Cyclotron Effective Mass Research Articles

Characteristic Heavy Fermion Properties in YbCu2Si2and YbT2Zn20(T: Co, Rh, Ir)

We studied the Fermi surface properties of YbCu 2 Si 2 and YbCu 2 Ge 2 with the tetragonal structure by measuring the de Haas–van Alphen (dHvA) oscillations, together with the energy band calculations. It was clarified that 4 f electrons contribute to the Fermi surface of a valence fluctuating compound YbCu 2 Si 2 , but not to that of a divalent compound YbCu 2 Ge 2 . Namely, the Fermi surface of YbCu 2 Si 2 contains the 4 f -components considerably and the corresponding cyclotron effective mass m c * of the main Fermi surface is large, m c * =30–40 m 0 ( m 0 : rest mass of an electron). We also studied the heavy fermion properties of YbT 2 Zn 20 (T: Co, Rh, Ir) with the cubic caged structure. The metamagnetic behavior or an abrupt nonlinear increase of magnetization was observed at 6 kOe in YbCo 2 Zn 20 , 63 kOe in YbRh 2 Zn 20 , and 97 kOe in YbIr 2 Zn 20 for H ∥ , which was measured at 60 mK in YbCo 2 Zn 20 and 1.3 K in YbRh 2 Zn 20 and YbIr 2 Zn 20 . The metamagnetic field is found to be a good pa...

De Haas-van Alphen effect in SmOs4P12

We have succeeded in growing single crystals of SmOs4P12 and measured the de Haas-van Alphen effect. An almost spherical Fermi surface, whose cyclotron effective masses are ranging 2.0-2.3 m0, has been observed.

Relation between Metamagnetic Transition and Quantum Critical Point in Heavy Fermion Compound YbIr2Zn20

We measured the electrical resistivity in magnetic field H under pressure P for a heavy fermion compound YbIr2Zn20. The quantum critical point is found to be defined as an electronic state where the metamagnetic transition field Hm becomes zero. This is realized at Pc ≊ 5.2 GPa. The most characteristic feature in the quantum critical pressure region is an anomalously large A value of the electrical resistivity p = p0 + AT2, reaching A = 380μΩ·cm/K2 at 5.0 GPa, which is, however, strongly reduced with increasing the magnetic field: A = 1.45μΩ·cm/K2 at 80 kOe. From the result of the de Haas-van Alphen experiment at ambient pressure, the corresponding cyclotron effective mass of conduction electrons at 5.0 GPa is 400 – 500 m0 (m0: rest mass of an electron).

Fermi surface of the electron-doped cuprate superconductor Nd2−xCexCuO4 probed by high-field magnetotransport

We report on the study of the Fermi surface of the electron-doped cuprate superconductor Nd2−xCexCuO4 by measuring the interlayer magnetoresistance as a function of the strength and orientation of the applied magnetic field. We performed experiments in both steady and pulsed magnetic fields on high-quality single crystals with Ce concentrations of x=0.13–0.17. In the overdoped regime of x>0.15, we found both semiclassical angle-dependent magnetoresistance oscillations (AMROs) and Shubnikov–de Haas (SdH) oscillations. The combined AMROs and SdH data clearly show that the appearance of fast SdH oscillations in strongly overdoped samples is caused by magnetic breakdown. This observation provides clear evidence for a reconstructed multiply connected Fermi surface up to the very end of the overdoped regime at x≃0.17. The strength of the superlattice potential responsible for the reconstructed Fermi surface is found to decrease with increasing doping level and likely vanishes at the same carrier concentration as superconductivity, suggesting a close relation between translational symmetry breaking and superconducting pairing. A detailed analysis of the high-resolution SdH data allowed us to determine the effective cyclotron mass and Dingle temperature, as well as to estimate the magnetic breakdown field in the overdoped regime.

Terahertz spectroscopy of quantum-well narrow-bandgap HgTe/CdTe-based heterostructures

The energy spectra of quantum-well narrow-bandgap Hg1 − y Cd y Te/Cd x Hg1 − x Te heterostructures have been studied. The dependences of the effective cyclotron mass on the density (in classical magnetic fields) and the transition energy (in quantizing fields) have been obtained from the cyclotron resonance measurements. These dependences confirm the near-linear dispersion law for the electrons with small mass at the band bottom (the minimum cyclotron mass measured is 0.003 m 0). The interband photoconductivity of the CdHgTe-based structures with the long-wavelength photoresponse edge lower than 6 meV has been demonstrated.

Fermi Surface Properties of Ferromagnet UCu2Si2

We have succeeded in growing a high-quality single crystal of UCu 2 Si 2 with a tetragonal structure by the Sn-flux method and measured the de Haas–van Alphen effect. UCu 2 Si 2 orders antiferromagnetically below T N =106 K and follows a successive ferromagnetic ordering at T C =100 K. Several de Haas–van Alphen branches are observed in the ferromagnetic state, ranging from 5×10 6 to 7×10 7 Oe. The corresponding cyclotron effective masses are moderately large, ranging from 1.4 to 4.2 m 0 , consistent with the electronic specific heat coefficient γ=20 mJ/(K 2 ·mol). These experimental results are approximately explained by the 5 f -itinerant spin- and orbital-polarized energy band model.

Quasiclassical cyclotron resonance of Dirac fermions in highly doped graphene

Cyclotron resonance in highly doped graphene has been explored using infrared magnetotransmission. Contrary to previous work, which only focused on the magneto-optical properties of graphene in the quantum regime, here we study the quasi-classical response of this system. We show that it has a character of classical cyclotron resonance, with an energy which is linear in the applied magnetic field and with an effective cyclotron mass defined by the position of the Fermi level m = E_F/v_F^2.

Strong Field Quenching of the Quasiparticle Effective Mass in Heavy Fermion Compound YbCo2Zn20

We found a metamagnetic like anomaly at H m ≃5 kOe in a heavy fermion compound YbCo 2 Zn 20 below the characteristic temperature T χ max =0.32 K where the ac-susceptibility shows a broad peak, suggesting that an electronic state with a very low Kondo temperature is realized. Interestingly, the metamagnetic like behavior was observed as two peaks at 4.0 and 7.5 kOe at 95 mK in the magnetic field dependence of the electronic specific heat C / T . The extremely large values of the electronic specific heat coefficient γ≃8000 mJ/(K 2 ·mol) and A =160 µΩ·cm/K 2 in the electrical resistivity ρ=ρ 0 + A T 2 at H =0 kOe are most likely due to the very low Kondo temperature. The \(\sqrt{A}\) value was, however, found to be strongly reduced from \(\sqrt{A}=12.6\) (µΩ·cm/K 2 ) 1/2 at 0 kOe to 0.145 (µΩ·cm/K 2 ) 1/2 at 150 kOe. Therefore, we considered that the corresponding cyclotron effective mass m c * , which was determined from the temperature dependence of the de Haas–van Alphen (dHvA) amplitude, is also reduced ...

Metamagnetic Behavior in Heavy-Fermion Compound YbIr2Zn20

The metamagnetic behavior in the heavy-fermion compound YbIr 2 Zn 20 with a cubic structure was studied by magnetization, de Haas–van Alphen (dHvA) oscillation, magnetoresistance, specific heat, thermal expansion, and magnetostriction measurements in single-crystalline samples. A metamagnetic anomaly at H m ≃100 kOe was found to exist in all field directions in the cubic crystal structure. The cyclotron effective mass m c * , the coefficient A in the Fermi liquid relation of electrical resistivity ρ=ρ 0 + A T 2 , and the electronic specific heat coefficient C / T indicate a peak at the metamagnetic field H m . The negative thermal expansion and negative volume magnetostriction suggest that the valence of the Yb ion gradually changes from a 4 f -itinerant state to a trivalent state with increasing magnetic field, and an almost trivalent state is realized above the metamagnetic field H m . On the other hand, the topology of the Fermi surface is approximately unchanged below and above H m in the dHvA experiment.

Magneto-optics of InAs/GaSb superlattices

We investigate the optical and electrical properties of a series of InAs/GaSb superlattices (SLs) as a function of InAs layer width d, from 21 to 55 Å, with a fixed GaSb layer width of 24 Å, corresponding to SLs with the cutoff wavelengths between 4 and 19 μm. Since the higher electron mass in InAs/GaSb SLs than in mercury cadmium telluride should lead to lower photodiode tunneling currents, we also measured the cyclotron effective mass for a very long wavelength infrared design SLs. For d<40 Å, the SLs were p-type, with hole mobilities of approximately 8 000 cm2/V s. For a high mobility p-type sample no hole cyclotron resonance signal was detected. However, the SLs with d≥40 Å were n-type, with electron mobilities increasing from 865 to 6126 cm2/V s. Cyclotron resonance data on an n-type SL sample yielded an electron cyclotron mass of 0.068 m0, which is three times the InAs bulk value of 0.023 m0. The mass enhancement was only partially accounted for by conduction band nonparabolicity, based on our 8×8 envelope function calculation.

5f-electronic states of neptunium compounds: NpGe3, NpRhGa5 and NpCd11

We studied the electronic states of three typical neptunium compounds, NpGe3, NpRhGa5 and NpCd11. Among them, NpGe3 and NpCd11 with the cubic crystal structure are paramagnets without magnetic ordering, while NpRhGa5 with the tetragonal structure is an antiferromagnet. At high temperatures, the 5f electrons in NpGe3 are almost localized, and the magnetic susceptibility χ(T) approximately follows the Curie-Weiss law. With decreasing temperature, χ(T) shows a broad peak around 50 K, indicating a moderate heavy fermion state at lower temperatures. In fact, the results of the de Haas-van Alphen (dHvA) experiments for NpGe3 are well explained by the 5f-itinerant band model; namely, the 5f electrons contribute to the Fermi surface and the cyclotron effective mass. The cyclotron mass is thus enhanced, ranging from 2.6 to 16 times the rest mass of the electron m0. In the antiferromagnet NpRhGa5, it was clarified from the results of dHvA experiments and energy band calculations that the 5f electrons contribute to the Fermi surface. The cyclotron mass varies from 8.1 to 11.7 m0, and the magnetic moment is 0.89 μB/Np. In NpCd11, the 5f electrons are localized in the whole temperature range and do not contribute to the Fermi surface. The corresponding cyclotron mass is thus light, below 1 m0, revealing no hybridization between the localized 5f electrons and the conduction electrons. The Fermi surface consists of small closed Fermi surfaces, reflecting the small Brillouin zone associated to the large unit cell of the crystal structure in NpCd11. The long Np-Np nearest-neighbor distance (6.568 Å) results in the well localized 5f 4states. Magnetic susceptibility and magnetization curves are well explained in a crystalline electric field (CEF) scheme assuming a singlet ground state and an excited triplet state separated by a 120 K energy gap.

Fermi surface properties of paramagnetic NpCd11 with a large unit cell

We succeeded in growing a high-quality single crystal of NpCd11 with the cubic BaHg11-type structure by the Cd-self flux method. The lattice parameter of a = 9.2968(2) Å and crystallographic positions of the atoms were determined by x-ray single-crystal structure analysis. From the results of the magnetic susceptibility and specific heat experiments, this compound is found to be a 5f-localized paramagnet with the singlet ground state in the crystalline electric field (CEF) scheme. Fermi surface properties were measured using the de Haas-van Alphen (dHvA) technique. Long-period oscillations were observed in the dHvA frequency range of 9.1 x 105 to 1.9 x 107 Oe, indicating small cross-sectional areas of Fermi surfaces, which is consistent with a small Brillouin zone based on a large unit cell. From the results of dHvA and magnetoresistance experiments, the Fermi surface of NpCd11 is found to consist of many kinds of closed Fermi surfaces and a multiply-connected-like Fermi surface, although the result of energy band calculations based on the 5f-localized Np3+(5f4) configuration reveals the existence of only closed Fermi surfaces. The corresponding cyclotron effective mass is small, ranging from 0.1 to 0.7 m0, which is consistent with a small electronic specific heat coefficient γ ≅ 10mJ/K2·mol, revealing no hybridization between the 5f electrons and conduction electrons.

Fermi surface properties of YbCu2Si2

AbstractWe succeeded in growing high‐quality single crystals of a heavy electron compound YbCu2Si2. The electronic specific heat coefficient γ is determined to be 150 mJ/K2·mol, which is consistent with the A value of the electrical resistivity from Kadowaki–Woods relation. We succeeded in observing the de Haas‐van Alphen (dHvA) oscillations. The dHvA frequencies and large cyclotron effective masses in YbCu2Si2 are highly different from those in a non‐4f reference compound YCu2Si2. From these dHvA results, the heavy electron state of YbCu2Si2 is characterized by the large contribution of 4f‐electrons to the topology of the Fermi surface and also to the strong enhancement of effective mass caused by the spin fluctuations.

Electron cyclotron effective mass in indium nitride

We report on cyclotron effective mass measurement in indium nitride epilayers grown on c-sapphire, using the thermal damping of Shubnikov-de-Haas oscillations obtained in the temperature range 2–70 K and under magnetic field up to 60 T. We unravel an isotropic electron cyclotron effective mass equal to 0.062±0.002m0 for samples having electron concentration near 1018 cm−3. After nonparabolicity and polaron corrections we estimate a bare mass at the bottom of the band equal to 0.055±0.002m0.

Terahertz photoresponse of a quantum Hall edge-channel diode

The Teraherz (THz) photoresponse of a two-dimensional electron gas in the quantum Hall regime is investigated. We use a sample structure which is topologically equivalent to a Corbino geometry combined with a cross-gate technique. This quasi-Corbino geometry allows us to directly investigate the THz-induced transport between adjacent edge-states, thus avoiding bulk effects. We find a pronounced photo voltage at zero applied bias, which rapidly decreases when an external current bias is applied. The photo voltage and its dependence on the bias current can be described using the model of an illuminated photodiode, resulting from the reconstruction of the Landau bands at the sample edge. Using the sample as a detector in a Fourier transform spectrometer setup, we find a resonant response from which we extract a reduced effective cyclotron mass. The findings support a non-bolometric mechanism of the induced photo voltage and the proposed edge-channel diode model.

Application of Berry's phase to the effective mass of Bloch electrons

Berry's phase, although well known since 1984, has received little attention among textbook authors of solid state physics. We attempt to address this lack by showing how the presence of the Berry's phase significantly changes a standard concept (effective mass) found in most solid state texts. Specifically, we show that the presence of a non-zero Berry curvature in Bloch systems makes the traditional concept of an inverse effective mass tensor M−1 problematic, since a routine application of Newton's second law leads to a circular definition. As a consequence, the related concept of cyclotron effective mass m* also requires modification. It is shown that m* is magnetic-field dependent in non-inversion symmetric systems. This has important ramifications for cyclotron resonance experiments, since such experiments yield m* and thereby purportedly give the components of M−1. This work represents a ‘case study’ in how Berry's phase effects can modify ‘standard’ solid-state topics in ways that students and instructors may find surprising.

Shubnikov–de Haas effect in n-CdSb:In under pressure

Magnetoresistance (MR) of single crystals of the group II–V semiconductor n-CdSb doped with In is investigated in magnetic fields B up to 7 T and temperatures T between 1.2 and 2.4 K under hydrostatic pressure p = 0–10 kbar. Shubnikov–de Haas (SdH) oscillations of MR observed up to B ∼ 4 T are characterized by a single period, giving evidence for one participating group of conduction band electrons. Pressure dependence of the SdH period and concentration reveal a second group of charge carriers, connected to a resonance impurity band with delocalized states. The SdH amplitude, A, exhibits non-universal behavior attributable to its sensitivity to scattering mechanism at low quantum numbers. The parameters characterizing the non-universality of A(T) and the pressure dependence of the cyclotron effective mass, mc(p), and of the concentration of conduction electrons, nSdH, are given. The dependences of mc and the Fermi energy on pressure are consistent with Kane-type non-parabolicity of the conduction band.

De Haas–van Alphen Effect and Fermi Surface Properties in High-Quality Single Crystals YbCu2Si2 and YbCu2Ge2

We succeeded in growing high-quality single crystals of a valence fluctuating compound YbCu 2 Si 2 and a divalent compound YbCu 2 Ge 2 . The magnetic susceptibility of YbCu 2 Si 2 follows the Curie–Weiss law with Yb 3+ at high temperatures, but reveals a broad peak around 40 K for H ∥[100], which is due to the formation of a 4 f -itinerant heavy fermion state at lower temperatures. This is also reflected in the temperature dependence of Hall coefficient, thermoelectric power and thermal expansion. The corresponding de Haas–van Alphen (dHvA) branches are approximately explained by the 4 f -itinerant LDA band model, and the 4 f -itinerant LDA+ U model is found to be much applicable to the dHvA data. The cyclotron effective masses of main Fermi surfaces are relatively large, being 30–40 m 0 , which is consistent with the electronic specific heat coefficient γ=150 mJ/(K 2 ·mol). These results indicate that the localized 4 f electrons at high temperatures become itinerant at low temperatures, forming a narrow ...

Antiferromagnetic Fluctuations in the Organic Superconductorκ−(BEDT−TTF)2Cu(NCS)2under Pressure

We measured the 13C-NMR spectrum and T1 of the quasi-two-dimensional organic superconductor kappa-(BEDT-TTF)2Cu(NCS)_{2} under pressure. This material was thought to show a relationship between T_{c} and the effective cyclotron mass m_{c};{*}, obtained from the Shubnikov-de Haas (SdH) effect. We found that kappa-(BEDT-TTF)2Cu(NCS)_{2} behaved as a Fermi liquid at low temperature under all pressures, and antiferromagnetic fluctuations were expected. The pressure dependence of the Korringa factor is similar to that of the effective cyclotron mass m_{c};{*}, suggesting that antiferromagnetic fluctuations contribute to the superconductivity of this material. We also found that, under pressure, T;{*} was shifted to 150 K, the temperature characteristic of the shift from bad metal to good metal.

Magnetoabsorption in InSb quantum-well heterostructures

Spin-resolved cyclotron resonance is observed in InSb/AlInSb quantum-well heterostructures. Spin-resolved transitions are identified for fields greater than 2.2 T and confirmed by k⋅p modeling. The cyclotron effective mass is calculated for a range of fields up to 11.5 T and is indicative of the strong nonparabolicity in this material. Resonant coupling is observed between the ground and first occupied subbands for normal-incidence excitation. This is explained in the context of conduction band-valance band mixing due to the narrow bandgap. Further resonant coupling is observed via interaction with a hybrid intersubband plasmon-LO phonon mode. This allows a quantitative estimation of the subband spacing and of the electron-phonon interactions in the quantum well.