Introduction of spin centers in single crystals of Ba2CaWO6−δ

Abstract

Developing the field of quantum information science (QIS) hinges upon designing viable qubits, the smallest unit in quantum computing. One approach to creating qubits is introducing paramagnetic defects into semiconductors or insulators. This class of qubits has seen success in the form of nitrogen-vacancy centers in diamond, divacancy defects in SiC, and P doped into Si. These materials feature paramagnetic defects in a low nuclear spin environment to reduce the impact of nuclear spin on electronic spin coherence. In this work, we report single crystal growth of Ba2CaWO6-δ, and the coherence properties of introduced W 5+ spin centers generated by oxygen vacancies. Ba2CaWO6-δ (δ = 0) is a B-site ordered double perovskite with a temperature-dependent octahedral tilting wherein oxygen vacancies generate W 5+ (d 1 ), S = ½, I = 0, centers. We characterized these defects by measuring the spin-lattice (T1) and spin-spin relaxation (T2) times from T = 5 to 150 K. At T = 5 K, T1 = 310 ms and T2 = 4 μs, establishing the viability of these qubit candidates. With increasing temperature, T2 remains constant up to T = 60 K and then decreases to T2 ~ 1 μs at T = 90 K, and remains roughly constant until T = 150 K, demonstrating the remarkable stability of T2 with increasing temperature. Together, these results demonstrate that systematic defect generation in double perovskite structures can generate viable paramagnetic point centers for quantum applications and expand the field of potential materials for QIS.

Twisting of 2D Kagomé Sheets in Layered Intermetallics

“…An alternative view of this structural change comes from a formal symmetry analysis: this polar disorder leads to activation of B 1 modes resulting in the transformation from the high-temperature to the low-temperature structure. Both amorphous and crystalline systems have been found to have excess low-temperature specific heat than predicted by the Debye model due to low-lying optic phonons, which can arise due to proximity to bond making or breaking or directional rearrangement, such as octahedral tilting in perovskites, 33 lone-pair driven disorder in pyrochlores, etc. ; 34 thus, a structure with evidence of temperature-dependent tilt may show thermodynamic impacts of those structural components.…”

“…This low-lying Einstein phonon mode in the heat capacity data indicates vibrationally active local modes in the structure. 33 This is naturally explained as arising from the thermally activated behavior of the bidirectional bilayer twisting. To see how universal this behavior is, single crystals of other materials of the MT 6 X 6 family, YCr 6 Ge 6 and LuFe 6 Ge 6 , were characterized using heat capacity measurements and X-ray diffraction.…”

Hexagonal Perovskites as Quantum Materials

“…In classical double perovskites, there are two different "M type" ions in an ordered array or a partially ordered array within the MO3 framework. Double perovskites can be written in the form A2MM'O6, where M and M' can be different ions such as in Sr2FeWO6, a material that has a particularly high magnetoresistance 51 or even the same M metal with different oxidation states, such as is seen in BaBiO3 (Ba2Bi 3+ Bi 5+ O6 formally) [52][53][54][55][56][57] , the basis for superconductivity in several perovskite oxides 58,59 . Disordered and partially ordered M-M' double perovskites are known.…”

Tools and Tricks for Single Crystal Growth

“…Under these conditions, oxygen vacancies form that change the color from white to dark blue, enabling absorption of near-IR laser light. 22 To correct the oxygen vacancies in the grown crystal, the single crystal is then annealed under oxygen for a long duration of time to regain its white color. Another method to promote absorption is shading the outer region of otherwise nonabsorbing crucibles (e.g., BN) with graphite to allow for light absorption and therefore successful heating, with the level of light absorption dependent on the amount of shading (darker shades will be better in light absorption−with the upper limit being the scenario of placing a BN crucible inside a C crucible).…”