Cross-relaxation and phonon bottleneck effects on magnetization dynamics in LiYF4:Ho3+

Frequency and dc magnetic field dependences of dynamic susceptibility in diluted paramagnets LiYF$_4$:Ho$^{3+}$ have been measured at liquid helium temperatures in the ac and dc magnetic fields parallel to the symmetry axis of a tetragonal crystal lattice. Experimental data are analyzed in the framework of microscopic theory of relaxation rates in the manifold of 24 electron-nuclear sublevels of the lowest non-Kramers doublet and the first excited singlet in the Ho$^{3+}$ ground multiplet $^5I_8$ split by the crystal field of S$_4$ symmetry. The one-phonon transition probabilities were computed using electron-phonon coupling constants calculated in the framework of exchange charge model and were checked by optical piezospectroscopic measurements. The specific features observed in field dependences of the in- and out-of-phase susceptibilities (humps and dips, respectively) at the crossings (anti-crossings) of the electron-nuclear sublevels are well reproduced by simulations when the phonon bottleneck effect and the cross-spin relaxation are taken into account

Numerical adiabatic potentials of orthorhombic Jahn-Teller effects retrieved from ultrasound attenuation experiments. Application to the SrF2:Cr crystal

A methodology is worked out to retrieve the numerical values of all the main parameters of the six-dimensional adiabatic potential energy surface (APES) of a polyatomic system with a quadratic T-term Jahn-Teller effect (JTE) from ultrasound experiments. The method is based on a verified assumption that ultrasound attenuation and speed encounter anomalies when the direction of propa- gation and polarization of its wave of strain coincides with the characteristic directions of symmetry breaking in the JTE. For the SrF2:Cr crystal, employed as a basic example, we observed anomaly peaks in the temperature dependence of attenuation of ultrasound at frequencies of 50-160 MHz in the temperature interval of 40-60 K for the wave propagating along the [110] direction, for both the longitudinal and shear modes, the latter with two polarizations along the [001] and [110] axes, respectively. We show that these anomalies are due to the ultrasound relaxation by the system of non-interacting Cr2+ JT centers with orthorhombic local distortions. The interpretation of the ex- perimental findings is based on the T2g (eg +t2g) JTE problem including the linear and quadratic terms of vibronic interactions in the Hamiltonian and the same-symmetry modes reduced to one interaction mode. Combining the experimental results with a theoretical analysis we show that on the complicated six-dimensional APES of this system with three tetragonal, four trigonal, and six orthorhombic extrema points, the latter are global minima, while the former are saddle points, and we estimate numerically all the main parameters of this surface, including the linear and quadratic vibronic coupling constants, the primary force constants, the coordinates of all the extrema points and their energies, the energy barrier between the orthorhombic minima, and the tunneling splitting of the ground vibrational states.Comment: 8 pages, 3 figure

NMR, high frequency EPR and magnetization studies of YF 3:Tm 3+ and TmF 3

Magnetic properties of single crystal and powder samples of thulium fluoride, TmF 3 (orthorhombic Pnma space group), and single crystals of YF 3 doped with the Tm 3+ ions are studied by NMR, high-frequency EPR and dc-magnetometry. It is shown that TmF 3 is a Van Vleck paramagnet. Zero field splitting between two lowest ground state energy levels (ground 3H 6 multiplet) of Tm 3+ ion in TmF 3 crystal lattice is found to be ∼6.5 cm -1. The 19F nuclear spin-lattice relaxation in TmF 3 at liquid helium temperatures is driven by the fluctuating magnetic fields created by Tm 3+ ions occupying the lowest excited singlet

Spectra and relaxation of electronic excitations in CsCdBr3:Yb3+ and CsCdBr3:Nd3+ monocrystals

Experimental and theoretical studies of the optical and EPR spectra, and the spin-lattice relaxation in CsCdBr3 crystals containing 0.1, 0.3 and 1.0 mol.% of impurity Yb3+ ions have been fulfilled. In the optical excitation spectrum, a broad charge transfer band has been detected in the wave-number range of 25000-35000 cm-1. The hybridization of the excited electron configuration corresponding to the charge transfer from the ligand (Br-) 4p closed shells on the ground 4f13 configuration of the ytterbium ion is considered to interpret the anomalously large crystal field splitting of the 2F5/2 multiplet. The EPR spectra with comparable intensities of the axial single-ion and symmetric dimer centres in the sample containing 0.3 mol.% of impurity Yb3+ ions were observed. Spin-lattice relaxation rates and linewidths in the EPR spectra of the single-ion and dimer centres were measured in the temperature range of 1.5 - 35 K at the frequency of 9.5 GHz at different directions of the applied magnetic field relative to the crystal symmetry axis. Experimental results are analyzed in the framework of the microscopic theory of the electron-phonon interaction with taking into account peculiarities of the phonon spectrum of the impurity CsCdBr3 lattice. High-frequency EPR spectra of dimer centres in CsCdBr3 crystals containing 0.2 and 0.5 mol.% of impurity Nd3+ ions were taken in the range of 205-250 GHz at 4.2 K in the magnetic fields up to 0.8 T parallel to the crystal symmetry axis. The crystal field splitting between the first excited and the ground Kramers doublets, and magnetic splitting factors of these doublets were determined. An estimate of the isotropic ferromagnetic exchange constant A = (2.3±0.3) 10-3 cm-1 in symmetric dimer centres formed by impurity Nd3+ ions was obtained from the zero-field splitting of the EPR signals

STABILIZATION ENERGIES OF THE JAHN-TELLER COMPLEXES IN CaF2:Cr2+ CRYSTAL

In CaF2 crystal doped with Cr2+ ions, attenuation of all the normal ultrasonic modes with the wave vector k were investigated at 26 -158 MHz in the temperature region of 4 - 170 K. The observed peaks of relaxation origin were interpreted as manifestation of the Jahn-Teller effect

Surgical Aid to Patients with Hepatopancreatobiliary Situations in Precovid Period and under Persistent Relapse of New Coronavirus Infection SARS-CoV-2

Introduction. The third wave of the new coronavirus infection (COVID-19) pandemic warrants total mobilisation of healthcare and social resources. In this respect, a pressing issue remains the provision of routine and emergency surgical care in patients with hepatopancreatobiliary diseases.Materials and methods. A retrospective analysis of the surgical outcomes in 5,040 hepatopancreatobiliary patients was carried out; this accounted for 51.1 % of the total abdominal surgeries.Results and discussion. Biliary lithiasis and its complications — choledocholithiasis with obstructive jaundice and residual choledocholithiasis — (54.4 %) as well as acute calculous cholecystitis (18.7 %) were operated most frequently. A sharp decrease over all hepatopancreatobiliary nosologies was registered for the surgical interventions in first pandemic year 2020. Thus, the median annual number of operations for biliary lithiasis and its complications was 550 (482–592 year-range) in the precovid period, while dropping to only 321 at the onset of pandemic (p <0.05). A first sixmonth survey of year 2021 revealed a growth of surgical activity for all hepatopancreatobiliary nosologies.Conclusion. Hepatopancreatobiliary operations prevail (54.4 % cases) in the total structure of level 3 abdominal surgical interventions. A high annual rate of surgical operations over nearly all hepatopancreatobiliary nosologies was interrupted in the first year of the new coronavirus infection outbreak. Meanwhile, the first half of 2021 showed a clear tend towards restoring the precovid statistical indicators, despite the stressful conditions of persistently relapsing COVID-19 that surgical facilities had faced

Rare-earth solid-state qubits

Quantum bits (qubits) are the basic building blocks of any quantum computer. Superconducting qubits have been created with a 'top-down' approach that integrates superconducting devices into macroscopic electrical circuits [1-3], whereas electron-spin qubits have been demonstrated in quantum dots [4-6]. The phase coherence time (Tau2) and the single qubit figure of merit (QM) of superconducting and electron-spin qubits are similar -- Tau2 ~ microseconds and QM ~10-1000 below 100mK -- and it should be possible to scale-up these systems, which is essential for the development of any useful quantum computer. Bottom-up approaches based on dilute ensembles of spins have achieved much larger values of tau2 (up to tens of ms) [7, 8], but these systems cannot be scaled up, although some proposals for qubits based on 2D nanostructures should be scalable [9-11]. Here we report that a new family of spin qubits based on rare-earth ions demonstrates values of Tau2 (~ 50microseconds) and QM (~1400) at 2.5 K, which suggests that rare-earth qubits may, in principle, be suitable for scalable quantum information processing at 4He temperatures