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Showing papers on "Effective mass (solid-state physics) published in 2017"


Journal ArticleDOI
TL;DR: Encapsulated 2D InSe expands the family of graphene-like semiconductors and, in terms of quality, is competitive with atomically thin dichalcogenides and black phosphorus.
Abstract: Encapsulated few-layer InSe exhibits a remarkably high electronic quality, which is promising for the development of ultrathin-body high-mobility nanoelectronics. A decade of intense research on two-dimensional (2D) atomic crystals has revealed that their properties can differ greatly from those of the parent compound1,2. These differences are governed by changes in the band structure due to quantum confinement and are most profound if the underlying lattice symmetry changes3,4. Here we report a high-quality 2D electron gas in few-layer InSe encapsulated in hexagonal boron nitride under an inert atmosphere. Carrier mobilities are found to exceed 103 cm2 V−1 s−1 and 104 cm2 V−1 s−1 at room and liquid-helium temperatures, respectively, allowing the observation of the fully developed quantum Hall effect. The conduction electrons occupy a single 2D subband and have a small effective mass. Photoluminescence spectroscopy reveals that the bandgap increases by more than 0.5 eV with decreasing the thickness from bulk to bilayer InSe. The band-edge optical response vanishes in monolayer InSe, which is attributed to the monolayer's mirror-plane symmetry. Encapsulated 2D InSe expands the family of graphene-like semiconductors and, in terms of quality, is competitive with atomically thin dichalcogenides5,6,7 and black phosphorus8,9,10,11.

985 citations


Journal ArticleDOI
TL;DR: Focusing on the regime of strong repulsive interactions, the many-body system is characterized by extracting the key properties of repulsive Fermi polarons: the energy E_{+}, the effective mass m^{*}, the residue Z, and the decay rate Γ.
Abstract: We employ radio-frequency spectroscopy to investigate a polarized spin mixture of ultracold ^{6}Li atoms close to a broad Feshbach scattering resonance. Focusing on the regime of strong repulsive interactions, we observe well-defined coherent quasiparticles even for unitarity-limited interactions. We characterize the many-body system by extracting the key properties of repulsive Fermi polarons: the energy E_{+}, the effective mass m^{*}, the residue Z, and the decay rate Γ. Above a critical interaction, E_{+} is found to exceed the Fermi energy of the bath, while m^{*} diverges and even turns negative, thereby indicating that the repulsive Fermi liquid state becomes energetically and thermodynamically unstable.

240 citations


Journal ArticleDOI
01 Feb 2017-ACS Nano
TL;DR: The zigzag and armchair directions of the as-grown 2D crystals are identified and it is shown that Sn deficiency is the main cause of the p-type conductivity.
Abstract: We study the anisotropic electronic properties of two-dimensional (2D) SnS, an analogue of phosphorene, grown by physical vapor transport. With transmission electron microscopy and polarized Raman spectroscopy, we identify the zigzag and armchair directions of the as-grown 2D crystals. The 2D SnS field-effect transistors with a cross-Hall-bar structure are fabricated. They show heavily hole-doped (∼1019 cm–3) conductivity with strong in-plane anisotropy. At room temperature, the mobility along the zigzag direction exceeds 20 cm2 V–1 s–1, which can be up to 1.7 times that in the armchair direction. This strong anisotropy is then explained by the effective mass ratio along the two directions and agrees well with previous theoretical predictions. Temperature-dependent carrier density determined the acceptor energy level to be ∼45 meV above the valence band maximum. This value matches a calculated defect level of 42 meV for Sn vacancies, indicating that Sn deficiency is the main cause of the p-type conductivity.

237 citations


Journal ArticleDOI
TL;DR: In this article, an adaptive hybrid metamaterial that possesses both a negative mass density as well as an extremely tunable stiffness by properly utilizing both the mechanical and electric elements is proposed.
Abstract: Achieving vibration and/or wave attenuation with locally resonant metamaterials has attracted a great deal of attention due to their frequency dependent negative effective mass density Moreover, adaptive phononic crystals with shunted piezoelectric patches have also demonstrated a tunable wave attenuation mechanism by controlling electric circuits to achieve a negative effective stiffness In this paper, we propose an adaptive hybrid metamaterial that possesses both a negative mass density as well as an extremely tunable stiffness by properly utilizing both the mechanical and electric elements A multi-physical analytical model is first developed to investigate and reveal the tunable wave manipulation abilities in terms of both the effective negative mass density and/or bending stiffness of the hybrid metamaterial The programmed flexural wave manipulations, broadband negative refraction and waveguiding are then illustrated through three-dimensional (3D) multi-physical numerical simulations in hybrid metamaterial plates Our numerical results demonstrate that the flexural wave propagation can essentially be switched between “ON/OFF” states by connecting different shunting circuits

168 citations


Journal ArticleDOI
TL;DR: Due to their ultra low lattice thermal conductivities coupled with high carrier mobilities, monolayer SnX2 materials may be promising materials for thermoelectric applications.
Abstract: Using density functional theory, we systematically investigate the lattice thermal conductivity and carrier mobility of monolayer SnX2 (X = S, Se). The room-temperature ultra low lattice thermal conductivities found in monolayer SnS2 (6.41 W m-1 K-1) and SnSe2 (3.82 W m-1 K-1) are attributed to the low phonon velocity, low Debye temperature, weak bonding interactions, and strong anharmonicity in monolayer SnX2. The predicted values of lattice thermal conductivity are lower than those of other two-dimensional materials such as stanene, phosphorene, monolayer MoS2, and bulk SnX2. High phonon-limited carrier mobilities are obtained for the monolayer SnX2. For example, the electron mobility of monolayer SnS2 is 756.60 cm2 V-1 s-1 and the hole mobility is 187.44 cm2 V-1 s-1. The electron mobility of these monolayers is higher than their hole mobility due to the low effective mass of electrons and low deformation constants, which makes them n-type materials. Due to their ultra low lattice thermal conductivities coupled with high carrier mobilities, monolayer SnX2 materials may be promising materials for thermoelectric applications.

159 citations


Journal ArticleDOI
Jin Hu1, Zhijie Tang1, Jinyu Liu1, Yanglin Zhu1, Jiang Wei1, Zhiqiang Mao1 
TL;DR: In the Dirac nodal-line semimetal ZrSiS, the extremely high Dirac fermion density gives rise to very strong de Haas-van Alphen quantum oscillations even at low magnetic fields as discussed by the authors.
Abstract: Topological semimetals harbor relativistic fermions featuring light effective mass, high mobility, and a nontrivial Berry phase. Quantum oscillations are an effective means to probe the properties of relativistic fermions. In the Dirac nodal-line semimetal ZrSiS, the extremely high Dirac fermion density gives rise to very strong de Haas--van Alphen quantum oscillations even at low magnetic fields, by which nearly massless Dirac fermions with surprisingly strong Zeeman effect are revealed.

156 citations


Journal ArticleDOI
23 Feb 2017
TL;DR: In this paper, the authors used Boltzmann transport calculations applied to ab initio band structures to extract a density-of-states effective mass from the Seebeck Coefficient and an inertial mass from electrical conductivity.
Abstract: The effective mass is a convenient descriptor of the electronic band structure used to characterize the density of states and electron transport based on a free electron model. While effective mass is an excellent first-order descriptor in real systems, the exact value can have several definitions, each of which describe a different aspect of electron transport. Here we use Boltzmann transport calculations applied to ab initio band structures to extract a density-of-states effective mass from the Seebeck Coefficient and an inertial mass from the electrical conductivity to characterize the band structure irrespective of the exact scattering mechanism. We identify a Fermi Surface Complexity Factor: $${N}_{{\rm{v}}}^{\ast }{K}^{\ast }$$ from the ratio of these two masses, which in simple cases depends on the number of Fermi surface pockets $$({N}_{{\rm{v}}}^{\ast })$$ and their anisotropy K *, both of which are beneficial to high thermoelectric performance as exemplified by the high values found in PbTe. The Fermi Surface Complexity factor can be used in high-throughput search of promising thermoelectric materials. A simple method for determining a material’s thermoelectric properties is developed by researchers in the United States and Belgium. Jeffrey Snyder from Northwestern University and his co-workers’ model could simplify the search for materials that efficiently generate electricity from waste heat. Even though the environment of an electron in a solid is very complex, the way an electron moves through a solid’s lattice of atoms can be treated as if it is moving in free space. However, because of the influence of its environment an effective mass, not its true mass, is used to model the movement of electrons and that material’s properties. But this effective-mass can be defined in several ways depending on which material property is being modeled. Snyder et al. determine that the ratio of two different effective masses, as computed from different electronic properties, could be a good method to identify novel thermoelectric materials and can be associated with the “complexity” of the electronic structure.

148 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reported electron-doped AgBi3S5 as a new high-performance nontoxic thermoelectric material, which is attributed to its unusual vibrational properties: double rattling phonon modes associated with Ag and Bi atoms.
Abstract: We report electron-doped AgBi3S5 as a new high-performance nontoxic thermoelectric material. This compound features exceptionally low lattice thermal conductivities of 0.5–0.3 W m–1 K–1 in the temperature range of 300–800 K, which is ascribed to its unusual vibrational properties: “double rattling” phonon modes associated with Ag and Bi atoms. Chlorine doping at anion sites acts as an efficient electron donor, significantly enhancing the electrical properties of AgBi3S5. In the carrier concentration range (5 × 1018–2 × 1019 cm–3) investigated in this study, the trends in Seebeck coefficient can be reasonably understood using a single parabolic band model with the electron effective mass of 0.22 me (me is the free electron mass). Samples of 0.33% Cl-doped AgBi3S5 prepared by spark plasma sintering show a thermoelectric figure of merit of ∼1.0 at 800 K.

142 citations


Journal ArticleDOI
TL;DR: In this article, a detailed theoretical analysis of Bose polarons in one-dimensional systems of ultracold atoms is presented, combining a nonperturbative renormalization group approach with numerically exact diffusion Monte Carlo calculations.
Abstract: Mobile impurity atoms immersed in Bose–Einstein condensates provide a new platform for exploring Bose polarons. Recent experimental advances in the field of ultracold atoms make it possible to realize such systems with highly tunable microscopic parameters and to explore equilibrium and dynamical properties of polarons using a rich toolbox of atomic physics. In this paper we present a detailed theoretical analysis of Bose polarons in one-dimensional systems of ultracold atoms. By combining a non-perturbative renormalization group approach with numerically exact diffusion Monte Carlo calculations we obtain not only detailed numerical results over a broad range of parameters but also qualitative understanding of different regimes of the system. We find that an accurate description of Bose polarons requires the inclusion of two-phonon scattering terms which go beyond the commonly used Frohlich model. Furthermore we show that when the Bose gas is in the strongly interacting regime, one needs to include interactions between the phonon modes. We use several theoretical approaches to calculate the polaron energy and its effective mass. The former can be measured using radio-frequency spectroscopy and the latter can be studied experimentally using impurity oscillations in a harmonic trapping potential. We compare our theoretical results for the effective mass to the experiments by Catani et al (2012 Phys. Rev. A 85 023623). In the weak-to-intermediate coupling regimes we obtain excellent quantitative agreement between theory and experiment, without any free fitting parameter. We supplement our analysis by full dynamical simulations of polaron oscillations in a shallow trapping potential. We also use our renormalization group approach to analyze the full phase diagram and identify regions that support repulsive and attractive polarons, as well as multi-particle bound states.

134 citations


Journal ArticleDOI
TL;DR: In this paper, a detailed theoretical analysis of Bose polarons in one dimensional systems of ultracold atoms is presented, combining a nonperturbative renormalization group approach with numerically exact diffusion Monte Carlo calculations, and they obtain not only detailed numerical results over a broad range of parameters but also qualitative understanding of different regimes of the system.
Abstract: Mobile impurity atoms immersed in Bose-Einstein condensates provide a new platform for exploring Bose polarons. Recent experimental advances in the field of ultracold atoms make it possible to realize such systems with highly tunable microscopic parameters and to explore equilibrium and dynamical properties of polarons using a rich toolbox of atomic physics. In this paper we present a detailed theoretical analysis of Bose polarons in one dimensional systems of ultracold atoms. By combining a non-perturbative renormalization group approach with numerically exact diffusion Monte Carlo calculations we obtain not only detailed numerical results over a broad range of parameters but also qualitative understanding of different regimes of the system. We find that an accurate description of Bose polarons requires the inclusion of two-phonon scattering terms which go beyond the commonly used Frohlich model. Furthermore we show that when the Bose gas is in the strongly interacting regime, one needs to include interactions between the phonon modes. We use several theoretical approaches to calculate the polaron energy and its effective mass. The former can be measured using radio-frequency spectroscopy and the latter can be studied experimentally using impurity oscillations in a harmonic trapping potential. We compare our theoretical results for the effective mass to the experiments by Catani et al. [PRA 85, 023623 (2012)]. In the weak-to-intermediate coupling regimes we obtain excellent quantitative agreement between theory and experiment, without any free fitting parameter. We supplement our analysis by full dynamical simulations of polaron oscillations in a shallow trapping potential. We also use our renormalization group approach to analyze the full phase diagram and identify regions that support repulsive and attractive polarons, as well as multi-particle bound states.

120 citations


Journal ArticleDOI
TL;DR: Modulated metamaterials, which exhibit either non-reciprocal behaviours or non-standard effective mass operators, offer promise for applications in the field of elastic wave control in general and in one-way conversion/amplification in particular.
Abstract: Time-reversal symmetry for elastic wave propagation breaks down in a resonant mass-in-mass lattice whose inner-stiffness is weakly modulated in space and in time in a wave-like fashion. Specifically, one-way wave transmission, conversion and amplification as well as unidirectional wave blocking are demonstrated analytically through an asymptotic analysis based on coupled mode theory and numerically thanks to a series of simulations in harmonic and transient regimes. High-amplitude modulations are then explored in the homogenization limit where a non-standard effective mass operator is recovered and shown to take negative values over unusually large frequency bands. These modulated metamaterials, which exhibit either non-reciprocal behaviours or non-standard effective mass operators, offer promise for applications in the field of elastic wave control in general and in one-way conversion/amplification in particular.

Journal ArticleDOI
TL;DR: In this article, the authors employ an eigenpolarization model including the description of direction dependent excitonic effects for rendering critical point structures within the dielectric function tensor of monoclinic b...
Abstract: We employ an eigenpolarization model including the description of direction dependent excitonic effects for rendering critical point structures within the dielectric function tensor of monoclinic b ...

Journal ArticleDOI
TL;DR: In this paper, a 2D tin-based chalcogenide material with high thermal stability and controllable superior carrier mobility was shown to have great potential in future flexible nano-electronic devices.
Abstract: Two dimensional (2D) materials are promising candidates for developing next-generation electronics. Monolayer tin(II) selenide (SnSe), which can be obtained by exfoliating bulk SnSe crystals at a low cleavage energy, is shown to be a nearly direct band gap semiconductor using first-principles calculations. By incorporating the anisotropic characteristics of effective masses, elastic modulus, and deformation potential with the longitudinal acoustic deformation potential scattering mechanism, we demonstrate that the charge carrier mobilities of monolayer SnSe strongly depend on the carrier type, valley index, transport direction, and biaxial strain. In particular, electron mobility is generally higher than hole mobility, and exhibits anisotropy of up to 241%. With increasing biaxial tensile strain, both electron mobility and hole mobility decline gradually, which is mainly attributed to a strain-induced heavier effective mass. Surprisingly, it is found that carrier mobilities can be enhanced by about 147% (electrons) and 968% (holes) via a small biaxial compressive strain, which effectively produces smaller effective masses of carriers and larger elastic modulus, suggesting the possibility of achieving high mobility of monolayer SnSe over a large number of substrates. Our results highlight a new promising 2D tin-based chalcogenide material with high thermal stability and controllable superior carrier mobility, having great potential in future flexible nano-electronic devices.

Journal ArticleDOI
TL;DR: An expanding spin-orbit coupled Bose-Einstein condensate whose dispersion features a region of negative effective mass is measured, observing a range of dynamical phenomena, including the breaking of parity and of Galilean covariance, dynamical instabilities, and self-trapping.
Abstract: Measurements of an expanding spin-orbit coupled Bose-Einstein condensate indicate that its dispersion features a region of negative effective mass.

Journal ArticleDOI
TL;DR: In this article, the authors use a nonperturbative renormalization group approach to develop a unified picture of the Bose polaron problem, where a mobile impurity is strongly interacting with a surrounding Bose-Einstein condensate (BEC).
Abstract: We use a nonperturbative renormalization group approach to develop a unified picture of the Bose polaron problem, where a mobile impurity is strongly interacting with a surrounding Bose-Einstein condensate (BEC). A detailed theoretical analysis of the phase diagram is presented and the polaron-to-molecule transition is discussed. For attractive polarons we argue that a description in terms of an effective Fr\"ohlich Hamiltonian with renormalized parameters is possible. Its strong-coupling regime is realized close to a Feshbach resonance, where we predict a sharp increase of the effective mass. Already for weaker interactions, before the polaron mass diverges, we predict a transition to a regime where states exist below the polaron energy and the attractive polaron is no longer the ground state. On the repulsive side of the Feshbach resonance we recover the repulsive polaron, which has a finite lifetime because it can decay into low-lying molecular states. We show for the entire range of couplings that the polaron energy has logarithmic corrections in comparison with predictions by the mean-field approach. We demonstrate that they are a consequence of the polaronic mass renormalization which is due to quantum fluctuations of correlated phonons in the polaron cloud.

Journal ArticleDOI
TL;DR: First-principles calculations of carrier dynamics in GaN are presented, focusing on electron-phonon (e-ph) scattering and the cooling and nanoscale dynamics of hot carriers, finding that e-ph scattering is significantly faster for holes compared to electrons and for hot carriers with an initial 0.5-1 eV excess energy.
Abstract: GaN is a key material for lighting technology. Yet, the carrier transport and ultrafast dynamics that are central in GaN light-emitting devices are not completely understood. We present first-principles calculations of carrier dynamics in GaN, focusing on electron–phonon (e-ph) scattering and the cooling and nanoscale dynamics of hot carriers. We find that e-ph scattering is significantly faster for holes compared to electrons and that for hot carriers with an initial 0.5–1 eV excess energy, holes take a significantly shorter time (∼0.1 ps) to relax to the band edge compared to electrons, which take ∼1 ps. The asymmetry in the hot carrier dynamics is shown to originate from the valence band degeneracy, the heavier effective mass of holes compared to electrons, and the details of the coupling to different phonon modes in the valence and conduction bands. We show that the slow cooling of hot electrons and their long ballistic mean free paths (over 3 nm at room temperature) are a possible cause of efficiency...

Journal ArticleDOI
TL;DR: In this paper, a new synthesis procedure for quantum-confined Cs2SnI6 nanocrystals with size-dependent band gaps in the long-visible to near-infrared (1.38-1.47 eV) was described.
Abstract: Tin-halide perovskite nanocrystals are a viable precursor for lead-free, high-efficiency active layers for photovoltaic cells. We describe a new synthetic procedure for quantum-confined Cs2SnI6 nanocrystals with size-dependent band gaps in the long-visible to near-infrared (1.38–1.47 eV). Hot injection synthesis produces particles with no organic capping ligands, with average diameters that increase from 12 ± 2.8 nm to 38 ± 4.1 nm with increasing reaction temperature. The band gap, energies of the first excitonic peak, ground-state bleach peak (in the transient absorption spectrum), and photoluminescence peak depend linearly on the inverse square of diameter, consistent with quantum-confined excitons with an effective mass of (0.12 ± 0.02)m0, where m0 is the mass of an electron, a factor of 4.6 smaller than that in the bulk material. Transient absorption measurements show that approximately 90% of the bleach amplitude decays within 30 ps, probably because of carrier trapping on unpassivated surface sites....

Journal ArticleDOI
TL;DR: The thermodynamic parameters of superconducting H3S and PH3 strongly deviate from the prediction of BCS theory due to the strong-coupling and retardation effects.
Abstract: The comparison study of high pressure superconducting state of recently synthesized H$_3$S and PH$_3$ compounds are conducted within the framework of the strong-coupling theory. By generalization of the standard Eliashberg equations to include the lowest-order vertex correction, we have investigated the influence of the nonadiabatic effects on the Coulomb pseudopotential, electron effective mass, energy gap function and on the $2\Delta(0)/T_C$ ratio. We found that, for a fixed value of critical temperature ($178$ K for H$_3$S and $81$ K for PH$_3$), the nonadiabatic corrections reduce the Coulomb pseudopotential for H$_3$S from $0.204$ to $0.185$ and for PH$_3$ from $0.088$ to $0.083$, however, the electron effective mass and ratio $2\Delta(0)/T_C$ remain unaffected. Independently of the assumed method of analysis, the thermodynamic parameters of superconducting H$_3$S and PH$_3$ strongly deviate from the prediction of BCS theory due to the strong-coupling and retardation effects.

Journal ArticleDOI
TL;DR: First-principles based methods are used to predict a very high zT value of 1.54 at 1200 K in p-type RuTaSb HH alloys, demonstrating that the p-types are promising as TE materials for high temperature power generation.
Abstract: Half-Heusler (HH) compounds are important high temperature thermoelectric (TE) materials and have gained ever-increasing popularity. In recent years, p-type FeNbSb-based heavy-band HH compounds have attracted considerable attention with the record-high zT value of 1.5. Here, we use first-principles based methods to predict a very high zT value of 1.54 at 1200 K in p-type RuTaSb alloys. The high band degeneracy and low band effective mass contribute to a high power factor. Although the electrical thermal conductivity is high due to the high carrier mobility and hence electrical conductivity, the total thermal conductivity is moderate because of the low lattice thermal conductivity. The predicted high zT demonstrates that the p-type RuTaSb HH alloys are promising as TE materials for high temperature power generation.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the optical properties of single crystals of light polarized parallel and perpendicular to the W-chain axis over a broad range of frequency and temperature, and quantitatively studied the temperature dependence of the plasma frequency, revealing a modest increase of the effective mass anisotropy in the plane upon cooling.
Abstract: We investigated the $ab$-plane optical properties of single crystals of ${\mathrm{WTe}}_{2}$ for light polarized parallel and perpendicular to the W-chain axis over a broad range of frequency and temperature. At far-infrared frequencies, we observed a striking dependence of the reflectance edge on light polarization, corresponding to anisotropy of the carrier effective masses. We quantitatively studied the temperature dependence of the plasma frequency, revealing a modest increase of the effective mass anisotropy in the $ab$ plane upon cooling. We also found strongly anisotropic interband transitions persisting to high photon energies. These results were analyzed by comparison with ab initio calculations. The calculated and measured plasma frequencies agree to within 10% for both polarizations, while the calculated interband conductivity shows excellent agreement with experiment.

Journal ArticleDOI
TL;DR: In this article, the authors reported an improved photocatalytic water splitting activity by P and As substitution at the N-site in the C2N monolayer using state-of-the-art hybrid density functional calculations.
Abstract: Exploiting earth-abundant and low-cost photocatalysts for high efficiency photocatalytic water splitting is of profound significance. Herein, we report an improved photocatalytic water splitting activity by P and As substitution at the N-site in the C2N monolayer using state-of-the-art hybrid density functional calculations. Our results show that the band gap can be reduced in C2N by increasing the concentrations of P and As substitution, and at the same time the obtained band gap value is higher than the free energy of water splitting except for As with concentrations of x = 0.333. This indicates that these new compositions of P/As substituted C2N monolayers are thermodynamically suitable to drive hydrogen evolution reaction. The calculated effective mass of charge carriers illustrates that charge transfer to the reactive sites would be easier in the substituted system than the pure C2N, and also our results suggest that the recombination rate would be lower in the substituted system, indicating the enha...

Journal ArticleDOI
TL;DR: In this paper, a theoretical study based on quantum Monte Carlo methods of the Bose polaron in one-dimensional systems with contact interactions is presented, where the ground-state energy of the impurity, its effective mass, and the contact parameter between the impurer and the bath are investigated.
Abstract: We present a theoretical study based upon quantum Monte Carlo methods of the Bose polaron in one-dimensional systems with contact interactions. In this instance of the problem of a single impurity immersed in a quantum bath, the medium is a Lieb-Liniger gas of bosons ranging from the weakly interacting to the Tonks-Girardeau regime, whereas the impurity is coupled to the bath via a different contact potential, producing both repulsive and attractive interactions. Both the case of a mobile impurity, having the same mass as the particles in the medium, and the case of a static impurity with infinite mass are considered. We make use of numerical techniques that allow us to calculate the ground-state energy of the impurity, its effective mass, and the contact parameter between the impurity and the bath. These quantities are investigated as a function of the strength of interactions between the impurity and the bath and within the bath. In particular, we find that the effective mass rapidly increases to very large values when the impurity gets strongly coupled to an otherwise weakly repulsive bath. This heavy impurity hardly moves within the medium, thereby realizing the ``self-localization'' regime of the Landau-Pekar polaron. Furthermore, we compare our results with predictions of perturbation theory valid for weak interactions and with exact solutions available when the bosons in the medium behave as impenetrable particles.

Journal ArticleDOI
TL;DR: In this paper, angle-resolved photoemission spectroscopy studies on a series of FeTe1−xSex monolayer films grown on SrTiO3 were performed.
Abstract: We performed angle-resolved photoemission spectroscopy studies on a series of FeTe1−xSex monolayer films grown on SrTiO3. The superconductivity of the films is robust and rather insensitive to the variations of the band position and effective mass caused by the substitution of Se by Te. However, the band gap between the electron- and hole-like bands at the Brillouin zone center decreases towards band inversion and parity exchange, which drive the system to a nontrivial topological state predicted by theoretical calculations. Our results provide a clear experimental indication that the FeTe1−xSex monolayer materials are high-temperature connate topological superconductors in which band topology and superconductivity are integrated intrinsically.

Journal ArticleDOI
TL;DR: In this paper, the authors derived a general methodology to obtain constraints for any PBH Extended Mass Distribution (EMD) and any observables in the desired mass range, starting from those obtained for a monochromatic distribution, they converted them into constraints for EMDs by using an equivalent, effective mass $M_{\rm eq}$ that depends on the specific observable.
Abstract: The model in which Primordial Black Holes (PBHs) constitute a non-negligible fraction of the dark matter has (re)gained popularity after the first detections of binary black hole mergers. Most of the observational constraints to date have been derived assuming a single mass for all the PBHs, although some more recent works tried to generalize constraints to the case of extended mass functions. Here we derive a general methodology to obtain constraints for any PBH Extended Mass Distribution (EMD) and any observables in the desired mass range. Starting from those obtained for a monochromatic distribution, we convert them into constraints for EMDs by using an equivalent, effective mass $M_{\rm eq}$ that depends on the specific observable. We highlight how limits of validity of the PBH modelling affect the EMD parameter space. Finally, we present converted constraints on the total abundance of PBH from microlensing, stellar distribution in ultra-faint dwarf galaxies and CMB accretion for Lognormal and Power Law mass distributions, finding that EMD constraints are generally stronger than monochromatic ones.

Journal ArticleDOI
TL;DR: In this paper, significant synergistic effects of d-orbital-unfilled transition metal doping on the crystal structure and electrical/thermal properties of Mohite-type ternary sulfide Cu2SnS3 are reported.
Abstract: Mohite-type ternary sulfide Cu2SnS3, which has been intensively studied in the photovoltaic field, has recently attracted much attention as an outstanding p-type eco-friendly thermoelectric material In the present work, significant synergistic effects of d-orbital-unfilled transition metal (Co) doping on the crystal structure and electrical/thermal properties of Cu2SnS3 are reported Crystal structure evolution with Co doping, involving not only monoclinic to cubic and tetragonal transitions but also the formation of a hierarchical architecture (Cu–S nano-precipitates, metal and S vacancies, and even nano-scaled stacking faults), is related to bond softening and intensified phonon scattering Thus, an ultralow lattice thermal conductivity of 090 W m−1 K−1 at 323 K to 033 W m−1 K−1 at 723 K was obtained Moreover, an increased effective mass is derived from the contribution of the Co 3d states to the inherent Cu 3d and S 3p states in the valence band, leading to a remarkable power factor (094 mW m−1 K−2, x = 020 at 723 K) with optimal doping As a result, the high ZT of ∼085 at 723 K elevates the modified Cu2SnS3 to the level of state-of-the-art mid-temperature eco-friendly sulfide thermoelectric materials

Journal ArticleDOI
TL;DR: In this article, the attenuation bandwidth in a one-dimensional finite chain with frequency graded linear internal resonators was investigated and it was shown that a properly tuned frequency graded arrangement of resonating units can extend the upper part of the attenuated band theoretically up to infinity and also increase the lower part of attenuation band by around 40% of an equivalent uniformly periodic metamaterial without increasing the mass.
Abstract: Depending on the frequency, waves can either propagate (transmission band) or be attenuated (attenuation band) while travelling through a one-dimensional spring-mass chain with internal resonators. The literature on wave propagation through a 1D mass-in-mass chain is vast and continues to proliferate because of its versatile applicability in condensed matter physics, optics, chemistry, acoustics, and mechanics. However, in all these areas, a uniformly periodic arrangement of identical linear resonating units is normally used which limits the attenuation band to a narrow frequency range. To counter this limitation of linear uniformly periodic metamaterials, the attenuation bandwidth in a one-dimensional finite chain with frequency graded linear internal resonators are investigated in this paper. The result shows that a properly tuned frequency graded arrangement of resonating units can extend the upper part of the attenuation band of 1D metamaterial theoretically up to infinity and also increases the lower part of the attenuation bandwidth by around 40% of an equivalent uniformly periodic metamaterial without increasing the mass. Therefore, the frequency graded metamaterials can be a potential solution towards low frequency and wideband acoustic or vibration insulation. In addition, this paper provides analytical expressions for the attenuation and transmission frequency limits for a periodic mass-in-mass metamaterial and demonstrates the attenuation band is generated by the high absolute value of the effective mass not only due to the negative effective mass.

Journal ArticleDOI
TL;DR: Effects of the extremely reduced cavity dimensions are observed as the light-matter coupled system is better described by an effective mass heavier than the uncoupled one, which opens the way to ultrastrong coupling at the single-electron level in two-dimensional electron systems.
Abstract: Ultrastrong light-matter coupling allows the exploration of new states of matter through the interaction of strong vacuum fields with huge electronic dipoles. By using hybrid dipole antenna-split ring resonator-based cavities with extremely small effective mode volumes Veff/λ03 ≃ 6 × 10–10 and surfaces Seff/λ02 ≃ 3.5 × 10–7, we probe the ultrastrong light-matter coupling at 300 GHz to less than 100 electrons located in the last occupied Landau level of a high mobility two-dimensional electron gas, measuring a normalized coupling ratio of ΩR/ωc = 0.36. Effects of the extremely reduced cavity dimensions are observed as the light-matter coupled system is better described by an effective mass heavier than the uncoupled one. These results open the way to ultrastrong coupling at the single-electron level in two-dimensional electron systems.

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate that the synergistic effect of band structure modification and chemical bond softening can be realized simultaneously in In & Mn doped SnTe bulk alloys.
Abstract: SnTe alloys, which have the same crystal structure as PbTe, have attracted increasing attention. Here, we demonstrate that the synergistic effect of band structure modification and chemical bond softening can be realized simultaneously in In & Mn doped SnTe bulk alloys. The Seebeck coefficient and power factor are synergistically improved by co-doping of In and Mn. In doping is known to introduce a resonance level. Mn doping reduces the separation of light- and heavy-valence bands. The combination of these effects significantly enhances the Seebeck coefficient at room temperature owing to around a factor of five times increase in the band effective mass. The reduction of thermal conductivity is from the decrease of both the electronic and phononic parts. The electronic thermal conductivity is decreased by the increase in defect scattering, as can be confirmed by the carrier mobility. The force constant of the bonds around the Te site is decreased due to the co-doping of In & Mn, which indicates that the chemical bonds are softened, which leads to low sound velocity and lower lattice thermal conductivity. As a result, the peak thermoelectric figure of merit, zT = 1.03 has been achieved for Sn0.89In0.01Mn0.1Te at 923 K. This strategy of using the synergistic effect of band structure modification and chemical bond softening could be applicable to other thermoelectric materials.

Journal ArticleDOI
TL;DR: In this paper, the authors compare the results of the canonical RMFT as a zeroth-order solution with the results obtained by the higher-order Gutzwiller wave function.
Abstract: Selected universal experimental properties of high-temperature superconducting (HTS) cuprates have been singled out in the last decade. One of the pivotal challenges in this field is the designation of a consistent interpretation framework within which we can describe quantitatively the universal features of those systems. Here we analyze in a detailed manner the principal experimental data and compare them quantitatively with the approach based on a single-band model of strongly correlated electrons supplemented with strong antiferromagnetic (super)exchange interaction (the so-called $t\ensuremath{-}J\ensuremath{-}U$ model). The model rationale is provided by estimating its microscopic parameters on the basis of the three-band approach for the Cu-O plane. We use our original full Gutzwiller wave-function solution by going beyond the renormalized mean-field theory (RMFT) in a systematic manner. Our approach reproduces very well the observed hole doping ($\ensuremath{\delta}$) dependence of the kinetic-energy gain in the superconducting phase, one of the principal non-Bardeen-Cooper-Schrieffer features of the cuprates. The calculated Fermi velocity in the nodal direction is practically $\ensuremath{\delta}$-independent and its universal value agrees very well with that determined experimentally. Also, a weak doping dependence of the Fermi wave vector leads to an almost constant value of the effective mass in a pure superconducting phase which is both observed in experiment and reproduced within our approach. An assessment of the currently used models ($t\ensuremath{-}J$, Hubbard) is carried out and the results of the canonical RMFT as a zeroth-order solution are provided for comparison to illustrate the necessity of the introduced higher-order contributions.

Journal ArticleDOI
TL;DR: In this article, the electronic structure and chemical bonding of three Sn2+ oxides of interest as p-type oxides: SnO and the two K2Sn2O3 polymorphs were analyzed.
Abstract: High mobility p-type transparent conducting oxides (TCOs) are critical to current and future optoelectronic devices such as displays, transparent transistors or solar cells. Typical oxides have flat oxygen-based valence bands leading to high hole effective masses and low mobilities. This makes the discovery of high hole mobility oxides very challenging. Sn2+ oxides are known to form Sn-s/O-p mixtures and dispersive valence bands (low hole effective mass). However, not all Sn2+ oxides exhibit low hole effective mass, pointing to the importance of structural factors. Here, we analyze the electronic structure and chemical bonding of three Sn2+ oxides of interest as p-type oxides: SnO and the two K2Sn2O3 polymorphs. We rationalize the differences in their hole effective masses by their Sn–O–Sn angles. As band dispersion is governed by the orbital overlap, Sn–O–Sn angles near 180° maximize the overlap and minimize the hole effective mass. We show that this principle is generalizable to a larger set of Sn2+ oxides. Our work leads to simple structural design principles for the development of low hole effective mass oxides based on Sn2+ (but also other reduced main group cations) offering a new avenue for the ongoing search for high mobility p-type TCOs.