arXiv subjects

Kenta Takata

Publications and source records attributed to Kenta Takata.

22 records · Page 2Linked to original sources

arXiv2014

Data Search by a Laser Ising Machine with Gradual Pumping or Coupling

We study two operational schemes for a coherent Ising machine based on an injection-locked laser network. These schemes gradually increase the pumping rate or the mutual coupling among the slave lasers. We numerically simulate the two schemes against a data search problem implemented with the Ising model in cubic graphs without frustration. We show the machine can achieve a better success probability and effective computational time to find a target/ground state with these gradual schemes than those with the abrupt introduction of the mutual injection which has been studied previously. The computational time simulated with typical parameters is almost constant up to the problem size M = 200 and turns into a nearly linear scale holding up to M = 1000.

quant-ph↗

arXiv2012

Valence-band structure of ferromagnetic semiconductor (InGaMn)As

To clarify the whole picture of the valence-band structures of prototype ferromagnetic semiconductors (III,Mn)As (III: In and Ga), we perform systematic experiments of the resonant tunneling spectroscopy on [(In_0.53Ga_0.47)_1-x Mn_x]As (x=0.06-0.15) and In_0.87Mn_0.13As grown on AlAs/ In_0.53Ga_0.47As:Be/ p+InP(001). We show that the valence band of InGaMnAs almost remains unchanged from that of the host semiconductor InGaAs, that the Fermi level exists in the band gap, and that the p-d exchange splitting in the valence band is negligibly small in (InGaMn)As. In the In0.87Mn0.13As sample, although the resonant peaks are very weak due to the large strain induced by the lattice mismatch between InP and InMnAs, our results also indicate that the Fermi level exists in the band gap and that the p-d exchange splitting in the valence band is negligibly small. These results are quite similar to those of GaMnAs obtained by the same method, meaning that there are no holes in the valence band, and that the impurity-band holes dominate the transport and magnetism both in the InGaMnAs and In_0.87Mn_0.13As films. This band picture of (III,Mn)As is remarkably different from that of II-VI-based diluted magnetic semiconductors.

cond-mat.mtrl-sci↗

arXiv2011

Comment on "Reconciling results of tunnelling experiments on (Ga,Mn)As" arXiv:1102.3267v2 by Dietl and Sztenkiel

We comment on the recent paper "Reconciling results of tunnelling experiments on (Ga,Mn)As" arXiv:1102.3267v2 by Dietl and Sztenkiel. They claimed that the oscillations observed in the d2I/dV2-V characteristics in our studies on the resonant tunneling spectroscopy on GaMnAs, are not attributed to the resonant levels in the GaMnAs layer but to the two-dimensional interfacial subbands in the GaAs:Be layer. Here, we show that this interpretation is not able to explain our experimental results and our conclusions remain unchanged.

cond-mat.mtrl-sci↗

arXiv2010

Universal valence-band picture of the ferromagnetic semiconductor GaMnAs

The origin of ferromagnetism in the prototype ferromagnetic semiconductor GaMnAs is still controversial due to the insufficient understanding of its band structure and Fermi level position. Here, we show the universal valence-band (VB) picture of GaMnAs obtained by resonant tunneling spectroscopy for a variety of surface GaMnAs layers with the Mn concentrations from 6 to 15% and the Curie temperatures from 71 to 154 K. We find that the Fermi level exists in the bandgap, and that the VB structure of GaAs is almost perfectly maintained in all the GaMnAs samples, i.e. VB is not merged with the impurity band. Furthermore, the p-d exchange splitting of VB is found to be quite small (only several meV) even in GaMnAs with a high Curie temperature (154 K). These results indicate that the VB structure of GaMnAs is quite insensitive to the Mn doping.

cond-mat.mtrl-sci↗