Observation of diamagnetic domains in beryllium

We have observed diamagnetic domains (Condon domains) in a beryllium single crystal in magnetic fields H⩽3 T (H∥[0001]) at liquid-helium temperatures. The formation of the domain structure was determined according to magnetic-breakdown quantum oscillations of the resistance thermoelectric power as well as according to the splitting of the resonance peak of the free spin precession frequency of muons (μSR). The alternation of a uniform state (with one μSR peak) and a state with domain structure (with two peaks) is consistent as regards the periodicity with the de Haas-van Alphen effect, the period is ΔH≅78 Oe, and the range of existence of domains and the difference in their magnetizations are ΔB=4πΔM=B ₂−B ₁≅30 Oe. Fiz. Tverd. Tela (St. Petersburg) 40, 524–526 (March 1998)     

On the origin of quantum oscillations in the mixed state of an anisotropic superconductor

For the vortex lattice in an anisotropic superconductor with well-separated cores (H _c1≪ B≪H _c2) it is shown that sizable de Haas-van Alphen oscillations are caused by the levels’ crossing of the energy threshold separating localized and extended states of excitations moving in the average magnetic field B. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 9, 705–710 (10 November 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

De Haas-van Alphen effect in unconventional superconductors

A theory of the de Haas-van Alphen effect in type-II p-wave and D-wave superconductors (the latter corresponds to the B _1g one-dimensional representation of group D _4h ) has been developed. Solutions for the order parameter and density of quasiparticle states near the upper critical field have been calculated. If the curve enclosing the extremal cross section of the Fermi surface in the plane perpendicular to the external magnetic field coincides with the line of nodes of the superconducting order parameter, the effect of the transition to the superconducting state on the amplitude of magnetization oscillations is negligible. If the line of nodes is oriented differently with respect to the applied magnetic field, the de Haas-van Alphen oscillations are suppressed in a manner qualitatively similar to the case of conventional superconductors. Zh. éksp. Teor. Fiz. 113, 2174–2192 (June 1998)     

de Haas-van Alphen oscillations and angular magnetoresistance oscillations in the organic metal κ-(BETS)2GaCl4

Quantum de Haas-van Alphen oscillations and semiclassical angular magnetoresistance oscillations are observed in the quasi-two-dimensional organic metal κ-(BETS)₂GaCl₄. The behavior of these oscillations attests to the existence of two cylindrical Fermi surface sheets with axes perpendicular to the conducting plane. The cross-sectional areas of these cylinders in the conducting plane are equal to about 20 and 100% of the corresponding cross section of the Brillouin zone. It is shown that the many-particle interaction can be suppressed significantly in this compound. Zh. éksp. Teor. Fiz. 115, 205–210 (January 1999)     

Influence of antiferromagnetic ordering on the de Haas-van Alphen effect in a semimetal

The distinctive characteristics of the de Haas-van Alphen effect in semimetals with antiferromagnetic long-range order are investigated theoretically. It is shown that the transition of the subsystem of localized spins from the canted antiferromagnetic phase to the ferromagnetic phase is accompanied by an abrupt change in the “frequency” of the magnetization oscillations of band carriers M _∼. In the below-critical range of magnetic fields, M _∼ is not a function periodic in 1/H. Significantly, the additional contribution to the phase of the oscillatory factors is proportional to H ² and is determined entirely by quantum fluctuations in the antiferromagnetic subsystem. Fiz. Tverd. Tela (St. Petersburg) 39, 204–210 (February 1997)     

On the anomalous H dependence of the amplitude of de Haas-van Alphen oscillations in CeCu2Si2

The de Haas-van Alphen effect is studied in heavy-fermion antiferromagnets near the spin-flip transition is studied. It is shown that the strong increase occurring in the amplitude of oscillations near the spin-flip point in an increasing magnetic field, as observed experimentally in CeCu₂Si₂, can be explained by strong single-site correlations and magnetic ordering in the subsystem of localized electronic states. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 4, 270–275 (25 February 1998)     

Feasibility of measuring the average sizes of diamagnetic domains by the μSR 2 method

Abtract One of the simplest examples of possible application of the μSR ² method for estimating the sizes of diamagnetic domains is analyzed in detail. The domains have been observed for the first time by means of the μ SR method in beryllium [G. Solt, C. Baines, V. S. Egorov et al., Hyperfine Interactions 104, 257 (1997)]. Results are given from a computer simulation of a μSR ² experiment to measure domain sizes in Be. An algorithm is described for processing the experimental results. It is graphically demonstrated that domain sizes can be estimated within the accelerator operating time allocated for an ordinary μSR experiment. Zh. éksp. Teor. Fiz. 115, 2133–2142 (June 1999)     

Anomalous anisotropies and field dependencies of the muon Knight shift and the relaxation rate in monocrystalline Bi

The angular dependence of the muon Knight shift,K _μ, and the muon relaxation rate in Bi at 11 K were measured in external magnetic fields up to 1 T. BothK _μ and the second moment,M ₂, are field dependent and involveP ₄ ⁰(cos θ) andP ₄ ³(cos θ) terms in the angular dependence. The Knight shift behaviour is discussed in terms of the dipole-dipole interaction and the de Haas-van Alphen effect, a consistent interpretation was not achieved in either case. The field dependence ofM ₂ is in complete contrast to the second moment calculations and points to a field dependent redistribution of the charge distribution around the interstitial site.     

Observation of the de Haas-van Alphen effect in powdered YbSn3 and CaSn3

In addition to the previously reported de Haas-van Alphen oscillation in a powder sample of YbIn₃, we now report the observation of the de Haas-van Alphen effect in YbSn₃ and CaSn₃ powders.     

Quantum oscillations of resistance and magnetization in the degenerate semiconductor n-HgCr2Se4

In the magnetic field range ΔH=8–60 kOe we observed and studied the anomalous oscillations in the magnetic field dependence of the resistance and magnetization of single crystals of n-HgCr₂Se₄. The absence of periodicity in 1/H in the ΔH=8–20 kOe range can be explained by the non-Fermi-liquid behavior of the electron subsystem and agrees with the theory of the de Haas-van Alphen in systems with intermediate valence. In stronger fields, ΔH=20–60 kOe, the amplitude of the fundamental harmonic decreases, with the number and amplitude of the higher-order harmonics increasing. As a result, noise is superimposed on the signal as magnetic field strength grows. The temperature dependence of the magnetization is the sum of the monotonic spin-wave contribution and the oscillating part. Zh. éksp. Teor. Fiz. 113, 1877–1882 (May 1998)     

Quantum and semiclassical oscillations in the organic metal (BEDO-TTF)2Clx(H2O)y

We study quantum (Shubnikov-de Haas and de Haas-van Alphen) oscillations and angular oscillations of the reluctance in the organic quasi-two-dimensional metal (BO)₂Cl_x(H₂O)_y. We show that the Fermi surface in this compound consists of a slightly corrugated cylinder with its axis perpendicular to the conducting plane. The cross section of the cylinder in this plane is a perfect circle of radius k _F≃3×10⁷ cm⁻¹. The effective carrier mass associated with this cylinder is m*=(1.65–2.0) m ₀ in the conducting plane, while the Dingle temperature is T _D=3–4 K. Zh. éksp. Teor. Fiz. 114, 1137–1146 (September 1998)     

Theory of the de Haas-van Alphen effect in doped semiconductors

The field dependence of the magnetization in doped semiconductors of the type InSb, InAs, GaAs, etc. is studied in high magnetic fields. The standard theory of the de Haas-van Alphen effect, mostly applicable to metals, is modified to include the long-range fluctuations of charge carriers. The experimental investigation of this effect can shed light on some open questions in semiconductor physics, e.g., the problem of tails in the electronic density of states. It is shown that in such systems the mean magnetization is sensitive to magnetic interactions. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 3, 181–186 (10 February 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Muons in type-II superconductors: μ+ diffusion in ultra-pure niobiumdiffusion in ultra-pure niobium

The diffusivityD _μ of positive muons (μ⁺) in the mixed state of superconducting high-purity, high-perfection niobium single crystals is investigated by measurements of the relaxation of the transverse muon spin polarization (μ⁺SR). The method makes use of the strong magnetic field gradients existing in the mixed state of Type-II superconductors and monitorsD _μ through the variation of the magnetic field felt by the μ⁺ during their diffusion through the crystals. For μ⁺ near the centres of the flux lines inNb it givesD _μ(4.6 K)=(8±2)·10⁻¹¹m²S⁻¹. The positive temperature coefficient ofD _μ indicates that at liquid-helium temperatures the diffusivity of μ⁺ inNb is mainly due to phonon-assisted tunnelling processes.     

de Haas-van Alphen effect and the Fermi surface of PrNi5

The Fermi surface of PrNi₅ has been studied by the measurements of the de Haas-van Alphen (dHvA) effect at temperatures between 0.3 and in magnetic fields up to 12 T. Two dHvA frequencies have been obtained. The electronic structure of PrNi₅ was calculated using the full potential linearized augmented plane wave method. Five sheets of the Fermi surface and the multiple extremal cross sections were determined. First and second sheet have a hole-like structure. The agreement between theory and experiment is obtained by a small downward shift ( 0.1 eV) of the Fermi energy which is probably due to an underestimation of the role of 4 f electrons. Received 9 May 2000 and Received in final form 20 September 2000     

de Haas-van Alphen effect in superconductors

A theory of the de Haas-van Alphen effect in type-II superconductors is proposed. The effect of the electron scattering by nonmagnetic impurities in a magnetic field in the potential produced by a nonuniform distribution of the order parameter in a mixed state is investigated. The magnitude of the order parameter and quasiparticle density of states are determined from the solution of the system of Gor’kov equations. It is shown that in the presence of even a small amount of impurities, the superconducting state near the upper critical field is gapless. In this region, the oscillatory (in the magnetic field) contribution to the density of states and the characteristic damping of the amplitude of the magnetization oscillations in the superconducting state are found. Zh. éksp. Teor. Fiz. 112, 1873–1892 (November 1997)     

Formation of Condon domains as a phase transition

It is shown, for the first time, that approaching the Condon domain phase in temperature from above is accompanied by critical temperature growth of the susceptibility thereby indicating formation of Condon domains, which occurs as a phase transition. The study is based on a recent measurement of the temperature dependence of the susceptibility in silver in magnetic field of 25 T under conditions of the nonlinear de Haas-van Alphen effect. Experimental results for the positive and negative slopes of the magnetization in one de Haas-van Alphen period are in good agreement with results of the calculations presented here. The Curie-Weiss law for the susceptibility is derived for a needle-type specimen. The Curie constant is calculated.     

De Haas-van Alphen effect and Seebeck effect in inversion layers and superlattices

Effect of collision broadening on the de Haas-van Alphen oscillations and the thermal voltage in two-dimensional systems is investigated in the quantum limit. It is shown that the limit of validity of the well-known thermodynamic expression for the Seebeck coefficient S_xx is further restricted due to the peculiar transport properties in two dimensions.     

Spatial correlation study of internal magnetic fields in magnets by μSR2-technique

It is shown that using position-sensitive detectors in μSR experiments to determine the muon stopping site in a target permits one to study correlation effects in μSR time histograms produced by the decay of muons stopping in the same domain, i.e. to obtain time correlators of μSR histograms of decays from a small region. These correlators contain information on the spatial correlation of magnetic fields in the sample under study. The proposed method (μSR²-technique) allows measuring correlation radii (r _c ) down to 10⁻⁵ cm in a bulk sample. Among interesting physical phenomena occuring overr _c≥3×10⁻⁶ cm are, for instance, long wavelength fluctuations of the order parameter near the phase transition point in ferromagnets and antiferromagnets and magnetic field correlations in magnet domains and spin glasses. One may use this method also on heavy-current accelerators producing pulsed muon beams to investigate the variation in time of spatial correlations in magnets, spin glasses and superconductors.     

Possible weakening of the many-body interactions in the organic quasi-two-dimensional metal α-(BETS)<Subscript>2</Subscript>NH<Subscript>4</Subscript>Hg(SCN)<Subscript>4</Subscript>

The behavior of the de Haas-van Alphen oscillations in the organic quasi-two-dimensional metal α-(BETS)₂NH₄Hg(SCN)₄ is comprehensively studied as a function of the angle between the magnetic-field direction and the normal to the conducting layers in it. The angular dependence of the oscillation amplitude has minima at angles of ±40° and ±62°, which are caused by the spin zero effect. The positions of these minima suggest that the electron-phonon and electron-electron interactions in this metal are significantly weakened.     

De Haas-van Alphen effect studies in dilute alloys of silver and gold

De Haas-van Alphen experiments have been used to determine the scattering temperatures which characterize the [111] neck and belly extremal orbits in some dilute alloys of silver and gold. The relaxation time is anisotropic withτ _N/τ _B≃2 in both Ag(Au) and Au(Ag) when the scattering is dominated by the solute. This anisotropy is in the opposite sense to that observed in another homovalent alloy Ag(Cu) and to that observed in the presence of charged impurities.