Quantum oscillations in a novel organic quasi-two-dimensional (BEDO-TTF)5[RbHg(SCN)4]2 metal

Quantum magnetization and magnetoresistance oscillations are detected in the quasi-two-dimensional organic metal (BEDO-TTF)₅[RbHg(SCN)₄]₂ for the first time. The magnetization oscillation spectrum corresponds to a calculated Fermi surface provided that a magnetic breakdown is realized. The magnetoresistance oscillation spectrum contains additional frequencies, one of which can unambiguously be related to quantum interference. An analysis of the angular dependence of the magnetoresistance oscillation amplitude indicates that the many-body interactions in this metal are weak.     

Reflectivity spectra of new organic metal (BEDO-TTF)5[CsHg(SCN)4]2

The polarized reflectivity and optical conductivity spectra of microcrystals of the new organic conductor (BEDO-TTF)₅[CsHg(SCN)₄]₂ based on the donor molecule bis(ethylenedioxy)tetrathiafulvalene (BEDO-TTF) have been studied in the spectral ranges 600–6500 and 9000–40000 cm^?1 at 300 K for three principal lattice directions. The optical evidence for the quasi-two-dimensional character of the conducting electronic system is obtained. The conclusion is made that the studied crystal is the quasi-two-dimensional semimetal with overlapping electron energy bands. The basic parameters of the electronic system of the crystal are determined in the framework of the Drude model. It is found that the allowed electron energy bands of the crystal are somewhat narrower than those of the previously studied structurally allied superconductor based on the same molecule. The features of vibrational structure are identified in the σ(ω) spectra for the specified three polarizations.     

Anomalous de Haas-van Alphen oscillations in CeCoIn5

We present de Haas-van Alphen oscillation measurements showing a strong spin dependence of the quasiparticle mass enhancement in the heavy fermion superconductor CeCoIn5 at high magnetic fields. There is evidence that the Fermi-liquid temperature dependence of the oscillations, embodied in the Lifshitz-Kosevich equation, is breaking down on the most strongly renormalized Fermi surface sheets.     

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)     

The influence of the chemical potential oscillations on the de Haas-van Alphen effect in quasi-two-dimensional compounds

The de Haas-van Alphen effect in quasi-two-dimensional metals is studied at arbitrary parameters. Oscillations of the chemical potential can substantially change the temperature dependence of harmonic amplitudes that is commonly used to determine the effective electron mass. The processing of the experimental data using the standard Lifshitz-Kosevich formula can therefore lead to substantial errors even in the strong harmonic damping limit. This can explain the difference between the effective electron masses determined from the de Haas-van Alphen effect and the cyclotron resonance measurements. The oscillations of the chemical potential and the deviations from the Lifshitz-Kosevich formula depend on the reservoir density of states that exists in organic metals due to open sheets of the Fermi surface. This dependence can be used to determine the density of electron states on open sheets of the Fermi surface. We present analytical results of the calculations of harmonic amplitudes in some limiting cases that show the importance of the chemical potential oscillations. We also describe a simple algorithm for a numerical calculation of the harmonic amplitudes for arbitrary reservoir density of states, arbitrary warping, spin-splitting, temperature, and Dingle temperature.     

De Haas-van Alphen effect in In2Bi

We report de Haas-van Alphen measurements in the intermetallic compound In₂Bi in magnetic fields up to 15T. At least three dHvA frequency branches could be followed continuously at all field directions indicating three ellipsoid-type pieces of the Fermi surface. The largest two ellipsoids are likely located along the Brillouin zone edge HK.     

First observation of De Haas-van Alphen oscillations in TiBe2: Polycrystalline material

De Haas-van Alphen oscillations have been observed in polycrystalline TiBe₂. A tentative interpretation is given in terms of a recent band-structure calculation.     

Wave shape of de Haas-van Alphen oscillations and effective mass in the two-dimensional organic conductor α-(BEDT-TTF)2KHg(SCN)4

De Haas-van Alphen (dHvA) oscillations in the two dimensional organic conductor α-(BEDT-TTF)₂KHg(SCN)₄ have been measured by a canti-lever technique at high magnetic fields up to 30 T. The wave shape of the dHvA oscillations undergoes a drastic change around the transition field B_K (24 T). The effective mass shifts 1.5 m₀ in the density wave phase (B<B_K) to 1.65 m₀ in the normal metallic phase (B>B_K). Based on the simulation, we have determined that the primary cause of the characteristic field dependence of the wave shape is the change in the effective mass.     

Shubnikov-de Haas oscillations in a new dual-layered quasi-two-dimensional organic metal (BETS)4CoBr4(C6H4Cl2)

The interlayer and intralayer resistances and Shubnikov-de Haas oscillations in a new dual-layered quasi-two-dimensional organic metal (BETS)₄CoBr₄(C₆H₄Cl₂) with a periodically varying structure of cation layers have been studied. It has been shown that the interlayer resistivity corresponds to an incoherent or weakly incoherent transport regime. The oscillations of the magnetoresistance have been described by a model of a chain of coherent magnetic breakdown orbits taking into account the quantum interference effect. The behavior of the interlayer transport, as well as quantum oscillations, is in good agreement with the theoretical calculations of the band structure.     

De Haas-van Alphen effect in rare-earth hexaborides (RE=Pr,Nd, Gd)

The de Haas-van Alphen (dHvA) effect has been measured for antiferromagnetic PrB₆, NdB₆, and GdB₆. The dHvA data of PrB₆ and NdB₆ show paramagnetic Fermi surfaces which arise from magnetic breakdown through the small antiferromagnetic gaps in high fields very similar to those of LaB₆. In contrast, the antiferromagnetic Fermi surfaces which arise from new magnetic Brillouin zone boundaries introduced by the magnetic order seem to be very different in PrB₆ and NdB₆, respectively. In GdB₆ dHvA oscillations could be observed for the first time. In all three compounds magnetic phase transitions have been observed in the dHvA measurements in the field range of 10–12 T.Dedicated to Professor Hund on the occasion of his 95th birthday     

de Haas-van Alphen oscillations in the underdoped high-temperature superconductor YBa2Cu3O6.5

The de Haas-van Alphen effect was observed in the underdoped cuprate YBa2Cu3O6.5 via a torque technique in pulsed magnetic fields up to 59 T. Above a field of approximately 30 T the magnetization exhibits clear quantum oscillations with a single frequency of 540 T and a cyclotron mass of 1.76 times the free electron mass, in excellent agreement with previously observed Shubnikov-de Haas oscillations. The oscillations obey the standard Lifshitz-Kosevich formula of Fermi-liquid theory. This thermodynamic observation of quantum oscillations confirms the existence of a well-defined, closed, and coherent, Fermi surface in the pseudogap phase of cuprates.     

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)     

Shubnikov-de Haas oscillations spectrum of the strongly correlated quasi-2D organic metal (ET)8[Hg4Cl12(C6H5Br)2] under pressure

Pressure dependence of the Shubnikov-de Haas (SdH) oscillations spectra of the quasi-two dimensional organic metal (ET)₈[ Hg₄Cl₁₂(C₆H₅Br)₂] have been studied up to 1.1 GPa in pulsed magnetic fields of up to 54 T. According to band structure calculations, its Fermi surface can be regarded as a network of compensated orbits. The SdH spectra exhibit many Fourier components typical of such a network, most of them being forbidden in the framework of the semiclassical model. Their amplitude remains large in all the pressure range studied which likely rules out chemical potential oscillation as a dominant contribution to their origin, in agreement with recent calculations relevant to compensated Fermi liquids. In addition to a strong decrease of the magnetic breakdown field and effective masses, the latter being likely due to a reduction of the strength of electron correlations, a sizeable increase of the scattering rate is observed as the applied pressure increases. This latter point, which is at variance with data of most charge transfer salts is discussed in connection with pressure-induced features of the temperature dependence of the zero-field interlayer resistance.     

Effect of the Fermi surface shape on the de Haas-van Alphen oscillations in layered conductors

In this paper, we theoretically analyze the effects of the Fermi surface (FS) shape on the magnetic oscillations in quantizing magnetic fields in quasi-two-dimensional layered conductors. The theory is developed based on a phenomenological model for the electron energy spectra introduced in the paper. The model enables various Fermi surface profiles to be taken into consideration; this gives it an advantage over the commonly used tight-binding approximation. It is shown that, when the FS curvature becomes zero at an effective cross-section with maximum/minimum cross-sectional area, this can significantly affect the amplitude, shape, and phase of the oscillations, as well as the field dependence of the amplitude. The text was submitted by the author in English.     

[Na(15-C-5)]2[Pd(SCN)4]配合物的合成与结构分析

研究了15-冠-5(15-C-5)与Na2[Pd(SCN)4]的反应,得到的配合物[Na(15-C-5)]2[Pd(SCN)4]通过元素分析、红外光谱、单晶X射线衍射进行了结构分析.该配合物为单斜晶系,空间群C2/c,晶体学数据: a=1.3525(6)nm,b=1.3729(6)nm,c=2.0312(9)nm,β=102.985(6)°,V=3.675(3)nm3,Z=4,F(000)=1696,R1=0.0288,wR2=0.0457.结构分析表明,该配合物由两个[Na(15-C-5)]+配阳离子和一个[Pd(SCN)4]2-配阴离子组成,二者通过Na-N相互作用形成二维网状结构.     

De Haas-van Alphen oscillations in the organic quasi-two-dimensional metal (ET)<Subscript>8</Subscript>[Hg<Subscript>4</Subscript>Cl<Subscript>12</Subscript>(C<Subscript>6</Subscript>H<Subscript>5</Subscript>Cl)<Subscript>2</Subscript>]

The behavior of de Haas-van Alphen oscillations in the quasi-2D organic metal (ET)₈[Hg₄Cl₁₂(C₆H₅Cl)₂] was studied in detail. The section of the Fermi surface of this metal is a two-dimensional network of magnetic breakdown orbits. Only two frequencies, which corresponded to allowed closed orbits, F_A and F_MB, were detected. This is in agreement with the earlier studies of Shubnikov-de Haas oscillations in this metal. The reason for the absence of other allowed frequencies remains unclear. The angular dependences of the amplitudes of F_A and F_MB oscillations contain a series of “spin zeros.” An analysis of their positions led us to suggest that many-particle interactions were weakened in (ET)₈[Hg₄Cl₁₂(C₆H₅Cl)₂].     

Unconventional field and angle dependences of the Shubnikov-de Haas oscillations spectra in the quasi two-dimensional organic superconductor (BEDO-TTF) 2ReO 4H 2O

We report on the inter-layer oscillatory conductance of the two-dimensional organic superconductor (BEDO-TTF)₂ReO₄H₂O measured in static and pulsed magnetic fields of up to 15 and 52 T, respectively. In agreement with previous in-plane studies, two Shubnikov-de Haas oscillation series linked to the two electron and the hole orbits are observed. The influence of the magnitude and orientation of the magnetic field with respect to the conducting plane is studied in the framework of the conventional two- and three-dimensional Lifshits-Kosevich (LK) model. Deviations of the data from this model are observed in low fields strongly tilted with respect to the normal to the conducting plane. In this latter case, the observed behaviour is consistent with an unexplained lowering of the cyclotron effective mass. At high magnetic field, the oscillatory data could have been compatible with the occurrence of a magnetic breakdown orbit built from the hole and electron orbits. However, the increase of the cyclotron effective mass, linked to the electron orbits, as the magnetic field increases above ∼12 T is consistent with a field-induced phase transition. In the lower field range, where the conventional LK model holds, the analysis of the angle dependence of the oscillations amplitude suggests significant renormalisation of the effective Landé factor. Received 22 August 2000 and Received in final form 20 December 2000