De Haas-van Alphen Experiments Research Articles

Orbital crossing in spin-split Fermi surfaces and anisotropic effective mass of the noncentrosymmetric heavy-fermion paramagnet UPt5

We report the single-crystal growth of the noncentrosymmetric cubic heavy-fermion paramagnet ${\mathrm{UPt}}_{5}$ and comparative Fermi surface studies of de Haas-van Alphen (dHvA) experiments and theoretical band calculations. We also present the results of single-crystal x-ray diffraction, electrical resistivity, heat capacity, and magnetization measurements using single crystals of ${\mathrm{UPt}}_{5}$. The dHvA experiments reveal nearly spherical split hole Fermi surfaces and largely split electron Fermi surfaces, which are in agreement with the results of a band-structure calculation. The largely split electron Fermi surfaces may be understood through the antisymmetric spin-orbit interaction derived from U-$5f$ and Pt-$5d$ electrons. We explain the observed unexpected dHvA frequencies quasiquantitatively based on orbital crossing using the coupled network analysis in the split hole Fermi surface pair. Furthermore, the temperature dependence of the dHvA amplitude reveals enhanced cyclotron effective masses of up to $29{m}_{0}$ and a peculiar anisotropic effective mass in the paramagnetic cubic heavy-fermion ${\mathrm{UPt}}_{5}$.

Quasi-one-dimensional magnetic interactions and conduction electrons in EuCu5 and EuAu5 with the characteristic hexagonal structure

ABSTRACTWe have succeed in growing single crystals of EuCu and EuAu with the hexagonal structure by the Bridgman method. Both compounds are known to be ferromagnets with Curie temperatures and 13 K, respectively, and the Eu-4f magnetic moments of EuCu are known to orient along the hexagonal c-axis or the [0001] direction by the Mössbauer experiment. The magnetisations at 2 K in EuCu and EuAu in the present experiment saturate at an extremely low field of 2 kOe for , with a Eu-moment of . On the other hand, the hard-axis magnetisations for [0001] saturate at a high field of 40 kOe. It is also found from the electrical resistivty measurement that the electrical resistivities along the current [0001] in EuCu and EuAu are about at room temperature, which are compared with the resistivities of 30–40 for [0001]. The quasi-one dimensional conductivities are also characteristic, which were clarified from the de Haas-van Alphen (dHvA) experiment and FLAPW energy band calculation for EuAu, revealing the existence of a large plate-like Fermi surface.

Magnetic field–induced type II Weyl semimetallic state in geometrically frustrated Shastry-Sutherland lattice GdB4

Weyl semimetal is a topologically non-trivial phase of matter with pairs of Weyl nodes in the k-space, which act as monopole and antimonopole pairs of the Berry curvature. Two hallmarks of the Weyl metallic state are the topological surface state called the Fermi arc and the chiral anomaly. It is known that the chiral anomaly yields anomalous magnetotransport phenomena. In this study, we report the emergence of the type II Weyl semimetallic state in the geometrically frustrated non-collinear antiferromagnetic Shastry-Sutherland lattice (SSL) GdB4 crystal. When we apply magnetic fields perpendicular to the non-collinear moments in the SSL plane, Weyl nodes are created above and below the Fermi energy along the M-A line (τ-band) because the spin tilting breaks the time-reversal symmetry and lifts band degeneracy while preserving C4z or C2z symmetry. The unique electronic structure of GdB4 under magnetic fields applied perpendicular to the SSL gives rise to a non-trivial Berry phase, detected in de Haas-van Alphen experiments, and chiral anomaly–induced negative magnetoresistance. The emergence of the magnetic field–induced Weyl state in the SSL presents a new guiding principle to develop novel types of Weyl semimetals in frustrated spin systems.

De Haas–van Alphen Experiment and Fermi Surface Properties in Field-Induced Ferromagnetic State of MnP

MnP is a prototype 3d-itinerant magnet but still a compound under considerable study. This is based on the characteristic magnetic phases including the helical, cone, and fan structures and a varie...

Splitting Fermi Surfaces and Heavy Electronic States in Non-Centrosymmetric U3Ni3Sn4

We report the single-crystal growth of the non-centrosymmetric paramagnet U3Ni3Sn4 by the Bridgman method and the Fermi surface properties detected by de Haas-van Alphen (dHvA) experiments. We have also investigated single-crystal U3Ni3Sn4 by single-crystal X-ray diffraction, magnetization, electrical resistivity, and heat capacity measurements. The angular dependence of the dHvA frequencies reveals many closed Fermi surfaces, which are nearly spherical in topology. The experimental results are in good agreement with local density approximation (LDA) band structure calculations based on the 5f-itinerant model. The band structure calculation predicts many Fermi surfaces, mostly with spherical shape, derived from 12 bands crossing the Fermi energy. To our knowledge, the splitting of Fermi surfaces due to the non-centrosymmetric crystal in 5f-electron systems is experimentally detected for the first time. The temperature dependence of the dHvA amplitude reveals a large cyclotron effective mass of up to 35m0, indicating the heavy electronic state of U3Ni3Sn4 due to the proximity of the quantum critical point. From the field dependence of the dHvA amplitude, a mean free path of conduction electrons of up to 1950A is detected, reflecting the good quality of the grown crystal. The small splitting energy related to the antisymmetric spin-orbit interaction is most likely due to the large cyclotron effective mass.

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.

Fermi surfaces of the pyrite-type cubic AuSb2 compared with split Fermi surfaces of the ullmannite-type cubic chiral NiSbS and PdBiSe

We grew high-quality single crystals of AuSb2 with the pyrite (FeS2)-type cubic structure by the Bridgman method and studied the Fermi surface properties by the de Haas-van Alphen (dHvA) experiment and the full potential LAPW band calculation. The Fermi surfaces of AuSb2 are found to be similar to those of NiSbS and PdBiSe with the ullmannite (NiSbS)-type cubic chiral structure because the crystal structures are similar each other and the number of valence electrons is the same between two different compounds. Note that each Fermi surface splits into two Fermi surfaces in NiSbS and PdBiSe, reflecting the non-centrosymmetric crystal structure.

Fermi Surfaces in the Antiferromagnetic, Paramagnetic and Polarized Paramagnetic States of CeRh2Si2 Compared with Quantum Oscillation Experiments

The large quantum oscillations observed in the thermoelectric power in the antiferromagnetic (AF) state of the heavy-fermion compound CeRh2Si2 disappear suddenly when entering in the polarized paramagnetic (PPM) state at Hc=26.5 T, indicating an abrupt reconstruction of the Fermi surface. The electronic band structure was [LDA+U] for the AF state taking the correct magnetic structure into account, for the PPM state, and for the paramagnetic state (PM). Different Fermi surfaces were obtained for the AF, PM, and PPM states. Due to band folding, a large number of branches was expected and observed in the AF state. The LDA+U calculation was compared with the previous LDA calculations. Furthermore, we compared both calculations with previously published de Haas-van Alphen experiments. The better agreement with the LDA approach suggests that above the critical pressure pc CeRh2Si2 enters in a mixed-valence state. In the PPM state under a high magnetic field, the 4f contribution at the Fermi level EF drops significantly compared with that in the PM state, and the 4f electrons contribute only weakly to the Fermi surface in our approach.

Magnetoresistance and Hall effect of antiferromagnetic uranium compound URhIn5

Magnetoresistance and Hall effect in URhIn5 have been measured across the antiferromagnetic transition temperature TN = 98 K. In the paramagnetic state, Hall coefficient is small and temperature independent. Below the TN, Hall coefficient suddenly changes to a negative value, suggesting that small light electron Fermi surface dominate electrical conductivity. The observation is consistent with small Fermi surfaces detected by previous de Haas-van Alphen experiment.

Magnetic Field Dependence of Specific Heat in KFe2As2 Single Crystals

The observed change in specific heat by the application of a magnetic field for high-quality superconducting KFe2As2 single crystals by Abdel-Hafiez et al. (Phys. Rev. B 85, 134533–134543 (2012)) is examined through the phenomenological Ginzburg–Landau (GL) theory of anisotropic type II superconductors. In doing so, it is proposed that the system contains two gaps along two perpendicular directions, i.e., parallel to the ab plane and parallel to the c-axis as per the prediction through an angle-resolved photoemission spectroscopy (ARPES) experiment by Terashima et al. (J. Phys. Soc. Jpn. 78(8), 083701–083704 (2009)) and a de Haas-van Alphen (dHvA) experiment by Sato et al (Phys. Rev. Lett. 103, 047002–047006 (2009)). The single equation for the change of specific heat (ΔC) derived from the GL theory used to study the anisotropic property of cuprate superconductors by Pattanaik et al. (Physica B 405, 3234–3238 (2010)) is now approximately splitted into two equations along these perpendicular directions. The analysis of this equation explains satisfactorily the specific heat anomaly near T c and determines the penetration depth anisotropic ratio γ as 4.98, which is close to the experimental value 5.0 near T c by Abdel-Hafiez et al. (Phys. Rev. B 85, 134533–134543 (2012)) and the calculated value 4.0 by Eskildsen et al. (Rep. Prog. Phys. 74, 124504–1245016 (2011)).

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.

Phase diagram of CeRh2Si2 under pressure studied by thermopower measurements

We report the evolution of thermoelectric power under hydrostatic pressure up to 17 kbar and at low temperature in the heavy fermion compound CeRh2Si2. These measurements were performed using a thermoelectric setup specially designed for piston cylinder pressure cells. The suppression of the antiferromagnetic order (AF) into a paramagnetic order (PM) state was studied and the (T, P) phase diagram was precisely obtained. The different magnetic transitions at low temperature as a function of pressure, AF1-AF2 transition at P'c and AF1-PM transition at Pc, show significant changes in the thermoelectric signal. This support reconstructions of the Fermi surface in agreement with previous de Haas van Alphen experiments.

Large Cyclotron Effective Mass Detected by de Haas–van Alphen Effect in YbCu2Si2

De Haas–van Alphen experiments were performed on the valence fluctuation compound YbCu2Si2. For the field direction close to the c-axis in the tetragonal structure, a very large cyclotron effective mass of 43 m0 was detected on branch β, which corresponds to the nearly cylindrical Fermi surface. This mass is one of the largest cyclotron masses detected experimentally in Yb compounds.

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.

Superconducting properties ofK1−xNaxFe2As2under pressure

The effect of hydrostatic pressure and partial Na substitution on the normal-state properties and the superconducting transition temperature ($T_c$) of K$_{1-x}$Na$_x$Fe$_2$As$_2$ single crystals were investigated. It was found that a partial Na substitution leads to a deviation from the standard $T^2$ Fermi-liquid behavior in the temperature dependence of the normal-state resistivity. It was demonstrated that non-Fermi liquid like behavior of the resistivity for K$_{1-x}$Na$_{x}$Fe$_2$As$_2$ and some KFe$_2$As$_2$ samples can be explained by disorder effect in the multiband system with rather different quasiparticle effective masses. Concerning the superconducting state our data support the presence of a shallow minimum around 2 GPa in the pressure dependence of $T_c$ for stoichiometric KFe$_2$As$_2$. The analysis of $T_c$ in the K$_{1-x}$Na$_{x}$Fe$_2$As$_2$ at pressures below 1.5 GPa showed, that the reduction of $T_c$ with Na substitution follows the Abrikosov-Gor'kov law with the critical temperature $T_{c0}$ of the clean system (without pair-breaking) which linearly depends on the pressure. Our observations, also, suggest that $T_c$ of K$_{1-x}$Na$_x$Fe$_2$As$_2$ is nearly independent of the lattice compression produced by the Na substitution. Further, we theoretically analyzed the behavior of the band structure under pressure within the generalized gradient approximation (GGA). A qualitative agreement between the calculated and the recently in de Haas-van Alphen experiments [T. Terashima et al., Phys.Rev.B89, 134520(2014)] measured pressure dependencies of the Fermi-surface cross-sections has been found. These calculations, also, indicate that the observed minimum around 2~GPa in the pressure dependence of $T_c$ may occur without a change of the pairing symmetry.

Fermi Surface and Magnetic Properties of Antiferromagnet EuBi3

EuBi3 with the AuCu3-type cubic structure is known to be a Eu-divalent antiferromagnet with the Neel temperature \(T_{\text{N}}\simeq 7.5\) K. We succeeded in growing a high-quality single crystal by the Bi self-flux method. The magnetization at 1.3 K for the magnetic field along the \(\langle 100\rangle\) direction increases linearly as a function of magnetic field, and saturates at a critical field \(H_{\text{c}}=225\) kOe, reaching a saturated magnetic moment of 7 µB/Eu. \(H_{\text{c}}\) is well explained by the magnetic exchange interaction based on a two-sublattice model, using the simple relation Hc = (kB/3µB)(TN-θp), namely, Hc [kOe]=4.9 (TN-θp) [K], where θp is the paramagnetic Curie temperature θp=-36 K. The present anti ferromagnetic state is found to be stable under pressures up to 8 GPa, where the Neel temperature increases with increasing pressure, being \(T_{\text{N}}=16.5\) K at 8 GPa. From the results of de Haas–van Alphen experiments on EuBi3 and energy band calculations for the non-\(4f\...

Heavy fermions and unconventional superconductivity in high-quality single crystals of rare-earth and actinide compounds

The f-electron system in rare-earth and actinide compounds exhibit a variety of characteristic properties including heavy fermions and unconventional superconductivity. The Fermi surface properties in rare-earth and actinide compounds are clarified by the de Haas-van Alphen experiments on the basis of the results of energy band calculations. The effect of pressure on the electronic states of CeRhIn5, CeIrSi3, and YbIr2Zn20 is studied in magnetic fields. An electronic instability, including unconventional superconductivity, occurs at 2.4 GPa in CeRhIn5 and 2.6 GPa in CeIrSi3. An abrupt non-linear increase in the magnetization, namely, a metamagnetic behavior, is found in the heavy fermion compounds, including YbT2Zn20 (T: Co, Rh, Ir). A super-heavy fermion state with a specific heat coefficient of 10 J/(K2·mol) is realized in YbIr2Zn20 under pressure.

LDA+DMFT study of the effects of correlation in LiFeAs

We discuss the role of electronic correlations in the iron-based superconductor LiFeAs by studying the effects on band structure, mass enhancements, and Fermi surface in the framework of density functional theory combined with dynamical mean field theory calculations. We conclude that LiFeAs shows characteristics of a moderately correlated metal and that the strength of correlations is mainly controlled by the value of the Hund's rule coupling $J$. The hole pockets of the Fermi surface show a distinctive change in form and size with implications for the nesting properties. Our calculations are in good agreement with recent angle-resolved photoemission spectroscopy and de Haas-van Alphen experiments.

Band Calculations for Ce Compounds with AuCu3-Type Crystal Structure on the Basis of Dynamical Mean Field Theory: II. CeIn3 and CeSn3

Band calculations for Ce compounds with the AuCu$_{3}$-type crystal structure were carried out on the basis of dynamical mean field theory (DMFT). The results of applying the calculation to CeIn$_{3}$ and CeSn$_{3}$ are presented as the second in a series of papers. The Kondo temperature and crystal-field splitting are obtained, respectively, as 190 and 390 K (CeSn$_{3}$), 8 and 160 K (CeIn$_{3}$ under ambient pressure), and 30 and 240 K (CeIn$_{3}$ at a pressure of 2.75 GPa). Experimental results for the photoemission spectrum are reasonably well reproduced. In CeSn$_{3}$, a Fermi surface (FS) structure similar to that obtained by a refined calculation based on the local density approximation (LDA) is obtained. In CeIn$_{3}$, the topology of the FS structure is different from that obtained by the LDA calculation but seems to be consistent with the results of de Haas-van Alphen experiments. Cyclotron mass of the correct magnitude is obtained in both compounds. The experimental result for the angular correlation of the electron-positron annihilation radiation is reasonably well reproduced on the basis of the itinerant 4f picture. A band calculation for CeIn$_{3}$ in the antiferromagnetic state was carried out, and it was shown that the occupied 4f state should have a very shallow level.

High-Quality Single Crystal Growth and Unique Electronic States under Magnetic Field and Pressure in Rare Earth and Actinide Compounds

The f electrons in rare earth and actinide compounds exhibit variety of characteristic properties including heavy fermions and unconventional superconductivity. Fermi surface properties in rare earth and actinide compounds such as CeSn 3 , USi 3 , NpGe 3 and PuIn 3 are clarified by the de Haas–van Alphen experiments on the basis of the results of energy band calculations. An abrupt nonlinear increase of magnetization, namely metamagnetic behavior is found in the heavy fermion compounds including YbT 2 Zn 20 (T: Co, Rh, Ir). An effect of pressure on the electronic state of YbIr 2 Zn 20 and antiferromagnets CeRhIn 5 and CeIrSi 3 are also studied in magnetic fields. The electronic instability including unconventional superconductivity occurs at about 2.4 GPa in CeRhIn 5 and 2.6 GPa in CeIrSi 3 .