Semiconducting Nature Research Articles

Structural, Electronic and Thermodynamic Properties of Double Perovskite Cs2NiF6: A First-Principles Study

The halide perovskite materials are being studied owing to their significant optical and thermoelectric properties and attractive applications in solar cells, LEDs, magnetic, optoelectronic, and temperature-resistive devices. Therefore, the electronic, structural, and thermodynamic properties of Cs2NiF6 have been examined utilizing the WIEN2k code's full-potential linearized augmented plane wave (FP-LAPW) approach based on the DFT. Cs2NiF6 crystallizes in the cubic structure, space group Fm-3m (225). Its band profile shows a semiconducting nature with a band gap of 1.79 eV. Further, we have estimated thermodynamic parameters such as bulk modulus, Debye temperature, and thermal expansion coefficient in temperatures varying from 0 to 1200K and pressures from 0 to 30 GPa using the QHD model.

Ca doped Y2/3Cu3Ti4O12: Structure and dielectric properties

In this study, we systematically examined the structure and dielectric properties of Y2/3-xCa3x/2Cu3Ti4O12 (x = 0.0, 0.05, 0.10, 0.15, and 0.20). X-ray diffraction (XRD) analysis revealed that the structure of all ceramics conformed to the CaCu3Ti4O12 ceramics database, specifically with JCPDS No. 75–2188, and no impurity phases were detected. The conducted experiments revealed a notable rise in the dielectric constant at elevated concentrations of Ca doping, ranging from 104 to 105. Conversely, the loss tangent values, lower than those of Y2/3Cu3Ti4O12, exhibited a decrease from 0.533 to 0.333 as x increased from 0 to 0.20. Synchrotron radiation, based on X-ray photoelectron spectroscopy, was employed to investigate the valence states of Ti and Cu ions. This observation is directly linked to the presence of oxygen vacancies within the lattice. Impedance spectroscopy analysis unveiled two distinct electrical states within the Ca-doped Y2/3Cu3Ti4O12 system. The first part corresponds to the semiconductive nature exhibited by the grain, while the subsequent part pertains to the insulative characteristics observed at the grain boundary. The remarkable dielectric permittivity observed in Ca-doped Y2/3Cu3Ti4O12 system ceramics can be attributed to the existence of a heterogeneous microstructure comprising semiconducting grains and insulating grain boundaries. The presence of Cu+ and Ti3+ ions could potentially account for the semiconductive state observed within the grains of Y2/3Cu3Ti4O12 ceramics.

Nonvolatile ferroelectric control of both magnetic anisotropy and half-metallicity in multiferroic heterostructures GdI2/Al2Te3

Nonvolatile all-electric spin manipulation is optimal for low-power and compact spintronic devices. Herein, using first-principles density functional theory, we propose a bilayer van der Waals (vdW) multiferroic heterostructure (HS) GdI2/Al2Te3 constructed of ferromagnetic electride GdI2 and ferroelectric (FE) semiconductor Al2Te3 to possess robust magnetoelectric coupling near room temperature. By reversing the electrical polarization states in Al2Te3, the magnetoelectric coupling not only allows the reversible switch of GdI2 from semiconductor to half-metal but also promotes the reversible transition of magnetocrystalline anisotropy from in-plane to out-of-plane. More importantly, the high Curie temperature (TC) of GdI2 and the unspoiled semiconducting nature of Al2Te3 in the HS predict the practical feasibility of this spin manipulation. Additionally, GdI2 exhibits substantial valley polarization when its magnetization direction changes to out-of-plane. These findings pave the way for achieving robust and efficient spin manipulation through all-electric control and also provide implications for multiferroic memory devices with highly efficient data reading and writing based on the HS.

Structural Elucidation, IR spectroscopy and DC electrical conductivity of Ni0.6Zn0.4GdyFe2-yO4 nanoferrites synthesized via a low-temperature citrate gel combustion method

In the present work, we report the detailed Powder XRD Rietveld refinement and elucidation of structural factors of Ni0.6Zn0.4GdyFe2-yO4 nanoferrites. The Ni0.6Zn0.4GdyFe2-yO4 nanoferrites synthesized via low-temperature citrate gel combustion technique for the various levels of Gd3+ ion concentration (y = 0.0, 0.1, 0.15 and 0.20). The generated structural factors signify the dependence on the concentration of Gd3+ ions. The prepared samples were found to crystallize in the Fd-3m space group and also identified their occupancies; some of the Fe3+ ions of the octahedral site at the 16d position will be replaced by Gd3+ ions. The lattice constant and crystallite size dropped to a low value for y = 0.1, and then, later, noticed the small increment. The crystallite sizes of the sample are to fall in the range of 26.1 nm–37.6 nm. The cation distribution among the tetrahedral (AII) and octahedral sites (BII) has been estimated. The obtained values correlate with Gd3+ ion concentration, and the radius variation of AII and BII sites signifies the migration of Fe3+ ions from the BII site to the AII sites. The force constant of Metal-Oxygen bonds was determined from the infrared spectrographs; the force constant was found to be relatively low with the BII site. The DC electrical conductivity infers the semiconducting nature and distinct phase of conductivity, which is attributed to the magnetic phase change due to temperature. The magnetic curie temperatures of the sample are obtained by the Arrhenius plot, which signifies the dependence of Gd3+ion concentration.

Comprehensive structural, optical, electrical, dielectric and magnetic analysis of co-precipitated Mg-Zn-Cu-Ce soft ferrites

The Mg0.6Zn0.2Cu0.2Fe2-xCexO4 series (0.0, 0.0125, 0.0250 and 0.0375) was prepared by coprecipitation and characterized by X-ray diffraction (XRD), UV–vis, Fourier transform infrared spectroscopy (FTIR), current and voltage (I-V), an LCR meter and a vibrating sample magnetometer (VSM). XRD analysis revealed a cubical structure with crystallite sizes ranging from 37.42 to 19.20 nm and lattice constants varying between 8.3938 and 8.4301 Å. Absorption bands, i.e., octahedral bands (533.87 – 533.99 cm−1) and tetrahedral bands (420.73 – 415.96 cm−1), were detected to confirm the occurrence of metal oxides. The ranges of the optical band gap energy (Eg = 2.782 – 2.756 eV) and DC resistivity (ρDC = 5.309 × 109 Ohm.cm to 2.071 × 1010 Ohm.cm) revealed the semiconducting nature of the composed ferrites. The dielectric constant and loss, AC conductivity and impedance were determined, and sample Mg0.6Zn0.2Cu0.2Fe0.0125Ce1.9875O4 exhibited the highest dielectric constant. The saturation magnetization (Ms = 12.7625 – 21.9460 emu/g) and remanence (Mr = 8.5460 – 15.6781 emu/g) increased, while the coercivity (Hc = 796.76 – 660.91 Oe) decreased. The determined values of the microwave frequency “ωm” indicate that ferrites are applicable in wireless communication systems.

Out‐of‐Plane Superexchange Interaction Enhanced Ferromagnetism in Semiconducting Monolayer Cr2Se3

Abstract2D magnetic semiconductors exhibit great potential for next‐generation spintronics, but realizing their full capabilities has been hindered by the low Curie temperatures (Tc) below 50 K observed in current materials. Here, a new mechanism to substantially enhance the Tc of 2D semiconducting materials through incorporating both in‐plane and out‐of‐plane superexchange interactions enabled by structural design is demonstrated. Specifically, monolayer Cr2Se3 is synthesized with a five‐layer Se–Cr–Se–Cr–Se atomic structure using molecular beam epitaxy (MBE). This unique structure not only possesses optimized in‐plane superexchange interaction but also incorporates out‐of‐plane Cr–Se–Cr couplings. Scanning tunneling spectroscopy (STS) and angular‐resolved photoemission spectroscopy (ARPES) confirm its semiconducting nature. Remarkably, the ferromagnetic phase transition observed by ARPES and Magnetic Force Microscopy (MFM) indicated that its Tc is up to 230 K. This not only establishes a new record for Tc in 2D ferromagnetic semiconductor materials but also introduces a novel approach to modulating materials' properties by manipulating the vertical dimension in 2D materials.

Universality of optoelectronic and thermoelectric properties of novel two-dimensional CrSiM2N (M=As, P and N[dbnd]Se, Te) monolayers and their vdWHs with MoTe2

In this study, we introduce a novel two-dimensional (2D) monolayer of CrSiM2N (M = As, P and NSe, Te) and explore its electronic properties. For the first time, we employ density functional theory and investigate the electronic and thermoelectric (TE) properties of CrSiM2N (M = As, P and NSe, Te) monolayers. Our calculated phonon band structure confirms that these monolayers are stable and can potentially be synthesized experimentally. The CrSiM2N (M = As, P and NSe, Te) monolayers exhibit an indirect band nature, with the CBM and VBM located at the K and G-points of the first Brillouin zone, respectively. We have also calculated the thermoelectric properties of these systems, which suggest that these monolayers could play a crucial role in enhancing the thermoelectric performance. Furthermore, we investigated the electronic, optical and thermoelectric properties of CrSiM2N (M = As, P and NSe, Te) and MoTe2 van der Waals heterostructures (vdWHs). The electronic band structure exhibits an indirect semiconductor nature, with the conduction band maxima and valence band minima originating from the CrSiM2N (M = As, P and NSe, Te) and MoTe2 monolayers, thereby confirming a type II band alignment. The optical properties indicate that these vdWHs can absorb a broad range of light, from the ultraviolet to the visible and infrared regions. We demonstrated that CrSiM2N (M = As, P and NSe, Te) monolayers exhibit p-type TE behavior, while their vdWHs counterparts exhibit n-type TE behavior.

Evidence of multifunctional properties of ferromanganite La0.5Ca0.5Mn0.5Fe0.5O3

Synthesis and characterization of the magnetic and electrical properties of the perovskite-type ferro-magnetite La0.5Ca0.5Mn0.5Fe0.5O3 are reported. Structural analysis reveals crystallization of the material in an orthorhombic structure, space group Pbnm (#62). The optical response suggests semiconductor-type behavior with bandgap Eg=2.3 eV. Susceptibility curves as a function of temperature and magnetization as a function of applied field suggest a soft ferromagnetic type response below room temperature, with evidence of disorder characterized by magnetic irreversibility at low temperatures and low applied fields. Resistivity measurements as a function of temperature and corroborate the semiconductor nature of the material and hysteretic I-V curves enhance its applicability in programmable logic memory devices. Band structure calculations around the Fermi level result in two different band gap values for the two spin up and spin down polarizations, as expected in ferromagnetic semiconductor materials. The hybridizations observed in the density of states curves as a function of energy suggest that the ferromagnetic character is due to double exchange mechanisms, coexisting with antiferromagnetic super-exchange, which is essentially due to the disorder of Fe3+ and Mn4+ cations in the octahedra along the three crystallographic axes.

Co contamination of Si: Plating & aging

Cobalt has emerged as a vital material in 10 nm technology for localized interconnect layers, potentially offering a compelling alternative to Cu-based interconnects. In this study, we subjected the contamination arising from the presence of cobalt atoms in silicon to comprehensive investigation, employing electron transmission electron microscopy (TEM) observations in conjunction with first-principles calculations. The results show that a dense CoSi layer with a thickness of a few nanometers is formed at the interface of cobalt and Si. The CoSi layer blocks the diffusion of Co atoms into Si. This is due to the semiconducting nature of the covalent bond formed between Co and Si, leading to the emergence of a forbidden zone at the Co/CoSi interface. The diffusion of Co into CoSi is governed by the atomic exchange mechanism, however, the local distortion of the periodic atomic potential due to the presence of the forbidden zone at the Co/CoSi interface hinders the diffusion of Co into Si. Therefore, the deposition of a Co metal layer on a Si chip does not require an additional barrier layer.

Theoretical exploration of PtSSe/ZrS2 Van der Waals heterostructure for solar energy conversion

In this work, the Solar energy conversion ability of van der Waals heterostructure (vWH) PtSSe/ZrS2 has been investigated by employing the density functional theory. The most stable configuration among the twelve possible configurations has been identified through assessments of cohesive energy, phonon dispersion curves, and ab initio molecular dynamics calculations. The electronic properties of the vWH PtSSe/ZrS2 have been calculated using the Heyd–Scuseria–Ernzerhof functional, indicating its semiconducting nature with a Type-II indirect band gap. The absorption coefficient analysis reveals that the vWH PtSSe/ZrS2 exhibits enhanced absorption characteristics across the entire ultraviolet and visible regions of the electromagnetic spectrum compared to its constituent monolayers, PtSSe and ZrS2. The determination of solar parameters has been done by utilizing the Shockley–Queisser method which demonstrates the superior photovoltaic performance in contrast to monolayers PtSSe and ZrS2. These results imply the promising prospects of vWH in photovoltaics, optoelectronic devices, and various other applications.

A Comprehensive Study of Cerium-Modified Bi2FeMnO6 Double Perovskite: Synthesis, Structure, Properties and Applications

This paper presents a detailed synthesis method by solid-state reaction route and typical characterization (structural, microstructural, dielectric, impedance, modulus, and optical properties) of a double perovskite material Bi2FeMn[Formula: see text]Ce[Formula: see text]O6. An orthorhombic crystal structure having an average crystallite size of 32.2[Formula: see text]nm is suggested by X-ray diffraction data (XRD). Scanning electron microscope (SEM) micrograph detects the presence of cylindrical nanorod-shaped distinct grains and well-defined grain boundaries in this material and the average grain size is 5.82[Formula: see text][Formula: see text]m. Furthermore, the purity and the presence of all constituent elements in the material were confirmed from energy dispersive X-ray (EDX) analysis and color mapping. Dielectric, impedance, modulus, and AC conductivity properties are studied within the temperature range of 25–500∘C and frequency range of 1[Formula: see text]kHz to 1[Formula: see text]MHz. The high dielectric constant at a low-frequency zone and low dielectric loss found in this material make it a promising candidate for better energy-storing devices. The negative temperature coefficient of resistance (NTCR) behavior is observed from the impedance study. The non-Debye relaxation is detected in the modulus study. The semiconducting nature of this material is verified by semicircular arcs observed in both Nyquist and Cole–Cole plots. The thermally activated conduction mechanism is confirmed by an AC conductivity study. The existence of Bi–O, Fe–O, Mn–O and Ce–O stretching vibrations are observed from the FTIR study and explain the presence of all constituent elements in the sample. The bandgap energy of 1.7[Formula: see text]eV is calculated from UV-DRS analysis and hence this material can be used for advanced optoelectronic and photovoltaic applications.

Photocatalytic degradation of Rhodamine B dye via Bi2O3 embedded BaO-P2O5-TeO2 glass nanocomposites: An ab initio study of structural, optical, and electrical transport properties

Bismuth incorporated glassy systems with composition xBi2O3-(1-x) [0.3BaO-0.3P2O5-0.4TeO2] (where x = 0.10, 0.15, 0.20, and 0.25) are synthesized by melt quenching technique. The glassy systems are examined for their structural, and surface morphological properties using XRD, SEM, and EDX analysis. A study of photocatalytic activity for the degradation of common organic dyes like Rhodamine B (RhB) dye under visible light is also carried out. From UV-vis absorbance data, the calculated optical band gap energy values declined from (2.99-2.56) eV, whereas the Urbach energy and refractive index values increased from (0.35 -0.52) eV, and (2.39 - 2.52), respectively with the rise of Bi2O3 content(x). Additionally, the fundamental processes of electrical conductivity have been studied within the framework of Jonscher's universal power law and the Almond-West formalism. The Mott and Greaves model asserts that the small polaron hopping model underlies DC conductivity; as Bi2O3 content increases, DC conductivity rises, but hopping distance (Rhop) and hopping energy (Whop) drop dramatically. The electrical conductivity study reveals the semi-conducting nature of the as-prepared samples. In our present study, we are focusing on the structural, optical, and electrical transportation properties, additionally, we investigated this class of glassy materials as a promising candidate for photocatalytic dye degradation. Our study reveals that RhB dye can degrade up to 75% within 340 min of visible light illumination. Moreover, the test demonstrates the production of superoxide radicals by the CB-electrons and hydroxyl radicals by the VB holes enables efficient photocatalytic dye degradation.

Rectification in Ionic Field Effect Transistors Based on Single Crystal Silicon Nanopore

AbstractIonic FETs have enormous potential for energy conversion, sensing, and ionic circuits due to their efficient regulation of the nanochannel. Here ionic FETs based on single‐crystal silicon nanopores and the rectification of the fabricated devices are studied. The electrical characterization results demonstrated that since the silicon‐based nanopores have the advantage of modulating the surface charge due to their semiconductor nature and benefitting from the effective 3D gating effect on the nanochannel, the magnitude and polarity of surface charge can be modulated by the gate voltage. The rectification effect can be adjusted by applying a certain voltage and fulfilling a transition between anion selectivity and cation selectivity when the surface charge polarity is reversed. Moreover, current–voltage characteristics of the reported ionic FET can be switched between ohmic and diode‐like regimes. The proposed ionic FETs supply a novel platform to study the ionic properties and have great potential to be applied in large‐scale ionic circuits due to their excellent performance. Finally, simulation results prove the surface charge modulated by the gate voltage determines the magnitude and direction of rectification, which is consistent with the reported experiment result.

Identification of Lightning Strike Damage Severity Using Pulse Thermography Through Integration of Thermal Data

Carbon fibre reinforced polymers (CFRP) structures, e.g., wind turbine blades, are suspectable to direct lightning strikes due to their semiconductive nature and ability to conduct current. It is critical to identify and evaluate lightning damage as it can cause premature failure of the primary load carrying components. Direct strike lightning damage has been traditionally identified and assessed by ultrasonic (UT) inspection, which is time consuming, usually requires contact, and does not directly provide a measure of damage severity. An appealing alternative to UT is pulsed thermography (PT), which takes minutes to conduct rather than hours and does not require a couplant. The aim of this work is to explore the application of pulse thermography to identify and evaluate the damage state of CFRP panels damaged by simulated lightning strike. A new analysis technique is presented that provides a damage severity metric which allows damage to be categorized, separated, and quantified.

Investigations of In2O3 Added SiC Semiconductive Thin Films and Manufacture of a Heterojunction Diode

This study involved direct doping of In2O3 into silicon carbide (SiC) powder, resulting in 8.0 at% In-doped SiC powder. Subsequently, heating at 500 °C was performed to form a target, followed by the utilization of electron beam (e-beam) technology to deposit the In-doped SiC thin films with the thickness of approximately 189.8 nm. The first breakthrough of this research was the successful deposition of using e-beam technology. The second breakthrough involved utilizing various tools to analyze the physical and electrical properties of In-doped SiC thin films. Hall effect measurement was used to measure the resistivity, mobility, and carrier concentration and confirm its n-type semiconductor nature. The uniform dispersion of In ions in SiC was as confirmed by electron microscopy energy-dispersive spectroscopy and secondary ion mass spectrometry analyses. The Tauc Plot method was employed to determine the Eg values of pure SiC and In-doped SiC thin films. Semiconductor parameter analyzer was used to measure the conductivity and the I-V characteristics of devices in In-doped SiC thin films. Furthermore, the third finding demonstrated that In2O3-doped SiC thin films exhibited remarkable current density. X-ray photoelectron spectroscopy and Gaussian-resolved spectra further confirmed a significant relationship between conductivity and oxygen vacancy concentration. Lastly, depositing these In-doped SiC thin films onto p-type silicon substrates etched with buffered oxide etchant resulted in the formation of heterojunction p-n junction. This junction exhibited the rectifying characteristics of a diode, with sample current values in the vicinity of 102 mA, breakdown voltage at approximately −5.23 V, and open-circuit voltage around 1.56 V. This underscores the potential of In-doped SiC thin films for various semiconductor devices.

Comparative study between oxide/soft ferrite, oxide/hard ferrite, and soft/hard ferrite nanocomposites: structural, electrical, and magnetic properties

Three binary nanocomposites (NCs): (0.5NiO/0.5Ni0.5Zn0.5Fe2O4), (0.5NiO/0.5BaFe12O19), and (0.5Ni0.5Zn0.5Fe2O4/0.5BaFe12O19) were prepared using the co-precipitation method followed by the wet ball-milling technique. X-ray diffraction analysis showed the production of NiO and Ni0.5Zn0.5Fe2O4 single phases, while the α-Fe2O3 secondary phase appeared in the BaFe12O19 and the 0.5Ni0.5Zn0.5Fe2O4/0.5BaFe12O19 nanocomposite. The transmission electron microscopy investigation and the selected area electron diffraction demonstrated the presence of the nanocomposites’ constituent phases. x-ray photoelectron spectroscopy identified the oxidation states found in the prepared samples (Ba2+, Ni2+, Ni3+, Zn2+, Fe3+, and O2−). The bandgap values (Eg) of the nanocomposites are in the range between 2.79 and 3.66 eV, which indicates their semiconductor nature. The DC conductivity experiment confirmed the semiconducting nature of all samples, and the activation energies ( EaH ) and ( EaL ) at high and low-temperature regions, respectively, were calculated from the Arrhenius equation. According to the vibrating sample magnetometer, the NCs exhibited ferromagnetic (FM) as showed by the M-H loops. In the oxide/soft ferrite NC, the dM/dH curve indicated strong exchange coupling interactions, while the hard and the soft magnetic phases in the oxide/hard ferrite and the soft/hard ferrite NCs were weakly exchanged coupled. Significant uses had been found for each of the three nanocomposites according to their constituent phases and properties.

Exploring the Mn doped BaTe alloy for spintronics and energy harvesting applications

In the present study, the ferromagnetic semiconductor behavior of Mn doped BaTe is reported along with their physical properties. The calculations are done by full potential linearized augmented plane wave (FP-LAPW) approach within spin-polarized density functional theory (SP-DFT). Formation energies were computed to satisfy the stability of reported alloys. The spin-polarization is included in the calculations to study the electronic (band structure (BS), density of states (DOS)) and magnetic characteristics. Ba1−xMnxTe elucidates the magnetic semiconductor nature with direct band gap (Eg) in both spin channels while indirect Eg (1.66 eV) is observed for pure BaTe compound. Stable ferromagnetic (FM) states are vindicated owing to the p-d hybridization which are contributors in inducing magnetic moments (μ B) at interstitial and non-magnetic sites. The optical parameters (reflectivity, absorption coefficient, refraction, optical conductivity and dielectric function) were computed within an energy range of 0–10 eV. Thermoelectric (TE) features are also figured using Boltaz-Trap code in terms of thermal and electrical conductivity, figure of merit, Seebeck coefficient and power factor. The analysis of optical parameters suggests that the considered alloys is active within visible to UV-range, having potential applications in optoelectronic, photovoltaic and thermoelectric applications.

Searching for new two-dimensional spintronic materials: Doping-induced magnetism in graphene-like SrS monolayer

In this work, doping approach is explored to induce feature-rich electronic and magnetic properties in graphene-like SrS monolayer and make it prospective spintronic two-dimensional (2D) candidate. For such goal, 3d transition metals (V, Cr, Mn, and Fe) and halogens (F, Cl, Br, and I) are selected as dopants at Sr and S sublattice, respectively. Pristine SrS single layer shows good dynamical and thermal stability. Its indirect-gap semiconductor nature is also asserted with energy gap of 2.87/3.81 eV obtained by PBE/HSE06 functional, generated by the separation in energy between S-3p and Sr-4d orbitals. The magnetic semiconducting with total magnetic moment of 2.00 μB is obtained by creating a single Sr vacancy, meanwhile S single vacancy preserves the non-magnetic nature. The monolayer is significantly magnetized by doping with transition metals, where large total magnetic moments of 3.00, 4.00, and 5.00 μB are obtained for the V-, Cr/Fe-, and Mn-doped SrS monolayer, respectively. In these cases, impurities play a key role on producing magnetic properties and generating the magnetic semiconductor nature. This feature-rich nature is also induced by doping with F atom, where a total magnetic moment of 1.00 μB is obtained that is originated mainly from Sr atoms closest to the doping site. Besides, Cl doping leads to the emergence of the half-metallicity. Importantly, the magnetization becomes significantly weaker according to increase the atomic number of halogen dopants, such that the non-magnetic nature is preserved by doping with I atom. This feature is attributed to the increase of the electronic hybridization. Results presented herein introduce the doped SrS monolayer as promising 2D spintronic materials, exhibiting novel properties that are not found in the pristine counterpart.

Competitive nature of weak anti-localization and weak localization effect in Cr-doped sputtered topological insulator Bi2Se3 thin film

In the present study, we have investigated the effect of magnetic Cr doping on the transport properties of a sputtered Bi2Se3 thin film on the SrTiO3 (110) substrate. The high-resolution x-ray diffraction and Raman spectroscopy measurements revealed the growth of rhombohedral Bi2Se3 thin films. Further electronic and compositional analysis was done by x-ray photoemission spectroscopy and Rutherford backscattering spectroscopy, and the x-value was estimated to be 0.18 in the Bi2−xCrxSe3 thin film. The variation in the resistivity with temperature (2–300 K) revealed the metallic nature in undoped Bi2Se3 up to 30 K and upturn resistivity below 30 K. The Cr-doped Bi2Se3 resistivity data show a traditional semiconducting nature up to 25 K and take an abrupt upturn resistivity below 25 K. The resistivity behavior of both samples was explained by adopting a model that consists of the total resistance, a combination of bulk and surface resistance in parallel. The bulk bandgap value determined by this method is obtained to be 256 meV in an undoped Bi2Se3 thin film. Magnetoconductance data of the undoped thin film revealed a weak anti-localization (WAL) effect, while the Cr-doped thin film showed a weak localization (WL) effect at low temperatures (<50 K). At low magnetic field and low temperature, a competing nature of WAL and WL effects was prominent in the Cr-doped film. A drastic increase in the electrical resistance suggests that Cr doping can significantly modify the electrical properties of Bi2Se3 thin films, which could have potential applications in futuristic devices.

Coexistence of Interacting Charge Density Waves in a Layered Semiconductor.

Coexisting orders are key features of strongly correlated materials and underlie many intriguing phenomena from unconventional superconductivity to topological orders. Here, we report the coexistence of two interacting charge-density-wave (CDW) orders in EuTe_{4}, a layered crystal that has drawn considerable attention owing to its anomalous thermal hysteresis and a semiconducting CDW state despite the absence of perfect Fermi surface nesting. By accessing unoccupied conduction bands with time- and angle-resolved photoemission measurements, we find that monolayers and bilayers of Te in the unit cell host different CDWs that are associated with distinct energy gaps. The two gaps display dichotomous evolutions following photoexcitation, where the larger bilayer CDW gap exhibits less renormalization and faster recovery. Surprisingly, the CDW in the Te monolayer displays an additional momentum-dependent gap renormalization that cannot be captured by density-functional theory calculations. This phenomenon is attributed to interlayer interactions between the two CDW orders, which account for the semiconducting nature of the equilibrium state. Our findings not only offer microscopic insights into the correlated ground state of EuTe_{4} but also provide a general nonequilibrium approach to understand coexisting, layer-dependent orders in a complex system.