In this study, by engineering the molecular structure, we optimize the spin Hall conductivity and the spin Hall angle in organics by more than five and three orders of magnitude, respectively. We identify two important characteristics of organic molecules, namely substitution of heavy elements and the torsion angles between constituent units of the polymer, which have significant effects on the spin Hall signal. These characteristics are directly related to the spin-orbit coupling and the energetic disorder, both of which offer a wide scope of chemical tunability in high-mobility polymers. We compute the spin Hall characteristics for easily synthesized molecules and identify candidates to exhibit the largest spin Hall signals in organic systems, several orders of magnitude larger than previously observed. The present study brings organic spintronics, by introducing polymers with much stronger spin Hall signal, closer to their inorganic counterparts.
Hall effect is detected in organic field-effect transistors, using appropriately shaped rubrene (C42H28) single crystals. It turned out that inverse Hall coefficient, having a positive sign, is close to the amount of electric-field induced charge upon the hole accumulation. The presence of the normal Hall effect means that the electromagnetic character of the surface charge is not of hopping carriers but resembles that of a two-dimensional hole-gas system.
We have observed the Hall effect in the field-induced accumulation layer on the surface of small-molecule organic semiconductor. The Hall mobility mu_H increases with decreasing temperature in both the intrinsic (high-temperature) and trap-dominated (low-temperature) conduction regimes. In the intrinsic regime, the density of mobile field-induced charge carriers extracted from the Hall measurements, n_H, coincides with the density n calculated using the gate-channel capacitance, and becomes smaller than n in the trap-dominated regime. The Hall data are consistent with the diffusive band-like m…
Hall effect measurements are important for elucidating the fundamental charge transport mechanisms and intrinsic mobility in organic semiconductors. However, Hall effect studies frequently reveal an unconventional behavior that cannot be readily explained with the simple band-semiconductor Hall effect model. Here, we develop an analytical model of Hall effect in organic field-effect transistors in a regime of coexisting band and hopping carriers. The model, which is supported by the experiments, is based on a partial Hall voltage compensation effect, occurring because hopping carriers respond …
The quantum anomalous Hall (QAH) phase is a novel topological state of matter characterized by a nonzero quantized Hall conductivity without an external magnetic field. The realizations of QAH effect, however, are experimentally challengeable. Based on ab initio calculations, here we propose an intrinsic QAH phase in DCA Kagome lattice. The nontrivial topology in Kagome bands are confirmed by the nonzero chern number, quantized Hall conductivity, and gapless chiral edge states of Mn-DCA lattice. A tight-binding (TB) model is further constructed to clarify the origin of QAH effect. Furthermore,…
Based on recently synthesized Ni3C12S12 class 2D metal-organic frameworks, we predict electronic properties of M3C12S12 and M3C12O12, where M is Zn, Cd, Hg, Be, or Mg with no M orbital contributions to bands near Fermi level. For M3C12S12, their band structures exhibit double Dirac cones with different Fermi velocities that are n and p type, respectively, which are switchable by few-percent strain. The crossing of two cones are symmetry-protected to be non-hybridizing, leading to two independent channels in 2D node-line semimetals at the same k-point akin to spin-channels in spintronics, rende…
We discuss the surface magnetotransport in the quantum Hall (QH) ferromagnetic state expected in the organic Dirac fermion system α-(BEDT-TTF)_2I_3. The QH ferromagnetic state is one of the possible ν=0 QH states in the two-dimensional Dirac fermion system resulting from the degeneracy breaking of the n=0 Landau level. It is characterized by the helical edge state. We have studied the interlayer surface transport via helical edge state in the multilayer QH ferromagnet, in which the bulk region is insulating. We have clarified that the surface conductivity is much less than e^2/h and decreases …
Exploration of spin-currents in organic semiconductors (OSECs) induced by resonant microwave absorption in ferromagnetic substrates has been of great interest for potential spintronics applications. Due to the inherently weak spin-orbit coupling (SOC) of OSECs, their inverse spin Hall effect (ISHE) response is very subtle; limited by the microwave power applicable under continuous-wave (cw) excitation. Here we introduce a novel approach for generating significant ISHE signals using pulsed ferromagnetic resonance, where the ISHE is ~2-3 orders of magnitude larger compared to cw excitation. This…
We present the results of first-principle calculations using the Vienna Ab-initio Simulation Package (VASP) for a new class of organometallics labeled TM3C6O6 (TM =Sc, Ti, V, Cr, Fe, Co, Ni and Cu) in the form of planar, two-dimensional, periodic free-standing layers. These materials, which can be produced by on-surface coordination on metallic surfaces, have a kagome lattice of TM ions. Calculating the structural properties, we show that all considered materials have local magnetic moments in the ground state, but four of them (with Fe, Co, Ni and Cu) show spin-crossover behavior by changing …
Metal-organic frameworks (MOFs) are an important class of materials that present intriguing opportunities in the fields of sensing, gas storage, catalysis, and optoelectronics. Very recently, two-dimensional (2D) MOFs have been proposed as a flexible material platform for realizing exotic quantum phases including topological and anomalous quantum Hall insulators. Experimentally, direct synthesis of 2D MOFs has been essentially confined to metal substrates, where the interaction with the substrate masks the intrinsic electronic properties of the MOF. Here, we demonstrate synthesis of 2D honeyco…
Spin-current injection into an organic semiconductor $\rm{κ\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$ film induced by the spin pumping from an yttrium iron garnet (YIG) film. When magnetization dynamics in the YIG film is excited by ferromagnetic or spin-wave resonance, a voltage signal was found to appear in the $\rm{κ\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$ film. Magnetic-field-angle dependence measurements indicate that the voltage signal is governed by the inverse spin Hall effect in $\rm{κ\text{-}(BEDT\text{-}TTF)_2Cu[N(CN)_2]Br}$. We found that the voltage signal in the $\rm{κ\text{-}(…
The interfacial structure plays a critical role in modern optoelectronics. Currently multilayer electrodes are used to optimize the injection and lifetime properties. The choice of interlayer is not universal, with different effects for the same material with different capping metals. Using a novel in-situ characterization method with X-ray photoelectron spectroscopy, the organic/inorganic interface in OLEDs was examined for two common cathode metals with a LiF interlayer. The impact of the interfacial layer on the performance of devices can be attributed to the bulk lattice matching of the in…
Organic semiconductors find increasing importance in spin transport devices due to the modulation and control of their properties through chemical synthetic versatility. The organic materials are used as interlayers between two ferromagnet (FM) electrodes in organic spin valves (OSV), as well as for magnetic spin manipulation of metal-organic complexes at the molecular level. In the latter, specifically, the substrate-induced magnetic switching in a paramagnetic molecule has been evoked extensively, but studied by delicate surface spectroscopies. Here we present evidence of the substantial mag…
In the last years, important non-linear optical results on sol-gel and polymeric materials have been reported, with values comparable to those found in crystals. These new materials contain push-pull chromophores either incorporated as guest in a high Tg polymeric matrix (doped polymers) or grafted onto the polymeric matrix. These systems present several advantages; however they require significant improvement at the molecular level - by designing optimized chromophores with very large molecular figure of merit, specific to each application targeted. Besides, it was recently stated in polymers…
We have experimentally tested the hypothesis of free charge carrier mediated spin-transport in the small molecule organic semiconductor Alq3 at room temperature. A spin current was pumped into this material by pulsed ferromagnetic resonance of an adjacent NiFe layer, while a charge current resulting from this spin current via the inverse spin-Hall effect (ISHE) was detected in a Pt layer adjacent on the other side of the Alq3 layer, confirming a pure spin current through the Alq3 layer. Charge carrier spin states in Alq3, were then randomized by simultaneous application of electron paramagneti…
Charge transfer between photoexcited quantum dots and molecular acceptors is one of the key limiting processes in most applications of colloidal nanostructures, most prominently in photovoltaics. An atomistic detailed description of this process would open new ways to optimize existing and create new structures with targeted properties. We achieve a one-to-one comparison between ab-initio non-adiabatic molecular dynamics calculations and transient absorption spectroscopy experiments, which allows us to draw a comprehensive atomistic picture of the charge transfer process, following the time ev…
This paper proposes a machine learning (ML) method to predict stable molecular geometries from their chemical composition. The method is useful for generating molecular conformations which may serve as initial geometries for saving time during expensive structure optimizations by quantum mechanical calculations of large molecules. Conformations are found by predicting the local arrangement around each atom in the molecule after trained from a database of previously optimized small molecules. It works by dividing each molecule in the database into minimal building blocks of different type. The …
Organic/inorganic donor-acceptor interfaces are gaining growing attention in organic photovoltaic applications as each component of the interface offers unique attributes. Here we use hybrid-density functional theory to examine the electronic structure of sexithiophene/ZnO interfaces. We find that interfacial molecular orientations strongly influence the adsorption energy, the energy level alignment, and the open circuit voltage. We attribute the orientation dependence to the varied strength of electronic coupling between the molecule and the substrate. Our study suggests that photovoltaic per…
We report the study of magnetotransport properties of regio-regular poly (3-hexyl thiophene) based organic diodes. The devices were fabricated using two different techniques of spin coating and inkjet printing. Positive magnetoresistance (MR) effect was observed at room temperature in all the devices. The highest MR magnitude reached up to 16% for some spin-coated devices and up to 10% in inkjet printed devices. The MR magnitude and line shapes were found to depend strongly on the measuring current. We observed deviation from the theoretically predicted Lorentzian or non-Lorentzian line shape …
Pure spin current based research is mostly focused on ferromagnet (FM)/heavy metal (HM) system. Because of the high spin orbit coupling (SOC) these HMs exhibit short spin diffusion length and therefore possess challenges for device application. Low SOC (elements of light weight) and large spin diffusion length make the organic semiconductors (OSCs) suitable for future spintronic applications. From theoretical model it is explained that, due to $π$ - $σ$ hybridization the curvature of the C$_{60}$ molecules may increase the SOC strength. Here, we have investigated spin pumping and inverse spin …
There is compelling evidence that charge carriers in organic semiconductors (OSs) self-localize in nano-scale space because of dynamic disorder. Yet, some OSs, in particular recently emerged high-mobility organic molecular crystals, feature reduced mobility at increasing temperature, a hallmark for delocalized band transport. Here we present the temperature-dependent mobility in two record-mobility OSs: DNTT (dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]-thiophene), and its alkylated derivative, C8-DNTT-C8. By combining terahertz photoconductivity measurements with fully atomistic non-adiabatic molecu…
EC-MOF/Phase-I: A computationally ready database of electrically conductive metal-organic frameworks with high-throughput structural and electronic properties
Modulation of the Nernst Thermoelectrics by Regulating the Anomalous Hall and Nernst Angles
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所凝聚态物理国家实验室）；Key Laboratory of Magnetic Molecules and Magnetic Information Materials of Ministry of Education & Research Institute of Materials Science, Shanxi Normal University（山西师范大学磁性分子与磁信息材料教育部重点实验室及材料科学研究所）
Despite the highly porous nature with significantly large surface area, metal organic frameworks (MOFs) can be hardly used in electronic, and optoelectronic devices due to their extremely poor electrical conductivity. Therefore, the study of MOF thin films that require electron transport or conductivity in combination with the everlasting porosity is highly desirable. In the present work, thin films of Co3(NDC)3DMF4 MOFs with improved electronic conductivity are synthesized using layer-by-layer and doctor blade coating techniques followed by iodine doping. The as-prepared and doped films are c…
The adsorption of two different organic molecules cyanidin glucoside (C$_{21}$O$_{11}$H$_{20}$) and TA-St-CA on anatase (101) and (001) nanowires have been investigated using the standard and the range separated hybrid density functional theory calculations. The electronic structures and optical spectra of resulting dye--nanowire combined systems show distinct features for these types of photochromophores. The lowest unoccupied molecular orbital of the natural dye cyanidin glucoside is located below the conduction band of the semiconductor while, in the case of TA-St-CA, it resonates with the …
System of Agentic AI for the Discovery of Metal-Organic Frameworks
University of California, Berkeley（加州大学伯克利分校）；Lawrence Berkeley National Laboratory（伯克利国家实验室）；Google DeepMind（谷歌DeepMind）；Kavli Energy NanoScience Institute（Kavli能源纳米科学研究所）
