We have studied the influence of piezoelectric fields on luminescence properties of GaInN strained quantum wells. Our calculation suggests that an electric field of 1.08 MV/cm is induced by the piezoelectric effect in strained Ga0.87In0.13N grown on GaN. The photoluminescence peak energy of the Ga0.87In0.13N strained quantum wells showed blue shift with increasing excitation intensity. Moreover, the well-width dependence of its luminescence peak energy was well explained when the piezoelectric fields were taken into account. These results clearly showed that the piezoelectric field induced the quantum-confined Stark effect.
The composition of alloys in strained ternary alloy layers, Al
x
Ga1-
x
N (0<x<0.25) and Ga1-
x
In
x
N (0<x<0.20), on thick GaN was precisely determined using the high-resolution X-ray diffraction profile. The band gap of strained AlGaN is found to increase almost linearly according to the AlN molar fraction, while that of strained GaInN has a large bowing parameter of 3.2 eV.
Two-dimensional density-matrix renormalization group method is employed to examine the ground state phase diagram of the Hubbard model on the triangular lattice at half-filling. The calculation reveals two discontinuities in the double occupancy with increasing the repulsive Hubbard interaction U at Uc1 ∼ 7.8t and Uc2 ∼ 9.9t (t being the hopping integral), indicating that there are three phases separated by first order transitions. The absence of any singularity in physical quantities for 0 ≤ U < Uc1 implies a metallic phase in this regime. For U > Uc2, the local spin density induced by an applied pinning magnetic field exhibits a three sublattice feature, which is compatible with the 120 • Néel ordered state realized in the limit of U → ∞. For Uc1 < U < Uc2, a response to the applied pinning magnetic field is comparable to that in the metallic phase with a relatively large spin correlation length, but showing neither valence bond nor chiral magnetic order, which therefore resembles gapless spin liquid. However, the spin structure factor for the intermediate phase exhibits the maximum at the K and K points in the momentum space, which is not compatible to spin liquid with a large spinon Fermi surface. The calculation also finds that the pairing correlation function monotonically decreases with increasing U and thus the superconductivity is unlikely in the intermediate phase.arXiv:1606.06814v2 [cond-mat.str-el]
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