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The magnetic field dependence of electronic transport, magnetic, and elastic properties in single crystals of PbTe were investigated in high magnetic fields up to 55 T. The magnetoresistance, magnetization, ultrasonic attenuation, and sound velocity showed clear quantum oscillations with pronounced Zeeman-splitting, which causes a large second harmonic in the frequency spectra. The ratio of the Zeeman to the cyclotron energy, which is regarded as an index of `Diracness' [H. Hayasaka and Y. Fuseya, J. Phys.: Condens. Matter \textbf{28,} 31LT01 (2016).], was determined to be 0.52 and 0.57 in samples with different carrier densities. We also pointed out that the effect of Zeeman-splitting seriously affects the Landau-level fan diagram analysis, which is widely used to extract the nontrivial Berry's phase from the quantum oscillations., Comment: to be published in Phys. Rev. B

This study examines the role of landforms in pond formation in alpine and subalpine regions of central Japan. Mountain ponds larger than ca. 50 m2 were detected by interpretation of stereo-paired aerial photographs, and mapped in areas over 2000 m (above sea level). The mapped ponds totaled 304 in the 1347 km2 study area. Mass movement landforms are the major sites of pond basins, comprising 66.5 % of the total number; 65 ponds occur in depressions in displaced masses downslope of ridges, and 137 occur in linear depressions along main ridges. These ponds occur frequently in the snowiest parts of the study area, although geological setting also affects pond formation. The second and third major types of landforms with ponds are of volcanic and glacial origins, accounting for 16.8 and 15.8 % of all ponds, respectively. Nearly 90 % of these mapped ponds have an area smaller than 1000 m2. The size distribution of ponds varies with origin type. Mass movement landforms have a greater range of pond sizes, including both small (

箱根町仙石原のススキ草原において，ローム層などの表層堆積物中の植物珪酸体と微粒炭の分析を行い，過去約1,000年間の植生変遷と人為活動との関係を検討した．ススキ草原内の深さ1.1mの試坑断面中から採取した41点の試料を分析した結果，草本起源の植物珪酸体7分類群，木本起源の植物珪酸体3分類群が認められた．ススキ属型の珪酸体は深度68cmから上方で多く検出され，それより下方ではネザサ節型の珪酸体が多く検出された．微粒炭は地表から深度62cmまで連続的に検出されたが，それより下方では不連続的に検出され，量も少なかった．土壌中に含まれる腐植の年代測定結果と合わせて考えると，調査地では西暦1200年頃までに火入れを伴う人為的影響を強く受けるようになり，ネザサ節のハコネダケが優占する植生から，ススキ草原が卓越する植生へと変化したと推察される．

Seebeck effect, Peltier effect, Thomson effect, electronic thermal conductivity, Hall effect, and Nernst effect are described on the basis of electronic conduction theory, taking account of effective mass anisotropy, nonparabolicity in E­k relation, and temperature dependent band gap. It is shown that the temperature dependence of the band gap does not modify the basic equations for the Seebeck coefficient, thermal conductivity, and Nernst coefficient. In narrow gap semiconductors, existence of minority carriers significantly enhances the electronic thermal conductivity, owing to the multiple carrier transport known as bipolar diffusion. Calibration coefficient £ for the Hall effect (RH ¼� £=en )i s increased by nonparabolicity in the E­k relation. Nernst coefficient gives useful information on scattering properties of the materials. [doi:10.2320/matertrans.E-M2012812]

This study examines vegetation succession and soil physico-chemical properties in the upper reaches of the O'Donell River, which have been affected by the seasonal lahar since the 1991 eruption of Mt. Pinatubo, central Luzon, the Philippines. Field surveys and physico-chemical analyses of lahar deposits and soil were carried out in areas including the living zone of the Aeta to understand the land recovery process along with land management practiced by the Aeta. Seedlings of Ararong (Trema orientalis) associated with root nodule bacteria are widely distributed on the lower lahar terraces and it was pointed out that Ararong is a pioneer plant. It is also the dominant species of tree and shrub layers on higher lahar terraces, and has a tendency to reduce its height in response to increases in coverage of herbs such as Talahib, Magkakamote, and Bureok. Vegetation succession was divided into the following stages (I–IV) based on an interpretation of the development of the geomorphological surface and a vegetation survey. The former surface soil of the 1991 pre-eruption was tentatively defined as the goal of land recovery and was classified as Stage V. A grain-size analysis of lahar deposits and soils in φ scale was carried out by the dry sieving method. Chemical properties of lahar deposits and soils were examined by analyzing total carbon (T-C), total nitrogen (T-N), total phosphorus content (T-P), C/N ratio, pH (H2O), cation exchange capacity (CEC), base saturation (BS), and total elemental composition. Lower terrace of post-eruption lahar deposits with no vegetation (Stage I) and lower terrace of lahar with Ararong seedlings or herbs (Talahib, Bureok) had low T-C contents 0.2–0.58 g kg-1, and no significant differences were recognized between the two stages. The higher terrace of lahars with Ararong of 2–5 m height and herb coverage (Stage III) and ridge area affected by the 1991 pyroclastic flow and/or fall deposits, currently used as fields with shifting cultivation (Stage IV), had an increased T-C content of from 0.37 to 8.9 g kg-1 in response to the increased density of the vegetation canopy and number of vegetation species, which showed an exponential increase towards Stage V (21 g kg-1). The T-N content showed a slight tendency of nitrogen accumulation occupied by Ararong and rhizobial nitrogen fixation. As far as we examined soil pH (H2O), T-N, CEC, and BS, the soil fertility of the shifting cultivated field and the secondary forest (stage III, IV) in the upper reaches of the O'Donell River is equivalent to that of the fields on plains of the Bambang and Pasig-Potrero rivers. Nitrogen fixation by root nodule bacteria of Ararong, and available phosphorus supply originating from apatite in the lahar deposits are both accelerated by the elution of organic acids from herbs such as Talahib. Potassium supply from the weathering of plagioclase and biotite, the major minerals of lahar deposits, is also the basic process responsible for land recovery on the upper slope of Mt. Pinatubo. Based on analytical data from this study, it is found that the activity of the Aeta people of burning down secondary forests of Ararong to open small areas of arable land is not a regulating factor against land restoration. The soil-forming process, which is closely related to vegetation management from the activities of local people, may help us to understand the ongoing sustainable development in the upper reaches of the O'Donell River.

We examined change in areal extent of mountain meadows and fields of deciduous shrubs and conifer saplings in the central western Cascade Range of Oregon, based on analysis of aerial photographs ta...

On-farm indigenous (Cordia africana) and exotic (Grevillea robusta) tree species were compared in terms of the quality of their utility and their agronomic traits in the Meru Central district of Kenya. These two species are the most common indigenous and exotic trees, respectively, among the recorded 117 trees on farms. Interviews with farmers and collected documents on tree felling and planting showed that farmers considered C. africana to be more useful than G. robusta. However, farmers wanted to plant more G. robusta than C. africana because the easily established and fast growing G. robusta has a higher short-term contribution to the household economy. The advantages of C. africana, however, should be redefined in terms of its long-term contribution to farmers; C. africana contributes to farming more effectively than does G. robusta. The lower growth performance and relative difficulty in the establishment of C. africana can be compensated for by its higher timber quality and coppicing ability.

The impacts of the 1997–1998 El Nino rains in the Mount Kenya region were heterogeneously distributed among agricultural villages in the area. The magnitude of these impacts on crop production depended on differences in the climatic and topographic conditions of the affected villages. Major food crops, especially beans and Irish potatoes, were ruined by the long-lasting rains in all villages, whereas banana and root crops, with the exception of Irish potatoes, received minimal damage. Because the less-susceptible crops were planted mainly in relatively humid villages on the upper slopes of the mountain, the differences in the impacts on the long-established upper and more recently settled lower villages became more apparent. Floods caused crop losses on the lower slopes but also deposited seeds of a useful tree species, resulting in a positive long-term impact of the El Nino rains. Farmers considered the El Nino rains to be much worse than a heavier rainfall event, the Mafuriko rains, experienced...

The cyclotron resonance of two-dimensional electron systems (2DES) of GaAs/AlGaAs heterostructures is investigated in a tilted magnetic field. In this study, the perpendicular (B⊥) and in-plane (B||) magnetic fields are changed systematically. More than two cyclotron resonances caused by B|| are observed. Further, the enhancement of cyclotron mass by B|| and its dependence on B⊥ and electron concentration of 2DES are also investigated in detail. These phenomena are well explained by the resonant subband Landau level coupling model.

We investigate the cyclotron resonance of corrugated lateral superlattices with ultrashort period (12 nm ) grown on (7 7 5)B GaAs substrates. In addition to the broad dips of cyclotron resonance compared with those of the unmodulated samples, the magnetic field dependence of observed cyclotron resonance spectra shows the anticross behavior or more complicated behavior. Several possible mechanisms on this behavior are discussed.

We investigate the influence of electron–electron interactions on cyclotron resonance (CR) of two-dimensional electron systems in tilted magnetic field. It is known that the electron–electron interactions affect the CR spectra in systems that have more than two cyclotron frequencies. In this study, this multi-component system is realized by applying the tilted magnetic field; the tilted magnetic field induces the resonant subband-Landau level coupling (RSLC) and a splitting of the CR spectrum is observed. Observed anomalous CR spectra cannot be explained by the RSLC with the single-electron picture. Present theoretical treatments cannot account for the result of our experiment.

We investigate different types of the breakdown of the quantum Hall effect (QHE), which are characterized by the sample width dependence of the critical current for the breakdown. The distinction of two different types of breakdown is thought to be the properties of the two-dimensional electron gas (2DEG) wafers, but it is not related directly to the 2DEG mobility and electron density determined by Hall measurement at low magnetic field. We observe the switching between linear and sublinear dependence of the QHE breakdown by varying temperature, gate voltage, and by illumination condition. The type of QHE breakdown is determined by the extent of potential fluctuations in the 2DEG, which are characterized by the random potential from ionized donors and by screening effects, comparing with those resulting from the thermal broadening of the electron distribution. The result of magnetocapacitance between 2DEG and Schottky gate also suggests that the 2DEG homogeneity play an important role in the breakdown of the QHE.

The in-plane magnetic field (B||) dependence of cyclotron resonance is investigated in both single and double layer two-dimensional electron systems by Fourier spectrometry in tilted magnetic fields. The observed B|| dependence of the cyclotron mass (mC) is complicated and varies with perpendicular magnetic field in the double layer system. The splitting of mC by B|| around filling factor 2 is observed in the single layer system.

We have studied the magnetic electron focusing effect (MEFE) and Weiss oscillations (WO) on two-dimensional electron gas (2DEG) in the magnetic fields parallel to the 2DEG plane ( B || ). The distortion of the Fermi loop in GaAs/AlGaAs 2DEG induced by the B || is observed in both MEFE and WO.

The in-plane magnetic field (B∥) dependence of cyclotron mass (mC) in two-dimensional electron system has been measured. In addition to the increment of mC with B∥, the split of mC by B∥ is observed near the filling factor of Landau level ν=2. Some possible origins on this splitting are discussed.

We have investigated the width of the compressible strips in the edge state by magnetocapacitance between two-dimensional electron gas and a metal gate. The detail of Landau level filling factor dependence of the width is measured around the quantum Hall plateaux, and the influence of confinement potential on the width has been studied by tuning the side gate voltage. It is confirmed that the width is mainly governed by the depletion region at the sample boundary; the spatially gentle confinement potential forms wider compressible and incompressible strips. The nonlocal resistance has been also studied in the samples with tunable confinement potential by side gate, which supports the result of the capacitance measurement.

We have measured the capacitance between adjacent edge channels ( C M ) in the GaAs/AlGaAs two-dimensional electron gas in the quantum Hall plateau to investigate the structure of edge channels. The value of C M is mainly determined by the ratio of edge channel width (compressible region) to the separation between them (incompressible region) and the length of the edge channels. However, the energy relaxation between the edge channels reduces the effective length of the adjacent edge channels. Only at ν =3 quantum Hall plateau, it is able to measure C M to investigate the width of incompressible region, since the energy relaxation between the ν =2 and 3 channel is small enough.

We investigate the breakdown of the quantum Hall effect (QHE) and observe a remarkable change in dependence of the critical current for the breakdown in sample width. Both linear and sub-linear dependences of the critical current on sample width are obtained for the same sample, depending on temperature, way of illumination, and gate bias voltage. The experimental results of the breakdown of the QHE are explained by comparing electron density fluctuations, which are characterized by the random potential from the ionized donors and by screening effects, with the thermal broadening of the electron energy distribution. It is suggested that the electron density fluctuations play an important role in the breakdown of the QHE.

In a vertically coupled dot, it is expected that generalized Kohn theorem is invalid. Then electron–electron interaction can be observed in far-infrared absorption. This interaction depends on the coupling between dots. We fabricated a vertically aligned double-dot array using a double heterostructure to investigate the coupling. The strength of the coupling depends on the confine potential of the dot. In far-infrared magneto-optical absorption measurements under pulsed photoexcitation, we observed peak shift of asymmetry states and increasing of absorption intensity of symmetry states of the dot. This is a result of the confined potential modulation by light. This indicates the possibility of optical control of the coupling.

Variation in the temperature dependence of the resistance and magnetic-field dependence of negative magnetoresistance (MR) with increasing gate voltage has been studied on an n-channel poly-Si MOS inversion layer. We find a crossover from strongly-localized (hopping) to weakly-localized (diffusive) regime in two dimensions around the sheet resistance of ≈6 kΩ with increasing gate voltage. In both regimes, the negative MR due to orbital motion is observed and explained by the quantum interference effects.

Far-infrared magneto-absorption of double-layer two-dimensional electron system has been measured by Fourier transform spectrometer in tilted magnetic fields. We have measured the dependence of cyclotron mass ( m C ) on the parallel ( B ∥ ) and perpendicular ( B ⊥ ) magnetic fields systematically. The obtained B ∥ dependence of m C is complicated and varies with B ⊥ , which cannot be explained by semi-classical theory.

Cyclotron resonance measurement of the double-layer two-dimensional electron system in tilted magnetic fields is made with far-infrared Fourier transform spectroscopy. Parallel magnetic field (B∥) dependence of the cyclotron mass is obtained by setting B∥ and the perpendicular magnetic field (B⊥) independently. We find a complicated behaviour of the cyclotron mass in tilted magnetic fields which is not explained by semiclassical theory.

Subalpine forest zone in the Japanese snowy mountains is characterized by a mosaic of coniferous forests and meadows.Abies mariesii thickets surround mesic meadows, forming a forest-meadow ecotone. Size and age structure of the thickets were studied to examine the stability of the forest-meadow boundaries on Mount Aizukomagatake in central Japan. The age structure indicates that the small height ofA. mariesii in the thickets was not due to the early stage of succession but due to adverse site conditions. In spite of their small stem height, they were as old as canopy trees in neighboringA. mariesii forests. Snow settling pressure madeA. mariesii thickets with broken main stems on the crest slopes, while snow glide pressure formed those with bending stems on leeward slopes. No evidence was found to show any major changes in the position of the forest-meadow boundaries in the size and age structure. The boundary position appears to have been almost steady for at least this century.

Time resolved magneto-optical absorption measurement of a quantum dot array is carried out. In contrast to two dimensional electron gas, a difference in the absorption between with and without photoexcitation can be clearly observed in a quantum dot array. From the time variation of the difference in the absorption, the peakshift is investigated. This may not depend simply on the carrier concentration. A photoexcited carrier may change the charge state around the dot.

We have evaluated the width of edge channels in the fractional and integer quantum-Hall (QH) regime by the magnetocapacitance measurement between a gate and two-dimensional electron system in GaAs/AlGaAs heterostructures. The frequency dependence of the magnetocapacitance between 100 Hz and 1 MHz has been measured at temperatures between 35 mK and 0.4 K. At the fractional QH regime, the total width of the edge channels is found to be 2.5 and 9 μm at 35 mK at the QH plateaux of filling factor ν= 1 3 and 2 3 , respectively. In the integer QH regime, the temperature dependence of the edge channel width is almost flat in the range of 35 mK–0.4 K. At the QH plateau of ν=1 due to spin-splitting Landau level, the width of total edge channel is almost the same value with that at ν=2. The width at ν=3 is also comparable to that at ν=4, although the residual bulk conductivity of ν=3 is an order of magnitude larger than that of ν=4.

We have investigated the anisotropy of Fermi surface of two-dimensional electron gas in GaAs/AlGaAs heterostructures induced by a strong parallel magnetic field. By means of a magnetic electron focusing effect, the anisotropy of the cyclotron diameter, that is, the anisotropy of the Fermi surface, is directly determined. The anisotropy of Fermi surface increases by 5–10% with increasing parallel magnetic field up to 6 T. It is found that the anisotropy is enlarged with increasing carrier density by illumination, while the anisotropy increases with decreasing carrier density by the gate voltage.

We report on an investigation of commensurability oscillations in antidot square-lattices, and show that the commensurate peaks in resistivity ρxxderive from two kinds of electron: runaway and quasipinned electrons. The runaway electrons, which skip away along the antidot arrays, increase the value of conductivity σxx; and the quasipinned electrons, which orbit some antidots for a long time, decrease the value of σxx. Therefore, by competition between the two different types of electron, the conductivity σxxis determined. The conductivity σyxin the antidot lattice always has dips at the peaks in ρxx. As a result, by combining the of values of σxxand σyx, the resistivity is determined through the orthodox relation of ρxx = σxx/ (σxx2 + σyx2).

The quantum Hall effect for the GaAs/AlGaAs heterostrcture is investigated by an ac capacitance measurement between the two-dimensional electron system (2DES) and the gate on GaAs/AlGaAs. The capacitance minima at the quantum Hall plateaus are mainly determined not by the 2DES area under the gate but by the edge length of 2DES. There exists the high conductive region due to the edge states along the 2DES boundary, when the bulk conductivity σxx is small enough at low temperatures and high magnetic fields. From the temperature and frequency dependence of the capacitance minima, it is found that the measured capacitance consists of the contribution from the edge states and that of the bulk state, which is treated as a distributed circuit of a resistive plate with the conductivity σxx. The evaluated width of edge states from the capacitance is much larger than the magnetic length and the cyclotron radius expected from the one-electron picture. This wide width of edge states can be explained by the compressible-incompressible strip model, in which the screening effect is taken into account. Further the bulk conductivity of less than 10-12 S (S=1/Ω) is measured by the capacitance of the Corbino geometry sample, where the edge states are absent and the capacitance is determined by only σxx in this geometry. The localization of the bulk state is investigated by the obtained σxx.

The low-temperature transport in high-mobility poly-Si TFT fabricated using laser annealing of amorphous Si film has been studied in the two-dimensional variable-range hopping (VRH) regime near the crossover between the weak and strong localization. The resistance follows the Efros-Shklovskii (ES) VRH as In R α T−1/2 below ∼ 20 K in the presence of a Coulomb gap in the density of states. The negative magnetoresistance ΔR R varies below ∼ 4 K as ∼ T−3/2B2 in low-magnetic fields and as ∼T−3/4B in moderate fields both in agreement with the theoretical predictions based on quantum interference.

In order to fabricate buried quantum structures using a total vacuum system which consists of low-energy focused ion beam and molecular beam epitaxy systems, the effects of growth interruption, passivation by As layers on GaAs and annealing after growth are investigated experimentally using δ-doping technique in the GaAs. It is found that the annealing at 800 °C for 10 s is not effective in reducing the interface states. It is concluded that the passivation by As layer is useful for the reduction of shallow interface state.

To predict the influence of global warming on high-mountain plants, we have started an experiment on Mt. Kisokomagatake (2956 m), the Central Japanese Alps, using the ITEX (International Tundra Experiment) method. Four small greenhouses (OTC: open-top-chamber) were set up in May 1995 to cover two alpine species: Arctous alpinus var. japonica and Diapensla lapponica. The temperatures at plant height and the ground were measured in each OTC as well as a control plot without OTC. The average temperature in OTCs was higher than that in the control plot by 0.9℃. In accordance with the temperature enhancement, the plants in OTCs underwent some phenological changes during the summer of 1995. The duration from the leaf emergence to the beginning of coloring in OTCs was longer than that in the control plot by 33 days. Leaf wilting was also delayed in OTCs. Thus, alpine plants responded sensitively to the environmental change in the OTC.

This study was conducted to clarify the characteristics of landform effects on fire behavior and post-fire regeneration and to examine regional differences in the effects of fire within a mixed-forest area with various topographic conditions in Hokkaido, northern Japan. Fire spread was controlled by topographic barriers such as ridges and valleys, although this was not clear in the areas with serpentinite. Fire frequency was higher on windward slopes of the prevailing wind, and the size of the burned area varied with the underlying geology, which controlled the areal extent of hillside slopes. In areas with terrace deposits, Wakkanai Formation or serpentinized rock, burned areas were large and included few unburned stands. The type of vegetation that grew following the fires varied with slope aspect and topographic position.Sasa grasslands often formed at wind-exposed sites. The grasslands were well developed in the three areas with the previously mentioned geology, where large-scale burning had occurred. Structure of the re-established forest stands was also affected by landforms. Canopy height and the maximum diameter at breast height varied with slope aspect, topographic position and elevation, as well as with stand age. Tree size was found to decrease at wind-exposed sites within high-elevation zones.

The results of low-temperature transport properties on high-mobility poly-Si thin film transistors (TFTs) have been examined by measurement of the resistance as a function of temperature, magnetoresistance (MR) and Hall effect. It has been shown that the transition between the two-dimensional (2D) weak and strong localization (WL and SL) occurs around the sheet resistance R = π h /e 2 (⋍ 13 kΩ), where ( 1 2 )k F l ∼ 1 , in the band-tail states, caused by potential fluctuations in the inversion layer of TFTs. In the barely SL regime, R at low temperatures is found to obey the Efros-Shklovskii variable-range hopping (VRH) law in the presence of the Coulomb gap in the density of states. In both regimes of WL and SL, a negative MR has been observed and interpreted by the quantum interference effect in each regime.

We investigate the transport properties in various antidot lattices. It is found that the fundamental peak on resistivity is determined by the conductivity perpendicular to the current flow direction in the case of smaller diagonal component of conductivity tensor than the off-diagonal one. Moreover, the peaks of conductivity are explained by the runaway trajectory, on which the electrons diffuse along the antidot array like as skipping over the antidots when the cyclotron diameter of electron corresponds to the antidot period, and the conductivity along the antidot period is enhanced. This is the origin of the fundamental peak in the commensurability oscillations.

In order to realize buried quantum structures using a total vacuum system which consists of low-energy focused ion beam and molecular beam epitaxy systems, the structures with passivation layers are discussed by numerical calculations. It is shown by the calculations that the device can be realized even if the growth-interrupted interfaces are passivated by thin GaAs layers if the thickness of each layer is designed carefully. The effect of growth interruption at the GaAs layer is studied experimentally. It is found that the interface-state density depends on the Si concentration at δ-doped layer.

We investigate the relation between commensurability oscillations and current flow direction in lateral two-dimensional anisotropic antidot lattices. The anisotropy is introduced as one-directional fluctuation or expansion of the lattice spacing. The fluctuation of the antidot location suppresses the peaks of commensurability oscillations. The suppression is dominated by the fluctuations perpendicular to the current flow direction. In one-directional expanded lattices, the peaks appear at the magnetic fields which correspond to the cyclotron motions with the diameter of the periods perpendicular to the current. These results suggest that the commensurability oscillations are determined only by the period along the direction perpendicular to the current.

Angular distribution of emitted electrons is investigated by using the magnetic electron focusing effect in a device with probes obliquely or vertically connected to a two dimensional electron gas, and by using low field magnetoresistance of the other device with two pairs of an emitter wire and a collector point contact. It is found that the distribution strongly depends on the structure just at the outlet of the wire rather than the wire direction.

Normal and superconducting properties of PtSi films with thicknesses of d=2–20 nm have been investigated. The superconducting transition has been observed on the thin films down to d=4 nm. The systematic reduction of the transition temperature with decreasing d (increasing the sheet resistance) has been explained by the localization and Coulomb interaction effects on superconductivity. The temperature dependence of the upper critical field indicates that the PtSi films behave as homogeneous superconductors.

The magnetic electron-focusing effect (MEFE) has been investigated in mesoscopic multiterminal samples of GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As heterostructures. The MEFE peaks are clearly observed even in a configuration where electrons seem to be reflected from an extra probe between an emitter and a collector probe. To clarify the reflection mechanism, the ``reflection'' peaks are studied in the samples with variously shaped extra probes and in the samples with two extra probes connected by a byway channel or an external circuit. In the reflection events, the electrons different from the electrons injected into the extra probe should be emitted from the extra probe, since the chemical potential of the extra probe becomes higher due to the accumulation of electrons in the extra probe.

The magnetic field dependence of the capacitance of a GaAs/AlGaAs heterostructure through a two-dimensional electron system (2DES) is measured in the quantum Hall regime. It is found that the values of the capacitance minima at the Hall plateaus are determined not by the 2DES area under the gate but by the edge length of the 2DES. These results cannot be explained by an existing interpretation of the magnetocapacitance, where the capacitance is directly related to the density of states of the 2DES. We suggest an alternative model in which the bottom values are essentially determined by the current carrying area at the edge. The widths of the current channels are estimated and compared with the recent theoretical and experimental estimates.