Quantum Oscillation Studies Research Articles

Numerical study of quantum oscillations of quasiparticle lifetime: Impurity spectroscopy and electric field and strain effects

Numerical study of quantum oscillations of quasiparticle lifetime: Impurity spectroscopy and electric field and strain effects

Comparative study of magnetic quantum oscillations in Hall and transverse magnetoresistance

Comparative study of magnetic quantum oscillations in Hall and transverse magnetoresistance

Experimental Detection of Topological Electronic State and Large Linear Magnetoresistance in SrSn4 Superconductor

AbstractWhile recent experiments confirm the existence of hundreds of topological electronic materials, only a few exhibit the coexistence of superconductivity (SC) and a topological electronic state. These compounds attract significant attention in forefront research because of the potential for the existence of topological SC, paving the way for future technological advancements. SrSn4 is known for exhibiting unusual SC below the transition temperature (TC) of 4.8 K. Recent theory predicts a topological electronic state in this compound, which is yet to be confirmed by experiments. Systematic and detailed studies of the magnetotransport properties of SrSn4 and its Fermi surface characterizations are also absent. For the first time, a quantum oscillation study reveals a nontrivial 𝝅‐Berry phase, very light effective mass, and high quantum mobility of charge carriers in SrSn4. Magnetotransport experiment unveils large linear transverse magnetoresistance (TMR) of more than 1200% at 5 K and 14 T. Angle‐dependent transport experiments detect anisotropic and fourfold symmetric TMR, with the maximum value (≈2000%) occurring when the angle between the magnetic field and the crystallographic b‐axis is 45°. The results suggest that SrSn4 is the first topological material with SC above the boiling point of helium that displays such high magnetoresistance.

Large Fermi surface in pristine kagome metal CsV3Sb5 and enhanced quasiparticle effective masses

The kagome metal CsV[Formula: see text]Sb[Formula: see text] is an ideal platform to study the interplay between topology and electron correlation. To understand the fermiology of CsV[Formula: see text]Sb[Formula: see text], intensive quantum oscillation (QO) studies at ambient pressure have been conducted. However, due to the Fermi surface reconstruction by the complicated charge density wave (CDW) order, the QO spectrum is exceedingly complex, hindering a complete understanding of the fermiology. Here, we directly map the Fermi surface of the pristine CsV[Formula: see text]Sb[Formula: see text] by measuring Shubnikov-de Haas QOs up to 29 T under pressure, where the CDW order is completely suppressed. The QO spectrum of the pristine CsV[Formula: see text]Sb[Formula: see text] is significantly simpler than the one in the CDW phase, and the detected oscillation frequencies agree well with our density functional theory calculations. In particular, a frequency as large as 8,200 T is detected. Pressure-dependent QO studies further reveal a weak but noticeable enhancement of the quasiparticle effective masses on approaching the critical pressure where the CDW order disappears, hinting at the presence of quantum fluctuations. Our high-pressure QO results reveal the large, unreconstructed Fermi surface of CsV[Formula: see text]Sb[Formula: see text], paving the way to understanding the parent state of this intriguing metal in which the electrons can be organized into different ordered states.

Interplay of Landau Quantization and Interminivalley Scatterings in a Weakly Coupled Moiré Superlattice.

Double-layer quantum systems are promising platforms for realizing novel quantum phases. Here, we report a study of quantum oscillations (QOs) in a weakly coupled double-layer system composed of a large-angle twisted-double-bilayer graphene (TDBG). We quantify the interlayer coupling strength by measuring the interlayer capacitance from the QOs pattern at low temperatures, revealing electron-hole asymmetry. At high temperatures when SdHOs are thermally smeared, we observe resistance peaks when Landau levels (LLs) from two moiré minivalleys are aligned, regardless of carrier density; eventually, it results in a 2-fold increase of oscillating frequency in D, serving as compelling evidence of the magneto-intersub-band oscillations (MISOs) in double-layer systems. The temperature dependence of MISOs suggests that electron-electron interactions play a crucial role and the scattering times obtained from MISO thermal damping are correlated with the interlayer coupling strength. Our study reveals intriguing interplays among Landau quantization, moiré band structure, and scatterings.

Unveiling the double-peak structure of quantum oscillations in the specific heat

Quantum oscillation phenomenon is an essential tool to understand the electronic structure of quantum matter. Here we report a systematic study of quantum oscillations in the electronic specific heat Cel in natural graphite. We show that the crossing of a single spin Landau level and the Fermi energy give rise to a double-peak structure, in striking contrast to the single peak expected from Lifshitz-Kosevich theory. Intriguingly, the double-peak structure is predicted by the kernel term for Cel/T in the free electron theory. The Cel/T represents a spectroscopic tuning fork of width 4.8kBT which can be tuned at will to resonance. Using a coincidence method, the double-peak structure can be used to accurately determine the Landé g-factors of quantum materials. More generally, the tuning fork can be used to reveal any peak in fermionic density of states tuned by magnetic field, such as Lifshitz transition in heavy-fermion compounds.

Correlation induced instability in topological nodal-line semimetal ZrSiS

Quantum phase transition hosts a quantum criticality around which the collective low-energy excitations are governed by quantum fluctuations. At this quantum critical regime, fluctuations alter the quasiparticle characteristics introducing some instabilities in the system. The experimental signatures of quantum criticality in topological Dirac materials are sparse. Here, we report the transport studies on nodal line semimetal ZrSiS, which is predicted to own excitonic instability at quantum criticality. Our quantum oscillation studies demonstrate a significant change in Berry phase at higher magnetic fields revealing a field-induced gap modification at the nodal line. Notably, the quasiparticle effective mass executes unique field-dependent oscillations, which is unexplainable from present theories. The temperature dependent oscillation amplitude dramatically departs from conventional Lifshitz–Kosevich theory. These unusual phenomena along with a zero field resistivity upturn collectively suggest the possibility of ZrSiS lying at the excitonic instability. Our findings will engender the systematic exploration of correlation induced phenomenon in topological materials.

Ab initio electronic structure of metallized NiS2 in the noncollinear magnetic phase

We investigate the electronic structure of the archetypical Mott insulator ${\mathrm{NiS}}_{2}$ by means of density functional theory calculations in which we explicitly account for the noncollinear antiferromagnetic order, as recently established in the isoelectronic analog $\mathrm{Ni}{(\mathrm{S},\mathrm{Se})}_{2}$. For metallic ${\mathrm{NiS}}_{2}$ under high pressures, our calculations predict a Fermi surface topology and volume which are in excellent agreement with recent quantum oscillation studies. However, we find that density functional theory wrongly predicts a metallic ground state even at ambient pressures, similar to previous nonmagnetic or collinear antiferromagnetic models. By including a Hubbard interaction $U$ and an on-site exchange interaction $J$, the metallic phase is suppressed, but even such an extended model fails to describe the nature of the metal-to-insulating phase transition and describes the insulating phase itself incorrectly. These results highlight the importance of more sophisticated computational approaches even deep in the insulating phase, far away from the Mott insulating phase transition.

Field-induced quasi-particle tunneling in the nodal-line semimetal HfSiS revealed by de Haas-van Alphen quantum oscillations

We present a de Haas--van Alphen quantum oscillation study of the Dirac nodal-line semimetal HfSiS up to 32 T to unravel the structure of the high-frequency magnetic breakdown spectrum that was previously obscured in transport experiments. Despite a threefold enhanced gap between adjacent electron and hole pockets relative to the sister compound ZrSiS, a large number of large-area magnetic breakdown orbits enclosing the nodal-loop are identified. All breakdown orbits are assigned by extracting their cyclotron masses. Moreover, one additional low-frequency magnetic breakdown orbit, previously absent in ZrSiS, is observed and attributed to the larger spin-orbit interaction in HfSiS.

Extremely High magnetoresistance and quantum Oscillation study of WTe2 Weyl Semimetal

Single crystals of WTe2 have been prepared using the flux method. Analysis of the x-ray diffraction pattern shows the pure phase of the sample. Temperature dependent resistivity indicates the metallic nature of the sample. The residual resistance ratio of the sample has been found very high providing further evidence of the good quality of the crystals. Extremely high magnetoresistance has been observed in the sample. Quantum oscillations have been seen at high field. Fast Fourier transformation of the quantum oscillations shows nearly the same size of the electron and hole pocket in the sample.

Anomalous charge transport of superconducting CuxPdTe2 under high pressure

By means of high-pressure resistivity measurements on single crystals, we investigate the charge transport properties of Cu$_x$PdTe$_2$, notable for the combination of topological type-II Dirac semimetallic properties with superconductivity up to $T_c = 2.5$ K. In both cases of pristine ($x = 0$) and intercalated ($x=0.05$) samples, we find an unconventional $T^4$ power law behavior of the low-temperature resistivity visible up to $\sim$40 K and remarkably stable under pressure up to 8.2 GPa. This observation is explained by the low carrier density $n$, which strongly reduces the $k$-region available for electron-phonon scattering, as previously reported in other low-$n$ two-dimensional systems, such as multilayer graphene and semiconductor heterostructures. Our data analysis complemented by specific heat measurements and supported by previous quantum oscillation studies and \textit{ab initio} calculations suggests a scenario of one-band charge transport. Within this scenario, our analysis yields a large value of transport electron-phonon coupling constant $\lambda_{tr} = 1.2$ at ambient pressure that appears to be strongly enhanced by pressure assuming a constant effective mass.

Fermi surfaces of the topological semimetal CaSn3 probed through de Haas van Alphen oscillations

In the search of topological superconductors, nailing down the Fermiology of the normal state is as crucial a prerequisite as unraveling the superconducting pairing symmetry. In particular, the number of time-reversal-invariant momenta (TRIM) in the Brillouin zone enclosed by Fermi surfaces is closely linked to the topological class of time-reversal-invariant systems, and can experimentally be investigated. We report here a detailed study of de Haas van Alphen quantum oscillations in single crystals of the topological semimetal CaSn3 with torque magnetometry in high magnetic fields up to 35 T. In conjunction with density functional theory based calculations, the observed quantum oscillations frequencies indicate that the Fermi surfaces of CaSn3 enclose an odd number of TRIM, satisfying one of the proposed criteria to realize topological superconductivity. Nonzero Berry phases extracted from the magnetic oscillations also support the nontrivial topological nature of CaSn3.

Quasi-two-dimensional relativistic fermions probed by de Haas–van Alphen quantum oscillations in LuSn2

We report de Haas--van Alphen (dHvA) quantum oscillation studies on a layered compound $\mathrm{Lu}{\mathrm{Sn}}_{2}$. Through the analyses of the dHvA oscillation data, we find this material has several 3D bands and one quasi-2D band hosting relativistic fermions. Compared to previously reported dHvA oscitations in $\mathrm{Y}{\mathrm{Sn}}_{2,}$, the oscillation component arising from the quasi-2D band is significantly enhanced. From structural analyses using single-crystal x-ray diffraction, we find the distorted Sn-square net layer is less corrugated than $\mathrm{Y}{\mathrm{Sn}}_{2,}$, which accounts for the enhancement of two dimensionality of the relativistic fermions created in this layer. This result suggests that the dimensionality of relativistic band in $\mathrm{RE}{\mathrm{Sn}}_{2}$ ($\mathrm{RE}=\mathrm{rare}$ earth) can be tuned by electronegativity of RE. Moreover, we also find the 3D relativistic bands are pushed closer to the Fermi level with respect to $\mathrm{Y}{\mathrm{Sn}}_{2,}$ due to enhanced spin-orbital coupling. These findings imply $\mathrm{RE}{\mathrm{Sn}}_{2}$ can be an interesting platform for seeking new topological states via the tuning of electronegativity, spin-orbital coupling, and magnetism.

Quantum oscillations of the magnetic torque in the nodal-line Dirac semimetal ZrSiS

We report a study of quantum oscillations (QO) in the magnetic torque of the nodal-line Dirac semimetal ZrSiS in the magnetic fields up to 35 T and the temperature range from 40 K down to 2 K, enabling high resolution mapping of the Fermi surface (FS) topology in the $k_z=\pi$ (Z-R-A) plane of the first Brillouin zone (FBZ). It is found that the oscillatory part of the measured magnetic torque signal consists of low frequency (LF) contributions (frequencies up to 1000 T) and high frequency (HF) contributions (several clusters of frequencies from 7-22 kT). Increased resolution and angle-resolved measurements allow us to show that the high oscillation frequencies originate from magnetic breakdown (MB) orbits involving clusters of individual $\alpha$ hole and $\beta$ electron pockets from the diamond shaped FS in the Z-R-A plane. Analyzing the HF oscillations we have unequivocally shown that the QO frequency from the dog-bone shaped Fermi pocket ($\beta$ pocket) amounts $\beta=591(15)$ T. Our findings suggest that most of the frequencies in the LF part of QO can also be explained by MB orbits when intraband tunneling in the dog-bone shaped $\beta$ electron pocket is taken into account. Our results give a new understanding of the novel properties of the FS of the nodal-line Dirac semimetal ZrSiS and sister compounds.

Intrinsic Bulk Quantum Oscillations in a Bulk Unconventional Insulator SmB6.

SummaryThe finding of bulk quantum oscillations in the Kondo insulator SmB6 proved a considerable surprise. Subsequent measurements of bulk quantum oscillations in other correlated insulators including YbB12 lent support to our discovery of a class of bulk unconventional insulators that host bulk quantum oscillations. Here we perform a series of experiments to examine evidence for the intrinsic character of bulk quantum oscillations in floating zone-grown single crystals of SmB6 that have been the subject of our quantum oscillation studies. We present results of thermodynamic, transport, and composition analysis experiments on pristine floating zone-grown single crystals of SmB6 and compare quantum oscillations with metallic LaB6 and elemental aluminum. These results establish the intrinsic origin of quantum oscillations from the insulating bulk of floating zone-grown SmB6. The similarity of the Fermi surface in insulating SmB6 with the conduction-electron Fermi surface in metallic hexaborides is at the heart of a theoretical mystery.

Magnetic breakdown and charge density wave formation: A quantum oscillation study of the rare-earth tritellurides

The authors explore the $R$Te${}_{3}$ family of materials as a clean model system in which to study a quantum phase transition between single and double charge density wave states. Quantum oscillation measurements reveal a significant reduction in the area of the Fermi surface across the quantum phase transition, but no obvious divergence of the electronic effective mass. Variation of the magnitude of the charge density wave gap across the rare-earth series leads to a particularly clear example of tunable magnetic breakdown.

Determination of the Fermi surface and field-induced quasiparticle tunneling around the Dirac nodal loop in ZrSiS

Unambiguous and complete determination of the Fermi surface is a primary step in understanding the electronic properties of topical metals and semi-metals, but only in a relatively few cases has this goal been realized. In this work, we present a systematic high-field quantum oscillation study up to 35 T on ZrSiS, a textbook example of a nodal-line semimetal with only linearly dispersive bands crossing the Fermi energy. The topology of the Fermi surface is determined with unprecedented precision and all pockets are identified by comparing the measured angle dependence of the quantum oscillations to density functional theory calculations. Comparison of the Shubnikov-de Haas and de Haas-van Alphen oscillations at low temperatures and analysis of the respective Dingle plots reveal the presence of significantly enhanced scattering on the electron pocket. Above a threshold field that is aligned along the c-axis of the crystal, the specific cage-like Fermi surface of ZrSiS allows for electron-hole tunneling to occur across finite gaps in momentum space leading to quantum oscillations with a complex frequency spectrum. Additional high-frequency quantum oscillations signify magnetic breakdown orbits that encircle the entire Dirac nodal loop. We suggest that the persistence of quantum oscillations in the resistivity to high temperatures is caused by Stark interference between orbits of nearly equal masses.

Fermi surface of PtCoO2 from quantum oscillations and electronic structure calculations

The delafossite series of layered oxides include some of the highest conductivity metals ever discovered. Of these, PtCoO2, with a room temperature resistivity of 1.8 microOhmcm for in-plane transport, is the most conducting of all. The high conduction takes place in triangular lattice Pt layers, separated by layers of Co-O octahedra, and the electronic structure is determined by the interplay of the two types of layer. We present a detailed study of quantum oscillations in PtCoO2, at temperatures down to 35 mK and magnetic fields up to 30 T. As for PdCoO2 and PdRhO2, the Fermi surface consists of a single cylinder with mainly Pt character, and an effective mass close to the free electron value. Due to Fermi-surface warping, two close-lying high frequencies are observed. Additionally, a pronounced difference frequency appears. By analysing the detailed angular dependence of the quantum-oscillation frequencies, we establish the warping parameters of the Fermi surface. We compare these results to the predictions of first-principles electronic structure calculations including spin-orbit coupling on Pt and Co and on-site correlation U on Co, and hence demonstrate that electronic correlations in the Co-O layers play an important role in determining characteristic features of the electronic structure of PtCoO2.

Fermi surface investigation of the semimetal TaAs2

The transversal magnetoresistance associated with the semimetal ${\mathrm{TaAs}}_{2}$ shows a parabolic field dependence that rises unrestrictedly to 2800 at 14 T and 1.8 K. Here, we report the results of a comprehensive quantum-oscillation study. Angular-dependent de Haas--van Alphen (dHvA) data were obtained with the method of cantilever-torque magnetometry. These were compared with the results of density-functional theory calculations, which predict a Fermi surface with two kinds of electron pockets, as well as two types of hole pockets. Only the electron pockets could be experimentally verified, whereas no evidence for the hole pockets is present in the measured dHvA frequencies.

Emergence of intrinsic superconductivity below 1.178 K in the topologically non-trivial semimetal state of CaSn3

Topological materials which are also superconducting are of great current interest, since they may exhibit a non-trivial topologically-mediated superconducting phase. Although there have been many reports of pressure-tuned or chemical-doping-induced superconductivity in a variety of topological materials, there have been few examples of intrinsic, ambient pressure superconductivity in a topological system having a stoichiometric composition. Here, we report that the pure intermetallic CaSn3 not only exhibits topological fermion properties, but also has a superconducting phase at ~1.178 K under ambient pressure. The topological fermion properties, including the nearly zero quasi-particle mass and the non-trivial Berry phase accumulated in cyclotron motions, were revealed from the de Haas–van Alphen (dHvA) quantum oscillation studies of this material. Although CaSn3 was previously reported to be superconducting with Tc = 4.2 K, our studies show that the Tc = 4.2 K superconductivity is extrinsic and caused by Sn on the degraded surface, whereas its intrinsic bulk superconducting transition occurs at 1.178 K. These findings make CaSn3 a promising candidate for exploring new exotic states arising from the interplay between non-trivial band topology and superconductivity, e.g. topological superconductivity (TSC).