Analysis Of Quantum Oscillations Research Articles

Enhancement of 2D topological semimetal transport properties by current annealing

Observation of intrinsic quantum transport properties of two-dimensional (2D) topological semimetals can be challenging due to suppression of high mobility caused by extrinsic factors introduced during fabrication. We demonstrate current annealing as a method to substantially improve electronic transport properties of 2D topological semimetal flakes. Contact resistance and resistivity were improved by factors up to 2×106 and 2×104, respectively, in devices based on exfoliated flakes of two topological semimetals, ZrSiSe and BaMnSb2. Using this method, carrier mobility in ZrSiSe was improved by a factor of 3800, resulting in observation of record-high mobility for exfoliated ZrSiSe. Quantum oscillations in annealed ZrSiSe appeared at magnetic fields as low as 5 T, and magnetoresistance increased by a factor of 104. We argue that a thermal process underlies this improvement. Finally, Raman spectroscopy and analysis of quantum oscillations in ZrSiSe indicate that the phonon modes and Fermi surface area are unchanged by current annealing.

Crystal growth and quantum oscillations in the topological chiral semimetal CoSi

We survey the electrical transport properties of the single-crystalline, topological chiral semimetal CoSi which was grown via different methods. High-quality CoSi single crystals were found in the growth from tellurium solution. The sample's high carrier mobility enables us to observe, for the first time, quantum oscillations (QOs) in its thermoelectrical signals. Our analysis of QOs reveals two spherical Fermi surfaces around the R point in the Brillouin zone corner. The extracted Berry phases of these electron orbits are consistent with the -2 chiral charge as reported in DFT calculations. Detailed analysis on the QOs reveals that the spin-orbit coupling induced band-splitting is less than 2 meV near the Fermi level, one order of magnitude smaller than our DFT calculation result. We also report the phonon-drag induced large Nernst effect in CoSi at intermediate temperatures.

Cyclotron resonance and the de Haas-van Alfven effect in the (BEDT-TTF)8Hg4Cl12(C6H5Cl)2 organic conductor

This paper reports on measurements of the de Haas-van Alfven effect in the quasi-two-dimensional organic conductor (BEDT-TTF)8Hg4Cl12(C6H5Cl)2 performed within the temperature range 0.33–1.44 K in magnetic fields of B≤50 T. An analysis of quantum oscillations together with cyclotron resonance data obtained in the 40–120-GHz frequency range revealed that the complex quantum-oscillation spectrum is formed by the fundamental frequencies α∼256 T and β∼670–610 T, as well as by combination and multiple frequencies. It is shown that the character of the temperature-induced oscillation-spectrum rearrangement can be interpreted within a model taking into account the existence of a magnetic phase transition at Tc∼0.9 K and the closeness of the fundamental frequency α with effective mass m*=1.48m0 to the spin damping condition.

Migration of Si IN δ-doped GaAs and Al xGa 1 − x As: Effect of substrate temperature

We have investigated the effect of substrate temperature, T S, during growth by molecular beam epitaxy on the migration of Si atoms in δ- (or planar) doped GaAs and Al 0.25Ga 0.75As. Determinations of the extent of Si migration were made through analysis of quantum oscillations in the magnetoresistance and independently by using secondary ion mass spectroscopy (SIMS). Analysis of magnetotransport data in δ-doped GaAs samples indicates that there is negligible spread in structures grown at T S⩽530 °C, while in structures grown at higher T S there is a measurable spread which increases with T S. For T S=640 °C, the Si spread is determ be = 180 Å. A similar analysis performed on the magnetoresistance of δ-doped Al 0.25Ga 0.75As samples reveals that the Si spreads further in Al 0.25Ga 0.75As than in GaAs (for a comparable T S). SIMS measurements performed on the same structures confirm these findings.

Power Spectrum Analysis of Quantum Oscillations of the Velocity of Sound in Antimony

By the power spectrum analysis of the quantum oscillations of the sound velocity in antimony, the geometrical factors G of the energy surfaces were studied. For holes it was found that G is ellipsoidal for the light mass directions. The coupling constants of holes with the sound wave were determined from the peak values of the power spectrum as follows: | C x d | 2 =20.0 ±1.0, | C x f | 2 =1.6 ±0.3, | C y d | 2 =5.65 ±0.30, | C y f | 2 =5.95 ±0.40 and | C z d | 2 =0.55 ±0.05 eV 2 . It was also found that for electrons G differs from the ellipsoid. The coupling constants were determined under the assumption that the densities of states of electrons and holes at zero magnetic field are given by the ellipsoidal models. The results are: | C x a | 2 =18.2 ±3.6, | C x b | 2 =8.66 ±1.7, | C y a | 2 =22.6 ±5.0, | C y b | 2 =2.78 ±0.55 and | C z a | 2 =0.475 ±0.043 eV 2 .

Quantum oscillations in the ultrasonic absorption in p-type PbSe

Analysis of quantum oscillations in the ultrasonic absorption in p-type PbSe indicates that the carriers are located in four equivalent 〈111〉 “ellipsoids”. At high carrier concentrations each “ellipsoid” appears to be compressed along its major axis.