Dependence Of G-factor Research Articles

Analogy and dissimilarity of excitons in monolayer and bilayer of MoSe2

Excitons in thin layers of semiconducting transition metal dichalcogenides are highly subject to the strongly modified Coulomb electron–hole interaction in these materials. Therefore, they do not follow the model system of a two-dimensional hydrogen atom. We investigate experimentally and theoretically excitonic properties in both the monolayer (ML) and the bilayer (BL) of MoSe2 encapsulated in hexagonal BN. The measured magnetic field evolutions of the reflectance contrast spectra of the MoSe2 ML and BL allow us to determine g-factors of intralayer A and B excitons, as well as the g-factor of the interlayer exciton. We explain the dependence of g-factors on the number of layers and excitation state using first principles calculations. Furthermore, we demonstrate that the experimentally measured ladder of excitonic s states in the ML can be reproduced using the approach with the Rytova–Keldysh potential that describes the electron–hole interaction. In contrast, the analogous calculation for the BL case requires taking into account the out-of-plane dielectric response of the MoSe2 BL.

Circular dichroism and enantio-selective catalytic effect of copper sulfide

Chiral inorganic nanomaterials provide a platform for a variety of applications. Chiral ligands are commonly used to induce chiroptical activity of nanoparticles through chiral transfer, while few materials have intrinsic chirality and the origins of their chirality are unclear as well. Here, several hexagonal copper sulfide (CuS) structures with achiral morphology which showed negative circular dichroism (CD) signals are reported. Although these CuS structures had variable maximum of anisotropic g-factor, the wavelength dependence of g-factor due to the structure-dependent chiroptical activity were similar for all these CuS structures, indicating that the negative CD activity could derive from some common microstructure in CuS. The simulation based on density functional theory (DFT) and time-dependent DFT (TDDFT) revealed that the CD may originate from (Cu3S3)2 nanostructure existing in hexagonal CuS. The enantio-selective catalysis of these homochiral CuS structure for oxidation of d-DOPA and l-DOPA was also investigated. All samples exhibited preferential catalysis of l-DOPA, which is conducive to distinguishing l-DOPA from d-DOPA. This work not only reveals the origin of CD in CuS inorganic structures with achiral morphology for the first time, but also provides a profound insight of applications of homochiral CuS structures in catalysis.

Electron g -factor of valley states in realistic silicon quantum dots

We theoretically model the spin-orbit interaction in silicon quantum dot devices, relevant for quantum computation and spintronics. Our model is based on a modified effective mass approach with spin-valley boundary conditions, derived from the interface symmetry under presence of perpendicular to the interface electric field. The g-factor renormalization in the two lowest valley states is explained by the interface-induced spin-orbit 2D (3D) interaction, favoring intervalley spin-flip tunneling over intravalley processes. We show that the quantum dot level structure makes only negligible higher order effects to the g-factor. We calculate the g-factor as a function of the magnetic field direction, which is sensitive to the interface symmetry. We identify spin-qubit dephasing sweet spots at certain directions of the magnetic field, where the g-factor renormalization is zeroed: these include perpendicular to the interface magnetic field, and also in-plain directions, the latter being defined by the interface-induced spin-orbit constants. The g-factor dependence on electric field opens the possibility for fast all-electric manipulation of an encoded, few electron spin-qubit, without the need of a nanomagnet or a nuclear spin-background. Our approach of an almost fully analytic theory allows for a deeper physical understanding of the importance of spin-orbit coupling to silicon spin qubits.

Zeeman spectroscopy of excitons and hybridization of electronic states in few-layer WSe2, MoSe2 and MoTe2

Monolayers and multilayers of semiconducting transition metal dichalcogenides (TMDCs) offer an ideal platform to explore valley-selective physics with promising applications in valleytronics and information processing. Here we manipulate the energetic degeneracy of the and valleys in few-layer TMDCs. We perform high-field magneto-reflectance spectroscopy on WSe2, MoSe2, and MoTe2 crystals of thickness from monolayer to the bulk limit under magnetic fields up to applied perpendicular to the sample plane. Because of a strong spin-layer locking, the ground state A excitons exhibit a monolayer-like valley Zeeman splitting with a negative g-factor, whose magnitude increases monotonically when crystal thickness decreases from bulk to a monolayer. Using kp calculations, we demonstrate that the observed dependence of g-factors for different materials is well accounted for by hybridization of electronic states in the and valleys. The mixing of the valence and conduction band states induced by the interlayer interaction decreases the g-factor with increasing layer number. The effect is the largest for MoTe2, followed by MoSe2, and the smallest for WSe2.

EPR studies of SmBa2Cu3O7-δ/MnFe2O4 superconducting composites

Electron paramagnetic resonance (EPR) studies are carried out on composite samples of SmBa2Cu3O7-δ/(MnFe2O4)x superconductors with 0.00 ≤ x ≤ 0.20 wt% at different temperatures 100K ≤ T ≤ 295K. An EPR signal of Cu2+ ions in the orthorhombic local symmetry is observed. Moreover, the EPR signal intensity increases as the temperature decreases from room temperature down to 100 K. The temperature dependence of g-factors indicates the pseudogap onset temperature (T*), corresponding to the peak of the observed curves between 127 K and 162 K. The number of spins (N) participating in EPR resonance are calculated as a function of both nanosized MnFe2O4 addition and temperature. In particular, it is shown that any EPR signal for SmBa2Cu3O7-δ/(MnFe2O4)x is probably due to small amount of spurious phases typically present in the samples such as BaCuO2. The presence of BaCuO2 is confirmed by magnetization-field (M-H) hysteresis measurements

G-factor modification in a bulk InGaAs epilayer by an in-plane electric field

We report on the modification of the g-factor by an in-plane electric field in an In$_{0.031}$Ga$_{0.969}$As epilayer. We performed external magnetic field scans of the Kerr rotation of the InGaAs film in order to independently determine the g-factor and the spin-orbit fields. The g-factor increases from $-0.4473\pm0.0001$ at 0 V/cm to $-0.4419\pm0.0001$ at 25 V/cm applied along the [1$\overline{1}$0] crystal axis. In addition, spatially-resolved spin measurements show a g-factor dependence on diffusive velocity. The change in g-factor with electric field can have a large effect on the determination of the internal spin-orbit and nuclear fields from Larmor precession frequency measurements.

Abrupt barrier contribution to electron spin splitting in asymmetric coupled double quantum wells

We have studied the behavior of the electronic energy spin-splitting of InGaAs-InAlAs based double quantum wells (narrow gap structures) under in-plane magnetic and transverse electric fields. We have developed an improved 8x8 version of the Transfer Matrix Approach that consider contributions from abrupt interfaces and external fields when tunneling through central barrier exists. We have included the Land\'e g-factor dependence on the external applied field. Also, we have calculated electron density of states and photoluminescence excitation. Variations of the electron spin-splitting energy lead to marked peculiarities in the density of states. Because the density of states is directly related to photoluminescence excitation, these peculiarities are observable by this technique.

Electron spin lifetime of a single antimony donor in silicon

We present measurements of the electron spin lifetime (T1) of a single Sb donor in Si. For a magnetic field (B) oriented along the [100] Si crystal direction and low temperature (T) such that kT≪gμB, we find T1−1=KB5, where K=1.7×10−3 Hz T−5. The T1−1∝B5 dependence is expected for donor electron spin relaxation due to g-factor dependence on crystal strain. The magnitude of T1 is within a factor of two of theoretical estimates and is in close agreement with values obtained for bulk donor ensembles.

Effects of sp-d exchange on a bound polaron and the g-factor of the exciton in a GaMnAs quantum dot

Magneto bound polaron in a GaMnAs/Ga0.6Al0.4As quantum dot is investigated with the inclusion of exchange interaction effects due to Mn alloy content and the geometrical confinement. The exciton binding energy and the optical transition energy are computed as functions of dot radius and the magnetic field strength for a fixed Mn alloy content (x=0.02) in a GaMnAs quantum dot. Numerical calculations are performed using variational method within a single band effective mass approximation. The spin polaronic energy of the heavy hole exciton is studied with the spatial confinement using a mean field theory in the presence of magnetic field strength. The magnetization as a function of dot radius is investigated in a GaMnAs/Ga0.6Al0.4As quantum dot. The magnetic field induced size dependence of g-factor is studied. The effective g-factor of conduction (valence) band electron (hole) is obtained in the GaMnAs quantum dot. The results bring out that (i) the geometrical dependence on sp-d exchange interaction in the GaMnAs/Ga0.6Al0.4As quantum dot has great influence with the magnetic field strength, (ii) the Landé factor is more sensitive if the geometrical confinement effect is included and (iii) the value of g-factor increases when the magnetic field strength is enhanced for all the dot radii. Our results are in good agreement with the other investigators.

Gyromagnetic factors and atomic clock constraints on the variation of fundamental constants

We consider the effect of the coupled variations of fundamental constants on the nucleon magnetic moment. The nucleon g-factor enters into the interpretation of the measurements of variations in the fine-structure constant, alpha, in both the laboratory (through atomic clock measurements) and in astrophysical systems (e.g. through measurements of the 21 cm transitions). A null result can be translated into a limit on the variation of a set of fundamental constants, that is usually reduced to alpha. However, in specific models, particularly unification models, changes in alpha are always accompanied by corresponding changes in other fundamental quantities such as the QCD scale, Lambda_QCD. This work tracks the changes in the nucleon g-factors induced from changes in Lambda_QCD and the light quark masses. In principle, these coupled variations can improve the bounds on the variation of alpha by an order of magnitude from existing atomic clock and astrophysical measurements. Unfortunately, the calculation of the dependence of g-factors on fundamental parameters is notoriously model-dependent.

Compositional dependence of g-factor and damping constant of (Gd100-xREx)FeCo alloy films (RE = Yb, Tm, Er)

Time domain magnetization dynamics of (Gd100-xREx)FeCo (RE = Yb, Tm, Er) alloy films with various compositions were measured by pump-probe method using a high energy ultra short pulse fiber laser, and their g-factors and damping constants were estimated. The g-factor of GdFeCo became large near the angular moment compensation point CA, which is qualitatively consistent with the simple mean field model. On the other hand, the damping constants took a maximum near magnetization compensation point, which is not described by the mean field model. Substitution of Tm or Er for Gd results in the significant increase of damping constant; (Gd90Tm10)FeCo and (Gd90Er10)FeCo exhibit roughly 3-6 times large damping constant compared to GdFeCo, while (Gd90Yb10)FeCo has almost the same damping constant as GdFeCo. This means that the damping constant is significantly modified by the orbital moment of RE atoms.

Angular and temperature-related specific features of averaging of hole effective masses in p-Ge at low temperatures

We report the results of an experimental study of the magnetoresistance ρxx and ρxy in two samples of p-Si/SiGe with low carrier concentrations p = 8.2 × 1010 cm-2 and p = 2 × 1011 cm-2. The research was performed in the temperature range of 0.3–2 K and in the magnetic fields of up to 18 T, parallel or tilted with respect to the two-dimensional (2D) channel plane. The large in-plane magnetoresistance can be explained by the influence of the in-plane magnetic field on the orbital motion of the charge carriers in the quasi-2D system. The measurements of ρxx and ρxy in the tilted magnetic field showed that the anomaly in ρxx, observed at filling factor ν = 3/2 is practically nonexistent in the conductivity σxx. The anomaly in σxx at ν = 2 might be explained by overlapping of the levels with different spins 0 ↑ and 1 ↓ when the tilt angle of the applied magnetic field is changed. The dependence of g-factor g*(Θ)/g*(00) on the tilt angle Θ was determined.

Magnetoresistance in dilute p-Si/SiGe in parallel and tilted magnetic fields

We report the results of an experimental study of the magnetoresistance $\rho_{xx}$ and $\rho_{xy}$ in two samples of $p$-Si/SiGe with low carrier concentrations $p$=8.2$\times10^{10}$ cm$^{-2}$ and $p$=2$\times10^{11}$ cm$^{-2}$. The research was performed in the temperature range of 0.3-2 K and in the magnetic fields of up to 18 T, parallel or tilted with respect to the two-dimensional (2D) channel plane. The large in-plane magnetoresistance can be explained by the influence of the \textit{in-plane} magnetic field on the orbital motion of the charge carriers in the quasi-2D system. The measurements of $\rho_{xx}$ and $\rho_{xy}$ in the tilted magnetic field showed that the anomaly in $\rho_{xx}$, observed at filling factor $\nu$=3/2 is practically nonexistent in the conductivity $\sigma_{xx}$. The anomaly in $\sigma_{xx}$ at $\nu$=2 might be explained by overlapping of the levels with different spins 0$\uparrow$ and 1$\downarrow$ when the tilt angle of the applied magnetic field is changed. The dependence of g-factor $g^*(\Theta)/g^*(0^0)$ on the tilt angle $\Theta$ was determined.

Compositional Dependence of g-Factor and Damping Constant of GdFeCo Amorphous Alloy Films

Time-domain magnetization dynamics of sputtered GdFeCo (30 nm) amorphous alloy films was measured by pump-probe method using high-power ultra-short pulse fiber laser. The effective g-factor g eff and effective damping constant alphaeff of the GdFeCo films were estimated by using a numerical calculation of Landau-Lifshitz-Gilbert equation. The precessional frequency took a maximum near the magnetization compensation composition C M of the GdFeCo, while the estimated g eff and alphaeff increased around the angular momentum compensation composition C A. The compositional dependences of g eff and alphaeff were roughly described by a mean-field model. The g eff and alphaeff were also estimated from the ferromagnetic resonance (FMR) spectra, and the data from the FMR spectra agreed well with those from the pump-probe measurement except for the composition near C M. The FMR method was unable to excite the magnetization near C M because of the small net magnetization.

Dependence of electron spin g-factor on magnetic field in quantum wells

The dependence of electron spin g-factor on magnetic field has been investigated in GaAs/AlGaAs quantum wells. We have estimated the electron g-factor from spin precession frequency in time-resolved photoluminescence measurements under a magnetic field in different configurations; the magnetic field perpendicular ( g ⊥) and parallel ( g ∥) to the quantum confinement direction. When the angle between the magnetic field and the confinement direction is 45°, we have found that g-factor varies depending on the direction of magnetic field and the circular polarization type of excitation light ( σ + or σ −). These dependences of g-factor exhibit main features of Overhauser effect that nuclear spins react back on electron spin precession. The value of g ⊥ and g ∥ corrected for the nuclear effects agree well with the results of four-band k·p perturbation calculations.

Effects of disorder on electron spin dynamics in a semiconductor quantum well

Using the spin of the electron to carry information, instead of or in addition to its charge, could provide advances in the capabilities of microelectronics. Successful implementation of spin-based electronics requires preservation of the electron spin coherence. In n-doped semiconductors, long spin-coherence times have been observed, with a maximum at a ‘magic’ electron density. Here, we vary the density in a two-dimensional electron gas, and show that spin coherence is lost because of the interplay between localization by disorder and dynamical scattering. By measuring the electron Lande g-factor dependence on density, we determine the density of states (DOS), which characterizes the disorder potential. Using our knowledge of the DOS, a simple model estimates the temperature and excitation intensity dependence of the g factor, qualitatively agreeing with experiments. This agreement confirms the importance of disorder and provides predictive power for designing spin-based electronic devices.

EPR Study of the Electronic States of β’-(BEDT-TTF)(TCNQ)

β′-(BEDT-TTF)(TCNQ) is a compound of BEDT-TTF (=ET) and TCNQ molecules aligned orthogonally with each other, forming two-dimensional sheets and one-dimensional columns of 1/4-filled π band, respectively. It is known that the metal-insulator transition occurs at 330 K at ambient pressure. We have measured the electronic spin susceptibility by means of the EPR-NMR method at 50 MHz, and the angular dependence of g-factor and line width of EPR both at Q (34 GHz) and W (94 GHz) band. We successfully confirmed that the antiferromagnetic transition occurs in ET sheets and TCNQ columns, independently.

Anisotropy of ESR parameters in organic ferromagnet TDAE-C 60

We study the anisotropy of ESR parameters using single crystal TDAE-C 60, which has two polymorphisms: the one is ferromagnetic a-phase and the other is non-ferromagnetic α′-phase. In both α′- and α-phase, the line-widths and g-factors show anisotropic angular dependences at room temperature, such as ΔH pp b > ΔH pp c ∼ ΔH pp a and g c > g b = g a. The anisotropic behaviour of g-factors in both phases suggest the uniaxial rotation of Jahn-Teller distorted C 60 molecules around the c-axis, which is the close-packing direction of C 60 molecules. In the α′-phase the temperature dependence of g-factors has a clear anomaly around 160 K. Below this temperature, the observed g-factors are in-between the monovalent C 60 and TDAE +, indicating the restoration of missing TDAE spins. In the α-phase, the g-factors continuously shift with decreasing temperature, become anisotropic below 230 K, and show no remarkable anomaly at the structural phase transition temperature. These results suggest that the difference exists in the mixing between the wave functions of C 60 and TDAE, which is possibly developed by the structural difference between α′- and α-phases. This difference separates the magnetic peculiarities of two polymorphisms in TDAE-C 60.

Magneto-optical response of CdSe nanostructures

We present theoretical calculations of the Land\'e g-factors of semiconductor nanostructures using a time-dependent empirical tight-binding method. The eigenenergies and eigenfunctions of the band edge states are calculated as a function of an external magnetic field with the electromagnetic field incorporated into the tight-binding Hamiltonian in a gauge-invariant form. The spin-orbit interaction and magnetic field are treated non-perturbatively. The g-factors are extracted from the energy splitting of the eigenstates induced by the applied magnetic field. Both electron and hole g-factors are investigated for CdSe nanostructures. The size and aspect ratio dependence of g-factors is studied. We observe that the electron g-factors are anisotropic and find that the calculated values agree quantitatively with experimental data. We conclude that the two distinct g-factor values extracted from time resolved Faraday rotation experiments should be assigned to the anisotropic in plane ($g_\parallel$) and out of plane ($g_z$) electron g-factors, rather than to isotropic electron and exciton g-factors. We find that the anisotropy in the electron g-factor depends on the aspect ratio of the nanocrystal. The g-factor anisotropy derived from the wurtzite structure and from the non-unity aspect ratio may cancel each other in some regime. We observe that hole g-factors oscillate as a function of size, due to size dependent mixing between the heavy hole-light hole components of the valence band edge states. Extension to the calculation of exciton g-factors is discussed.

Electron g-factor in a gated InAs-inserted-channel In 0.53Ga 0.47As/In 0.52Al 0.48As heterostructure

We report on electron g-factor in an InAs-inserted In 0.53Ga 0.47As/In 0.52Al 0.48As heterostructure. The gate voltage dependence of g-factor is obtained from the coincidence method. The obtained g-factor values are surprisingly smaller than the g-factor value of bulk InAs, and it is close to the bare g-factor value of In 0.53Ga 0.47As. The large change in g-factor is observed by applying the gate voltage. The obtained gate voltage dependence is not simply explained by the energy dependence of g-factor.