Van Alphen Measurements Research Articles

Fermi surface of the chiral topological semimetal PtGa

PtGa is a topological semimetal with giant spin-split Fermi arcs. Here, we report on angular-dependent de Haas–van Alphen (dHvA) measurements combined with band-structure calculations to elucidate the details of the bulk Fermi surface of PtGa. The strong spin–orbit coupling leads to eight bands crossing the Fermi energy that form a multitude of Fermi surfaces with closed extremal orbits and results in very rich dHvA spectra. The large number of experimentally observed dHvA frequencies make the assignment to the equally large number of calculated dHvA orbits challenging. Nevertheless, we find consistency between experiment and calculations verifying the topological character with maximal Chern number of the spin-split Fermi surface.

Fermi surface topology and large magnetoresistance in the topological semimetal candidate PrBi

We report a detailed magnetotransport study on single crystals of PrBi. The presence of $f$-electrons in this material raises the prospect of realizing a strongly correlated version of topological semimetals. PrBi shows a magnetic field induced metal insulator transition below $T \sim 20$ K and a very large magnetoresistance ($\approx 4.4 \times 10^4~$) at low temperatures ($T= 2$ K). We have also probed the Fermi surface topology by de Haas van Alphen (dHvA) and Shubnikov de Haas (SdH) quantum oscillation measurements complimented with density functional theory (DFT) calculations of the band structure and the Fermi surface. Angle dependence of the SdH oscillations have been carried out to probe the possible signature of surface Dirac fermions. We find three frequencies corresponding to one electron ($\alpha$) and two hole ($\beta$ and $\gamma$) pockets in experiments, consistent with DFT calculations. The angular dependence of these frequencies is not consistent with a two dimensional Fermi surface suggesting that the transport is dominated by bulk bands. Although the transport properties of this material originate from the bulk bands, the high mobility and small effective mass are comparable to other compounds in this series proposed as topologically nontrivial.

Quantum magnetotransport and de Haas–van Alphen measurements in the three-dimensional Dirac semimetal Pb0.83Sn0.17Se

Magnetoresistance (MR), Hall resistance and magnetization of the Pb0.83Sn0.17Se crystals have been measured in magnetic field up to 15 T and 5 T, respectively, and temperatures from 1.7 K up to 300 K. A large linear and temperature dependent MR is observed in magnetic field up to 15 T. The de Haas–van Alphen (dHvA) and Shubnikov de Haas effects (SdH) of Pb0.83Sn0.17Se crystals have been clearly seen in the temperature range from 30 K down to 1.7 K and magnetic field as low as 2 T. The dHvA and SdH oscillations reveal single frequency of around 8 T which confirms the existence of a single Fermi surface cross section. Influence of isothermal annealing of Pb0.83Sn0.17Se crystals in Se vapours has been investigated. By increasing the annealing temperature from 433 °C up to 440 °C, transition from n to p-type conductivity has been observed. The dHvA and SdH effects clearly reflect the existence of a nontrivial Berry’s phase owing to the linear band dispersion which is the signature of a three-dimensional Dirac fermion in the Pb0.83Sn0.17Se crystals [1].

Magnetotransport and de Haas–van Alphen measurements in the type-II Weyl semimetal TaIrTe4

The layered ternary compound ${\mathrm{TaIrTe}}_{4}$ has been predicted to be a type-II Weyl semimetal with only four Weyl points just above the Fermi energy. Performing magnetotransport measurements on this material we find that the resistivity does not saturate for fields up to 70 T and follows a $\ensuremath{\rho}\ensuremath{\sim}{B}^{1.5}$ dependence. Angular-dependent de Haas--van Alphen measurements reveal four distinct frequencies. Analyzing these magnetic quantum oscillations by use of density functional theory calculations we establish that in ${\mathrm{TaIrTe}}_{4}$ the Weyl points are located merely $\ensuremath{\sim}40--50$ meV above the chemical potential.

Effects of oxygen plasma etching on Sb2Te3 explored by torque detected quantum oscillations

De Haas–van Alphen measurements evidence that oxygen plasma etching strongly affects the properties of the three-dimensional topological insulator Sb2Te3. The quantum oscillations in magnetization down to low temperature (T ≥ 2 K) and high magnetic field (B ≤ 7 T) have been systematically investigated using a high-sensitive cantilever torque magnetometer. The effective mass and the oscillation frequency obtained from de Haas–van Alphen measurements first increase and then decrease as the oxygen plasma etching time increases from 0 to 12 min, corresponding to an up- and down-shift of the Dirac point. We establish the cantilever torque magnetometer as a powerful contactless tool to investigate the oxygen sensitivity of the surface state in topological insulators.

Chiral and non‐chiral p‐wave superconducting states from correlated hopping interactions

Understanding anisotropic superconductivity has been one of the major theoretical challenges in the solid state physics. In this paper, we report a comparative study of chiral and non‐chiral p‐wave superconducting states by means of a generalized Hubbard Hamiltonian within the BCS formalism. The single‐electron parameters were obtained by fitting ab initio band structure data supported by de Haas–van Alphen measurements in Sr2RuO4 and the electron correlation parameter was determined by the experimental critical temperature (Tc). This study was carried out by looking at Tc, superconducting gap, Helmholtz free energy, and electronic specific heat. The results show that both chiral and non‐chiral p‐wave superconducting states possess the same Tc but different superconducting energy gaps. Moreover, both states have almost the same Helmholtz free energy, which leads to their possible coexistence. Finally, the calculated electronic specific heats without adjustable parameters for both p‐wave superconducting states are compared with the experimental data obtained from Sr2RuO4, observing a better agreement for the non‐chiral case for temperatures much lower than Tc.

Small and nearly isotropic hole-like Fermi surfaces in LiFeAs detected through de Haas–van Alphen effect

LiFeAs is unique among the arsenic based Fe-pnictide superconductors because it is the only nearly stoichiometric compound which does not exhibit magnetic order. This is at odds with electronic structure calculations which find a very stable magnetic state and predict cylindrical hole- and electron-like Fermi surface sheets whose geometry suggests spin fluctuations and a possible instability toward long-range ordering at the nesting vector. In fact, a complex magnetic phase diagram is indeed observed in the isostructural NaFeAs compound. Previous angle-resolved photoemission (ARPES) experiments revealed the existence of both hole and electron-like surfaces, but with rather distinct cross-sectional areas and an absence of the nesting that is thought to underpin both magnetic order and superconductivity in the pnictide family of superconductors. These ARPES observations were challenged by subsequent de Haas--van Alphen (dHvA) measurements which detected a few, electron-like Fermi surface sheets in rough agreement with the original band calculations. Here, we show a detailed dHvA study unveiling additional, small and nearly isotropic Fermi surface sheets in LiFeAs single crystals, which ought to correspond to hole-like orbits, as previously observed by ARPES. Therefore, our results reconcile the apparent discrepancy between ARPES and the previous dHvA results. The small size of these Fermi surface pockets suggests a prominent role for the electronic correlations in LiFeAs. The absence of gap nodes, in combination with the coexistence of quasi-two-dimensional and three-dimensional Fermi surfaces, favor an $s$-wave pairing symmetry for LiFeAs. But similar electron-like Fermi surfaces combined with very different hole pockets between LiFeAs and LiFeP suggest that the nodes in the gap function of LiFeP might be located on the hole pockets. This would be difficult to reconcile with the current understanding of the $s\ifmmode\pm\else\textpm\fi{}$ scenario.

Fermi surface topology and de Haas–van Alphen orbits in PuIn3and PuSn3compounds

Since the recent discovery of plutonium-based superconductors such as PuCoIn$_{\rm 5}$, systematic studies of the electronic properties for plutonium compounds are providing insight into the itinerancy-localization crossover of Pu 5$f$ electrons. We are particularly interested in understanding the Fermi surface properties of PuIn$_{3}$ compound, which serves as the building block for the PuCoIn$_{\rm 5}$ superconductor. Motivated by the first observation of quantum oscillation and renewed interest in the de-Hass van-Alphen (dHvA) measurements on PuIn$_{\rm 3}$, we study the Fermi surface (FS) topology and the band dispersion in both paramagnetic and antiferromagnetic state of PuIn$_{\rm 3}$, based on density functional theory with generalized gradient approximation. We compare the results with its isostructural paramagnetic compound PuSn$_{\rm 3}$. We show the detailed Fermi surfaces of compounds PuIn$_{\rm 3}$ and PuSn$_{\rm 3}$ and conclude that the FS topology of an antiferromagnetic PuIn$_3$ agrees better with dHvA measurements. In addition, we show the magnetization of the antiferromagnetic order can alter the angle dependence and values of the effective mass for the dHvA orbits. We point out the accurate determination of the magnetic order orientation with respect to the crystal orientation is crucial to advance the understanding of the electronic structures of the PuIn$_{\rm 3}$ compound.

Band-dependent emergence of heavy quasiparticles in CeCoIn5

We investigate the low temperature ($T<2$ K) electronic structure of the heavy fermion superconductor CeCoIn${}_{5}$ (${T}_{c}=2.3$ K) by angle-resolved photoemission spectroscopy (ARPES). The hybridization between conduction electrons and $f$ electrons, which ultimately leads to the emergence of heavy quasiparticles responsible for the various unusual properties of such materials, is directly monitored and shown to be strongly band dependent. In particular the most two-dimensional band is found to be the least hybridized one. A simplified multiband version of the periodic Anderson model (PAM) is used to describe the data, resulting in semiquantitative agreement with previous bulk sensitive results from de Haas--van Alphen measurements.

High-resolution angle-resolved photoemission study of electronic structure and electron self-energy in palladium

In this study, we investigate the electronic structure and electron self-energy of palladium single crystals using polarization-dependent high-resolution angle-resolved photoemission spectroscopy. The observed Fermi surfaces and energy-band dispersions agree with those given by the band-structure calculation. A detailed comparison between the observed and theoretical band dispersions of the ${\ensuremath{\Sigma}}_{1}$ band forming the electronlike Fermi surface indicates an electron-electron coupling parameter of ${\ensuremath{\lambda}}_{ee}\ensuremath{\sim}0.02$. Near the Fermi level, a kink structure in the energy-band dispersion exists at $\ensuremath{\sim}\ensuremath{-}20$ meV, in agreement with the Debye energy. The electron-phonon coupling parameter is estimated to be ${\ensuremath{\lambda}}_{ep}=0.39\ifmmode\pm\else\textpm\fi{}0.05$ at 8 K for the ${\ensuremath{\Sigma}}_{1}$ band, which is consistent with the theoretical values of ${\ensuremath{\lambda}}_{ep}=0.35--0.41$. Furthermore, analyses of the self-energy indicate a possible contribution from the electron-paramagnon interaction in the energy range of $\ensuremath{-}50\ensuremath{\sim}\ensuremath{-}150$ meV. The evaluated electron-paramagnon coupling parameter is ${\ensuremath{\lambda}}_{em}\ensuremath{\sim}0.06$ for the ${\ensuremath{\Sigma}}_{1}$ band. We found that the magnitudes of ${\ensuremath{\lambda}}_{ep}$ and ${\ensuremath{\lambda}}_{em}$ depend on the Fermi surface points. The total effective mass enhancement factor is estimated to be $1+{\ensuremath{\lambda}}_{ep}+{\ensuremath{\lambda}}_{ee}+{\ensuremath{\lambda}}_{em}\ensuremath{\sim}1.5$ for the ${\ensuremath{\Sigma}}_{1}$ band, which is close to the values ${m}^{*}/{m}_{b}\ensuremath{\sim}1.5--1.7$ given by the de Haas--van Alphen and electron specific-heat measurements.

Cyclotron Resonance in Fe-based Superconductor KFe2As2

We report cyclotron resonance (CR) measurements for the Fe-based superconductor KFe2As2. Only one series of CR with an effective mass of 3.4me (me is the free electron mass) is observed. The CR signal is attributed to the quasi-two-dimensional α Fermi surface at the Γ point. Our main finding is that the effective mass obtained from the CR is significantly smaller than that obtained from the de-Haas van Alphen (dHvA) measurements. This is the direct evidence of the mass enhancement by electronic correlation. A comparison between the CR and dHvA measurements shows that both intra- and interband electronic correlations contribute to the mass enhancement in KFe2As2.

Using the de Haas–van Alphen Effect to Map Out the Closed Three-Dimensional Fermi Surface of Natural Graphite

The Fermi surface of graphite has been mapped out using de Haas-van Alphen (dHvA) measurements at low temperature with in-situ rotation. For tilt angles θ>60° between the magnetic field and the c axis, the majority electron and hole dHvA periods no longer follow a cos(θ) behavior demonstrating that graphite has a three-dimensional closed Fermi surface. The Fermi surface of graphite is accurately described by highly elongated ellipsoids. A comparison with the calculated Fermi surface suggests that the Slonczewski-Weiss-McClure trigonal warping parameter γ(3) is significantly larger than previously thought.

De Haas–van Alphen Effect and Fermi Surface Properties in V5Si3

We succeeded in growing high-quality single crystals of V 5 Si 3 with a high melting point of 2010 °C, and carried out the electrical resistivity, specific heat, magnetic susceptibility, and the de Haas–van Alphen measurements to clarify the electronic properties. The Fermi surface is small in volume and is well explained by the result of energy band calculations. The cyclotron mass is in the range from 5.3 to 0.2 m 0 ( m 0 : rest mass of an electron), consistent with the electronic specific heat coefficient γ= 9.7 mJ/(K 2 ·mol).

Numerical extraction of de Haas–van Alphen frequencies from calculated band energies

A new algorithm for extracting de Haas–van Alphen frequencies and effective masses from calculated band energies is presented. The algorithm creates an interpolated k-space “super cell,” which is broken into slices perpendicular to the desired magnetic field direction. Fermi surface orbits are located within each slice, and de Haas–van Alphen frequencies and effective masses are calculated. Orbits are then matched across slices, and extremal orbits determined. This technique has been successful in locating extremal orbits not previously noticed in the complicated topology of existing UPt 3 band-structure data; these new orbits agree with experimental de Haas–van Alphen measurements on this material, and solidify the case for a fully-itinerant model of UPt 3.

Spin Density Wave Ordering in CeIrSi3

Pressure induced superconductivity discovered in CeRhSi3 and CeIrSi3 has attracted much attention due to their being heavy fermion superconductors without inversion symmetry. It is also pointed out that both of them lie close to the quantum critical point, and interestingly Ce 4f electrons are itinerant even in their antiferromagnetic phase in sharp contrast to CeRhIn5 in which Ce 4f electrons are localized in the antiferromagnetic phase. The itinerant character of the Ce 4f electron in CeRhSi3 was pointed out by de Haas–van Alphen (dHvA) measurements. When Ce 4f electrons are localized, the Fermi surfaces (FSs) in CeRhSi3 will be very similar to those in LaRhSi3. On the other hand, the observed dHvA frequencies and then FSs in CeRhSi3 are totally different to those in LaRhSi3, and these results are interpreted as a strong indication of the itinerant character of Ce 4f electrons in CeRhSi3. The angle-resolved photoemission study in CeIrSi3 indicates that the Ce 4f electrons in CeIrSi3 are also itinerant. The observed FSs in CeIrSi3 are substantially larger than those in LaIrSi3 and they contact each other at Brillouin zone boundaries. The ground states of Ce ions in CeIrSi3 and CeRhSi3 are determined to be 7 doublets through the susceptibility studies, and their magnetic moments order antiferromagnetically at low temperatures. A neutron diffraction study of those magnetic structures may provide important information on the possible itinerant character of Ce 4f electrons in CeIrSi3 and CeRhSi3. The magnetic structure of CeRhSi3 was determined by our previous study. CeRhSi3 shows an antiferromagnetic phase below TN 1⁄4 1:6K with the magnetic moment of ord 1⁄4 0:13 B/Ce. The magnetic moments lie in the c plane and form a longitudinal spin-density wave with a propagation vector 1⁄4 ð0:215; 0; 1=2Þ, being consistent with a picture that the Ce 4f electrons are itinerant. Recently, we also succeeded in observing magnetic peaks in CeIrSi3 by neutron diffraction. The magnetic peaks appear below TN 1⁄4 5:0K at Q 1⁄4 G 1 and at Q 1⁄4 G 2 with 1 1⁄4 ð0:265; 0; 0:43Þ and 2 1⁄4 ð 0:265; 0; 0:43Þ, and G denotes the fundamental reciprocal vector for the BaNiSn3-type structure. In contrast to the magnetic structure of CeRhSi3, the observed magnetic structure is incommensurate both along the a and c directions. The single crystal sample used in the present study was grown by Czochralsky pulling method in a tetra-arc furnace at Tohoku university. The X-ray powder diffraction measurements at room temperature confirmed only the Bragg peak lines expected for the BaNiSn3-type structure. The size of the crystal was 3mm in diameter and 35mm long whose weight was 1.1 g. Neutron diffraction measurements were carried out with the GPTAS triple-axis spectrometer installed at 4G in the JRR-3 research reactor at Japan Atomic Energy Agency. The incident momentum of ki 1⁄4 3:83 A 1 was adopted to avoid large absorption of Ir atoms with a set of collimators of 400-800-400. To reduce the higher order contaminations, two PG filters were utilized. The one was placed at the position before the monochromator and the other just before the analyzer. The crystal was mounted to the He gas closed cycle refrigerator whose base temperature is 0.75K, and it was aligned with the (0 1 0) axis vertical so that the (h0l) zone can be observed. The lattice parameters at 1 K was a 1⁄4 1:487 A , and c 1⁄4 0:642 A . The (h0l) reciprocal plane in CeIrSi3 is shown in Fig. 1 in which the fundamental reflections for the BaNiSn3-type structure are denoted by open circles, while observed magnetic satellites are denoted by yellow filled circles (for the propagation vector 1) and star-shape blue symbols (for the propagation vector 2). The dashed circles indicate the position at which the aluminum powder lines are observed. In order to find the magnetic peaks in CeIrSi3, we carried out a two-dimensional survey scans around the Q 1⁄4 ð0:215; 0; 2:5Þ at which the magnetic peak was observed in CeRhSi3. The scans were carried out for the range with h: 0.10–0.30 and l: 2.34–2.48 which is indicated by a gray hatch in Fig. 1, and the observed intensity distribution is depicted as a contour map in Fig. 2. We discovered a weak peak at Q 1⁄4 ð0:265; 0; 2:43Þ. We noted that the peak is actually a single peak and dips of intensity around Q 1⁄4 Magnetic Bragg Nuclear Bragg 111 200 ( h 0 l ) zone CeIrSi3

LDA+DMFTspectral functions and effective electron mass enhancement in the superconductor LaFePO

In this Letter we report the first LDA+DMFT results (method combining Local Density Approximation with Dynamical Mean-Field Theory) for spectral properties of superconductor LaFePO. Calculated {\bf k}-resolved spectral functions reproduce recent angle-resolved photoemission spectroscopy (ARPES) data [D. H. Lu {\it et al}., Nature {\bf 455}, 81 (2008)]. Obtained effective electron mass enhancement values $m^{*}/m\approx$ 1.9 -- 2.2 are in good agreement with infrared and optical studies [M. M. Qazilbash {\it et al}., Nature Phys. {\bf 5}, 647 (2009)], de Haas--van Alphen, electrical resistivity, and electronic specific heat measurements results, that unambiguously evidence for moderate correlations strength in LaFePO. Similar values of $m^{*}/m$ were found in the other Fe-based superconductors with substantially different superconducting transition temperatures. Thus, the dynamical correlation effects are essential in the Fe-based superconductors, but the strength of electronic correlations does not determine the value of superconducting transition temperature.

Fermi Surface and Mass Enhancement in KFe2As2 from de Haas–van Alphen Effect Measurements

We report on a band structure calculation and de Haas–van Alphen measurements of KFe 2 As 2 . Three cylindrical Fermi surfaces are found. Effective masses of electrons range from 6 to 18 m e , m e being the free electron mass. Remarkable discrepancies between the calculated and observed Fermi surface areas and the large mass enhancement (\({\gtrsim}3\)) highlight the importance of electronic correlations in determining the electronic structures of iron pnicitide superconductors.

Fermi surface ofα-uranium at ambient pressure

We have performed de Haas--van Alphen measurements of the Fermi surface of $\ensuremath{\alpha}$-uranium single crystals at ambient pressure within the ${\ensuremath{\alpha}}_{3}$ charge-density wave (CDW) state from 0.020--10 K and magnetic fields to 35 T using torque magnetometry. The angular dependence of the resulting frequencies and the effective masses were measured. The observation of quantum oscillations within the ${\ensuremath{\alpha}}_{3}$ CDW state gives insight into the effect of the charge-density waves on the Fermi surface. We observed no signature of superconductivity in either transport or magnetization down to 0.020 K at ambient pressure.

Fermi surface ofMoO2studied by angle-resolved photoemission spectroscopy, de Haas–van Alphen measurements, and electronic structure calculations

A comprehensive study of the electronic properties of monoclinic ${\text{MoO}}_{2}$ from both an experimental and a theoretical point of view is presented. We focus on the investigation of the Fermi body and the band structure using angle-resolved photoemission spectroscopy, de Haas--van Alphen measurements, and electronic structure calculations. For the latter, the full-potential augmented spherical wave method has been applied. Very good agreement between the experimental and theoretical results is found. In particular, all Fermi surface sheets are correctly identified by all three approaches. Previous controversies concerning additional holelike surfaces centered around the $Z$ and $B$ points could be resolved; these surfaces were artifacts of the atomic-sphere approximation used in the old calculations. Our results underline the importance of electronic structure calculations for the understanding of ${\text{MoO}}_{2}$ and the neighboring rutile-type early transition-metal dioxides. This includes the low-temperature insulating phases of ${\text{VO}}_{2}$ and ${\text{NbO}}_{2}$, which have crystal structures very similar to that of molybdenum dioxide and display the well-known prominent metal-insulator transitions.

Magnetic-Field Dependence of theYbRh2Si2Fermi Surface

Magnetic-field-induced changes of the Fermi surface play a central role in theories of the exotic quantum criticality of ${\mathrm{YbRh}}_{2}{\mathrm{Si}}_{2}$. We have carried out de Haas--van Alphen measurements in the magnetic-field range $8\text{ }\text{ }\mathrm{T}\ensuremath{\le}H\ensuremath{\le}16\text{ }\text{ }\mathrm{T}$, and directly observe field dependence of the extremal Fermi surface areas. Our data support the theory that a low-field ``large'' Fermi surface, including the Yb $4f$ quasihole, is increasingly spin split until a majority-spin branch undergoes a Lifshitz transition and disappears at ${H}_{0}\ensuremath{\approx}10\text{ }\text{ }\mathrm{T}$, without requiring $4f$ localization at ${H}_{0}$.