Magnetoconductance Research Articles

The magneto thermoelectric coefficients of double quantum dots in series connected to ferromagnetic electrodes

In this paper, the charge and spin magneto coefficients of a double quantum dots system coupled in series connected to ferromagnetic electrodes with collinear magnetic alignments at finite bias voltage are theoretically investigated based on Green’s functions in a linear response regime. Magneto and spin magneto thermopower are estimated as a function of the thermal gradient and quantum dot energy levels. Magneto conductance and spin magneto conductance are also studied. The results showed that the positions of the peaks can be controlled for each value of polarization, and the magneto conductance is negative where the charge conductance for parallel alignment is lesser than that for antiparallel alignment except in the case of high spin polarization and ferromagnetic spin exchange. Enhancing the magneto thermoelectric coefficients of double quantum dots is a promising step in creating adaptable magnetic switching for thermoelectric generations, which could find use in thermal energy-based logic circuits or heat control applications.

Energy Gain and Loss Processes in OLEDs with Spacer‐Separated Electron–Hole Pairs Investigated by Magnetic Field Effects

AbstractInterfacial or diluted exciplex organic light emitting diodes (OLEDs) with spacer‐separated electron–hole pairs have emerged as a promising approach for precise tuning the energy level of charge‐transfer (CT) excitons and the improvement in device performance. However, their microscopic energy gain and loss mechanisms are not well understood. In this study, magnetic field effects (MFEs) including magneto‐electroluminescence (MEL), magneto‐conductance (MC), and magneto‐efficiency (Mη) in two series of donor‐spacer‐acceptor type exciplex‐based OLEDs, which exhibited opposite distance‐dependent device performances, are studied to explore the microscopic dynamics of spacer‐separated electron–hole pairs. Intersystem crossing (ISC) between CT excitons and between polaron‐pairs, reverse intersystem crossing (RISC) between CT excitons, triplet–triplet annihilation (TTA), scattering and dissociation channels of triplet‐charge annihilation (TQA), and additional Dexter energy transfer (DET) processes are identified. The decreased external quantum efficiency (EQE) and MEL with increasing thickness of space layer in Configuration II devices are attributed to an activation of the potential DET process from the lowest triplet of spacer‐separated CT excitons to the lowest triplet of Bphen caused by their smaller energy gaps. The study offers in‐depth insights into the exciton utilization and energy loss, which may allow better design and optimization of space‐modulated OLEDs.

Molecular Control of Triplet-Pair Spin Polarization and Its Optoelectronic Magnetic Resonance Probes.

ConspectusPreparing and manipulating pure magnetic states in molecular systems are the key initial requirements for harnessing the power of synthetic chemistry to drive practical quantum sensing and computing technologies. One route for achieving the requisite higher spin states in organic systems exploits the phenomenon of singlet fission, which produces pairs of triplet excited states from initially photoexcited singlets in molecular assemblies with multiple chromophores. The resulting spin states are characterized by total spin (quintet, triplet, or singlet) and its projection onto a specified molecular or magnetic field axis. These excited states are typically highly polarized but exhibit an impure spin population pattern. Herein, we report the prediction and experimental verification of molecular design rules that drive the population of a single pure magnetic state and describe the progress toward its experimental realization.A vital feature of this work is the close partnership among theory, chemical synthesis, and spectroscopy. We begin by presenting our theoretical framework for understanding spin manifold interconversion in singlet fission systems. This theory makes specific testable predictions about the intermolecular structure and orientation relative to an external magnetic field that should lead to pure magnetic state preparation and provides a powerful tool for interpreting magnetic spectra. We then test these predictions through detailed magnetic spectroscopy experiments on a series of new molecular architectures that meet one or more of the identified structural criteria. Many of these architectures rely on the synthesis of molecules with features unique to this effort: rigid bridges between chromophores in dimers, heteroacenes with tailored singlet/triplet-pair energy level matching, or side-group engineering to produce specific crystal structures. The spin evolution of these systems is revealed through our application and development of several magnetic resonance methods, each of which has different sensitivities and relevance in environments relevant to quantum applications.Our theoretical predictions prove to be remarkably consistent with our experimental results, though experimentally meeting all the structural prescriptions demanded by theory for true pure-state preparation remains a challenge. Our magnetic spectra agree with our model of triplet-pair behavior, including funneling of the population to the ms = 0 magnetic sublevel of the quintet under specified conditions in dimers and crystals, showing that this phenomenon is subject to control through molecular design. Moreover, our demonstration of novel and/or highly sensitive detection mechanisms of spin states in singlet fission systems, including photoluminescence (PL), photoinduced absorption (PA), and magnetoconductance (MC), points the way toward both a deeper understanding of how these systems evolve and technologically feasible routes toward experiments at the single-molecule quantum limit that are desirable for computational applications.

Low temperature charge transport study of MWCNT/PEDOT:PSS composites: insulating to metallic regime

Multiwall carbon nanotube (MWCNT)/poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) composites have been examined for their temperature and magnetic field dependent conductivity behavior. The conductivity ratio, σ r (σ 300 K/ σ 2 K), is significantly impacted by the sulfuric acid post-treatment of the composites and a slight alteration in MWCNTs loading. By adjusting the loading of MWCNTs in the composites, the charge transport is tuned from insulating to metallic regime. For the low loading of MWCNTs (0.04 wt%), charge transport of the composite lies in the insulating regime and follows a variable range hopping model. At moderate loading of MWCNTs, the transport of the composites lies in the critical regime and the temperature dependent conductivity follows a power law model. As the MWCNTs loading increases to 4 wt%, transport of the composites shifts to the metallic regime with σ r ∼ 2.8. The temperature dependent conductivity has been explained by using electron-electron interactions and weak localization effects and the conductivity follows ∼T 1/2 and ∼T 3/4 dependence in different temperature regimes. Wave function shrinkage and forward interference effects have been used to evaluate the magnetoconductance (MC) of the samples located in the insulating regime. For the composites lying in the metallic regime, a dominant contribution from weak localization explains the behaviour of the MC. However, for those in the critical regime a combined effect of weak localization and electron-electron interactions has been observed.

Interplay of structural chirality, electron spin and topological orbital in chiral molecular spin valves

Chirality has been a property of central importance in physics, chemistry and biology for more than a century. Recently, electrons were found to become spin polarized after transmitting through chiral molecules, crystals, and their hybrids. This phenomenon, called chirality-induced spin selectivity (CISS), presents broad application potentials and far-reaching fundamental implications involving intricate interplays among structural chirality, topological states, and electronic spin and orbitals. However, the microscopic picture of how chiral geometry influences electronic spin remains elusive, given the negligible spin-orbit coupling (SOC) in organic molecules. In this work, we address this issue via a direct comparison of magnetoconductance (MC) measurements on magnetic semiconductor-based chiral molecular spin valves with normal metal electrodes of contrasting SOC strengths. The experiment reveals that a heavy-metal electrode provides SOC to convert the orbital polarization induced by the chiral molecular structure to spin polarization. Our results illustrate the essential role of SOC in the metal electrode for the CISS spin valve effect. A tunneling model with a magnetochiral modulation of the potential barrier is shown to quantitatively account for the unusual transport behavior.

Effect of active layer thickness on the charge recombination and dissociation in bulk heterojunction polymer solar cells under open circuit conditions

Bulk heterojunction organic photovoltaic cells (OPVs), which are based on anthracene-containing poly (p-phenylene-ethynylene)-alt-poly (p-phenylene-vinylene) (PPE-PPV) polymer denoted (AnE-PVstat) and phenyl C60 butyric acid methyl ester (PCBM). The active layer thickness was varied from 100 nm to 300 nm. The solar cell parameters and magnetoconductance (MC) effect were analyzed, and the results showed a positive MC effect (+MC) for active layer thicknesses of 100 nm, 150 nm, and 200 nm, while a negative MC effect (-MC) was observed for thicknesses of 250 nm and 300 nm. The Power conversion efficiency (PCE) of 4 ℅ was achieved for an active layer thickness of 200 nm. The triplet-doublet quenching (TQD) model was used to describe the MC effect, which is influenced by triplet-charge reactions on the current based on density matrix formalism using the Stochastic Liouville Equation. The dissociation and recombination rates of the T-D pairs increased with the thickness for thinner layers (100, 150, 200 nm) while decreased for thicker layers (250 nm and 300 nm).

Sign Inversion of Magnetoconductance in Organic Semiconductors by Different Spin-Mixing Channels at Charge-Transfer Interfaces

Organic semiconductors have shown obvious spin-related magnetoconductance (MC) even without the involvement of any magnetic elements, bringing an emerging research field called as organic spintronics. Tuning the MC sign is crucial to realize practical application based on these spin effects. Herein, we report the manipulation of MC signs in organic photodiode based on the ground-state and excited-state charge–transfer (CT) interfaces at room temperature. Different to the traditional CT interfaces that normally show positive MC, the ground-state CT (GSCT) interface presents negative MC due to the dominant spin-mixing channel from weakly bound polaron-pairs states, in which a main reverse intersystem crossing from the triplet to singlet states will lead to the opposite signs of magnetic field dependence. By adjusting the ground-state or excited-state CT process in one tandem device under electric and optical excitations, the device could reveal a low-field controlled current inverter. Our work shows the important role of organic CT states in the manipulation of the spin-related magneto-optoelectronic properties in organic semiconductors.

Transverse magnetoconductance in two-terminal chiral spin-selective devices.

The phenomenon of chirality induced spin selectivity (CISS) has triggered significant activity in recent years, although many aspects of it remain to be understood. For example, most investigations are focused on spin polarizations collinear to the charge current, and hence longitudinal magnetoconductance (MC) is commonly studied in two-terminal transport experiments. Very little is known about the transverse spin components and transverse MC - their existence, as well as any dependence of this component on chirality. Furthermore, the measurement of the CISS effect via two-terminal MC experiments remains a controversial topic. Detection of this effect in the linear response regime is debated, with contradicting reports in the literature. Finally, the potential influence of the well-known electric magnetochiral effect on CISS remains unclear. To shed light on these issues, in this work we have investigated the bias dependence of the CISS effect using planar carbon nanotube networks functionalized with chiral molecules. We find that (a) transverse MC exists and exhibits tell-tale signs of the CISS effect, (b) transverse CISS MC vanishes in the linear response regime establishing the validity of Onsager's relation in two-terminal CISS systems, and finally (c) the CISS signal remains present even in the absence of electric magneto chiral effects, suggesting the existence of an alternative physical origin of CISS MC.

Mediation of exciton concentration on magnetic field effects in NPB : Alq3-based heterojunction OLEDs.

Organic light-emitting diodes (OLEDs) are considered one of the most promising new display technologies owing to their advantages, such as all-solid-state, high color gamut, and wide viewing angle. However, in terms of special fields, the brightness, lifetime, and stability of the devices need further improvement. Therefore, heterojunction devices with different concentrations were prepared to regulate device brightness. The brightness of the bulk heterojunction device is enhanced by 9740 cd m-2, with a growth rate of about 26.8%. The impact of various temperatures and various exciton concentrations on the device magneto-conductance (MC) and magneto-electroluminescence (MEL) was investigated. Experimental results demonstrate that the exciton concentration inside the device can be tuned to improve optoelectronic properties and organic magnetic effects. The complex spin mixing process inside the bulk heterojunction device is deeply investigated, which provides a reliable basis for the design of bulk heterojunction devices.

Enhanced reverse inter-system crossing process of charge-transfer stated induced by carrier balance in exciplex-type OLEDs

The reverse inter-system crossing (RISC, CT<sup>3</sup> → CT<sup>1</sup>) process in charge transfer (CT<sup>1</sup> and CT<sup>3</sup>) states is an effective approach to improving the energy utilization rate of excited states, and precise control and full use of the RISC process have important scientific significance and application prospect for fabricating and realizing the efficient exciplex-type organic light-emitting diodes (OLEDs). The conventional exciplex-type OLEDs based on m-MTDATA: Bphen have received extensive attention among researchers owing to the fact that the energy difference between CT<sup>1</sup> and CT<sup>3</sup> around zero promotes the efficient occurrence of RISC process. But up to now, only transient photoluminescence can infer the existence of RISC process in experiment, which is quite unfavorable for the comprehensive understanding and application of this process to design high-performance OLEDs. Fortunately, in this paper, a series of balanced and unbalanced exciplex-based devices are prepared by changing the donor-acceptor blending ratio in the emitting layer (<i>x</i>% <i>m</i>-MTDATA:<i>y</i>% Bphen; <i>x</i>%, <i>y</i>% is the weight percent) and the carrier density flowing through the device. The RISC process of CT states is directly observed via analyzing fingerprint magneto-conductance (MC) traces of the balanced device at room temperature, and the balanced device has higher electroluminescence (EL) efficiency than the unbalanced device. Specifically, the low-field MC curves of unbalanced device only show an inter-system crossing (ISC) line shape, whereas those from the balanced exciplex device present an RISC line shape at low bias-current and the conversion into an ISC line shape with the further increase of bias current. The line shape transition from RISC to ISC is attributed to the triplet-charge annihilation (TQA) process caused by excessive charge carries under high bias current. Combining the physical microscopic mechanism of device, the above-mentioned MC curves of various exciplex devices can be explained as follows: under the same bias current, extra holes or electrons are generated in the emitter layer of unbalanced devices due to the mismatch of donor-acceptor molecular concentrations. These superfluous holes or electrons will react with the CT<sup>3</sup> state, which aggravates the TQA process in the device and weakens the RISC process in which the CT<sup>3</sup> state participates. That is to say, there are strong TQA process and weak RISC process in unbalanced exciplex device. Contrarily, the strong RISC process and weak TQA process in the balanced exciplex device are beneficial to the occurrence of delayed fluorescence, resulting in its EL efficiency higher than that of the unbalanced device. This work not only deepens the physical understanding of the influence of donor-acceptor blending ratio on the carrier balance in exciplex devices, but also paves the way for designing highly efficient OLED by fully employing the RISC process of balanced device.

Trap-Filling Magnetoconductance as an Initialization and Readout Mechanism of Triplet Exciton Spins.

Photoexcited triplet states are promising candidates for hybrid qubit systems, as they can be used as a controlling gate for nuclear spins. But microwave readout schemes do not generally offer the sensitivity needed to approach the single-molecule limit or the scope to integrate such systems into devices. Here, we demonstrate the possibility of electrical readout of triplet spins at room temperature through a specific mechanism of magnetoconductance (MC) in polycrystalline pentacene. We show that hole-only pentacene devices exhibit a positive photoinduced MC response that is consistent with a trap-filling mechanism. Spin and magnetic-field-dependent quenching of photogenerated triplets by holes quantitatively explains the MC response we observe. These results are distinct in both sign and proposed mechanism compared to previous reports on polyacene materials and provide clear design rules for future spintronic devices based on this spin-sensing mechanism.

Effect of gold nanoparticles on photoelectric properties and magnetic effects of light-emitting diodes

<p indent="0mm">In this study, four different kinds of green light-emitting devices with gold nanoparticles modified anode have been successfully fabricated by vacuum thermal evaporation and spin-coating. The device structure is ITO/Au-NPs/MoO₃/NPB/Alq₃/CBP/CsCl/Al. The photoelectric properties, magneto-electroluminescence (MEL) and magneto-conductance(MC) curves of the devices were measured at room temperature. The MEL and MC curves of the device with the CBP film thickness of <sc>15 nm</sc> were measured at ambient temperature ranging from 245 to <sc>9 K.</sc> Experimental results show that the stability of the devices improves after spinning a layer of nano-gold film on the surface of ITO. The value for maximum brightness is <sc>14710 cd/m²,</sc> and current efficiency is <sc>4.79 cd/A.</sc> The efficiency roll-off ratio of 5.47% at luminance of <sc>11890 cd/m².</sc> In addition, MC curves completely opposite line type appear at <sc>195 K</sc> compared with room-temperature. The mechanisms show that main reason for improving the stability of device is that the nanoparticles were adsorbed to the anode surface and defects are effectively passivated. Non-lorentz equation was applied to well fit the MC curve at <sc>245 K</sc> under <sc>7 V,</sc> and the fitting result <italic>B</italic>₂=297.37 mT. The reverse intersystem crossing (RISC) process inside device reverses the MC line from positive to negative, triplet excitons break through the barriers to conversion to singlet excitons and increase the utilization rate of triplet excitons. We deeply explore the low-efficiency roll-off devices and micro-mechanisms based on Au-NPs, and provide a feasible idea and researchable method for designing high-stability devices in the future.

Conversions from Normal to Abnormal Current‐Dependent ISC and from Abnormal to Normal Current‐Dependent RISC Processes in Exciplex‐Based OLEDs

AbstractIntersystem crossing (ISC) and reverse ISC (RISC) are important spin‐mixing processes for obtaining high quantum efficiency in exciplex‐based organic light‐emitting diodes (EB‐OLEDs) and often show normal current (I) dependencies which weaken with increasing I. Surprisingly, herein, using magneto‐conductance (MC) as a fingerprint probing tool, an unreported conversion from normal to abnormal I‐dependent ISC processes is observed at 300 K from relatively‐unbalanced EB‐OLEDs with the low electron‐injection barrier and the high hole mobility. More amazingly, after improving carrier injection balance through replacing the hole‐injection layer, a conversion from abnormal to normal I‐dependent RISC processes with increasing I is observed from the relatively‐balanced EB‐OLEDs for the first time. These two conversions are reasonably analyzed by fitting and decomposing MC traces of the devices. Furthermore, transition I of the conversion from abnormal to normal I‐dependent RISC processes decreases from 50 to 5 μA as the temperature reduces from 300 to 150 K, and only the normal I‐dependent RISC process is observed at 100 and 20 K due to high driving voltages. Obviously, this work deepens the full understandings of I‐dependent ISC and RISC processes in EB‐OLEDs and has the potential applications for the achievement of high‐performance devices.

Essential Role of Triplet Diradical Character for Large Magnetoresistance in Quinoidal Organic Semiconductor with High Electron Mobility.

A diradicaloid molecule with high semiconducting performance is synthesized based on the quinoidal benzo[1,2‐b:4,5‐b′]dithiophene structure. The diradical character is investigated by quantum chemical calculations and variable temperature electron spin resonance. The diode devices based on this molecule show a large change in electric current in magnetic fields below 100 mT with a strong dependence on the measurement temperatures; as the population of the triplet diradicals increases at high temperatures, the magnetoconductance (MC) values increase. As a result, a MC of −19.4% is achieved at 120 °C, which is the largest negative MC observed for organic molecules to date. In contrast, a smaller diradicaloid molecule based on quinoidal thieno[3,2‐b]thiophene without thermally accessible triplet state shows no MC, indicating the essential role of the triplet diradicals. The strong correlation between the MC and the triplet diradical concentrations suggests that the charge conduction in the diradicaloid is suppressed through a spin‐blocking mechanism, which can be controlled through the magnetic modulation of the hyperfine fields. The compound forms high‐crystallinity thin films and has high monopolar electron transport in organic field‐effect transistors, with an average mobility of 1.01 cm2 V−1 s−1 for edge‐cast films.

Dynamic Behaviors of Exciplex States in Rubrene/ C60 -Based OLEDs with Sub-Band-Gap Turn-On Electroluminescence

Although the origin of sub-band-gap electroluminescence has been extensively studied for organic light-emitting diodes (OLEDs) with a planar heterojunction of rubrene-fullerene (${\mathrm{C}}_{60}$), the dynamic behaviors of exciplexes formed at the $\mathrm{rubrene}/{\mathrm{C}}_{60}$ interface are still vague. Herein, employing magnetoconductance (MC) and magnetoelectroluminescence (MEL) detection techniques, we find an unreported reverse intersystem crossing (RISC, ${\mathrm{EX}}^{3}$ \ensuremath{\rightarrow} ${\mathrm{EX}}^{1}$) from triplet to singlet exciplexes dominated at the $\mathrm{rubrene}/{\mathrm{C}}_{60}$ interface. Besides this RISC evolution channel, the triplet exciplexes also participate in another two processes: one is the scattering channel of triplet-charge annihilation (TCASC, ${\mathrm{EX}}^{3}$ + $\stackrel{\ensuremath{\leftarrow}}{e}$ \ensuremath{\rightarrow} ${S}_{0}$+ \ensuremath{\downarrow}e) with excessive charge carriers, which is disadvantageous for RISC to occur, and the other is Dexter-energy transfer to produce a triplet exciton (${\mathrm{EX}}^{3}$ \ensuremath{\rightarrow} ${T}_{1}$) in rubrene followed by triplet-triplet annihilation (TTA, ${T}_{1}$+ ${T}_{1}$ \ensuremath{\rightarrow} ${S}_{1}$+ ${S}_{0}$ \ensuremath{\rightarrow} h\ensuremath{\nu}\ensuremath{\uparrow} + 2${S}_{0}$). This TTA is the physical origin of sub-band-gap EL because TTA needs no respective injection of electrons and holes into the LUMO and HOMO energy levels and requires no direct recombination of LUMO electrons with HOMO holes in rubrene. Moreover, both the bias-current dependences of MC and MEL traces reveal that the RISC process is more obvious in relatively balanced devices due to weak TCASC processes, and they show a monotonic decrease and nonmonotonic variation in unbalanced and relatively balanced $\mathrm{rubrene}/{\mathrm{C}}_{60}$-based OLEDs, respectively, because of the combined effects of the applied electrical field and the TCASC process. Theoretically, a stronger RISC process should be observed in devices by inserting a thin bathocuproine (BCP) interlayer to modify the $\mathrm{rubrene}/{\mathrm{C}}_{60}$ interface due to the increased separation distance between electron and hole in exciplex states, but the opposite experimental results are obtained because of strong TCASC channels simultaneously occurred with the insertion of a BCP interlayer. The RISC process decreases monotonically upon lowering the operational temperature due to its endothermic property. This work deepens our comprehensive understanding of the dynamic behaviors of exciplexes and the physical origin of sub-gap EL features in $\mathrm{rubrene}/{\mathrm{C}}_{60}$-based OLEDs.

In-depth analysis of anisotropic magnetoconductance in Bi2Se3 thin films with electron–electron interaction corrections

A combination of out-of-plane (OOP) and in-plane (IP) magnetoconductance (MC) study in topological insulators (TI) is often used as an experimental technique to probe weak anti-localization (WAL) response of the topological surface states (TSSs). However, in addition to the above WAL response, weak localization (WL) contribution from conducting bulk states are also known to coexist and contribute to the overall MC; a study that has so far received limited attention. In this article, we accurately extract the above WL contribution by systematically analyzing the temperature and magnetic field dependency of conductivity in Bi2Se3 films. For accurate analysis, we quantify the contribution of electron–electron interactions to the measured MC which is often ignored in the WAL studies. Moreover, we show that the WAL effect arising from the TSSs with finite penetration depth, for OOP and IP magnetic field can together explain the anisotropic magnetoconductance (AMC) and, thus, the investigated AMC study can serve as a useful technique to probe the parameters like phase coherence length and penetration depth that characterise the TSSs in 3D TIs. We also demonstrate that increase in bulk-disorder, achieved by growing the films on amorphous SiO2 substrate rather than on crystalline Al2O3(0001), can lead to stronger decoupling between the top and bottom surface states of the film.

Magnetoconductance in epitaxial bismuth quantum films: Beyond weak (anti)localization

The complex behavior of magnetoconductance of Bi films grown epitaxially on Si(111) with a thickness of 20--100 bilayers (BL) was measured at $T$= 9 K in magnetic fields up to $B=4\phantom{\rule{0.16em}{0ex}}\mathrm{T}$, oriented in-plane parallel and perpendicular to the electric dc current $I$. Contributions to magnetoconductance (MC) by diffuse scattering, by weak localization (WL) as well as by weak antilocalization (WAL) were identified. All these components to MC turned out to be isotropic in two dimensions, i.e., no dependence on angle between $B$ and $I$ within the surface plane was found. Only for $B\phantom{\rule{0.16em}{0ex}}\ensuremath{\perp}\phantom{\rule{0.16em}{0ex}}I$ an increase of MC was detected that is, to first approximation, $\ensuremath{\propto}{B}^{2}$. It is ascribed to ballistic scattering between the Rashba-split interfaces that allow Umklapp scattering without spin flip. While MC within the surface states, dominant at small thicknesses, $d$, shows negligible diffuse scattering under the chosen geometry, their quantum corrections are characterized by WAL with $\ensuremath{\alpha}=\ensuremath{-}0.3$ and a coupling strength that decays $\ensuremath{\propto}1/d$ with layer thickness. The admixing of quantized bulk states, which dominates MC above 50 BL, not only increases diffuse scattering, it introduces WL in combination with WAL. Presumably due to hybridization with the surface states, it also modifies strongly the WAL component for $d&gt;60$ BL. Thus our findings suggest an intriguing interplay in magnetotransport between 2D and quantized 3D states at the Fermi surface of ultrathin bismuth quantum films and provide further deep insight into the electronic transport in quantized and partly spin split bands.

Evidence for spin-orbit and e−e Coulomb interaction from a magnetotransport study on CaCu3Ru4O12 thin films

$\mathrm{Ca}{\mathrm{Cu}}_{3}{\mathrm{Ru}}_{4}{\mathrm{O}}_{12}$ (CCRO) is considered a $d$-electron-based heavy-fermion metallic system with intriguing electronic properties. The magnetotransport measurements on metallic CCRO thin films reveal weak antilocalization (WAL) effects; however, it is not straightforward to infer whether the same originates from $e\text{\ensuremath{-}}e$ Coulomb interaction (EEI), spin-orbit interaction (SOI), or both present in CCRO. By evaluating quantum correction to sheet conductance for CCRO metallic thin films in the two-dimensional limit, it is observed that SOI gives rise to a dominant contribution to negative magnetoconductance (MC) in the weak-field regime. Based on weak localization (WL) and WAL analysis, SOI and inelastic scattering lengths (${l}_{so}$ and ${l}_{\ensuremath{\phi}}$) are obtained to be 30 and 74 nm, respectively, which indicates that WAL $({l}_{so}&lt;{l}_{\ensuremath{\phi}})$ remains at play. The anisotropic effect of SOI is reflected in the field-direction-dependent in-plane and out-of-plane MC measurements. The presence of the EEI contribution is evidenced from (i) the linear increment (positive slope) of sheet conductance with $ln(T)$ in the quantum interference regime [only the WAL effect should otherwise show a negative slope with $ln(T)]$ and (ii) $ln(T)$ dependence of the Hall coefficient with a negative slope. Further, in the high-magnetic-field regime where WL or WAL is not valid, MC follows $ln(B)$-type behavior, indicating the presence of EEI. These findings have implications for the basic understanding of quantum magnetotransport properties in the presence of SOI and EEI in CCRO.

Intra‐Island Coulomb Correlations in PEDOT:PSS Thin Films; Saturation of Spin Polarization Magnetoresistance

AbstractMagnetic field and temperature dependence of the magneto‐conductance (MC) of thin films made of self‐p‐doped poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) having room temperature conductivity of ≈200 S cm−1 in the range of fields B = 0–14 T and temperatures T = 1.8–300 K are reported. At B = 0 and for current parallel to the film surface, the conductance follows a variable range hopping mechanism in two dimensions. It is shown that the finite Coulomb correlations, U, within the nano‐crystalline PEDOT islands dominates MC at low temperatures and high fields. At T = 1.8 K, the intra‐island Coulomb correlation spin polarization mechanism is already saturated for B &gt; 10 T establishing a finite minimum of ≈2 meV for U. This small value of U is in line with the delocalized nature of the holes within the PEDOT islands and the relatively high conductivity that makes it essential in organic opto‐electronics.

Gate-Modulated Quantum Interference Oscillations in Sb-Doped Bi2Se3 Topological Insulator Nanoribbon

Topological insulator nanoribbons (TI NRs) provide a useful platform to explore the phase-coherent quantum electronic transport of topological surface states, which is crucial for the development of topological quantum devices. When applied with an axial magnetic field, the TI NR exhibits magnetoconductance (MC) oscillations with a flux period of h/e, i.e., Aharonov-Bohm (AB) oscillations, and h/2e, i.e., Altshuler-Aronov-Spivak (AAS) oscillations. Herein, we present an extensive study of the AB and AAS oscillations in Sb doped Bi$_2$Se$_3$ TI NR as a function of the gate voltage, revealing phase-alternating topological AB oscillations. Moreover, the ensemble-averaged fast Fourier transform analysis on the Vg dependent MC curves indicates the suppression of the quantum interference oscillation amplitudes near the Dirac point, which is attributed to the suppression of the phase coherence length within the low carrier density region. The weak antilocalization analysis on the perpendicular MC curves confirms the idea of the suppressed coherence length near the Dirac point in the TI NR.