficient with temperature by considering the relative variation of the free carrier concentrations with temperature in different bands in alloys of bismuth in addition to variation of other parameters. Calculations have been made to see the effect of the overlap on Hall coefficient for different values of band overlap. The experimental curves are in satisfactory agreement with the theoretical calculations.

Hall effect of single layer, tetragonal Tl 2Ba 2CuO 6+δ near optimal doping

We report measurements of the Hall effect in single crystals of Tl 2Ba 2CuO 6+δ near optimum doping. In principle, this is an ideal material for an investigation of the quality of the well-known linear and quadratic temperature dependences of the resistivity and inverse Hall angle, since crystals of this material have a simple tetragonal crystal structure with one CuO 2 layer per formula unit, and little disorder.

Effect of pressure on the electrical resistivity and Hall effect in single crystals of CeRhSb

The Hall effect and electrical resistivity have been measured under pressure up to 7.3 kbar using purified single crystals of CeRhSb. Electrical resistivity and especially the Hall coefficient show a large increase under pressure at low temperatures. These results could be due to an increase of the gap energy under pressure (confirmed by an Arrhenius plot of the resistivity and Hall effect data). These pressure effects are anisotropic and the minimum is for I a, H b. It is notable that the b direction coincides with the minimum lattice constant of the orthorhombic structure.

Pressure dependence of the Hall effect in single crystals of CeNiSn

Abstract The pressure dependence of the Hall effect in single crystals of CeNiSn (J‖b, H‖a; J‖a, H‖b; J‖b, H‖c) has been measured. The Hall coefficient RH decreases with pressure in the low-temperature range, indicating a decrease of gap energy under pressure due to the decrease of slope in the log ϱ versus 1/T dependence. A crossover temperature is observed in the slope of this dependence.

Influence of oxygen stoichiometry on the Hall effect of single crystals of YBa 2Cu 3O y

We report Hall effect measurements on YBa 2Cu 3O y single crystals for 6.5⩽ y⩽7. Just below T c superconducting fluctuations lead to non-linear variations of the Hall voltage against the magnetic field. In the normal state the Hall coefficient strongly increases with oxygen removal and displays at higher temperatures a T −1 variation.

Anomalous hall effect in mixed valence compounds

We have studied the Hall effect of single crystals of CeNi and UPt 3 compounds, and of a polycrystalline sample of CeNi 0.95Pt 0.05. Our measurements confirm the existence of predominant skew scattering effects in mixed valence compounds. They also evidence some new aspects of the Hall effect, such as the strongly non-linear variation of the Hall resistivity as a function of the magnetization.

Transport properties and ultrasonic propagation in single crystal Gd 65.4-Y 34.6

Measurements have been carried out on the elastic constants, ultrasonic attenuation, resistivity, thermoelectric power and Hall effect of single crystals of a Gd 65.4-Y 34.6 alloy over a temperature range from 300 down to 70 K. This temperature range allows the various magnetic phases of the alloy to be studied in detail. The alloy first orders at a Néel temperature of 200 K into a spiral spin antiferromagnetic phase which on further cooling transforms to a ferromagnetic phase at a Curie temperature of 132 K. The behaviour of both the elastic and the transport properties at the Néel temperature indicate the presence of unusual pretransitional effects.

Reversal of the Hall field in indium

The Hall effect in single crystal has been investigated at 63 kOe over the 6–280 K temperature range. The Hall coefficient reverses sign as a function of temperature. The high temperature value is less negative then theoretical predictions.

Anisotropic temperature dependence of the hall effect in Cu and some Cu [sbnd]Zn crystals

The Hall effect in single crystals of Cu ( RRR = 2312) and Cu containing 76, 172 and 1100 ppm Zn has been studied in the temperature range 4.2–80°K (i.e. through the low-field/high-field transition). The temperature dependence of the effect is given for H along [111], [110], [100], [211], and other directions which show either a single open orbit or all closed orbits. It is shown how the qualitative features of this dependence can be explained in terms of the known topology of the Fermi surface. Comparable results are also given for polycrystalline samples of Cu, and Cu with 78, and 940 ppm Zn. These indicate that of the singular topological features associated with the open Fermi surface of Cu only orbits of the four-cornered rosette and dog's bone type contribute to the Hall effect in a polycrystal. Some further evidence is given to support the view that the anomalous maximum in the temperature dependence of the effect in a polycrystal, which is centred at about 50°K, arises from the low-field/high-field transition.

Hall effect in single crystals of a ζ-Cu-Ge alloy

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Oscillatory Hall effect in tin due to magnetic breakdown

The Hall effect in single crystals of tin shows oscillations at temperatures below 4.2 K when B lies along, or very near, the [001] axis. The amplitude of the oscillations has a sharp maximum 1° away from the axis and has vanished by 4°. The oscillations are explained in terms of the migration of electrons by magnetic breakdown between the e 5 1 and δ 1 1 orbits, as has already been invoked to account for oscillatory magneto-resistance. To account for the existence of off-axis Hall oscillations when, as is known, breakdown is confined to a fairly narrow central zone, it is found necessary to include collisions of the electrons with impurities even though these are rare enough for ω c т to be as large as 200. The theory is developed in terms of diffusion of electrons on a limited orbit-network, and an explicit expression derived for the angular variation of oscillatory amplitude, which is found to agree well when independent estimates of the relevant parameters are used.

Electronic Properties of Tetracyanoquinodimethane (TCNQ) Salts: Hall Effect in Crystals of the Triethylammonium (TCNQ)2 Complex

AbstractA report is given of a successful measurement of the Hall effect in single crystals of the organic salt triethylammonium (TCNQ)2 at room temperature. A Hall mobility of the order of 0.6 cm2/Vs was found, the sign of the Hall constant being that appropriate for hole carriers. A study of the thermoelectric power sign was in agreement with the existence of holes. Study of the temperature dependence of the conductance indicated that some electrically active, gaseous impurities, which were believed to act as acceptors, were present in the samples. An interpretation of the experimental results is presented, including a discussion of the effect of the impurities on the electronic properties of the material. Some indications about the conduction process are suggested on the basis of a two‐band model.

Galvanomagnetic Studies of Sn-Doped Bi. II. Negative Fermi Energies

Studies of the Shubnikov-de Haas effect and the Hall effect in single crystals of bismuth doped with tin are extended to excess hole concentration beyond 2\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$, the upper limit achieved in earlier reported work. For dopings greater than about 3\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$, the Fermi level lies below the bottom of the $L$-point conduction band, so that the Fermi energy measured from this band edge is negative. The passage of the Fermi level into the forbidden gap at the $L$ point is accompanied by the disappearance of electron quantum oscillations and by a decrease by two orders of magnitude in the magnetoresistance at 4.2\ifmmode^\circ\else\textdegree\fi{}K. At about 5\ifmmode\times\else\texttimes\fi{}${10}^{18}$ excess holes/${\mathrm{cm}}^{3}$, a large magnetoresistance effect reappears, and low-field quantum oscillations, which are attributed to light holes at the $L$ point, are observed. The dependence of the light-hole periods on magnetic field orientation suggests that the longitudinal mass is smaller for $L$-point holes [${L}_{a}(3)$] than for electrons [${L}_{s}(3)$], as is predicted by Golin's band-structure calculation. $T$-point hole oscillations are observed for excess hole concentrations up to ${10}^{19}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ and measurements have been extended to fields of 90 kOe to study their anisotropy. The anisotropy is consistent with a $T$-point hole surface which is a prolate ellipsoid of revolution for excess hole concentrations up to 3\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$, but the surface becomes less prolate as tin is added. Data on this surface are compared with the predictions of a six-band $\mathrm{k}\ifmmode\cdot\else\textperiodcentered\fi{}\ensuremath{\pi}$ calculation derived from Golin's pseudopotential theory, using the matrix elements at $T$ which he calculated; good agreement is obtained. It is pointed out that the analysis of band nonparabolicity in an earlier paper which makes use of the Abrikosov-Falkovski dispersion relation underestimates the magnitude of the ${{T}_{45}}^{\ensuremath{-}}(1)\ensuremath{-}{{T}_{6}}^{+}(3)$ direct gap at $T$. On the basis of the six-band model, the observed nonparabolicity is found to be consistent with the gap estimated by Golin.

The Low-Temperature Transport Properties of NbSe2

The resistivity and Hall effect of single crystals of the two-layer structure of NbSe2 were measured from about 5° to 300°K. A sign change was observed in the Hall coefficient at about 26°K; above this temperature the samples were p type, and below, n type.