Cylindrical Fermi Surface Research Articles

Slow oscillations of magnetoresistance in layered organic metals

We show that the slow oscillations observed, in addition to the fundamental Shubnikov-de Haas oscillations, in the interlayer magnetoresistance of β-(BEDT-TTF) 2 IBr 2 do not reveal a separate small group of carriers but are ultimately determined by the weak warping of the cylindrical Fermi surface. We propose a simple explanation of the phenomenon based on interfering contributions from oscillating relaxation time and Fermi velocity to the Shubnikov-de Haas effect.

Magnetic and Fermi surface properties of UTGa 5 (T: Fe, Co and Pt)

We succeeded in growing high-quality single crystals of UTGa 5 (T: Fe, Co and Pt) by the self-flux method, and measured the de Haas–van Alphen effect. With increasing the number of 3d-electrons, from Fe to Pt, the Fermi surface is found to change systematically, indicating cylindrical Fermi surfaces in UFeGa 5 and UPtGa 5.

An unusual hollow cylindrical Fermi surface of a quasi-two-dimensional compound CeAgSb2

Abstract We have carried out the de Haas-van Alphen (dHvA) experiment, together with electrical resistivity, magnetic susceptibility, magnetization and specific heat experiments on a high-quality single-crystal CeAgSb2, which has a small net ferromagnetic moment of 0.4 μB per Ce atom. The bulk magnetic properties are well explained by the crystalline electric field scheme. On the other hand, large dHvA frequencies of 108 Oe, which correspond to cylindrical Fermi surfaces, were detected by the dHvA measurement for the magnetic field along the tetragonal [001] direction, indicating the quasi-two-dimensional electronic structure. The dHvA branches of CeAgSb2 are highly different from those with small dHvA frequencies of 107 Oe for the reference compounds LaAgSb2 and YAgSb2 which exhibit a semimetallic character. The dHvA results have been compared with the results of the energy band calculations. It was concluded that the 4f electron is mainly localized and that the Fermi surface of CeAgSb2 is similar to tha...

An unusual hollow cylindrical Fermi surface of a quasitwo-dimensional compound CeAgSb<SUB>2</SUB>

An unusual hollow cylindrical Fermi surface of a quasitwo-dimensional compound CeAgSb<SUB>2</SUB>

Fermi surface in new layered organic conductors (BEDT-TTF) 3Br( pBIB) and (BEDT-TTF) 3Cl(DFBIB)

We report the measurements of Shubnikov–de Haas (SdH) oscillation and angular dependent magnetoresistance oscillation (ADMRO) in a new layered organic conductor (BEDT-TTF) 3Br( pBIB), where pBIB stands for p-bis(iodoethynyl)benzene. When magnetic fields are applied perpendicular to the layers, two distinct SdH oscillations are clearly observed, which arise from the two extremal cross-sectional areas of the slightly warped cylindrical Fermi surface (FS). The cross-sectional areas correspond to 50.9 and 51.6% of the first Brillouin zone. From the analysis of the ADMRO, the area of FS is estimated to be 52.5% of the first Brillouin zone. The ADMRO data also shows that the anisotropy of the FS is enhanced by change of Br( pBIB) for Cl(DFBIB), where DFBIB stands for 1,4-difluoro-2,5-bis(iodoethynyl)benzene. These results are consistent with the band calculation.

5f-itinerant Antiferromagnetism and Fermi surface property in UGa3, UFeGa5, UNiGa5 and UPtGa5

We measured the magnetic susceptibility and de Haas-van Alphen (dHvA) oscillation in UGa3 and UTGa5 (T: Fe, Ni and Pt). The susceptibility in UGa3 and UTGa5 is almost temperature-independent. It does not follow the Curie-Weiss law in the paramagnetic region, being dominated by a Pauli-like contribution, although UGa3 and UTGa5 (T: Ni and Pt) order antiferro-magnetically. The electronic state in UTGa5 is unique, indicating quasi-two dimensionality. Nearly cylindrical Fermi surfaces are formed by itinerant-5f electrons.

Magnetic molecular conductors based on BETS molecules and divalent magnetic anions [BETS = bis(ethylenedithio)tetraselenafulvalene

Several conducting salts based on BETS [where BETS = bis(ethylenedithio)tetraselenafulvalene] molecules and divalent magnetic anions such as the (CoCl(4))(2-), (CoBr(4))(2-), and (MnBr(4))(2-) were prepared. Electrocrystallization by using the (CoCl(4))(2-) anion gave two kinds of crystals. Block-shaped crystals were cleared to be (BETS)(2)CoCl(4), which is an insulator with the high-spin state of cobalt 3d spin. On the other hand, the X-ray crystal structure analysis of a plate-shaped crystal of the (CoCl(4))(2-) salt revealed the system to be kappa-(BETS)(4)CoCl(4)(EtOH), which is metallic down to 0.7 K. The electronic band structure calculation gave a typical two-dimensional cylindrical Fermi surface. However, there is only very weak antiferromagnetic interaction between the S = 3/2 cobalt 3d spins because of its anion-solvent-intermingled layer structure. On the other hand, the electrocrystallization by using the (MnBr(4))(2-) anion yielded the plate-shaped black crystals of the (MnBr(4))(2-) salt. Crystal structure analysis of the (MnBr(4))(2-) salt showed that the salt is theta;-(BETS)(4)MnBr(4)(EtOH)(2) with alternating donor and anion-solvent mixed layers. The stacking direction in one donor layer is perpendicular to those of the neighboring layers. The electrical and magnetic properties of the theta;-(BETS)(4)MnBr(4)(EtOH)(2) salt showed the metallic behavior down to approximately 30 K and the paramagnetism of the high-spin manganese 3d spins. Band structure calculation of this salt gave an elliptical cylindrical Fermi surface. Because the Fermi surfaces of the adjacent donor layers are rotated to each other by 90 degrees, the theta-(BETS)(4)MnBr(4)(EtOH)(2) salt becomes a two-dimensionally isotropic metal.

Fermi surface and internal magnetic field of the organic conductorsλ−(BETS)2FexGa1−xCl4

Shubnikov--de Haas (SdH) oscillations have been examined for organic conductors $\ensuremath{\lambda}\ensuremath{-}(\mathrm{BETS}{)}_{2}{\mathrm{Fe}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Cl}}_{4}$ $(x=0,$ 0.45, 0.78, and 1.0). In spite of the variety of the magnetic phases, no significant difference is found in the Fermi surface among them. All the salts have similar cylindrical Fermi surfaces, whose cross-sectional areas correspond to $\ensuremath{\sim}15%$ of the first Brillouin zone. For $x\ensuremath{\ne}0,$ two different SdH frequencies are observed, which are ascribed to the internal magnetic field ${H}_{J}$ due to the exchange interaction between the localized Fe moments and the conduction electron spins. The value of ${H}_{J}$ for $x=1.0$ is estimated to be 32 T and decreases with decreasing x. The large ${H}_{J}$ suggests that the field-induced superconductivity for $\ensuremath{\lambda}\ensuremath{-}(\mathrm{BETS}{)}_{2}{\mathrm{FeCl}}_{4}$ is understood in terms of the Jaccarino-Peter effect.

De Haas–van Alphen Effect in Quasi-Two-Dimensional Material La2RhIn8

We have grown a single crystal of La 2 RhIn 8 with the tetragonal structure and have measured the de Haas–van Alphen (dHvA) effect and magnetoresistance in the 4 He temperature region up to 9 T. The two dHvA frequencies α=6220 T and β=400 T were observed for the field along the [001] direction. The corresponding cross-sectional areas of the Fermi surfaces of α and β are about 33 and 2% of the Brillouin zone base area, respectively. The cyclotron mass m c * for the α is about 0.7 m 0 , where m 0 is the free electron mass. The angular dependence of the dHvA frequencies suggests that the frequency α originates from a large cylindrical Fermi surface elongated the c -axis, and the frequency β corresponds to a small pocket. The result of the magnetoresistance suggests that La 2 RhIn 8 is an uncompensated metal.

Magnetic and Fermi surface properties of UNiGa5

In order to investigate the magnetic structure and Fermi surface properties of UNiGa5, we have performed elastic neutron scattering and de Haas-van Alphen(dHvA) experiments. In the neutron scattering experiment using a single crystalline sample, we determined the antiferromagnetic propagation vector Q=(1/2,1/2,1/2) in UNiGa5. In the dHvA experiment, we observed four branches. Two branches indicate cylindrical Fermi surface and the other two branches correspond to ellipsoidal ones. The cyclotron mass was not large, ranging from 1.3 to 3.1m0.

Fermi surface studies in the magnetic-field-induced superconductorλ−(BETS)2FeCl4

Measurements of the Shubnikov--de Haas (SdH) and angular-dependent magnetoresistance oscillations were performed to study the Fermi surface for a magnetic-field-induced superconductor $\ensuremath{\lambda}\ensuremath{-}(\mathrm{BETS}{)}_{2}{\mathrm{FeCl}}_{4}.$ We found two SdH oscillations ascribed to the minimum and maximum cross-sectional areas of corrugated cylindrical Fermi surface, which are estimated to be $14%$ and $17%$ of the first Brillouin zone, respectively. The mass of the conduction electrons is $4.1 {m}_{0},$ suggesting the enhancement due to many-body effects. Assuming a parabolic energy band, we obtain a Fermi energy of $\ensuremath{\sim}20 \mathrm{meV}$ and an interlayer transfer integral of $\ensuremath{\sim}1 \mathrm{meV}.$

Periodic orbit resonances in κ-(ET) 2I 3

We have observed periodic orbit resonances in the normal state of the organic superconductor κ-(ET) 2 I 3 . Frequency dependent studies allow for a determination of the cyclotron mass, which can then be compared with the effective mass obtained by other techniques. Tilting the sample in the applied magnetic field enhances the resonance harmonics and enables investigation of the warping of the nearly cylindrical Fermi surface; our findings confirm recent theoretical predictions for quasi-two-dimensional conductors.

The Yamaji Ocsillations of the Ultrasonic Attenuation in the Quasi Two Dimensional Systems with the Periodically Undulating Fermi Surfaces

The ultrasonic attenuation is investigated for such quasi two dimensional systems with periodically undulating cylindrical Fermi surfaces as organic metals and superlattices. We obtained the most general forms of the ac-nonlocal magnetoconductivity, which becomes the dc-local magnetoconductivity obtained earlier in the limit of the high magnetic strength, where both the frequency and wave number can be assumed to become zero. The directional dependence of the magnetic field on the ultrasonic attenuation, one of what we call the Yamaji oscillations, appears in the high-field limits, only for longitudinal waves propagating parallel to the c -axis and for transverse waves polarized along the c -axis in the case of propagation in the plane perpendicular to the c -axis.

ChemInform Abstract: Bulk and Surface Electronic Structure of the Layered Sub-Nitrides Ca2N and Sr2N.

The binary sub-nitrides M2N (M = Ca and Sr) have the anti-CdCl2 layered structure. First-principles calculations show that these sub-nitrides are best described as ionic compounds with one electron in the “van der Waals gap” between the calcium (strontium) layers. The nitrogen 2p states show rather localized character with a bandwidth of about 2 eV. The compounds have a quasi-two-dimensional electronic structure with a cylindrical Fermi surface perpendicular to the layer direction. Calculations also show that the surface M2N slab has density of N 2s, 2p states shifted toward to a lower energy (about 1 eV) with respect to the bulk. These layered compounds may have an application as cathode material for polymer LED devices.

Charge-density-wave instabilities and quantum transport in the monophosphate tungsten bronzes with m = 5 alternate structure

Resistivity, thermoelectric power and magnetotransport measurements have been performed on single crystals of the quasi two-dimensional monophosphate tungsten bronzes (PO2)4(WO3)2m for m=5 with alternate structure, between 0.4 K and 500 K, in magnetic fields of up to 36 T. These compounds show one charge density instability (CDW) at \(\) 160 K and a possible second one at \(\) 30 K. Large positive magnetoresistance in the CDW state is observed. The anisotropic Shubnikov-de Haas and de Haas-van Alphen oscillations detected at low temperatures are attributed to the existence of small electron and hole pockets left by the CDW gap openings. Angular dependent magnetoresistance oscillations (AMRO) have been found at temperatures below \(\) 30 K. The results are discussed in terms of a weakly corrugated cylindrical Fermi surface. They are shown to be consistent with a change of the Fermi surface below \(\) 30 K.

Cylindrical Fermi surfaces formed by a fiat magnetic Brillouin zone in uranium dipnictides

Abstract We succeeded in growing high-quality single crystals of UX2 (X = Bi, Sb, As or P) by the self-flux and chemical transport methods and carried out de Haasvan Alphen and Shubnikov-de Haas experiments. We found quasi-two-dimensional Fermi surfaces in these U compounds. Fermi surfaces of UBi2 are found to consist of one spherical Fermi surface and two cylindrical Fermi surfaces. Each Fermi surface in UBi2 changes into two cylindrical surfaces in USb2 and UAs2. This change in the Fermi surfaces is well explained on the basis of a fiat magnetic Brillouin zone. The quasi-two-dimensional character of the Fermi surfaces is mainly due to the conduction electrons in the U piane, including the 5f electrons. The itinerant nature of 5f electrons is reflected in the large cyclotron masses. The magnetic breakthrough (breakdown) phenomenon is also discussed for USb2.

Cylindrical Fermi surfaces formed by a flat magnetic Brillouin zone in uranium dipnictides

Cylindrical Fermi surfaces formed by a flat magnetic Brillouin zone in uranium dipnictides

Bulk and Surface Electronic Structure of the Layered Sub-Nitrides Ca2N and Sr2N

The binary sub-nitrides M2N (M = Ca and Sr) have the anti-CdCl2 layered structure. First-principles calculations show that these sub-nitrides are best described as ionic compounds with one electron in the “van der Waals gap” between the calcium (strontium) layers. The nitrogen 2p states show rather localized character with a bandwidth of about 2 eV. The compounds have a quasi-two-dimensional electronic structure with a cylindrical Fermi surface perpendicular to the layer direction. Calculations also show that the surface M2N slab has density of N 2s, 2p states shifted toward to a lower energy (about 1 eV) with respect to the bulk. These layered compounds may have an application as cathode material for polymer LED devices.

Observation of dia- and paramagnetic domains in beryllium and white tin by muon spin rotation spectroscopy

Dia- and paramagnetic (Condon) domains in simple metals, produced at low temperatures and in high magnetic fields via the cooperative effect of electrons in Landau orbitals, are observable by the muon spin rotation (μSR) technique. For beryllium, domains were seen for T<3.5 K in fields 1<H<3 T through a well resolved splitting of the muon precession frequency, the split lines reappearing in each de Haas–van Alphen (dHvA) period as the applied field H varies. The beat in the dHvA oscillations allowed varying of the amplitude χ0 of the differential susceptibility, the key parameter determining domain properties. The data points in the (B,T) plane show that the standard formula for χ0(B,T) fails to describe the phase diagram, a consequence of the nearly cylindrical Fermi surface of Be. For white tin, preliminary data indicate the presence of domains by the oscillatory behavior of the μSR linewidth at T=0.1 K in fields of H≈1 T, arising from electrons in the pocket of the Fermi surface in the sixth zone.

Dimensional Crossover and Angular Dependent Magnetoresistance of Magnetic Graphite Intercalation Compounds; MCl2GIC's (M=Cu and Co)

In order to consider the dimensionality and the interaction between conduction electrons and localized magnetic moments, angular dependences of the magnetoresistance of magnetic GIC's, stage-1 and stage-2 MCl 2 GIC's (M=Cu and Co) were measured. The c -axis (perpendicular to the graphite layers) resistance of stage-1 CuCl 2 GIC shows a typical angular dependent magnetoresistance oscillation (ADMRO) which is commonly observed in several quasi two-dimensional (2D) electron systems with a periodically-warped cylindrical Fermi surface. This proves a band conduction along the c -axis in spite of extremely large anisotropy in conductivity (ρ c /ρ a = 10 5 ). On the other hand, stage-2 CoCl 2 GIC shows a larger MR for the magnetic field along the c axis than that along the graphitic plane. In addition, ADMRO is absent in this compound. These suggest that the c -axis conduction is governed by incoherent interlayer hoppings. The angular dependence of MR in stage-2 CuCl 2 and stage-1 CoCl 2 GIC's show an intermedia...