Ultrasonic evaluation of the Jahn–Teller effect parameters. Application to ZnSe:Cr^{2 +}

Abstract

A method is constructed that uses ultrasonic experiments to evaluate the parameters of the Jahn-Teller (JT) effect in impurity centers in crystals. The method is based on measurements of temperature dependent attenuation and phase velocity and does not require assumptions about mechanisms of relaxation. The results are illustrated by measurements performed on the impurity system ZnSe:Cr(2+), in which the Cr(2+) ion has a threefold degenerate T term in the ground state, subject to the [Formula: see text] JT problem. Ultrasound propagation anomalies show that the main JT distortions of the tetrahedral environment of the Cr(2+) ion are of tetragonal E type and hence the lowest branch of the adiabatic potential energy surface (APES) is formed in accordance with the [Formula: see text] problem. With dopant concentration 3.8 × 10(18) cm(-3) the modulus of the constant of linear vibronic coupling to tetragonal E type vibrations is determined by two independent experiments: |F(E)| = 5.49 × 10(-5) dyn revealed from attenuation measurements, while a slightly different value |F(E)| = 5.57 × 10(-5) dyn emerges from phase velocity measurements. Contributions of other active vibronic modes to the elastic modulus C(l) = (C(11) + C(12) + 2C(44))/2 are analyzed and it is shown that the influence of the totally symmetric mode is negligible. Using additional information about this system obtained from independent sources, we also estimated the primary force constant in the E direction (K(E)≈(1.4-4.2) × 10(4) dyn cm(-1)) and orthorhombic and trigonal saddle points of the APES in the five-dimensional space of the tetragonal and trigonal coordinates, their stabilization energies being E(JT)(O)≈81-450 cm(-1) and E(JT)(T)≈48-417 cm(-1), respectively (the variations of the K(E), E(JT)(O) and E(JT)(T) values are due to different literature data for E(JT)(E)). With these data the APES of the JT linear [Formula: see text] problem for the Cr(2+) ion in the ZnSe:Cr(2+) system is revealed.

Динамика фотоиндуцированных изменений упругих характеристик кристаллов ниобата лития, допированных ян-теллеровскими ионами Fe-=SUP=-2+-=/SUP=-

“…Неоднородное по сечению увеличение затухания акустических волн до лазерного облучения в образцах можно также связать с неравномерным распределением ионов Fe 2+ по образцам. В этом случае значение α JT будет, согласно современным представле-ниям [14], связано с изменением упругих модулей C i j и временем релаксации τ между состояниями туннели-рующих через барьер электронов:…”

“…Однако полученные в работе [13] методом синхротронной дифрактометрии значения фотодеформации ε ∼ 10 −4 не соответствуют величинам фотоиндуцированных полей (E ph ∼ 10 7 V/m), достигнутых с помощью облучения ксеноновой лампой образца НЛ, содержащего ионы железа. Это обстоятель-ство не позволяет объяснить полученные результаты только пьезоэффектом, хотя сам факт влияния примерно такой же концентрации ионов Fe 2+ , Cr 2+ , Ni 2+ , V 2+ на упругие характеристики полупроводниковых кристаллов типа ZnSe был обнаружен в работе [14]. Причем са-ми авторы объясняют полученные результаты именно присутствием ЯТ-эффекта в допирующих ионах.…”

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

“…Hence we can define these constants from the experimental data on ultrasonic attenuation using the method introduced in Refs. 5,6 . As it was shown in these papers, relaxation attenuation of the shear ultrasonic waves is given by the following expression:…”

“…Along with traditional methods of investigation of electronic structure, dynamics and local symmetry of crystal dopants and other active centers in polyatomic systems by means of experimental electron spin resonance (ESR) and pulse techniques using electron spin echo (ESE, ES-EEM spectroscopy) [1][2][3][4] , recent studies of II-VI:3d and III-V:3d crystals by means of ultrasonic experiments demonstrated the efficiency of this novel approach in obtaining important information about the structure and properties of Jahn-Teller effect (JTE) centers in such crystals [5][6][7][8] . Ultrasonic experiments are uniquely suited for investigation of JTE problems because the interaction of the ultrasound wave of strain produces characteristic anomalies in speed, relaxation, and attenuation when its direction of propagation and polarization coincides with the direction of JTE distortions.…”

Magnetoacoustic Relaxation by Cr2+ Jahn–Teller Centers Revealed from Elastic Moduli

“…But in view of possible application in quantum computing, magneto‐acoustic investigation is deemed to be important. We have performed such experiments in wurtzite CdSe:Cr 2+ , fluorite SrF 2 :Cr 2+ , and sphalerite ZnSe:Cr 2+ single crystals. All of these materials manifest the JTE but only ZnSe:Cr 2+ exhibits magnetic field dependence of the acoustic properties.…”