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The electromagnetic response of Dirac semimetals in the infrared and terahertz frequency ranges is attracting growing interest for potential applications in optoelectronics and nonlinear optics. The interplay between the free-carrier response and interband transitions in the gapless, linear dispersion relation plays a key role in enabling novel functionalities. Here we investigate ultrafast dynamics in thin films of a photoexcited Dirac semimetal Cd$_3$As$_2$ by probing the broadband response functions as complex quantities in the multiterahertz region (10-45 THz, 40-180 meV, or 7-30 $\mu$m), which covers the crossover between the inter and intraband response. We resolve dynamics of the photoexcited nonthermal electrons which merge with originally existing carriers to form a single thermalized electron gas and how it is facilitated by high-density excitation. We also demonstrate that a large reduction of the refractive index by 80% dominates the nonequilibrium infrared response, which can be utilized for designing ultrafast switches in active optoelectronics., Comment: 20 pages

As the need for ever greater transistor density increases, the commensurate decrease in device size approaches the atomic limit, leading to increased energy loss and leakage currents, reducing energy efficiencies. Alternative state variables, such as electronic spin rather than electronic charge, have the potential to enable more energy-efficient and higher performance devices. These spintronic devices require materials capable of efficiently harnessing the electron spin. Here we show robust spin transport in Cd3As2 films up to room temperature. We demonstrate a nonlocal spin valve switch from this material, as well as inverse spin Hall effect measurements yielding spin Hall angles as high as θSH = 1.5 and spin diffusion lengths of 10-40 μm. Long spin-coherence lengths with efficient charge-to-spin conversion rates and coherent spin transport up to room temperature, as we show here in Cd3As2, are enabling steps toward realizing actual spintronic devices.

We investigated ultrafast broadband (12-45 THz) response functions of a photoexcited Dirac semimetal Cd3As2. Under periodic driving at 30 THz, we observed coherent nonlinear response dominated by stimulated Rayleigh scattering between the photon-dressed states.

The three-dimensional Dirac semimetal is a parent phase for a variety of topological phases that can be generated by tuning parameters in material growth or device operation. Notably, it has recently been found that cadmium arsenide, which is ordinarily a three-dimensional Dirac semimetal, can nevertheless realize a three-dimensional topological insulator in (001)-oriented films about 50-nm thick. In this work, we study the quantum Hall effect in thin (001)-oriented cadmium arsenide films, their thickness ranging from 12 to 24 nm. When the carrier density is kept approximately constant across the different films, quantum transport reveals an identical underlying picture. The result is shown to be consistent with the transport's origin in the surface states of a three-dimensional topological insulator, but problematic for a perspective in which the quantum Hall effect originates from the confined subbands of the bulk band structure. These thin-film results complement previous studies of the quantum Hall effect in 50-nm-thick films.

Topological protection against localization causes electrical transport phenomena in disordered topological materials to differ from those in topologically trivial systems. For example, a transition between a regime of weak localization to one of weak antilocalization can occur in systems such as topological insulators and topological semimetals when an external potential is applied across the system. Here, we report on the transverse magnetoresistance of thin films of cadmium arsenide, a topologically nontrivial, as we tune the electronic states and the Fermi level. We show that the appearance of weak localization and weak antilocalization sensitively reflects the relative contributions of multiple transport channels involving both gapless (massless) and gapped (massive) Dirac fermion states present in these films. The data are consistent with expectations of the different topological states of these films. Weak (anti-)localization phenomena can, therefore, serve as a probe of the types of Dirac fermions present in topological semimetals.

Cadmium arsenide (Cd3As2) is one of the first materials to be discovered to belong to the class of three-dimensional topological semimetals. Reported room temperature crystal structures of Cd3As2 reported differ subtly in the way the Cd vacancies are arranged within its antifluorite-derived structure, which determines if an inversion center is present and if Cd3As2 is a Dirac or Weyl semimetal. Here, we apply convergent beam electron diffraction (CBED) to determine the point group of Cd3As2 thin films grown by molecular beam epitaxy. Using CBED patterns from multiple zone axes, high-angle annular dark-field images acquired in scanning transmission electron microscopy, and Bloch wave simulations, we show that Cd3As2 belongs to the tetragonal 4/mmm point group, which is centrosymmetric. The results show that CBED can distinguish very subtle differences in the crystal structure of a topological semimetal, a capability that will be useful for designing materials and thin film heterostructures with topological states that depend on the presence of certain crystal symmetries., Accepted for publication in Physical Review Materials

Recently, Cd3As2 has attracted intensive research interest as an archetypical Dirac semimetal, hosting three-dimensional linear-dispersive electronic bands near the Fermi level. Previous studies have shown that single-crystalline Cd3As2 has an anomalously low lattice thermal conductivity, ranging from 0.3 W/mK to 0.7 W/mK at 300 K, which has been attributed to point defects. In this work, we combine first-principles lattice dynamics calculations and temperature-dependent high-resolution Raman spectroscopy of high-quality single-crystal thin films grown by molecular beam epitaxy to reveal the existence of a group of soft optical phonon modes at the Brillouin zone center of Cd3As2. These soft phonon modes significantly increase the scattering phase space of heat-carrying acoustic phonons and are the origin of the low lattice thermal conductivity of Cd3As2. Furthermore, we show that the interplay between the phonon-phonon Umklapp scattering rates and the soft optical phonon frequency explains the unusual non-monotonic temperature dependence of the lattice thermal conductivity of Cd3As2. Our results further suggest that the soft phonon modes are potentially induced by a Kohn anomaly associated with the Dirac nodes, in analogy to similar, nonetheless weaker, effects in graphene and Weyl semimetals., 7 pages, 4 figure. Comments are welcome

In this paper we report a detailed analysis of the temperature-dependent optical properties of epitaxially grown cadmium arsenide (Cd$_3$As$_2$), a newly discovered three-dimensional Dirac semimetal. Dynamic Fermi level tuning -- instigated from Pauli-blocking in the linear Dirac cone -- and varying Drude response, generate large variations in the mid and far-infrared optical properties. We demonstrate thermo-optic shifts larger than those of traditional III-V semiconductors, which we attribute to the obtained large thermal expansion coefficient as revealed by first-principles calculations. Electron scattering rate, plasma frequency edge, Fermi level shift, optical conductivity, and electron effective mass analysis of Cd$_3$As$_2$ thin-films are quantified and discussed in detail. Our ab initio density functional study and experimental analysis of epitaxially grown Cd$_3$As$_2$ promise applications for nanophotonic and nanoelectronic devices, such as reconfigurable metamaterials and metasurfaces, nanoscale thermal emitters, and on-chip directional antennas.

We report on the growth and transport properties of strained thin films of the three-dimensional Dirac semimetal ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$. Epitaxial heterostructures, consisting of (112)-oriented ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ films, are grown on nearly lattice matched $({\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{In}}_{x})\mathrm{Sb}$ buffer layers on (111) GaAs substrates by molecular beam epitaxy. The epitaxial coherency strain breaks the fourfold rotational symmetry, which protects the bulk Dirac nodes in ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$. All strained films exhibit the quantum Hall effect with most carriers residing in the two-dimensional states, irrespective of the sign of the biaxial stress. The Hall mobility monotonically increases as the biaxial stress is changed from compressive towards tensile. Furthermore, pronounced anisotropy is seen in the transport properties. The results show that the quantum Hall effect, which is quite similar to that of unstrained (112)-oriented films, is independent of the presence of bulk Dirac nodes. Its appearance is consistent with the topological surface states that are a characteristic of the topological ${\mathbb{Z}}_{2}$ invariant.

Recent development of topological materials has opened up a new paradigm of material research. Unique electronics properties make these materials interesting to study new physics of materials. Thin film epitaxial growth gives an additional control parameter to design different experiments. For example, even though Cd 3 As 2 is a 3D Dirac semimetal, thin film Cd 3 As 2 shows 2D transport with quantum hall effect with surface Dirac node. Along with interesting physics, unique properties of this material can be exploited for a new class of electronics materials. High mobility $(\sim 20,000\ \mathrm{cm}^{2}/\mathrm{Vs})$ and high Fermi velocity $(2\times 10^{6}\mathrm{m}/\mathrm{s})$ make Cd 3 As 2 a suitable candidate for RF devices. In this abstract, we report the first demonstration of field effect transistors (FETs) with Cd 3 As 2 channel.

In a Weyl orbit, the Fermi arc surface states on opposite surfaces of the topological semimetal are connected through the bulk Weyl or Dirac nodes. Having a real-space component, these orbits accumulate a sample-size-dependent phase. Following recent work on the three-dimensional Dirac semimetal cadmium arsenide (Cd3As2), we have sought evidence for this thickness-dependent effect in quantum oscillations and quantum Hall plateaus in (112)-oriented Cd3As2 thin films grown by molecular beam epitaxy. We compare quantum transport in films of varying thickness at apparently identical gate-tuned carrier concentrations and find no clear dependence of the relative phase of the quantum oscillations on the sample thickness. We show that small variations in carrier densities, difficult to detect in low-field Hall measurements, lead to shifts in quantum oscillations that are commensurate with previously reported phase shifts. Future claims of Weyl orbits based on the thickness dependence of quantum transport data require additional studies that demonstrate that these competing effects have been disentangled.

(001)-oriented thin films of the three-dimensional Dirac semimetal cadmium arsenide can realize a quantum spin Hall insulator and other kinds of topological physics, all within the flexible architecture of epitaxial heterostructures. Here, we report a method for growing (001) cadmium arsenide films using molecular beam epitaxy. The introduction of a thin indium arsenide wetting layer improves surface morphology and structural characteristics, as measured by x-ray diffraction and reflectivity, atomic force microscopy, and scanning transmission electron microscopy. The electron mobility of 50-nm-thick films is found to be 9300 cm2/Vs at 2 K, comparable to the highest-quality films grown in the conventional (112) orientation. This work demonstrates a simple experimental framework for exploring topological phases that are predicted to exist in proximity to the three-dimensional Dirac semimetal phase.

Despite the significant advances made in the field of metamaterials and metasurfaces in recent years, many applications of such devices are hampered by the lack of active refractive index tuning. Here, we report on a new class of tunable quantum materials based on 3D topological Dirac semimetals with extremely high electrical and thermal refractive index tuning. Realized optical reflectivity data, performed on thin films of Cd3As2 over a broad range of frequencies demonstrate larger than traditional thermo-optic shifts in III-V semiconductors. Dynamic Fermi level tuning, instigated from the Pauli blocking in the linear Dirac cone, offers large and tunable absorption peak in the mid-infrared region. In contrast to recent efforts in 3D Dirac semimetals which are mostly focused on single crystal Cd3As2, our data based on MBE-grown Cd3As2 can galvanize newfound applications in the field of meta-optics and can enable several applications such as ultra-thin programmable optical devices, photodetectors, and on-chip directional antennas.

The surfaces of a three-dimensional topological insulator each host a single Dirac fermion, which, in a strong magnetic field, contribute to the transverse conductance in integer-and-a-half multiples of the conductance quantum. The direct observation of this extra half integer, the hallmark of the two-dimensional Dirac state, is usually thwarted by the fermion doubling theorem—top and bottom surfaces are not measured independently. Here, we employ a Corbino measurement geometry in which a current, induced by an ac magnetic field, is driven around the ring, as a complementary measurement to the conventional Hall bar geometry. As the device enters the quantum Hall regime, the transverse voltage reaches a series of plateaus when the current is carried by the incompressible bulk states. We compare the results with the corresponding Hall bar measurements.

Epitaxial strains offer unique opportunities to obtain topological states in thin films and heterostructures that do not exist in their bulk counterparts. Here, we investigate the point group symmetries of coherently strained films of cadmium arsenide (Cd3As2), a prototype three-dimensional Dirac semimetal, by convergent beam electron diffraction. We report a loss of the fourfold rotational axis and adoption of the orthorhombic mmm point group in (112)-oriented films under biaxial compressive stress. (001)-oriented Cd3As2 films that are under a small biaxial tensile stress retain the fourfold rotational symmetry that protects the bulk nodes but adopt the non-centrosymmetric 4mm point group symmetry. This, in turn, suggests that (001) films adopt a different crystal structure in biaxial tension, one that differs in the arrangement of the ordered Cd vacancies that are an inherent feature of the crystal structure of Cd3As2 and that are key to its nodal electronic structure. Density functional theory calculations confirm the experimental findings of the stability of the non-centrosymmetric structure under biaxial tension, whereas the centrosymmetric structure is stable under biaxial compression. The results show that bulk Cd3As2 is already close to structural instability and showcase the extraordinary tunability of the topological states of Cd3As2.

The discovery of the 3D Topological Dirac semimetal Cd3As2 presents a new class of semimetals because of its unique electronic structure and transport properties, demonstrating potential in novel topological devices. Promising properties of Cd3As2 include its topological surface states, ultrahigh electron mobility, and linear band dispersion. We evaluated the effect of inversion asymmetry on quantum confinement of Cd3As2 by measuring its electronic properties with and without hybridization through the quantum transport simulation package Kwant. Due to confinement, Cd3As2 exhibits a similar state to a 3D topological insulator because the transport in the bulk state becomes gapped, causing the surface state to dominate transport similar to 3D topological insulators. Thus, we can compare transport properties and band structure of Cd3As2 with other known 3D topological insulators such as HgTe and (Bi1-x Sb x )2Te3 through the analysis of previous electrostatic gating studies. We observe the lifting of the spin degeneracy due to inversion asymmetry and demonstrate that Cd3As2 provides a promising platform for topological device applications.

In-plane magnetoresistance effects in the three-dimensional Dirac semimetal cadmium arsenide are studied as a function of film growth orientation, film thickness, and surface Fermi level. For films with the Fermi level near the bulk nodes, which are gapped for very thin films, a pronounced planar Hall effect is observed due to the combination of magnetoresistance effects from the Berry phase and orbital magnetoresistance. At high Fermi levels, surface state transport produces weaker magnetoresistance effects. The results are discussed in the context of detecting signatures of the chiral anomaly.

We investigate (001)-oriented films of the topological semimetal cadmium arsenide (Cd3As2) grown by molecular beam epitaxy on lattice-matched III–V AlxIn1−xSb buffer layers. Magnetotransport studies and analysis of thin film microstructures are used to determine the influence of dislocations on their carrier mobilities. We show that only a minority of the threading dislocations present in the buffer layers extend into the Cd3As2 films. Threading dislocations are shown to reduce the mobilities of carriers residing in the topological surface states, while bulk transport was unaffected by a change in the dislocation density across an order of magnitude. Thick (001) Cd3As2 films exhibit electron mobilities of up to 41 000 cm2 V−1 s−1 at 2 K. The results provide insights into the influence of extended defects on the transport properties of a prototype topological semimetal.

La2NiMnO6 has been reported to exhibit a paramagnetic to ferromagnetic transition with a transition temperature of similar to 260 K. However, most of its magnetic properties, such as the saturation ...

Three-dimensional topological Dirac semimetals are a new state of matter. The authors report on experiments that directly access the electronic structure of two-dimensional states in the prototype topological Dirac semimetal Cd${}_{3}$As${}_{2}$. By modulating the carrier density of very thin, epitaxial Cd${}_{3}$As${}_{2}$ films, using the electric field effect, the authors tune the electronic states through a two-dimensional Dirac point, as evidenced by a minimum in the density of states. Moreover, the linear energy dispersion and the presence of a zero-energy Landau level establish the topological nature of the two-dimensional states in this three-dimensional Dirac semimetal.

Epoxy matrix nanocomposites with nickel nanoparticles of two different sizes were processed and characterized to investigate their structure-magnetic prop- erty correlations. Crystal structure, morphology, density, resistivity and magnetic properties of the nanocomposites withdifferentfillercontentswerecomparedfordifferentsize scales. Nanocomposites with 25 nm nanoparticles showed higher coercivity, higher frequency stability and lower loss, though the permeability was suppressed. Coarser nickel particles (100 nm) showed a permeability of *5.5 but sta- bility only up to 200 MHz. The structure-magnetic property correlations were validated using analytical models to pro- vide valuable design guidelines for permeability and fre- quency-stability in particulate nanocomposites.

Realizing the quantum Hall effect in topological materials is notoriously difficult due to remanent bulk conduction in the material. This feat has now been achieved in a Dirac semimetal by growing a sufficiently thin film of the material, thus eliminating bulk conduction.

RAPID COMMUNICATIONS PHYSICAL REVIEW B 95, 241113(R) (2017) Negative magnetoresistance due to conductivity fluctuations in films of the topological semimetal Cd 3 As 2 Timo Schumann, 1,* Manik Goyal, 1 David A. Kealhofer, 2 and Susanne Stemmer 1,† Materials Department, University of California, Santa Barbara, California 93106-5050, USA Department of Physics, University of California, Santa Barbara, California 93106-9530, USA (Received 9 April 2017; revised manuscript received 5 June 2017; published 26 June 2017) Recently discovered Dirac and Weyl semimetals display unusual magnetoresistance phenomena, including a large, nonsaturating, linear transverse magnetoresistance and a negative longitudinal magnetoresistance. The latter is often considered as evidence of fermions that have a defined chirality. Classical mechanisms, due to disorder or nonuniform current injection, can, however, also produce negative longitudinal magnetoresistance. Here, we report on magnetotransport measurements performed on epitaxial thin films of Cd 3 As 2 , a three-dimensional Dirac semimetal. Quasilinear positive transverse magnetoresistance and negative longitudinal magnetoresistance are observed. By evaluating films of different thickness and by correlating the temperature dependence of the carrier density and mobility with the magnetoresistance characteristics, we demonstrate that both the quasilinear positive and the negative magnetoresistance are caused by conductivity fluctuations. Chiral anomaly is not needed to explain the observed features. DOI: 10.1103/PhysRevB.95.241113 Recent experimental realizations of three-dimensional topological semimetals have opened up numerous exciting opportunities to test quasiparticle behavior that mimics mass- less, relativistic Dirac or Weyl fermions. A signature of Weyl fermions is the “chiral anomaly”, when charge flows from one Weyl node to one of opposite chirality under parallel electric and magnetic fields, thereby giving rise to an unusual negative longitudinal magnetoresistance (MR) [1,2]. In Dirac semimet- als the Dirac nodes split into Weyl nodes in the magnetic field and similar physics is expected. Recent observations [3–9] of longitudinal negative MR in Dirac and Weyl semimetals have therefore generated significant attention. While most studies consider the negative longitudinal MR to be evidence of the chiral anomaly, current jetting has been proposed as an alternative explanation [10,11]. Current jetting arises under inhomogeneous current injection into high-mobility materials that have a large conductivity anisotropy [12]. It leads to a strong preference of the current to flow in the direction of the magnetic field, resulting in a negative longitudinal MR [12]. Other studies claim to have ruled out current jetting caused by nonuniform current injection [7]. Negative longitudinal MR can also be due to conductivity fluctuations and has been reported for disordered semiconductors [13,14]. A recent study [15] showed that mobility fluctuations are a likely origin of linear, positive transverse MR in Cd 3 As 2 , a three-dimensional Dirac semimetal [16–20]. Most studies that attribute the negative longitudinal MR to chiral anomaly have been carried out on bulk materials. Thin films offer several important advantages towards resolving the origin of the negative longitudinal MR in Dirac and Weyl semimetals. In particular, thin-film-device geometries are much less susceptible to current jetting. Furthermore, the effects of nonuniformities can be studied by varying the film thickness and growth conditions. In this work, we study the magnetotransport properties of epitaxial Cd 3 As 2 thin films. schumann.timo@gmx.net stemmer@mrl.ucsb.edu We show that both the transverse positive MR and the negative longitudinal MR are due to conductivity fluctuations. Cd 3 As 2 films were grown by molecular beam epitaxy on relaxed, 180-nm-thick GaSb buffer layers on GaAs (111)B ¯ direction), as de- substrates (1 ◦ miscut towards the [ 1 ¯ 12] scribed elsewhere [21]. The beam equivalent pressure was 2 × 10 −6 Torr, the substrate temperatures ranged between 150 ◦ C and 170 ◦ C, and the growth time was between 5 min and 60 min (see Table I). Surface morphologies were investigated by optical, atomic force, and scanning electron microscopies. The film’s structure and alignment with the substrate were probed by x-ray diffraction (XRD) using Cu Kα radiation. The films were patterned into Hall bar structures with widths and lengths of 100 μm using standard optical lithography and Ar + ion milling. The thicknesses of the Cd 3 As 2 layers were deter- mined by scanning electron microscopy of the patterned Hall bar structures. Magnetoresistance measurements were carried out in a Quantum Design Dynacool PPMS, at temperatures between 300 K and 2 K and magnetic fields up to 9 T. DC excitation currents of 10 μA were used in all measurements. Shubnikov–de Haas oscillations were detected in the thinnest films (See Fig. S1 in the Supplemental Material [22]). Representative optical and atomic force micrographs of a Cd 3 As 2 film are shown in Figs. 1(a) and 1(b). In most areas, the film is smooth with atomically stepped surfaces ˚ matches the interplanar [Fig. 1(b)]. The step height (∼4 A) spacing of the Cd 3 As 2 (112) planes, which form the surface [21]. The defects in the optical micrograph [Fig. 1(a)] are likely areas that grew in a three-dimensional (island) growth mode. Their density was about 10 3 −10 4 cm −2 . Out-of-plane XRD confirmed single-phase, epitaxial Cd 3 As 2 [Fig. 1(c)]. High-resolution XRD showed Laue fringes from the GaSb buffer layer and for the thinnest Cd 3 As 2 layers [arrows in Fig. 1(d)]. The three-dimensional carrier densities determined from low-field Hall measurements were similar for all films grown at 150 ◦ C (see Table I) and ranged from ∼(0.8−1.8) × 10 17 cm −3 at 2 K to (5.0−8.0) × 10 17 cm −3 at 300 K. These carrier densities are lower than those of single crystals reported in the literature (typically > 10 18 cm −3 [15,17,23]), indicating ©2017 American Physical Society

Cadmium arsenide (Cd3As2) is a three-dimensional Dirac semimetal with many unique electronic properties that are of interest for future device applications. Here, we demonstrate field effect transistors using Cd3As2 as the channel material. We show that current densities exceed 5 A/mm and that very low contact resistances can be achieved even in unoptimized device structures. These properties make Cd3As2 of great interest for future high-speed electronics. We report on the current modulation characteristics of field effect transistors as a function of temperature. At low temperatures, the modulation exceeds 70%. We discuss material and device engineering approaches that can improve the device performance at room temperature.

Low-temperature magnetotransport studies are reported for (112)Cd3As2 films grown on (111)CdTe by molecular beam epitaxy as a function of the Cd3As2 film thickness. All films show Shubnikov-de Haas oscillations. An even-integer quantum Hall effect is observed for films thinner than 70 nm. For the thinnest films, the bulk is gapped and transport at low temperatures occurs only via the gapless, two-dimensional states. The lowest Landau level is reached at ∼10 T, and the longitudinal resistance nearly vanishes at the plateaus in the Hall resistance. The results are discussed in the context of the current theoretical understanding of topological surface states in three-dimensional Dirac semimetals.

Three-dimension (3D) Dirac semimetals are a newly discovered class of topological materials that have attracted significant interest. Their electronic structure exhibits a linear dispersion relation around the Fermi energy, making them a three-dimensional analogue of graphene. Epitaxial heterostructures of these materials open a path for the manipulation of topological electronic states by strain engineering, electron confinement, or electrostatic gating, all of which may enable new electronic devices. Here, we discuss the growth of epitaxial thin films of Cd3As2, a 3D Dirac semimetal, by molecular beam epitaxy. We report on their structure, magnetotansport properties, and field gating experiments using high-k dielectrics. The films are shown to grow in the low-temperature, vacancy ordered, tetragonal Dirac semimetal phase. Extremely high room temperature mobilities (~20,000 cm2/Vs) are achieved in epitaxial layers on III-V substrates. Unusual transport characteristics are observed, such as a negative longitudinal magnetoresistance, i.e., when the magnetic field is applied parallel to the direction of electric current. We vary the film parameters and study their influence on the magnetotransport to distinguish between ‘classical’ phenomena and effects originating from the unique electronic structure.

We report on Raman and Ni K-edge x-ray absorption investigations of a NiS(2-x)Se(x) (with x = 0.00, 0.50/0.55, 0.60, and 1.20) pyrite family. The Ni K-edge absorption edge shows a systematic shift going from an insulating phase (x = 0.00 and 0.50) to a metallic phase (x = 0.60 and 1.20). The near-edge absorption features show a clear evolution with Se doping. The extended x-ray absorption fine structure data reveal the evolution of the local structure with Se doping which mainly governs the local disorder. We also describe the decomposition of the NiS(2-x)Se(x) Raman spectra and investigate the weights of various phonon modes using Gaussian and Lorentzian profiles. The effectiveness of the fitting models in describing the data is evaluated by means of Bayes factor estimation. The Raman analysis clearly demonstrates the disorder effects due to Se alloying in describing the phonon spectra of NiS(2-x)Se(x) pyrites.