Large Effective Mass Research Articles

Observation of floating surface state in obstructed atomic insulator candidate NiP2

Obstructed atomic insulator is recently proposed as an unconventional material, in which electric charge centers localized at sites away from the atoms. A half-filling surface state would emerge at specific interfaces cutting through these charge centers and avoid intersecting any atoms. In this article, we utilized photoemission spectroscopy and density functional theory calculations to study one of the obstructed atomic insulator candidates, NiP2. A floating surface state with large effective mass that is close to the Fermi level and isolated from all bulk states is resolved on the (100) cleavage plane, implying better catalytic activity in this plane than the previously studied surfaces. Density functional theory calculation results elucidate that this floating surface state is originated from the obstructed Wannier charge centers, albeit underwent surface reconstruction. Our findings not only shed lights on the study of obstructed atomic insulators, but also provide possible route for development of new catalysts.

First‐Principle Investigation of zb‐TiGe: A Promising Narrow Bandgap Semiconductor

Using first‐principle calculations, a new compound semiconductor based on titanium (Ti) is predicted. It has been observed that Ti when alloyed with germanium (Ge) can crystallize in the zincblende symmetry, and exhibits semiconducting nature with a narrow bandgap. To test the robustness of the semiconducting nature, the structural properties and electronic band structure have been modeled using three different exchange–correlation functionals, namely, local density approximation, generalized gradient approximation, and Perdew‐Burke‐Ernzerhof for solids. With a nominal composition of 1:1, TiGe exhibits a direct bandgap of 0.58 eV at the “X” point of the Brillouin zone. From lattice dynamics, the structural stability of the compound has been established. The new semiconductor is characterized in detail for its electronic band structure, carrier effective mass, charge density distribution, and linear optical properties. Zb‐TiGe exhibits large effective mass for conduction band holes and tentatively becomes a prototype system to study heavy holes resulting in carrier condensation at the bottom of the conduction band. The linear optical properties of the TiGe are found to be suitable for photosensitive devices in the infrared region. In addition, TiGe may find application in deep‐UV and far‐UV regions because of the surface plasmon resonance at 6.4 eV.

Abnormal Relaxation Behavior of Excited Electrons in the Flat Band of Kagome Compound Nb3Cl8.

Carrier dynamics is crucial in semiconductors, and it determines their conductivity, response time, and overall functionality. In flat bands (FBs), carriers with high effective masses are predicted to host unconventional transport properties. The FBs usually overlap with other trivial energy bands, however, making it difficult to accurately distinguish their carrier dynamics. In this paper, we have investigated the flat-band carrier dynamics of excited electrons in Nb3Cl8, which hosts ideal nonoverlapping FBs near the Fermi level. The optical transition between Hubbard bands is abnormally weakened, exhibiting weak interband absorption and its related slow photoresponse with a time constant of ∼120 s, which are associated with flat-band Mottness-induced large electron effective mass and parity-forbidden transitions. Besides, the localized states created by chlorine vacancies also act as trapping centers for carriers with a time constant of ∼600 s, which are similar to those of the compact localized states of the FB, making the relaxation behavior even more extraordinary. The presence and impacts of atomic defects are confirmed experimentally and theoretically. This work has revealed the abnormal flat-band carrier dynamics of Nb3Cl8, which is essential for understanding the optical, electrical, and thermal transport properties of flat-band materials.

Ag nanoparticles at p-Si/ MAPbI3 perovskite interface: improved photo responsivity and response speed in photodetection

Although enhanced performances of photovoltaic devices by embedding metal nanoparticals in charge transport layer, doping into active layer bulk, decorating the active layer surface, and inserting at the interface between semiconductor and the electrode were reported, the effect of incorporating metal NPs at the interface of single crystal semiconductor and perovskite is rarely tackled. Herein the effects of incorporating Ag nanoparticals (AgNPs) at p-Si/MAPbI3 perovskite interface on the photodiode performances were investigated. The results showed that compared with reference device (without AgNPs) the photoresponsivity of the device incorporating AgNPs is greatly improved with the exception for light with wavelengths fall in the spectral range where AgNPs have strong optical absorption. This effect is extremely significant for relatively shorter wavelengths in visible region, and a maximal improvement of around 10.6 times in photoresponsivity was achieved. The physical origin of the exception for spectral range that AgNPs have strong optical absorption is the cancelation of scatter resulted enhancement through AgNPs by band-to-band absorption resulted reduction of photocurrent, in which the generated electron has energy near the fermi level and the hole has large effective mass, which relax by nonradiative recombination, thus making not contribution to the photocurrent. More importantly, the AgNP decorated device showed much faster photo response speed than reference device, and a maximal improvement of around 7.9 times in rise and fall time was achieved. These findings provide a novel approach for high responsive and high speed detection for weak light.

The Bound Band Structure in a Strong Attractive Dirac Comb

Abstract: The Dirac comb problem in quantum mechanics is revisited by estimating its energy band structure, including the band gap, bandwidth, and the effective mass at band edges. The case of an attractive strong Dirac comb potential is considered. Our findings show the existence of a single bound energy band state, which is flat with a small width and a large effective mass at both of its edges; positive at its lower edge and negative at its upper edge. Keywords: Dirac comb, Bound energy, Band structure, Dispersion relation, Band gap, Bandwidth, Effective mass.

(Invited) Doping Mechanisms and Defect Passivation of p-Type SnOx for Tfts and Bipolar Devices

Despite the outstanding achievements in multiple areas such as displays and energy, oxide electronics has been limited to single-polar (n-type) applications due to the facile generation of oxygen vacancies as native donors. On the contrary, the processing of p-type oxides is restrained due to the high formation energy of native acceptors. Furthermore, the oxygen 2p orbitals of the majority of oxide semiconductors are anisotropic and localized to the valence band maximum (VBM), resulting in a large effective mass of holes and hence low carrier mobility.Hybrid orbital electronic configurations with cation d10 (closed shell structure) and cation s2 (pseudo-closed structure) have been suggested initially in complex oxides (e.g., CuMO2 where M= Al, Ga, and In; and SrCu2O2) to delocalize the oxygen 2p orbitals from the VBM. However, these complex oxides require high temperatures to process and are difficult to engineer the electrical properties of carrier density and carrier mobility due to the correlated nature of multi-cation species. Several single-cation p-type oxides such as PbO, Bi2O3, and SnO have emerged as well, where the energy level of a unique s-orbital of cations is similar to oxygen 2p orbitals, forming strong hybrid structures. In addition, a simpler single-cation structure leads to easier control of electrical properties required in practical device applications such as thin film transistors (TFT) and complementary logic inverters.We previously reported scalable processing of p-type SnOx through thermodynamic-based interfacial reactions as well as reactive sputtering.1 More recently, we also suggested multi-modal encapsulation to enhance TFT on- and off-state behaviors and identified a defect complex as an effective p-type doping agent.2 However, challenges remain since the TFT off-state current is large, and the defect/trap state density is high.In this presentation, we share our approaches to engineer the off-state current and passivate the defect/trap states. In addition to channel thickness optimization, intrinsic (Sn vacancy or oxygen interstitial) and extrinsic (H-related species) doping strategies to adjust channel carrier density will be compared. The performance of several surface treatments (oxygen plasma and UV) and TFT back channel encapsulations (SiO2 and Al2O3) will be systematically compared. Then, the device performance of optimized p-type SnO TFTs and complementary inverters with n-type InZnO TFTs will be discussed.References Lee et al., ACS Applied Materials & Interfaces, 13 (46), 55676–55686 (2021)Lee et al., ACS Applied Materials & Interfaces, 14 (48), 53999–54011 (2022) AcknowledgmentsThis work was partially supported by National Science Foundation, Award number ECCS-1931088 and CBET-2207302.

Layered oxyiodide CdBiO2I: An efficient visible light responsive and scalable photocatalyst

Developing high-performance visible-light driven photocatalyst (λ≥420 nm) makes significance for the efficient utilization of solar energy. Mass production and easy recycling are equally important for the practical application of powdery photocatalyst. However, it is challenging to meet the above requirements at the same time. In this work, we develop an efficient visible-light responsive layered oxyiodide CdBiO2I nanosheets prepared by a facile direct precipitation method at ambient atmosphere, and demonstrate its upgradable features well fitting potential application. CdBiO2I has a layered crystal structure consisting of [CdBiO2]+ layer and I– single layer, differing from that of BiOI composed of [BiO2]2+ layer and I- double layers. It displays an absorption edge of 520 nm in visible region, with a band gap of 2.52 eV. CdBiO2I has a large intrinsic effective mass difference of hole/electron, exceeding BiOI by 8-fold, which results in much higher charge separation efficiency and production of more reactive species (superoxide radicals and holes). The degradation efficiency of CdBiO2I nanosheets for tetracycline hydrochloride reaches 84% under the visible light irradiation within 1 h, in which the degradation rate is 10 times that of BiOI. In addition, mass production (12 g catalyst at one time) and immobilization onto porous polyurethane foam of CdBiO2I powder are also demonstrated, which indicates the scalable properties and easy recovery of the catalyst, highlighting the advantages of the current preparation method and prefiguring its potential in practical applications. This work may enlighten future research on the exploitation of solar-driven catalyst with high efficiency and strong practical applicability.

Unusual Dzyaloshinskii-Moriya Interaction in Graphene/Fe3GeTe2 Van der Waals Heterostructure.

Dzyaloshinskii-Moriya interaction (DMI) is shown to induce a topologically protected chiral spin texture in magnetic/nonmagnetic heterostructures. In the context of van der Waals spintronic devices, graphene emerges as an excellent candidate material. However, due to its negligible spin-orbit interaction, inducing DMI to stabilize topological spins when coupled to 3d-ferromagnets remains challenging. Here, it is demonstrated that, despite these challenges, a sizeable Rashba-type spin splitting followed by significant DMI is induced in graphene/Fe3GeTe2. This is made possible due to an interfacial electric field driven by charge asymmetry together with the broken inversion symmetry of the heterostructure. These findings reveal that the enhanced DMI energy parameter, resulting from a large effective electron mass in Fe3GeTe2, remarkably contributes to stabilizing non-collinear spins below the Curie temperature, overcoming the magnetic anisotropy energy. These results are supported by the topological Hall effect, which coexists with the non-trivial breakdown of Fermi liquid behavior, confirming the interplay between spins and non-trivial topology. This work paves the way toward the design and control of interface-driven skyrmion-based devices.

Estimation of Maximum <i>zT</i> in Cu<sub>3</sub>SbSe<sub>4</sub> for Different Starting Materials Content

Cu<sub>3</sub>SbSe<sub>4</sub> is considered a promising thermoelectric material because of its large effective mass and low thermal conductivity, originating from its unique lattice structure. However, Cu<sub>3</sub>SbSe<sub>4</sub> has intrinsically low carrier concentration and relatively high electric resistance which limit performance. Recently, a <i>zT</i> improvement in Cu<sub>3</sub>SbSe<sub>4</sub> was reported where doping/precipitation is controlled by changing the content of the starting materials. However, the effect of these changes in starting content on electronic band structures has not been studied. Here, we investigate how the change in starting materials content (<i>x</i> varying from 6 to 20) affects band parameters like density-of-states effective mass (<i>m<sub>d</sub></i> *), non-degenerate mobility (<i>μ<sub>0</sub></i>), weighted mobility (<i>μ<sub>W</sub></i>), and B-factor using the Single Parabolic Band (SPB) model. For <i>x</i> greater than 8, precipitation of the secondary phase (CuSe) was observed, and the band parameters changed differently for <i>x</i> greater than 8. The <i>m<sub>d</sub></i> * increases up to <i>x</i> = 8 and then rapidly decreases for <i>x</i> > 8. For <i>μ<sub>0</sub></i>, an overall decrease is observed for increasing <i>x</i>, but the rate of decrease is suppressed for <i>x</i> > 8. The <i>μ<sub>W</sub></i> reaches the maximum at <i>x</i> = 8. As <i>x</i> increases, the experimental lattice thermal conductivity also increases, especially for <i>x</i> > 8. Therefore, the B-factor, which is directly related to the theoretical maximum zT, becomes maximum at = 8. Hence the SPB model predicts a maximum <i>zT</i> of 0.0484 for <i>x</i> = 8 at 300 K, which is 15.5% higher than the experimental <i>zT</i> of 0.0419, which can be achieved by tuning the Hall carrier concentration to 4.44 × 10<sup>19</sup> cm<sup>-3</sup>.

Enhancing thermoelectric performance of AB2Sb2-type Zintl phase through band shaping and lattice distortion

AB2Sb2-type Zintl phases, especially Mg3Sb2, have garnered widespread attention in virtue of their nontoxic constituent elements and outstanding thermoelectric performance in n-type materials. However, the p-type counterpart of AB2Sb2 still struggles with a low figure of merit zT, primarily because of the limited valence band degeneracy, large band effective mass, and relatively high thermal conductivity. Here we simultaneously optimize the electrical and thermal transports of p-type AB2Sb2-based materials through shaping the band edge and distorting the crystal lattice. By alloying Zn at Mg2 site and Ca at Mg1 site, we successfully decorate the crystal lattice of Mg3Sb2 in real space and thereby modify the band structure in reciprocal space. Zn alloying promotes the band degeneracy while Ca alloying reduce the single band effective mass, which largely promotes the transport of charge carriers. Moreover, the distorted crystal lattice effectively blocks the heat-carry phonons to reduce the lattice thermal conductivity κL. A high zT of 0.81 is finally realized at 750 K in our Zn/Ca co-alloyed samples, which is three times larger than that of Mg3Sb2 matrix. Our work opens new possibilities for the synthetic optimization of both electrical and thermal transports in Zintl phase and other thermoelectric systems.

Comparative Analysis of Thiophene-Based Interlayer Cations for Enhanced Performance in 2D Ruddlesden-Popper Perovskite Solar Cells.

2D Ruddlesden-Popper (RP) perovskites have appeared as a promising prospective material owing to their tunable optoelectronic peculiarities and structural stability. The choice of interlayer cations greatly influences the performance of the 2D RP perovskites. In this study, through theoretical calculations and experimental investigation, we demonstrate the intrinsic and device performance differences between two perovskites based on cations of thiophenemethylamine (TMA) and thiopheneethylamine (TEA). Using density functional theory (DFT) calculations, it exposes that as compared to (TMA)2PbI4, (TEA)2PbI4 exhibits more pronounced distortion of [PbI6]4- units and possesses a wider band gap and larger effective mass. The experimental results on the TMA- and TEA-based 2D perovskites further show that when TEA is used as the interlayer cation, the crystallization process tends to form more low-n phases, which hinder charge transfer and decrease light harvesting. On the other hand, when TMA is used as the interlayer cation, excessive low-n phases are not observed, and the thin film exhibits excellent quality with significantly improved electron mobility. The (TMA)2(FA)n-1PbnI3n+1 (n = 5) perovskite device shows a remarkable conversion efficiency of 16.56%, much higher than that of TEA-based devices (PCE = 2.58%). Moreover, the unencapsulated devices based on TMA were able to maintain 88% of their initial efficiency even after being exposed to the environment (RT, RH = 30 ± 5%) for a duration of 1080 h. These findings provide important insights into the differences between thiophene-based cations and the selection of organic interlayer cations for 2D RP perovskite solar cells.

Large effective mass and ultralow thermal conductivity lead to high thermoelectric performance in the high-entropy semiconductor MnGeAgBiTe4

The partial substitution of Mn with Ge in the phase-separated MnTe–AgBiTe2 alloy effectively stabilizes a single solid solution and improves the thermoelectric performance.

Influence of defects induced by plasma-bombarded monolayer WS<sub>2 </sub>on optical properties of bound excitons

<sec>Monolayer transition metal dichalcogenides (TMDCs) exhibit exceptional properties including atomic-scale thickness, direct bandgap, and strong spin-orbit coupling, which make them have great potential applications in spintronics, optoelectronics, and other fields. Usually, materials contain various structural defects, which are either formed during preparation and growth or induced by subsequent treatments. These defects can significantly change their physicochemical properties. Consequently, controlling and comprehending defects is an important approach to adjusting the properties of these materials.</sec><sec>Herein, we use Ar<sup>+</sup> plasma to bombard monolayer WS<sub>2,</sub> which is exfoliated mechanically, thereby introducing defects whose density is controlled by changing the bombardment duration. The photoluminescence (PL) and Raman spectroscopic measurements at different temperatures and power values are utilized to investigate the optical properties of the defects. Furthermore, time-resolved photoluminescence is employed to unveil the dynamic behaviors of free and trapped excitons.</sec><sec>The bombardment can introduce different types of defects into typical two-dimensional (2D) TMDCs such as MoS<sub>2</sub> and WS<sub>2</sub>. Single sulfur vacancies are frequently generated, while other defects like double sulfur vacancies or metal atom vacancies can also occur. Exciton effects dominate the optical properties of monolayer TMDCs due to reduced screening and large effective mass. At low temperatures, bound exciton emissions arise from trapped states. Our measurements reveal two types of defect-bound excitons from the PL spectra at around 1.85 eV (X<sup>B1</sup>) and 1.55 eV (X<sup>B2</sup>). Meanwhile, the Raman peaks of the samples before and after treatment exhibit no obvious changes, indicating that the lattice structure remaines unchanged. After the Ar<sup>+</sup> bombardment, the intensity of the free neutral exciton significantly decreases to 1/6 of untreated WS<sub>2</sub>, owing to the free exciton population and the increased non-radiative centers. The dynamic processes of these two bound excitons are considerably slower than the neutral exciton’s, showing the typical dynamic behavior of defect-bound excitons. Furthermore, comparison between the PL under vacuum condition and the PL under atmospheric condition shows that the intensities of the two bound excitons exhibit opposing behaviors. In an atmospheric environment, neutral excitons and bound exciton X<sup>B1</sup> possess higher intensities. In the vacuum, the strength of neutral exciton and X<sup>B1</sup> decrease quickly, while the intensity of deep-level bound exciton X<sup>B2</sup> increases.</sec><sec>In summary, we observe two bound exciton states arising from specific vacancy states in monolayer WS<sub>2</sub> after Ar<sup>+</sup> bombardment. Their energy values are 200 meV and 500 meV lower than those of the neutral exciton, with a splitting energy value being about 300 meV. The detailed evolution of the relative spectral weight with temperature and excitation power are presented. This work provides insights into the generation, control, and characteristic spectra of defects in 2D materials.</sec>

Fractional Quantum Hall State at Filling Factor ν=1/4 in Ultra-High-Quality GaAs Two-Dimensional Hole Systems.

Single-component fractional quantum Hall states (FQHSs) at even-denominator filling factors may host non-Abelian quasiparticles that are considered to be building blocks of topological quantum computers. Such states, however, are rarely observed in the lowest-energy Landau level, namely at filling factors ν<1. Here, we report evidence for an even-denominator FQHS at ν=1/4 in ultra-high-quality two-dimensional hole systems confined to modulation-doped GaAs quantum wells. We observe a deep minimum in the longitudinal resistance at ν=1/4, superimposed on a highly insulating background, suggesting a close competition between the ν=1/4 FQHS and the magnetic-field-induced, pinned Wigner solid states. Our experimental observations are consistent with the very recent theoretical calculations that predict that substantial Landau level mixing, caused by the large hole effective mass, can induce composite fermion pairing and lead to a non-Abelian FQHS at ν=1/4. Our results demonstrate that Landau level mixing can provide a very potent means for tuning the interaction between composite fermions and creating new non-Abelian FQHSs.

(Invited) Better GaN Substrates Are the Key to Advancing GaN Device Technology

Gallium nitride (GaN) is a semiconductor that has an unusual combination of extreme values of fundamental physical and chemical properties. Its wide bandgap (3.4 eV at room temperature) results in a low intrinsic carrier density and thus low leakage and dark currents. These properties combined with its direct gap are crucial requirements for photo-detectors and high-temperature electronic applications. Despite the relatively large carrier effective masses, which lead to lower carrier mobilities, the high electron saturation velocity and high breakdown field make possible the fabrication of high frequency electronic devices. In addition, its relatively high thermal conductivity opens the possibility to realize a number of high-power device applications. These unique characteristics have made possible the fabrication of a variety of optoelectronic and electronic devices capable of performing at extreme operation conditions of current, voltage, temperature, and in harsh environments. GaN and its alloys and heterostructures with InN and AlN have resulted in devices with superior performance for a variety of applications. Despite this unprecedented and not fully developed semiconductor materials success, the realization of high-performance and high-yield devices will require native GaN substrates with well-controlled physical properties.Presently, Hydride Vapor Phase Epitaxy (HVPE) and Ammonothermal (Ammono-GaN) bulk growth are the only two methods that have successfully demonstrated the manufacture of GaN boules. The first, a fast-growth non-equilibrium process, only reproduces the starting substrate dimensions, while the latter, a slow-growth equilibrium process, allows increasing boule dimensions under controlled growth conditions. Despite the impressive accomplishments recently achieved by these growth methods, much work still needs to be done to establish a fully satisfactory bulk growth method for this material. Heteroepitaxial HVPE-GaN suffers from high dislocation densities, while Ammono-GaN suffers from high oxygen incorporation. Recent results suggest that Ammono-GaN wafers can be successfully used as seeds to grow thick freestanding GaN wafers by HVPE [1]. This approach resulted on HVPE-GaN wafers with orders of magnitude reduced extended defect and lower oxygen impurity concentrations. However, the relatively high background concentration of pervasive impurities is still preventing the realization of high performance devices. In this work, we illustrate how defect-sensitive optical techniques can be used to assist the optimization procedures at various stages of growth [2]. A brief review of defect-sensitive optical spectroscopic techniques employed to evaluate structural, optical, and electronic properties of the state-of-the-art bulk and thick-film (quasi-bulk) Nitride substrates and homoepitaxial films is presented. Defects control the performance of devices and feeding back knowledge of defects to growth efforts is key to advancing technology.References J. A. Freitas, Jr., J.C. Culbertson, N.A. Mahadik, T. Sochacki, M. Iwinska, and M.S. Bockowski, J. Crystal Growth 456 (2016) 113.J. A. Freitas, Jr., J.C. Culbertson, and E. R. Glaser, Crystals, 12 (2022) 1294.

An ab‐initio study of structural, opto‐electronic and thermoelectric aspects of zinc sulfide and zinc telluride

AbstractIn this study, structural, electronic, optical and thermoelectric aspects of Zinc Sulfide (ZnS) and Zinc Telluride (ZnTe) have been explored in detail. These calculations have been done by utilizing FP‐LAPW method via Density Functional Theory (DFT). In order to attain accurate band gaps, opto‐electronic properties are evaluated with modified Becke Johnson potential (mBJ). From band structure plots, both ZnS and ZnTe reveals direct (Γv–ΓC) band gap semiconductors in nature with bandgap value equal to 3.5 and 2.3 eV while in Density Of States (DOS) major influence is observed due to p states of S/Te and d state of Zn. Prominent variation of optical responses such as high values of imaginary dielectric constants 𝜀1 (ω) and n (ω) refractive index suggests that ZnS and ZnTe are applicant materials for future photonics and microelectronic devices. The thermoelectric aspects were explored by Boltz Trap code to determine electrical and thermal conductivities, Seebeck coefficients, power factors and figure of merit. The figure of merits is closer to 1 while compared with p‐type ZnS and ZnTe, n‐type ZnS and ZnTe has good thermoelectric properties, which are attributed to low thermal conductivity of the hole and larger effective mass. The goal of this research is to investigate not only the detailed physical aspects but also to provide an overview of its future applications in optoelectronics, displays, sensors and microelectronic industry.

Intrinsically large effective mass and multi-valley band characteristics of n-type Bi2[sbnd]Bi2Te3 superlattice-like films

Thermoelectric superlattices are expected to decouple the strong correlation between various thermoelectric parameters, and are an important strategy for excellent thermoelectric performances. The superlattices of (Bi2)m(Bi2Te3)n homologous series are well-known for low lattice thermal conductivity and intriguing topological surface states. However, the impacts of electronic structure on the thermoelectric performance were still not well-understood in (Bi2)m(Bi2Te3)n. To cope with this issue, Bi2Bi2Te3 superlattice-like films with adjustable Bi2/(Bi2+Bi2Te3) molar ratio (R) were successfully fabricated by the molecular beam epitaxy technique. Angle-resolved photoemission spectroscopy measurements combined with theoretical calculations revealed the conduction band evolution from single-valley to multi-valley as R ≥ 0.30, leading to intrinsically high carrier effective mass and improved thermoelectric power factor. Also, the superlattice film (R = 0.46) with the structure close to Bi4Te3 possesses the topological surface state feature around the high symmetry point. As a result of the high effective mass of 3.9 m0 and very high electron density of 2.31 × 1021 cm−3, the film with R = 0.46 acquired the highest power factor of 1.49 mW·m−1·K−2 at 420 K, outperforming that of other (Bi2)m(Bi2Te3)n superlattices. This work lays an essential foundation on understanding the electronic structure and further improving thermoelectric performances of (Bi2)m(Bi2Te3)n homologous series.

Large composite fermion effective mass at filling factor 5/2

The 5/2 fractional quantum Hall effect in the second Landau level of extremely clean two-dimensional electron gases has attracted much attention due to its topological order predicted to host quasiparticles that obey non-Abelian quantum statistics and could serve as a basis for fault-tolerant quantum computations. While previous works have establish the Fermi liquid (FL) nature of its putative composite fermion (CF) normal phase, little is known regarding its thermodynamics properties and as a result its effective mass is entirely unknown. Here, we report on time-resolved specific heat measurements at filling factor 5/2, and we examine the ratio of specific heat to temperature as a function of temperature. Combining these specific heat data with existing longitudinal thermopower data measuring the entropy in the clean limit we find that, unless a phase transition/crossover gives rise to large specific heat anomaly, both datasets point towards a large effective mass in the FL phase of CFs at 5/2. We estimate the effective-to-bare mass ratio m*/me to be ranging from ~ 2 to 4, which is two to three times larger than previously measured values in the first Landau level.

Physical mechanism on ladderphane copolymers with electron localization and phonon delocalization for capacitive energy storage

In this article, the properties of trapezoidal polymer PSBNP-co-PTNI for capacitive energy storage are investigated theoretically, stimulated by the recent experimental reports [Chen et al., Nature 615, 62 (2023)]. The flatband structures of PSBNP-co-PTNI copolymer reveal that very large effective mass of electron results in Anderson electron localization and then small electric conductance. The TNI doping significantly decreases optical absorption in an ultraviolet region, which can significantly suppress photocurrent. Raman spectrum demonstrates that phonon Debye temperature can be significantly decreased, due to the U-process of phonon scattering by TNI doping, and then results in the phonon delocalization, and then the large thermal conductivity and thermal capacity. The simultaneous regulations on decreasing electric conductivity and on increasing thermal conductivity can significantly increase the ability of capacitive energy storage. The unit-length dependent thermal electric current manifests that the thermal electric current can be significantly decreased by slightly increase in length of copolymer. Overall, our research contributes to the understanding of the impact of TNI doping on the energy storage properties of the polymer and provides a valuable reference for future research focused on polymer energy storage.

Enhancing sensitivity in mode-localized tilt sensors based on asymmetrically coupled resonators

Mode-localized tilt sensors with amplitude ratio (AR) outputs have been proven to have a significant improvement in sensitivity over conventional frequency outputs, and the coupling stiffness between the coupled resonators is the key to sensitivity. The resonators in tilt sensors are designed identically to form coupling and have an equivalent response to the external perturbation. This paper proposes a new method to improve the sensitivity without weakening the coupling stiffness between resonators by exploiting the asymmetry of coupled resonators. Using the amplitude ratio of the asymmetrically resonators with a smaller effective mass to the resonator with a larger effective mass as the output, the sensitivity of the mode-localized tilt sensor will be increased approximately by a factor of the ratio of the effective masses of the two resonators compared to symmetrically coupled resonators. Sensitivity can be increased to twice the original using asymmetrically coupled resonators, which has been verified both in theoretical analysis and finite element method (FEM) simulation.