Showing papers on "Effective mass (solid-state physics) published in 1993"
TL;DR: In this article, a two-dimensional electron system in an external magnetic field, with Landau-level filling factor \ensuremath{
u}=1/2, can be transformed to a mathematically equivalent system of fermions interacting with a Chern-Simons gauge field such that the average effective magnetic field acting on the fermion is zero.
Abstract: A two-dimensional electron system in an external magnetic field, with Landau-level filling factor \ensuremath{
u}=1/2, can be transformed to a mathematically equivalent system of fermions interacting with a Chern-Simons gauge field such that the average effective magnetic field acting on the fermions is zero. If one ignores fluctuations in the gauge field, this implies that for a system with no impurity scattering, there should be a well-defined Fermi surface for the fermions. When gauge fluctuations are taken into account, we find that there can be infrared divergent corrections to the quasiparticle propagator, which we interpret as a divergence in the effective mass ${\mathit{m}}^{\mathrm{*}}$, whose form depends on the nature of the assumed electron-electron interaction v(r). For long-range interactions that fall off slower than 1/r at large separation r, we find no infrared divergences; for short-range repulsive interactions, we find power-law divergences; while for Coulomb interactions, we find logarithmic corrections to ${\mathit{m}}^{\mathrm{*}}$. Nevertheless, we argue that many features of the Fermi surface are likely to exist in all these cases. In the presence of a weak impurity-scattering potential, we predict a finite resistivity ${\mathrm{\ensuremath{\rho}}}_{\mathit{x}\mathit{x}}$ at low temperatures, whose value we can estimate. We compute an anomaly in surface acoustic wave propagation that agrees qualitatively with recent experiments. We also make predictions for the size of the energy gap in the fractional quantized Hall state at \ensuremath{
u}=p/(2p+1), where p is an integer. Finally, we discuss the implications of our picture for the electronic specific heat and various other physical properties at \ensuremath{
u}=1/2, we discuss the generalization to other filling fractions with even denominators, and we discuss the overall phase diagram that results from combining our picture with previous theories that apply to the regime where impurity scattering is dominant.
1,014 citations
TL;DR: The first-principles orthogonalized linear-combination-of-atomic-orbitals method in the local-density approximation for wurtzite crystals shows that the calculated equilibrium volume and the bulk modulus are in good agreement with recent experimental data.
Abstract: Using the first-principles orthogonalized linear-combination-of-atomic-orbitals method in the local-density approximation, the electronic structures and the linear-optical properties of ten wurtzite crystals, BeO, BN, SiC, AlN, GaN, InN, ZnO, ZnS, CdS, and CdSe are investigated. Results on band structures, density of states, effective masses, charge-density distributions, and effective charges are presented and compared. Optical properties of the ten wurtzite crystals up to a photon energy of 40 eV are calculated and the dielectric functions are resolved into components perpendicular and parallel to the z axis. The calculated results are compared with the available experimental data and other recent calculations. The structural properties of the wurtzite crystals are also studied by means of local-density total-energy calculations. It is shown that the calculated equilibrium volume and the bulk modulus are in good agreement with recent experimental data.
560 citations
TL;DR: Using the recently developed exact envelope-function theory, an explicit form for the effective-mass Hamiltonian is derived for the valence bands of a semiconductor quantum well or superlattice and it is shown that the correct form of the Hamiltonian gives physically reasonable results.
Abstract: Using the recently developed exact envelope-function theory, an explicit form for the effective-mass Hamiltonian is derived for the valence bands (including the spin-orbit split-off band) of a semiconductor quantum well or superlattice. It is shown that the correct form of the Hamiltonian gives physically reasonable results, while the commonly used ``symmetrized'' form can produce nonphysical solutions for the heavy-hole subbands in which the quantum-well effective mass is very sensitive to the difference in Luttinger parameters between the well and the barrier. This problem arises because the correct boundary conditions for the heavy-hole states are determined exclusively through interaction with other p states, while the symmetrized boundary conditions implicitly incorporate the much larger s-state interaction, hence they substantially overestimate the magnitude of the interband coupling.
211 citations
TL;DR: In this paper, the muon spin relaxation (µSR) measurements of TI-2Ba2CuO6+δ (TI-2201) in high-transition-temperature (high-Tc ) copper oxide superconductors have revealed remarkable correlations between Tc and ns/m* in the underdoped region, followed by a saturation with increasing carrier doping, implying that either ns no longer scales with the normal-state carrier density nn, and/or m* for a superconducting pair becomes much larger than the value expected
Abstract: THE magnetic field penetration depth λ is a basic parameter of superconductivity, related to ns/m* (superconducting carrier density/effective mass) as λ-2 ∝ ns/m* in the limit where the coherence length ζ is much shorter than the mean free path l (the 'clean limit'). Muon spin relaxation (µSR) measurements1,2 of λ in high-transition-temperature (high-Tc ) copper oxide superconductors have revealed remarkable correlations between Tc and ns/m*: Tc increases linearly with ns/m* in the underdoped region, followed by a saturation with increasing carrier doping. Here we report µSR measurements of λ in ceramic specimens of of the superconductor TI-2Ba2CuO6+δ (TI-2201) in the 'overdoped' region where Tc decreases with increasing hole doping. Recent measurements of upper critical field and resistivity3confirm that overdoped TI-2201 lies well in the clean limit with a ζ<
187 citations
TL;DR: The effective Hamiltonian describing the motion of electrons in compositionally graded crystals is constructed which is valid throughout a given energy band and part way into the gaps, as well as the appropriate turning point connection rules.
Abstract: : We construct the effective Hamiltonian describing the motion of electrons in compositionally graded crystals which is valid throughout a given energy band and part way into the gaps. The effective Hamiltonian, constructed from the band structures of uniform crystals, also includes the effects of a slowly varying applied scalar potential U(r). Near the edges of a nondegenerate band, this effective Hamiltonian reduces to an effective mass Hamiltonian with position dependent mass (one of several forms previously appearing in the literature): H sub eff = 1/2 pi(1/m*(r)) sub ij pj + Epsilon(r) + U(r), where Epsilon(r) is the energy of the band edge as a function of position. The analogous effective mass Hamiltonian for degenerate bands is also derived. Next, we examine more general states-not restricted to the vicinity of a band edge in crystals with composition and applied potential variation in one direction. We obtain a WKB-type solution for the envelope functions, as well as the appropriate turning point connection rules.
159 citations
TL;DR: In this paper, the authors focus on the emergence of limiting configurations of the Reissner-Nordstrom field that have vanishing effective mass everywhere within the sphere and show that these configurations prevent the existence of naked singularities, and demand that the effective gravitational mass be everywhere non-negative.
Abstract: The energy conditions of general relativity are satisfied by all experimentally detected fields. We discuss their interpretation and application to charged spheres. It is found that they prevent the existence of naked singularities, and demand that the effective gravitational mass be everywhere non-negative. We focus on the emergence of limiting configurations-sources of the Reissner-Nordstrom field that have vanishing effective mass everywhere within the sphere. These configurations have a number of interesting features. Among them we find that, near the center, the limiting form of the equation of state isρ+3p=0. Notably this is the only equation of state consistent with the existence of zero-point electromagnetic field, and it has been considered in different contexts, in discussions of cosmic strings and in derivations of (3+1) properties of matter from (4+1) geometry. The consistency of these configurations with the Einstein-Maxwell equations is shown by means of explicit examples. These configurations can be interpreted as due to selfinteracting gravitational effects of the zero-point electromagnetic field.
155 citations
TL;DR: The binding energies of donors in both finite and infinite GaAs•(Ga,Al)As spherical quantum dots are calculated as a function of the donor position for different radii within the effective mass approximation.
Abstract: The binding energies of hydrogenic donor in both finite and infinite GaAs‐(Ga,Al)As spherical quantum dots are calculated as a function of the donor position for different radii within the effective‐mass approximation. It is observed an enhancement of the binding energy of donors in quantum dots when compared to results in quantum wells and quantum‐well wires, which is an expected consequence of the higher geometrical electronic confinement in these systems. The density of impurity states as a function of the donor binding energy was also calculated. As a general feature it presents structures associated with special impurity positions that may be important in the understanding of the absorption and photoluminescence experiments of doped quantum dots.
139 citations
TL;DR: A tight-binding model in the three-center representation, with an orthogonal sp 3 set of orbitals and interactions up to third neighbor, is introduced and gives a good description of bulk Si and Ge and reproduces known results for their band structures.
Abstract: A tight-binding model in the three-center representation, with an orthogonal ${\mathit{sp}}^{3}$ set of orbitals and interactions up to third neighbor, is introduced. This model gives a good description of bulk Si and Ge and reproduces known results for their band structures, including the lowest conduction band, their density of states, effective masses, deformation potentials, and dielectric function. Also, this is an efficient model as far as computer time is concerned; therefore, it is most appropriate for application to superlattices (SL's). In particular, it is used to study the electronic properties of some strained Si/Ge superlattices. Their band structure, confinement of superlattice states, transition probabilities, effective masses, and spin splittings were investigated and the influence of the strain and superlattice periodicity was studied. It was found that under specific conditions of growth, some SL's can be direct-gap materials. Finally, the comparison with experimental results shows that the present model is a realistic one and can be used to describe the electronic properties of the strained Si/Ge SL's and clarify many of the points that are under debate.
112 citations
TL;DR: The plasma frequency of the carriers is found to increase upon cooling, a very unusual phenomenon which, together with Hall-effect measurements, may imply that the effective mass of the carrier decreases upon cooling.
Abstract: The temperature dependence of infrared reflection spectra of single crystals of n-type strontium titanate doped with 0.3 to 1.5 at. % niobium are reported from 10 to 5 000 cm -1 in the temperature range 80-900 K. Results are analyzed by means of various factorized forms of the dielectric function. A decoupling scheme allows the temperature dependence of the plasmon to be deduced. The plasma frequency of the carriers is found to increase upon cooling, a very unusual phenomenon which, together with Hall-effect measurements, may imply that the effective mass of the carriers decreases upon cooling
102 citations
TL;DR: Calculations of the hole mobility in a strained SiGe quantum well on (001) Si are carried out for the case of a narrow well in which the subband splittings are large due to quantum-size effects and results indicate that hole mobilities could be possible in narrow SiGe wells as a result of the favorable modifications in band structure and scattering.
Abstract: Calculations of the hole mobility in a strained SiGe quantum well on (001) Si are carried out for the case of a narrow well in which the subband splittings are large due to quantum-size effects. An envelope-function model for the valence-band structure and hole wave functions in an infinite square well and calculations of scattering rates in a single parabolic band with an isotropic effective mass are used to delineate limitations on mobility imposed by lattice scattering, background impurities, alloy scattering, and interface roughness. Additional scattering mechanisms associated with compositional fluctuations in the SiGe layer are also discussed. Narrow wells (60 \AA{}) with high Ge content (40%) have large subband splittings and exhibit a light mass for hole densities well beyond ${10}^{12}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$. Scattering rates in such structures are greatly reduced as a result of the light mass and large subband splittings. Numerical results indicate that hole mobilities in the mid ${10}^{3}$ ${\mathrm{cm}}^{2}$/V s at room temperature and in the mid ${10}^{4}$ ${\mathrm{cm}}^{2}$/V s at low temperature could be possible in narrow SiGe wells as a result of the favorable modifications in band structure and scattering.
85 citations
TL;DR: In this paper, the conduction and valence bands of porous silicon are shifted relative to the bands for bulk silicon, as expected in the quantum confinement model for the optical properties of the porous silicon.
Abstract: Photoemission and x‐ray absorption spectroscopy show that both the conduction and valence bands of porous silicon are shifted relative to the bands for bulk silicon, as expected in the quantum confinement model for the optical properties of porous silicon. The shift in the valence band is larger than the shift in the conduction band and proportional to it, with a proportionality constant that is consistent with effective mass theory. No oxygen is detected in the as‐prepared porous silicon.
TL;DR: The electron optical-phonon coupling is studied in GaAs/Al x Ga 1-x As quantum wells as due to the interface modes, the confined slab mode in the well, and the half-space modes in the barriers.
Abstract: The electron optical-phonon coupling is studied in GaAs/Al x Ga 1-x As quantum wells as due to the interface modes, the confined slab modes in the well, and the half-space modes in the barriers. The polaron binding energy and effective mass are calculated and the relative importance of the different phonon modes is investigated as a function of the width of the quantum well. The full-energy spectrum, i.e., the discrete energy levels in the well and the continuum energy spectrum above the barrier, are included as intermediate states. The polaron binding energy and effective mass go continuously from the three-dimensional (3D) Al x Ga 1-x As to the 3D GaAs results when the well width varies from zero to infinity
TL;DR: In this article, a generic expression for the valence-band structure of strained group-IV semiconductors (Si, Ge, and Si1−xGex alloys) is presented.
Abstract: A generic expression is presented for the valence‐band structure of strained group‐IV semiconductors (Si, Ge, and Si1−xGex alloys) that takes into account spin‐orbit coupling. The valence band is obtained using k⋅p perturbation theory coupled with deformation potential theory. The band‐structure equation is put into a simplified form that can be readily used, viz., ∑i=03 ∑j=03−iaijEkjk2i=0, where k is the wave‐vector magnitude, Ek is the energy at k, and the coefficients aij are functions of band parameters and strain components. The band structure of strained silicon is qualitatively analyzed in relation to the well‐established piezoresistivity coefficients. Furthermore, a new coefficient is introduced that describes the first‐order change in carrier concentration effective mass per unit applied stress for different stress directions.
TL;DR: The low-T magnetic order in the metal helps to deconvolute contributions from charge correlations and spin fluctuations and helps to understand the evolution with pressure P and band filling y of the heat capacity, Hall coefficient, and resistivity at the approach to the Mott-Hubbard metal-insulator transition.
Abstract: We study the evolution with pressure P and band filling y of the heat capacity, Hall coefficient, and resistivity at the approach to the T→0 Mott-Hubbard metal-insulator transition (MIT) in highly correlated V_(2-y)O_3. Under P, the electronic effective mass m* diverges at the MIT with a negligible change in carrier concentration n away from half-filling. Conversely, in the doped system m* actually decreases as the MIT is approached, while n increases linearly with y. The low-T magnetic order in the metal helps us deconvolute contributions from charge correlations and spin fluctuations.
TL;DR: In this paper, it was shown that a spin gap opens and the linear coefficient of the specific heat decreases and then vanishes at the transition point of MT2 in sharp contrast with MT1.
Abstract: One type of Mott transition (MT1) is characterized by diverging enhancement of the charge effective mass when one approaches a Mott insulator from the side of the paramagnetic metal. Another fundamentally different type of Mott transition (MT2) is shown to exist when a spin gap opens. The linear coefficient of the specific heat γ decreases and then vanishes at the transition point of MT2 in sharp contrast with MT1. As an example, a dimerized t - J model is shown to undergo MT2. The underlying pairing mechanism determines the character of MT2. Recent controversial experimental results on the Mott transitions in copper oxides and other strongly correlated systems are discussed from the above viewpoint.
TL;DR: In this article, a curve-fitting procedure is developed to fit the reflectivity spectra with or without phonon-plasmon coupling, and the effective mass determined from 'plasma edge' measurements agrees well with the simple Kane model for n below 2.7*1019 cm-3.
Abstract: Nondestructive optical methods, based on measurements of the 'plasma edge' and the Moss-Burstein shift, are investigated as contactless alternatives to Hall measurements for determining carrier concentrations. Infrared reflection and transmission spectra of undoped and Si-doped InAs grown on GaAs by MBE are studied. A curve-fitting procedure is developed to fit the reflectivity spectra with or without phonon-plasmon coupling. The range of carrier concentrations over which these optical methods can provide useful characterization is evaluated. The effective mass determined from 'plasma edge' measurements agrees well with the simple Kane model for n below 2.7*1019 cm-3. For n above 4*1019 cm-3, the sample effective mass deviates considerably from the simple Kane model. Excitonic structure in the absorption edge is reported for high-purity undoped samples.
TL;DR: In this paper, a singularity in the charge susceptibility at the Mott transition point δ→0 is observed, leading to the anomaly of the charge mass m c * ∝|δ| -1, where δ is the doping concentration.
Abstract: Two-dimensional Hubbard model with both nearest- and next-nearest-neighbor transfers is studied. A singularity in the charge susceptibility at the Mott transition point δ→0 is observed, leading to the anomaly of the charge mass m c * in the form m c * ∝|δ| -1 , where δ is the doping concentration. The singularity is similar to that in the case without the next-nearest-neighbor transfer. This indicates that the singularity in the charge mass is a universal nature of this model, irrespective of its band structure.
TL;DR: In this paper, a single-band effective mass equation was used to analyze the waveguiding properties of the ballistic electron waveguides with and without spatially varying effective mass, and it was shown that heterostructure wells, homostructure voltage-induced wells, and heterostructured barriers can act as waveguiders for ballistic electrons.
Abstract: Semiconductor slab electron waveguides with and without spatially varying effective mass are analyzed using the single-band effective-mass equation. Starting with ballistic electron incidence on a potential energy/effective mass interface, expressions for the phase shift, the lateral shift, and the time delay upon total internal reflection are found. It is shown that heterostructure wells, homostructure voltage-induced wells, and heterostructure barriers can act as waveguides for ballistic electrons, and that the waveguiding is described by a single dispersion relation. The guided mode wave functions, dispersion curves, cutoffs, group velocity. effective mass, density of states, and ballistic guided current density are determined. >
TL;DR: In this article, a new integrable model of a strong correlated electronic system is formulated as a model of hole superconductivity, which is solved by using the Bethe ansatz.
Abstract: A new integrable model of a strong correlated electronic system is formulated as a model of hole superconductivity. The model is solved by using the Bethe ansatz. The critical exponents describing the decrease of correlation functions on long distances are derived. The behaviour of these correlations indicates that Cooper pairs of holes are formed in the repulsive region of the model. This conclusion is also confirmed by the calculation of the conductivity and the effective transport mass. In the attractive region, the model is a highly conducting system in which the current carriers with small effective mass are 'light fermions'.
TL;DR: The observation of the spin-doublet splitting of cyclotron resonance (CR) in a two-dimensional electron gas (2DEG) shows that the g factor of a 2DEG has a smaller energy dependence than that of bulk electrons.
Abstract: We report the observation of the spin-doublet splitting of cyclotron resonance (CR) in a two-dimensional electron gas (2DEG). Two discernible CR peaks, originating from spin-conserved transitions between adjacent sets of spin-split Landau states, are observed at a magnetic field as low as 4.4 T. The observed doublet features in the vicinity of even and odd integer filling factors are attributed to the linear dependence of the g factor and effective mass on the electron energy, respectively. In addition, our data show that the g factor of a 2DEG has a smaller energy dependence than that of bulk electrons.
TL;DR: A modified Schrodinger equation has been obtained for calculating the energy-wave-vector dispersion relationship of the two-band Kane model and has been applied to the case of a two-dimensional electron gas.
Abstract: A modified Schrodinger equation has been obtained for calculating the energy-wave-vector dispersion relationship of the two-band Kane model and has been applied to the case of a two-dimensional electron gas. The equation is applicable when the isoenergetic surfaces are not spheres and it is expressed as an infinite series whose summation provides compact solutions. With this equation, the transverse energy levels can he obtained by using an effective mass which is independent of the transverse energy, but there is a dependence of these energy levels on the parallel energy
TL;DR: In this article, the cyclotron mass in a parabolic quantum dot with weak magnetic field normal to the plane of the quantum dot is investigated theoretically, and it is shown that for weak magnetic fields (omega(c) much less than omega(LO), the mass of a parabolized quantum dot can be split into two cycloton masses (m+* and m-*).
Abstract: Cyclotron resonance of magnetopolarons in a parabolic quantum dot with weak magnetic field normal to the plane of the quantum dot is investigated theoretically. It is shown that for weak magnetic field (omega(c) much less than omega(LO)), the cyclotron mass in a parabolic quantum dot is split into two cyclotron masses (m+* and m-*). One (m+*) is larger than the bare band mass for large quantum dots but is lower than the bare band mass for small quantum dots, and with decreasing the effective confinement length of the quantum dot, the negative mass renormalization for the small quantum dots is important. The other (m-*) is greater than the bare band mass and might be a measurable effect for the small quantum dots.
TL;DR: The proton's effective mass grows significantly with density, and at higher densities the proton impurity can be localized, similar to that of the polaron in solids.
Abstract: We study interactions of a proton impurity with density oscillations of the neutron matter in a Debye approximation. The proton-phonon coupling is of the deformation-potential type at long wavelengths. It is weak at low density and increases with the neutron matter density. We calculate the proton's effective mass perturbatively for a weak coupling, and use a canonical transformation technique for stronger couplings. The proton's effective mass grows significantly with density, and at higher densities the proton impurity can be localized. This behavior is similar to that of the polaron in solids. We obtain properties of the localized proton in the strong-coupling regime from variational calculations, treating the neutron matter in the Thomas-Fermi approximation.
TL;DR: In this paper, the electronic structure of α-nodes was calculated within the local density approximation for the description of excitation energies, and the band structure was corrected to agree with energy differences at points of high symmetry by introducing additional external potentials on the atomic sites as well as on the interstitial positions of the diamond lattice.
Abstract: The electronic structure of \ensuremath{\alpha}-Sn is calculated within the local-density approximation. As a result of the inadequacies of this approximation for the description of excitation energies, the band structure is corrected to agree with energy differences at points of high symmetry by introducing additional external potentials on the atomic sites as well as on the interstitial positions of the diamond lattice. The resulting band structures are used to obtain effective masses as well as hydrostatic deformation potentials.
TL;DR: In this paper, a time dependent theoretical approach to calculate the electronic properties of semiconductor nanoclusters is presented, which can be applied to ground and excited electronic states without using the effective mass approximation or perturbative expansions.
Abstract: We present a time dependent theoretical approach to calculating the electronic properties of semiconductor nanoclusters. The technique can be applied to ground and excited electronic states without using the effective mass approximation or perturbative expansions. The effects of surface properties on the electronic structure can be calculated at an atomic level. We illustrate the method with calculations of ground state densities of states for CdS and CdSe crystallites between 19 and 33 A in diameter. The size‐dependence of the bandwidths and band gap is studied, and the influence of surface states and surface polarity is discussed. The calculated shift in the valence band edge with cluster size is compared with experimental results from valence‐band photoemission. Good agreement is obtained.
TL;DR: In this paper, the tunneling effective mass of electrons in undoped a−Si:H has been determined from measurements on Schottky diodes operating with high reverse fields.
Abstract: The tunneling effective mass of electrons in undoped a‐Si:H has been determined from measurements on Schottky diodes operating with high reverse fields. Under these conditions, the change of current with electric field is a sensitive function of effective mass. The tunneling effective mass was measured to be 0.09±0.02 me for a range of different samples giving a tunneling constant of ≊40 A.
TL;DR: In this article, the lowest-order constrained variational method is used to calculate the equation of state of hot nuclear matter for a wide range of densities of interest in heavy-ion collisions and astrophysics.
Abstract: The lowest-order constrained variational method is used to calculate the equation of state of hot nuclear matter. The calculations are performed for a wide range of densities of interest in heavy-ion collisions and astrophysics. A realistic nuclear Hamiltonian that contains N-N and N- Delta interactions and fits N-N scattering as well as nuclear matter saturation data is used. Besides spin, isospin, total angular momentum and density dependence, the correlation functions are also arranged to depend on the temperature of the system. The liquid-vapour phase equilibrium, as well as the behaviour of the effective mass in nuclear matter, is discussed.
TL;DR: In this paper, angle-resolved two-photon photoemission was used to measure changes in the binding energy and dispersion of image states for a Xe monolayer on the Ag(111) surface.
TL;DR: The spin-resolved cyclotron resonance of a two-dimensional electron gas in an InAs quantum well sandwiched by AlSb barriers is investigated and it is concluded that the effective mass is enhanced as a result of the penetration of electron wave functions into the barrier.
Abstract: The spin-resolved cyclotron resonance of a two-dimensional electron gas in an InAs quantum well sandwiched by AlSb barriers has been investigated to determine the energy dependence of the effective mass. We observe variations of the cyclotron mass correlated with the filling factor due to the linear dependence of the effective mass and Land\'e g factor on the electron energy. The experimental results are analyzed by the envelope-function approximation under a four-band k\ensuremath{\cdot}p model which leads to a renormalized effective mass in the well. Excellent agreement with experiment is achieved and we are able to conclude that the effective mass is enhanced as a result of the penetration of electron wave functions into the barrier.
TL;DR: In this article, the fabrication and characterization of a high-quality two-dimensional electron system in the X-point valley of an AlAs quantum well was reported, which has a density of ns=2.5×1011 cm−2 and low-temperature mobility μ=3×104 cm2/V
Abstract: We report the fabrication and characterization of a high‐quality two‐dimensional electron system in the X‐point valley of an AlAs quantum well. The modulation doped structure has a density of ns=2.5×1011 cm−2 and low‐temperature mobility μ=3×104 cm2/V s. Cyclotron resonance data reveal an effective mass mc=0.46m0, indicating that the X‐point conduction valleys with heavy in‐plane mass are occupied. In the magnetotransport data, we observe quantum Hall states at consecutive integral Landau‐level fillings (ν), implying that the degeneracy of these valleys is lifted. Our data at high magnetic fields show well‐developed fractional quantum Hall states at ν=1/3 and 2/3 with a gap of 1/3Δ=1.3K for the ν=1/3 state at B≊30 T.