32 research outputs found
Theoretical Description of Pulsed RYDMR: Refocusing Zero-Quantum and Single Quantum Coherences
A theoretical description of pulsed reaction yield detected magnetic resonance (RYDMR) is proposed. In RYDMR, magnetic resonance spectra of radical pairs (RPs) are indirectly detected by monitoring their recombination yield. Such a detection method is significantly more sensitive than conventional electron paramagnetic resonance (EPR), but design of appropriate pulse sequences for RYDMR requires additional effort because of a different observable. In this work various schemes for generating spin-echo like signals and detecting them by RYDMR are treated. Specifically, we consider refocusing of zero-quantum coherences (ZQCs) and single-quantum coherences (SQCs) by selective as well as by non-selective pulses and formulate a general analytical approach to pulsed RYDMR, which makes an efficient use of the product operator formalism. We anticipate that these results are of importance for RYDMR studies of elusive paramagnetic particles, notably, in organic semiconductors
Quantum phase slips in the presence of finite-range disorder
To study the effect of disorder on quantum phase slips (QPS) in
superconducting wires, we consider the plasmon-only model where disorder can be
incorporated into a first-principles instanton calculation. We consider weak
but general finite-range disorder and compute the formfactor in the QPS rate
associated with momentum transfer. We find that the system maps onto
dissipative quantum mechanics, with the dissipative coefficient controlled by
the wave (plasmon) impedance Z of the wire and with a superconductor-insulator
transition at Z=6.5 kOhm. We speculate that the system will remain in this
universality class after resistive effects at the QPS core are taken into
account.Comment: 4 pages, as accepted at Phys. Rev. Letter
Higher triplet state of fullerene C70 revealed by electron spin relaxation
Spin-lattice relaxation timesT1 of photoexcited triplets 3C70 in glassy
decalin were obtained from electron spin echo inversion recovery dependences.
In the range 30–100 K, the temperature dependence of T1 was fitted by the
Arrhenius law with an activation energy of 172 cm−1. This indicates that the
dominant relaxation process of 3C70 is described by an Orbach-Aminov mechanism
involving the higher triplet state t2 which lies 172 cm−1 above the lowest
triplet state t1. Chemical modification of C70fullerene not only decreases the
intrinsic triplet lifetime by about ten times but also increases T1 by several
orders of magnitude. The reason for this is the presence of a low-lying
excited triplet state in 3C70 and its absence in triplet C70 derivatives. The
presence of the higher triplet state in C70 is in good agreement with the
previous results from phosphorescence spectroscopy
Non-Equilibrium and Quantum Coherent Phenomena in the Electromechanics of Suspended Nanowires
Strong coupling between electronic and mechanical degrees of freedom is a
basic requirement for the operation of any nanoelectromechanical device. In
this Review we consider such devices and in particular investigate the
properties of small tunnel-junction nanostructures that contain a movable
element in the form of a suspended nanowire. In these systems, electrical
current and charge can be concentrated to small spatial volumes resulting in
strong coupling between the mechanics and the charge transport. As a result, a
variety of mesoscopic phenomena appear, which can be used for the transduction
of electrical currents into mechanical operation. Here we will in particular
consider nanoelectromechanical dynamics far from equilibrium and the effect of
quantum coherence in both the electronic and mechanical degrees of freedom in
the context of both normal and superconducting nanostructures.Comment: 20 pages, 13 figures, figures update
Kondo effect in quantum dots
We review mechanisms of low-temperature electronic transport through a
quantum dot weakly coupled to two conducting leads. Transport in this case is
dominated by electron-electron interaction. At temperatures moderately lower
than the charging energy of the dot, the linear conductance is suppressed by
the Coulomb blockade. Upon further lowering of the temperature, however, the
conductance may start to increase again due to the Kondo effect. We concentrate
on lateral quantum dot systems and discuss the conductance in a broad
temperature range, which includes the Kondo regime
Pulse EPR and ENDOR study of 1,2,3-benzodithiazolyl, 2,1,3-benzothiaselenazolyl and 1,2,3-benzodiselenazolyl radicals
Structure of the Charge-Transfer State in PM6/Y6 and PM6/Y6:YT Composites Studied by Electron Spin Echo Technique
Nowadays, Y-shaped non-fullerene acceptors become increasingly important in organic photovoltaics (OPV). Their use in binary and ternary bulk heterojunction composites continuously pushes up the efficiency of OPV devices. However, the mechanism of OPV performance enhancement by the third component of a ternary composite is rarely understood. In the present work, pulse EPR technique was used to reveal the similarities and the differences of photoinduced charge separation process in binary PM6/Y6 and ternary PM6/Y6:Y-T composites, where PM6 is polymer donor, Y6 and Y-T are different non-fullerene acceptors. Out-of-phase electron spin echo signal was detected for both composites, which is the signature of the charge-transfer state (CT state) formed at the donor/acceptor interface upon exciton splitting. Nearly identical distribution of the distances between the electron and the hole constituting the CT state was obtained for these composites from the analysis of this signal. In both cases the average electron-hole distance was 3.5 nm. It implies that OPV efficiency increase with Y-T addition is not caused by the increased probability of CT state dissociation followed by free charge generation for PM6/Y6:Y-T composite