dHvA Branches Research Articles

First Observation of the de Haas–van Alphen Effect and Fermi Surfaces in the Unconventional Superconductor UTe2

We report the first observation of the de Haas–van Alphen (dHvA) effect in the novel spin-triplet superconductor UTe2 using high quality single crystals with a high residual resistivity ratio (RRR) over 200. The dHvA frequencies, named α and β, are detected for the field directions between c- and a-axes. The frequency of branch β increases rapidly with the field angle tilted from c- to a-axis, while branch α splits, owing to the maximal and minimal cross-sectional areas from the same Fermi surface. Both dHvA branches, α and β reveal two kinds of cylindrical Fermi surfaces with a strong corrugation at least for branch α. The angular dependence of the dHvA frequencies is in very good agreement with that calculated by the generalized gradient approximation (GGA) method taking into account the on-site Coulomb repulsion of U = 2 eV. It indicates that the main Fermi surfaces are experimentally detected. The observed cyclotron effective masses are large in the range from 32 to 57 m0. They are approximately 10–20 times lager than the corresponding band masses, consistent with the mass enhancement obtained from the Sommerfeld coefficient, γ and the calculated density of states at the Fermi level. The local density approximation (LDA) calculations of ThTe2 assuming U4+ with the 5f2 localized model are in less agreement with our experimental results, in spite of the prediction for two cylindrical Fermi surfaces, suggesting a mixed valence states of U4+ and U3+ in UTe2.

Fermi surfaces properties of AuAl2, AuGa2, and AuIn2 with the CaF2-type cubic structure

We grew high-quality single crystals of AuAl2, AuGa2, and AuIn2 with the fluorite (CaF2)-type cubic structure and determined the Fermi surface properties by the de Haas-van Alphen (dHvA) experiments using full-potential LAPW bad calculations. The Fermi surface and optical properties for three compounds were once studied from an interest of colors because AuAl2 has a striking bright reddish-purple color, whereas AuGa2 and AuIn2 are, respectively, neutral and bluish. The detected dHvA frequencies in the present study are found to be in a wide range of (0.1–13)×107Oe. The main dHvA branches for three compounds are in excellent agreement with the theoretical ones, but some dHvA branches with small dHvA frequencies are slightly deviated from the theoretical ones, especially in AuGa2 and AuIn2.

Magnetic field-induced Fermi surface reconstruction and quantum criticality in

We present detailed results of the field evolution of the de Haas–van Alphen (dHvA) effect in . A magnetic field-induced reconstruction of the Fermi surface is clearly shown to occur inside the antiferromagnetic state, in an applied field of around T, which is evidenced by the appearance of several new dHvA branches. The angular dependence of the dHvA frequencies reveals that the Fermi surfaces of at and are similar. The results suggest that the Ce-4f electrons in become itinerant at due to the Kondo effect, prior to the field-induced quantum critical point (QCP) at T. The electronic states at the field-induced QCP are therefore different from that of the pressure-induced QCP where a dramatic Fermi surface reconstruction occurs exactly at the critical pressure, indicating that multiple types of QCP may exist in .

Fermi Surface and Magnetic Properties in Ferromagnet CoS2 and Paramagnet CoSe2 with the Pyrite-type Cubic Structure

We succeeded in growing high-quality single crystals of pyrite-type cubic compounds CoSe2 and CoS2 using a transport agent of CoBr2 and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization, and the de Haas–van Alphen (dHvA) effect. We confirmed that CoSe2 is an exchange-enhanced paramagnet revealing a broad maximum at around 50 K in the temperature dependence of the magnetic susceptibility. The electronic specific heat coefficient is moderately large, γ = 18 mJ/(K2·mol). On the other hand, CoS2 is a ferromagnet with a Curie temperature TC = 122 K and an ordered moment μs = 0.93 μB/Co. The γ value of 21 mJ/(K2·mol) in CoS2 is slightly larger than that of CoSe2. A large ordered moment, together with a large γ value, is a characteristic feature in CoS2 because CoS2 is a half-metallic spin state in the ferromagnetic state. Correspondingly, we detected a main dHvA branch with a large cyclotron effective mass of 13m0 in the dHvA experiments. The detected dHvA branches in CoS2 and CoSe2 are discussed on the basis of the results of energy band calculations, revealing a broken four-fold-symmetry in the angular dependence of the dHvA frequency.

Magnetic and Fermi Surface Properties of Ferromagnets EuPd2 and EuPt2

We succeeded in growing single crystals of the ferromagnets EuPd2 and EuPt2 with the Laves-type cubic structure by the Bridgman method, namely, heating constituting materials in a Mo crucible up to a high temperature of about 1500 °C. The ferromagnetic properties of EuPd2 and EuPt2 with Curie temperatures of 74 and 100 K, respectively, were confirmed from the results of electrical resistivity, specific heat, and magnetization measurements. The ordered moment is 7 μB/Eu, revealing the Eu-divalent ferromagnetism. The present Eu-divalent electronic state is found to be robust against high pressures of up to 8 GPa and is not changed into the Eu-trivalent state. We also carried out de Haas–van Alphen (dHvA) experiments for EuPd2. The detected dHvA branches in EuPd2 are well explained by the relativistic linearized augmented plane wave (RLAPW) energy band calculations for SrPd2, revealing a closed hole Fermi surface and compensated four closed electron Fermi surfaces.

Large Cyclotron Mass and Large Ordered Moment in Ferromagnet CoS2 Compared with Paramagnet CoSe2

We succeeded in growing high-quality single crystals of the pyrite-type cubic compounds CoSe2 and CoS2 using the transport agent CoBr2 and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization, and de Haas–van Alphen (dHvA) effect. We confirmed that CoSe2 is an exchange-enhanced paramagnet revealing a broad maximum at around 50 K in the temperature dependence of the magnetic susceptibility. The electronic specific heat coefficient is moderately large, γ = 18 mJ/(K2·mol). On the other hand, CoS2 is a ferromagnet with a Curie temperature TC = 122 K and an ordered moment μs = 0.93 μB/Co. The γ of 21 mJ/(K2·mol) of CoS2 is slightly larger than that of CoSe2. A large ordered moment, together with a large γ, is characteristic of CoS2 because CoS2 is a half-metallic spin state in the ferromagnetic state. Correspondingly, we detected a main dHvA branch with a large cyclotron effective mass of 13m0 in the dHvA experiments. The detected dHvA branches in CoS2 and CoSe2 are discus...

Superconducting and Fermi Surface Properties of Single Crystal Zr2Co

We succeeded in growing single crystals of a superconductor Zr2Co with the tetragonal structure by the Bridgman method and carried out electrical resistivity, magnetic susceptibility, magnetization, specific heat, and de Haas–van Alphen (dHvA) experiments. Superconductivity is a characteristic revealing that the electronic specific heat at 1.45 K in the form of Ce/T in the superconducting state increases not linearly but as a function of \(\sqrt{H} \) up to a magnetic field close to the upper critical field Hc2 = 11 kOe. The superconducting transition temperature Tsc is found to increase markedly with increasing pressure from Tsc = 5.2 K at ambient pressure to 9.5 K at 8 GPa. From the dHvA experiment, several kinds of dHvA branches are detected, which are well explained by the results of the energy band calculation. The main conduction electrons are Zr-4d and Co-3d electrons.

Mass Enhancement of Nearly Trivalent Compound EuCo2Si2: Studied by the de Haas-van Alphen Experiments and Energy Band Calculations

We succeeded in growing single crystals of EuCo2Si2 by the Bridgman method, and carried out the de Haas-van Alphen (dHvA) experiments. EuCo2Si2 was previously studied from a viewpoint of the trivalent electronic state on the basis of the magnetic susceptibility and X-ray absorption experiments, whereas most of the other Eu compounds order magnetically, with the divalent electronic state. The detected dHvA branches in the present experiments are found to be explained by the results of the full potential linearized augmented plane wave energy band calculations on the basis of a local density approximation (LDA) for YCo2Si2 (LDA) and EuCo2Si2 (LDA + U), revealing the trivalent electronic state. The detected cyclotron effective masses are moderately large, ranging from 1.2 to 2.9 m0.

De Haas–van Alphen Effect in Rh2Ga9and Ir2Ga9without Inversion Symmetry in the Crystal Structure and Related Compounds T2Al9(T: Co, Rh, Ir) with Inversion Symmetry

We succeeded in growing high-quality single crystals of Rh2Ga9 and Ir2Ga9 with the non-centrosymmetric (distorted Co2Al9-type) monoclinic structure by the Ga-self flux method, and carried out the de Haas–van Alphen (dHvA) experiments. The Fermi surface is found to be split into two different Fermi surfaces, reflecting the non-centrosymmetric crystal structure. A magnitude of the antisymmetric spin–orbit interaction or a splitting energy between the two Fermi surfaces are determined to be 56 K for dHvA branch α and 45 K for branch β in Rh2Ga9, where these dHvA branches correspond to main Fermi surfaces. The present splitting values are compared with 290 and 130 K in Ir2Ga9, respectively. The splitting energy is found to be larger in the Ir-5d conduction electrons than in the Rh-4d conduction electrons. The split dHvA branches in Rh2Ga9 and Ir2Ga9 are also compared with the single dHvA branch in Co2Al9, Rh2Al9, and Ir2Al9 with inversion symmetry in the crystal structure.

De Haas-van Alphen Effect and Fermi Surface Properties in Ferromagnet LaCo2P2 and Related Compounds

We grew single crystals of a ferromagnet LaCo2P2 and an antiferromagnet CaCo2P2, and clarified the magnetic properties by measuring the electrical resistivity, specific heat, magnetic susceptibility, and magnetization. For LaCo2P2, we also carried out the de Haas-van Alphen (dHvA) experiment. Detected dHvA branches are well explained by the results of energy band calculations using a full-potential linearized augmented plane wave method within the local spin density approximation, where the ferromagnetic state is assumed. The cyclotron effective masses are (2–3)m0 (m0: rest mass of an electron). The present relatively large cyclotron masses in LaCo2P2 are due to ferromagnetic correlations of Co-3d conduction electrons, which are compared with much larger cyclotron masses of (3–7)m0 for a nearly ferromagnet SrCo2P2.

De Haas–van Alphen Effect and Fermi Surface Properties in Nearly Ferromagnet SrCo2P2

We grew high-quality single crystals of SrCo2P2 with the ThCr2Si2-type tetragonal structure, and clarified the Fermi surface properties by carrying out de Haas–van Alphen (dHvA) experiments and energy band calculations. SrCo2P2 is known to be a nearly ferromagnetic compound, where the magnetic susceptibility follows the Curie–Weiss law above 200 K, with the effective magnetic moment μeff = 1.72 μB/Co, but becomes almost constant below about 100 K. The electronic specific heat coefficient γ is thus relatively large, being γ = 40 mJ/(K2·mol). Detected dHvA branches possess the corresponding cyclotron effective masses \(m_{\text{c}}^{*}\), ranging from 0.87 to 7.2 m0 (m0: rest mass of an electron). The angular dependences of the dHvA frequencies are well explained by the results of full-potential linearized augmented plane wave (FLAPW) energy band calculations, revealing a multiply-connected band 25th hole Fermi surface and a compensated nearly cylindrical band 26th electron Fermi surface. It is thus conclud...

Magnetic and Fermi Surface Properties of Antiferromagnet EuCd11

We succeeded in growing a high-quality single crystal of EuCd11 with the BaCd11-type tetragonal structure by the Cd self-flux method, and measured the electrical resistivity, specific heat, magnetic susceptibility, magnetization, and de Haas–van Alphen (dHvA) oscillations, together with the electrical resistivity under high pressures up to 8 GPa. The antiferromagnetic ordering was confirmed to occur at the Néel temperature TN = 2.7 K, and the antiferromagnetic state was found to change into the field-induced ferromagnetic state with 7 μB/Eu above a critical field Hc \( \simeq \) 15 kOe for both the magnetic fields H || [100] and [001], revealing a typical Eu-divalent antiferromagnet. Reflecting the large lattice parameters of a = 11.93 Å and c = 7.682 Å with the caged structure, where each Eu atom is surrounded by a polyhedron of 22 Cd atoms, the Brillouin zone and the corresponding Fermi surfaces are small in volume. The detected dHvA branches are well explained by the full potential linear augmented plane wave (FLAPW) energy band calculations for the non-4f reference compound SrCd11, revealing ellipsoidal Fermi surfaces with complicated concave and convex shapes. The present Eu-divalent electronic state is found to be robust against high pressures up to 8 GPa, and does not change into the Eu-trivalent state.

Chiral-Structure-Driven Split Fermi Surface Properties in TaSi2, NbSi2, and VSi2

We carried out de Haas–van Alphen (dHvA) experiments for TaSi2, NbSi2, and VSi2 with the hexagonal chiral structure, and compared them with the results of energy band calculations. The Fermi surface is found to be split into two different Fermi surfaces, reflecting the non-centrosymmetric crystal structure. A magnitude of the antisymmetric spin–orbit interaction or a splitting energy between the two Fermi surfaces is determined to be 493 K for dHvA branch α (α′) and 564 K for branch β (β′), where these dHvA branches correspond to main Fermi surfaces. The present splitting values are compared with 209 and 244 K in NbSi2, and 19 and 39 K in VSi2, respectively. The splitting energy is found to be larger in the Ta-5d conduction electrons than those with the Nb-4d and V-3d conduction electrons.

De Haas–van Alphen Effect and Fermi Surface Properties of EuPd3 with the Trivalent Electronic State

EuPd3, which is in the trivalent (Eu3+) electronic state, is a rare compound because most Eu compounds are in the divalent (Eu2+) electronic state and order magnetically. The electronic state of EuPd3 was previously studied by Mossbauer, magnetic susceptibility, and X-ray absorption experiments using polycrystalline samples. We succeeded in growing single crystals of EuPd3 by the Bridgeman method and carried out a de Haas–van Alphen (dHvA) experiment. The dHvA branches detected in EuPd3 are well explained by the results of the full potential linear augmented plane wave (FLAPW) energy band calculation based on a local density approximation (LDA) with additional treatments for EuPd3, revealing the trivalent electronic state. Conduction electrons are mainly Pd-4d electrons. The cyclotron effective masses are determined from the temperature dependence of the dHvA amplitude, ranging from 0.3 to 1.0m0 (m0: rest mass of an electron), which are also consistent with the corresponding band masses.

Chiral Crystal Structure and Split Fermi Surface Properties in TaSi2

We carried out a de Haas–van Alphen (dHvA) experiment in TaSi2 with the hexagonal chiral structure, together with an energy band calculation. The Fermi surface is found to be split into two different Fermi surfaces, reflecting the non-centrosymmetric crystal structure. The magnitude of the antisymmetric spin–orbit interaction or the splitting energy between the two Fermi surfaces is determined to be 493 K for dHvA branch α (α'), 564 K for branch β (β'), and 617 K for branch γ (γ'), where these dHvA branches correspond to the main Fermi surfaces. The present splitting values are compared with 19, 39, and 110 K, respectively, observed in a similar compound, VSi2. The splitting energy is found to be larger in Ta-\(5d\) conduction electrons than in V-\(3d\) conduction electrons. Furthermore, we found a magnetic breakthrough effect for branches γ (γ') and α (α'), of which the circulating orbits are separate but are nearly degenerate in three and two regions, respectively.

Split Fermi Surface Properties of VSi2without Mirror Planes in the Chiral Crystal Structure

VSi2 is hexagonal in the crystal structure, and the basal plane stacks along the [0001] direction. Interestingly, each plane is rotated by 60\circ relative to the neighboring one. Therefore, there exist no mirror planes in this chiral structure. We carried out a de Haas–van Alphen (dHvA) experiment and clarified the Fermi surface properties. Each dHvA branch was found to be split into two branches on the basis of the antisymmetric spin–orbit interaction. The magnitude of the antisymmetric spin–orbit interaction in this chiral structure was determined for the first time to be 19 K for dHvA branch α (dHvA frequency \(F = 7.9 \times 10^{7}\) Oe and cyclotron mass \(m^{*}_{\text{c}} = 1.6\) \(m_{0}\)), 39 K for branch β (\(F = 4.1 \times 10^{7}\) Oe and \(m^{*}_{\text{c}} = 3.4\) \(m_{0}\)), and 110 K for branch γ (\(F = 1.8 \times 10^{7}\) Oe and \(m^{*}_{\text{c}} = 2.3\) \(m_{0}\)). These dHvA branches correspond to the main Fermi surfaces, which are well explained by the results of the energy band calculations based on the full potential linear augmented plane wave (FLAPW) method. The present values are mainly due to the V-\(3d\) conduction electrons.

High Field Magnetoresistance and de Haas–van Alphen Effect in LaRu2Al10

We have measured the magnetoresistance and de Haas–van Alphen (dHvA) effect in LaRu 2 Al 10 , which is a reference compound of CeRu 2 Al 10 that exhibits an unusual transition at T 0 ≃27 K. The magnetoresistance increases with increasing magnetic field at low temperatures in the wide field directions, suggesting that LaRu 2 Al 10 is a compensated metal without an open orbit. From the dHvA experiments, about three dHvA frequency branches whose cyclotron effective masses are close to 1 m 0 ( m 0 : rest mass of an electron) were detected. The observed dHvA branches for the main Fermi surface are well explained by the results of band structure calculation based on a full potential linearized augmented-plane-wave (FLAPW) method and local-density approximation (LDA), that demonstrates the multiply connected Fermi surface with no nesting property in LaRu 2 Al 10 .

Fermi Surface Property and Characteristic Crystalline Electric Field Effect in PrIr2Zn20

We measured the de Haas–van Alphen (dHvA) oscillations, electrical resistivity, magnetic susceptibility, magnetization, and specific heat of PrIr 2 Zn 20 , which has recently been suggested as a heavy-fermion superconductor. Several dHvA branches with small frequencies ranging from 0.33×10 6 to 8.00×10 6 Oe were detected in the dHvA experiment, which were well explained by the results of energy band calculations for LaIr 2 Zn 20 using the lattice parameter of PrIr 2 Zn 20 . Moreover, the cyclotron effective mass is small, i.e., less than 1 m 0 ( m 0 : rest mass of an electron). This means that 4 f electrons are fully localized and do not contribute to the Fermi surface. Similar dHvA results were obtained for the reference compound LuIr 2 Zn 20 . Thus, superconductivity in PrIr 2 Zn 20 , which has been observed very recently below 0.05 K, is not due to heavy quasiparticles. In fact, the present superconductivity disappears at a magnetic field of 20 Oe. From the experimental results of magnetic susceptibili...

Low-Temperature Magnetic Orderings and Fermi Surface Properties of LaCd11, CeCd11, and PrCd11with a Caged Crystal Structure

We succeeded in growing single crystals of cage-structure compounds RCd11 (R: La, Ce, and Pr) and precisely studied their low-temperature magnetic and electronic properties by measuring electrical resistivity, magnetic susceptibility, magnetization, specific heat, and the de Haas–van Alphen (dHvA) effect. We found antiferromagnetic ordering at 0.44 and 0.39 K in CeCd11 and PrCd11, respectively, and clarified the magnetic phase diagrams of the compounds. In addition, low-lying crystalline electric field (CEF) schemes were proposed from the specific heat results of both compounds. From the present study, the antiferromagnetic ordering in PrCd11 is found to be of the exchange-induced type with a singlet ground state. From the dHvA experiment, we detected small dHvA branches ranging from 7 � 10 5 to 2 � 10 7 Oe, which correspond to small Fermi surfaces. This is mainly due to a small Brillouin zone based on a large unit cell. Moreover, the dHvA frequencies and cyclotron masses are approximately the same among RCd11, revealing a localized character of 4f electrons in CeCd11 and PrCd11.

Magnetic and Fermi Surface Properties of CePd5Al2 and PrPd5Al2

We succeeded in growing single crystals of the antiferromagnet CePd 5 Al 2 and the paramagnet PrPd 5 Al 2 with a tetragonal crystal structure by the Bridgman method, and studied the magnetic and Fermi surface properties by measuring the electrical resistivity, magnetic susceptibility, magnetization, specific heat, and de Haas–van Alphen (dHvA) oscillation. We constructed the crystalline electric field (CEF) scheme from the experimentally observed anisotropic magnetic susceptibility and magnetization of CePd 5 Al 2 and PrPd 5 Al 2 . In both compounds, the B 2 0 value in the CEF parameters is negative and large, implying that the magnetic easy axis is the [001] direction. The present magnetism of CePd 5 Al 2 and PrPd 5 Al 2 is highly different from that of the heavy fermion superconductor NpPd 5 Al 2 with the magnetic easy axis of the [100] direction. From the dHvA experiment for CePd 5 Al 2 and PrPd 5 Al 2 , we observed a few dHvA branches, which correspond to nearly cylindrical band-32 hole and band-33 el...