W. Joss

Magnetic field dependence of the many-body enhancement on the Fermi surface of CeB6

Abstract Low-temperature high-field specific heat measurements are presented which show that the density of states of the itinerant electrons in the Kondo lattice CeB6 decreases strongly with field. CeB6 is an ordered heavy electron system with a zero field electronic specific heat coefficient γ of about 250 mJ/mol K2. The specific heat was measured with the heat pulse method at temperatures as low as 0.3 K and in steady magnetic fields as high as 22 T. At 22 T the linear term in the specific heat was found to be five times smaller than in zero field. The observed field dependence in the electronic specific heat is in good agreement with the field dependence of the cyclotron mass recently found in de Haas-van Alphen experiments.

High-field magnetoconductance of electrons on liquid helium

For the first time electrons on liquid helium have been subjected to magnetic fields as high as 22 T. The magnetoconductance has been measured in the temperature range 1.5–2 K, where the mobility of the electrons is dominated by the scattering with helium vapor atoms. Since helium is a diamagnetic liquid, the presence of field gradients has to be taken into account in high magnetic fields. The conductance data inherently contain the effect of the field-induced deformation of the helium surface. An estimation of this effect is presented. The corrected data are discussed within quantum transport theory.

De Haas-van Alphen effect in CeB6 in fields up to 52T: Reduction of the cyclotron mass and new frequencies

Abstract The de Haas-van Alphen effect is used to study CeB 6 in pulsed fields up to 52 T. Two cyclotron orbits are observed; a previously unreported orbit may be due to magnetic breakdown. The cyclotron masses corresponding to these orbits decrease with increasing field.

Magnetostriction of Heavy-Fermion UPt3 in Magnetic Fields up to 24 Tesla

The high-magnetic-field anomaly at 20 T in heavy-fermion UPt3 has been studied by means of magnetostriction measurements on a single-crystalline sample at liquid helium temperatures. The data for a field direction in the basal plane reveal an orthorhombic distortion of the hexagonal crystal structure. An explanation for this distortion is offered in terms of a (antiferromagnetic) spin-fluctuation model.

Magneto-oscillations in YBa2Cu3O7-δ in high magnetic fields

Abstract Magneto-oscillatory signals have been observed in the magnetization of samples of oriented YBa 2 Cu 3 O 7− δ powders. The experiments have been performed in pulsed magnetic fields up to 52 T. The Fourier transform of these signals analyzed as a function of 1/ B is dominated by two peaks at frequencies very close to the dHvA frequencies reported by Fowler et al. (Phys. Rev. Lett. 58 , 534 (1992)). The field dependence of the amplitude of the oscillations is in qualitative agreement with that predicted by a recent theory of Maniv et al .

Magnetoconductance of electrons on liquid helium in the extreme quantum limit

Abstract Measurements of the longitudinal magnetoconductivity σ xx of the nondegenerate two-dimensional system of electrons on the surface of liquid helium are presented for magnetic fields up to 22T in the temperature range 0.4K . For temperatures above 1.6 K our experimental results are in good agreement with a quantum magnetotransport theory of short-range scattering within broadened Landau levels. If the temperature is reduced below 1.5 K, a deviation of the experimental data from the theoretical calculations is observed for magnetic fields between 2 T and 10 T. At temperatures T where the conductvity of the surface electrons is determined by the scattering between electrons and ripplons, the magnetic field dependence of our measurements of 1/σ xx (B) for high fields is rather poorly reproduced by the existing theories.

Origin of the resistivity increase in gadolinium hydride halides: GdXH(D)y (X-Cl, Br, I; 0.67<y<1.0)

The electrical resistivity of GdXHy (X-Cl, Br, I; 0.67<y<1.0) undergoes a strong increase (several orders of magnitude for X-Br, I) at low temperatures ( <20 K) when the hydrogen concentration y approaches its lower limit of 0.67. Here, we report on resistivity measurements on samples exposed to a special thermal treatment and in high magnetic fields. In both cases, the resistivity increase changes significantly. A slow cooling rate from 450 to 200 K favors the increase which seems to indicate that a better ordering of the H atoms enhances the resistivity at low temperatures. On the other hand, the magnetoresistivity measurements reveal that the resistivity increase can be completely suppressed by magnetic fields up to 20 T. This result emphasizes the strong connection between the electrical and the magnetic properties since the magnetic field will counteract the magnetic order.

Electronic structure of AsF5 intercalated graphite from de Haas-Van Alphen measurements

Abstract The oscillatory magnetization of stage 1 and stage 2 AsF 5 intercalated graphite was studied with the de Haas-van Alphen effect in magnetic fields up to 22 T. Using the quasi-static torque method it was possible to determine the absolute value of the magnetization of sealed, chemically active samples. For the stagee 1 samples we found the expected frequency of ⋍ 1700 T , corresponding to the charge transfer of ⋍ 0.3 electron per AsF 5 . From the angular dependence of the de Haas-van Alphen frequencies and the cyclotron effective masses we conclude that the Fermi surface is cylindrical. The Landau levels are well separated at 20 T compared with their broadening due to imperfections. The magnetization oscillations have sinusoidal shape with little higher harmonics, which indicates that the number of carriers in the graphite layers and the chemical potential are both field dependent.

Theory of the de Haas-van Alphen effect in quasi-two-dimensional conductors

Abstract According to the Peierls theory, the de Haas-van Alphen oscillations should have a saw-tooth form in an ideal two-dimensional electron gas when the chemical potential is pinned to a Landau level during the entire de Haas-van Alphen period (constant number of carriers) or when a reservoir of carriers exists (fixed chemical potential). Recent experiments indicate that neither of these conditions are fulfilled, during a single period in AsF 5 intercalated graphite. We have studied both: analytically and numerically the smoothing out of the saw tooth form of the magnetization, at finite temperature, due to an external reservoir of carriers.

Magnetic field dependence of the cyclotron effective mass in the Kondo lattice CeB6

We report the first observation of a field‐dependent mass in a hybridizing f‐electron system. CeB6 is an ordered moment heavy fermion system with an electronic specific heat coefficient γ of order 225–300 mJ/moleu2009K2. Using the de Haas–van Alphen effect at temperatures as low as 60 mK in steady magnetic fields as large as 22 T, we observe a cyclotron orbit of frequency 8680 T for fields along the [100] direction. The mass of this orbit was measured at eight fixed fields and found to decrease from 18me to 8me as the field increases from 12 to 22 T. The observed Fermi surface is very similar to that of LaB6, indicating that the f‐electrons are largely local rather than itinerant in CeB6, a picture confirmed by bandstructure calculations. The observed field dependence of the cyclotron mass is consistent with the low‐energy scale of the system as measured, for example, by the Kondo temperature. Our results are compared with Fermi surface observations in other heavy fermion systems.