@conference {339, title = {A Multi-functional Spintronic Device Driven by Spin-orbit Interactions}, year = {2016}, month = {25{\textendash}27 Jan 2016}, pages = {O3-NP1 01}, publisher = {Annual Meeting of the Physical Society of the Republic of China}, address = {National Sun Yat-sen University, Kaohsiung}, abstract = {We propose a simple two-terminal device that operates simultaneously as (i) a spin inverter for an incident polarized electron, (ii) a spin polarizer for an unpolarized source and (iii) a tunable spin current attenuator at certain range of electron energies. The device consists of a U-shaped nanowire with a uniform Dresselhaus spin-orbit coupling and a spatially-modulated Rashba spin-orbit coupling along the curved section. The latter is implemented through a tunable gate voltage at every alternating segment along the wire{\textquoteright}s arc. This multi-purpose device does not need magnetic components or an external magnetic field to carry out the different functions as enumerated above. We discuss how the interplay of the wire{\textquoteright}s geometry and the spin-orbit interaction present in the device drives its spin transport.}, url = {http://psroc2016.conf.tw}, author = {Carlos Baldo III and Cristine Villagonzalo} } @article {baldo2016a, title = {Spin inverter and polarizer curved nanowire driven by Rashba and Dresselhaus spin-orbit interactions}, journal = {Physica E}, volume = {83}, year = {2016}, note = {cited By 0; Article in Press}, pages = {498-504}, abstract = {
We propose in theory a curved nanowire structure that can both serve as a spin inverter and a spin polarizer driven by a periodic Rashba spin{\textendash}orbit coupling (SOC) and a uniform Dresselhaus SOC. The curved section of the U-shaped quasi-one dimensional nanowire with an arc of radius R and circumferential length πR is divided into segments of equal length initially having only its inherent homogeneous Dresselhaus SOC. Then a Rashba-type SOC is applied at every alternating segment. By tuning the Rashba SOC strength and the incident electron energy, this device can flip the spin at the output of an incoming spin-polarized electron. On the other hand, this same device acts as a spin filter for an unpolarized input for which an outgoing electron with a non-zero polarization can be achieved without the application of an external magnetic field. Moreover, the potential modulation caused by the periodic Rashba SOC enables this device to function as an attenuator for a certain range of incident electron energies that can make the probability current density drop to 10^(-4) of its otherwise magnitude in other regimes.
}, doi = {10.1016/j.physe.2015.11.024}, author = {Carlos F Baldo III and Cristine Villagonzalo} } @inproceedings {baldo-spp-2015, title = {Electron spin polarization along a one-dimensional wire with periodic Rashba and uniform Dresselhaus spin-orbit couplings}, booktitle = {Proceedings of the 33rd Samahang Pisika ng Pilipinas Physics Congress}, year = {2015}, month = {3{\textendash}6 Jun 2015}, pages = {SPP-2015-3B-05}, address = {University of Northern Philippines, Vigan City}, abstract = {
We investigate the transmission of an electron spin on a one-dimensional wire with a periodic Rashba spin-orbit couplings (SOC) and a constant contribution from a Dresselhaus SOC. The straight wire is divided into initially uniform segments and the Rashba SOC is turned on every alternating segment. Eigenvalues and eigenfunctions for both without and with Rashba SOC segments are analytically derived. From these obtained values, we numerically calculate the net polarization at the output. We find in our result that regardless of the initial spin orientation, the output polarization turns out to be spin-up polarized. The modulation effect of the segment length of the wire via a periodic Rashba SOC is manifested by the appearance of an energy gap whose width increases with larger Rashba coupling strength. On the other hand, the position of the gap can be tuned by setting the strength of the Dresselhaus SOC. We find that for electrons with Fermi energies falling within this gap, the output spin current is unpolarized.
}, author = {Carlos F Baldo III and Cristine Villagonzalo} } @conference {349, title = {Optimal curvilinear transport of a spin-polarized electron with Rashba and Dresselhaus spin-orbit coupling in a uniform magnetic field}, year = {2015}, month = {7{\textendash}11 Jan 2015}, pages = {C3-13}, publisher = {9th International Conference on Computational Physics}, address = {National University of Singapore}, abstract = {The spin-polarized transport of an electron along a curved-one dimensional wire with Rashba and Dresselhaus spin-orbit couplings (SOCs) and a uniform perpendicular magnetic field is considered in this study. Here we analytically derived the appropriate eigenenergies and eigenvalues of the system and numerically determine the output transmission coefficients. Spin polarization, probability current density and conductance are then obtained using transfer matrix approach to examine the dependence of spin transport on the radius, R, of curved wire, on the external magnetic field, B, and on the SOCs strengths.
From our results, we find the condition, B ≈ R^(1/3), at which there would be no spin switching regardless of the SOC strengths. A value of R beyond this condition will no longer have a spin reversal. Moreover, for a material with sufficiently strong SOCs, regardless of its type, the effect of the external magnetic field is reduced. The effective SOC strength follows the standard form equation of a circle in which the Rashba SOC and the Dresselhaus SOC are the component coordinates. From here, we optimize the probability current density by properly tuning the Rashba coupling strength for a given value of B, R and Dresselhaus SOC.}, url = {http://www.physics.nus.edu.sg/iccp9/}, author = {Carlos F Baldo III and Cristine Villagonzalo} } @conference {baldo-qpcmp-2015, title = {Spin switching in a spin-orbit coupled transport in a curved nanowire}, year = {2015}, month = {22{\textendash}23 Apr 2015}, publisher = {Workshop on Theories in Quantum Phenomena and Condensed Matter Physics}, address = {University of the Philippines Los Ba{\~n}os, Laguna}, url = {https://imsp.uplb.edu.ph/index.php/component/content/article/17-imsp-news/research/370-workshop-on-theories-in-quantum-phenomena-and-condensed-matter-physics}, author = {Carlos F Baldo III} } @inproceedings {baldo-spp-2014, title = {Magnetoconductance of a spin polarized electron along a curved one-dimensional wire}, booktitle = {Proceedings of the 32nd Samahang Pisika ng Pilipinas Physics Congress}, year = {2014}, month = {17{\textendash}20 Oct 2014}, pages = {SPP2014-1A-6}, address = {University of the Philippines Diliman, Quezon City}, abstract = {
In this paper, we revisit our transport studies on the motion of a spin-polarized electron along a curved quantum wire under the presence of a uniform perpendicular magnetic field B and both the Rashba and Dresselhaus spin-orbit couplings (SOCs). Then from the previously derived output transmission coefficients, we numerically determine the magnetoconductance of the electron motion along the curved wire. Our results agree with our earlier reports that for large effective SOCs, the effects of B on spin switching is reduced. Moreover, we found that for a given energy\ E, the desired high MC ratio can be achieved by tuning B. Finally, with large R the MC reduces significantly due to adiabatic transport.
}, author = {Carlos F Baldo III and Cristine Villagonzalo} } @article {Baldo201493, title = {Spin-orbit coupled transport in a curved quantum wire}, journal = {Physica E}, volume = {63}, year = {2014}, note = {cited By 0}, pages = {93-98}, abstract = {
We study the interplay of both Rashba and Dresselhaus spin{\textendash}orbit couplings (SOCs) and a uniform perpendicular magnetic field B on the transport of a spin-polarized electron along a curved quantum wire. Eigenenergies and eigenfunctions of the system were analytically solved in the presence of both SOCs for a confinement radius R. From the transmission coefficients, the spin transport properties such as spin polarization, probability current density and spin conductance were computed numerically to determine their dependence on the SOCs, B and R. We find the condition for B that if it is beyond R1/3, no spin reversal will occur. Our results show that for a sufficiently large SOC strength, regardless of its inversion asymmetry origin, the effect of the external magnetic field is reduced. Finding the optimal effective SOC strength is essential in achieving suitable magneto-transport properties for possible spintronic device applications.
}, doi = {10.1016/j.physe.2014.05.013}, author = {Carlos F Baldo III and Cristine Villagonzalo} } @inproceedings {baldo-spp-2013, title = {Spin switching on a quantum wire with spin orbit coupling in a uniform magnetic field}, booktitle = {Proceedings of the 31st Samahang Pisika ng Pilipinas Physics Congress}, year = {2013}, month = {23{\textendash}25 Oct 2013}, pages = {SPP2013-5B-4}, address = {University of San Carlos, Cebu City}, abstract = {
In this paper, the interplay of a uniform perpendicular magnetic field and the radius of curvature on the spin transport along a curved quantum wire with Rashba and Dresselhaus spin-orbit interactions is investigated. From the analytic calculations of the system{\textquoteright}s eigenenergies and eigenfunctions, transmission coefficients were numerically determined using transfer-matrix approach and were used to calculate the probability current densities and output polarization. Our results show that the spin orientation of the initially spin-polarized electron can be switched for smaller values of radius of curvature of the curved quantum wire. However, the range of spin switching is largely dependent on the threading magnetic field and on the strength of the spin-orbit interactions.
}, author = {Carlos F Baldo III and Cristine Villagonzalo} } @article {BaldoIII2012, title = {Low-lying spin excitations due to next-nearest neighbour interactions in a ferromagnetic lattice with a body-centred cubic (bcc) crystal structure}, journal = {J. Phys. Conf. Ser.}, volume = {400}, number = {PART 3}, year = {2012}, note = {cited By 0}, pages = {032007}, abstract = {
Spin excitations due to the next-nearest-neighbour interactions are investigated for a ferromagnetic lattice with a body-centred cubic (bcc) crystal structure. Using the three-dimensional Heisenberg spin model in a uniform external magnetic field, both the nearest-neighbour (NN) and next-nearest-neighbour (NNN) exchange interactions are considered. The spin wave energies at low temperatures are calculated for which the system is close to its ground state. From the dispersion plots, the additional exchange interactions by the NNN cause an increase in the spin excitation energies. Furthermore, there is a critical NNN/NN exchange ratio for which the effect of the NNN interactions becomes evident as characterized by the presence of two maximum energy peaks in the energy spectra.
}, doi = {10.1088/1742-6596/400/3/032007}, author = {Carlos F Baldo III and Cristine Villagonzalo} } @inproceedings {244, title = {Rashba and Dresselhaus spin-orbit interactions in a curvilinear motion of a spin-polarized electron}, booktitle = {Proceedings of the 30th Samahang Pisika ng Pilipinas Physics Congress}, year = {2012}, month = {22{\textendash}24 Oct 2012}, pages = {SPP-2012-054}, address = {De La Salle Health Sciences Institute, Dasmari{\~n}as, Cavite}, abstract = {
To see the effects of both Rashba and Dresselhaus spin-orbit interactions on a spin-polarized electron along a curved path, we obtain the system{\textquoteright}s exact energy spectrum taking into account the Zeeman effect. This approximates the motion of an electron in a one-dimensional wire. Our results show that the lifted degeneracy between spins of opposite polarization does not only depend on both Rashba and Dresselhaus coupling constants, but also on the radius of curvature.
}, author = {Carlos F Baldo III and Cristine Villagonzalo} } @inproceedings {baldospp2010, title = {Spin waves in a simple ferromagnetic cubic lattice using the Heisenberg model with nearest and next-nearest neighbor interactions}, booktitle = {Proceedings of the 28th Samahang Pisika ng Pilipinas Physics Congress}, year = {2010}, month = {25{\textendash}27 Oct 2010}, pages = {SPP-2010-006}, address = {Meralco Management and Leadership Development Center, Antipolo City}, abstract = {
We study the combined effect of the nearest and the next-nearest neighbor interactions on the spin wave dispersion of an isotropic cubic ferromagnet in a uniform magnetic field using the Heisenberg model. Near the groundstate, the components of the spin angular momentum perpendicular to the applied field are negligible as compared to the parallel spin component. Hence, the dispersion relation and the ground state energy estimate of the system are obtained by considering the spin fluctuations along the plane normal to the magnetic field. The results herein are compared to the case where only the effect of the nearest neighbors are present.
}, author = {Carlos F Baldo III and Cristine Villagonzalo} }