Abstract Three dimensional topological insulators, as a new phase of quantum matters, are characterized by an insulating gap in the bulk and metallic state on surface. Particularly, most insulators have narrow band gaps, hence promising applications area terahertz optoelectronics. In this work, we experimentally demonstrate electronically-tunable intensity modulator based Bi 1:5 Sb 0:5 Te 1:8 Se 1:2 single crystal, one insulators. A relative frequency-independent modulation depth ~62% over...

Abstract Solution‐processed organic–inorganic hybrid perovskites are promising emitters for next‐generation optoelectronic devices. Multiple‐colored, bright light emission is achieved by tuning their composition and structures. However, there very little research on exploring optically active organic cations perovskites. Here, unique room‐temperature phosphorescence from reported employing novel cations. Efficient activated designing a mixed‐cation perovskite system to suppress nonradiative...

Abstract Apart from broadband absorption of solar radiation, the performance photovoltaic devices is governed by density and mobility photogenerated charge carriers. The latter parameters indicate how many free carriers move away their origin, fast, before loss mechanisms such as carrier recombination occur. However, only lower bounds these are usually obtained. Here we independently determine both in a perovskite film use time-resolved terahertz spectroscopy. Our data reveal modification...

We study the temperature-dependent phonon modes of organometallic lead iodide perovskite CH3NH3PbI3 thin film across terahertz (0.5–3 THz) and temperature (20–300 K) ranges. These are related to vibration Pb–I bonds. found that two in tetragonal phase at room split into four low-temperature orthorhombic phase. By use Lorentz model fitting, we analyze critical behavior this transition. The carrier mobility values calculated from mode frequencies, via theoretical approaches, agree reasonably...

Strong spin-orbit coupling, resulting in the formation of spin-momentum-locked surface states, endows topological insulators with superior spin-to-charge conversion characteristics, though dynamics that govern it have remained elusive. Here, an all-optical method is presented, which enables unprecedented tracking ultrafast a prototypical insulator Bi2 Se3 /ferromagnetic Co heterostructure, down to sub-picosecond timescale. Compared pure or Co, giant terahertz emission observed...

Excellent-performance terahertz (THz) modulators based on graphene/ionic liquid/graphene sandwich structures are demonstrated. The modulation covers a broadband frequency range from 0.1 to 2.5 THz with depth of up 99% by applying small gate voltage 3 V. outstanding performance the proposed devices is due conical band structure graphene and powerful gating effect ionic liquid in proximity graphene. As service our authors readers, this journal provides supporting information supplied authors....

Strong second-order optical nonlinearities often require broken material centrosymmetry, thereby limiting the type and quality of materials used for nonlinear devices. Here, we report a giant highly tunable terahertz (THz) emission from thin polycrystalline films centrosymmetric Dirac semimetal PtSe2. Our PtSe2 THz is turned on at oblique incidence locked to photon momentum incident pump beam. Notably, find an emitted efficiency that giant: It two orders magnitude larger than standard...

We report measurements of the magnetic penetration depth in single crystals ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ down to 0.04 K using a tunnel-diode based, self-inductive technique. observe power law temperature dependence below 0.8 K, with no sign second phase transition nor crossover predicted for multiband superconductor. A suggests that gap function has nodes, inconsistent candidate $p$-wave states. argue nonlocal effects, rather than impurity scattering, can explain observed ${T}^{2}$...

We report measurements of quasiparticle relaxation dynamics in the high-temperature superconductor (Ba,K)Fe2As2 optimally doped, underdoped, and undoped regimes. In underdoped sample, spin-density wave (SDW) order forms at approximately 85 K, followed by superconductivity 28 K. find emergence a normal-state that suppresses SDW temperature T{*} 60 K argue this is precursor to superconductivity.

Using terahertz time-domain spectroscopy, the real part of optical conductivity [$\sigma_{1}(\omega)$] twisted bilayer graphene was obtained at different temperatures (10 -- 300 K) in frequency range 0.3 3 THz. On top a Drude-like response, we see strong peak $\sigma_{1} (\omega)$ $\sim$2.7 We analyze overall response using disorder-dependent (unitary scattering) model, then attribute 2.7 THz to an enhanced density states that energy, is caused by presence van Hove singularity arising from...

Room-temperature phosphorescence (RTP) has a much longer lifetime than fluorescence as it involves triplet excitons. This extended enables the design of advanced optoelectronics and biological sensing technologies. Despite omnipresence states, harnessing these excitons remains challenging for most organic materials because forbidden transitions between singlet states. Here, we report novel organic–inorganic hybrid perovskites based on conjugated cations with low-lying energy levels to...

Lead halide perovskite semiconductors have low-frequency phonon modes within the lead sublattice and thus are considered to be soft. The soft lattice is important in defining their interesting optoelectronic properties. Electron–phonon coupling governs hot-carrier relaxation, carrier mobilities, lifetimes, among other electronic characteristics. Directly observing interplay between free charge carriers phonons can provide details on how impact these properties (e.g., exciton populations...

As a light absorber in photovoltaic applications, hybrid organic-inorganic halide perovskites should have long and balanced diffusion lengths for both the separated electrons holes before recombination, which necessitates high carrier mobility. In polar semiconductors, room-temperature mobility is often limited by scattering between carriers lowest-frequency optical phonon modes. Using terahertz time-domain spectroscopy, we examine temperature evolution of these modes CH3NH3PbBr3 obtained...

Spin–charge conversion is a spin–orbit coupling phenomena where electrical currents can generate transverse spin and vice versa. It one of the central topics in spintronics widely applied to manipulate charge degrees freedom materials. Previous research on spin–charge was mainly carried out by transport measurements, which lies (quasi)equilibrium DC/low-frequency limit. The recent development THz emission spectroscopy this field provides additional insights into dynamics process, i.e., its...

Solid-state infrared-to-visible photon up-conversion is important for spectral-tailoring applications. However, existing systems not only suffer from low efficiencies and a need high excitation intensity, but also exhibit limited selection of materials complex fabrication processes. Herein, we propose sensitizer with bulk-heterojunction structure, comprising both an energy donor acceptor, triplet-triplet annihilation devices. The occurs through charge separation at the donor-acceptor...

We report measurements of the magnetic penetration depth $\ensuremath{\lambda}$ in single crystals ${\mathrm{P}\mathrm{r}\mathrm{O}\mathrm{s}}_{4}{\mathrm{S}\mathrm{b}}_{12}$ down to 0.1 K, with ac field applied along $a$, $b$, and $c$ directions. In all three orientations, $\ensuremath{\lambda}\ensuremath{\sim}{T}^{2}$ superfluid density ${\ensuremath{\rho}}_{s}\ensuremath{\sim}{T}^{2}$ for $T<0.3{T}_{c}$. Data are best fit by $^{3}\mathrm{H}\mathrm{e}$ A-phase-like gap multidomains, each...

Magnetic polarons have been proposed to play important roles in doped wide band gap oxides that exhibit weak room temperature ferromagnetism. Here, we report the experimental evidence supporting polaronic magnetism and transport Ag-doped ZnO. Temperature dependent resistivity data suggest conduction mechanism of Mott Efros variable range hopping. The observed ferromagnetism its dependence are explained using percolation-based model partially ordered bound magnetic polarons.

Topological insulators are electronic materials with an insulating bulk and conducting surface. However, due to free carriers in the bulk, properties of metallic surface difficult detect characterize most topological insulator materials. Recently, a new Bi1.5Sb0.5Te1.7Se1.3 (BSTS) was found, showing high resistivities 1–10 Ω.cm greater contrast between compared other Bi-based insulators. Using Terahertz Time-Domain Spectroscopy (THz-TDS), we present complex conductivity BSTS single crystals,...

Abstract Terahertz time‐domain spectroscopy is a noncontact, coherent technique that can probe dynamics of carriers, phonons and excitons, the interplay among these degrees freedom, which determines functionalities system. In past few years, lead‐halide perovskites have shown to be promising class materials in areas solar cells, light emitting diodes, lasers, photodetectors, field‐effect transistors. electronic photonic devices, knowledge charge carriers other low‐energy excitations crucial...

Abstract Inorganic perovskites have recently attracted much attention as promising new nanocrystalline materials that interesting fundamental phenomena and great potential in several applications. Herein, we reveal unusual structural electronic changes cesium lead bromide (CsPbBr 3 ) a function of temperature using high-resolution spectroscopic ellipsometry, transmission electron microscopy terahertz spectroscopy measurements supported by first-principles calculations. New dual phases...

The generation and detection of ultrafast spin current, preferably reaching a frequency up to terahertz, is the core spintronics. Studies have shown that Weyl semimetal WTe2 great potential in generating currents. However, prior studies been limited static measurements with in-plane orientation. In this work, we demonstrate picosecond spin-photocurrent Td-WTe2 thin film via terahertz time domain spectroscopy circularly polarized laser excitation. anisotropic dependence circular photogalvanic...

In the development of highly efficient photovoltaic cells, solid perovskite systems have demonstrated unprecedented promise, with figure merit exceeding nineteen percent efficiency. this paper, we investigate optical and vibrational properties organometallic cubic CH3NH3PbI3 using first-principles calculations. For accurate theoretical description, go beyond conventional density functional theory (DFT), calculate conductivity relativistic quasi-particle correction. Incorporating these...

Abstract A remarkable feature of vanadium dioxide is that it can be synthesized in a number polymorphs. The conductivity mechanism the metastable layered polymorph VO 2 ( B ) thin films has been investigated by terahertz time-domain spectroscopy (THz-TDS). In ), critical temperature 240 K marks appearance non-zero Drude term observed complex conductivity, indicating evolution from pure insulating state towards metallic state. contrast, THz well-known M 1) well fitted only modification model...